RU2560881C1 - Method of producing 2',4,4'-trinitrobenzanilide from aniline and 4-nitrobenzoic acid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing 2',4,4'-trinitrobenzanilide, which is an intermediate product in the synthesis of 5(6)-amino-2-(4-aminophenyl)benzimidazole - a monomer for producing heat-resistant high-strength fibres. The method includes acylating aniline with 4-nitrobenzoic acid while heating with distillation of reaction water and separating 4-nitrobenzanilide, followed by nitration thereof with nitric acid in a sulphuric acid medium and separating the end product. The method is characterised by that acylation is carried out under pressure at molar ratio of aniline to 4-nitrobenzoic acid of (2-20):1. The 4-nitrobenzanilide is separated in powder form and after nitration thereof, the obtained 2',4,4'-trinitrobenzanilide is separated from the reaction solution by diluting to sulphuric acid concentration of 30-85 wt %. Further, the product is recrystallised from an aromatic solvent or from a mixture of an amide solvent with water.

EFFECT: method cuts the duration of acylation, improves the quality of the product and reduces the amount of wastes.

3 cl, 2 tbl, 8 ex

Description

The present invention relates to the field of organic chemistry and relates to a method for producing 2 ′, 4,4′-trinitrobenzanilide (TNBA), which is an intermediate product of the synthesis of 5 (6) -amino-2- (4-aminophenyl) benzimidazole - a monomer to obtain heat-resistant high-strength fibers .

A known method of producing TNBA by acylation of 2,4-dinitroaniline 4-nitro-benzoyl chloride (patent RU 2348612 C2, IPC C07C 233/80, publ. 10.03.2009). The disadvantage of this method is the use of hard-to-reach starting compounds -2,4-dinitroaniline and 4-nitrobenzoyl chloride, the need for the use of highly toxic phosgene, thionyl chloride or phosphorus chlorides for the synthesis of 4-nitrobenzoyl chloride, high corrosivity of the working media.

A known method of producing TNBA by acylation of aniline with 4-nitro-benzoyl chloride, followed by nitration of the resulting 4-nitrobenzanilide with nitric acid in 93% sulfuric acid (L.F. Myasnikova, I.L. Vaysman, S.S.Gluzman, N.I. . Fayngold, D. A. Novokhatka, S. G. Panina. Journal of Applied Chemistry, Volume 50, No. 6, pp. 1428-1430 (1977)). TNBA is isolated by pouring a solution of TNBA in a mixture of sulfuric and nitric acid residues into water. Data on the quality of TNBA obtained by this method — the composition and melting point, are not given in the published description. When reproducing this method, it was found that the resulting TNBA has a low melting point of 170-180 ° C (literary value 194-195 ° C, patent RU 2348612), when it was restored, intense resinification was observed. The disadvantage of this method is the low quality of TNBA, the use of inaccessible 4-nitrobenzoyl chloride, high corrosiveness of the working environment.

A known method of producing TNBA by acylation of aniline with 4-nitro-benzoyl chloride followed by nitration of the resulting 4-nitrobenzanilide with nitric acid in an environment of excess sulfuric acid as a solvent (L.G. Matveev, G.F. Levchenko, E.A. Kudryavtseva, I.A. Abramov Journal of Applied Chemistry, Volume 57, No. 1, pp. 132-134 (1984)). TNBA is isolated by pouring the reaction mass into water. The TNBA obtained by this method had a low melting point — from 170 to 190 ° C. Using thin-layer chromatography, impurities of dinitrobenzanilides and isomeric 2 ′, 4,6′-trinitrobenzanilide were found in it. The disadvantage of this method is the low quality of TNBA, the use of inaccessible 4-nitrobenzoyl chloride, and the high corrosivity of the working media.

