Abstract
The composition of the N-diketohydrindylidene histidinato chromium(III) complex formed by interaction of ninhydrin with the [Cr(histidine)(H2O)(3)](2+) complex has been determined using Job's method of continuous variations. The reaction is slow and the kinetic studies were carried out under varying conditions of pH, temperature and [ninhydrin]. The observed pseudo-first order rate constant under these conditions follow the rate equation: 1/k(obs) = 1/{K(t)k(3)[N]} + 1/k(3). The reaction has the features of a template mechanism which proceeds through coordination of ninhydrin to the [Cr(histidine)](2+) complex. The reaction is expected to involve the combination of two ligands (ninhydrin and histidine) attached to the same Cr-III (CLAM reaction). The Cr-III ion provides a better opportunity for the reaction of ninhydrin and histidine by assembling their reactive groups together. On the basis of the observed data the probable mechanism has been proposed.