A preparation method of 2,3,3,3-tetrafluoropropylene

Abstract

The present invention relates to a preparation method of an organofluorine compound, and more particularly to a preparation method of 2,3,3,3-tetrafluoropropene, wherein the method is based on 2,3-dichloro-1,1,1-trifluoropropane as a raw material, and under the joint action of a Lewis acid catalyst and a fluorinating agent, 2-chloro-1,1,1,2-tetrafluoropropane is reacted to obtain 2,3,3,3-tetrafluoropropene, and finally the 2-chloro-1,1,1,2-tetrafluoropropene prepared is reacted with an alkali, and hydrogen chloride is removed to obtain 2,3,3,3-tetrafluoropropene. The method in this application has the advantages that reaction conditions are mild and selectivity is high, so that the preparation efficiency of 2,3,3,3-tetrafluoropropene can be significantly improved during the reaction. In addition, the separation and collection difficulty of product can also be effectively reduced by the method in the present invention, and the manufacturing cost of 2,3,3,3-tetrafluoropropene is reduced.

Description

Technical Field

[0001] The present invention relates to a method for preparing an organic fluorine compound, in particular to a method for preparing 2,3,3,3-tetrafluoropropylene. Background Art

[0002] 2,3,3,3-Tetrafluoropropene (1234yf) is a new refrigerant widely used in automotive cooling. Compared to traditional refrigerants, 2,3,3,3-Tetrafluoropropene offers numerous advantages, including environmental friendliness, energy efficiency, and safety. Compared to the traditional refrigerant R134a, 1234yf has a lower ozone depletion potential and global warming potential, thus meeting environmental standards. Furthermore, due to its superior thermal properties, 1234yf enables vehicles to achieve higher cooling efficiency and lower energy consumption. Consequently, several countries and regions have begun adopting 1234yf as a refrigerant for automotive air conditioning, while the traditional refrigerant R134a is facing a gradual phase-out.

[0003] Currently, the production of 2,3,3,3-tetrafluoropropene still has shortcomings: for example, it requires relatively high consumption of raw materials and energy, is prone to side reactions that reduce product purity and yield, and requires additives and auxiliary agents to improve the properties of the reaction process and increase yield. However, these additives and auxiliary agents reduce production costs and product purity, and increase the risk of environmental pollution.

[0004] For example, the patent with the announcement number CN101979364B discloses a method for preparing 2,3,3,3-tetrafluoropropene, which comprises the following steps: first, using 3,3,3-trifluoropropene CF3CH=CH2(I) as a raw material, subjecting it to an addition reaction with chlorine under ultraviolet light to prepare 3,3,3-trifluoro-1,2-dichloropropane CF3CHClCH2Cl(II), using halogenated alkane as a solvent, and the reaction temperature is -10℃-100℃; second, reacting the compound of formula (II) with an alkali metal hydroxide as a catalyst and a high molecular weight polyether or a macromolecular ether as a co-catalyst; at 0 The method comprises removing HCl at -150°C to generate CF3CCl=CH2(III). In the third step, compound (III) is reacted with HF to generate CF3CClFCH3(IV). The reaction is carried out using SnCl4 and TiCl4 fluorosulfonic acid as catalysts, an aprotic inhibitor, a reaction temperature of 5-100°C, and a pressure of 0.2-1.0 MPa. In the fourth step, compound (IV) is subjected to a de-HCl reaction in the presence of an alkali metal catalyst at a temperature of 0-100 degrees, a pressure of 0-0.5 MPa, and an organic amine halide as a phase transfer catalyst to generate FO-1234yf. In the first step of this method, side reactions are prone to occur during the addition of 2,3,3,3-trifluoropropene to chlorine, resulting in a low yield and selectivity of 2,3,3,3-trifluoro-1,2-dichloropropane, and thus a low overall yield of 2,3,3,3-tetrafluoropropene.

