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  • 1990-1994  (43)
  • 1960-1964  (14)
  • 1920-1924
  • 1810-1819
  • 1800-1809
  • Catalysis
  • Synthetic methods
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 25 (1994), S. 97-103 
    ISSN: 1572-879X
    Keywords: Catalysis ; partial oxidation ; oxidative coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relative reactivity of ethane and ethylene compared to methane over the Ca/Ni/K catalyst was determined. The reactivities are in the order of ethylene 〉 ethane ≫methane. The catalyst was also studied using temperature-programmed reaction, desorption and decomposition.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer-aided materials design 1 (1994), S. 169-176 
    ISSN: 1573-4900
    Keywords: Zeolites ; Catalysis ; Lattice simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Lattice simulations and quantum mechanical techniques are used to study the energetics involved in the activation of the Ni-zeolite-Y catalyst, which requires migration of the Ni2+ cation from the S1 (hexagonal prism) to the supercage. We show that the barrier to migration of the nickel ions may be overcome by interaction of the migrating ion with molecules such as H2O, NH3 and C2H2 in the supercage, thereby explaining the role of the latter species in the activation process.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2373-2379 
    ISSN: 0009-2940
    Keywords: Chelating ligands ; Molybdenum complexes ; Peroxo complexes ; Catalysis ; Olefine epoxidation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N,N-Chelate Ligands - Applications in Molybdenum-Catalyzed Epoxidation of Olefins*Oxodiperoxomolybdenum complexes 4 of substituted 2-[3(5)-pyrazolyl]pyridines (2a-g) were synthesized in order to control the solubility of these complexes in organic solvents. Alkyl side chains (butyl, octyl, octadecyl) increase the solubility of the complexes and enable spectroscopic investigations in solution. Due to the symmetry of the ligands the peroxo complexes 4 appear in two isomeric forms, with the terminal oxo ligand in the trans position either to pyridine or to pyrazole. The latter isomer of (C5H4NC3H2N2CH2COOEt)MoO(O2)2 (4f) was characterized by an X-ray structure analysis. The alkyl-substituted peroxo complexes are active catalysts for the epoxidation of olefins with tert-butyl hydroperoxide.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 691-696 
    ISSN: 0009-2940
    Keywords: Molecule-induced radical formation, kinetics of ; Catalysis ; ESR spectroscopy ; Radical clock ; Isokinetic relationship ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bimolecular Formation of Radicals by H-Transfer, 7[1].  -  Bimolecular Formation of Radicals via H-Transfer with Catalysis by 7H-Benz[de]anthraceneThe transfer hydrogenation of α-methylstyrene (2) by 9,10-dihydroanthracene (1) (DHA) with 7H-benz[de]anthracene (8) as a catalyst proceeds already at 210-260°C. Isotopic labeling, ESR spectroscopy, radical clock experiments, solvents effects, and thermochemical calculations support the postulated stepwise radical mechanism induced by bimolecular formation of radicals.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 1040-0397
    Keywords: Molybdenim ; Adsorptive stripping voltammetry ; Catalysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The adsorptive collection of the molybdenum (VI) complex of 2-(2′-thiazolylazo)-p-cresok (TAC), coupled with the catalytic current of the adsorbed complex, yield an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were found with the use of a stirred acetate buffer (pH 2.9) supporting electrolyte, a TAC concetration of 1.0 × 10-5 M, and a concentration of 0.1 M potassium nitrate. In addition, a preconcentration potential of -0.13 V (vs. Ag/AgCl), equilibrium time of 30 seconds, and an anodic scan rate of 200 mV/s from -0. 93 to -0. 20 was used. A catalytic effect was observed when nitrate was present. The response was found to be linear over a concentration range of 0.0 to12.0 μg L-1 Mo (VI). For a preconcentration time of 3 minutes, the detection limit was found to be 11 pM. Possible interferences by anions and other trace metals were investigated. The interference by copper may be masked by CDTA, and sequential determination with molybdenum is possible. The merits of the procedure are demonstrated in the analysis of sea and mineral water.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 1040-0397
    Keywords: Nickel ; Nicotinamide ; Catalysis ; Polarography ; catalytic wave ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catalytic reduction of Ni (II) in the presence of nicotihamide (NA) at pH 〈 7 was studied by direct-current and differential-pulse polarography (DPP). The prewave (with E1/2 around -0.78 V (versus saturated calomel electrode (SCE)) shows the typical behavior of an electrode process with regeneration of the reactant by a second-order, rate-determining chemical reaction. This reaction consists in the formation of the reducible nickel complex. The kinetics of the electrode process was studied by means of an adapted form of the equation derived by Koutecký for electrochemical reactions with a parallel chemical step. The rate constant for the formation of nickel-nicotinamide complex is slightly dependent en pH and buffer composition and ranges between 4.5 and 6.7 × 103 mole-1 L s-1. This electrode process enables the selective determination of Ni (II) in presence of a large excess of cobalt. For example, nickel impurity in cobalt salts can be determined by DPP, in acetate buffer (pH 4.6) containing 0.01 M nicotinamide and about 0.1 M cobalt salt sample.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 49-58 
    ISSN: 0170-2041
    Keywords: Catalysis ; Guanidine ; Ion pair ; Phosphoric acid diester ; Staphylococcal nuclease, model of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acceleration of Substitution Reactions of a Phosphoric Acid Diester by Bis(guanidinium) CompoundsIon-pair coordination of phosphoric acid diesters with positively charged guanidines may cause large rate accelerations in substitution reactions. Here we present a comparative study on the catalytical influence of several mono- bis- and tris(guanidines) and of other cationic compounds. Large rate effects occur if 1,3-bis(aminomethyl)benzene or 1,2-ethylenediamine are used as spacers. Further acceleration can be achieved by exchanging guanidinium groups by 2-aminoimidazolines. The 4800-fold rate enhancement seen in the best case demonstrates the importance of the bis(guanidinium) moiety of staphylococcal nuclease and gives good perspectives towards future uses of guanidinium compounds as RNA cleaving agents.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 913-937 
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This personal journey through the enlarging landscape of heterogeneous catalysis, pure and applied, starts with the discovery in 1823 of a dramatic example of the synthesis of water that was to serve as the basis of the first commercial exploitation of catalysis, Dobereiners lighter (tinder box). The quickening pace of successive industrial innovations and of academic insight during the intervening 170 years are summarized and the turning points, both major and minor, identified. Although new concepts and new ideas emerged in relative profusion, few exhibited the longevity predicted for them at birth by their proponents. Some concepts, like broken milestones on a vanished road, have ceased to retain their significance. Some have survived, even flourished. But in catalysis, as in most other branches of natural science, new tools and new techniques, rather than new concepts, tend to hold sway. And just as experimental advances in enzymology and immunology have led to the design of remarkable new biocatalysts so also, but not yet at the same level of delicate control, have the tools and techniques of solid-state chemistry (including novel preparative and computational procedures), generated many powerful rationally designed inorganic catalysts.
