Method for producing dicyclohexyl disulfide

[Technical field]

The present invention relates to a method for producing dicyclohexyl disulfide useful as a raw material for a rubber vulcanization retarder of tires and the like, and for producing industrial sodium chloride.

[Background art]

In general, industrial methods for producing dicyclohexyl disulfide include a method of reacting sodium disulfide and chlorocyclohexane with each other. In this production method, the waste liquid produced in the production process contains large amounts of sodium chloride, sulfides, organic materials and the like produced as byproducts, and the offensive odor and color of the waste liquid pose a large problem. Further, if the waste liquid is discharged as it is, it pollutes rivers and the ocean. Thus, the treatment that allows the waste liquid to be discharged without adversely affecting the environment is not easy.

Presently the following methods are available. The insoluble matter produced as a byproduct is removed from the reaction mixture, and subsequently the oil layer is separated from the reaction mixture, to reuse the remaining water layer partially or wholly for the reaction between sodium disulfide and chlorocyclohexane. On the other hand, there is also a method of treating the insoluble matter produced as a byproduct using an oxidizing agent, for changing it into wastewater with less environmental load (see patent documents 1 and 2). This method is excellent in that the influence on the environment can be reduced. However, actually the wastewater has the following serious defect since the inorganic salt concentration is high. That is, depending on the environmental regulations and the like of respective districts, the wastewater cannot be discharged into rivers or the ocean. In addition, the method has a disadvantage that useful resources such as sodium chloride contained in the insoluble matter produced as a byproduct cannot be used.

[Prior art documents] [Patent documents]

[Patent document 1] Chinese patent application, publication number CN 101070296 [Patent document 2] Japanese patent application, publication number JP 2007-326850 A

[Summary of the invention]

[Problems to be solved by the invention]

The object of this invention is to provide an industrially advantageous method for producing dicyclohexyl disulfide and sodium chloride for allowing resources to be effectively used without adversely affecting the environment at all.

[Means for solving the problems]

This invention is a method for producing dicyclohexyl disulfide in which sodium disulfide and chlorocyclohexane are reacted with each other using a hydrous solvent to synthesize dicyclohexyl disulfide; by acidifying at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

Further, this invention is a method for producing sodium chloride, by acidifying at least a portion of the reaction mixture containing sodium chloride produced by reacting sodium disulfide and chlorocyclohexane with each other using a hydrous solvent, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

[Effect of the invention]

This invention can provide an industrially practical method for producing dicyclohexyl disulfide, N-(cyclohexylthio) phthalimide and sodium chloride at low cost without adversely affecting the environment at all.

[Modes for carrying out the invention]

This invention is a method for producing dicyclohexyl disulfide in which sodium disulfide and chlorocyclohexane are reacted with each other using a hydrous solvent to synthesize dicyclohexyl disulfide; by acidifying at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

Further, this invention is a method for producing sodium chloride, by acidifying at least a portion of the reaction mixture containing sodium chloride produced by reacting sodium disulfide and chlorocyclohexane with each other using a hydrous solvent, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

In this invention when sodium disulfide and chlorocyclohexane are reacted with each other, a hydrous solvent is used. The hydrous solvent can also be water used as a solvent. To improve the mixed state between chlorocyclohexane and sodium disulfide in the water used as a solvent, a hydrophilic solvent other than water can also be used together with water. As the hydrophilic solvent, it is preferred to use an alcohol, and it is more preferred to use methanol or ethanol. As the hydrous solvent, hydrous methanol or hydrous ethanol is preferred.

In the case where an alcohol is used as a hydrophilic solvent, it is preferred that the alcohol content based on the amount of the entire hydrous solvent is 90 wt% or less. A more preferred range is 20 to 80 wt%. If the alcohol content is 90 wt% or less, the yield and productivity of dicyclohexyl disulfide can be kept high.

The amount of the hydrous solvent used is normally 0.1 to 10 times the weight of chlorocyclohexane. A preferred range is 0.5 to 5 times. If the amount of the hydrous solvent used is in a range from 0.1 to 10 times the weight of chlorocyclohexane, the yield and productivity of dicyclohexyl disulfide can be kept high.

The method for producing the sodium disulfide used in this invention is not limited. Sodium disulfide offered by others, or synthesized before use, or synthesized simultaneously in the reaction solution with chlorocyclohexane can also be used.

It is preferred that the amount of sodium disulfide used is 0.1 to 2 molar times the amount of chlorocyclohexane. A more preferred range is 0.3 to 1 molar time. If the amount of sodium disulfide used is 0.1 to 2 molar times the amount of chlorocyclohexane, the yield of cyclohexyl disulfide is high and the loss of chlorocyclohexane used as a raw material can be reduced.

