Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative
AbstractThe 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
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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.
Skotnicki K, De la Fuente JR, Cañete A, Bobrowski K. Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative. Molecules. 2014; 19(11):19152-19171.Chicago/Turabian Style
Skotnicki, Konrad; De la Fuente, Julio R.; Cañete, Alvaro; Bobrowski, Krzysztof. 2014. "Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative." Molecules 19, no. 11: 19152-19171.