Limitations of the transition-state variation model. Part 3. Solvolyses of electron-rich benzenesulphonyl chlorides

Abstract

Rate constants for solvolyses of 4-methoxy-2,6-dimethylbenzenesulphonyl chloride 3(Z = OMe) and of 4-methyl- and 4-methoxybenzenesulphonyl chlorides 4(Z = Me and OMe) are reported for aqueous binary mixtures with acetone, ethanol and methanol. Some additional rate constants are reported for aqueous acetonitrile and dioxane mixtures, as well as product selectivities (S) in alcohol–water mixtures. For each binary mixture, rates of solvolyses of 3(Z = OMe)vs. Y_Cl or Y are approximately bilinear. As water is added to alcohol, S values for solvolyses of 3(Z = OMe) pass through a maximum and for solvolyses of 4-methoxybenzenesulphonyl chloride 4(Z = OMe) the position of the maximum shifts to more aqueous media. For solvolyses of 4-methylbenzenesulphonyl chloride 4(Z = Me), S values are shifted such that they reach a plateau rather than a maximum, and the rate–rate profiles with Y_Cl are approximately linear rather than bilinear. All of the rate–rate profiles show ‘dispersion’ into separate correlations for the various binary mixtures. These substituent effects follow the same trends as corresponding solvolyses of benzoyl chloride and strengthen recent proposals that solvolyses of 3(Z = Me) proceed via competing (dual) reaction channels.