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Originally appearing in Volume V22, Page 691 of the 1911 Encyclopedia Britannica.
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CH8.CO + NH3 + CO•CH3 CH3•C-NH-G.CH3 The resulting dihydro-compound is then oxidized with nitrous acid, the ester hydrolysed and the resulting acid heated with lime; carbon dioxide is eliminated and a trisubstituted pyridine of the type CH C(CHI) is obtained. The reaction is apparently a R•C' \N general one for all aldehydes. On the course \CH :C(CH3)/ of the reaction see also C. Beyer, Ber., 1891, 24, p. 1662, and E. Knoevenagel, Ber., 1898, 31, p. 738. In this reaction the proportions of aldehyde and acetoacetic ester may be interchanged and ay disubstituted pyridines are then obtained. Of the other methods for preparing pyridine homologues mention may be made of the discovery by A. Ladenburg that the pyridinium alkyl iodides rearrange themselves when strongly heated and yield a and y alkyl pyridines (Ber., 1883, 16, p. 1410 seq. ; Ann., 1888, 247, p. I). S. Ruhemann prepared 7-substituted dioxypyridines by condensing alkyl-dicarboxy-glutaconic esters with ammonia. R'02C)2C:CR•CH(CO2R')2-,R'02Co.c CRH•NC•COH•CO2R'-HHOC:CRNC. On Of •C OH M. Scholtz (Ber., 1895, 28, p. 1726) prepared aa- methylphenylpyridine by distilling cinnamenylidene acetoxime, CSHSCH:CH•CH:CH•C(:N•OH).CH3= H C•CHc H2O CeHs•c•N :C•CHs-- The 1.5 diketones of the type inset, when heated with ammonia, also yield pyridine derivatives. Alkyl pyridines -CO\ /CO- are also obtained by heating aldehyde >C:CH•CH< ammonias alone or with aldehydes and -CO CO- ketones (A. v. Baeyer, Ann., 187o, 155, pp. 281, 294; J. Pldchl, Ber., 1S87, 20, p. subjoined table shows the chief homologues of pyridine: Name. Formula. Position Remarks. of Sub- stituent. Picolines C5H4(CHa)N a Liqquid, b.p. 129°. Oxi- Lutidines CSH4(C2H5)N y dizes to picolinic acid. a, /3, y, Condenses readily with aldehydes. Liquid, b.p. 143°. Oxi- dizes to nicotinic acid. Does not condense with aldehydes. Liquid, b.p. 144-145°. Three isomers. All liquids. The /3 com- pound is a decompo- sition product of cinchonine, quinine, strychnine and bru- cine. CSH3(CHa)2N aa', ay, a,B' Five isomers. All /3l3', /37. liquids. Collidines C5H4(CaH1)N a, P. Liquids. The a com- C5H3(CH3)(C2H5)N a, y. pound is a decomposi- CSH2(CHa)3N a'a, y(3, tionproductof conine. ay, a/3' Both contain the nor- aya' mal propyl group. ay/3' Containing the isopro- Lis.rou p. qu1id Liquid, b. . 171-172°. Prepared by the Hantzsch synthesis. Found in coal-tar. Pyridine carboxylic acids are usually prepared by oxidizing the homologues of the base; they also result as decomposition products of various alkaloids. The more important are shown in the table. Name. Formula. Position Remarks. of Sub- stituent. Picolinic C5H4(CO2H)N a M.p. 137°. Easily solu- acid. ble in water. Yellow coloration with FeSO4. Position of carboxyl group deter- mined by synthesis from a-naphthyl- amine (Z. Skraup and A. Cobenzl, Monals., Nicotinic C5H4(CO2H)N p 1883, 4, p. X36). acid. M.p. 228—229 . An oxi- dation product of nicotine, hydrastine Quinolinic C6H3(CO2H)2N a$ and berberine. Con- acid. C5H3(CO2H)2N py stitution determined Cincho- C6H2(CO2H)2N apy by synthesis from meronic C6H2(CO2H)3N ayf3' p-naphthylamine acid. (Skraup). a-Carbo- M.p. 192—195° with