Nitriles
(nitriles of carboxylic acids), RC≡N, organic derivatives of hydrocyanic acid. Their structural isomers are isonitriles.
The first representative of the nitrile series is hydrogen cyanide, HCN (formonitrile). The lower aliphatic nitriles are liquids with an unpleasant odor, and the higher aliphatic nitriles are solid crystalline compounds. The simplest aromatic nitrile is benzonitrile, which is a colorless liquid with a pleasant bitter almond odor. Some properties of nitriles are given in Table 1.
| Table 1. Properties of nitriles | ||
|---|---|---|
| Baling point (° C) | Density at 20°C (g/cm3) | |
| *At 41°C **d1515 | ||
| Acetonitrile, CH3CN.............. | 81.6 | 0.783 |
| Propionitrile, C2H5CN............. | 98 | 0.785 |
| Butyronitrile, C3HH7CN............. | 118 | 0.794 |
| Stearonrtrile, C17H35CN............ | 357 | 0.818* |
| Benzonitrile, C6H5CN............. | 190.7 | 1.0102** |
Nitriles reduce to primary amines, RNH2. Nitriles with unsaturated hydrocarbon residues polymerize readily. For example, polyacrylonitrile fibers are produced by industrial polymerization of acrylonitrile. Formonitrile, or hydrocyanic acid, HCN, is used in the production of acrylonitrile; meth-acrylonitrile is used in the production of water glass.
Under the action of acids and bases, nitriles are hydrolized to carboxylic acids (II):
The reaction may be stopped at the stage of formation of the amide (I). The reverse reaction (splitting-off of water from the amide or the ammonium salt of the carboxylic acid) is one of the main methods for production of nitriles. Another method is the reaction of alkyl halides with potassium cyanide, KCN.