The method for synthesizing the sodium disulfide used in this invention can be, for example, the following method. That is, the method can be a method of reacting sodium sulfide and sulfur with each other in a hydrous solvent. Since the reaction between sodium sulfide and sulfur takes place quantitatively, the amount of sulfur used is normally 0.5 to 1.5 molar times the amount of sodium sulfide. A preferred range is 0.8 to 1.2 molar times.

The method for producing the chlorocyclohexane used in this invention is not limited. The method for producing the chlorocyclohexane used in this invention can be, for example, the following method. That is, the method can be a method of reacting cyclohexane and chlorine with each other, or a method of reacting cyclohexanol or cyclohexene and hydrogen chloride with each other, etc.

In this invention, as a reaction accelerator, preferably an alkali metal hydroxide such as sodium hydroxide can be made to exist together. It is preferred that the amount of the alkali metal hydroxide used is not larger than 1 molar times the amount of chlorocyclohexane. A more preferred range is 0.05 to 0.5 molar times. As the amount of the alkali metal hydroxide used, not larger than 1 molar time the amount of chlorocyclohexane is effective, and the loss of chlorocyclohexane can be reduced.

In this invention, it is preferred that the temperature of the reaction between sodium disulfide and chlorocyclohexane is 50 to 150 °C. A more preferred range is 70 to 120 °C. If the reaction temperature is 50 to 150 °C, the reaction rate is fast, and the yield of dicyclohexyl disulfide can be enhanced. It is preferred that the time of the reaction between sodium disulfide and chlorocyclohexane is 1 to 24 hours. A more preferred range is 5 to 15 hours. If the reaction time is 1 to 24 hours, the yield of dicyclohexyl disulfide can be enhanced. The pressure of the reaction can be normal pressure, and can also be a higher pressure.

In this invention, as the method for reacting sodium disulfide and chlorocyclohexane with each other, normally sodium disulfide and chlorocyclohexane are mixed in a reactor. Either sodium disulfide or chlorocyclohexane can be placed in the reactor at first. For example, after sodium disulfide is synthesized in a reactor, chlorocyclohexane can be added.

In this invention, if sodium disulfide and chlorocyclohexane are reacted with each other, the intended dicyclohexyl disulfide is produced after completion of reaction, and sodium chloride is produced as a byproduct.

In this invention, at least a portion of the reaction mixture containing sodium chloride produced as a byproduct is acidified, and subsequently the acidified reaction mixture is neutralized to recover sodium chloride.
In this invention, the chlorocyclohexane and sodium sulfide respectively used as raw materials, the sodium sulfide derived from sodium disulfide and the like may remain partially without being reacted as the case may be. In this case, the reaction mixture is separated into an oil layer containing dicyclohexyl disulfide, chlorocyclohexane and the like, and a water layer containing sodium chloride, sodium sulfide and the like.

This invention is a method for producing dicyclohexyl disulfide in which sodium disulfide and chlorocyclohexane are reacted with each other using a hydrous solvent to synthesize dicyclohexyl disulfide; by acidifying at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

Further, this invention is a method for producing sodium chloride, by acidifying at least a portion of the reaction mixture containing sodium chloride produced by reacting sodium disulfide and chlorocyclohexane with each other using a hydrous solvent, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

In this invention, it is preferred that at least a portion of the reaction mixture containing sodium chloride produced as a byproduct is a solid component and/or a liquid component.

In the case where a portion of the reaction mixture containing sodium chloride produced as a byproduct is a solid, it is desirable to collect the solid component containing sodium chloride, sodium sulfide and the like from the reaction mixture, for separation from a liquid. The solid component containing sodium chloride produced as a byproduct can be naturally precipitated after completion of reaction, or some treatment can also be applied after completion of reaction, to cause precipitation.

In order to naturally precipitate the solid component containing sodium chloride produced as a byproduct, the following examples can be presented. That is, there are a method of using a bad solvent of sodium chloride such as an alcohol in advance as the hydrous solvent used for the reaction, a method of reducing the amount of the hydrous solvent, and the like. In order to naturally precipitate the solid component containing sodium chloride produced as a byproduct, it is preferred to use a hydrous alcohol as a solvent for performing the reaction. It is more preferred to use hydrous methanol or hydrous ethanol as a solvent.

As the method for applying some treatment to the solid component containing sodium chloride produced as a byproduct, to cause precipitation, the following examples can be presented. That is, there are a method of adding a bad solvent of sodium chloride such as an alcohol to the reaction mixture after completion of reaction, a method of distilling away the solvent, to cause precipitation, and the like.

In this invention, as the method for collecting the solid component containing sodium chloride produced as a byproduct, normally centrifugal filtration, pressure filtration, centrifugal precipitation or the like can be performed. Further, when the solid content is collected, the solid component can also be washed (rinsed) using a solvent. As examples of the rinse solvent, enumerated are alcohols, water, etc.

