A method for preparing fluorine-containing enol

Abstract

The present invention provides a method for preparing fluorine-containing olefin ether, and belongs to the technical field of organic fluorine chemical synthesis. The method comprises subjecting fluorine-containing alkanes to a dehalogenation reaction under the conditions of a metal dehalogenating agent, a nitrogen-containing aprotic polar solvent, and a fluorine-containing cosolvent, to prepare fluorine-containing olefin ether; wherein, on the basis of using aprotic polar solvents as solvents for the dehalogenation reaction of fluorine-containing alkanes, a fluorine-containing cosolvent is added to the reaction system to reduce the viscosity of the reaction system, and no complex salt is generated, which is convenient for subsequent distillation or rectification separation and recovery of the fluorine-containing cosolvent. Under the conditions of keeping the reaction process stable and maintaining a high yield, the amount of aprotic polar solvent is reduced, and the fluorine-containing cosolvent can be recycled and reused, thereby reducing the cost and the generation of three wastes.

Description

Technical Field

[0001] The invention relates to a method for preparing fluorine-containing olefin ether, in particular to a method for preparing fluorine-containing olefin ether by dechlorination reaction of fluorine-containing alkane, belonging to the technical field of organic fluorine chemical synthesis. Background Art

[0002] Fluorinated olefin ethers are a class of chemical intermediates with important industrial significance and are important monomers for the synthesis of high-performance fluororubbers, fluororesins, etc. At present, the preparation methods of fluorinated olefin ethers mainly include: 1. Preparation of acyl fluoride precursors by high-temperature salt cracking or solvent cracking. This preparation method usually produces a certain amount of hydrogen-containing ether by-products, which have a boiling point close to that of fluorinated olefin ethers, that is, the separation and purification of the products is more difficult; 2. Preparation by reacting fluorohaloalkane precursors with metal dehalogenating agents in organic solvents. The solvent used in the reaction is usually a non-protonic polar solvent.

[0003] Generally speaking, simple fluorinated olefins (such as trifluorochloroethylene, difluorodichloroethylene, etc.) can use alcohols (such as methanol, ethanol, isopropanol, etc.) as solvents. For example, in patent document CN105801335A, ethanol is used as solvent to prepare difluorodichloroethylene by dechlorination. However, the disadvantages of alcohol solvents include: low flash point, flammability and explosion, safety hazards in industrial production, and weaker dehalogenation reaction activity than aprotic polar solvent system, extremely low yield and generation of hydrogen-containing ether by-products. Therefore, aprotic polar solvents are often used in fluorinated olefin ether synthesis reactions. Commonly used aprotic polar solvents include: amides (such as: DMF, DMAc), nitriles (such as: acetonitrile, propionitrile), N-methyl-2-pyrrolidone, tetrahydrofuran, dimethyl sulfoxide, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, among which perfluoromethyl vinyl ether, perfluorosulfonyl fluoride vinyl ether, perfluoronitrile vinyl ether, etc. mostly use aprotic polar solvents. For example, in patent document US6388139B1, N-methyl-2-pyrrolidone or DMF is used as a solvent to prepare perfluorosulfonyl fluoride vinyl ether by dechlorination; in patent document CN1775722A, DMF is used as a solvent to prepare perfluoromethyl vinyl ether by dechlorination.

[0004] In addition, patent document CN1299711 discloses "a method for recovering alcohol solvents after dechlorination reaction by filtering and then distilling", but when the solvent system is changed to a non-protonic polar solvent, the zinc halide generated by dehalogenation will form a stable complex (1:2) with the non-protonic polar solvent, for example: DMF and ZnCl2 form a stable complex ZnCl2·2DMF (Synthesis, characterization, and thermochemistry of adducts of zinc, cadmium and mercury halides with N, N-dimethylformamide. Chem. 1983, 22, 136-140), and the solvent cannot be completely recovered by distillation.

[0005] In the existing preparation process of fluorinated olefin ether, the dehalogenation kettle residue contains complexes, unreacted metal dehalogenating agent and excess solvent, which is very difficult to recover. If only the solvent is recovered, the remaining metal dehalogenating agent in the kettle residue loses the isolation of the solvent and will come into contact with the air, which may cause the risk of oxidation and spontaneous combustion, and the required storage conditions are very harsh; if the reactor residue is comprehensively recycled, a series of post-processing steps are required, which requires high equipment and labor investment and huge energy consumption (Organic Fluorine Industry, 2019 (01), Research on Comprehensive Utilization of Dechlorination Kettle Residue of Perfluoromethyl Vinyl Ether).

[0006] In summary, it is necessary to seek a new solvent system that can adapt to the dehalogenation requirements of a wide range of raw materials, while maintaining a stable reaction process and a high yield, and at the same time, can achieve easy recovery and reuse of part of the solvent. Summary of the invention

[0007] The present invention aims at the deficiencies of the prior art and provides a method for preparing fluorinated olefin ethers. In the technical scheme, on the basis of using a non-protonic polar solvent as the solvent for the dehalogenation reaction of fluorinated alkanes, a fluorinated co-solvent is added to the reaction system to reduce the viscosity of the reaction system, and no complex salt is generated, which is convenient for subsequent distillation or rectification separation and recovery of hydrofluoroether solvents. Under the condition of keeping the reaction process stable and maintaining a high yield, the amount of non-protonic polar solvent is reduced, and the fluorinated amine solvent can be recycled and reused, which reduces the cost and reduces the generation of three wastes.

[0008] In order to achieve the above technical objectives, the following technical solutions are proposed:

[0009] A method for preparing fluorine-containing olefin ethers comprises subjecting fluorine-containing alkanes to a dehalogenation reaction under the conditions of a metal dehalogenating agent, a nitrogen-containing aprotic polar solvent and a fluorine-containing cosolvent to prepare fluorine-containing olefin ethers;

[0010] Wherein, the fluorinated alkane is represented by the following structural formula (I):

[0011] CF2X1-CFX2-OR f 1 -(O) y -R f 2 X3

[0012] (I)

[0013] In formula (I), X1 is Cl, Br or I, X2 is Cl, Br or I, X3 is F, Br, I, SO2F, CN or COOR, R f 1 is a straight-chain or branched perfluoroalkyl group having 1 to 5 carbon atoms, R f 2 is a linear or branched perfluoroalkyl group having 0 to 3 carbon atoms, R is a linear or branched alkyl group having 1 to 3 carbon atoms, and y = 0 or 1;

[0014] Wherein, the fluorine-containing olefin ether is represented by the following structural formula (II);

[0015] CF2=CF-OR f 1 -(O) y -R f 2 X3

[0016] (Ⅱ)

[0017] In formula (II), R f 1 is a straight-chain or branched perfluoroalkyl group having 1 to 5 carbon atoms, R f 2 It is a straight chain or branched perfluoroalkyl group having 0-3 carbon atoms, X3 is F, Br, I, SO2F, CN or COOR, R is a straight chain or branched alkyl group having 1-3 carbon atoms, and y=0 or 1.

[0018] Furthermore, the fluorine-containing alkane includes CF2ClCFClOCF3, CF2ClCFClOCF2CF3, CF2ClCFClOCF2OCF3, CF2ClCFClOCF2CF2SO2F, CF2ClCFClOCF2CF2Br, CF2BrCFBrOCF2CF(CF3)OCF2CF2SO2F, CF2BrCFBrOCF2CF2CF2COOCH3 or CF2BrCFBrOCF2CF2CF2CF2CN.

[0019] Furthermore, the fluorine-containing ether includes CF2=CFOCF3, CF2=CFOCF2CF3, CF2=CFOCF2OCF3, CF2=CFOCF2CF2SO2F, CF2=CFOCF2CF2Br, CF2=CFOCF2CF(CF3)OCF2CF2SO2F, CF2=CFOCF2CF2CF2COOCH3 or CF2=CFOCF2CF2CF2CF2CN.

[0020] Furthermore, the metal dehalogenating agent refers to a metal element that removes halogen atoms from adjacent carbon atoms in a reducing manner when reacting with a fluorinated alkane and forms a double bond between two adjacent carbon atoms. Preferably, the metal dehalogenating agent is one or a combination of any two or more of magnesium, aluminum, copper and zinc. More preferably, the metal dehalogenating agent is zinc or a combination of zinc and other metals.

[0021] Furthermore, the average particle size of the metal dehalogenating agent is 40-150 μm, and activation treatment is not required, so it is easy to use in the preparation process of fluorine-containing olefin ether.

[0022] Further, the molar amount of the metal dehalogenating agent is 1-3 times the molar amount of the fluorinated alkane. Preferably, the molar amount of the metal dehalogenating agent is 1.2-1.8 times the molar amount of the fluorinated alkane.

[0023] Further, the nitrogen-containing aprotic polar solvent is one or a combination of any two or more of triethylamine, tetramethylethylenediamine, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N,N-diisopropylformamide, N-methylpyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI) and N,N-dimethylpropyleneurea (DMPU). Preferably, the nitrogen-containing aprotic polar solvent is one or a combination of any two or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0024] Further, the molar amount of the nitrogen-containing aprotic polar solvent is 1-6 times the molar amount of the fluorinated alkane. Preferably, the molar amount of the nitrogen-containing aprotic polar solvent is 1.5-3 times the molar amount of the fluorinated alkane.

[0025] Furthermore, the mass ratio between the nitrogen-containing aprotic polar solvent and the fluorine-containing co-solvent is 0.1-1.

[0026] Furthermore, the fluorinated cosolvent is a hydrofluoroether solvent, which is represented by the following structural formula (III):

[0027] R f 3 OR f4

[0028] (III)

[0029] In formula (III), R f 3 is a linear or branched polyfluoroalkyl or polyfluoroalkoxy group having 1 to 6 carbon atoms, R f 4 is a linear or branched polyfluoroalkyl or polyfluoroalkoxy group having 1 to 6 carbon atoms, and R f 3 and R f 4 They are not perfluoroalkyl or perfluoroalkoxy at the same time.

[0030] Furthermore, the hydrofluoroether solvent is ethyl tetrafluoroethyl ether (EtO(CF2)2H), propyl tetrafluoroethyl ether (PrO(CF2)2H), isopropyl tetrafluoroethyl ether (iPrO(CF2)2H), butyl tetrafluoroethyl ether (BuO(CF2)2H), methyl hexafluoroisopropyl ether (MeOCH(CF3)2), ethyl hexafluoropropyl ether (EtOCF2CFHCF3), propyl hexafluoropropyl ether (PrOCF2CFHCF3), isopropyl hexafluoropropyl ether (iPrOCF2CFHCF3), butyl hexafluoropropyl ether (BuOC F2CFHCF3), methyl heptafluoroisopropyl ether (MeOCF(CF3)2), ethyl heptafluoroisopropyl ether (EtOCF(CF3)2), methyl heptafluoro-n-propyl ether (MeO(CF2)2CF3), ethyl heptafluoro-n-propyl ether (EtO(CF2)2CF3), methyl nonafluoroisobutyl ether (MeOCF2CF(CF3)2), methyl nonafluorobutyl ether (MeO(CF2)3CF3), ethyl nonafluorobutyl ether (EtO(CF2)3CF3), trifluoroethyl tetrafluoroethyl ether (CF3CH2O(CF2)2H), tetrafluoro Propyl tetrafluoroethyl ether (CF2HCF2CH2O(CF2)2H), octafluoropentyl tetrafluoroethyl ether (CF2H(CF2)3CH2O(CF2)2H), trifluoroethyl hexafluoropropyl ether (CF3CH2OCF2CFHCF3), tetrafluoropropyl hexafluoropropyl ether (CF2HCF2CH2OCF2CFHCF3), octafluoropentyl hexafluoropropyl ether (CF2H(CF2)3CH2OCF2CFHCF3), 1-methoxy-2-(1,1,2,2-tetrafluoroethoxy)ethane (H(CF2)2OCH2C H2OCH3), 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane (H(CF2)2OCH2CH(CH3)2), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (H(CF2)2O(CH2)2O(CF2)2H), 1,3-bis(1,1,2,2-tetrafluoroethoxy)propane (H(CF2)2O(CH2)3O(CF2)2H), cyclohexyl tetrafluoroethyl ether (CyO(CF2)2H) or cyclohexyl hexafluoropropyl ether (CyOCF2CFHCF3). The boiling point of the hydrofluoroether solvent is 30-200°C, and they are all fluorine-containing inert liquids with low viscosity and high molecular stability. They are often used in industry as heat-conducting coolants, dielectric fluids, precision instrument cleaning fluids, etc. The hydrofluoroether solvent is used as an excellent reaction solvent and co-solvent in the technical solution. It can not only dissolve fluorinated alkanes, but also improve the dispersibility of metal dechlorinating agents, reduce the viscosity of the reaction system, and will not form complex salts with metal halides. In practical applications, hydrofluoroethers with a slightly lower boiling point than nitrogen-containing aprotic polar solvents can be selected as co-solvents, which are convenient for subsequent recovery by conventional distillation or rectification separation methods, thereby reducing the amount of organic solvents used.

