ICSE Class 10 Answered

There are several methods for preparing carboxylic acids.

(i) From alcohols: Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate (KMnO4) in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7) and chromium trioxide (CrO3) in acidic media.

 (ii) From aldehydes: Oxidation of aldehydes in presence of mild oxidizing agents like Tollen’s reagent (ammoniacal solution of AgNO3) or Fehling reagent (Fehling solution A (aqueous solution of CuSO4) + Fehling solution B (aqueous solution of sodium potassium tartarate)) forms carboxylic acids 

(iii) From alkylbenzenes: Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate. 

From alkenes: Suitably substituted alkenes are oxidised to carboxylic acids on oxidation with acidic potassium permanganate or acidic potassium dichromate

From Nitriles: Nitriles on hydrolysis in presence of dilute acids or bases forms amide which on further hydrolysis gives carboxylic acid. 

(vi) From Grignard reagent: Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which on hydrolysis forms carboxylic acids.

 (vii) From acyl halides and anhydrides: Acid chlorides when hydrolysed  with water give carboxylic acids .On basic hydrolysis  carboxylate ions are formed which on further acidification forms corresponding carboxylic acids. Anhydrides on hydrolysis forms corresponding acid(s) 

 (viii) From esters: Acidic hydrolysis of esters gives directly carboxylic acids while basic hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids.