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  • 1995-1999  (654)
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  • Physical Chemistry  (1,158)
  • Heterocycles
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  • 1
    Electronic Resource
    Electronic Resource
    Syntheses of Batzelline A, Batzeline B, Isobatzelline A, and Isobatzelline B (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1173-1183 
    Details
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Pyrroloquinoline ; Total synthesis ; Heterocycles ; Alkaloids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characterized by the presence of a methylthio substituent at C-2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Intramolecular Copper- and Rhodium-Mediated Carbenoid Reactions of α-(Propargyloxy)silyl-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1213-1221 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Copper(I) triflate catalyzes the transformation of α-[(2-alkynyl)oxy]silyl-α-diazoacetates 1a-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)ethenes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as catalyst, 1a-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are formed when 1a,c,e (containing terminal alkyne functions) are treated with catalytic amounts of copper(I) chloride. The experimental observations are explained in terms of metal-mediated intramolecular cyclopropenation and subsequent metal-assisted ring-opening of the strained bicyclic cyclopropene leading to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasilines 3a,c,e is also described.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    The Preparation of 2,3,5-Tri- and 2,3-Disubstituted Furans by Regioselective Palladium(0)-Catalyzed Coupling Reactions: Application to the Syntheses of Rosefuran and the F5 Furan Fatty Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2045-2057 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Palladium ; Cross-coupling ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5-acceptor-substituted 2,3-dibromofurans 1 and 2 underwent a regioselective Pd0-catalyzed coupling reaction at the C-2 carbon atom. With alkynes the corresponding 2-alkynylfurans 4 and 5 were accessible (49-97% yield). Alkyl-, aryl-, and alkenylzinc reagents gave the 2-substituted furans 8 starting from compound 2 (66-84% yield). The 2-allylfurans 8e and 8f were obtained by a regioselective Stille coupling in 79% and 73% yield. The latter reaction was also applied to the parent 2,3-dibromofuran (27) and yielded the substitution product 28 (60% yield). Subsequent Pd0-catalyzed reactions to introduce a methyl group in 3-position by a methyldebromination were successfully conducted for 2-alkynyl-3-bromofurans with MeZnCl and PdCl2(PPh3)2 as the catalyst in THF (reflux) to yield compounds 13-16 and 24 (67-76%) and with SnMe4 and PdCl2[P(o-Tol)3]2 as the catalyst in DMA (90 °C) for the 2-allyl-3-bromofuran 8e to yield 18 (70%). The more facile reaction of the 2-alkynylfurans relative to those of furans bearing an sp3-carbon atom at C-2 appears to be due to steric reasons. Studies on the 2-alkyl-3-bromofuran 20 supported this notion. With the regioselective coupling methodology the terpene rosefuran (22) was prepared in four steps starting from furan 2 (35% yield overall). The F5 furan fatty acid (26) was synthesized from furan 1 in five steps (29% yield overall).
    Additional Material: 4 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of (-)-Cytoxazone, a Novel Cytokine Modulator Isolated from Streptomyces sp. (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2965-2967 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohol ; Asymmetric synthesis ; Cell signaling ; Dihydroxylations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cytoxazone [(4R,5R)-(-)-5-hydroxymethyl-4-(4-methoxyphenyl)-2-oxazolidinone, 1], a new immunosuppressant, was synthesized by starting from p-methoxycinnamyl alcohol (2) employing the Sharpless asymmetric dihydroxylation as the key reaction in 26% overall yield (7 steps).
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Borane Insertion into Group-4 Metal-to-Carbon Bonds: The Reaction of HB(C6F5)2 with (η2-Formaldehyde)zirconocene Dimer and with (Butadiene)zirconocene (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2243-2247 
    Details
    ISSN: 1434-1948
    Keywords: Metallaoxirane ; HBR2 addition ; (Formaldehyde)zirconocene ; (Butadiene)zirconocene ; Heterocycles ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (η2-Formaldehyde)zirconocene dimer (8) cleanly adds one or two molar equivalents of the borane HB(C6F5)2 by insertion of the H-[B] unit into the zirconium-carbon bond of the metallaoxirane moieties to form the mono- and bis-insertion products 16 and 17, respectively. These systems contain five-membered heterocyclic rings that are built up by connecting five different elements, namely H, B, C, O, and Zr. The bis(borane) insertion product 17 was characterized by an X-ray crystal structure analysis. (Butadiene)zirconocene reacts with HB(C6F5)2 in a similar way by insertion of the H-[B] unit into the (butadiene)C4-Zr linkage to form the metallacycle 18.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Insights into the Staudinger Reaction: Experimental and Theoretical Studies on the Stabilization of cis-Phosphazides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1659-1664 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Iminophosphorane ; Staudinger reaction ; Heterocycles ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Staudinger-model reaction H3P (1) + HN3 (2) → H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N-N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis -3is 8.2 kcal mol-1 more stable than trans -3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor-acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New Inorganic Metallacycles and the First Six-Membered Covalent “True” Heterocycle - Oxidation of RC(E)NHPPh2 (E = O or S; R = H2N, Ph, or Py) with O, S, or Se to Give RC(E)NHP(E′)Ph2 (E′ = O, S, Se) and Their Coordination Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1445-1452 
    Details
    ISSN: 1434-1948
    Keywords: Metallacycles ; Solid-state structures ; Heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct oxidation of PhC(O)NHPPh2, H2NC(S)NHPPh2, (C5H4N)C(S)NHPPh2 with O2, S8, or Se gives [PhC(O)NHP(O)Ph2] (1), [H2NC(S)NHP(S)Ph2] (2), [H2NC(O)NHP-(S)Ph2] (3), [PhC(O)NHP(S)Ph2] (4), [(C5H4N)C(S)NHP(S)Ph2] (5), and [H2NC(S)NHP(Se)Ph2] (6). Deprotonation of 1, 2, 4-6 with potassium tert-butoxide gives K[PhC(O)NP(O)Ph2] (7), K[H2NC(S)NP(S)Ph2] (8), K[PhC(O)NP(S)Ph2] (9), K[(C5H4N)C(S)NP(S)Ph2] (10), and K[H2NC(S)NP(Se)Ph2] (11). Reaction of 4with KOBu and [Cu(Ph3P)2][NO3] gives [Cu(Ph3P)(PhC(O)NP(S)Ph2)] (12) which is the first crystallographically characterised example of a non-ionic six-membered “true” heterocycle (i.e. a ring in which every heterocatom is different). 9 and 10 were treated with [PdCl2(COD)] to give [Pd{PhC(O)NP(S)Ph2}2] (13) and [Pd{(C5H4N)C(O)NP(S)Ph2}2] (14), respectively The anion of 8 coordinates to zinc forming [Zn{H2NC(S)NP(S)Ph2}2] (15). Treatment of 2 or 8 with [PtCl2(COD)] gives [Pt{H2NC(S)NP(S)Ph2}{H2NC(S)NHP(S)Ph2}]+Cl- (16) and [Pt{H2NC(S)NP(S)Ph2}2] (17), respectively. The X-ray structures of 12, 15-17are reported.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Syntheses, Structures, and Coordination of Diborylbipyridines and Bipyridinediborates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 393-398 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Bipyridine ; Crystal structures ; Donor-acceptor interaction ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6,6′-Bis(diethylboryl)-2,2′-bipyridine (1a) was obtained in low yield by in situ deprotonation of 2,2′-bipyridine in the presence of diethyl(methoxy)borane. 6,6′-Dilithio-2,2′-bipyridine reacts with various alkoxyboranes leading to bipyridinediborates 2 in good yields. The derivatives 2b and 2c allow the formation of the free diborylbipyridines 1b and 1c. The coordination properties of the diboryl-bipyridines as tetrafunctional donor-acceptor compounds have been used for the formation of the copper complex 4 and of the adduct 5 which is built from diborylbipyridine and a dihydroxydiboroxan derivative. The composition of the products follows from spectroscopic data and from X-ray structure analyses for 2f, 4, and 5.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and Structure of 2-Hydro-, 2-Alkyl-, 2-Alkynyl-, and 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 491-497 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Hydrides ; Tin ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (4a) and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH4. Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium or by the ethylenediamine adduct of lithium acetylide. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the complex 9a the compound 3a serves as an η1 ligand towards the [Cr(CO)5] unit via the cyano group. These novel compounds were characterized by 1H-, 11B-, 13C-, and 119Sn-NMR spectroscopy, as well as by X-ray structure analyses of 4b, 8a, and 9a.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Reactions of 1,8-Diheterocyclotetradeca-4,11-diynes with (η4-Cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 499-504 
    Details
    ISSN: 1434-1948
    Keywords: Alkynes ; Heterocycles ; Cyclizations ; Cobalt ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following monocyclic and bicyclic 14-membered diynes were treated with [CpCo(cod)]: 1-oxacyclotetradeca-4,11-diyne (2), 1,8-dioxacyclotetradeca-4,11-diyne (3), cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (5), 1,1,8,8-tetramethyl-1,8-disilacyclotetradeca-4,11-diyne (6), 1-allyl-1-azacyclotetradeca-4,11diyne (7), 1,8-dipropyl-1,8-diazacyclotetradeca-1,11-diyne (8), 1,8-diallyl-1,8-diazacyclotetradeca-4,11-diyne (9), 1,8-diazabicyclo[6.6.4]octadeca-4,11-diyne (10), 1,8-diazabicyclo[6.6.6]eicosa-4,11-diyne (11), 1,10-diazabicyclo[8.6.6]docosa-13,19-diyne (12) and 1,12-diazabicyclo[10.6.6]tetracosa-15,21-diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15-26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X-ray studies. Common to all structures is a boat-like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.
    Additional Material: 1 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Synthesis, X-ray Crystal Structures and Reactivity Towards Alkynes of Gold(I)-Phosphinine Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2233-2241 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Heterocycles ; Phosphinines ; Gold ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.
    Additional Material: 5 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Intramolecular Donor-Assisted Cyclization of Organotin Compounds (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 887-898 
    Details
    ISSN: 1434-1948
    Keywords: Tin ; Phosphorus ; Intramolecular coordination ; O ligands ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New intramolecularly coordinated organotin compounds containing the monoanionic O,C,O-coordinating ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- have been synthesized by substitution reactions starting from organotin halides. In view of the enhanced reactivity of the intramolecularly coordinated compounds {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}SnR2R′ (2, R = Ph, R′ = CH2SiMe3; 3, R = R′ = Ph; 6, R = R′ = Cl), cationic tin species are suggested to occur as intermediates in the formation of the heterocyclic compounds [1(Sn),3(P)-Ph2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (8), [1(Sn), 3(P)-Ph(Me3SiCH2)SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (15), and {[1(Sn),3(P)-Cl2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)]C6H2}2 (16). The latter compounds are formed by intramolecular cyclizations of pentacoordinate cationic tin species under elimination of ethyl halide. Furthermore, the synthesis of [1(Sn),3(P)-Ph2SnOP(O)(OH)-5-tert-Bu-7-P(O)(OH)2]C6H2 (13) is described. Reaction of 8 with an excess of Me3SiBr leads to the unexpected formation of {2-[P(O)(OEt)(OSiMe3)]-4-tert-Bu-6-[P(O)(OEt)2]C6H2}SnPhBr2 (9) as a result of an O-Sn bond cleavage initiated by Me3SiBr and subsequent reaction of the intermediate with further Me3SiBr under Sn-C bond cleavage. The high donor capacity and the rigidity of the new ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- are demonstrated by X-ray diffraction analyses of the tetraorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1-oxaphosphastannoles 8 and 16 are discussed.
    Additional Material: 5 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Cyclic Ketiminoboranes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 7-9 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Diazaboroles ; Heterocycles ; Ketiminoboranes ; Crystal Structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclocondensation reaction of benzil-bis(trimethylsilylimin) (3) and Cl2B-NiPr2 via silicon-boron exchangeresults in the solvent-dependent formation of the 1,3,2-diazaborole 1a or the 1,3,6,8,2,7-tetraazadiborecin 2a. Using the more rigid 9,10-bis(trimethylsilylimino)phenanthrene instead of 3 only the five-membered heterocycle 4,5-biphenylene-2-diisopropylamino-1,3,2-diazaborole (1b) is formed. The cyclic ketiminoboranes are characterized by NMR and X-ray diffraction data. The 1,3,2-diazaborole ring is almost planar, while the conformation of the 1,3,6,8,2,7-tetraazadiborecin has the shape of a figure-eight loop.
