JP5152521B2 - Method for dehydrohalogenating halogenated compounds - Google Patents

Description

  The present invention relates to a novel dehydrohalogenation method of a halogenated compound, and more particularly, to a method of dehydrohalogenating a dihydrohalogenated alkane compound and / or a monohydrohalogenated alkene compound to obtain a perfluoroalkyne or fluoroalkene. .

Conventionally, a method of obtaining an alkene compound or an alkyne compound by causing a dehalogenation reaction by reacting a hydrogenated halogenated hydrocarbon having a hydrogen atom and a halogen atom on adjacent carbon atoms with a basic compound is known. It has been.
For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-320874), a dihydrohalogenoalkane compound and / or a monohydrohalogenoalkene compound and a metal fluoride are brought into contact with each other at a temperature of 500 ° C. or higher in a gas-phase flow system. Thus, a method has been proposed in which a dehalogenation reaction is advanced to obtain a perfluoroalkyne compound. Here, the metal fluoride is supported on a carrier, and the dehalogenation reaction is allowed to proceed by circulating the vaporized hydrohalogenoalkane compound and / or monohydrohalogenoalkene compound in a reaction tube filled with the metal fluoride. Yes.
In Patent Document 2 (Japanese Patent Publication No. 2005-504097), a hydrogenated alkane having a hydrogen atom and a halogen atom on adjacent carbon atoms is contacted with an alkali metal hydroxide in the presence of a phase transfer catalyst. Thus, a method has been proposed in which the dehalogenation reaction proceeds to obtain a halogenated alkene in good yield. Since this reaction proceeds in the presence of a phase transfer catalyst, it is carried out in a liquid state under high pressure.
In Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-146717), a dehydrohalogenation reaction is advanced by bringing a dihydrofluoroalkane compound and / or a monohydrofluoroalkene compound into contact with a basic compound, and a perfluoroalkyne compound is obtained. The method of obtaining is proposed. Specifically, a method has been proposed in which a basic compound is used as a solid, a product is obtained by solid-liquid reaction, and then the product is isolated by distillation of the liquid part.
Furthermore, in patent document 4 (Unexamined-Japanese-Patent No. 2004-292329), the dehalogenate is produced | generated by the gas-solid reaction which filled the reaction tube with the basic compound and the reaction similar to patent document 3.

JP 2007-320874 A JP 2005-504097 gazette Japanese Patent Laid-Open No. 2003-146917 JP 2004-292329 A

  An object of the present invention is to provide an industrially advantageous dehydrohalogenation method that does not require a high temperature or a catalyst, has a high recovery rate, and is industrially advantageous.

As a result of examination of the related art by the present inventors, it has been confirmed that each has a problem. In the method of Patent Document 1, a dihydrohalogenoalkane compound and / or a monohydrohalogenoalkene compound is reacted in a vaporized state, so that a high temperature condition of 500 ° C. or higher is required. In order to implement such high temperature conditions safely industrially, special equipment is required, which is not suitable for mass production. The phase transfer catalyst suitably used in Patent Document 2 is expensive, and in order to reuse it, there is a problem that a step of recovering from the reaction system is required. When the method of Patent Document 3 was actually carried out at an industrial level, the recovery rate of the raw material after the reaction was low, and there was a problem of productivity. The method of Patent Document 4 has a problem that raw materials and intermediates adhere to the solid surface, resulting in a decrease in reactivity.
In order to solve the above-mentioned problems, the present inventors have conducted extensive research on the dehydrohalogenation method. As a result, the gasified halogenated compound is bubbled into the basic compound solution (bubble flow injection). Thus, when they are brought into contact with each other, it has been found that the dehydrohalogenation reaction proceeds efficiently, and the present invention has been completed based on this finding. According to this method, an alkene or alkyne can be obtained with a high recovery rate and yield, and is particularly suitable for a method for producing perfluoroalkyne or fluoroalkene.