[0031] Furthermore, the fluorine-containing cosolvent is a fluorine-containing amine cosolvent, which is represented by the following structural formula (IV):

[0032] R f 5 R f 6 NR f 7

[0033] (IV)

[0034] In formula (IV), R f 5 , R f 6 and R f 7 It is a linear or branched perfluoroalkyl or perfluoroalkoxy group having 1 to 5 carbon atoms, and may be the same or different.

[0035] Further, the fluorine-containing amine cosolvent is perfluoromethylmorpholine, perfluorotriethylamine, perfluoromethylethylpropylamine, perfluorotripropylamine, perfluorodiethylpropylamine, perfluorodibutylmethylamine, perfluorotributylamine, perfluorodibutylethylamine or perfluorotripentylamine, etc. Wherein, the fluorine-containing amine cosolvent is a fluorine-containing inert liquid, has high molecular stability, is non-toxic, non-flammable, and is commonly used as electrical insulating oil, heat-conducting coolant, dielectric fluid, precision instrument cleaning fluid, etc. in industry. The fluorine-containing amine cosolvent can dissolve the fluorine-containing alkane of the dehalogenation raw material. It is used as an excellent reaction solvent and cosolvent in the present technical solution, which can not only dissolve the fluorine-containing alkane, but also improve the dispersibility of the metal dechlorination agent, reduce the viscosity of the reaction system, and will not generate complex salts with metal halides. In practical applications, fluorine-containing amines with a boiling point slightly lower than that of nitrogen-containing aprotic polar solvents can be selected as cosolvents, and it is convenient to use conventional distillation or rectification separation to recover the fluorine-containing amine solvents, and reduce the amount of organic solvents used. Preferably, the fluorine-containing amine co-solvent is perfluorotriethylamine, perfluorotripropylamine or perfluorotributylamine which are widely used in industry.

[0036] Furthermore, the fluorine-containing cosolvent is a fluorine-containing alcohol cosolvent, which is represented by the following general structural formula (V):

[0037] X4R f 8 CH2OH

[0038] (V)

[0039] In formula (V), X4 is H or F, R f 8 It is a linear or branched perfluoroalkyl or perfluoroalkoxy group having 1 to 10 carbon atoms.

[0040] Furthermore, the fluorine-containing alcohol cosolvent is trifluoroethanol, tetrafluoropropanol, pentafluoropropanol, 1,1,1,3,3,3-hexafluoro-2-isopropanol, heptafluorobutanol, 1H,1H,5H-octafluoro-1-pentanol, nonafluoro-1-pentanol, undecafluoro-1-hexanol, 1H,1H,7H-dodecafluoro-1-heptanol, tridecafluoro-1-heptanol, pentafluoro-1-octanol, 1H,1H,9H-hexadecanoyl-1-nonanol, 2-perfluoropropoxy-2,3,3,3-tetrafluoropropanol or 1H,1H-2,5-bis(trifluoromethyl)-3,6-dioxoperfluorononanol. Wherein, the fluorine-containing alcohol cosolvent introduces a large number of strongly electronegative fluorine atoms, and compared with ordinary hydrocarbon alcohols, the alcohol hydroxyl group of the fluorine-containing alcohol is relatively inert, therefore, the fluorine-containing alcohol has a higher molecular stability, and it can dissolve the fluorine-containing alkane of the dehalogenation raw material, and is an excellent reaction solvent and cosolvent. In the present technical scheme, the fluorine-containing alcohol cosolvent solvent can dissolve the fluorine-containing alkane, improve the dispersibility of the metal dechlorination agent, reduce the viscosity of the reaction system, and will not generate complex salts with metal halides. In practical applications, fluorine-containing alcohols with a slightly lower boiling point than nitrogen-containing non-protonic polar solvents can be selected as cosolvents, and it is convenient to use conventional distillation or rectification separation to recover the fluorine-containing alcohol solvents, and reduce the amount of organic solvents used. Preferably, the fluorine-containing alcohol cosolvent is a cleaning agent widely used in industry such as tetrafluoropropanol or 1H, 1H, 5H-octafluoro-1-pentanol, because its price is relatively cheap.

[0041] Furthermore, in the preparation method of the fluorine-containing enol ether, the reaction temperature is 20-180° C.; preferably, the reaction temperature is 50-120° C. Generally, a higher reaction temperature can accelerate the reaction rate, but considering the boiling points of the reaction raw materials, solvent system and product, the reaction temperature is ultimately limited to 20-180° C.

[0042] In addition, in the preparation method of the fluorinated olefin ether, the reaction time is related to the reaction temperature, the type of fluorinated alkane, the type of solvent, the type of metal dechlorinating agent and the particle size. After comprehensive consideration, the reaction time is controlled within 8 hours, thereby ensuring the reaction efficiency while avoiding the formation of excessive by-products.

