Ab initio study of the oxidation of CH3SH to CH3SSCH3

The thermodynamic and kinetic aspects of the oxidation of methanethiol to dimethyl disulfide by oxygen were studied using ab-initio molecular techniques. The reaction was considered as a multi-step process. Geometrical parameters and molecular energies for critical points were determined and characterized at the MP2(Full)/6-31G* level. Afterwards, a study was carried out employing different methods of theoretical model chemistry (G2, G2(MP2), G3 and CBS-4 MB), for which the equilibrium geometry at MP2(Full)/6-31G* was assumed as starting point. The steps governing the rate of the whole reaction were determined and prove to be the same for any level of theory employed. Although the MP2(Full)/6-31G* level is able to afford a good qualitative description of the reaction pathway, the quantitative aspect is less satisfactory. Results from the methods of theoretical model chemistry, on the other hand, accord well with experimental data, if available, and are very useful for studying the thermodynamic and kinetic aspects of chemical reactions.