Thus, according to the present invention, a halogenated compound represented by the following formula is gasified and bubbled into a solution of the basic compound, thereby bringing the halogenated compound into contact with the basic compound. A method for hydrogenation is provided.
R ¹ —CHX—CHY—R ² (1)
R ³ —CH═CX—R ⁴ (2)
(In Formula (1), R ¹ and R ² are each independently a C 1-6 perfluoroalkyl group, and R ¹ and R ² may combine to form a ring. X And Y are each independently one halogen atom selected from the group consisting of F, Cl, Br and I.
In Formula (2), R ³ and R ⁴ are each independently a C 1-6 perfluoroalkyl group, and R ³ and R ³ may be bonded to form a ring. X is one halogen atom selected from the group consisting of F, Cl, Br and I. )
Here, the equivalent of the basic compound is preferably 2 to 15 equivalents relative to the number of moles of the halogenated compound to be reacted. The concentration of the basic compound in the basic compound solution is preferably 50 to 80% by weight. It is preferable to use an alkali metal hydroxide as the basic compound.
In Formula (1), R ¹ is preferably a perfluoromethyl group, and R ² is preferably a perfluoroethyl group. It is preferable that either R ³ or R ^{4 in} the formula (2) is a perfluoromethyl group and the other is a perfluoroethyl group.
Furthermore, the product obtained by dehydrohalogenating a halogenated compound is preferably perfluoroalkyne. It is preferable that the perfluoroalkyne compound is perfluoro-2-pentyne.
In the above-described method for dehydrohalogenating a halogenated compound, it is preferable to separate a dehydrohalogenated product from an unreacted halogenated compound and react the unreacted halogenated compound again.

The present invention relates to a method for dehydrohalogenating a halogenated compound, wherein the gasified halogenated compound is brought into contact with the basic compound by bubbling into a solution of the basic compound.
As a halogenated compound suitable for dehydrohalogenation by this method, a dihydrohalogenated alkane compound and / or a monohydrohalogenated alkene compound can be used.

The dihydrohalogenated alkane compound is not particularly limited as long as it becomes a gas under conditions such as normal temperature, high temperature, and pressure, but its boiling point is 25 at normal pressure because of easy handling and easy vaporization. The thing of -100 degreeC is preferable, and the compound shown by the said Formula (1) is especially preferable. Among these, it is preferable that R ¹ in the formula (1) is a perfluoromethyl group and R ² is a perfluoroethyl group. At this time, X and Y may be any of F, Cl, Br, and I, but F is preferable because it has a low boiling point and is easily vaporized.
Specific examples of suitable dihydrohalogenated alkane compounds include 1,1,1,2,3,4,4,4-octafluorobutane, 1,1,1,2,2,3,4,5,5. , 5-decafluoropentane, 1,1,1,2,3,4,4,5,5,6,6,6-tridecafluorohexane.

The monohydrohalogenated alkene compound is not particularly limited as long as it becomes a gas under conditions of room temperature, high temperature, and pressure, but the boiling point is normal temperature and normal pressure because of ease of handling and ease of vaporization. And those of 25 to 100 ° C. are preferred, and the compound represented by the formula (2) is preferred. The compound represented by the formula (2) can be used in either cis form or trans form. Also, a cis-type or trans-type mixture may be used. Among these, it is preferable that either R ³ or R ^{4 in} the formula (2) is a perfluoromethyl group and the other is a perfluoroethyl group. At this time, X may be any of F, Cl, Br, and I, but F is preferred because it has a low boiling point and is easily vaporized.
Specific examples of suitable monohydrohalogenated alkene compounds include 1,1,1,2,4,4,4-heptafluoro-2-butene, 1,1,1,2,4,4,5,5. , 5-Nonafluoro-2-pentene, 1,1,1,3,4,4,5,5,5-Nonafluoro-2-pentene, 1,1,1,2,4,4,5,5,6 , 6,6-dodecafluoro-2-hexene, 1,1,1,3,4,4,5,5,6,6,6-dodecafluoro-2-hexene, 1,1,1,2,2 3,5,5,6,6,6-dodecafluoro-3-hexene.

