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  • 2000-2004  (14)
  • 1985-1989  (39)
  • 1975-1979  (23)
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  • Catalysis
  • Free radicals
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  • 1
    ISSN: 1438-2385
    Keywords: Mayonnaise ; Structure ; Volatiles ; Free radicals ; Sensory analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of toxicology 73 (2000), S. 588-593 
    ISSN: 1432-0738
    Keywords: Key words Polychlorinated biphenyls (PCB) ; Synaptosomes ; Reactive oxygen species (ROS) ; Free radicals ; Mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In this paper the effect of polychlorinated biphenyls (PCBs) on the production of reactive oxygen species (ROS) in rat synaptosomes is elucidated. The effect of methylmercury (MeHg) on rat synaptosomes was included as a positive control since several studies have investigated the ability of this substance to produce ROS. The exposure of the synaptosomes to the congener 2,2-dichlorobiphenyl (2,2′-DCB; 12.5 μM) produced a linear increase in the formation of 2′,7′-dichlorofluorescein (DCF) as a measure for the production of ROS. The congeners 2,2′-DCB (12.5 μM) and 3,3′-DCB (12.5 μM) stimulated, as expression of ROS production, a significant increase in DCF formation formation compared to the control. The congeners 2-chlorobiphenyl (2-CB) and 2,2′,6-trichlorobiphenyl (2,2,6′-TCB) were active at 50 μM, whereas 2,2′,4,4′,5,5′-hexachlorobiphenyl (2,2′,4,4′,5,5′-HCB), 4,4′-DCB and 2,2′,6,6′-tetrachlorobiphenyl (2,2′,6,6′-TeCB) were not active at this concentration. The increased formation of ROS in response to 2,2′-DCB and MeHg in the synaptosomes was dependent on extracellular Ca2+. A phospholipase C inhibitor, U73122, was shown to significantly decrease the ROS formation induced by 2,2′-DCB, but did not reduce the ROS formation induced by MeHg. Ethanol (1%), a phospholipase D modulator, reduced the ROS formation induced by MeHg and by 2,2′-DCB by 33 and 52%, respectively. Wortmannin (25 nM), an inhibitor of phosphatidylinositol 3-kinase, completely inhibited the ROS formation induced by MeHg and 2,2′-DCB. It appears that the ROS-stimulating PCBs are the same congeners found to be neuroactive in other types of study. Phospholipase C and D and phosphatidylinositol 3-kinase seem to be involved in the intracellular signalling system that leads to ROS formation during PCB exposure.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    JBIC 5 (2000), S. 2-15 
    ISSN: 1432-1327
    Keywords: Iron-sulfur clusters ; Cluster interconversions ; Electron transfer ; Sensing and regulating ; Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    JBIC 5 (2000), S. 213-217 
    ISSN: 1432-1327
    Keywords: Key words Nitric oxide ; Nitrosothiols ; Copper(I) ; Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Copper and other transition metal ions and their complexes are catalysts for the decomposition of nitrosothiols. In this way they catalyze the biological functions of nitrosothiols. The kinetics and mechanism of the reaction of two nitrosothiols, S-nitrosothiolactic acid and S-nitrosoglutathione (GSNO), with copper(I) are reported. The kinetics of the reaction of Cu(MeCN) n + (n=0–3) with the nitrosothiols were studied. The results indicate that Cu+ aq is the active species in the GSNO system, with k(Cu+ aq+GSNO)=(9.4 ±2.0)×107 dm3 mol−1 s−1 . The results also indicate that the Cu(MeCN) n + (n=0–3) complexes react with S-nitrosothiolactic acid. Transient species are formed in these processes. The results suggest that these species contain copper(I) and thiol. The results shed light on the catalytic role of copper complexes in the decomposition of S-nitrosothiols.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1438-2199
    Keywords: Keywords: Amino acids ; Quinolinic acid ; Kynurenines ; Melatonin ; Deprenyl ; Antioxidants ; Free radicals ; Reactive oxygen species ; Neuroprotection ; Neurotoxicity ; Excitotoxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary. Several differences exist between quinolinic acid and N-methyl-D-aspartate (NMDA) in the potency and pharmacology of their neurotoxic actions in the brain, suggesting that quinolinic acid may act by mechanisms additional to the activation of NMDA receptors, possibly involving lipid peroxidation. In the present review, studies are considered which have attempted to determine whether free radicals might contribute to the neuronal damage induced by quinolinic acid. Following Injections into the hippocampus of anaesthetised rats, quinolinic acid induced damage is prevented by melatonin, by an action not blocked by the melatonin receptor blocker luzindole. Deprenyl, but not the non-selective monoamine oxidase inhibitor nialamide, also prevent quinolinic acid-induced damage. In vitro, seversl groups have shown that quinolinic acid can induce lipid peroxidation of brain tissue The results suggest that free radical formation contributes significantly to quinolinic acid-induced damage in vivo.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 203 (2000), S. 17-21 
    ISSN: 1573-4919
    Keywords: Free radicals ; Ca-Mg-ATPase ; ischaemia ; coronary artery ; immune-response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Endo/sarcoplasmic reticulum (ER) Ca2+-pumps are important for cell survival and communication but they are inactivatedby reactive oxygen species (ROS).We have previously reported that the Ca2+-pump isoform SERCA3a is more resistant than SERCA2b to damage by peroxide. Since peroxide and superoxide differ in their redox potentials, we now report the effects of superoxide on the two Ca2+-pump isoforms. We isolated microsomes from HEK293 cells transiently transfected with SERCA2b or SERCA3a cDNA. We exposed these microsomes to superoxide which was generated using xanthine plus xanthine oxidase and catalase to prevent accumulation of peroxide due to superoxide dismutation. Superoxide damaged the Ca2+- transport activity of both isoforms but SERCA3a was damaged at higher concentrations of superoxide and upon longer periods of exposures than was SERCA2b. Thus the SERCA3a isoform is more resistant than SERCA2b to inactivation by both superoxide and peroxide. (Mol Cell Biochem 000: 000-000, 1999)
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Reaction kinetics and catalysis letters 69 (2000), S. 145-152 
    ISSN: 1588-2837
    Keywords: Catalysis ; methane ; lanthanum oxide ; stronlium ; nickel ; copper
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methane transformation over Ni and Cu modified Sr2+/La2O3 catalysts has been studied. These species favor formation of reducible mixed oxides and change the surface reactivity of the Sr2+/La2O3 system, modifying the reaction mechanism, since Sr2+/La2O3 favors methane oxidative coupling but with copper methane combustion is favored and nickel favors partial oxidation.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1434-193X
    Keywords: Bicyclo[1.1.1]pentane ; Haloarenes, cross-coupling of ; Propellanes ; Palladium ; Catalysis ; Small-ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Radical addition reactions of organyl iodides 7a-s onto [1.1.1]propellane (2) followed by halogen-lithium exchange and transmetallation with zinc chloride, as well as additions of Grignard reagents to 2, have furnished a variety of 3-substituted bicyclo[1.1.1]pentyl-1-magnesium (14) and -zinc (19) derivatives. The latter have been coupled with various alkenyl, aryl, and biaryl halides and triflates under NiCl2dppe, Pd(PPh3)4, or PdCl2(dppf) catalysis to give a number of 1,3-disubstituted bicyclo[1.1.1]pentyl derivatives 17, 20, and 23, several of which exhibit liquid crystalline properties, in moderate to very good yields. The coupling products 20ca, 23ab, 23ae, 23ff, and 23fg have been further transformed to yield bicyclo[1.1.1]pentyl derivatives 32, 24ab, 24ae, 27ff, and 27fg, respectively, bearing alkynyl, cyano, and/or alkenyl groups.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 701-705 
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Catalysis ; Addition reactions ; N ligands ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quaternary stereocenters were constructed with an enantioselectivity of up to 91% ee under aerobic conditions and at ambient temperature in the Michael reaction of β-dicarbonyl compounds and methyl vinyl ketone with Ni(OAc)2·4H2O and optically active trans-1,2-diaminocyclohexane as a chiral catalyst.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 655-658 
    ISSN: 1434-1948
    Keywords: Molybdenum ; Copper ; Oxidation ; Alcohols ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of activated primary and secondary alcohols to the corresponding aldehydes and ketones can be carried out with molecular oxygen, in the presence of the bimetallic molybdenum-copper system MoO2(acac)2-Cu(NO3)2 as catalyst.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 225-237 
    ISSN: 1434-193X
    Keywords: Lithium ; Arenes ; Catalysis ; Organolithium ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The applications of arene-catalyzed lithiation reactions during recent years are reviewed. This methodology has been used to obtain functionalized organolithium compounds from halogenated as well as nonhalogenated materials, such as heterocycles, sulfones, triflates, ethers, thioethers, amides, and esters. This arene-catalyzed lithiation has also been used in the preparation of polylithiated intermediates. Sub-stoichiometric amounts of the arene may be supported on a polymeric material, its catalytic activity being as efficient as in the solution version.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1434-193X
