WO2012073976A1 - Aqueous solution of piperazine-n, n'-bis-carbodithioate, and production method for same - Google Patents

Abstract

Provided is an industrial production method for increasing the ratio of piperazine-N, N'-bis-carbodithioate which has excellent heavy metal treatment ability, when producing a piperazine carbodithioate useful as a heavy metal treatment agent and without requiring distilling off of carbon disulfide by inert gas. Specifically provided is a method for producing an aqueous solution of piperazine-N, N'-bis-carbodithioate characterized by the presence of a hydrophobic solvent during reaction, in a method for producing piperazine carbodithioate by mixing piperazine, at least the reaction equivalent of carbon disulfide relative to piperazine, and an alkali metal hydroxide, and reacting same.

Description

Piperazine-N, N'-biscarbodithioate aqueous solution and method for producing the same

The present invention relates to an aqueous piperazine carbodithioate aqueous solution useful as a heavy metal treating agent and a method for producing the same, and more particularly, an aqueous solution of piperazine-N, N′-biscarbodithioate not containing piperazine-N-carbodithioate and The manufacturing method is provided.

環境 Environmental problems, especially environmental pollution problems associated with waste disposal, are common issues not only in Japan but around the world. In Japan, fly ash generated from waste incineration is treated at a managed final disposal site after heavy metals are insolubilized with chelating agents to prevent contamination of heavy metals in soil and groundwater by waste incineration ash. Technology is established.

As chelating agents that can insolubilize heavy metals in fly ash, carbodithioates of various amines are used, but piperazine carbodithioates not only have the ability to immobilize heavy metals but also generate no harmful gases when used, and are stable. And it is widely used as a drug excellent in safety (see, for example, Patent Document 1).

On the other hand, recently, in Asian countries around Japan, it has begun to consider the treatment of fly ash after waste incineration with a chelating agent for safe treatment. Accordingly, worldwide demand for chelating agents for fly ash treatment is increasing.

As piperazine carbodithioate having excellent performance as a heavy metal treating agent, two chemical structures of piperazine-N, N′-biscarbodithioate and piperazine-N-carbodithioate may exist, but piperazine -N, N'-biscarbodithioate has a higher ability to treat heavy metals.

Piperazine carbodithioate must be aged after mixing piperazine, carbon disulfide and alkali metal hydroxide in an aqueous solution and reacting at a low temperature (about 40 ° C) below the boiling point of carbon disulfide. It is. Conventional aging has been carried out under alkali-excess conditions in order to inhibit the decomposition of the carbodithioate.

Conventionally, as a method for producing a piperazine carbodithioate having a high heavy metal treating capacity and a high ratio of piperazine-N, N′-biscarbodithioate, an excess of carbon disulfide is used during the reaction, and finally, an unreacted carbon disulfide is used. A method of distilling (removing) carbon disulfide with an inert gas is known (see, for example, Patent Document 1). Also known are a method of dividing and mixing the raw materials during the reaction and a method of reacting in the presence of piperazine carbodithioic acid (see, for example, Patent Documents 2 and 3).

However, the conventional method of increasing the piperazine-N, N′-biscarbodithioate ratio using excess carbon disulfide requires a distillation process with a large amount of nitrogen gas after the reaction, which is industrially necessary. It was not a preferable method. In addition, the method of dividing and mixing carbon disulfide and alkali metal hydroxide in an aqueous solution of piperazine can improve the ratio of piperazine-N, N′-biscarbodithioate, but increases the number of divisions to a large number. There is a problem that the operation is complicated.
The same applies to the method of reacting in the presence of piperazine carbodithioic acid, and the ratio of piperazine-N, N′-biscarbodithioate can be improved, but piperazine carbodithioic acid is an insoluble solid. When uniform reaction becomes difficult or when piperazinecarbodithioic acid is deposited in a reaction vessel (especially a stirring blade), reaction control may become difficult, and improvement has been demanded.

Japanese Patent No. 3391173 Japanese Unexamined Patent Publication No. 2003-221389 Japanese Unexamined Patent Publication No. 2008-143810

In order to produce a heavy metal treating agent comprising piperazine-N, N′-biscarbodithioate that does not contain piperazine-N-carbodithioate, a distillation treatment with an inert gas or a solid piperazinecarbodithioate is used. It was necessary to control the reaction during the precipitation.
An object of the present invention is to provide an industrially useful piperazine-N, N′-biscarbodithioic acid that does not contain piperazine-N′-carbodithioate and does not require the distillation of carbon disulfide with an inert gas. It is to provide a method for producing a salt.

