SYNTHESIS OF 3-BROMO-l-PHENYLPROP-l-ENE (Cinnamyl bromide)

• Chlorotrimethylsilane (2.7 g, 25mmol) (1) (CAUTION) is added to a solution of lithium bromide (1.74g, 20mmol) in dry acetonitrile (20 ml) (2) with good stirring under a nitrogen atmosphere. 

• Cinnamyl alcohol (1.34 g, lOmmol) is then added and the reaction mixture heated under reflux for 12 hours. 

• The progress of the reaction is monitored by t.l.c. on silica gel plates with hexane as the eluant. 

• On completion of the reaction (12 hours), the reaction mixture is taken up in ether (50 ml), washed successively with water (2 x 25 ml), sodium hydrogen carbonate solution (10%, 50 ml) and finally brine, and dried over anhydrous sodium sulphate. 

• Evaporation of the ether affords the pure bromide in 93 per cent yield. 

• The product may be recrystallised from ethanol and has m.p. 31-32 °C; CAUTION this compound is lachrymatory.

Notes to keep in mind:

1. Chlorotrimethylsilane is distilled over sodium hydroxide pellets.

2.  Acetonitrile is purified and stored over molecular sieves.