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis and 1H-, 15N-, 31P-, 183W-Multinuclear Magnetic Resonance Study of the Cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4] and Their W(CO)5 Complexes (dobp = 2,2′-dioxybiphenyl) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1015-1020 
    Details
    ISSN: 1434-1948
    Keywords: Cyclotriphosphazenes ; Oxypyridine ; Carbonyltungsten compounds ; NMR spectroscopy ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of [N3P3(dobp)2Cl2] and [N3P3(dobp)Cl4] with a mixture of HOC5H4N-4 and K2CO3 in acetone give the cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4], respectively. These compounds react with [W(MeOH)(CO)5] in methanol to give mixtures of the polymetallic complexes [N3P3(dobp)2(OC5H4N-4)2{W(CO)5}x] (x = 1, 2) and [N3P3(dobp)(OC5H4N-4)4{W(CO)5}x] (x = 1-4), which are unstable in solution, slowly undergoing loss of the pentacarbonyl moiety. A complete characterization by multinuclear 1H, 15N, 31P, 183W magnetic resonance has revealed that the complexation of the N atom of one 4-oxypyridine ligand by the W(CO)5 fragment has a measurable effect on other parts of the phosphazene molecule very far away from the coordination site. The changes observed in δ183W have been used to identify the components in mixtures of compounds incorporating different numbers of tungsten atoms in the molecule. The characterization of less sensitive nuclei has been accomplished by means of indirect detection methods.
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  • 15
    Electronic Resource
    Electronic Resource
    Novel Condensed Thionated Bis(phosphonic) Acid Salts with a Rigid Naphthalene-1,8-diyl Backbone (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2327-2333 
    Details
    ISSN: 1434-1948
    Keywords: Heterocycles ; Organo-phosphorus compounds ; Dithiadiphosphetane disulfides ; Phosphonates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New salts of thionated (naphthalene-1,8-diyl)bis(phosphonic) acid monoanhydrides [PPh4+]2[C10H6PS2(μ-S)PS22-] (2) and [K+]2[C10H6PS2(μ-S)POS2-]·H2O (3) both containing the C3P2S ring, were prepared in high yields by the reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (1) with NaHS and PPh4Cl, or KOH, respectively, in water. The derivative 3, containing a P=O terminal bond as well as P-S-P bridge, undergoes, in acid conditions, a rearrangement reaction leading to the O,S-symmetrically substituted derivative [K+]2[C10H6PS2(μ-O)PS22-] (4) containing a C3P2O heterocycle. Dipotassium salt 4 was converted into the bis(tetraphenylphosphonium) salt 5 by the treating with PPh4Cl. Hydrolysis of [PyH+][C10H6P(S)(NHMe)(μ-S)PS22-] (15) led to [CH3NH3+][PyH+][C10H6POS(μ-O)POS2-]·1.5 Py (6). New compounds were characterised by 31P{1H}-, 1H- and 13C{1H}-NMR, FT-IR, ES-MS and in the cases 2-6 by X-ray structure determination. The 31P{1H}-NMR spectra of these mixed O,S-derivatives are briefly discussed.
    Additional Material: 5 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    Synthesis, Structure and Reactivity of 3,4-Dihydro-2H-1,2,4,3-triazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1193-1198 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Triazaboroles ; Heterocycles ; Halogens ; Cyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,4-Dihydro-2,4-diphenyl-2H-1,2,4,3-triazaboroles 3a, 3b, and 4 were synthesized by cyclocondensation of N1,N3-diphenylformamidrazone (1) with dibromophenylborane, dibromomethylborane, and boron trichloride. 3-Chloro-3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (4) was converted into 3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (5) by treatment with LiAlH4. The corresponding 3-cyanato and 3-cyano derivatives 6 and 7 resulted from the reaction of 4 with AgOCN and AgCN, respectively. Compound 7 was transformed into the bis(1,2,4,3-triazaborolyl)oxane 8 by silver oxide. Compounds 1-8 were characterized by elemental analyses and spectroscopic methods (1H, 11B, and 13C NMR; IR; MS). The molecular structure of 8 was established by single-crystal X-ray diffraction analysis.
    Additional Material: 2 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    The Synthesis of Novel Cyclic β-Amino Acids as Intermediates for the Preparation of Bicyclic β-Lactams (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2433-2441 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Lactams ; Schiff bases ; Nitrogen heterocycles ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several derivatives of homopipecolic acid are prepared by α-amino alkylation of malonic acid with cyclic imines 6 and 7. These are prepared on a large scale and with different substitution patterns. The β-amino acids 8 and 9 were formed in high yield and with remarkable diastereoselectivity if chiral imines are used as starting materials. The diastereoselectivity of the amino alkylation leading to homopipecolic acid analogues is compared to those of thiazolidineacetic acids by epimerisation experiments. A method for resolution of the obtained racemic β-amino acids by diastereomeric salt formation is described. The β-amino acids 9 and 15 were converted into their corresponding carbacepham analogues 14 and isopenam 16. The isopenam endo-16 was selectively epimerised by mild basic treatment of the N/S-acetal to give an exo-configured precursor of isopenicillin G.
    Additional Material: 2 Tab.
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  • 18
    Electronic Resource
    Electronic Resource
    Pd-Catalyzed Asymmetric Allylic Alkylation of 3-Acetoxy-N-(tert-butyloxycarbonyl)-1,2,3,6-tetrahydropyridine - Preparation of Key Intermediates for Natural Product Synthesis (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2515-2521 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Heterocycles ; Palladium ; Alkylations ; Allyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient synthesis of racemic tetrahydropyridine 1 was developed. Pd-catalyzed allylic alkylation of 1 with malonate and dimethylacetoxymalonate as nucleophiles with the phosphanylcarboxylic acid L1 and the dihydrooxazol L2 as ligands, were carried out and gave enantiomeric excesses of up to 98%. Absolute configurations were determined for all compounds described. From the alkylation products (+)- and (-)-2a, and (+)- and (-)-2b a variety of versatile, nonracemic chiral intermediates were prepared.
    Additional Material: 1 Tab.
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  • 19
    Electronic Resource
    Electronic Resource
    Nucleophilic Substitution Reactions with the 3-Borane-1,4,5-trimethylimidazol-2-ylidene Anion. - Unexpected Formation of an Imidazabole Isomer (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 789-793 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Carbenes ; Heterocycles ; Imidazoles ; X-ray structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic carbene 3-borane-1,4,5-trimethylimidazol-2-ylidene anion (1-) reacts with the electrophiles CH3I, (CH3)3SiCl, (CH3)3SnCl, and the bromodiazaboroline 7 to form the 2-substituted imidazoles 4, 5, 6, and 8. With triethylborane, the anionic carbene borane adduct 9- is obtained. An unexpected result was achieved when chlorodimethoxyborane and HBCl2 · S(CH3)2 were used as electrophiles. In both cases only the imidazabole 14a could be isolated. Imidazole 5, the imidazole borane adduct 3a and the imidazabole 14a were characterized by X-ray structure analyses.
    Additional Material: 3 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Carbon=Carbon Hydrogenation of Silicon-Functionalized Silaheterocycles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1095-1102 
    Details
    ISSN: 1434-1948
    Keywords: Silanorbornenes ; Silanorbornanes ; Silicon-functionalized olefins ; Silacyclobutanes ; Hydrogenations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Catalytic hydrogenation of olefins containing functionalized silicon groups affords the saturated products in good yields. Chloro and alkoxy substituents at the silicon atom remain unaffected and, in the case of heterocyclic compounds, the cyclic or bicyclic moieties remain intact. The 2-silanorbornanes 4, 5, and 6 were synthesized from the corresponding 2-silanorbornenes 1, 2, and 3, and organosilanes 13 and 14 possessing the cyclopentyl group, were prepared from the cyclopentenyl-substituted precursors 10 and 12. The 3-vinyl-substituted silacyclobutanes 15, 17, and 18 were also hydrogenated in a simple apparatus with diethyl ether or THF as solvent, and Pd/C as a recoverable catalyst system. A basic organosilicon compound, trichloro(vinyl)silane, is hydrogenated in a nearly quantitative yield to form the saturated trichloro(ethyl)silane; this emphasizes the general applicability of this method.
    Additional Material: 2 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Synthesis of N-Acetylglucosaminyl and Diacetylchitobiosyl Amides of Heterocyclic Carboxylic Acids as Potential Chitinase Inhibitors (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2293-2297 
    Details
    ISSN: 1434-193X
    Keywords: Carboxylic acid amides ; Chitinase ; Chitobiose ; Heterocycles ; Enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(Dimethylamino)oxazoline-4-carboxylic acids 5 were prepared by condensation of binucleophilic amino acids 4and O-ethyl-N,N-dimethylisourea 3. New heterocyclic N-acetylglucosaminyl amides and chitobiosyl amides 8 were obtained by the coupling of tetraacetylglucosamine 6a or heptaacetylchitobiosylamine 6b with acid chlorides of heterocyclic carboxylic acids 2 or 5a and subsequent deacetylation. Based on their substitution patterns, compounds 8were expected to have inhibitory activity towards chitinases. Enzyme assays showed that glycosyl amides 8 indeed were moderate inhibitors of chitinases, the diacetylchitobiosyl amides 8d-f generally having higher inhibitory activities than the N-acetylglucosaminyl amide derivatives 8a-c. Inhibitory activities depended on the chitinase tested.
    Additional Material: 2 Tab.
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  • 22
    Electronic Resource
    Electronic Resource
    2-Substituted 5-Acetyl-4-Thiazolyl Triflates as Useful Building Blocks for the Preparation of Functionalized Thiazoles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3117-3126 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Thiazoles ; Pyrido[3,4-c]thiazoles ; Triflates ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 2-substituted 5-acetyl-4-thiazolyl triflates 2are useful building blocks for the preparation of functionalised thiazoles by means of palladium-catalysed cross-coupling reactions with organometallic reagents and alkoxycarbonylation and deoxygenation reactions. The combination of palladium-catalysed coupling of 2 together with 1-alkynes/6-endo-dig annulation reactions in the presence of ammonia leads to functionalised pyrido[3,4-c]thiazoles in satisfactory yields. The utilisation of uncatalysed displacement reactions of the triflate group represents a very simple method for the synthesis of 4-N-,4-O-, and 4-S-substituted thiazoles.
    Additional Material: 2 Tab.
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  • 23
    Electronic Resource
    Electronic Resource
    Silicon-Oxygen Heterocycles from Thermal, Photochemical, and Transition-Metal-Catalyzed Decomposition of α-(Alkoxysilyl and Alkenyloxysilyl)-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1939-1946 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolysis of (ethoxy)silyl-, (propyloxy)silyl-, and (isopro-pyloxy)silyl-substituted diazoacetates 1a-c leads to tetrahydro-1,2-oxasiloles 2a-c by intramolecular C-H insertion of a carbene intermediate. Photochemical or catalytic decomposition of (allyloxysilyl)diazoacetates 3a-e results in intramolecular cyclopropanation which provides 3-oxa-2-silabicyclo[3.1.0]hexane systems 5a-e. In contrast, the thermal reaction of 3b-d gives rise to 2,5-dihydro-1,2-oxasiloles 4b-d, which are likely to be formed on a pyrazoline rather than a carbene route. For (3-butenyloxysilyl)diazoacetate 3f, all modes of decomposition generate the 3-oxa-2-silabicyclo[4.1.0]heptane system 7. Fluoride-induced cleavage of the bicyclic systems 5b-d provides trans-2-hydroxyalkyl-1-cyclopropanecarboxylates 9 diastereospecifically.
    Additional Material: 1 Tab.
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  • 24
    Electronic Resource
    Electronic Resource
    An Easy Access to 1-Azaspiropentane-2-carboxamides - The First Derivatives of a New Type of Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2017-2024 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Azaspiropentanes ; Heterocycles ; Peptides ; Strained molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azaspiropentanecarboxamides 10 and 12 are formed with remarkable ease in two steps in a one-pot operation from methyl 2-chloro-2-cyclopropylideneacetate (4) by addition of a primary amine in tetrahydrofuran and subsequent treatment with sodium hydride/triethylamine in the presence of another equivalent of a primary amine or ammonia. Achievable yields of the amides 10, 12 were moderate to good (27-59%, 12-48%), while the corresponding esters 9 could only be obtained in poor yields (4-14%). The new α-amino acid amides are surprisingly stable, and they can be incorporated into small peptides as demonstrated with the preparation of the glycine 13e and the spirocyclopro-paneoxazoline derivative 14e.