In this invention, at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, is acidified. In order to acidify the solid component, it is preferred to add water to the solid component. It is more preferred to completely dissolve the solid component into water, to form an aqueous solution. In this invention, it is further more preferred that the solid component containing sodium chloride is collected from the reaction mixture and that subsequently water is added to the solid component, to form an aqueous solution. In this invention, it is preferred that at least a portion of the produced reaction mixture containing sodium chloride is acidified, and especially that the sodium sulfides adversely affecting the environment are removed to recover refined sodium chloride. In this invention, it is more preferred that sodium chloride is recovered as a refined sodium chloride aqueous solution.

In order to acidify at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, an acid is added. As the acid, an inorganic acid is preferred. Hydrochloric acid and sulfuric acid are more preferred. There is no limit to the concentration of the acid. It is preferred to add an acid for keeping the hydrogen ion concentration of the mixture containing sodium chloride at pH 6 or lower. A more preferred hydrogen ion concentration is pH 4 to 5.

In this invention, it is preferred that the solid component containing sodium chloride is collected from the reaction mixture, that from the remaining liquid component, an oil layer is separated, and that the water layer in which a small amount of sodium chloride remains is partially or entirely used for the reaction between sodium disulfide and chlorocyclohexane. The re-reaction (second reaction) between sodium disulfide and chlorocyclohexane can be performed like the initial reaction (the initial reaction for reacting sodium disulfide and chlorocyclohexane with each other, to synthesize dicyclohexyl disulfide).

For example, after completion of the reaction between sodium disulfide and chlorocyclohexane, at first the solid component containing sodium chloride is collected from the reaction mixture by centrifugation, and subsequently the oil layer of the filtrate obtained as the liquid component is separated. Sodium sulfide and/or sulfur is added to the remaining water layer, and the mixture is mixed and heated to synthesize sodium disulfide, then the re-reaction with chlorocyclohexane being performed. The re-reaction can be repeated multiple times, and further the water layer can be effectively used. Thus, it is not necessary any more to throw away the water layer that adversely affects the environment.

In this invention, at least a portion of the reaction mixture containing sodium chloride is acidified, so that preferably the sodium sulfides coexisting in the reaction mixture can be released as a gas containing hydrogen sulfide and absorbed by a sodium hydroxide aqueous solution for recovery. In order to release the gas containing hydrogen sulfide, an acid can also be added to a portion of the reaction mixture, or a portion of the reaction mixture can also be added to an acid. In this invention, preferably an acid is added to the reaction mixture. It is preferred that the amount of the sodium hydroxide of the sodium hydroxide aqueous solution used for absorption is not smaller than 1 molar time the amount of the sodium sulfide or hydrogen sulfide contained, and 2 molar times or more are more preferred. The gas absorbing device is available as liquid drop type, bubble type, liquid film type and the like, and is not particularly limited. In a laboratory, using a gas washing bottle as the gas absorbing device is preferred. For reliable absorption, multiple gas absorption devices are used. The sodium sulfide recovered in the sodium hydroxide aqueous solution can be industrially effectively used. It is preferred that the sodium sulfide recovered in the sodium hydroxide aqueous solution is used in the method for producing dicyclohexyl disulfide and sodium chloride of this invention.

In this invention, at least a portion of the reaction mixture containing sodium chloride is acidified and subsequently a base is added to the acidified reaction mixture, for neutralization. As the base used, an inorganic base is preferred. More preferred is sodium hydroxide. The base can also be added as an aqueous solution, and a solid base can also be added directly as it is. It is preferred that the amount of the base used is such that the hydrogen ion concentration of the mixture containing sodium chloride is adjusted to a pH range from 6 to 8. An amount for adjusting to pH 7 is more preferred. If the hydrogen ion concentration is adjusted to a pH range from 6 to 8, the quality of sodium chloride is good.

In this invention, it is preferred to treat the recovered sodium chloride or sodium chloride aqueous solution using an oxidizing agent, to decompose the slight amount of remaining sulfides. If an oxidizing agent is added to perform oxidation treatment, normally reducing sulfides or offensive odor can be removed to enhance the quality of sodium chloride. It is preferred that the oxidizing agent used in this invention is a peroxide, oxygen, air, hypochlorite, chlorine, ozone or the like. More preferred oxidizing agents are hydrogen peroxide, air and sodium hypochlorite. It is preferred that the concentration of hydrogen peroxide is 1 to 80 wt%, and a more preferred range is 5 to 50 wt%. It is preferred that the concentration of sodium hypochlorite is 1 to 50 wt%, and a more preferred range is 5 to 15 wt%. It is preferred that the amount of the oxidizing agent used is not smaller than 0.001 molar time the amount of the sodium chloride recovered, and a more preferred range is 0.01 to 1 molar time. If the amount of the oxidizing agent used is too small, the effect is too low, and too large an amount is economically disadvantageous. In this invention, multiple oxidation treatments can also be combined. For example, hydrogen peroxide water and sodium hypochlorite aqueous solution can be added to perform oxidation treatment, and subsequently air can also be further introduced into the liquid for oxidation and deodorization. It is preferred that the temperature of oxidation treatment is 25 °C or higher, and a more preferred range is 60 to 100 °C. If the temperature is too low, the oxidation is slow, and too high a temperature may be uneconomical as the case may be. It is preferred that the oxidation treatment time is 0.1 hour or more, and a more preferred range is 0.2 to 4 hours. If the time is too short, the oxidation does not take place, and too long a time may be uneconomical as the case may be. After the sodium chloride aqueous solution is subjected to oxidation treatment, it may contain an insoluble matter or may be turbid as the case may be, and considering quality, it is preferred to filter the sodium chloride aqueous solution.