A known method of producing TNBA by acylation of aniline with 4-nitrobenzoic acid, followed by nitration of the resulting 4-nitrobenzanilide with nitric acid in a monohydrate medium - 98.5-100% sulfuric acid (German patent 70862, NCI 22, publ. 1893). Acylation is carried out with a molar ratio of aniline: 4-nitro-benzoic acid equal to 1.075: 1, i.e. close to stoichiometric. The mixture is heated at a temperature of 220-230 ° C for 8 hours, driving off the water formed during the reaction. After completion of the reaction, the product solidifies in a solid melt, which is crushed, ground, washed with dilute hydrochloric acid to remove unreacted aniline and a dilute soda solution to remove unreacted 4-nitrobenzoic acid. 4-nitro-benzanilide is obtained in good yield, which is dissolved at a temperature of 15-20 ° C in a five-fold amount of monohydrate, cooled to 5-10 ° C and nitrated at this temperature with a mixture of fuming nitric acid and monohydrate. With vigorous stirring, the nitromass is slowly poured onto ice and washed with water from acids to a neutral reaction. The resulting 2 ′, 4,4′-trinitrobenzanilide contains as an impurity the meta-isomer (obviously 2 ′, 4,6′-trinitrobenzanilide). Quality indicators of 2 ′, 4,4′-trinitrobenzanilide are not given. The disadvantages of the method are the formation of a crystalline melt of 4-nitrobenzanilide, which must be crushed, incomplete conversion of reagents, which necessitates washing with solutions of acid and an alkaline agent, which is accompanied by the formation of chemically contaminated wastewater, and the long duration of the stage of production of 4-nitrobenzanilide.

A known method of producing 4-nitrobenzanilide by acylation of aniline with 4-nitrobenzoic acid with a molar ratio of reagents equal to 1.0: 1.0 by heating in the temperature range 170-210 ° C with distillation of the reaction water for 3 to 6 hours and subsequent nitration of the resulting 4 -nitrobenzanilide with concentrated nitric acid in a monohydrate medium (US Patent 4109093, IPC С07С 235/18, publ. 1978). Nitration of 4-nitrobenzanilide is carried out in monohydrate with a mixture of nitric acid with a density of 1.52 g / cm ³ with monohydrate with a gradual increase in temperature from 0 ° C to 25 ° C. The target product was isolated by pouring the reaction solution into a mixture of water and ice, taken in a weight ratio of 2: 3. The yield of 2 ′, 4,4′-trinitrobenzanilide is 90%. The method described in US patent 4109093, identical to the method proposed in German patent 70862, and has the same disadvantages. The stoichiometric ratio of reagents at the stage of synthesis of 4-nitrobenzanilide leads to the formation of a product in the form of crystalline melt, contaminated with the starting compounds due to incomplete conversion of the reagents, aniline and 4-nitrobenzoic acid. This, in turn, necessitates the crushing, grinding of crystalline melt, washing of 4-nitrobenzanilide with acid and alkaline aqueous solutions. As a result, a large number of chemically contaminated effluents are formed. A large amount of chemically contaminated effluents is additionally formed during the precipitation of 2 ′, 4,4′-tri-nitrobenzanilide from its solution in sulfuric acid by pouring ice and water into a mixture. The disadvantages of the method are also the long duration of the aniline acylation step with 4-nitrobenzoic acid and the low quality of the target product. Using high performance liquid chromatography, we found that the 2 ′, 4,4′-trinitro-benzanilide obtained under the conditions of the method described in US Pat. No. 4,109,093 contains only 94% of 2 ′, 4,4′-trinitrobenzanilide and contains 1 as an impurity % of isomeric 2 ′, 4,6′-trinotrobenzanilide, 0.3% of a compound with a molecular weight of 377 corresponding to tetranitrobenzanilide, and other compounds.

Closest to the technical nature of the proposed method is the method described in US patent 4109093.

The aim of the invention is to improve the process of obtaining 2 ′, 4,4′-trinitrobenzanilide by acylation of aniline with 4-nitrobenzoic acid followed by nitration of the resulting 4-nitrobenzanilide, which consists in reducing the duration of acylation, improving the quality of 2 ′, 4,4′-trinitrobenzanilide, eliminating the need crushing, grinding and washing 4-nitrobenzanilide, reducing waste.