In the method of reacting piperazine, carbon disulfide having a reaction equivalent amount or more with respect to the piperazine, and an alkali metal hydroxide in an aqueous solution, the present inventors present a hydrophobic solvent during the reaction, Piperazine-N, N'-biscarbodithioate containing no piperazine-N-carbodithioate without any reaction control during the distillation process with inert gas after the reaction or the precipitation of piperazinecarbodithioic acid The inventors have found that an aqueous solution can be produced, and have completed the present invention.
That is, the present invention has the following gist.
(1) In a method for producing a piperazine carbodithioate in which an aqueous solution is mixed with piperazine, carbon disulfide having a reaction equivalent or more with respect to the piperazine, and an alkali metal hydroxide, and reacted. A method for producing an aqueous solution of piperazine-N, N′-biscarbodithioate, characterized by comprising an organic solvent.
(2) The manufacturing method as described in said (1) whose molar ratio of carbon disulfide with respect to piperazine is 2.00 times equivalent or more and 3.00 times equivalent or less.
(3) The manufacturing method as described in said (1) or (2) whose molar ratio of the alkali metal hydroxide with respect to piperazine is 1.95 times equivalent or more and 2.05 times equivalent or less.
(4) The production method according to any one of (1) to (3) above, wherein the solubility of the hydrophobic solvent in water is 1% by weight or less.
(5) The production method according to any one of the above (1) to (4), wherein the amount of the hydrophobic solvent is 100 to 10,000% by weight based on excess carbon disulfide.
(6) The production method according to any one of the above (1) to (5), wherein the hydrophobic solvent is at least one selected from the group consisting of n-hexane, n-heptane, toluene, chlorobenzene, and dichlorobenzene. .
(7) The production method according to any one of (1) to (6), wherein the alkali metal hydroxide is potassium hydroxide and / or sodium hydroxide.
(8) After completion of the reaction, the alkali metal hydroxide is further mixed with the piperazine carbodithioate aqueous solution composed of piperazine-N, N′-biscarbodithioate from which the hydrophobic solvent has been separated. 7) The manufacturing method in any one of.
(9) An aqueous piperazine-N, N′-biscarbodithioate aqueous solution characterized by not containing piperazine-N-carbodithioate.
(10) The piperazine-N, N′-biscarbodithioate aqueous solution according to (9) above, wherein the piperazine-N, N′-biscarbodithioate is a potassium salt.

The production method of the present invention does not contain piperazine-N-carbodithioate without subjecting excess carbon disulfide to distillation with an inert gas or controlling the reaction during precipitation of solid piperazine carbodithioic acid. A heavy metal treatment agent comprising piperazine-N, N′-biscarbodithioate can be produced, and a stable heavy metal treatment effect can be obtained in terms of performance.

6 is a ¹³ C-NMR spectrum of the aqueous solution obtained in Example 6. ^{1 is} a ¹ H-NMR spectrum of an aqueous solution obtained in Example 6. 3 is a ¹³ C-NMR spectrum of an aqueous solution obtained in Comparative Example 1. 2 is a ¹ H-NMR spectrum of an aqueous solution obtained in Comparative Example 1.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

The present invention relates to an aqueous piperazine-N, N′-biscarbodithioate aqueous solution that does not contain piperazine-N-carbodithioate. When piperazine-N-carbodithioate is not included, the heavy metal treatment ability is high, a stable heavy metal treatment effect can be obtained in terms of performance, and further, the reduction of the treatment ability in long-term storage can be suppressed. it can. In the present invention, “not containing piperazine-N-carbodithioate” means that piperazine-N-carbodithioate is not detected by ¹ H-NMR and ¹³ C-NMR.

Examples of the piperazine-N, N′-biscarbodithioate in the piperazine-N, N′-biscarbodithioate aqueous solution of the present invention include alkali metal salts such as potassium salt and sodium salt. Of these, potassium salts are particularly preferred.

The method for producing an aqueous piperazine-N, N′-biscarbodithioate salt solution of the present invention comprises piperazine, carbon disulfide having a reaction equivalent or more to the piperazine, and an alkali metal hydroxide in the aqueous solution. In the method for producing piperazine carbodithioate to be mixed and reacted, a hydrophobic solvent is present during the reaction.

