A method for preparing cis-1,2-dibromoethylene based on steric hindrance effect

Abstract

This invention discloses a method for preparing cis-1,2-dibromoethylene based on steric hindrance, belonging to the field of technical organic synthesis. The method includes the following steps: (a) providing reactors A and B connected in series. Bromine is added to reactor A, and a solvent and configuration-selective catalyst are added to reactor B. This invention employs a series reactor system. Under the synergistic effect of a copper / crown ether composite catalyst and ultraviolet light, a highly selective addition reaction of acetylene with bromine is achieved by controlling the solvent system, reaction temperature, and material ratio. Using acetonitrile or perfluoroalkane as solvent, and copper chloride and crown ethers (such as 15-crown-5) as catalysts, the reaction is carried out at 30-80℃ under 200-400nm ultraviolet light. The selectivity of cis-1,2-dibromoethylene is ≥95%, which has advantages such as mild reaction conditions, solvent recyclability, and suitability for industrial production. Furthermore, the cis selectivity is improved to ≥95%; the content of the byproduct tetrabromoethane is <0.5%; and the solvent recovery rate is >98%.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and in particular relates to a method for preparing cis-1,2-dibromoethylene based on steric hindrance effect. Background Technology

[0002] cis-1,2-dibromoethylene is a bromine-containing organic compound with excellent solubility and thermal stability, and can be used as a flame retardant additive, polymer crosslinking agent, and stereochemical synthesis intermediate. Developing an efficient synthesis process for cis-1,2-dibromoethylene has significant industrial and economic value.

[0003] The synthesis method for 1,2-dibromoethylene is the direct acetylene synthesis method. This method involves the direct reaction of acetylene (C2H2) with bromine at a certain temperature to obtain a mixture of cis-1,2-dibromoethylene and trans-1,2-dibromoethylene. 1,2-Dibromoethylene is an important flame retardant and pharmaceutical intermediate. Its cis configuration (CAS 590-12-5) exhibits unique reactivity due to steric hindrance. Traditional synthesis methods have the following drawbacks: Direct bromination: Acetylene reacts directly with bromine to produce a cis / trans mixture (ratio approximately 1:2), requiring complex separation; Electrolysis: High energy consumption, products contain brominated byproducts; Metal-catalyzed methods: prone to over-bromination to produce tetrabromoethane; Therefore, existing synthetic methods produce many byproducts and have uncontrollable configurations, which greatly limits the preparation of 1,2-dibromoethylene. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing cis-1,2-dibromoethylene based on steric hindrance. This method employs a series reactor system, utilizing a copper / crown ether composite catalyst and ultraviolet light. By controlling the solvent system, reaction temperature, and material ratio, a highly selective addition reaction of acetylene and bromine is achieved. Acetonitrile or perfluoroalkanes are used as solvents, and copper chloride and crown ethers (such as 15-crown-5) are used as catalysts. The reaction is carried out at 30-80℃ under 200-400nm ultraviolet light, achieving a selectivity of ≥95% for cis-1,2-dibromoethylene. This method solves the technical problems of numerous byproducts and uncontrollable configuration in traditional processes, and offers advantages such as mild reaction conditions, recyclable solvents, and suitability for industrial production.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing cis-1,2-dibromoethylene based on steric hindrance effect, comprising the following steps: (a) Provide reactor A and reactor B connected in series, wherein bromine is added to reactor A and solvent and configuration-selective catalyst are added to reactor B; (b) Bromine flows into reactor B through the bottom pipe, while acetylene gas is introduced into reactor B at the same time; (c) Control the temperature of reactor B and turn on ultraviolet light to initiate the addition reaction of bromine and acetylene to generate cis-1,2-dibromoethylene; (d) Collect the reaction solution, remove the solvent and recover the catalyst to obtain cis-1,2-dibromoethylene.

[0006] Preferably, the solvent is acetonitrile, perfluorooctane, perfluoropentane, or perfluorohexane, and the mass ratio of the solvent to bromine is 2-8:1.

