Method for producing thiol compounds

Abstract

This method for producing a thiol compound comprises a light irradiation step in which a thiol compound having a color or a composition including said thiol compound is irradiated with light. In the light irradiation step, the composition is preferably irradiated with light including light having a wavelength of 250-600 nm.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thiol compound. This application claims priority based on Japanese Patent Application No. 2020-095577, filed on June 1, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, from the viewpoint of energy saving and productivity improvement, there has been a demand for curable resins with good curability that can be cured quickly with low energy. As such curable resins, curable resins containing thiols have attracted attention. For example, Patent Documents 1 and 2 describe photocurable resin compositions containing a thiol compound. Patent Document 3 describes photocuring a resin composition containing a thiol compound followed by thermal curing. Patent Documents 4 to 7 describe resin compositions containing a thiol compound that are excellent in low-temperature curing properties.

[0003] Patent Document 8 describes a method for producing a mercaptocarboxylic acid polyhydric alcohol ester by esterifying a mercaptocarboxylic acid or a mercaptocarboxylic acid ester with a polyhydric alcohol. Patent Document 8 also describes that the produced tetrakis(3-mercaptobutanoic acid) pentaerythritol ester is a pale yellow liquid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5801556 [Patent Document 2] Patent No. 6468315 [Patent Document 3] Patent No. 6184003 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-93887 [Patent Document 5] Japanese Patent Application Laid-Open No. 2017-43721 [Patent Document 6] Japanese Patent Application Laid-Open No. 2016-12131 [Patent Document 7] Japanese Patent Application Laid-Open No. 2016-104875 [Patent Document 8] Japanese Patent Application Laid-Open No. 2011-084479 [Patent Document 9] Patent No. 5713886 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, curable resins used for specific applications, such as optical materials and the outer surfaces of final products, are required to have little coloration and excellent transparency. In recent years, there has been a demand for improving the curability of curable resins used for such specific applications. However, thiol compounds are typically colored in yellow, orange, brown, red, or the like. It is difficult to incorporate colored thiol compounds into curable resins that require transparency in order to improve their curability. For this reason, there is a demand for a technology that can reduce the coloration of thiol compounds.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a thiol compound that can reduce the coloration of the thiol compound. [Means for solving the problem]

[0007] [1] A method for producing a thiol compound, comprising a light irradiation step of irradiating a colored thiol compound or a composition containing the thiol compound with light.

[0008] [2] The method for producing a thiol compound according to [1], wherein the light includes light having a wavelength of 250 nm to 600 nm. [3] The Hazen color number of the thiol compound or the composition is 100 or more, The method for producing a thiol compound according to [1] or [2], wherein the light irradiation step is carried out until the Hazen color number of the thiol compound or the composition becomes less than 100.

[0009] [4] The method for producing a thiol compound according to any one of [1] to [3], wherein the thiol compound contains a thiol having at least one secondary mercapto group. [5] The method for producing a thiol compound according to any one of [1] to [3], wherein the thiol compound contains one or both of 3-mercaptocarboxylic acid and a 3-mercaptocarboxylic acid ester. [6] The method for producing a thiol compound according to [5], wherein the thiol compound contains one or both of 3-mercaptobutanoic acid and a 3-mercaptobutanoic acid ester.

[0010] [7] The method for producing a thiol compound according to [6], wherein the 3-mercaptobutanoic acid ester is any one of compounds represented by the following formulas (1) to (4):

[0011] [ka] (In formula (1), R 1 represents a hydrogen atom or a group represented by formula (5). (In formula (2), R 2 , R 3 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (3), R 4 , R 5 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (4), R 6 , R 7 , R 8 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (5), * indicates the bonding position with the compounds represented by formulas (1) to (4).)

[0012] [8] The method for producing a thiol compound according to [6], wherein the 3-mercaptobutanoic acid ester is any one of the compounds represented by the following formulas (6) to (9):

[0013] [ka]

[0014] [9] The method for producing a thiol compound according to any one of [1] to [8], wherein the composition contains the thiol compound and at least one solvent selected from the group consisting of toluene, xylene, cyclohexane, methylcyclohexane, acetonitrile, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl acetate, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and water. [Effects of the Invention]

[0015] The method for producing a thiol compound of the present invention includes a light irradiation step of irradiating a colored thiol compound or a composition containing a colored thiol compound with light, thereby reducing the coloration of the thiol compound. DETAILED DESCRIPTION OF THE INVENTION

[0016] In order to solve the above problems, the present inventors have conducted extensive research as described below. Typically, compounds are stored in a light-shielded environment to prevent the compounds from being altered by light energy. Thiol compounds were also thought to be altered when exposed to light, so they were stored in a light-shielded environment like other general compounds.

[0017] However, as a result of intensive research by the present inventors, it was found that even if a thiol compound is colored, the thiol compound can be decolorized by exposing it to light. This is presumably due to the fact that unspecified impurities in the colored thiol compounds are decomposed by light energy, resulting in a change such as becoming a colorless substance. Thiol compounds generally contain impurities such as by-products produced during synthesis and excess raw materials. Thiol compounds are purified as needed during and / or after production. Therefore, the amount of impurities contained in thiol compounds used as materials for curable resins is minimal. However, the details of the impurities that color the inherently colorless and transparent thiol compounds have not been clarified. Therefore, the method for removing them is unknown, and it is presumed that they may not be sufficiently removed.

