Halogen oxidation, mechanism

Much of tills chapter concerns ET reactions in solution. However, gas phase ET processes are well known too. See figure C3.2.1. The Tiarjioon mechanism by which halogens oxidize alkali metals is fundamentally an electron transfer reaction [2]. One might guess, from tliis simple reaction, some of tlie stmctural parameters tliat control ET rates relative electron affinities of reactants, reactant separation distance, bond lengtli changes upon oxidation/reduction, vibrational frequencies, etc. 

Since carbon-halogen bond cleavage is not a favorable process, and since both carbon and oxygen atoms have an even number of electrons, the oxidation proceeds either via free radicals or via carbenes and triplets. As a result, the oxidation mechanisms are considerably simpler than with hydrocarbons. Section III of this review treats free radical oxidation, whereas Section IV treats oxidation by processes not involving free radicals. In this discussion a free radical is considered to be a species with an odd number of electrons carbenes and triplets are called biradicals and are not included in this category. 

The atmospheric oxidation of dimethyl sulfide (DMS) and DMSO has been reviewed. Kinetics of oxidation of DMS and DMSO with OH and NO3 radicals and with halogen and halogen oxides have been described and the mechanistic aspects have been discussed.244 A review of recent studies of the mechanism and kinetics of the gas-phase oxidation of dimethyl ether has mentioned the pressure dependence of the... 

The field of halogen oxidation has developed primarily in two directions. The first is the preparation of aldonic acids by oxidation with bromine in acid solution. The second is the use of alkaline hypoiodite as a quantitative oxidant. Little work has been done on the mechanism of these reactions. The conditions under which the reactions are carried out have usually been established empirically without extensive study. The further use of solutions of known concentration and the comparison of various oxidants under similar conditions are to be desired. Critical oxidation potentials of various sugars used in relation to possible oxidants and ranges of pH might yield promising results. 

Friedel-Crafts and Grignard processes applied to, 6, 251-289 halogen oxidation of simple, 3, 129-184 infrared spectra of, 12, 13-33 mechanisms of replacement reactions in chemistry of, 9, 1-57 metabolism of, 2, 119-160 3, 229-250 orthoesters of, 1, 77-127 periodate oxidation of, 11, 1-41 the dialdehydes" from, 16, 105-158 physicochemical properties of, 16,11-51 radiation chemistry of, 16, 13-58 and related compounds, paper chromatography of, 9, 303-353 relative reactivities of hydroxyl groups of, 8, 1-44... 

Reaction with Cl2 or C12/A1C13 probably involves initial attack of the electrophile Cl+. However, in view of the oxidative properties of halogens, a mechanism involving electron transfer cannot be excluded. The exact mechanism of the reaction is difficult to determine. Possible pathways are represented on Scheme 60. 

As an alternative to the mechanism above, it is possible that the reaction outlined in Eq. (49) proceeds by way of an oxidative-promoted insertion, in which a 17-electron alkyl carbonyl is formed which then rapidly undergoes insertion to produce an acyl complex. This redox-promoted reaction appears to occur in a rather large number of cases involving the action of metal or halogen oxidizing agents on metal alkyl carbonyls [Eq. (50)] (Ref. 221, and... 

Platt, U. (1995) The chemistry of halogen compounds in the Arctic troposphere, in Tropospheric Oxidation Mechanisms, K. H. Becker, ed., European Commission, Report EUR 16171 EN, Luxembourg, pp. 9-20. 

CHEMICAL MODIFICATION The following chemical modifications of cis-1,4-polyisoprene are employed as a convenient way of altering physical and mechanical properties hydrohalogenation, halogenation, oxidation, ozonolysis, hydrogenation, carbene addition, cyclization. ... 

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