Preparation method of perfluoro-2, 3-dimethyl-2-pentene

Abstract

The invention discloses a preparation method of perfluoro-2, 3-dimethyl-2-pentene, which comprises the following steps of: initiating a trifluoromethylation reagent to generate trifluoromethyl ions by using an initiator containing fluorine ions or carbonate ions in an aprotic solvent by adopting a continuous flow micro-reaction process; then, the trifluoromethyl ions and the perfluoro-2-methyl-2-pentene are subjected to a reaction, and the perfluoro-2, 3-dimethyl-2-pentene is generated. The method is short in reaction time, high in preparation efficiency, simple in process, low in cost, few in three wastes, high in product yield and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the field of chemical synthesis, and particularly to a method for preparing perfluoro-2,3-dimethyl-2-pentene by a continuous flow microreaction process. Background Art

[0002] Perfluoro-2,3-dimethyl-2-pentene is an organic compound with the English name 1,1,1,4,4,5,5,5-octafluoro-2,3-bis(trifluoromethyl)-2-pentene, CAS number 58621-65-1, and the molecular formula C7F 14 , molecular weight 350.05, and the structural formula is as follows:

[0003]

[0004] Perfluoro-2,3-dimethyl-2-pentene is a perfluoroolefin compound. This type of compound contains a carbon-carbon double bond and has a relatively high reactivity with OH radicals, so its atmospheric lifetime is short and its global warming potential (GWP) is low, making it environmentally friendly; fluorine substitution can significantly reduce the polarizability of the compound molecule, thereby reducing its dielectric constant and having good insulation performance; and it has excellent heat transfer performance and is an ideal liquid cooling medium. In recent years, this type of compound has been well applied in the liquid cooling technology of data centers.

[0005] Currently, there is no relevant report on a large-scale preparation method of perfluoro-2,3-dimethyl-2-pentene.

[0006] The literature "J. Chem. Soc., Perkin Trans. 1, 1981: 1064-1067" reported a method for preparing perfluoro-2,3-dimethyl-2-pentene by the reaction of hexafluoropropene and perfluoro-2-butene catalyzed by cesium fluoride. The conversion rate of the substrate in this method is not high, and the yield is only 70%, and cesium fluoride is used as the catalyst, resulting in a high cost.

[0007]

[0008] The literature "Journal of Fluorine Chemistry, 27(1985): 71-84" reported a method for preparing perfluoro-2,3-dimethyl-2-pentene by the high-temperature pyrolysis of perfluorocyclic oxides. In (5dm 3 / h) In a dry nitrogen stream, perfluorocyclooxide (112.5 g) was introduced into a glass pyrolysis tube at 305 - 310 °C over 5.5 hours, and the product was collected using a glass cold trap cooled with liquid air. After separation, perfluoro-2,3-dimethyl-2-pentene (0.5 g), perfluoro-2-methyl-1-butene (0.42 g), perfluoro-2,3-dimethylhexene (0.6 g), and other products were obtained. This method has harsh reaction conditions, many by-products, poor selectivity for the target product, a very low yield of perfluoro-2,3-dimethyl-2-pentene, a long reaction time, and cannot be applied on a large scale.

[0009]

[0010] The literature "Journal of Fluorine Chemistry 196(2017)128–134" reported a method for preparing perfluoroolefins by the reaction of hexafluoropropene trimer and trimethyl(trifluoromethyl)silane in a polar aprotic solvent catalyzed by potassium bifluoride. However, the products obtained by this method are a mixture of mono-substituted and di-substituted trifluoromethylated products, with poor reaction selectivity. In addition, this reaction is carried out in conventional glassware, where the catalyst and the raw materials are in two immiscible phases, and the two phases are brought into contact by magnetic stirring. The reaction system is prone to long reaction times and low yields due to insufficient contact between the materials. At the same time, it is also easy to have local hot spots due to insufficient cooling systems, which can lead to boiling over of the system and splashing of the materials, posing a large safety risk and making it difficult to carry out industrial production.

