The anomalous behaviour of isoquinoline relative to quinoline and its significance in relation to structure and reactivity

Abstract

Vapour phase catalytic oxidation of quinoline over a vanadia base catalyst yielded nicotinic acid, while vapour phase catalytic ammoxidation gave 3‐cyano‐pyridine, the benzenoid ring undergoing cleavage in both cases. The isomeric molecule, isoquinoline, was however found to behave in sharp contrast, undergoing an unexpected reaction in its transformation into phthalimide during identical conditions of oxidation and into ortho‐phthalonitrile during ammoxidation, the pyridine ring undergoing cleavage in both cases, with the appearance of the heterocyclic ring nitrogen in a reactive functional group. The significance of these observations is discussed in relation to structure and reactivity and possible reaction mechanisms are suggested.