Topic 24 of 34
Choose between acid-base reaction and changing the acyl group
Salt formation leaves the carbon skeleton intact; reduction and substitution transform the functional group.
A-Level 9476 (2026-2027)
Choose between acid-base reaction and changing the acyl group
Salt formation leaves the carbon skeleton intact; reduction and substitution transform the functional group.
| Transformation | Reagents/conditions | Representative equation |
|---|---|---|
| Salt with reactive metal | Suitable metal such as sodium or magnesium. | 2CH3COOH + Mg → (CH3COO)2Mg + H2. |
| Salt with alkali | Aqueous hydroxide. | CH3COOH + OH- → CH3COO- + H2O. |
| Salt with carbonate | Aqueous carbonate; effervescence. | 2CH3COOH + CO32- → 2CH3COO- + CO2 + H2O. |
| Ester | Alcohol, concentrated H2SO4 catalyst, heat. | CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O. |
| Acyl chloride | PCl5. | CH3COOH + PCl5 → CH3COCl + POCl3 + HCl. |
| Primary alcohol | LiAlH4 in dry ether, followed by aqueous work-up. | CH3COOH + 4[H] → CH3CH2OH + H2O. |
Carboxylic acids usually release CO2 with hydrogencarbonate or carbonate, unlike phenol under the ordinary test conditions. The acid-base products of benzoic acid follow the same pattern as ethanoic acid. In esterification, the acid-derived part keeps its carbonyl and the alcohol contributes the group attached through oxygen.
For a reversible esterification, using one reactant in excess or removing a product can improve equilibrium yield. Concentrated sulfuric acid catalyses the reaction; changing catalyst amount alone does not change the equilibrium constant at fixed temperature. Reflux supports heating, while subsequent separation, washing, drying and distillation may be selected according to the product's solubility and volatility.