METADIAZINES

PYRIMIDINES  Or MIAZINES, in organir chemistry, a series of heterocyclic compounds containing a rin1 complex, composed of four carbon atoms and two nitrogen atoms the nitrogen atoms being in the meta-position . The oxyderiva tives of the tetrahydro- 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-di- ketones with the amidines (A . Pinner, Ber., 1893, 26, p . 2125) . N CHs CH2•CO(CH3) + N HN C6H6_> CHsCH C(CH3)Clv,CsHb . The 0-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 13o° C. and 18o° C . 3CH3CN =C4HN2(CH3)2•NH2[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, C6H9N2 (dimethyl-aminopyrimidine—2.4.6), melts at 18o—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 18o° 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(CH2)3Br+C6H6C(:NH) •NH2 =2HBr+C4H7N2(C6Hs)[2] . The 2.6-diketo-tetrahydropyrimidines or uracils may be considered as the ureides of ,B-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, C5He02N2, has long been known, having first been synthesized by R . Behrend (see PURIN) . It crystallizes in needles which melt at 3200 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 (O .

Gerngross,

Bee., 1905, 38, 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.; O . Isay, ibid., 1906, 39, P .

251 .