[0043] The beneficial technical effects brought about by adopting this technical solution are:

[0044] 1) The present invention adopts a specific fluorine-containing cosolvent (such as: hydrofluoroether solvents, fluorine-containing amine cosolvents, fluorine-containing alcohol cosolvents), and adds a fluorine-containing cosolvent to a nitrogen-containing aprotic polar solvent, which can dissolve fluorine-containing alkanes, improve the dispersibility of metal dechlorination agents, and reduce the viscosity of the reaction system. Under the conditions of maintaining a stable reaction process and maintaining a high yield, the amount of aprotic polar solvent can be reduced, and the content of by-product hydrogen ether can be reduced to less than 0.5%;

[0045] 2) In the present invention, the fluorine-containing co-solvent will not form a complex salt with the metal halide, and after the reaction is completed, it can be separated and recovered by conventional methods such as distillation or rectification, and can be reused after recovery, thereby reducing the residue in the reactor, and has the dual value of economy and environmental protection;

[0046] 3) In the present invention, a metal dehalogenating agent with an average particle size of 40-150 μm is used, and activation treatment is not required, which can ensure that the dehalogenation reaction maintains a certain reaction speed from beginning to end, taking into account the reaction yield and efficiency, and at the same time can avoid the metal dehalogenating agent from agglomerating to block the reactor or affect the normal operation of stirring. DETAILED DESCRIPTION

[0047] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example 1

[0049] In a 1-liter four-necked flask equipped with mechanical stirring, constant pressure dropping funnel, reflux condensing tube and thermometer catheter, 200g ethyl tetrafluoro ether, 110g DMAC, 55g zinc powder (325 mesh, average particle size of about 50 microns) are added, and 200g of CF2ClCFClOCF3 with a content of 91.4% is added in advance in the constant pressure dropping funnel. Start stirring, after the water bath is warmed to 50°C, the reflux condensing tube is passed through -20°C refrigerant, and CF2ClCFClOCF3 is gradually dripped at a certain flow rate, and the generated product is connected to the collection cold trap of dry ice alcohol cooling by the air guide tube for collection. After the reaction is started, heat release is obvious, and a certain feeding rate is maintained to maintain an internal temperature of 50-60°C. After the dropwise addition is completed, the water bath temperature is raised to 70°C and continued to stir for 30min, and the total reaction time is 5.5h. After the reaction is completed, the cold trap collects 127.5g of product.

[0050] GC analysis: The main product is CF2=CFOCF3, with a content of 94.2%, CHF2CF2OCF3 content of 0.13%, and a reaction yield of 97.3%. Its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376MHz,CDCl3)δ(ppm):-62.7(s,3F,CF3-O-),-118.4(m,F,OC=CF),-125.9(m,F,OC=CF),-140.7(m,F,O-CF=C); GC-MS m / z:69(CF3 + ),78(C2F2O + ),81(C2F3 +),97(C2F3O + ),119(C2F5 + ),147(C3F5O + ),166M + , further proving that the product is perfluoromethyl vinyl ether.

[0051] Recovery of fluorinated co-solvent: After the reaction was completed, the temperature was lowered to 50°C and the reaction residue was treated with a water jet vacuum pump. The extract was collected with an ice water cold trap to obtain a total of 193 g of collected material. Among them, the content of ethyl tetrafluoroethyl ether was 98.2%, and the recovery rate of ethyl tetrafluoroethyl ether was 94.8%. There were 223 g of residues that needed to be treated as hazardous waste.

[0052] Comparative Example 1

[0053] Based on Example 1, a control example of Example 1 is designed to further illustrate the technical solution.

[0054] The details include:

[0055] 310 g of DMAC was used to replace 110.0 g of DMAC in Example 1, and ethyl tetrafluoroethyl ether was not added. The rest was the same as in Example 1.

[0056] After the reaction, 124.5 g of product was collected. GC analysis showed that the CF2=CFOCF3 content was 92.7%, the CHF2CF2OCF3 content was 1.3%, and the reaction yield was 90.1%.

[0057] After the reaction, the reaction residue was treated with a water jet vacuum pump at 70°C for 1 hour, and then the temperature was raised to 120°C and replaced with an oil pump for 1 hour. The extract was collected with an ice-water cold trap, and a total of 113 g of the collected product was obtained, of which the DMAC content was 95.6% and the DMAC recovery rate was 38.9%. There were 318 g of residues that needed to be treated as hazardous waste.

[0058] Comparative Example 2

[0059] Based on Example 1, a control example of Example 1 is designed to further illustrate the technical solution.

[0060] The details include:

[0061] 310 g of ethanol was used to replace the ethyl tetrafluoroethyl ether and DMAC in Example 1, and the rest was the same as in Example 1.

[0062] No product was collected after 4 hours of reaction. After the temperature dropped to 30°C, 5 g of elemental iodine was added. The temperature was raised to 70°C and the reaction was continued with stirring for 5 hours. There was still 134 g of raw material left without being added. 12.7 g of material was collected in the cold trap.

[0063] GC analysis: CF2=CFOCF3 content is 75.13%, CHF2CF2OCF3 content is 12.1%, and the reaction yield is only 7.5%.

[0064] Comparative Example 3

[0065] Based on Example 1, a control example of Example 1 is designed to further illustrate the technical solution.

[0066] The details include:

[0067] 310 g of diethylene glycol dimethyl ether was used to replace the ethyl tetrafluoroethyl ether and DMAC in Example 1, and the rest was the same as in Example 1.

[0068] After 6 h of reaction at 70°C, no product was obtained. 10 g of anhydrous zinc chloride was added and the reaction was continued at 90°C for 4 h, but still no product was obtained.

[0069] Comparative Example 4

[0070] Based on Example 1, a control example of Example 1 is designed to further illustrate the technical solution.

[0071] The details include:

[0072] 200 g of fluoroether oil (brand L2-06, Chenguang Boda Company) was used to replace the ethyl tetrafluoroethyl ether in Example 1, and the rest was the same as Example 1; the internal temperature was raised to 85°C and the raw materials were added dropwise to react. The temperature fluctuated greatly during the reaction, and the feed flow rate needed to be adjusted frequently to avoid excessive reflux and lowering of the internal temperature. The reaction was terminated after 9 hours to obtain 122 g of the product.