In the method for producing dicyclohexyl disulfide of this invention, it is preferred to refine the intended dicyclohexyl disulfide. The method for refining dicyclohexyl disulfide can be a method of distilling away such impurities as cyclohexene produced as a byproduct and unreactive chlorocyclohexane from the separated oil layer after completion of reaction. Further in order to obtain highly pure dicyclohexyl disulfide, a method of distilling dicyclohexyl disulfide is preferred.

The obtained dicyclohexyl disulfide can be mainly used as a raw material of N-(cyclohexylthio)phthalimide that is one of rubber vulcanization retarders. For example, chlorine gas is reacted with dicyclohexyl disulfide in an organic solvent, to prepare a cyclohexyl sulfenyl chloride solution, and then the solution is reacted with a mixture consisting of phthalimide, base and organic solvent. The reaction mixture is post-treated and crystallized. Thus, N-(cyclohexylthio)phthalimide with industrially usable quality can be obtained.

Further, the refined sodium chloride produced in this invention can be used for regenerating cation exchange resins. In general, cation exchange resins are supplied in the sodium ion form. For example, they are used to release sodium ions and to capture calcium, magnesium and other metal ions according to the ion selectivity tendency of metal species. If the sodium chloride aqueous solution of this invention is made to act on the ion exchange resins exchanged by other metal ions subsequently, the cation exchange resins can be regenerated in the sodium ion form again. Cation exchange resins are available as strong acid cation exchange resins and weak acid cation exchange resins. Strong acid cation exchange resins are preferred, and sulfonic acid cation exchange resins are more preferred.

In particular, the refined sodium chloride produced in this invention is suitable for regenerating the cation exchange resins used for softening the feed water, washing water and cooling water of industrial boilers. For example, if hard water such as groundwater is fed through an ion exchange resin packing an ion exchange tower or the like, softened water can be obtained. During the period, the cation exchange resin captures calcium ions, magnesium ions and the like, and declines in ion exchange capability. Subsequently, if a solution containing approx. 10 wt% of the refined sodium chloride of this invention is passed through the ion exchange tower, the metal ions on the resin can be replaced by sodium ions, to restore the ion exchange capability.

Thus, according to this invention, the sodium chloride and the like thrown away in the past can be effectively used as useful resources and as industrially useful compounds without adversely affecting the environment at all.

[Examples]

This invention is explained below in more detail in reference to examples. Example 1 (Reaction using hydrous methanol as a solvent)

An autoclave was charged with 140 g of 60 wt% sodium sulfide (crystallization water 56.0 g, sodium sulfide 84.0 g, 1.08 moles (molecular weight 78.1)), 31.4 g of sulfur (0.978 mole (atomic weight 32.1)), 12. 1 g of sodium hydroxide (0.303 mole (molecular weight 40.0)), 80.0 g of methanol and 130 g of water, and was heated at 65 °C for 0.5 hour, to produce sodium disulfide. After cooling, the autoclave was opened and charged with 190 g of 95 wt% chlorocyclohexane (chlorocyclohexane 181 g, 1.53 moles (molecular weight 118.6)) (total 584 g), and heated at 100 °C and at a gauge pressure of 200 kPa for 8 hours, to perform the initial reaction. After cooling, from the initial reaction mixture, a solid component containing sodium chloride produced as a byproduct was collected by filtration. Thus, 110 g of a solid component could be obtained. The amount of the filtrate was 440 g. The solid component contained 78.0 g (1.33 moles (molecular weight 58.44)) of sodium chloride. A liquid component containing sodium chloride produced as a byproduct adhered to the solid component.

Subsequently the filtrate was separated to obtain 280 g of the water layer containing remaining sodium chloride and 160 g of the oil layer of the initial reaction. The water layer had a strong offensive odor of sulfur compounds and was a deep black liquid with a large environmental load. The oil layer was subjected to gas chromatography. The dicyclohexyl disulfide concentration of the oil layer was 84.4 wt% (dicyclohexyl disulfide 135 g, 0.586 mole (molecular weight 230.4), reaction yield 76.6 %).

