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Originally appearing in Volume V22, Page 698 of the 1911 Encyclopedia Britannica.
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C4H5N PYRROL or C41;T4•NH, an organic base found in coal-tar and Dippel's oil. It may be synthetically prepared by the dry distillation of ammonium mucate, or, better, by heating it with glycerin to 180-200° C. (H. Schwanert, Ann., 186o, 116, p. 257); by passing the vapour of diethylamine through a red-hot tube; by distilling succinimide with zinc dust (C. A. Bell, Ber., 188o, 13, p. 877); by distilling calcium pyroglutaminate: H02C' CH(NH2)'CH2'CH2 CO2H = C4H4NH+CO2+2H20 (L. Haitinger, Monats., 1882, 3, p. 228); and by boiling succinic dialdehyde.with ammonia and glacial acetic acid (C. Harries, Ber., 1901, 34, p. 1497). It is a feebly basic, colourless liquid which boils at 13o° C., and possesses a smell resembling that of chloroform. It is slightly soluble in water, and turns brown on exposure to air. It has to some extent the character of a secondary amine; the hydrogen of the imino group can he replaced by potassium. It is resinified by the action of concentrated mineral acids. On warming solutions of pyrrol in dilute acid, ammonia is evolved, and an amorphous powder of variable composition, known as pyrrol-red, separates out. The pyrrol ring is easily broken, e.g. hydroxylamine gives the dioxime of succinic aldehyde. Pyrrol is readily converted into pyridine derivatives by acting with bromoform, chloroform, or methylene iodide on its potassium salt, /3-brom-and /3-chlorpyridine being obtained with the first two compounds, and pyridine itself with the last. Iodine in alkaline solution converts pyrrol into iodol (tetra-iodopyrrol), crystallizing in yellowish-brown needles, which decompose on heating. It may also be prepared by heating tetra-brom- or tetra-chlorpyrrol with potassium iodide in alcoholic solution (German patent, 384231 1886). It is used as an antiseptic. Zinc dust and hydrochloric acid reduce pyrrol to pyrrolin (dihydropyrrol), C4H6•NH, a liquid which boils at 9o° C. (748 mm.); it is soluble in water and has strongly basic properties and an alkaline reaction. Hydriodic acid at high temperature reduces pyrrol to pyrrolidine (tetra-hydropyrrol), C4HSNH. Pyrrolidine has also been prepared by A. Thiele (Ber., 1905, 38, p. 4Ip4) from ,B-chlorpropionic aldehyde diethyl acetal. The chlorine atom in this compound is replaced by the cyano-group, which is then reduced to. the CH2NH2. group and coupled up with benzene sulphochloride to form the compound C6H5S02NH(CH2)2.CH(OC2H6)2• This substance easily splits out alcohol, and the ring compound then formed yields pyrrolidine on reduction by sodium in amyl alcohol solution. An a-pyrrolidine carboxylic acid and its hydroxy derivatives have been detected by E. Fischer among the products of hydrolysis of proteids. R. Willstatter (Ber., 1900, 33, p. 1164) obtained this acid by the action of a methyl alcoholic solution of ammonia on dibrompropylmalonic ester at 140° C., the diamide formed being then hydrolysed either by hydrochloric acid or baryta water : CH2•CBr(CO2H)2 CH2• (CONH2) CH2• CH(CO2H) I —s I )NH—a >NH. CH2•CH2Br CH2 CH2 CH2 CH2 Numerous substitution derivatives of pyrrol are known. The N-derivatives are prepared by the action of alkyl halides and acid chlorides on potassium pyrrol. The C-derivatives have been prepared in various ways. L. Knorr, by the action of ammonia on aceto-acetic ester, obtained 19-imidobutyric ester, which with nitrous acid yields a-isonitroso-$-imidobutyric ester, CH3.C(:NH)•C(:N•OH)•CO2C2H6. Reduction of this ester leads to the formation of ammonia, hydroxylamine, and dimethyl pyrrol dicarboxylic ester, HN/C(CH3) : C44 •CO2R \C(CO2R) :C•CH3• He also found that diaceto succinic ester reacts with compounds of the type NH2R(R=H, CH2, OH, NHC6H6, &c.) to form pyrrol derivatives :propionic acid with 'hydroxylamine. It is monobasic and yields salts which only crystallize with great difficulty; when liberated from these salts by a mineral acid it forms a syrupy non-volatile mass. In aqueous solution it gives a red colour with ferric chloride. It shows characteristic ketone reactions, yielding a bisulphite compound and combining with hydro-cyanic acid to form the nitrile of a-oxyisosuccinic acid. When warmed with baryta water it gives uvitic acid. Pyruvic nitrile, or acetyl cyanide, CH3CO•CN, may be prepared by the action of silver cyanide on acetyl chloride ; or of acetyl chloride on nitrosoacetone (L. Claisen and O. Manasse, Ber., .1887, 2o, p. 2196). It is a liquid which boils at 93° C. and with caustic alkalis polymerizes to diacetyldicyanide.
End of Article: C4H5N PYRROL
PYRRHUS (c. 318–272 B.C.)

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