Boron tribromide, replacement

Boron tribromide replaces fluonne with bromine on tertiary or secondary carbons however, trifluoromethyl groups are inert in this reaction [70] (equation 57). 

The original method1 reported for the preparation of trichloroborazine involves the use of borazine. However, this procedure is not recommended because of the difficulty of preparing this heterocycle and its hydrolytic instability. More recently, this trichloroborazine has been prepared directly from ammonium chloride and boron trichloride at elevated temperatures with or without a solvent.2-8 Ammonium chloride may be replaced by a primary aliphatic or aromatic amine or its hydrochloride, and organodihaloboranes can be used in place of the boron trichloride to give the respective N- and B-substituted borazines.6 Boron tribromide has been used in analogous reactions to yield -B,/ , .B"-tribromoborazines.6... 

Rearrangement. Tertiary A -benzylglycinamides are subject to [l,2]-rearrangement by consecutive treatment with BBr3 and Et3N to afford phenylalaninamide analogues. The transformation cannot be effected by replacing boron tribromide with boron trifluoride. 

The dibromide is obtained when the boron trichloride in the above equation is replaced by the tribromide. It crystallises in colourless tablets, M.pt. S2" to 34" C., B.pt. 99" to 101" C. at 20 mm., fumes strongly in air, has a pungent smell, and is decomposed by water giving phenyl... 

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