[0011]

[0012] In summary, the existing methods for preparing perfluoro-2,3-dimethyl-2-pentene disclosed in the prior art have deficiencies such as poor reaction selectivity and low yield, or harsh reaction conditions and difficult reaction process control, or ineffective removal of reaction heat and large safety risks, or long reaction times and high preparation costs, or being batch reactions, difficult to achieve automated control, and difficult to achieve industrial production. Summary of the Invention

[0013] To solve the above technical problems, the inventors creatively used perfluoro-2-methyl-2-pentene as the raw material. First, in an aprotic solvent, fluoride ions or carbonate ions were used to conduct nucleophilic attack on trimethyl(trifluoromethyl)silane to generate trifluoromethyl ions. Then, these trifluoromethyl ions reacted with the raw material to obtain the target product perfluoro-2,3-dimethyl-2-pentene. At the same time, by coupling a microreactor with high mass and heat transfer efficiency, a preparation method of perfluoro-2,3-dimethyl-2-pentene was proposed, which has a simple process, low cost, few three wastes, high product yield, is suitable for industrial production, has a short reaction time, and high production efficiency.

[0014] The object of the present invention is achieved by the following technical solutions:

[0015] A preparation method of perfluoro-2,3-dimethyl-2-pentene, comprising the following steps: in an aprotic solvent, trimethyl(trifluoromethyl)silane reacts with perfluoro-2-methyl-2-pentene under the action of an initiator to generate perfluoro-2,3-dimethyl-2-pentene, and the initiator contains fluoride ions or carbonate ions.

[0016] The reaction equation of the present invention is shown in Formula I:

[0017]

[0018] The initiator conducts a nucleophilic attack on trimethyl(trifluoromethyl)silane to generate a trifluoromethyl ion. Subsequently, this anion conducts an addition-elimination reaction on perfluoro-2-methyl-2-pentene to obtain the target product perfluoro-2,3-dimethyl-2-pentene. Taking the fluoride ion as an example of the initiator, the reaction mechanism is shown in Formula II:

[0019]

[0020] In an aprotic solvent, the fluoride ion, as the initiator, attacks trimethyl(trifluoromethyl)silane to generate an intermediate I with nucleophilic activity. Subsequently, the carbon-silicon bond in the intermediate I breaks, and the trifluoromethyl part attacks perfluoro-2-methyl-2-pentene to obtain an intermediate II, and at the same time, a by-product trimethylfluorosilane is generated. The intermediate II can also act as an initiator to attack trimethyl(trifluoromethyl)silane to obtain an intermediate III with nucleophilic activity. Subsequently, through a similar pathway, the carbon-silicon bond in the intermediate III breaks, and the trifluoromethyl part attacks another molecule of perfluoro-2-methyl-2-pentene to start the catalytic cycle, and the remaining part obtains the target product perfluoro-2,3-dimethyl-2-pentene through elimination.

[0021] The reaction of the present invention is carried out in a microreactor. The microreactor can strengthen heat transfer and mass transfer, accelerate the progress of the reaction, and avoid the generation of local hot spots. The present invention conducts the nucleophilic substitution reaction of trimethyl(trifluoromethyl)silane through a microchannel reactor. By optimizing the microchannel reaction process and conditions, perfluoro-2,3-dimethyl-2-pentene is prepared in a continuous flow mode with a high yield.

[0022] The reaction described in the present invention is generally an exothermic reaction. If not controlled, "hot spots" will exist locally in the reaction system, and the overall temperature will rise rapidly, which will cause side reactions such as chain breakage and rearrangement, resulting in low reaction selectivity and low product yield. The continuous flow microreaction process with functions of enhanced heat transfer and enhanced mass transfer is adopted, which is conducive to realizing automatic control. The continuous flow microreaction process described in the present invention uses a microreactor as a liquid-liquid phase microreactor. Compared with the traditional jacketed kettle reactor, the microreactor has a larger specific surface area, and the specially designed channels with special shapes conducive to rapid mixing can play the role of enhancing heat transfer and mass transfer; specifically, the structural type of the liquid-liquid phase microreactor is a chip-type or (and) coil-type microchannel reactor; the channel shape is, for example, a simple shape such as a cylindrical shape or a cuboid shape or (and) the channel shape is a shape or structure such as a heart shape, a rhombus shape and a structure with baffles inside to enhance the mixing effect; its characteristic is that the specific surface area ≥ 5000m 2 / m 3 , the microchannel diameter ≥ 0.1 mm, and the channel length ≥ 1000 mm; preferably, its specific surface area ≥ 20000m 2 / m 3 , the microchannel diameter is 0.3 mm - 3 mm, and the channel length ≥ 5000 mm.

