STEPWISE MECHANISMS OF THE AMINOLYSES OF 4-NITROPHENYL AND 2,4-DINITROPHENYL O-ETHYL DITHIOCARBONATES IN AQUEOUS-ETHANOL

The reactions of the title substrates with a series of secondary alicyclic amines are subjected to a kinetic study in 44 wt% aqueous ethanol, at 25.0 degrees C, ionic strength 0.2 M (maintained with KCl). Pseudo-first-order kinetics are found under amine excess. The order in amine obtained is one in the reactions of all amines. The Bronsted-type plots for the overall second-order rate coefficients are biphasic with slopes beta(1) = 0.3 (high pK(a)), beta(2) = 0.95 (low pK(a)) for the aminolysis of the 4-nitro derivative, and beta(1) = 0.3 and beta(2) = 0.80 for the aminolysis of the dinitro compound; the pK(a) values at the curvature center are pK(a)(0) = 9.8 and 9.5, respectively. From a comparison of these pK(a)(0) values with those found in the same reactions in water and the shapes of the Bro;nsted-type plots, it is concluded that these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate in the reaction pathway. (C) 1995 John Wiley & Sons, Inc.