Title of Invention

PROCESS FOR PRODUCING 2-CHLORO-3, 3, 3-TRIFLUOROPROPENE Technical Field

The present invention relates to a process for producing 2-chloro-3, 3, 3-trifluoropropene .

Background Art

2-Chloro-3, 3, 3-trifluoropropene (HCFO-1233xf) represented by the chemical formula: is a useful compound as an intermediate for producing various fluorocarbons, and also as a monomer component of various kinds of polymers. The possibility of using 2-chloro-3, 3, 3-trifluoropropene as a blowing agent or a propellant has also been suggested.

A known process for preparing HCFC-1233xf comprises reacting anhydrous hydrogen fluoride (HF) in a gas phase in the presence of a catalyst. For example, Patent Literature (PTL) 1 listed below discloses a process comprising fluorination of

1,1,2,3-tetrachloropropene (HCO-1230xa, CC1 ₂ =CC1CH ₂ C1) in a gas phase in the presence of a chromium-based catalyst. Patent

Literature 2 listed below also reports a process comprising fluorination of 1,1,2,3-tetrachloropropene in a gas phase in the presence of a chromium-based catalyst. Further, Patent Literature 3 teaches that 1,1,2,3-tetrachloropropene (HCO-1230xa) ,

1,1,1,2,3-pentachloropropane (HCC-240db) , 2,3,3,3- tetrachloropropene (HCC-1230xf) , etc. can be fluorinated using a stabilizer for minimizing catalyst deterioration.

However, the processes disclosed in the above

literatures suffer from various disadvantages. For example, further improvement in the yield of HCFO-1233xf is required, the use of a catalyst is costly, and many products are produced by the reaction in addition to the target product, i.e., HCFO-1233xf, resulting in unsatisfactory selectivity. Further, since catalytic activity tends to decrease as a reaction proceeds, many attempts, such as using a stabilizer for the purpose of minimizing catalyst deactivation, have been made.

Non-Patent literature (NPL) 1 teaches a process for producing HCFO-1233xf, comprising subjecting 1, 2-dichloro-3, 3, 3- trifluoropropane (HCFC-243db) to a dehydrochlorination reaction in an alkaline solution using an airtight container. However, this process is problematic because it takes a long time for the reaction to be completed, the yield is as low as about 50%, and the production efficiency is unsatisfactory.

Further, a method comprising subjecting 1,1,1,2,3- tetrachloropropane (HCC-240db) as a starting material to

dehydrochlorination in a solution containing an alcohol and an aqueous alkali metal hydroxide solution to produce 1,1,1,2- trichloropropene, and subjecting the produced 1,1,1,2- trichloropropene to fluorination using SbF ₃ , has also been reported (see Non-Patent literature 2) . However, in this process, the use of highly corrosive SbF ₃ as a fluorinating agent requires a specific reactor; in addition, because SbF ₃ is used in one equivalent per equivalent of HCFO-1233xf, a large amount of SbCl ₃ is generated as a by-product. Therefore, in order to recycle

SbCl ₃ as SbF ₃ , a fluorination treatment with hydrogen fluoride is required. Because of this, the operation becomes complicated, and thus is not appropriate for industrial production.

As described above, an economically suitable process for readily producing HCFO-1233xf at a high yield has not yet been accomplished at present.

Citation List

Patent Literature

PTL 1: WO 2007/079431 A2

PTL 2: WO 2008/054781 Al

PTL 3: WO 2009/015317 Al

Non Patent Literature

NPL 1: J.C.S., Haszeldine, R.N., 2495-2504 (1951)

NPL 2: J.C.S., Haszeldine, R.N., 3371-3378 (1953) Summary of Invention

Technical Problem

The present invention has been accomplished in view of the foregoing problems found in the prior art. A main object of the present invention is to provide a novel process that can produce 2-chloro-3, 3, 3-trifluoropropene (HCFO-1233xf) at a high yield under industrially advantageous conditions. Solution to Problem

The present inventors conducted extensive research to achieve the above object. As a result, they found that when a fluorine-containing alkane represented by a specific formula is used as a starting material and mixed with an aqueous solution containing an alkali metal hydroxide or an alkali earth metal hydroxide in a liquid phase in the presence of a catalyst to perform a dehydrohalogenation reaction, the reaction is allowed to proceed at a relatively low temperature, and the target 2- chloro-3, 3, 3-trifluoropropene (HCFO-1233xf) can be obtained at a very high yield. The present inventors found that the above- described process is greatly advantageous for industrial purposes. Thereby, the present invention was accomplished.

