Antioxidant properties of derivatives of 3,4-dihydropyrimidin-2-one with sterically hindered phenolic substituent in heterocycle

Abstract

In the processes of free-radical oxidation of organic compounds, the inhibitory action of the inhibitor is mainly due to either the breakdown of the reaction chains on its molecules, or the slowdown of the decomposition of intermediate hydroperoxides, or both at the same time. We analysed the inhibitory properties of 4-[3,5-di(tert-butyl)-4-hydroxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one (I) and 4-[4-methoxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one (II) gasometry and hydroperoxide decomposition methods. These compounds were obtained by the three-component Biginelli reaction. The decomposition of cumene hydroperoxide in dimethylformamide under these conditions is described by a first-order kinetics equation. The first compound significantly inhibits the decomposition of hydroperoxide. The dependence of the effective rate constant of the decomposition of cumene hydroperoxide on the first concentration is described by the equation: . The second compound also slows the decomposition of hydroperoxide, but much less than the first compound. Therefore, both the phenolic moiety and the urea moiety of the dihydropyrimidinone cycle take part in slowing the cumene hydroperoxide decomposition. Initiated oxidation of cumene happened at 343 K with the presence of the initiator azodiisobutyronitrile. The concentration of the first compound varied from 1,5·10-4 to 2,5·10-3 mol/l. With a concentration of the first compound 1,25·10-3 and 2,5·10-3 mol/l, the duration of the induction period exceeds 80 min. In the concentration range (1,5÷6,3)·10-4 mol/l the linear change in the duration of the induction period is observed. 4-[3,5-Di(tert-butyl)-4-hydroxyphenyl]-5-aminocarbonyl-6-methyl-3,4-dihydropyrimidin-2-one is a more effective inhibitor than the ionol due to the urea moiety of the dihydropyrimidinone cycle. Confirmation is the notable antioxidant activity of the second compound. In conclusion, 4- [3,5-di (tert-butyl)-4-hydroxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one is a bifunctional inhibitor.