Why bromobenzene cannot be used effectively in a Gabriel amine synthesis?

Answer 1

The Gabriel synthesis is a method for the preparation of primary amines from potassium phthalimide and an alkyl halide. Bromobenzene cannot be used effectively in a Gabriel amine synthesis because it is an aryl halide, which is generally unreactive towards nucleophilic substitution reactions due to the stability of the aryl carbon-halide bond. The reaction conditions of the Gabriel synthesis involve the use of strong base (such as KOH or NaOH), which can induce the elimination of the halide group to form an alkene instead of the desired amine product. Therefore, aryl halides like bromobenzene are not suitable substrates for the Gabriel synthesis.

Answer 2

Gabriel synthesis include 3 steps:

1. deprotonation of imide
2. direct S_N2 reaction
3. hydrolysis of imde to amine

when bromobenze was used, the second step will fail as all carbons on benzene ring are sp2 hyrbridized carbon, which is not reactive towards SN2 reaction.