QUINAZOLINES (Phenmiazines or benzopyrimidines), in organic chemistry, heterocyclic compounds of the structure shown in the inset formula.
| (4) | |
|
N(3) |
| (2) | |
| N(1) |
They may be regarded as resulting from the fusion of a benzene with a pyrimidine nucleus in the 5.6 position. They are isomeric with the cinnolines, phthalazines and quinoxalines. They may be obtained by the action of alcoholic ammonia on the acidyl derivatives of orthoaminobenzaldehydes and ortho-aminoketones (A. Bischler, Ber., 1891–95):
C6H4
|
CHO | +NH3 = C6H4
|
CH : N |
| | | + 2 H2O; | ||
| NH.CO.R | 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 (C6H2N8) 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 Δ1, Δ2, Δ3, denoting that the double linkage is between the first and second, second and third, and third and fourth atoms in the diazine ring. The Δ1 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, Bef., 1889–1896). 4-Keto-dihydroquinazoline (β-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. 124);or by heating anthranilic acid with form amide (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 Δ2 series is obtained by heating acidyl-orthoaminobenzylamines with zinc chloride, whilst the Δ3 series, which is only known in the form of its keto derivatives (a-quinazolines), results from the fusion of urea with ortho-aminobenzaldehydes and benzophenones, the elements of water and of ammonia being eliminated (S. Gabriel and Th. Posner, Bef., 1895, 28, p. IO37). They possess feeble basic and phenolic characters. The tctra-hydroquinazolines are obtained by reducing the quinazolines and dihydroquinazolines and by condensing ortho-aminobenzylamine with aldehyde's (M. Busch, Jour. prak. 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 HgN.C6H4.CH2NHR (M. Busch, Bef., 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.