Patent GB-713622-A (GB)
Title: Process for the preparation of aromatic parahydroxyamines
IPC: C07C215/76
Filed: 1952-12-04
Abstract: Aromatic parahydroxyamines are prepared by the reduction of a mononitro derivative of an aromatic hydrocarbon containing not more than two benzene rings or a monochloro or dichloro derivative thereof, the nitro group being attached to an aromatic nucleus which is unsubstituted in the position para thereto, the reduction being effected by adding the nitro compound and hydrogen to a suspension of hydrogenation catalyst in an aqueous solution containing from 1 to 25 per cent by weight of sulphuric acid, at a temperature of from 50 DEG to 145 DEG  C., the partial pressure of hydrogen being maintained below 760 mm. of mercury and the rate of addition of the nitro compound being such that at no time does the amount of unreacted nitro compound in the suspension exceed its solubility therein. Specified nitro compounds are nitrobenzene, orthonitrotoluene, ortho-nitrochlorobenzene, meta-nitrochlorobenzene, 2 : 5 - dichloronitrobenzene, 2-nitrobiphenyl and 1-nitronaphthalene.  The nitro compound, which may be in the form of a concentrated sulphuric acid solution, is conveniently added to the reaction mixture by increments, each increment being less than 0.8 per cent of the weight of dilute acid solution and being added after the preceding increment has been substantially reduced.  The hydrogenation catalyst is preferably platinum supported on a porous material such as charcoal, and for a catalyst comprising 1 per cent platinum supported on charcoal the amount used (including support) is preferably from 0.1 to 3 per cent of the weight of the dilute acid solution.  Other suitable catalysts, which should be acid insensitive, include palladium, rhodium, and the sulphides of certain heavy metals such as molybdenum, cobalt and tungsten.  The proportion of parahydroxyamine in the reaction product is increased by the presence in the acid suspension of from 0.01 to 0.2 per cent by weight (based on weight of dilute acid solution) of a water-soluble quaternary ammonium compound, especially one containing an alkyl group having at least ten and not more than eighteen carbon atoms or a betaine having a normal alkyl radical of fourteen to sixteen carbon atoms substituted on its methylene carbon.  Examples of such compounds include octadecyl trimethyl ammonium chloride, octadecyl dimethyl ethyl ammonium bromide, dioctadecyl dimethyl ammonium chloride, dipentadecyl dimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, C-cetyl betaine and C-dodecyl betaine.  Compounds such as tetramethyl ammonium chloride are also effective.  The proportion of amines produced as by-products may be controlled by suitable adjustment of temperature, partial pressure of hydrogen, acid concentration, quantity of catalyst and amount of quaternary ammonium compound. These amines may be separated from the parahydroxyamines by any convenient method, e.g. by neutralizing the sulphuric acid with brine followed by steam distillation.  The examples describe the preparation of the following mixtures:-para-aminophenol and aniline, 3-methyl-4-amino-phenol and ortho-toluidine, 4-aminonaphthol and 1 - aminonaphthalene, 3-chloro - 4 - amino - phenol and ortho - chloroaniline, 2 - amino - 5 - hydroxy biphenyl and 2 - aminobiphenyl, and 2 : 5 - dichloro - 4 - aminophenol with ortho-chloroaniline, meta-chloroaniline and 2 : 5-dichloroaniline. Specifications 493,960 and 536,415 are referred to.