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

Zavitsanos K, Petrou AL - Bioinorg Chem Appl (2010)

Bottom Line: The corresponding activation parameters are DeltaH(2(2,4)) ( not equal) = 45, 13 kJ/mol(-1), DeltaS(2(2,4)) ( not equal) = -185, 9 J mol(-1) K(-1), DeltaH(2(2,5)) ( not equal) = 54, 55 kJ/mol(-1), and DeltaS(2(2,5)) ( not equal) = -154, 8 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.

View Article: PubMed Central - PubMed

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

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 k(1(obs)) = k(1)[DHBA] + C and the corresponding activation parameters are DeltaH(1(2,4)) ( not equal) = 49, 5 kJ/mol(-1), DeltaS(1(2,4)) ( not equal) = -103, 7 J mol(-1) K(-1), DeltaH(1(2,5)) ( not equal) = 60, 3 kJ/mol(-1), and DeltaS(1(2,5)) ( not equal) = -68, 0 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 DeltaH(2(2,4)) ( not equal) = 45, 13 kJ/mol(-1), DeltaS(2(2,4)) ( not equal) = -185, 9 J mol(-1) K(-1), DeltaH(2(2,5)) ( not equal) = 54, 55 kJ/mol(-1), and DeltaS(2(2,5)) ( not equal) = -154, 8 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.

No MeSH data available.


A possible mechanism of the reactions of Chromium(III) with 2,4-and 2,5-dihydroxybenzoic acids in weak acidic aqueous solutions.
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Related In: Results  -  Collection


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sch1: A possible mechanism of the reactions of Chromium(III) with 2,4-and 2,5-dihydroxybenzoic acids in weak acidic aqueous solutions.

Mentions: Thus, for the first attack, a reaction between [Cr(OH)]2+ and the protonated molecule of the ligand can be proposed (Scheme 1), the reaction resulting in proton release (pH decrease). Upon the chelation reaction that follows, proton release takes also place resulting in further pH decrease. Hence for the reactions of 2,4-DHBA and 2,5-DHBA with chromium(III), the mechanism which can be proposed, according to the experimental results (rate laws), is


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

Zavitsanos K, Petrou AL - Bioinorg Chem Appl (2010)

A possible mechanism of the reactions of Chromium(III) with 2,4-and 2,5-dihydroxybenzoic acids in weak acidic aqueous solutions.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2913840&req=5

sch1: A possible mechanism of the reactions of Chromium(III) with 2,4-and 2,5-dihydroxybenzoic acids in weak acidic aqueous solutions.
Mentions: Thus, for the first attack, a reaction between [Cr(OH)]2+ and the protonated molecule of the ligand can be proposed (Scheme 1), the reaction resulting in proton release (pH decrease). Upon the chelation reaction that follows, proton release takes also place resulting in further pH decrease. Hence for the reactions of 2,4-DHBA and 2,5-DHBA with chromium(III), the mechanism which can be proposed, according to the experimental results (rate laws), is

Bottom Line: The corresponding activation parameters are DeltaH(2(2,4)) ( not equal) = 45, 13 kJ/mol(-1), DeltaS(2(2,4)) ( not equal) = -185, 9 J mol(-1) K(-1), DeltaH(2(2,5)) ( not equal) = 54, 55 kJ/mol(-1), and DeltaS(2(2,5)) ( not equal) = -154, 8 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.

View Article: PubMed Central - PubMed

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

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 k(1(obs)) = k(1)[DHBA] + C and the corresponding activation parameters are DeltaH(1(2,4)) ( not equal) = 49, 5 kJ/mol(-1), DeltaS(1(2,4)) ( not equal) = -103, 7 J mol(-1) K(-1), DeltaH(1(2,5)) ( not equal) = 60, 3 kJ/mol(-1), and DeltaS(1(2,5)) ( not equal) = -68, 0 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 DeltaH(2(2,4)) ( not equal) = 45, 13 kJ/mol(-1), DeltaS(2(2,4)) ( not equal) = -185, 9 J mol(-1) K(-1), DeltaH(2(2,5)) ( not equal) = 54, 55 kJ/mol(-1), and DeltaS(2(2,5)) ( not equal) = -154, 8 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.

No MeSH data available.