KINETICS OF INTRAMOLECULAR ALKYL RADICAL ATTACK ON SULFUR IN DISULFIDES AND THIOESTERS

The 4-(alkyldithio)butyl radicals 8a and c, and the 4-(phenyldithio)bu tyl radical 8b, generated from the corresponding esters of N-hydroxypy ridine-2(1H)-thione, undergo fast exo-cyclisation by S(H)i attack at s ulfur. Similarly, the 5-(alkyldithio)pentyl radical 8d undergoes 1,6-r ing formation. The rate constants for cyclisation were determined by p hotolysis of the radical precursors in the presence of appropriate thi ols. Butyl and pentyl radicals bearing omega-acetylthio or omega-benzo ylthio substituents also undergo ring closure but much more slowly. Th e kinetics of these intramolecular S(H)2 reactions are discussed and c ompared with those for the intermolecular attack of hexyl radicals on diphenyl disulfide and on dibutyl disulfide.