A method of synthesizing n,o-dimethyl-n'-nitroisourea

Abstract

The application relates to the fine chemical technology field and discloses a method for synthesizing N,O-dimethyl-N'-nitroisourea, which specifically comprises the following steps: mixing urea and an imidazole ionic liquid, adding dimethyl carbonate drop by drop under temperature rising, performing heat preservation reaction, opening a vacuum, continuously removing low-boiling substances in a slow temperature rising process, cooling, stirring, adding fuming nitric acid drop by drop, stirring and temperature rising, performing heat preservation reaction, cooling and standing to separate layers, pumping the upper concentrated nitric acid into nitrogen dioxide and oxygen, waiting for reuse, adding 4-6 times of water into the lower ionic liquid and N,O-dimethyl-N'-nitroisourea mixture, stirring and temperature rising, separating layers, taking the upper layer of N,O-dimethyl-N'-nitroisourea-containing aqueous solution, slowly cooling, precipitating white solids, filtering, washing with ice water, drying, and obtaining N,O-dimethyl-N'-nitroisourea, so that the shortcomings of traditional synthesis methods, i.e. the necessity of using dimethyl sulfate and sulfuric acid to generate dangerous waste salt of sodium sulfate and waste mixed acid with high COD, are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fine chemical technology, more particularly, to a method for synthesizing N,O-dimethyl-N'-nitroisourea. BACKGROUND

[0002] There are two methods for synthesizing N,O-dimethyl-N'-nitroisourea in the prior art: 1. urea is subjected to methylation reaction with dimethyl sulfate to generate O-methylisourea, O-methylisourea is subjected to nitration reaction with fuming nitric acid under the condition of concentrated sulfuric acid to generate O-methyl-N-nitroisourea, and then amine exchange reaction is performed with monomethylamine to generate N,O-dimethyl-N'-nitroisourea; 2. methyl isocyanate is reacted with ammonia to generate N-methylurea, N-methylurea is reacted with dimethyl sulfate to generate monomethyl sulfate, and finally nitration reaction is performed with fuming nitric acid under the condition of concentrated sulfuric acid to generate N,O-dimethyl-N'-nitroisourea.

[0003] In the prior art, dimethyl sulfate is used for methylation reaction, which produces a large amount of wastewater containing sulfate, which is further converted into hazardous waste salt containing sodium sulfate that cannot be disposed of, and concentrated sulfuric acid is also used as a solvent, which produces a large amount of waste mixed acid with high COD, and since the product is crystallized out after the mixed acid is diluted with water and cooled, the waste mixed acid cannot be recycled and reused. SUMMARY

[0004] In view of the above, a method for synthesizing N,O-dimethyl-N'-nitroisourea is provided to solve the problems in the prior art.

[0005] The technical scheme of the present application is as follows:

[0006] The present application provides a method for synthesizing N,O-dimethyl-N'-nitroisourea, characterized in that the method comprises the following steps:

[0007] S1. First, urea is mixed with an imidazole-based ionic liquid, dimethyl carbonate is added dropwise while being heated, the heating temperature is 50-70 DEG C, and the first stage of methylation reaction is carried out under insulation;

[0008] S2. The vacuum is opened, the vacuum control pressure is-0.085±0.005 MPa, the temperature is slowly raised to 120-140 DEG C, and the second stage of methylation reaction is carried out after slow heating for 4 hours, during which low-boiling substances are continuously removed;

[0009] S3. After the reaction is completed, the temperature is lowered, stirring is carried out, fuming nitric acid is added dropwise, the temperature is raised, and the reaction is carried out under insulation;

[0010] S4. The temperature is lowered, and the mixture is allowed to stand and separate into two layers, the lower layer is a mixed liquid, and the upper layer is concentrated nitric acid;

[0011] S5, take the upper layer concentrated nitric acid pump into nitrogen dioxide and oxygen, converted into fuming nitric acid, reused in step S3;

[0012] S6, take the lower layer mixed liquid to add 4-6 times amount of water, stir to warm, separate layers, the upper liquid is N, O-dimethyl-N'-nitroisourea containing aqueous solution, the lower liquid is urea and imidazole ionic liquid containing mixed liquid;

[0013] S7, take the lower layer liquid vacuum warming to remove water, reuse to step S1;

[0014] S8, take the upper liquid, slowly cool, precipitate white solid, filter, ice water washing, drying to obtain N, O-dimethyl-N'-nitroisourea.

