CS254443B1 - Preparation method of 5-amino-2-acylaminiphenols - Google Patents

Abstract

A reduction of 5-nitro-2-acylaminophenols is described sodium polysulfide in the presence of magnesium sulfate to give 5-amino-2-acylaminophenols.

Description

The present invention provides a novel process for the preparation of 5-amino-2-acylaminophenols by reducing 5-nitro-2-acylaminophenols with sodium polysulfide.

The preparation of 5-amiho-2-acylaminophenols by the reduction of the corresponding nitro compounds by a variety of alkaline or acidic reduction procedures does not proceed satisfactorily. The reduction is either not performed at all or in an imperfect manner, the resulting products are obtained with poor yield and poor quality. In addition, the above procedures are not described in the scientific or patent literature. The patent literature describes the preparation of the above compounds only by hydrogenation of the corresponding nitro compounds on a Raney nickel catalyst under pressure (DE 1,946,652; BE 594,973; Res. Discl. 1983 235,352-3). Said hydrogenation is specific to a particular structure of substances of this type and has no universal activity. Thus, for example, hydrogenation of 5-nitro-2- (o-chlorobenzoyl) aminophenol in dimethylforniamide in the presence of Raney-nickel at 30 MPa at 150 ° C affords the corresponding 5-amino-2- (o-chlorobenzoyl) aminophenol. On the other hand, hydrogenation of 2-furanoyl-5-nitrophenol, 2-benzoyl-5-nitrophenol or 2- (p-toluyl) amino-5-nitrophenol gives the corresponding amino compounds in very low yield (5-20%) and in very impure form. Some substances, such as 2-furanoyl-amino-5-nitrophenol, are reduced on the furan nucleus and possibly even cleaved during reduction. The pressure-free hydrogenation on the platinum catalyst shows a similar course.

According to the invention, the reduction of 5-nitro-2-acylaminophenols (I) to 5-amino-2-acylaminophenols (II) can be carried out with sodium polysulphide in aqueous medium at 40 ° C. 2-Acylaminophenol sc is dissolved in a solution of 2.5 N sodium hydroxide solution, sc sc magnesium sulfate is added and an equivalent amount of sodium polysulfide is added with stirring sc.

The reaction is complete after stirring for 4-5 hours. By slowly dripping conc. hydrochloric acid is rendered alkaline to neutral (conjugate yellow), the precipitate is filtered off with suction, the filter cake is redissolved in 2.5 N sodium hydroxide solution, undissolved, the sulfur formed in the reaction is filtered off with suction and the filtrate is acidified with conc. hydrochloric acid until neutral. After washing with water, the product is dried.

The yields are almost quantitative and the reduction proceeds universally, regardless of the structure of 5-nitro-2-acylaminophenol. The material thus prepared is suitable, without further purification, for the preparation of coloring agents.

Example 1

5.08 g of 5-nitro-2-benzoylaminophenol was dissolved in 20 ml of 2.5 N sodium hydroxide solution and the resulting solution was mixed with a solution of 5.7 g of crystalline magnesium sulfate in 7 ml of water. 13 ml of an aqueous solution of sodium polysulfide containing 259 g of NaHS / l were added to the solution with stirring. After stirring for 5 hours, the solution was slowly acidified with conc. hydrochloric acid for neutral reaction and after another. The precipitated product was aspirated with stirring for 30 minutes. The filter cake was stirred in sodium hydroxide solution and the resulting suspension was aspirated again and the aspirated cake was washed on the filter. After acidification, conc. hydrochloric acid, washed with water and dried 3.46 g, i.e. 90% of the theory of 5-amino-2-benzoylaminophenol of m.p. Mp 215-218 ° C.

Example 2

21.2 g of 5-nitro-2- (o-chlorobenzoyl) aminophenol was dissolved in 100 ml of 2.5 N sodium hydroxide solution and the resulting solution was mixed with a solution of 20.5 g of crystalline magnesium sulfate in 36 ml of water. While stirring, 33 ml of an aqueous solution of sodium polysulfide containing 259 g of NaHS / l were added to the solution. After stirring for 5 hours, the reaction was terminated by chromatography / SILUFOL, 4: 1 benzene-ethanol system, detection: UV radiation - dark spot unreacted nitro compounds + + Erlich reagent - yellow amine color or CD 3 developing agent in 10% carbonate solution Sodium: yellow spot of unreacted nitro compounds and blue spot formed by amino compounds. When the reaction was complete, the solution was acidified with conc. hydrochloric acid for neutral reaction and after brief stirring the suspension was aspirated. The filter cake was redissolved in 2.5 N sodium hydroxide, the precipitated sulfur was aspirated and the filtrate was concentrated. hydrochloric acid eliminates the desired amino compound. After suctioning off the precipitated product, washing with water and drying, 5-amino-2- (o-chlorobenzoylamino) phenol of m.p. 118-120 [deg.] C. in a yield of 18.5 g, i.e. 95% of theory.

Example 3

60.6 g of 5-nitro-2-furanoylaminophenol was dissolved in 200 ml of 2.5 N sodium hydroxide solution and the resulting solution was mixed with a solution of 69 g of crystalline magnesium sulfate in 121 ml of water. 110 ml of aqueous sodium polysulfide solution were added to the solution with stirring, and after stirring for five hours and a negative chromatographic test, the solution was acidified with conc. hydrochloric acid for neutral reaction. After stirring for half an hour, the precipitated product was aspirated, the filter cake was reslurried in sodium hydroxide solution, the suspension was aspirated, the precipitated sulfur was washed on the filter with water, and the filtrate was acidified with conc. hydrochloric acid for neutral reaction. The precipitated 5-amino-2-furanoylaminophenol was aspirated

254 443 and washed on the filter with water. After drying, the product was obtained with a th. 217 DEG-222 DEG C. in a yield of 49.2 g, i.e. 87% of theory.

Example 4

64.5 g of 5-nitro-2-lauroylaminophenol were dissolved in 200 ml of 2.5 N sodium hydroxide solution and the resulting solution was mixed with a solution of 54.2 g of crystalline magnesium sulfate in 95 ml of water. 85 ml of aqueous sodium polysulfide solution (in 1 liter of 259 g NaHS solution) were added to the solution with stirring, and after stirring for five hours and a negative chromatographic test, the solution was acidified with conc. hydrochloric acid. The precipitate was aspirated and the filter cake was redissolved in sodium hydroxide solution. The resulting suspension was aspirated again and the filtrate was acidified with conc. hydrochloric acid for neutral reaction. The precipitated 5-amino-2-lauroylaminophenol was aspirated, washed on the filter with water and dried. M.p. 125-140 ° C in a yield of 55 g, i.e. 94.8% of theory.

Claims (1)

SUBJECT OF THE INVENTION A process for the preparation of 5-amino-2-acylaminophenols of formula II OH H ₂ N wherein R represents an alkyl residue of C 1 or phenyl, o-chlorophenyl. o-toluyl, furanoyl and ureide residue by reduction of 5-nitro-2-acylaminophenols of formula I OH .NHCOR O ₂ n wherein R is as defined above, characterized in that the reduction is carried out with sodium polysulphide in an aqueous alkaline medium, in the presence or absence of magnesium sulfate, at a temperature of 10 to 80 ° C. ·