This goal is achieved by the proposed method for the production of 2 ′, 4,4′-tri-nitrobenzanilide by acylation of aniline with 4-nitrobenzoic acid when heated with distillation of reaction water, isolation of the intermediate 4-nitrobenzanilide followed by nitration with nitric acid in sulfuric acid and isolation and purification of the target product.

The proposed method is characterized in that the acylation is carried out under pressure at a molar ratio of aniline: 4-nitrobenzoic acid, equal to (2 ÷ 20): 1,4-nitro-benzanilide is isolated in powder form and after its nitration the target 2 ′, 4,4 ′ trinitro-benzanilide is isolated from the reaction solution by dilution to a sulfuric acid concentration of 30-85% by weight and then recrystallized from an aromatic solvent or a mixture of an amide solvent with water. As an aromatic solvent, one of a number is used: chlorobenzene, ortho-dichlorobenzene, nitrobenzene or mixtures thereof. As an amide solvent, one of the series is used: dimethylformamide, dimethylacetamide, N-methylpyrrolidone.

The use of excess pressure allows you to increase the acylation temperature and thereby accelerate the reaction, reduce the duration of the process. The dependence of the boiling temperature of aniline on pressure is given below (DR Stell. Tables of vapor pressure of individual substances. Publishing house "IL". - M., 1949).

So at a pressure of 0.4 MPa, you can increase the reaction temperature at the end of the process to 240 ° C. In this case, the reaction rate increases three times.

Aniline is an effective solvent for 4-nitrobenzanilide.

The solubility data of 4-nitrobenzanilide obtained by us are given below.

Therefore, it is advisable to conduct acylation in excess of aniline as a solvent at a molar ratio of aniline: 4-nitrobenzoic acid in the range (2 ÷ 20): 1.

The use of a sufficient excess of aniline provides the quantitative conversion of 4-nitrobenzoic acid to the target 4-nitrobenzanilide, the quantitative yield of the target product, the absence of an impurity of 4-nitrobenzoic acid in it. In this case, a solution of 4-nitrobenzanilide in aniline is formed, from which the target product can be isolated by crystallization, followed by filtration or distillation of the aniline solvent in the form of an azeotrope with water. The resulting powdered 4-nitrobenzanilide is of high quality, has a melting point of 217 ° C, can be easily prepared for dissolution in concentrated sulfuric acid for subsequent nitration. Such preparation is carried out by drying the powdered 4-nitrobenzanilide from water.

4-Nitrobenzanilide is isolated in the form of a powder, which makes it possible to further process it into 2 ′, 4,4′-trinitrobenzanilide - an intermediate of the synthesis of 5 (6) -amino-2- (4-aminophenyl) benzimidazole by nitration.

Nitration of 4-nitrobenzanilide is carried out in a solution of concentrated sulfuric acid at temperatures below 25 ° C. The powdery form of 4-nitrobenzanilide allows you to prepare its solution in sulfuric acid at low temperatures, which eliminates the processes of destruction and sulfonation.

Since the quantitative conversion of 4-nitrobenzoic acid to 4-nitrobenzanilide and aniline is provided, it is completely regenerated as an azeotrope, and the water used to distill the aniline is recycled, the acylation step is low-waste.

Due to the high speed, acylation can be organized in a continuous manner.

At the stage of synthesis of 2 ′, 4,4′-trinitrobenzanilide by nitration of 4-nitrobenzanilide in concentrated sulfuric acid, the isolation of the target product by diluting sulfuric acid to a concentration in the range of 30-85% by mass solves two problems. Firstly, a significant reduction in the amount of chemically contaminated acidic wastewater is provided, since sulfuric acid with a concentration of 30-85% can be regenerated and returned to the process. Secondly, due to strong dilution when pouring nitromass into water, all impurities co-precipitate together with the target product, which leads to 2 ′, 4,4′-trinitrobenzanilide containing less than 95% by weight of the main substance. Isolation from 30-85% sulfuric acid can increase the content of 2 ′, 4,4′-trinitrobenzanilide to 97.5-98.0%.

