Electrophilic catalysis of sulphate (–SO3–) group transfer: hydrolysis of salicyl sulphates assisted by intramolecular hydrogen bonding

Abstract

The hydrolysis of substituted salicyl sulphates has been measured over a range of pH values at 70 °C to obtain kinetic parameters for hydronium ion (K_H) and carboxylic acid (K_p) catalysis. A Jaffé treatment of the carboxy-catalysis parameter for a range of nuclear substituents yields ρ_phenol 1.51; ρ_carboxy 0 indicates that the carboxy-function does not ionise on going from the ground-to the transition-state, consistent with hydrogen bonding rather than catalysis through proton transfer. The change in ‘effective’ charge on the phenol oxygen on going from the ground-to the transition-state confirms less build up of negative charge than in the uncatalysed hydrolysis of aryl sulphates.