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PYRAZINES, PIAZINES
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See also:PYRAZINES, PIAZINES , Or PARADIAZINES, in organic See also:chemistry, a See also:group of compounds containing a See also:ring See also:system composed of 4 See also:carbon atoms and 2 See also:nitrogen atoms, the nitrogen atoms being in the See also:para position: The di- and tri-methyl derivatives are found in the fusel oil obtained by See also:fermentation of See also:beet-See also:root See also:sugar (E. C. See also:Morin, Comptes rendus, 1888, 106, p. 36o). They were first prepared synthetically by reducing the isonitrosoketones. They may also be prepared by the inner condensation of a-aminoaldehydes or a-aminoketones in the presence of a mild oxidizing See also:agent, such as mercuric chloride or See also:copper sulphate in boiling alkaline See also:solution (L. See also:Wolff, Ber., 1893, 26, p. 183o; S. See also:Gabriel, ibid. p. 2207); and by the See also:action of See also:ammonia on a-halogen ketonic compounds (W. Staedel and L. Rugheimer, Ber., 1876, 9, p. 563; V. See also:Meyer and E. Braun, Ber., 1888, 21, p. 19). They are also formed when See also:grape sugar is heated with ammonia or when See also:glycerin is heated with ammonium chloride and ammonium phosphate (C. Stoehr, Journ. prakt. Chem., 1895 (2), 51, p. 450; 1896 (2), 54, p. 481). They are feeble basic compounds which distil unchanged. They are mostly soluble in See also:water and somewhat hygroscopic in See also:character. Their salts are easily dissociated. They See also:form characteristic compounds with mercuric and auric chlorides. Their alkyl derivatives readily oxidize to pyrazine carboxylic acids. Pyrazine, C4H4N2, crystallizes from water in prisms, which have a See also:heliotrope odour. It melts at 55° C. and boils at 115° C. It may also be obtained by elimination of carbon dioxide from the pyrazine dicarboxylic See also:acid formed when quinoxaline is oxidized with alkaline See also:potassium permanganate (S. Gabriel). 2.5•-Dimethylpyrazine, or ketine, C4H2(See also:CH3)2N2, is obtained by reducing isonitrosoacetone, or by See also:heating glycerin with ammonium chloride and ammonium phosphate. It boils at 153° C. Two classes of dihydropyrazines are known, namely the 1.4 and 2.3• dihydro-compounds, corresponding to the formulae II. and III., pyrazine being I.: HC•N•CH HC•NH•CH HC•N•See also:CH2 See also:H2C.NH.CH2 HC•N•CH HC•NH•CH HC•]V•CH2 H2C•NH•C. H2 I (Pyrazine) II (1.4 dihydro) III (2.3 dihydro) IV (Piperazine). Those of the former type are obtained by condensing a-bromketones with See also:primary See also:amines (A. T. See also:Mason, Journ. Chem. See also:Soc., 1893, 63, p. 1355) ; the latter type result on condensing alkylene diamines with a-See also:diketones. The 2.3 derivatives are somewhat unstable compounds, since on heating they readily give up two See also:hydrogen atoms. Tetrahydropyrazines of the 1.2.3.4 type have also been obtained (L. Garzini, Ber., 1891, 24, 956 R). Hexahydropyrazine or piperazine (See also:formula IV. above), also known as diethylene diamine, may be prepared by reducing pyrazine, or, better, by combining See also:aniline and See also:ethylene bromide to form See also:diphenyl diethylene diamine, the dinitroso See also:compound of which hydrolyses to_para-dinitrosophenol and pipera- zine. It is a strong See also:base, melting at 104° and boiling at 145°–146° It is used in See also:medicine on See also:account of the high solubility of its See also:salt with uric acid. Additional information and CommentsThere are no comments yet for this article.
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