tetramethylammonium

Tetramethylammonium refers to the quaternary ammonium cation with formula (CH3)4N+. It forms a family of salts in which this cation is paired with various anions, such as chloride, hydroxide, or fluoride. The cation is tetrahedral at nitrogen and bears a permanent positive charge, making the salts generally water-soluble.

Common examples include tetramethylammonium chloride and tetramethylammonium hydroxide (TMAH). TMAH, in particular, is a widely used strong base in chemical processing and microfabrication, where it serves as a developer for photoresists and as an etchant for silicon.

Preparation: tetramethylammonium salts are typically formed by quaternization of a tertiary amine with an alkyl halide or by metathesis of a suitable salt. For example, treating trimethylamine with methyl chloride yields tetramethylammonium chloride.

Safety and handling: quaternary ammonium salts can be irritants to skin and eyes. Tetramethylammonium hydroxide is caustic and toxic, and all tetramethylammonium compounds should be handled with appropriate protective equipment and disposed of according to regulations. In industry, their use is usually restricted to controlled environments.