RU2797410C1 - Method for obtaining para-aminophenol by reduction of para-nitrosophenol with ammonium sulfide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: new method for the production of para-aminophenol by the reduction of para-nitrosophenol with ammonium sulfide by the reduction of para-nitrosophenol. This method includes the following steps: a) preparing a solution of p- nitrosophenol in an aqueous ammonia solution; b) providing an aqueous solution of ammonium sulfide; c) simultaneously feeding the solutions from steps a) and b) with a flow ratio corresponding to a molar ratio of p- nitrosophenol to (NH₄)₂S from 1:1.5 to 1:2.5 into an inert atmosphere reactor with stirring, and forced maintenance of temperature in the range from 40 to 50°C; d) after complete addition of the solutions from steps a) and b) evacuation of the reaction mixture until the complete removal of ammonia while forcibly maintaining the temperature in the range from 40 to 50°C; e) removing the vacuum and cooling the reaction mixture to 18-20°C; f) withdrawing the reaction mixture from the reactor into a nutsche filter; g) separating the solid para-aminophenol on the filter and washing it with water; h) unloading para-aminophenol from the nutsche filter and drying it at a temperature not exceeding 55°C with the receipt of the finished product.

EFFECT: cheap and readily available reagents, as well as cost-effective waste disposal, allows, without the use of special equipment, to obtain and isolate the product, that are hardwarily and technologically simple, providing high purity and high yield, and also guarantees a product that is stable upon further drying, transportation and storage.

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Description

The present invention relates to the field of chemical technology, in particular to a new method for the production of para- aminophenol by the reduction of para- nitrosophenol with ammonium sulfide.

Para- aminophenol is a valuable product of organic synthesis. This compound serves as a raw material for the production of drugs (paracetamol), dyes, and is used as an antioxidant in the production of rubber. Therefore, there is still considerable interest in the research and production areas in the development and implementation of new effective methods for the synthesis of para- aminophenol that meet the modern realities of constantly rising raw material prices and tightening requirements for ensuring environmental friendliness of production.

Currently, there are several approaches to the industrial production of para- aminophenol in the state of the art, where the main method of synthesis is the reduction of para- nitro- or para- nitrosophenol. At the same time, para- nitrosophenol is used extremely rarely as a starting compound, since it is an insufficiently stable substance. Of the reduction methods, catalytic hydrogenation with hydrogen (RU2461543, CN104447362A, SU536167A1, DE1280258B) and electrolytic reduction (DE2256003A1) can be distinguished. However, these methods require expensive catalysts and high energy costs, as well as due to the use of high hydrogen gas pressures, special precautions and special hardware design.

Also quite common in the prior art is the so-called "sulfide" recovery method. As reagents for the "sulfide" method, it is known to use sulfides and polysulfides of sodium, hydrogen sulfide, sulfur dioxide, dithionite, sodium bisulfite or metabisulfite (CN103772217A, CN104356007A, US3177256, US3223727).

Various options for the reduction of p- nitrophenol are described, for example, the reaction of the sodium salt of p- nitrophenol with a 43% aqueous solution of sodium hydrosulfide (US3177256); or the reaction of para- nitrophenol with ammonium thiosulfate (CN103772217A).

US Pat. No. 3,223,727 discloses a procedure for the reduction of p- nitrosophenol with sodium hydrosulfide in an alkaline medium, wherein the reaction proceeds at 40-50°C in just 15 minutes. Sulfur dioxide is used in this process to neutralize and isolate the product, which requires complex hardware design and essential precautions.

Chinese patent CN104356007A describes that p- nitrosophenol can be reduced by the action of 10% sodium sulfide solution at 45-48°C.

A similar approach is used by the authors of patent PL54012B1, according to which para- nitrosophenol reacts with sodium sulfide in an alkaline medium (pH 8.8-10.2), para- aminophenol is precipitated from the reaction mixture using ammonium sulfate, and the resulting para- aminophenol is not further purified and is immediately used in further transformations.

