Nucleophilic substitution reactions of phenacyl benzenesulphonates with anilines in methanol–acetonitrile mixtures

Abstract

The nucleophilic substitution reactions of phenacyl benzenesulphonates with anilines in methanol–acetonitrile have been studied. A stronger nucleophile was found to cause less bond cleavage, while a better leaving group led to less bond formation, in complete agreement with predictions by the potential energy surface model. The reactions were also found to adhere to the Bell–Evans–Polanyi principle as well as the reactivity–selectivity principle, and hence constituted a good example of a thermodynamically controlled reaction series. Cross interaction constants, ρ_ij, for the reaction series were used to characterize the transition state structure. The α-carbonyl group was shown to provide a ‘shunt’ in the resonance in the transition state, which resulted in a remarkable decrease in the cross interaction between substituents in the nucleophile and those in the substrate. The magnitudes of ρ_ij indicated that in the transition state bond breaking had progressed very little but bond formation was substantial. Consideration of cross interaction constants led us to conclude that the involvement of a bridged transition state is unlikely.