Method for producing S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate

Abstract

The purpose of the present invention is to provide a method for producing high-purity S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate by efficiently removing starting materials used for the synthesis and specific impurities produced during the synthesis from S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. The present invention provides a method for producing S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, the method comprising: a step (reaction step) in which 2,3-dimercapto-6-methylquinoxaline is converted into an alkali metal salt or an alkaline earth metal salt, and is subsequently reacted with a phenyl chloroformate in the presence of a phase-transfer catalyst; and a purification step which is characterized by purifying S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate with use of an acetic acid ester, the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate having been obtained by the reaction.

Description

[Technical Field]

[0001] The present invention relates to a method for producing S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, which is useful as a vulcanizing agent for polymers. [Background technology]

[0002] S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate is a compound widely used as an agricultural chemical and is also known to be useful as a vulcanizing agent for polymers.

[0003] The following methods are known for producing this compound: For example, Patent Document 1 describes that this compound can be synthesized by reacting 2,3-dimercapto-6-methylquinoxaline with phosgene in the presence of sodium hydroxide as an acid acceptor.

[0004] On the other hand, Patent Document 2 describes a method that does not use phosgene, in which 2,3-dimercapto-6-methylquinoxaline is converted into a metal salt and reacted with phenyl chloroformate in the presence of a phase transfer catalyst. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 3,510,486 [Patent Document 2] Japanese Patent Application Publication No. 11-80133 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the method described in Patent Document 2, when S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate is used as a vulcanizing agent for a polymer, if raw materials used in the synthesis or specific impurities generated remain in S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, they may affect vulcanization.

[0007] An object of the present invention is to provide a production method by which raw materials used in the synthesis and specific impurities generated can be efficiently removed from S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate to obtain high-purity S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. [Means for solving the problem]

[0008] Means for Solving the Problems The present inventors have conducted extensive research in order to achieve the above-mentioned object, and as a result have found that by using a specific solvent for purifying S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, raw materials used in the synthesis and specific impurities produced can be efficiently removed from S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, thereby obtaining high-purity S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, and have thus completed the present invention.

[0009] That is, the present invention provides the following aspects. Item 1. A step (reaction step) of converting 2,3-dimercapto-6-methylquinoxaline into an alkali metal salt or alkaline earth metal salt, and then reacting the salt with a phenyl chloroformate in the presence of a phase transfer catalyst to obtain S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate; and a purification step of purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction using an acetic acid ester. Item 2. The production method according to Item 1, wherein the acetate ester is one or more selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, and isobutyl acetate. Item 3. The method according to Item 1 or 2, wherein the purification using acetate esters in the purification step is performed by one or more of immersion, recrystallization, and solvent extraction. [Effects of the Invention]

[0010] The process of the present invention makes it possible to obtain high-purity S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate by reducing the raw materials used in the synthesis and the specific impurities produced. The S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the process of the present invention is useful as a vulcanizing agent for polymers. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method for producing S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate by converting 2,3-dimercapto-6-methylquinoxaline into an alkali metal salt or alkaline earth metal salt, and then reacting the salt with a phenyl chloroformate in the presence of a phase transfer catalyst (reaction step); and a purification step of purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction using an acetate ester. By providing this configuration, the present invention can obtain highly pure S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate in good yield.

[0012] Reaction process In the reaction step of the production method of the present invention, 2,3-dimercapto-6-methylquinoxaline is converted into an alkali metal salt or alkaline earth metal salt, and then the salt is reacted with a phenyl chloroformate in the presence of a phase transfer catalyst to obtain S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. The reaction step can be carried out, for example, according to the description in JP-A-11-80133.

[0013] The 2,3-dimercapto-6-methylquinoxaline used in the reaction step can be easily synthesized by a common method. For example, it can be easily obtained by reacting 2,3-dihalogeno-6-methylquinoxaline (e.g., 2,3-dichloro-6-methylquinoxaline, 2,3-dibromo-6-methylquinoxaline, etc.) with NaSH in the presence of sulfur. Alternatively, commercially available products may be used.

[0014] When converting 2,3-dimercapto-6-methylquinoxaline into an alkali metal salt or alkaline earth metal salt, a hydroxide of an alkali metal or alkaline earth metal can be used. Examples of hydroxides of alkali metals or alkaline earth metals that can be used include sodium hydroxide, potassium hydroxide, and calcium hydroxide. Examples of carbonates that can be used include sodium carbonate, potassium carbonate, sodium bicarbonate, and calcium carbonate. These can be used alone or in combination of two or more. Among these, hydroxides of alkali metals or alkaline earth metals are preferred, with sodium hydroxide, potassium hydroxide, and calcium hydroxide being more preferred.

