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1 Solutions 2 Electrochemistry 3 Chemical Kinetics 4 The d-and f-Block Elements 5 Coordination Compounds 6 Haloalkanes and Haloarenes 7 Alcohols, Phenols and Ethers 8 Aldehydes, Ketones and Carboxylic Acids 9 Amines 10 Biomolecules

8 Aldehydes, Ketones and Carboxylic Acids

8.1 Nomenclature and Structure of Carbonyl Group 8.2 Preparation of Aldehydes and Ketones 8.3 Physical Properties 8.4 Chemical Reactions 8.5 Uses of Aldehydes and Ketones 8.6 Nomenclature and Structure of Carboxyl Group 8.7 Methods of Preparation of Carboxylic Acids 8.8 Physical Properties of Carboxylic Acids 8.9 Chemical Reactions of Carboxylic Acids 8.10 Uses of Carboxylic Acids

Methods of Preparation of Carboxylic Acids

NCERT Reference: Chapter 8 – Aldehydes, Ketones and Carboxylic and Carboxylic Acids – Pages 206–207

Quick Notes

  • Oxidation of primary alcohols and aldehydes gives carboxylic acids.
  • Alkylbenzenes undergo side-chain oxidation to give aromatic acids.
  • Nitriles and amides hydrolyse under acidic or basic conditions to give acids.
  • Grignard reagents form acids upon reaction with CO2 and hydrolysis.
  • Acyl halides, anhydrides, and esters convert to acids through hydrolysis.

Full Notes

Carboxylic acids can be synthesised from a wide range of starting materials, including alcohols, aldehydes, hydrocarbons, nitriles, Grignard reagents, and derivatives of acids. Each method targets the formation of the carboxyl group by oxidation, hydrolysis, or nucleophilic substitution.

From Primary Alcohols and Aldehydes

Primary alcohols are easily oxidised to carboxylic acids using strong oxidising agents. Common oxidising agents include:

Potassium permanganate (KMnO4) or Potassium dichromate (K2Cr2O7)

NCERT Class 12 Chemistry schematic showing oxidation of a primary alcohol to a carboxylic acid using KMnO4 or K2Cr2O7.

Chromium trioxide (CrO3) in acidic medium (Jones reagent).

NCERT Class 12 Chemistry diagram of Jones reagent (CrO3 in acid) oxidising alcohols to acids.

Aldehydes are also oxidised to carboxylic acids using mild oxidising agents.

From Alkylbenzenes

Aromatic carboxylic acids are prepared by oxidising alkylbenzenes with chromic acid or acidic/alkaline KMnO4.

NCERT Class 12 Chemistry reaction scheme showing oxidation of toluene with KMnO4/heat to benzoic acid.

From Nitriles and Amides

Hydrolysis of nitriles (RCN) and amides (RCONH2) leads to the forming of carboxylic acids.

The nitrogen-containing groups are replaced by the hydroxyl of the acid.

NCERT Class 12 Chemistry pathways showing acidic and basic hydrolysis of nitriles to carboxylic acids and amides to acids.

From Grignard Reagents

Grignard reagents (RMgX) react with carbon dioxide to form the magnesium salt of a carboxylic acid, which yields the acid upon hydrolysis.

NCERT Class 12 Chemistry scheme showing RMgX reacting with CO2 to give RCOOMgX and then RCOOH after hydrolysis.

Steps:

  1. RMgX + CO2 → RCOOMgX
  2. RCOOMgX + H3O+ → RCOOH + Mg2+ + X

For Example: CH3MgBr + CO2 → CH3COOH (after hydrolysis)

From Acyl Halides and Acid Anhydrides

Both acyl halides and acid anhydrides undergo hydrolysis to form carboxylic acids.

From Esters

Esters undergo hydrolysis in acidic or basic conditions to form the corresponding carboxylic acid and an alcohol.

NCERT Class 12 Chemistry diagram showing acid-catalysed hydrolysis of an ester to a carboxylic acid and alcohol.

Summary