Nitration acetyl aniline

Problem 23.9 Nitration of un-acetylated aniline yields a mixture of about tvvo-thirds meta and one-third para product. Since almost all the aniline is in the form of the anilinium ion, how do you account for the fact that even more meta product is not obtained ... 

On acetylation it gives acetanilide. Nitrated with some decomposition to a mixture of 2-and 4-nitroanilines. It is basic and gives water-soluble salts with mineral acids. Heating aniline sulphate at 190 C gives sulphanilic add. When heated with alkyl chlorides or aliphatic alcohols mono- and di-alkyl derivatives are obtained, e.g. dimethylaniline. Treatment with trichloroethylene gives phenylglycine. With glycerol and sulphuric acid (Skraup s reaction) quinoline is obtained, while quinaldine can be prepared by the reaction between aniline, paraldehyde and hydrochloric acid. 

Direct nitration of aniline and other arylamines fails because oxidation leads to the formation of dark colored tars As a solution to this problem it is standaid practice to first protect the ammo group by acylation with either acetyl chloride or acetic anhydride... 

Mononltroanllines or Nitroanilines, OjN.Q" H4.NHj, exist in three isomeric forms ortho-, meta-, and para. They are commercially available and extensively used in industry. None of these isomers can be obtained in good yield by direct nitration of aniline and it is necessary to employ indirect methods such as che Holleman method of acetylation of aniline to acetanilide followed by nitration(Ref 2) or by ammonolysis... 

SAMPLE SOLUTION (a) Because direct nitration of aniline is not a practical reaction, the amino group must first be protected as its A/-acetyl derivative. 

In the nitration of aniline in strongly acid medium one is concerned with the reaction of the anilinium ion, without resonance, with the N02+ ion. Electrons are withdrawn from the phenyl nucleus by the —NH3+ group and so meta and para nitraniline is produced but not ortho. If the aniline is first acetylated then mainly ortho and para nitraniline is produced through the R effect. 

Pentryl. See 2-(2 , 4, 6-TrInitro-N-nitranilino Ethanol Nitrate under Aniline ethanol and Derivatives A425-L to A42 )-R Pentryl Homologs A429-R Peracetic Acid, Benzylester. See Acetyl-benzyl peroxide A55-L P hen acyl Azide. See a>-Azido acetophenone under Acetophenone A47-R Phenazone. See Antipyrine A471-R Phenetidine. See Aminophenetole A240-R Phenyl Abietate. See under Abietic Acid A4rL... 

For the preparation of o-nitroaniline the method outlined above may be used. Nitration at a temperature of 40° is employed so as to increase the proportion of the o-nitroacetanilide to 25 per cent. Another variation is to treat aniline with excess of acetic anhydride and then with nitric acid. Acetanilide is first formed, which in the presence of acetic anhydride nitrates to give a larger proportion of the ortho isomer. The nitrating agent is assumed to be acetyl nitrate, CHaCOONOs. Finally, a number of indirect methods are... 

Treating aniline with acetic anhydride, or refluxing together aniline with glacial acetic acid, yields acetanilide (21). Nitration with mixed acids affords p-nitroacetanilide hydrolysis of the acetyl group gives p-nitroaniiine (15b). 

Derivation From aniline by nitration after acetylation, with subsequent removal of the acetyl group by hydrolysis from m-nitrobenzoic acid. 

Derivation (1) From p-chloronitrobenzene, (2) from aniline by nitration after acetylation, (3) from acetanilide. 

Nitration of aniline as the acetyl derivative by mixed acid gives p-nitro-acetanilide as the main product, together with a little of the ortho-compound. The relative amounts are shifted very greatly in favor of the ortho-compound... 

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. 

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