The role of water release from the cyclodextrin cavity in the complexation of benzoyl chlorides by dimethyl-β-cyclodextrin

The influence of temperature on the solvolysis of substituted benzoyl chlorides in the presence of dimethyl-β-cyclodextrin (DM-β-CD) was studied. Based on the influence of the DM-β-CD concentration on chemical reactivity in this process, the cyclodextrin has a catalytic effect on the solvolysis of 4-nitrobenzoyl chloride (4-NO2) but an inhibitory effect on that of 4-methoxy-(4-MeO), 3-chloro-(3-Cl) and 3-trifluoromethyl-(3-CF3) benzoyl chlorides. These disparate effects are related to a difference in reaction mechanism; thus, DM-β-CD catalyses associative solvolysis and inhibits dissociative solvolysis. Examining the influence of temperature on the solvolytic process allowed the stoichiometry of the host–guest complexes formed to be established. The formation constants for the complexes of meta-substituted benzoyl chlorides increased with increasing temperature. On the other hand, the equilibrium formation constants for the 1:1 host–guest complexes of para-substituted benzoyl chlorides exhibited the opposite trend. The equilibrium formation constant for 2:1 host–guest complexes for the para-substituted benzoyl chlorides increased with increasing temperature. These differences are ascribed to the release of water from the DM-β-CD cavity during the formation of the host–guest complex.