  Although the basic compound used in the present invention is not particularly limited, for example, alkali metal such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide Or alkaline earth metal hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, bicarbonate Carbonates of alkali metals or alkaline earth metals such as barium;

Organic alkali metal compounds such as methyl lithium, ethyl lithium, n-butyl lithium, s-butyl lithium, t-butyl lithium, phenyl lithium, lithium diisopropylamide; dimethyl magnesium, diethyl magnesium, methyl magnesium chloride, methyl magnesium bromide, ethyl magnesium Organic alkaline earth metal compounds such as bromide and phenylmagnesium bromide;

Alkoxide compounds such as sodium methoxide, sodium ethoxide, sodium propoxide, potassium t-butoxide; hydride compounds such as sodium hydride, potassium hydride, calcium hydride, lithium aluminum hydride, sodium borohydride; tetramethylammonium And quaternary ammonium hydroxides such as hydroxide and tetrabutylammonium hydroxide; ammonia; and the like.

Among these basic compounds, inorganic base compounds such as alkali metal hydroxides and alkaline earth metal hydroxides are preferable, and as described later, the solubility in water, which is a suitable solvent, is good, and precipitation during the reaction Alkali metal hydroxides with no fear are more preferable. Potassium hydroxide, rubidium hydroxide, and cesium hydroxide are more preferable, and potassium hydroxide is most preferable.
The basic compounds may be used alone or in combination of two or more.

  As the solvent for dissolving the basic compound, it is preferable to select a raw material halogenated compound and a solvent in which the product does not dissolve, and alcohol compounds such as methanol, ethanol, propanol and t-butanol; glycols such as polyethylene glycol and diglyme Compounds; Amide compounds such as dimethylformamide and N-methylpyrrolidone; Sulfoxide compounds such as dimethyl sulfoxide; Ether compounds such as tetrahydrofuran; Water and the like can be used. It is particularly preferred to use

  The amount of the basic compound used is 2 to 15 equivalents, preferably 4 to 12 equivalents, more preferably 6 to 10 equivalents, relative to the number of moles of the halogenated compound. If the amount of the basic compound used is too small, the purity of the product tends to decrease. On the other hand, if the amount is too large, the amount of waste increases, which is not preferable.

  Although the concentration of the basic compound solution is not particularly limited, it is preferably 50 to 85% by weight because it is difficult to produce a by-product, and particularly preferably 55 to 80% by weight from the viewpoint of recovery.

  The upper limit of the reaction temperature is the boiling point of the basic compound solution, and is preferably 10 ° C. lower than the boiling point. The lower limit of the reaction temperature is the freezing point of the solution of the basic compound, but it is preferable to set the boiling point of the raw material compound as the lower limit from the viewpoint of unreacted raw material and product recovery efficiency.

  In the present invention, the method of gasifying the raw material dihydrohalogenated alkane compound and / or monohydrohalogenated alkene compound is not particularly limited, and a known method may be used. As a suitable method, a method of introducing a raw material into a heat exchanger and gasifying it can be mentioned.

There is no particular limitation on the method of bubbling the gasified halogenated compound into the basic compound solution, but there is usually a method in which the gasified halogenated compound is pressurized and the gas is circulated through the solution through the nozzle. Adopted.
The nozzle may have a structure in which a single bubble emerges, or may have a structure in which a plurality of bubbles are generated using a known technique such as a shower nozzle. Further, the number of nozzles attached to the reactor is not particularly limited.
The size of gas bubbles emerging from the nozzle can be controlled by the diameter of the nozzle. If the size of the bubbles is too large, the progress of the dehydrohalogenation reaction will be slow (especially, the production efficiency of alkyne having a carbon-carbon triple bond will be reduced). It tends to be easier.
The gas supply amount can be controlled by the degree of pressurization to the gasified halogenated compound. If the supply amount is too large, the progress of the dehydrohalogenation reaction will be slow (especially, the production efficiency of alkyne having a carbon-carbon triple bond will be reduced). It is in.
The linear velocity of the gas to be blown can be controlled by the nozzle diameter and the gas supply amount. If the linear velocity is too high, the progress of the dehydrohalogenation reaction will be slow (especially, the production efficiency of the alkyne having a carbon-carbon triple bond will be reduced). It is in.

