Method for directly preparing biurea from benzophenone azine

Abstract

The invention provides a method for directly preparing biurea from benzophenonetazine, which comprises the following steps of: adding an acid catalyst into a mixed solution of benzophenonetazine, urea and an organic solvent, heating for reaction, and finally centrifugally separating to directly obtain the biurea. The benzophenonetazine and the urea are used as raw materials, the raw materials are dissolved in the reaction solvent, the reaction product biurea is not dissolved in the reaction solvent, the product is easy to separate and purify, inorganic salt and ammonia nitrogen wastewater are not generated in the reaction, the technological process is simple, and the method has the advantages of being easy to implement industrially and remarkable in economic benefit.

Description

A method for the direct preparation of biuret from benzophenone azohydride Technical Field

[0001] This invention belongs to the field of organic synthesis, specifically relating to a method for the direct preparation of biuret from benzophenone azobenzene under catalytic conditions. Background Technology

[0002] Biuret, chemically known as hydrazine dicarboxamide, is a white or light brown powder in its pure form. It is stable at room temperature and insoluble in alcohols, ethers, and water. Biuret is a key intermediate in the industrial synthesis of azodicarbonamide (AC foaming agent), an important chemical product. It is also widely used in applications such as runway anti-skid, gear anti-skid, high-grade cable fire-retardant protection, and high-grade highway anti-skid and anti-melting.

[0003] Currently, the main synthetic routes for biuret include the hydrazine hydrate-urea condensation method, the hydrazine salt-urea method, and the hydrazine carbonate-urea method. Among these, the hydrazine hydrate-urea method is the most widely used in existing industrial practice due to the availability of raw materials and relatively low cost. This method is usually carried out in an aqueous system by heating hydrazine hydrate and urea under acidic conditions to achieve a condensation reaction. However, all of the above methods share a common technical bottleneck: they all rely on a high concentration of hydrazine hydrate as a key raw material. Currently, industrially, hydrazine hydrate is mainly produced through the Raschig process or the urea process. The Raschig process uses chlorine and sodium hydroxide as raw materials to generate sodium hypochlorite, which is then oxidized by ammonia to produce a low concentration (1%~2%) of hydrazine hydrate. Finally, a high concentration of hydrazine hydrate solution is obtained through a concentration process. The Raschig process is widely used due to its low raw material cost, but its high energy consumption and large amount of inorganic salt byproducts limit its further development. The urea process involves reacting chlorine and sodium hydroxide to generate sodium hypochlorite, which is then oxidized by adding urea to produce hydrazine. The urea process can yield high concentrations of hydrazine hydrate, and the technology is relatively mature and stable. However, the production process generates large amounts of complex wastewater containing high concentrations of inorganic salts and ammonia nitrogen (NaCl, NaCO3, NH4Cl, NH3), leading to complicated subsequent treatment and severe environmental compliance pressures on enterprises, significantly limiting the economic viability of the process. Furthermore, hydrazine hydrate itself is chemically unstable, and high-concentration hydrazine hydrate has extremely strong reducing properties, classifying it as a highly hazardous chemical. Its storage, transportation, and use pose significant safety risks, requiring extremely strict safety management of production equipment. In addition, the synthetic route from hydrazine hydrate to biuret is lengthy, involving multiple processes such as concentration and purification, resulting in a complex overall process, high energy consumption, and environmental problems such as byproducts like ammonia and ammonium salts. Summary of the Invention

[0004] To address the shortcomings of the aforementioned technologies, this invention avoids the use of hydrazine hydrate and provides a method for directly preparing biuret from benzophenone azide. This method features a simple process flow, produces no inorganic salts or ammonia nitrogen wastewater, is environmentally friendly, and is easily implemented on an industrial scale with significant economic benefits.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for directly preparing biuret from benzophenone azohydride includes the following steps:

[0007] (1) Add benzophenone azo, urea and acid catalyst to a high-pressure reaction tube and purge the reaction tube with nitrogen for protection;

[0008] (2) Add the solvent to the high-pressure reaction tube and stir until homogeneous;

[0009] (3) Heat the reaction tube to 120-180℃ and stir continuously for 24-48 hours;

[0010] (4) Cool the reaction tube to room temperature, centrifuge the resulting turbid reaction solution, and wash and dry the resulting precipitate to obtain biuret;

[0011] The mass ratio of benzophenone azo, urea, acidic catalyst, and solvent is 20:10:1-2:80-100.

