Ultrasonic-enhanced continuous synthesis method of FOX-7

Abstract

The invention discloses a continuous synthesis method of ultrasonic enhanced FOX-7. The method comprises the following steps: continuously introducing a concentrated sulfuric acid solution of 6-hydroxy-2-methylpyrimidine-4-ketone and a nitric-sulfuric acid mixed solution into a tubular reactor, wherein the tubular reactor is tightly arranged around an ultrasonic vibration rod; the reaction liquid enters a continuous stirring kettle after staying in the tubular reactor for a period of time, then nitration reaction liquid in the continuous stirring kettle is introduced into a large amount of ice-water mixture for hydrolysis reaction, and FOX-7 is obtained after filtering, washing and drying. According to the invention, the mass transfer rate and the nitrification rate in the tubular reactor are intensified by adopting ultrasound creatively, so that the reaction efficiency is remarkably improved; by reasonably setting the residence time in the tubular reactor, solid products are effectively prevented from being separated out, and the problem of blockage in the tubular reactor is solved. Under the optimal condition, the yield of FOX-7 reaches 92%, and the purity is not lower than 99.3%.

Description

Technical Field

[0001] The invention relates to the field of energetic material synthesis, and in particular to an ultrasonically enhanced 1,1-diamino-2,2-dinitroethylene (FOX-7) continuous synthesis process. Background Art

[0002] 1,1-Diamino-2,2-dinitroethylene (FOX-7) is a new type of low-friction, low-impact-sensitivity insensitive energetic material, and is an insensitive explosive with high application value. Its sensitivity is lower than that of the commonly used explosive cyclotrimethylene trinitramine (RDX), and it has good energy performance and detonation performance. It has good compatibility with the main components of modified double-base propellants, and has good application prospects in propellants. It is one of the most widely used energetic materials today. There are several different synthetic routes for FOX-7. The most commonly used one is the synthetic process using 2-methyl-4,6-dihydroxypyrimidine or 2-methyl-4,6-dipyrimidone as raw materials through nitration and hydrolysis reactions.

[0003] Chinese patent 201410705615.4 adopts an intermittent process to synthesize FOX-7. Specifically, a mixed acid nitrating agent is continuously added to an intermittent reactor pre-added with 2-methyl-4,6-dihydroxypyrimidine and an inert solvent, and the nitration reaction is completed at room temperature. Then water is added to the reaction system for hydrolysis, and FOX-7 is obtained after post-treatment, realizing the one-pot preparation of FOX-7. However, due to the use of an intermittent process, this method has the disadvantages of a long reaction cycle, a large amount of hazardous materials online, and low efficiency. Therefore, there are documents that use a tubular reactor continuous process to synthesize FOX-7 to solve the problems of the intermittent process, but the process has not yet made a major breakthrough. The main reason is that no matter whether the tubular reactor uses a hose or a hard pipe, and whether the pipe diameter is thick or thin, solids will precipitate during the nitration process, causing pipe blockage. Chinese patent CN202011402646.4 reports a method for synthesizing 1,1-diamino-2,2-dinitroethylene (FOX-7), in which a concentrated sulfuric acid solution of 2-methylpyrimidine-4,6-dione, a mixed acid solution of concentrated sulfuric acid and fuming nitric acid, and an inert solvent are mixed in a microchannel reactor and reacted to generate a FOX-7 precursor. Although this method solves the problem of solid precipitation in the continuous process of the tubular reactor causing pipeline blockage by introducing an inert solvent and realizes continuous nitration, the use of an inert solvent not only requires the separation and recovery of the inert solvent after the reaction is completed, but also introduces new impurities into the system, and the yield is low (up to about 80%). Summary of the invention

[0004] The purpose of the present invention is to provide an ultrasound-enhanced FOX-7 continuous synthesis method, which aims to improve the purity and yield of a continuous process in a tubular reactor.

