Preparation method of malononitrile
This invention proposes a two-step method to prepare malononitrile. It utilizes readily available and inexpensive dimethyl malonate and ammonia to prepare malonamide at room temperature and pressure, and then dehydrates it at room pressure to prepare malononitrile. The malononitrile is then purified by distillation. This method solves the environmental and cost problems of malononitrile preparation in existing technologies and achieves green preparation with high purity and high yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU XIANMEIDA MATERIAL TECH CO LTD
- Filing Date
- 2026-03-27
- Publication Date
- 2026-05-12
AI Technical Summary
Existing methods for preparing malononitrile suffer from problems such as the use of highly toxic raw materials, harsh reaction conditions, high equipment requirements, high energy consumption, and the generation of a large amount of solid waste, making it difficult to achieve green, environmentally friendly, and low-cost high-purity preparation.
Malonamide is prepared by reacting dimethyl malonate with ammonia at room temperature and pressure. Subsequently, malononitrile is prepared by using a dehydrating agent at room pressure and purified by distillation. The process is carried out in two steps to avoid high temperature, high pressure and highly toxic substances, and to use inexpensive and readily available raw materials and environmentally friendly dehydrating agents.
It achieves high purity (≥99.5%) and high yield (≥75%) of malononitrile, reduces production costs, simplifies operation procedures, reduces solid waste, and meets the needs of high-end application fields.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for preparing malononitrile. Background Technology
[0002] Malononitrile is an important organic synthesis intermediate. In addition to its wide application in pharmaceuticals, pesticides, and dyes, it is also used in electronic chemicals and new energy materials, and is also involved in the extraction of precious metals and the synthesis of polymers.
[0003] Currently, industrial methods for preparing malononitrile mainly fall into two categories: synthesis and dehydration. Synthesis typically uses acetonitrile and chlorocyanide, or chloroacetonitrile and hydrogen cyanide, or chloroethane and sodium cyanide as raw materials, reacting them in the presence of a catalyst. This method commonly uses highly toxic cyanides or chlorocyanides, imposing extremely high requirements on production safety and environmental protection, and the reaction conditions are often quite harsh. Dehydration methods mostly use cyanoacetamide as a raw material, dehydrating it under the action of dehydrating agents such as phosphorus oxychloride, phosphorus pentoxide, or phosgene. Although the cyanoacetamide route avoids the direct use of highly toxic gases, cyanoacetamide itself is usually obtained by the amination of cyanoacetate, and its production process may still involve cyanide-containing raw materials. Furthermore, traditional dehydrating agents generate large amounts of phosphorus-containing solid waste, placing significant environmental pressure on the industry.
[0004] Technical information related to the preparation method of malononitrile can be found in publicly available Chinese patent documents. A typical example is a method for preparing malononitrile disclosed in CN118619847A, which uses malonic acid or dimethyl malonate as raw materials and reacts with ammonia in a one-step catalytic reaction under high temperature and pressure to obtain the product. That is, a one-step direct catalytic amination method without intermediate separation. Although the raw materials are readily available, this method has harsh reaction conditions, high equipment requirements, high energy consumption, and uses a specific composite metal oxide catalyst, which is not conducive to reducing production costs and simplifying the process.
[0005] Therefore, it is of positive significance to explore a preparation method that uses readily available raw materials, has a simple process, mild reaction conditions, is environmentally friendly, and can obtain high-purity malononitrile. Summary of the Invention
[0006] The objective of this invention is to provide a method for preparing malononitrile, which uses inexpensive and readily available starting materials, is environmentally friendly, and has mild reaction conditions. The malononitrile obtained by the two-step process of amine reaction and dehydration has the advantages of high purity, low preparation cost, simple operation, and safety and environmental protection.
[0007] The objective of this invention is achieved by providing a method for preparing malononitrile, comprising the following steps: A) Preparation of malondiamide: Dimethyl malonate and ammonia water are mixed and stirred at room temperature and pressure, and the stirring time is controlled. After the stirring reaction is completed, malondiamide solid is obtained through post-processing. B) Synthesis of malononitrile: The malonamide obtained in step A) is dissolved in an organic solvent, a dehydrating agent is added, and the reaction is stirred under normal pressure. The stirring time and temperature are controlled. After the reaction is completed, the organic solvent is recovered by distillation to obtain crude malononitrile. C) Refining: The crude malononitrile obtained in step B) is distilled, and the fraction is collected to obtain high-purity malononitrile with a gas chromatographic purity of over 99.5%.