    Keywords: Macrocycles ; Palladium ; Polymers ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Preparation of the 15-membered cycle (E,E,E)-1,6,11-tris[(2,4,6-triisopropylphenyl)sulfonyl]-1,6,11-triazacyclopentadeca3,8,13-triene (8) is reported. This cyclic triolefin forms a stable Pd0 complex 9 which catalyzes several cross-coupling reactions and can be recovered. Anchoring to a polystyrene framework affords a solid version of the catalyst, which is recovered by simple filtration and reused without loss of catalytic activity.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 15
    ISSN: 1437-160X
    Keywords: Rheumatoid factor ; IgG ; Free radicals ; Gamma globulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Alteration of IgG by oxygen-derived free radicals has been implicated in an in vivo process which renders IgG autoantigenic and leads to the production of rheumatoid factor (RF) and the perpetuation of inflammation, as in rheumatoid arthritis (RA). In this study the impact of UV irradiation on IgG was investigated as well as the ability of RF to bind to UV-altered gamma globulin. Inhibition studies of the binding of 125I aggregated human gamma globulin (AHG) to RF-coated sepharose beads show that UV-irradiated IgG is able to bind RF to the same extent as AHG. Binding studies to 125I-C1q proved that UV-irradiated IgG could bind the first complement component, but also that the complement system could be activated as illustrated by the C3a generation. These results support the hypothesis that free radical damage to gamma globulins plays a role in the chronicity of the inflammatory reaction in RA.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Archives of dermatological research 281 (1989), S. 40-44 
    ISSN: 1432-069X
    Keywords: Hermansky-Pudlak syndrome ; Calcium ; Free radicals ; Keratinocyte cell cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Cell cultures of keratinocytes, established from four Hermansky-Pudlak, syndrome (HPS) homozygotes yielded low membrane-associated thioredoxin reductase activities compared with normal healthy adult controls. This low activity has been shown to be caused by a special sensitivity of the enzyme to calcium. 45Calcium has been used to compare the kinetics for the transport and bioaccumulation of this regulatory cation in keratinocyte cultures of a kindred with HPS (i.e., one HPS homozygote, one HPS obligate heterozygote, one normal family member, and healthy adult controls). The results show that both HPS-homozygous and-heterozygous cells bind more extracellular calcium than noncarriers of this genetic defect, and HPS homozygous cells appear to have a defective calcium transport system.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Archives of dermatological research 281 (1989), S. 362-365 
    ISSN: 1432-069X
    Keywords: Dithranol ; Platelet activating factor ; Prostaglandins ; Histamine ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of different pharmacological substances on dithranol-induced irritative dermatitis were studied in mice. Pretreatment of the animals with a specific platelet activating factor (PAF) antagonist, BN 52021, significantly reduced the ear swelling in a dose-dependent manner. The cyclooxygenase inhibitor indomethacin, the antihistamine clemastine, and the antioxidant superoxide dismutase also proved to be effective in the reduction of the dermatitis. The results provide evidence of the coinvolvement of PAF, prostaglandins, histamine, and reactive oxygen radicals in dithranol-induced irritative dermatitis in mice.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Pharmacy world & science 11 (1989), S. 199-206 
    ISSN: 1573-739X
    Keywords: Cataract ; Free radicals ; Multiple organ failure ; Oxygen ; Reflex sympathetic dystrophy ; Respiratory distress syndrome, adult ; Stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The early involvement of free radicals in the evolution of life may explain their ubiquitous presence and vital physiological role. Imbalance between protection against free radicals and their generation, explains the likely association of various diseases with toxic oxygen species. An elaborate defence system against oxygen-free radicals exists. The effects of oxidative stress are manifold. Direct demonstration of oxygen radicals in intact biological systems is difficult. Frequently, effect-related measurements are used in this respect. The clinical conditions adult respiratory distress syndrome and multiple organ failure, reflex sympathetic dystrophy and sugar cataract are discussed and the role of oxygen radicals in the aetiology of these diseases are described.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    European journal of plastic surgery 12 (1989), S. 111-116 
    ISSN: 1435-0130
    Keywords: Orgotein ; Superoxide dismutase ; Free radicals ; Ischemia-reperfusion ; Inflammation ; Burns ; Catalase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Free radicals are incriminated as being responsible for cellular lesions during irradiation, inflammatory phenomena, and the syndrome of ischemia followed by reperfusion. These 3 processes are of interest to plastic surgeons. It would be useful to protect the tissue from the free radicals during irradiation for breast cancer with a view to secondary reconstruction in tissue of unproved quality. Limiting the inflammatory phenomena in burned patients would also be helpful. The ischemic reperfusion syndrome occurs in flap surgery, in microsurgery and during all surgical procedures which involve clamping pedicles. Finally shock, which causes an ischemic reperfusion syndrome over the entire organism, also favors the formation of free radicals and it is interesting to consider the possibility of combating the free radicals in the shock accompanying extensive burns. Among the enzymes destined to fight these radicals, superoxide dismutase was the first to be discovered and is the best known, since it has been the subject of numerous animal experiments and many applications in humans. Currently it seems more efficient than other substances in combating ischemic type lesions.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 533-535 
    ISSN: 0009-2940
    Keywords: Free radicals ; Triphenylmethyl radicals ; ESR measurements ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Sterically Hindered Free Radicals, XIX. - Stable 4,4′,4″-Trisubstituted Triphenylmethyl RadicalsThe title radicals (4-R—C6H4)3C. (1), R = F, Cl, Ph, OMe, NO2, tBu, OEt, SMe, CN, CF3, have been prepared, the latter four for the first time, and the ESR spectra have been recorded. aoH, amH, and apR are listed. The intensities of the ESR signals remain constant within the accessible range of -30 to + 100°C. Within this range these radicals are kinetically stable and do not dimerize like other trityls by, e.g., α,p-, α,o-, α,α -recombinations.
    Notes: Die Titelradikale (4-R—C6H4)3C· (1), R = F, Cl, Ph, OMe, NO2, tBu, OEt, SMe, CN, CF3, wurden dargestellt, davon die vier letzten erstmalig, und mittels ESR-Spektroskopie vermessen. aoH, amH und apR werden angegeben. Die ESR-Signale bleiben im gesamten zugänglichen Temperaturbereich - 30 bis + 100°C in ihrer Intensität unverändert. Daraus folgt, daß alle diese Radikale im genannten Temperaturbereich kinetisch stabil sind, also nicht wie andere Trityle zu Dimerisierungen, etwa α,p-, α,o-, α,α-, neigen.
    Additional Material: 1 Tab.
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  • 21
    ISSN: 0570-0833
    Keywords: Metallo-ene reaction ; Ene reaction ; Synthetic methods ; Catalysis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C—O→C—;Pd-→ C—C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon-carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.
    Additional Material: 11 Tab.
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  • 22
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 135-145 
    ISSN: 0570-0833
    Keywords: Reaction mechanisms ; Heterogeneous catalysis ; C-H activation ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterogeneous catalysis is changing from an empirical art to an exact science. The various methods for the analysis of solids and surfaces, constantly refined by materials science and surface science, seem to be almost unlimited. The increasing availability of atomic resolution microscopy as well as synchrotron radiation allows the characterization of catalyst particles, surface structures, surface processes and surface intermediates. We have learned to determine the surface structure sensitivity of catalytic reactions. Thermodynamic and kinetic data of catalytic reactions are now determined routinely. Isotopic exchange and labeling experiments provide information about reactant-catalyst interactions. How much have we learned through these techniques about the nature or mechanism of heterogeneously catalyzed reactions? The following article attempts to summarize the progress and the problems encountered in mechanistic studies of C—H bond formation and activation in a hydrogen atmosphere as an example for the present state of the understanding of reaction mechanisms in heterogeneous catalysis.
    Additional Material: 6 Ill.
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  • 23
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 708-715 
    ISSN: 0570-0833
    Keywords: Solid ion conductors ; Ion conductors ; Heterogeneous catalysis ; Conducting materials ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical measurement of oxygen activity using ion-conducting solid electrolytes (λ-sensors) has become widely known, at least since the application of three-way catalysts in the postcombustion of exhaust gases from spark-ignition engines. However, the use of solid ion conductors is not limited to control devices. There are various other potential applications and numerous problems which can be studied: the formation of oxides in the course of catalytic reactions on metal surfaces, the improvement of selectivity and yield of catalytic reactions, such as the epoxidation of ethylene on silver catalysts and, finally, the cogeneration of electrical energy during oxidation reactions, such as the partial oxidation of methanol to formaldehyde.
