RU2283307C1 - Method for preparing 5(6)-amino-2-(4'-aminophenyl)-benzimidazole - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of 5(6)-amino-2-(4'-aminophenyl)-benzimidazole. Method involves the acylation reaction of 2,4-dinitroaniline with 4-nitrobenzoyl chloride in the presence ferric chloride as a catalyst in a solvent medium chosen from chlorobenzene, para-xylene, technical mixture of xylenes, toluene or ethylbenzene at boiling the reaction mass followed by crystallization after cooling the reaction mixture and the following reduction of synthesized 2,4',4-trinitrobenzanilide with powder-like iron in dimethylacetamide or dimethylformamide aqueous solution at temperature 96-101°C and the cyclodehydration reaction of synthesized 2',4',4-triaminobenzanilide with sulfuric acid aqueous solution in the presence of ammonia aqueous solution at temperature 100-101°C, and the following isolation of formed 5(6)-amino-2-(4'-aminophenyl)-benzimidazole as crystallohydrate of monosulfate and its neutralization with ammonia. Invention provides the development of the technological process for synthesis of the end product that excludes using hydrogen and expensive catalysts, enhancing the yield of salt and preventing formation of acid waste, effective isolation of 5(6)-2-(4'-aminophenyl)-benzimidazole salt with only trace amounts of impurities.

EFFECT: improved and effective method of synthesis.

9 cl, 1 tbl, 10 ex

Description

The present invention relates to the field of organic chemistry and relates to a method for producing 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole, hereinafter DABI, used in the synthesis of heat-resistant polymers and fibers.

A known method for producing 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole by hydrogenation in the presence of Raney nickel or palladium 2,4-dinitroaniline in alcohol, followed by condensation of the resulting triaminobenzene in the form of a phosphate salt with n-aminobenzoic acid in 105 -116% polyphosphoric acid at 140-145 ° С (A.S. USSR 498298, C 07 D 235/18, 09/13/1976). However, the method requires the use of expensive catalysts and hydrogen, which requires the creation and operation of an appropriate structure - hydrogen production, purification, etc. In addition, the formation of a large amount of phosphorus-containing waste pollutes the environment.

There is also known a method for producing DABI by cyclodehydration of 2 ¹ , 4 ¹ , 4-tri-aminobenzanilide, hereinafter TABA, in the presence of formic acid salt when heated in hydrochloric acid, followed by isolation of the target product by neutralization with an alkaline agent (AS USSR 1438178, C 07 D 235/18, 07.27.1995). The disadvantage of this method is the use of concentrated hydrochloric acid when heated to 107 ° C, which makes special demands on the corrosion resistance of the equipment.

In turn, the used TABA is obtained by hydrogenation of 2 ¹ , 4 ¹ , 4-tri-nitrobenzanilide, hereinafter TNBA, in a solvent medium in the presence of a palladium catalyst on a support containing iron and / or nickel (RU 2041200 C1, C 07 C 233 / 80, 12/25/1995), or in the presence of a palladium catalyst on a support additionally containing boron (AS USSR 546608, C 07 C 103/20, 04/20/1977). The use of hydrogen under pressure and expensive palladium catalysts also complicate the process, which leads to the high cost of TABA and DABI based on it.

There is also a method for producing TNBA by acylation of 2,4-dinitroaniline with 4-nitrobenzoic acid in the presence of an activator, polychlorocyclophosphazene and a catalyst, N-oxides of pyridine or β- and γ-picoline in chlorobenzene medium (AS USSR 1025093, C 07 C 233 / 66, 02.20.1999). The disadvantages of this method include the use of complex activators and catalysts.

A known method of producing DABI by catalytic reduction and cyclization of TNBA with hydrogen in aqueous solutions of hydrochloric or phosphoric acids, followed by isolation of DABI by alkali neutralization (US patent 4417056, C 07 D 235/18, 11/22/1983). In this case, metals of the eighth group of the Periodic Table, such as nickel, platinum, palladium, rhodium and ruthenium, are used as a catalyst. The disadvantages of this method include the use of expensive catalysts based on precious metals, the implementation of the recovery of gaseous hydrogen.