[0023] The polar aprotic solvent described in the present invention can dissolve the initiator or form a suspension with the initiator, and there is no particular limitation on the specific compound. Specifically, the solvent is, for example, at least one or a mixture of 1,3-dimethyl-2-imidazolidinone (DMI), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and acetonitrile (CH3CN); preferably, the polar aprotic solvent is selected from at least one of 1,3-dimethyl-2-imidazolidinone (DMI), acetonitrile (CH3CN), and N,N-dimethylformamide (DMF).

[0024] The initiator contains fluoride ions or carbonate ions, and there is no particular limitation on the specific compound. For example, the fluoride ions are selected from sodium fluoride, potassium fluoride, cesium fluoride, potassium bifluoride, and tetrabutylammonium fluoride, and the carbonate ions are selected from at least one of cesium carbonate and potassium carbonate; preferably, the initiator contains fluoride ions and is selected from at least one of tetrabutylammonium fluoride, potassium fluoride, and potassium bifluoride.

[0025] The concentration of the initiator in the polar aprotic solvent is not particularly limited, and it can be completely dissolved or form a suspension. Specifically, the molar concentration of the initiator in the polar aprotic solvent is 0.01 - 0.5 mol / mL; preferably, the molar concentration of the initiator in the polar aprotic solvent is 0.01 - 0.1 mol / mL.

[0026] The trifluoromethyltrimethylsilane can be commercially available or prepared by reacting a haloalkane with trimethylchlorosilane (Me3SiCl) in the presence of a reducing agent. The haloalkanes include trifluoromethane, trifluorobromomethane, trifluoroiodomethane, etc. There is no particular limitation on the trifluoromethylating reagent obtained by any method.

[0027] The inventors of this patent obtained the optimal process flow and process parameters of the reaction through multiple experiments.

[0028] Through multiple experiments, it was found that when generating trifluoromethyl ions, a certain amount of energy is required for the reaction. The addition-elimination reaction of trifluoromethyl ions with the substrate perfluoro-2-methyl-2-pentene to obtain the target product perfluoro-2,3-dimethyl-2-pentene is a catalytic cycle reaction and will generate a large amount of heat. If the heat is not removed in time, a violent reaction will occur, resulting in a decrease in the yield and even accidents such as material flushing. Therefore, when the initiator and the trifluoromethylating reagent react to generate trifluoromethyl ions, the reaction needs to be carried out at a relatively high temperature, and the reaction system needs to be heated; when the trifluoromethyl ions generated in the first step react with the substrate to generate the target product, heat needs to be removed in time when entering the cyclic catalytic reaction stage, and the reaction temperature needs to be strictly controlled. The reaction needs to be carried out at a relatively low temperature to react safely and obtain a better yield.

[0029] Specifically, the preparation method is divided into two-stage reactions in a microchannel reactor. The first-stage reaction is that the initiator and the trifluoromethylating reagent are pre-cooled and then generate trifluoromethyl ions in the microchannel reactor module 1. The reaction requires heating, and the temperature T1 of the first-stage reaction is controlled at 10-40 °C; preferably, the temperature T1 of the first reaction stage is 15-30 °C. The second-stage reaction is that trifluoromethyl ions react with the substrate to generate the target product. The reaction requires cooling, and the temperature T2 of the second-stage reaction is controlled at -10-30 °C; preferably, the temperature T2 of the second reaction stage is 5-20 °C.

[0030] In the preparation method of the present invention, the continuous flow microchannel process is adopted, which can effectively improve the reaction rate and reduce the occurrence of side reactions. Compared with traditional reactors such as batch reactors, the reaction time can be greatly shortened, but the reaction time needs to be strictly controlled. If the reaction time is short, the raw materials cannot be completely converted, resulting in a low yield of the target product; if the reaction time is too long, the by-products increase and the product selectivity decreases. It is necessary to adopt a strategy of segmentally controlling the reaction time according to the characteristics of this preparation method. The first stage is that the residence time (i.e., the reaction time) of the reaction between the initiator and the trifluoromethylating reagent is greater than 8 s; preferably, the reaction time of the first stage is 8-50 s. The second stage is that trifluoromethyl ions react with the substrate to generate the target product, and the residence time (i.e., the reaction time) is greater than 30 s; preferably, the reaction time of the second stage is 30-200 s.

