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Oxidation of Aldehydes to Carboxylic Acids

Oxidation of Aldehydes to Carboxylic Acids: Introduction

Starting materials

  • Aldehyde
  • Oxidizing agent in aqueous acidic solution

Reaction principle

Initially, water is added to the carbon atom of the carbonyl group in the presence of an acidic catalyst to form a hydrate which is subsequently oxidized to the carboxylic acid.

Fig.1

The red numbers in the equation represent oxidation numbers which clearly show that carbon is oxidized from +I to +III and chromium is reduced from +VI to +IV. However, the chromium(IV) compound is very unstable and reacts immediately with the solvent.

Application

This is a very common method to prepare aromatic carboxylic acids. In most cases, the oxidation of aldehydes is the second step in the preparation of carboxylic acids from primary alcohols:

Fig.2

Biological importance

In the human body, alcohol dehydrogenase (ADH) metabolizes primary alcohols to aldehydes. This is followed by a consecutive oxidation to acetate. Aldehyde poisoning takes place in some people if the corresponding enzymes required for the oxidation to acetates are missing.

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