For this reaction, a known method such as a batch method, a semi-batch method, or a continuous method can be used. A semibatch system is preferred in which a basic compound is charged into a reactor and the product is recovered while continuously supplying raw materials.
In the present invention, the reaction apparatus is not particularly limited, and those which are usually used industrially may be adopted. Preferably, a stainless steel reactor is used.
From the viewpoint of reaction efficiency, it is preferable to stir the solution while bubbling the gasified halogenated compound into the basic compound solution using a reactor equipped with a stirring blade, and the rotation speed of the stirring blade Is usually 0.01 × G to 3 × G, preferably 0.1 × G to 2 × G.

In the present invention, when an alkyne is obtained as a dehydrohalogenated product, any compound of the formula (1) and the formula (2) may be used as a raw material.
When only the alkane of the formula (1) is used as the raw material, the unreacted raw material alkane and the alkene as the reaction intermediate are recovered together with the product alkyne. When a mixture of the alkane of the formula (1) and the alkene of the formula (2) is used as a raw material, the unreacted raw material alkane and alkene are recovered together with the product alkyne. Moreover, when only the alkene of said Formula (2) is used as a raw material, alkyne and unreacted alkene are collect | recovered. These unreacted raw materials and reaction intermediates are preferably separated from the product alkyne and used again for the reaction.
The method for separating the alkyne from the unreacted raw material and the reaction intermediate is not particularly limited, but it is convenient and preferable to separate the alkyne by distillation.

The dehydrohalogenation method of the present invention is suitable for obtaining a fluoroalkene compound.
Examples of the fluoroalkene compound include 1,1,1,2,4,4,4-heptafluoro-2-butene, 1,1,1,2,2,4,5,5,5-nonafluoro-2. Pentene, 1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene, 1,1,1,2,4,4,5,5,6,6,6-dodeca Fluoro-2-hexene, 1,1,1,3,4,4,5,5,6,6,6-dodecafluoro-2-hexene, 1,1,1,2,2,3,5,5 , 6,6,6-dodecafluoro-2-hexene and the like. Among these, 1,1,1,2,2,4,5,5,5-nonafluoro-2-pentene and 1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene Is more preferably produced.

The dehydrohalogenation method of the present invention is suitable for obtaining a perfluoroalkyne compound.
Examples of the perfluoroalkyne compound include perfluoro-2-butyne, perfluoro-2-pentyne, perfluoro-2-hexyne, perfluoro-3-hexyne, perfluoro-2-heptin, and perfluoro-3- Examples include heptine. Among these, perfluoro-2-pentyne is more preferably produced.

In the present invention, perfluoroalkyne and fluoroalkene can be selectively obtained by controlling the solution temperature of the basic compound. Specifically, when the solution temperature is high, perfluoroalkyne tends to be obtained, and conversely, when the solution temperature is low, fluoroalkene tends to be obtained.
Perfluoroalkynes and fluoroalkenes are useful as fluorine-containing monomers, raw materials for producing pharmaceuticals and agricultural chemicals, etching agents, refrigerants, and the like. In particular, perfluoro-2-pentyne has a boiling point of 5 ° C., and is useful as a raw material for producing fluorine-containing polymers, medical and agricultural chemicals, and an etching agent.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. The analysis of the reaction product was performed by gas chromatography (GC) method (apparatus: HP6890 manufactured by Hewlett-Packard Co., column: Ultra ALLOY + -1 (s) manufactured by Frontier LAB).

Example 1
An autoclave (330 ml) equipped with a paddle blade and an inner nozzle having an inner diameter of 1 mm was charged with 276 g (4.12 mol) of commercially available potassium hydroxide pellets (KOH 85 wt%, water 15 wt%) and water 26.8 g, The autoclave was heated to 150 ° C. to prepare a 77.5 wt% potassium hydroxide aqueous solution. When potassium hydroxide is dissolved, the tip of the inner nozzle is immersed in the solution by 33 mm from the liquid surface. Using a liquid feed pump, 1,1,1,2,3,4,4,5,5,5-decafluoropentane is supplied to a heat exchanger heated to 100 ° C. and vaporized at 1.5 g / min. This was supplied to an autoclave using an inner nozzle and bubbled. During the reaction, the aqueous potassium hydroxide solution in the autoclave was continuously stirred at 0.25 × G. 1,1,1,2,3,4,4,5,5,5-decafluoropentane (175.6 g, 0.70 mol) was continuously fed, and the reaction mixture distilled from the autoclave was dried ice- Collected with a methanol trap. The yield of the collected product was 155 g, and the recovery rate was 95.6 mol% (raw material basis).
When this was analyzed by GC, perfluoro-2-pentyne (alkyne), 1,1,1,2,4,4,5,5,5-nonafluoro-2-pentene (alkene A), 1,1,1, 3,4,4,5,5,5-nonafluoro-2-pentene (alkene B) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (raw material) Included. The yield of the alkyne based on the raw material charged was 23.9 mol%, and the total yield of the reaction intermediates A and B was 28.6 mol%.

