EA024484B1 - Process for preparing 5-amino-2-(4-aminophenyl)-1h-benzimidazole - Google Patents

Abstract

The invention relates to the field of organic chemistry and concerns a process for preparing 5-amino-2-(4-aminophenyl)-1H-benzimidazole (DABI), which is applied in production of fibre-forming polymers with special characteristics, for instance for production of para-amide highly strong heat-resistant fibres. Provided is the process for preparing DABI, characterised in that 2',4',4-triaminobenzanilide is subjected to cyclodehydration at 90-110°C in the presence of formic acid or its salt initially in the medium of diluted hydrochloric acid solution, obtained DABI muriate is separated by introduction of concentrated hydrochloric acid, with further processing with activated coal in water solution at 90-110°C and medium pH 0.5-3.0, the target product is separated by neutralisation with gaseous ammonia or ammonia water. A product with main substance content not lower than 99.2 wt.% is obtained by the provided process.

Description

The present invention relates to the field of organic chemistry and relates to a method for producing 5amino-2- (4-aminophenyl) -1H-benzimidazole (DAFBI), which is used in the manufacture of fiber-forming polymers with special characteristics, for example, for the production of high-temperature resistant paraamide fibers.

In the preparation of aramid fibers, the purity of the products used is very important, in particular the purity of DAFBI, which is one of the main components in the production of fiber. This is due to the fact that the strength characteristics of fibers obtained on the basis of DAFBI monomer largely depend on its purity, i.e. from the content of organic and inorganic impurities. The mass fraction of DAFBI should not be lower than 99.2%, that is, no more than 2 units, melting point 235.5-236 ° C).

A known method of producing DAFBI by hydrogenation of 2,4-dinitroaniline in alcohol in the presence of Raney nickel or palladium, followed by condensation of the obtained triaminobenzene in the form of a phosphoric acid salt with p-aminobenzoic acid in 105-116% polyphosphoric acid at 140-145 ° C (5I 498298, S07E 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. The resulting product is not clean enough (melting point 230-231 ° C).

A known method of producing DAFBI by catalytic reduction and cyclization of trinitrobesanilide (TNBA) with hydrogen in aqueous solutions of hydrochloric or phosphoric acids, followed by the release of DAFBI by neutralization with alkali (I8 4417056, S07E 235/18, 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.

A known method of producing DAFBI by cyclodehydration of 2 ', 4', 4-triaminobenzanilide (TABA) with an aqueous solution of sulfuric acid with the addition of aqueous ammonia at a temperature of 100-110 ° C, followed by isolation of the formed DAFBI in the form of a monosulfuric acid crystalline hydrate and its neutralization with an aqueous solution ammonia in the presence of complexon - Trilon B at a temperature of 15-20 ° С with adjusting the pH of the medium to 8.5-9.0 and subsequent heating to 60-75 ° С (KN2283307, С07Э 235/18, 2005). The disadvantages of this technology include the occurrence of all the main chemical stages not in solution, but in suspension. The mass in the solution is homogeneous only at high temperatures, which requires hot cleaning filtration to prevent the precipitation of sulfuric acid salt even with slight cooling. In addition, there is no possibility of express analysis, because the sample precipitates after being taken for analysis or during determination. This leads to the fact that the process is difficult to carry out and control, in addition, the duration of the process, including the TABA cyclodehydration reaction (4-5 hours), significantly increases. In addition, dilute sulfuric acid exhibits more severe corrosion of the material, even alloy equipment based on chrome-nickel-molybdenum steel EP-567 is not suitable, but in hydrochloric acid EP-567 can be used. In addition, the product is not pure enough (color more than 2.3, melting point 234-235 ° C), i.e. additional cleaning is required for its use in the manufacture of heat-resistant fibers.

The technology for producing DAFBI using hydrochloric acid is more economical and simple.

