Pyrimidines

Pyrimidines, METADIAZINES or Miazines, in organic chemistry, a series of heterocyclic compounds containing a ring complex, composed of four carbon atoms and two nitrogen atoms, the nitrogen atoms being in the meta-position. The oxyderivatives of the tetrahydroand 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 I. 3-diketones with the amidines (A. Pinner, Ber., 1893, 26, p. 2125).

CH3 CH 2 CO(CH 3) + N 5 3 C .

H HN CEH?Chch C(Ch3)N.Cs The ketonic esters under like treatment yield oxypyrimidines, whilst if cyanacetic ester be employed then amino-oxypyrimidines are obtained. By using urea, guanidine, thiourea and related compounds instead of amidines, one obtains the uracils. The cyanalkines (aminopyrimidines) 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 0 C. and C.

3CH 3 CN = C4HN2(CH3)2NH2[2.4.6].

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, C 6 H 9 N 3 (dimethyl-aminopyrimidine -2.4. 6), melts at 180-181°C. 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 trimethylene bromide: Br(CH 2) 3 Br+C 6 H 5 C (:NH) NH 2 = 2HBr+C 4 H 7 N 2 (C 6 H 5) [2]. The 2.6-diketo-tetrahydropyrimidines or uracils may be considered as the ureides of /-aldehydo, and 0-ketonic acids. Uracil and its homologues may be obtained in many cases from the hydrouracils by the action of bromine, and subsequent elimination of the elements of hydrobromic acid; or by the condensation of aceto-acetic ester and related substances with urea, thiourea, guanidine, &c. Uracil, C4H402N2, crystallizes in colourless needles, is soluble in hot water and melts with decomposition at 335° C. Hydrouracil, C4H602N2, 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 0-aminopropionic acid with urea; by the electrolytic reduction of barbituric acid (J. Tafel, Ber., 1900, 33, p. 3385), and by the condensation of acrylic acid with urea at 210-220° C. (E. Fischer, Ber., 1901, 34, p. 3759). It crystallizes in needles and is soluble in water. It melts at 275° C. 4-Methyluracil, C5H602N2, 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 (Thymin) is obtained from the corresponding methyl bromhydrouracil (E. Fischer); or from 2.4. 6-trichlor-5-methylpyrimidine by the action of sodium methylate. This yields a 2.4-dimethoxy-5-methyl-6-chlorpyrimidine, which on reduction and subsequent treatment with hydrochloric acid is converted into thymin (0. Gerngross, Ber., 1905, 3 8, p. 3394). For methods of preparation and properties of numerous other pyrimidine compounds see T. B. Johnson, Journ. Biol. Chem., 1906, &c.; Amer. Chem. Journ., 1906, &c.; W. Traube, Ber., 1900, &c.; 0. Isay, ibid., 1906, 39, P. 251.

N:CHN N:C(CH3)N NHCONH ' 'CH :CHCH NH2C :CH CCH 3 CH :CH 0  Pyrimidine Cyanmethine Uracil