The closest analogue of the proposed method is a three-stage method for producing DABI by dinitration of N- (4 ¹ -nitrobenzoyl) aniline with concentrated nitric acid in the presence of concentrated sulfuric acid to obtain TNBA in the first stage, followed by reduction of TNBA to TABA using sodium sulfide, polysulfide or ammonium on the second stage and cyclodehydration of TABA in a medium of concentrated hydrochloric acid when heated to 100 ° C to DABI in the third stage (UK patent 1531161, C 07 D 235/18, 01/01/1978). The product is isolated by diluting the reaction mass with large amounts of ice and neutralizing the hydrochloric acid salt with ammonia. DABI is purified by recrystallization from ethanol, which complicates the technology and leads to loss of product. In addition, working with large amounts of concentrated hydrochloric and nitric acids requires the use of expensive equipment made of high alloy steels and alloys and leads to the formation of a large amount of acid waste requiring neutralization.

The objective of the present invention is to develop a technologically advanced method for producing DABI, devoid of these drawbacks, eliminating the use of hydrogen and expensive palladium and platinum catalysts and conducting cyclodehydration of TABA in DABI in high acid environments, isolating the DABI salt by adding a large amount of concentrated hydrochloric acid to the reaction mass.

The problem is solved by the described method for producing 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole (DABI), characterized in that 2,4-dinitroaniline is acylated with 4-nitrobenzoyl chloride in the presence of a ferric chloride catalyst in an organic solvent, such as chlorobenzene, n-xylene, a technical mixture of xylenes, toluene or ethylbenzene, when the reaction mixture is boiled and 2,4 ¹ , 4-trinitrobenzanilide crystallized after cooling of the reaction mixture is neutralized with aqueous ammonia, after which the resulting 2,4 ¹ , 4 -tri-nitrobenzanilines d is reduced with powdered iron in an aqueous solution of dimethylacetamide or dimethylformamide at a temperature of 96-101 ° C, followed by the introduction of sodium sulfite and separation of the formed precipitate of iron oxide, with further cooling of the remaining aqueous amide solution and separation of crystallized upon cooling 2 ¹ , 4 ¹ , 4- triaminobenzanilide, which is then subjected to cyclodehydration in an aqueous solution of sulfuric acid in the presence of an aqueous solution of ammonia at a temperature of 100-101 ° C, followed by isolation of the resulting 5 (6 ) -amino-2- (4 ¹ -aminophenyl) benzimidazole in the form of crystalline salt of monosulfate salt and its neutralization with ammonia.

The achievement of the objectives of the invention contributes to the following conditions:

- the catalyst in the form of ferric chloride or as an aqueous solution of ferric chloride or crystalline anhydrous ferric chloride and the solvent is added to the aqueous paste of 2,4-dinitroaniline, followed by joint dehydration by azeotropic distillation of water with a solvent, after which the solvent is added to the remaining mass, 4- nitrobenzoyl chloride and carry out acylation;

- use a 50% aqueous solution of ferric chloride;

- use a 10% aqueous solution of dimethylacetamide or dimethylformamide and the water-amide mother liquor obtained after cooling and crystallization of 2 ¹ , 4 ¹ , 4-triaminobenzanilide is recycled to the reduction stage of 2,4 ¹ , 4-trinitrobenzanilide with preliminary adjustment of pH≤7 ;

- cyclodehydration with a solution of sulfuric acid is carried out in the presence of activated carbon;

- the allocation of 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole in the form of crystalline monosulfate salt is carried out by crystallization from the cooled reaction mass, then the sulfuric acid mother liquor is purified by heating with activated carbon and after filtering from activated carbon sent for recycling to the stage of cyclodehydration;

- the obtained crystalline hydrate of the monosulfate salt of 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole is purified by recrystallization from an aqueous solution of sulfuric acid in the presence of activated carbon or without it, followed by recycling of the resulting sulfate mother liquor to the recrystallization stage;

- neutralization of crystalline hydrate of monosulfur salt of 5 (6) -amino-2- (4 ^1- aminophenyl) benzimidazole is carried out by adding the obtained crystalline hydrate of monosulphate salt of 5 (6) -amino-2- (4 ^1- aminophenyl) benzimidazole in the form of an aqueous paste to aqueous ammonia solution in the presence of Trilon B at a temperature of 15-20 ° C, followed by heating to 60-75 ° C and adjusting the pH of the medium to 8.5-9.0;

- the obtained 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole is subjected to drying in an inert gas stream in a stepwise mode at a temperature of 100-135 ° C and 150-170 ° C in the second stage.

