The palladium(II)-picolylamine promoted hydrolysis of amino acid esters; kinetic evidence for inter-and intramolecular mechanisms

Abstract

The hydrolysis of amino acid esters is catalysed by the palladium(II) complex [Pd(Pic)]2+ (Pic = 2-picolylamine). The reaction has been studied by the pH-stat technique. The overall PdII chelate-promoted hydrolysis of the ethyl esters of glycine and alanine may be accounted by inter-and intramolecular mechanisms depicted in Eqns (1) and (2) respectively. [Pd(Pic)(NH2CH(R)CO2R')]2+ + OH -k1/→[Pd(Pic)(NH2CH(R)CO2] + + R'OH (1) [Pd(Pic)(NH2CH(R)CO2R')(OH)] + k2/→[Pd(Pic)(NH2CH(R)CO 2)]+ +R'OH (2) The kinetic data for histidine and methionine methyl esters are fitted assuming that hydrolysis proceeds solely by the intermolecular mechanism [Eqn (1)]. The rate enhancement compared with the free ester is discussed in terms of the structure of the complex. Activation parameters associated with the hydrolysis have been determined and discussed. © 2011 Science Reviews 2000 Ltd.