Kinetics and mechanism of the aminolysis of ethyl aryl carbonates in acetonitrile

摘要

The aminolysis reactions of ethyl aryl carbonates with benzylamines in acetonitrile at 25.0 degrees C are investigated. The base-catalyzed path, k(2), disappears when strong nucleophiles (X = p-CH3O and p-CH3) react with a substrate activated by a strong nucleofuge (Z = p-NO2. The large magnitude of rho(x) (-1.7 to -2.5), rho(z) (3.4 to 4.3), and rho(xz) (1.4) values, and relatively large k(H)/k(D) (1.6 to 1.8) found for the uncatalyzed path (k(1)) can be accounted for in terms of a stepwise mechanism with rate-limiting expulsion of the phenoxide leaving group. The catalyzed process (k(2)) is characterized by the much smaller magnitude of rho(x) (-1.0 to -1.7), rho(z) (0.4 to 0.7), and rho(xz) (0.2), the larger k(H)/k(D) (2.1 to 2.5) values, and the lower Delta H-double dagger values (1.8-1.9 kcal mol(-1)) than those of the uncatalyzed process (k(1)) with large negative Delta S-double dagger values (-65 to -67 cal K-1 mol(-1)). These results are consistent with four- and six-centered transition states for the two processes, k(1) and k(2), respectively. [References: 43]