Perkin Reaction Mechanism

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Mechanism of Perkins Reaction

Perkin’s reaction is an organic reaction proposed by William Henry Perkin, an English Chemist, in the year 1868. The reaction belongs to the Carbonyl compounds and is used to make ɑ-, and β-unsaturated aromatic acids. Perkin used this reaction to make cinnamic acids. When an acid anhydride and aromatic aldehyde react with each other in the presence of a weak base, they condense to give the desired product. Condensation means the removal of water. The reaction is generally used in the synthesis of phytoestrogenic stilbene resveratrol in the laboratory. We will describe the mechanism of Perkins reaction and the step-by-step mechanism of perkin condensation under this topic.

Perkins Reaction With Mechanism

As mentioned above, the Perkin mechanism involves the condensation of an aldehyde and carboxylic acid anhydride with a weak base acting as a catalyst. Mainly, Sodium or Potassium salt of an acid is used which results in the formation of unsaturated aromatic acids. Perkin performed this reaction using the sodium salt of salicylaldehyde and acid anhydride, after heating this mixture at 453K, coumarin was obtained as the final product.

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Perkin Condensation Reaction Mechanism

The steps involved in the mechanism of Perkin condensation reaction are as follows.

  • The first step involves the removal of H+ ions using a weak base by carboxylate ion, which results in the formation of resonance stabilized carbanion, i.e., a species involving carbon-containing negative charge.

  • The second step involves the nucleophilic addition of the carbanion to the carbonyl carbon of aldehyde which will result in the formation of a tetrahedral intermediate.

  • The third step involves protonation of the tetrahedral intermediate by acetic acid which is formed in-situ. 

  • The fourth step involves condensation, i.e., the removal of a water molecule from the hydroxy derivative.

  • The last step involves hydrolysis, i.e., breaking of bonds using water, resulting in the formation of unsaturated acid as the product.

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This is the most accepted and simplest mechanism of Perkin reaction so far. There are various approaches suggested, so a few steps may differ. So, here we have explained the Perkin reaction with mechanism.

Applications of Perkin Reaction Mechanism

  • Perkin Condensation is used for the synthesis of cinnamic acid in laboratories. Cinnamic acids are naturally occurring unsaturated aromatic carboxylic acids that are found commonly in cinnamon and shea butter.

  • It is used to synthesize ɑ-, and β-unsaturated aromatic acids, which are greatly used in the pharmaceutical sector.

FAQ (Frequently Asked Questions)

Question 1: Which Catalyst is used in the Perkin Condensation Mechanism?

Answer: The Perkins Condensation mechanism involves sodium or potassium salts of acid as a catalyst. These alkali salts act as a weak base that is suitable for this reaction because stronger bases result in undesirable changes in the aromatic entities present in the reaction.

Question 2: Which Intermediate is Involved and What is the Final Product of Perkin Reaction?

Answer: Intermediates are formed during the reactions, which cannot be isolated and they are theoretically assumed to plan how the mechanism would be. The intermediate involved in the reaction is the Tetrahedral entity which is formed by an attack of carbanion on the carbonyl carbon. The end product formed in the perkin reaction is ɑ,β-unsaturated aromatic acid.

Question 3: Describe the Perkin Reaction and the Mechanism of Perkins’s Reaction.

Answer:  Perkin Reaction is a type of chemical reaction that involves the aldol condensation of an organic acid anhydride and an aromatic aldehyde to yield an ɑ, 𝛃-unsaturated aromatic acid.

Benzaldehyde when heated with acetic anhydride in the presence of sodium acetate it forms cinnamic acid as a product.

C2 H5CH=O + CH−CO−O−COCH3   C5H5CH=CH−COOH + CH3 COOH3
Perkins’s condensation mechanism consists of five steps. The first step involves deprotonation using a weak base. The second step involves the formation of a carbanion. The third step involves the Attack of this carbanion on the carbon of the carbonyl compound. The fourth step involves condensation and the last step involves hydrolysis which results in the formation of the final product.