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Encyclopedia Britannica - Main :: PRE-PYR |
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PURIN, C5H4N4 , in chemistry , the name given by Emil Fischer to the parent substance of a large group of compounds, the more important of which are sarcine, xanthine, uric acid, adenine, paraxanthine, guanine, theophylline, theobromine and caffeine. Its formula
2.6.8 trichlor purin (see below sub Uric acid), hydriodic acid and phosphonium iodide at o, with zinc dust and water, the zinc double
NHCH N:CH N:CH N:CH N:CH ONO2-CICCNO2--> C1CCNO2->HCCNH2- HC .NH i i NH-CO N uiCl iiNH2 ii N~ Ni >CH. NCNH2 g-.8 Purin crystallizes in microscopic needles, which melt at 216 C. It possesses the properties of both an acid and a base. It is characterized by its ready solubility in water and by its stability towards oxidizing agents. Oxypurins.Sarcine or hypoxanthine, C5H4N40, is 6-oxypurin. It is found in many animal liquids and organs and in the seeds of many plants, and was discovered by J. Scherer in milk (Ann. 185o, 73, p. 328) and by A. Strecker in muscle. It crystallizes in needles which decompose at 15o C. It was synthesized by E. Fischer (Ber., 1897, 30, p. 2228) by heating
caustic
3-Methylhypoxanthine was synthesized by W. Traube and F. Winter (Arch. Pharm., 1906, 244, p. 11), whilst 8-oxypurin was obtained by E. Fischer and L. Ach in 1897 (Ber., 30, p. 2213), and by 0. Isay (Ber., 1906, 39, p. 251). Xanthine, C5H4N402, or 2.6-dioxypurin, was discovered in 1817 by Marcet in a urinary calculus; it also occurs in various animal organs (the liver , pancreas and muscular tissue ), in urine, and in beetroot juice. It may be prepared by boiling nuclein with water (A. Kossel, Zeit. physiol. Chem., 188o, 4, p. 290) ; by the decomposition of guanine with nitrous acid (A. Strecker, Ann., 1858, 1o8, p.141) ; and by heating
CO.CH2 CO ICH2 CO.C:NOH COCNH2 CO-ICNH NHCN~NHC NH-~NHC:NH3NHCNH2~NH CNa' CONH2 CONH CONH CONH CONH It decomposes when heated, giving ammonia, carbon dioxide and hydrocyanic acid. It possesses both acid and basic properties. When heated with concentrated hydrochloric acid to 220 C, it decomposes into carbon dioxide, ammonia, glycine and formic acid. Potassium chlorate and hydrochloric acid oxidize it to alloxan and urea. Methylation of its lead salt gives theobromine. The isomeric 6.8-dioxypurin was prepared by E. Fischer and L. Ach (loc. cif). 1-Methylxanthine was found in urine by M. Kruger and G. Salomon (Zeit. physiol. Chem., 1897, 24, p. 364) ; 3-methylxanthine was obtained by E. Fischer and F. Ach.(Ber., 1898, 30, 1980) from 3-methyl uric (1)N=CH(6) (2)HC(5)C.NH(7) (3) NC N>CH (8) (4) (9) Purin. it to amalic acid or tetramethyl alloxantin (Fr. Rochleder, Ann. 1849, 71, p. 1), and that hydrolysis with baryta gave caffeidine (A. Strecker, Ann., 1862, 123, p. 360), which could be further hydrolysed to sarcosine, methylamine, formic acid and carbon dioxide (O. Schultzen, Zeil. f. Chemie, 1867, p. 614). Fischer confirmed these results and showed further that oxidation with chlorine water gave monomethyl urea and dimethyl alloxan, pointing to the presence of three methyl groups in the molecule. Further, on bromination, a brom-derivative is obtained which on treatment with alcoholic potash yields ethoxy-caffeine, which readily hydrolyses to hydroxy-caffeine. This substance behaves as an unsaturated compound and combines with a molecule of bromine to form a derivative which on treatment with alcoholic potash yields diethoxy-hydroxycaffeine. Diethoxy-hydroxycaffeine on hydrolysis with concentrated hydrochloric acid yields apocaffeine, C7H7N30s, and hypo-acid; and 7-methylxanthine or heteroxanthine, which is found in human urine, may be obtained from theobromine (E. Fischer, Ber., 1897, 30, p. 2400; see also ibid., 1898, 31, p. 