[0015] Preferably, in step S1, the holding time is 2 hours.

[0016] Preferably, in step S3, the cooling temperature is 5-15℃, the stirring temperature is 25-30℃, and the holding reaction time is 6 hours.

[0017] Preferably, in step S4, the cooling temperature is 10-15℃.

[0018] Preferably, in step S6, the stirring temperature is 30-40℃.

[0019] Preferably, in step S8, the slowly cooling temperature is 0-5℃.

[0020] Preferably, the imidazole ionic liquid is 1-butyl-3-methylimidazolium hexafluoroantimonate.

[0021] Preferably, the imidazole ionic liquid is 1-hexyl-3-methylimidazolium hexafluoroantimonate. Beneficial effects

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] 1. A more green and environmentally friendly methylating agent dimethyl carbonate is used instead of dimethyl sulfate, which eliminates the possibility of producing sulfate from the source;

[0024] 2. Imidazole ionic liquid is used instead of concentrated sulfuric acid for nitration, which avoids the generation of a large amount of high-concentration COD waste acid;

[0025] 3. The ionic liquid and concentrated nitric acid after reaction are recycled and reused, reducing the pollution to the environment. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The chemical reaction schematic diagram of the present application. DETAILED DESCRIPTION

[0027] Clearly, the described embodiments are merely a part of the embodiments of the present application, rather than all the embodiments, based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application. Example 1

[0028] 60 g (1 mol) of urea and 150 g of 1-butyl-3-methylimidazolium hexafluoroantimonate ionic liquid were added into a 500 mL flask, and the temperature was raised to 60°C, 90 g (1 mol) of dimethyl carbonate was added dropwise, and the first stage of methylation reaction was carried out for 2 hours. The vacuum was opened, the pressure was controlled to be -0.085±0.005 MPa, and the temperature was slowly raised to 130°C to continue the reaction for 4 hours, and in this process, the low-boiling substances were continuously removed, and the second stage of methylation reaction was carried out. After the reaction was completed, N,O-dimethyl-isourea was generated. The reaction system was cooled to 10°C, and 193 g (3 mol) of fuming nitric acid was added dropwise under stirring, and after the addition was completed, the temperature was raised to 25-30°C, and the reaction was carried out for 6 hours. After the reaction was completed, the temperature was lowered to 10-15°C, and the layers were separated after standing, the lower layer was a mixture of ionic liquid and N,O-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid was absorbed with nitrogen dioxide and oxygen, and was converted into fuming nitric acid, which was recovered and reused. 700 g of water was added to the mixture of the lower layer of ionic liquid and the product, and the temperature was raised to 30-40°C under stirring, and the layers were separated. After the lower layer of ionic liquid was removed by vacuum heating, the water was recovered and reused, and the upper layer of N,O-dimethyl-N'-nitroisourea aqueous solution was slowly cooled to 0-5°C to precipitate white solid, which was filtered, washed with ice water, and dried to obtain 124 g of N,O-dimethyl-N'-nitroisourea with a content of 98% and a yield of 93%. Example 2

[0029] Into a 500 mL flask, 60 g (1 mol) urea and 150 g of 1 -hexyl-3-methylimidazolium hexafluoroantimonate ionic liquid were added, and the temperature was raised to 60 °C. Then, 90 g (1 mol) dimethyl carbonate was added dropwise, and the first stage of methylation was carried out for 2 hours. The vacuum was opened, and the pressure was controlled at -0.085 ± 0.005 MPa. The temperature was slowly raised to 130 °C, and the second stage of methylation was carried out for 4 hours. During the process, low-boiling substances were continuously removed. After the reaction was completed, N,0-dimethyl- isourea was generated. The reaction system was cooled to 10 °C, and 193 g (3 mol) fuming nitric acid was added dropwise under stirring. After the addition was completed, the temperature was raised to 25-30 °C, and the reaction was carried out for 6 hours. After the reaction was completed, the temperature was lowered to 10-15 °C, and the mixture was allowed to stand and separate into two layers. The lower layer was a mixture of ionic liquid and N,0-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid was used to absorb nitrogen dioxide and oxygen, and was converted into fuming nitric acid, which was recycled. 700 g of water was added to the mixture of ionic liquid and product in the lower layer, and the temperature was raised to 30-40 °C. The mixture was separated into two layers. The ionic liquid in the lower layer was recovered after the water was removed by vacuum heating. The aqueous solution containing N,0-dimethyl-N'-nitroisourea in the upper layer was slowly cooled to 0-5 °C to precipitate white solids. The solids were filtered, washed with ice water, and dried to obtain 125 g of N,0-dimethyl-N'-nitroisourea with a content of 98% and a yield of 94%. Example 3