In order to perform re-utilization (second reaction), 280 g of the water layer of the initial reaction was placed in an autoclave that was charged with 95 g of 60 wt% sodium sulfide (crystallization water 38 g, sodium sulfide 57 g, 0.730 mole), 20.6 g (0.643 mole) of sulfur, 5.5 g (0.14 mole) of sodium hydroxide, 7.0 g of methanol and 6.0 g of water and heated at 65 °C for 0.5 hour, to produce sodium disulfide. After cooling, the autoclave was opened and charged with 190 g of 95 wt% chlorocyclohexane (chlorocyclohexane 181 g, 1.53 moles) (total 604 g), being heated at 100 °C and at a gauge pressure of 200 kPa for 8 hours to perform the second reaction. After cooling, from the second reaction mixture, a solid component containing sodium chloride produced as a byproduct was collected by filtration, to obtain 120 g of a solid component. The amount of the filtrate was 460 g. The solid component contained 80.0 g (1.37 moles) of sodium chloride. A liquid component containing sodium chloride produced as a byproduct adhered to the solid component.

The filtrate was separated to obtain 300 g of the water layer and 160 g of the oil layer of the second reaction. The water layer had a strong offensive odor of sulfur compounds and was a deep black liquid considered to adversely affect the environment such as polluting rivers. The oil layer was subjected to gas chromatography. The dicyclohexyl disulfide concentration of the oil layer was 83.1 wt% (dicyclohexyl disulfide 133 g, 0.577 mole, reaction yield 75.5 %).

As described above, the water layer of the initial reaction, which could adversely affect the environment, could be effectively used for the second reaction (re-reaction) without being thrown away at all and without any problem.

In succession, 300 g of the water layer of the second reaction can be used for the third reaction as described above, and the water layer of the second reaction with a large environmental load can be effectively used in the third reaction (re-reaction) without being thrown away at all.

The dicyclohexyl disulfide concentration was analyzed by gas chromatography under the following conditions. Gas chromatograph: Shimadzu GC-17A Column: NB-1, length 60 m x inner diameter 0.25 mm, film thickness 0.40 um Column temperature: 70 -> 270 °C, 5 °C/min Carrier He gas pressure: 180 kPa (70 °C) Injection port-FID detector temperature: 270 °C (Treatment of solid components)

The solid components produced as byproducts in the initial reaction and in the second reaction were mixed. From the mixture, 175 g (sodium chloride 120 g, 2.06 moles; sodium sulfide 8.6 g, 0.11 mole) was taken and dissolved into 300 ml of water, to form a blackish green sodium chloride aqueous solution. The solution had an offensive odor of sulfur compounds. To the solution, 30 ml of 30 wt% hydrochloric acid (35 g, hydrogen chloride 10.4 g, 0.28 mole (molecular weight 36.46)) was added with stirring, and the temperature of the liquid rose from 20 °C to 50 °C, the pH being kept at 4. The hydrogen sulfide gas simultaneously released was introduced into a gas washing bottle containing 160 ml of 30 wt% sodium hydroxide aqueous solution (214 g, sodium hydroxide 64 g, 1.6 moles), to be absorbed, and 500 g of a crude sodium chloride aqueous solution remained.

On the other hand, further 6.0 ml of 30 wt% sodium hydroxide aqueous solution (8.0 g; sodium hydroxide 2.4 g, 0.06 mole) was added to 500 g of the crude sodium chloride aqueous solution acidified by adding hydrochloric acid as described above, for neutralization, to keep the liquid temperature at 50 °C and the pH at 7. Then, 5.0 g of 30 % hydrogen peroxide water (hydrogen peroxide 1.5 g, 0.044 mole (molecular weight 34.0)) was added, and the mixture was heated at 80 °C for 0.5 hour. Air was bubbled from the bottom of the aqueous solution at the same temperature for 0.5 hour, to remove the odor. Subsequently, the liquid was cooled to a temperature of 50 °C, and the insoluble matter was filtered away with filter paper. Thus, 510 g of colorless transparent 26 wt% refined sodium chloride aqueous solution (specific gravity 1.2) could be obtained. The refined sodium chloride aqueous solution contained 137 g (2.34 moles) of sodium chloride and 1.5 g of sodium sulfate (molecular weight 142.1). (Regeneration of cation exchange resin)

The refined sodium chloride aqueous solution recovered as described above was diluted with deionized water, to prepare 400 ml of 10 wt% salt water at room temperature. Fifty grams of a strong acidic styrene-based cation exchange resin (total exchange capacity 4.5 mmol/g, produced by Shanghai Yuanye Bio-Technology Co., Ltd.) used for softening the groundwater for a boiler was placed in a separating funnel. The salt water prepared as described above was added to it, and the resin as immersed was allowed to stand for one day. Then, the salt water was extracted from the bottom of the separating funnel, and added again into the separating funnel. Likewise the salt water was extracted.
In succession, 2000 ml of non-treated groundwater (hardness 8.0 milligram equivalents/L) was passed through the separating funnel, and the treated water was recovered. The recovered water was titrated with EDTA. As a result, the hardness was 0.01 milligram equivalent/L. The hardness was less than 0.04 milligram equivalent/L and had no problem in view of softening, and the water could be used for the boiler.

