pyridine(redirected from Pyridinium salt)
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azine(ăz`ēn), C5H5N, colorless, flammable, toxic liquid with a putrid odor. It melts at −42°C; and boils at 115.5°C;. Chemically, it is a heterocyclic aromatic tertiary amine (see under amino groupamino group,
in chemistry, functional group that consists of a nitrogen atom attached by single bonds to hydrogen atoms, alkyl groups, aryl groups, or a combination of these three. An organic compound that contains an amino group is called an amine.
..... Click the link for more information. ). Its molecule resembles that of benzene, one carbon-hydrogen unit in the benzene ring being replaced with a nitrogen molecule. It is miscible with water and with most organic solvents. Its aqueous solution is slightly alkaline. Pyridine is used as a solvent, as a denaturant for alcohol, and as a starting material in the synthesis of other compounds. Compounds that can be derived from pyridine include antihistamines and vitamins. Pyridine is obtained from bone oil or from coal tar by destructive distillation, which decomposes alkaloids that contain it. Alkaloids that contain pyridine include coniine, piperine (the alkaloid in pepper), and nicotine (present in tobacco); free pyridine is present in tobacco smoke.
a heterocyclic compound. Colorless liquid with a characteristic odor. Melting point, — 41.6°C; boiling point, 115.3°C; density, 0.9832 g/cm3 (at 20°C). The structural formula
Pyridine is a weak base that is miscible in all proportions with water and most organic solvents. It forms salts with acids as well as with alkyl halides (RX); the alkyl halide salts are called N-alkyl pyridinium salts and have the general formula C5H5N-RX. Pyridine also forms complexes with FeCl2, S02, S03, Br2, and H20. It is oxidized by peracids (RCOOOH)to give N-oxides.
Pyridine exhibits the properties of an aromatic compound, although—unlike benzene—it does not undergo electrophilic substitution readily: it is nitrated, sulfonated, and brominated only at about 300°C, primarily with the resultant formation of ss-derivatives. Nucleophilic substitution occurs more easily with pyridine than with benzene. For example, pyridine reacts with NaNH2 to give α-aminopyridine and with KOH to give a- hydroxypyridine. Pyridine is reduced by sodium in ethanol or by hydrogen over a nickel catalyst at 120°C to give piperidine. The pyridine ring can be cleaved by, for example, the action of bases on pyridinium salts to form glutaconic dialdehyde (HOCCH=CHCH2COH) or the corresponding glutaconic-dialdehyde derivative. The pyridine nucleus is a structural component of many alkaloids, vitamins, and drugs, including anabasine, nicotine, nicotinic acid, and nikethamide.
Pyridine is toxic, with a maximum permissible vapor concentration in the air of 0.0015 mg/l. Coal tar, which contains about 0.08 percent pyridine, is the major source. A mixture of pyridine and its homologues, the pyridine bases, are extracted with dilute sulfuric acid from the light and medium fractions of the tar oils in coal tar. After neutralization, the desired compounds are separated by distillation.
Pyridine is widely used in industrial organic synthesis as a solvent and in the production of dyes, pesticides, and drugs. Derivatives of pyridine, for example, 2-methyl-5-vinylpyridine, are used in the production of vinylpyridine lattices. Pyridine N-sulfur trioxide (C5H5N -S03) is a mild sulfonating agent.
E. P. LUR’E