Nitration of Simple Heterocycles

Abstract

Two results of interest in the study of comparative heterocyclic chemistry have been reported recently. Nitration of 4-hydroxyquinoline is said to give c. 50 per cent of 3-nitro-4-hydroxyquinoline¹, whereas quinazoline provides not less than 56 per cent of the 6-nitro-derivative². In identifying the product from 4-hydroxyquinoline, the authors¹ depended on (a) the proved difference of its 4-chloro-derivative from 5-nitro-4-chloroquinoline, its assumed difference from 8-nitro-³ and 6-nitro-4-chloroquinoline³, and (b) the assumed identity of the derived aminoquinoline, m.p. 94°, with 3-aminoquinoline⁴. We find that the chloro-derivative of the chief nitration product gives a strong mixed melting point depression with genuine 3-nitro-4-chloroquinoline⁵. Further, whereas the former may be crystallized from methanol, such treatment hydrolyses the latter. By analogy with 4-hydroxycinnoline⁶ and 4-hydroxyquinazoline⁷, we expected kynurin to give chiefly 6-nitro-4-hydroxyquinoline on nitration. In fact, the nitro-chloroquinoline, m.p. 144–145°, prepared as described by Mosher et al.¹, gave no melting point depression on admixture with genuine 6-nitro-4-chloroquinoline, m.p. 144–145°³. The derived 4-phenoxy-compounds, m.p. 117–118°, Were also identical (found for genuine 6-nitro-4-phenoxyquinoline: C, 66.6; H, 4.0; N, 11.4; C₁₅H₁₀O₃N₂ requires C, 67.6; H, 3.8; N, 10.5 per cent).