On the Mechanism of the Thermal and Photolytic Cyclization of Diphenylamines to Carbazoles

The product of photolysis of di‐ p ‐tolyamine in petroleum ether is 3,6‐dimethylcarbazole. The primary product of gas‐phase thermolysis of di‐ p ‐tolylamine at 850–1000°/0.01–0.05 Torr is also 3,6‐dimethylcarbazole. In the higher temperature range monomethylcarbazole and carbazole are also formed. Thermolysis of tetra‐ p ‐tolylhydrazine at 800–1000° gives only di‐ p ‐tolylamine, the latter decomposing further in the higher temperature range. It is concluded that carbazole formation involves in both cases an electrocyclization of the ortho ‐positions, and not a rearrangement, and that diphenylaminyl is not an intermediate.