    Additional Material: 2 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    New Heterocycles from the Reaction between Some Natural α-Amino Acid Hydrazides and Formaldehyde (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2943-2948 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; α-Amino acid phenylhydrazides ; Heterocycles ; Cyclization reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L-tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality.
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  • 26
    Electronic Resource
    Electronic Resource
    Synthesis Mediated by Ring-Closing Metathesis - Applications in the Synthesis of Azasugars and Alkaloids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 959-968 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
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  • 27
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    Electronic Resource
    A New Strategy for the Asymmetric Synthesis of 1,3-Oxathiolane-Based Nucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1455-1458 
    Details
    ISSN: 1434-193X
    Keywords: Nucleoside analogues ; 1,3-Oxathiolanes ; Chiral sulfoxides ; Heterocycles ; Antiviral agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A ready asymmetric synthesis of 3′-oxathionucleosides has been accomplished in three main steps from benzoyloxyethanal. The synthesis is characterized by high overall yield and considerable enantiomeric excesses. It represents a general synthetic path to prepare a wide range of heterosubstituted sulfur-containing nucleoside analogues.
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  • 28
    Electronic Resource
    Electronic Resource
    Novel Stereoelectronic Behavior of Bicyclic Glycosyl Donors: Application to the Synthesis of Both 2-Deoxy-α- and -β-Glycosides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1869-1874 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Heterocycles ; Electrostatic interactions ; Glycosylation ; Glycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pairs of novel stereoisomeric, cyclic glycosyl donors exhibit different behaviors in glycosylation processes. In the pair of α-gluco (1) and β-manno (2), the former exhibits reversability with its glycoside product whereas the latter does not. In the α-gluco (3) and β-manno (4) set, the former undergoes glycosyl transfer via an isolable intermediate whereas the latter does not. The differing anomeric effects exerted in the ground states are proposed as the force which explains the differences in behavior.
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  • 29
    Electronic Resource
    Electronic Resource
    Synthesis of the Enantiomers of 2-sec-Butyl-4,5-dihydrothiazole and (1R,5S,7R)-3,4-Dehydro-exo-brevicomin, Pheromone Components of the Male Mouse, Mus musculus (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2167-2173 
    Details
    ISSN: 1434-193X
    Keywords: Acetals ; Heterocycles ; Mouse ; Mus musculus/ Pheromones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two components [2-sec-butyl-4,5-dihydrothiazole (1) and 3,4-dehydro-exo-brevicomin (2)] of a male-produced pheromone of the mouse Musmusculus have been synthesized in optically active forms. The enantiomers of 1 were obtained with an enantiomeric purity of ca. 92% ee and were found to be readily racemizable. Asymmetric dihydroxylation was employed as the key reaction (15→16) allowing the preparation of (1R,5S,7R)-2 with ca. 94% ee.
    Additional Material: 1 Tab.
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  • 30
    Electronic Resource
    Electronic Resource
    Umpolung of Reactivity of Lithium Trimethylsilyldiazomethane at the C-5 Position of 6-Substituted Uracil Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2751-2755 
    Details
    ISSN: 1434-193X
    Keywords: Lithium ; Lithium trimethylsilyldiazomethane ; Heterocycles ; Uracil derivatives ; Pyrazolo[4,3-d]pyrimidindiones ; Pyrazolo[4,3-d]pyrimidindiones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic addition of TMSC(Li)N2 at the low reactive C-5 position of the uracil ring of C-6 substituted uracil derivatives is reported. The ratio of C-5 versus C-6 nucleophilic addition of TMSC(Li)N2 dramatically depends on the stereoelectronic properties of the C-6 substituent. In particular, substituents characterized both by sterically bulky and/or electron-withdrawing (EWG) effects appear to direct the nucleophile mainly (methyl, chloromethyl or halogen) or completely (isopropyl) toward the C-5 position. The fine-tuned substituent selectivity found in the nucleophilic addition of TMSC(Li)N2 to C-6 substituted uracils plays a leading role in the synthesis of new trimethylsilyl-1H-[4,3-d]pyrimidin-5,7-dione derivatives, which can in turn be easily modified through known silicon chemistry.
    Additional Material: 1 Ill.
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  • 31
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    Electronic Resource
    Synthesis and Structure of Gallium/Silicon Heterocycles with a Ga2Si2 and a Ga3Si Framework⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 745-749 
    Details
    ISSN: 1434-1948
    Keywords: Gallium ; Silicon ; Heterocycles ; Main group elements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Ga2X4· 2 dioxane with four equivalents of (Me3Si)3SiLi(thf)3 (= hypersilyllithium) affords for X = Br a 1,3,2,4-disiladigalletane together with tetrahedral hypersilylgallium(I). For X = Cl an anionic 1,2,3,4-silatrigalletanate, a four-membered heterocycle with a Ga3 unit, is isolated. These primary examples of gallium/group-14 heterocycles have been investigated by NMR spectroscopy as well as by X-ray single-crystal structure analysis. In addition, the synthesis and structure of bis(hypersilyl)gallium chloride is described. This monomeric molecule has a nearly T-shaped Si2GaCl framework.
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  • 32
    Electronic Resource
    Electronic Resource
    2,3-Dihydroimidazol-2-ylidene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1517-1520 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic carbenes ; Heterocycles ; Decarboxylation ; Photochemistry ; Matrix isolation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of imidazole-2-carboxylic acid (3) - matrix-isolated in argon at 10 K - with a wavelength of 254 nm leads to decarboxylation and the formation of a complex between 2,3-dihydroimidazol-2-ylidene and carbon dioxide (1·CO2). Upon irradiation of 2,3-dihydroimidazol-2-ylidene (1) with λ = 254, 193, and 185 nm no imidazole can be detected. On the other hand flash vacuum pyrolysis of imidazole-2-carboxylic acid (3) produces imidazole and carbon dioxide. 2,3-Dihydroimidazol-2-ylidene (1) - the possible intermediate - cannot be trapped under these conditions.
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  • 33
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    Electronic Resource
    Kinetics of the [2+ + 4]-Cycloaddition Reactions of 1,3-Dithian-2-ylium Ions with 1,3-Dienes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1919-1922 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbocations ; Dienes ; Cycloadditions ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the [2+ + 4] cycloadditions of 1,3-dithian-2-ylium ions (1) with 1,3-dienes was investigated photometrically in dichloromethane. The second-order rate constants determined for the reactions of 1 with 2,3-dimethyl-1,3-butadiene (2a) and isoprene (2b) were identical to those calculated for the first step of a stepwise cycloaddition pathway by the correlation lg k = s (E + N). Though a concerted cycloaddition pathway is not excluded by this finding, it is obvious that the transition states of these reactions are not noticeably stabilized by the simultaneous formation of two new σ bonds.
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  • 34
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    Electronic Resource
    A General Route to the Monomeric Subunits of the Macrotetrolides - A Short Synthesis of Methyl Nonactate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2073-2078 
    Details
    ISSN: 1434-193X
    Keywords: Sultones ; Intramolecular Diels-Alder reaction ; Desulfurization ; Heterocycles ; Actic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A highly stereoselective and flexible sultone route to actic acids, the monomeric subunits of the macrotetrolides, has been developed and exemplified for nonactic acid (2a). Due to the extensive application of tandem transformations, only six steps were needed to secure methyl nonactate (20) from furan.
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  • 35
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    Preparation, Structure and Reactivity of 2-Chloro-, 2-Fluoro- and 2-Iodo-2,3-dihydro-1H-1,3,2-diazaboroles (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1145-1152 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Halogens ; Isocyanides ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of differently substituted 2-chloro-, 2-fluoro- and 2-iodo-2,3-dihydro-1H-1,3,2-diazaboroles have been prepared by various methods. 1,3-Di-tert-butyl-2-fluoro-2,3-dihydro-1H-1,3,2-diazaborole (3a), 1,3-di-tert-butyl-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5a), 1,3-bis(2,6-dimethyl-phenyl)-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5b), 2-chloro-4,5-dimethyl-1,3-dineopentyl-2,3-dihydro-1H-1,3,2-diazaborole (5c), and 1,3-di-tert-butyl-2-iodo-2,3-dihydro-1H-1,3,2-diazaborole (6a) were formed from the corresponding lithiated Z-1,2-diaminoethenes, by treatment with BF3·OEt2, BCl3, or BI3 in n-hexane. Compounds 3a, 5a, and 5b are also available by sodium amalgam reduction of the adduct (tBu)(BF3)N=CH-CH=N(BF3)(tBu) (2a), and the borolium salts [RNa=CH-CH=Nb(R)BCl2]X (Na-B) (4a: R = tBu, X = BCl4 and 4b: R = 2,6-Me2C6H2, X = Cl) respectively. The iodo derivative (2,6-Me2C6H2)-Na-CH=CH-Nb(2,6-Me2C6H2)BI (Na-B) (6b) was synthesized in a redox reaction between the 1,4-diazabutadiene 1b and BI3. The novel compounds were characterized by 1H-, 11B- and 13C-NMR spectroscopy, as well as by an X-ray structure analysis of 6b.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1998/98047_s.pdf or from the author.
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  • 36
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    Electronic Resource
    New P,N-Chelate Ligands Based on Pyridyl-Substituted Phosphaferrocenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    Details
    ISSN: 1434-1948
    Keywords: Chelates ; P,N ligands ; Phosphaferrocene ; Catalysis ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new pyridyl-substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α-picoline to 2-formyl-3,4-dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N-chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru-bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P-coordinated phospha-ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven-membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X-ray diffraction. The ligands 3 and 6 were tested in the palladium-catalyzed asymmetric alkylation of 1,3-diphenylallyl acetate.
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  • 37
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    Electronic Resource
    Isoelectronic Arduengo-Type Carbene Analogues with the Group IIIa Elements Boron, Aluminum, Gallium, and Indium (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 305-310 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carbene homologues ; Boron ; Isoelectronic analogues ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While Arduengo-type carbenes are now well established for the Group IVa elements carbon, silicon and germanium, they are experimentally unknown for the isoelectronic anions with the Group IIIa elements boron, aluminum, gallium, and indium. In the present quantum chemical investigations, the bonding features of this class of compounds are explored. As a result, they are predicted to be stable species with sizeable singlet-triplet energy separations and electron affinities. Hence, they may be considered as valid targets for experimental investigations. An analysis of the electron density distribution in the case of boron and aluminum reveals a strongly polar B-N bond for the former, and a half Al-N bond with positive charge at the aluminum, emphasizing the donor-acceptor formulation for the latter.
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  • 38
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    Electronic Resource
    On the Homoconjugation of Two Acceptor Groups (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1615-1623 
    Details
    ISSN: 1434-193X
    Keywords: Homoconjugation ; Cyclovoltammetry ; ESR spectroscopy ; Diketones ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclovoltammetric investigations have been carried out on 3,3,6,6-tetramethylcyclohexane-1,2,4,5-tetrone (4), bicyclo-[3.2.2]nonane-6,7,8,9-tetrone (5), and several of their congeners, such as 6,13-dihydro-6,6,13,13-tetramethylquin-oxalino[2.3-b]phenazine (13), 5,10-dihydro-5,5,10,10-tetra-methylpyrazino[2,3-g]quinoxaline (17), and 6,13-dihydro-6,13-propanoquinoxalino[2,3-b]phenazine (20). For 5 and 20 a large difference (ΔE° ≥400 mV) between the first and second reduction potentials was found. The ESR results of the radical anion 20•- are in support of a strong homoconjugation. ESR studies of 4•-, 13•-, and 17•- also reveal a symmetrical displacement of the unpaired electron over both acceptor groups on the ESR time scale which, however, based on the small potential difference ΔE° ≤ 200 mV can be most likely described to a fast electron exchange.