In the present invention, the presence of a hydrophobic solvent during the reaction makes it possible to capture excess carbon disulfide, which has conventionally been required to be distilled off after the reaction, in the hydrophobic solvent, and piperazine-N, N′-biscarbodithio By separating the two phases from the piperazine carbodithioate aqueous solution containing an acid salt as a main component, it becomes easy to take out only the necessary aqueous solution phase. In addition, unnecessary side reactions due to excess carbon disulfide can be suppressed. In addition, hydrophobic solvents that capture excess carbon disulfide can be reused. When the hydrophobic solvent is reused, excess carbon disulfide is already trapped in the solvent, so that the use of excess carbon disulfide can be reduced in the next reaction.
Here, the excess carbon disulfide represents carbon disulfide obtained by subtracting the reaction equivalent of carbon disulfide from the reaction equivalent of carbon disulfide.

Piperazine-N-carbodithioate is not contained in the piperazine carbodithioate aqueous solution mainly composed of piperazine-N, N′-biscarbodithioate obtained by the production method of the present invention. Therefore, when ¹³ C-NMR was measured, no peak derived from piperazine-N-carbodithioate near 47 ppm was observed, and when ¹ H-NMR was measured, piperazine-N near 2.8 ppm was observed. -No peaks derived from carbodithioate are observed.

In the production method of the present invention, the amount of carbon disulfide used in the reaction is preferably such that the molar ratio of carbon disulfide to piperazine is in the range of 2.00 times equivalent or more and 3.00 times equivalent or less. It is preferably 0.01 times equivalent or more and 2.5 times equivalent or less, particularly preferably 2.05 times equivalent or more and 2.5 times equivalent or less. By making the amount of carbon disulfide used within the above range, piperazine-N-carbodithioate is not produced, the production rate of piperazine-N, N′-biscarbodithioate is not reduced, and Excessive carbon disulfide does not become large, and the production efficiency of piperazine-N, N′-biscarbodithioate is not lowered.

In the production method of the present invention, the amount of alkali metal hydroxide used in the reaction is preferably such that the molar ratio of alkali metal hydroxide to piperazine is 1.95 times equivalent or more and 2.05 times equivalent or less. 97 times equivalent or more and 2.02 times equivalent or less are preferable.

In the production method of the present invention, after completion of the reaction, 0.1% of alkali metal hydroxide is added to 100 parts by weight of piperazine-N, N′-biscarbodithioate aqueous solution obtained by separating the hydrophobic solvent. It is preferable to add to 3.0 parts by weight, particularly 0.3 to 1.5 parts by weight. By adding an excessive amount of alkali metal hydroxide, it is possible to further stabilize the piperazine-N, N′-biscarbodithioate aqueous solution. The alkali metal hydroxide can be added as it is or as an aqueous solution of an alkali metal hydroxide, and is particularly preferably added as an aqueous solution.

The hydrophobic solvent used in the production method of the present invention is not particularly limited, and examples thereof include hydrocarbons such as n-pentane, n-hexane, n-heptane, benzene, toluene, chlorobenzene, dichlorobenzene, chloroform, diethyl ether. , Ethyl acetate, methylene chloride and the like. Among these solvents, particularly when the solubility in water is high, the amount of the hydrophobic solvent mixed in the piperazine carbodithioate aqueous solution containing piperazine-N, N′-biscarbodithioate as a main component increases. Therefore, hydrocarbons such as n-pentane, n-hexane and n-heptane having a solubility in water of 1% by weight or less, benzene, toluene, chlorobenzene, dichlorobenzene, chloroform and the like are preferable, and particularly 0.1% by weight. The following hydrocarbons such as n-pentane, n-hexane and n-heptane, toluene, chlorobenzene, dichlorobenzene and the like are preferable. Of these, hydrocarbons such as n-hexane and n-heptane having a low specific gravity and a large specific gravity difference from the aqueous solution of piperazine-N, N′-biscarbodithioate are preferable. Moreover, you may use it, mixing 2 or more types of these compounds.

In the present invention, the amount of the hydrophobic solvent to be present during the reaction is preferably from 100 to 10,000% by weight, particularly preferably from 200 to 2000% by weight, based on excess carbon disulfide. By making the usage-amount of a hydrophobic solvent into this range, since the capture effect of carbon disulfide does not fall, it is not necessary to distill off carbon disulfide, and there is no possibility of causing unnecessary side reactions. In addition, since carbon disulfide is not captured too much, there is no possibility of remaining piperazine-N-carbodithioate, and piperazine carbodithioic acid mainly composed of piperazine-N, N′-biscarbodithioate The production efficiency of the salt solution is not reduced.

