Hydrolysis of Nitriles to Carboxylic Acids

A nitrile can also be converted into a carboxylic acid by hydrolysis, a reaction in which water breaks bonds in the molecule.OCR's conditions are to heat the nitrile with dilute aqueous acid, for example dilute hydrochloric acid, HCl(aq). The C≡N group becomes a −COOH group and the nitrogen is released as an ammonium ion:R−CN + 2H₂O + H⁺ → R−COOH + NH₄⁺With hydrochloric acid, the ammonium ion ends up as ammonium chloride, NH₄Cl:R−CN + 2H₂O + HCl → R−COOH + NH₄ClWorked example: ethanenitrile is heated with dilute HCl(aq).CH₃CN + 2H₂O + HCl → CH₃COOH + NH₄ClThe product is ethanoic acid. As in reduction, the carbon atom of the nitrile group is kept, and it becomes the carbon of the carboxyl group. So the acid has the same number of carbon atoms as the nitrile.This gives a two-step route from a haloalkane to a carboxylic acid with one more carbon atom: iodomethane → ethanenitrile (KCN in ethanol) → ethanoic acid (dilute acid, heat). Note that 2 moles of water are needed per mole of nitrile, because both the C=O and the O−H oxygen atoms come from water.