Replacement of oxygen in carboxyl or alkoxycarbonyl groups

Carboxylic acids and their esters are converted into the corresponding alcohols by reduction of their carbonyl group to a methylene group, and three methods are available for this purpose, namely  

The reduction of carboxylic esters by sodium and alcohol, discovered by Bouveault and Blanc in 1903, is carried out under very drastic conditions.519 The usual procedure is to drop one mole of the ester in absolute alcohol directly on to six gram-atoms of sodium lumps and then to heat the mixture until all the sodium is dissolved, this requiring several hours under reflux. The whole is treated with water and worked up for the alcohol produced. 

Use of absolute alcohol is essential since otherwise substantial amounts of acid are formed by hydrolysis. Ethanol is generally used, but sometimes 1-butanol since this permits a higher reaction temperature. 

The yields can be increased by adding substances such as C02 and NH4C1 that destroy the alkoxide formed and by maintaining specific conditions.520 

Reduction proceeds smoothly with fatty acid esters, but not with aromatic esters whose carboxylic ester group is attached directly to a benzene ring., / -Unsaturated esters give the related saturated alcohols, but double bonds that are not conjugated to the alkoxycarbonyl group are, in general, not reduced by this method. 

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