The use of sulfides has a number of advantages: the cheapness of reagents and the technically uncomplicated isolation of the product. However, due to the low chemical activity of the reducing agent, a significant excess of the reducing agent is required to carry out this transformation. As a result, a large amount of liquid waste is generated, which must be disposed of. Also, the reaction is accompanied by the release of a noticeable amount of toxic hydrogen sulfide, which requires additional devices to capture and neutralize it, and strict control over the state of the environment.

Thus, at present, there is still a significant need to develop new methods for obtaining a para- aminophenol product valuable in chemical technology, eliminating or at least minimizing the previously mentioned disadvantages of the prior art and providing a specialist in this field with a wider choice of means and technologies for achieving the necessary characteristics of para- aminophenol, in particular for use in further synthetic chains.

Therefore, the objective of the present invention was to provide a new method for the production of para- aminophenol, which is characterized by ease of implementation from the hardware and technological points of view, the availability and low cost of the starting reagents and solvents, as well as the cost-effective disposal of the resulting waste, which at the same time would provide reproducible production of a stable final product. product with high yields and high purity without additional purification steps.

This problem was solved by means of a new method for the production of para- aminophenol by the reduction of para- nitrosophenol, which includes the following stages:

a) preparation of a solution of p- nitrosophenol in an aqueous ammonia solution;

b) providing an aqueous solution of ammonium sulfide;

c) simultaneously feeding the solutions from steps a) and b) with a flow ratio corresponding to a molar ratio of p- nitrosophenol to (NH ₄ ) ₂ S from 1:1.5 to 1:2.5 into an inert atmosphere reactor with stirring, and forced maintenance of temperature in the range from 40 to 50°C;

d) after complete addition of the solutions, evacuation of the reaction mixture until the complete removal of ammonia while forcibly maintaining the temperature in the range from 40 to 50°C;

e) removing the vacuum and cooling the reaction mixture to 18°C - 20°C;

f) withdrawing the reaction mixture from the reactor into a suction filter;

g) separating the solid para- aminophenol on the filter and washing it with water;

h) unloading para- aminophenol from the suction filter and drying it at a temperature not exceeding 55°C to obtain the finished product.

As previously shown in the review of the prior art, there are several approaches to the industrial production of para- aminophenol, with the main precursor for its production being para- nitrophenol. The use of para- nitrosophenol has a very limited distribution.

This is due to the fact that para- nitrophenol as a starting material for the reduction reaction to para- aminophenol looks more attractive due to its greater chemical stability. However, p- nitrophenol is a less accessible and more expensive raw material for production, since it cannot be obtained in high yield directly from phenol by the nitration reaction due to the low regioselectivity of this reaction.

para -Nitrosophenol, in turn, can be obtained with high yield and selectivity directly from phenol, however, it has a lower chemical stability, which imposes special requirements for the implementation of the process of its reduction: sufficiently mild process conditions must be provided to exclude the formation of by-products and, as a result, guarantee the required purity of the final product. Therefore, when such a reduction method is discovered, the general synthetic approach based on the nitrosation of phenol and the reduction of para -nitrosophenol to para -aminophenol becomes significantly more profitable due to the almost doubling of the total yield of the final product.

The inventors have succeeded in finding a method for the reduction of para -nitrosophenol that meets the necessary requirements.

The proposed method according to the invention is based on the reduction reaction of p- nitrosophenol using ammonium sulfide as a reducing agent in an aqueous ammonia solution (Scheme 1)

Said method according to the invention makes it possible to realize the following advantages:

- obtaining the final para- aminophenol with high purity, since when reducing para- nitrosophenol with ammonium sulfide, the reducing sulfide medium effectively prevents the formation of colored impurities, which leads to a slightly colored crystalline product;

- the use of an aqueous solution of ammonia as a solvent makes it easy to separate it from the resulting product, which contributes to the simple isolation of para- aminophenol in an individual form;

- para- aminophenol is obtained in a stable form without the addition of additional stabilizers, which means that there is no decomposition during further drying, transportation and storage, since the sulfide medium acts as an antioxidant and preservative,

- during the reaction, a complex ammonium-polysulfite mixture is formed as liquid drains, which can be used as a feedstock for the production of sulfur fertilizers, which reduces the amount of unclaimed reaction waste and significantly increases the economic viability of the method as a whole;

- the target para- aminophenol is isolated from the reaction mixture in crystalline form by simple filtration, while providing >98% purity.