    Additional Material: 31 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 2009-2023 
    ISSN: 0570-0833
    Keywords: Photochemistry ; Synthetic methods ; Fine chemicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner.
    Additional Material: 21 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 17 (1993), S. 1-10 
    ISSN: 1572-879X
    Keywords: Catalysis ; effect of pressure ; structure insensitive reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract At 445 K, and equimolar ratio of reactants, the turnover rate for CO oxidation on unsupported and supported Pd is constant within experimental error between ≈ 0.1 and 100 mbar. As first proposed in 1922 by Langmuir, the overall rate is the rate of adsorption on a surface almost saturated with CO. Thus the rate is proportional to the ratio of concentrations of O2 and CO and is pressure independent. At quasi-saturation, the few vacant sites form an ideal dilute solution in the CO-Pd solvent. Adsorption on these sites is dominated by pressure invariant interactions with the solvent. Hence, the rate obeys Langmuir kinetics and the reaction is structure insensitive.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Pharmacy world & science 15 (1993), S. 123-127 
    ISSN: 1573-739X
    Keywords: Catalysis ; Drug stability ; Mitomycins ; Reaction kinetics ; Reaction mechanisms ; Stereoisomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The acid-catalyzed degradation of mitomycin C is supposed to be governed, to a certain extent, by the protonation status of the aziridine nitrogen in the molecule as well as the protonation degree of the opened aziridine function in a key intermediate species, formed during mitomycin degradation. In order to obtain information about the contribution of the protonation degrees of these functions in controlling the degradation processes, we investigated the degradation of 1a-acetylmitomycin C in acidic aqueous solutions. In the presence of 0.001 mol/l phosphate buffers five 1-hydroxy and mono-acetyl mitosenes are formed, whereas in 1.0 mol/l acetate buffers a total of eight products could be identified, two of them being diacetyl mitosenes. Over the whole pH range studied the formation of 1,2-Z-mitosenes prevails, indicating that, contrary tomitomycin C, a pH-independent factor controls the ultimate 1,2-stereochemistry.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1039-1045 
    ISSN: 0009-2940
    Keywords: Hydrogen transfer ; Radical formation, molecule induced ; C—H bond dissociation enthalpies, determination of ; Catalysis ; Coal pyrolysis ; Phenalene ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bimolecular Formation of Radicals by H-Transfer, 2[1]. - H-Transfer Reactions of PhenaleneThe uncatalysed H transfer from phenalane (7) to α1-methyl-styrene (2) and the selfreaction (d) of phenalene (7) are quantitative transformations in the presence of an excess of 9,10-dihydroanthracene (1) (DHA) in diphenyl ether at 200-250°C. In this system phenalene (7) is consumed only in reaction (d) because the phenalenyl radicals (9) are captured by DHA (1) to give phenalene (7) and 9,10-dihydroanthryl radicals (3). The latter disproportionate rapidly. Accordingly, phenalene (7) acts as a catalyst for the hydrogenation of α1-methylstyrene (2) by DHA (1). The activation parameters of the two reactions (e) and (d) were obtained from kinetic experiments between 200-250°C. They allow the determination of the C—H bond enthalpy δHdiss of phenalene (7) (65.3 kcal mol-1) at the methylene position.
    Additional Material: 2 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2393-2396 
    ISSN: 0009-2940
    Keywords: Platinum complexes ; Cyclobutadiene complexes ; Alkyne dimerization ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Characterization of Platinumcyclobutadiene Complexes by the Reduction of Hexachloroplatinic AcidHexachloroplatinic acid is reduced in 1-butanol in the presence of an alkyne R-C≡C-R′ (R, R′ = Me, Et, nPr) to give platinumcyclobutadiene complexes [PtCl2(C4R2R2′)] (1). H[PtCl3(CH3CH2CH=CH2)] (2) is an intermediate which is isolated as bis(triphenylphosphoranylidene)ammonium salt (PPN-salt) [PPN][PtCl3(CH3CH2CH=CH2)] (3). The molecular structure of [PtCl2(C4Et4)] (1b) shows in the solid state a planar cyclobutadiene ring with internal bond angles of 93(3) and 87(2)°. The Pt-C bond lengths are 208(2) and 210(2) pm. The ethyl groups are pushed out of the ring plane, away from the Pt atom, with an angle of 7(2)°.
    Additional Material: 1 Ill.
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  • 14
    ISSN: 0044-2313
    Keywords: Rhodium( I) Complex Salts ; Preparation ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Catalytic Properties of Rhodium(I) Complex Salts of the Type [Rh(COD)(o-Py(CH2)2 P(Ph)(CH2)3ZR)]PF6 (Z = O, NH).In dichloromethane solutions were reacted [Rh(COD)Cl]2 (COD = cis,cis-1.5-cyclooctadiene) with each of the four new ligands of the type o-Py(CH2)2P(Ph)(CH2)3ZR in the presence of the halogen scavenger TIPF6 at 0°C to complex salts [Rh(COD) (o-Py(CH2)2P(Ph)(CH2)3ZR]PF6 (ZR = OC2H5, I; OPh, II; NHPh, III; NHcyclo—C6H11, IV). The Rh1 complex cation in the obtained compounds I - IV coordinates besides the bedentate COD group the ligand donor atoms P und pyridinic N and the remaining donor atom Z is uncoodinated in an assumed square planar ligand geometry at the Rh central atom. In 1.4 dioxane solutions the complex catalysts I - IV polymerize at 25°C the substrate phenylacetylene (PA) to polyphenylacetylene (PPA): values of TON [h-1] between 352 (I) and 876 (IV), and average molecular weights Mw (GPC measurements) between 238 000 (I) and 199 900 (IV). These given values exhibit a dependency on the ZR group in complexes I - IV. The microstructure of isolated PPA is cis-transoidal. It is formed stereospezific and, based on MNDO calculations, is thermodynamically favoured. For the purpose of comparison, from both the newly synthesized compounds of the type [Rh(COD)DBN- (or DBU)Cl] (DBN = 1.5-Diazabi-cyclo[4.3.0.]non-5-en, DBU = 1.8-Diazabicycl0[5.4.0]- undec-7-en) was obtained a larger value of TON with 1292 (or 1327) [h-], but a lower value of M, with 166200 (or 131200). These catalysts including I -IV polymerize PA to PPA at a lower reaction temperature with improved selectivity and larger values of Mw as hitherto known catalyst systems.