Further recrystallization from aromatic solvents or a mixture of an amide solvent and water allows to obtain 2 ′, 4,4′-trinitrobenzanilide with a basic substance content of 98.5-99.5% by mass. At the same time, its melting point rises to 196-197 ° C.

The proposed method can significantly improve the process of obtaining 2 ′, 4,4′-trinitrobenzanilide, simplify the process design, reduce the amount of waste, improve the quality of the product.

The invention is illustrated by examples, which are not intended to give an exhaustive description of the method.

Example 1. Obtaining 4-nitrobenzanilide

In a stainless steel reactor with a capacity of 0.5 dm ³ , equipped with a stirrer, a sleeve for measuring temperature, a bottom valve, an electric heating system, a condensation system for collecting an aniline-water azeotrope, consisting of a condenser, a receiver and a throttling valve, 167 g (1.0 g-mol) of 4-nitrobenzoic acid and 186 g (2.0 g-mol) of freshly distilled aniline. The molar ratio of aniline: 4-nitro-benzoic acid is 2: 1. The reaction mass is heated with stirring, while driving away water and raising the temperature to 240 ° C, maintaining a pressure of 0.4 MPa in the system. The process of distillation of water is completed in 1.5 hours.

The reaction mass is cooled to 70 ° C, 150 cm ^{3 of} water are introduced and the aniline is distilled off in the form of an azeotrope, returning the aqueous layer after separation of the distillate. After distillation of the aniline is completed, additional water is added and the aqueous suspension of 4-nitrobenzanilide is filtered.

The precipitate was dried at 100 ° C in vacuo. The yield of 4-nitrobenzanilide 239.6 g (99% of theory). The powder is white. Melting point 217 ° C.

Example 2. Obtaining 4-nitrobenzanilide

88 g (0.527 g mol) of 4-nitrobenzoic acid and 345 g (3.71 g mol) of aniline are charged to the reactor described in Example 1. The molar ratio of aniline: 4-nitrobenzoic acid is 7: 1. The mixture is heated with stirring, while driving water away to a temperature of 240 ° C. The process is completed in 1.5 hours at a pressure of 0.4 MPa.

After the completion of water distillation, the reaction mass is poured into a crystallizer, where it is cooled to 10 ° C. A suspension of crystallized 4-nitrobenzanilide is filtered. The paste is introduced into 500 cm ^{3 of} water and the aniline is distilled off in the form of an azeotrope with water, returning the aqueous layer after separation of the distillate. The aqueous suspension of 4-nitrobenzanilide is filtered, the precipitate is dried in vacuum at 100 ° C.

The yield of 4-nitrobenzanilide is 124.9 g (98% of theory). White powder, melting point 217 ° C.

The mother liquor from filtering an aniline suspension of 4-nitrobenzanilide, the mass of which is 235 g, is loaded into the reactor, 4-nitrobenzoic acid and aniline are loaded in quantities corresponding to the charge in the initial synthesis. The process is carried out as described above. After five experiments with recycle of the aniline mother liquor with a total load of 440 g of 4-nitrobenzoic acid, the yield of 4-nitrobenzanilide was 631 g (99% of theory). The crystalline powder is white. Melting point 217 ° C.

Example 3. Obtaining 4-nitrobenzanilide

34 g (0.20 g mol) of 4-nitrobenzoic acid and 335 g (3.6 g mol) of aniline are charged to the reactor described in Example 1. The molar ratio of aniline: 4-nitrobenzoic acid is 18: 1. The process is conducted under conditions similar to those described in example 2. The reaction ends in 1 hour at a pressure of 0.4 MPa. The isolation of 4-nitrobenzanilide and the recycling of the aniline mother liquor are carried out using the same techniques as in Example 2. The yield of 4-nitrobenzanilide is 46.3 g (94% of theory). White crystalline powder. Melting point 217 ° C.