In the present invention, the hydrophobic solvent present during the reaction can be present during the reaction by various methods, and is not particularly limited. For example, a method of adding a hydrophobic solvent from the beginning together with a raw material, a method of adding a hydrophobic solvent during the reaction, a method of adding a hydrophobic solvent to carbon disulfide in advance and adding it to the reaction system can be exemplified.

It is preferable to use potassium hydroxide and / or sodium hydroxide as the alkali metal hydroxide used in the production method of the present invention.

In the production method of the present invention, a piperazine-N, N′-biscarbodithioate aqueous solution containing no piperazine-N-carbodithioate in the piperazine carbodithioate aqueous solution can be produced. By not containing piperazine-N-carbodithioate, the ability to fix heavy metals is particularly enhanced, and more stable performance can be expected.

In the production method of the present invention, the method of mixing the raw materials during the reaction is not particularly limited, and examples thereof include a method of continuous addition or divided addition while maintaining the raw material composition ratio of the present invention. In particular, a method of adding carbon disulfide and an alkali metal hydroxide to a solution containing piperazine and a hydrophobic solvent in two or more divided portions; adding piperazine to a solution containing carbon disulfide and a hydrophobic solvent; and A method in which the alkali metal hydroxide is alternately divided into two or more is added. Further, a method of adding carbon disulfide and an alkali metal hydroxide to a solution containing piperazine and a hydrophobic solvent in two or more portions alternately in this order; adding a solution containing carbon disulfide and a hydrophobic solvent to piperazine, A method in which the alkali metal hydroxide is alternately divided into two or more parts and added in the order of alkali metal hydroxide is more preferable.

In the production method of the present invention, the temperature at the time of reaction and aging is not particularly limited, and is preferably room temperature (20 ° C.) to 45 ° C., particularly preferably 30 to 45 ° C.

In the present invention, the concentration of piperazine-N, N′-biscarbodithioate in the aqueous solution after completion of the reaction is not particularly limited, and may be a concentration that can be appropriately used as a heavy metal treating agent. % By weight is preferable, and 30 to 45% by weight is particularly preferable.

In the present invention, by further adding piperazine, it is possible to prevent a decrease in processing capacity for longer-term storage. The amount of piperazine added is not particularly limited. Since piperazine carbodithioate is stable, 0.1 to 2 parts by weight per 100 parts by weight of piperazine-N, N′-biscarbodithioate aqueous solution. In particular, 0.2 to 1 part by weight is preferable. Piperazine can be added as a solid or as an aqueous solution of piperazine, and is particularly preferably added as an aqueous solution.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
In the examples, NMR (nuclear magnetic resonance) measurement ( ¹³ C-NMR and ¹ H-NMR) was performed using Gemini-200 manufactured by VARIAN, using heavy water as a solvent, and 3-trimethylsilylpropion as a standard substance. sodium _{acid-2,2,3,3-d 4} was performed using.

Example 1
To a 1 L (liter) four-necked flask equipped with a stirrer, a thermometer, a condenser, and a dropping funnel, 189.4 g of water, 56.0 g (0.65 mol) of anhydrous piperazine, and 75.0 g of n-hexane were collectively added. First, piperazine was dissolved at 35 ° C. Carbon disulfide (123.8 g, 1.63 mol) and 48.5 wt% aqueous potassium hydroxide solution (150.4 g, 1.30 mol) were each divided into four portions and reacted dropwise at 40 ° C over 6 hours with stirring. I let you.
The molar ratio of alkali metal hydroxide to piperazine is 2.00 times equivalent, the molar ratio of carbon disulfide is 2.50 times equivalent, and the hydrophobic solvent (n-hexane) contains excess disulfide. The concentration of piperazine-N, N′-biscarbodithioate in the aqueous solution was 40.9% by weight based on carbon.
Next, after aging for 15 minutes, a yellow transparent liquid (aqueous solution) separated from the n-hexane phase was obtained. The obtained yellow liquid was separated with a separatory funnel, collected, stirred for 15 minutes, and then added with 5.2 g of 48.5 wt% potassium hydroxide aqueous solution and filtered.

As a result of measuring ¹³ C-NMR of the obtained aqueous solution, only peaks derived from the main component piperazine-N, N′-biscarbodithioate were observed at around 53 ppm and around 210 ppm, and were around 47 ppm and 55 ppm. No peak derived from the nearby piperazine-N-carbodithioate was observed.