[0073] GC analysis: CF2=CFOCF3 content is 93.2%, CHF2CF2OCF3 content is 0.1%, and the yield is 88.8%.

[0074] After the reaction, the system was in a yellow powdery paste state with poor fluidity. The reactor residue was subjected to vacuum distillation under the condition of oil pump evacuation. When the external temperature rose to 175°C, the weight loss was about 12.5%, which showed that fluoroether oil was difficult to recover by vacuum distillation. Only 1 / 3 of the extracted material could be collected with ice water, and the remaining 2 / 3 was lost.

[0075] Example 2

[0076] Based on Example 1, this example is further improved, 193 g of ethyl tetrafluoroethyl ether recovered in Example 1 is used, and the rest is the same as Example 1.

[0077] After the reaction, 122 g of product was collected in a cold trap, and GC analysis showed that the content of CF2=CFOCF3 was 93.3%, the content of CHF2CF2OCF3 was 0.28%, and the reaction yield was 89.8%. After the reaction, 185 g of ethyl tetrafluoroethyl ether with a content of 97.6% was recovered, and the recovery rate of ethyl tetrafluoroethyl ether was 95.3%.

[0078] Example 3

[0079] In a 2-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 400g of octafluoropentyl hexafluoropropyl ether, 150g NMP, 80g zinc powder (200 mesh, average particle size of about 80 microns) were added, and 350g of CF2ClCFClOCF2CF2SO2F with a content of 93% was added in advance in the constant pressure dropping funnel. Stirring was started, and after the oil bath was heated to 50°C, the reflux condenser was passed into an ice-water mixture, and CF2ClCFClOCF2CF2SO2F was gradually added dropwise at a certain flow rate. After the addition was completed, the temperature was raised to 90°C within 1h to terminate the reaction, the temperature was lowered to 50°C and the reflux condenser was removed, and the temperature was raised to 80-110°C for atmospheric distillation, and the generated product was connected to an ice-water cold trap through an air guide tube for collection, and a total of 243.5g of product was collected.

[0080] GC analysis: The product is mainly CF2=CFOCF2CF2SO2F, with a content of 95.8%, CHF2CF2OCF2CF2SO2F content of 0.31%, raw material 0.27%, octafluoropentyl hexafluoropropyl ether 2.6%, and the reaction yield is 91.9%. Its nuclear magnetic resonance fluorine spectrum is 19 FNMR (376MHz,CDCl3)δ(ppm):45.3(m,F,-SO2F),-83.7(m,2F,-OCF2-C),-112.1(m,2F,-CF2SO2F),-113.5(m,F,OC=CF),-121.8(m,F,OC=CF),-135.5(m,F,O-CF=C), proving that the product is perfluoro(3-oxa-4-pentene)sulfonyl fluoride.

[0081] Recovery of octafluoropentyl hexafluoropropyl ether: The residue in the reactor was subjected to reduced pressure distillation under the condition of oil pump vacuum, the external temperature was maintained at 100°C, and the extract was collected with an ice-water cold trap to obtain a total of 384 g of collected material, of which the content of octafluoropentyl hexafluoropropyl ether was 98.6%, and the recovery rate of octafluoropentyl hexafluoropropyl ether was 94.7%.

[0082] Example 4

[0083] In a 1-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 300 g of ethyl nonafluorobutyl ether, 60 g of DMF, 40 g of zinc powder (325 mesh, average particle size of about 50 microns) were added, and 150 g of CF2ClCFClOCF2OCF3 with a content of 89% was added in advance in the constant pressure dropping funnel. Stirring was started, and after the water bath was heated to 50°C, an ice-water mixture was introduced into the reflux condenser, and CF2ClCFClOCF2OCF3 was gradually added dropwise at a certain flow rate. After the addition was completed, the temperature was raised to 70°C within 1 hour to terminate the reaction, and the reflux condenser was removed to room temperature, and then the temperature was raised to 50-60°C for atmospheric distillation. The generated product was connected to an ice-water cold trap through an air guide tube for collection, and a total of 101.7 g of product was collected.

[0084] GC analysis: The product is mainly CF2=CFOCF2OCF3, with a content of 91.6%, CHF2CF2OCF2OCF3 content of 0.29%, raw material 0.2%, ethyl nonafluorobutyl ether 4.3%, reaction yield 91.1%. Its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376MHz,CDCl3)δ(ppm):-56.1(m,2F,-OCF2O-),-60.4(t,3F,CF3-O-),-116.5(m,F,OC=CF),-123.4(m,F,OC=CF),-138.5(m,F,O-CF=C); GC-MS m / z:69(CF3 + ),81(C2F3 + ),97(C2F3O + ),119(C2F5 + ),147(C3F5O + ),185(C3F7O + ),232M + , further proving that the product is perfluoromethoxymethylene vinyl ether.

[0085] Recovery of ethyl nonafluorobutyl ether: The reactor residue was treated to obtain 284 g of collected material, in which the content of ethyl nonafluorobutyl ether was 98.2% and the recovery rate of ethyl nonafluorobutyl ether was 93%.

[0086] Embodiment 5-9

[0087] In addition, on the basis of Examples 1-4, different raw materials and solvent systems were replaced respectively, and the results were shown in Table 1 below. The product characteristics of each example are as follows:

[0088] CF2=CFOCF2CF2Br, its nuclear magnetic resonance fluorine spectrum is 19F NMR (376MHz,CDCl3)δ(ppm):-64.3(m,2F,-CF2Br),-88.2(m,2F,-OCF2-CF),-113.7(m,F,OC=CF),-121.1(m,F,OC=CF),-135.4(m,F,O-CF=C), indicating that the product is 2-bromotetrafluoroethyl trifluorovinyl ether;

[0089] CF2=CFOCF2CF2CF2COOCH3, its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376MHz,CDCl3)δ(ppm):-86.5(d,2F,-OCF2-C),-117.5(m,F,OC=CF),-120.6(t,2F,-CCF2-COOCH3),-124.8(m,F,OC=CF),-127.5(d,2F,-OCF2-CF2-CF2),-139(m,F,O-CF=C), indicating that the product is perfluoro-5-oxa-6-heptenoic acid methyl ester;

