The oxidation of several series of secondary alcohols 2-9, ethers 10-17, and related derivatives 18 and19, by dimethyldioxirane, 1, in acetone at 25°C produced the corresponding ketones in good to excellent yields for all but two cases. (The exceptions: oxidation of 1-methoxy-2-methyl-1-phenylpropane (48%) and 1-methoxy-2,2-dimethyl-1-phenylpropane (24%).) The oxidation of the secondary alcohols was found to yield k2 values that were roughly 10-fold greater than those of the corresponding methyl ethers. The rate constant for oxidation of a silyl ether was slightly lower than that for the corresponding methyl ether while that for the ester derivative was roughly half the value. For oxidation of alcohols and methyl ethers, the k2 values became smaller as the R " series (Me, Et, nPr, iPr, and tBu) increased in steric bulk (ρ* = 1.7; r = 0.998 and ρ* = 3.2; r = 0.95, respectively). The Hammett study for the oxidation of the methyl ethers of α-methyl-p-benzyl alcohols (10, 20-25) yielded a ρ value of -0.74. The activation parameters for oxidation of the parent compound of the ether series (1-methoxy-1-phenylethane) were ΔH = 14.8 ± 0.5 kcal/mol, ΔS = -21.9 eu, ΔG = 21.3 kcal/mol, k2 (25°C) = 1.6 × 10-3 M-1 s-1. The mechanistic aspects of the oxidation are discussed in relation to two mechanistic extremes: (a) direct insertion of the oxygen atom into the CH bond and (b) direct abstraction of the H by dimethyldioxirane to yield a caged-radical pair, with subsequent coupling to hemi-ketal intermediates that fragment to yield acetone, alcohol or water, and ketone as the final products.Key words: dimethyldioxirane, oxidation.
在25°C下,通过二甲基过氧化苯甲酰,对几系列次级醇2-9、醚10-17以及相关衍生物18和19在丙酮中进行氧化,产生相应的酮类产物,除两种情况外,产率良好至极好。(两种例外情况:1-甲氧基-2-甲基-1-苯基丙烷的氧化产率为48%,1-甲氧基-2,2-二甲基-1-苯基丙烷的氧化产率为24%。)发现次级醇的氧化产率的k2值大约比相应的甲基醚高10倍。硅醚氧化的速率常数略低于相应的甲基醚,而酯衍生物的速率常数大约是其值的一半。对于醇类和甲基醚的氧化,k2值随着R"系列(Me,Et,nPr,iPr和tBu)的立体体积增大而变小(ρ* = 1.7;r = 0.998和ρ* = 3.2;r = 0.95,分别)。对α-甲基-p-苄醇(10,20-25)甲基醚的氧化进行的Hammett研究得到了-0.74的ρ值。对于醚系列的母体化合物(1-甲氧基-1-苯乙烷)的氧化激活参数为ΔH = 14.8 ± 0.5 kcal/mol,ΔS = -21.9 eu,ΔG = 21.3 kcal/mol,k2(25°C)= 1.6 × 10-3 M-1 s-1。讨论了氧化的机理方面,涉及两种机理极端:(a)氧原子直接插入CH键和(b)二甲基过氧化苯甲酰直接提取氢,产生一个笼罩的自由基对,随后与半缩醛中间体结合,分解产生丙酮、醇或水以及酮类作为最终产物。关键词:二甲基过氧化苯甲酰,氧化。