If you’re drinking it, alcohol is alcohol right? But alcohols can in fact be categorised as primary, secondary and tertiary depending on the number of carbon atoms.
And this classification is very important as each type of alcohol holds different properties.
These different behaviours can be see when alcohol is oxidised. The alcohols are oxidised by strong oxidising agents. Commonly potassium dichromate in the presence of dilute acid is the reagent of choice.
It is also useful because on oxidation it gives a colour change from orange to green which is helpful in being able to monitor the reaction process.
Primary alcohols will get turned inco aldehydes, secondary alcohols into ketones and tertiary alcohols are not oxidised.
When a primary alcohol is partially oxidised it produces organic acid and aldehyde.
It can be difficult to tell the difference between aldehydes and ketones as they have similar physical properties.
Their boiling points are similar, but so are many of the other physical properties of aldehydes and ketones. In both, the dominant intermolecular force is a dipole-dipole interaction from C=O, and they are of the same size.
We can test for the presence of aldehydes using Tollens reagent. If aldehydes are present the colourless solution produces a grey precipitate of silver, or a silver mirror on the test tube. Aldehydes reduce the diamminesilver(I) ion to metallic silver. Because the solution is alkaline, the aldehyde itself is oxidised to a salt of the corresponding carboxylic acid.
If we are wanting to oxidise a primary alcohol all the way to a carboxylic acid then it is important to make sure than the aldehyde does not escape before it is oxidised – this is done using reflux apparatus.
Secondary alcohols have only one hydrogen on the carbon atom that holds the alcohol group. This means that although they can be oxidised to ketones, the oxidation can go no further. Hence, there is no need to use distillation apparatus and the reaction may be carried out using reflux.