Oxidation of Alcohols

Primary and secondary alcohols (only) are able to undergo oxidation. The most common oxidants for alcohols are:

1. Acidified potassium permanganate (H⁺/MnO₄^-)
2. Acidified potassium dichromate (H⁺/Cr₂O₇^2-)

In both primary and secondary alcohols, the observations for each oxidant are the same, but the organic products are different. There is no reaction with tertiary alcohols.

OBSERVATIONS

Permanganate: the purple colour disappears (it is reduced to Mn²⁺ ions)

Dichromate: when heated, the orange colour becomes green/blue (it is reduced to Cr³⁺ ions)

ORGANIC PRODUCTS

Primary Alcohol

In both cases, a primary alcohol is first oxidised to an aldehyde:

If we wanted to stop the reaction at this point (because we want the aldehyde but not the carboxylic acid, we would use apparatus called distillation. This works because the aldehyde has a lower boiling point than any of the reactants, so distills away when it is produced:

SOURCE: https://www.123rf.com/visual/search/80631818

The aldehyde is then further oxidised to a carboxylic acid:

Reflux is used to ensure that all reagents fully react. The boiling point of the carboxylic acid is too high for it to escape out the top of the condenser: