Nitration of Bromobenzene Study Notes

Objectives

• Perform Electrophilic Aromatic Substitution (EAS).
• Analyze product distribution to understand substituent effects.

Nitration Reagents

• Electrophile: $NO_2^+$ (nitronium ion)
• Source:
  • $HNO<em>3 + H</em>2SO_4$ (sulfuric acid protonates nitric acid)
  • Fuming nitric acid for stronger nitration (less water).
• Other sources of $NO_2^+$ include:
  • $NO<em>2^+BF</em>4^-$ in aprotic solvent
  • $CH<em>3COONO</em>2$ (acetyl nitrate).

Reaction Conditions

• Temperature control is critical to suppress dinitration; keep temp below $60^ ext{o}C$.
• Monitor phase separation of reactants and products (bromobenzene and product).

Product Isomers

• Possible products:
  • Ortho,
  • Meta,
  • Para
• Major product expected: Para isomer is more stable.

Experimental Procedure

1. Apparatus Setup:

   • Use a round-bottom flask (RBF) with a condenser.
   • Insert thermometer into solution to monitor temperature closely.

2. Reagent Addition:

   • Add concentrated sulfuric acid to dilute nitric acid (add acid to acid).
   • Control temperature and reaction by adding bromobenzene slowly; swirling enhances mixing.

3. Work Up:

   • Quench reaction by pouring mixture into ice water to precipitate products.
   • Isolate solid products via vacuum filtration.
   • Crystallize in 95% ethanol, filter, and dry.
   • Save mother liquor for TLC analysis.

Purification Processes

• Fractional Crystallization:
  • Initial crystals are mostly para isomers (less soluble).
  • Use TLC for analysis (compare against standards).

Analysis and Waste Disposal

• Analyze final products via melting point, TLC, and NMR.
• Waste categories include:
  • Aqueous acid waste for first filter filtrate
  • Halogenated waste for TLC solutions and remaining mother liquors.

Discussion Questions

• What is the role of sulfuric acid in nitration?
• Discuss reaction success based on product analysis (TLC, melting point).
• Expected outcomes for acetophenone nitration at different temperatures.