    Notes: In Dichlormethanlösung wurde [Rh(COD)Cl]2 (COD = cis,cis-1.5-Cyclooctadien) mit vier neuen dreizähnigen Liganden vom Typ o-Py(CH2)2P(Ph)(CH2)3ZR in Gegenwart des Halogenfängers TIPF6 bei 0°C zu Komplexsalzen [Rh(COD)(o-Py(CH2)2P(Ph)(CH2)3ZR)] PF6 (ZR = OC2H5, I; OPh, II; NHPh, III; NHcyclo—C6H11, IV) umgesetzt. Das Rhodium-Komplexkation in den abgetrennten Verbindungen I - IV koordiniert aufgrund von 1H-, 31P-, 13C-NMR und IR-Meßergebnissen außer der zweizähnigen COD-Gruppe die Donoratome Phosphor und Pyridinstickstoff und läßt in der angenommenen quadratisch-planaren Koordinationsgeometrie ein vorhandenes Z-Donoratom ungebunden. Die Komplexkatalysatoren I - IV polymerisieren in 1,4-Dioxanlösung bei 25°C das Substrat Phenylacetylen (PA) zu Polyphenylacetylen (PPA): Werte für TON [h-1] von 352(I) und 876(IV) und mittlere Molmassen Mw (GPC-Meßresultate) zwischen 238 000(I) und 199 900(IV). Diese Werte der Lösungs-Fällungspolymerisation zeigen eine Abhängigkeit von der unkoordinierten ZR-Gruppe in Komplexen I - IV. Die Mikrostruktur des isolierten PPA ist cis-transoidal. Sie entsteht stereospezifisch und ist nach MNDO-Rechnungen die thermodynamisch begünstigte. Von den zu Vergleichszwecken dargestellten neuen Rhodium(I)-Komplexen des Typs [Rh(COD)DBN(bzw. DBU)Cl] (DBN = 1,5-Diazabicyclo[4.3.0]-non-5-en, DBU = 1,8-Diazabicyclo[5.4.0]undec-7-en) wird unter analogen Reaktionsbedingungen für PA ein höherer TON-Wert 1 292 (bzw. 1 327) [h-1], aber kleinerer Mw-Wert von 166 200 (bzw. 131 200) erhalten. Gegenüber bisher bekannten Katalysatorsystemen polymerisieren diese Komplexkatalysatoren einschließlich I - IV PA zu PPA bei milderen Reaktionstemperaturen, verbesserter Selektivität und höheren Mw-Werten.
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 336-358 
    ISSN: 0570-0833
    Keywords: Carbohydrates ; Chiral auxiliaries ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbohydrates are inexpensive natural products in which numerous functional groups and stereogenic centers are combined in one molecule. By directed regio-and stereoselective formation of derivatives they can be converted into efficient chiral auxiliaries for controlling asymmetric syntheses. Stereoelectronic effects and pre-orientation of the reactive and shielding groups through formation of complexes can often be used for effective diastereofacial differentiation. In aldol reactions and alkylations on carbohydrate ester enolates intramolecular complexation promotes simultaneous elimination with formation of ketene. The steric, stereoelectronic, and coordinating properties of carbohydrate templates can also be used selectively to attain high levels of asymmetric induction in processes such as Diels-Alder reactions, hetero-Diels-Alder reactions, [2 + 2] cycloadditions, cyclopropanations, and Michael additions. It was possible with bicyclic, strongly stereodifferentiating carbohydrate auxiliaries to achieve a diastereoselective synthesis of carboxylic acid derivatives branched in the β position by a new 1,4-addition of alkylaluminum halides to α,β-unsaturated N-acylurethanes, in which methylaluminum halides and higher alkyl- or arylaluminum compounds behave mechanistically in a strikingly different manners. As complex ligands in chiral reagents and promoters, carbohydrates allow highly stereoselective reductions and aldol reactions that lead, amongst others, to chiral alcohols and β-hydroxy-α-amino acids in excellent enantiomeric excesses. Glycosylamines offer the possibility of versatile stereoselective applications: in the presence of Lewis acids the corresponding aldimines permit high-yielding syntheses of enantiomerically pure α-amino acids by Strecker and Ugi reactions, controlled by steric and stereoelectronic effects and by complex formation. They can be used with equal efficiency for asymmetric syntheses of chiral homoallylamines and for asymmetric Mannich syntheses of β-amino acids and chiral heterocycles, for example alkaloids.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 164-189 
    ISSN: 0570-0833
    Keywords: Metals ; Reactivity ; Activation ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Today, the synthetic chemist has a large repertoire of metal activation methods at his disposal. After a first breakthrough was made at the beginning of the seventies with the introduction of the Rieke metals, a series of further, in part more efficient methods were describes, based on which not only classical metal-induced reactions could be substantially improved but also completely new reactions could be discovered. In this article the individual activation methods are discussed and compared as far as is possible using the currently available data. Especially noteworthy are the metal-graphite combinations because of their unsurpassed reactivity and concomitant easy preparation and manipulation. As shown by numerous applications of these reagents on polyfunctional substrates, particularly natural products, high reactivity of the metal and excellent selectivity are by no means precluded. Besides the purely preparative aspects also insights gained so far into the general principles and limits of metal activation are outlined, and attempts at determining the morphology of highly dispersed systems are reported.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 1010-1022 
    ISSN: 0570-0833
    Keywords: Natural products ; Polycycles ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 12 (1992), S. 105-115 
    ISSN: 1572-879X
    Keywords: Catalysis ; clean fuels ; reformulated gasoline ; ethers ; oil refining ; natural gas conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract New and more stringent environmental legislation is expected to have a major impact on the refining industry. Reformulated gasoline which is currently being introduced into parts of the United States is an example of the shift towards “cleaner” burning fuels. To achieve future government specifications for such fuels significant changes will likely be required in refinery operations to produce products with good combustion characteristics and reduced emissions. Catalysis is expected to play a dominant role in both modifying existing processes and developing new routes to these more environmentally acceptable fuels. Both new and improved catalysts systems which will be required for the production of so-called reformulated gasoline are discussed. For example, oxygenated components in gasoline such as methyl tertiary butyl ether (MTBE) will continue to be required on a large scale necessitating new process and catalyst technology to achieve improved economics. Natural gas can be considered as a “clean” feedstock from which to produce liquid fuels of high quality. A number of new process routes to convert remote natural gas into readily transportable liquid fuels are also discussed. This area of technology offers considerable scope for further major improvements based on innovation in the field of syngas catalysis.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 12 (1992), S. 147-155 
    ISSN: 1572-879X
    Keywords: Catalysis ; zeolites ; palladium ; ion exchange ; solid-state ; hydrogenation ; hydroisomerisation ; ethylbenzene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bifunctional catalysts containing an acidic as well as a hydrogenation/dehydrogenation function were prepared by solid-state ion exchange. Preparation and properties of Pd-loaded H-ZSM-5 are described in detail. The catalytic behavior of the reduced catalysts was investigated using hydrogenation and hydroisomerisation of ethylbenzene as a test reaction. The catalytic performance of the catalysts could be significantly improved by concomitant incorporation of Ca2+. This was advantageously achieved in a two-step procedure, where first a solid-state ion exchange with CaCl2 and subsequently a second solid-state ion exchange with PdCl2 was carried out. A Ca, H-ZSM-5 with 1.5 wt-% Pd obtained via this two-step procedure and subsequent reduction in H2 exhibited high activity, long life-time and good selectivity with respect to hydrogenation and hydroisomerisation of ethylbenzene to ethylcyclohexane and dimethylcyclohexanes, respectively. Electron micrographs of the reduced catalyst showed finely dispersed palladium with maximum size of about 2.0 nm.
