Pyridine

Description

Pyridine is a solvent for many organic compounds and anhydrous metallic salts chemicals. Contained in Karl Fischer reagent, it induced contact dermatitis in a laboratory technician.

Description

Pyridine is a colorless liquid with a foul odor and several hazardous properties. In the late 1840s, physician/chemist Thomas Anderson at the University of Edinburgh produced several liquids by heating animal bones to high temperatures. One of these turned out to be pyridine, which he named after the Greek word pyr (fire).
About 20 years later, chemists Wilhelm (aka Guglielmo) K?rner at the University of Milan (Italy) and James Dewar at the University of Cambridge (UK), working separately, elucidated the structure of pyridine. The two chemists were friends, but they disagreed about which of them was the first to conceive of the structure. An interesting account of this episode is given by Alan J. Rocke at Case Western Reserve University (Cleveland) in a 1988 article.
In 1881, German chemist Arthur Rudolf Hantzsch at the University of Leipzig (Germany) developed a cumbersome, low-yielding synthesis of pyridine. Later, in 1924, Russian chemist Aleksei Chichibabin came up with an improved method, which is still in use today: a reaction between formaldehyde, acetaldehyde, and ammonia over a transition-metal fluoride catalyst to give dihydropyridine, followed by high-temperature catalytic oxidation to pyridine. Several other methods are also used, including the oxidative dealkylation of alkylpyridines.
Pyridine’s structure is isoelectronic with that of benzene, but its properties are quite different. Pyridine is completely miscible with water, whereas benzene is only slightly soluble. Like all hydrocarbons, benzene is neutral (in the acid–base sense), but because of its nitrogen atom, pyridine is a weak base.
In industry and in the lab, pyridine is used as a reaction solvent, particularly when its basicity is useful, and as a starting material for synthesizing some herbicides, fungicides, and antiseptics. Current worldwide pyridine production is ≈20,000 t/year, valued at about US$600 million.

The Uses of Pyridine

Pyridine is used directly in the denaturation of alcohol (ACGIH 1986; HSDB 1989; NSC 1978) and as a solvent in paint and rubber preparation (ACGIH 1986; HSDB 1989; NSC 1978) and in research laboratories for functions such as extracting plant hormones (Santodonato et al. 1985). Half of the pyridine produced today is used as an intermediate in making various insecticides and herbicides for agricultural applications (ACGIH 1986; Harper et al. 1985; Santodonato et al. 1985). Approximately 20% goes into the production of piperidine (Harper et al. 1985; Santodonato et al. 1985) which is commercially significant in the preparation of chemicals used in rubber vulcanization and agriculture (NSC 1978). Pyridine is also used as an intermediate in the preparation of drugs (antihistamines, steroids, sulfa-type and other antibacterial agents) dyes, water repellents, and polycarbonate resins (ACGIH 1986; Harper et al. 1985; NSC 1978; Santodonato et al. 1985). Pyridine is also approved by the Food and Drug Administration (FDA) for use as a flavoring agent in the preparation of foods (Harper et al. 1985; HSDB 1989) .