A kinetic study is reported for the reactions of 4-nitrophenyl phenyl carbonate (5) and thionocarbonate (6) with a series of alicyclic secondary amines in 80 mol% H(2)O-20 mol% DMSO at 25.0 +/- 0.1 degrees C. The plots of k(obsd) vs. amine concentration are linear for the reactions of 5. On the contrary, the plots for the corresponding reactions of 6 curve upward as a function of increasing amine concentration, indicating that the reactions proceed through two intermediates (i.e., a zwitterionic tetrahedral intermediate T(+/-) and its deprotonated form T(-)). The Brønsted-type plot for 5 the reactions of with secondary amines exhibits a downward curvature, i.e., the slope decreases from 0.98 to 0.26 as the pK(a) of the conjugate acid of amines increases, implying that the reactions proceed through T(+/-) with a change in the rate-determining step (RDS). The k(N) values are larger for the reactions of with secondary amines than for those with primary amines of similar basicity. Dissection of k(N) values for the reactions of 5 into the microscopic rate constants (i.e., k(1) and k(2)/k(-1) ratio) has revealed that k(1) is larger for the reactions with secondary amines than for those with isobasic primary amines, while the k(2)/k(-1) ratio is nearly identical. On the other hand, for reactions of 6, secondary amines exhibit larger k(1) values but smaller k(2)/k(-1) ratios than primary amines. The current study has shown that the reactivity and reaction mechanism are strongly influenced by the nature of amines (primary vs. secondary amines) and electrophilic centers (C[double bond]O vs. C[double bond]S).

A kinetic study is reported for aminolysis of O-Y-substituted phenyl thionobenzoates (1a-f) and O-4-nitrophenyl X-substituted thionobenzoates (2a-f) in 80 mol % H2O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The reaction proceeds through one or two intermediates (i.e., a zwitterionic tetrahedral intermediate T(+/-) and its deprotonated form T(-)) depending on the basicity difference between the nucleophile and nucleofuge, that is, the reaction proceeds through T(+/-) when the leaving aryloxide is less basic than the attacking amine, but through T(+/-) and T(-) when the leaving group is more basic than the amine. However, the reaction mechanism is not influenced by the electronic nature of the substituent X in the nonleaving group. The Hammett plot for the reactions of 2a-f with benzylamine is consisted of two intersecting straight lines, which might be interpreted as a change in the rate-determining step (RDS). However, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation, indicating that the nonlinear Hammett plot is not due to a change in the RDS but caused by stabilization of the ground-state of the substrate through resonance interaction between the electron-donating substituent X and the thionocarbonyl moiety.