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 14 (1992), S. 101-106 
    ISSN: 1572-879X
    Keywords: Catalysis ; aromatization ; propane ; ZSM-5 ; hydrogen acceptor ; intermetallic compound ; hydride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the hydride-forming intermetallic compound Zr2Fe on the aromatization of propane over high-silica zeolites of CVM type (Russian equivalent of ZSM-5) modified by Zn, Ga or Pt cations has been investigated. Aromatics yield and selectivity of aromatization are shown to increase essentially as a result of releasing hydrogen elimination by the intermetallic acceptor. The effect of hydrogen acceptor on propane conversion and product distribution appeared to be different depending on the composition of the catalyst used. Possible changes in the reaction mechanism in hydrogen removal conditions are discussed.
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  • 21
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    Springer
    Journal of molecular evolution 35 (1992), S. 1-6 
    ISSN: 1432-1432
    Keywords: Sugar synthesis ; Glyceraldehyde ; Iron(III) hydroxide oxide ; Catalysis ; Aldol condensation ; Prebiotic ; Molecular evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Iron(III) hydroxide oxide [Fe(OH)O] efficiently catalyzed the condensation of 25 MM dl-glyceraldehyde to ketohexoses at 25°C (pH 5–6). At 16 days the yields were sorbose (15.2%), fructose (12.9%), psicose (6.1%), tagatose (5.6%), and dendroketose (2.5%) with 19.6% of triose unreacted. Analysis at 96 days showed no decomposition of hexoses. Under these conditions Fe(OH)O also catalyzed the isomerization and rearrangement of glyceraldehyde to dihydroxyacetone and lactic acid, respectively. In these reactions, about 10% of the glyceraldehyde was oxidized to glyceric acid with concurrent reduction of the iron(III) to iron(II). The partial reduction of Fe(OH)O did not noticeably reduce its ability to catalyze hexose synthesis. The relationship of these results to prebiotic sugar synthesis is discussed.
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  • 22
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    Chromatographia 34 (1992), S. 398-410 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Catalysis ; Hydrodenitrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Many important parameters of surface catalysed reactions can be determined simultaneously, under nonsteady state conditions using Reversed-Flow Gas Chromatography. A simple, slightly modified gas chromatograph is required. The distorted diffusion bands, obtained experimentally for reactant and product(s), can be analysed mathematically, using simple PC programs, to give the pre-exponential factors and the exponential coefficients of a function consisting of the sum of two-four exponential functions of time. From these, and some geometrical and diffusional characteristics of the reaction cell, the values of adsorption, desorption and reaction rate constants, the overall mass transfer coefficients in the gas and in the solid catalyst, and the adsorption equilibrium constant, for both reactant and product(s) can be calculated. The above parameters were determined at various temperatures and over three catalysts for the hydrodenitrogenation of piperidine ton-pentane, an industrially important hydrotreating process. The results obtained can help to understand the mechanism of reactions on solid surfaces and to confirm experimentally theoretical calculations on adsorption and surface reactions.
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  • 23
    ISSN: 1040-0397
    Keywords: Catalysis ; flow analysis ; modified electrodes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for a layer, containing catalytic centers, coated on an electrode and used for the mediation of analyte in a flowing stream is proposed and solved. The model applies to a situation of a Gaussian concentration profile of analyte impinging on the outer edge of the mediating layer. It was found that the important parameters that limit the current magnitude are the diffusion coefficient of the analyte through the layer, the effective electron diffusion coefficient through the layer and the rate of reaction between the mediator and the analyte. On evaluation of literature data, it was found that layers, high catalyst loading and with high rates of electron exchange, lead to linear peak current height versus concentration plots.
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  • 24
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    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 167-182 
    ISSN: 1040-0397
    Keywords: Catalysis ; reaction mechanism ; channel electrode ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The shape of the current-voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution-flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pathways.
    Additional Material: 22 Ill.
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  • 25
    ISSN: 0570-0833
    Keywords: Alkaloids ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oriental plant Yuzuriha (Daphniphyllum macropodum) elaborates a fascinating family of polycyclic, squalene-derived alkaloids that provide a test for state-of-the-art methods of organic synthesis. The intriguing structures of these natural products have inspired us to design and explore two rather different approaches for their laboratory synthesis. This article recounts and contrasts these two different syntheses. The first approach was based on a method of synthetic design that emphasizes efficient construction of the polycyclic skeleton of the molecule (Corey's “network analysis”). A strategic bond was identified and the synthesis planned around the late formation of this bond. The synthesis that was designed by this approach proceeded smoothly until the point where it was necessary to remove functional groups that had been incorporated solely for the purpose of forming the strategic bond. Although the problems were eventually overcome, the resulting synthesis was too long and did not control the configuration of one of the stereocenters. The second approach was based on a possible biosynthesis of one of the alkaloids and provided surprisingly easy access to the simpler members of the family. The success of this synthesis led to a concrete proposal about the biosynthesis of the alkaloids and to the discovery of the astonishing transformation depicted in Scheme 27. In this marvelous reaction, an acyclic squalene derivative is converted by successive treatment with ordinary commodity chemicals into a pentacyclic alkaloid. The transformation involves the formation of four carbon-carbon bonds, two carbon-nitrogen bonds, and one carbon-hydrogen bond!
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  • 26
    ISSN: 1572-879X
    Keywords: Catalysis ; rare-earths ; lanthanides ; ytterbium ; oligomerization ; polymerization ; ethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ytterbium catalysts such as YbCl3/n-BuLi and (Cp2YbCl)2/RLi (R = Me, t-Bu, n-Bu,-CH2SiMe3) have been applied for the C-C-linkage of ethylene. Highly linear oligomers (n-alkanes) and polymers (high molecular weight polyethylene) were obtained. A reaction mechanism based on ytterbium-hydrides is proposed.
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  • 27
    ISSN: 1572-879X
    Keywords: Catalysis ; platinum ; microemulsion ; isomerisation ; hydrogenolysis ; hexanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Platinum catalysts have been prepared by depositing on alumina monodispersed particles of platinum prepared in reversed micellar solution. After deposition, the particles are well dispersed on the support and the size distribution has a sharp maximum around 2 nm. The isomerization and hydrogenolysis of hexanes were studied in order to get more information about the particle size effects on the selectivities of Pt catalysts in these reactions. It was found that this catalyst exhibits the same selectivities as a low dispersed ordinary platinum catalyst. These selectivity values are quite different from the ones given by a highly dispersed classical catalyst in spite of the fact that the catalysts have fairly similar average particle size. Such results confirm the conclusions previously proposed that isomerisation via cyclic mechanism and non selective hydrogenolysis of hexanes take place only on platinum particles smaller than 1 nm.
