Silicon Effects. V. .BETA.-Silicon Effect in the Solvolysis of 2-Phenylethyl Compounds.
作者:Fumie Hayakawa、Sin-ichiro Watanabe、Nobujiro Shimizu、Yuho Tsuno
DOI:10.1246/bcsj.66.153
日期:——
The rates of the solvolysis of 2-aryl-2-(trimethylsilyl)ethyl compounds, ArCH(SiMe3)CH2X (4: X = Cl and OCOCF3; Ar = C6H5 and p-MeOC6H4), have been measured in various solvents at 25°C. The solvolysis of the chloride, 4 (X = Cl; Ar = C6H5), exhibited an m value of 0.90 in aqueous dioxane consistent with rate-determining ionization; it gave (2-ethoxy-2-phenylethyl) trimethylsilane together with styrene in ethanol indicating a 1, 2-SiMe3 migration during the solvolysis. The p-MeO-substitution effect, kp–MeO/kH, was measured with the trifluoroacetates to be 2.1, in contrast to a factor of 269 observed in solvolysis of 1-aryl-2-(trimethylsilyl)ethyl compounds (1), indicating that distinct intermediates are involved in ionization of the two regioisomeric systems, 1 and 4.
在 25°C 的各种溶剂中测量了 2-芳基-2-(三甲基硅基)乙基化合物 ArCH(SiMe3)CH2X (4: X = Cl 和 OCOCF3; Ar = C6H5 和 p-MeOC6H4)的溶解速率。氯化物 4(X=Cl;Ar=C6H5)在二噁烷水溶液中的溶解度 m 值为 0.90,与决定速率的电离相一致;在乙醇中生成了(2-乙氧基-2-苯基乙基)三甲基硅烷和苯乙烯,表明在溶解过程中发生了 1,2-SiMe3 迁移。在三氟乙酸盐中测出的 p-MeO 取代效应(kp-MeO/kH)为 2.1,而在 1-芳基-2-(三甲基硅基)乙基化合物 (1) 的溶解过程中观察到的系数为 269,这表明 1 和 4 这两个异构体系统的电离过程涉及不同的中间产物。