The nitration of some methyl substituted indole-3-aldehydes

The reactions of some methyl derivatives of indole-3-aldehyde with nitric acid in acetic acid medium have been investigated. 2-Methylindole-3-aldehyde gives the 6-nitro derivative, together with some 2-methyl-3-nitro- and 2-methyl-3,6-dinitroindole. 1-Methylindole-3-aldehyde gives 4- and 6-nitro derivatives, 1-methyl-3-nitroindole, 1-methyl-5-nitroisatin, N-formyl-N-methyl-5-nitro-anthranilic acid and N-methyl-5-nitroanthranilic acid. 1,2-Dimethylindole-3-aldehyde gives 1,2-dimethyl-3-nitroindole, 1,2-dimethyl-3,6-dinitroindole, N-methyl-4-nitroanthranilic acid and 4- and 6-nitro-2-methylaminobenzonitrile.