The method comprises the following steps: synthesizing O, N-dimethyl-Napos; green and environment-friendly method for-nitroisourea

Abstract

The invention relates to the technical field of fine chemical engineering, and provides a green and environment-friendly method for synthesizing O, N-dimethyl-N '-nitroisourea, which specifically comprises the following steps: mixing urea with an imidazole ionic solution, heating, dropwise adding dimethyl carbonate, carrying out heat preservation reaction, opening vacuum, continuously removing low-boiling-point substances in the slow heating process, cooling, stirring, dropwise adding fuming nitric acid, and carrying out heat preservation reaction to obtain the O, N-dimethyl-N'-nitroisourea. The preparation method comprises the following steps: stirring, heating, carrying out heat preservation reaction, cooling, standing and layering, taking upper concentrated nitric acid, pumping nitrogen dioxide and oxygen into the concentrated nitric acid for reuse, taking a lower ionic liquid and O, N-dimethyl-N '-nitroisourea mixture, adding 4-6 times of water, stirring, heating, layering, taking an upper aqueous solution containing O, N-dimethyl-N'-nitroisourea, slowly cooling, filtering, washing, and drying to obtain the O, N-dimethyl-N '-nitroisourea. And separating out white solid, filtering, washing with ice water, and drying to obtain O, N-dimethyl-N '-nitroisourea, so that the defect that hazardous waste salt of sodium sulfate and waste mixed acid of high-concentration COD (Chemical Oxygen Demand) are generated due to the fact that dimethyl sulfate and sulfuric acid must be used in a traditional synthesis method is overcome.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and more specifically, to a green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea. Background Technology

[0002] There are currently two existing methods for synthesizing O,N-dimethyl-N'-nitroisourea: 1. Methylating urea with dimethyl sulfate to generate O-methylisourea, then nitrating O-methylisourea with fuming nitric acid under concentrated sulfuric acid conditions to generate O-methyl-N-nitroisourea, which is then subjected to an amine exchange reaction with monomethylamine to generate O,N-dimethyl-N'-nitroisourea; 2. Reacting methyl isocyanate with ammonia to generate N-methylurea, then reacting it with dimethyl sulfate to generate monomethyl sulfate, and finally nitrating it with fuming nitric acid under concentrated sulfuric acid conditions to generate O,N-dimethyl-N'-nitroisourea.

[0003] Existing technologies all use dimethyl sulfate for methylation reactions, which generates a large amount of sulfate-containing wastewater, which is then converted into hazardous waste salt containing sodium sulfate that cannot be treated. At the same time, concentrated sulfuric acid is required as a solvent, generating a large amount of waste mixed acid with high COD. Since the product is obtained by diluting the mixed acid with water and then cooling and crystallizing it, this waste mixed acid cannot be recycled and reused. Summary of the Invention

[0004] To address this issue, we propose a green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea to solve the problems existing in the above-mentioned technologies.

[0005] The technical solution of the present invention is as follows: This invention proposes a green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea, characterized by comprising the following steps: S1. First, mix urea with an imidazole ion solution, heat the mixture and add dimethyl carbonate dropwise, and keep it warm to carry out the first stage of methylation reaction. S2. Open the vacuum, slowly heat up and continue the reaction for 4 hours. During this process, remove low-boiling substances continuously to carry out the second stage of methylation reaction. S3. After the reaction is complete, cool down, stir, add fuming nitric acid dropwise, stir and heat up, and keep the reaction at this temperature. S4. Cool down, let stand and separate into layers. The lower layer is a mixed solution, and the upper layer is concentrated nitric acid. S5. Take the upper layer of concentrated nitric acid and pump in nitrogen dioxide and oxygen to convert it into fuming nitric acid, which is then reused in step S3. S6. Take the lower layer of the mixture and add 4-6 times the amount of water. Stir and heat to separate the layers. The upper layer is an aqueous solution containing O,N-dimethyl-N'-nitroisourea, and the lower layer is a mixture containing urea and imidazole ions. S7. Remove the lower layer of liquid, vacuum heat it to remove water, and reuse it in step S1; S8. Take the upper liquid, slowly cool it down, a white solid precipitates out, filter, wash with ice water, and dry to obtain O,N-dimethyl-N'-nitroisourea.

