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Abstract:

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.

Registro:

Documento: Artículo
Título:Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes
Autor:Destaillats, H.; Turjanski, A.G.; Estrin, D.A.; Hoffmann, M.R.
Filiación:W. M. Keck Laboratories, California Institute of Technology, Pasadena, CA 91125, United States
Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina
Palabras clave: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
Año:2002
Volumen:15
Número:5
Página de inicio:287
Página de fin:292
DOI: http://dx.doi.org/10.1002/poc.480
Título revista:Journal of Physical Organic Chemistry
Título revista abreviado:J Phys Org Chem
ISSN:08943230
CODEN:JPOCE
Registro:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_08943230_v15_n5_p287_Destaillats

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Citas:

---------- APA ----------
Destaillats, H., Turjanski, A.G., Estrin, D.A. & Hoffmann, M.R. (2002) . Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes. Journal of Physical Organic Chemistry, 15(5), 287-292.
http://dx.doi.org/10.1002/poc.480
---------- CHICAGO ----------
Destaillats, H., Turjanski, A.G., Estrin, D.A., Hoffmann, M.R. "Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes" . Journal of Physical Organic Chemistry 15, no. 5 (2002) : 287-292.
http://dx.doi.org/10.1002/poc.480
---------- MLA ----------
Destaillats, H., Turjanski, A.G., Estrin, D.A., Hoffmann, M.R. "Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes" . Journal of Physical Organic Chemistry, vol. 15, no. 5, 2002, pp. 287-292.
http://dx.doi.org/10.1002/poc.480
---------- VANCOUVER ----------
Destaillats, H., Turjanski, A.G., Estrin, D.A., Hoffmann, M.R. Molecular structure effects on the kinetics of hydroxyl radical addition to azo dyes. J Phys Org Chem. 2002;15(5):287-292.
http://dx.doi.org/10.1002/poc.480