[0031] The material ratio of the preparation method of the present invention is an important factor affecting the reaction yield. Specifically, the molar ratio of the initiator to trimethyl(trifluoromethyl)silane is (0.1 - 1.0):1; preferably, the molar ratio of the initiator to trimethyl(trifluoromethyl)silane is (0.1 - 0.3):1. The molar ratio of trimethyl(trifluoromethyl)silane to perfluoro-2-methyl-2-pentene is (1 - 3.0):1; preferably, the molar ratio of trimethyl(trifluoromethyl)silane to perfluoro-2-methyl-2-pentene is (1.1 - 1.6):1.

[0032] In a specific embodiment of the present invention, the preparation method of perfluoro-2,3-dimethyl-2-pentene of the present invention comprises the following steps:

[0033] Dissolve the initiator in an aprotic solvent, with the initiator concentration being 0.01 - 0.1 mol / L, and pump 1 is used to transport it into the precooling module 1 of the microchannel reactor for precooling, with the precooling temperature being greater than or equal to the first-stage reaction temperature T1. This is stream 1.

[0034] Meanwhile, pump 2 is used to transport trimethyl(trifluoromethyl)silane into the precooling module 2 of the microchannel reactor for precooling, with the precooling temperature being greater than or equal to the first-stage reaction temperature. This is stream 2.

[0035] After streams 1 and 2 pass through the precooling modules 1 and 2, they are merged into the reaction module 1 of the microchannel reactor to initiate the generation of trifluoromethyl ions. This is the first-stage reaction. By controlling the flow rates of pumps 1 and 2, the molar ratio of the initiator to trimethyl(trifluoromethyl)silane is (0.1 - 0.3):1, the residence time of the materials in the reaction module 1 of the microchannel reactor is 8 s - 50 s, and the reaction temperature of the reaction module 1 of the microchannel reactor is controlled at 15 - 30 °C.

[0036] The material containing trifluoromethyl ions after the reaction in the reaction module 1 of the microchannel reactor (this is stream 4) enters the reaction module 2 of the microchannel reactor; meanwhile, pump 3 is used to transport the substrate perfluoro-2-methyl-2-pentene into the precooling module 3 of the microchannel reactor for precooling, with the precooling temperature being less than or equal to the second-stage reaction temperature T2. This is stream 3. After being precooled by the precooling module 3, stream 3 enters the reaction module 2 of the microchannel reactor for the second-stage reaction, where the target product perfluoro-2,3-dimethyl-2-pentene is generated. By controlling the flow rates of pumps 2 and 3, the molar ratio of trimethyl(trifluoromethyl)silane to perfluoro-2-methyl-2-pentene is (1.1 - 1.6):1, the residence time of the materials in the microchannel reactor 2 is 30 s - 200 s, and the reaction temperature of the reaction module 2 of the microchannel reactor is controlled at 5 - 20 °C.

[0037] The crude product after sufficient mixing and reaction in the reaction module 2 of the microchannel reactor flows out through the reaction module 2 of the microchannel reactor (this is stream 5).

[0038] The crude product stream 5 is allowed to stand for liquid-liquid separation, and the lower layer liquid is taken and further rectified to obtain the target product perfluoro-2,3-dimethyl-2-pentene; the upper layer liquid contains the initiator active ions and can be mixed with the stream 4 for recycling.

[0039] The trifluoromethyl reagent used in the present invention is sensitive to water. If the system contains a large amount of water, its reaction activity will be significantly reduced. Therefore, the reaction equipment and instruments used in the present invention need to be dehydrated. Specifically, the equipment and pipelines can be pre-purged with dry nitrogen.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. The present invention adopts a continuous flow microreaction process, which can timely remove the reaction heat, has a low safety risk, is easy to realize automatic control, and is easy to realize industrial production.