A known method of producing DAFBI by cyclodehydration of TABA in a medium of concentrated hydrochloric acid when heated to 100 ° C, the allocation of the target product by diluting the reaction mass with a large amount of ice and neutralizing the hydrochloric acid salt with aqueous ammonia. The obtained DAPBI is purified by recrystallization from ethanol (OV1531161, С07Э 235/18, 1978; И84109093; С07 |) 235/14; C07O 235/18, 1978).

The disadvantage of this method is the use of concentrated hydrochloric acid during cyclodehydration with simultaneous heating to 100 ° C for 3 hours, which 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 product is not clean enough with temperature melting not more than 235 ° C.

Closest to the proposed invention is a method for producing DAFFI by cyclodehydration of TABA, in the presence of formic acid or its salt at 90-100 ° C, initially in dilute hydrochloric acid followed by isolation of the reaction product with concentrated hydrochloric acid, treatment of the obtained hydrochloric acid salt of DAFBI with activated carbon at 90-100 ° C, by filtration and isolation of the target product by neutralizing the filtrate with an aqueous ammonia solution to a pH of 9.3 (8I No. 1438178, С07О 235/18, 1995).

The disadvantage of this method is the lack of purity of the target product (the content of the main substance in the dry finished product is 92-93%, the color index exceeds 1.8 units, the melting point is 234.6-234.8 ° C).

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The technical problem solved by the invention is to obtain in a simple and economical way a high-purity product suitable for use in the production of aramid fiber.

To solve this problem, we propose a method for producing DAFBI, including cyclodehydration of TABA when heated in a dilute hydrochloric acid medium in the presence of formic acid or its salt, isolating the obtained hydrochloric acid salt of 5-amino-2- (4-aminophenyl) -1benzimidazole, and adjusting the chloride content hydrogen in the reaction mass up to 14-20 wt.% by introducing a concentrated solution of hydrochloric acid, purification of hydrochloric acid salt with activated carbon in an aqueous solution at 90-110 ° C, separation of coal and the selection of the target product a solution to a pH of 9–10, in which according to the invention the cyclodehydration is carried out at 100-110 ° C, the hydrochloric acid salt is purified with activated carbon at a pH of 0.5-3.0, and the target product is isolated in the presence of a complexing agent.

At the stage of purification of an aqueous solution of hydrochloric acid salt DAFBI with activated carbon, the pH of the medium is adjusted to a value of 0.5-3.0 by supplying gaseous ammonia or an aqueous solution of ammonia (ammonia water).

In this case, in the case of neutralization with gaseous ammonia, it is used in a mixture with nitrogen in a volume ratio of 1: 1-4.

Trilon B (disodium salt of ethylenediaminetetraacetic acetic acid), HEDPA (hydroxyethylidene diphosphonic acid), etc. are used as complexing agents.

The process of cyclodehydration in a dilute hydrochloric acid medium at elevated temperature (100-110 ° C) allows to achieve a more complete conversion of TABA to DAFBI, which, in turn, helps to increase the purity of the target product, and the cleaning of DAFBI salt with activated carbon when heated and pH environment in the range of 0.5-3.0 allows you to effectively carry out the cleaning process, because under these conditions, the conversion of acidic impurities to gummy products is not observed and the most selective removal of impurities by an adsorbent (activated carbon) is observed, which allows to obtain the target product with a content of the main substance in a dry product of at least 99.2% and a color index of not more than 2 units, usually in the range of 0.5-1.5 units. In addition, the purification of DAFBI salt at the indicated pH values additionally significantly reduces the corrosion of equipment. The introduction of a complexing agent at the stage of isolation of the target product by neutralization allows to reduce the content of iron ions in the finished product to trace amounts.

The proposed method is illustrated by the following examples.

