Tetramethyl orthosilicate


Tetramethyl orthosilicate is the chemical compound with the formula Si4. This molecule consists of four methoxy groups bonded to a silicon atom. The basic properties are similar to the more popular tetraethyl orthosilicate, which is usually preferred because the product of hydrolysis, ethanol, is less toxic than methanol.
Tetramethyl orthosilicate hydrolyzes to SiO2:
In organic synthesis, Si4 has been used to convert ketones and aldehydes to the corresponding ketals and acetals, respectively.

Safety

The hydrolysis of Si4 produces insoluble SiO2 and CH3OH. Even at low concentrations inhalation causes lung lesions, and at slightly higher concentrations eye contact with the vapor causes blindness. Worse, at low concentrations 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 toxic formaldehyde in the liver; methanol splashes to the eye cause only moderate and reversible eye irritation.