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  • 39
    Electronic Resource
    Electronic Resource
    2-(Het)aryl-Substituted 7-Azabicyclo[2.2.1]heptane Systems (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1997-2001 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Acetylcholine receptor ; Palladium ; C-C coupling ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epibatidine (1) is a recently discovered trace alkaloid found in the skin of a Latin-American poisonous frog. Its remarkably high analgetic activity is accompanied by high toxicity. Therefore, in order to tune its biological activity, a convergent and efficient synthetic pathway was sought to synthesize epibatidine derivatives with different (het)aryl substituents. The hydro(het)arylation of the key intermediate 7-azabicycloheptene (10) represents such an approach. The synthesis of 10 by a Diels-Alder reaction of an N-activated pyrrole (7) with ethynyl p-tolyl sulfone (6) and subsequent steps has been optimized. The crucial last step, the reductive cleavage of the vinyl sulfone 9, has been replaced by a high-yield fluoride-induced degradation of the β-silylated sulfone 12 to give 10. A number of structurally different racemic epibatidine analogs (16b-e) can be prepared by palladium-catalyzed hydro(het)arylation of 10 with iodo(het)arenes 15b-e in good yields.
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  • 40
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    Electronic Resource
    Borane-Substituted Imidazol-2-ylidenes: Syntheses, Structures, and Reactivity⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 843-849 
    Details
    ISSN: 1434-1948
    Keywords: Boranes ; Carbenes ; Carbene complexes ; Heterocycles ; Imidazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of the Lewis acids BH3 and BEt3 with trimethylimidazole (1) lead to the borane adducts 2a and 2b. Deprotonation of 2a with n-butyllithium results in the formation of the novel N-borane-substituted imidazol-2-ylidene anion 3a- whereas deprotonated 2b rearranges unexpectedly to the anionic compound 3b-. This can be transformed into the carbene-borane adduct 4 by methylation. The reaction of 3a- with [Mn(CO)5Br] yields the carbene complex 5. Surprisingly, 3a- attacks Fe(CO)5 at a carbon atom which leads to the iron acyl complex anion 6-. The compositions of the products follow from spectroscopic and analytical data and from X-ray structure analyses for Li(thp)+3a-, Li(thf)2+3b- and Li(thp)3+6-.
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  • 41
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    Electronic Resource
    The Synthesis of Perylenebisimide Monocarboxylic Acids (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 847-851 
    Details
    ISSN: 1434-193X
    Keywords: Fluorescent dyes ; Perylenes ; Heterocycles ; Carboxylic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and properties of perylene-bisimides 4 with one carboxylic acid anchor group are described. The properties of 4 are strongly influenced by the spacer between the carboxylic acid group and the imide moeity. Dyes with aliphatic (4d-4g) and aromatic (4a-4c) spacers have been prepared.
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  • 42
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    Electronic Resource
    Alkoxycarbonylcarbene Transfer to Semicyclic Enaminones - A Route to Cyclopenta[b]pyrrole and Indole Ring Systems (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1177-1187 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Heterocycles ; Enaminones ; Indoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper-catalyzed decomposition of alkyl diazoacetates in the presence of semicyclic enaminones 1a-o leads primarily to enamino esters 2 which constitute formal products of C-C insertion of the carbene unit. In the case of N-methyl (1a-e) and N-benzyl (1f-i) enaminones, 2a-i are accompanied by 2,3,5,6-tetrahydroindoles 3a-i, in which two carbene moieties are incorporated. At 250 °C, compounds 2b-e, which could not be isolated in pure form, undergo cyclocondensation to form 1,2,3,5-tetrahydrocyclopenta-[b]pyrroles 4b-e. In contrast, 2f-i can be isolated as Z,E mixtures and are transformed thermally into 4f-i only in the presence of silica gel. Carbene transfer to N-phenyl enaminones 1j-m and N-methyl enamino esters 1n,o leads only to the 1:1 adducts, enamino esters 2j-o, which do not undergo the cyclocondensation reaction under the previous conditions. Dehydrogenation of tetrahydroindoles 3c-e with tetrachloro-p-benzoquinone can be controlled to give either 1,2-dihydroindole-6,7-dicarboxylates 5 or indole-6,7-dicarboxylates 6.
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  • 43
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    Electronic Resource
    Generation of 6,7-Dihydro-5H-1,3,4-thiadiazolo[3,2-a]pyridines  -  Unexpected Products in the Reaction of 5-Ethylthio-1,3,4-thiadiazole-2-amine and 3-(Dimethylamino)propiophenones (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1201-1203 
    Details
    ISSN: 1434-193X
    Keywords: 1,3,4-Thiadiazoles ; Pyridines ; Cyclizations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of 6,8-diaroyl-6,7-dihydro-5H-1,3,4-thiadiazolo[3,2-a]pyridines 4a-e was prepared by the reaction of 5-ethylthio-1,3,4-thiadiazole-2-amine (1) and p-substituted 3-(dimethylamino)propiophenones 2a-e in pyridine. The unexpected cyclization process was established by NMR and X-ray diffraction measurements.
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  • 44
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    Electronic Resource
    Synthesis of Hetaryl Glycosides and Their Glycosyl Donor Properties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Substitution ; Carbohydrates ; Anomeric O-hetarylation ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomeric O-hetarylation of tetra-O-benzyl- and tetra-O-acetylglucose (1a, b) can be directly performed with electron-deficient heteroaromatic/heterocyclic systems 2-14, which contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-trifluoropyrimidine (16), can be employed for successive anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O- and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even be advantageous.
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  • 45
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    Electronic Resource
    2-Chloro-1,4-benzodithiin 1,1,4,4-Tetraoxide - A Conjunctive Dienophile for the Preparation of Tetrasubstituted Polycyclic Olefins (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2775-2784 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Cycloadditions ; Diatomic carbon ; Sulfones ; Alkenes ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Chloro-1,4-benzodithiin 1,1,4,4-tetraoxide 11 is a reactive dienophile that forms Diels-Alder adducts with a number of dienes. Adducts 17a-j undergo facile dehydrochlorination to give 2,3-substituted 1,4-benzodithiin tetraoxides 18a-j, which react further with another molecule of diene (the same or a different one) affording the “double” adducts 19-23. Upon reductive desulfonylation with sodium amalgam, the latter are transformed to tetrasubstituted polycyclic olefins 24-27. These olefins correspond to the cycloadducts that would theoretically have been formed by the cycloaddition of diatomic carbon with two molecules of diene, reacting in a Diels-Alder fashion.
    Additional Material: 4 Ill.
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  • 46
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    Electronic Resource
    Isoquinolinium N-Arylimides and Some Cycloadditions to Heterocumulenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 379-385 
    Details
    ISSN: 1434-193X
    Keywords: Isoquinolinium N-arylimides ; Azomethine imines ; Cycloadditions ; Heterocycles ; 1,3-Dipoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The red isoquinolinium N-arylimides 19-23 are azomethine imines of which the C=N bond is part of an aromatic ring. The N-(4-nitrophenyl)imide 22 and the N-(2-pyridyl)imide 23 were obtained crystalline; in solution the latter equilibrates with the hexahydrotetrazine 24 as its dimer. The N-phenylimide 19 is not stable; an isolated solid appears to be a tetramer. Generated by deprotonation of 11-13, the N-arylimides 19-21 undergo in situ cycloadditions to carbon disulfide, phenyl isocyanate, phenyl isothiocyanate, and diphenylketene. The storable CS2 adduct 29 offers a neutral source of theN-phenylimide 19, since a cycloreversion equilibrium is established in solution.
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  • 47
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    Electronic Resource
    Cycloaddition-Elimination Reactions of 5-Imino-1,2,4-thiadiazolidin-3-ones and 5-Imino-1,2,4-dithiazolidin-3-ones with Electron-Rich Double Bonds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 515-520 
    Details
    ISSN: 1434-193X
    Keywords: Cycloaddition ; Elimination ; Heterocycles ; 1,2,4-Thiadiazolidines ; 1,2,4-Dithiazolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Imino-1,2,4-thiadiazolidin-3-ones 1 react with compounds containing electron-rich double bonds such as enamines and ester enolates to afford the 2-iminothiazolidines 3, 4, and 10 in cycloaddition-elimination reactions. The less reactive 5-imino-1,2,4-dithiazolidin-3-ones 2 only give the 2-iminothiazolidines 3 or 4 with enamines; with ester enolates the 5-alkylidene-1,2,4-dithiazolidines 12 are formed. The reaction products with enamines undergo hydrolysis and elimination to form the corresponding hydroxy compounds 5, 6 or the unsaturated compounds 7, 8, depending on the size of the fused ring.
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  • 48
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    Electronic Resource
    Synthesis of Stegobiol and Its Oxidation to Stegobinone, the Components of the Female-Produced Sex Pheromone of the Drugstore Beetle (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1135-1141 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Lipases ; Oxidations ; Pheromones ; Stegobinone ; Stegobium paniceum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystalline (-)-stegobinone [(2S,3R,1′R)]-2,3-dihydro-2,3,5-trimethyl-6-(1′-methyl-2′-oxobutyl)-4H-pyran-4-one (1)], the major component of the female-produced sex pheromone of the drugstore beetle (Stegobium paniceum L.), was synthesized by oxidation of crystalline and the minor component (-)-stegobiol [(2S,3R,1′S,2′S)-2,3-dihydro-2,3,5-trimethyl-6-(2′-hydroxy-1′-methylbutyl)-4H-pyran-4-one (2)] under the appropriate conditions using Jones's chromic acid, Dess-Martin's periodinane or Ley's ruthenium reagent. The latter (2) was synthesized by employing lipase and the Sharpless epoxidation for the introduction of the proper chiral centers. The streostructure of 1 was comfirmed by X-ray analysis.
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  • 49
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    Electronic Resource
    Thermal Isomerization of 1,3-Dipolar Cycloadducts of 3,4-Dihydro-β-carboline 2-Oxide (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1391-1395 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Nitrones ; 1,3-Dipolar cycloadditions ; β-Carbolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal isomerization of the 1,3-dipolar cycloadducts of 3,4-dihydro-β-carboline 2-oxide is studied using 1H-NMR spectroscopy. Stereoisomerizations of the cis or syn cycloadducts with dipolarophiles such as methyl crotonate, methyl cinnamate, and methyl methacrylate into the trans or anti cycloadducts are observed. On the other hand, regioisomerization of the 1-substituted cycloadduct with nitroethylene into the 2-substituted cycloadduct is also observed.
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  • 50
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    Electronic Resource
    Selective Bromination of 4,5-Dimethylthiazole with N-Bromosuccinimide (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 593-594 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; NBS bromination ; Selective bromination ; Polybrominated thiazole ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical bromination of 4,5-dimethylthiazole (1) was carried out using different stoichiometries of N-bromosuccinimide in the presence of 2,2′-azobisisobutyronitrile. Mono-, tri- and tetrabromo compounds 2, 5, and 6 were obtained in good yields with regioselectivity while the dibromo derivatives 3 and 4 were formed without any selectivity. Substitution at the thiazole ring occurred in the presence of silica gel or in the perfluoro ether FC-77 (C8F16O), affording the 2-bromothiazole 7. The order of reactivity observed was 5-Me 〉 4-Me 〉 C-2. Structural assignment of compounds 2-7 was made by chemical correlations and NMR spectroscopy.
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  • 51
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    Reaction of Ambident Dianions with Oxalic Acid Dielectrophiles - Effect of the Heteroatoms of the Dinucleophile on the Regiochemistry of Cyclization (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1467-1470 
    Details
    ISSN: 1434-193X
    Keywords: Ambident dianions ; Regioselectivity ; Heterocycles ; C-C coupling ; Oxalyl dielectrophiles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Y-Shaped ambident dianions 1-6 were reacted with dielectrophilic oxalic acid-bis(imidoyl)dichlorides 7 providing a convenient access to novel N-heterocycles 8-13 containing a heteroanalogous oxalic acid unit. The cyclization reactions generally proceeded with good regioselectivity which is controlled by the heteroatoms of the dianion reagents.
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  • 52
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    The First 1,10-Diaza[2.2]metacyclophanes - Strained Medium Membered Heterocycles⋆ (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1471-1477 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Dilution principle ; Heterocycles ; Medium membered rings ; Ring strain ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-protected 1,10-diaza[2.2]metacyclo- and 1,10-diaza-[2]metacyclo[2](2,6)-pyridinophanes 4 and 5 have been synthesized for the first time using high dilution conditions. The free secondary diamine 7 was obtained from 4 by alkaline hydrolysis. - Quantum chemical calculations support the hypothesis that 7 is one of the most strained anti-hetera[2.2]metacyclophanes known. This is also evident from the 1H-NMR spectrum of 7, which shows one of the strongest high field shifts for the intraannular protons in comparison to other anti-[2.2]metacyclophanes.