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  • 28
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    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1173-1180 
    ISSN: 0009-2940
    Keywords: Bis(2-oxazolines) ; Chelating ligands ; Zinc complexes ; Catalysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinitriles (5-7, 12, 13) react with enantiomerically pure β-amino alcohols (8 - 11,17) under zinc chloride catalysis to give optically active C2-symmetric bis(oxazolines). 1,2-Bis(2-oxazolin-2-yl)benzenes 1a - e are obtained under mild reaction conditions. 1H-NMR spectroscopy indicates the formation of 1:1 complexes 23 of these compounds with ZnCl2. The energy required for a conformational interconversion of zinc dichloride complex 23e was determined by variable-temperature 1H-NMR studies. An X-ray structure analysis was performed with the substituted [1,2-bis(2-oxazolinyl)benzene]zinc dichloride complex 23a.
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  • 29
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    Chemie Ingenieur Technik - CIT 63 (1991), S. 170-171 
    ISSN: 0009-286X
    Keywords: Air blowing ; Asphalt ; Catalysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 30
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    Applied Organometallic Chemistry 5 (1991), S. 167-172 
    ISSN: 0268-2605
    Keywords: Catalysis ; ethylation ; organosodium ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Study of the catalytic ethylation of p-t-butyltoluene in the presence of organosodium compounds, and of toluene in the presence of organopotassium compounds, was carried out at an ethylene pressure of 40 bar.Various yields of different products were obtained after 23 h of reaction in the presence of different tertiary polyamines used to complex and solubilize the organoalkali compounds.A higher initial ethylation rate was observed in the presence of organosodium than in the presence of organopotassium species. However, the thermal stability of organopotassium species being higher, much higher yields were observed in their presence in catalytic ethylation reactions than those observed previously.The results obtained concerning metallation or ethylation of hindered alkylaromatics may be interpreted by an anionic mechanism and the activation by a steric effect.
    Additional Material: 3 Ill.
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  • 31
    ISSN: 0749-1581
    Keywords: meso-Tetra(α, β, α, β-o-camphanylamidophenyl)porphyrin ; Rhodium complex ; Catalysis ; 1H and 13C NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a new chiral porphyrin, meso-tetra(α, β, α, β-o-camphanylamidophenyl)porphyrin, and its Mn(III) and Rh(III) derivatives is reported. Complete resonance assignments of both the 1H and 13C spectra of the ligand has been achieved via homo- and hetero-nuclear 2D NMR. Insertion of metal ions into the porphyrin ring was performed both in order to test the catalytic properties of the resulting complexes and to characterize the effect of of metal coordination on the spatial distribution of the bulky substituents. The Mn complex was then tested in catalytic chiral epoxidation reactions, giving low enantiomeric excesses (20%). The 2D NMR spectra of the Rh derivative indicate the existence of four molecular species generated by the interaction of the metal atom with the peripheral substituents of the porhyrin ring. In fact, a complex combination of axial coordination, together with the chirality of the camphanyl substituents, removed the symmetry of the porphyrin plane.
    Additional Material: 8 Ill.
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  • 32
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Retro reactions ; Computer chemistry ; Nobel lecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 33
    ISSN: 0570-0833
    Keywords: Chirality transfer ; Carbonyl compounds ; Addition ; Enantioselectivity ; Synthetic methods ; Alcohols ; Reaction mechanisms ; Catalysis ; Alkylation ; Organometallic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic addition of organometallic reagents to carbonyl substrates constitutes one of the most fundamental operations in organic synthesis. Modification of the organometallic compounds by chiral, nonracemic auxiliaries offers a general opportunity to create optically active alcohols, and the catalytic version in particular provides maximum synthetic efficiency. The use of organozinc chemistry, unlike conventional organolithium or -magnesium chemistry, has realized an ideal catalytic enantioselective alkylation of aldehydes leading to a diverse array of secondary alcohols of high optical purity. A combination of dialkylzinc compounds and certain sterically constrained β-dialkylamino alcohols, such as (-)-3-exo-dimethylaminoiso- borneol [(-)-DAIB], as chiral inducers affords the best result (up to 99% ee). The alkyl transfer reaction occurs via a dinuclear Zn complex containing a chiral amino alkoxide, an aldehyde ligand, and three alkyl groups. The chiral multiplication method exhibits enormous chiral amplification: a high level of enantioselection (up to 98%) is attainable by use of DAIB in 14% ee. This unusual nonlinear effect is a result of a marked difference in chemical properties of the diastereomeric (homochiral and heterochiral) dinuclear complexes formed from the dialkylzinc and the DAIB auxiliary. This phenomenon may be the beginning of a new generation of enantioselective organic reactions.
    Additional Material: 19 Ill.
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  • 34
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    Angewandte Chemie International Edition in English 30 (1991), S. 238-264 
    ISSN: 0570-0833
    Keywords: 3-Amino-2H-azirines ; Azirines ; Amino acids ; Peptides ; Heterocycles ; Synthetic methods ; 2-Aminoisobutyric acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recent upswing in peptide chemistry has been accompanied by an increasing interest in nonproteinogenic amino acids. These include the α,α-disubstituted glycines, the best known of which is Aib (2-aminoisobutyric acid, 2-methylalanine). These α-amino acids occur in natural oligopeptides such as the peptaibols, a class of membrane-active ionophores that has been isolated from fungal cultures. The twofold substitution at the α-C atom of the amino acids severely restricts the conformational freedom of the peptides and causes particular secondary structures to be favored; thus, α, α-disubstituted α-amino acids induce the formation of β turns or helices. 3-Amino-2H-azirines are ideal synthons for the construction of oligopeptides, cyclic peptides and depsipeptides (peptolides) containing such α,α-disubstituted α-amino acids. The presence of the ring strain in these molecules means that they can be used in peptide coupling without the need for additional activating reagents. Using 3-amino-2H-azirines a large array of heterocycles containing α, α-disubstituted α-amino acids as structural elements within their skeleton can be synthesized. The driving force in these reactions is the release of the strain on the three-membered ring, which usually takes place in a ring-expansion reaction. The mechanistic elucidation of these reactions, which can be quite complex, contains some surprises.
    Additional Material: 7 Ill.
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  • 35
    ISSN: 0570-0833
    Keywords: Rearrangement ; Synthetic methods ; Cyanides ; Isocyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Until recently the isocyanide-cyanide rearrangement was of interest almost solely as an example of a unimolecular gas-phase reaction, and kinetic studies had been carried out in only a few simple cases. Kinetic measurements in solution were made possible only by the discovery and suppression of a parallel free-radical chain process which leads to the same products. The rate of the isomerization is almost independent of the structure of the starting material and of the substituents present. An exception is provided by extreme steric hindrance in three dimensions which, as in tris-α-substituted triptycyl isocyanides, leads to a considerable increase in the activation energy. The results can be interpreted in terms of a purely sigmatropic mechanism, as predicted by ab initio calculations. The preparative application of this rearrangement reaction requires the suppression of side reactions and can best be carried out by flash pyrolysis; yields are then almost quantitative. Allyl isocyanides react without allyl isomerization, optically active isocyanides with complete retention of configuration. New, economically interesting syntheses for the known nonsteroidal anti-inflammatory drugs ibuprofen and (S)-naproxene are described. The application of the useful synthetic building blocks, the optically active β-acyloxy cyanides, which are formed from optically active α-amino acids, will be demonstrated.
