Intermediates in the photolysis of alkyl sulfides and disulfides in dilute glass matrices

Abstract

Simple alkyl sulfides and disulfides have been photolysed at 253.7 nm in dilute rigid glasses of 3-methylpentane, and the reactions which occur both at 77 K and in the glass at higher temperatures have been studied using epr and optical spectroscopy. The end products of photolysis have been determined using glc at room temperature. In sulfides, C—S bond cleavage leads to 'hot' radical pairs that react with each other giving rise to the main diamagnetic products observed, or react with nearby solvent molecules in the matrix by hydrogen abstraction yielding RSH and the solvent derived radicals (M•) which dominate the initial epr spectrum at 77 K. Thiyl radicals (RS•) are produced in significant amounts only after the sulfide glasses have been warmed slightly to allow the cage reaction,[Formula: see text]to occur. Pethiyl radicals (RS2•) are not ordinarily observed in sulfide photolyses. Photolysis of disulfide-containing glasses gives rise to S—S bond rupture and mainly diamagnetic products, or to C—S bond cleavage resulting in the formation of solvent radicals and RS2. Very little RS• is generated on warming the matrices. As with ethyl mercaptan photolysis, radicals corresponding to α-hydrogen abstraction of the substrate are obtained for both ethyl sulfide and disulfide. The spectral characteristics and photolytic behaviour of the sulfur containing radical species have been investigated where possible.