Trialkoxysilane Grafting in Alcohols: A Simple Approach towards Modified Silica-Based Materials

The grafting of trialkoxysilanes is the most common method for the surface functionalization of silica gel, and it is usually carried out in the presence of toluene or other solvents such as acetonitrile or acetone. Here, we replaced these solvents with alcohols to afford silica materials containing alkoxy groups linked to the silicon atom. The grafting of <i>N,N</i>-dimethyl-3-amino- or 3-amino-propyltrimethoxysilane was carried out in the presence of several alcohols containing an unsubstituted alkyl chain (C7 and C14), a PEG functionalized chain, or an amino-substituted chain (<i>N,N</i>-dimethylamino, pyridyl). Materials were characterized via solid-state ¹³C- and ²⁹Si CPMAS NMR and thermogravimetric analysis to prove that alcohols are not "innocent" solvents but take part in the reaction and lead to [RSi(OR¹)-(OSi)₂] systems where the OR¹ group proceeds from the alcohol used in the synthesis. As a proof of concept, we briefly studied the catalytic activity of some of these materials with the aim of showing how different modifications can influence the course of a selected reaction. Finally, a quaternary ammonium salt (QAS)-based silica was prepared containing both an alkyl-QAS and an alkoxy-QAS linked to silicon atoms. This could represent an interesting approach for the development of new antifouling-based materials and, overall, the described strategy could be useful for the preparation of new organosilica materials.