[0005] For example, patent publication number EP2546224B1 discloses a method for producing fluorinated olefins. Specifically, CCl2=CClCH2Cl is fluorinated using a mixture of Cr2O3 and FeCl3 / C as a catalyst to synthesize the compound CF3CCl=CH2. CF3CCl=CH2 is then converted to CF3CFClCH3 using SbCl5 as a catalyst, and finally selectively converted to 1234yf. However, this method requires high temperatures and a catalyst containing heavy metal chromium, resulting in a complex process that can easily lead to safety issues and poses significant environmental risks. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art methods for synthesizing 2,3,3,3-tetrafluoropropene, such as excessive side reactions, difficulty in preparing catalysts, significant environmental hazards, and low overall yield and selectivity. A new method for preparing 2,3,3,3-tetrafluoropropene is provided to overcome the above defects.

[0007] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions:

[0008] The present invention provides a method for preparing 2,3,3,3-tetrafluoropropene, comprising the following steps:

[0009] 2,3-dichloro-1,1,1-trifluoropropane is used as a raw material, and 2-chloro-1,1,1,2-tetrafluoropropane is obtained by reaction under the combined action of a Lewis acid catalyst and a fluorinating agent. Finally, the prepared 2-chloro-1,1,1,2-tetrafluoropropane is reacted with a base to remove hydrogen chloride to obtain 2,3,3,3-tetrafluoropropene.

[0010] In this application, 2-chloro-1,1,1,2-tetrafluoropropane (244bb) is first prepared in a liquid phase using 2,3-dichloro-1,1,1-trifluoropropane (243db) as a raw material. During this process, due to the combined action of a Lewis acid and a fluorinating agent, 2,3-dichloro-1,1,1-trifluoropropane (243db) undergoes rearrangement and fluorination, with both reactions occurring simultaneously. The presence of a Lewis acid catalyst causes 2,3-dichloro-1,1,1-trifluoropropane to undergo a rearrangement reaction to become 2,2-dichloro-1,1,1-trifluoropropane. 2,2-dichloro-1,1,1-trifluoropropane immediately undergoes halogen exchange fluorination with the fluorinating agent in situ, ultimately exchanging a chlorine atom at position 2 for a fluorine atom, thereby obtaining the key intermediate product 2-chloro-1,1,1,2-tetrafluoropropane (244bb). The relevant reaction process is shown in Formula (I) below:

[0011]

[0012] Formula (I).

[0013] 2,3-dichloro-1,1,1-trifluoropropane is typically used as the starting material. Because it has two chlorine atoms at the 2- and 3-carbon positions, fluorination preferentially replaces the chlorine at the 3-position, yielding 2-chloro-1,1,1,3-tetrafluoropropane. This chemical is a precursor for preparing 1234ze. For example, patents EP2634165 and WO2008 / 54781 disclose vapor-phase fluorination processes for 243db. The present invention employs a process in which 2,3-dichloro-1,1,1-trifluoropropane is first rearranged to 2,2-dichloro-1,1,1-trifluoropropane in the presence of a polar mixed solvent and a catalyst. This is followed by in-situ liquid-phase fluorination in a reactor to yield 2-chloro-1,1,1,2-tetrafluoropropane, thus avoiding the production of 2-chloro-1,1,1,3-tetrafluoropropane.

[0014] Regarding the rearrangement step of 2,3-dichloro-1,1,1-trifluoropropane, the applicant discovered that patent application CN113292392A already mentions a rearrangement reaction between saturated hydrochlorofluorocarbons and a method for producing fluorinated alcohols. Unlike the aforementioned patent, the present invention emphasizes that the saturated hydrochlorofluorocarbons undergo a fluorination reaction immediately after the rearrangement reaction to obtain a saturated hydrochlorofluorocarbon with a higher fluorine content, rather than producing a fluorinated alcohol.

