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Photochemical Reaction with Bromine

Hazards

  • Bromine is corrosive and toxic.
  • Dichloromethane is a carcinogen and affects the nervous system when inhaled.
  • Toluene is flammable and toxic.

Materials

  • Two vials of toluene (about 10 ml each)
  • 5% bromine in DCM solution
  • Plastic eyedropper

Procedure

  1. Add a few drops of the bromine solution rapidly to each of the vials of toluene. Show the class the orange solution produced.
  2. Place one of the vials on the overhead projector and watch this solution decolorize rapidly. The vial not placed on the overhead will decolorize much more slowly.

This demo can be scaled up to be done in small hydrometer cylinders. Students will be able to see the the bromine fading out starting from the bottom and moving up the cylinder.

Discussion

The halogenation reaction is a substitution reaction that takes place by a free radical mechanism.

a diagram of the reaction: toluene and bromine yielding Ch2Br

\$\ce{CH3Ph + Br2 ->[{hν}]  CH2BrPh}\$

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