Primary and secondary alcohols are oxidised by common oxidising agents such as potassium manganate(VII), KMnO4, or acidified sodium dichromate(VI), Na2Cr2O7.
If you gently heat a primary alcohol in the presence of an oxidising agent, the hydroxyl group forms a carbonyl group at the end of the molecule – we have made an aldehyde. However, unless you distil off the aldehyde as it is formed it will be oxidised further forming a carboxylic acid functional group. The oxidising agent is itself reduced as signalled by a change in colour.
Secondary alcohols are oxidised to a ketone (the carbonyl group is in the middle of the carbon chain in the molecule) when heated under reflux with an oxidising agent. Heating under reflux for a period of time ensures that the reaction goes to completion. Once again, the oxidising agent is reduced as this is a redox reaction.
Tertiary alcohols are not oxidised as the reaction would involve breaking a C-C bond rather than a C-H bond.