[0090] CF2=CFOCF2CF2CF2CF2CN, its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376MHz,CDCl3)δ(ppm):-86.7(d,2F,-OCF2-C),-108(d,2F,-CF2-CN),-117.2(m,F,OC=CF),-125.1(m,F,OC=CF),-127.5(m,4F,-OCF2-CF2-CF2-CF2-CN),-139(m,F,O-CF=C), indicating that the product is 4-nitrile octafluorobutyl trifluorovinyl ether;

[0091] CF2=CFOCF2CF3, its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376MHz,CDCl3)δ(ppm):-88.4(s,3F,CF3-C-),-93.6(m,2F,C-CF2-O),-119.4(m,F,OC=CF),-126.2(m,F,OC=CF),-138.7(m,F,O-CF=C); GC-MS m / z:69(CF3 + ),78(C2F2O + ),81(C2F3 + ),97(C2F3O + ),119(C2F5 + ),147(C3F5O + ),185(C3F7O + ),216M +, further proving that the product is perfluoroethyl vinyl ether;

[0092] CF2=CFOCF2CF(CF3)OCF2CF2SO2F, its nuclear magnetic resonance fluorine spectrum is 19 F NMR (376 MHz, CDCl3) δ (ppm): 45.1 (m, F, -SO2F), -79.2 (m, 2F, -OCF2-CF), -80.3 (m, 3F, CF3-CF), -84.3 (m, 2F, -OCF2-C), -112.4 (m, 2F, -CF2SO2F), -113.7 (m, F, OC=CF), -121.5 (m, F, OC=CF), -135.0 (m, F, O-CF=C), -145.2 (m, F, O-CF-CF2), proving that the product is perfluoro(4-methyl-3,6-dioxa-7-octenyl)sulfonyl fluoride.

[0093] Table 1

[0094]

[0095] Example 10

[0096] In a 1-liter four-necked flask equipped with mechanical stirring, constant pressure dropping funnel, reflux condensing tube and thermometer catheter, 200g perfluorotriethylamine, 110g DMAC, 52g zinc powder (325 mesh, average particle size of about 50 microns) are added, and 200g of CF2ClCFClOCF3 with a content of 91.4% is added in advance in the constant pressure dropping funnel. Start stirring, after the water bath is warmed to 50°C, the reflux condensing tube is passed through -20°C refrigerant, and CF2ClCFClOCF3 is gradually dripped at a certain flow rate, and the generated product is connected to the collection cold trap of dry ice alcohol cooling by the air guide tube for collection. After the reaction is started, heat release is obvious, and a certain feeding rate is maintained to maintain an internal temperature of 50-60°C. After the dropwise addition is completed, the water bath temperature is raised to 70°C and continued to stir for 30min, and the total reaction time is 4.5h. After the reaction is completed, the cold trap collects 131.5g of product.

[0097] GC analysis: CF2=CFOCF3 content is 95.2%, CHF2CF2OCF3 content is 0.12%, and the reaction yield is 97.8%.

[0098] Recovery of perfluorotriethylamine: After the reaction is completed, the temperature is lowered to 50°C and the reaction residue is treated with a water jet vacuum pump. The extract is collected with an ice water cold trap to obtain a total of 201g of the collected material. Among them, the content of perfluorotriethylamine is 97.6%, and the recovery rate of perfluorotriethylamine is 98.1%. There are 217g of residues that need to be treated as hazardous waste.

[0099] Embodiment 11

[0100] Based on Example 10, this example further includes:

[0101] 201 g of perfluorotriethylamine recovered in Example 10 was used, and the rest was the same as in Example 10.

[0102] After the reaction, 128 g of product was collected in a cold trap, and GC analysis showed that the content of CF2=CFOCF3 was 95.8%, the content of CHF2CF2OCF3 was 0.15%, and the reaction yield was 94.5%. After the reaction, 195 g of perfluorotriethylamine with a content of 97% was recovered, and the recovery rate of perfluorotriethylamine was 96.4%.

[0103] Example 12

[0104] In a 1-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 300g of perfluorotributylamine, 150g of NMP, 83g of zinc powder (200 mesh, average particle size of about 80 microns) were added, and 350g of 93% CF2ClCFClOCF2CF2SO2F was added in advance in the constant pressure dropping funnel. Stirring was started, and after the oil bath was heated to 50°C, the reflux condenser was passed into an ice-water mixture, and CF2ClCFClOCF2CF2SO2F was gradually added dropwise at a certain flow rate. After the addition was complete, the temperature was raised to 90°C within 1h to terminate the reaction, the temperature was lowered to 50°C and the reflux condenser was removed, and the temperature was raised to 80-110°C for atmospheric distillation. The generated product was collected by connecting the air guide tube to an ice-water cold trap, and a total of 247g of product was collected.

[0105] GC analysis: CF2=CFOCF2CF2SO2F content is 95.4%, CHF2CF2OCF2CF2SO2F is 0.24%, raw material is 0.2%, perfluorotributylamine is 1.7%, and reaction yield is 90.7%.

[0106] Recovery of perfluorotributylamine: The residue in the reactor was subjected to reduced pressure distillation under the condition of oil pump vacuum, the external temperature was maintained at 120°C, and the extract was collected with an ice-water cold trap to obtain a total of 287.5 g of the collected material, of which the perfluorotributylamine content was 96.3% and the perfluorotributylamine recovery rate was 92.3%.

[0107] Example 13

[0108] In a 1-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 280g of perfluorotripropylamine, 70gDMF, 45g zinc powder (100 mesh, average particle size of about 150 microns) were added, and 180g of 89% CF2ClCFClOCF2OCF3 was added in advance in the constant pressure dropping funnel. Stirring was started, and after the water bath was heated to 50°C, the reflux condenser was passed into an ice-water mixture, and CF2ClCFClOCF2OCF3 was gradually added dropwise at a certain flow rate. After the addition was completed, the temperature was raised to 85°C within 1h to terminate the reaction, and the reflux condenser was removed to room temperature, and then the temperature was raised to 50-70°C for atmospheric distillation. The generated product was connected to an ice-water cold trap through an air guide tube for collection, and a total of 124.3g of product was collected.

