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Bioinorganic Chemistry and Applications
Volume 2010 (2010), Article ID 348692, 8 pages
http://dx.doi.org/10.1155/2010/348692
Research Article

Kinetics and Mechanism of the Reaction between Chromium(III) and 2,3-Dihydroxybenzoic Acid in Weak Acidic Aqueous Solutions

Laboratory of Inorganic Chemistry, University of Athens, Panepistimioupolis, 15771 Athens, Greece

Received 17 November 2009; Accepted 10 March 2010

Academic Editor: Spyros P. Perlepes

Copyright © 2010 Athinoula L. Petrou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The reaction between chromium(III) and 2,3-dihydroxybenzoic acid (2,3-DHBA) takes place in at least three stages, involving various intermediates. The ligand (2,3-DHBA)-to-chromium(III) ratio in the final product of the reaction is 1 : 1. The first stage is suggested to be the reaction of with the ligand in weak acidic aqueous solutions that follows an mechanism. The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are  kJ, ,  kJ, and . These two stages are proposed to proceed via associative mechanisms. The positive value of can be explained by the opening of a four-membered ring (positive entropy change) and the breaking of a hydrogen bond (positive entropy change) at the associative step of the replacement of the carboxyl group by the hydroxyl group at the chromium(III) center (negative entropy change in associative mechanisms). The reactions are accompanied by proton release, as shown by the pH decrease.