Thus, the method according to the invention is characterized by cheap and readily available reagents, as well as cost-effective disposal of waste, allows, without the use of special equipment, to obtain and isolate the product, which is simple from the hardware and technological point of view, providing high purity and high yield, and also guarantees the receipt of the product. , stable during further drying, transportation and storage.

Detailed description of the essence of the technical solution

The figure 1 shows one of the options for a possible installation scheme for implementing the method according to the invention

The following detailed description of the method is given for the sake of clarity with reference to FIG. 1 installation option, however, does not impose any restrictions on the hardware implementation of the method proposed in the invention.

At the first technological stage a) in the container E2.1 , a saturated solution of para- nitrosophenol is prepared in 10-25% of the mass. aqueous solution of ammonia. The lower limit of the specified concentration range of aqueous ammonia solution is due to the fact that at a lower concentration, the solubility of p- nitrosophenol decreases significantly and, as a result, the volume of the reaction solution and subsequent drains increases, and the upper limit is determined by the maximum possible concentration of ammonia in water under standard conditions.

According to the invention, p- nitrosophenol can be used to obtain the solution in step a) both in dry and wet state with a water content of up to 50% by weight, calculated on the weight of p- nitrosophenol. Wet p- nitrosophenol has a greater chemical stability, since in this case oligomerization processes are inhibited.

Step b) of the process according to the invention comprises providing an aqueous solution of ammonium sulfide. In the context of the present invention, the term " providing an aqueous solution of ammonium sulfide " is understood to mean both loading into a container E2.2 a prepared aqueous solution of ammonium sulfide from commercial sources, and preparing a solution directly in a container E2.2, for example, by passing a weak current of hydrogen sulfide gas through aqueous solution of ammonia (see RU2154608C1). According to the invention in stage b) provide a solution containing from 15 to 48% of the mass. ammonium sulfide, preferably from 15 to 25% of the mass. In addition, in a preferred embodiment, the resulting solution additionally contains from 5 to 15 wt.% ammonium hydroxide. The addition of the specified amount of ammonium hydroxide allows you to maintain the pH of the solution in the range> 9, at which ammonium sulfide exhibits greater stability, and as a result, there are no processes of disproportionation and turbidity of the solution due to the release of elemental sulfur.

At the next technological stage c), pumps H2.1 and H2.2 simultaneously supply solutions to the reactor R2.1 through a T-shaped mixer T2.1 , the feed rate is chosen so that the ratio of flows corresponds to the molar ratio of p- nitrosophenol to ( NH ₄ ) ₂ S in the range from 1:1.5 to 1:2.5. This ratio makes it possible to carry out the reduction reaction until the complete conversion of p- nitrosophenol into the product and at the same time does not lead to the formation of by-products due to a significant excess of ammonium sulfide.

In a preferred embodiment, the R2.1 reactor is equipped with a thermostatic coil that has two modes of operation: both heating and cooling, which allows it to be used in a wide range of operating temperatures at different stages of the process.

Before starting the supply of reaction solutions, a weak current of an inert gas, preferably nitrogen or argon, is supplied to the reactor R2.1 through tap 1 . The resulting mixture from the mixer T2.1 is fed into the reactor P2.1 where it is stirred using a standard agitator, providing effective mixing, in which all the solids of the reaction mixture are constantly in suspension, and the temperature of the reaction mixture in the reactor P2.1 is maintained in the range from 40 to 50°C, more preferably in the range from 42-45°C. Control over the temperature of the reaction mixture is carried out using a thermocouple TT2.1 . Since the reaction proceeds with heating, the coolant coil in the P2.1 reactor at this stage of the process operates in the cooling mode.