Example 1

380 ml of 7.2% hydrochloric acid, 50.5 g of TABA, sodium formate in a molar ratio to TABA of 0.12: 1 are charged into a flask with a stirrer, a thermometer and a reflux condenser. The mixture is heated with stirring in an oil bath to 100-110 ° C, incubated for 40 minutes and dosed to the reaction mass of 530 ml of 30% hydrochloric acid (to the content of HCl in the reaction mass of 14-20%). It is maintained at 95-110 ° C for 15 minutes, cooled to 10-30 ° C. The resulting suspension (hydrochloric acid salt DAFBI) is filtered off, washed with a 16-18% hydrochloric acid solution and squeezed. Obtain 112 g of a paste of hydrochloric acid salt DAFBI containing 44.8 g (40%) of the basic substance, 30 g (26.8%) of hydrogen chloride and water.

The obtained hydrochloric acid salt of DAFBI is suspended at a temperature of 15-25 ° C in 520 ml of distilled water, a 6.5-7.5% aqueous solution of DAFBI salt is obtained, a mixture of gaseous ammonia and nitrogen is dosed in a volume ratio of 1: 1 until the medium reaches pH 0.5-1.0, 9 g of charcoal activated carbon is added to the prepared suspension and incubated for 20-30 minutes in an oil bath at 90-100 ° C, then the coal is filtered off and washed with water. The filtrate is cooled to 20-30 ° C.

In purified from dyeing impurities a solution of hydrochloric acid salt DAFBI, having a color of 1.4 units. and containing 20 mg / l of iron ions, a solution of 0.11 g of Trilon B in 15 ml of water (molar ratio of Trilon B: Pe = 1.2: 1) is added and incubated for 15 minutes. The resulting solution is treated at 20-30 ° C with a mixture of gaseous ammonia and nitrogen in a volume ratio of 1: 1 at a speed of 30 l / h. When the pH of the medium reaches 9.0-9.5, the flow of ammonia is stopped, the suspension is kept under stirring for 60 minutes and filtered. The precipitate is washed with water and dried. 41.3 g of DAFBI are obtained with a basic substance content of 99.3% (by GLC), 1 mp = 235.8 ° C. the color is 1.3 units, the iron content is 0.0001%, and the yield on loaded TABA is 87.5%.

Example 2

380 ml of a 7.0% hydrochloric acid solution, 50.5 g of TABA are loaded into a flask with a stirrer, a thermometer and a reflux condenser, sodium formate is added in a molar ratio to TABA 0.12: 1.

To carry out cyclodehydration of TABA, the reaction mixture is heated with stirring in an oil bath to 100-110 ° C, after 40 minutes, it is dosed to the reaction mass of 550 ml of 30% hydrochloric acid (to the content of HCl in the reaction mass of 15-20%) and kept at 95-110 ° C for another 15 minutes, then cooled to 10-20 ° C with constant stirring and the resulting suspension is filtered. Get a paste of hydrochloric acid salt DAFBI containing 38% of the basic substance.

The obtained hydrochloric acid salt of DAFBI is mixed with water to obtain a 6.5-7.5% aqueous solution of the DAFBI salt and treated with a mixture of gaseous ammonia with nitrogen in a volume ratio of 1: 2 until the medium reaches pH 1.5-2.0.

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9 g of charcoal activated carbon are added to the prepared suspension, heated to 95-105 ° C and held for 20-30 minutes, cooled to 50-60 ° C. Then the coal is filtered off and washed with water. The filtrate is cooled to 20-30 ° C. Get purified from coloring impurities a solution of hydrochloride salt DAFBI, having a color of 1.1 units. and containing 20 mg / l of iron ions.

Trilon B in molar ratio to iron ions of 1.5: 1 is added to the resulting solution of hydrochloric acid salt of DAFBI, it is kept under stirring for 15 minutes and filtered.

To obtain the target product, the resulting solution of hydrochloric acid salt DAFBI is neutralized to pH 9.0-9.5 with a mixture of ammonia and nitrogen in a volume ratio of 1: 2. A suspension of DAFBI in a solution of ammonium chloride is obtained, and the resulting suspension is filtered. The precipitate is washed with water and dried. Obtain 41 g DAFBI with a basic substance content of 99.4% (by GLC), 1pl. 236 ° C, color 1.0 units, ash content 0.01%, iron content 0.0001%, yield 87.1%, calculated on loaded TABA.

