Oxidation and reaction of trolox c, a tocopherol analog, in aqueous solution. A pulse-radiolysis study
作者:Michael J. Thomas、Benon H. J. Bielski
DOI:10.1021/ja00191a031
日期:1989.4
by 10sup 4}. The rate constant versus pH plot is consistent with a scheme that involves three reactions of the protonated and the unprotonated forms of 2. Intermediate 3 undergoes slow pH-dependent decomposition to 2-hydroxy-2-methyl-4-(2,5,6-trimethyl-2,4-dioxo-2,5-cyclohexadienyl)butanoic acid, 4. The same first-order rate constant was found for the decay of 3 and the appearance of 4. Simultaneous
Trolox c, 3,4-dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carb acid, 1,一种水溶性的 α}-tocopherol 类似物,被氧化Brsub 2}sup minus}} 得到苯氧基自由基 2。这些自由基通过二阶、pH 依赖性过程歧化得到 1 和不稳定的中间体 3,鉴定为 4,5-二氢-3, 6,8,9-四甲基-2H-3,9a-epoxy-1-benzoxepin-2,7(3H)-dione,在 235 nm 处有很强的紫外吸收。歧化速率常数随着 pH 值的增加而降低,最大的变化发生在 pH 值 2 和 9 之间,在那里它降低了 10sup 4}。速率常数与 pH 值关系图与涉及质子化和非质子化形式 2 的三个反应的方案一致。中间体 3 经历缓慢的 pH 依赖性分解为 2-羟基-2-甲基-4-(2