Properties of Disulphides and Polysulphides

Several papers have appeared describing the cleavage of disulphides and diselenides with phosphines. A two-step mechanism applies to the reduction of a disulphide with Ph3P in aqueous media, and the intermediate Ph3PSAr ArS hydrolyses to ArSH + PhaPO. More complex disulphides containing acetamido-alkyl and o a-di(ethoxycarbonyl)alkyl substituents give oxazole and trisulphide side-products during reduction with PhaP. Conversion of dimethyl diselenide with (R2N)aP into dimethyl selenide, and photochemical deselenation of diethyl diselenide to diethyl selenide with PhaPMe, which involves an EtSe radical chain mechanism, have been described. 

Photolysis of disulphides in aldehyde solvents gives thiol-esters, Irradiation of dibenzyl diselenides at wavelengths longer than ca. 300 nm gives selenides  

Furukawa, S. Kato, and S. Hayashi, Chem. andPharm. Bull. (Japan), 1974,22, 2987. 

Burton and J. M. Shreeve, Inorg. Nuclear Chem. Letters, 1976, 12, 373. 

Methyl bis(methylthio)sulphonium hexachloroantimonate, MeS(SMe)s SbClg-, -9 8 prepared by methylthiolation of the disulphide, shows useful methylthiolating properties e.g. alkenes give 5-methylthiiranium salts. Methylation of a trisulphide with MejO BF4- gives the analogous salt MeS(SR)a BF.  

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