[0005] The technical solution to achieve the purpose of the present invention is: an ultrasonically enhanced 1,1-diamino-2,2-dinitroethylene (FOX-7) continuous synthesis method, comprising:

[0006] A mixed solution of 6-hydroxy-2-methylpyrimidin-4-one and concentrated sulfuric acid is used as raw material 1, and a nitric-sulfuric acid mixture is used as raw material 2. Raw materials 1 and 2 are introduced into a tubular reactor, and the tubular reactor is tightly arranged around an ultrasonic vibrator. After the reaction liquid stays in the tubular reactor for a period of time, it enters a continuous stirring kettle. After staying in the continuous stirring kettle for a period of time, the nitration reaction liquid after the reaction is continuously introduced into a large amount of ice-water mixture for hydrolysis reaction. The product obtained by the hydrolysis reaction is vacuum filtered, washed, and vacuum dried.

[0007] Preferably, 6-hydroxy-2-methylpyrimidin-4-one is added to concentrated sulfuric acid to dissolve, and the resulting mixed solution is used as raw material 1. The temperature is maintained below 30° C. during the dissolution process, wherein the mass ratio of 6-hydroxy-2-methylpyrimidin-4-one to concentrated sulfuric acid is 1:6-20, preferably 1:14.

[0008] Preferably, the nitric acid in the nitric-sulfuric acid mixture is fuming nitric acid, and the sulfuric acid is concentrated sulfuric acid, wherein the mass ratio of the fuming nitric acid to the concentrated sulfuric acid is 1:1-2, preferably 1:1.5.

[0009] Preferably, raw material 1 and raw material 2 are introduced into a tubular reactor to ensure that the molar ratio of 6-hydroxy-2-methylpyrimidin-4-one to fuming nitric acid in the nitric-sulfuric acid mixture is 1:5-8, preferably 1:6.

[0010] Preferably, the tubular reactor can use an acid-resistant and corrosion-resistant hose or hard pipe. In order to ensure the ultrasonic effect, a PTFE hose is preferred.

[0011] Preferably, the temperature of the reaction liquid in the tubular reactor is controlled to be 30-40°C.

[0012] Preferably, in order to ensure that the temperature of the reaction liquid in the tubular reactor is 30-40°C, cooling circulating water is arranged around the tubular reactor, and the temperature of the cooling circulating water is controlled at 20°C.

[0013] Preferably, the ultrasonic frequency of the ultrasonic vibrator is 20kHz-40kHz, and the power density (power of the ultrasonic vibrator / area of ​​the ultrasonic vibrator) of the ultrasonic vibrator acting on the tubular reactor is 0.05-0.2W / cm 2 The lower the power density, the lower the yield. The higher the power density, the less change in yield and purity. The higher the temperature of the reaction liquid in the reactor, the more likely it is to cause the intermediate to decompose, and the more dangerous it is. The preferred value is 0.16W / cm 2 .

[0014] Preferably, the residence time of the reaction solution in the tubular reactor is 10-30 s, preferably 30 s. When the residence time is set to not more than 30 s, no solid precipitation will occur in the tubular reactor. If the residence time is too short, the conversion rate will be reduced.

[0015] Preferably, the average residence time in the continuous stirred tank is 5-20 min, preferably 10 min.

[0016] Preferably, in the hydrolysis reaction, the volume ratio of the reaction liquid to the ice-water mixture is 1:2-15, preferably 1:10, and the reaction liquid and the ice-water mixture are mixed and allowed to stand for 5-10 hours.

[0017] Compared with the existing synthesis process, the present invention has the following significant advantages: (1) under the assistance of ultrasound, the time required for the nitration reaction process is significantly shortened, the residence time in the tubular reactor does not exceed 1 minute, and the residence time in the continuous stirring reactor does not exceed 15 minutes. The main reason for this advantage is that ultrasound can significantly improve the mass transfer of the nitration liquid in the tubular reactor and promote the nitration reaction rate; (2) within the set time of the present invention, no solid precipitation occurs in the tubular reactor, which completely solves the problem of tubular reactor blockage; (3) using the synthesis process of the present invention, the yield and purity of FOX-7 obtained exceed those reported in existing literature and patents, and the atom economy is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the FOX-7 continuous synthesis device.

[0019] Figure 2 This is the HPLC test result of the product FOX-7.

[0020] Figure 3 This is the XRD characterization result of the product FOX-7. DETAILED DESCRIPTION

[0021] The present invention is further described below by way of examples, but the present invention is not limited by the following examples.