117). Theophylline, C5(CH3)2H202N4, or I.3-dimethyl-2.6-dioxypurin, was isolated by A. Kossel from tea-leaves (Ber., 1888, 21, p. 2164). It was synthesized by E. Fischer and L. Ach (Ber., 1895, 28, p. 3135) from I.3-dimethyl uric acid, which on treatment with phosphorus pentachloride yields chlortheophylline, from which theophylline is obtained by reduction with hydriodic acid. W. Traube (Ber., 1900, 33, p. 3035) formed the nitroso derivative of iminodimethyl barbituric acid (obtained by the action of phosphorus oxychloride on cyanacetic acid and dimethyl urea), and reduced it by ammonium sulphide to 1.3-dimethyl-4.5-diamino-2.6-dioxypyrimidine, the formyl derivative of which, when heated to 250 C., loses the elements of water and yields theophylline (cf. Xanthine). It behaves as a weak base. When oxidized by potassium chlorate and 'hydrochloric acid it yields dimethylalloxan. Its silver salt on methylation yields caffeine. The isomeric Paraxanthine, or I.7-dimethyl-2.6-dioxypurin, occurs in urine. It has been obtained from theobromine (E. Fischer, Ber., 1897, 30, p. 2400); from I.7-dimethyl uric acid (E. Fischer and H. Clemm, Her., 1898, 31, p. 2622); and from 8-chlorcaffeine (E. Fischer, Ber., 1906, 39, p. 423). On methylation it yields caffeine. A third isomer Theobromine, or 3.7-dimethyl-2.6-dioxy urin, is found in the cocoa-bean (from Theobroma cacao) and in the kola-nut. It is obtained by methylating xanthine, or from 3.7-dimethyl uric acid (E. Fischer, Ber., 1897, 30, p. 1839). This acid, by the action of phosphorus oxychloride and pentachloride, is converted into 3.7-dimethyl-6-chlor-2.8-dioxypurin, which with ammonia gives the corresponding amino compound. This substance with phosphorus oxychloride yields 3.7-dimethyl-6-amino-2-oxy-8-chlorpurin, which on reduction with hydriodic acid leads to 3.7-dimethyl-6-amino-2-oxypurin, from which theobromine is obtained by the action of nitrous acid. It is also obtained by W. Traube's method (Bee., 1900, 33, p. 3047) from cyanacetyl methyl urea, which gives 3-methyl-4.5-diamino-2.6-dioxypyrimidine, whose formyl derivative yields 3-methylxanthine, from which theobromine is obtained by methylation. It crystallizes in anhydrous needles which sublime at 290-295 C. It behaves as a weak base. Potassium chlorate and hydrochloric acid oxidize it to methyl alloxan and methyl urea, chromic acid mixture oxidizes it to carbon dioxide, methylamine and methylparabanic acid. When boiled with baryta it yields carbon dioxide, ammonia, methylamine, formic acid and sarcosine. Methylation of its silver salt yields caffeine. Caffeine, C5H(CH3)3N402, is I.3.7-trimethyl-2.6-dioxypurin. For its general properties and method of extraction see CAFFEINE. It may be synthesized by methylating chlortheophylline and reducing the resulting product (E. Fischer and L. Ach, Ber., 1895, 28, p. 3135) ; by the action of phosphorus oxychloride on tetramethyl uric acid, the resulting chlorcaffeine being reduced (Bet., 1897, 30, p. 3010); from dimethylalloxan (Ber., 1897, 30, p. 564); from 3-methyl uric acid (Ber., 1898, 31, p. 1980), and from I.3-dimethyl-4.5-diamino-2.6-dioxypyrimidine (W. Traube, Ber., 1900, 33, p. 3042). The three latter methods may be outlined as follows. Dimethylalloxan (I.) condenses with methylamine in the presence of sulphurous acid to form an addition product (II.), which on hydrolysis yields 1.3.7-trimethyl uramil; this substance gives with potassium cvanate, 1.3.7-trimethyl pseudo-uric acid (III.), which on dehydration yields I.3.7-trimethyl uric acid (hydroxycaffeine) ; this substance with phosphorus pentachloride gives chlercaffeine, which yields caffeine (IV.) on reduction: H3CNCO H3C.NIICO H3CNCIIO OC CO-+ O(: 6HNHCH3sOC CHN End of Article: PURIN, C5H4N4 If you wish, you can link directly to this article.
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