[0007] Preferably, the configuration-selective catalyst is a combination of copper chloride / basic copper carbonate and crown ether, wherein the crown ether is selected from 15-crown-5, 18-crown-6 or 12-crown-4.

[0008] Preferably, the mass ratio of the copper catalyst to the crown ether is 1:1.5-3, and the total amount of catalyst added is 0.1%-1% of the bromine mass.

[0009] Preferably, the ultraviolet light wavelength is 200-400 nm.

[0010] Preferably, the reaction temperature is 30-80℃.

[0011] Preferably, the molar ratio of bromine to acetylene is 1:1-1.2.

[0012] Preferably, both reactor A and reactor B are equipped with stirring devices, and reactor B is equipped with a jacketed heating system and an ultraviolet light source.

[0013] Preferably, the acetylene gas has a purity of ≥99.5% and an introduction rate of 100-300 mL / min.

[0014] Preferably, the product separation is performed by rotary evaporation to remove solvent, vacuum filtration and GC analysis, with a selectivity of ≥95% for cis-1,2-dibromoethylene.

[0015] The beneficial effects of this invention are: This invention employs a series reactor system. Under the synergistic effect of a copper / crown ether composite catalyst and ultraviolet light, and by controlling the solvent system, reaction temperature, and material ratio, a highly selective addition reaction of acetylene and bromine is achieved. Acetonitrile or perfluoroalkanes are used as solvents, and copper chloride and crown ethers (such as 15-crown-5) are used as catalysts. The reaction is carried out at 30-80℃ under 200-400nm ultraviolet light. The selectivity of cis-1,2-dibromoethylene is ≥95%. It has the advantages of mild reaction conditions, solvent recyclability, and suitability for industrial production. Furthermore, the cis selectivity is improved to ≥95%. The content of the byproduct tetrabromoethane is <0.5%, and the solvent recovery rate is >98%. Attached Figure Description

[0016] The advantages of the present invention, both above and / or other aspects, will become clearer and more readily understood through the following detailed description taken in conjunction with the accompanying drawings, which are merely illustrative and do not limit the invention, wherein: Figure 1 This is a schematic diagram of the process flow of the reaction system of the present invention; Figure 2 This is a chromatogram of the product sample analyzed according to the present invention.

[0017] In the diagram: a, bromide feed pump; b, high-pressure acetylene storage bottle; c, reactor A; d, reactor B; e, absorption unit. Detailed Implementation

[0018] In the following text, reference will be made to the appendix. Figure 1-2 This invention describes an embodiment of a method for preparing cis-1,2-dibromoethylene based on steric hindrance.

[0019] The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the invention, and are illustrative and exemplary, and should not be construed as limiting the implementation or scope of the invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0020] The accompanying drawings in this specification are schematic diagrams to aid in illustrating the concept of the invention, and schematically show the shapes of the various parts and their interrelationships. Please note that, in order to clearly demonstrate the structure of the components in the embodiments of the invention, the drawings are not drawn to the same scale. The same reference numerals are used to indicate the same parts.

[0021] Example: A method for preparing cis-1,2-dibromoethylene based on steric hindrance includes the following steps: (a) Provide reactors A and B connected in series. 200 mL of bromine is added to reactor A, and 400 mL of solvent and configuration-selective catalyst is added to reactor B. The copper chloride / crown ether (e.g., 18-crown-6) composite system locks the cis configuration of the acetylene anion through the macrocyclic steric hindrance effect of the crown ether. Specifically, 400 mL of degassed acetonitrile + 2 g of catalyst (CuCl2:18-crown-6=1:2) is added to reactor B. The dual-reactor series design (reactor A stores bromine, reactor B reacts) avoids local overheating. Reactor B is equipped with a jacketed oil bath heating and an internal ultraviolet irradiation light source. (b) Bromine flows into reactor B through the bottom pipe, while acetylene gas is introduced into reactor B at 200 mL / min with 99.5% acetylene, and then heated in an oil bath at 60°C. (c) Control the temperature of reactor B and turn on the 365nm ultraviolet lamp to irradiate ultraviolet light. React for 4 hours to initiate the addition reaction of bromine and acetylene to generate cis-1,2-dibromoethylene. Ultraviolet light induces homolytic cleavage of bromine and precisely controls the free radical addition path. (d) Collect the reaction solution, remove the solvent and recover the catalyst to obtain cis-1,2-dibromoethylene.

