Oxidation of alcohols and aldehydes Flashcards
What can the reaction of alcohols with oxidising agents be used to determine?
to distinguish between primary, secondary, and tertiary alcohols
What is oxidation?
the gain of 1 oxygen atom/the loss of 2 hydrogen atoms
What is the oxidising agent?
the chemical that supplies the oxygen/removes the hydrogen
How do we represent the oxidant?
[O]
What is an example of an oxidising agent?
acidified potassium dichromate (VI)
What happens to a primary alcohol when oxidised?
primary alcohol +[O] —-> aldehyde +[O] —-> carboxylic acid
What happens to a secondary alcohol when oxidised?
secondary alcohol+[O] —-> ketone
What happens to a tertiary alcohol when oxidised?
nothing
What do you always get as a product when an alcohol has undergone oxidation?
a water molecule
What happens to acidified potassium dichromate solution when an alcohol is oxidised?
it goes from orange solution of potassium dichromate (VI) changes to a green solution containing chromium (III) ions
How can we control the oxidation of primary alcohols?
by altering the reaction conditions;
-if a primary alcohol is oxidised using distillation apparatus, any aldehyde formed with distil off immediately from the mixture, as the aldehyde boiling point is lower than the alcohol/carboxylic acid
-if a primary alcohol is oxidised under reflux, the aldehyde formed cannot escape, and is further oxidised to form a carboxylic acid
Why can’t ketones be oxidised further?
they don’t have a hydrogen atom attached to the carbon with the C=O bond
What are the reaction conditions for this oxidation?
K2Cr2O7 + dilute H2SO4 + warm
Why can tertiary alcohols not be oxidised?
they don’t have a hydrogen atom bonded to the carbon carrying the -OH group, and this is usually removed during the oxidation process
