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Molecules 2014, 19(11), 19152-19171; doi:10.3390/molecules191119152

Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative

1
Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, Dorodna 16, Warszawa 03-195, Poland
2
Departamento de Quimica Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 223, Santiago 1, Chile
3
Departamento de Química Orgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Correo 22, Santiago, Chile
*
Author to whom correspondence should be addressed.
Received: 9 October 2014 / Revised: 12 November 2014 / Accepted: 13 November 2014 / Published: 19 November 2014
(This article belongs to the Special Issue Free Radicals and Radical Ions)
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Abstract

The kinetics and spectral characteristics of the transients formed in the reactions of OH and N3 with quinoxalin-2(1H)-one (Q), its methyl derivative, 3-methylquinoxalin-2(1H)-one (3-MeQ) and pyrazin-2-one (Pyr) were studied by pulse radiolysis in aqueous solutions at pH 7. The transient absorption spectra recorded in the reactions of OH with Q and 3-MeQ consisted of an absorption band with λmax = 470 nm assigned to the OH-adducts on the benzene ring, and a second band with λmax = 390 nm (for Q) and 370 nm (for 3-MeQ) assigned, inter alia, to the N-centered radicals on a pyrazin-2-one ring. The rate constants of the reactions of OH with Q and 3-MeQ were found to be in the interval (5.9–9.7) × 109 M–1·s–1 and were assigned to their addition to benzene and pyrazin-2-one rings and H-abstraction from the pyrazin-2-one nitrogen. In turn, the transient absorption spectrum observed in the reaction of N3 exhibits an absorption band with λmax = 350 nm. This absorption was assigned to the N-centered radical on the Pyr ring formed after deprotonation of the respective radical cation resulting from one-electron oxidation of 3-MeQ. The rate constant of the reaction of N3 with 3 MeQ was found to be (6.0 ± 0.5) × 109 M–1·s–1. Oxidation of 3-MeQ by N3 and Pyr by OH and N3 confirms earlier spectral assignments. With the rate constant of the OH radical with Pyr (k = 9.2 ± 0.2) × 109 M–1·s‒1, a primary distribution of the OH attack was estimated nearly equal between benzene and pyrazin-2-one rings. View Full-Text
Keywords: quinoxalin-2-ones; radicals; pulse radiolysis; hydroxyl radicals; azide radicals quinoxalin-2-ones; radicals; pulse radiolysis; hydroxyl radicals; azide radicals
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Skotnicki, K.; De la Fuente, J.R.; Cañete, A.; Bobrowski, K. Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative. Molecules 2014, 19, 19152-19171.

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