[0022] The mass ratio of the solvent to bromine is 2-8:1, and the temperature is 30-80℃ (preferably 60℃).

[0023] The configuration-selective catalyst is a combination of copper chloride / basic copper carbonate and crown ether, wherein the crown ether is selected from 15-crown-5, 18-crown-6 or 12-crown-4.

[0024] The mass ratio of copper catalyst to crown ether is 1:1.5-3, and the total amount of catalyst added is 0.1%-1% of the bromine mass.

[0025] The ultraviolet light wavelength is 200-400 nm.

[0026] The reaction temperature is 30-80℃.

[0027] The molar ratio of bromine to acetylene is 1:1-1.2.

[0028] Both reactor A and reactor B are equipped with stirring devices. Reactor B is equipped with a jacketed heating system and an ultraviolet light source.

[0029] Acetylene gas purity ≥ 99.5%, introduction rate 100-300 mL / min, Br2:C2H2 molar ratio 1:1-1.2.

[0030] The product was separated by rotary evaporation to recover acetonitrile, filtration to obtain mother liquor, and GC analysis: yield 93.5%, cis selectivity 95.2%, and cis-1,2-dibromoethylene selectivity ≥95%.

[0031] It should be noted that this invention breaks through the bottleneck of configuration control by designing a composite catalyst (copper / crown ether) and a UV photoinitiation system. Compared with the traditional catalyst-free preparation method with a cis product yield of only 33%, the technical solution of this invention improves the cis selectivity to ≥95%; the content of the by-product tetrabromoethane is <0.5%; and the solvent recoverability is >98%.

[0032] The results of changing the solvent (perfluorooctane, etc.), catalyst ratio (1:1.5-3), and temperature (30-80℃) are shown in Table 1. Example 1: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed acetonitrile into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / acetonitrile reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the acetonitrile phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 93%, and the selectivity is 95%.

[0033] Example 2: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed acetonitrile into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / acetonitrile reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the acetonitrile phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 50°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 93.2%, and the selectivity is 95.1%.

[0034] Example 3: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed acetonitrile into the system from the feed port of the second reactor B, add 1.5 g of composite catalyst, control the liquid level of the system, and construct a bromine / acetonitrile reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the acetonitrile phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 93.3%, and the selectivity is 95.8%.

[0035] Example 4: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 500 ml of pre-degassed acetonitrile into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / acetonitrile reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the acetonitrile phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 93.2%, and the selectivity is 95.1%.

[0036] Example 5: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed perfluorooctane into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / perfluorooctane reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the perfluorooctane phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 92%, and the selectivity is 94%.

[0037] Example 6: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed perfluorohexane into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / perfluorohexane reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the perfluorohexane phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 91%, and the selectivity is 92%.

[0038] Example 7: (1) Start the bromine feed pump, inject 200 ml of bromine into the system from the feed port of the first reactor A, inject 400 ml of pre-degassed perfluoron-pentane into the system from the feed port of the second reactor B, add 2 g of composite catalyst, control the liquid level of the system, and construct a bromine / perfluoron-pentane reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the perfluoron-pentane phase; (3) Start the jacket heating system of the second reactor B to maintain the reaction system at the set temperature of 60°C; simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B, sample and analyze the product composition by gas chromatography, the yield of cis-1,2-dibromoethylene is 93%, and the selectivity is 95%.

