A level Chemistry · Edexcel 9CH0 · Topic 17C
Carboxylic acids
Key points
- Carboxylic acids contain –COOH; they have high boiling points because they form hydrogen-bonded dimers.
- Short-chain acids dissolve in water and are weak acids: they react with metals, bases and carbonates (fizzing with Na₂CO₃ is a test).
- Preparation: oxidise a primary alcohol or aldehyde under reflux with acidified dichromate, or hydrolyse a nitrile with dilute acid.
- Reduction with LiAlH₄ in dry ether gives a primary alcohol.
- With PCl₅ they form acyl chlorides (steamy HCl fumes).
- Esterification: heat with an alcohol and a concentrated sulfuric acid catalyst; the reaction is reversible.
- Name salts as -oate, e.g. sodium ethanoate.
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Carboxylic acids, with the –COOH group, give vinegar, citrus fruit and nettle stings their sharpness. They are weak acids, they have surprisingly high boiling points, and they are the starting point for esters, acyl chlorides and amides.
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