Carboxylic acids and derivatives
Carboxylic acids and esters
Carboxylic acids (RCOOH) are made by oxidising primary alcohols or aldehydes (reflux with acidified dichromate) or hydrolysing nitriles with acid. They are weak acids: react with metals (H₂), bases (salt + water) and carbonates (CO₂: the test that distinguishes them from phenols and alcohols). LiAlH₄ reduces them to primary alcohols. With alcohols and conc. H₂SO₄ they form esters, named alkyl-first (methyl ethanoate). Ester hydrolysis: acid (reversible, gives acid + alcohol) or alkaline (irreversible, gives carboxylate salt + alcohol: saponification). Esters are used as flavourings, solvents and plasticisers; fats are triesters of glycerol.
≈ 45 minAcyl chlorides and acylation
Acyl chlorides (RCOCl) are made from carboxylic acids with SOCl₂, PCl₅ or PCl₃. The carbonyl carbon is very δ+ (bonded to O and Cl), so they react vigorously at room temperature with nucleophiles by nucleophilic addition–elimination, giving off steamy HCl fumes: water → carboxylic acid; alcohol (or phenol) → ester; ammonia → primary amide; primary amine → N-substituted amide. Acid anhydrides ((RCO)₂O) react the same way but more slowly, releasing RCOOH instead of HCl; ethanoic anhydride is preferred industrially for aspirin (cheaper, safer, less corrosive). Ease of hydrolysis: acyl chloride ≫ alkyl chloride ≫ aryl chloride.
≈ 45 min