Mechanism of the reactions of substituted anilines with phenyl 2,4,6-trinitrophenyl ether in benzene: evidence for a cyclic transition state involving an eight-membered ring

Abstract

Rates and activation parameters have been determined for the reactions of phenyl 2,4,6-trinitrophenyl ether with substituted anilines in benzene. For some of the nucleophiles, the rates decrease with increasing temperature in the range 5–35 °C resulting in negative activation enthalpies (ΔH^‡–3.1 to –27.3 kJ mol^–1). This is strong evidence for a stepwise mechanism involving (at least) a pre-equilibrium. These base-catalysed nucleophilic substitution reactions are sensitive to the nature of the arylated amine as indicated by the Hammett's constant (ρ–7.7).