Example 2 (Treatment of liquid component)

In the reaction using hydrous methanol as a solvent described in Example 1, the solid component obtained in the initial reaction was collected from the reaction mixture, and the filtrate was separated. From 280 g of the water layer containing remaining sodium chloride of the initial reaction, 48 g (methanol 13 g, sodium chloride 2.0 g, 0.034 mole; sodium sulfide 4.8 g, 0.062 mole) was taken. The water layer of the initial reaction was a blackish green liquid having an offensive odor of sulfur compounds.

Sixteen milliliters of 30 wt% hydrochloric acid (19 g, hydrogen chloride 5.6 g, 0.154 mole) was added to 48 g of the water layer of the initial reaction with stirring. The temperature of the water layer rose from 20 °C to 40 °C, and the pH of the water layer became 2. Two point one grams of hydrogen sulfide (0.062 mole (molecular weight 34.1)) released by adding 30 wt% hydrochloric acid was introduced into 36 g of 30 wt% sodium hydroxide aqueous solution (sodium hydroxide 10.8 g, 0.270 mole), to absorb it, thereby obtaining sodium sulfide. As the water layer, 67 g of a crude sodium chloride aqueous solution (methanol 13 g, sodium chloride 9.2 g, 0.158 mole) remained.

Subsequently, 4.0 g of 30 wt% sodium hydroxide aqueous solution (sodium hydroxide 1.2 g, 0.030 mole) was added to the crude sodium chloride aqueous solution, for neutralization, to adjust the pH to 7. The temperature of the crude sodium chloride aqueous solution was 30 °C. Then, 2.7 g of 30 % hydrogen peroxide water (hydrogen peroxide 0.81 g, 0.024 mole) was added, and the mixture was heated at 80 °C for 0.5 hour. Air was bubbled from the bottom of the aqueous solution at 80 °C for 0.5 hour, to remove the odor and methanol. Further, the liquid cooled to a temperature of 50 °C, and the insoluble matter was filtered away with filter paper. Thus, 58 g of colorless transparent 19 wt% refined sodium chloride aqueous solution (specific gravity 1.2) could be obtained. The refined sodium chloride aqueous solution contained 11 g of sodium chloride and 0.3 g of sodium sulfate. The refined sodium chloride aqueous solution could be used for regenerating cation exchange resins as described in Example 1. Example 3 (Reaction using hydrous ethanol as a solvent)

The initial reaction as described in Example 1 was performed, except that the same amount of ethanol was supplied instead of methanol and that the mixture (total 584 g) was heated at 100 °C and at normal pressure for 12 hours, and the solid component was treated likewise.

In the initial reaction, 103 g of a solid component was obtained. The amount of the filtrate was 460 g. The solid component contained 72.1 g (1.23 moles) of sodium chloride. A liquid component containing sodium chloride produced as a byproduct adhered to the solid component.

Then, the filtrate was separated into 300 g of the water layer and 152 g of the oil layer of the initial reaction. The water layer had a strong offensive odor of sulfur compounds and was a deep black liquid with a large environmental load. The oil layer was subjected to gas chromatography. The dicyclohexyl disulfide concentration of the oil layer was 59.2 wt% (dicyclohexyl disulfide 90.0 g, 0.391 mole, reaction yield 51.1 %).

In succession, as described above, 300 g of the water layer of the initial reaction can be used in the second reaction, and the water layer of the initial reaction with a large environmental load can be effectively used in the second reaction (re-reaction) without being thrown away at all. (Treatment of solid component)

Eighty eight grams (sodium chloride 62 g, 1.1 moles; sodium sulfide 4.4 g, 0.056 mole) was taken out of the solid component produced as a byproduct in the initial reaction, and 150 ml of water was added to it for dissolution. A blackish green sodium chloride aqueous solution was obtained and had an offensive odor of sulfur compounds. As described in Example 1, the solution was treated to be acidified, and 230 g of a crude sodium chloride aqueous solution remained.

Then, as described in Example 1, the crude sodium chloride aqueous solution was treated for neutralization and the like, to obtain 235 g of colorless transparent 30 wt% refined sodium chloride aqueous solution (specific gravity 1.2). The refined sodium chloride aqueous solution contained 70.5 g of sodium chloride and 1.0 g of sodium sulfate. Example 4 (Method for producing N-(cyclohexylthio)phthalimide)

One hundred and sixty gams of the oil layer (dicyclohexyl disulfide 133 g, 0.577 mole) obtained in the second reaction of Example 1 was concentrated at normal pressure and at 80 to 120°, and further concentrated under reduced pressure at 20 to 85 kPa, to obtain 140 g of refined dicyclohexyl disulfide (purity 94 %).

