Bromination of trans-cinnamic acid
Purpose and Introduction
The halogenation of of trans-cinnamic acid using pyridinium tribromide was connected in the organic solvent glacial acetic acid in order to verify and test which addition mechanism the reaction would follow. In the anti-addition mechanism, bromines attach themselves on opposite sides of the alkene functional group in a compound. In a syn-addition, the attach to the same side of the alkene.
The reaction synthesis was completed by using a reflux system to produce to crude product, and a vacuum filter to yield a solid, crude product. Recrystallization of the solid product was performed, allowing the impurities of the solid to be removed while slowly crystallizing and the product. The melting point of the final recrystallized product was taken to compare and verify to that of the which stereoisomer of 2,3,-dibromo- 3-phenylpropanoic acid is produced, and therefore, determine which addition mechanism took place for the halogenation reaction.
The character of the halogenation anti mechanism begins with the electrophilic addition of bromine to trans-cinnamic acid. The bromine is an induced dipole electrophile, which is attacked by the alkene and forms the bridged-ion intermediate. The large size of the bromide atom results in the nucleophilic bromide anion performing a “backside attack” similar to that of SN2. The resulting product is a vicinal dibromide with a trans or anti relationship. As there are two…