The EPR spectra of thiyl radical spin adducts produced by photolysis of disulfides in the presence of 2,4,6-tri-tert-butylnitrosobenzene and 5,5-dimethyl-1-pyrroline N-oxide

Abstract

A series of thiyl radicals prepared by the photolysis of the parent disulfide have been trapped using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,4,6-tri-tert-butylnitrosobenzene (BNB). The EPR spectra of the resulting spin adducts show proton hyperfine interactions from the δ-protons of the alkyl group of the thiyl, thus allowing definitive radical assignments to be made. For thiyl BNB spin adducts, a characteristic nitrogen coupling constant is observed. For secondary and tertiary thiyls, two adducts arise from addition to the nitrogen and oxygen of the nitroso group. The extent of reaction at the oxygen increases with increasing disulfide concentration. This is attributed to the formation of a complex between the thiyl and the parent disulfide, whose bulk favours its addition to the less sterically hindered oxygen position. The rate constant for the reaction of PrⁱS˙ radicals with (PrⁱS)₂ to form the complex is 240 times lower than that for reaction with BNB. Direct addition of PrⁱS˙ to the nitrogen of BNB is 11.5 times more efficient than to oxygen.