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  • 36
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    Angewandte Chemie International Edition in English 30 (1991), S. 1387-1416 
    ISSN: 0570-0833
    Keywords: Calicheamicins ; Synthetic methods ; Antitumor agents ; Antibiotics ; Enediynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, biologically active substances from nature often provide excitement, stimulation, challenges, and opportunities for the scientific and medical communities. Experience and wisdom dictate investigation of their chemistry and pursuit of their chemical synthesis for more often than not, the rewards for both chemistry and medicine are great. The enediyne anticancer antibiotics are a rapidly emerging class of such compounds derived from bacterial sources. Combining unprecedented and highly unusual molecular architecture, phenomenal biological activities and fascinating modes of action, these DNA cleaving compounds burst onto the scene in the latter half of the 1980s when their structures became known, and they rapidly moved to center stage. Today the enediyne family includes the neocarzinostatin chromophore, the calicheamicins, the esperamicins, and the dynemicins, and soon the number of family members is certain to increase. These molecules elicited extensive research activities in chemical, biological, and biomedical circles and inspired the design of a number of novel molecular assemblies to probe and mimic their chemical and biological actions. A new body of synthetic technology and several novel synthetic strategies have already been devised to address the challenges posed by these molecules, and several new DNA cleaving agents have been designed and synthesized. This article summarizes the chemistry and biology of the enediynes and discusses mechanistic, synthetic, molecular design, and DNA cleavage aspects associated with the field.
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  • 37
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    Angewandte Chemie International Edition in English 30 (1991), S. 1531-1546 
    ISSN: 0570-0833
    Keywords: Amino acids ; Asymmetric synthesis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Amino acids protected at nitrogen in quite different ways can be transformed without racemization into the corresponding α-amino aldehydes. Provided one chooses the right protecting groups (e.g., two benzyl residues on nitrogen) it is possible for the first time to carry out Grignard-like, aldol, and Me3SiCN additions, and hetero-Diels-Alder reactions with a high degree of nonchelation control. If the reactions of classical carbanions turn out to be nonselective, transmetalation, for example into organotitanium reagents, constitutes an important tool in controlling stereoselectivity. Diastereoselectivity can be reversed by specific variation of the protecting group and reagent. “Protecting-group tuning”, “metal tuning”, and “ligand tuning” are very useful in reactions of α-amino aldimines as well. The α-amino aldehydes can also be converted by Wittig reactions into electron-poor γ-amino olefins, which in turn undergo stereoselective cuprate, Michael, and cycloadditions.
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  • 38
    ISSN: 0570-0833
    Keywords: Arene ligands ; Intermediates ; Cocondensation ; Sandwich complexes ; Synthetic methods ; Iron ; Metal atoms ; Cobalt ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 1969, P. L. Timms reported the first preparative cocondensation reactions of metal vapors with organic and inorganic substrates. The use of this technique in preparative chemistry soon spread rapidly, but in recent years there has been less activity in this sector. If metal atom reactions are not utilized primarily for the formation of new products, but for the synthesis of highly reactive intermediates, a new synthetic strategy may be developed. Our aims are reaction sequences which, based on an effective cocondensation reaction, lead gradually and selectively to new substance classes. This principle can be illustrated by the example of the cocondensation products of arenes and iron, cobalt, or nickel vapor, which decompose between -70 and -50°C. The classes of products accessible by this method extend from clusters, through π-complexes, organophosphorus and organoboron cage compounds to pure organic cycloaddition products.
    Additional Material: 13 Ill.
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  • 39
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Reaction mechanisms ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Despite the great importance of heterogeneous catalysis, research in this field has long been characterized by its empiricism. Now, however, thanks to the rapid development of methods in surface physics, the elementary steps can be identified at the atomic level and the underlying principles understood. Defined single crystal surfaces are employed as models, based on the analysis of the surfaces of ‘real’ catalysts. Direct images, with atomic resolution, can be obtained using scanning tunneling microscopy, while electron spectroscopic methods yield detailed information on the bonding state of adsorbed species and the influence of catalyst additives (promotors) upon them. The successful application of this approach is illustrated with reference to the elucidation of the mechanism of ammonia synthesis. The catalyst surface is usually transformed under reaction conditions, and, as the processes involved are far-removed from equilibrium, such transformations can lead to intrinsic spatial and temporal self-organization phenomena. In this case, the reaction rate may not remain constant under otherwise invariant conditions but will change periodically or exhibit chaotic behavior, with the formation of spatial patterns on the catalyst surface.
    Additional Material: 20 Ill.
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  • 40
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    Angewandte Chemie International Edition in English 29 (1990), S. 977-991 
    ISSN: 0570-0833
    Keywords: Biaryls ; Arenes ; Synthetic methods ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and utilization of specific biaryl systems, particularly those which suffer hindered rotation, is a demanding goal not only in the synthesis of natural products and Pharmaceuticals, but also for example in the discovery of new reagents for asymmetric synthesis. This article will attempt to provide a topical review of modern, efficient processes for the specific preparation of biaryls. This appears to be of particular urgency, since, under the pressure of continually increasing demand, a wealth of new or modified synthetic approaches to the ever more important biaryl systems has been realized in recent years. The high standard which has been reached in this field is impressively demonstrated by regio- and stereoselective syntheses of important biaryl natural products such as steganone, ancistrocladine, ancistrocladisine, and dioncophylline A. Besides the utilization of asymmetric induction in the actual coupling step, the thermodynamically or kinetically controlled torsion of biaryl axes belongs to the most important concepts discussed.
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  • 41
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    Angewandte Chemie International Edition in English 29 (1990), S. 609-626 
    ISSN: 0570-0833
    Keywords: Oxy-Cope rearrangement ; Ring expansion ; Cope rearrangement ; Diastereoselectivity ; Rearrangement ; Ketones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Convergency is a highly serviceable aspect of organic synthesis, particularly when its application is accompanied by high levels of chirality transfer and regiocontrol. A reaction that is notably well suited to these objectives is the oxy-Cope rearrangement. In addition, the benefits that can accrue from suitable condensation of β γ-unsaturated ketones with a vinyl organometallic and subsequent [3,3] sigmatropic shift are substantive enhancement in structural complexity and the ability to generate a myriad of polycyclic frameworks. Another profitable feature is the complementary regeneration of the carbonyl group in a new structural context. In view of the pivotal role played by the carbonyl functionality in synthetic transformations, reacquisition of such a reaction site translates into heightened chemical versatility. The trajectories followed by vinyl organometallics as they engage in 1,2 addition to ketones are gradually being understood. Proper diastereoselective control of this bond-making process, when coupled with full awareness of the chair or boat topography adopted during the ensuing oxy-Cope electronic reorganization, provides for exciting new strategy-level dimensions not often available in other contexts. The use of this two-step sequence as a prelude to a third chemical event clearly serves to expand the possibilities for molecular construction still more. While a considerable amount of the work to date has focused on the preparation of rather elaborate carbocyclic molecules, principally with a view to gaining access to complex natural products, the possibilities for heterocyclic synthesis are currently being accorded increased attention.
