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

Molecules

Konrad Skotnicki¹  Julio R. De la Fuente³  Alvaro Ca༞te²  Krzysztof Bobrowski¹ 

[1] Centre of Radiation Research and Technology, Institute of Nuclear Chemistry and Technology, Dorodna 16, Warszawa 03-195, Poland; E-Mail:;Departamento de Química Orgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Correo 22, Santiago, Chile; E-Mail:;Departamento de Quimica Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 223, Santiago 1, Chile; E-Mail:

关键词: quinoxalin-2-ones;    radicals;    pulse radiolysis;    hydroxyl radicals;    azide radicals;   

DOI  :  10.3390/molecules191119152

来源: mdpi

【 摘 要 】

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 λ_max = 470 nm assigned to the OH-adducts on the benzene ring, and a second band with λ_max = 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 λ_max = 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.

【 授权许可】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland.