Reactions of thiyl radicals. III. Photochemical equilibrium in the photolysis of liquid disulfide mixtures

Abstract

The photolysis of mixtures of liquid methyl disulfide and ethyl disulfide at room temperature at wavelengths greater than 2300 Å has been investigated. The sole detectable product is methyl ethyl disulfide which reaches a photostationary state concentration after relatively short irradiation periods. For various initial mixtures, the concentration of the three disulfides in the photostationary state can be correlated in terms of an equilibrium constant, K = [RSSR′]/[RSSR]1/2[R′SSR′]1/2, whose value is 2.05 ± 0.04. The quantum yield of unsymmetrical disulfide formation in the initial stages of the reaction is 330 for an absorbed intensity of 4.70 × 10−2 μeinstein/min when the incident radiation is confined to λ = 2600 + 50 Å. The exceptionally high efficiency of the overall process is ascribed to the chain-propagating step[Formula: see text]which likely proceeds through attack of the thiyl radical on the S—S disulfide linkage.