[0042] 4. The present invention adopts a specially designed process flow to precisely control the reaction process, with milder reaction conditions, shorter reaction time, high preparation efficiency, and good selectivity and high yield of the target product. Description of the Drawings

[0044] Figure 1 It is the mass spectrum of the product perfluoro-2,3-dimethyl-2-pentene in Example 1 of the present invention;

[0045] Figure 2 It is the 19 F-NMR spectrum of the product perfluoro-2,3-dimethyl-2-pentene in Example 1 of the present invention;

[0046] Figure 3 It is the 13 C-NMR spectrum of the product perfluoro-2,3-dimethyl-2-pentene in Example 1 of the present invention;

[0047] Figure 4 It is the process flow schematic diagram of the preparation method in Example 1 of the present invention. 112 is the initiator solution / suspension, 113 is trimethyl(trifluoromethyl)silane, 114 is the substrate perfluoro-2-methyl-2-pentene, 21 is the peristaltic pump 1, 22 is the peristaltic pump 2, 23 is the peristaltic pump 3, 115 is the stream 1, 116 is the stream 2, 117 is the stream 3, 118 is the stream 4(118), 119 is the stream 5, 24 is the microchannel reactor, 241 is the precooling module 1, 242 is the precooling module 2, 243 is the precooling module 3, 244 is the reaction module 1, and 245 is the reaction module 2. Detailed Embodiments

[0048] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions, and equivalent solutions that may be included within the scope of the claims.

[0049] Example 1

[0050] In this example, a microreactor is used. Specifically, a microchannel reactor formed by combining ten microchannel reaction modules made of G1 silicon carbide material is used. The liquid holdup of reaction module 1 is 10 mL, and the liquid holdup of reaction module 2 is 90 mL.

[0051] The equipment and pipelines are purged with dry nitrogen to make the equipment and pipelines fully dry.

[0052] The initiator potassium fluoride is mixed with the aprotic solvent 1,3-dimethyl-2-imidazolidinone (DMI) to form a potassium fluoride solution / suspension, and the concentration of potassium fluoride is 0.02 mol / mL

[0053] The above initiator solution / suspension (112) is transported into the precooling module 1 (241) of the microchannel reactor by a peristaltic pump 1 (21) for precooling. The precooling temperature is 25 °C, and the flow rate is 1.2 mL / min (0.024 mol / min). This is stream 1 (115).

[0054] At the same time, trifluoromethyltrimethylsilane (113) is transported into the precooling module 2 (242) of the microchannel reactor by a peristaltic pump 2 (22) for precooling. The precooling temperature is 25 °C, and the flow rate is 18.0 mL / min (0.12 mol / min). This is stream 2 (116).

[0055] At the same time, the substrate perfluoro-2-methyl-2-pentene (114) is transported into the precooling module 3 (243) of the microchannel reactor by a peristaltic pump 3 (23) for precooling. The precooling temperature is 0 °C, and the flow rate is 18.5 mL / min (0.1 mol / min). This is stream 3 (117).

[0056] After streams 1 and 2 pass through the precooling modules 1 and 2, they enter the reaction module 1 (244) simultaneously. After being fully mixed and reacted in the reaction module 1, they become stream 4 (118) and enter the reaction module 2 (245) of the microchannel reactor;

[0057] At the same time, after stream 3 is precooled by the precooling module 3 (243), it enters the reaction module 2 (245) of the microchannel reactor; Streams 3 and 4 are fully mixed and reacted in the reaction module 2 (245) of the microchannel reactor to form a crude product, which flows out of the reaction module 2 (245) of the microchannel reactor as stream 5 (119).

[0058] The molar ratio of potassium fluoride to trimethyl(trifluoromethyl)silane is 0.2:1, and the molar ratio of trimethyl(trifluoromethyl)silane to the substrate perfluoro-2-methyl-2-pentene is 1.2:1; in the first-stage reaction, the residence time of the materials in the reaction module 1 (244) of the microchannel reactor is 33 s, and the reaction temperature is 25 °C; in the second-stage reaction, the residence time of the materials in the reaction module 2 (245) of the microchannel reactor is 147 s, and the reaction temperature is 10 °C.

[0059] The above reaction was continued for 30 minutes, and a total of 900 g (3.00 mol) of the substrate perfluoro-2-methyl-2-pentene was introduced.

[0060] The stream 5 (119) was collected, allowed to stand and separate into layers, the lower layer liquid was taken, and the target product perfluoro-2,3-dimethyl-2-pentene (1010 g, 2.90 mol) was obtained by rectification. The molar yield of the target product was 96.7% (calculated based on the substrate perfluoro-2-methyl-2-pentene). The upper layer liquid after layer separation contains initiator active ions and can be mixed with the stream 4 for recycling.

