Question

A product of Perkin reaction is:
(A) α, β – unsaturated aldehyde
(B) β – cyclohexyl α, β – unsaturated aldehyde
(C) β – aryl – α, β – unsaturated acid
(D) all of the above

Answer 1

Hint: We have already learned about the Perkin reaction which is an organic reaction that is used to make cinnamic acids. On conducting the same in laboratory it gives an α, β-unsaturated aromatic acid by the aldol condensation of an aromatic aldehyde and an acid anhydride, in the presence of an alkali salt of the acid.

Complete step by step solution:
The Perkin reaction involves the condensation of a carboxylic acid anhydride and an aldehyde in the presence of a weak base, often the sodium or potassium salt of the acid or triethylamine, to give unsaturated carboxylic acids. The first example of this reaction was described by Perkin in 1868 and involves a synthesis of coumarin by heating the sodium salt of salicylaldehyde with acetic anhydride. The reaction is generally applicable only to aromatic aldehydes. $$C_6{H}_5-CHO+R-C{H}_2(CO)-O-(CO)C{H}_2-R\stackrel{base}{\to }{C}_6{H}_5-CHC(R)COOH+RC{H}_{2}COOH$$
Hence, the correct answer should be Option (C) β – aryl – α, β – unsaturated acid.

Additional information:
> The alkali salt of the acid anhydride is used as a catalyst. However, other bases can be used for this purpose.
> This reaction is used for the synthesis of phytoestrogenic stilbene resveratrol in the laboratory.
> Cinnamic acid was first synthesized by the base-catalyzed condensation of acetyl chloride and benzaldehyde, followed by hydrolysis of the acid chloride product.

Notes: We can prepare cinnamic acid by another way: the Knoevenagel condensation reaction. The reactants for this are benzaldehyde and malonic acid in the presence of a weak base, followed by acid-catalyzed decarboxylation.
Perkin Reaction is very important to develop our knowledge and is an essential topic from the examination point of view.