[0008] In a specific embodiment of the present invention, the mass concentration of ammonia in step A) is 20-30%; the molar ratio of dimethyl malonate to ammonia is 1:2-6.
[0009] In another specific embodiment of the present invention, the molar ratio of dimethyl malonate to ammonia is 1:3-5.
[0010] In another specific embodiment of the present invention, the stirring reaction time mentioned in step A) is controlled to be 120-360 min.
[0011] In another specific embodiment of the present invention, the post-processing described in step A) includes: after the reaction is completed, removing excess ammonia under reduced pressure, and then sequentially cooling, crystallizing, filtering and drying.
[0012] In another specific embodiment of the present invention, in step B), the organic solvent is one or more of dichloroethane, dichloromethane, and chloroform.
[0013] In a further specific embodiment of the present invention, the organic solvent is dichloroethane.
[0014] In a further specific embodiment of the present invention, the dehydrating agent in step B) is phosgene or solid phosgene, and the molar ratio of malondiamide to the dehydrating agent is 1:1-1.5.
[0015] In yet another specific embodiment of the present invention, the molar ratio of malondiamide to dehydrating agent is 1:1.1-1.3.
[0016] In yet another specific embodiment of the present invention, the control of the subsequent reaction time in step B) is to control the subsequent reaction time to 240-600 min and the temperature to 60-90°C.
[0017] In another specific embodiment of the present invention, the subsequent reaction time is controlled to be 300-420 min, and the temperature is controlled to be 75-80°C.
[0018] In a further specific embodiment of the present invention, the distillation in step C) is vacuum distillation, and the distillation conditions are: vacuum degree -0.09 to -0.1 MPa, and the fraction collected at 105-115°C.
[0019] Compared with existing technologies, the technical solution provided by this invention has the following advantages: Since dimethyl malonate and ammonia, the starting materials, are bulk chemical products, highly toxic raw materials such as sodium cyanide, hydrogen cyanide, and chlorocyanide can be avoided, eliminating safety hazards and environmental pressures at the source and significantly reducing raw material costs. Since both reactions are carried out under normal pressure, without the need for high temperature and high pressure, it has advantages such as less stringent equipment requirements, low energy consumption, simple and safe operation, concise process, short process route, and environmental friendliness. Since the byproducts of the dehydration reaction are absorbable gases such as pure HCl and CO2, no large amount of solid waste is generated, post-processing is simple, and it easily meets the requirements for industrial-scale production. Since the malononitrile prepared by the method of this invention has a purity of over 99.5% as detected by gas chromatography, it can meet the demand for high-purity raw materials in high-end application fields such as pharmaceuticals and pesticides. Detailed Implementation
[0020] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all parts and percentages are by weight.
[0021] Example 1: A) Preparation of malondiamide: 118 g (1.0 mol) of dimethyl malonate was added to a 500 mL four-necked flask equipped with a stirrer, thermometer, and dropping funnel. 270 g of 25% ammonia solution (approximately 4.0 mol NH3) was slowly added dropwise while stirring at room temperature (25°C). After the addition was complete, the reaction was continued to be stirred at room temperature and pressure for 240 min. After the reaction was complete, unreacted ammonia gas was removed under reduced pressure. The reaction solution was then cooled to 0–5°C, resulting in the precipitation of a large amount of white crystals. The crystals were filtered, the filter cake was washed with a small amount of cold water, and dried under vacuum at 50°C to constant weight, yielding 86.5 g of white solid malonamide, with a yield of 85.0% (based on dimethyl malonate). B) Synthesis of malononitrile: Add 102 g (1.0 mol) of malondiamide prepared in step A and 300 mL of dichloroethane to a 500 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, and gas absorption device. Stir until dissolved, heat to 75 °C, and then slowly introduce 115 g (approximately 1.15 mol) of phosgene, controlling the introduction rate to ensure stable reflux of the reaction system. After the introduction is complete, continue stirring at this temperature for 360 min. The tail gases (HCl and CO2) produced in the reaction are absorbed by alkaline solution. After the reaction is complete, stop heating, cool to room temperature, and first recover most of the dichloroethane by atmospheric distillation to obtain crude malononitrile. C) Refining (i.e., preparing the finished product): The crude malononitrile obtained in step B) was subjected to vacuum distillation at a vacuum degree of -0.095 MPa, and the fraction at 105-115℃ was collected to obtain 59.8 g of colorless liquid malononitrile. After cooling, it became a colorless crystalline solid, which is the solid malononitrile. The yield was 90.6% (based on malonamide), and the purity was 99.7% as determined by gas chromatography.
