(i) An aromatic compound 'A' on treatment with aqueous ammonia and heating forms compound 'B' which on heating with `Br_(2)` and KOH forms a compound 'C' of molecular formula `C_(6)H_(7)N`. Write the structures and IUPAC names of compound A, B and C.
(ii) Lactose act as reducing sugar. Justify this statement.

Explanation

(i) Step-1: To find out the structure of compounds .B. and .C..
1. Since compound .C. with molecular formula `C_(6)H_(7)N` is formed from compound .B. on treatment with `Br_(2)+KOH` (i.e., Hoffmann bromamide reaction). Therefore, compound .B. must be an amide and .C. must be an amine. The only amine having the molecular formula `C_(6)H_(7)N` is `C_(6)H_(5)NH_(2)` (i.e., aniline or benzenamine).
2. Since .C. is aniline, therefore, the amide from which it is formed must be benzamide `(C_(6)H_(5)CONH_(2))`. Thus, compound .B. is benzamide:
The chemical equation showing the conversion of .B. to .C. is
`" "underset(underset((M.F.=C_(7)H_(7)NO))("Benzamide (B)"))(C_(6)H_(5)CONH_(2)) underset(("Hoffmann bormamide reaction"))overset(Br_(2)//KOH)(rarr) underset(underset((M.F.=C_(6)H_(7)N))("Benzenamine (C)"))(C_(6)H_(5)NH_(2))`
Step-2: To find out the structure of compound .A.. Since compound .B. is formed from compound .A. by treatment with aqueous ammonia and heating. Therefore, compound .A. must be benzoic acid or benzenecarboxylic acid.
`" "underset(underset("or Benzoic acid (A)")("Benzenecarboxylic acid"))(C_(6)H_(5)COOH) underset((ii)Delta)overset((i)Aq.NH_(2))(rarr) underset("Benzamide(B)")(C_(6)H_(5)CONH_(2))`
(ii) `*` Lactose is a disaccharide and contains one galactose unit and one glucose unit.
`*` In lactose, the `beta-D` galactose and `beta-D` glucose are linked by `beta-1,4-` glycosidic bond.
`*` The aldehyde carbon is not involved in the glycosidic bond hence it retains its reducing property and is called a reducing sugar.