Oxidation of alcohols

Oxidising an alcohol forms a C=O bond and removes an O–H and a C–H hydrogen together, so it is also called dehydrogenation.

A primary alcohol is oxidised first to an aldehyde and then to a carboxylic acid. Strong oxidising agents such as acidified potassium permanganate take it straight through to the acid.

To stop at the aldehyde, anhydrous CrO₃ is used. Pyridinium chlorochromate (PCC), a complex of CrO₃ with pyridine and HCl, gives the aldehyde in better yield.

A secondary alcohol is oxidised by chromium trioxide (CrO₃, chromic anhydride) to a ketone, which resists further mild oxidation.

A tertiary alcohol has no hydrogen on the –OH carbon and is not oxidised under these conditions. Under strong conditions such as KMnO₄ with heat, C–C bonds break and a mixture of acids with fewer carbons forms.

Passing alcohol vapour over heated copper at 573 K dehydrogenates primary and secondary alcohols to aldehydes and ketones, while tertiary alcohols are dehydrated to alkenes.

In the body methanol is oxidised to methanal and then to methanoic acid, which can cause blindness and death. Treatment is an intravenous infusion of diluted ethanol, which keeps the enzyme busy so the kidneys can excrete the methanol.