Example 2
The same operation as in Example 1 was carried out except that 75.0 g of n-hexane was changed to 75.0 g of p-dichlorobenzene. The obtained liquid was yellow and transparent, and as a result of ¹³ C-NMR measurement, only peaks derived from piperazine-N, N′-biscarbodithioate as a main component were observed at around 53 ppm and around 210 ppm. No peaks derived from piperazine-N-carbodithioate at around 47 ppm and around 55 ppm were observed.

Example 3
The same operation as in Example 1 was performed except that 75.0 g of n-hexane was changed to 75.0 g of n-heptane and 106.6 g (1.40 mol) of carbon disulfide (alkaline metal water was added to piperazine). Molar ratio of oxide is 2.00 times equivalent and carbon disulfide is 2.15 times equivalent Hydrophobic solvent (n-heptane): 987% by weight based on excess carbon disulfide Piperazine in aqueous solution N, N′-biscarbodithioate concentration is 40.9% by weight.) The obtained liquid was yellow and transparent, and as a result of ¹³ C-NMR measurement, only peaks derived from piperazine-N, N′-biscarbodithioate as a main component were observed at around 53 ppm and around 210 ppm. No peaks derived from piperazine-N-carbodithioate at around 47 ppm and around 55 ppm were observed. Furthermore, as a result of measuring ¹ H-NMR, no peak derived from piperazine-N-biscarbodithioate near 2.8 ppm was observed.

Example 4
The same operation as in Example 1 was performed except that n-hexane separated in Example 1 was used and the amount of carbon disulfide added was changed to 104.0 g (1.37 mol). The obtained liquid was yellow and transparent, and as a result of ¹³ C-NMR measurement, only peaks derived from piperazine-N, N′-biscarbodithioate as a main component were observed at around 53 ppm and around 210 ppm. No peaks derived from piperazine-N-carbodithioate at around 47 ppm and around 55 ppm were observed.

Example 5
Into a 500 mL (milliliter) four-necked flask equipped with a stirrer, a condenser, and two dropping funnels, 58.8 g of water, 101.5 g (1.33 mol) of carbon disulfide, and 25.0 g of n-heptane were batched. Preparation, 186.6 g (0.65 mol) of 30 wt% piperazine aqueous solution and 150.4 g (1.30 mol) of 48.5 wt% potassium hydroxide aqueous solution were divided into three parts, respectively, and 30 wt% piperazine aqueous solution, 48.5 wt% The same operation as in Example 1 was performed except that the aqueous potassium hydroxide solution was alternately dropped in the order of% potassium hydroxide aqueous solution. The molar ratio of alkali metal hydroxide to piperazine is 2.00 times equivalent, the molar ratio of carbon disulfide is 2.05 times equivalent, and the hydrophobic solvent (n-heptane) is in excess of 2 The amount was 1000% by weight with respect to carbon sulfide, and the concentration of piperazine-N, N′-biscarbodithioate in the aqueous solution was 40.9% by weight.
The obtained liquid (aqueous solution) was yellow and transparent. As a result of measuring ¹³ C-NMR, only peaks derived from the main component piperazine-N, N′-biscarbodithioate were found at around 53 ppm and around 210 ppm. And peaks derived from piperazine-N-carbodithioate at around 47 ppm and around 55 ppm were not observed. Furthermore, as a result of measuring ¹ H-NMR, no peak derived from piperazine-N-biscarbodithioate near 2.8 ppm was observed.

Example 6
Into a 500 mL (milliliter) four-necked flask equipped with a stirrer, a thermometer, a condenser, and a dropping funnel, 189.4 g of water, 56.0 g (0.65 mol) of anhydrous piperazine, and 5.0 g of n-heptane were collectively added. First, piperazine was dissolved at 35 ° C. 99.5 g (1.31 mol) of carbon disulfide and 148.9 g (1.29 mol) of 48.5 wt% potassium hydroxide aqueous solution were each divided into 4 parts, and the whole amount was alternately taken over 6 hours at 40 ° C. with stirring. The reaction was carried out dropwise.
The molar ratio of alkali metal hydroxide to piperazine is 1.98 equivalents, the molar ratio of carbon disulfide is 2.01 equivalents, and the hydrophobic solvent (n-heptane) is in excess of 2 The amount was 1010% by weight based on carbon sulfide, and the concentration of piperazine-N, N′-biscarbodithioate in the aqueous solution was 40.9% by weight. After aging for 15 minutes, a yellow transparent liquid (aqueous solution) separated from the n-heptane phase was obtained. The obtained yellow liquid was separated with a separatory funnel, collected, stirred for 15 minutes, and then added with 6.7 g of 48.5% by weight potassium hydroxide aqueous solution and filtered.

