Aromatic acids: Prepration, Reaction

Aromatic acids, also known as aromatic carboxylic acids, are organic compounds that contain both a carboxyl group (-COOH) and an aromatic ring. These compounds play a significant role in organic chemistry and have various applications. Below is a detailed note on the general methods of preparation and reactions of aromatic acids.

General Methods of Preparation

1. Carbonylation of Arenes:

The carbonylation of arenediazonium salts can prepare aromatic acids. This involves the treatment of arenediazonium tetrafluoroborates with carbon monoxide (CO) in the presence of a palladium catalyst.

Example: Ar-N₂⁺BF₄⁻ + CO + Pd catalyst → Ar-COOH + BF₄⁻ + N₂

2. Hydrolysis of Acid Chlorides:

Aromatic acid chlorides, obtained from the Friedel-Crafts acylation of aromatic compounds with acyl chlorides, can be hydrolyzed to form aromatic acids.

Example: Ar-COCl + H₂O → Ar-COOH + HCl

3. Oxidation of Alkylbenzenes:

Alkylbenzenes can be oxidized to form aromatic acids using strong oxidizing agents such as potassium permanganate (KMnO₄) or chromic acid (H₂CrO₄).

Example: Cumene (isopropylbenzene) can be oxidized to benzoic acid.

Reactions of Aromatic Acids

1. Esterification:

Aromatic acids ca undergo esterification reactions to form aromatic esters. This involves the reaction with alcohols in the presence of an acid catalyst.

Example: Ar-COOH + R-OH → Ar-COO-R + H₂O

2. Amide Formation:

Aromatic acids react with ammonia or amines to form amides.

Example: Ar-COOH + NH₃ → Ar-CONH₂ + H₂O

3. Halogenation:

Aromatic acids can undergo halogenation reactions, replacing a hydrogen atom on the aromatic ring with a halogen (Cl, Br, or I).

Example: Ar-COOH + X₂ → Ar-COO-X + HX (where X = Cl, Br, I)

4. Decarboxylation:

Aromatic acids, particularly those with electron-withdrawing groups, can undergo decarboxylation reactions to form the corresponding benzene derivative. This process is often initiated by heating or using reagents like soda lime (NaOH/CaO).

Example: Ar-COOH → Ar-H + CO₂

5. Reduction to Alcohols:

Aromatic acids can be reduced to the corresponding alcohols using reducing agents like lithium aluminum hydride (LiAlH₄).

Example: Ar-COOH + LiAlH₄ → Ar-CH₂OH + H₂O

6. Claisen Condensation:

Aromatic acids can participate in Claisen condensation reactions with esters to form β-ketoesters.

Example: Ar-COOH + R’-COOR” → Ar-COO-R’ + R”-COOH

7. Grignard Reactions:

Aromatic acids can react with Grignard reagents to form tertiary alcohols.

Example: Ar-COOH + RMgX → Ar-CH₂-R + Mg(OH)X

8. Acylation:

Aromatic acids undergo acylation reactions, replacing the carboxyl group with an acyl group, often catalyzed by Lewis acids.

Example: Ar-COOH + Ac₂O → Ar-CO-Ac + HOAc (Ac = acetyl group)

These reactions demonstrate the versatility of aromatic acids in organic synthesis, allowing for forming a wide range of derivatives with different functional groups. The choice of reaction depends on the desired product and the specific functional groups present in the starting material.

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Post

Phenols -General Methods of Preparation and Reactions of Phenols

Phenols are organic compounds characterized by a hydroxyl (-OH) group directly attached to an aromatic benzene ring (Ar-OH). Distinguished from alcohols by the aromatic ring, phenols exhibit unique chemical properties. The hydroxyl group imparts acidic and nucleophilic traits, rendering phenols weak acids. They are prevalent in natural sources, serving as antioxidants in plants, while synthetic […]

Acidity of aromatic acids

Aromatic acids, also known as aromatic carboxylic acids, are organic compounds that contain both a carboxyl group (-COOH) and an aromatic ring. The aromatic ring’s unique electronic and structural features influence aromatic acid’s acidity. Understanding the acidity of aromatic acids is crucial in predicting their reactivity and behavior in various chemical reactions. Here’s a note […]

Resorcinol – Structure and Uses

Resorcinol is an aromatic organic compound with the molecular formula C6H4(OH)2. Also known as 1,3-dihydroxybenzene, resorcinol features a benzene ring with two hydroxyl (-OH) groups situated at adjacent carbon positions (1,3 positions) on the ring. This white crystalline solid exhibits phenolic properties, participating in various chemical reactions typical of phenols. Resorcinol finds application in industries […]