[0022] The synthetic formula of FOX-7 of the present invention is as follows:

[0023]

[0024] In order to verify the effect of the continuous synthesis method of FOX-7 described in the present invention, the continuous synthesis device used in the experiment is as follows Figure 1 As shown, a tubular reactor (1 m long, 1.6 mm inner diameter, made of polytetrafluoroethylene (PTFE)) is tightly wound around an ultrasonic vibrator (5 cm in radius, 30 cm in height), and the area of ​​the ultrasonic vibrator is 950 cm 2Then, it was completely immersed in a water tank with a water temperature of 20°C, and the ultrasonic frequency was set to 40kHz and the power was 150w. At this time, the power density was 0.16W / cm 2 about.

[0025] Example 1:

[0026] Based on the continuous synthesis device adopted by the present invention, the synthesis method comprises the following steps:

[0027] (1) 50.2 g of 6-hydroxy-2-methylpyrimidin-4-one was added to 380 ml of concentrated sulfuric acid and dissolved. During the dissolution process, the temperature was kept below 30° C. Ultrasound was turned on to accelerate the dissolution rate. The 6-hydroxy-2-methylpyrimidin-4-one concentrated sulfuric acid mixed solution was recorded as raw material 1;

[0028] (2) Dissolve 135 ml of fuming nitric acid in 160 ml of sulfuric acid to prepare a nitric-sulfur mixed acid solution, which is referred to as raw material 2;

[0029] (3) Using a medium-pressure constant flow pump, raw materials 1 and 2 were continuously introduced into the tubular reactor through a three-way adapter at a volume ratio of 1.8:2.2 (i.e., the molar ratio of 6-hydroxy-2-methylpyrimidin-4-one and fuming nitric acid was 1:6). The reaction liquid stayed in the tubular reactor for 30 seconds and then was continuously introduced into a continuous stirred reactor (CSTR). The average residence time of the nitration reaction liquid in the continuous stirred reactor was 10 minutes, and the reaction temperature was set to 20°C. Then, a peristaltic pump was used to continuously pass the nitration reaction liquid in the stirred reactor into a beaker containing 1750 mL of ice-water mixture, and the entire continuous process continued to operate stably for 2 hours.

[0030] (4) The beaker was left to stand overnight (about 10 hours). A large amount of bright yellow solid precipitated. The suspension was filtered, the filter cake was washed with water and ethanol, and vacuum dried at 50°C for 8 hours. After drying, the FOX-7 sample was obtained, and 54.65 g of yellow solid FOX-7 was obtained (XRD as Figure 3 The yield was 92.0% and the purity was 99.3% (HPLC test results were shown in Figure 2 shown).

[0031] Example 2:

[0032] The implementation process of Example 2 was the same as that of Example 1, except that the residence time of the reaction solution in the tubular reactor was set to 10 s. 18.35 g of FOX-7 was obtained, with a yield of 30.9% and a purity of 98.3%.

[0033] Example 3:

[0034] The implementation process of Example 3 was the same as that of Example 1, with the only difference being that the reaction solution was kept in the tubular reactor for 60 seconds. Due to the precipitation of solid inside the tubular reactor, the reaction could not proceed continuously, so the experiment was stopped for experimental safety.

[0035] Example 4:

[0036] Example 4 The implementation process is the same as Example 1, the only change is: the residence time of the reaction solution in the CSTR is 20 minutes. FOX-754.77g is obtained with a yield of 92.2% and a purity of 99.2%.

[0037] Example 5:

[0038] Example 5 The implementation process is the same as Example 1, the only change is: the residence time of the reaction solution in the CSTR is 5 minutes. FOX-742.95g is obtained with a yield of 72.3% and a purity of 98.1%.

[0039] Example 6:

[0040] Example 6 The implementation process is the same as Example 1, the only change is: the molar ratio of 6-hydroxy-2-methylpyrimidin-4-one and fuming nitric acid is changed to 1:4.5. FOX-742.53g is obtained with a yield of 71.6% and a purity of 97.6%. Example 7:

[0041] Example 7 The implementation process is the same as Example 1, the only change is: the mass ratio of 6-hydroxy-2-methylpyrimidin-4-one and concentrated sulfuric acid is changed to 1:25. FOX-733.50g is obtained with a yield of 56.4% and a purity of 98.2%.

