AMINOLYSIS OF PHENYL 2-FUROATES IN ACETONITRILE

Kinetic studies of the reaction of Z-phenyl 2-furoates with X-benzylam ines in acetonitrile at 55.0 degrees C were carried out. The magnitude s of the rho(x) (-1.1 similar to -1.9), rho(z) (1.8 similar to 2.5) an d rho(xz) (1.19) obtained for the reaction series are large, suggestin g a stepwise mechanism with a rate-limiting breakdown of the zwitterio nic intermediate, T+/-. The suggested mechanism is supported by the no rmal secondary kinetic isotope effects observed (k(H)/k(D) = 1.04 simi lar to 1.21). The inductive electron-withdrawing (sigma(1) = 0.04) and resonance electron donating (sigma(R) = - 0.19) effects of the 2-fura n group on the rate are smaller than those of the phenyl and ethoxy gr oups, as expected for the formation of a relatively stable zwitterioni c intermediate. A dual-substituent parameter analysis of the rates of the aminolysis of six p-nitrophenyl R-carbonyl esters indicated that t he rate-retarding resonance-electron-donating effect (sigma(R)) is as important as the rate-accelerating inductive-electron-withdrawing effe ct (sigma(1)) of the R group.