[0061] In this example, gas chromatography analysis was used, and the analytical instrument was Shimadzu GC-2014; chromatographic column: SH-1301 (inner diameter 0.25 mm, length 60 m). GC analysis method: High-purity nitrogen and hydrogen were used as carrier gases, the detector temperature was 250 °C, the vaporization chamber temperature was 220 °C, column temperature: 33 °C (10 min) at 10 °C / min to 200 °C (5 min); the flow rate of the carrier gas (nitrogen) was 30 mL / min, the air flow rate was 400 mL / min, the hydrogen flow rate was 40 mL / min, the split ratio at the injection port was 30.0, and the injection volume was 0.1 μL.

[0062] By GC-MS, 19 F NMR, 13 C NMR were used to determine the structure of the target product. GC / MS, m / z: 350 (M · ), 331 (M - F), 281 (M - CF3), 212 (M - 2CF3); 19 F-NMR (564 MHz) (ppm, DMSO-d6): δ -60.1 (s, 3F), -61.1 (s, 3F), -61.7 (s, 3F), -76.8 (m, 3F), -101.3 (s, 2F); 13 C-NMR (150 MHz) (ppm DMSO-d6) (hydrogen-fluorine synchronous decoupling): 137.78, 136.1, 118.5, 118.41, 118.36, 117.5, 112.5.

[0063] Comparative Example 1

[0064] Potassium fluoride (41.8 g, 0.72 mol) was taken and dried in an oven for 4 hours; 72 mL of 1,3-dimethyl-2-imidazolidinone (DMI) was transferred into a container equipped with a thermometer and a stirrer. Under nitrogen protection, the dried potassium fluoride was added, and stirring was continued to obtain a DMI solution / suspension with a potassium fluoride concentration of 0.01 mol / mL.

[0065] Under nitrogen protection, the above-mentioned DMI solution of potassium fluoride was added to a glass reactor equipped with a thermometer, a condenser, and a constant-pressure dropping funnel. The reactor was placed in a cold trap, and perfluoro-2-methyl-2-pentene (900.0 g, 3.0 mol) was added. Then, a trifluoromethylating reagent (511.2 g, 3.6 mol) was slowly added dropwise at 0 °C. After the addition was complete, the mixture was maintained at 10 °C for 1 h, slowly heated to 25 °C, and stirred for 8 h. After the reaction was completed, the reaction solution was transferred to a separatory funnel, allowed to stand for stratification, and the lower layer was taken. The target product, perfluoro-2,3-dimethyl-2-pentene (383 g, 1.1 mol), was obtained by rectification, and the product yield was 36.7% (calculated based on the substrate perfluoro-2-methyl-2-pentene).

[0066] In Comparative Example 1, a glass reaction kettle was used, the two-phase contact was insufficient, the conversion rate was low, the selectivity was low, and the yield was low.

[0067] Examples 2 to 5

[0068] The operating procedures of Examples 2 to 5 were the same as those of Example 1, except that: the initiator was changed, and the molar yields of the target product perfluoro-2,3-dimethyl-2-pentene are shown in Table 1.

[0069] Table 1 Molar yields of the target product in Examples 2 to 5

[0070] Serial number Initiator Molar yield of target product (%) Example 2 <![CDATA[KHF2]]> 95.3% (2.86 mol) Example 3 Tetrabutylammonium fluoride 97.3% (2.92 mol) Example 4 <![CDATA[Cs2CO3]]> 94.3% (2.84 mol) Example 5 <![CDATA[KCO3]]> 93.3% (2.80 mol)

[0071] As can be seen from Table 1, the target product can be obtained in a relatively high yield by using an initiator containing fluoride ions or carbonate ions in this preparation method.

[0072] Comparative Example 2

[0073] The operating procedure was the same as that of Example 1, except that: the initiator was changed to KCl, and the molar yield of the target product perfluoro-2,3-dimethyl-2-pentene was 10%.

[0074] It can be seen from Comparative Example 2 that when KCl was used as the initiator, the yield was low. It is speculated that although KCl can initiate trimethylsilyl trifluoride to generate trifluoromethyl ions and simultaneously generate TMSCl, its catalytic activation effect on trimethylsilyl trifluoride is poor, resulting in a low yield.

[0075] Examples 6 to 10

[0076] The operating steps of Examples 6 to 10 are the same as those of Example 1, with the only difference being: changing the solvent while keeping other operations unchanged.

[0077] The molar yields of the target product perfluoromethyl-2,3-dimethyl-2-pentene in Examples 6 to 10 are shown in Table 2.

