Metal/bromide-catalysis

It is known that the oxidation of alkyl-substituted aromatic hydrocarbons in acetic acid on metal bromide catalysis follows the one-electron transfer mechanism (Sheldon and Kochi 1981). The rate-determining stage is the one-electron transfer from the substrate to the metal ion in the highest oxidation state (Digurov et al. 1986). As a result, an unstable cation-radical is formed that... 

Metal bromide catalysis is widely used in industry for oxidation of alkylaromatic compounds to their corresponding acids. The mechanism for this catalytic process has been investigated for over 20 years but it is still not established despite numerous papers on this subject This work presents results of our investigations on the kinetics and mechanisms of cobalt bromide catalysis. 

Reactions between R02 and Go(II) or Mn(II) are discussed in terms of the methods of rate constant determination, the values of the rate constants and the effect of media on rate constants. A synergistic effect of Mn(II) addition is also discussed. The effect of the media is discussed in terms of the coordination ability of the solvent with Go(II) ion as well as the proton donor property of the solvent. It is concluded that the presence of a proton donor in the coordination sphere of Co(n) is required for hydroperoxide formation but at the same time this prevents the peroxy radical from reacting with the cobalt(II) ion. As a result, a bell-shaped dependence of the rate constant on the acetic acid and water concentration is observed. Our data explain some of the controversial literature data on solvent effects for the kinetics of metal bromide catalysis. 

Metal bromides, 4 322-330 Metal can food packaging, 18 37-39 Metal-carbene complexes, 26 926 Metal-carbon compounds, 4 648, 650 Metal-carbon eutectic fixed points, 24 454 Metal carbonyl catalysts, supported, 16 75 Metal carbonyl complexes, 16 73 Metal carbonyls, 15 570 16 58-78 bonding and structure of, 16 59-64 from carbon monoxide, 5 12 in catalysis, 16 72-75 economic aspects of, 16 71 health and safety aspects of, 16 71 heteronuclear, 16 69-71 high nuclearity, 16 66-69 high nuclearity carbonyl clusters, 16 64-66... 

Competition between Homolytic and Heterolytic Catalytic Decompositions of Hydroperoxides Reactions of Transition Metals with Free Radicals Reactions of Transition Metal Ions with Dioxygen Catalytic Oxidation of Ketones Cobalt Bromide Catalysis Oscillating Oxidation Reactions... 

The solvation of ionic species involved in a reaction has to be considered. Furthermore, many reactions involve metal-ion catalysis in which the principles of hard and soft acids and bases come into play. Thus a large soft metal may facilitate the reaction of the softer iodides, allowing a harder base to react at the carbon centre. Finally, there are radical reactions based on the alkyl halides, particularly bromides and iodides, involving homolytic fission of the C-X bond. 

Parteriheimer, W. Metodology and scope of metal/bromide autoxidation of hydrocarbon, Catalysis Today, 1991, 23, 69. 

Carbonylation of allylic and benzylic chlorides was carried out by transition-metals (as catalysis) to give P,y-unsaturated acids. However, the above method gave low yields. It is found that carbonylation of benzyl bromide and chloride could be carried out by stirring with an aqueous sodium hydroxide and an organic solvent using a PTC and a cobalt catalyst. Even benzylic mercaptan could be carbonylated to give esters under high pressure and temperature (Scheme 142) ... 

Partenheimer, W., 1995. Methodology and scope of metal/bromide autoxidation of hydrocarbons. Catalysis Today 23, 69-158. 

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising composite systems, for separation and catalysis, respectively. 

The reader is referred the recent book by Bell and Pines [2] for a more complete overview of the various methods and objectives in NMR studies of solid acids and other heterogeneous catalysis. In the present contribution we illustrate the application of H, and MAS NMR to two archetypal solid acids, Brpnsted sites in zeolites and solid metal halides such as aluminum chloride and bromide powders which exhibit "Lewis superacidity". An important characteristic of the more recent work is the integration of quantum chemical calculations into the design and interpretation of the NMR experiments. 

Palladium NHC systems for the hydrodehalogenation of aryl chlorides and bromides and polyhalogenated aromatic substrates originate from about the same time as the first reports on Ni chemistry, and show many similarities. Initial efforts showed that the combination of PdCdba) (2 mol%), one equivalent of imidazolium chloride and KOMe produced an effective system for the reduction of 4-chlorotolu-ene, especially upon use of SIMes HCl 2 (96% yield of toluene after 1 h at 100°C) [7]. Interestingly, higher ligand to metal ratios severely inhibited the catalysis with only 7% yield of toluene achieved in the same time in the presence of two equivalents of SIMes HCl 2. Variation of the metal source (Pd(OAc)2, Pd(CjHjCN)jClj), alkoxide (NaOMe, KO Bu, NaOH/ ec-BuOH) or imidazolium salt (IMes HCl 1, IPr HCl 3, lAd HCl, ICy HCl) all failed to give a more active catalyst. 

These reactions are subject to catalysis by certain transition metal ions and with small amounts of MnBr2 or CuCl the reaction proceeds satisfactorily with alkyl bromides.134... 

At the end of this first stage of the chemical catalysis process, the metalloporphyrin is left under the form of a metal(III) bromide. The reaction that closes the catalytic loop is thus the reduction of this species into the metal(I) complex by means of two successive electron transfers from the electrode. This is a fast process since the electrode potential is adjusted so as to reduce rapidly the metal(II) complex. 

An additional report describes Te/Zn exchange of diaryl tellurides and diaryl ditelluride by treatment with Zn under Ni catalysis." The resulting Zn derivatives submitted to trans-metallation with CuCN-2LiCl and subsequent allylation with aUyhc bromide, furnishes the expected product in high yield. 

Hydrogenation catalysis, by matrix isolated metal clusters, 23 91 Hydrogen bromide irradiation of, 5 169 PES of, 16 78, 83 Hydrogen chloride di.splaced, 34 151 PES of, 16 78, 83 Hydrogen cyanide... 

Low reactive aryl chlorides are converted to the respective organomagnesium species in excellent yields through transition metal catalysis using 2 mol% FeCU (4-6, equation 3). Alternatively, a safe and reproducible method for activation of aryl chlorides or bromides 7 uses microwave irradiation (equation 4). In a synthesis of a novel HIV-1 protease inhibitor, microwave irradiation was essential to generate the starting arylmagnesium halide as well as to promote the subsequent Kumada coupling reaction. ... 

The formation of arylzinc reagents can also be accomplished by using electrochemical methods. With a sacrificial zinc anode and in the presence of nickel 2,2-bipyridyl, polyfunctional zinc reagents of type 36 can be prepared in excellent yields (Scheme 14) . An electrochemical conversion of aryl halides to arylzinc compounds can also be achieved by a cobalt catalysis in DMF/pyridine mixture . The mechanism of this reaction has been carefully studied . This method can also be applied to heterocyclic compounds such as 2- or 3-chloropyridine and 2- or 3-bromothiophenes . Zinc can also be elec-trochemically activated and a mixture of zinc metal and small amounts of zinc formed by electroreduction of zinc halides are very reactive toward a-bromoesters and allylic or benzylic bromides . ... 

Catalysis by chlorides of Cr(III) and Co(II), metals which normally exhibit the d2sp2 octahedral geometry directs the coupling of either cis- or /ranr-diphenylvinylmagnesium bromide, (26) or (28) to form the cis-cis-... 

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