Specifically, the present invention provides the following process for producing 2-chloro-3, 3, 3-trifluoropropene.

1. A process for producing 2-chloro-3, 3, 3-trifluoropropene

represented by the chemical formula: CF ₃ CC1=CH ₂ , comprising:

mixing a fluorine-containing alkane, in a liquid state, represented by the formula: CF ₃ CHC1CH ₂ X, wherein X is halogen, with an aqueous solution containing at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides in the presence of a catalyst to perform a dehydrohalogenation reaction of the fluorine-containing alkane. 2. The process for producing 2-chloro-3, 3, 3-trifluoropropene according to Item 1, wherein the catalyst is at least one member selected from the group consisting of phase-transfer catalysts and aprotic solvents.

3. The process for producing 2-chloro-3, 3, 3-trifluoropropene according to Item 1 or 2, wherein the reaction is performed at a temperature ranging from 0°C to 30°C.

4. The process for producing 2-chloro-3, 3, 3-trifluoropropene according to any one of Item 1 to 3,

wherein the dehydrohalogenation reaction is continuously performed while the produced fluorine-containing alkene represented by the formula: CF ₃ CC1=CH ₂ is collected by distillation.

5. A process for producing 2-chloro-3, 3, 3-trifluoropropene, comprising the steps of :

(i) producing 2-chloro-3,.3, 3-trifluoropropene by the process according to any one of Items 1 to 4,

(ii) removing precipitates in a reaction solution obtained in step(i),

(iii) adding a fluorine-containing alkane represented by the formula: CF3CHCICH2X, wherein X is halogen, and at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides to the reaction solution, and

(iv) performing a dehydrohalogenation reaction of the fluorine-containing alkane by the process according to any of Items 1 to 4.

Hereinafter, the production process of the present invention is described in detail.

Starting Compound

According to the present invention, a fluorine- containing alkane represented by the formula: CF3CHCICH2X, wherein

X is halogen, is used as a starting material. This fluorine- containing alkane is a known compound that can be easily obtained.

In the above-mentioned formula, F, CI, Br, I, etc. can be

exemplified as the halogen.

Reaction Process

In the production process of the present invention, a fluorine-containing alkane represented by the above formula is used in a liquid state as a starting compound. The process comprises mixing this fluorine-containing alkane with an aqueous solution containing at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides to perform a dehydrohalogenation reaction of the starting compound by a liquid phase reaction in a two-phase reaction system.

In the production process of the present invention, potassium hydroxide, sodium hydroxide, cesium hydroxide, or the like can be used as the alkali metal hydroxide. As the alkali earth metal hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, strontium hydroxide, or the like can be used. The alkali metal hydroxides and alkali earth metal hydroxides mentioned above may be used alone, or in a combination of two. or more .

There is no particular limitation to the concentration of metal hydroxide in the aqueous solution containing at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides. Generally, aqueous solutions having a concentration of from about 5 wt% to saturation ca be used. In particular, when an aqueous solution having a concentration of from about 20 to about 50 wt% is used, the specific gravity of the aqueous solution will be close to that of a fluorine-containing alkane, which is used as a starting material. This achieves excellent dispersibility therebetween, allowing the reaction to efficiently proceed, and enabling a reduction in the amount of the below-mentioned catalyst used.

The amount of the aqueous solution containing a metal hydroxide may be adjusted so that the amount of the metal

component contained therein is about 1 to about 1.5 equivalents, per equivalent of a fluorine-containing alkane represented by the formula: CF ₃ CHC1CH ₂ X, used as a starting material. Specifically, when a hydroxide of an alkali metal, which is a monovalent metal, is used as the metal hydroxide, an aqueous solution may contain the alkali metal hydroxide in an amount of about 1 to about 1.5 mol, per 1 mol of a fluorine-containing alkane represented by the formula: CF ₃ CHC1CH ₂ X. When a hydroxide of an alkaline earth metal, which is a divalent metal, is used as the metal hydroxide, an aqueous solution may contain the alkali earth metal hydroxide in an amount of about 0.5 to 0.75 mol, per 1 mol of the fluorine- containing alkane represented by the formula: CF3CHCICH2X .

In the production process of the present invention, a fluorine-containing alkane represented by the formula: CF ₃ CHC1CH ₂ X is mixed with an aqueous solution containing at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides in the presence of a catalyst. This allows a dehydrohalogenation reaction of the fluorine-containing alkane to proceed at the interface between the fluorine-containing alkane phase and a water phase containing the metal hydroxide, thereby producing the target 2-chloro-3, 3, 3- trifluoropropene (HCFO-1233xf) .