[0015] The amount of alkali metal or alkaline earth metal hydroxide added may be 1.0 to 5.0 times by mole, preferably 1.5 to 4.0 times by mole, and more preferably 2.5 to 3.0 times by mole, relative to 2,3-dimercapto-6-methylquinoxaline.

[0016] The alkali metal salt or alkaline earth metal chloride of 2,3-dimercapto-6-methylquinoxaline can usually be converted into a metal chloride by reacting 2,3-dimercapto-6-methylquinoxaline with an alkali metal or alkaline earth metal hydroxide, carbonate, or the like in water or an alcohol solvent such as methanol. The temperature and time for the metal chloride can be adjusted as appropriate, but the temperature may be from room temperature to 100°C, preferably from 50°C to 100°C, and the time may be from 0.5 hours to 100 hours, preferably from 1 hour to 50 hours, and more preferably from 1 hour to 10 hours.

[0017] The alkali metal or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline is reacted with phenyl chloroformates in the presence of a phase transfer catalyst to give S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate.

[0018] Examples of the phase transfer catalyst include quaternary ammonium salts, pyridinium salts, and quaternary phosphonium salts. More specifically, tetra-n-butylammonium bromide, tetra-n-butylammonium chloride, trioctylmethylammonium chloride, Nn-octylpyridinium chloride, and tetrabutylphosphonium chloride are mentioned. These may be used alone or in combination of two or more. The amount of the phase transfer catalyst used is usually 0.1 to 20 mol %, and preferably 1 to 5 mol %, based on the 2,3-dimercapto-6-methylquinoxaline.

[0019] Examples of phenyl chloroformates include phenyl chloroformate, methylphenyl chloroformate, chlorophenyl chloroformate, fluorophenyl chloroformate, bromophenyl chloroformate, nitrophenyl chloroformate, trifluoromethylphenyl chloroformate, and butylphenyl chloroformate. These may be used alone or in combination of two or more. Among these, phenyl chloroformate, methylphenyl chloroformate, chlorophenyl chloroformate, fluorophenyl chloroformate, and bromophenyl chloroformate are preferred, and phenyl chloroformate and methylphenyl chloroformate are more preferred.

[0020] The amount of phenyl chloroformates used may be in the range of 1.0 to 5.0 times by mole, preferably 2.0 to 5.0 times by mole, relative to 2,3-dimercapto-6-methylquinoxaline.

[0021] The alkali metal or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline can be used in the reaction with phenyl chloroformates as an aqueous solution, powder, or solvent slurry. Typically, 2,3-dimercapto-6-methylquinoxaline and an alkali metal or alkaline earth metal hydroxide or carbonate are converted into a metal salt in water or an alcoholic solvent such as methanol. A solvent such as an aromatic hydrocarbon (e.g., toluene or xylene), a ketone (e.g., methyl isobutyl ketone), or a halogenated hydrocarbon (e.g., 1,2-dichloroethane) is then added, followed by azeotropic dehydration or solvent substitution to obtain a slurry of the alkali metal or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline. The slurry of the alkali metal or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline can be filtered and isolated, or used directly in the reaction with phenyl chloroformates.

[0022] The reaction solvent used in the reaction of an alkali metal salt or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline with a phenyl chloroformate can be a solvent or a mixture thereof. Examples of the solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as 1,2-dichloroethane, dichloromethane, and chloroform; ethers such as diethyl ether, dioxane, and tetrahydrofuran; ketones such as acetone and methyl isobutyl ketone; and polar solvents such as dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile. These solvents may be used alone or in combination.

[0023] The reaction temperature is usually −30 to 200° C., preferably in the range of 0 to 100° C. The reaction time is affected by the reaction temperature and is not necessarily limited, but is usually 0.5 to 100 hours, preferably 0.5 to 48 hours, and more preferably 0.5 to 10 hours. The reaction is usually carried out by adding a phenyl chloroformate dropwise to a reaction solvent containing an alkali metal salt or alkaline earth metal salt of 2,3-dimercapto-6-methylquinoxaline and a phase transfer catalyst, but the reverse may also be done, or simultaneous dropwise addition is also possible.

[0024] The S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction can be easily isolated from the reaction solution by a common procedure such as filtration.

[0025] The S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction contains raw materials used in the synthesis (such as a phase transfer catalyst) and specific impurities (such as diphenyl carbonate) that are produced. In the production method of the present invention, in order to remove these impurities, the product is subjected to a purification step using acetate esters.