    Additional Material: 9 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 1173-1192 
    ISSN: 0570-0833
    Keywords: Cyclization ; Allylic alkylation ; Alkylation ; Synthetic methods ; Palladium ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The history of ring systems in organic chemistry parallels their synthetic accessibility. Transition-metal-catalyzed cyclizations offer a new opportunity to create carbo- and heterocyclic compounds with great facility. Among these methods, allylic alkylations catalyzed by palladium have proven unusually productive because of the extraordinary chemo-, regio-, and diastereoselectivity and the continuing possibility for the development of enantioselectivity. The rules for ring closure differ from those for non-transition-metal-catalyzed reactions. A major benefit is the ability to generate medium (eight-, nine-, ten-, and eleven-membered) and large rings in preference to normal (five-, six- and seven-membered) rings. With the appropriate substrate, efficient macrocyclizations are possible under conditions of normal concentrations. A second major benefit derives from the complementary stereochemistry of the metalcatalyzed substitution (net retention of configuration) compared to non-metal-catalyzed reactions (inversion of configuration). Further, the requirement for the substrate to conform to the transition-metal template may impose a stereochemical preference in the intermediate that ultimately translates into the thermodynamically less stable organic product regardless of the stereochemistry of the starting material. While more work has focused on carbocyclic synthesis, the possibilities for heterocyclic synthesis are just beginning to be tapped. In addition to forming heterocycles by C—C bond formation, use of a heteroatom as a nucleophile has already proven effective for oxygen and nitrogen, with other nucleophiles awaiting investigation. New dimensions for cyclization via allylic alkylation arise by generating the requisite π-allylpalladium intermediates by methods other than palladium(0)-initiated allylic ionizations. In addition, metals other than palladium will clearly expand the possibilities, but as yet remain untapped.
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  • 25
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 969-980 
    ISSN: 0570-0833
    Keywords: Stereoselectivity ; Reaction mechanisms ; Synthetic methods ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regio- and chemoselectivities of free radical reactions are often high and largely predictable; systematic studies have now shown that the stereoselectivity of free radical reactions can also be directed. Examples involving five- and six-membered cyclic radicals will be used to show how steric and stereoelectronic effects influence the diastereoselectivity of reactions of cyclic radicals with olefins. The temperature, the solvent, and the nature of the radical scavenger used also play a role, so that, if the correct reaction conditions are used, the stereoselectivity of reactions for cyclic reactants can be very high. Lower stereoselectivities are often observed for reactions between acyclic radicals and acyclic alkenes. However, preliminary experiments have indicated that under certain conditions such systems can also react in a stereoselective manner.
    Additional Material: 9 Tab.
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  • 26
    ISSN: 1434-4475
    Keywords: Alkynes ; Catalysis ; Dinitrogen complex ; Nitriles ; Pyrimidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Der Komplex [CoH(N2)(PPh 3)3] katalysiert Oligomerisations- und Cyclisierungsreaktionen von Alkinen unter milden Bedingungen. Die Cyclotrimerisierung von Propinsäureethylester ergibt die drei möglichen Isomeren von Tricarbethoxybenzol; Phenylacetylen reagiert hauptsächlich zu linearen Dimeren (vor allemtrans-PhC≡CCH=CHPh) und Trimeren; lineare Dimere herrschen auch bei 3-Hexin vor, während 1-Octin (mit langer Alkylkette) vorwiegend zu 2-Octin isomerisiert wird. In allen Fällen werden ebenfalls höhere Oligomere gebildet. Außer bei Propinsäureethylester entstehen ebenfalls in geringer Menge hydrierte Dimere (z. B.trans,trans-PhCH=CHCH=CHPh aus Phenylacetylen). Eine neue Art von Cocyclisierungsreaktion mit einem Nitril (NCMe) scheint bei der Bildung (in geringer Ausbeute) von 4,6-Dimethyl-5-phenyl-pyrimidin aus Phenylacetylen vorzuliegen. Alkinole reagieren unter den Versuchsbedingungen nicht.
    Notes: Abstract The complex [CoH(N2)(PPh 3)3] catalyses oligomerization and cyclization reactions of alkynes under mild conditions. Hence, alkyne cocyclotrimerization to benzene derivatives was mainly observed for ethyl propiolate, affording the three possible isomers of tricarbethoxybenzene; phenylacetylene undergoes mainly linear dimerization totrans-PhC≡CCH=CHPh and trimerization; linear dimers are also the predominant products from 3-hexyne, but 1-octyne (with a long chain) undergoes mainly isomerization to 2-octyne; higher oligomers are also usually formed. Except for ethyl propiolate, hydrogenated dimers are detected in low yields (e.g.trans,trans-PhCH=CHCH=CHPh from phenylacetylene), whereas 3-hexene is formed in considerable yield from 3-hexyne. A novel type of cocyclization reaction with a nitrile (NCMe) appears to occur with phenylacetylene to give (although in low yield) 4,6-dimethyl-5-phenyl-pyrimidine. Alkynols are unreactive under the chosen conditions.
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  • 27
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    Archives of dermatological research 280 (1988), S. 137-139 
    ISSN: 1432-069X
    Keywords: Vitiligo ; Calcium ; Free radicals ; Keratinocyte cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 45Ca2+ has been used to measure the kinetics for the uptake, efflux, and “steady state” of this regulatory cation in keratinocytes grown from the involved and uninvolved skin of one donor (JM) with vitiligo. Cells grown from uninvolved skin yielded a very rapid uptake and efflux of this isotope before reaching “steady state”. A similar profile has been found for keratinocytes from normal healthy adult controls. However, cells established from vitiliginous skin showed a slow uptake of 45Ca2+ before reaching the same “steady state” as the controls. 45Ca2+ efflux has not been observed in vitiliginous keratinocytes. Furthermore, vitiliginous keratinocytes yielded a higher concentration of extracellular bound 45Ca2+ compared with keratinocytes from uninvolved skin. Since Ca2+ has been found to be an allosteric inhibitor of membrane-associated thioredoxin reductase, this defect in Ca2+ transport may explain the proposed breakdown in free radical defense in vitiligo. These findings may also shed some more light on the etiology of this disorder.
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  • 28
    ISSN: 1619-7089
    Keywords: Radiolabeled free fatty acids ; Free radicals ; Myocardial metabolism ; Allopurinol ; Superoxide dismutase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In a canine model of reversible global ischemia, the residual quantity of 123I was assessed following a bolus injection of 15-p-(123I)-iodophenyl pentadecanoic acid (123I-IPPA). This technique was used to assess changes in free fatty acid metabolism following the utilization of three cardioplegic formulations. Cardioplegic arrest was initiated with Tyers' iso-osmolar (IO) solution (Group A); IO+superoxide dismutase (SOD) (Group B) and IO+allopurinol (Group C). Pre and post operative scanning were completed with 2–5 mCi 123I-IPPA. Clearance was assessed by IPPA time activity curve analysis generating t 1/2 (half lives in min) for the early and late phases of the curve. The assessment between groups demonstrated that the elimination of 123I-IPPA products (early phase) was faster from the lateral wall in groups B and C versus group A (14±12 min, 13±9 min and 24±10 min, respectively). The elimination of IPPA (late phase) was also faster from the lateral wall in groups B and C when compared to group A (240±270 min, 132±85 min and 416±238 min). Examining the changes between control and postoperative values for each area of the left ventricle within each group demonstrated no significant, changes for groups B and C. Group A, however, demonstrated significantly increased t 1/2 values for the lateral wall (early and late phases) and the apical wall (late phase). From this study it can be concluded that following 2 h of reversible global ischemia and reperfusion, the assessment of turnover of 123I-IPPA can be used to differentiate the effectiveness of various cardioplegic formulations. It appears that cardioplegic solutions supplemented with allopurinol and SOD (groups B and C) may be better able to protect myocardial fatty acid metabolism compared to Tyers' iso-osmolar solution (group A).
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  • 29
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    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 2 (1988), S. 91-92 
    ISSN: 0268-2605
    Keywords: Catalysis ; dehydrogenation ; hydrosilane ; disilane ; platinum complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dimethylphenylsilane was catalytically dehydrogenated and condensed in the presence of platinum complexes to give 1,1,2,2-tetramethyl-1,2-diphenyl-disilane.
    Additional Material: 1 Tab.
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  • 30
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    Angewandte Chemie International Edition in English 27 (1988), S. 643-660 
    ISSN: 0570-0833
    Keywords: Catalysis ; Electrocatalysis ; Chain catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Parallel to organic electrocatalysis, the field of organotransition metal electrocatalysis has developed explosively since 1980. The theoretical and experimental foundations established by Feldberg in 1971 (ECE mechanism) have been applied, using fast electrochemical techniques, to various organometallic reactions such as isomerization, ligand exchange, chelation, decomplexation, and CO insertion and extrusion. Most of the work performed to date concerns ligand exchange reactions of N-donors and P-donors in mononuclear compounds, initiated by oxidants (or anodes) and of carbonyls and P-donors in clusters, initiated by reducing agents (or cathodes). The preparative aspects of electrocatalysis have already been impressively developed in cluster chemistry and indicate that the technique is extremely useful. This review first delineates the principles and characteristics of electrocatalysis applied in organotransition metal chemistry, and then, after outlining the choice of efficient initiating reagents, goes on to describe the systems up to August 1986.