Example 3

The process is carried out analogously to example 1, but instead of sodium formate, 98.5% formic acid 2.5 g is used at the stage of cyclodehydration, and the pH of the medium at the stage of purification of hydrochloric acid salt is maintained within 1.0-1.5 by the supply of gaseous ammonia. Obtain 43.5 g of DAFBI with a basic substance content of 99.2%, 1pl. 235.5 ° C, chroma 1.4 units, iron content 0.0001%, yield 86.5% in terms of loaded TABA.

Example 4

The process is carried out analogously to example 1, but instead of Trilon B use OEDFK. Obtain 41.0 g DAFBI with a basic substance content of 99.2, 1pl. 235.5 ° C, chroma 1.4 units, iron content 0.0001%, yield 86.8% on loaded TABA.

Example 5

The process is carried out analogously to example 1, but the neutralization is carried out with a mixture of ammonia and nitrogen in a volume ratio of 1: 4 with a volumetric flow rate of 10 to 15 l / h at the stage of purification until the pH of the medium reaches 0.51.0 and at the stage of isolation of DAFBI to pH 9 5-10 at a temperature not exceeding 25 ° C. Obtain 53.6 g of paste DAFBI with a mass fraction of the main substance of not less than 75%; the product yield from the stages of separation and washing with water is 95%. After drying, a product is obtained with a melting point of 234.7 ° C, a basic substance content of 99.3 1pl. 235.5 ° C, chroma 1.4 units, the total yield of the product, considering loaded TABA - 87%.

Example 6

90 ml of 10% hydrochloric acid, 15 g (100%) TABA and 0.37 g of formic acid are charged into a flask with a stirrer, thermometer and reflux condenser. The mixture is heated with stirring in an oil bath to 100-110 ° C, incubated for 45 minutes and dosed to the reaction mass of 82 ml of 28% hydrochloric acid (to the content of HC1 in the reaction mass of 14-20%). It is kept at 95-110 ° C for 15 minutes, cooled to 10-30 ° C, the resulting suspension of hydrochloric acid salt DAFBI is filtered off, washed with 16-18% hydrochloric acid solution and squeezed. 45.3 g of a paste of hydrochloric acid salt DAFBI are obtained, containing 12.6 g of the basic substance, 5 g of hydrogen chloride and water. Yield 90.75% of theoretical.

The obtained hydrochloric acid salt of DAFBI is suspended at a temperature of 15-25 ° C in 180 ml of distilled water, adjusted with 20% ammonia water to pH 1.0-1.5, in the prepared solution with a color of 20 units. 3 g of charcoal activated carbon are introduced, the coal suspension is heated to a temperature of 95-105 ° C and maintained at this temperature for 30 minutes. Then the coal is filtered off, the filtrate is cooled to 20-30 ° C.

0.3 g Trilon B is added to a solution of DAFBI hydrochloride acid salt, purified from coloring impurities, having a color of 1.5 units, and held for 15 minutes. Ammonia water is poured into the resulting solution of hydrochloric acid salt DAFBI at such a rate that the temperature in the mass is not more than 25 ° C until the pH of the medium reaches 9.5-10. When the required pH value is reached, the flow of ammonia water is stopped, the suspension is kept under stirring for 60 minutes and filtered. The precipitate is washed with water and dried. Obtain 11.6 g of DAFBI with 1 mp. = 235.5 ° C. with a basic substance content of 99.2%, a color of 1.4 units, the yield, calculated on loaded TABA, was 82.8%.

The use of gaseous ammonia can significantly simplify the technological scheme by eliminating equipment for the absorption of gaseous ammonia by water, containers for receiving and dosing aqueous ammonia, pumps and filters, reduce the amount of waste by 5-10%, increase the accuracy of adjusting the pH of the medium, and reduce the ash content in the finished product and its color. The supply of gaseous ammonia in a mixture with nitrogen in a volume ratio of 1: 1-4 improves the hydrodynamics of the process and eliminates the oxidation of the resulting monomer.

