Oxidation of Alcohols
Alcohols can be obtained by reduction of other, more oxidized, functions. It is easy to imagine the reverse process, that is, that alcohols can be oxidized relatively easily.
PRIMARY ALCOHOLS
In a primary alcohol, the carbon bearing the OH group has a formal oxidation state of -1, which leaves it several oxidation possibilities.
Many oxidation reagents are inorganic salts, like KMnO4 or K2Cr2O7, only water soluble. Water forms hydrates with aldehydes, making the oxidation process even easier.
It is thus very difficult to stop the alcohol oxidation at the aldehyde stage.
In order to accomplish it, one has to use reagents with at least an organic part, making them soluble in organic solvents and hence avoiding the presence of water.
Pyridinium chlorochromate
PCC
PCC is soluble in organic solvents.
Its reaction with primary alcohols is selective and does stop at the aldehyde.
A plausible mechanism for this reaction is the following:
SECONDARY ALCOHOLS
They can be transformed into ketones, without breaking the molecule, something that can easily happen if reaction conditions are harsh.
A probable mechanism for this reaction can be as follows:
TERTIARY ALCOHOLS
Tertiary alcohols cannot be oxidized without breaking the molecule because they lack a hydrogen that could be eliminated.
In fact, they are pretty resistant to oxidation.