[0022] Example 2: A) Preparation of malondiamide: The operation steps were the same as in Example 1, except that the molar ratio of dimethyl malonate to ammonia was 1:2 (i.e., 136g of 20% ammonia was added dropwise), and the reaction time was 180min. Finally, 72.5g of malonamide was obtained, with a yield of 71.2%.
[0023] B) Synthesis of malononitrile: To a 500 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, and gas absorption device, add 102 g (1.0 mol) of malondiamide prepared in step A and a mixed solvent of 150 mL of dichloroethane and 150 mL of dichloromethane. Stir until dissolved, raise the temperature to 78 °C, and then slowly introduce 120 g (approximately 1.2 mol) of phosgene, controlling the introduction rate to ensure stable reflux of the reaction system. After the introduction is complete, continue stirring at this temperature for 300 min. After the reaction is complete, the post-treatment is the same as in Example 1 to obtain crude malononitrile.
[0024] C) Refining (i.e., preparing the finished product): The crude malononitrile obtained in step B) was subjected to vacuum distillation at a vacuum degree of -0.098 MPa. The fraction collected at 105-115℃ yielded 58.5 g of colorless liquid malononitrile, which turned into a colorless crystalline solid after cooling. The yield was 88.6%, and the purity was 99.6% as determined by gas chromatography.
[0025] Example 3: A) Preparation of malondiamide: The operation steps were the same as in Example 1, except that the molar ratio of dimethyl malonate to ammonia was 1:5 (i.e., 243g of 28% ammonia was added dropwise), and the reaction time was 360min. Finally, 84.2g of malonamide was obtained, with a yield of 82.7%.
[0026] B) Synthesis of malononitrile: To a 500 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, and gas absorption device, add 102 g (1.0 mol) of malondiamide prepared in step A and 300 mL of dichloroethane. Stir to dissolve the malondiamide, heat to 80 °C, and then add 119 g of solid phosgene (approximately 0.4 mol, equivalent to 1.2 mol of phosgene) all at once. Continue stirring and maintaining the temperature at this point for 420 min. After the reaction is complete, the post-treatment is the same as in Example 1 to obtain crude malononitrile.
[0027] C) Refined: The crude malononitrile obtained in step B) was subjected to vacuum distillation at a vacuum degree of -0.092 MPa, and the fraction at 105-115℃ was collected to obtain 59.0 g of colorless liquid malononitrile, which was a colorless crystalline solid after cooling. The yield was 89.4%, and the purity was 99.5% as determined by gas chromatography.
[0028] Example 4: A) Preparation of malondiamide: The operation steps were the same as in Example 1, except that the molar ratio of dimethyl malonate to ammonia was 1:6 (i.e., 278g of 25% ammonia was added dropwise), and the reaction time was 120min. Finally, 70.1g of malonamide was obtained, with a yield of 68.9%.
[0029] B) Synthesis of malononitrile: To a 500 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, and gas absorption device, add 102 g (1.0 mol) of malondiamide prepared in step A and 300 mL of dichloroethane. Stir until dissolved, heat to 60 °C, and then slowly introduce 110 g (approximately 1.1 mol) of phosgene, controlling the introduction rate to ensure stable reflux of the reaction system. After the introduction is complete, continue stirring at this temperature for 600 min. After the reaction is complete, the post-treatment is the same as in Example 1 to obtain crude malononitrile.
[0030] C) Refined: The crude malononitrile obtained in step B) was subjected to vacuum distillation at a vacuum degree of -0.09 MPa, and the fraction at 105-115℃ was collected to obtain 54.2 g of colorless liquid malononitrile, which was a colorless crystalline solid after cooling. The yield was 82.1%, and the purity was 99.4% as determined by gas chromatography.
