Flashcards · 9701 · AS Topic 18

Carboxylic acids and derivatives (AS Level) flashcards

10 cards on AS Topic 18, subtopics 18.1 to 18.2. Pick a subtopic or study them all.

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Three ways to make a carboxylic acid: Oxidise a primary alcohol or aldehyde with acidified K₂Cr₂O₇, heating under reflux; hydrolyse a nitrile (dilute acid, or dilute alkali then acidify); hydrolyse an ester (then acidify).
Reactions of carboxylic acids with metals, alkalis and carbonates: Reactive metal → salt + hydrogen. Alkali or metal oxide → salt + water. Carbonate → salt + water + CO₂ (effervescence), e.g. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
Test that identifies a carboxylic acid: Add a carbonate (e.g. Na₂CO₃): effervescence of CO₂. Alcohols do not do this.
Reducing a carboxylic acid: LiAlH₄ in dry ether gives a primary alcohol: CH₃COOH + 4[H] → CH₃CH₂OH + H₂O. NaBH₄ is not strong enough.
Nitrile hydrolysis and the carbon count: The –C≡N carbon becomes –COOH, so the acid has the same number of carbons as the nitrile (ethanenitrile → ethanoic acid).

Esterification: reagents and conditions: Carboxylic acid + alcohol, concentrated H₂SO₄ catalyst, heat under reflux ⇌ ester + water. It is reversible, so the yield is limited.
Name the ester from ethanol and propanoic acid: Ethyl propanoate: the alcohol part first, then the acid part.
Acid and alkaline hydrolysis of esters: Dilute acid, reflux: carboxylic acid + alcohol, reversible. Dilute NaOH, reflux: carboxylate salt + alcohol, goes to completion.
Why does alkaline hydrolysis of an ester go to completion?: The carboxylate salt formed cannot react with the alcohol, so the reverse reaction cannot happen.
Uses of esters: Volatile with fruity smells: flavourings and perfumes. Also solvents and plasticisers.