[0006] Preferably, in step S1, the temperature is raised to 50-70°C and the holding time is 2 hours.

[0007] Preferably, in step S2, the vacuum control pressure is -0.085±0.005MPa, and the temperature is slowly increased to 120℃-140℃.

[0008] Preferably, in step S3, the cooling temperature is 5-15℃, the stirring and heating temperature is 25-30℃, and the heat preservation reaction time is 6 hours.

[0009] Preferably, in step S4, the cooling temperature is 10-15℃.

[0010] Preferably, in step S6, the stirring and heating temperature is 30-40℃.

[0011] Preferably, in step S8, the temperature for slow cooling is 0-5℃.

[0012] Preferably, the imidazole ionic solution is a 1-butyl-3-methylimidazolium hexafluoroantimonate solution.

[0013] Preferably, the imidazole ionic solution is a 1-hexyl-3-methylimidazolium hexafluoroantimonate solution. Beneficial effects

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Use dimethyl carbonate, a more environmentally friendly methylating agent, instead of dimethyl sulfate to eliminate the possibility of sulfate formation at the source; 2. Use imidazole ionic solutions instead of concentrated sulfuric acid for nitration to avoid generating large amounts of high-concentration COD waste acid; 3. The ionic liquid and concentrated nitric acid after the reaction are recycled and reused, reducing environmental pollution. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the chemical reaction of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0017] 60 g (1 mol) of urea and 150 g of 1-butyl-3-methylimidazolium hexafluoroantimony ionic liquid were added to a 500 mL flask. The temperature was raised to 60 °C, and 90 g (1 mol) of dimethyl carbonate was added dropwise. The mixture was kept at this temperature for 2 hours to carry out the first stage of methylation. Vacuum was then applied, and the pressure was controlled at -0.085 ± 0.005 MPa. The temperature was slowly raised to 130 °C, and the reaction continued for 4 hours, during which low-boiling substances were continuously removed to carry out the second stage of methylation. After the reaction was complete, O,N-dimethyl-N'-nitroisourea was generated. The reaction system was cooled to 10 °C, and 193 g (3 mol) of fuming nitric acid was added dropwise with stirring. After the addition was complete, the temperature was raised to 25-30 °C with stirring, and the reaction was kept at this temperature for 6 hours. After the reaction was complete, the temperature was lowered to 10-15 °C, and the mixture was allowed to stand and separate into layers. The lower layer was a mixture of ionic liquid and O,N-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid absorbs nitrogen dioxide and oxygen, converting it into fuming nitric acid, which is then recycled. 700g of water is added to the mixture of the lower ionic liquid and the product, and the mixture is stirred and heated to 30-40℃, resulting in separation. The lower ionic liquid is removed by vacuum heating and then recycled. The upper layer, containing an aqueous solution of O,N-dimethyl-N'-nitroisourea, is slowly cooled to 0-5℃ to precipitate a white solid. This solid is filtered, washed with ice water, and dried to obtain 124g of O,N-dimethyl-N'-nitroisourea, with a purity of 98% and a yield of 93%. Example 2

[0018] 60 g (1 mol) of urea and 150 g of 1-hexyl-3-methylimidazolium hexafluoroantimony ionic liquid were added to a 500 mL flask. The temperature was raised to 60 °C, and 90 g (1 mol) of dimethyl carbonate was added dropwise. The mixture was kept at this temperature for 2 hours to carry out the first stage of methylation. Vacuum was then applied, and the pressure was controlled at -0.085 ± 0.005 MPa. The temperature was slowly raised to 130 °C, and the reaction continued for 4 hours, during which low-boiling substances were continuously removed to carry out the second stage of methylation. After the reaction was complete, O,N-dimethyl-N'-nitroisourea was generated. The reaction system was cooled to 10 °C, and 193 g (3 mol) of fuming nitric acid was added dropwise with stirring. After the addition was complete, the temperature was raised to 25-30 °C with stirring, and the reaction was kept at this temperature for 6 hours. After the reaction was complete, the temperature was lowered to 10-15 °C, and the mixture was allowed to stand and separate into layers. The lower layer was a mixture of ionic liquid and O,N-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid absorbs nitrogen dioxide and oxygen, converting it into fuming nitric acid, which is then recycled. 700g of water is added to the mixture of the lower ionic liquid and the product, and the mixture is stirred and heated to 30-40℃, resulting in separation. The lower ionic liquid is removed by vacuum heating and then recycled. The upper layer, containing an aqueous solution of O,N-dimethyl-N'-nitroisourea, is slowly cooled to 0-5℃ to precipitate a white solid. This solid is filtered, washed with ice water, and dried to obtain 125g of O,N-dimethyl-N'-nitroisourea, with a purity of 98% and a yield of 94%. Example 3