[0026] Purification process The purification step in the production method of the present invention is characterized by purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained in the reaction step using an acetate ester, which allows for the removal of raw materials used in the synthesis (such as a phase transfer catalyst) and specific impurities produced (such as diphenyl carbonate) with a high yield of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate.

[0027] In the purification step in the production method of the present invention, any purification method may be used as long as purification is performed using acetate esters. For example, impurities may be removed by immersing S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate in acetate esters, S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate may be recrystallized using acetate esters, or S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate may be solvent extracted using acetate esters. Purification can also be performed by combining these methods. The purification step in the production method of the present invention does not include spray-washing using acetate esters. Spray-washing may be performed before or after the purification step in the production method of the present invention.

[0028] Among these, it is preferable to immerse S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate in acetate esters because this method can provide high yield and high purity. In other words, by contacting the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction with acetate esters for a certain period of time or longer, impurities contained in the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate can be efficiently removed.

[0029] The solvent used in the purification step is not particularly limited as long as it is an acetate ester. Examples include acetate esters having an alkyl group (preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms), such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert-butyl acetate, n-pentyl acetate, n-hexyl acetate, isoamyl acetate, n-heptyl acetate, and n-octyl acetate; geranyl acetate, vinyl acetate, phenyl acetate, furfuryl acetate, benzyl acetate, and linalyl acetate. These may be used alone or in combination of two or more. Among these, acetate esters having an alkyl group are preferred, and methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, and isobutyl acetate are more preferred. The solvent used in the purification step in the production method of the present invention may contain an acetate ester, or a mixed solvent with other solvents may be used. When a mixed solvent is used, the content of acetate esters in the mixed solvent may be 50% by weight or more, preferably 75% by weight or more, and more preferably 90% by weight or more. By using acetate esters in the purification process, raw materials used during synthesis (such as a phase transfer catalyst) and specific impurities (such as diphenyl carbonate) that are generated and are contained in the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction can be efficiently removed.

[0030] Examples of other solvents when a mixed solvent with acetate esters is used as the solvent for the purification step include alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, etc., ether solvents such as tetrahydrofuran, diethyl ether, methyl tert-butyl ether, aromatic hydrocarbon solvents such as benzene, toluene, etc., aliphatic hydrocarbon solvents such as pentane, hexane, heptane, cyclohexane, etc., halogenated solvents such as methylene chloride, 1,2-dichloroethane, etc., ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, etc., and nitrile solvents such as acetonitrile, propionitrile, etc. These may be used alone or in combination of two or more.

[0031] In the purification step, S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate is purified using acetate esters, which makes it possible to remove raw materials used in the synthesis (such as a phase transfer catalyst) and specific impurities produced (such as diphenyl carbonate).Furthermore, in the purification step, S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate is purified using acetate esters, making it possible to obtain high-purity S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate in high yield.

[0032] The amount of acetate esters used in the purification step can be appropriately determined, but for example, it may be 1 to 200 times the weight of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate, preferably 5 to 100 times, and more preferably 10 to 50 times.

[0033] In the purification step, the contact time between S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and the acetate esters (preferably the immersion time when immersion is performed) is not particularly limited, but may be, for example, 1 minute or more, preferably 0.5 to 72 hours. The temperature of the acetate esters in the purification step may be below the boiling point of the solvent, preferably 0 to 50°C.

[0034] The S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate that has been subjected to the purification step can be recovered by a conventional method such as filtration or vacuum drying. It may also be washed with a solvent, if necessary. The purification step in the production method of the present invention can be repeated multiple times depending on the purpose, thereby removing impurities from the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. [Example]

[0035] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0036] Example 1: Examination of solvents used in the purification process The following experiment was conducted to find a solvent that could efficiently remove impurities contained in S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate during the purification process. S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and diphenyl carbonate were added to each solvent, and their solubilities were confirmed. A rating of ◯ was given to solvents in which S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate was poorly soluble and diphenyl carbonate was highly soluble. A rating of × was given to solvents in which S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate was highly soluble and diphenyl carbonate was highly soluble, and to solvents in which S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate was poorly soluble and diphenyl carbonate was highly soluble. The results are shown in Table 1.

[0037] [Table 1]

[0038] As shown in Table 1, we found that ethyl acetate, an acetate ester, is a solvent that can efficiently remove impurities from S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate because it has low solubility for S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and high solubility for diphenyl carbonate. Other solvents either have high or low solubility for both S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and diphenyl carbonate, and are not suitable for removing impurities from S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate by themselves. Table 1 shows that by purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction using acetate esters, specific impurities (e.g., diphenyl carbonate) that are produced can be removed with a good yield of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate.