A glass flask was charged with 87 g of thus obtained refined dicyclohexyl disulfide (purity 94 %, 0.35 mole) and 127 g of a toluene/cyclohexane mixed solvent (toluene 15 wt%), and a cooling medium was used to cool to -20 °C. Twenty milliliters of chlorine (30 g, 0.43 mole (molecular weight 70.9)) gathered in a glass cylinder was blown into the glass flask with stirring in a liquid temperature range from -20 to -10 °C, taking 1.5 hours, to chlorinate dicyclohexyl disulfide, thereby obtaining a cyclohexyl sulfenyl chloride solution (0.70 mole).

Then, the glass flask was charged with 103 g of phthalimide (0.70 mole (molecular weight 147.1)), 129 ml of triethylamine (93 g, 0.92 mole (molecular weight 101.2)), and 127 g of a toluene/cyclohexane mixed solvent (toluene 15 wt%), and hot water was used to heat the mixture up to 60 °C. The cyclohexyl sulfenyl chloride solution prepared as described above was cooled at -10 °C. With stirring, the cyclohexyl sulfenyl chloride solution was added into the flask at 60 to 65 °C, taking 1.5 hours. Then, stirring was continued at 60 to 65 °C for 1 hour, to obtain a reaction mixture containing N-(cyclohexylthio)phthalimide, unreactive phthalimide, triethylammonium chloride, etc.
At 60 to 65 °C, 163 g of hot water was added to the reaction mixture containing N-(cyclohexylthio)phthalimide, to dissolve the ammonium salt and the like, and subsequently, unreactive phthalimide and the like were filtered away. In order to remove the excessive triethylamine and the like from the filtrate into the water layer in a temperature range from 60 to 65 °C, sulfuric acid was added for neutralization. Further, in order to remove the phthalimide remaining in the oil layer, in a temperature range from 60 to 65 °C, 48 wt% caustic soda was added for separating the water layer. The remaining oil layer was cooled to 10 °C, to crystallize crude N-(cyclohexylthio)phthalimide. The crystals were collected by filtration and dried to obtain 159 g of a refined product (purity 99 %, N-(cyclohexylthio)phthalimide content 157 g, 0.60 mole (molecular weight 261.3)) and 280 g of crystallization mother liquor (N-(cyclohexylthio)phthalimide content 6 g, 0.02 mole). The total yield of N-(cyclohexylthio)phthalimide with respect to phthalimide was 89 % (163 g, 0.62 mole), and the crystallization rate of refined N-(cyclohexylthio)phthalimide was 96 %.

The N-(cyclohexylthio)phthalimide concentration was analyzed by gas chromatography under the following conditions. Gas chromatograph: Shimadzu GC-17A Column: NB-1, length 60 m x inner diameter 0.25 mm, film thickness 0.40 um Column temperature: 70 ->• 270 °C, 5 °C/min Carrier He gas pressure: 180 kPa (70 °C) Injection port-FID detector temperature: 270 °C Example 5 (Reaction using recovered sodium sulfide)

As in the treatment of the solid component of Example 1, the solid component was dissolved into water, and the solution was adjusted to acidic pH 4. The released hydrogen sulfide gas was introduced into a gas washing bottle containing 30 wt% sodium hydroxide aqueous solution, to absorb it. The process of dissolving the solid component into water, adjusting to acidic pH 4, and introducing the released hydrogen sulfide gas into a gas washing bottle containing 30 wt% sodium hydroxide aqueous solution, to absorb it was repeated till the gas absorption became unlikely to occur, thereby obtaining 27 wt% sodium sulfide aqueous solution.

A reaction was performed as described in Example 1, except that 311 g of 27 wt% sodium sulfide aqueous solution (water 227 g, sodium sulfide 84.0 g, 1.08 moles) was used and that sodium sulfide and water were not supplied (total 625 g), to obtain 100 g of a solid component. The amount of the filtrate was 500 g. The solid component contained 76.0 g (1.30 moles) of sodium chloride. A liquid component containing sodium chloride produced as a byproduct adhered to the solid component.

Then, the filtrate was separated to obtain 342 g the water layer containing remaining sodium chloride ant 158 g of the oil layer of the initial reaction. The water layer had a strong offensive odor of sulfur compounds and was a deep black liquid with a large environmental load. The oil layer was subjected to gas chromatography. The dicyclohexyl disulfide concentration of the oil layer was 83.5 wt% (dicyclohexyl disulfide 132 g, 0.573 mole, reaction yield 74.9 %).