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  • 53
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    Unprecedented 1,3-Dipolar Cycloaddition of Azomethine Ylides Derived from Difluorocarbene and Imines to Carbonyl Compounds. - Synthesis of Oxazolidine Derivatives (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 133-137 
    Details
    ISSN: 1434-193X
    Keywords: Azomethine ylides ; Difluorocarbene ; Cycloadditions ; Heterocycles ; Oxazolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iminiodifluoromethanides generated by the reaction of difluorocarbene with benzaldehyde and benzophenone imines undergo regioselective 1,3-dipolar cycloaddition to aldehydes to give oxazolidine derivatives.
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  • 54
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    Total Synthesis of TAN-1057 A/B, a New Dipeptide Antibiotic from Flexibacter sp. PK-74 (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 777-783 
    Details
    ISSN: 1434-193X
    Keywords: Antibiotics ; Dipeptides ; Heterocycles ; β-Amino acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: TAN-1057 (1a, b) - a new natural dipeptide antibiotic active against methicillin resistant strains of Staphylococcus aureus - was synthesized starting from Nα, Nδ, Nω-tri-Z-L-arginine 20b via the corresponding diazoketone 21b. This upon photolysis rearranged to the ketene which was trapped by (±)-2,4,5,6-tetrahydro-5-methylamino-2-ureidopyrimidin-4-one (3) to yield the fully protected dipeptide 23 (30%). The latter was deprotected by hydrogenolysis to give the final compound as a mixture of two epimers - TAN-1057A, B - isolated previously from a strain of Flexibacter sp. PK-74. The intermediate 3 was prepared from 3-amino-2-(N-Z-N-methylamino)propionic acid methyl ester hydrochloride (16) and 2-methyl-2-thiopseudobiuret hydroiodide (18) in one step in 35% yield.
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  • 55
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    Kinetics of liquid phase synthesis of tert-amyl methyl ether from tert-amyl alcohol and methanol catalyzed by ion exchange resin (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 137-143 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of tert-amyl methyl ether (TAME) from methanol (MeOH) and tert-amyl alcohol (TAA) in the liquid phase was studied by using an ion exchange resin, Amberlyst15 (A15) in the H+ form. Experiments were carried out in a stirred batch reactor under atmospheric pressure. The effects of catalyst size, agitation speed, temperatures, feed ratio and water on the reaction rate were investigated. Both of intraparticle and external diffusion effects could be neglected in this system. The dehydration of TAA could be decreased by increasing the ratio of MeOH/TAA and the reaction rates were greatly inhibited by water.A kinetic model which considered the inhibition of water was proposed. The experimental results agreed well with the model. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 137-143, 1998.
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    Proton transfer involving nucleic acids: A temperature-jump study of the systems sulphonephthaleins-double stranded poly(A) and sulphonephthaleins-double stranded poly(C) (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 161-169 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of proton transfer between poly(A - AH) (partially protonated double-stranded polyadenylic acid) and CPR (chlorophenol red), and between poly(C - H - C) (partially protonated double-stranded polycytidylic acid) and the indicators CPR, BCP (bromocresol purple), and BCG (bromocresol green) have been investigated at 25°C and ionic strength 0.1 M (NaClO4) by the temperature-jump method. The acidic proton of poly(C - H - C) is engaged in a hydrogen bond (N3H+----N3) which is believed to contribute to stabilizing the double-strand conformation, whereas the acidic proton of poly(A - A - H) does not form hydrogen bonds. The analysis of the dependence of the relaxation times on the concentrations of the reactants has enabled the evaluation of the rate constants for the direct proton transfer and for the protolysis paths. The rate constants for proton recombination with the deprotonated forms of the polynucleotides and the indicators are of the order of magnitude expected for diffusion controlled processes involving oppositely charged ions (k2=(0.2-1.6)×1010 M-1s-1). The direct proton transfer from poly(C - H - C) to BCG is thermodynamically disfavored and its rate constant, k1, is lower than k2 by about three orders of magnitude. The (thermodynamically favored) proton transfers from poly(A - A - H) to CPR and from poly(C - H - C) to CPR and BCP are characterized by similar values of k1. This result indicates that the hydrogen bonds in poly(C - H - C) are very weak and suggests that the stabilization of the double-stranded conformation of this polynucleotide could be ascribed to the large number of hydrogen bonds rather than to their specific strength. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 161-169, 1998.
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    A dual-phase oscillatory behavior in Belousov-Zhabotinsky system with vanillin as the substrate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 201-206 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dual-phase oscillations are observed in Belousov-Zhabotinsky system with 4-hydroxy-3-methoxybenzaldehyde (vanillin) as the substrate and manganous sulphate or ammonium Ce(IV) sulphate as the catalyst. The nonoscillatory period of time between the two phases decreases with increase in the concentration of the catalyst and the substrate. Under uncatalyzed and ferroin catalyzed conditions the system exhibits single-phase oscillations. The first-phase oscillations are due to vanillin whereas the second-phase oscillations are brought about by 4-hydroxy-3-methoxybenzoic acid (vanillic acid) formed during the course of the first-phase reactions. The reactions are explained with relevant steps of the FKN mechanism. © 1998 John Wiley & Sons, Inc. Int J. Chem. Kinet 30: 201-206, 1998.
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    A wide range modeling study of dimethyl ether oxidation (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 229-241 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at 1 and 10 atm, 0.2≤φ≤2.5, and 800≤T≤1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, φ=1.0 and 650≤T≤1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates, and products pertinent to the oxidation of DME. These data test the kinetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock-tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g., the primary reference fuels, n-heptane and iso-octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 229-241, 1998.
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    Micellar effect upon the reaction of hydroxide ion with coumarin (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 273-276 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cationic micelles of cetyltrimethylammonium bromide, CTABr, speed attack of hydroxide ion upon coumarin by a factor of c.a-2, due to a concentration effect. The first-order rate constants, kobs, at a given hydroxide ions concentration go through maxima with increasing surfactant concentration. The overall micellar effects in these cationic micelles can be treated in terms of the pseudo-phase ion exchange model. Analysis of the data shows that second-order rate constant at the micellar surface is smaller than the second-order rate constant in water. Anionic micelles of sodium dodecyi sulfate, SDS, inhibit the same reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 273-276, 1998.
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    Kinetics and mechanism of the oxidation of diols by pyridinium bromochromate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 285-290 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: kobs=a+b[H+]. The oxidation of [1,1,2,2-2H4]ethanediol exhibited a primary kinetic isotope effect (kH/k D=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 285-290, 1998.
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    Fast and reliable numerical methods to simulate complex chemical kinetic mechanisms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 349-358 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Models that simulate atmospheric photochemistry require the use of a stiff ordinary differential equations (ODEs) solver. Since the simulation of the chemical transformations taking place in the system takes up to 80 percent of the CPU time, the numerical solver must be computationally fast. Also, the residual error from the solver must be small. Because most accurate solvers are relatively slow, modelers continue to search for timely, yet accurate integration methods. Over the past years an extensive number of articles have been dedicated to this subject. One of the highly debated questions is whether one should construct specialized algorithms or instead use general methods for stiff ODEs. In the present article we use the second alternative. We apply three linearly (semi-)implicit methods from the classical stiff ODE literature which we modified to implement the sparse routines to solve the system of equations describing a complex kinetic mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 349-358, 1998
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    Hydrogen autoignition at pressures above the second explosion limit (0.6-4.0 MPa) (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 385-406 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The investigation of high-pressure autoignition of combustible mixtures is of importance in providing both practical information in the design of combustion systems and fundamental measurements to verify and develop chemical kinetic models. The autoignition characteristics of hydrogen-oxygen mixtures at low pressures have been explored extensively, whereas few measurements have been made at high pressures. The present measurements extend the range of pressures up to 4 MPa, where few measurements have yet been reported.Using a rapid compression machine equipped with a specially designed piston head, hydrogen autoignition pressure traces were measured at pressures above the second explosion limit (p=0.6-4 MPa, T=950-1050 K). The measured pressure records show a more gradual pressure increase during induction time in this regime than in the low-pressure regime, indicating that the energy release becomes significant at conditions over the second explosion limit.By comparing the measurements and a thermodynamic model which incorporates the heat transfer and energy release, a modified reaction rate constant for H2O2+H=HO2+H2, one of the most important reactions for hydrogen oxidation at high pressure, and the reaction with the largest uncertainty, is suggested in this work as k17=2.3 . 1013exp(-4000/T) cm3/mol-s. The modeled pressure history with the modified reaction rate agrees well with the measured values during the induction period over the range of conditions tested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 385-406, 1998
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    Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part II. Pyrolysis in pyrex reactors packed with platinum foils or PbO-treated pyrex rods (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 439-450 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isobutane pyrolysis has been studied at 20-200 torr initial pressures and 773-793 K, in a packed reactor treated with PbO and in a reactor packed with platinum foils. These packings strongly inhibit product formation and this effect is explained by the occurrence of the heterogeneous termination step:\documentclass{article}\pagestyle{empty}\begin{document}$ \rm H\cdot\mathrel{\mathop{\relbar\joinrel\longrightarrow}^{walls}} product $\end{document}at the reactor walls. The reaction has been modeled in the temperature and pressure range on the basis of a kinetic scheme which has been proposed for the homogeneous reaction and step (w) with the following values of kw:$$\eqalign{(k_{_{w}})_{_{\rm{PbO}}}&=3.7\ 10^{8}\ \rm{exp} \left[-{9000\over \rm{T}}\right]\rm{S}^{-1}\cr(k_{_{w}})_{_{\rm{Pt}}}&=15000\ \rm{S}^{-1}\ \rm{at\ any\ temperature}\cr}$$for both types of packing. The corresponding sticking coefficients of hydrogen atoms are:$$\eqalign{\gamma _{_{\rm{PbO}}} &=160\ \rm{exp} \left[-{9000\over \rm{T}}\right]\cr\gamma _{_{\rm{Pt}}} &=0.03\cr}$$© 1998 John Wiley & Sons, Inc. Int J Chem. Kinet 30: 439-450,1998
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    Rate constants for the gas-phase reactions of selected dibasic esters with the OH radical (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 471-474 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with the dibasic esters dimethyl succinate [CH3OC(O)CH2CH2C(O)OCH3], dimethyl glutarate [CH3OC(O)CH2CH2CH2C(O)OCH3], and dimethyl adipate [CH3OC(O)CH2CH2CH2CH2C(O)OCH3] at 298±3 K. The rate constants obtained were (in units of 10-12 cm3 molecule-1 s-1): dimethyl succinate, 1.4±0.6; dimethyl glutarate, 3.3±1.1; and dimethyl adipate, 8.4±2.5, where the indicated errors include the estimated overall uncertainty of ±25% in the rate constant for cyclohexane, the reference compound. The calculated tropospheric lifetimes of these dibasic esters due to gas-phase reaction with the OH radical range from 1.4 days for dimethyl adipate to 8.3 days for dimethyl succinate for a 24 h average OH radical concentration of 1.0×106 molecule cm-3. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 471-474, 1998