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  • 42
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    Angewandte Chemie International Edition in English 29 (1990), S. 1320-1367 
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Future of chemistry ; Chemistry today ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review article is an attempt to sketch the important developments in organic synthesis during the past 25 years, and to project them into the future. - The primary motivations that once induced chemists to undertake natural product syntheses no longer exist. Instead of target structures themselves, molecular function and activity now occupy center stage. Thus, inhibitors with an affinity for all the important natural enzymes and receptors have moved to the fore as potential synthetic targets. - New synthetic methods are most likely to be encountered in the fields of biological and organometallic chemistry. Enzymes, whole organisms, and cell cultures for enan-tioselective synthesis of specific substances have already been incorporated into the synthetic arsenals of both research laboratories and industry. In addition, designing appropriate analogues to transition states and intermediates should soon make it possible, with the aid of the mammalian immune system and gene technology, to prepare catalytically active monoclonal antibodies for almost any reaction; perhaps, more important, such processes will increasingly come to be applied on an industrial scale.-The discovery of truly new reactions is likely to be limited to the realm of transition-metal organic chemistry, which will almost certainly provide us with additional “miracle reagents” in the years to come. As regards main group elements (“organoelemental chemistry”), we can surely anticipate further stepwise improvements in experimental procedures and the broader application of special techniques, leading to undreamed of efficiency and selectivity with respect to known procedures. The primary center of attention for all synthetic methods will continue to shift toward catalytic and enantioselective variants; indeed, it will not be long before such modifications will be available with every standard reaction for converting achiral educts into chiral products. Analysis, spectroscopy, structure determination, theory, and electronic data processing have all become indispensable in organic synthesis. Only with the aid of these “tools” will the methods of organic chemistry permit selective syntheses of ever larger and more complex systems on both the molecular and supramolecular levels. - Examples have been introduced throughout this discourse to illustrate its many themes, and a very comprehensive bibliography should help the interested reader become more familiar with important keywords and authors.[The list of references is also available upon request in the form of a Microsoft Word© file on diskette.] - This article will have served its intended purpose if it changes the minds of some of those who claim organic chemistry is a mature science, and if it causes students to discover the vitality and forcefulness with which organic synthesis is meeting new challenges and attempting to fulfill old dreams.Er zeigt uns so in seinem wissenschaftlichen Leben, daß die Chemie nicht von einer Theorie, nicht von einer Methode aus zu erschöpfen ist, und daß Erkenntnis und Nutzen in ihr untrennbar verwoben sind.“He showed us through his scientific life that chemistry cannot be exploited fully with the aid of a single theory or a single methodology, and that it is a field in which knowledge and application are inextricably linked.” G. Bugge: Das Buch der großen Chemiker, Vol. 2, 4th reprint, Verlag Chemie, Weinheim 1974.R. Koch, writing about Louis Pasteur
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  • 43
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    Angewandte Chemie International Edition in English 29 (1990), S. 235-244 
    ISSN: 0570-0833
    Keywords: Homogeneous catalysis ; Nickel ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10-15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon-carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis. - This review is primarily concerned with nickel-catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.
    Additional Material: 3 Ill.
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  • 44
    ISSN: 0570-0833
    Keywords: Proton transfer ; Catalysis ; Enzyme catalysis ; Hydrolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid-base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid-base and enzymatic catalysis.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 45
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 93-101 
    ISSN: 0570-0833
    Keywords: Organometallic catalysts ; Catalysis ; Reaction mechanisms ; Lithium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n-heptane as solvent indicate the following sequence of reactions: 1. formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, and proof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler-type catalyst. All the reactions can be formulated in the form of cyclic structures with electron-deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 46
    ISSN: 0570-0833
    Keywords: Quinones ; Quinones ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If catechol or other hydroquinones are dehydrogenated in the presence of a nucleophilic reagent, the latter reacts, usually by Michael addition, with the quinone formed in situ. The wide range of possible variations offered by this synthetic method is comprehensively described in the present paper. procedures are given for carrying out typical reactions.
    Type of Medium: Electronic Resource
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  • 47
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 185-191 
    ISSN: 0570-0833
    Keywords: Coordination modes ; Catalysis ; Cyclooctatetraenes ; Reppe chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relationship between the structure and the catalytic activity of nickel(II) complexes in the synthesis of cyclooctatetraene by the method of W. Reppe is discussed. The cyclotetramerization of acetylene takes place within labile Ni(II)-acetylene π-complexes. Inhibition tests have made it probable that four molecules of acetylene are grouped around the nickel ion in the transition state, in a configuration which favors the formation of the eight-membered ring.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 48
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 250-260 
    ISSN: 0570-0833
    Keywords: Unsaturated fatty acids ; Fatty acids ; Carbonyl olefination ; Synthetic methods ; Wittig reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that carbonyl olefination, i.e. the reaction of carbonyl compounds with alkylidene phosphoranes, can be sterically controlled. In some cases cis-olefins can be obtained by proper choice of the reaction conditions; trans-olefins are formed only in the presence of suitable structural factors. These cis-and trans-olefination reactions have opened new, stereo-specific routes to unsaturated and polyunsaturated fatty acids with differing positions and sequences of cis- and trans-double bonds and to ω-hydroxy and branched chain fatty acids.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 49
    ISSN: 0570-0833
    Keywords: Cyclization ; Dialdehydes ; Nitromethane ; Carbohydrates ; Polyalcohols ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Condensation of nitromethane with suitable diadehydes in alkaline medium provides a general method of cyclization, in which the methyl group of the nitromethane is incorporated into the ring. This method leads to 5-, 6-, and 7-membered rings and is equally applicable to aliphatic, aromatic, and sugar dialdehydes. For example, glyoxal is converted into 1,4-dideoxy-1,4-dinitro-neo-inositol, and glutaraldehyde into trans-2-nitrocyclohexane-1,3-diol, while the corresponding cyclization of xylo-trihydroxyglutaraldehyde leads to deoxy-nitroinositols having the scyllo, myo-1, and muco-3 configurations.-In the case of aromatic dialdehydes, the cyclization is accompanied by elimination of water. Thus, phthalaldehyde, naphthalene-2,3-dicarboxaldehyde, and homophthalaldehyde yield, respectively, 2-nitroindenol, 2-nitrobenzindenol, and 2-nitronaphthalene. -Application of the method to sugar dialdehydes (aldehydic diglycol derivatives of monosaccharides formed by periodate oxidation) constitutes an excellent synthesis of 3-amino sugars, since 3-deoxy-3-nitropyranoses are formed smoothly on cyclization, and the corresponding 3-amino derivatives are obtained by hydrogenation. Thus, the reaction sequence: periodate oxidation → cyclization with nitromethane → hydrogenation, leads in the case of α-and β-D-pentosides to 3-amino-3-deoxy-D-and-L-pentosides, respectively, with ribo, xylo, and arabino configurations. α-D-hexosides give derivatives with gluco, manno, and galacto configurations. 3-Amino-3,6-dideoxyglucosides of the D-and L-series are obtained from 6-deoxy-D-or-L-hexosides, respectively, and 3-aminohexosans with gulo, ido, and altro configurations are obtained from 1,6-anhydro sugars. Cyclization of the dialdehydes obtained from sedoheptulose and methyl 4,6-O-ethylidene-α-D-glucoside by periodate oxidation, leads to 3-nitro and, after hydrogenation, to 3-amino derivatives of 3-deoxyheptopyranoses.