Example 7

The process is carried out analogously to example 1, but instead of sodium formate, 98.5% formic acid 2.5 g is used instead of sodium formate, and the pH of the medium at the stage of cleaning the hydrochloric acid salt is maintained within the range of 3.0-3.5 by feeding gaseous ammonia. The obtained hydrochloric acid salt of DAFBI is suspended at a temperature of 15-25 ° C in 520 ml of distilled water, a 6.5-7.5% aqueous solution of hydrochloric acid salt of DAFBI is obtained, a mixture of gaseous ammonia and nitrogen in a volume ratio of 1: 1 to when the pH of the medium reaches 3.0-3.5, 9 g of activated wood charcoal is added to the prepared suspension and incubated for 20-30 minutes in an oil bath at 90-100 ° С, then the coal is filtered off and washed with water. The filtrate is cooled to 20-3 0 ° C.

In a solution of hydrochloric acid salt DAFBI purified from coloring impurities, having a color of 3.5 units. and containing 20 mg / l of iron ions, a solution of 0.11 g of Trilon B in 15 ml of water (molar ratio of Trilon B: Pe = 1.2: 1) is added and incubated for 15 minutes. The resulting solution is treated at 20-30 ° C with a mixture of gaseous ammonia and nitrogen in a volume ratio of 1: 1 at a speed of 30 l / h. When the pH of the medium reaches 9.0-9.5, the flow of ammonia is stopped, the suspension is kept under stirring for 60 minutes and filtered. The precipitate is washed with water and dried.

Get 39 g of DAFBI with a basic substance content of 99.0%, 1pl. 234.5 ° C, chroma 2.3 units, iron content 0.0050%, yield 77.6% in terms of loaded TABA.

Example 8

The process is carried out analogously to example 1, but instead of sodium formate, 98.5% formic acid 2.5 g is used in the cyclodehydration stage, and the pH of the medium in the purification stage of hydrochloric acid salt is maintained in the range of 0.3-0.5.

The obtained hydrochloric acid salt of DAFBI is suspended at a temperature of 15-25 ° C in 520 ml of distilled water, a 6.5-7.5% aqueous solution of DAFBI salt is obtained, a mixture of gaseous ammonia and nitrogen is dosed in a volume ratio of 1: 1 until the medium reaches pH 0.3-0.5, 9 g of charcoal activated carbon is introduced into the prepared suspension and incubated for 20-30 minutes in an oil bath at 90-100 ° C, then the charcoal is filtered off and washed with water. The filtrate is cooled to 20-30 ° C.

In purified from coloring impurities a solution of hydrochloric acid salt DAFBI, having a color of 2.8 units. and containing 20 mg / l of iron ions, a solution of 0.11 g of Trilon B in 15 ml of water (molar ratio of Trilon B: Pe = 1.2: 1) is added and incubated for 15 minutes. The resulting solution is treated at 20-30 ° C with a mixture of gaseous ammonia and nitrogen in a volume ratio of 1: 1 at a speed of 30 l / h. When the pH of the medium reaches 9.0-9.5, the flow of ammonia is stopped, the suspension is kept under stirring for 60 minutes and filtered. The precipitate is washed with water and dried. Get 38.5 g DAFBI with a basic substance content of 89.9% (by HPLC), 1PL. = 234.8 ° C, chroma 2.3 units, iron content 0.0060%, yield on loaded TABA was 76.6%.

When the pH value is below 0.5, the DAFBI salt-acid salt does not completely dissolve in water; at the stage of coal purification, the DAFBI hydrochloric acid salt is less effective than in examples 1-6.

Data on the above examples in comparison with the prototype are presented in the table.