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    Kinetics and modeling of the thermal reaction of propene at 800 K. Part iii. Propene in the presence of small amounts of oxygen (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 503-522 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal reaction of propene was examined around 800 K in the presence of less than 20% oxygen. At initial time, the production of H2, CH4, C2H4, C2H6, allene, C3H8, 1,3-butadiene, butenes, 3- and 4-methylcyclopentene, a mixture of 1,4- and 1,5-hexadienes, methylcyclopentane (or dimethylcyclobutane), 4-methylpent-1-ene, and hex-1-ene, was observed along with hydrogen peroxide, CO, and small quantities of ethanal and CO2. Oxygen increases the initial production of hydrogen and of most hydrocarbons and, particularly, that of C6 dienes and of cyclenes. However, the production of allene, methylcyclopentane (or dimethylcyclobutane), and 4-methylpent-1-ene is practically not affected. A kinetic study confirms the mechanism proposed for the thermal reaction of propene. Formation of allene, thus, involves a four-center-unimolecular dehydrogenation of propene, that of 4-methylpent-1-ene is explained by an ene bimolecular reaction while methylcyclopentane (or dimethylcyclobutane) probably arises from a bimolecular process involving a biradical intermediate. Other products arise from a conventional chain radical mechanism.A kinetic scheme is proposed in which chains are primarily initiated by the bimolecular step:C3H6+O2→HO2·+C3H5·which competes with the second-order initiation of propene pyrolysis. Since allene production is not affected by oxygen, it is concluded that allyl radicals are not dehydrogenated by oxygen; but they oxidize in a branching step involving allylperoxyl radicals; r. radicals other than methyl, and allyl are dehydrogenated according to the conventional process:r·+O2→unsaturated+HO2·and account for the production of a large excess of C6 diolefins, methylcyclopentenes, and hydrogen peroxide, when r. stands for C6H11, the allyl adduct. Hydrogen peroxide gives rise to a degenerate branching of chains. Based on the proposed scheme, a modeling of the reaction is shown to account fairly well for the concentration-time profiles. Rate constants of many steps are evaluated and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 503-522, 1998
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    Branching ratios for BrO production from reactions of O(1D) with HBr, CF3Br, CH3Br, CF2ClBr, and CF2HBr (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 555-563 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Laser-flash photolysis of RBr/O3/SF6/He mixtures at 248 nm has been coupled with BrO detection by time-resolved UV absorption spectroscopy to measure BrO product yields from O(1D) reactions with HBr, CF3Br, CH3Br, CF2ClBr, and CF2HBr at 298±3 K. The measured yields are: HBr, 0.20±0.04; CF3Br, 0.49±0.07; CH3Br, 0.44±0.05; CF2ClBr, 0.31±0.06; and CF2HBr, 0.39±0.07 (uncertainties are 2σ and include estimates of both random and systematic errors). The results are discussed in light of other available information or O(1D)+RBr reactions. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 555-563, 1998
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    Determination of the rate constants for the gas-phase reactions of methyl butenol with OH radicals, ozone, NO3 radicals, and Cl atoms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 589-594 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO3 radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: kOH=(3.9±1.2)×10-11 cm3 molecule-1 s-1, kO3=(8.6±2.9)×10-18 cm3 molecule-1 s-1, kNO3=(8.6±2.9)×10-15 cm3 molecule-1 s-1, and kCl=(4.7±1.0)×10-10 cm3 molecule-1 s-1. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O3, NO3, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589-594, 1998
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    Kinetic stability of 1,1,1-Trifluoroethane (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 621-628 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,1,1-Trifluoroethane has been decomposed in comparative rate single-pulse shock-tube experiments. The rate expression for elimination at ca. 2.5 bar and in the temperature range of 1050 to 1200 K has been found to be\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=7.0\times 10^{14}\ exp(-37260/T)s^{-1} $\end{document}The experimental conditions appear to be such that the unimolecular reaction is at the beginning of the fall-off region and we find that for step sizes down between 500 and 1000 cm-1 the high-pressure rate expression is in the range\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=2.0\times 10^{15}\ exp(-38300/T)\ to\ 4\ \times\ 10^{15}\ exp(-39000/T)s^{-1} $\end{document}where the smaller rate parameters refer to the larger step size down. The results are compared with those from an earlier study and the anomalously high A-factor is noted. It is suggested that the existing rate expressions for the fluorinated ethanes may need to be reevaluated. © 1998 John Wiley & Sons, Inc., Int J Chem Kinet: 30: 621-628, 1998
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    Rate constant for the gas-phase reaction of hydroxyl radical with the natural hydrocarbon bornyl acetate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 497-502 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase reaction of bornyl acetate (bicyclo[2,2,1]-heptan-2-ol-1,7,7-trimethyl-acetate) with hydroxyl radical has been studied. A relative method was used to determine the rate constant for this reaction, with n-octane as reference compound.Methyl nitrite photolysis experiments were carried out in an environmental smog chamber at atmospheric pressure and (294±2) K. The rate constant determined for bornyl acetate is k=(13.9±2.2)×10-12 cm3 molecule-1 s-1.The experimental rate constant has been compared with the rate constants calculated with the structure-activity relationship (SAR) and with the evolution trend of the acetate rate constants. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 497-502, 1998
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    Atmospheric chemistry of acetone: Kinetic study of the CH3C(O)CH2O2+NO/NO2 reactions and decomposition of CH3C(O)CH2O2NO2 (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 475-489 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pulse radiolysis was used to study the kinetics of the reactions of CH3C(O)CH2O2 radicals with NO and NO2 at 295 K. By monitoring the rate of formation and decay of NO2 using its absorption at 400 and 450 nm the rate constants k(CH3C(O)CH2O2+NO)=(8±2)×10-12 and k(CH3C(O)CH2O2+NO2)=(6.4±0.6)×10-12 cm3 molecule-1 s-1 were determined. Long path length Fourier transform infrared spectrometers were used to investigate the IR spectrum and thermal stability of the peroxynitrate, CH3C(O)CH2O2NO2. A value of k-6≈3 s-1 was determined for the rate of thermal decomposition of CH3C(O)CH2O2NO2 in 700 torr total pressure of O2 diluent at 295 K. When combined with lower temperature studies (250-275 K) a decomposition rate of k-6=1.9×1016 exp (-10830/T) s-1 is determined. Density functional theory was used to calculate the IR spectrum of CH3C(O)CH2O2NO2. Finally, the rate constants for reactions of the CH3C(O)CH2 radical with NO and NO2 were determined to be k(CH3C(O)CH2+NO)=(2.6±0.3)×10-11 and k(CH3C(O)CH2+NO2)=(1.6±0.4)×10-11 cm3 molecule-1 s-1. The results are discussed in the context of the atmospheric chemistry of acetone and the long range atmospheric transport of NOx. © John Wiley & Sons, Inc. Int J Chem Kinet: 30: 475-489, 1998
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    The fluorine atom initiated oxidation of CF3CFH2 (HFC-134a) studied by FTIR spectroscopy (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 541-554 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experiments have been carried out on the oxidation of CF3CFH2 (HFC-134a). Reaction was initiated by continuous photolysis of F2 in the near-ultraviolet. The F atoms produced abstracted a hydrogen atom from CF3CFH2 initiating oxidation in gas mixtures containing O2 and made up to a total pressure of 700 torr with N2. Product yields were measured using Fourier-transform infrared (FTIR) spectroscopy. Experiments were performed with several different partial pressures of O2 present, and at three temperatures; 298, 323, and 357 K. The major products were HC(O)F, CF3C(O)F, and CF3O3CF3, consistent with H atom abstraction by O2 and CC bond scission being the dominant loss processes for CF3CFHO radicals:\documentclass{article}\pagestyle{empty}\begin{document}$ CF3CFHO+O2 \rightarrow CF3C(O)F+HO2 (4a) $\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$ CF3CFHO+M \rightarrow CF3+HC(O)F+M (4b) $\end{document}The following expression was derived for the ratio of rate constants for these reactions:k4a/k4b=(3.8±1.6)×10-24 exp[(2400±500)/T]cm3 molecule-1 (viii)The main fate of the CF3 radicals was formation of CF3O3CF3 and small amounts of CF3OH were detected. The results of the present experiments in which F atoms were used to initiate reaction are in good agreement with those of previous studies in which Cl atoms were employed to initiate the oxidation of HFC-134a. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 541-554, 1998
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    Photoreduction of IrCl62- complex in alcohol solutions and its reaction with hydroxyalkyl radicals (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 711-719 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemistry of IrCl62- complex in simple alcohols have been studied using laser-flash photolysis. Single electron transfer from the solvent molecule to the light-excited complex has been shown to be the primary photochemical process. Quantum yields of the photoreduction of IrCl62- complex and the rate constants of its reaction with hydroxyalkyl radicals were determined at 200-330 K. Deviations of the rate constants from Debye-Smoluchowski equation for diffusion-controlled reactions are discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 711-719, 1998
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    The hydroxyl radical reaction rate constant and atmospheric transformation products of 2-butanol and 2-pentanol (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 745-752 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of +2-butanol (2BU, CH3CH2CH(OH)CH3) and 2-pentanol (2PE, CH3CH2CH2CH(OH)CH3). 2BU and 2PE react with OH yielding bimolecular rate constants of (8.1±2.0)×10-12 cm3molecule-1s-1 and (11.9±3.0)×10-12 cm3molecule-1s-1, respectively, at 297±3 K and 1 atmosphere total pressure. Both 2BU and 2PE OH rate constants reported here are in agreement with previously reported values [1-4]. In order to more clearly define these alcohols' atmospheric reaction mechanisms, an investigation into the OH+alcohol reaction products was also conducted. The OH+2BU reaction products and yields observed were: methyl ethyl ketone (MEK, (60±2)%, CH3CH2C((DOUBLEBOND)O)CH3) and acetaldehyde ((29±4)% HC((DOUBLEBOND)O)CH3). The OH+2PE reaction products and yields observed were: 2-pentanone (2PO, (41±4)%, CH3C((DOUBLEBOND)O)CH2CH2CH3), propionaldehyde ((14±2)% HC((DOUBLEBOND)O)CH2CH3), and acetaldehyde ((40±4)%, HC((DOUBLEBOND)O)CH3). The alcohols' reaction mechanisms are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. Labeled (18O) 2BU/OH reactions were conducted to investigate 2BU's atmospheric transformation mechanism details. The findings reported here can be related to other structurally similar alcohols and may impact regulatory tools such as ground level ozone-forming potential calculations (incremental reactivity) [5]. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 745-752, 1998
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    Reduction of iodine by hydroxylamine within the pH range 0.7-3.5 (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 785-797 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of iodine by hydroxylamine within the [H+] range 3×10-1-3×10-4 mol.L-1 was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH3OH+]0/[I2]0 ratio below 15, [H+] around 0.1 mol.L-1, and ionic strength around 0.1 mol.L-1), the [I2] and [I3-] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I2+I-⇔I3-, 2 I2+NH3OH++H2O→HNO2+4 I-+5 H+, NH3OH++HNO2→N2O+2 H2O+H+, and 2 HNO2+2 I-+2 H+→2 NO+I2+2 H2O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h).The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H+] is above 4×10-2 mol.L-1 at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH2OH and NH3OH+ as the reducing reactive species. The additional rate suppression by H+ at low pH would be connected to the existence of H2OI+ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785-797, 1998
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    Kinetics of the reactions of OH radicals with some oxygenated volatile organic compounds under simulated atmospheric conditions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 839-847 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some relative rate experiments have been carried out at room temperature and at atmospheric pressure. This concerns the OH-oxidation of some oxygenated volatile organic compounds including methanol (k1), ethanol (k2), MTBE (k3), ethyl acetate (k4), n-propyl acetate (k5), isopropyl acetate (k6), n-butyl acetate (k7), isobutyl acetate (k8), and t-butyl acetate (k9). The experiments were performed in a Teflon-film bag smog chamber. The rate constants obtained are (in cm3 molecule-1 s-1): k1=(0.90±0.08)×10-12; k2=(3.88±0.11)×10-12; k3=(2.98±0.06)×10-12; k4=(1.73±0.20)×10-12; k5=(3.56±0.15)×10-12; k6=(3.97±0.18)×10-12; k7=(5.78±0.15)×10-12; k8=(6.77±0.30)×10-12; and k9=(0.56±0.11)×10-12. The agreement between the obtained rate constants and some previously published data has allowed for most of the studied compounds to point out a coherent group of values and to suggest recommended values. Atmospheric implications are also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 839-847, 1998
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    Reactivity of the bis[1-Hydroxy-2-(Salicylideneamino)Ethane]Manganese(II) complex toward hydrogen peroxide: Kinetics and intermediates of reaction (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 889-897 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic studies of the oxidation of the bis[1-hydroxy-2-(salicylideneamino)ethane]manganese(II) complex by hydrogen peroxide in acetonitrile solutions, at (30.0±0.2)°C, are described. A first-order dependence on the total manganese and the peroxide concentrations was verified, leading to the rapid formation of a Mn(III) intermediate, monitored by stopped-flow measurements, at 394 nm, with a rate constant kf=(1.15±0.03)×105 mol-1 dm3 s-1. The participation of hydroxyl radicals in the process was detected by spin-trapping EPR spectra. The final product was monitored both by EPR spectra, and spectrophotometrically by the slow decay of the intermediary Mn(III) species, with a rate constant kd=(2.60±0.09) s-1. It was identified as the corresponding mononuclear Mn(IV) complex, and characterized by different spectroscopic techniques. Comparative results of the reactivity of the starting complex versus molecular oxygen, leading to the same final product, were also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 889-897, 1998
