Alcohols

• You can test whether you have a primary, secondary or tertiary alcohol.

  Primary alcohols - carbons attached to one other carbon and a functional group.

  Secondary alcohols - attached to two other carbons and a functional group.

  Tertiary alcohols - attached to three other carbons and a functional group.
• Method:

  1. Add 10 drops of the alcohol to 2cm3 of acidified potassium dichromate solution in a test tube.
  2. Warm the mixture gently in a hot water bath.
  3. Watch for a colour change.
• Results:

  • Primary - orange solution turns green as an aldehyde forms
  • If you carry on heating, the aldehyde will be oxidised further to give a carboxylic acid.
  • Secondary - orange solution turns green as a ketone forms.
  • Tertiary - no change.
• To test between primary (-> aldehyde) and secondary (-> ketone):

  1. Add excess alcohol to 2cm3 of acidified potassium dichromate solution in a round bottomed flask.
  2. Set up the flask as part of distillation apparatus.
  3. Gently heat the flask. The alcohol will be oxidised and the product will be distilled off immediately so you can collect it.
  4. Then carry out the aldehyde or ketone test with the products.