Gas-Chromatographic Identification of Unusual Unstable Products of the Partial Hydrolysis of Tetraethoxysilane

Abstract

Gas chromatographic analysis of a long-stored sample of tetraethoxysilane (tetraethyl orthosilicate) showed that it lacked the main component due to the hydrolysis of this compound by traces of water. Instead, ethanol and three other components with retention indices (RIs) of 537 ± 2 (no. 1), 608 ± 1 (no. 2, the most abundant component), and 727 ± 3 (no. 3) on a column with a HP-5 stationary phase were detected. These components are unstable, and they cannot be isolated preparatively; as a result, they have not been characterized previously. To identify them, the chemical properties of this sample were characterized, and the recurrent approximations of the RIs of the detected components and their correlation with the retention indices of structural analogs were considered. It was established that they were congeners of the initial tetraethoxysilane, namely, exotic products of its partial hydrolysis—triethoxysilanol (C2H5O)3SiOH, diethoxysilanediol (C2H5O)2Si(OH)2, and ethoxysilanetriol (C2H5O)Si(OH)3. In accordance with published data, some silanediols R2Si(OH)2 and silanetriols RSi(OH)3 are stable, especially, compounds containing substituents capable of conjugation with vacant d orbitals of silicon atoms. Among them are phenyl- (π–d conjugation systems) and alkoxy-substituted (p–d systems) silanediols and silanetriols. The identified products of partial hydrolysis of tetraethoxysilane belong to the latter type.