Thermochemistry and kinetics of the reaction of methyl mercaptan with iodine

The gas‐phase reaction CH 3 SH + I 2 has been studied spectrophotometrically over the temperature range of 476–604 K. It was found that the reaction undergoes H abstraction by I at ≤575 K, leading to the formation of MeSI and followed by a secondary reaction which leads to the formation of MeSSMe:Taking into consideration the effect of reaction (2), the equilibrium constant K 1 (554 K) has been evaluated to be 0.025 ± 0.004. This value was combined with the estimated values S   298 0(CH 3 SI, g ) = 73.7 ± 1.0 eu and 〈ΔC   p 1,554 0 〉 = 0.87 ± 0.3 eu to obtain Δ H   1,298 0= 4.03 ± 0.73 kcal/mol. This yields Δ H   f 298 0(CH 3 SI, g ) = 7.16 ± 0.73 kcal/mol when combined with known thermochemical values for CH 3 SH, HI, and I 2 . A kinetic study was vitiated by the concurrent heterogeneous reaction of MeSH and I 2 at lower temperatures and the rather complicated chemistry occurring at elevated temperatures. However, attempts at measuring rate constants at 554 K lead to a lower limit of Δ H   f 298 0(CH 3 S·, g ) ≥ 29.5 ± 2 kcal/mol when an estimated value of A = 10 10.8 ± 0.2 L/mol·s for the reactioncis used. DH   298 0(CH 3 S–I) is estimated to be 49.3 ± 1.7 kcal/mol. The bond strengths of some divalent sulfurs and the reaction mechanisms are discussed. A crude estimate of DH 0 (H–CH 2 SH) = 96 ± 1 kcal has been obtained from the kinetic data.