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Oxidation 1

Chemistry: Cambridge International A Level, topic 3.4.2

Oxidation of Alcohols

There are different kinds of alcohols, and as always in chemistry, they all have slightly different reactions.

Oxidation

Oxidation

  • Each of the kinds of alcohol can be oxidised to different extents.
  • The rule is that you can break carbon-hydrogen bonds, but not a carbon-carbon bond.
  • Primary alcohols can be oxidised twice.
  • Secondary alcohols can be oxidised once.
  • Tertiary alcohols cannot be oxidised.
  • The usual oxidising agent, for all, is acidified potassium dichromate(V).
Primary alcohols

Primary alcohols

  • Two possible oxidation reactions for primary alcohols:
  • They can be oxidised to aldehydes.
  • If you change the experimental conditions, you can also oxidise them to carboxylic acids.
Secondary alcohols

Secondary alcohols

  • One possible oxidation reaction for secondary alcohols:
  • You can oxidise them to a ketone.
    • You cannot oxidise it further without breaking carbon-carbon bonds.
Tertiary alcohols

Tertiary alcohols

  • You can’t oxidise a tertiary alcohol at all!
  • Tertiary alcohols have three carbon groups bonded to the alcohol carbon.
  • The only way to add more oxygen involves breaking carbon-carbon bonds.

Ketones and Aldehydes

Ketones and aldehydes are functional groups that can be produced by the oxidation of alcohols.

Ketones

Ketones

  • When you oxidise a secondary alcohol, the molecule you get is called a ketone.
  • Ketones have a carbon double bonded to an oxygen atom, and two other single carbon-carbon bonds.
  • The simplest ketone, propanone (acetone), is shown here.
Naming ketones

Naming ketones

  • We use the general name:
  • Alkan-X-one:
    • Propanone.
    • Butanone.
    • Pentan-2-one or pentan-3-one.
  • The numbers are used on longer alkanes to show on which carbon the ketone group lies.
Aldehydes

Aldehydes

  • You can oxidise a primary alcohol to an aldehyde.
  • An aldehyde has a carbon-oxygen double bond and at least one carbon-hydrogen bond.
  • The simplest aldehyde, methanal (formaldehyde), is shown here.
Naming aldehydes

Naming aldehydes

  • We use the general name:
  • Alkanal:
    • Propanal.
    • Butanal.
    • Pentanal.
  • Here, there is no need for any numbers as the aldehyde group must lie on one of the end carbons.
Carboxylic acids

Carboxylic acids

  • You can oxidise an aldehyde to a carboxylic acid.
  • You cannot oxidise a ketone to a carboxylic acid.
  • The simplest acid, methanoic acid (formic acid), is shown here.

Test yourself on Oxidation 1

  • How many oxidations can a secondary alcohol undergo?

  • An aldehyde comes from the oxidation of which of the following?

  • What is the molecule CH3CH2CH2COCH3 called?

  • What type of alcohol is oxidised to form an aldehyde?

  • Which of the following can be oxidised to a carboxylic acid?

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