Oxidation of organic compounds with chromic acid

Chemicals necessary

acetone  F   R 11    S (2)-9-16-23-33

distilled water

ethanol  F    R 11    S (2)-7-16

or denatured alcohol

propanal  F Xi   R 11-36/37/38     S (2)-9-16-29

sulphuric acid potassium dichromate solution T+ C   N    R 21-25-26-35-37/38-41-43-46-49-50/53    S (1/2)-26-45-53-60-61

Other alcohols, aldehyes and ketones can be used. Diluted chromosulphuric acid can also be used.

Equipment necessary

3 test tubes
test tube rack
burner (if possible alcohol-)

Test procedure

• Safety goggles. Due to offensive smells, perhaps ventilation.
• Respectively add a couple of drops of alcohol, propanal or acetone into the test tubes.
• Add 1 ml of water to each.
• Add 2-3 drops of sulphuric acid potassium dichromate solution to each. The solutions all become yellow.
• Heat each with the burner until a noticeable vaporization occurs (in the case of acetone and propanal clearly before the boiling point!).
• The alcohol- and the aldehyde solutions have become green, the acetone solution remains yellow.

Disposal

All solutions are disposed of as heavy metal waste.

Elucidation

The yellow/orange Cr(VI) is in a acidic solution (in the form of chromic acid), especially when warm, a strong oxidant and is reduced to a green Cr(III). Similiarly alcohol and aldehyde are oxidized to carboxylic acid respectively. In the case of aceton a comparable transformation is not possible.

Photos

Ethanol (left) und propanal (middle) reduced Cr(VI), acetone (right) not.

Literature

Own procedure modelled after a school experiment.