Explain the chemical reactions of the following:
(i) Rosenmund Reduction
(ii) Cannizzaro Reaction
(iii) Gattermann aldehyde synthesis
(iv) Perkin's Reaction

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Solution

(i) Rosenmund Reduction: Aldehydes are obtained by the reduction of acid chloride with hydrogen in boiling xylene in presence of a catalyst $P d$ suspended in $B a S O_{4}$
$C H_{3} C O C l + 2 H P d / B a S O_{4} - ----- \to X y l e n e C H_{3} C H O + H C l$
$C_{6} H_{5} C O C l + 2 H P d / B a S O_{4} - ----- \to X y l e n e C_{6} H_{5} C H O + H C l$
(ii) Cannizzaro Reaction: Aldehydes which do not contain $α$ -hydrogen like $H C H O$ , $C_{6} H_{5} C H O$ react with Conc. $N a O H$ solution to form methyl alcohol and foarmic acid. This reaction is called Cannizzaro's reaction.
$2 H C H O + N a O H ⟶ H C O O N a + C H_{3} O H$
Formaldehyde Sodium formate Methyl alcohol
$2 C_{6} H_{5} C H O + N a O H ⟶ C_{6} H_{5} C H_{2} O H + C_{6} H_{5} C O O N a$
Benzaldehyde Benzel alcohol Sodium benzoate
(iii) Gattermann aldehyde synthesis: When benzene react with $H C N$ and $H C l$ gas in the presence of anhydrous $A l {C l}_{3}$ , Benzaldehyde is obtained. This reaction is known as Gattermann aldehyde synthesis.
$C_{6} H_{6} + H C N + H C l A n h y d r o u s {A l C l}_{2} - --------- \to H_{2} O C_{6} H_{5} C H O + N H_{3} + H C l$
Benzene Benzaldehyde
(iv) Perkin's Reaction: When Benzaldehyde is heated with acetic anhydride in the presence of sodium acetate, it gives an unsaturated acid.
$C_{6} H_{5} C H O + {(C H_{3} C O)}_{2} O C H_{3} C O O N a - ------- \to Δ C_{6} H_{5} C H = C H C O O H + C H_{3} C O O H$
Benzaldedhyde Acetic anhydride Cinnamic acid

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