(a) Illustrate the following name reactions giving suitable example in each cases:
(i) Clemmensen reduction
(ii) Hell-Volhard-Zelinsky reaction
(b) How are the following conversions carried out?
(i) Ethylcyanide to ehtanoic acid
(ii) Butan-1-ol to butanoic acid
(iii) Benzoic acid to m-bromobenzoic acid

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Solution

(a) (i) Clemmensen reduction
The carbonyl group of aldehydes and ketones is reduced to CH_2 group on treatment with zinc-amalgam and concentrated hydrochloric acid. This is known as Clemmensen reduction. (Ref. image 1)

(ii) Hell-volhard-zelinsky (HVZ) reaction
Carboxylic acids having an $^I \pm$ - hydrogen are halogenated at the at the $^I \pm -$ position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give $^I \pm -$ halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.
$R - C H_{2} - C O O H (i) X_{2} / R e d p h o s p h o r u s - ------------ \to (i i) H_{2} O R - C H - C O O H$
$\begin{matrix} | X X & = & C l . B r \end{matrix} a - H a l o c a r b o x y l i c a c i d$

(b)- (i) (Ref. image 2)

(ii) $C H_{3} C H_{2} C H_{2} C H_{2} C H_{2} O H (i) K_{2} C r_{2} O_{2} / H_{2} S O_{4} - ----------- \to (I i i) D i l . H_{2} S O_{4} C H_{3} C H_{2} C H_{2} C O O H$
Butanol Butanoic acid

(iii) (Ref. image 3)

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