Nitriles

Nitriles are organic compounds that contain the cyano group (-C≡N) bonded to an alkyl, alkenyl, or aryl group. The general formula is R-CN, where R represents the carbon-containing substituent. Nitriles are often referred to as cyanides in some contexts, but cyanide more commonly denotes the anion CN−.

Physicochemical properties of nitriles vary with the substituent, but they are typically colorless liquids or solids with moderate polarity. The cyano group imparts polarity and affects boiling points, with many nitriles serving as polar aprotic solvents. Acetonitrile is among the most widely used nitriles in laboratories and industry due to its solvent properties and low nucleophilicity.

Synthesis and sources include several common routes. Nucleophilic substitution of alkyl halides with cyanide salts (R-X + NaCN or KCN) yields R-CN. The Fischer nitrile synthesis converts aldoximes (R-CH=NOH) into nitriles using dehydrating conditions. Dehydration of primary amides (RCONH2 → R-CN) can be accomplished with reagents such as POCl3 or other dehydrating agents. Hydrocyanation of alkenes adds HCN across a double bond to form nitriles. Industrial routes also include ammoxidation of alkanes, such as the production of acrylonitrile from propylene in the presence of ammonia and oxygen.

Uses and significance include major industrial polymers and specialty chemicals. Polyacrylonitrile (PAN) is a key precursor for carbon fibers and synthetic fibers, while nitrile rubber (NBR) combines acrylonitrile and butadiene for oil and fuel resistance. In synthesis, nitriles are versatile intermediates convertible to amines, carboxylic acids, amides, and other functionalities. In laboratories, acetonitrile and related nitriles are common solvents and chromatography solvents.

Safety considerations include toxicity and potential release of hydrogen cyanide under certain conditions; acrylonitrile is particularly hazardous and requires careful handling.