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

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]+ + ROH (1) [Pd(Pic)(NH2CH(R)CO2R(OH)]+ + k2→[Pd(Pic)(NH2CH(R)CO2)] + ROH (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. [ABSTRACT FROM AUTHOR]