Patent GB-619877-A (GB)
Title: Improvements in or relating to the production of aromatic amines
IPC: C07C209/18
Filed: 1946-06-13
Abstract: A primary aromatic amine or a mixture of primary aromatic amines are obtained by completely replacing hydroxy groups in a phenol or a mixture of phenols with amino groups by heating to a high temperature and under a high pressure a phenol or a mixture of phenols and an amine in the presence of a small proportion, e.g. 1 per cent by weight of the phenol, of a salt of ammonium, a primary or secondary amine and a strong acid other than sulphurous or nitric acid. Secondary amines are also obtained.  By phenol is meant any compound of the benzene or naphthalene series in which the hydroxyl group is directly attached to the nucleus and which does not already contain amino groups, but other groups which do not react with ammonia or amines may be present.  By amine is meant any primary or secondary amine of the aliphatic, alicyclic, aralkyl and aromatic series excepting diarylamines.  The salt employed may be formed in situ and may be a salt of the amine to be produced or a salt of the amine used for aminating the phenol. The ammonia or amine may be used in the presence or absence of a solvent or may be employed in a molecular excess.  The strong acid may be hydrochloric, hydrobromic, hydriodic, sulphuric, phosphoric or p-toluene sulphonic acid.  In examples: (1) aniline and diphenylamine are prepared from phenol, ammonia and with or without ammonium chloride; (2) o-toluidine and 2 : 21-dimethyl-diphenylamine are prepared from o-cresol, ammonia, ammonium chloride; (3) meta - toluidine and 3 : 31-dimethyl-diphenylamine are prepared from metal-cresol, ammonia and ammonium chloride; (4) para-toluidine and 4 : 41 - dimethyl - diphenylamine are prepared from para-cresol, ammonium chloride and ammonia; (5) 1 : 3-xylidine-5 and 3 : 31-5 : 51-tetramethyl-diphenylamine are prepared from 1 : 3-xylenol-5, ammonia and ammonium chloride; (6) 1 : 3-xylidine-5 is prepared from 1 : 3-xylenol-5, ammonia and with or without 1 : 3-xylidine-5 hydrochloride; (7) 1 : 2-xylidine-4 and 3 : 31-4 : 41 tetramethyl-diphenylamine are prepared from 1 : 2-xylenol-4, ammonia and ammonium chloride; (8) 3 : 4 : 5-trimethylaniline and 3 : 31 - 4 : 41 - 5 : 51 - hexamethyl - diphenylamine are prepared from 1 : 2 : 3-tri-methyl-5-hydroxybenzene, ammonia and ammonium chloride; (9), (10), (11) aniline and diphenylamine are prepared from phenol, ammonia and ammonium bromide or phosphate or p-toluene-sulphonate; (12) 1 : 3-xylidine-5 and 3 : 31-5 : 51-tetramethyl-diphenylamine are prepared from 1 : 3-xylenol-5, ammonium sulphate and ammonia.  The reaction may be carried out in a continuous manner by separately pumping the phenol and ammonia or amine through preheaters into a reaction zone wherein the salt is also present or is introduced, separately withdrawing the reaction product and the gaseous effluent, separating the reaction product into amines and unchanged phenol and recycling the phenol, and recovering the ammonia or amine from the gaseous effluent and recycling it.  The gaseous effluent may be expanded and cooled whereby the condensing water of reaction yields a concentrated solution of ammonia, the uncondensed ammonia is recycled, and the ammonia is recovered from the solution and recycled.  Preferably, the gaseous effluent is withdrawn through an absorbent to remove any volatilized salt carried by the effluent. The salt may be introduced into the reaction with the phenol in the form of a solution or slurry, or it may be sublimed into the reaction zone with the ammonia stream, or it may be produced in situ by introducing into the reaction zone the anhydrous acid from which it is formed.  The amines may be obtained from the reaction product by means of aqueous hydrochloric acid and regenerated by the addition of alkali. Unchanged phenol in the reaction product is extracted with aqueous caustic alkali and regenerated by the addition of acid. Prior to extraction, the reaction product may be diluted with a water-immiscible solvent, and the extraction carried out continuously.  In the case where the amines are extracted with hydrochloric acid, the solvent layer containing phenol and secondary amines may be dried, the solvent stripped therefrom and the phenol separated from the secondary amines before recycling. When the phenols are extracted with aqueous caustic alkali, the alkaline layer is separated from the solvent layer containing primary and secondary amines, and the solvent is stripped therefrom.  The required aromatic amines may be purified by conversion into formyl derivatives which are recrystallized and then hydrolysed to regenerate the amines.