Download Oxidation of alcohols

Oxidation of alcohols
Let us look at the basic reaction of an alcohol with a strong oxidising agent.
The oxidising agent can be shown as [O].
The square brackets mean that oxygen is not present as an atom but is supplied
during the reaction.
Two hydrogen atoms are lost from the alcohol molecule, forming a carbonyl group,
C=O.
The organic product can be an aldehyde or a ketone, depending on whether a
primary or a secondary alcohol has been oxidised.
Propan-1-ol is a primary alcohol.
What happens when it is oxidised by acidified potassium dichromate(Vl)?
During the reaction, the orange potassium dichromate(Vl) solution changes to a
green solution that contains chromium(lll) ions.
An aldehyde is formed when a primary alcohol is oxidised. Here, propanal is
formed from propan-1-ol.
Water is also formed in the reaction.
If the primary alcohol is oxidised using distillation apparatus, the aldehyde distils off
and is not oxidised further to a carboxylic acid.
Propan-1-ol is a primary alcohol.
Aldehydes are formed when primary alcohols are oxidised at room temperature or
using distillation.
Something different happens when an excess of oxidising agent is used at high
temperature.
The primary alcohol is oxidised to form an aldehyde, which is oxidised further to
form a carboxylic acid.
Water is also formed in the reaction.
If a primary alcohol is oxidised under reflux with excess oxidising agent, the
aldehyde formed is oxidised to form a carboxylic acid.
Propan-2-ol is a secondary alcohol.
What happens when it is oxidised by acidified potassium dichromate(Vl)?
During the reaction, the orange potassium dichromate(Vl) solution changes to a
green solution that contains chromium(lll) ions.
A ketone is formed when a secondary alcohol is oxidised. Here, propanone is
formed from propan-2-ol.
Water is also formed in the reaction.
Tertiary alcohols, like 2-methylpropan-2-ol, cannot be oxidised by acidified
potassium dichromate(Vl).