Nitration of Indoles. IV. The Nitration of 2-Phenylindole

Nitration of 2-phenylindole (1) follows the orientation rules previously established for 2-methylindole, except that trinitration has not been observed. Thus, nitration of 1 in concentrated sulfuric acid gives 5-nitro-2-phenylindole (8), while nitration of 1 in concentrated nitric acid gives 3,6-dinitro-2-phenylindole (4) and further nitration of 8 in concentrated nitric acid gives 3,5-dinitro-2-phenylindole (9). Catalytic hydrogenation of 8 gives 5-amino-2-phenylindole (12). The nitration product of 2-phenylisatogen (13) and nitric acid has been shown to be 5-nitro-2-phenylisatogen (14), an observation of interest because of the structural resemblance of 13 to the conjugate acid (15) of 1.