[0042] Comparative Example 1:

[0043] The implementation process of Comparative Example 1 is the same as that of Example 1, the only change is that the power of the ultrasonic generator is set to 50W, that is, the power density is 0.05W / cm 2 The obtained FOX-747.58g was 80.1% in yield and 98.7% in purity.

[0044] Comparative Example 2:

[0045] Comparative Example 2 was implemented in the same manner as Example 1, with the only difference being that the ultrasonic vibrator was turned off. As a result, 11.94 g of FOX-7 was obtained, with a yield of 20.1% and a purity of 97.1%.

[0046] Comparative Example 3:

[0047] Comparative Example 3 The implementation process is the same as Example 1, the only change is: the frequency of the ultrasonic generator is set to 30kHz. FOX-751.50g is obtained with a yield of 86.7% and a purity of 98.4%.

[0048] Comparative Example 4:

[0049] The implementation process of Comparative Example 4 is the same as that of Example 1, with the only change being that the hydrolysis reaction in step (3) is carried out in water at room temperature. During the hydrolysis process, heat is released severely, and the reaction liquid quickly reaches its own boiling point, forming a gas-liquid mixture that sprays out rapidly, causing the hydrolysis reaction to fail.

Claims

1. An ultrasonically enhanced continuous synthesis method of 1,1-diamino-2,2-dinitroethylene, characterized in that: include: A mixed solution of 6-hydroxy-2-methylpyrimidin-4-one and concentrated sulfuric acid is used as raw material 1, and a nitric-sulfuric acid mixture is used as raw material 2. Raw materials 1 and 2 are introduced into a tubular reactor, and the tubular reactor is tightly arranged around an ultrasonic vibrator. After the reaction liquid stays in the tubular reactor for a period of time, it enters a continuous stirring kettle. After staying in the continuous stirring kettle for a period of time, the nitration reaction liquid after the reaction is continuously introduced into a large amount of ice-water mixture for hydrolysis reaction. The product obtained by the hydrolysis reaction is vacuum filtered, washed, and vacuum dried.

2. The method according to claim 1, characterized in that 6-Hydroxy-2-methylpyrimidin-4-one is added to concentrated sulfuric acid to dissolve, and the obtained mixed solution is used as raw material 1. The temperature is kept below 30° C. during the dissolution process, wherein the mass ratio of 6-hydroxy-2-methylpyrimidin-4-one to concentrated sulfuric acid is 1:6-20, preferably 1:

14.

3. The method according to claim 1, characterized in that The nitric acid in the nitric-sulfuric acid mixture is fuming nitric acid, and the sulfuric acid is concentrated sulfuric acid, wherein the mass ratio of the fuming nitric acid to the concentrated sulfuric acid is 1:1-2, preferably 1:1.

5.

4. The method according to claim 1, characterized in that Raw materials 1 and 2 are introduced into a tubular reactor to ensure that the molar ratio of 6-hydroxy-2-methylpyrimidin-4-one to the fuming nitric acid in the nitric-sulfuric acid mixture is 1:5-8, preferably 1:

6.

5. The method according to claim 1, characterized in that The temperature of the reaction liquid in the tubular reactor was controlled at 30-40°C.

6. The method according to claim 1, characterized in that The ultrasonic frequency of the ultrasonic vibrator is 20kHz-40kHz, and the power density of the ultrasonic vibrator acting on the tubular reactor is 0.05~0.2W / cm 2 , preferably 0.16W / cm 2 .

7. The method according to claim 1, characterized in that The residence time of the reaction solution in the tubular reactor is 10-30 s, preferably 30 s.

8. The method according to claim 1, characterized in that The average residence time in the continuous stirred tank is 5-20 min, preferably 10 min.

9. The method according to claim 1, characterized in that In the hydrolysis reaction, the volume ratio of the reaction liquid to the ice-water mixture is 1:2-15, preferably 1:

10.

10. The method according to claim 1, characterized in that The reaction liquid was mixed with the ice-water mixture and then allowed to stand for 5-10 hours.

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