The usable catalysts may be those that are active in a dehydrohalogenation reaction. In particular, at least one

catalyst selected from the group consisting of phase-transfer catalysts and aprotic polar solvents is preferably used. By performing the aforementioned dehydrohalogenation reaction in the presence of such a catalyst, the target 2-chloro-3, 3, 3- trifluoropropene (HCFO-1233xf) can be produced as a result of the liquid phase reaction, at a high yield in a shorter period of time and at a relatively low reaction temperature.

Examples of phase-transfer catalysts include, but are not particularly limited to, tetrabutylammonium bromide (TBAB) , trimethylbenzylammonium bromide, triethylbenzylammonium bromide, trioctylmethylammonium chloride (TOMAC) , and like quaternary ammonium salts; tetrabutylphosphonium chloride (TBPC) , and like phosphonium salts; 15-crown-5, 18-crown-6, and like crown ethers; etc.

There is no limitation to the aprotic polar solvents, as long as they have a polarity and no active protons . Examples thereof include tetrahydrofuran, 1, 2-dimethoxyethane, propylene carbonate, acetonitrile, dimethylformamide, dimethyl sulfoxide, bis (2-methoxyethyl) ether, 1,4-dioxane, diethyl ether, diisopropyl ether, and the like.

These catalysts may be used alone, or in a combination of two or more. Of these, trioctylmethylammonium chloride (TOMAC), which is a phase-transfer catalyst, is particularly preferable.

The amount of the catalyst is not particularly limited. It is preferable that a phase-transfer catalyst is used in an amount of about 0.3 to about 5 parts by weight, and that an aprotic polar solvent is used in an amount of about 10 to about 50 parts by weight, based on 100 parts by weight of a fluorine- containing alkane represented by the formula: CF ₃ CHC1CH ₂ X.

According to the production process of the present invention, by mixing an aqueous solution containing at least one metal hydroxide selected from the group consisting of alkali metal hydroxides and alkali earth metal hydroxides, a fluorine- containing alkane represented by the formula: CF3CHCICH2X, and a catalyst, a dehydrohalogenation reaction of the fluorine- containing alkane is allowed to proceed. These components are added in an arbitrary order. Further, there is no limitation to the stirring method; a method by which each component can be homogeneously mixed may be appropriately employed. The reaction can proceed by, for example, causing a sufficient mechanical stirring of an aqueous solution containing a metal hydroxide and a catalyst, and adding a fluorine-containing alkane represented by the formula: CF ₃ CHC1CH ₂ X dropwise to the resulting aqueous solution.

The reaction temperature may be adjusted to a

temperature range in which both the aqueous metal hydroxide solution and the fluorine-containing alkane can exist as a liquid, generally about 0°C to about 30 °C. According to the present invention, the target 2-chloro-3, 3, 3-trifluoropropene (HCFO- 1233xf) can be obtained at a high yield at the aforementioned relatively low reaction temperature.

In the production process of the present invention, in particular, it is preferable to use a reaction apparatus in which a distillation column is attached to a reactor for mixing an aqueous solution containing a metal hydroxide, a fluorine- containing alkane, and a catalyst. With this reaction apparatus, 2-chloro-3, 3, 3-trifluoropropene can be continuously produced by using the starting materials in liquid state, and by performing a dehydrohalogenation reaction at a temperature exceeding about 14 °C, which is a boiling point of target 2-chloro-3, 3, 3- trifluoropropene, for example, at 14°C or more and 30°C or less, and continuously isolating and collecting the produced 2-chloro- 3, 3, 3-trifluoropropene by distillation. In particular, it is preferable that this reaction be performed at a temperature of from about 1 °C to about 20 °C. An excessively high reaction temperature is not preferable because the starting materials are easily incorporated into the reaction product collected by

distillation. In contrast, an excessively low reaction

temperature is also not preferable because the reaction product is dissolved in the reaction solution, which allows the reaction to further proceed, producing a by-product, i.e., a propyne compound, which is easily incorporated into the reaction product collected by distillation.

In the above-mentioned method, 2-chloro-3, 3, 3- trifluoropropene can be continuously produced by appropriately adding to the reactor the fluorine-containing alkane and the metal oxide consumed during the reaction. Recycling of Reaction Solution

In the production process of the present invention, a metal halide is produced as a by-product, other than the target 2-chloro-3, 3, 3-trifluoropropene . Generally, a metal halide is low in solubility compared with the metal hydroxide used as a

starting material, and will thus be precipitated in a reaction solution. For example, the solubility of KOH (20°C) is 110 g/100 cc, whereas the solubility of KC1 is 34 g/100 cc.

