Abstract
Fluorenone, dissolved in 96 and 100 % sulphuric acid, has been allowed to react with sodium azide and the resultant mixtures diluted with both water and anhydrous methanol. 9-Methoxyphenanthridine, the product to be expected from nucleophilic attack by the methanol, was not formed and phenanthridine was obtained in good yield from all experiments. The formation of this compound both under anhydrous conditions and in the presence of water shows Smith's mechanism for the ketonic Schmidt reaction, which involves dehydration to a Beckmann-type intermediate and subsequent rehydration, to be unlikely. An alternative mechanism involving a hydrogen-bonded cyclic intermediate is suggested. The rate of decomposition of 9-azidofluorene in anhydrous sulphuric-acetic acid has been followed by the measurement of the evolution of nitrogen under constant-pressure conditions. Determination of initial rates and times for half and seven-tenths reaction showed the decomposition to be substantially of the first order both in azide-concentration, with values of 1.09, 1.04, and 1.02, and in acid-strength of the solution, as given by hO (negative antilogarithm of Hammett's Acidity Function HO), with values 1.03, 1.07, and 1.09. The activation energy of the reaction, measured between 25 and 45 was found to be approximately 23.4 kcal. /mole. A mechanism for the acid-catalysed rearrangement of 9-azidofluorene to phenanthridine is put forward in which reaction proceeds via the decomposition and rearrangement of the mono-protonated azide (which probably exists largely as the ion-pair with bisulphate ion) present in equilibrium with the more stable non-protonated azide. The evidence for simultancity of rearrangement and nitrogen-release is discussed both for the above azide and for the diarylazido-methanes and -ethanes which have been investigated by McEwen and his co-workers.