Write equations, with reagents and conditions, for: (i) the Hell-Volhard-Zelinsky reaction (ii) decarboxylation (iii) Kolbe electrolysis (iv) esterification (v) the reaction with thionyl chloride.

1. 1 · HVZ reaction. CH₃COOH → (i) Cl₂, red phosphorus (ii) H₂O → ClCH₂COOH; the α-hydrogen is replaced.
2. 2 · Decarboxylation. CH₃COONa + NaOH → (CaO, heat) CH₄ + Na₂CO₃; soda lime; one carbon fewer.
3. 3 · Kolbe electrolysis. 2CH₃COONa + 2H₂O → (electrolysis) CH₃CH₃ + 2CO₂ + H₂ + 2NaOH.
4. 4 · Esterification. CH₃COOH + C₂H₅OH ⇌ (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O; reversible, so water is removed.
5. 5 · Thionyl chloride. RCOOH + SOCl₂ → RCOCl + SO₂ + HCl; gaseous by-products escape.
6. 6 · Link to real life. Esters made this way give the fruity smells used in perfumes and flavours.
7. 7 · Close in one line. So the same -COOH group can be halogenated, removed, doubled up or turned into derivatives.

Scoring tip: Name each reaction before you write it, and write the catalyst or condition (red P, CaO, electrolysis, conc. H₂SO₄) on the arrow.