Tetramethylammonium tribromide

Tetraalkylammonium salts that have poor stability can be freshly prepared by the procedure in eq 1. Stoichiometric amounts of tetraalkylammonium (methyl, ethyl, butyl…) bromide and sodium bromide are dissolved into hot water (1 L/mol of sodium bromide) and concd nitric acid (2.2 mol/mol NaBr) is slowly added with stirring. The reaction starts after few min and can be quite exothermic. When the temperature of the mixture returns to rt, the orange precipitate is filtered, washed with ethanol and ether, and dried.

Tetramethylammonium tribromide is a hygroscopic solid and should be stored under dry conditions. Purity more than 98%; stable bromine degree (1 g = 3.18 mequiv Br2) when correctly handled. Avoid washing reaction vessels with acetone. Less toxic than bromine, but handle in a fume hood.