[0015] Halogen exchange fluorination is a method of replacing other halogens with fluorine to produce fluorine compounds containing fluorine atoms. The existing halogen exchange fluorination methods usually involve exchanging halogen-containing compounds with inorganic halides such as potassium fluoride at high temperatures. However, conventional halogen exchange fluorination methods have the following two drawbacks: (1) the reaction temperature is high, resulting in uncontrollable reaction progress; (2) for polyhalogen compounds, all halogens may be exchanged during the halogen exchange process.

[0016] This application utilizes a liquid-phase halogen exchange fluorination process, where 2-chloro-1,1,1,2-tetrafluoropropane (244bb) is prepared by reacting an organic base-hydrogen fluoride complex with 2,2-dichloro-1,1,1-trifluoropropane. The applicant discovered that the properties of the solvent significantly influence the reaction conditions for halogen exchange fluorination. The applicant discovered that adding a certain amount of a nitrogen-containing compound as a cosolvent, which forms hydrogen bonds with hydrogen fluoride, can modulate the nucleophilicity of the fluoride ion. Therefore, by selecting nitrogen-containing heterocyclic compounds of varying basicity to form hydrogen bonds with hydrogen fluoride, the nucleophilicity of the fluoride ion can be controlled. The applicant discovered that the most preferred nitrogen-containing compounds are those that form strong hydrogen bonds with hydrogen fluoride and are sterically hindered organic bases. In the fluorination reaction, in an aprotic polar solvent and a nitrogen-containing compound cosolvent, the fluoride ion is "naked," resulting in a greater nucleophilicity, which increases the binding capacity of the nucleophile to the carbon atom. Fluoride ion and carbon are in the same period, with similar orbital sizes, good overlap, and large FC bond energy. Therefore, the nucleophilicity of fluoride ion is the greatest in the co-solvent, which enables the fluorination reaction to occur under mild process conditions, thereby significantly improving the selectivity of monofluorinated substitution products in the co-solvent.

[0017] Finally, in this application, during the preparation of 2,3,3,3-tetrafluoropropene (1234-yf) from 2-chloro-1,1,1,2-tetrafluoropropane (244bb), it was discovered that the final product, 2,3,3,3-tetrafluoropropene (1234-yf), undergoes a distinct phase transition at room temperature and pressure compared to the raw material, 2-chloro-1,1,1,2-tetrafluoropropane (244bb). For example, at room temperature and pressure, 2-chloro-1,1,1,2-tetrafluoropropane (244bb) is in the liquid phase, while the final product, 2,3,3,3-tetrafluoropropene (1234-yf), is in the gaseous phase. Therefore, after the preparation of 2,3,3,3-tetrafluoropropene (1234-yf), it can be separated from 2-chloro-1,1,1,2-tetrafluoropropane (244bb), thus preventing the introduction of impurities into the product. Therefore, the technical means of the present invention can effectively reduce the difficulty of collection and purification during the reaction process, which is beneficial to industrial production.

[0018] Therefore, in summary, the present invention, through a two-step reaction, can improve the production efficiency of 2,3,3,3-tetrafluoropropene (1234-yf) under milder reaction conditions. It also effectively reduces the difficulty of product separation and collection, and prevents the introduction of impurities into the product.

[0019] Preferably, the preparation process of 2-chloro-1,1,1,2-tetrafluoropropane is carried out in a mixed solvent of an aprotic polar solvent and a co-solvent.

[0020] Preferably, the co-solvent is a nitrogen-containing compound, and its addition amount is 5-20% of the mass of the aprotic solvent to form a mixed solvent.

[0021] Preferably, the co-solvent is any one of 1,3-dimethylpropyleneurea, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoramide, imidazole, quinoline, isoquinoline, and other substituted or unsubstituted nitrogen-containing five-membered ring compounds, substituted or unsubstituted nitrogen-containing six-membered ring compounds, or a combination of any two or more co-solvents.

