Abstract

The reactions of a series of secondary alicyclic amines with 4-methylphenyl and 4-methoxyphenyl chloroformates are subjected to a kinetic investigation in water, at 25.0°C, ionic strength 0.2 M (KCI). Under amine excess, pseudo-first-order rate coefficients (kobs) are found for all reactions. Plots of kobs vs [NH] (NH is the free amine) are linear, with the slope (kN) pH independent, except the reactions of l-(2-hydroxyethyl)piperazine with both substrates at pH 6.2-7.3. The Brönsted-type plots for the kN values for the aminolysis of both chloroformates are linear, with slopes ca. 0.3, which is consistent with rate-determining formation of a zwitterionic tetrahedral intermediate (T±). With the PKa and log kN data for the present reactions, together with those for the same aminolysis of phenyl and 4-nitrophenyl chloroformates, two dual parametric equations are found for log kN as a function of pKa of the nucleophile, Hammett sigma of the "nonleaving" group, and pKa of the "nonleaving" group, with coefficients ?N = 0.3, ?nlg = 0.7, and ?nlg = -0.2, respectively. © 2001 John Wiley & Sons, Inc.