The reactions of the title substrate (1) with a series of secondary alicyclic amines are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0ЊC, ionic strength 0.2 M (KCl). Under amine excess over the substrate, pseudo-first-order rate coefficients (k obs ) are obtained. Plots of k obs against [NH], where NH is the free amine, are nonlinear upwards, except the reactions of piperidine, which show linear plots. According to the kinetic results and the analysis of products, a reaction scheme is proposed with two tetrahedral intermediates, one zwitterionic and another anionic with a kinetically significant proton transfer from Ϯ Ϫ
(T ) (T ), to an amine to yield (k 3 step). By nonlinear least-squares fitting of an equation derived
T T from the scheme to the experimental points, the rate microcoefficients involved in the reactions are determined. Comparison of the kinetics of the title reactions with the linear k obs vs.
[NH] plots found in the same aminolysis of O-ethyl 4-nitrophenyl dithiocarbonate (2) in the same solvent shows that the rate coefficient for leaving group expulsion from (k 2 ) is larger Ϯ T for 2 due to a stronger push by EtO than PhO. The k 3 value is the same for both reactions since both proton transfers are diffusion controlled. Comparison of the title reactions with the same aminolysis of phenyl 4-nitrophenyl thionocarbonate (3) in water indicates that (i) the k 2 value is larger for the aminolysis of 1 due to the less basic nucleofuge involved and the small solvent effect on k 2 , (ii) the k 3 value is smaller for the reactions of 1 due to the more viscous solvent, (iii) the rate coefficient for amine expulsion from is larger for the Ϯ T (k )
Ϫ1
aminolysis of 1 than that of 3 due to a solvent effect, and (iv) the value of the rate coefficient for amine attack (k 1 ) is smaller for the aminolysis of 1 in aqueous ethanol, which can be explained by a predominant solvent effect relative to the electron-withdrawing effect from the nucleofuge.