According to the invention, it has been found that an effective method for introducing a ferric chloride catalyst into the acylation process is to add an aqueous solution of ferric chloride to an aqueous paste of 2,4-dinitroaniline, followed by dehydration by azeotropic distillation of the water with a solvent. This technique provides a high catalytic activity of ferric chloride and allows the use of ~ 50% aqueous solution of ferric chloride, which is a technical product. Along with this, it is also possible to use crystalline hydrate or anhydrous ferric chloride. It was shown that the acylation process proceeds smoothly in paraxylene as well as in chlorobenzene, in a free boiling regime without blowing hydrogen chloride with an inert gas and applying increased pressure. The maximum temperature of the reaction mixture is 135 ° C in chlorobenzene and 139 ° C in n-xylene. The conversion of 3,4-dinitroaniline reaches 99% or more. Received TNBA meets the requirements for a technical product suitable for processing in TABA. It was also shown that along with the above, it is possible to use such solvents as a technical mixture of xylenes, toluene or ethylbenzene.

Water in the process of reducing TNBA to TABA with iron powder in the presence of an electrolyte is a source of hydrogen.

The most effective solvents for the recovery process is a 10% by volume solution of dimethylacetamide or dimethylformamide in water. The separation of the TABA solution in the water-amide medium from the precipitate of iron oxide can be carried out without neutralizing the reaction mass.

By adding a reducing agent, sodium sulfite, directly to the reaction mass, before the solution is separated from the iron oxide precipitate, the best quality of TABA and the possibility of recycling the water-amide mother liquor for the next reduction operation are ensured.

To implement the TABA cyclodehydration process, a system is used that ensures the process proceeds at low acidity and, therefore, its selectivity, as well as the possibility of efficient separation of the DABI salt from the reaction mass by crystallization. The selectivity of the process as a whole is determined by the value of the acidity of the medium H _about . For the implementation of cyclodehydration TABA use a solution of sulfuric acid, the acidity of which is reduced by adding an aqueous solution of ammonia. Under these conditions, 5 (6) -amino-2- (4'-aminophenyl) benzimidazole crystallizes from the reaction solution in the form of crystalline hydrate of the monosulfuric salt DABI · H ₂ SO ₄ · H ₂ O.

The mother liquor after separation of the salt DABI · H ₂ SO ₄ · H ₂ O by filtration is purified by treatment with activated carbon OU-B and sent for recycling to the stage of cyclodehydration. Such a recycling can be carried out repeatedly. This achieves a significant reduction in the consumption of sulfuric acid and the amount of production waste.

Purification of the DABI · H ₂ SO ₄ · H ₂ O salt is carried out by recrystallization from ~ 12% sulfuric acid in the presence of OU-B coal and is also carried out with recycling of the sulfuric acid mother liquor.

DABI salt · H ₂ SO ₄ · Н ₂ O of a bright salad greenish color. Its composition is confirmed by elemental analysis:

Element S N FROM N Calculated 9.41 4.70 45.88 16.47 Found 9.43 5.27 44,20 15.98

Acid-base titration of the salt revealed that its individual samples contain 28.8-31.0% H ₂ SO ₄ (according to the theory of 28.8%). Crystal hydrate is stable when heated to 110-130 ° C. Salt loses the water molecule and passes into DABI · H ₂ SO ₄ when heated to 160-180 ° C. After drying at 160-180 ° C for 6-8 hours, the DABI · H ₂ SO ₄ salt still contains 0.3% water. Separate samples of the DABI · H ₂ SO ₄ salt contain 30.5-30.6% of H ₂ SO ₄ (30.43% in theory). In air at room temperature, the anhydrous salt quickly enough again goes into crystalline hydrate. The crystalline hydrate DABI · H ₂ SO ₄ · H ₂ O is practically insoluble in water at room temperature.

The DABI base is isolated by neutralizing with ammonia an aqueous suspension of salt. It is shown that an effective process of neutralization is provided by the gradual addition of salt to an aqueous solution of ammonia. This achieves high mobility of the suspension in the process of neutralization. The process proceeds smoothly and quantitatively at a temperature of 15-20 to 70-75 ° C.

