Experiment 8:

1
Experiment 8

• BROMINATION OF STILBENE
• A GREEN SYNTHESIS

2
Objectives

• To perform a Green Chemistry synthesis and
  determine chemical yield.
• To purify and isolate the product by
  recrystallization and vacuum filtration.
• To determine the degree of product purity using
  TLC analysis.

3
Introduction to Green Chemistry

• Green Chemistry the design of chemical products
  and processes that reduce or eliminate the use
  and generation of hazardous substances.
• A PERFECT chemical reaction would be one that
  is
• Selective forming the desired product ONLY.
• Efficient converting all atoms of starting
  materials and reagents to product.
• Non-hazardous is safer to the chemist and the
  environment.

4
Bromination Reactions

• A typical bromination reaction is carried out
  using chlorinated solvents and elemental bromine,
  both of which are hazardous to the environment.
• Refer to McMurray text pages 208-210.

5
Bromination Reactions

• Todays synthesis is performed by generating the
  Br2 in situ, by the oxidation of aqueous HBr
  with H2O2, using ethanol as the solvent, which is
  a much more environmentally safe chemical than
  any chlorinated solvent.
• The mechanism for this reaction is shown below.

6
Experimental Procedure(Synthesis)
7
Experimental Procedure(Product Isolation)
8
Safety Concerns.

• Goggles are required at all times during the lab!
• 30 Hydrogen peroxide is a very strong oxidizer
  and will burn your skin if you get any on
  yourself. One person per group should handle the
  H2O2 using gloves

9
Waste Management

• Place filtrate from recrystallization in
  container labeled, Organic Waste (Stilbene).
• Place solid product in container labeled,
  Dibromostilbene, student prep.
• Place TLC solvent in beaker labeled, TLC solvent
  waste.
• Place used TLC capillaries in broken glass
  container.