Aldehydes and Ketones

Production

Aldehydes are produced by oxidising a primary alcohol, using distillation. Distillation removes the aldehyde before it can further oxidise to become a carboxylic acid.

This was covered in an earlier post, about the oxidation of alcohols.

Reactions

Aldehydes can be further oxidised to carboxylic acids.

Both aldehydes and ketones can be reduced back to their respective alcohols by NaBH₄.

Nomenclature

ALDEHYDES

The aldehyde functional group is always on the terminal carbon. That means we number the carbon with the C=O bond as "1". We then number all other side chains and functional groups from this carbon:

KETONES

Once we have five (or more) carbons, we need to identify which carbon the C=O functional group is on. In Level 3, the ketone will be the "main" functional group is anything you need to name, so you give it the lowest number possible:

Beyond high school, we use the "oxo-" prefix, whenever a ketone (or aldehyde) is in a compound containing any of these: carboxylic acid, acid chloride, ester, or amide.

Testing - Aldehyde or Ketone?

If you know a compound is either an aldehyde or a ketone, there is an experiment we can do to confirm which it is. This uses Tollens' Reagent. Silver diammine ions can be reduced to silver metal. It is sometimes called the "silver mirror test". It only works for aldehydes, not for ketones.

Start the video at 2:20 if you want to skip how they make the Tollens' Reagent: