Question 22 of 32intermediate🔧 ApplyShort Answer4 marks

How will you convert benzene into (i) p-nitrobromobenzene (ii) m-nitrochlorobenzene (iii) p-nitrotoluene (iv) acetophenone?

(i)
Answer

Benzene undergoes halogenation with Br2Br_2 in the presence of anhydrous AlBr3AlBr_3 to form bromobenzene. Bromobenzene then undergoes nitration with HNO3HNO_3 in the presence of H2SO4H_2SO_4 to yield pp-nitrobromobenzene.

(ii)
Answer

Benzene undergoes nitration with HNO3HNO_3 in the presence of H2SO4H_2SO_4 to form nitrobenzene. Nitrobenzene then undergoes halogenation with Cl2Cl_2 in the presence of anhydrous AlCl3AlCl_3 to yield mm-nitrochlorobenzene.

(iii)
Answer

Benzene undergoes Friedel-Crafts alkylation with CH3ClCH_3Cl in the presence of anhydrous AlCl3AlCl_3 to form toluene. Toluene then undergoes nitration with HNO3HNO_3 in the presence of H2SO4H_2SO_4 to yield pp-nitrotoluene.

(iv)
Answer

Benzene undergoes Friedel-Crafts acylation with acetyl chloride (CH3COClCH_3COCl) in the presence of anhydrous AlCl3AlCl_3 to directly form acetophenone.

Explanation

The conversions rely on the directing effects of substituents in electrophilic substitution reactions. Halogen atoms are ortho/para-directing, so bromobenzene yields the para-nitrated product. The nitro group is meta-directing, so nitrobenzene yields the meta-chlorinated product. The methyl group in toluene is ortho/para-directing, leading to p-nitrotoluene. Friedel-Crafts acylation directly introduces the acetyl group to form acetophenone.

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