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Demonstration Experiment on Video

Oxidation of the Butanol Isomers

Objective: Distinction between primary, secondary and tertiary Alcohol

Peter Keusch




German version




Chemicals:
1-butanol  (d = 0.8098)
2-butanol  (d = 0.8080)
Tert-butanol  (d = 0.7887)
potassium dichromate
conc. sulfuric acid

Test reagent:  0.99 g K2Cr2O7 in 1000 mL of dist. water + 300 mL of conc. H2SO4

Apparatus and glass wares:
hot plate
thermometer
3 conical measures, graduated, 500 mL
beaker 1500 mL
measuring cylinder 100 mL
3 snap-cap vials 20 mL
3 glass stirring rods


Hazards and safety precautions:

Potassium dichromate: Hexavalent chromium compounds are generally more toxic than trivalent chromium compounds. May be fatal if absorbed through the skin, if swallowed or inhaled. Contains chromium (VI), a known cancer hazard. Allergen. Skin eye and respiratory irritant. May act as a sensitizer.
Tert-butanol is harmful if inhaled. Skin and respiratory irritant. Severe eye irritant.
Conc. sulfuric acid is highly toxic. Causes severe burns. May be fatal if swallowed. May cause cancer through inhalation. Very destructive of mucous membranes.

Safety goggles and protective gloves must be worn. The experiment should be performed under a portable fume cupboard giving all-round visibility!


Experimental procedure:

Three conical measures are each filled with 400 ml of acidic dichromate solution heated to 40°C.

9.682 g of tert. butanol is added to the third conical measure. Afterwards 1-butanol (9.946 g) and 2-butanol (9.924 g), respectively, is added simultaneously to the conical measures 1 or 2, respectively.


Results:

The orange color of the dichromate solution in the samples, treated with primary and secondary butanol, respectively, turns green and finally green-blue. The orange color of the solution in conical measure 3 remains unchanged.




Video clip (Download RealPlayer .rm file)



Alternative:   Microscale Projection Experiment
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Discussion:

The most important reaction of alcohols is their oxidation to carbonyl compounds. Primary alcohols yield either aldehydes or carboxylic acids, depending on the conditions used. Secondary alcohols yield ketones - and tertiary alcohols do not react under the usual oxidizing conditions.

·   Under the given reaction conditions tert-butanol proves to be stable.

·   Primary and secondary butanol reduce orange Cr2O7 2- ions to Cr (aq) 3+ ions, which appear green-blue.



equations



Waste disposal:  Also the dichromate solution in conical measure 3 is to be reduced to Cr 3+. The Cr 3+-solution is mixed with ammonium chloride. The precipitate - Cr(OH)3 - is mixed with ammonia. Either filter or let stand for a week to let the precipitate settle out. The supernatent liquid can be washed down the drain with 50 times its volume of water. The precipitate should be washed with hot water, dried, packaged and labelled, and then taken to a toxic waste disposal.


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