# 1911 Encyclopædia Britannica/Pyrimidines

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​PYRIMIDINES, METADIAZINES or MIAZINES, in organif chemistry, a series of hetero cyclic compounds containing a rin; complex, composed of four carbon atoms and two nitrogen atoms the nitrogen atoms being in the meta-position. The oxyderiva tives of the tetra hydro- and hexahydro-pyrimidines are the uracils and the ureides of malonic acid (see PURIN). The purins themselves may be considered as a combination of the pyrimidine and glyoxaline ring systems; For formulae see below; the numbers about the first ring explain the orientation of pyrimidine derivatives.
The pyrimidines may be obtained by condensing 1-3-dike tones with the amidines (A. Pinner, Bef., 1893, 26, p. 2125). CH, -CO + NHVC-CeH5 CH, -C:Nl-Q;C6H5. CH2-CO(CH3) HN °> CH:C(CH3)~N
The B-ketonic esters under like treatment yield oxypyrimidines, whilst if cyan acetic ester be employed then amino-oxypyrimi dines are obtained. By using urea, guanidine, thiourea and related compounds instead of amidines, one obtains the uracils. The cyanalkines (amino pyrimidines) were first obtained, although their constitution was not definitely known, by E. Frankland and H. Kolbe (Ann. 1848, 65, p. 269) by heating the nitriles of acids with metallic sodium or with sodium ethylate between 130° C. and I8O° C.
=C4HN2(CH3)¢'NH2[2'4j6].V
Pyrimidine, C4H4N2, itself is a water-soluble base which melts at 21° C. and possesses a narcotic smell. Its methyl derivatives yield the corresponding carboxylic acids when oxidized by potassium permanganate. The amino derivatives are stable bases which readily yield substitution derivatives when acted upon by the halogen elements. Cyanmethine, CSHQN3 (dimethyl-amino pyrimidine-2-4-6), melts at ISO'-ISIQC. The simple oxypyrimidines are obtained by the action of nitrous acid on the amino derivatives, or by heating these latter with concentrated hydrochloric acid to 180° C. They show both basic and phenolic properties and are indifferent to the action of reducing agents. Acid oxidizing agents, however, completely destroy them. By the action of phosphorus pentachloride, the hydroxyl group is replaced by chlorine. Hydropyrimidines.-The dihydro derivatives are most probably those compounds which are formed in the condensation of acidyl derivatives of acetone, with urea, guanidine, &c. Tetrahydropyrimidines are obtained by the action of amidines on trim ethylene bromide: Br(CH2)3Br-}-C6H5C(:NH)~NH2=2HBr-I-C4H7N2(C<, H5)[2]. The 2-6-diketo-tetra hydro pyrimidines or uracils may be considered as the ureides of B-aldehydo, and B-ketonic acids. Uracil and its homologies may be obtained in many cases from the hydrouracils b the action of bromine, and subsequent elimination of the elements oi, hydro bro mic acid; or by the condensation of aceto-acetic ester and related substances with urea, thiourea, guanidine, &c. Uracil, C4H4O2N2, crystallizes in colourless needles, is soluble in hot water and melts with decomposition at 335° C. Hydrauracil, C4H6O2N2, is obtained by the action of bromine and caustic alkalis on succinamide (H. Weidel and E. Roithner, Monats., 1896, 17, p. 172); by the fusion of 6-amino prop ionic acid with urea; by the electrolytic reduction of barbituric acid (J. Tafel, Bef., 1900, 33, p. 3385)¢ and by the condensation of acrylic acid with urea at 2IO~220° C. (E. Fischer, Ber., 1901, 34, p. 3759). It crystallizes in needles and is soluble in water. It melts at 275° C. 4-Methyluraeil, C5H@O2N¢, has long been known, having first been synthesized by R. Behrend (see PURIN). It crystallizes in needles which melt at 320° C. and is soluble in caustic alkalis. On oxidation with potassium permanganate it is converted into acetyl urea, together with other products. 5-Methyluracil (Thyrnin) is obtained from the corresponding methyl bromhydrouracil (E. Fischer); or from 2-4-6-trichlor-5-methyl pyrimidine by the action of sodium methyl ate. This yields a 2~4-dimethoxy-5-methyl-6-chlorpyrimidine, which on reduction and
subsequent treatment with hydrochloric acid is converted into thymin (O. Gerngross, Bef., 1905, 38, p. 3394). For methods of preparation and properties of numerous other. pyrimidine compounds see T. B.Johnson, foam. Biol. Chem., 1906, &c.; Amer. Chem. foum., 1906, &c.; W. Traube, Bef., 1900, &c.; O. Isay, ibid., 1906, 39» P- 251-I
N:CH-lélf N:C(CHa).-N NH-CO-NH
CH:CH~CH NH2-C:CH-C-CH3 CH:CH-CO
6 5 4
Pyrimidine Cyanmethine Uracil