(Example 2)
A 60 wt% aqueous potassium hydroxide solution obtained from 175 g (2.64 mol) of potassium hydroxide pellets (KOH 85 wt%, water 15 wt%) and 73 g of water was used, and the autoclave was brought to 110 ° C., The reaction mixture was collected in the same manner as in Example 1 except that the amount of 1,2,3,4,4,5,5,5-decafluoropentane supplied was 111 g (0.44 mol). The yield of the collected product was 105 g, and the recovery rate was 100 mol% (raw material basis). The yield of the alkyne based on the raw material charged was 0.6 mol%, and the total yield of alkene A and alkene B was 57.8 mol%.

(Example 3)
Stirring of the aqueous potassium hydroxide solution in the autoclave was carried out using 85% aqueous potassium hydroxide solution obtained by melting 157 g (6.01 mol) of potassium hydroxide pellets (KOH 85% by weight, water 15% by weight) at 150 ° C. The reaction mixture was collected in the same manner as in Example 1 except that the speed was 1.57 × G. The yield of the collected product was 151 g, and the recovery rate was 86.6 mol% (raw material basis). The yield of the alkyne based on the raw material charged was 26.4 mol%, and the total yield of alkene A and alkene B was 46.1 mol%.

(Comparative Example 1)
Without vaporizing 1,1,1,2,3,4,4,5,5,5-decafluoropentane (175.6 g, 0.70 mol) at 1.5 g / min using a liquid feed pump The reaction mixture distilled from the autoclave was collected by a dry ice-methanol trap in the same manner as in Example 1 except that it was continuously supplied to the autoclave. The yield of the collected product was 168 g, and the recovery rate was 97.9 mol% (based on raw materials). The yield of the alkyne based on the raw material charged was 1.1 mol%, and the total yield of alkene A and alkene B was 21.2 mol%.

(Comparative Example 2)
A commercial blend of potassium hydroxide pellets (85% by weight of KOH, 15% by weight of water) 157 g (6.01 moles) was charged in an autoclave (100 ml) equipped with a Max blend blade and a horizontal condenser, and melted at 150 ° C. 1,1,1,2,3,4,4,5,5,5-decafluoropentane (0) at a rate of 1.5 g / min. 4 mol) was added dropwise. During the reaction, the aqueous potassium hydroxide solution in the autoclave was continuously stirred at 1.75 × G. The temperature of the refrigerant flowing through the condenser was set to -11 ° C. A part of the reaction mixture flowing out from the autoclave was liquefied with a condenser and returned to the autoclave, and the reaction was carried out while extracting a part from the system. The reaction mixture extracted out of the system was collected with a dry ice-methanol trap. The yield of the collected product was 66 g, and the recovery rate was 77.4 mol% (raw material basis), which was a low recovery rate. The yield of the alkyne based on the raw material charged was 30.5 mol%, and the total yield of alkene A and alkene B was 26.6 mol%.