[0109] GC analysis showed that the content of CF2=CFOCF2OCF3 was 93.1%, CHF2CF2OCF2OCF3 was 0.35%, the raw material was 0.18%, the perfluorotripropylamine was 1.3%, and the reaction yield was 94.3%.

[0110] Recovery of perfluorotripropylamine: The reactor residue was treated to obtain 277 g of collected material, wherein the content of perfluorotripropylamine was 97.2% and the recovery rate of perfluorotripropylamine was 96.2%.

[0111] Examples 14-18

[0112] In addition, based on Examples 10-13, different raw materials and solvent systems were replaced, and the results were shown in Table 2 below.

[0113] Table 2

[0114]

[0115] Embodiment 19

[0116] In a 1-liter four-necked flask equipped with mechanical stirring, constant pressure dropping funnel, reflux condensing tube and thermometer catheter, 200g tetrafluoropropanol, 110g DMAC, 52g zinc powder (325 mesh, average particle size of about 50 microns) are added, and 200g of CF2ClCFClOCF3 with a content of 91.4% is added in advance in the constant pressure dropping funnel. Start stirring, after the water bath is warmed to 50°C, the reflux condensing tube is passed through -20°C refrigerant, and CF2ClCFClOCF3 is gradually dripped at a certain flow rate, and the generated product is connected to the collection cold trap of dry ice alcohol cooling by the air guide tube for collection. After the reaction is started, heat release is obvious, and a certain feeding rate is maintained to maintain an internal temperature of 50-60°C. After the dropwise addition is completed, the water bath temperature is raised to 70°C and continued to stir for 30min, and the total reaction time is 4h. After the reaction is completed, the cold trap collects 128.2g of product.

[0117] GC analysis showed that the CF2=CFOCF3 content was 94.5%, the CHF2CF2OCF3 content was 0.1%, and the reaction yield was 94.6%.

[0118] Recovery of tetrafluoropropanol: After the reaction is completed, the temperature is lowered to 50°C and the reaction residue is treated with a water jet vacuum pump. The extract is collected with an ice water cold trap to obtain a total of 195g of collected material. Among them, the tetrafluoropropanol content is 98.3%, and the tetrafluoropropanol recovery rate is 95.8%. There are 230g of residues that need to be treated as hazardous waste.

[0119] Embodiment 20

[0120] Based on Example 19, this example goes a step further, using 195 g of tetrafluoropropanol recovered in Example 19, and the rest is the same as Example 19.

[0121] After the reaction, 126.7 g of product was collected in a cold trap. GC analysis showed that the content of CF2=CFOCF3 was 93.8%, the content of CHF2CF2OCF3 was 0.12%, and the reaction yield was 92.8%. After the reaction, 188 g of tetrafluoropropanol with a content of 98.6% was recovered, and the recovery rate of tetrafluoropropanol was 96.7%.

[0122] Embodiment 21

[0123] In a 2-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 400g of 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 130g of NMP, 80g of zinc powder (200 mesh, average particle size of about 80 microns) were added, and 350g of CF2ClCFClOCF2CF2SO2F with a content of 93% was added in advance in the constant pressure dropping funnel. Stirring was started, and after the oil bath was heated to 50°C, an ice-water mixture was introduced into the reflux condenser, and CF2ClCFClOCF2CF2SO2F was gradually added dropwise at a certain flow rate. After the addition was completed, the temperature was raised to 90°C within 1h to terminate the reaction, the temperature was lowered to 50°C and the reflux condenser was removed, and the temperature was raised to 80-110°C for atmospheric distillation, and the generated product was connected to the ice-water cold trap through a gas guide tube for collection, and a total of 241.2g of product was collected.

[0124] GC analysis: CF2=CFOCF2CF2SO2F content is 94.3%, CHF2CF2OCF2CF2SO2F content is 0.5%, raw material is 0.9%, octafluoropentanol is 3.4%, and reaction yield is 87.6%.

[0125] Recovery of octafluoropentanol: The residue in the reactor was subjected to reduced pressure distillation under the condition of oil pump vacuum, the external temperature was maintained at 80°C, and the extract was collected by ice water cold trap, and a total of 372.8g of the collected product was obtained, of which the octafluoropentanol content was 98.3% and the octafluoropentanol recovery rate was 91.6%.

[0126] Embodiment 22

[0127] In a 1-liter four-necked flask equipped with mechanical stirring, a constant pressure dropping funnel, a reflux condenser and a thermometer catheter, 240g of heptafluorobutanol, 80g of DMF, 45g of zinc powder (100 mesh, average particle size of about 150 microns) and 160g of 89% CF2ClCFClOCF2OCF3 were added in advance in the constant pressure dropping funnel. Stirring was started, and after the water bath was heated to 50°C, an ice-water mixture was introduced into the reflux condenser, and CF2ClCFClOCF2OCF3 was gradually added dropwise at a certain flow rate. After the addition was completed, the temperature was raised to 85°C within 1h to terminate the reaction, and the reflux condenser was removed to room temperature, and then the temperature was raised to 50-70°C for atmospheric distillation. The generated product was connected to an ice-water cold trap through an air guide tube for collection, and a total of 110.2g of product was collected.

[0128] GC analysis: CF2=CFOCF2OCF3 content is 92.2%, CHF2CF2OCF2OCF3 content is 0.4%, raw material is 0.5%, heptafluorobutanol is 6.2%, and the reaction yield is 93.2%.

[0129] Recovery of heptafluorobutanol: The residue in the reactor was treated to obtain 236.8 g of collected material, in which the content of heptafluorobutanol was 97.6% and the recovery rate of heptafluorobutanol was 96.3%.

[0130] Examples 23-26

[0131] In addition, based on Examples 19-22, different raw materials and solvent systems were replaced, and the results were shown in Table 3 below.