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  • 77
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    Determination of the isomerization rate constant HOCH2CH2CH2CH(OO·)CH3 →HOC·HCH2CH2CH(OOH)CH3. Importance of intramolecular hydroperoxy isomerization in tropospheric chemistry (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 875-887 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant of the title reaction is determined during thermal decomposition of di-n-pentyl peroxide C5H11O(—)OC5H11 in oxygen over the temperature range 463-523 K. The pyrolysis of di-n-pentyl peroxide in O2/N2 mixtures is studied at atmospheric pressure in passivated quartz vessels. The reaction products are sampled through a micro-probe, collected on a liquid-nitrogen trap and solubilized in liquid acetonitrile. Analysis of the main compound, peroxide C5H10O3, was carried out by GC/MS, GC/MS/MS [electron impact EI and NH3 chemical ionization CI conditions]. After micro-preparative GC separation of this peroxide, the structure of two cyclic isomers (3S*,6S*)3α-hydroxy-6-methyl-1,2-dioxane and (3R*,6S*)3α-hydroxy-6-methyl-1,2-dioxane was determined from 1H NMR spectra. The hydroperoxy-pentanal OHC(—)(CH2)2(—)CH(OOH)(—)CH3 is formed in the gas phase and is in equilibrium with these two cyclic epimers, which are predominant in the liquid phase at room temperature. This peroxide is produced by successive reactions of the n-pentoxy radical: a first one generates the CH3C·H(CH2)3OH radical which reacts with O2 to form CH3CH(OO·)(CH2)3OH; this hydroxyperoxy radical isomerizes and forms the hydroperoxy HOC·H(CH2)2CH(OOH)CH3 radical. This last species leads to the pentanal-hydroperoxide (also called oxo-hydroperoxide, or carbonyl-hydroperoxide, or hydroperoxypentanal), by the reaction HOC·H(CH2)2CH(OOH)CH3+O2→O(=)CH(CH2)2CH(OOH)CH3+HO2.The isomerization rate constant HOCH2CH2CH2CH(OO·)CH3→HOC·HCH2CH2CH(OOH)CH3 (k3) has been determined by comparison to the competing well-known reaction RO2+NO→RO+NO2 (k7). By adding small amounts of NO (0-1.6×1015 molecules cm-3) to the di-n-pentyl peroxide/O2/N2 mixtures, the pentanal-hydroperoxide concentration was decreased, due to the consumption of RO2 radicals by reaction (7). The pentanal-hydroperoxide concentration was measured vs. NO concentration at ten temperatures (463-523 K). The isomerization rate constant involving the H atoms of the CH2(—)OH group was deduced:\documentclass{article}\pagestyle{empty}\begin{document}$ k_{3}\rm =(6.4\pm 0.6)\times 10^{10}\hbox{exp}\{-(16,900\pm 700)\hbox{cal mol}^{-1}/RT\}s^{-1} $\end{document}or per H atom:\documentclass{article}\pagestyle{empty}\begin{document}$ k_{3\rm (H)}\rm =(3.2\pm 0.3)\times 10^{10}\hbox{exp}\{-(16,900\pm 700)\hbox{cal mol}^{-1}/RT\}s^{-1} $\end{document}The comparison of this rate constant to thermokinetics estimations leads to the conclusion that the strain energy barrier of a seven-member ring transition state is low and near that of a six-member ring. Intramolecular hydroperoxy isomerization reactions produce carbonyl-hydroperoxides which (through atmospheric decomposition) increase concentration of radicals and consequently increase atmospheric pollution, especially tropospheric ozone, during summer anticyclonic periods. Therefore, hydrocarbons used in summer should contain only short chains (〈C4) hydrocarbons or totally branched hydrocarbons, for which isomerization reactions are unlikely. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 875-887, 1998
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    Modeling of the oxidation of n-octane and n-decane using an automatic generation of mechanisms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 949-959 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Detailed modeling of the oxidation of n-octane and n-decane in the gas phase was performed by using mechanisms written by means of a software recently developed in our laboratory. This computer-aided design of mechanisms permits the automatic generation of detailed oxidation and combustion kinetic models in the case of paraffins and isoparaffins [1]. For n-octane, the predictions of the model were compared with experimental results obtained by Dryer and Brezinsky by means of a turbulent plug flow reactor (1080 K, 1 atm) [2]. The experimental study of Balès-Guéret et al., performed in a perfectly stirred reactor (922-1033 K, 1 atm) [3], was used as a basis of comparison for the modeling of the oxidation of n-decane. Considering that no fitting of any kinetic parameter was done, the agreement between the computed and the experimental values is satisfactory both for conversions and for the distribution of the products formed. This modeling has required improvement in the generation of the secondary reactions of alkenes, which are the main primary products obtained during the oxidation of these two alkanes in the range of temperature studied and for which reaction paths are detailed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 949-959, 1998
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    Oxidation of L-glutamine by manganese(iii) in aqueous sulfuric acid, acetic acid, and pyrophosphate media: A kinetic and mechanistic study (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 7-19 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Manganese(III) solutions were prepared by known electrochemical methods in sulfuric acid, acetic acid, and pyrophosphate media. The nature of the oxidizing species present in manganese(III) solutions was characterized by spectrophotometric and redox potential measurements. Kinetics of oxidation of L-glutamine by manganese(III) in sulfuric acid (1.5 M), acetic acid (60% v/v), and pyrophosphate (pH=1.3) media at 313 K, 323 K, and 328 K, respectively, have been studied. Three different rate laws have been obtained for the three media. Effects of varying ionic strength, solvent composition, and added anions, such as fluoride, chloride, perchlorate, pyrophosphate, and bisulfate, have been investigated. There is evidence for the existence of free radicals as transient species. Activation parameters have been evaluated using Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 7-19, 1998.
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    Study of the effects of concentration and pH on the dissociation kinetics of Fe(II)-fulvic acid complexes (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 63-67 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of reagent concentration and the pH in the kinetic behavior of the dissociation of Fe(II)-fulvic acid complexes were studied using a spectrophotometric technique. The results show that this behavior is not strongly affected by the concentration of fulvic acid, the concentration of the metal cation on the ratio of these concentrations and that variations in pH are more important in the dissociation process. A possible explanation based in the relative influence of proton concentration on the stability of the complexes is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 63-67,1998.
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    Kinetics and mechanism of reaction of toluidine blue with acidic bromate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 111-120 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The detailed kinetics of the reaction of toluidine blue {phenothiazine-5-ium, 3-amino-7(dimethylamino)-2-methyl chloride, tolonium chloride, TB+Cl-} with potassium bromate and with aqueous bromine reaction were studied. In most of the experiments, the kinetics were monitored by following the rate of consumption of TB+ at 590 nm with excess acid and bromate. The reaction exhibited complex kinetic behavior. Initial reaction was slow and after an induction time, the TB+ concentration decreased fast. It had first-order dependence on both TB+ and bromate, and second-order dependence on H+. Under excess bromate conditions, the stoichiometric ratio of TB+ to bromate was 1:1. Demethylated sulfoxides were found at the reaction products. Sharp increase in the overall potential synchronized with the increase in bromine levels and the fast depletion of [TB+]. The role of bromide ion and bromine in the reaction was established. A multi-step reaction mechanism is proposed consistent with the experimental results. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 111-120, 1998.
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    Kinetic study of the nitrosation of N-alkylureas in dioxane-acetic acid mixtures (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 145-150 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constants were determined for the nitrosation reactions of the following substrates: Methyl (MU), Ethyl (EU),Propyl (PU)Butyl (BU), and Allylurea (AU). The rate equation found at a constant pH was: v=k[HNO2] [Urea]. The reactions were carried out in predominantly organic media(dioxane-acetic acid-water) with differing polarities. The proposed reaction mechanism involves the proton transfer from the protonated N-alkyl-N-nitrosourea to the acetate anion. As the polarity of the medium decreased, an approximation of the rate constants of the nitrosation of the different substrates was observed. This approximation can be interpreted as a function of the impediment generated by the R alkyl radical in the rate controlling step. Accordingly, the substrate reactivity will be associated with the ease in which the protonated N-alkyl-N nitrosurea can transfer the proton to the acetate anion. The results achieved in this study are in accordance with there activities observed in the nitrosation of these substrates in aqueous media MU≫(EU≈PU≈BU)〉AU. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 145-150, 1998.
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    The pyrolysis of azetidine: Shock-tube kinetics similarities and contrasts with two analogs (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 185-191 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of decomposition of azetidine {(CH2)3N(SINGLEBOND)H)} was measured using single-pulse shock-tube techniques, over the temperature range 855-1100 K, in high argon dilution. These data confirm and extend an earlier investigation that utilized the very low-pressure pyrolysis method. A brief survey of many reports regarding the interesting features of azetidine is presented. In two appendices the thermodynamic and kinetic data on trimethylene sulfide, oxide, and immine are intercompared. New ab-initio calculations are cited for the parent species and their fragmentation products. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 185-191, 1998.
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  • 84
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    Oxidation of manganese(II) by ozone and reduction of manganese(III) by hydrogen peroxide in acidic solution (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 207-214 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Manganese(II) is oxidized by ozone in acid solution, k=(1.5±0.2)×103 M-1 s-1 in HClO4 and k=(1.8±0.2)×103M-1 s-1 in H2SO4. The plausible mechanism is an oxygen atom transfer from O3 to Mn2+ producing the manganyl ion MnO2+, which subsequently reacts rapidly with Mn2+ to form Mn(III). No free OH radicals are involved in the mechanism. The spectrum of Mn(III) was obtained in the wave length range 200-310 nm. The activation energy for the initial reaction is 39.5 kJ/mol. Manganese(III) is reduced by hydrogen peroxide to Mn(II) with k(Mn(III)+H2O2)=2.8×103M-1 s-1 at pH 0-2. The mechanism of the reaction involving formation of the manganese(II)-superoxide complex and reaction of H2O2 with Mn(IV) species formed due to reversible disproportionation of Mn(III), is suggested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 207-214, 1998.
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  • 85
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    Belousov-Zhabotinskii type oscillations with amino acids or peptides as organic substrates in the presence of Mn2+ and Fe(phen)32+ as coupled catalysts (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 243-247 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nine amino acids, aspartic acid, glycine, serine, tyrosine, alanine, glutamic acid, threonine, cystine, phenylalanine, and two peptides, and two peptides, glycine-glycine peptide, glutamic acid-cystine-glycine peptide, give rise to damped oscillations of the Belousov-Zhabotinskii(BZ) type in a batch reactor. Both Mn2+ and Fe(phen)32 are essential for most of those oscillations; and the oscillations in [Mn3+] and [Fe(phen)33+] are also observed. The role of two metallic ions played in the oscillations are analyzed, showing that Mn2+ catalyzes the oxidation of the amino acids or peptides by BrO3- to produce some intermediates which effectively reduce Br2 to Br- catalyzed by Fe(phen)32+. © 1998 John Wiley & Sons, Inc. Int. J. Chem Kinet 30: 243-247, 1998.
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    Concerted mechanism of the reactions of 2,4-dinitrophenyl 4-cyanobenzoate with secondary alicyclic amines in aqueous ethanol (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 267-272 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title reactions are subjected to a kinetic analysis in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 (KCl). With a large excess of amine over the substrate, pseudo-first-order rate coefficients (kobs) are obtained, which are linearly dependent on the amine concentration. The nucleophilic rate constants (kN) are determined from plots of kobs vs. amine concentration. The Brönsted-type plot obtained with the kN values is linear, with slope β=0.63. The magnitude of this slope suggests that the mechanism is concerted, as opposed to a stepwise process with rate-determining breakdown of a zwitterionic tetrahedral intermediate (T±), in which the value of β is usually 0.8-1.0. The pyridinolysis of the same substrate in the same solvent is stepwise with the breakdown of T± as the rate-determining step. The change to a concerted mechanism for the title reactions is attributed to the superior nucleofugality of the alicyclic amines, compared to the isobasic pyridines, which destabilizes kinetically the “intermediate” T± in such a way that it does not exist, and the mechanism becomes enforced concerted. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 267-272, 1998.
