A level Chemistry · Edexcel 9CH0 · Topic 17D
Carboxylic acid derivatives
Key points
- Acyl chlorides (–COCl) are very reactive because the carbonyl carbon is strongly δ+.
- They react by addition–elimination: with water → carboxylic acid + HCl; with alcohols → ester; with ammonia → primary amide; with amines → N-substituted amide. All release steamy HCl fumes.
- Esters are sweet-smelling and used in flavourings and perfumes.
- Acid hydrolysis of an ester is reversible (gives acid + alcohol); alkaline hydrolysis (saponification) goes to completion, giving a carboxylate salt + alcohol.
- Polyesters form by condensation between a diol and a dicarboxylic acid (or diacyl chloride), losing water (or HCl) at each link; they can be hydrolysed, so are more biodegradable than addition polymers.
- Draw the repeat unit with the ester link –COO– and trailing bonds.
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Acyl chlorides and esters are made from carboxylic acids by replacing the –OH. Acyl chlorides are highly reactive and are used to make esters and amides quickly and completely; esters are pleasant-smelling compounds used in flavourings…
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