Sulfonyl Chloride Kinetics. Part II. Solvolysis of a Series of Benzenesulfonyl Chlorides: An Unexpected Heat Capacity Variation

Abstract

First order rate constants for the solvolysis of a series of 4-X-benzenesulfonyl chlorides (where X = MeO, Me, Br, and NOz) were measured by the conductance method in HzO over the approximate temperature range of 0 to 25". Pseudothermodynamic parameters, AG*, AH*, AS*, and ACp* were derived and the high accuracy of the rate constants enabled an estimation of dACp*/dT.A trigonal bipyramidal transition state is favored for the nucleophilic attack which is probably by an SN2 type mechanism. A novel explanation for the effect of 4-methoxy on ACp* involves a temperature dependent water-solute interaction, which has general applicability to the behavior of 4-methoxy substituents.On a mesurd, par la methode de la conductivite, dans I'eau et a des temperatures entre 0 et 25 "C, les constantes de vitesse du premier ordre pour la solvolyse d'une sirie de chlorures de benzenesulfonyles substituis en position 4. On en a dtrive les parametres pseudothermodynamiques AG*, AH*, AS*, et ACp* et grlce a la grande precision des mesures, on a pu estimer la valeur de dAC,*/dT.On favorise un etat de transition trigonal et bipyramidal pour I'attaque nucleophile qui est probablement un mecanisme SN2. Une nouvelle explication pour l'effet du groupement methoxy en position 4 sur ACp* implique une interaction entre l'eau et le solute qui serait dependante de la temperature; cette explication serait d'application generale chaque fois que des substituants methoxyle en position 4 seraient impliqub.

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

“…In this connection there is a related factor which deserves comment. In an investigation of the hydrolysis of substituted benzenesulfonyl chlorides (43) it was found that the AC,* for the p-methoxy member was less negative than expected by comparison with other members of the series. This was attributed to a temperature dependent interaction of the water with the methoxy group, an effect which increased with increasing temperature as the equilibrium in cooperative water structure moved toward a greater number of unbonded water molecules (44).…”

Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides

“…In a subsequent paper [ 29 ], for the solvolyses of benzenesulfonyl chloride and its p -MeO, p -Me, p -Br, and p -NO 2 derivatives specific rates of hydrolysis were measured in the 0 °C to 25 °C range. The thermodynamic parameters, ∆ G # , ∆ H # , and ∆ S # and the above mentioned second-order parameter ∆ C p # were derived.…”

“…The ∆ C p # values correlated very well against ∆ S # values, except for an unusually low value for the p -MeO derivative. Arguments to explain this [ 29 ] were presented at length but do not seem to be totally convincing.…”

“…In a third paper [ 30 ], kinetic solvent isotope effects ( k sie values) were reported as k H2O / k D2O for the same group of benzenesulfonyl chlorides as reported on in part II [ 29 ]. Differences are found, as one might predict, in the nucleophilic processes for attack by water on sulfur rather than on carbon, indicating differences in the detailed bimolecular processes.…”