Example 4
Commercially available potassium hydroxide pellets (KOH 85 wt%, water 15 wt%) 8.19 kg (124.3 mol) in a SUS reactor (15 L) equipped with a Max blend blade and an inner nozzle with an inner diameter of 7.5 mm 828.4 g of water was charged, and the reactor was heated to 150 ° C. to prepare a 77.5 wt% aqueous potassium hydroxide solution. When potassium hydroxide is dissolved, the tip of the inner nozzle is immersed in the solution by 56 mm from the liquid surface. 1,1,1,2,2,4,5,5,5-nonafluoro-2-pentene and 1,1,1,3,4,4,5 at 29.5 g / min using a feed pump , 5,5-nonafluoro-2-pentene was supplied to a heat exchanger heated to 100 ° C. and vaporized. This was supplied to the reactor using an inner nozzle and bubbled. During the reaction, the aqueous potassium hydroxide solution in the reactor was continuously stirred at 0.41 × G. 1,1,1,2,2,4,5,5,5-nonafluoro-2-pentene and 1 of 1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene 4.8 kg (20.7 mol) of a 1: mixture was continuously fed, and the reaction mixture distilled from the reactor was collected by a dry ice-methanol trap. The yield of the collected product was 4.3 kg, and the recovery rate was 92.0 mol% (raw material basis).
When this was analyzed by GC, perfluoro-2-pentyne (alkyne), 1,1,1,2,4,4,5,5,5-nonafluoro-2-pentene (raw material), 1,1,1,3 4,4,5,5,5-nonafluoro-2-pentene (raw material). The yield of the alkyne based on the raw material charged was 27.6 mol%.

As a result of bubbling the raw material in an aqueous potassium hydroxide solution having a concentration of 77.5% by weight in Example 1, alkyne was obtained in a yield of 23.9 mol%. The recovery rate was as high as 95.6 mol%. Since the fluorinated unreacted raw materials and reaction intermediates can be used again for the reaction, a high recovery rate is an advantage. In Example 2, when the reaction temperature was changed to 110 ° C. and the potassium hydroxide concentration was changed to 60% by weight, the yield of alkyne decreased to 0.6%, but the total amount of alkene A and alkene B was 57.8 mol. The yield was as high as%. This result suggests that the alkene can be selectively obtained by changing the reaction temperature and the base concentration to suppress the formation of alkyne. In Example 3, when the stirring speed of the potassium hydroxide aqueous solution was increased, the production of alkene tended to increase, but there was no significant difference in the yield of alkene and alkyne.
When the raw material was dropped in the liquid and reacted, the yield of alkyne was as low as 1.1 mol% (Comparative Example 1), and the overall recovery of the alkyne was as high as 30.5 mol%. The rate was as low as 77.4 mol% (Comparative Example 2).
As a result of reaction using alkene as a raw material in Example 4, alkyne was obtained in a yield of 27.6 mol%. The recovery rate at this time was as high as 92.0 mol%.

Claims (9)

A method of dehydrohalogenating a halogenated compound, characterized in that a halogenated compound represented by the following formula is gasified and bubbled into a solution of the basic compound to contact with the basic compound.
R ¹ —CHX—CHY—R ² (1)
R ³ —CH═CX—R ⁴ (2)
(In Formula (1), R ¹ and R ² are each independently a C 1-6 perfluoroalkyl group, and R ¹ and R ² may combine to form a ring. X And Y are each independently one halogen atom selected from the group consisting of F, Cl, Br and I.
In formula (2), R ³ and R ⁴ are each independently a C 1-6 perfluoroalkyl group, and R ³ and R ⁴ may be bonded to form a ring. X is one halogen atom selected from the group consisting of F, Cl, Br and I. ) The process according to claim 1, wherein the equivalent amount of the basic compound is 2 to 15 equivalents relative to the number of moles of the halogenated compound to be reacted. The method according to claim 1 or 2, wherein the concentration of the basic compound in the basic compound solution is 50 to 85% by weight. The method according to claim 1, wherein an alkali metal hydroxide is used as the basic compound. The method according to claim 1, wherein R ^{1 in the} formula (1) is a perfluoromethyl group and R ² is a perfluoroethyl group. The method according to claim 1, wherein either R ³ or R ^{4 in} the formula (2) is a perfluoromethyl group, and the other is a perfluoroethyl group. The method according to any one of claims 1 to 6, wherein the product obtained by dehydrohalogenating the halogenated compound is perfluoroalkyne. The method according to claim 7, wherein the perfluoroalkyne compound is perfluoro-2-pentyne. 2. The method according to claim 1, wherein the dehydrohalogenated product and the unreacted halogenated compound are separated, and the unreacted halogenated compound is reacted again.