PYRIMIDINES, METADIAZINES or MIAZINES, a series of nitrogenous organic substances which play an important part in physiological processes. They possess a cyclic structure as shown in the formula (III.) of pyrimidine itself, and the group includes cyclic urea derivatives (ureides) and also compounds of the uric acid or purine group.
Pyrimidine is best prepared from barbituric acid (malonyl urea, formula I.) by the action of phosphorus oxychloride and by reduction of the resulting 2 :4 : 6-trichloropyrimidine (formula II.).
Pyrimidine is a crystalline base of narcotic odour and dis solves readily in water; it melts at 21° C and boils at 124° C. Derivatives of pyrimidine are of great physiological importance and take part in many fundamental life processes. They have been shown by Kossel (1893) to be present in the cell nucleus where synthetic changes associated with the growth of the cell are taking place.
Uracil (2 :6-dioxypyrimidine, formula IV.), a white crystalline powder, sparingly soluble in cold but more readily soluble in hot water, melts with evolution of gas at 338° C. It was recognised as
a hydrolytic product of nucleic acids from yeast in 19oo by A. Ascoli and was synthesised by E. Fischer and Roeder in i9o1 by heating urea with acrylic acid. This condensation gave dihydro uracil which was successively converted into monobromo-deriva tive and uracil.
Thymine or 5-methyl-2:6-dioxypyrimidine (formula V.) is ob Cytosin (2-oxy-6-aminopyrimidine, formula VI.) was synthe sised by H. Wheeler and Treat B. Johnson in 1903 and identified by Kossel and Neumann in 1894 as a hydrolytic product of thy monucleic acid. It crystallises from water in colourless, nacreous plates decomposing at 320-325° C. It is converted by nitrous acid into uracil (v. supra) and is oxidised by barium permanganate into oxalic acid and biuret. (See UREA.) For methods of preparation and properties of numerous pyrimi dine derivatives see T. B. Johnson, Jour. Biol. Chem., 1906; Amer. Chem. Journ., 1906; bourn. Amer. Chem. Soc., 1911 et seq.