[0022] Preferably, the Lewis acid catalyst is a metal halide and / or a metal oxide, wherein the halogen is chlorine or fluorine.

[0023] Preferably, the Lewis acid catalyst is any one or more of aluminum trichloride, ferric trichloride, tin trichloride, boron trifluoride, niobium pentachloride, iron oxide, and zinc oxide.

[0024] Preferably, the solvent used in the rearrangement and selective halogen exchange fluorination process in (S.1) is an aprotic polar solvent.

[0025] Further preferably, the aprotic polar solvent in the rearrangement process in (S.2) includes a mixture of any one or more of dimethyl sulfoxide, sulfolane, acetonitrile, N,N-dimethylformamide, nitrobenzene, N-methylpyrrolidone, acetic anhydride, and acetone.

[0026] Preferably, in the process of preparing 2-chloro-1,1,1,2-tetrafluoropropane, the reaction temperature is 30-150° C., and the reaction time is 12-72 hours.

[0027] Preferably, the organic base in the organic base-hydrogen fluoride complex includes any one of trimethylamine, triethylamine, diisopropylethylamine, diisopropylamine, dimethylisopropylamine, N,N-dimethylformamide, pyridine, piperidine, imidazole, N-methylimidazole, morpholine, pyrrolidine, and hexamethylphosphoric acid triamide.

[0028] Correspondingly, it is further preferred that the organic base-hydrogen fluoride complex is any one of trimethylamine-hydrogen fluoride complex, triethylamine-hydrogen fluoride complex, diisopropylethylamine-hydrogen fluoride complex, diisopropylamine-hydrogen fluoride complex, dimethylisopropylamine-hydrogen fluoride complex, N,N-dimethylformamide-hydrogen fluoride complex, pyridine-hydrogen fluoride complex, piperidine-hydrogen fluoride complex, imidazole-hydrogen fluoride complex, N-methylimidazole-hydrogen fluoride complex, morpholine-hydrogen fluoride complex, pyrrolidine-hydrogen fluoride complex, and hexamethylphosphoric triamide-hydrogen fluoride complex.

[0029] Preferably, the base in the process of removing hydrogen chloride includes any one of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide.

[0030] Preferably, the reaction temperature during the removal of hydrogen chloride is 35-90° C., and the product is introduced into a cold well, thereby condensing and liquefying 2,3,3,3-tetrafluoropropene, thereby facilitating the collection of 2,3,3,3-tetrafluoropropene.

[0031] Therefore, compared with the prior art, this application has the following beneficial effects:

[0032] The method of the present invention has the advantages of mild reaction conditions and high selectivity, thereby significantly improving the efficiency of preparing 2,3,3,3-tetrafluoropropene during the reaction process. In addition, the method of the present invention can effectively reduce the difficulty of separating and collecting the product and reduce the production cost of 2,3,3,3-tetrafluoropropene. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below generally represent only a portion of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0034] The 2,3-dichloro-1,1,1-trifluoropropane used in this example is a commercially available product. Some methods for preparing 2,3-dichloro-1,1,1-trifluoropropane are disclosed in the prior art, as shown below.

[0035] Preparation method 1 of raw material 2,3-dichloro-1,1,1-trifluoropropane:

[0036] It is prepared by synthesizing from cheap raw materials carbon tetrachloride (CCl4) and ethylene, that is, ethylene and carbon tetrachloride react to produce 1,1,1,4-tetrachloropropane, 1,1,1,4-tetrachloropropane reacts with HF to generate 3-chloro-1,1,1-trifluoropropane, 3-chloro-1,1,1-trifluoropropane removes HCl in the presence of a base (such as KOH) to obtain 3,3,3-trifluoropropene, and then Cl2 is added to obtain 2,3-dichloro-1,1,1-trifluoropropane.