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  • 31
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    Angewandte Chemie International Edition in English 27 (1988), S. 661-678 
    ISSN: 0570-0833
    Keywords: Carbon dioxide ; C1 synthetic unit ; Transition metals ; C-C coupling ; Homogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carbon dioxide molecule has been of limited importance as a synthetic unit in organic chemistry. When it is coordinated to transition metals, however, completely new possibilities arise; CO2 can bond to metal complexes in a variety of ways and can enter into insertion and coupling reactions, or become catalytically attached to other substrates. The formation of C—C bonds between carbon dioxide and unsaturated hydrocarbons under conditions of homogeneous catalysis makes available new synthetic routes to industrially interesting organic compounds.
    Additional Material: 11 Ill.
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  • 32
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    Angewandte Chemie International Edition in English 27 (1988), S. 1127-1144 
    ISSN: 0570-0833
    Keywords: Organometallic compounds ; Surface chemistry ; Carbonyl ligands ; Metal oxides ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal carbonyls react on metal oxide surfaces to give a wide range of structures analogous to those of known compounds. The reactions leading to formation of surface-bound metal carbonyls are explained by known molecular organometallic chemistry and the functional group chemistry of the surfaces. The reaction classes include formation of acid-base adducts as the oxygen of a carbonyl group donates an electron pair to a Lewis acidic center; nucleophilic attack at CO ligands by basic surface hydroxyl groups or O2⊖ ions; ion-pair formation by deprotonation of hydrido carbonyls to give carbonylate ions; interaction of bifunctional complexes with surface acid-base pair sites such as [Mg2⊕O2⊖]; and oxidative addition of surface hydroxyl groups to metal clusters. The reactions of surface-bound organometallic species include redox condensation and cluster formation on basic surfaces (paralleling the reactions in basic solution) as well as oxidation of mononuclear metal complexes and oxidative fragmentation of metal clusters by reaction with surface hydroxyl groups. Most supported metal carbonyls are unstable at high temperatures, but some, including osmium carbonyl cluster anions on the basic MgO surface, are strongly stabilized in the presence of CO and are precursors of catalysts for CO hydrogenation at 550 K.
    Additional Material: 18 Ill.
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  • 33
    ISSN: 0570-0833
    Keywords: Rhenium ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homogeneous catalysis as the major industrial outlet of organometallic basic research has been enjoying great benefit from organotransition metal species that promote bond forming between hydrocarbon fragments. Most of the commercially important processes that serve to produce large-volume organic feedstock chemicals such as linear α-olefins (Shell Higher Olefins Process), linear aldehydes (hydroformylation), acetaldehyde (Wacker-Hoechst), acetic acid (Monsanto), adiponitrile (DuPont hydrocyanation of butadiene) operate at low-valent metal centers. It is thus hardly surprising that by far the most part of organometallic research during the past few decades has been directed towards an understanding and the improvement of these catalytic reactions as well as towards the related stoichiometric chemistry. As a matter of consequence, our present knowledge on high-valent organotransition metal compound is comparatively shallow, nor do we know much about the chemical relationship and interconvertability of high and low oxidation states within a given class of compounds. In this article I want to point out some ostensibly challenging perspectives of future organometallic research by describing a novel class of high oxidation state organorhenium compounds as well as by speculating on possible generalizations for other transition metals.
    Additional Material: 18 Ill.
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  • 34
    ISSN: 0570-0833
    Keywords: Heterogeneous catalysis ; Solid-state reactions ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterogeneous catalysts are generally assumed to be multiphasic and multicomponent; many of them are, and this is one of the resons why disentangling the factors that govern their mode of action is so difficult. But there is a large class of heterogeneous catalysts where the solid is monophasic and where the activity may be envisaged as being dispersed in a spatially uniform fashion throughout its bulk. This is true both of zeolites and many other microporous catalysts on the one hand, and of certain mixed metal oxides, where the non-stoiohiometry is inextricably mingled with the catalysis, on the other. By recognizing this broad classification numerous operational advantages follow: the performance of existing catalysts and the design of those yet to be prepared can be placed on a rational footing; moreover, the myriad techniques of solid-state chemistry and physics, often regarded as inapplicable to the subtle and special problems of surface chemistry, are seen to be of direct relevance as probes for the structure and properties of proven uniform heterogeneous catalysts as well as for the synthesis and development of new ones. This review, which draws analogies with and lessons from the chemistry of enzyme catalysts, focuses largely on the catalytic conversions of hydrocarbons over zeolites, clays, microporous AlPO4 and a wide range of metal oxides.
    Additional Material: 32 Ill.
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  • 35
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    Angewandte Chemie International Edition in English 27 (1988), S. 226-246 
    ISSN: 0570-0833
    Keywords: Zeolites ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.
    Additional Material: 2 Ill.
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  • 36
    ISSN: 0570-0833
    Keywords: Organonickel compounds ; Polymerization ; Hydrogenation ; Homogeneous catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One hundred years of organonickel chemistry have generated a wealth of new knowledge and a history of examples of accidental discoveries which have finally led to industrial applications. The historical development is associated with the names of Mond, Sabatier, Reppe and Ziegler and, with the methods and techniques available today, many of the original discoveries and unsolved problems are attracting renewed attention. For example, 70 years were to go by before a synthesis first conceived by Sabatier could finally be realized. The path leading from nickel-catalyzed hydrogenation to highly enantioselective homogeneous catalysts is one of the contributions to organonickel chemistry which is described here.
    Additional Material: 19 Ill.
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  • 37
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    Biology and fertility of soils 5 (1987), S. 120-125 
    ISSN: 1432-0789
    Keywords: Fungal melanins ; Humic acid ; Infrared analysis ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Humic acid-type polymers (melanins) synthesized in culture media by the fungi Aspergillus glaucus, Eurotium echinulatum, Hendersonula toruloidea, Stachybotrys atra and Aspergillus sydowi were analysed for elemental composition, functional group content, infrared (IR) and electron spin resonance (ESR) properties. Results were discussed in comparison with range values referred for soil humic acids. The fungal polymers showed significant differences in carboxyl and nitrogen content and C/H atomic ratios, reflecting a different degree of condensation (aromaticity) among the various samples. IR analysis gave evidence of: (a) the predominant aromatic character of melanins from A. glaucus, E. echinulatum and H. toruloidea; (b) the high content of aliphatic and olefinic components of S. atra melanin; (c) the typical presence of amide bonds in the nitrogen-richest melanins from A. sydowi and H. toruloidea; and (d) the generally low amount of free carboxyl groups, which often appeared involved in hydrogen bonds. ESR spectra showed that all the melanins studied contained appreciable concentrations of organic free radicals of prevailing semiquinonic nature and of the same order of magnitude commonly measured in humic acids from soil and other sources. The free electron concentration was shown to be directly related to the C/H atomic ratio and to the degree of aromaticity shown by IR analysis. This indicated that the highest free radical content in the melanins from E. echinulatum and A. glaucus was associated with the highest presence of condensed aromatic structures. Humic acid-type polymers synthesized by soil fungi may, therefore, contribute to the total free radical content of soil humic substances and play important roles in all reactions involving free radicals in soils and related environments.
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  • 38
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    European journal of applied physiology 56 (1987), S. 313-316 
    ISSN: 1439-6327
    Keywords: Fatigue ; Free radicals ; Lipid peroxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The possibility that plasma levels of malonaldehyde (MDA) are altered by exercise has been examined. The presence of MDA has been recognized to reflect peroxidation of lipids resulting from reactions with free radicals. Maximal exercise, eliciting 100% of maximal oxygen consumption ( $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ ) resulted in a 26% increase in plasma MDA (P〈0.005). Short periods of intermittent exercise, the intensity of which was varied, indicated a correlation between lactate and MDA (r 2=0.51) (p〈0.001). Blood lactate concentrations increased throughout this exercise regimen. A significant decrease (10.3%) in plasma MDA occurred at 40% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ . At 70% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ plasma MDA was still below resting values, however the trend to an increase in MDA with exercise intensity was evident. At exhaustion, plasma MDA and lactate were significantly greater than at rest. These results suggest, that exhaustive maximal exercise induces free radical generation while short periods of submaximal exercise (i.e. 〈70% $$\dot V_{{\text{O}}_{{\text{ 2 max}}} } $$ ) may inhibit it and lipid peroxidation.
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  • 39
    ISSN: 0268-2605
    Keywords: Hydrosilylation ; Acetylene ; Trichlorosilane ; Silica ; Rhodium ; Ruthenium ; Catalysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive-consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115-140°C allowed us to evaluate the activation energy, Ea, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol-1 for the selected rhodium and ruthenium supported complexes.
    Additional Material: 3 Ill.
