Tsivgoulis Gerasimos M, Afroudakis Pantelis A, Ioannou Panayiotis V
Department of Chemistry, University of Patras, Patras, Greece.
J Inorg Biochem. 2004 Apr;98(4):649-56. doi: 10.1016/j.jinorgbio.2004.01.016.
Ascorbic acid in the presence of a catalytic amount of iodine reduces arsenic acid in methanol giving the arsenious acid bound to the 2-methyl hemi-ketal of dehydroascorbic acid, 5, in 1:1 and in a more stable 2:1 5/As(III) molar ratio. Removal of the As(III) and treating the 2-methyl hemi-ketal of dehydroascorbic acid with refluxing acetonitrile affords the pure, crystalline dehydroascorbic acid dimer in good yields. Ascorbic acid also binds to As(III) of H(3)AsO(3) in a 1:1 and 2:1 ascorbic acid/As(III) molar ratio. The 1:1 complex is not stable and by expulsion of H(3)AsO(3) is transformed to the more stable 2:1 complex. The data do not permit distinguishing the 2:1 complexes between AsL(2)(H(2)O)H(+) or AsL(LH)(H(2)O) where L is the bis deprotonated and LH is the mono deprotonated 2-methyl hemi-ketal of dehydroascorbic acid or ascorbic acid. The 2:1 ascorbic acid/As(III) complex is oxidized by dioxygen, in a solvent-dependent manner, to dehydroascorbic acid implying dioxygen activation by the bound As(III). With thiophenol the same complex gives quantitatively triphenyl trithioarsenite, As(SPh)(3).
在催化量碘存在下，抗坏血酸可将甲醇中的砷酸还原，生成与脱氢抗坏血酸的2-甲基半缩酮（5）以1:1及更稳定的2:1 5/As(III)摩尔比结合的亚砷酸。除去As(III)并将脱氢抗坏血酸的2-甲基半缩酮用回流的乙腈处理，可高产率地得到纯的结晶脱氢抗坏血酸二聚体。抗坏血酸还能以1:1和2:1抗坏血酸/As(III)摩尔比与H₃AsO₃中的As(III)结合。1:1配合物不稳定，通过排出H₃AsO₃可转化为更稳定的2:1配合物。这些数据无法区分[AsL₂(H₂O)]⁻H⁺或AsL(LH)(H₂O)之间的2:1配合物，其中L是脱氢抗坏血酸或抗坏血酸的双去质子化形式，LH是单去质子化的2-甲基半缩酮。2:1抗坏血酸/As(III)配合物在溶剂依赖的方式下被双氧氧化为脱氢抗坏血酸，这意味着结合的As(III)可激活双氧。与苯硫酚反应时，相同的配合物定量生成三苯基三硫代亚砷酸盐As(SPh)₃。
