RU2177939C2 - Method of synthesis of azobisformamide - Google Patents

Abstract

FIELD: organic chemistry, chemical technology. SUBSTANCE: invention relates to the improved method of synthesis of azobisformamide used as a foaming agent. Invention describes method of synthesis of azobisformamide by condensation of urea with hydrazine hydrate in acid medium at increased temperature followed by oxidation of hydrazobisformamide in the presence of bromine. Synthesis of hydrazobisformamide is carried out at boiling point of reaction mass and pH 4-6 followed by its oxidation without isolation to the end product using oxidative-reductive system hydrogen peroxide-bromine at 20-70 C. EFFECT: simplified technology, increased yield of product, sewage refining.

Description

 The invention relates to an improvement in the method of producing azobisformamide used as a blowing agent.

The industrial method for producing azobisformamide includes three separate schemes:
- obtaining a salt of hydrazine from hydrazine hydrate and mineral acid;
- condensation of the hydrazine salt with urea to form hydrazobisformamide;
- oxidation of hydrazobisformamide with gaseous chlorine in the presence of a bromine-containing catalyst to azobisformamide / TU 113-38-110-91 "Azodicarbonamide (porphore ChKhZ-21)"; The technological regulations of the installation for the production of porphore CHKhZ-21, 1965, Chernorechensky Chemical Plant.

 The disadvantages of this method are its multi-stage, the complexity of the hardware design, the presence of highly concentrated salt wastewater, the use of highly toxic gaseous chlorine, which made it possible to locate the production of azobisformamide only in plants where there is a special warehouse and territorial capabilities for storing chlorine.

 The methods for producing azobisformamide described in the literature are based on the use of hydrazobisformamide as the starting material. Potassium permanganate, sodium hypochlorite, alkali metal dichromates, hydrogen peroxide in combination with hydrobromic acid, its salts, hydrochloric acid and other compounds are used as oxidizing agents / ed. testimonial. Czechoslovakia 235393, MKI C 07 C 107/02, 1983; patent CPP 90091, MKI C 07 C 103/00, 1984; patent CPP 91669, MKI C 07 C 103/00, 1985; patent CPP 91670 MKI C 07 C 103/00, 1985; patent CPP 92105, MKI C 07 C 107/02, 1985; patent CPP 92106, MKI C 07 C 107/02, 1985; patent CPP 92109 MKI C 07 C 107/02, 1985; patent CPP 97229, MKI C 07 C 107/02, 1987; author testimonial. Czechoslovakia 244312, MKI S 07 S 107/02, 1984 /.

 The disadvantages of these methods are the low yield of azobisformamide, the complexity of the process and equipment design, the need to obtain hydrazobisformamide as a commercial product and (as in chlorine oxidation) a large amount of mineralized wastewater.

The closest and proposed are:
- a method for producing hydrazobisformamide by condensation of urea with hydrazine hydrate in the presence of mineral acid (H ₂ SO ₄ ) in an aqueous medium at 80-120 ^o C for 2-10 hours. After cooling the mass to room temperature, the product is filtered off, washed with water and dried. The yield of hydrazobisformamide is 94%, counting on hydrazine / patent CPP 90402, MKI C 07 C 109/00, 1984 /;
- a method of producing azobisformamide by oxidation of hydrazobisformamide with sodium dichromate in the presence of bromine and sulfuric acid, taken in a ratio of 1: 0.5-1.5: 0.01-0.3: 1.5-2.5 at 10-25 ^o C. The reaction time is 1-6 hours. The product yield of 96.5, counting on hydrazobisformamide / patent CPP 92108, MKI C 07 With 107/02, 1985 /.

 The yield of azobisformamide in terms of hydrazine is 90.7%.

 This method has all the disadvantages indicated for the above analogues. In addition, the need to use more sulfuric acid (from 1.5 to 2.5 parts by weight per 1 part by weight of hydrazobisformamide) and bichromate together with the need to treat wastewater from chromium, the lack of bichromate and its high cost make this method uncompetitive for industrial use even compared to the chlorine oxidation method.

 The objective of the present invention is to simplify the technology of obtaining azobisformamide, increase product yield, refinement of wastewater.

The problem is solved by the proposed method for producing azobisformamide, namely, that hydrazine hydrate is condensed with urea in the presence of mineral acid and, without isolating the intermediate product - hydrazobisformamide, in the same reactor it is oxidized with a redox system hydrogen peroxide - bromine to the final product. The yield of azobisformamide is 94-97%, counting on hydrazine. The gas number is 260-270 cm ³ / g. The decomposition temperature of 190-205 ^o C.

