Dimethylsulfoxide-mediated oxidations

A very mild oxidation procedure that tolerates a variety of other functional groups is the oxidation of alcohols to aldehydes and ketones by the dimethyl sulfoxide (DMSO). A DMSO solution of the alcohol is treated with one of the several electrophilic dehydrating reagents. The alcohol is oxidized to the aldehyde or ketone and DMSO is reduced to dimethyl sulfide (DMS), which is a volatile liquid (b.p. 37°C). Since pure DMSO freezes at 18°C and an oxidation reaction is carried out at —50°C or lower, a co-solvent such as methylene chloride or THF (tetrahydrofuran) is needed. 

But the Pfitzner-Moffatt oxidation is not in much use because the Swern oxidation gives better yield and fewer side products. For example, methyl 12-hydroxydodecanoate (7.11) on treatment with DMSO and oxalyl chloride [(COCl)2] in CF12C12 followed by treatment with triethylamine yields 87% methyl 12-oxododecanoate (7.12). 

4-terf-butylcyclohexanol (7.13) on treatment with ( 113)28 and NCS in toluene followed by the reaction with Et3N yields 4-tert-butylcyclohexanone (7.14) in 100% yield. 

Because of the foul smell of DMS, several odourless versions of Corey-Kim and Swern oxidations have been reported. For example, odourless dodecyl methyl sulfide (Dod-S-Me) is an alternative to DMS in Corey-Kim oxidations. 

Similarly, when dodecyl methyl sulfoxide (C12H25SOCH3) is used in the Swern oxidation, the odourless Dod-S-Me by-product instead of foul-smelling DMS is formed. 

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Iron complexes or microsomal nonheme iron are undoubtedly obligatory components in the microsomal oxidation of many organic compounds mediated by hydroxyl radicals. In 1980, Cohen and Cederbaum [27] suggested that rat liver microsomes oxidized ethanol, methional, 2-keto-4-thiomethylbutyric acid, and dimethylsulfoxide via hydrogen atom abstraction by hydroxyl radicals. Then, Ingelman-Sundberg and Ekstrom [28] assumed that the hydroxylation of aniline by reconstituted microsomal cytochrome P-450 system is mediated by hydroxyl radicals formed in the superoxide-driven Fenton reaction. Similar conclusion has been made for the explanation of inhibitory effects of pyrazole and 4-methylpyrazole on the microsomal oxidation of ethanol and DMSO [29],... 

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