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

Petrou AL, Thoma V, Tampouris K - Bioinorg Chem Appl (2010)

Bottom Line: The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are DeltaH( not equal) (2(obs)) = 61.2 +/- 3.1 kJmol(-1), DeltaS( not equal) (2(obs)) = -91.1 +/- 11.0 JK(-1)mol(-1), DeltaH( not equal) (3(obs)) = 124.5 +/- 8.7 kJmol(-1), and DeltaS( not equal) (3(obs)) = 95.1 +/- 29.0 JK(-1)mol(-1).These two stages are proposed to proceed via associative mechanisms.The reactions are accompanied by proton release, as shown by the pH decrease.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Inorganic Chemistry, University of Athens, Panepistimioupolis, 15771 Athens, Greece.

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(2)O)(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 DeltaH( not equal) (2(obs)) = 61.2 +/- 3.1 kJmol(-1), DeltaS( not equal) (2(obs)) = -91.1 +/- 11.0 JK(-1)mol(-1), DeltaH( not equal) (3(obs)) = 124.5 +/- 8.7 kJmol(-1), and DeltaS( not equal) (3(obs)) = 95.1 +/- 29.0 JK(-1)mol(-1). These two stages are proposed to proceed via associative mechanisms. The positive value of DeltaS( not equal) (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.

No MeSH data available.


2,3-Dihydroxybenzoic acid (2,3-DHBA).
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Related In: Results  -  Collection


getmorefigures.php?uid=PMC2902047&req=5

fig1: 2,3-Dihydroxybenzoic acid (2,3-DHBA).

Mentions: The aim of this work is to study and determine the kinetics and suggest a mechanism of the substitution reactions between chromium(III) and 2,3-DHBA. Knowledge of the mechanism will further contribute in the understanding of the role of organic ligands in the uptake of metals by plants because metal ions are transferred by organic ligands from the roots to certain parts of the plants. Such ligands are humic substances and products of their decomposition, that is, organic acids. One of such organic ligands is 2,3-DHBA (Figure 1).


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

Petrou AL, Thoma V, Tampouris K - Bioinorg Chem Appl (2010)

2,3-Dihydroxybenzoic acid (2,3-DHBA).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2902047&req=5

fig1: 2,3-Dihydroxybenzoic acid (2,3-DHBA).
Mentions: The aim of this work is to study and determine the kinetics and suggest a mechanism of the substitution reactions between chromium(III) and 2,3-DHBA. Knowledge of the mechanism will further contribute in the understanding of the role of organic ligands in the uptake of metals by plants because metal ions are transferred by organic ligands from the roots to certain parts of the plants. Such ligands are humic substances and products of their decomposition, that is, organic acids. One of such organic ligands is 2,3-DHBA (Figure 1).

Bottom Line: The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters are DeltaH( not equal) (2(obs)) = 61.2 +/- 3.1 kJmol(-1), DeltaS( not equal) (2(obs)) = -91.1 +/- 11.0 JK(-1)mol(-1), DeltaH( not equal) (3(obs)) = 124.5 +/- 8.7 kJmol(-1), and DeltaS( not equal) (3(obs)) = 95.1 +/- 29.0 JK(-1)mol(-1).These two stages are proposed to proceed via associative mechanisms.The reactions are accompanied by proton release, as shown by the pH decrease.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Inorganic Chemistry, University of Athens, Panepistimioupolis, 15771 Athens, Greece.

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(2)O)(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 DeltaH( not equal) (2(obs)) = 61.2 +/- 3.1 kJmol(-1), DeltaS( not equal) (2(obs)) = -91.1 +/- 11.0 JK(-1)mol(-1), DeltaH( not equal) (3(obs)) = 124.5 +/- 8.7 kJmol(-1), and DeltaS( not equal) (3(obs)) = 95.1 +/- 29.0 JK(-1)mol(-1). These two stages are proposed to proceed via associative mechanisms. The positive value of DeltaS( not equal) (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.

No MeSH data available.