The Hofmann Rearrangement. II. Kinetic Substituent Effects of ortho-, meta-, and para-Substituted N-Chlorobenzamides

The reaction rates of the Hofmann rearrangement of ortho-, meta-, and para-substituted N-chlorobenzamides were measured under the same reaction conditions as were used for the preceding N-bromo series. The rate constants of the N-chloroamides were found to be slightly larger than those of the N-bromoamides. The relative values of the activation entropy and the activation enthalpy of N-chloro- and N-bromo-derivatives were approximately −4 e.u. and −1.3 kcal/mol respectively. The LFER between the two series was excellent, indicating that the reaction mechanism was almost the same for both series. The effects of the leaving group on the reactivity of ortho-substituents were discussed in terms of the ortho/para rate ratios and the relative values of the activation parameters of ortho- and para-substituents.