Q16-20P - Organic Chemistry (Mcmurry)

Question

Styrene, the simplest alkenylbenzene, is prepared commercially for use in plastics manufacture by catalytic dehydrogenation of ethylbenzene. How might you prepare styrene from benzene using reactions you’ve studied?

Step-by-Step Solution

Answer

Step 1: Preparation of alkenylbenzene.

Alkylbenzene is obtained by the FriedelCrafts reaction of benzene with alkylhalide in the presence of ${\mathbf{AlCl}}_3$ .The alkyl group is transformed into an olefinic group by halogenations followed by dehydrohalogenation with alcoholic KOH.

Step 2: Preparation of styrene from benzene

Benzene undergoes Friedal-Crafts reaction when treated with ethyl chloride in the presence of ${\mathrm{AlCl}}_3$ to give ethylbenzene. Bromination of ethylbenzene in the benzyl position with NBS results in the formation of bromoethylbenzene which eliminates HBr when treated with ethanolic KOH to produce styrene.

Preparation of styrene from benzene