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  • 40
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    Angewandte Chemie International Edition in English 26 (1987), S. 190-203 
    ISSN: 0570-0833
    Keywords: Homogeneous hydrogenation ; Hydrogenation ; Synthetic methods ; Catalysis ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
    Additional Material: 12 Ill.
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  • 41
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    Angewandte Chemie International Edition in English 26 (1987), S. 309-319 
    ISSN: 0570-0833
    Keywords: EPR spectroscopy ; Automotive microparticle sources ; X-ray photoelectron spectroscopy ; Environmental chemistry ; Catalysis ; Photoelectron spectroscopy ; Microparticles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the last fifteen years the necessity for efficient environmental protection has become generally accepted. However, before practical measures can be taken, a comprehensive assessment of the present environmental situation should be made, taking into consideration the risks involved in as well as the positive effects of any planned environmental changes - whether natural or man made. This clearly calls for close cooperation between the various scientific disciplines. For example, the treatment of exhaust fumes from motor vehicles has been of primary importance in measures taken to restrict the recent damage caused to woodland areas. The introduction of 3-Way-Catalyst technology has been regarded as a viable countermeasure. The following report is intended to describe a method for examining some side effects of catalyst usage. Accordingly, the chemical composition of microparticles emitted from combustion motors through the use of catalysts will be examined and some possible changes in the environment caused by such particles will be briefly considered. As in the area of research into catalysts for industrial synthesis a knowledge of the surface structure of such particles, i.e. the boundary layer between emission product and environment, is necessary in the investigation into their effects. Consequently, a surface sensitive technique from solid state physics, X-ray photoelectron spectroscopy (XPS or ESCA) has found novel use in the area of environmental analysis. In the following report emphasis will be placed on the description of measurement techniques and the interpretation of the results obtained. After a critical consideration of the experimental methods, examples from two different series of measurements on diesel and Otto motors equipped with soot filters or 3-way-catalysts respectively, will be given. Hopefully, this report will also stimulate establishment of the use of EPS in environmental research techniques.
    Additional Material: 17 Ill.
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  • 42
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    Angewandte Chemie International Edition in English 26 (1987), S. 170-189 
    ISSN: 0570-0833
    Keywords: Free radicals ; Zwitterions ; Diradicals ; Quantum chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A knowledge of the geometries at which excited molecules return to the electronic ground state (S0) is essential for the understanding of the structures of photoproducts. Particularly good candidates are geometries corresponding to local minima on the S1 (lowest excited singlet) and T1(lowest triplet) surfaces, as well as S0-S1 conical intersections (funnels). Given sufficient effort, such geometries can nowadays be found numerically for small enough molecules. Still, it is interesting to ask whether more approximate, but also more general, statements can be made concerning the geometries at which the S0 and S1 surfaces closely approach each other. Since many of these are biradicaloid geometries, it is logical to examine the properties of biradicals and related species at some length. After reviewing the two-electron two-orbital model for molecules at biradicaloid geometries, we formulate the conditions under which the S0 and S1 surfaces touch. The results obtained for the simple model are supported by ab initio large-scale configuration interaction (CI) calculations for the twisting of ethylene in the polarizing field of a positive charge and for the twisting of charged double bonds and π-donor-to-π-acceptor single bonds, and by similar calculations for “push-pull” perturbed cyclobutadienes, some of which are predicted to have nearly degenerate S0, S1, and T1 states. The likely consequences of these results for the detailed description of the mechanisms of cis-trans isomerization, the formation of twisted internal charge-transfer (TICT) states, proton translocation, and possibly of the initial step in vision, as well as for the understanding of the regiospecificity of singlet photocycloaddition, are summarized.
    Additional Material: 16 Ill.
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  • 43
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    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 1 (1987), S. 281-284 
    ISSN: 0268-2605
    Keywords: Catalysis ; Brooke rearrangment ; Iridium ; Palladium ; Platinum ; Complexes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes [IrH(CO)(PPh3)3], trans-[IrCI(CO)- (PPh3)2], [RhH(PPh3)4], [Pd(PPh3)4], [Pt(trans-stilbene)(PPh3)2] and [Pt(η3-CH2-COCH2)-(PPh3)2] catalyse the rearrangement of Me3SiCH2C(O)CH2Cl to CH2=C(OSiMe3)-CH2Cl.
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  • 44
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    Monatshefte für Chemie 117 (1986), S. 617-619 
    ISSN: 1434-4475
    Keywords: Catalysis ; Photochemistry ; Supported platinum complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Ultraviolettbetrahlung des siliziumverknüpften Komplexes Pt(C2O4)L 2 [L=(H3CO)3Si(CH2)2PEt 2] ergab eine [SiO2]-L 2Pt-Spezies, die die Hydrosilierung von Olefinen katalysiert oder unter Bildung eines Oberflächen-Dicarbonylkomplexes 2 CO addiert.
    Notes: Abstract Ultraviolet irradiation of the silica attached complex Pt(C2O4)L 2, [L=(H3CO)3Si(CH2)2PEt 2], yields a [SiO2]-L 2Pt species that catalyzes olefin hydrosilation or adds 2 CO to yield a surface dicarbonyl complex.
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  • 45
    ISSN: 1434-4475
    Keywords: Catalysis ; Dinitrogen complexes ; Ethyldiazoacetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Komplexetrans-[Mo(N2)2(dppe)2] (dppe=Ph 2PCH2CH2PPh 2) reagieren mit NN=CHCOOEt in benzolischer Lösung zuPh-N=N-CH3 als organischem Hauptprodukt. Andererseits wird bei der Bestrahlung vontrans-[W(N2)2(dppe)2] inTHF-Lösung in der Gegenwart von Ethyldiazoacetat das PhosphazenPh 2P(N2CHCOOEt)(CH2CH2)P(N2CHCOOEt)Ph 2 gebildet; in feuchter Lösung erleidet die Phosphazen-Bindung eine teilweise Hydrolyse und die Phosphonium-Spezies [Ph 2P(NHNCHCOOEt)(CH2CH2)P(NHNCHCOOEt)Ph 2]2+ scheint gebildet zu werden.
    Notes: Abstract Complextrans-[Mo(N2)2(dppe)2] (dppe=Ph 2PCH2CH2PPh 2) reacts with NN=CHCOOEt in benzene solution to afford benzene-azomethane,Ph-N=N-CH3, as the main organic product. However, the phosphazene speciesPh 2P(N2CHCOOEt)(CH2CH2)P(N2CHCOOEt)Ph 2 is formed by irradiating aTHF solution oftrans-[W(N2)2(dppe)2] in the presence of ethyldiazoacetate; in moist solution, the phosphazene bonds undergo a partial hydrolysis, and the phosphonium species [Ph 2P(NHNCHCOOEt)(CH2CH2)P(NHNCHCOOEt)Ph 2]2+ appears to be formed.
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  • 46
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    Pharmacy world & science 8 (1986), S. 300-301 
    ISSN: 1573-739X
    Keywords: Anoxia ; Biotransformation ; Calcium paradox ; Doxorubicin ; Free radicals ; Ischemia ; Vitamin E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 47
    ISSN: 0570-0833
    Keywords: Cholesterol homeostasis ; Receptors ; Catalysis ; Nobel lecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 16 Ill.
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  • 48
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    Angewandte Chemie International Edition in English 25 (1986), S. 508-524 
    ISSN: 0570-0833
    Keywords: Cross-coupling ; Organotin compounds ; Electrophilicity ; Palladium ; Catalysis ; C-C coupling ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross-coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon-carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.
    Additional Material: 1 Ill.
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  • 49
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    Angewandte Chemie International Edition in English 25 (1986), S. 960-970 
    ISSN: 0570-0833
    Keywords: Phase-transfer catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of Phase Transfer Catalysis (PTC) represents a major step forward in the employment of many organic reactions and renders them very convenient and useful processes. These reactions involve the application of nucleophiles in general, anions and bases in particular, in reactions carried out in a water-organic solvent system. They can be performed both in the laboratory and on an industrial scale. The ease of application of PTC processes is the main reason for their increasing utilization in industry. An outstanding achievement of this technique is the employment of aqueous bases in reactions which traditionally would otherwise require a strong base in a nonaqueous medium. The classical procedures that require severe anhydrous conditions, expensive solvents and dangerous bases such as metal hydrides and organometallic reagents are now replaced by aqueous solutions of, e.g., sodium or potassium hydroxides (PTC/OH processes). In contrast to the extensive synthetic applications of PTC/OH systems, the detailed mechanisms of these processes have been the subject of a great deal of controversy and various mechanisms have been suggested. However, it would seem that our knowledge concerning the mechanistic aspects of such reactions has now reached the stage where it can be used to advantage in synthesis planning. A better understanding of the various factors which influence the reaction would undoubtedly help to optimize PTC/OH processes such as to enable higher yields in shorter reaction times at lower temperatures. The importance of, inter alia, the catalyst will be pointed out and it is highly recommended that such catalysts be always available in the laboratory, for the range of organic reactions that they can efficiently, conveniently and safely catalyze is vast indeed.
