Para-Nitroacetanilide

Recrystallise the crude pale yellow product from methylated spirit, filter at the pump, wash quickly with a few ml. of fresh spirit, and then drain and dry. The yellow o-nitroacetaniiide remains in the filtrate, whilst the p nitroacetanilide is obtained as colourless ciy stals, m.p. 214°. A second recrystallisation of the para compound should not be necessary. Yield of pure product, 8 g. 

Compounds containing two primary amino groups attached to a benzene ring can be prepared by the reduction of dinitro compounds and of nitroanilines, usually with tin or stannous chloride and hydrochloric acid or with iron and very dilute hydrochloric acid. Para-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylaniline from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetanilide,. which may be hydrolysed to the diamine. 

Para-nitroaniline was obtained by A. W. Hofmann [1] who nitrated acetanilide to p- nitroacetanilide which was then hydrolysed with a sodium hydroxide solution. 

Although protonation of the amine leads to the anilinium salt which is a deactivating substituent, nitration of aniline in nitric acid sulfuric acid yields 60% para and 34% meta substitution, whilst nitration of acetanilide gives 79% para and 19% ortho nitroacetanilides. 

The nitration of acetanilide with mixed acid yields nitroacetanilides in which the ortho para ratio is less than 0.1. When the nitration medium is nitric acid, this ratio is 0.7, when acetyl nitrate in acetic anhydride is used, the product is almost entirely o-nitroacetanilide. No satisfactory explanation has been given for these results. The 40-50 per cent yield of m-nitro-aniline that results from the nitration of aniline in mixed acid or in nitric acid can be explained in the following manner. In the strong acids, nitric and sulfuric acid, aniline is largely ionized. 

Suppose, however, that we need o-nitroaniline. The synthesis that we just outlined would obviously not be a satisfactory method, for only a trace of o-nitroacetanilide is obtained in the nitration reaction. (The acetamido group is purely a para director in many reactions. Bromination of acetanilide, for example, gives/>-bromoacetanilide almost exclusively.)... 

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