PYRIDINE, is a liquid organic base formed during the destructive distillation of a great variety of nitrogenous organic substances such as bone, coal, shale and lignite. It has been detected in crude petroleum and fusel oil, and is also a charac teristic decomposition product of various alkaloids (q.v.) either heated alone or with zinc dust. Pyridine was discovered and isolated in a pure state by T. Anderson (1851) from bone oil, which, together with coal tar, is its chief commercial source, and which is obtained in the preparation of bone black or animal charcoal by distilling bones in a closed retort. For the extraction from coal tar or bone oil, the light oil boiling up to 120° C is taken and the basic constituents are extracted by washing with dilute sulphuric acid and removing the acid layer. The bases, which have dissolved in the acid, are liberated by the addition of excess of caustic soda and separate as a dark oily layer at the surface of the liquid. After drying they are fractionally distilled in order to separate pyridine from its higher homologues which inevitably accompany it when obtained from these sources. Syn thetically pyridine may be prepared by distilling allylethylamine over lead oxide ; by passing acetylene and hydrocyanic acid through a red-hot tube ; by heating pyrrole with sodium methoxide and methylene iodide ; also by heating isoamyl nitrate with phos phoric oxide. These methods are of theoretical interest only. When required very pure, it is made by distilling nicotinic acid with lime.
of forming loose additive compounds on the nitrogen atom that it is a useful "carrier" in the halogenation of various materials. At high temperatures it reacts with sulphuric acid to form a sulphonic acid. As a base it combines with acids to form crystal line salts, such as the hydrochloride, which is very soluble in water. With many inorganic salts such as mercuric, auric and platinic chlorides, it forms double salts or addition compounds, many of which are highly crystalline and sparingly soluble in cold water. Pyridine combines with alkyl iodides to form pyri dinium alkyliodides which are often highly crystalline and have definite melting points. Nascent hydrogen reduces pyridine to piperidine, (see p. 798), whilst hydriodic acid reduces it to n-pentane. Pyridine is a strong base; its aqueous solution turns red litmus blue. It is a tertiary amine possessing a ring structure that is expressed symbolically by the following formulae: 0', and a', the positions a and a', (3 and 0', being equivalent.