P-Nitroacetanilide

Prepared by heating p-nitrochlorobenzene with concentrated aqueous ammonia in an autoclave at 170°C. It is also prepared by alkaline hydrolysis of p-nitroacetanilide or by nitrating and hydrolysing benzylideneaniline. 

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. 

Heat a mixture of 15 g. of p-nitroacetanilide and 75 ml. of 70 per cent, sulphuric acid (1) under a reflux water condenser for 20-30 minutes or until a test sample remains clear upon dilution with 2-3 times its volume of water. The p-nitroaniline is now present in the hquid as the sulphate. Pour the clear hot solution into 500 ml. of cold water and precipitate the p-nitroanihne by adding excess of 10 per cent, sodium hydroxide solution or of concentrated ammonia solution. When cold (cool the mixture in ice water, if necessary), filter the yellow crystalline precipitate at the pump, wash it well with water, and drain thoroughly. Recrystallise it from a mixture of equal volumes of rectified (or methylated) spirit and water or from hot water. Filter, wash and dry. The yield of p-nitroanihne, m.p, 148°, is 11 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. / ara-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylanihne from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetaniUde,.which may be hydrolysed to the diamine. 

When p-nitroacetanilide is heated to 200-250 C in the presence of small quantities of sulphuric acid, it gives rise to a very spectacular decomposition and the formation of a huge quantity of carbonised foam . This extraordinary reaction is called black snake . 

Add 26 g. of flnely-powdered, dry acetanihde to 26 ml. of glacial acetic acid contained in a 500 ml. beaker introduce into the well-stirred mixture 92 g. (60 ml.) of concentrated sulphuric acid. The mixture becomes warm and a clear solution results. Surround the beaker with a freezing mixture of ice and salt, and stir the solution mechanically. Support a separatory funnel, containing a cold mixture of 16 5 g. (11 ml.) of concentrated nitric acid and 12-6 g. (7 ml.) of concentrated sulphuric add, over the beaker. When the temperature of the solution falls to 0-2°, run in the acid mixture gradually while the temperature is maintained below 10°. After all the mixed acid has been added, remove the beaker from the freezing mixture, and allow it to stand at room temperature for 1 hour. Pour the reaction mixture on to 260 g. of crushed ice (or into 500 ml. of cold water), whereby the crude nitroacetanihde is at once precipitated. Allow to stand for 15 minutes. Alter with suction on a Buchner funnel, wash it thoroughly with cold water until free from acids (test the wash water), and drain well. RecrystaUise the pale yellow product from alcohol or methylated spirit (see Section IV,12 for experimental details), filter at the pump, wash with a httle cold alcohol, and dry in the air upon filter paper. [The yellow o-nitroacetanilide remains in the filtrate.] The yield of p-nitroacetanilide, a colomless crystalline solid of m.p. 214°, is 20 g. 

P(0)(0Me)H and [TpAr Me]Zn0P(0)(0R)2, respectively (Scheme 26) (35). In addition, [TpAr Me]ZnOH also cleaves activated esters and amides in a stoichiometric fashion, as illustrated in Scheme 27. Kitajima has described a similar amide cleavage reaction between the copper and nickel hydroxide complexes [Tp JMtOH) (M = Ni, Cu) and p-nitroacetanilide to give [TpPr 2]M p2-MeC(0)NC6H4N02 [Eq. (34)] (198). 

The basic hydrolysis of p-nitroacetanilide is retarded by a-CD, whereas that of trifluoroacetanilide and its m-nitro derivative is modestly enhanced... 

Nitration leads similarly to p-nitroacetanilide, which can be hydrolysed to p-nitroaniline ... 

Protection of the amino group by acetylation, as in acetanilide, therefore usually permits monosubstitution reactions with appropriate electrophilic reagents to proceed smoothly. Thus with bromine, p-bromoacetanilide is the main product the small quantity of the ortho isomer simultaneously formed can be easily eliminated by recrystallisation (Expt 6.67) hydrolysis of p-bromoacetanilide gives p-bromoaniline. Nitration leads similarly to p-nitroacetanilide which can be hydrolysed to p-nitroaniline (Expt 6.68). 

Investigate by thin-layer chromatography the effectiveness of the recrystallisation process in the following way. Load a 20 x 5 cm thin-layer plate (Silica Gel G) with approximately 3 mm diameter spots of concentrated solutions (in acetone) of the crude and the recrystallised product. Concentrate a portion of the ethanolic mother-liquor and similarly apply to the plate. Develop the chromatogram with a toluene-ethyl acetate mixture (4 1) and dry the plate. Mark the positions of the visible spots and leave the plate in a tank of iodine vapour to reveal the rest of the components. The recrystallised p-nitroacetanilide (RF 0.07) should be free from the pale yellow o-isomer (RF 0.36) these compounds are revealed by the iodine treatment. 

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