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

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          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 [Cr(H 2O) 5(OH)] 2+ with the ligand in weak acidic aqueous solutions that follows an I d mechanism. The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are Δ H 2(obs) = 61.2 ± 3.1 kJmol −1, Δ S 2(obs) = −91.1 ± 11.0 JK −1mol −1, Δ H 3(obs) = 124.5 ± 8.7 kJmol −1, and Δ S 3(obs) = 95.1 ± 29.0 JK −1mol −1. These two stages are proposed to proceed via associative mechanisms. The positive value of Δ S 3(obs) 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.

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          Most cited references46

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          Kinetics and Mechanism of Reactions of Transition Metal Complexes

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            Chemical Kinetics and Reactions Mechanisms

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              General Principles of Biochemistry of the Elements

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                Author and article information

                Journal
                Bioinorg Chem Appl
                BCA
                Bioinorganic Chemistry and Applications
                Hindawi Publishing Corporation
                1565-3633
                1687-479X
                2010
                31 May 2010
                : 2010
                : 348692
                Affiliations
                Laboratory of Inorganic Chemistry, University of Athens, Panepistimioupolis, 15771 Athens, Greece
                Author notes
                *Athinoula L. Petrou: athpetrou@ 123456chem.uoa.gr

                Academic Editor: Spyros P. Perlepes

                Article
                10.1155/2010/348692
                2902047
                20634986
                62ba9ef8-a510-475a-840e-a3a974099bb0
                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.

                History
                : 17 November 2009
                : 10 March 2010
                Categories
                Research Article

                Biochemistry
                Biochemistry

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