🚀 Quick Guide: How to Make Haloalkanes

Haloalkanes (alkyl halides) pop up everywhere—from anesthetics to PVC pipes. Below you’ll find student-friendly tricks to whip them up in the lab, plus NEET-worthy highlights.

1 🎯 From Alcohols (R-OH ➔ R-X)

  • With Concentrated HX
    R-OH + HX \(\xrightarrow[\text{ZnCl}_2]{\text{heat}}\) R-X + H2O
    • ZnCl2 helps primary and secondary alcohols.
    • Tertiary alcohols just shake with HCl—no heat!
    • Reactivity order: 3° > 2° > 1° :contentReference[oaicite:0]{index=0}
  • With Phosphorus Halides
    3 R-OH + PCl3 → 3 R-Cl + H3PO3
    (PBr3 and PI3 form in situ from red P + Br2/I2) :contentReference[oaicite:1]{index=1}
  • With Thionyl Chloride (SOCl2)
    R-OH + SOCl2 → R-Cl + SO2 ↑ + HCl ↑
    • Both by-products are gases, so you collect almost pure R-Cl. 😊 :contentReference[oaicite:2]{index=2}

2 🔥 From Hydrocarbons

2.1 Alkanes → Haloalkanes (Free-Radical Steps)

  • Cl2 or Br2 + light/heat breaks into radicals.
  • You get a messy mix of mono- and poly-halogen products—separating them is tough. :contentReference[oaicite:3]{index=3}

2.2&nbsp>Alkenes → Haloalkanes

  • Add HX (Markovnikov rule)
    Propene + HBr gives mostly 2-bromopropane.
    \( \mathrm{CH_3CH\!=\!CH_2 + HBr \rightarrow CH_3CHBrCH_3} \) :contentReference[oaicite:4]{index=4}
  • Add X2 (Br2/Cl2)
    Bromine in CCl4 loses its brown color—hello, vic-dibromide! 🧪 :contentReference[oaicite:5]{index=5}

3 🔄 Halogen Exchange

  • Finkelstein Reaction
    R-Cl (or R-Br) + NaI (dry acetone) → R-I + NaCl↓ (or NaBr↓)
    • Precipitated salt drives the reaction forward. :contentReference[oaicite:6]{index=6}
  • Swarts Reaction
    R-Cl (or R-Br) + AgF → R-F + AgCl↓
    • CoF2, SbF3, Hg2F2 also work. :contentReference[oaicite:7]{index=7}

🌟 High-Yield NEET Nuggets

  1. Thionyl chloride makes pure R-Cl because SO2 and HCl escape as gases. :contentReference[oaicite:8]{index=8}
  2. Order of alcohol reactivity with HX: 3° > 2° > 1°. :contentReference[oaicite:9]{index=9}
  3. Markovnikov addition decides the major haloalkane from alkenes. :contentReference[oaicite:10]{index=10}
  4. Finkelstein swaps Cl/Br for I using NaI in dry acetone—watch the precipitate. :contentReference[oaicite:11]{index=11}
  5. Swarts is your go-to for R-F; AgF (or similar) pulls it off smoothly. :contentReference[oaicite:12]{index=12}

Keep practicing mechanisms, and you’ll ace those haloalkane questions! 💪