The results of ¹³ C-NMR measurement of the obtained aqueous solution are shown in FIG. Only peaks derived from the main component piperazine-N, N′-biscarbodithioate are observed around 53 ppm and 210 ppm, and peaks derived from piperazine-N-carbodithioate at around 47 ppm and around 55 ppm are observed. Not observed. Further, the result of ¹ H-NMR measurement is shown in FIG. A peak derived from piperazine-N-biscarbodithioate near 2.8 ppm was not observed.

Comparative Example 1
The same operation as in Example 1 was performed except that the amount of carbon disulfide was 98.0 g (1.29 mol) (the molar ratio of carbon disulfide to piperazine was 1.98 times equivalent). . The obtained liquid (aqueous solution) was yellow and transparent. As a result of measuring ¹³ C-NMR (FIG. 3), the main component, piperazine-N, N′-biscarbodithioate, was around 53 ppm and 210 ppm. In addition to the derived peaks, peaks derived from piperazine-N-carbodithioate were observed at around 47 ppm and around 55 ppm. Further, as a result of measuring ¹ H-NMR (FIG. 4), a peak derived from piperazine-N-biscarbodithioate in the vicinity of 2.8 ppm was observed.

The piperazine-N, N′-biscarbodithioate obtained was obtained because no carbon disulfide was used in excess of the reaction equivalent (molar ratio of carbon disulfide to piperazine is 2.00 times equivalent). The aqueous solution contained piperazine-N-carbodithioate.

Comparative Example 2
The same operation as in Example 1 was performed except that n-hexane was not used. Since a hydrophobic solvent was not used, unreacted carbon disulfide was visually confirmed after completion of ripening, and distillation with an inert gas was necessary.

The aqueous solution of piperazine carbodithioate obtained by the production method of the present invention can treat heavy metals in soil, wastewater, incinerated ash, fly ash and other heavy metal containing materials with high performance and is industrially useful. .

In addition, Japanese Patent Application No. 2010-266294 filed on November 30, 2010, Japanese Patent Application No. 2011-074065 filed on March 30, 2011, and Japan Application filed on August 22, 2011 The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-180509 are hereby incorporated herein by reference as the disclosure of the specification of the present invention.

Claims (10)

In a method for producing piperazine carbodithioate, in which an aqueous solution is mixed with piperazine, carbon disulfide having a reaction equivalent or more with respect to the piperazine, and an alkali metal hydroxide, the hydrophobic solvent is removed during the reaction. A method for producing an aqueous solution of piperazine-N, N′-biscarbodithioate, characterized in that it is present. The manufacturing method according to claim 1, wherein the molar ratio of carbon disulfide to piperazine is 2.00 times equivalent or more and 3.00 times equivalent or less. The manufacturing method according to claim 1 or 2, wherein the molar ratio of the alkali metal hydroxide to piperazine is 1.95 times equivalent or more and 2.05 times equivalent or less. The production method according to any one of claims 1 to 3, wherein the solubility of the hydrophobic solvent in water is 1% by weight or less. The production method according to any one of claims 1 to 4, wherein the amount of the hydrophobic solvent is 100 to 10,000% by weight based on excess carbon disulfide. 6. The production method according to claim 1, wherein the hydrophobic solvent is at least one selected from the group consisting of n-hexane, n-heptane, toluene, chlorobenzene, and dichlorobenzene. The production method according to any one of claims 1 to 6, wherein the alkali metal hydroxide is potassium hydroxide and / or sodium hydroxide. After completion of the reaction, an alkali metal hydroxide is further mixed with the piperazine carbodithioate aqueous solution composed of piperazine-N, N′-biscarbodithioate from which the hydrophobic solvent has been separated. 8. The production method according to any one of 7 above. Piperazine-N, N′-biscarbodithioate aqueous solution characterized by not containing piperazine-N-carbodithioate. The piperazine-N, N'-biscarbodithioate aqueous solution according to claim 9, wherein the piperazine-N, N'-biscarbodithioate is a potassium salt.

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