[0037] Preparation method 2 of raw material 2,3-dichloro-1,1,1-trifluoropropane: Using 3,3,3-trifluoropropene as raw material: preheat 3,3,3-trifluoropropene and chlorine to 100-150°C respectively, mix them in a mixer and then enter a reactor loaded with a catalyst for reaction, wherein the molar ratio of 3,3,3-trifluoropropene to chlorine is 0.5:1-2:1, the reaction temperature is 100-150°C, and the reaction pressure is 0-1.0MPa.

[0038] It should be noted that the above-listed methods for preparing 2,3-dichloro-1,1,1-trifluoropropane are for reference only and are not intended to be the scope of protection required by the claims.

[0039] Example 1

[0040] (S.1) At room temperature, a mixture of 8.3 g of 2,3-dichloro-1,1,1-trifluoropropane, 50 ml of dimethyl sulfoxide, and 5 g of 1,3-dimethylpropyleneurea was injected into a reactor. Subsequently, 1 g of aluminum trichloride and 17 ml of triethylamine hydrogen fluoride complex (Et3N·3HF) were added. The reaction was stirred for 2 hours. The temperature was then raised to 90°C and the reaction was continued with stirring for 24 hours. After completion of the reaction, the reaction solution was poured into 500 ml of ice water and neutralized with concentrated aqueous ammonia. The organic phase was separated, dried over MgSO4, and purified by distillation. Gas chromatography confirmed the yield of 6.72 g of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) (yield 89.7%).

[0041] (S.2) Under nitrogen protection, add 50 ml of potassium tert-butoxide (6.8 g) in tetrahydrofuran to the reactor, cool the reactor to -5 degrees Celsius, and then add 2-chloro-1,1,1,2-tetrafluoropropane (7.5 g) to the reactor. Then, slowly heat the mixture to 65 degrees Celsius while stirring to react, producing a large amount of gas. The gas is introduced into a cold well with dry ice as the refrigerant. After stirring for 4 hours, the reaction is stopped and the product in the cold well is collected. Gas chromatography confirms that 5.49 g of 2,3,3,3-tetrafluoropropene (HFO-1234yf) is obtained (yield 96.3%).

[0042] Example 2

[0043] (S.1) At room temperature, a mixture of 8.3 g of 2,3-dichloro-1,1,1-trifluoropropane, 50 ml of dimethyl sulfoxide, and 2.5 g of 1,3-dimethyl-2-imidazolidinone was added to a nickel-iron alloy reactor. Subsequently, 1 g of aluminum chloride and 17 ml of Et3N·3HF were added. The reaction mixture was heated to 50°C with stirring for 5 hours, then to 80°C for another 12 hours. After completion of the reaction, the reaction mixture was poured into 500 ml of ice water and neutralized with concentrated aqueous ammonia. The organic phase was separated, dried over MgSO4, and purified by distillation. Gas chromatography confirmed the yield of 6.29 g of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) (yield 83.9%).

[0044] Step (S.2) is as described in Example 1.

[0045] Example 3

[0046] (S.1) At room temperature, add 1 g of aluminum chloride, 8.3 g of 2,3-dichloro-3,3,3-trifluoropropane, and 50 ml of dimethyl sulfoxide to a nickel-iron alloy reactor. Heat the mixture to 100°C with stirring and allow to react for 36 hours. The reactor temperature is then lowered to 20°C. Hexamethylphosphoramide (10 g) and Et₃N·3HF (17 ml) are then added to the reactor. Heat the mixture to 80°C with stirring and allow to react for 12 hours. After the reaction, pour the reaction mixture into 500 ml of ice water and neutralize it with concentrated ammonia. The organic phase is separated, dried over MgSO₄, and purified by distillation. Gas chromatography confirms the yield of 4.32 g of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) (yield 57.7%).

[0047] Step (S.2) is as described in Example 1.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is that the addition of 1,3-dimethylpropyleneurea in step (S.1) was omitted, and 2.06 g of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) was finally separated (yield 27.6%).

