Question

Carboxylic acid derivative is used in reaction(s): (A) Aldol condensation (B) Perkin reaction (C) Claisen condensation (D) Knovenagal reaction

Short answer

The correct options are (B) Perkin reaction and (C) Claisen condensation as they involve carboxylic acid derivatives in their reactions.

Step-by-step solution

Understand Aldol Condensation

Aldol condensation is a reaction between two aldehydes or ketones in the presence of a base or an acid catalyst. It results in the formation of a β-hydroxy ketone (aldol) or aldehyde (related) compound as a product. This reaction does not involve a carboxylic acid derivative; therefore, option (A) is incorrect.

Understand Perkin Reaction

The Perkin reaction is an organic reaction in which an aromatic aldehyde reacts with an anhydride of a carboxylic acid in the presence of a weak base like acetic anhydride / acetic acid, leading to the formation of α,β-unsaturated carboxylic acids as the primary product. It employs a carboxylic acid derivative (anhydride); thus, option (B) is correct.

Understand Claisen Condensation

Claisen condensation is a reaction between an ester and an enolizable aldehyde/ketone or another ester, in which both the reactants have α-hydrogen atoms, in the presence of a base. It results in the formation of a β-keto ester or a β-diketone. Since esters are involved in the reaction, it's a carboxylic acid derivative. Option (C) is correct.

Understand Knovenagal Reaction

Knovenagal reaction is a reaction of non-enolizable aldehydes or ketones with active methylene compound in the presence of a mild base to form α,β-unsaturated carbonyl compounds. The reaction does not involve carboxylic acid derivatives in any part of the process. Therefore, option (D) is incorrect. Based on our understanding of the reactions, the correct options are (B) Perkin reaction and (C) Claisen condensation.

Key concepts

Aldol Condensation

Aldol condensation is a reaction that involves the enolizable aldehydes or ketones and is typically catalyzed by either a base or an acid. The result is the formation of a product known as a β-hydroxy ketone or an aldol. It occurs via the formation of enolate ions in the case of base-catalyzed reactions. These ions are highly nucleophilic and attack the carbonyl carbon of another aldehyde or ketone, leading to the condensation product. However, it is important to note that aldol condensation does not involve any carboxylic acid derivatives. Thus, in the context of reactions involving carboxylic acid derivatives, Aldol condensation is not applicable.

Perkin Reaction

The Perkin Reaction is a classic organic synthesis method used to produce α,β-unsaturated carboxylic acids. This reaction involves an aromatic aldehyde reacting with the anhydride of a carboxylic acid. The reaction mechanism generally requires a weak base such as the acetate ion from acetic anhydride. The process involves the formation of an enolate that attacks the carbonyl carbon of the aldehyde, creating an intermediate that undergoes dehydration to produce the unsaturated product. Anhydrides, which are a category of carboxylic acid derivatives, are crucial to this reaction, making the Perkin Reaction a suitable example of reactions involving carboxylic acid derivatives.

Claisen Condensation

Claisen condensation is a reaction that traditionally involves two ester molecules reacting in the presence of a strong base, leading to the formation of a β-keto ester or a β-diketone. The reaction proceeds through the formation of an enolate ion from one ester molecule which then attacks another ester molecule’s carbonyl carbon. The strong base, such as sodium ethoxide or sodium hydride, facilitates this ion formation. Because esters are derivatives of carboxylic acids, Claisen condensation is uniquely significant in organic synthesis involving carboxylic acid derivatives. This reaction can also happen with an enolizable aldehyde or ketone, although the most common substrates are esters.

Knovenagal Reaction

The Knovenagal reaction stands out as a method to synthesize α,β-unsaturated carbonyl compounds. It does not involve carboxylic acid derivatives. Instead, it requires non-enolizable aldehydes or ketones to react with an active methylene compound such as malononitrile or ethyl acetoacetate in the presence of a mild base. The base facilitates deprotonation of the active methylene compound, forming a carbanion which then attacks the carbonyl group of the aldehyde or ketone. This process results in the condensation and dehydration necessary to form a double bond in the unsaturated product, but without the involvement of any carboxylic acid derivatives.