[15625-56-6] · C4H12Br3N · Tetramethylammonium Tribromide · (MW 313.87)
(mild brominating agent)
Physical Data: mp 118-119 °C.
Solubility: slightly sol H2O, alcohols, other organic solvents; slowly dissolves in acetone, reacting to form a lachrymatory solution.
Form Supplied in: anhydrous orange powder.
Preparative Methods: 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.
Purification: by recrystallization from glacial acetic acid.
Handling, Storage, and Precautions: this hygroscopic solid 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.
Application of tetramethylammonium tribromide as a brominating reagent is well known.1 Tetramethylammonium tribromide allows double bond bromination under mild conditions and with good yields, and in some cases permits the bromination of aryl compounds at the a-position.2 Cyclohexene leads to 1,2-dibromocyclohexane; toluene gives benzyl bromide. The bromination of fluorene and methylnaphthalene has also been reported.
Michel J. L. Fournier
Université Pierre et Marie Curie, Paris, France