silanols

Silanols are compounds containing the silicon–oxygen–hydrogen moiety Si–OH. In organosilicon chemistry the term commonly refers to silyl alcohols, R3SiOH, in which a silicon atom bearing three carbon substituents carries a single hydroxyl group. In materials science, silanol groups (Si–OH) terminate siloxane networks on silica and related oxides.

Silanol groups are polar and capable of hydrogen bonding. They readily participate in condensation reactions, forming siloxane (Si–O–Si) linkages with loss of water. On solid supports such as silica, silanols can be isolated, vicinal, or geminal, influencing surface properties such as hydrophilicity and Brønsted acidity. Silanol counts can be altered by thermal treatment, leaving siloxane bridges.

Synthesis and applications: Organosilanols can be prepared by hydrolysis of chlorosilanes or alkoxysilanes and by oxidation of Si–H or Si–C bonds under appropriate conditions. Surface silanols arise from controlled hydrolysis of siloxane networks. Silanols are widely used to functionalize surfaces through silanization, by reacting Si–OH with organosilane reagents to graft desired functionalities. They also serve as intermediates in silicone chemistry and as sites for catalysis or adsorption on oxide supports.

Characterization: Infrared spectroscopy detects O–H stretching bands for silanols, while solid-state NMR and temperature-programmed dehydration studies reveal silanol type and density. Dehydration converts silanols to siloxanes, weakening hydrogen bonding and reducing surface acidity.