de- cincho- composition into nico- meronic tinic acid. Formed acid. by oxidation of Berbero- quinoline. nic M.p. 258—2590. Formed acid. by oxidation of quin- ine, cinchonine, and of isoquinoline. M.p. 249-250°. Crystal- hies with IIH2O. An oxidation product of cinchonine, quinine and papaverine. M.p. 243°. An oxida- tion product of ber- berine. Gives a red coloration with FeSO4. Boiling with glacial acetic acid gives cinchomeronic acid. Trigonelline, C7H7NO2, the methyl betaine of nicotinic acid, was discovered in 1885 by E. Jahns (Ber., 1885, 18, p. 2518), and is found in the seeds of Trigonella and Strophanthus hispidus. It is very soluble in water. With baryta it yields methylamine, and when heated with concentrated hydrochloric acid, to 26o° C. it yields methyl chloride and nicotinic acid. It was synthesized by A. Hantzsch (Ber., 1886, 19, p. 31) by condensing methyl iodide and potassium nicotinate at 150° C. the resulting iodide being then decomposed by moist silver oxide. A. Pictet (Ber., 1897, 30, p. 2117) obtained it by oxidizing nicotine methyl hydroxide with potassium permanganate. Apophyllenic acid, C8H7NO4•H20, the methyl betaine of cinchomeronic acid, was synthesized by W. Roser (Ann., 1886, 234, p. 118). Piperidine or hexa-hydropyridine, C6H21N, was first obtained in 1848 by distilling piperine with lime. It is formed in the hydrolysis of piperine by alcoholic potash, by the reduction of trimethylene cyanide (A. Ladenburg) and by the action of alkalis on e-chloramylamine, Cl(CH2)s•NH2 (S. Gabriel, Ber., 1892, 25, p. 42I). It is also produced in the electrolytic oxidation of N-nitroso piperidine in sulphuric acid solution (F. B. Ahrens, Ber., 1898, 31, p. 2275). It is a liquid which boils at 105—106° C., and possesses an ammoniacal smell. It is readily soluble in water, alcohol and ether, and is a very powerful base. It is oxidized to pyridine by heating with concentrated sulphuric acid to 300° C., or with nitrobenzene to 250° C., or with silver acetate to 180° C. Being an imide it readily yields a nitroso derivative, and N-alkyl and acidyl derivatives. The piperidine ring is easily split. When heated with fuming hydriodic acid to 300° C. it yields normal pentane and ammonia, and hydrogen peroxide oxidizes it to glutarimide and to a piperidinium oxide or oxime (R. Wolffenstein, Ber., 1904, 37, p. 3228). A. W. Hofmann (Ber.. 1881, 14, p. 66o), by a process of exhaustive methylation and distillation, obtained the unsaturated hydrocarbon piperylene, C H2: C H • C H2 • CH : CH2, from piperidine (see also A. Ladenburg, Ann., 1894, 279, P. 344)- C6HnN(+CH3I) — C5HI0N(CH3)2I (+AgOH) —j C6H,6N(CH3)2.OH (distil) 1 CiH9N(CH3)3.OHE--(+AgOH)C5H9N(CH3)3I<—(-}CHsI)C6H9N(CHs)2 (distil) C1H2+N(CH3)3+H20 J. v. Braun (Bee., 1904, 37, p. 2915) showed that benzoyl piperidine, when heated with phosphorus pentachloride to 20o° C. in sealed tubes, yields benzonitrile, and pentamethylene dichloride, thus leading to a simple method of preparing pentamethylene compounds. At 125—130° C. the compound C6H2C•Cl:N(C112)s•G is obtained; this with water yields benzoylamidochloramylamine C6H5CONH(CH2)5Cl, which when heated with hydrochloric acid tc 17o—18o° C. furnishes e-chloramylamine, NH2(CH2)SCI. a-Propyl, piperidine is the alkaloid conine (q.v.).
End of Article: CH8

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