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QUINAZOLINES (Phenmiazines or benzopyrimidines), in organic chemistry, heterocyclic compounds of the structure shown in the inset formuk. They may be regarded as resulting ( 4 j from the fusion of a benzene with a pyrimidine N( . nucleus in the 5.6 position. They are isomeric with the cinnolines, phthakzines and quinoxalines. They may be obtained by the action of alcoholic ammonia on the acidyl derivatives of orthoaminobenzaldehydes and ortho-aminoketones (A. Bischler, Ber., /CHO /CH : N 1891-95) iCeH/ +NH 3 = C 6 H/ | +2H 2 O; X NH.CO.R X N : CR and_from the corresponding dihydro compounds on oxidation with potassium permanganate. They are stable, tertiary bases, and may be distilled without decomposition; they form addition products with alkyl iodides and double salts with mercuric and platinum chlorides. On reduction with sodium in presence of alcohol they yield dihydro derivatives. Those in which the -CH group adjacent to the benzene nucleus is unsubstituted are oxidized by chromic acid to ketodihydroquinazolines (quinazolones).

Quinazoline (C 6 H 2 Ns) is obtained by oxidizing its dihydro- derivative with potassium ferricyanide. The dihydro derivatives exist in three different series, since the addition of two atoms of hydrogen in the diazine ring can take place in three different positions, namely, in the 3.4, 1.4 and 1.2 positions, and these different types are distinguished by the symbols Ai, Aa, A3, denoting that the double linkage is between the first arid second, second and third, and third and fourth atoms in the diazine ring. The Ai series, which are obtained by the elimination of the elements of water from the acidyl derivatives of ortho-aminobenzylamines, are rather strong bases which form stable salts and yield the corresponding keto derivatives on oxidation (C. Paal, Ber., 1889-1896). 4-Keto-dihydroquinazoline (/3-quinazolone) is formed by oxidizing the dihydro base with potassium permanganate; by boiling acidyl-ortho-aminobenzamide with water (A. Weddige, Jour. prak. Chem., 1885, (2)31, p. 1 24); or by heating anthranilic acid with formamide (S. Niementowski, Ber., 1895, 28, p. 443). It reacts both in the enol and keto forms, yielding both N-ethers and O-ethers, the latter being obtained by the action of sodium alcoholates on 4- chlorquinazolines. The A2 series is obtained by heating acidyl- orthoaminobenzylamines with zinc chloride, whilst the A3 series, which is only known in the form of its keto derivatives (o-auinazolincs), results from the fusion of urea with ortho-aminobenzaidehydes and benzophenones, the elements of water and of ammonia being eliminated (S. Gabriel and Th. Posner, Ber., 1895, 28, p. 1037). They possess feeble basic and phenolic characters. The tctra- nydroquinazolines are obtained by reducing the quinazolines and dihydroquinazolines and by condensing ortho-ammobenzylamine with aldehydes (M. Busch, Jour. frak. Chem., 1896, (2) 53, p. 414). The ring is easily split on hydrolysis, giving rise to ortho-disubstituted benzenes. The keto derivatives of this series result by the action of carbonyl chloride on ortho-aminobenzylamines of the type H,N.C,H 4 .CH,NHR (M. Busch, Ber., 1892, 25, p. 2853), or from the urea derivatives of ortho-aminobenzylamine. They are weak bases which are indifferent to both acids and alkalis, and which on oxidation yield the corresponding 2-4-diketo derivatives.

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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