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PYRIDINE

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Originally appearing in Volume V22, Page 690 of the 1911 Encyclopedia Britannica.
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PYRIDINE , C51-15N, an organic See also:

base, discovered by T. See also:Anderson (Trans. See also:Roy. See also:Soc. Edin., 1851, 20, p. 251) in See also:bone oil. It is also found among the See also:distillation products of bituminous See also:coal, See also:lignite, and various shales, and has been detected in fusel oil and crude See also:petroleum. It is a decomposition product of various alkaloids (See also:nicotine, sparteine, cinchonine, &c.), being formed when they are strongly heated either alone or with See also:zinc dust. It may be synthetically prepared by distilling allyl ethylamine over heated See also:lead See also:oxide (W. Konigs, Ber., 1879, 12, p. 2341) by passing a mixture of See also:acetylene and hydrocyanic See also:acid through a red-hot See also:tube (W. See also:Ramsay, Ber., 1877, 10, p.

736); by See also:

heating See also:pyrrol with See also:sodium methylate and methylene iodide to 2o0° C. (M. Dennstedt and J. See also:Zimmermann, Ber., 1885, 18, p. 3316); by heating isoamyl nitrate with See also:phosphorus pentoxide (E. T. See also:Chapman and M. H. See also:Smith, See also:Ann., 1868, Sup p1. 6, p. 329); and by heating piperidine in acetic acid See also:solution with See also:silver acetate (J. Tafel, Ber., 1892, 25, p.

1619). The amount of pyridine produced in most of these processes is very small, and the best source for its preparation is the " See also:

light-oil " fraction of the coal-See also:tar distillate. The basic constituents are removed by dilute sulphuric acid, the acid layer removed, and the bases liberated by See also:alkali, separated, dried, and fractionally distilled. Pyridine is a colourless liquid of a distinctly unpleasant, penetrating odour. It boils at 114.5° C., and is miscible with See also:water in all proportions. It is a See also:tertiary base, and combines readily with the alkyl halides to See also:form pyridinium salts. Nascent See also:hydrogen reduces it to piperidine, C5H11N (see below), whilst hydriodic acid above 300° C. reduces it to n-pentane (A. W. See also:Hofmann, Ber., 1883, 16, p. 59o). •It is a very See also:stable See also:compound, chromic and nitric acids being without See also:action upon it, whilst the See also:halogens only yield substitution derivatives with difficulty. It reacts with sulphuric acid only at high temperatures, yielding a sulphonic acid.

It forms addition compounds with mercuric and auric chlorides. On the constitution of the pyridine See also:

nucleus, see Korner, Gior. dell' acad. di See also:Palermo, 1869, and C. Riedel, Ber., 1883, 16, p. 1609. As regards the See also:isomerism of the pyridine substitution products, three mono-derivatives are known, the different positions being indicated by the See also:Greek letters a, /3 and y, as shown in the inset See also:formula. This 4 e formula also allows of the existence of six di-deriva- tives, six tri-derivatives, three tetra- and one penta- derivative, when the substituent See also:groups are identi-°` \N%a cal; all of which are in agreement with known facts. The three monochlorpyridines are known, the a and y compounds resulting from the action of phosphorus pentachloride on the corresponding oxypyridines, and the fl compound from the action of See also:chloroform on See also:potassium pyrrol. a-Aminopyridine, C5H4N•See also:NH2, is formed by heating 5-aminopyridine-2-carboxylic acid. It is a crystalline solid which melts at 56° C. and boils at 204° C. It can only be diazotized in the presence of concentrated sulphuric acid, and even then the See also:free diazonium sulphate is not stable, readily passing in the presence of water to a-oxypyridine. $-Aminopyridine is obtained by heating $-pyridyl See also:urethane with fuming hydrochloric acid until no more See also:carbon dioxide is liberated (T. See also:Curtius and E. See also:Mohr, Ber., 1898, 31, p.

2493), or by the action of See also:

bromine and See also:caustic soda on the See also:amide of nicotinic acid (F. Pollak, Monats., 1895, 16, p. 54). It melts at 64° C. and boils at 250-252° C. The aminopyridines are readily soluble in water, and resemble the aliphatic See also:amines in their See also:general chemical properties. The oxypyridines may be prepared by distilling the corresponding oxypyridine carboxylic acids with See also:lime, or by fusing the pyridine carboxylic acids with caustic potash. The mono-oxypyridines are easily soluble in water and possess only feeble basic properties. The compound is hydroxylic in See also:character, whilst the a and y derivatives behave frequently as if they possess the tautomeric ketostructure, yielding according to the conditions of the experiment either N- or 0-See also:ethers (H. v. Pechmann, Ber., 1895, 28, p._1624), thus corresponding to the formulae CH CH C.OH CO HC/\CH HC" CH HC/\CH HC CH HC\ jC•OH HC\/CO HC'\ CH HC/I CH N NH N~ NH a-oxypyridine a-pyridone y-oxypyridine 7-pyridone The homologues of pyridine may be synthesized in various ways. One of the most important is the so-called " collidine " See also:synthesis of A. Hantzsch (Ann., 1882, 215, p. I ; Ber., 1882, 15, p.

End of Article: PYRIDINE

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