Q56E - Organic Chemistry (Mcmurry)

Question

Starting with benzene as your only source of aromatic compounds,

how would you synthesize the following substances? Assume that you

can separate ortho and para isomers if necessary.

(a) p-Chloroacetophenone (b) m-Bromonitrobenzene

(c) o-Bromobenzenesulfonic acid (d) m-Chlorobenzenesulfonic acid

Step-by-Step Solution

Answer

Answer

The synthesis of benzene gives the following product:

Step-by-step Solution Step 1: Isomers

Isomers are molecules or polyatomic ions having identical molecular formulas but the distinct arrangement of atoms in space.

In organic chemistry ortho, meta and para are isomers of a compound generally cyclic in nature. They are used to indicate the position of non-hydrogen substituents on a hydrocarbon.

Step 2: Synthesis of compounds (a) and (b)

It is necessary to introduce substituents in the proper order when synthesizing substituted aromatic rings. A group that is introduced out of order will not have the proper directing effect. 

Mostly in these types of reactions, a mixture of ortho and para isomer may be formed.

(a) Benzene reacts with chlorine molecule in the presence of Lewis acid to give chlorobenzene, which further participates in Friedel-Crafts acylation to produce p-Chloroacetophenone.

                             Benzenechlorobenzenep-Chloroacetophenone

(b) Benzene undergoes nitration to produce nitrobenzene which further reacts with bromine in the presence of FeBr₃ to synthesize m-bromonitrobenzene.

                            Benzene nitrobenzenem-Bromonitrobenzene

Step 3: Synthesis of compounds (c) and (d)

(c) Benzene undergoes bromination to produce bromobenzene, which further takes part in sulphonation reaction to produce o-Bromobenzenesulfonic acid

(d) Benzene undergoes sulphonation and then reacts with chlorine molecule to synthesize m-Chlorobenzenesulfonic acid.

                   Benzenebenzenesulfonic acid m-Chlorobenzenesulfonic acid