12.23 : 醛和酮氧化成羧酸

Since aldehydes contain an easily abstractable proton, they are more readily oxidized than ketones.

In the case of aldehydes, both weak and strong oxidizing agents can convert them into corresponding carboxylic acids. When the oxidant is chromic acid, a hydrate intermediate is observed.

Aldehydes readily react with atmospheric oxygen. So, stored aldehyde samples undergo autoxidation and often contain traces of acid contaminants.

On the other hand, ketones are more resistant and oxidize only in the presence of strong oxidizing agents at higher temperatures.

For example, nitric acid converts cyclohexanone—via its enol form—to adipic acid, which is used to synthesize polymers.

In functional-group analysis, Tollens reagent—a mild oxidizing agent comprising diaminosilver(I) ions—can selectively oxidize an aldehyde in the presence of other oxidizable groups.

As the aldehyde gets oxidized, silver reduces to its metallic form, which precipitates to give a distinct mirror-like deposit on the surface of the glassware.