Comparative nucleophilic reactivities in carboxylate, phosphinate, and thiophosphate esters cleavage

Abstract

Nucleophilic substitution reaction of p‐nitrophenyl acetate (PNPA), p‐nitrophenyldiphenyl phosphinate, and pesticide parathion with different α‐nucleophiles [I] have been studied at 27 °C in different pH in the presence of a novel cationic surfactant. The kinetic study was performed spectrophotometrically under pseudo‐first order conditions with the α‐nucleophile in excess. The pKa of nucleophiles have also been determined by kinetic method. In the presence of surfactant, the rate constant increased with increasing surfactant concentration up to a limiting value. This behavior has been analyzed in quantitative terms on the basis of pseudo‐phase model of micellar catalysis. Finally the nucleophilic reactivity of hydroxamate ions has been compared with other α‐nucleophiles, like oxime, hydroxybenzotriazole, and 2‐iodosobenzoic acid (IBA). The order of cleavage of electrophilic centers, that is, CO, PO, and PS have also been discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Reaction mechanisms : Part (iii) Polar reactions

“…58 The kinetics of cleavage of carboxylate 96, phosphinate 97 and thiophosphate 98 with different a-effect nucleophiles, N-phenylbenzohydroxamate 99, butane-2,3dione monoximate 100, 1-hydrobenzotriazolate 101 and 2-iodosobenzoate 102, have been investigated in the presence of cationic surfactant cetyltriphenylphosphonium bromide 103 (Scheme 26). 59 The reactivity order towards the a-nucleophiles was found to be 96 (CQO) 4 97 (PQO) 4 98 (PQS) which was attributed to a reduction in the electrophilicity of the central atom in the PQO and PQS esters.…”

Effects of Surfactants on the Rate of Chemical Reactions

“…In the latter case, the interaction of anionic surfactants with neutral substrates increases the electronic repulsion between the resulted complex and hydroxide ions. On the other hand, the reaction rates of a number of nucleophiles (other than hydroxide ion) with neutral [71][72][73] and anionic [74][75][76][77][78][79] substrates are increased in the presence of cationic surfactants. It was observed that the increase in the chain length of cationic surfactants [75] and adding TX-100 [79] to the reaction media decreases the reaction rate.…”

Kinetic study on effect of novel cationic dimeric surfactants for the cleavage of carboxylate ester

“…Simanenko and co‐workers have studied a detailed kinetic study of nucleophilic cleavage of some phosphate and sulphonate esters in the presence of imidazolium surfactants bearing moieties of alpha‐nucleophiles, namely oximate hydroxamate, amidoximate group. Our research groups have also previously carried out extensive studies of reactivity in micellar media and other colloidal aggregates.…”