The kinetics and mechanism of the reaction of p-nitrocumyl bromide with azide ions in dimethyl sulfoxide. Evidence for a heterolytic reaction

Abstract

The reaction of p-nitrocumyl bromide 1 with azide ions in [²H₆]dimethyl sulfoxide does not show the strong photochemical catalysis and inhibition by electron acceptors and radical traps characteristic of the reactions of the corresponding chloride in dipolar aprotic solvents and used as evidence for a S_RN1 reaction. Instead, the bromide reacts by a heterolytic mechanism that is approximately first-order with respect to both the substrate and the lithium azide. The results can be interpreted in terms of the preassociation mechanism proposed by Richard and Amyes for the reaction of p-nitrocumyl chloride with azide ions in aqueous trifluoroethanol but there is some evidence for the participation of the azide ion in heterolysis of the C–Br bond.