Bifunctional catalysis in the condensation of silanols and alkoxysilanes
作者:Hsien-Kun Chu、Robert P. Cross、David I. Crossan
DOI:10.1016/0022-328x(92)80018-s
日期:1992.2
alkoxysilane by catalyst followed by its condensation with the silanol is deemed insufficient to explain the catalysis. Reaction of catalyst with the alkoxysilane to form an intermediate followed by silanolcondensation with this intermediate is also considered and cannot be ruled out. Rate considerations, however, favors a cyclic transition state where bifunctional catalysis is invoked. With the slow triethylamine
研究了模型硅烷醇九甲基四硅氧烷-1-醇与甲基三甲氧基硅烷的缩合反应,形成1,1-二甲氧基十甲基五硅氧烷。使用各种催化剂来研究缩合速率。CCl 3 COOH> Et 2 NOH> CH 3 COOH>MeEtCNOH> Et 3的反应顺序观察到N用于催化。由烷氧基硅烷由催化剂缓慢质子化,然后与硅烷醇缩合形成过渡态被认为不足以解释该催化作用。还考虑了催化剂与烷氧基硅烷反应形成中间体,然后与该中间体进行硅烷醇缩合反应,因此不能排除。但是,速率方面的考虑有利于调用双功能催化的循环过渡态。随着缓慢的三乙胺催化,还需要另一种机理。提出了一种过渡态,其中胺充当碱,协助质子在硅烷醇上解离。