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Bioinorganic Chemistry and Applications
Volume 2010, Article ID 832768, 10 pages
http://dx.doi.org/10.1155/2010/832768
Research Article

Kinetics and Mechanisms of the Chromium(III) Reactions with 2,4- and 2,5-Dihydroxybenzoic Acids in Weak Acidic Aqueous Solutions

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

Received 10 April 2010; Accepted 26 May 2010

Academic Editor: Spyros Perlepes

Copyright © 2010 Kimon Zavitsanos and Athinoula L. Petrou. 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 reactions of 2,4- and 2,5-dihydroxybenzoic acids (dihydroxybenzoic acid, DHBA) with chromium(III) in weak acidic aqueous solutions have been shown to take place in at least two stages. The first stage of the reactions has an observed rate constant and the corresponding activation parameters are  kJ/mol−1, J mol−1 K−1,  kJ/mol−1, and  J mol−1 K−1. These are composite activation parameters and the breaking of the strong intramolecular hydrogen bonding in the two ligands is suggested to be the first step of the (composite) first stage of the reactions. The second stage is ligand concentration independent and is thus attributed to a chelation process. The corresponding activation parameters are  kJ/mol−1,  J mol−1 K−1,  kJ/mol−1, and  J mol−1 K−1. The activation parameters support an associative mechanism for the second stage of the reactions. The various substitution processes are accompanied by proton release, resulting in pH decrease.