How are haloalkanes prepared from (i) alcohols and (ii) alkenes? Write equations, and name the reactions used for halogen exchange.

1. 1 · Open with the idea. Haloalkanes are made by replacing the -OH of alcohols, by adding HX or X₂ to alkenes, or by swapping one halogen for another.
2. 2 · From alcohols.
   • R-OH + HCl (anhydrous ZnCl₂) → R-Cl + H₂O
   • 3R-OH + PBr₃ → 3R-Br + H₃PO₃
   • R-OH + PCl₅ → R-Cl + POCl₃ + HCl
   • R-OH + SOCl₂ → R-Cl + SO₂ + HCl (best method)
3. 3 · From alkenes.
   • CH₃CH=CH₂ + HI → CH₃CHICH₃ (Markovnikov)
   • CH₂=CH₂ + Br₂ (in CCl₄) → BrCH₂CH₂Br
4. 4 · Halogen exchange.
   • Finkelstein: R-Br + NaI (dry acetone) → R-I + NaBr
   • Swarts: CH₃Br + AgF → CH₃F + AgBr
5. 5 · Link to real life. Freon refrigerants are made from CCl₄ by the Swarts reaction.
6. 6 · Close in one line. So the reagent you choose depends on the halogen you want and how pure the product must be.

Scoring tip: Write the condition (ZnCl₂, dry acetone, CCl₄) above the arrow; examiners give part of the mark for it.