[0078] Table 2 Molar yields of the target product in Examples 6 to 10

[0079] Serial number Solvent Molar yield of target product (%) Example 6 N,N-Dimethylformamide (DMF) 95.3% (2.86 mol) Example 7 N,N-Dimethylacetamide (DMAc) 94.7% (2.84 mol) Example 8 N-Methylpyrrolidone (NMP) 93.7% (2.81 mol) Example 9 Dimethyl sulfoxide (DMSO) 93.0% (2.79 mol) Example 10 <![CDATA[Acetonitrile (CH3CN)]]> 96.0% (2.88 mol)

[0080] As can be seen from Table 2, the target product can be obtained in a relatively high yield by using an aprotic solvent in this preparation method.

[0081] Comparative Example 3

[0082] The operating steps are the same as those of Example 1, with the only difference being: changing the solvent to absolute ethanol; the molar yield of the target product perfluoromethyl-2,3-dimethyl-2-pentene is 1.3% (0.04 mol).

[0083] In Comparative Example 3, absolute ethanol was used as the solvent, resulting in a low yield. This is because ethanol contains a hydroxyl group that can be protonated in solution and belongs to a polar protic solvent, which has a solvent effect that causes an adverse reaction with the initiator or substrate, leading to the inability of the substrate to continuously undergo trifluoromethylation reaction, thus resulting in a low yield.

[0084] Example 11

[0085] The operation is the same as that of Example 1, with the only difference being: the concentration of the initiator is 0.01 mol / L, and the molar yield of the target product perfluoromethyl-2,3-dimethyl-2-pentene is 96.0% (calculated based on the substrate perfluoromethyl-2-methyl-2-pentene).

[0086] Example 12

[0087] The operation is the same as that of Example 1, with the only difference being: the concentration of the initiator is 0.08 mol / L, and the molar yield of the target product perfluoromethyl-2,3-dimethyl-2-pentene is 97.0% (calculated based on the substrate perfluoromethyl-2-methyl-2-pentene).

[0088] Example 13

[0089] The operation is the same as that of Example 1, with the only difference being: the concentration of the initiator is 0.5 mol / L, and the molar yield of the target product perfluoromethyl-2,3-dimethyl-2-pentene is 96.7% (calculated based on the substrate perfluoromethyl-2-methyl-2-pentene).

[0090] Examples 14 to 22

[0091] The operating procedures of Examples 18 to 26 are the same as those of Example 1, except that: the reaction temperature is changed, and the molar yields of the target product perfluorinated 2,3-dimethyl-2-pentene are shown in Table 3.

[0092] Table 3 Molar yields of the target product in Examples 14 to 22

[0093] Serial number The first-stage microchannel reactor (°C) The second-stage microreactor (°C) Molar yield of target product (%) Example 14 15 10 96.33 (2.89 mol) Example 15 10 10 92.67 (2.85 mol) Example 16 30 10 97.33 (2.92 mol) Example 17 25 0 96.33 (2.89 mol) Example 18 25 5 97.33 (2.92 mol) Example 19 25 15 97.67 (2.93 mol) Example 20 25 20 97.00 (2.91 mol) Example 21 25 30 93.67 (2.81 mol) Example 22 40 10 96.67 (2.90 mol)

[0094] Comparative Examples 4 to 7

[0095] The operating procedures of Comparative Examples 4 to 7 are the same as those of Example 1, except that: the reaction temperature is changed, and the molar yields of the target product perfluorinated 2,3-dimethyl-2-pentene are shown in Table 4.

[0096] Table 4 Molar yields of the target product in Comparative Examples 4 to 7

[0097]

[0098]

[0099] It can be seen from Examples 14 to 22 and Comparative Examples 4 to 7 that the reaction temperature has a very significant effect on the product yield. The target product can be prepared in high yield within the range of 15 - 30 °C for the first-stage reaction temperature and 5 - 20 °C for the second-stage reaction temperature; in Comparative Example 4, the first-stage reaction temperature is too low, which causes the reaction of generating trifluoromethyl ions to proceed slowly and cannot enter the cyclic catalytic reaction in the second-stage reaction to further generate the target product, so the yield is low; although the first-stage reaction temperature is 25 °C, which is suitable for generating trifluoromethyl ions, the second-stage reaction temperature in Comparative Example 6 is too low, and the trifluoromethylation reaction rate is slow; in Comparative Example 7, the second-stage reaction temperature is too high, the trifluoromethylation reaction is violent, the by-products increase, the selectivity decreases, and the yields of the target products are all very low.