    Type of Medium: Electronic Resource
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  • 50
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 24-29 
    ISSN: 0570-0833
    Keywords: 3-Aminoquinazol-4-one ; 3-Aminobenzotriazin-4-one ; Quinazolones ; Benzotriazinones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the derivatives of 3-aminoquinazol-4-one and 3-aminobenzotriazin-4-one are compounds with narcotic, sedative, analgetic, and muscle-relaxant properties. Of special interest are compounds with one or several urethane groups and those substituted in the 3-position by a morpholine moiety.
    Additional Material: 4 Tab.
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  • 51
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 225-238 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review discusses syntheses leading to a new type of N-vinylpyridinium salts, to novel anionocyanines, to aminophenazines and alloxazines, as well as to (aza-) dehydroquinolizinium, acridizinium, and morphanthridizinium salts. In addition, Mannich reactions and aminoalkylations at active methylene groups of cycloimmonium salts, and their reactions with amines are treated. The possibilities offered by the “Ortoleva-King” reaction are demonstrated using numerous examples, such as a new route leading to the yohimbine skeleton.
    Type of Medium: Electronic Resource
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  • 52
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 309-323 
    ISSN: 0570-0833
    Keywords: s-Triazines ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and properties of s-triazine are discussed. Nucleophilic reagents (even water) readily attack s-triazine. Thus, open-chain and heterocyclic compounds, e.g. formamidines, aminomethylene compounds, and triazole, pyridine, and pyrimidine deravatives are accessible from s-triazine. With amidines and imido ethers substituted triazines are obtained (by trans-triazination).The latter are formed via open-chain intermediates.
    Additional Material: 11 Tab.
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  • 53
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 380-393 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cleavage of N-phenylpyridinium or N-vinylpyridinium salts with secondary aliphatic amines leads to aromatic amino compounds or enamines which are often unobtainable by other routes. The other fragment, glutacondialdehyde or its monoanil, gives azulenes, as shown by Ziegler and Hafner, as well as König; these compounds can also be prepared from alkylpyridinium salts with cyclopentadienylsodium (Hafner). Syntheses of labile aldehydes which are otherwise difficult to obtain and of α-ketocarboxylic acids, starting from pyridinium salts and proceeding via nitrones or α-cyanoanils, are illustrated by many new examples. Benzimidazoles, benzothiazoles, and amidines are accessible from pyridinium salts via nitrones or α-cyanoanils; cyanoanils can be transformed into quinoxalines (including xanthopterine), perimidines, etc. Furthermore, nitrosonaphthols and nitrosonaphthylamines react with pyridinium salts containing an active methylene group on the nitrogen, leading to new ring systems. Further synthetic possibilities arise from nucleophilic displacements of the pyridine in pyridinium salts by SN 2 reactions. Combination of the route via nitrones with the methods of Arndt-Eistert, Ortoleva-King, or with chloromethylation constitutes a significant enlargement of its range of application. The formation of α-cyanoanils from diazoketones permits synthesis of α-keto-β-amino acids from α-amino acids, or of phenylglyoxylic acids from benzoic acids by chain extension.
    Type of Medium: Electronic Resource
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  • 54
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 8-21 
    ISSN: 0570-0833
    Keywords: Addition ; Immonium ions ; Isocyanides ; Amino acids ; Synthetic methods ; Alkylidene ammonium ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The α-addition of immonium ions and anions (OH-, SeH-, S2O3 2-, N3- NCO- NCS-, R—CO2 -, RO—CO2-) to isonitriles, accompanied by secondary reactions provides a means for the one-stage synthesis of organic nitrogen compounds starting with two to five different components. Thus, by the condensations of amines (ammonia, primary, and secondary aliphatic and aromatic amines, hydrazines) and aldehydes or ketones with isonitriles and acids, a number of α-aminocarboxylic acid amides, thioamides, selenoamides, 1,5-disubstituted retrazoles, hydantoin imides, thiohydantoin imides, α-acylamino carboxylic acid amides, oligopeptide derivatives, β-lactams, derivatives of penicillanic acid, urethanes, diacylimides, and various hydrazine derivatives, can be prepared. The reactions are easily carried out and take place under mild conditions. Yields of more than 90% are frequently encountered.
    Additional Material: 4 Tab.
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  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 80-88 
    ISSN: 0570-0833
    Keywords: Oxidation ; Palladium ; Catalysis ; Alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of olefins to carbonyl compounds with palladium compounds, especially the oxidation of ethylene to acetaldehyde, is at present carried out on a technical scale. The reaction takes place via a palladium-olefin complex, the formation of which is inhibited by halide ions. Hydrolysis to the carbonyl compound is inhibited by hydrogen ions. The knowledge gained by studying the reaction of olefins with pure solutions of palladium salts allows important conclusions to be drawn concerning the action of technical catalyst solutions containing copper and palladium chloride.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 56
    ISSN: 0570-0833
    Keywords: Amides ; Azolides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 57
    ISSN: 0570-0833
    Keywords: Michael addition ; Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By Michael addition of the active methylene groups in pyridinium salts onto suitable acceptor compounds, α-pyridones, substituted pyridines, particularly pyridinecarboxylic acids and pyridylpyridines, including the minor alkaloid of tobacco nicotelline and annelized pyridines, can be prepared by a simple procedure and generally in good yields. From the Michael adducts, polycyclic aromatic hydrocarbons, e.g. substituted fluoranthenes and “bisfluoranthenes” can be prepared; internal Michael addition leads to pyrrolinopyrdinium salts. For example, Michael addition of pyridinium salts onto quinones gives phenacyl substituted quinones, from which benzofurans and cinnolines can be readily obtained.
    Type of Medium: Electronic Resource
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