Aminolysis of 3,4-Dinitrophenyl Cinnamate and Benzoate 2:Activation Parameters and Transition-State Structures

摘要

The apparent second-order rate constants(K_N)have been dissected into the microscopic rate constants(i.e.,k1 and k2/k_(-1))associated with the reactions of Y-substituted phenyl cinnamates(5a-g)with piperidine and morpholine on the assumption that the reactions proceed through a stepwise mechanism with a change in the rate-determining step(RDS).The k1 value is larger for the reactions with the more basic piperidine,and increases with decreasing the basicity of the leaving aryloxides.However,the k2/k_(-1)ratio is almost the same for the reaction of 3,4-dinitrophenyl cinnamate(5a)with piperidine and for that with morpholine,which is not possible if the reactions proceed through a stepwise mechanism.Thus,the aminolysis of 5a-g has been proposed to proceed through a concerted mechanism.The activation parameters(DELTA H and DELTA S)have been measured for the reactions of 3,4-dinitrophenylbenzoate(1a)and cinnamate(5a)with morpholine from the kinetic study performed at 5 different temperatures in 80 mol% H2O/20 mol% DMSO.The reaction of 5a results in a lager enthalpy of activation(DELTA H)but a less negative entropy of activation(DELTA S)than that of la.