[0050] Comparative Example 2

[0051] (S.1) A mixture of 8.3 g of 2,3-dichloro-1,1,1-trifluoropropane (25 g) of 1,3-dimethylpropyleneurea (25 g) was added to a reaction vessel. Aluminum chloride (1 g) and Et₃N·3HF (17 ml) were then added. The mixture was heated to 80°C with stirring for 24 h. After completion, the reaction mixture was poured into 500 ml of ice water and neutralized with concentrated ammonia. The organic phase was separated, dried over MgSO₄, and purified by distillation. Gas chromatography confirmed the yield of 4.79 g of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) (yield 63.9%).

[0052] As shown in Examples 1 to 3, the preparation method of the present invention can produce 2,3,3,3-tetrafluoropropene from 3,3,3-trifluoropropene under relatively mild reaction conditions. Compared to the prior art, the method of the present invention has the advantages of mild reaction conditions, high selectivity, and low cost of reaction raw materials. This significantly improves the production efficiency of 2,3,3,3-tetrafluoropropene during the reaction process, effectively reduces the difficulty of product separation and collection, and reduces the production cost of 2,3,3,3-tetrafluoropropene.

[0053] Comparing Example 1 with Comparative Example 1, we can see that in Comparative Example 1, the absence of a nitrogen-containing heterocyclic compound co-solvent in step (S.1) significantly weakened the nucleophilicity of the fluoride ion in the reaction system, leading to a significant decrease in the yield of 2-chloro-1,1,1,2-tetrafluoropropane. However, Comparative Example 2 shows that excessive addition of a nitrogen-containing heterocyclic compound co-solvent results in excessive nucleophilicity of the fluoride ion, leading to a significant increase in difluorosubstituted products and a significant decrease in the yield of the final target product, 2-chloro-1,1,1,2-tetrafluoropropane.

[0054] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for preparing 2,3,3,3-tetrafluoropropene, characterized in that: The following steps are involved: The method uses 2,3-dichloro-1,1,1-trifluoropropane as a raw material, carries out a liquid-phase reaction in a mixed solvent of an aprotic polar solvent and a nitrogen-containing compound as a co-solvent under the joint action of a Lewis acid catalyst and a triethylamine-hydrogen fluoride complex as a fluorinating agent, wherein the co-solvent is 1,3-dimethylpropyleneurea or hexamethylphosphoramide, to obtain 2-chloro-1,1,1,2-tetrafluoropropane. Finally, the prepared 2-chloro-1,1,1,2-tetrafluoropropane is reacted with a base to remove hydrogen chloride to obtain 2,3,3,3-tetrafluoropropene.

2. The method for preparing 2,3,3,3-tetrafluoropropene according to claim 1, wherein: The Lewis acid catalyst is a metal halide and / or a metal oxide, wherein the halogen is chlorine or fluorine.

3. The method for preparing 2,3,3,3-tetrafluoropropene according to claim 2, wherein: The Lewis acid catalyst is any one or more of aluminum trichloride, ferric trichloride, tin tetrachloride, boron trifluoride, niobium pentachloride, iron oxide, and zinc oxide.

4. The method for preparing 2,3,3,3-tetrafluoropropene according to claim 1, wherein: In the process of preparing 2-chloro-1,1,1,2-tetrafluoropropane, the reaction temperature is 30~150°C and the reaction time is 12~72h.

5. The method for preparing 2,3,3,3-tetrafluoropropene according to claim 1, wherein: The amount of the co-solvent added is 5-20% of the mass of the aprotic solvent to form a mixed solvent.

6. The method for preparing 2,3,3,3-tetrafluoropropene according to claim 1, wherein: The aprotic polar solvent includes a mixture of any one or more of dimethyl sulfoxide, sulfolane, acetonitrile, N,N-dimethylformamide, nitrobenzene, N-methylpyrrolidone, acetic anhydride, and acetone.

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