After the complete supply of solutions from E2.1 and E2.2 at the technological stage d), the supply of inert gas to the reactor is stopped using valve 1 , the reactor is disconnected from communication with the external atmosphere by valve 2, and the reaction mixture is evacuated to remove excess ammonia, for which connect the reactor R2.1 to the vacuum system through the tap 3 . Preferably the removal of ammonia is carried out at a pressure in the range of 150 to 300 mmHg, more preferably at a pressure of about 250 mmHg (control by vacuum gauge B2.1 ), and a temperature in the range of 40 to 50°C. (control by thermocouple TT2.1 ). The distillation of excess ammonia is accompanied by cooling of the reaction mixture, so the coil with coolant in the reactor P2.1 at this stage of the method operates in heating mode. A gradual increase in temperature in the reactor indicates the completion of the distillation. When stripping ammonia, it is preferable to provide a vapor recovery device, such as an acid spray scrubber or a cold trap, to eliminate harmful emissions.

At the next technological stage f) the R2.1 reactor is disconnected from the vacuum system with a valve 3 , communication with the external atmosphere is restored with a valve 2 , and the reaction mass is cooled to 15 - 18 ° C (control by a thermocouple TT2.1 ). In the R2.1 reactor, an abundant precipitation of para- aminophenol crystalline precipitate is observed.

Then, in step f), the reaction mixture is completely drained from the reactor R2.1 into the suction filter F2.1 by opening the tap 4 .

To separate solid para- aminophenol from the reaction mixture at stage g), the lower part of the suction filter is connected to the vacuum system with a valve 6 , filtered off, and the precipitate is squeezed out on the filter. The suction filter is disconnected from the vacuum system with tap 6 , by opening tap 8 a portion of pure water is supplied and the precipitate of para- aminophenol in the filter is washed using a manual stirrer MP2.1 , vacuum is applied and the washing phase is sucked off. The washing procedure is repeated one more time.

In a preferred embodiment of the method, at stage g), after washing twice with pure water with a pump H2.3 , a portion of distilled water, slightly saturated with SO ₂ , is fed from tank E2.3 to the suction filter for additional washing, clarification and stabilization of the resulting para- aminophenol.

The precipitate on the filter is squeezed out, by opening the tap 7 the combined filtrate is poured from the bottom of the suction filter into a container E2.4 for storage and / or further processing. The resulting liquid plums are a complex ammonium-polysulfite mixture, which can be used as a feedstock for the production of sulfur fertilizers. Since there is a significant excess of ammonia in the initial reaction mixture, the main component after the reduction reaction is ammonium thiosulfate. As additional impurities in plums, ammonium sulfate and ammonium sulfite are present. A solution of ammonium thiosulfate with a concentration of 10% in itself is a ready-made fertilizer, which contains two extremely important plant nutrients - nitrogen and sulfur. Also, ammonium thiosulfate can be used to produce complex fertilizers, for example, mixed with urea. This approach reduces the amount of unclaimed reaction waste and significantly increases the economic viability of the method as a whole.

In the last process step h), the precipitate of crude para- aminophenol is discharged from the suction filter and dried by any mild drying method known to the specialist (for example, under reduced pressure) at a temperature not exceeding 55 ° C. After drying, solid para- aminophenol is obtained with a purity exceeding 98 % and a yield of more than 80%.