The main problem of drying DABI is the formation of DABI · Н ₂ О crystalline hydrate from aqueous solutions, which actively loses water when rapidly heated to 138-145 ° С and at the same time it melts. Further, as water is removed, it hardens to form a solid melt. To avoid this phenomenon, the drying process is carried out stepwise, heating the paste, and then the DABI crystalline hydrate at a temperature of from 100 to 130-135 ° C with constant inert gas purging. In this case, crystalline hydrate gives off water without melting. At the final stage of drying, the temperature is increased to 160-165 ° C.

The invention is illustrated by the following examples.

Example 1. The synthesis of TNBA in chlorobenzene

In a 3-liter flask equipped with a stirrer, thermometer and direct refrigerator, load 800 g of an aqueous paste of 2,4-dinitroaniline containing 708 g of dry matter, and 4.3 g of ferric chloride in the form of a 50% aqueous solution. 1.7 L of chlorobenzene was added and water was distilled off with stirring as an azeotrope with chlorobenzene. Azeotrope distillation begins at 90 ° C. By the end of the distillation, the temperature in the vapor reaches 135 ° C.

After the distillation of water is complete, the direct refrigerator is reversed, chlorobenzene is added in an amount equal to distilled with an azeotrope, and 758 g of 4-nitrobenzoyl chloride dissolved in 1380 ml of chlorobenzene. The reaction mass is heated with stirring. At a temperature of 90-100 ° C, an intensive evolution of hydrogen chloride begins, which, having passed through a reflux condenser, is trapped in an aqueous solution of alkali in a system connected to a water ring vacuum pump.

The reaction mixture gradually over 2 hours, heated to reflux (134-135 ° C) and maintained at this temperature for 2 ^hours. By this time, the evolution of hydrogen chloride ceases. The content of 2,4-dinitroaniline in the sample of TNBA taken from the reaction mass is 0.1 wt.%.

The reaction mixture in the flask is cooled to 10-15 ° C, the crystallized precipitate of TNBA is filtered off, washed on the filter with chlorobenzene and transferred to a 5-liter flask equipped with a stirrer and a direct refrigerator. 2.5 L of distilled water was added to the flask and the chlorobenzene contained in TNBA was distilled off as an azeotrope with water at a vapor temperature of 90-100 ° C.

An aqueous suspension of TNBA in the flask is cooled to 60-70 ° C, 0.5 L of distilled water is added and 350 ml of a 0.25% aqueous ammonia solution are neutralized with stirring until the pH of the aqueous extract of TNBA 7-8 is reached.

Obtain 1541 g of an aqueous paste containing 1233 g of TNBA (96% of theory), mp. 194-195 ° C, the content of 2,4-dinitroaniline 0.07 wt.%, 4-nitrobenzoic acid 0.1 wt.%, PH of the aqueous extract 6.

Example 2. Synthesis of TNBA in n-xylene

The synthesis is carried out as described above. The charge is 800 g of an aqueous paste of 2,4-dinitroaniline containing 708 g of dry matter, 794 g of 4-nitrobenzoyl chloride and 3080 ml of n-xylene. 7.2 g of FeCl ₃ · 6H ₂ O are charged as a catalyst. When dehydrating a mixture of aqueous paste of 2,4-dinitroaniline and crystalline ferric chloride by azeotropic distillation, the vapor temperature rises from 90 ° C to 139 ° C. During acylation at a temperature of 90 ° C, the evolution of hydrogen chloride begins. Gradually, over 2.5 hours, the temperature was raised to a boiling point of 139 ° C and kept under stirring for 3 hours. The content of 2,4-dinitroaniline in the TNBA sample taken from the reaction mass is 0.05 wt.%. The yield of TNBA 1232 g (95.9% of theoretical), the appearance is a crystalline powder of a yellow-greenish color, mp. 195-196 ° C, the content of 2,4-dinitroaniline 0.05 wt.%, 4-nitrobenzoic acid 0.08 wt.%, PH of the aqueous extract 6.

Examples 3-5 (Synthesis of TNBA in various organic solvents) are given in the table.

