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  • Title: Preparation and characterization of bonded silica hydride intermediate from triethoxysilane and dimethylmethoxysilane using supercritical carbon dioxide and dioxane as reaction medium.
    Author: Ashu-Arrah BA, Glennon JD, Albert K.
    Journal: J Chromatogr A; 2012 May 04; 1236():42-50. PubMed ID: 22446079.
    Abstract:
    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-CO(2) and dioxane as reaction solvent. Under sc-CO(2) reaction conditions (at temperature and pressure of 100 °C, 414 bar, respectively and 3h reaction time), the surface coverages of SiH (evaluated from %C obtained from elemental analysis) prepared with DMMS (3.39 μmol/m(2)) and TES (4.46 μmol/m(2)) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 μmol/m(2), SiH, DMMS and 0.69 μmol/m(2), SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO(2) 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 ∼84.4% of SiH prepared from TES in sc-CO(2) estimated from (29)Si 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-CO(2) is more superior to 33.3% efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO(2) being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO(2) 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-CO(2) 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.
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