[0100] Examples 23 to 25

[0101] The operating procedures of Examples 23 to 25 are the same as those of Example 1, except that: the material flow rate is changed, thereby changing the reaction time, and the molar yields of the target product perfluorinated 2,3-dimethyl-2-pentene are shown in Table 5.

[0102] Table 5 Molar yields of the target product in Examples 23 to 25

[0103] Serial number The first-stage reaction time (s) The second-stage reaction time (s) Molar yield of target product (%) Example 23 42 191 97.33 (2.92 mol) Example 24 16 72 96.00 (2.88 mol) Example 25 8 36 90.67 (2.72 mol)

[0104] Comparative Example 8

[0105] The operation steps of Comparative Example 8 were the same as those of Example 1, except that: the material flow rate was changed, and the flow rates of pumps 1, 2, and 3 were 7.2, 108.0, and 111.0 mL / min, respectively, so as to change the reaction time, and the reaction times of the first and second stages were 5 s and 24 s, respectively.

[0106] The molar yield of the target product perfluoromethyl-2-pentene was 40.33% (1.21 mol).

[0107] From Examples 25 to 27 and Comparative Example 8, it can be seen that the residence time (i.e., reaction time) of the material in the microchannel reactor significantly affects the yield of the target product. In Comparative Example 8, the residence time was too short, the reaction was incomplete, resulting in a low substrate conversion rate and a significant decrease in the product yield.

Claims

1. A method for preparing perfluoro-2,3-dimethyl-2-pentene, characterized in that: The preparation method includes: in an aprotic solvent, trifluoromethyltrimethylsilane reacts with perfluoro-2-methyl-2-pentene under the action of an initiator to generate perfluoro-2,3-dimethyl-2-pentene, and the initiator is an initiator containing fluoride ions or carbonate ions.

2. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The initiator contains fluoride ions or carbonate ions, and the fluoride ions are selected from at least one of sodium fluoride, potassium fluoride, cesium fluoride, potassium bifluoride, and tetrabutylammonium fluoride, and the carbonate ions are selected from at least one of cesium carbonate and potassium carbonate.

3. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 2, characterized in that: The fluoride ions of the initiator are selected from at least one of tetrabutylammonium fluoride, potassium fluoride, and potassium bifluoride.

4. The method for preparing perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The aprotic solvent is selected from at least one of 1,3-dimethyl-2-imidazolidinone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

5. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The initiator is dissolved in the aprotic solvent, and the molar concentration of the initiator in the solution is 0.01 - 0.5 mol / mL.

6. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 5, characterized in that: The initiator is dissolved in the aprotic solvent, and the molar concentration of the initiator in the solution is 0.01 - 0.1 mol / mL.

7. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The molar ratio of the initiator to trifluoromethyltrimethylsilane is (0.1 - 0.3):1, and the molar ratio of trifluoromethyltrimethylsilane to the substrate perfluoro-2-methyl-2-pentene is (1.1 - 1.6):

1.

8. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The preparation method adopts a continuous flow microchannel process. This reaction includes a first-stage reaction temperature T1 and a second-stage reaction temperature T2, where T1 is 10 - 40 °C and T2 is -10 - 30 °C.

9. The preparation method of perfluoro-2,3-dimethyl-2-pentene according to claim 8, characterized in that: The preparation method adopts a continuous flow microchannel process. This reaction includes a first-stage reaction temperature T1 and a second-stage reaction temperature T2, where T1 is 15 - 30 °C and T2 is 5 - 20 °C.

10. The method for preparing perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The preparation method adopts a continuous flow microchannel process. It is characterized by segmentally controlling the reaction time. The residence time of the first reaction segment is 8 - 50 s, and the residence time of the second reaction segment is 30 s - 200 s.

11. The method for preparing perfluoro-2,3-dimethyl-2-pentene according to claim 1, characterized in that: The reactor is a liquid-liquid microreactor, and the reactor type is a microchannel reactor. It is characterized by a specific surface area ≥ 5000 m2 / m3, a microchannel diameter ≥ 0.1 mm, and a channel length ≥ 1000 mm.

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