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

2010 ◽  
Vol 2010 ◽  
pp. 1-10 ◽  
Author(s):  
Kimon Zavitsanos ◽  
Athinoula L. Petrou
Keyword(s):  
Hydrogen Bonding ◽  
Aqueous Solutions ◽  
Activation Parameters ◽  
Intramolecular Hydrogen Bonding ◽  
Dihydroxybenzoic Acid ◽  
Proton Release ◽  
Second Stage ◽  
Ph Decrease ◽  
Intramolecular Hydrogen ◽  
Two Stages

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 constantk1(obs)=k1[DHBA]+Cand the corresponding activation parameters areΔH1(2,4)≠=49,5 kJ/mol−1,ΔS1(2,4)≠=−103,7J mol−1K−1,ΔH1(2,5)≠=60,3 kJ/mol−1, andΔS1(2,5)≠=−68,0 J mol−1K−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 areΔH2(2,4)≠=45,13 kJ/mol−1,ΔS2(2,4)≠=−185,9 J mol−1K−1,ΔH2(2,5)≠=54,55 kJ/mol−1, andΔS2(2,5)≠=−154,8 J mol−1K−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.

scholarly journals Reaction of Chromium(III) with 3,4-Dihydroxybenzoic Acid: Kinetics and Mechanism in Weak Acidic Aqueous Solutions

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Kimon Zavitsanos ◽  
Konstantinos Tampouris ◽  
Athinoula L. Petrou
Keyword(s):  
Aqueous Solutions ◽  
Coordination Sphere ◽  
Activation Parameters ◽  
Experimental Results ◽  
Ligand Concentration ◽  
Water Molecules ◽  
Dihydroxybenzoic Acid ◽  
Proton Release ◽  
Three Stages ◽  
Ph Decrease

The interactions between chromium(III) and 3,4-dihydroxybenzoic acid (3,4-DHBA) were studied resulting in the formation of oxygen-bonded complexes upon substitution of water molecules in the chromium(III) coordination sphere. The experimental results show that the reaction takes place in at least three stages, involving various intermediates. The first stage was found to be linearly dependent on ligand concentrationk1(obs)_=k0+k1(obs)[3,4-DHBA], and the corresponding activation parameters were calculated as follows:ΔH1(obs)≠=51.2±11.5 kJ mol−1,ΔS1(obs)≠=−97.3±28.9 J mol−1 K−1(composite activation parameters) . The second and third stages, which are kinetically indistinguishable, do not depend on the concentrations of ligand and chromium(III), accounting for isomerization and chelation processes, respectively. The corresponding activation parameters areΔH2(obs)≠=44.5±5.0 kJ mol−1,ΔS2(obs)≠=−175.8±70.3 J mol−1 K−1. The observed stages are proposed to proceed via interchange dissociative (Id, first stage) and associative (second and third stages) mechanisms. The reactions are accompanied by proton release, as is shown by the pH decrease.

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

2010 ◽  
Vol 2010 ◽  
pp. 1-8 ◽  
Author(s):  
Athinoula L. Petrou ◽  
Vladimiros Thoma ◽  
Konstantinos Tampouris
Keyword(s):  
Aqueous Solutions ◽  
Activation Parameters ◽  
Entropy Change ◽  
Hydroxyl Group ◽  
Positive Entropy ◽  
Dihydroxybenzoic Acid ◽  
Three Stages ◽  
Ph Decrease ◽  
Two Stages ◽  
Mechanism Of The Reaction

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(H2O)5(OH)]2+with the ligand in weak acidic aqueous solutions that follows anIdmechanism. The second and third stages do not depend on the concentrations of chromium(III), and their activation parameters areΔH≠=61.2±3.1 kJmol−1,ΔS≠=−91.1±11.0 JK−1mol−1,ΔH≠=124.5±8.7 kJmol−1, andΔS≠=95.1±29.0 JK−1mol−1. These two stages are proposed to proceed via associative mechanisms. The positive value ofΔS≠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.

