Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes

The effect of the molecular structure of azobenzene and related azo dyes on their reactivity towards ·OH radicals in water was investigated by performing ultrasonic irradiation experiments on their aqueous solutions and density functional theory (DFT) calculations. Sonolysis of azobenzene, methyl or...

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Autores principales: Destaillats, H., Turjanski, A.G., Estrin, D.A., Hoffmann, M.R.
Formato: JOUR
Materias:
Azo dyes
Hydroxyl radical addition
Kinetics
Molecular structure
Addition reactions
Carboxylic acids
Free radicals
Hydrogen bonds
Isomers
Photodegradation
Probability density function
Rate constants
Solutions
Thermodynamics
Ultrasonic effects
Non-buffered solutions
Solvation
Sonolysis
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_08943230_v15_n5_p287_Destaillats
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id todo:paper_08943230_v15_n5_p287_Destaillats
record_format dspace
spelling todo:paper_08943230_v15_n5_p287_Destaillats2023-10-03T15:41:58Z Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes Destaillats, H. Turjanski, A.G. Estrin, D.A. Hoffmann, M.R. Azo dyes Hydroxyl radical addition Kinetics Molecular structure Addition reactions Carboxylic acids Free radicals Hydrogen bonds Isomers Molecular structure Photodegradation Probability density function Rate constants Solutions Thermodynamics Ultrasonic effects Non-buffered solutions Solvation Sonolysis Azo dyes The effect of the molecular structure of azobenzene and related azo dyes on their reactivity towards ·OH radicals in water was investigated by performing ultrasonic irradiation experiments on their aqueous solutions and density functional theory (DFT) calculations. Sonolysis of azobenzene, methyl orange, o-methyl red and p-methyl red was performed at a frequency of 500 kHz and 50 W applied power under air saturation. Under such irradiation conditions, these molecules were shown to decompose through ·OH radical addition reactions taking place in the bulk liquid. The ortho isomer of methyl red reacted at significantly higher rates (nearly 30% higher) than the other three studied compounds in non-buffered aqueous solutions. In contrast, measurements performed at lower pH (10 mM HNO3), at which the carboxylic group vicinal to the azo group is protonated, yielded a similar reaction rate for all four substrates, i.e. the specific acceleration observed in the ortho-substituted dye disappeared with protonation. These results were rationalized by the computation of formation energies of the adduct originated in the ·OH addition to the azo group, performing DFT calculations combined with the polarized continuum model (PCM) of solvation. The calculations suggest that intramolecular H-bonding in the o-methyl red-OH adduct provides extra stabilization in that particular case, which correlates with the observed higher addition rates of ·OH radical to the anionic form of that isomer in non-buffered solutions. On the other hand, the energy changes calculated for the ·OH addition to an o-methyl red molecule which is protonated in the carboxylic group (representative of the situation at pH 2) do not differ significantly from those computed for the other three molecules studied. Copyright © 2002 John Wiley & Sons, Ltd. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_08943230_v15_n5_p287_Destaillats
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Azo dyes
Hydroxyl radical addition
Kinetics
Molecular structure
Addition reactions
Carboxylic acids
Free radicals
Hydrogen bonds
Isomers
Molecular structure
Photodegradation
Probability density function
Rate constants
Solutions
Thermodynamics
Ultrasonic effects
Non-buffered solutions
Solvation
Sonolysis
Azo dyes
spellingShingle Azo dyes
Hydroxyl radical addition
Kinetics
Molecular structure
Addition reactions
Carboxylic acids
Free radicals
Hydrogen bonds
Isomers
Molecular structure
Photodegradation
Probability density function
Rate constants
Solutions
Thermodynamics
Ultrasonic effects
Non-buffered solutions
Solvation
Sonolysis
Azo dyes
Destaillats, H.
Turjanski, A.G.
Estrin, D.A.
Hoffmann, M.R.
Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
topic_facet Azo dyes
Hydroxyl radical addition
Kinetics
Molecular structure
Addition reactions
Carboxylic acids
Free radicals
Hydrogen bonds
Isomers
Molecular structure
Photodegradation
Probability density function
Rate constants
Solutions
Thermodynamics
Ultrasonic effects
Non-buffered solutions
Solvation
Sonolysis
Azo dyes
description The effect of the molecular structure of azobenzene and related azo dyes on their reactivity towards ·OH radicals in water was investigated by performing ultrasonic irradiation experiments on their aqueous solutions and density functional theory (DFT) calculations. Sonolysis of azobenzene, methyl orange, o-methyl red and p-methyl red was performed at a frequency of 500 kHz and 50 W applied power under air saturation. Under such irradiation conditions, these molecules were shown to decompose through ·OH radical addition reactions taking place in the bulk liquid. The ortho isomer of methyl red reacted at significantly higher rates (nearly 30% higher) than the other three studied compounds in non-buffered aqueous solutions. In contrast, measurements performed at lower pH (10 mM HNO3), at which the carboxylic group vicinal to the azo group is protonated, yielded a similar reaction rate for all four substrates, i.e. the specific acceleration observed in the ortho-substituted dye disappeared with protonation. These results were rationalized by the computation of formation energies of the adduct originated in the ·OH addition to the azo group, performing DFT calculations combined with the polarized continuum model (PCM) of solvation. The calculations suggest that intramolecular H-bonding in the o-methyl red-OH adduct provides extra stabilization in that particular case, which correlates with the observed higher addition rates of ·OH radical to the anionic form of that isomer in non-buffered solutions. On the other hand, the energy changes calculated for the ·OH addition to an o-methyl red molecule which is protonated in the carboxylic group (representative of the situation at pH 2) do not differ significantly from those computed for the other three molecules studied. Copyright © 2002 John Wiley & Sons, Ltd.
format JOUR
author Destaillats, H.
Turjanski, A.G.
Estrin, D.A.
Hoffmann, M.R.
author_facet Destaillats, H.
Turjanski, A.G.
Estrin, D.A.
Hoffmann, M.R.
author_sort Destaillats, H.
title Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
title_short Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
title_full Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
title_fullStr Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
title_full_unstemmed Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
title_sort molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
url http://hdl.handle.net/20.500.12110/paper_08943230_v15_n5_p287_Destaillats
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AT estrinda molecularstructureeffectsonthekineticsofhydroxylradicaladditiontoazodyes
AT hoffmannmr molecularstructureeffectsonthekineticsofhydroxylradicaladditiontoazodyes
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