From the above examples it can be seen that in comparison with the prototype and other known technologies, the target product obtained by the claimed method has improved quality characteristics. Moreover, the proposed technology is more simple and economical.

Download / Mode Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Prototype Cyclodehydration TABA | The concentration of salt. you 7.2 7.0 7.2 7.2 7.2 10 7.2 7.2 7.3 Formate: TABA 0.12: 1 0.12: 0.12: 0.12: 1 0.12: 1 0.02: 1 * 0.12: 1 * 0.12: 1 * 0.05-0.25: 1 T. process, city C. 100-110 100-110 100-110 g 100-110 100-110 100-110 100-110 100-110 90-100 Min time 40 40 40 40 40 45 40 40 60 Isolation of hydrochloric salt DABI, Sod.NS! in the reaction. mass% 14-20 15-20 14-20 14-20 14-20 14-20 14-20 14-20 17 Teraturarad. C 95-110 95-110 95-110 95-110 95-110 95-110 95-110 95-110 90-100 Min time fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen fifteen Purification of hydrochloric acid salt DABI activated charcoal | Neutralization ΝΗγ Ν ·> eleven 1: 2 1: 1 1: I 1: 4 20% of am.water eleven I: 1 Oats PH 0.5-1.0 1.5-2.0 1.0-1.5 pH 0.5-1.0 pH 0.5-1.0 1.0-1.5 3.0-3.5 0.3-0.5 out The selection of the target product | | Correlation. Trilon B; and he. gland 1.2: 1 1.5: 1 1.2: 1 1.2: 1 (OEDFK) 1.2: 1 1.2: 1 1.2: 1 1.2: 1 Ots. Neutralization ΝΗ ₃ : Ν ₂ eleven 1: 2 1: 1 eleven 1: 4 20% of am.water eleven eleven 12.5% am water pH after neutralization 9.0-9.5 9.0-9.5 9.0-9.5 9.0-9.5 9.0-9.5 9.0-9.5 9.0-9.5 9.0-9.5 8.85-9.2 Quality indicators of the finished DABI! T square city. C 235.8 236 235.5 235.5 235.5 235.5 234.5 234.8 234.6-234.8 Soda.Main 99.3 99.3 99,2 99,2 99,2 99,2 98.5 98.6 92.7 Color 1.3 units 1,0 1.4 1.4 1.4 1.4 2,3 2,3 1.8-3.15 Soda.iokov iron 0.0001% 0.0001% 0.0001% 0.0001% 0.0001% 0.0001% 0.005 0.006 Not identified. Exit 87.5% 87.1 86.5 86.8 87 82.8 77.6 76.6 90.8-93.8

* - Formic acid used.

Claims (3)

CLAIM 1. A method of obtaining 5-amino-2- (4-aminophenyl) -1H-benzimidazole, including the cyclodehydration of 2 ', 4', 4-diaminobenzanilide when heated in a medium of dilute hydrochloric acid in the presence of formic acid or its salt, highlighting the resulting salt acid salt of 5-amino-2- (4-aminophenyl) 1H-benzimidazole, bringing the content of hydrogen chloride in the reaction mass to 14-20 wt.% by introducing a concentrated solution of hydrochloric acid, purifying the hydrochloric acid salt with activated carbon in an aqueous solution at 90- 110 ° C, the separation of coal and the selection of the target product neutralization to pH 9-10, wherein the cyclodehydration is carried out at 100-110 ° C, hydrochloride salt purification with activated carbon is performed at pH 0.5-3.0, and selection is carried out in the presence of a complexing agent of the title product. 2. The method according to claim 1, characterized in that at the stage of purification of the hydrochloric acid salt of 5-amino-2- (4-aminophenyl) -1H-benzimidazole activated carbon, the pH of the medium is adjusted to a value of 0.5-3.0 with an ammonia gas or ammonia water solution. 3. The method according to claim 1 or 2, characterized in that the gaseous ammonia is used in a mixture with nitrogen in a volume ratio of 1: 1-4.