CS254448B1 - Preparation method of the pure 3-aminophenol - Google Patents

Abstract

The present invention relates to a process for the preparation of pure 3-aminophenol from the crude product produced alkaline melting of 3-aminobenzenesulfonic acid. The essence is the acidification of the dissolved amine inorganic acid, preferably hydrochloric acid. 3-aminophenol is used as a semi-finished product drugs, herbicides and dyes.

Description

The invention relates to a process for preparing pure

3-aminophenol from the crude product produced by the alkaline melting of 3-aminobenzenesulfoacid.

3-Aminophenol is an important raw material in the manufacture of pharmaceuticals, herbicides and dyes. The starting material for its preparation is 3-aminobenzenesulfonic acid (methanil). Alkaline melting with potassium hydroxide yields an impure, dark brown colored crude 3-aminophenol containing unreacted methanilic acid and 5-10 wt. diphenylamine derivatives, especially 4-amino-4‘-hydroxy-diphenylamine and 4,4‘-dihydroxydiphenylamine. The most efficient way to purify 3-aminophenol from these impurities is by distillation under reduced pressure. Its design is not easy.

Due to the significant decomposition of 3-aminophenol at temperatures above 165 ° C it is necessary to distil at an absolute pressure below 1.3 kPa and with the addition of stabilizers to the batch. The high melting point of 122 ° C with significant sublimation at this temperature requires special treatment in the condensation of the distillate. Pure distilled 3-aminophenol must be immediately crystallized or flaked to avoid discoloration in the presence of air. The light products are stabilized against oxidation by a suitable admixture. The yield of distillation varies from 70 to 78% of the 100% of 3-aminoquinol. Residues need to be disposed of by incineration and handling is very unpleasant.

These disadvantages are overcome by the process for preparing pure 3-aminophenol from the crude product produced by the alkaline melting of methanilic acid according to the invention. The essence is that the solution of 3-aminophenol purified by carbonation at 60-65 ° C and pH 5.2 is acidified with an inorganic acid such as hydrochloric acid to pH 4.2-3.5 and after cooling to 35-45 ° C the pure product is isolated. The yield of pure 3-aminophenol is lower (40 to 55%) than in the case of distillation, but the difference is compensated by the fact that by neutralization of the mother liquors it is possible to regenerate

3-Aminophenol with increased content of diphenylamines. This regenerate is light yellow colored, contains no water-insoluble substances and can be advantageously used for purposes where the increased content of diphenylamine derivatives does not interfere, for example for the production of certain types of dyes.

Crystallization product - pure 3-aminophenol. with a content of diphenylamine derivatives of less than 1% by weight. It is only slightly yellow to slightly brown in color, well crystalline and does not need to be dried for the vast majority of applications because it is further processed in an aqueous medium. It will fully replace distilled 3-aminolenol for the preparation of pharmaceutical drugs and herbicides.

In order to further elucidate the invention, an exemplary embodiment is given below.

Example

In a batch of 1,500 ml of water, 450 g of wet crude were dissolved with the gradual heating of 65 ° C

3-aminophenol, very dark brown in color, containing 88.1.5% (396.5 g) of dry matter. Content

4-amino-4 ' -hydroxydiphenylamine 5.50%, 4.4 ' -dihydroxydiphenylamine 0.13% and methanilic acid 0.17% in dry matter. It also contains inorganic salts, water-insoluble impurities and resins.

The solution is first acidified to pH 5.2 by the addition of 4 ml of 32.5% hydrochloric acid and filtered by filtration after stirring with activated carbon. This eliminates the precipitated resin fractions. The scleration may be repeated as necessary and the resulting filtrate decolorized by the addition of 0.5 to 1 g of sodium dithionite.

The purified 3-aminophenol solution was further acidified with hydrochloric acid to pH in the region

4.2 to 3.5 (preferably 4.0) and 3-aminophenol are crystallized from the solution by cooling to 40 ° C. At this temperature, filtration and washing of the crystals with 40 ° C with warm water are performed. The obtained wet 3-aminophenol is slightly yellow colored, nicely crystalline and contains 0.4% diphenylamine derivatives. Yield 238 g, with a dry matter content of 77.7%, i.e. 46.6 per feed of crude 3-aminophenol solids.

From the mother liquors, neutralization with 26% aqueous ammonia to pH 6.5, salting out 190 g of crystalline sodium chloride and cooling to 25 ° C gives the remaining 3-aminophenol 165 g (dry matter 78.2%) containing 10.6% of derivatives. diphenylamine in dry matter. The total crystallization yield is 79.1 percent of the initially seeded dry crude 3aminophenol.

SUBJECT OF THE INVENTION

Claims (1)

SUBJECT OF THE INVENTION Process for the preparation of pure 3-aminophenol from crude 3-aminophenol produced by the alkaline melting of metanilic acid, characterized in that the solution of 3-aminophenol purified by filtration and activated carbon at 60 to 65 ° C and pH 5.2 is further acidified best with inorganic acid dilute hydrochloric acid to pH 4.2-3.5 and after cooling to crystallization at 35-45 ° C, pure 3-aminophenol is isolated by filtration.