Example 4. Obtaining 2 ′, 4,4′-trinitrobenzanilide

10 g of 4-nitrobenzanilide are dissolved in 25 cm ^{3 of} monohydrate at a temperature of (-5) -0 ° С, a mixture of 3.8 cm ^{3 of} nitric acid with a density of 1.52 g / cm ³ with 25 cm ^{3 of} monohydrate is gradually added. The resulting solution was diluted by mixing with 65% sulfuric acid to a concentration of sulfuric acid after mixing 82.5% of the mass. The precipitate formed is filtered off, washed with small amounts of 75% sulfuric acid and water, and recrystallized from ortho-dichlorobenzene. The yield of 2 ′, 4,4′-tri-nitrobenzanilide was 10.7 g (78% of theory). The content of the main substance of 98.5% (HPLC). T pl. 196 ° C.

Example 5. Obtaining 2 ′, 4,4′-trinitrobenzanilide

The synthesis is carried out similarly to that described in example 4, a sulfuric acid solution of 2 ′, 4,4′-trinitrobenzanilide is diluted to a sulfuric acid concentration of 30% by mass, and recrystallization of 2 ′, 4,4′-TNBA is carried out from nitrobenzene. Obtain 11.25 g of 2 ′, 4,4′-TNBA (82% of theory). The content of the main substance of 99.5% (HPLC), T pl. 197 ° C.

Example 6. Obtaining 2 ′, 4,4′-trinitrobenzanilide

The synthesis is carried out analogously to that described in example 4. The sulfuric acid solution of 2 ′, 4,4′-trinitrobenzanilide is diluted to a sulfuric acid concentration of 50% by mass. The precipitated 2 ′, 4,4′-TNBA is recrystallized from chlorobenzene. Yield 2 ′, 4.4′-TNBA 9.88 g (79% of theory), basic substance content 98.8% (HPLC). T pl. 196 ° C.

Example 7. Obtaining 2 ′, 4,4′-trinitrobenzanilide

The synthesis is carried out similarly to that described in example 4, the sulfuric acid solution of 2 ′, 4,4′-trinitrobenzanilide is diluted to a sulfuric acid concentration of 60% by mass, and the recrystallization of 2 ′, 4,4′-TNBA is carried out from a mixture of nitrobenzene: chlorobenzene 1: 1 by volume. Yield 2 ′, 4.4′-TNBA 11.05 g (80.5% of theory), basic substance content 99.3% (HPLC). T pl. 197 ° C.

Example 8. Obtaining 2 ′, 4,4′-trinitrobenzanilide

The synthesis is carried out similarly to that described in example 4, using 93.4% sulfuric acid instead of monohydrate. The sulfuric acid solution is diluted with 40% sulfuric acid to a sulfuric acid concentration of 75%. The precipitated precipitate 2 ′, 4,4′-TNBA is recrystallized from a mixture of dimethylacetamide-water containing 80% by volume of dimethylacetamide. Yield 2 ′, 4.4′-TNBA 9.81 g (74.3% of theory). The content of the main substance of 99.1% (HPLC). T pl. 197 ° C.

Claims (3)

1. The method of obtaining 2 ′, 4,4′-trinitrobenzanilide by acylation of aniline with 4-nitrobenzoic acid when heated with distillation of the reaction water and isolation of 4-nitrobenzanilide followed by nitration with nitric acid in sulfuric acid and the isolation of the target product, characterized in that acylation lead under pressure at a molar ratio of aniline: 4-nitrobenzoic acid equal to (2 ÷ 20): 1, 4-nitrobenzanilide is isolated in the form of a powder and after its nitration, the obtained 2 ′, 4,4′-trinitrobenzanilide is isolated from the reaction solution pouring to a sulfuric acid concentration of 30-85 wt.% and then recrystallized from an aromatic solvent or from a mixture of an amide solvent with water. 2. The method according to claim 1, characterized in that as an aromatic solvent use one of the series: chlorobenzene, ortho-dichlorobenzene, nitrobenzene or mixtures thereof. 3. The method according to claim 1, characterized in that one row is used as the amide solvent: dimethylformamide, dimethylacetamide, N-methylpyrrolidone.