Table.
Synthesis of TNBA in various organic solvents. Example No. Solvent Download, g Temperature ° C Time hour TNBA output Characteristic TNBA Name Download, g 2,4-dinitro-aniline (DND) in terms of the main substance 4-nitro-benzoyl chloride FeCl ₃ in terms of the basic substance g % of theoretical Mp, ° C Content, wt.% pH of the aqueous extract Bottom 4-nitro-benzoic acid 3 Technical mixture of xylenes 65 16.41 18.29 0,091 anhydrous powder 100-136 2.2 27.8 93.5 194-195 0.005 0.09 6 four Toluene 130 16.41 18.29 0,091 FeCl ₃ • 6Н ₂ О 100-113 4.0 27.6 92.7 192-193 0.006 0.08 6 5 Ethylbenzene 65 16.41 18.29 0,091 50% aqueous solution 90-137 3.0 28.1 94.2 194-196 0.004 0,07 6

Example 6. The restoration of TNBA in TABA in water-dimethylacetamide solution.

A 3-liter flask equipped with a stirrer, a thermometer and a reflux condenser is charged with 2500 ml of a 10% (by volume) solution of dimethylacetamide in water, 634 g of finely divided metal iron powder and 9.55 g of ammonium chloride as an electrolyte. The mixture is heated to 96-98 ° C and 280 g of wet paste containing 240 g of TNBA are gradually added over 1-1.5 hours. In this case, the temperature rises to 100-101 ° C (boiling of the reaction mass). After completion of the addition of TNBA, the reaction mass is stirred for 30 minutes, 6 g of sodium sulfite are added and filtered from iron oxide. The precipitate of iron oxide is washed on the filter with a 10% solution of dimethylacetamide in water, heated to 96-98 ° C. The mother and wash filtrates are combined, cooled with stirring to 10-5 ° C. Precipitated light beige crystals of 2 ¹ , 4 ¹ , 4-triaminobenzanilide are filtered off, washed with 600 ml of water. The uterine filtrate is sent for recycling to the subsequent operation to restore TNBA to TABA, after preliminary adjustment to pH≤7 by adding dilute hydrochloric acid.

Get 200 g of water paste TABA, containing 161 g of dry matter (92% of theoretical), appearance - crystalline powder of light beige color, TPL. 208-210 ° C, chroma 15 units.

Example 7. The restoration of TNBA in TABA in water-dimethylformamide solution

The synthesis is carried out in the device described above. 2500 ml of a 10% (by volume) solution of dimethylformamide in water, 634 g of finely divided metal iron powder and 37.2 g of concentrated hydrochloric acid (HCl content ~ 35 wt.%) Are loaded into the flask. The mixture is heated to boiling with stirring and 280 g of wet TNBA paste containing 240 g of the basic substance are gradually added, maintaining the temperature of the reaction mixture at 98-101 ° C under mild boiling.

After completion of the addition of TNBA, the reaction mass is kept at boiling for 15 minutes, 6 g of sodium sulfite are added and filtered from iron oxide. The precipitate of iron oxide on the filter is washed with a 10% solution of dimethylformamide in water, heated to 96-98 ° C. The mother and wash filtrates are combined, cooled with stirring to 10-5 ° C. Precipitated light beige crystals of TABA are filtered off, washed with 600 ml of water.

The uterine filtrate is recycled to the subsequent recovery of TNBA in TABA after preliminary adjustment to pH≤7 by the addition of dilute hydrochloric acid.

Get 203.4 g of an aqueous paste TABA, containing 163.7 g of dry matter (93.5% of theoretical), the appearance is a crystalline powder of light beige color, Tm. 207-210 ° C, color 12 units.

Example 8. The synthesis of salt DABI · N ₂ OSO ₄ · H ₂ O

In a heated glass reactor with a volume of 25 l, equipped with a stirrer, thermometer and reflux condenser, load 12.62 l of water, 1603 ml of sulfuric acid with a density of 1.832 (94.3 wt.%). 552 ml of a 25% aqueous ammonia solution and 2693 g of an aqueous TABA paste containing 1800 g of the basic substance. The initial concentration of sulfuric acid in the reaction mass of the specified composition is 10.4 wt.%. The molar ratio of TABA: H ₂ SO ₄ : NH ₃ : H ₂ O = 1: 38: 1: 105. The mass is heated with stirring to a temperature of 100-101 ° C for 1.5 hours and maintained at this temperature for 3 hours, then cooled to 10-12 ° C.