    Additional Material: 5 Ill.
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  • 50
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    Angewandte Chemie International Edition in English 24 (1985), S. 553-565 
    ISSN: 0570-0833
    Keywords: Free radicals ; Organomercury compounds ; Synthetic methods ; Organotin compounds ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C—C bond formation is one of the most important synthetic steps in the construction of organic molecules. In the last few years it has been increasingly achieved by radical addition to alkenes. In such reactions the adduct radicals have to be trapped by an donor subsequent to the C—C bond formation in order to prevent polymerization. This task can be accomplished with organotin and organomercury hydrides, the use of which has led to new synthetic methods. The occurrence of radical chain reactions in which reactions take place between radicals and nonradicals is decisive for the success of the synthesis. In these cases small amounts of radical initiators suffice and numerous functional groups may be used in the C—C bond-forming reactions. The yields and selectivities of these radical reactions are often very high.
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  • 51
    ISSN: 0570-0833
    Keywords: Organocobalt compounds ; Pyridines ; Catalysis ; Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cocyclization of alkynes with cyano compounds using organocobalt catalysts of the type [YCoL] has evolved into a versatile and technically useful method for synthesizing pyridine and its derivatives. An important advance came with the realization that the organo group Y remains attached to the cobalt throughout the catalytic cycle. This opened up the possibility of optimizing the catalyst by varying the controlling ligand Y.
    Additional Material: 11 Ill.
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  • 52
    ISSN: 0570-0833
    Keywords: Organomagnesium compounds ; Magnesium hydrides ; Hydrides ; Hydrogen storage ; Catalysis ; Organolithium compounds ; Lithium hydrides ; Energy storage ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A recent development in homogeneous catalysis is the discovery of catalysts that are active for the lithiation of 1-alkenes to alkenyllithium compounds and lithium hydride as well as for the hydrogenation of lithium and magnesium under mild conditions. The catalytically prepared magnesium hydride is highly reactive and adds to 1-alkenes to give diorganomagnesium compounds and can also be used in the preparation of, for example, silane and “active” magnesium. The use of metal hydrides in hydrogen storage is discussed: hydrogenation/dehydrogenation experiments show that the catalytically prepared magnesium hydride (which can be doped with a second metal) can be used as a high-temperature hydrogen storage material.
    Additional Material: 8 Ill.
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  • 53
    ISSN: 0570-0833
    Keywords: Allylpalladium compounds ; Palladium ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of transition-metal complexes as homogeneous catalysts for the production of organic chemicals is of considerable industrial significance. Although palladium complexes have not attained the same importance as, for example, those of rhodium or cobalt, palladium is nonetheless one of the most versatile metals for synthetic organic purposes. An understanding of the role played by the metal in these reactions is essential for their optimal utilization. This necessarily entails a detailed study of the chemistry of the palladium-carbon bond. In this article we concentrate on η3-allylpalladium complexes, which are frequently involved as intermediates in the Pd-catalyzed transformations of dienes. The study of their behavior gives a deeper insight into the individual steps of a catalytic cycle.
    Additional Material: 12 Ill.
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  • 54
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    Calcified tissue international 29 (1979), S. 95-99 
    ISSN: 1432-0827
    Keywords: ESR ; Radiation ; Free radicals ; Enamel ; ENDOR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary An asymmetric ESR signal and an outer doublet signal centered atg=2.00 produced in human tooth enamel by X-irradiation have been studied over a temperature range from liquid helium temperature to 380° K. The line shape of the asymmetric signal for an enamel crystallite is Lorentzian at room temperature. The temperature dependence of the integrated intensity of the asymmetric signal suggests that the signal follows a singlet-triplet model with the exchange interaction of 0.022 eV. Below about 60° K the asymmetric signal becomes broad as the temperature is decreased. The ENDOR line of the asymmetric signal shows that there exists interaction between the centers and protons. The temperature dependence of the integrated intensity of the double signal is analogous to that of the asymmetric signal.
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  • 55
    ISSN: 0570-0833
    Keywords: Donor-acceptor systems ; Substituent effects ; Free radicals ; Radicophiles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.
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  • 56
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    Angewandte Chemie International Edition in English 18 (1979), S. 421-429 
    ISSN: 0570-0833
    Keywords: Triphase catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Triphase catalysis (TC) has recently been introduced as a unique form of heterogeneous catalysis in which the catalyst and each of a pair of reactants are located in separate phases. Based on this concept, new synthetic methods have been developed for aqueous phase-organic phase reactions using a solid phase catalyst. Although it is only at an early stage of development, TC shows considerable potential for practical use. Our mechanistic understanding of these highly complex catalytic systems is at present very limited and detailed examination will be required before their relationship to phase-transfer, micellar, and interfacial catalysis becomes clear.
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  • 57
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    Angewandte Chemie International Edition in English 18 (1979), S. 837-846 
    ISSN: 0570-0833
    Keywords: C-C coupling ; Synthetic methods ; Catalysis ; Silanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reagent hydrosilane/carbon monoxide opens up new possibilities for organic synthesis. Four cases will be discussed: 1. The reaction of olefins with hydrosilane (trialkylsilane) and carbon monoxide in the presence of Co, Ru, and Rh complexes leads to enol silyl ethers having one more carbon atom that the olefins. 2. Cyclic ethers underto carbonylative ring opening to ω-siloxyaldehydes when reacted with hydrosilane and carbon monoxide in the presence of Co2(CO)8 as catalysts 3. Aldehydes are catalytically converted into the next higher α-siloxyaldehydes or 1,2-bis(siloxy)alkenes depending on the reaction conditions used. 4. The reaction of alkyl acetates proceeds in various ways depending on the nature of the alkyl group; enol silyl ethers or alkenes are optained.-Mechanisms of these Co2(CO)8 catalyzed reactions using hydrosilane and carbon monoxide are discussed in which HCo(CO)n or R3SiCo(CO)nL function as catalytically active agents. With these species there are four types of catalytic cycles.-The synthetic possibilities of these catalytic reactions have still not been fully explored.
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  • 58
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    Angewandte Chemie International Edition in English 18 (1979), S. 173-180 
    ISSN: 0570-0833
    Keywords: Homolysis ; Free radicals ; Anchimeric effect ; Neighboring-group effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical reactions of the type R1—a—b—R2→•a—b—R1 + •R2 are feasible if the new bond formed between b and R1 is considerably stronger than the old bond between a and R1. Furthermore, both the radical fragments formed must be resonance stabilized. An example of this reaction type is the thermolysis of benzyl trimethylsilylmethyl ethers, in which the trimethylsilyl group (with empty orbitals) migrates to the oxygen atom (with lone pairs). Assumption of a cyclic reactive intermediate with pentacoordinated silicon explains the observed intramolecular nature and the negative entropy of activation of such homolyses.
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  • 59
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    Calcified tissue international 25 (1978), S. 99-104 
    ISSN: 1432-0827
    Keywords: Low temperature ashing ; Enamel ; Bone mineral ; Gas trapping ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Low temperature ashing by excited gas (LTA) causes crystallographic and paramagnetic alterations of the human bone and tooth enamel mineral. On the one hand, LTA induces variations of thea lattice parameter. These variations depend upon the nature of the gas used, but are little affected by its degree of excitation. Trapping of gas molecules in the crystal structure is demonstrated. On the other hand, LTA produces two preponderant paramagnetic centers in bone and enamel samples at 20°C. Their inorganic origin is clearly indicated. One of the two radicals has been identified as O3 − (g1=2.002, g2=2.010, g3=2.016) and the other as CO 3 3− (g‖=1.996, g⊥=2.003). Variations of thea lattice parameter and trapping of paramagnetic gas species do not seem to be directly related.
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  • 60
    ISSN: 1432-0827
    Keywords: Bone mineral ; Calciphylaxis ; Calcinosis ; ESR ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The evolution of the mineral constituents of subcutaneous calcinosis induced in rats by topical calciphylaxis was studied by the method of quantitative chemical analysis, and after treatment with excited gases by electron spin resonance (ESR) analysis. Chemical data show that the genesis of the subcutaneous calcinosis does not significantly alter the concentration of Ca, P, F, CO3, Mg, and Fe in the mineral phase of the femoral bone of calciphylactic rats. In the calcinosis an important increase of the fluoride concentration is noticed in function of the time after challenging. There is also a high concentration of Mg2+ ions in the early stages of the experimental calcification. Iron injected for the challenging is continuously present in the calciphylactic tissue after this treatment. This suggests that subcutaneous calcinosis might be a means of fixing certain heavy metal ions. After treatment with excited gases, the proportions of the trapped CO3 3− and O3 − radicals are of the same order of magnitude in calciphylactic tissue after 12 days and observations in bone mineral. These suggest that after 12 days the mineral of the calciphylactic tissue has a crystalline state close to that of bone.