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    Comment: A kinetic study of chlorine radical reactions with ketones by laser-photolysis technique by Olsson et al. (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 309-310 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Critical considerations on the methods for evaluating kinetic parameters from nonisothermal experiments (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 313-327 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By surveying the most used methods for evaluating the kinetic parameters from nonisothermal experiments, a new classification scheme of the methods is proposed. For each method the number of principles and theoretical approximations required to derive the equation which grounds it, is considered as a comparison criterion. The methods are, finally, classified into classes of equivalence.As a result of the analysis it is also suggested that the activation energy, as calculated from nonisothermal data, should be given as a range of values instead of a unique value. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 313-327, 1998.
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    Temperature dependence of the gas-phase reactions F+CHFO, CFO+F, and CFO+CFO (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 329-333 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate coefficients for the reactions CHFO+F, CFO+F and the self-reaction of CFO were determined over the temperature range of 222-298 K. A computer controlled discharge-flow system with mass spectrometric detection was used. The results are expressed in the Arrhenius form (with energies in J):CHFO+F→CFO+HF:k1(T)=(9.7±0.7)·10-12 exp[-(5940±150)/RT] cm3 molecule-1 s-1CFO+F+M→CF2O+M:FORMULA DISC=“MATH”〉k2(T)=(2.60±1.17)·10-10 exp[-(10110±1250)/RT cm3 molecule-1 s-1FORMULACFO+CFO→CF2O+CO:k3(T)=(3.77±2.7)·10-10 exp[-(8350±2800)/RT] cm3 molecule-1 s-1© 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 329-333, 1998
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    Kinetics and mechanism of the pyrolysis of 1-chloro-1,1-difluoroethane in the presence of additives (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 359-366 
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal dehydrochlorination CF2ClCH3→CF2(DOUBLEBOND)CH2+HCl has been studied in a static system between 597 and 664 K in the presence of CCl4, C2Cl6, CF2(DOUBLEBOND)CH2, HCl, and CF3CH3. A kinetic radical and molecular reaction model has been developed. In addition to describing earlier results on the acceleration of the pyrolysis by CCl4 and the further acceleration by HCl, this model describes quantitatively up to conversions of 20% (i) the dependence of the catalytic effect of CCl4 at low concentrations, (ii) the stronger catalytic effect of C2Cl6, and (iii) the inhibitory effect of added CF2CH2 and CF3CH3 when CCl4 is used as a catalyst. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 359-366, 1998
    Additional Material: 6 Ill.
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  • 91
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    Kinetics and mechanism of oxidation of aspirin by bromamine-T, N-bromosuccinimide, and N-bromophthalimide (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 407-414 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the oxidation of aspirin (ASP) by bromamine-T (BAT), N-bromosuccinimide (NBS), and N-bromophthalimide (NBP) has been studied in aqueous perchloric acid at 303 K. The oxidation reaction follows identical kinetics with first-order in [oxidant], fractional-order in [ASP], and inverse fractional-order in [H+]. Under identical experimental conditions the extent of oxidation with different oxidizing agents is in the order: NBS 〉 BAT 〉 NBP. The rate decreased with decreasing dielectric constant of the medium. The variation of ionic strength and the addition of the reaction products and halide ions had no significant effect on the reaction rate. The solvent isotope effect was studied using D2O. Kinetic parameters were evaluated by studying the reaction at different temperatures. The reaction products were identified by GC-MS. The proposed reaction mechanism and the derived rate law are consistent with the observed kinetic data. Formation and decomposition constants for ASP-oxidant complexes have been evaluated. Decarboxylation, bromination, and loss of acetic acid gave 2,4,6-tribromophenol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 407-414, 1998
    Additional Material: 8 Ill.
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  • 92
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    Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part I. Pyrolysis in an unpacked pyrex reactor (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 425-437 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20-100 torr initial pressures and 750-793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self-inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425-437, 1998
    Additional Material: 5 Ill.
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  • 93
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    Kinetics and mechanism of isatin ring opening in aqueous binary mixtures of methanol and acetonitrile cosolvents (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 463-469 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent effects on the kinetics of hydrolysis of isatin by sodium hydroxide have been investigated within the temperature range (30-55°C) in methanol-water and acetonitrile-water media of varying solvent compositions up to 70% (v/v) of the organic solvent component. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions; log k was correlated with both log [H2O] and the reciprocal of the dielectric constant. The first correlation was observed to be linear while the second was nonlinear. Finally a mechanism for the isatin ring opening was proposed, which accounts for the role and the effect of the solvent on the reaction rate. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 463-469, 1998
    Additional Material: 4 Ill.
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  • 94
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    Reaction of 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) derived radicals with hydroperoxides. Kinetics and mechanism (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 565-570 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tert-Butyl hydroperoxide and hydrogen peroxide readily react with the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The reaction is inhibited by ABTS and protons, and can be interpreted in terms of a mechanism comprising a partially reversible electron transferROOH+ABTS•+↔ ROO · + ABTS + H+ (1)followed by the self-reactions of the hydroperoxide derived radicals and reactions between them and another ABTS derived radical. A complete kinetic analysis allows an evaluation of the rate constant for reaction (1). A value of 0.2 M-1 s-1 was obtained for both compounds. The back reaction of process (1) is more relevant when tert-butyl hydroperoxide is employed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 565-570, 1998
    Additional Material: 5 Ill.
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  • 95
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    Kinetic study of the Ce(iii)- or Mn(ii)-catalyzed Belousov-Zhabotinsky reactions with mixed organic acid/ketone substrates (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 595-604 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a stirred batch reactor, the Ce(III)- or Mn(II)-catalyzed Belousov-Zhabotinsky reaction with mixed organic acid/ketone substrates exhibits oscillatory behavior. The organic acids studied here are: dl-mandelic acid (MDA), dl-4-bromomandelic acid (BMDA), and dl-4-hydroxymandelic acid (HMDA), and the ketones are: acetone (Me2CO), methyl ethyl ketone (MeCOEt), diethyl ketone (Et2CO), acetophenone (MeCOPh), and cyclohexanone ((CH2)5CO). The effects of bromate ion, organic acid, ketone, metal-ion catalyst, and sulfuric acid concentrations on the oscillatory patterns are investigated. Both conventional and stopped-flow methods are applied to study the kinetics of the oxidation reactions of the above organic acids by Ce(IV) or Mn(III) ion. The order of relative reactivities of the oxidation reactions of organic acids in 1 M H2SO4 is Mn(III)(SINGLEBOND)HMDA reaction 〉 Ce(IV)(SINGLEBOND)HMDA reaction 〉 Mn(III)(SINGLEBOND)BMDA, reaction 〉 Mn(III)(SINGLEBOND)MDA reaction 〉 Ce(IV)(SINGLEBOND)BMDA reaction 〉 Ce(IV)(SINGLEBOND)MDA reaction. Spectrophotometric study of the bromination reactions of the above ketones shows that these reactions are zero-order with respect to bromine and first-order with respect to ketone and that ketone enolization is the rate-determining step. The order of relative rates of bromination or enolization reactions of ketones in 1 M H2SO4 is (CH2)5CO≫(MeCOEt, Et2CO, Me2CO)〉MeCOPh. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet:30: 595-604, 1998
    Additional Material: 10 Ill.
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  • 96
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    Inhibition of chemical oscillations by bromide ion in the Briggs-Rauscher reaction (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 641-646 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of bromide ions to the component solutions of the Briggs- Rauscher oscillating system produces a variety of phenomena, depending on the sequence of the addition and on the initial bromide concentration. If the addition is made some minutes after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations last for five or six cycles, then suddenly ceases. If the addition is made immediately after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations do not start at all. The addition of bromide ions to an actively oscillating BR reaction causes a rapid suppression of the oscillations. Our observations may be accounted for by a mechanism involving the IBr species. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 641-646, 1998
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  • 97
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    Parabenzoquinone pyrolysis and oxidation in a flow reactor (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 683-697 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An experimental and theoretical study of the pyrolysis and oxidation of parabenzoquinone has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 600-1500 K. The main variables considered are temperature, oxygen concentration, and presence of CO. A detailed reaction mechanism for the pyrolysis and oxidation chemistry of parabenzoquinone is proposed, which provides a good description of the experimental results. Both the experimental work and the kinetic mechanism proposed for the pyrolysis and oxidation of parabenzoquinone represent the first systematic study carried out for this important aromatic compound.Our pyrolysis results confirm that the primary dissociation channel for p-benzoquinone leads to CO and a C5H4O isomer, presumably cyclopentadienone. However, significant formation of CO2 during the pyrolysis may indicate the existence of a secondary dissociation channel leading to CO2 and a C5H4 isomer. Under oxidizing conditions, consumption of p-benzoquinone occurs mainly by dissociation at lower temperatures. As the temperature increases interaction of OC6H4O with the radical pool becomes more significant, occurring primarily through hydrogen abstraction reactions followed by ring opening reactions of the OC6H3O radical. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 683-697, 1998
    Additional Material: 9 Ill.
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  • 98
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    Rate coefficients for the reactions of hydrogen atoms with 1-bromopropane, 2-bromopropane, 1-bromobutane, and 2-bromobutane (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 721-727 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate coefficients for the reactions of hydrogen atoms with n-C3H7Br, s-C3H7Br, n-C4H9Br, and s-C4H9Br were determined in a discharge flow-reactor at 298 K and a pressure of 4 mbar. Molecular-beam sampling and subsequent mass-spectrometric detection with electron-impact ionisation was used for the measurement of the bromo-hydrocarbon concentration. The rate coefficients obtained are (in 1010 cm3 mol-1 s-1): 2.3±1.2 for n-C3H7Br, 2.3±1.2 for s-C3H7Br, 2.4±1.2 for n-C4H9Br, and 2.8±1.4 for s-C4H9Br. The results are compared with predictions from bond-energy bond-order (BEBO) calculations, where a reasonable agreement is found. Furthermore, also by BEBO calculations, the relative importance of bromine abstraction as compared to hydrogen abstraction is estimated. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 721-727, 1998
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  • 99
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    Rate constants for the reactions of methylvinyl ketone, methacrolein, methacrylic acid, and acrylic acid with ozone (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 769-776 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants for the reaction of ozone with methylvinyl ketone (H2C(DOUBLEBOND)CHC(O)CH3), methacrolein (H2C(DOUBLEBOND)C(CH3)CHO), methacrylic acid (H2C(DOUBLEBOND)C(CH3)C(O)OH), and acrylic acid (H2C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm3 molecule-1 s-1): methylvinyl ketone (5.4±0.6)×10-18; methacrolein (1.3±0.14)×10-18; methacrylic acid (4.1±0.4)×10-18; and acrylic acid (0.65±0.13)×10-18. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769-776, 1998
    Additional Material: 7 Ill.
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  • 100
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    Determination of propagation and termination rate constants by using an extension to the rotating-sector method: Application to PLPC and DLPC bilayers (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 753-767 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extension to the rotating-sector method, which is usually applied to determine propagation and termination rate constants, is presented. The analytical treatment developed accounts for the simultaneous presence of a thermal initiation and of a first-order termination process. The applicability of the rotating-sector method is thus extended to situations where the rate in dark is higher than 5% of the rate in the presence of light, and more accurate estimates of the rate constants are obtained than before for any values of the “dark” rate. A previously published experiment on the application of the rotating-sector method to the autoxidation of styrene was reanalyzed. The estimates obtained for the propagation and the termination rate constants were 11% and 19% higher than the previous estimates, respectively. Finally, the improved rotating-sector method was also applied to the experimental determination of propagation (kp) and termination rate constants (2×kt) for both 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLPC) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) liposomes. The following results were obtained at 37°C: for PLPC kp =16.6 M-1s-1, and 2×kt=1.27×105 M-1s-1; for DLPC kp(intermolecular)=(13.3-13.9) M-1s-1, kp(intramolecular)=(4.7-5.4) s-1, and 2×kt=(0.99-1.05)×105 M-1s-1. The separation of the intermolecular and intramolecular propagation rate constants for DLPC was made possible both by a special adaptation of the rotating-sector equations to substrates with two oxidizable moieties, and by the experimental determination of the ratio between partially oxidized DLPC molecules (only one acyl is oxidized) and fully oxidized DLPC molecules (both acyls are oxidized). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 753-767, 1998
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