Replacement of nitrogen by carboxyl-oxygen

Since nitriles are usually conveniently accessible their conversion into carboxylic acids is important for aliphatic, aromatic hydrocarbon and heterocyclic chemistry. Hydrolysis of the nitrile group requires energetic conditions, such as treatment with strong acid or alkali. The individual case will decide whether acid or alkali is used. Where possible, acid hydrolysis is preferable, especially by concentrated hydrochloric acid, and, to increase the solubility of the nitrile, this is often carried out in presence of acetic acid. For the same reason alkaline hydrolysis is effected in presence of alcohol or pyridine, sometimes under pressure. Primary cyanides are hydrolysed more easily than secondary or tertiary ones, and aliphatic more easily than aromatic. The last traces of the nitrile and of the amide formed as intermediate are not always easy to remove. In some cases hydrolysis is stopped at the amide stage and completed by a different process, e.g., by means of nitrous acid (see page 345).621 

For conversion of aliphatic dinitriles into dicarboxylic acids it is best to use concentrated hydrochloric acid, e.g., for the preparation of glutaric acid from the dinitrile.622 Aromatic nitriles such as a-tolunitrile are hydrolysed by ca. 75% sulfuric acid. 

Nitriles that are hard to hydrolyse, such as a/T/za-disubstituted benzonitriles, are effectively converted into carboxylic acids in 100% phosphoric acid,624 although polyphosphoric acid converts simpler aromatic and aliphatic nitriles only to the amide stage, giving these in good yield in 1 hour at 110°.625 

Dilute sulfuric acid is used for hydrolysis of phenylacetonitrile (benzyl cyanide) to phenylacetic acid 626 

The nitrile (700 g), concentrated sulfuric acid (840 ml), and water (1150 ml) are heated, with stirring, for 3 h. The yield is 77.5 % (630 g) of phenylacetic acid. 

---