Influence of steric effects on the kinetics of ethyltrimethoxysilane hydrolysis in a fast sol-gel system

Kinetic study of methyltriethoxysilane (MTES) hydrolysis by FTIR spectroscopy under different temperatures and solvents

“…The hydrolysis of trifunctional alkoxysilane with larger alkoxy groups is much slower [21]. Therefore, the E a value (8.2 kcal/mol) in this study is higher than that (6.4 kcal/mol) of methyltrimethoxysilane (MTMS) reported previously [25,26], because ethoxyl has larger steric effect than methoxyl to block the water attacking Si atom.…”

“…Generally the mechanism for alkoxysilane hydrolysis under acid conditions is a fast, reversible protonation step, followed by S N 2 attack by water [13,25]. Kinetics studies showed that steric hindrance to nucleophilic attack at silicon was more important than inductive effects in affecting the overall rate of hydrolysis.…”

Di̇ş Heki̇mli̇ği̇nde Si̇lan Uygulamalari

“…Silikonda bimoleküler nükleofilik yer değiştirme (SN 2 ) reaksiyonu gerçekleşir. 26 Merkezi silikon atomu 5-trigonal bipirimidal durumuna geçer. Daha sonra nükleofil ile silikon atomu arasında yeni bir bağ oluşur.…”

Resin Bonding to Silicatized Zirconia with Two Isocyanatosilanes and a Cross-linking Silane. Part II: Mechanistic Approach

“…The first hydrolysis step of silane to silanol (≡SiOH) is a fast and reversible protonation of the alkoxy group of the silane which enhances the leaving group ability. Then, it is followed by a bimolecular nucleophilic substitution (S N 2) reaction [5]. This involves the backside attack of a nucleophile (an electron-rich species) to the electrophile (an electron-deficient species), i.e the central silicon atom, to produce a penta-coordinate trigonal bipyramidal transition state.…”

“…Chambers et al [5] have studied the steric and inductive effects of alkoxy groups on the acid-catalyzed hydrolysis of ethyltrimethoxysilane and tetramethoxysilane. An alkoxy group is a better electron-donating substituent than a hydroxyl group and so the rate of hydrolysis should decrease with more hydroxyl substitutions.…”