[0019] 60 g (1 mol) of urea and 150 g of recycled 1-butyl-3-methylimidazolium hexafluoroantimony ionic liquid were added to a 500 mL flask. The temperature was raised to 60 °C, and 90 g (1 mol) of dimethyl carbonate was added dropwise. The mixture was kept at this temperature for 2 hours to carry out the first stage of methylation. Vacuum was then applied, and the pressure was controlled at -0.085 ± 0.005 MPa. The temperature was slowly raised to 130 °C, and the reaction continued for 4 hours, during which low-boiling substances were continuously removed to carry out the second stage of methylation. After the reaction was complete, O,N-dimethyl-isourea was generated. The reaction system was cooled to 10 °C, and 193 g (3 mol) of recycled fuming nitric acid was added dropwise with stirring. After the addition was complete, the temperature was raised to 25-30 °C with stirring, and the reaction was kept at this temperature for 6 hours. After the reaction was complete, the temperature was lowered to 10-15 °C, and the mixture was allowed to stand and separate into layers. The lower layer was a mixture of ionic liquid and O,N-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid absorbs nitrogen dioxide and oxygen, converting it into fuming nitric acid, which is then recycled. 700g of water is added to the mixture of the lower ionic liquid and the product, and the mixture is stirred and heated to 30-40℃, resulting in separation. The lower ionic liquid is removed by vacuum heating and then recycled. The upper layer, containing an aqueous solution of O,N-dimethyl-N'-nitroisourea, is slowly cooled to 0-5℃ to precipitate a white solid. This solid is filtered, washed with ice water, and dried to obtain 128g of O,N-dimethyl-N'-nitroisourea, with a purity of 98% and a yield of 96%.

[0020] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea, characterized in that, Includes the following steps: S1. First, mix urea with an imidazole ion solution, heat the mixture and add dimethyl carbonate dropwise, and keep it warm to carry out the first stage of methylation reaction. S2. Open the vacuum, slowly heat up and continue the reaction for 4 hours. During this process, remove low-boiling substances continuously to carry out the second stage of methylation reaction. S3. After the reaction is complete, cool down, stir, add fuming nitric acid dropwise, stir and heat up, and keep the reaction at this temperature. S4. Cool down, let stand and separate into layers. The lower layer is a mixed solution, and the upper layer is concentrated nitric acid. S5. Take the upper layer of concentrated nitric acid and pump in nitrogen dioxide and oxygen to convert it into fuming nitric acid, which is then reused in step S3. S6. Take the lower layer of the mixture and add 4-6 times the amount of water. Stir and heat to separate the layers. The upper layer is an aqueous solution containing O,N-dimethyl-N'-nitroisourea, and the lower layer is a mixture containing urea and imidazole ions. S7. Remove the lower layer of liquid, vacuum heat it to remove water, and reuse it in step S1; S8. Take the upper liquid, slowly cool it down, a white solid precipitates out, filter, wash with ice water, and dry to obtain O,N-dimethyl-N'-nitroisourea.

2. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S1, the temperature is raised to 50-70℃ and held for 2 hours.

3. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S2, the vacuum control pressure is -0.085±0.005MPa, and the temperature is slowly increased to 120℃-140℃.

4. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S3, the cooling temperature is 5-15℃, the stirring temperature is 25-30℃, and the holding time is 6 hours.

5. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S4, the cooling temperature is 10-15℃.

6. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S6, the stirring temperature is 30-40℃.

7. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: In step S8, the temperature is slowly reduced to 0-5℃.

8. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: The imidazole ion solution is a 1-butyl-3-methylimidazolium hexafluoroantimonate solution.

9. The green and environmentally friendly method for synthesizing O,N-dimethyl-N'-nitroisourea according to claim 1, characterized in that: The imidazole ion solution is a 1-hexyl-3-methylimidazolium hexafluoroantimonate solution.

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