 The difference between the proposed method and the known one is the production of azobisformamide from hydrazine hydrate in one reactor without isolation of intermediate products and the use of a redox system hydrogen peroxide - bromine.

The technology for producing azobisformamide is as follows: water, urea, hydrazine hydrate, sulfuric acid are sequentially loaded into the reaction flask. Heated the contents of the flask to a boiling point, held for 6 hours, maintaining the pH of the reaction mass within 4-6. At the end of the exposure, the contents of the flask are cooled to room temperature, the mother liquor is decanted, and the precipitate is washed with water. After washing, pour water into the flask, acidify the reaction mass to pH 1-2, load bromine and add hydrogen peroxide, maintaining the temperature of the reaction mass in order to eliminate losses of bromine and process safety in the range of 20-70 ^o C. After completion of the addition, give hydrogen peroxide exposure 1-5 hours, filtered, washed the product on the filter with water until neutral, dried.

 The invention is illustrated by the following examples.

EXAMPLE 1
In a reaction flask equipped with a mechanical stirrer, reflux condenser, thermometer and dropping funnel, 320 ml of water, 268.8 g of urea, 74.6 g of 68.3% hydrazine hydrate, 90 cm ^{3 of} concentrated sulfuric acid are successively charged. Heat the contents of the flask to a boiling point and incubate for 6 hours, maintaining a pH of 4-6. At the end of the exposure, the reaction mass is cooled to room temperature, settled for 20-30 minutes and the mother liquor is decanted. Then the precipitate is washed twice with water. After that, 320 ml of water is poured into the flask, the mass is acidified to pH 1-2, and 3.5 cm ^{3 of} bromine are charged. Raise the temperature to 45 ^o C and give 127 cm ^{3 of} 39.7% hydrogen peroxide, maintaining the temperature not higher than 65 ^o C. Then the mass is kept at 65-70 ^o C for 1 hour, cooled to room temperature, filtered, washed with the target product water until neutral. They are drying. Obtain 183 g of azobisformamide, which is 97.3%, counting on hydrazine. The decomposition temperature is 198 ^o C. Gas number 267 cm ³ / year

EXAMPLE 2
In an enameled reactor with a capacity of 1 m ³ , equipped with a stirrer, a jacket, a thermometer sleeve, a heat exchanger, measuring devices for sulfuric acid and hydrogen peroxide, pour 320 dm ^{3 of} water, turn on the stirrer, load 269 kg of urea, 75 kg of 67.8% hydrazine hydrate and 165 kg of concentrated sulfuric acid, heated to boiling point and maintained under these conditions for 6 hours, maintaining the pH of the reaction mass 4-6. At the end of the exposure, it is cooled to 20-25 ^o C, it settles for 1 hour, the mother liquor is decanted, the precipitate is washed twice with water. Then water is poured into the reactor and 15 kg of concentrated sulfuric acid and 5 dm ^{3 of} bromine are successively charged. The temperature of the reaction mixture is raised to 45 ^{° C.} and the addition of 154 kg of 37% hydrogen peroxide is started, maintaining the temperature within the range of 50-60 ^° C. After the completion of the addition, the hydrogen peroxide is held for 3 hours at 55-60 ^° C. The contents of the reactor are then cooled to 20-25 ^o With and the resulting suspension of the finished product is passed to the stage of filtration and washing with water until neutral. Dry the product at 80-100 ^o C.

175 kg of azobisformamide are obtained, which is 94.6%, based on the loaded hydrazine. The decomposition temperature is 192 ^o C. The gas number is 272 cm ³ / g.

 The technical result of the proposed method is to obtain azobisformamide with high yield and quality, simplifying the process, reducing the amount of concentrated mineralized wastewater. Compared with the industrial method, the sanitary and environmental characteristics of production are also significantly improved due to the rejection of the use of toxic chlorine, and it becomes possible to organize the production of azobisformamide in enterprises of general organic synthesis.

Claims (1)

A method of producing azobisformamide of condensation of urea with hydrazine hydrate in an acidic environment at elevated temperature followed by oxidation of hydrazobisformamide in the presence of bromine, characterized in that the synthesis of hydrazobisformamide is carried out at a boiling point of the reaction mixture and a pH of 4-6 and, without isolating, oxidize it to the end product oxidatively the reducing system, hydrogen-bromine peroxide at 20-70 ^o C.