Preparation and characterization of bonded silica hydride intermediate from triethoxysilane and dimethylmethoxysilane using supercritical carbon dioxide and dioxane as reaction medium

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• 作者：Benjamin A. Ashu-Arrah^a ; ^{b.ashuashuarrah@ucc.ie} ; Jeremy D. Glennon^a ; ^{j.glennon@ucc.ie} ; Klaus Albert^b
• 关键词：Chemical functionalization ; Silica hydride (SiH) ; Triethoxysilane (TES) and dimethylmethoxysilane (DMMS) ; Supercritical CO2 and dioxane ; Surface coverage and conversion efficiency ; Bonding methodology
• 刊名：Journal of Chromatography A
• 出版年：2012
• 期刊代码：47_00219673
• 类别：ch
• 出版时间：4 May, 2012
• 卷：1236
• 期：Complete
• 页码：42-50
• 文件大小：717 K

摘要

This research examines bonding methodology, surface coverage and silanol conversion efficiencies on the preparation of silica hydride (SiH) intermediate from triethoxysilane (TES) and dimethylmethoxysilane (DMMS) using sc-CO₂ and dioxane as reaction solvent. Under sc-CO₂ reaction conditions (at temperature and pressure of 100 掳C, 414 bar, respectively and 3 h reaction time), the surface coverages of SiH (evaluated from%C obtained from elemental analysis) prepared with DMMS (3.39 渭mol/m²) and TES (4.46 渭mol/m²) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 渭mol/m², SiH, DMMS and 0.69 渭mol/m², SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO₂ is due to the inherent trialkoxy moiety of the TES that favours siloxane crosslinkage, forming polymeric surface attachments to yield a higher ligand density than the monomeric DMMS ligand. A conversion efficiency of 鈭?4.4%of SiH prepared from TES in sc-CO₂ estimated from ²⁹Si CP/MAS NMR analysis is comparable to TES silanization in dioxane or toluene. Moreover, silica hydride (SiH) conversion efficiency of ca. 42.4%achieved for the hydride intermediate prepared from DMMS in sc-CO₂ is more superior to 33.3%efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO₂ being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO₂ were characterized using elemental analysis, thermogravimetric analysis (TGA), BET surface area, Fourier transform infrared (FI-IR) and solid state NMR spectroscopy. Silica hydride technology/chemical functionalization of silica in sc-CO₂ avoid extended purification steps (i.e. filtration and washing), generation of waste organic solvent and the need of costly or energy consuming drying processing with improved modification efficiency.