Comparative Example (Treatment of solid component)

One hundred and seventy five grams of a solid component (sodium chloride 120 g, 2.06 moles; sodium sulfide 8.6 g, 0.11 mole) similar to the solid component used in Example 1 was taken and dissolved into 300 ml of water, to prepare a blackish green sodium chloride aqueous solution having an offensive odor of sulfur compounds. Fifty seven grams of 30 % hydrogen peroxide water (hydrogen peroxide 17 g, 0.5 mole) was added to 475 g of the crude sodium chloride aqueous solution, and the mixture was heated at 80 °C for 0.5 hour. Air was bubbled from the bottom of the aqueous solution at 80 °C for 0.5 hour, to remove the odor. Further, the liquid was cooled to a temperature of 50 °C, and the insoluble matter was filtered away with filter paper. Thus, 530 g of lightly yellow turbid 23 wt% refined sodium chloride aqueous solution (specific gravity 1.2) was obtained. The refined sodium chloride aqueous solution contained 120 g of sodium chloride and 16 g of sodium sulfate.

The solution contains much sodium sulfate. Consequently it cannot be industrially used as a regenerant of cation exchange resins and the like. Further, since the inorganic salt concentration is high, it cannot be discharged into rivers and the ocean as it is.

[Industrial application]

This invention can provide an industrially advantageous dicyclohexyl disulfide production method without adversely affecting the environment. Further, the invention allows byproducts such as sodium chloride to be recovered and effectively used without adversely affecting the environment.

The dicyclohexyl disulfide produced in this invention can be a raw material of N-(cyclohexylthio)phthalimide that is mainly one of rubber vulcanization retarders.

The sodium chloride produced in this invention can be used for regenerating the cation exchange resins used for softening the feed water, washing water and cooling water of industrial boilers.

Claims

[Claim 1] A method for producing dicyclohexyl disulfide in which sodium disulfide and chlorocyclohexane are reacted with each other using a hydrous solvent to synthesize dicyclohexyl disulfide; by acidifying at least a portion of the reaction mixture containing sodium chloride produced as a byproduct, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

[Claim 2] The method for producing dicyclohexyl disulfide, according to claim 1, wherein at least the portion of the reaction mixture containing sodium chloride produced as a byproduct is a solid component and/or a liquid component.

[Claim 3] The method for producing dicyclohexyl disulfide, according to claim 2, wherein the solid component containing sodium chloride is collected from the reaction mixture, and subsequently water is added to the solid component, for preparing an aqueous solution.

[Claim 4] The method for producing dicyclohexyl disulfide, according to claim 3, wherein the solid component containing sodium chloride is collected from the reaction mixture; subsequently an oil layer containing dicyclohexyl disulfide is separated from the filtrate; and the water layer containing remaining sodium chloride is reused for the reaction between sodium disulfide and chlorocyclohexane.

[Claim 5] The method for producing dicyclohexyl disulfide, according to claim 1, wherein at least the portion of the reaction mixture containing sodium chloride produced as a byproduct is acidified to release a gas containing hydrogen sulfide, and the released gas containing hydrogen sulfide is absorbed by a sodium hydroxide aqueous solution, for recovering as a sodium sulfide aqueous solution.

[Claim 6]The method for producing dicyclohexyl disulfide, according to claim 1, wherein the hydrous solvent is hydrous methanol or hydrous ethanol.

[Claim 7] A method for producing N-(cyclohexylthio)phthalimide by using the dicyclohexyl disulfide produced by the method described in claim 1 as a raw material.

[Claim 8] A method for producing sodium chloride, by acidifying at least a portion of the reaction mixture containing sodium chloride produced by reacting sodium disulfide and chlorocyclohexane with each other using a hydrous solvent, and subsequently neutralizing the acidified reaction mixture for recovering sodium chloride.

[Claim 9] The method for producing sodium chloride, according to claim 8, wherein at least the portion of the reaction mixture containing sodium chloride produced as a byproduct is a solid component and/or a liquid component.

[Claim 10] The method for producing sodium chloride, according to claim 9, wherein thesolid component containing sodium chloride is collected from the reaction mixture, and subsequently water is added to the solid component, to prepare an aqueous solution.

[Claim 11] The method for producing sodium chloride, according to claim 8, wherein at least the portion of the reaction mixture containing sodium chloride produced as a byproduct is acidified to release a gas containing hydrogen sulfide, and the released gas containing hydrogen sulfide is absorbed by a sodium hydroxide aqueous solution, for recovering as a sodium sulfide aqueous solution.

[Claim 12] The method for producing sodium chloride, according to claim 8, wherein the hydrous solvent is hydrous methanol or hydrous ethanol.

[Claim 13] A sodium chloride using method for using the sodium chloride recovered by the sodium chloride production method set forth in claim 8, as a regenerant of cation exchange resins.