Product-Rate Correlations for Solvolyses of 2,4-Dimethoxybenzenesulfonyl Chloride

Abstract

The solvolysis rate constants of 2,4-dimethoxybenzenesulfonyl chloride (1) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the N-T solvent nucleophilicity scale and Y-Cl solvent ionizing scale, with sensitivity values of 0.93 +/- 0.14 and 0.65 +/- 0.06 for 1 and m, respectively. These 1 and m values can be considered to support a S(N)2 reaction pathway. The activation enthalpies (Delta H-not equal) were 12.4 to 14.6 kcal.mol(-1) and the activation entropies (Delta S-not equal) were -15.5 to -32.3 cal-mol(-1).K-1, which is consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effects (SKIE) were 1.74 to 1.86, which is also in accord with the S(N)2 mechanism and was possibly assisted using a general-base catalysis. The values of product selectivity (S) for solvolyses of 1 in alcohol/water mixtures was 0.57 to 6.5, which is also consistent with the proposed bimolecular reaction mechanism. Third-order rate constants, k(ww) and k(aa), were calculated from the rate constants (k(obs)), together with k(aw) and k(wa) calculated from the intercept and slope of the plot of 1/S vs. [water]/[alcohol]. The calculated rate constants, k(calc) (k(ww), k(aw), k(wa) and k(aa)), are in satisfactory agreement with the experimental values, supporting the stoichiometric solvation effect analysis.