[0012] Preferably, the acidic catalyst in step (1) is one of p-toluenesulfonic acid, trichloroacetic acid, and trifluoromethanesulfonic acid.

[0013] Preferably, the solvent in step (2) is one of sulfolane, dioxane, and ethanol.

[0014] Preferably, in step (3), the temperature is raised to 150-170℃ and the reaction is continuously stirred for 30-36 hours.

[0015] The present invention particularly prefers trifluoromethanesulfonic acid as the acidic catalyst, ethanol or sulfolane as the solvent, and the reaction temperature as 150-170°C, with continuous stirring for 30-36 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses benzophenone azide and urea as raw materials. The raw materials are soluble in the reaction solvent, while the reaction product biuret is insoluble in the reaction solvent. The product is easy to separate and purify. The one-step synthesis reaction has a simple process flow. Moreover, the reaction process does not produce inorganic salts and ammonia nitrogen wastewater, which can significantly reduce environmental pollution problems. It has the characteristics of being easy to implement industrially and having significant economic benefits. Attached Figure Description

[0017] Figure 1 shows the biuret prepared in Example 1.1 H NMR spectrum.

[0018] Figure 2 shows the DSC spectrum of the biuret prepared in Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below through specific embodiments. The described embodiments are merely some embodiments of the present invention, not all embodiments, and the protection scope of the present invention is not limited thereto. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0020] In this embodiment of the invention, the steps for preparing biuret from benzophenone azo dyes are as follows:

[0021] (1) Take 20 parts of benzophenone azo, 10 parts of urea and 1-2 parts of acid catalyst and add them to the high-pressure reaction tube. Nitrogen gas is passed through the reaction tube for protection.

[0022] (2) Add 80-100 parts of solvent to the high-pressure reaction tube and stir until homogeneous;

[0023] (3) Heat the reaction tube to 120-180℃ and stir continuously for 24-48 hours;

[0024] (4) Cool the reaction tube to room temperature, centrifuge the resulting turbid reaction solution, and wash and dry the precipitate with distilled water to obtain biuret;

[0025] The acidic catalyst mentioned in step (1) is one of p-toluenesulfonic acid, trichloroacetic acid, and trifluoromethanesulfonic acid. The solvent mentioned in step (2) is one of sulfolane, dioxane, and ethanol.

[0026] The characterization test method in this embodiment of the invention is as follows:

[0027] 1) Determination of biuret yield (Y.%)

[0028] Y.% = m1 / m2 × 100%

[0029] In the above formula, m1 is the mass of the separated biuret, and m2 is the theoretical maximum mass of biuret calculated based on the amount of benzophenone azo added.

[0030] 2) The proton NMR spectrum of biuret (H2N) 1 H NMR determination

[0031] An appropriate amount of dried biuret was dissolved in deuterated DMSO and analyzed on a Bruker Avance III 600MHz nuclear magnetic resonance spectrometer. 1 H NMR determination.

[0032] 3) Differential scanning calorimetry (DSC) determination of biuret

[0033] A suitable amount of dried biuret was placed on a Netzsch Polyma 214 (Germany) for DSC testing. The temperature scan range was 20 °C to 300 °C, under N2 atmosphere, with a heating rate of 20 °C / min.

[0034] Example 1

[0035] 1.0 g of benzophenone azide, 0.5 g of urea, 0.05 g of trifluoromethanesulfonic acid, and 5.0 g of ethanol were added to a 50 mL stainless steel reactor. Nitrogen gas was introduced into the reactor for deoxygenation protection. The reactor was then heated to 170 °C and stirred for 30 h. The reaction mixture was then cooled and centrifuged. The precipitate was washed with distilled water and dried under vacuum to obtain 0.220 g of biuret, with a yield of 67.1%. The obtained biuret... 1 The H NMR spectrum is shown in Figure 1; the DSC spectrum of the obtained biuret is shown in Figure 2.

