🚀 Preparation of Haloarenes – quick, clear, and fun!

1. Swarts reaction 🔄 (quick route to fluoro-arenes)

Pop in a metal fluoride such as AgF, Hg2F2, CoF2, or SbF3. The fluoride ion kicks out the older halogen and you form an aryl fluoride – neat and tidy! :contentReference[oaicite:0]{index=0}

Example (written in KaTeX/MathJax): \( \ce{C6H5Br + AgF -> C6H5F + AgBr} \)

2. Electrophilic substitution of arenes ⚡

  • Simply let chlorine or bromine react with an arene in the presence of a Lewis-acid buddy such as Fe or FeCl3. \( \ce{C6H6 + Cl2 ->[FeCl3] C6H5Cl + HCl} \) :contentReference[oaicite:1]{index=1}
  • Chlorine and bromine give ortho- and para-products. Their melting points differ a lot, so separating them is easy 👍 :contentReference[oaicite:2]{index=2}
  • Iodination needs an oxidising pal (HNO3 or HIO4) to mop up the HI that forms: \( \ce{C6H6 + I2 ->[HNO3] C6H5I + HI} \) :contentReference[oaicite:3]{index=3}
  • Fluorine gas reacts too wildly, so we skip direct fluorination here 💥 :contentReference[oaicite:4]{index=4}

3. Diazonium route 🎩 (Sandmeyer & friends)

Start with a primary aromatic amine. Chill it in mineral acid, add NaNO2, and you get a diazonium salt. Now swap the –N2+ group for a halogen:

Sandmeyer reaction 🔧

  • For Cl or Br, stir the fresh diazonium solution with CuCl or CuBr: \( \ce{C6H5N2+ Cl- ->[CuCl] C6H5Cl + N2} \) \( \ce{C6H5N2+ Br- ->[CuBr] C6H5Br + N2} \) :contentReference[oaicite:5]{index=5}

Iodination shortcut ⚡

  • No copper needed! Just shake the diazonium salt with KI: \( \ce{C6H5N2+ Cl- + KI -> C6H5I + KCl + N2} \) :contentReference[oaicite:6]{index=6}

💡 Important NEET nuggets

  1. Lewis-acid magic: Remember Fe/FeCl3 catalyses Cl2 or Br2 electrophilic substitution on benzene. :contentReference[oaicite:7]{index=7}
  2. Regioselectivity matters: Ortho vs para products separate easily because of their distinct melting points. :contentReference[oaicite:8]{index=8}
  3. Sandmeyer = halogen swapper: CuCl/CuBr replace diazonium – handy one-step route to aryl chlorides/bromides. :contentReference[oaicite:9]{index=9}
  4. HI issue in iodination: Always add an oxidiser (HNO3/HIO4) so HI doesn’t reverse the reaction. :contentReference[oaicite:10]{index=10}
  5. Fluorine caution: Direct fluorination is too violent; use Swarts reaction instead. :contentReference[oaicite:11]{index=11}

You’ve got this! Practice the equations, visualise the steps, and ace those haloarene questions 😎