E. Castro, M. Andújar, P. Campodónico
2002
Citations
0
Influential Citations
12
Citations
Journal
International Journal of Chemical Kinetics
Abstract
The reactions of 4-methylphenyl 4-nitrophenyl carbonate (MPNPC) and 4-methylphenyl 2,4-dinitrophenyl carbonate (MPDNPC) with a series of secondary alicyclic amines are subjected to a kinetic investigation in 44 wt% ethanol–water, at 25.0°C, ionic strength 0.2 M (KCl). Under amine excess over the substrate, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against [amine] are linear, with kN as slopes. A biphasic Bronsted-type plot for kN is obtained for the aminolysis of MPNPC, with slopes β1 = 0.2 (high pKa) and β2 = 0.9 (low pKa). This is in accordance with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T±), and a change in the rate-determining step, from formation to breakdown of T± as the amine pKa decreases. For the aminolysis of MPDNPC, a slightly curved Bronsted-type plot for kN is obtained, with β1 = 0.1 (low pKa) and β2 = 0.55 (high pKa). This is consistent with a concerted mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 309–315, 2002