Stepwise mechanisms of the aminolyses of 4‐Nitrophenyl and 2,4‐Dinitrophenyl O‐Ethyl Dithiocarbonates in aqueous Ethanol

Abstract

The reactions of the title substrates with a series of secondary alicyclic amines are subjected to a kinetic study in 44 wt% aqueous ethanol, a t 25.0°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 p1 = 0.3 (high pK,), p2 = 0.95 (low pX,) for the aminolysis of the 4-nitro derivative, and p1 = 0.3 and pz = 0.80 for the aminolysis of the dinitro compound; the pK, values at the curvature center are pK: = 9.8 and 9.5, respectively. From a comparison of these pK; values with those found in the same reactions in water and the shapes of the Bronsted-type plots, it is concluded that these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate in the reaction pathway. 0 1995 John Wiley & Sons, Ine.

Kinetics and mechanism of the aminolysis of O‐phenyl 4‐nitrophenyl dithiocarbonate in aqueous ethanol

“…The values of the Brönsted slopes obtained in this work when the k 1 and the k 2 steps are rate determining are in agreement with the corresponding values found in the aminolysis of similar compounds, both in aqueous ethanol and water [3 -6,8,13 -15]. This is another proof that the rate microcoefficients in Table II cating a stepwise mechanism and a change in the rate determining step, from k 2 to k 1 as the amine basicity increases [4]. Since the reactions of the present work show nonlinear plots of k obs vs.…”

“…The value ␤ ϭ 0.25 of this slope is consistent with a stepwise mechanism where the formation of the tetrahedral intermediate is rate-limiting [4,5].…”

“…In the present work we compare our kinetic results with those obtained in the same aminolysis of O-ethyl 4-nitrophenyl dithiocarbonate (2) in the same solvent [4] ("acyl" group effect), and phenyl 4-nitrophenyl thionocarbonate (3) in water [5] (leaving group and solvent effects).…”

“…Also, the ␤ ϭ 0.53 reactions of anilines with O-ethyl substituted phenyl dithiocarbonates in acetonitrile have been found to be concerted [2]. In contrast, the reactions of secondary alicyclic amines with O-ethyl phenyl, O-ethyl 4-ni- [3], and through biphasic Brönsted plots, in the other cases [4].…”

Structure-reactivity correlation in the reactions of pyrrolidine with O-ethyl S-aryl dithiocarbonates in aqueous ethanol

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ethyl S- (2,4,6-trinitrophenyl) [2,3]. In the reaction of O-ethyl Sphenyl dithiocarbonate the zwitterionic tetrahedral intermediate formed by the amine attack can be deprotonated to yield an anionic intermediate in a kinetically significant step [2].

EtO 9 CS 9 S(PhX) ϩ HNR 1 R 2 9: EtO 9 C(S) 9 NR 1 R 2 ϩ XPhSH (1) We have also studied the above reactions in water [4] and those of the same amines with the other three O-

INTRODUCTION

We have studied the mechanism of the reactions of a series of secondary alicyclic amines (HNR 1 R 2 ϭ piperidine, piperazine, 1-(2-hydroxyethyl)piperazine, morpholine, 1-formylpiperazine, and piperazinium ion) with O-ethyl S-(X-phenyl) dithiocarbonates (X ϭ H, p-nitro, 2,4-dinitro, and 2,4,6-trinitro), see eq.

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