Electron transfer. 83. Reductions of unsaturated esters with vitamin B12s [cob(I)alamin]
Electron transfer. 83. Reductions of unsaturated esters with vitamin B12s [cob(I)alamin]
复制标题
电子转移。
DOI：
10.1021/ic00246a031
复制
发表时间：
1986
影响因子：
4.6
通讯作者：
E. Gould
中科院分区：
文献类型：
--
作者：
G. Pillai;E. Gould
在水介质中，维生素B12s （cob (I) alamin）可将马来酸和富马酸的二酯迅速还原为琥珀酸酯。乙炔二羧酸二甲酯分两个阶段还原：第一阶段（非常迅速）生成富马酸酯，然后较慢地转化为琥珀酸酯。反应在氧化还原伙伴中都是一级反应，在最高酸度下反应最快。动力学行为与B12s分为不活跃的非质子化形式，中等活性的单质子化形式和非常活跃的双质子化形式一致。提出后者是Co-H物质，具有类似氢化物的特征，以特定速率bbb104m ' s ' 1（25℃）氧化。乙炔酯和烯烃酯的相对反应活性（速率比为4-105）表明，这些反应与母体二酸的反应一样，在性质上是异裂解（2e）而不是均裂解（le）。乙炔二羧酸盐还原为富马酸盐是一种净反式加成反应，其烯烃-碳离子中间体可以保持其几何构型。
The diesters of maleic and fumaric acid are rapidly reduced to succinic esters by vitamin B12s (cob (I) alamin) in aqueous media. The dimethyl ester of acetylenedicarboxylic acid is reduced in two stages: the first (very rapid) stage yields a fumaric ester, which is then converted more slowly to succinate. Reactions are first order each in redox partners and are fastest at highest acidities. Kinetic behavior is consistent with the partition of B12s into an inactive nonprotonated, a moderately reactive monoprotonated, and a very reactive diprotonated form. It is proposed that the latter is a Co-H species, having hydride-like character, which is oxidized at a specific rate> 104 M" 1 s" 1 (25 C). The relative reactivities of acetylenic and olefinic esters (rate ratios 4—105) indicate that these reactions, like those of the parent diacids, are heterolytic (2e) rather than homolytic (le) in nature. The reduction of acetylenedicarboxylate to fumarate is a net trans addition for which an olefinic-carbanion intermediate, which may maintain its geometric configuration, is suggested.