Benzyltrimethylammonium hydroxide

Benzyltrimethylammonium hydroxide, also known as Triton B or trimethylbenzylammonium hydroxide, is a quaternary ammonium salt that functions as an organic base. It is usually handled as a solution in water or methanol. The compound is colourless, although the solutions often appear yellowish. Commercial samples often have a distinctive fish-like odour, presumably due to the presence of trimethylamine via hydrolysis.

Together with the benzyltriethylammonium salt, benzyltrimethylammonium hydroxide is a popular phase-transfer catalyst.

It is used in aldol condensation reactions and base-catalyzed dehydration reactions. It is also used as a base in Ando's Z-selective variant of Horner-Wadsworth-Emmons Olefination reactions.

Relative to tetramethylammonium hydroxide, benzyltriethylammonium hydroxide is more labile. In 6M NaOH at 160 °C their half-lives are 61.9 and 4 h, respectively.