Quinic acid and hypervalent chromium: a spectroscopic and kinetic study

Abstract

The redox reaction between an excess of quinic acid (QA) and Cr^VI involves the formation of intermediates, namely, Cr^IV and Cr^V species, which in turn react with the organic substrates. As observed with other substrates that have already been studied, Cr^IV does not accumulate during this reaction because of the rate of the reaction. Its rate of disappearance is several times higher than that of the reaction of Cr^VI or Cr^V with QA. Kinetic studies indicate that the redox reaction proceeds via a combined mechanism that involves the pathways Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III, which is supported by the observation of superoxo-Cr^III (CrO₂²⁺) ions, free radicals, and oxo-Cr^V species as intermediates and the detection of Cr^VI ester species. The present study reports the complete rate laws for the QA/chromium redox reaction.