In the production process of the present invention, the precipitate of a metal halide, such as the produced KC1, or the like, is separated by filtration from the reaction solution.

Thereafter, a fluorine-containing alkane and a metal hydroxide, which are used as starting materials, are added to this reaction solution to readjust the concentrations of these components.

Thereby, 2-chloro-3, 3, 3-trifluoropropene can be continuously produced. In this way, the catalyst contained in the reaction solution can be effectively used, and the amount of waste fluid can be greatly reduced. Further, the metal halide collected by filtration can also be better utilized.

Advantageous Effects of Invention

The production process of the present invention can be performed in a liquid phase at a relatively low temperature without using a catalyst that is difficult to handle, and can produce the target 2-chloro-3, 3, 3-trifluoropropene at a high yield.

For this reason, the method of the present invention is industrially advantageous as a production process of 2-chloro- 3,3, 3-trifluoropropene .

Description of Embodiments

Hereinafter, the present invention is described in more detail with reference to Examples.

Example 1

A 50 wt% aqueous potassium hydroxide solution (1,000 g) and Aliquat 336 (tradename, produced by Aldrich)

(trioctylmethylammonium chloride (TOMAC) ) (3.0 g) , which is a phase-transfer catalyst, were added to a 1-liter three-necked flask equipped with a thermometer for measuring the reactor temperature, a thermometer for measuring the temperature at the top of rectification column, a dropping funnel, an Oldershaw-type rectification column (five plates) , a rectification head, a cold finger trap using dry ice/acetone, and a receiver. The resulting mixture was cooled in a water bath to 10 °C. While stirring the cooled mixture with a magnetic stirrer, 1, 2-dichloro-3, 3, 3- trifluoropropane (HCFC-243db) (700 g, 4.2 mol) was added dropwise from a dropping funnel so that the temperature inside the reactor maintained 20 °C or lower.. When the temperature inside the reactor reached 14°C or higher, gas was generated. When the temperature at the top of the rectification column reached 13°C, the reflux ratio (return: distillate) was changed to 2 : 1 from the total reflux. The distillate was collected until the temperature at the top of the rectification column reached 15°C. Thereby, 530 g of the fraction containing the target 2-chloro-3, 3, 3- trifluoropropene (HCFO-1233xf) was obtained. The purity as measured by a gas chromatographic analysis was 99.2%; thus, the yield at this time was 97%.

Example 2

The same reaction was performed in the same manner as in Example 1, except that 220 g (1.32 mol) of 2-dichloro-3, 3, 3- trifluoropropane (HCFC-243db) , 95 g of 60 wt% aqueous sodium hydroxide solution, and 1.0 g of Aliquat 336 (produced by

Aldrich) were used. Thereby, 174 g of a fraction containing the target 2-chloro-3, 3, 3-trifluoropropene (HCFO-1233xf) was obtained. The purity as measured by a gas chromatographic analysis was

99.1%; thus, the yield at this time was 96%.

Example 3

The same reaction was performed in the same manner as in Example 1, except that 180 g (1.08 mol) of 2-dichloro-3, 3, 3- trifluoropropane (HCFC-243db) , 280 g of 50 wt% aqueous potassium hydroxide solution, and, in place of the phase-transfer catalyst, 30.0 g of dimethylacetamide, which is an aprotic polar solvent, were used. Thereby, 108 g of a fraction containing 2-chloro-

3, 3, 3-trifluoropropene (HCFO-1233xf) was obtained. The purity as measured by a gas chromatographic analysis was 99.0%; thus, the yield at this time was 89%. Example 4

The residue in the three-necked flask, obtained after the reaction of Example 1 was concentrated, and the precipitated KC1 was separated by filtration under reduced pressure. The amount of the filtrate at this time was 250 g, and Aliquat 336, which is a phase-transfer catalyst, remained in the filtrate. A 60 wt% aqueous KOH solution (750 g) was added to the resulting filtrate, and the resulting mixture was cooled in a water bath to 10°C, followed by a reaction as in Example 1 using 1, 2-dichloro- 3, 3, 3-trifluoropropane (HCFC-243db) (700 g, 4.2 mol). Thereby, 525 g of a fraction containing the target 2-chloro-3, 3, 3- trifluoropropene (HCFO-1233xf) was obtained. The purity as measured by a gas chromatographic analysis was 99.4%; thus, the yield at this time was 95.2%.