Reactivity of 4,9-diazapyrene
Heating 5,10-dimethyl-4,9-diazapyrene with nitric acid to 200°C does not bring about disruption of the heteroring but leads to the formation of nitro derivatives of 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene. 4,9-Diazapyrene is a weak base that forms quaternary salts only under severe conditions. Piperidine replaces two chlorine atoms in 5,10-dichloro-4,9-diazapyrene, whereas only monosubstitution occurs in the case of 1,6-dibromo-5,10-dimethyl-4,9-diazapyrene. Calculations by the Hückel MO method, in agreement with the experimental data, characterize 4,9-diazapyrene as a strong electron acceptor and indicate that the effect of conjugation is propagated primarily along the periphery of the molecule rather than between the heterorings.