The precipitate of the sulfate salt DABI · N ₂ SO ₄ · N ₂ O is filtered off, washed with 6 l of water in two stages with repulpation.

Get 3578 g of an aqueous paste of salt DABI · N ₂ SO ₄ · N ₂ O gray, containing 2200 g of the main substance (87% of theory).

When filtering and washing the salt, 15 kg of mother liquor are formed, which is treated with 220 g of activated carbon OU-B (in terms of the main substance) when heated to 100 ° C for 30 minutes. The purified mother liquor after filtration from coal is sent for recycling to the next step for the synthesis of the DABI · H ₂ SO ₄ · Н ₂ O salt. With successive recycling of the mother sulphate, the yield of the DABI · Н ₂ SO ₄ · Н ₂ O salt monotonously increases, reaching 95-97% . In this case, a decrease in the quality of salt is not observed. Recycling of the mother liquor with preliminary coal cleaning can be carried out an unlimited number of times. The resulting salt DABI · H ₂ SO ₄ · H ₂ O does not have a purple or violet hue, indicating the presence of oxidation products of triaminobenzene, in contrast to the salt DABI · 3HCl in accordance with the closest analogue.

Example 9. Purification of salt DABI · N ₂ SO ₄ · H ₂ O

The salt is purified by recrystallization from ~ 12% sulfuric acid. 1954 pastes of DABI · H ₂ SO ₄ · Н ₂ О salt containing 1800 g of anhydrous DABI · H ₂ SO ₄ salt, 14 L of water (including water introduced with salt paste), 2.089 kg 94 are loaded into a 25 L heated glass reactor , 3% sulfuric acid with a density of 1.832 and 250 g of activated carbon (in terms of the main substance). The mass is heated with stirring to a temperature of 100 ° C and maintained at this temperature for 30 minutes. The hot solution is filtered off from coal. The charcoal on the filter is washed with 1.5 L of 12% sulfuric acid, attaching a wash filtrate to the main one.

The mother liquor is then cooled to 10-5 ° C. The precipitated crystals of the DABI · H ₂ SO ₄ · H ₂ O salt are filtered off, washed successively with 1.5 L of 12% sulfuric acid and 6 L of distilled water. Sulfuric acid filtrates are recycled for the subsequent salt recrystallization operation, and the aqueous filtrate is sent to neutralization.

Get 2050 g of an aqueous paste of salt containing 1618 g of crystalline hydrate DABI · H ₂ SO ₄ · H ₂ O or 1532 g of salt DABI · H ₂ SO ₄ calculated on the anhydrous salt (85.1% of theory). The color of salt is 28.7 units. In subsequent operations with the recycling of the mother sulphate, the yield of the DABI · H ₂ SO ₄ · H ₂ O salt monotonously increases, reaching 97.15% of the theoretical by the 6th operation (5 cycles).

Example 10. Isolation of DABI - base and its drying

11.36 liters of distilled water, 1.71 kg of 25% ammonia water, 1 liter of 5% Trilon B solution are loaded into a glass apparatus with a capacity of 25 l with heating, equipped with a stirrer, thermometer and reflux condenser, and the solution is mixed. 3500 g of an aqueous paste of DABI salt containing 3352 g of salt in terms of DABI · H ₂ SO ₄ are added to the solution with stirring over 0.5 hours. The temperature rises from 18-20 ° C to 29-30 ° C. The suspension is stirred for 15 minutes, then heated to 65-70 ° C for ~ 1.5 hours and kept at this temperature for 1 hour. If necessary, adjust the pH of the medium by adding ammonia water, bringing its value to pH 8.5-9. The total exposure time at 65-70 ° C for 2 hours. DHABI suspension in an aqueous ammonium sulfate solution was cooled to 30-40 ° C, filtered, washed with 18 liters of distilled water until no anion SO ₄ ^- in the washing waters (the sample with barium chloride). Wash water is used in subsequent salt neutralization operations. 3798 g of an aqueous paste of the DABI salt are obtained, containing 58.85% g of the basic substance. The paste is dried in a stream of inert gas in a stepwise mode at a temperature in the first stage of 100-135 ° C and then in the second stage of 150-160 ° C. 2235 g of DABI are obtained (96.6% of theory).

