How can the following conversion be carried out:

(i) Aniline to bromobenzene

(ii) Chlorobenzene to 2-chloroacetophenone

(iii) Chloroethane to butane.

OR

What happens when

(i) chlorobenzene is treated with Cl₂/FeCl₃.

(ii) Ethyl choride is treated with AgNO₂.

(iii) 2-bromopentane is treated with alcoholic KOH?

Write the chemical equations in support of your answer.

(i)

When aniline is treated with nitrous acid or sodium nitrite and HCl at chilled temperatures, it gets converted to a diazonium salt benzene diazonium chloride, which undergoes Sandmeyer’s reaction where treatment with CuBr gives Bromobenzene, or it can also undergo Gatterman’s reaction where the diazonium salt is treated with HBr in presence of Cu powder to give bromobenzene.

(ii)

The reaction follows Friedel Craft’s acylation mechanism. According to this reaction, when a substituted benzene compound like chlorobenzene is treated with acetic anhydride in presence of anhydrous AlCl₃, it forms 2-chloroacetophenone/o-chloroacetophenone as a major product, and p-chloroacetophenone as a minor product. This is an electrophilic subsitution reaction.

(iii)

Chloroethane undergoes Wurtz reaction where an alkyl halide on treatment with Na and dry ether give hydrocarbons with double the number of carbons. Chloroethane undergoes this reaction to give butane.

OR

(i)

When chlorobenzene is treated with Cl₂/FeCl₃, it undergoes chlorination to give dichlorobenzene with 1,4-dichlorobenzene as major product and 1,2-dichlorobenzene as minor product.

(ii)

When ethyl chloride is treated with AgNO₂, ethyl chloride undergoes nucleophilic substitution and substitutes the chloride with –NO₂, giving nitroethane.

(iii)

When 2-bromopentane is treated with alcoholic KOH, it undergoes elimination reaction by Saytzeff rule. The compound has more than one β-hydrogen, hence there will be more than one product. In dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms. Hence the major product is pent-2-ene and the minor product is pent-1-ene.