What is combustion?
Write a definition
Write an equation of combustion for
the following alcohols:
• Ethanol
• Methanol
• Propanol
• Combustion – The process of burning
by reacting a fuel with oxygen
• C2H5OH (l) + 3O2 (g)2CO2 (g) + 3H2O (l)
• CH3OH (l) + 1½O2 (g)CO2 (g) + 2H2O (l)
• C3H7OH (l) + 4½O2 (g)3CO2 (g) + 4H2O (l)
Oxidation of Alcohols
Oxidation of Alcohols
• Primary and secondary alcohols can be
oxidised using an oxidising agent.
• Suitable oxidising agent is a solution
containing acidified dichromate ions
H+ /Cr2O72• During the reaction, the acidified potassium
dichromate changes colour from orange to
green.
• Alcohols fall into different classes depending on
how the -OH group is positioned on the chain of
carbon atoms
• In a primary (1°) alcohol, the carbon which carries
the -OH group is only attached to one alkyl group.
• In a secondary (2°) alcohol, the carbon with the OH group attached is joined directly to two alkyl
groups
Primary Alcohols
• On gentle heating with potassium dichromate a primary
alcohol can be oxidised to produce an aldehyde.
On stronger heating in excess acidified dichromate alcohol will pass
through aldehyde stage to form carboxylic acid.
• Reflux – the continual boiling and condensing
of a reaction mixture to ensure that the
reaction takes place without the contents of
the flask boiling dry.
Secondary and Tertiary Alcohols
• Oxidised by dichromate ions to produce
ketones.
Ketones can’t be oxidised any further
• Tertiary alcohols are resistant to oxidation so
don’t react.