In some cases, the DABI yields ranged from 96.6-98.1% of the theoretical. Appearance - crystalline powder of light beige color, mp. 234-235 ° C, the mass fraction of the residue after calcination is 0.004%, the color is 2.3 units, the mass fraction of water is 0.1%, impurities insoluble in hydrochloric acid in trace amounts.

Claims (9)

1. The method of obtaining 5 (6) -amino-2- (4 ^1- aminophenyl) benzimidazole (DABI), characterized in that 2,4-dinitroaniline is acylated with 4-nitrobenzoyl chloride in the presence of a ferric chloride catalyst in an environment of an organic solvent from the chlorobenzene series , para-xylene, a technical mixture of xylenes, toluene or ethylbenzene, when the reaction mixture is boiled and 2,4 ¹ , 4-trinitrobenzanilide crystallized after cooling the reaction mixture is neutralized with aqueous ammonia, after which the resulting 2,4 ¹ , 4-trinitrobenzanilide is reduced with powdered iron to an aqueous solution of dimethylacetamide or dimethylformamide at a temperature of 96-101 ° C, followed by the introduction of sodium sulfite and separation of the precipitate of iron oxide, with further cooling of the remaining aqueous amide solution and the separation of 2 ¹ , 4 ¹ , 4-triaminobenzanilide crystallized upon cooling, which is further subjected to cyclodehydration in an aqueous solution of sulfuric acid in the presence of an aqueous solution of ammonia at a temperature of 100-101 ° C followed by isolation of the resulting 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole in the form crystalline hydrate of monosulfate salt and its neutralization with ammonia. 2. The method according to claim 1, characterized in that the catalyst in the form of ferric chloride or in the form of an aqueous solution of ferric chloride or a crystalline powder of anhydrous ferric chloride and the solvent are added to the aqueous paste of 2,4-dinitroaniline, followed by combined dehydration by azeotropic distillation of water with solvent, after which solvent, 4-nitro-benzoyl chloride is added to the remaining mass and acylation is carried out. 3. The method according to claim 2, characterized in that a 50% aqueous solution of ferric chloride is used. 4. The method according to claims 1 and 2, characterized in that a 10% aqueous solution of dimethylacetamide or a 10% aqueous solution of dimethylformamide is used and the water-amide mother liquor obtained after cooling and crystallization of 2 ¹ , 4 ¹ , 4-triaminobenzanilide to the recovery stage of 2,4 ¹ , 4-trinitrobenzanilide with preliminary adjustment of pH≤7. 5. The method according to claim 1, characterized in that the cyclodehydration solution of sulfuric acid is carried out in the presence of activated carbon. 6. The method according to claims 1 and 2, characterized in that the allocation of 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole in the form of crystalline monosulfuric acid salt is carried out by crystallization from a cooled reaction mass, then sulfur the acid mother liquor is purified by heating with activated carbon and, after filtration, the activated carbon is recycled to the cyclodehydration stage. 7. The method according to claim 6, characterized in that the obtained crystalline hydrate of monosulfur salt of 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole is purified by recrystallization from an aqueous solution of sulfuric acid in the presence of activated carbon or without it, followed by recycling of the obtained sulfuric acid mother liquor at the stage of recrystallization. 8. The method according to claims 1 and 2, characterized in that the neutralization of the crystalline hydrate of monosulfuric acid salt of 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole is carried out by adding the obtained crystalline hydrate of monosulfuric acid salt 5 (6) - amino-2- (4 ¹ -aminophenyl) benzimidazole in the form of an aqueous paste to an aqueous solution of ammonia in the presence of Trilon B at a temperature of 15-20 ° C followed by heating to 60-75 ° C and adjusting the pH of the medium to 8.5-9, 0. 9. The method according to claim 8, characterized in that the obtained 5 (6) -amino-2- (4 ¹ -aminophenyl) benzimidazole is dried in a stream of inert gas in a stepwise mode at a temperature of 100-135 ° C in the first stage and 150 -170 ° C in the second stage.