[0036] Example 2

[0037] Add 1.0 g of benzophenone azide, 0.5 g of urea, 0.1 g of p-toluenesulfonic acid, and 5.0 g of sulfolane to a 50 mL stainless steel reactor. Purge the reactor with nitrogen for deoxygenation protection, then heat the reactor to 180 °C and stir for 24 h. Afterward, cool the reactor, centrifuge the reaction mixture, wash the precipitate with distilled water, and vacuum dry to obtain 0.197 g of biuret, with a yield of 60.2%.

[0038] Example 3

[0039] 1.0 g of benzophenone azide, 0.5 g of urea, 0.05 g of trifluoromethanesulfonic acid, and 5.0 g of dioxane were added to a 50 mL stainless steel reactor. Nitrogen gas was introduced into the reactor for deoxygenation protection. The reactor was then heated to 120 °C and stirred for 48 h. The reaction mixture was then cooled and centrifuged. The precipitate was washed with distilled water and dried under vacuum to obtain 0.184 g of biuret, with a yield of 56.1%.

[0040] Example 4

[0041] Add 1.0 g of benzophenone azide, 0.5 g of urea, 0.1 g of trichloroacetic acid, and 5.0 g of ethanol to a 50 mL stainless steel reactor. Purge the reactor with nitrogen for deoxygenation protection, then heat the reactor to 180 °C and stir for 36 h. Afterward, cool the reactor, centrifuge the reaction mixture, wash the precipitate with distilled water, and vacuum dry to obtain 0.176 g of biuret, with a yield of 53.7%.

[0042] Example 5

[0043] 1.0 g of benzophenone azide, 0.5 g of urea, 0.05 g of trifluoromethanesulfonic acid, and 4.0 g of sulfolane were added to a 50 mL stainless steel reactor. Nitrogen gas was introduced into the reactor for deoxygenation protection. The reactor was then heated to 150 °C and stirred for 36 h. The reaction mixture was then cooled and centrifuged. The precipitate was washed with distilled water and dried under vacuum to obtain 0.207 g of biuret, with a yield of 63.0%.

[0044] Example 6

[0045] 1.0 g of benzophenone azide, 0.5 g of urea, 0.1 g of p-toluenesulfonic acid, and 4.0 g of ethanol were added to a 50 mL stainless steel reactor. Nitrogen gas was introduced into the reactor for protection, and then the reactor was heated to 140 °C. After stirring for 40 h, the reaction mixture was cooled and centrifuged. The precipitate was washed with distilled water and dried under vacuum to obtain 0.201 g of biuret, with a yield of 61.3%.

Claims

1. A method for directly preparing biuret from benzophenone azohydride, characterized in that: The method includes the following steps: (1) adding benzophenone azo, urea, and acidic catalyst into a high-pressure reaction tube, and protecting the reaction tube with nitrogen gas; (2) adding solvent into the high-pressure reaction tube and stirring evenly; (3) heating the reaction tube to 120-180℃ and stirring continuously for 24-48h; (4) cooling the reaction tube to room temperature, centrifuging the resulting turbid reaction solution, and washing and drying the resulting precipitate to obtain biuret; the mass ratio of benzophenone azo, urea, acidic catalyst, and solvent is 20:10:1-2:80-100.

2. The method as described in claim 1, characterized in that: The acidic catalyst mentioned in step (1) is one of p-toluenesulfonic acid, trichloroacetic acid, and trifluoromethanesulfonic acid.

3. The method as described in claim 1, characterized in that: The solvent mentioned in step (2) is one of sulfolane, dioxane, and ethanol.

4. The method as described in claim 1, characterized in that: In step (3), the temperature is raised to 150-170℃ and the reaction is stirred continuously for 30-36 hours.

5. The method as described in claim 1, characterized in that: The acidic catalyst is trifluoromethanesulfonic acid, the solvent is ethanol or sulfolane, the reaction temperature is 150-170℃, and the reaction is carried out with continuous stirring for 30-36 hours.

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