L. R. Yakupova, R. A. Sakhautdinova, E. Pankratyev
Nov 25, 2012
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11
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Journal
Kinetics and Catalysis
Abstract
The antiradical activity of 5-amino-6-methyluracil in the initiated radical-chain oxidation of 1,4-dioxane as a model system was studied quantitatively. The rate constant k7 of its reaction with the peroxyl radical of 1,4-dioxane was measured to be (5.6 ± 1.8) × 105 L mol−1 s−1 at 333 K. The effect of the methyl substituents in the 1- and 3-positions of the uracil ring and in the amino group on the rate constant of inhibition was studied. The strengths of all N-H bonds in the 5-amino-6-methyluracil and its derivatives were calculated in the G3MP2B3 approximation and were compared with the measured rate constants of inhibition. By the example of the reaction of 5-amino-6-uracil with i-PrO2⊙, different attack pathways of the peroxyl radical at the N-H bonds of uracil were analyzed in the UB3LYP/6-311+G(d,p) approximation. The lowest activation barrier (5.8 kJ/mol) was observed for peroxyl radical attack on the (C5)N-H bonds. The site responsible for the inhibition activity of the compound is the amino group.