Legend:

P2.1 Reactor

F2.1 Nutsch filter

T2.1 T-shaped liquid mixer

L2.1 Loading hatch for maintenance of the reactor R2.1

M2.1 Mechanical stirrer

MP2.1 Agitator with manual drive for stirring sediment in the suction filter

H2.1 Peristaltic pump for supplying a solution of p- nitrosophenol to the reactor P2.1

H2.2 Peristaltic pump for supplying ammonium sulfide solution to the reactor P2.1

H2.3 Peristaltic pump for supplying water saturated with SO ₂ to the suction filter F2.1 for washing the precipitate

E2.1 Container for storing para- nitrosophenol solution

E2.2 Ammonium sulphide storage tank

E2.3 Tank for storing water saturated with SO ₂ for rinsing

E2.4 Storage container for polysulfite drains

ТТ2.1 Reactor temperature sensor

B2.1 Vacuum gauge

1 Inert gas supply valve to the reactor

2 Valve for connection to the external atmosphere of the reactor Р2.1

3 Valve for connecting the R2.1 reactor to the vacuum system

4 Valve for draining the reaction mass from the reactor R2.1 into the suction filter F2.1

5 Valve for connection to the external atmosphere of the suction filter F2.1

6 Nutsch filter F2.1 connection valve to the vacuum system

7 Valve for draining the filtrate from the suction filter F2.1

8 Shut-off valve on the clean water supply line for flushing into the suction filter F2.1

9 Shut-off valve on the line for supplying water saturated with SO ₂ to the suction filter F2.1 for washing the sediment

The invention is further explained in more detail with the help of exemplary embodiments, which, however, do not limit the scope of the present invention.

EXAMPLES

Example 1 Synthesis of para- aminophenol by reduction of para- nitrosophenol with ammonium sulfide

To carry out the synthesis, a laboratory setup was used, created in accordance with the scheme shown in figure 1.

The following operating parameters and flows were used:

Total reactor volume 35 l Reactor working volume 27 l Capacity E2.1 10 l Capacity E2.2 20 l Capacity E2.3 5 l Capacity E2.4 50 l Pump capacity H2.1 120 ml/min Pump capacity H2.2 230 ml/min Pump performance H2.3 200 ml/min

The initial reagents used were para- nitrosophenol obtained in a laboratory by means of phenol nitrosation (purity 95-97%), a commercial solution of 25% aqueous ammonia, and a commercial solution of ammonium sulfide in aqueous ammonia with a concentration of 20 wt.% (NH ₄ ) ₂ S (CAS No. 12135-76-1) and 9.5 wt% NH ₄ OH.

Synthesis technique :

In vessel E2.1, 1420 g of p- nitrosophenol (in terms of dry weight) were dissolved in 3950 g of 25% aqueous ammonia. In parallel, 8270 g of an aqueous solution of ammonium sulfide containing 20% wt. (NH ₄ ) ₂ S and 9.5% wt.% NH ₄ OH were loaded into container E2.2 . In the reactor P2.1 , equipped with a stirrer with a top drive, a weak stream of nitrogen was supplied through the valve 1 , and the pumps H2.1 and H2.2 carried out the simultaneous supply of solutions from E2.1 and E2.2 through the T-shaped mixer T2.1 to reactor P2.1 , with feed rates providing 2.03 equivalents of ammonium sulfide to p- nitrosophenol. In the P2.1 reactor, the resulting reaction mixture was stirred and the temperature was maintained in the range of 42-45°C using a submerged coil operating in conjunction with a TT2.1 thermocouple. The reaction proceeded with heating, so the coolant coil in the P2.1 reactor operated in the cooling mode.

After about 37 minutes of feeding solutions, both reaction solutions were consumed.

After that, to distill excess ammonia from the reaction mixture, the nitrogen supply was stopped, the reactor was disconnected from communication with the external atmosphere by tap 2, and connected to the vacuum system through tap 3 .

Excess ammonia was distilled off for 3.5 hours with constant stirring at a pressure of 250 mm Hg (control by vacuum gauge B2.1 ) and a temperature of 40-50°C (control by thermocouple TT2.1 ). The distillation was accompanied by cooling of the reaction mixture; therefore, the coil with the coolant in the R2.1 reactor operated in the heating mode.

