Silver-assisted DMSO

Oxidation. Oxidation of alkyl halides by DMSO requires high temperatures (100-150°), and yields are relatively low except for primary iodides (1, 303). Epstein and Ollinger11 find that halides can be oxidized to carbonyl compounds by DMSO at room temperature (4-48 hours) in the presence of silver perchlorate as assisting agent. Chlorides are relatively unreactive, but bromides and iodides are oxidized relatively easily. Yields are higher with primary halides than with secondary halides. Cyclohexyl halides are oxidized to only a slight extent to cyclohexanone, the main product being cyclohexene, formed by elimination. 

Erickson and co workers of the hydrolysis reactions of [PtCl(dmso) (amino acid)] (dmso is cis to N amino acids are glycine, sarcosine, or N,N-dimethylglycine) revealed a second-order assistance by Ag" which dominated the conversions to the aquo ions, [Pt(OH2)(dmso)(amino acid)]. The relative importance of the unassisted (ki) path and the silver ion assisted (kAg) path is expressed by the ratio ki/(ki + kAg[Ag ]). The authors suggested the operation of reactions (1) and (2), based on chloride bridges to Ag, to account for the acceleration. Some structures described in Section 5.7 lend support to this type of interaction. 

The direct oxidation of alkyl halides to carbonyl compounds by DMSO occurs in good yield under mild conditions in the presence of silver ion, which assists formation of the alkoxysulphonium intermediate silver perchlorate is the salt of choice, other salts competing nucleophilically with DMSO for the substrate. Oxidation of primary halides stops cleanly at the aldehyde stage, except when an excess of silver salt is present. As has been already described, sodium tetracarbonylferrate converts alkyl bromides into the homologous aldehydes this conversion is most successful with primary halides, n-decanal being obtained in 77% yield from n-nonyl bromide. 

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