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  • 61
    ISSN: 1420-9136
    Keywords: Electron paramagnetic resonance ; Free radicals ; Matrix isolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract With some special adaptations the technique of matrix isolation followed by detection through electron paramagnetic resonance (EPR) can also be used for the measurement of atmospheric radical concentrations. A light weight cryogenic sampling device has been constructed. It uses condensation of atmospheric CO2 or H2O at 77 K for matrix formation and trapping of the radicals. The sampler has been flown on a balloon for stratospheric sampling. First data on stratospheric, HO2 and NO2 at 32 km altitude have been obtained on a flight on 8 August 1976 and will be reported.
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  • 62
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    Calcified tissue international 25 (1978), S. 191-195 
    ISSN: 1432-0827
    Keywords: ESR ; Apatites ; Radiation ; Free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Free radicals generated in synthetic apatitic calcium phosphates by X-ray radiation were investigated by electron spin resonance (ESR) spectroscopy. Among the species stable enough at −188° C to be identified were hydrogen atoms, phosphate radicals, and oxygen anion radicals. The ESR spectra were markedly dependent on the specific surface of the mineral. Oxygen radicals dominated the spectra of low specific surface samples while phosphate radicals were the predominant species at higher specific surfaces. Our studies suggest that the oxygen radicals are more stable in the bulk of the crystal while the hydrogen atoms and the phosphate radicals are stabilized at or near the crystal surface. It was concluded that the surface species are potentially capable of serving as probes of biologically relevant mineral-organic interfaces.
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  • 63
    ISSN: 1432-2234
    Keywords: ZnII complexes (ab initio study) ; Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Zinc is one of the most important biological metals involved in the catalytic site of many enzymes. SCFab initio computations with good quality basis sets are reported for monoadducts of ZnII with various biologically significant ligands, and the fundamental features of the binding are characterized, using in particular energy decomposition scheme, population analysis and difference density curves. A test of the possibility of using pseudopotentials in this domain is also reported.
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  • 64
    ISSN: 1432-2234
    Keywords: ZnII complexes (ab initio study) ; Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Zinc is one of the most important biological metals involved in the catalytic site of many enzymes. SCFab initio computations with good quality basis sets are reported for monoadducts of ZnII with various biologically significant ligands, and the fundamental features of the binding are characterized, using in particular energy decomposition scheme, population analysis and difference density curves. A test of the possibility of using pseudopotentials in this domain is also reported.
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  • 65
    ISSN: 0570-0833
    Keywords: Oxygenation ; Alkanes ; Synthetic methods ; Superacidic systems ; Catalysis ; Magic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Owing to the ready availability of the starting materials, the functionalization of saturated hydrocarbons for preparing chemical intermediates and products represents an attractive goal. The possibility of converting alkane in a controlled way into alcohols, ketones etc., i.e. to oxyfunctionalize them, is particularly challenging. After a short account of previous methods used for the oxidation of alkanes, particular emphasis will be given to recently developed reactions of alkanes with oxygenating agents in superacidic media.
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  • 66
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    Angewandte Chemie International Edition in English 17 (1978), S. 505-515 
    ISSN: 0570-0833
    Keywords: Pyridines ; Alkynes ; Nitriles ; Synthetic methods ; Cobalt catalysts ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Soluble organocobalt catalysts permit selective formation of substituted pyridines under mild conditions in a single step: mono-, di-, and trisubstituted pyridines can be obtained at will in high conversions and high yields from nitriles and alkynes. Polynuclear derivatives such as bipyridines can also be prepared by this method.
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  • 67
    ISSN: 0570-0833
    Keywords: 4-Dialkylaminopyridines ; Amino pyridines ; Acylation ; Catalysis ; Synthetic methods ; Pyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs.
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  • 68
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    Angewandte Chemie International Edition in English 17 (1978), S. 657-670 
    ISSN: 0570-0833
    Keywords: Polymeric catalysts ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present-day position in the field of polymeric catalysts is outlined. The following selected groups of polymeric catalysts are discussed: synthetic hydrolases, immobilized enzymes, phase-transfer catalysts, nucleophilically active bases, polymers with conjugated π-systems, photosensitizers, polymers as carriers for catalytically active metals or ions, and immobilized homogeneous catalysts. Polymeric catalysts have the following valuable properties: insoluble polymeric catalysts are readily separable from reaction solutions and can often be re-used without loss of activity; a hydrophobic matrix protects the organometallic active center from deactivation by oxygen and water; by fixation of finely divided metals on an ion exchanger, multistage reactions may be effected successively in one reactor. Polymeric carriers may influence the catalytic properties; for example, in the case of immobilized enzymes on polyionic carriers the pH of the activity maximum may be shifted.
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  • 69
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    Angewandte Chemie International Edition in English 16 (1977), S. 449-459 
    ISSN: 0570-0833
    Keywords: Entropy ; Binding energy ; Enzyme catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Why are enzyme-catalyzed reactions so much faster than uncatalyzed reactions, and why are enzymes so specific? What is the effect of mere approximation of enzyme and substrate, and what is the influence of the strain energy? Attempts to answer these questions have led to comparisons between entropy changes in intermolecular and intramolecular reactions, and to determinations of the intrinsic energy of the bond arising by non-covalent interaction between enzyme and substrate.
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  • 70
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    Angewandte Chemie International Edition in English 16 (1977), S. 493-505 
    ISSN: 0570-0833
    Keywords: Phase-transfer catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phase-transfer catalysis (PTC) has grown into a versatile preparative method in the last few years. The most notable new developments include the use of crown ethers as phase-transfer catalysts and the introduction of solid-liquid PTC. Some representative examples have been selected from the large number of new PTC reactions and some of them are summarized in tables.
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  • 71
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    Angewandte Chemie International Edition in English 16 (1977), S. 817-826 
    ISSN: 0570-0833
    Keywords: Titanium tetrachloride ; Synthetic methods ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium tetrachloride can accelerate numerous organic reactions. Valuable syntheses of, e.g., allyl sulfides, amides, enamines, and ketones are based upon transformations of functional groups with TiCl4. Particular mention should also be made of carbon-carbon linkage with TiCl4 which permits the synthesis of hydroxy ketones and carbonyl compounds of the Michael adduct type. TiCl4 reduced in situ is suitable for the reduction of chloroarenes or the linkage of two aldehyde molecules to give an alkene.
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  • 72
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    Angewandte Chemie International Edition in English 16 (1977), S. 285-293 
    ISSN: 0570-0833
    Keywords: Evolution ; Enzyme catalysis ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new function derived from kinetic data, the efficiency function, can be used to quantify the efficiency of a catalyst. For freely diffusing species the maximum efficiency is unity. The enzyme triose phosphate isomerase has an efficiency of 0.6 and is thus almost a perfect catalyst. The efficiency of the acetate ion as catalyst for the same reaction is 2.5 × 10-11. This increase in catalytic efficiency is discussed in terms of three types of evolutionary improvement: the uniform binding of the substrate to the enzyme, changes in the internal thermodynamics of the bound states, and more effective catalysis of elementary steps. These concepts are illustrated for triose phosphate isomerase.
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  • 73
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    Theoretical chemistry accounts 42 (1976), S. 87-90 
    ISSN: 1432-2234
    Keywords: McLachlan method ; Free radicals ; Radical anions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A recent modification to the McLachlan method is corrected. This modification, when correctly applied to odd alternant hydrocarbons, reproduces McLachlan's results instead of improving their agreement with experiment. The modification is irrelevant and erroneous for radical anions.
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  • 74
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    Angewandte Chemie International Edition in English 15 (1976), S. 586-592 
    ISSN: 0570-0833
    Keywords: Environmental chemistry ; Automotive exhaust gases ; Exhaust gases ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon monoxide, hydrocarbons, and nitrogen oxides can be simultaneously transformed into inoffensive substances on multifunctional catalysts. Consisting of noble metals or base metal oxides deposited on an inert support, these catalysts can be used in monolithic form or as granular packings. Compared with other methods of automotive exhaust detoxification, multifunctional catalysts are distinguished by incurring fuel savings.
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  • 75
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    Angewandte Chemie International Edition in English 15 (1976), S. 150-156 
    ISSN: 0570-0833
    Keywords: Catalysis ; Analytical methods ; Trace analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Catalyzed reactions are becoming increasingly improtant in analytical chemistry, and especially in trace analysis. The acceleration of a particular reaction (indicator reaction) promoted by the catalyst provides information about the catalyst concentration. Substances which lower or raise the activity of a catalyst (inhibitors or activators, respectively) can likewise be determined in this way. The course of a reaction is usually monitored by physical measuring techniques. Various methods of conducting these kinetic-catalytic studies are discussed in this article. - Use of catalyzed reactions for end point detection in volumetric analysis is also feasible.
