Reactions of chloromethyl silanes with hydrated Aerosil silicas

Abstract

Methyl chlorosilane vapours react with the surface hydroxyls of Aerosil silicas at temperatures above about 250°C. Infra-red spectroscopic studies on deuterium exchanged samples show that only the external hydroxyl-groups are affected. The trimethyl-and dimethyl-substituted chlorosilmes react selectively but completely with the isolated or single surface hydroxyls, whereas the monomethyl and tetrachloro compounds also react with some of the interacting hydrogen-bonded surface groups. Analyses of the solid reaction products from the dimethyl and trimethyl chlorosilane+silica reactions suggest that these compounds react largely 1 : 1 with the single surface hydroxyls although 1 : 2 bridging reactions occur on preheating the solid to temperatures of the order of 500°C. By comparing these results with those reported earlier it is suggested that the selectivity of reactions of this type is controlled largely by the stereochemistry of the activated transition-state structure of the organic molecule.

Flame-made nanoparticles for nanocomposites

“…Therefore it is not surprising that first attempts to passivate surface silanol groups were undertaken with respect to these composites [65]. Methyltrichloro-(MTCS [66,67]), dimethyldichloro-(DMDCS [66][67][68]) or trimethylchlorosilanes (TMCS [67][68][69]) were applied for gas phase functionalization from room temperature to 300 [66] or 400 • C [67]. The presence of NH 3 catalyzed the reaction and resulted in a high surface coverage of organosilanes at relatively lower reaction temperatures than without catalyst [69].…”

Implications of silica on biorefineries – interactions with organic material and mineral elements in grasses

“…Organic molecules can also interact with silica, but depending on the form of interaction they either prevent dissolution of silica or induce it by forming a soluble complex. Reaction of silica with trimethylchlorosilane results in a chemisorbed surface layer of alkyltrimethylsilane, which make silica particles hydrophobic and prevent their dissolution . On the other hand, o‐dihydroxy arylenes, as for example catechol, form soluble complexes with silicon which are stabile in aqueous solutions, but however not stabile toward atmospheric pressure …”

“…Reaction of silica with trimethylchlorosilane results in a chemisorbed surface layer of alkyltrimethylsilane, which make silica particles hydrophobic and prevent their dissolution. 2,41 On the other hand, o-dihydroxy arylenes, as for example catechol, form soluble complexes with silicon which are stabile in aqueous solutions, but however not stabile toward atmospheric pressure. 2,42 In aqueous solutions at pH 8 and room temperature, amorphous silica and to some extent quartz were solubilized by various o-dihydroxy arylenes.…”

Effect of catalyst preparation conditions on the performance of eggshell cobalt/SiO2 catalysts for Fischer–Tropsch synthesis

“…De Boer and Vleeskens [16] argue that the silica loses this adsorbed water at around 120 o C in ambient air, unless it is present in micropores, where the loss is at 180 o C. Drying under a vacuum, at low temperature is also an effective technique to remove all the surface adsorbed water. Armistead and Hockey [17] found that removal of the silanol group takes place around 400-450 o C in ambient air where half of the hydroxyl groups leave the silica surface creating large siloxane areas that do not rehydrate readily.…”