Intramolecular Hydrogen Bonding Facilitates Electrocatalytic Reduction of Nitrite in Aqueous Solutions

2019 ◽  
Vol 58 (14) ◽  
pp. 9443-9451 ◽  
Author(s):  
Song Xu ◽  
Hyuk-Yong Kwon ◽  
Daniel C. Ashley ◽  
Chun-Hsing Chen ◽  
Elena Jakubikova ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Aqueous Solutions ◽  
Intramolecular Hydrogen Bonding ◽  
Electrocatalytic Reduction ◽  
Intramolecular Hydrogen

Synthesis and P.M.R. study of 2-(2',4'-Dihydroxy-6'-methylbenzoyl)-3,6-dihydroxybenzoic acid and its methyl ethers

1975 ◽  
Vol 28 (3) ◽  
pp. 657 ◽  
Author(s):  
BW Au-Yeung ◽  
T Chan ◽  
SW Tam
Keyword(s):  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Potassium Hydroxide ◽  
Chemical Shifts ◽  
Intramolecular Hydrogen Bonding ◽  
Dihydroxybenzoic Acid ◽  
Alcoholic Potassium Hydroxide ◽  
Intramolecular Hydrogen ◽  
Aryl Methyl ◽  
Methoxybenzoic Acid

The syntheses of 2-(2?,4?-dihydroxy-6?-methylbenzoyl)-3,6- dihydroxybenzoic acid (4) and its methyl ethers are described. Treatment of 6-hydroxy-2-(2?-hydroxy-4?-methoxy-6?-methylbenzoyl)-3- methoxybenzoic acid (8) with alcoholic potassium hydroxide gave 2- hydroxy-6-methoxy-8-methyl-9-oxoxanthene-1-carboxylic acid (9). Comparison of the p.m.r. spectra of these structurally related 2- benzoylbenzoic acids revealed that the chemical shifts of the aryl methyl and the ring protons are significantly influenced by the existence of intramolecular hydrogen bonding.

Theoretical study of intramolecular hydrogen bonding and molecular geometry of 2-trifluoromethylphenol

10.1002/jcc.2 ◽  
1996 ◽  
Vol 17 (16) ◽  
pp. 1804-1819 ◽  
Author(s):  
Attila Kov�cs ◽  
Istv�n Kolossv�ry ◽  
G�bor I. Csonka ◽  
Istv�n Hargittai
Keyword(s):  
Hydrogen Bonding ◽  
Theoretical Study ◽  
Molecular Geometry ◽  
Intramolecular Hydrogen Bonding ◽  
Intramolecular Hydrogen

Seven-Membered Intramolecular Hydrogen Bonding of Phenols: Database Analysis and Phloroglucinol Model Compounds

2012 ◽  
Vol 2012 (24) ◽  
pp. 4483-4492 ◽  
Author(s):  
Ronald K. Castellano ◽  
Yan Li ◽  
Edwin A. Homan ◽  
Andrew J. Lampkins ◽  
Iris V. Marín ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Model Compounds ◽  
Database Analysis ◽  
Intramolecular Hydrogen

scholarly journals NMR of Natural Products as Potential Drugs

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3763
Author(s):  
Poul Erik Hansen
Keyword(s):  
Natural Products ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Density Functional Theory Calculations ◽  
Intramolecular Hydrogen Bonding ◽  
Chemical Equilibria ◽  
Nmr Techniques ◽  
Intramolecular Hydrogen

This review outlines methods to investigate the structure of natural products with emphasis on intramolecular hydrogen bonding, tautomerism and ionic structures using NMR techniques. The focus is on 1H chemical shifts, isotope effects on chemical shifts and diffusion ordered spectroscopy. In addition, density functional theory calculations are performed to support NMR results. The review demonstrates how hydrogen bonding may lead to specific structures and how chemical equilibria, as well as tautomeric equilibria and ionic structures, can be detected. All these features are important for biological activity and a prerequisite for correct docking experiments and future use as drugs.

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