[0030] Into a 500 mL flask, 60 g (1 mol) urea and 150 g of 1 -hexyl-3-methylimidazolium hexafluoroantimonate ionic liquid were added, and the temperature was raised to 60 °C. Then, 90 g (1 mol) dimethyl carbonate was added dropwise, and the first stage of methylation was carried out for 2 hours. The vacuum was opened, and the pressure was controlled at -0.085 ± 0.005 MPa. The temperature was slowly raised to 130 °C, and the second stage of methylation was carried out for 4 hours. During the process, low-boiling substances were continuously removed. After the reaction was completed, N,0-dimethyl- isourea was generated. The reaction system was cooled to 10 °C, and 193 g (3 mol) fuming nitric acid was added dropwise under stirring. After the addition was completed, the temperature was raised to 25-30 °C, and the reaction was carried out for 6 hours. After the reaction was completed, the temperature was lowered to 10-15 °C, and the mixture was allowed to stand and separate into two layers. The lower layer was a mixture of ionic liquid and N,0-dimethyl-N'-nitroisourea, and the upper layer was concentrated nitric acid. The upper layer of concentrated nitric acid was used to absorb nitrogen dioxide and oxygen, and was converted into fuming nitric acid, which was recycled. 700 g of water was added to the mixture of ionic liquid and product in the lower layer, and the temperature was raised to 30-40 °C. The mixture was separated into two layers. The ionic liquid in the lower layer was recovered after the water was removed by vacuum heating. The aqueous solution containing N,0-dimethyl-N'-nitroisourea in the upper layer was slowly cooled to 0-5 °C to precipitate white solids. The solids were filtered, washed with ice water, and dried to obtain 125 g of N,0-dimethyl-N'-nitroisourea with a content of 98% and a yield of 94%.

[0031] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art, according to the technical solution of the present application and the improved concept thereof, makes equivalent replacement or change within the technical range disclosed by the present application, and should be covered within the protection scope of the present application.

Claims

1. A method of synthesizing N, O-dimethyl-N'-nitroisourea, characterized by, The method comprises the following steps: S1, firstly mixing urea with imidazole ionic liquid, warming and dropping dimethyl carbonate, warming temperature to 50-70℃, holding for the first stage of methylation reaction; S2, opening the vacuum, vacuum control pressure is-0.085±0.005MPa, slowly warming to 120-140℃, continuing to react for 4 hours after slowly warming, removing low boiling point substances during the process, for the second stage of methylation reaction; S3, after the reaction is completed, cooling, stirring, dropping fuming nitric acid, stirring and warming, holding for reaction; S4, cooling, standing and separating, the lower layer is mixed liquid, and the upper layer is concentrated nitric acid; S5, taking the upper layer concentrated nitric acid, pumping into nitrogen dioxide and oxygen, converting into fuming nitric acid, and recycling to step S3; S6, taking the lower layer mixed liquid, adding 4-6 times amount of water, stirring and warming, separating, the upper layer liquid is N,O-dimethyl-N'-nitroisourea aqueous solution, and the lower layer liquid is urea and imidazole ionic liquid mixed liquid; S7, taking the lower layer liquid, vacuum warming and removing water, recycling to step S1; S8, taking the upper layer liquid, slowly cooling, precipitating white solid, filtering, ice water washing, drying to obtain N,O-dimethyl-N'-nitroisourea.

2. A process for the synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: In step S1, the holding time is 2 hours.

3. A process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: In step S3, the cooling temperature is 5-15℃, the stirring and warming temperature is 25-30℃, and the holding reaction time is 6 hours.

4. A process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: In step S4, the cooling temperature is 10-15℃.

5. The process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: In step S6, the stirring and warming temperature is 30-40℃.

6. A process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: In step S8, the slowly cooling temperature is 0-5℃.

7. The process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: The imidazole ionic liquid is 1-butyl-3-methylimidazolium hexafluoroantimonate.

8. A process for synthesis of N, O-dimethyl-N'-nitroisourea as claimed in claim 1, wherein: The imidazole ionic liquid is 1-hexyl-3-methylimidazolium hexafluoroantimonate.

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