Then the reactor was disconnected from the vacuum system, contact with the external atmosphere was restored, and the reaction mass was cooled to 16°C. Abundant precipitation of a crystalline precipitate was observed in the reactor. The reaction mixture was kept under these conditions for 30 min.

By opening the valve 4 , the reaction mixture was completely poured from the reactor P2.1 into the suction filter F2.1 . The lower part of the suction filter was connected to the vacuum system with a stopcock 6 , the precipitate of para- aminophenol was filtered out and squeezed out on the filter. The suction filter was disconnected from the vacuum system with tap 6 , by opening tap 8 1.5 l of pure water was supplied and the precipitate of para- aminophenol in the filter was washed using a manual stirrer MP2.1 , the vacuum was reapplied and the washing phase was sucked off. The washing procedure with clean water was repeated once more.

After that, 1.5 l of distilled water slightly saturated with SO ₂ was supplied to the suction filter by pump H2.3 from vessel E2.3 .

The precipitate on the filter was squeezed out, and by opening tap 7 , the combined filtrate was poured from the bottom of the suction filter into a container E2.4 for storage and further processing.

The precipitate of crude p- aminophenol was unloaded from the suction filter and dried in a vacuum oven at reduced pressure and at a temperature of 55°C for 16 hours.

This gave 1045 g (yield 82% of theory) of crystalline para- aminophenol with a purity of 98.9% (HPLC).

¹ H NMR (300 MHz, DMSO-d6) δ 4.36 (s, 2H), 6.46 (d, J=8.7 Hz, 2H), 6.52 (d, J=8.7 Hz, 2H), 8.32 (s, 1H).

¹³ C NMR (300 MHz, DMSO-d6) δ 115.8, 116.1, 141.0, 148.8.

Thus, as can be seen from the presented example, the proposed method according to the invention makes it possible to obtain and isolate para- aminophenol from cheap and readily available reagents, without the use of special equipment, providing high purity and modern yield, and also implies cost-effective waste disposal.

Claims (15)

1. A method for the production of para- aminophenol by the reduction of para- nitrosophenol, which includes the following steps: a) preparation of a solution of p- nitrosophenol in an aqueous ammonia solution; b) providing an aqueous solution of ammonium sulfide; c) simultaneously feeding the solutions from steps a) and b) with a flow ratio corresponding to a molar ratio of p- nitrosophenol to (NH ₄ ) ₂ S from 1:1.5 to 1:2.5 into an inert atmosphere reactor with stirring, and forced maintenance of temperature in the range from 40 to 50°C; d) after complete addition of the solutions from step a) and b) evacuation of the reaction mixture until the complete removal of ammonia while forcibly maintaining the temperature in the range from 40 to 50°C; e) removing the vacuum and cooling the reaction mixture to 18-20°C; f) withdrawing the reaction mixture from the reactor into a suction filter; g) separating the solid para- aminophenol on the filter and washing it with water; h) unloading para- aminophenol from the suction filter and drying it at a temperature not exceeding 55°C to obtain the finished product. 2. Method according to claim 1, characterized in that the solution in step a) is prepared from wet p- nitrosophenol and 25% by weight aqueous ammonia solution. 3. The method according to p. 1, characterized in that the solution provided in step b) contains from 15 to 25% of the mass. ammonium sulfide. 4. The method according to p. 1, characterized in that the solution provided in step b) additionally contains from 5 to 15% of the mass. ammonium hydroxide. 5. The method according to p. 1, characterized in that the temperature in step c) is maintained in the range from 42 to 45°C. 6. The method according to p. 1, characterized in that at stage g) additional washing is carried out with distilled water, slightly saturated with SO ₂ . 7. The method according to one of paragraphs. 1-6, characterized in that the liquid plums obtained at stage g) are a complex ammonium-polysulfite mixture, which is sent as a feedstock to the production of sulfur-containing fertilizers.

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