[0031] Compared with the existing one-step high-temperature and high-pressure catalytic method using dimethyl malonate as a raw material (such as CN118619847A mentioned in the background section), the preparation methods of Examples 1 to 4 of this invention have outstanding substantive features and significant progress. First, by creatively splitting the reaction into two steps—"room-temperature and atmospheric-pressure amination" and "intermediate-temperature dehydration"—and successfully separating the key intermediate malonamide, this invention fundamentally eliminates the dependence on harsh conditions of high temperature (350-450℃) and high pressure (0.1-5 MPa), as well as the use of specific composite metal oxide catalysts. This greatly reduces equipment investment and energy consumption, simplifies process operation, and improves the safety of the production process. Second, while achieving green substitution of raw materials and completely eliminating the use of highly toxic cyanide, the product yield (90.6% in Example 1, total yield 77.0%) and product purity (above 99.5%) of this invention are comparable to those of the aforementioned high-temperature and high-pressure route. This efficient and high-purity conversion achieved under mild conditions overcomes the technical prejudice held by those skilled in the art that malonate must undergo a one-step catalytic process under high temperature and high pressure to effectively prepare malononitrile, fully demonstrating the inventiveness and industrial application value of this invention.
[0032] The malononitrile products prepared by Examples 1-4 of the present invention were subjected to performance tests, and the purity was analyzed by gas chromatography. The results are shown in the table below:
[0033] Note: The overall yield is based on dimethyl malonate and is the product of the yields from the two steps.
[0034] As shown in the table above, using the preferred reaction conditions of this invention (Examples 1 and 2), high-purity malononitrile with a purity of over 99.5% can be obtained with a high overall yield. When the reaction conditions deviate from the preferred range of this invention (e.g., the amination time in Example 3 is too short, or the dehydration solvent / temperature in Example 4 is inappropriate), the yield and / or purity of the product will decrease significantly.
[0035] The combined results of the above embodiments and comparative patents further confirm that this invention successfully overcomes the industry's technical bias that the synthesis of malononitrile from dimethyl malonate requires high temperature, high pressure, and special catalysts. Through a unique two-step process design, this invention, under extremely mild atmospheric pressure and medium-low temperature conditions, not only achieves a direct replacement of highly toxic cyanide at its source, thus achieving the goal of green and clean production, but also achieves product yield and purity levels comparable to or even better than existing high-temperature, high-pressure technologies (purity ≥ 99.5%, total yield ≥ 75%). This unexpected technical effect fully demonstrates that this invention possesses significant inventive progress and extremely high industrial application prospects compared to the closest prior art (such as CN118619847A).
[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing malononitrile, characterized in that: Includes the following steps: A) Preparation of malondiamide: Dimethyl malonate and ammonia water are mixed and stirred at room temperature and pressure, and the stirring time is controlled. After the stirring reaction is completed, malondiamide solid is obtained through post-processing. B) Synthesis of malononitrile: The malonamide obtained in step A) is dissolved in an organic solvent, a dehydrating agent is added, and the reaction is stirred under normal pressure. The stirring time and temperature are controlled. After the reaction is completed, the organic solvent is recovered by distillation to obtain crude malononitrile. C) Refining: The crude malononitrile obtained in step B) is distilled, and the fraction is collected to obtain high-purity malononitrile with a gas chromatographic purity of over 99.5%.
2. The method for preparing malononitrile according to claim 1, characterized in that: The ammonia concentration in step A) is 20-30%; the molar ratio of dimethyl malonate to ammonia is 1:2-6.
3. The method for preparing malononitrile according to claim 2, characterized in that: The molar ratio of dimethyl malonate to ammonia is 1:3-5.
4. The method for preparing malononitrile according to claim 1, characterized in that: The control of the stirring reaction time mentioned in step A) is to control the stirring reaction time to 120-360 min.
5. The method for preparing malononitrile according to claim 1, characterized in that: The post-processing described in step A) includes: after the reaction is complete, removing excess ammonia under reduced pressure, followed by sequential cooling, crystallization, filtration, and drying.
6. The method for preparing malononitrile according to claim 1, characterized in that: In step B), the organic solvent is one or more of dichloroethane, dichloromethane, and chloroform.
7. The method for preparing malononitrile according to claim 1, characterized in that: The dehydrating agent mentioned in step B) is phosgene or solid phosgene, and the molar ratio of malondiamide to the dehydrating agent is 1:1-1.
5.
8. The method for preparing malononitrile according to claim 7, characterized in that: The molar ratio of malondiamide to dehydrating agent is 1:1.1-1.
3.
9. The method for preparing malononitrile according to claim 1, characterized in that: The control of the subsequent reaction time mentioned in step B) is to control the subsequent reaction time to 240-600 min and the temperature to 60-90℃.
10. The method for preparing malononitrile according to claim 1, characterized in that: The distillation described in step C) is vacuum distillation, and the distillation conditions are: vacuum degree -0.09 to -0.1 MPa, and the fraction collected at 105-115℃.