[0039] Example 2 24.0 g of sodium hydroxide was dissolved in 190 ml of water, and 50.0 g of 2,3-dimercapto-6-methylquinoxaline was added thereto and stirred at room temperature for 1 hour. Next, 500 ml of toluene was added, and azeotropic dehydration was performed. After cooling, 3.9 g of tetra-n-butylammonium bromide was added, and a solution of 78.9 g of phenyl chloroformate and 95 ml of toluene was added dropwise over 60 minutes at 40-45°C. The mixture was then stirred at 45°C for 3 hours. After the reaction was completed, the mixture was filtered at 80°C while still hot, and the resulting inorganic salts were removed. The mixture was then heated to 90°C to dissolve the solids, then cooled to 25°C at a rate of 0.1°C per minute. After reaching 25°C, stirring was continued for 13 hours, and the precipitated solid was collected by filtration. 400 ml of ethyl acetate was added to 47.7 g of the obtained solid (29.6 g of pure S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate), and the solid was immersed at room temperature for 1 hour, followed by filtering again. After washing with another 400 ml of ethyl acetate and vacuum drying, 27.0 g of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate was obtained. The yield was 48%. Table 2 shows the purity and impurity content of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. The purity and impurity content of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate were analyzed using the measurement methods described below.

[0040] Comparative Example 1 28.8 g of sodium hydroxide was dissolved in 227 ml of water, and 60.0 g of 2,3-dimercapto-6-methylquinoxaline was added. The mixture was stirred at room temperature for 1 hour. 692 ml of toluene was then added, and azeotropic dehydration was performed. After cooling, 4.6 g of tetra-n-butylammonium bromide was added, and a solution of 94.7 g of phenyl chloroformate and 131 ml of toluene was added dropwise over 60 minutes at 40-45°C. The mixture was then stirred at 45°C for 3 hours. After the reaction was complete, the mixture was filtered at 80°C while hot to remove the inorganic salts. The mixture was then heated to 90°C to dissolve the solids, then cooled to 25°C at a rate of 0.1°C per minute. After reaching 25°C, stirring was continued for 13 hours. The solid (70.6 g) obtained by filtration was washed with 240 ml of ethyl acetate (contact time: 30 seconds) and then vacuum dried to obtain 43.8 g of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. The yield was 65%. Table 2 shows the purity and impurity content of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate. The purity and impurity content of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate were analyzed using the measurement methods described below.

[0041] Measurement method for S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and diphenyl carbonate The purity of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate and the amount of diphenyl carbonate contained in S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate were analyzed using high performance liquid chromatography under the following conditions. Equipment used: Shimadzu LC-2030 Column used: Osaka Soda SP-120-5-ODS-P (4.6 mm I.D. x 150 mm) Flow rate: 1.0mL / min Developing solvent: MeCN / H2O (ratio: 1 / 1) Temperature: 40℃ Wavelength: 254nm

[0042] Measurement method for tetra-n-butylammonium bromide The tetra-n-butylammonium bromide contained in S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate was analyzed using NMR. The content was calculated based on the proton ratio between the chemical shift of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate (7.91 ppm, 1H min) and the chemical shift of tetra-n-butylammonium bromide (1.00 ppm, 12H min). Equipment used: JEOL ECZS-400 Deuterated solvent: DMSO-D6

[0043] [Table 2]

[0044] As shown in Table 2, by not only washing the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained in the reaction but also contacting it with ethyl acetate for a certain period of time, it was possible to efficiently remove impurities such as tetra-n-butylammonium bromide and diphenyl carbonate contained in the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate to less than 0.1%. As a result, S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate with a high purity of 99.6% was obtained. Table 2 shows that by purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction using acetate esters, the raw materials used in the synthesis (phase transfer catalyst, etc.) and specific impurities produced (e.g., diphenyl carbonate, etc.) can be removed with a good yield of S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate.

Claims

1. a step of converting 2,3-dimercapto-6-methylquinoxaline into an alkali metal salt or alkaline earth metal salt, and then reacting the salt with a phenyl chloroformate in the presence of a phase transfer catalyst to obtain S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate (reaction step); and a purification step of purifying the S,S-(6-methylquinoxaline-2,3-diyl)dithiocarbonate obtained by the reaction using an acetic acid ester.

2. 2. The method according to claim 1, wherein the acetate ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, and isobutyl acetate.

3. 3. The method according to claim 1, wherein the purification using an acetic acid ester in the purification step is performed by one or more of immersion, recrystallization, and solvent extraction.

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