16.5: Oxidation of Aldehydes
- Page ID
- 415632
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- Objective 2
ldehydes and ketones are much alike in many of their reactions, owing to the presence of the carbonyl functional group in both. They differ greatly, however, in one most important type of reaction: oxidation. Aldehydes are readily oxidized to carboxylic acids, whereas ketones resist oxidation.
The aldehydes are, in fact, among the most easily oxidized of organic compounds. They are oxidized by oxygen (O2) in air to carboxylic acids.
\[2RCHO + O_2 \rightarrow 2RCOOH \label{14.10.1} \]
The ease of oxidation helps chemists identify aldehydes. A sufficiently mild oxidizing agent can distinguish aldehydes not only from ketones but also from alcohols. Tollens’ reagent, for example, is an alkaline solution of silver (Ag+) ion complexed with ammonia (NH3), which keeps the Ag+ ion in solution.
\[H_3N—Ag^+—NH_3 \label{14.10.2} \]
When Tollens’ reagent oxidizes an aldehyde, the Ag+ ion is reduced to free silver (Ag).
Deposited on a clean glass surface, the silver produces a mirror (Figure \(\PageIndex{1}\)). Ordinary ketones do not react with Tollens’ reagent.
Although ketones resist oxidation by ordinary laboratory oxidizing agents, they undergo combustion, as do aldehydes.