Projection Experiment: Oxidation of 1,3,5-Triphenylverdazyl

Demonstration of Microscale Projection Experiments - Chemistry en miniature

Oxidation of 1,3,5-Triphenylverdazyl

Peter Keusch

German version

Chemicals:
10 ^{- 3} M 1,3,5-triphenylverdazyl solution (31 mg, dissolved in 100 mL ethanol 96 %)
bromine water 0.1 %
ethanol 96 %
Sn(II) chloride

Hazards and safety precautions:

Bromine is highly toxic if inhaled, ingested or comes in contact with the skin.

Bromine water is harmful if ingested or inhaled. Prolonged skin contact can cause burns. Eye irritant - lengthy contact will lead to eye damage.
Sn(II) chloride is harmful if swallowed. Eye, skin and respiratory irritant.

Ethanol is highly flammable.

Safety glasses, protective gloves and good ventilation. The preparation of bromine water should be performed under a laboratory fume hood!

Experimental procedure:

Three test tubes are set up as shown in the table below.

Test tube 1 1 mL of triphenylverdazyl solution
Test tube 2 1 mL of triphenylverdazyl solution 1 drop of bromine water
Test tube 3 1 mL of triphenylverdazyl solution, 1 drop of bromine water

Results:

When bromine water is added to T3 and T4, the green solutions turn red violet (Photo 1). A Pasteur pipette contains some SnCl₂ crystals in its narrow end. The crystals are introduced into the solution of T3 by gentle sqeezing of the pipette bulb. After a couple of minutes a decolorization occurs (Photo 2).

Photo 1
Photo 2

Discussion:

· The green triphenylverdazyl (radical) is oxidized by bromine to the violet verdazylium ion (1).

· SnCl₂ reduces verdazylium ion to the colorless "Leucoverdazyl" (2).

Reference:
Demonstration Experiment on Video Oxidation of 1,3,5-Triphenylverdazyls

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