Tetramethyl orthosilicate

Tetramethyl orthosilicate hydrolyzes to SiO₂:

Si(OCH₃)₄ + 2 H₂O → SiO₂ + 4 CH₃OH

In organic synthesis, Si(OCH₃)₄ has been used to convert ketones and aldehydes to the corresponding ketals and acetals, respectively.

Safety

The hydrolysis of Si(OCH₃)₄ produces insoluble SiO₂ and CH₃OH (methanol). Even at low concentrations inhalation causes lung lesions, and at slightly higher concentrations eye contact with the vapor causes blindness. Worse, at low concentrations (200 ppm/15 min) the damage is often insidious, with onset of symptoms hours after exposure. The mode of action is the precipitation of silica in the eyes and/or lungs. Contrary to common information, including several erroneous MSDS sheets, the methanol produced is only a risk through chronic exposure and is a comparatively small concern. The mechanisms of methanol toxicity are well established, methanol causes blindness via conversion to formaldehyde, then to toxic formic acid in the liver; methanol splashes to the eye cause only moderate and reversible eye irritation.