[0039] Comparative example without catalysis: (1) Start the bromine feed pump and inject 200 ml of bromine into the system from the feed port of the first reactor A and 400 ml of pre-degassed acetonitrile into the system from the feed port of the second reactor B. Control the liquid level of the system and construct a bromine / acetonitrile reaction system in reactor B; (2) Under stirring, continuously pass high-purity acetylene gas (purity ≥99.5%) into the second reactor B at a flow rate of 100-300 ml / min to ensure that acetylene is uniformly dispersed and dissolved in the acetonitrile phase; (3) Start the jacket heating system of the second reactor B and maintain the reaction system at the set temperature of 60°C; Simultaneously turn on the ultraviolet light source device configured in reactor B and adjust the wavelength of the ultraviolet device to 400 nm; (4) Connect the collection unit to the outlet of the second reactor B and sample the product composition by gas chromatography. The yield of cis-1,2-dibromoethylene is 33% and the yield of trans-1,2-dibromoethylene is 64%.

[0040] In summary, this method for preparing cis-1,2-dibromoethylene based on steric hindrance utilizes a series reactor system. Under the synergistic effect of a copper / crown ether composite catalyst and ultraviolet light, and by controlling the solvent system, reaction temperature, and material ratios, a highly selective addition reaction of acetylene and bromine is achieved. Using acetonitrile or perfluoroalkanes as solvents, and copper chloride and crown ethers (such as 15-crown-5) as catalysts, the reaction is carried out at 30-80℃ under 200-400nm ultraviolet light. The selectivity for cis-1,2-dibromoethylene is ≥95%, offering advantages such as mild reaction conditions, solvent recyclability, suitability for industrial production, and improved cis selectivity to ≥95%. The content of the byproduct tetrabromoethane is <0.5%, and the solvent recovery rate is >98%.

[0041] The technical features disclosed above are not limited to the combinations of the disclosed features with other features. Those skilled in the art can also make other combinations of the technical features according to the purpose of the invention to achieve the purpose of the invention.

Claims

1. A method for preparing cis-1,2-dibromoethylene based on steric hindrance, characterized in that, Includes the following steps: (a) Provide reactor A and reactor B connected in series, wherein bromine is added to reactor A and solvent and configuration-selective catalyst are added to reactor B; (b) Bromine flows into reactor B through the bottom pipe, while acetylene gas is introduced into reactor B at the same time; (c) Control the temperature of reactor B and turn on ultraviolet light to initiate the addition reaction of bromine and acetylene to generate cis-1,2-dibromoethylene; (d) Collect the reaction solution, remove the solvent and recover the catalyst to obtain cis-1,2-dibromoethylene.

2. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, The solvent is acetonitrile, perfluorooctane, perfluoropentane, or perfluorohexane, and the mass ratio of the solvent to bromine is 2-8:

1.

3. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, The configuration-selective catalyst is a combination of copper chloride / basic copper carbonate and crown ether, wherein the crown ether is selected from 15-crown-5, 18-crown-6 or 12-crown-4.

4. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 3, characterized in that, The mass ratio of copper catalyst to crown ether is 1:1.5-3, and the total amount of catalyst added is 0.1%-1% of the bromine mass.

5. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, The ultraviolet light wavelength is 200-400 nm.

6. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, The reaction temperature is 30-80℃.

7. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, The molar ratio of bromine to acetylene is 1:1-1.

2.

8. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, Both reactor A and reactor B are equipped with stirring devices. Reactor B is equipped with a jacketed heating system and an ultraviolet light source.

9. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, Acetylene gas purity ≥ 99.5%, and introduction rate 100-300 mL / min.

10. The method for preparing cis-1,2-dibromoethylene based on steric hindrance effect according to claim 1, characterized in that, Product separation was achieved by rotary evaporation for solvent removal, vacuum filtration, and GC analysis, with a selectivity of ≥95% for cis-1,2-dibromoethylene.

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