[0132] Table 3

[0133]

[0134] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a fluorine-containing alkenyl ether, characterized in that: The method comprises taking a fluorine-containing alkane as a raw material, carrying out a dehalogenation reaction under the conditions of a metal dehalogenating agent, a nitrogen-containing non-protonic polar solvent and a fluorine-containing co-solvent to prepare a fluorine-containing olefin ether; Wherein, the fluorinated alkane is represented by the following general structural formula (I): CF2X1-CFX2-O-R f 1 -(O) y -R f 2 X3 （I） In formula (I), X1 is Cl, Br or I, X2 is Cl, Br or I, X3 is F, Br, I, SO2F, CN or COOR, R is a linear or branched alkyl group having 1 to 3 carbon atoms, R f 1 is a straight-chain or branched perfluoroalkyl group having 1 to 5 carbon atoms, R f 2 is a straight-chain or branched perfluoroalkyl group having 0 to 3 carbon atoms, y=0 or 1; Wherein, the fluorine-containing olefin ether is represented by the following structural formula (II); CF2=CF-O-R f 1 -(O) y -R f 2 X3 （Ⅱ） In formula (II), R f 1 is a straight-chain or branched perfluoroalkyl group having 1 to 5 carbon atoms, R f 2 is a linear or branched perfluoroalkyl group having 0 to 3 carbon atoms, X3 is F, Br, I, SO2F, CN or COOR, R is a linear or branched alkyl group having 1 to 3 carbon atoms, y = 0 or 1; The nitrogen-containing aprotic polar solvent is one or a combination of any two or more of triethylamine, tetramethylethylenediamine, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diisopropylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and N,N-dimethylpropyleneurea; The fluorinated cosolvent is a hydrofluoroether solvent, a fluorinated amine cosolvent or a fluorinated alcohol cosolvent; The hydrofluoroether solvent is ethyl tetrafluoroethyl ether, propyl tetrafluoroethyl ether, isopropyl tetrafluoroethyl ether, butyl tetrafluoroethyl ether, methyl hexafluoroisopropyl ether, ethyl hexafluoropropyl ether, propyl hexafluoropropyl ether, isopropyl hexafluoropropyl ether, butyl hexafluoropropyl ether, methyl heptafluoroisopropyl ether, ethyl heptafluoroisopropyl ether, methyl heptafluoro-n-propyl ether, ethyl heptafluoro-n-propyl ether, methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, trifluoroethyl tetrafluoroethyl ether, tetrafluoropropyl tetrafluoroethyl ether, oc ...ethyl heptafluoroisopropyl ether, ethyl Fluoropentyl tetrafluoroethyl ether, trifluoroethyl hexafluoropropyl ether, tetrafluoropropyl hexafluoropropyl ether, octafluoropentyl hexafluoropropyl ether, 1-methoxy-2-(1,1,2,2-tetrafluoroethoxy)ethane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, 1,3-bis(1,1,2,2-tetrafluoroethoxy)propane, cyclohexyl tetrafluoroethyl ether or cyclohexyl hexafluoropropyl ether; The fluorine-containing amine cosolvent is perfluoromethylmorpholine, perfluorotriethylamine, perfluoromethylethylpropylamine, perfluorotripropylamine, perfluorodiethylpropylamine, perfluorodibutylmethylamine, perfluorotributylamine, perfluorodibutylethylamine or perfluorotripentylamine; The fluorine-containing alcohol co-solvent includes trifluoroethanol, tetrafluoropropanol, pentafluoropropanol, 1,1,1,3,3,3-hexafluoro-2-isopropanol, heptafluorobutanol, 1H,1H,5H-octafluoro-1-pentanol, nonafluoro-1-pentanol, undecafluoro-1-hexanol, 1H,1H,7H-dodecafluoro-1-heptanol, tridecafluoro-1-heptanol, pentafluoro-1-octanol, 1H,1H,9H-hexadecanofluoro-1-nonanol, 2-perfluoropropoxy-2,3,3,3-tetrafluoropropanol or 1H,1H-2,5-bis(trifluoromethyl)-3,6-dioxoperfluorononanol.

2. The method for preparing a fluorine-containing alkenyl ether according to claim 1, characterized in that: The fluorine-containing alkanes include CF2ClCFClOCF3, CF2ClCFClOCF2CF3, CF2ClCFClOCF2OCF3, CF2ClCFClOCF2CF2SO2F, CF2ClCFClOCF2CF2Br, CF2BrCFBrOCF2CF(CF3)OCF2CF2SO2F, CF2BrCFBrOCF2CF2CF2COOCH3 or CF2BrCFBrOCF2CF2CF2CF2CN.

3. The method for preparing a fluorine-containing alkenyl ether according to claim 1 or 2, characterized in that: The fluorine-containing olefin ethers include CF2=CFOCF3, CF2=CFOCF2CF3, CF2=CFOCF2OCF3, CF2=CFOCF2CF2SO2F, CF2=CFOCF2CF2Br, CF2=CFOCF2CF(CF3)OCF2CF2SO2F, CF2=CFOCF2CF2CF2COOCH3 or CF2=CFOCF2CF2CF2CF2CN.

4. The method for preparing a fluorine-containing alkenyl ether according to claim 1, characterized in that: The metal dehalogenating agent is one of magnesium, aluminum, copper and zinc or a combination of any two or more thereof.

5. The method for preparing a fluorine-containing alkenyl ether according to claim 1 or 4, characterized in that: The average particle size of the metal dehalogenating agent is 40-150 μm.

6. The method for preparing fluorine-containing alkenyl ether according to claim 5, characterized in that: The molar amount of the metal dehalogenating agent is 1-3 times the molar amount of the fluorinated alkane.

7. The method for preparing fluorine-containing alkenyl ether according to claim 1, characterized in that: The molar amount of the nitrogen-containing aprotic polar solvent is 1-6 times the molar amount of the fluorine-containing alkane.

8. The method for preparing fluorine-containing alkenyl ether according to claim 1, characterized in that: The mass ratio between the nitrogen-containing aprotic polar solvent and the fluorine-containing co-solvent is 0.1-1.

9. The method for preparing fluorine-containing alkenyl ether according to claim 1, characterized in that: In the preparation method of the fluorine-containing enol ether, the reaction temperature is 20-180° C. and the reaction time is controlled within 8 hours.

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