Mechanistic Analysis of 4-Methylthiobenzoyl Chloride in Solvolysis

Abstract

The solvolysis mechanism of 4-methylthiobenzoyl chloride (1) was studied by kinetic methods, and these results were compared with 4-methoxy (2) and 3,4,5-trimethoxybenzoyl chlorides (3) reported previously. The analysis of kinetic data was carried out using both the simple and extended Grunwald-Winstein (G-W) equations, thermodynamic parameters, and kinetic solvent isotope effects (KSIE). In fact, 4-methylthiobenzoyl chloride (1) has a sulfur atom which is bigger in size and has more electrons than oxygen in the para-position. The results were obtained and showed typical dispersed plots from the simple (R = 0.939) and extended G-W equations (l/m = 0.33, R = 0.952) for all data, and when the data from some of the most dispersed points were removed, the correlation coefficients were improved remarkably. Thermodynamic parameters revealed that the change of enthalpies were 16.2 +/- 17.6 kJ/mol and the change of entropies were -16.5 +/- -8.6 J/K-mol. The KSIE of MeOH/MeOD was 1.42. The above results for 4-methylthiobenzoyl chloride supported a unimolecular pathway, or more precisely, a dissociated S(N)2 mechanism classified by l/m ratio.