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  • 76
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    Angewandte Chemie International Edition in English 14 (1975), S. 783-789 
    ISSN: 0570-0833
    Keywords: Free radicals ; Aminyl radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recent interest in aminyl free radicals, especially in their electronic structure, has led to many investigations in this area. This report reviews the main features of the generation of aminyls, their reactivity, and electronic properties.
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  • 77
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 8 (1969), S. 97-107 
    ISSN: 0570-0833
    Keywords: Transition metals ; Oxidation ; Hydrocarbons ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The way in which dissolved transition metal compounds affect the liquid-phase oxidation of hydrocarbons is demonstrated for compounds of cobalt, copper, and manganese. Kinetic investigations on model systems and comparisons with the non-catalyzed reaction show that the catalysts participate in all the oxidation steps.
    Additional Material: 10 Ill.
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  • 78
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 7 (1968), S. 36-44 
    ISSN: 0570-0833
    Keywords: Photolysis ; Iodoaromatic compounds ; Dehydrobenzene ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Under appropriate conditions, the photolysis of iodoaromatic compounds yields derivatives of biphenyl and phenanthrene, as well as organometallic compounds. Ring closures of o-terphenyls to triphenylenes and of benzanilides to phenanthridones are described. The formation of dehydrobenzene (benzyne) on photolysis of 1,2-diiodobenzene in solution has been established. The photolysis of various substituted iodoaromatic compounds or of substances such as CH3I, ICN, ICH3, COOH, or RC≡CI, provides a general method for the generation of a large variety of free radicals in solution. The potential uses of photochemically initiated exchanges of iodine in ArI for 131I, Li, D, Cl, or Br are noted.
    Additional Material: 2 Tab.
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  • 79
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 7 (1968), S. 507-519 
    ISSN: 0570-0833
    Keywords: Radical reactions ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Free radicals can be produced in the gas phase and then condensed together with the molecules of an inert gas; they can also be generated and trapped in isolated sites in rigid solids. IR and ESR spectra of trapped radicals provide information concerning their structure and chemical properties. The techniques employed for producing and studying radicals are reviewed and a number of recent IR and ESR investigations of trapped radicals are discussed. The last part of the article deals exclusively with the applications of the rotating cryostat to the study of the ESR spectra and reactions of trapped radicals at low temperatures.
    Additional Material: 5 Ill.
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  • 80
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 6 (1967), S. 34-40 
    ISSN: 0570-0833
    Keywords: Spin density distribution ; 2,4,6-Triphenylphenoxyl ; Free radicals ; EPR spectroscopy ; Phenoxyl ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6-triphenylphenoxy radical was determined by electron spin resonance spectroscopy and quantum-mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum-mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with 13C in positions 1,2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the 17O-coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.
    Additional Material: 7 Ill.
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  • 81
    ISSN: 0570-0833
    Keywords: Ziegler-Natta catalysts ; Catalysis ; Polymerization ; Polyethylene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cp2TiCl2 and Cp2TiEtCl (Cp = cyclopentadienyl, Et = ethyl), in combination with aluminum alkyls, have been studied as model catalyst systems for the polymerization of ethylene in toluene. The activity of these systems resides in the presence of a complex molecule involving an alkylated Ti(IV) and an alkylated Al species, linked together by chlorine bridge bonds. The environment of the Ti is of octahedral symmetry with one vacant site available for the coordination of ethylene. The bridged Al-alkyl causes a destabilization of the Ti-alkyl bond (“trans effect”), thus rendering it active for polymerization. The reduction Ti(IV) → Ti(III), inevitable in these systems, involves the irreversible change from octahedral to tetrahedral symmetry with loss of the catalytic activity. Polymerization and reduction are supposed to occur at the same catalyst site. Magnetic methods (susceptibility and EPR) as well as the kinetics of polymerization were used in the investigation of these catalyst systems.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 82
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 6 (1967), S. 124-133 
    ISSN: 0570-0833
    Keywords: Allyl halides ; Catalysis ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Allyl compounds react with carbon monoxide, or with carbon monoxide and acetylene, in the presence of tetracarbonylnickel as catalyst. These catalysts are involved also in coupling reactions and addition reactions of activated olefins and ketones. Reactions of this type can be used for the preparation of unsaturated aliphatic acids, esters, nitriles, hydrocarbons, alicyclic ketones, keto acids, keto esters, diketones, lactones, phenols, and other compounds. The reactions proceed via π-allylnickel complexes.
    Additional Material: 5 Tab.
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  • 83
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 5 (1966), S. 6-15 
    ISSN: 0570-0833
    Keywords: Radical reactions ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paper describes the application and limitations of magnetic methods to the problems of free-radical chemistry (detection and quantitative investigation of the free-radical state, relationships between structure and free-radical formation, “distribution” of the unpaired electron, detection of mesomeric C, O, N, P, As, and Sn radicals, g-factors, triplet states, and hyperfine structure). The problem of the diradical is described, and the paper closes with a discussion of the “Selwood effect”.
    Additional Material: 4 Ill.
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  • 84
    ISSN: 0570-0833
    Keywords: Free radicals ; Polyamides ; Fibers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation of free radicals during the process of drawing of spun fibers was observed for the first time with two polyoxamides. The fibers turn red, and an ESR signal can be detected. Both, color and ESR absorption are not permanent. The decrease in the intensity of the ESR absorption and the change in the optical reflectance with time, as well as the dependence of the decoloration on temperature were investigated. The action of high-energy radiation on the polyoxamides also leads to a red coloration and gives rise to ESR signals. It is concluded that the red color is due to free radicals associated with the oxamido group.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 85
    ISSN: 0570-0833
    Keywords: Butadiene ; Oligomers ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of new catalyst systems based on transition-metal compounds have been developed for the oligomerization and co-oligomerization of butadiene. These catalysis promote dienylations and the formation of other C—C linkages, and make possible the synthesis of new open-chain and cyclic compounds from butadiene.
    Additional Material: 1 Tab.
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  • 86
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 4 (1965), S. 341-347 
    ISSN: 0570-0833
    Keywords: Promotors ; Catalysis ; Ammonia synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An attempt is made to give a phenomenological description of the relationships between the catalytic activity and the distribution of the promotors in the reduced ammonia catalyst. Investigations were carried out on series of catalysts whose compositions were gradually brought closer to that of technical ammonia catalysts by the addition to iron of one new activator (Al2O3, K2O, CaO, MgO, SiO2) at a time.
    Additional Material: 7 Ill.
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  • 87
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 4 (1965), S. 856-867 
    ISSN: 0570-0833
    Keywords: EPR spectroscopy ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The more recent applications of electron paramagnetic resonance (EPR) to organic chemistry include the investigation of triplet states, donor-acceptor complexes, short-lived free-radical intermediates, and reaction kinetics. The principles of the theoretical calculations required to obtain the maximum information from EPR spectra are outlined for free radicals containing π-electron systems. EPR intensities, line widths, hyperfine splitting, and g factors permit the determination of free-radical yields, ionic charges, rotation frequencies in rotamers, electron density distributions, electronegativities, intramolecular torsion angles, solvent effects (resulting from hydrogen bonding), and π-orbital energies. - The production of free radicals with the aid of initiation reaction in flow systems, by irradiation, and by electrolysis seems particularly promising.
    Additional Material: 2 Ill.
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  • 88
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 525-538 
    ISSN: 0570-0833
    Keywords: Radical reactions ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present article an attempt is made to summarize the steric requirements and the influence of neighboring groups which determine the course of intramolecular radical reactions. Steroids are used as substrates for these reactions, since here the spatial arrangement of the ring members and the distances between substituents are largely fixed. Furthermore, intramolecular free-radical reactions are of practical importance in steroid chemistry in connection with substitution at non-activated carbon atoms. Almost all the reactions discussed begin with the formation of an oxygen radical by oxidation of an alcohol with lead tetraacetate or by homolysis of the corresponding hypoiodite.
    Type of Medium: Electronic Resource
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  • 89
    ISSN: 0570-0833
    Keywords: Free radicals ; Radical reactions ; Sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic free radicals of monovalent sulfur have not been hitherto observed in solution or in melts. Steric hindrance and resonance stabilization, which are responsible for the stability of the triarylmethyl, diphenylnitrogen, and phenoxyl radicals, are apparently insufficient to stabilize the organic free radicals of monovalent sulfur in such concentrations that they can be detected by current physical methods. - It was only in 1963 that aminopolysulfur radicals (R2N—Sn—S·) were detected in solution, and arylsulfur radicals (Ar-S·) and phenylselenium radicals were isolated at ca. -180°C. - Organically bound sulfur can be stabilized in the free-radical state if association of the radicals is prevented by fixing in a crystal lattice (“cystine radical”), by repulsion between radical ions (sulfinium salts), or by freezing-in (arylsulfur radicals).
    Additional Material: 1 Ill.
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  • 90
    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.
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  • 91
    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.
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  • 92
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    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.
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  • 93
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    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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