Reactions of Thiyl Radicals. VII. Photolysis of Methyl Sulfide Vapor

Abstract

The photolysis of methyl sulfide vapor has been investigated as a function of substrate pressure, exposure time, and temperature in the wavelength range 2000 to 2300 Å. The effects of added propane, sulfur hexafluoride, and 2-methylpentane have been studied. The principal products of the decomposition are CH4, C2H6, CH3SSCH3, and CH3SH. The data indicate direct C—S bond scission in the primary process giving rise to "hot" CH3 and CH3S radicals. A mechanism in which disproportionation of methylthiyl radicals is a very minor process is proposed.The reactions of CH3 and CH3S radicals with methyl sulfide have been examined also by photolyzing CH3SSCH3 and CH3COCH3 in the presence of CH3SCH3. Quantum yields at 2288 Å have been determined as a function of several variables. A number of rate parameters for the reactions of methyl radicals and methylthiyl radicals have been calculated.

Mechanism of the reaction of oxygen atoms, O(3P) with dimethyl disulfide

“…The observed ratios are 1.8 < -AH2S/ACH3S(0)2SCH3 < 3.3 and 0.9 < ACH,SH/ ACH3S(0)?SCH3 < 1.6, with the ratios increasing with increasing H2S. These ratios are smaller than the simple mechanism predicts because the product CH,SH will compete with H2S in reactions [6]- [9]. With increasing concentrations of H2S, CH,SH would be less competitive, and the ratios should increase, as observed.…”

“…If these are the only additional channels responsible for loss of oxygen atoms, the disproportionation reactions would account for 32% of the oxygen atoms, leading to an overall ratio of disproportionation/ recombination of 0.47 for reactions [3] and [4]. ation/recombination ratio of 0.4 for CH3S radicals (8), later work suggests that disproportionation is insignificant (9,10).…”

“…But because addition of 400 pmol of CH,SH leads to nearly complete depletion of CH,S(O),SCH,, CH,SH must react also with the intermediate product of reaction [4], i.e., Alternatively, the CH,SH could potentially intercept the CH,SO radical directly, and prevent the formation of CH,S(0)2SCH, before reactions [3] and [4] occur. However, in estimating the rate constant of reaction [9] it should be remembered that this reaction may be endothermic (estimated AH = +9 5 10 kcal/mol).…”

“…Thus, H2S must react with CH,S(O)SCH, analogously to CH,SH i.e., Also, because addition of 80 pmol of H2S causes the yield of CH,S(0)2SCH, to be so small as to be undetectable, either one or both of reactions [I31 and [I41 (the analogs of reactions [8] and [9]) must occur, although reaction [I41 may be endothermic.…”

Reactions of thiyl radicals. XII. Triplet mercury photosensitized decomposition of ethyl sulfide in the gas phase

“…Methyl sulfide has been studied in both direct (1) and Hg-sensitized decomposition (2), but only the direct photolysis of ethyl sulfide has been investigated (3).…”