Effects of zwitterionic vesicles on the reactivity of benzoyl chlorides.

A systematic study on the solvolysis reaction of substituted benzoyl chlorides in the presence of zwitterionic vesicles of dipalmitoyl phosphatidylcholine (DPPC) has been performed. Size, shape, surface charge, and polarity of the interface of the vesicular aggregates were determined using various techniques. The application of the pseudophase formalism allowed us to obtain the thermodynamic and kinetic coefficients characteristic of the reaction. The effects of vesicular aggregates on the solvolysis of benzoyl chlorides, which are known to be sensitive to the physical properties of the medium, depend on the nature of the substrate. For benzoyl chlorides with electron-donating groups, which react predominantly through a dissociative mechanism which is strongly affected by medium properties, the rate constant decreases as the vesicle concentration increases. On the other hand, for benzoyl chlorides with electron-withdrawing groups, which react mainly via an associative pathway, DPPC vesicles catalyze the solvolysis reaction.