[0018] Therefore, the present inventors conducted further studies and found that by irradiating a colored thiol compound or a composition containing the same with light, the coloration of the thiol compound can be reduced regardless of the type of thiol compound, and thus conceived the present invention.

[0019] The method for producing a thiol compound of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments. The method for producing a thiol compound of the present embodiment includes a light irradiation step of irradiating a colored thiol compound or a composition containing the same with light.

[0020] "Colored thiol compounds" The colored thiol compound contains unspecified impurities. The colored thiol compound is not particularly limited as long as it has a higher Hazen color number than the pure substance. For example, the colored thiol compound has a Hazen color number of 100 or more, and may have a Hazen color number of 80 or more, 40 or more, or 20 or more. Generally, if the Hazen color number is 10 or more, the color can be confirmed visually.

[0021] The colored thiol compound has at least one mercapto group. The mercapto group may be any of a primary mercapto group, a secondary mercapto group, and a tertiary mercapto group. The colored thiol compound may have two or more mercapto groups selected from a primary mercapto group, a secondary mercapto group, and a tertiary mercapto group. The colored thiol compound may be only one type, or two or more types.

[0022] Examples of thiol compounds having a primary mercapto group include 3-mercaptopropionic acid, 3-mercaptopropionic acid esters, bisphenol A type thiol, and polyether polymer type thiol. Examples of 3-mercaptopropionic acid esters include esters of 3-mercaptopropionic acid with an alcohol selected from the group consisting of 1,4-butanediol, 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trimethylolpropane, and pentaerythritol. Specifically, pentaerythritol tetrakis(3-mercaptopropionate) and trimethylolpropane tris(3-mercaptopropionate) can be used. As the bisphenol A thiol, for example, bisphenol A thiol QX11 manufactured by Mitsubishi Chemical can be used. As the polyether polymer type thiol, for example, polyether polymer type thiol CAPCURE 3-800 manufactured by Cognis can be used.

[0023] Examples of thiol compounds having a secondary mercapto group include 3-mercaptobutanoic acid, 3-mercaptobutanoic acid esters, etc. Examples of 3-mercaptobutanoic acid esters include esters of 3-mercaptobutanoic acid with an alcohol selected from the group consisting of 1,4-butanediol, 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trimethylolpropane, and pentaerythritol.

[0024] Preferably, the colored thiol compound comprises a thiol having at least one secondary mercapto group. The colored thiol compound preferably contains one or both of 3-mercaptocarboxylic acid and 3-mercaptocarboxylic acid ester, and more preferably contains one or both of 3-mercaptobutanoic acid and 3-mercaptobutanoic acid ester. Specifically, the 3-mercaptobutanoic acid ester is preferably any one of the compounds represented by the following formulas (1) to (4): When the colored thiol compound contains any one of the compounds represented by the following formulas (1) to (4), the effect of reducing the coloration of the thiol compound by irradiating it with light is significant.

[0025] [ka] (In formula (1), R 1 represents a hydrogen atom or a group represented by formula (5). (In formula (2), R 2 , R 3 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (3), R 4 , R 5 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (4), R 6 , R 7 , R 8 each independently represents a hydrogen atom or a group represented by formula (5). (In formula (5), * indicates the bonding position with the compounds represented by formulas (1) to (4).)

[0026] The 3-mercaptobutanoic acid ester is more preferably any one of 1,4-bis(3-mercaptobutyryloxy)butane represented by the following formula (6), 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione represented by the following formula (7), trimethylolpropane tris(3-mercaptobutyrate) represented by the following formula (8), and pentaerythritol tetrakis(3-mercaptobutyrate) represented by the following formula (9).

[0027] [ka]

[0028] The thiol compound can be produced by a conventionally known method. For example, 3-mercaptocarboxylic acids such as 3-mercaptobutanoic acid can be synthesized by a method of reacting an α,β-unsaturated carboxylic acid with hydrogen sulfide in the presence of a basic compound in an aqueous solution, as described in Patent Document 9.

[0029] For example, 3-mercaptobutanoic acid esters such as the compounds represented by formulas (6) to (9) can be synthesized by synthesizing 3-mercaptobutanoic acid and then esterifying the 3-mercaptobutanoic acid with a polyhydric alcohol, as described in Patent Document 8.

[0030] (composition) The composition of this embodiment contains a colored thiol compound and, as necessary, contains a solvent and / or other compounds that are not thiol compounds. The Hazen color number of a composition containing a colored thiol compound is, for example, 100 or more. The Hazen color number of a composition containing a colored thiol compound may be 80 or more, 40 or more, or 20 or more. Generally, if the Hazen color number is 10 or more, the color can be confirmed visually.

[0031] [solvent] The composition of the present embodiment may contain a solvent as needed, which can be appropriately selected depending on the type of thiol compound and the wavelength of light irradiated in the light irradiation step. Examples of solvents that can be used include organic solvents such as hydrocarbons, alcohols, esters, ketones, and ethers, and / or water. Specifically, it is preferable to use at least one solvent selected from the group consisting of toluene, xylene, cyclohexane, methylcyclohexane, acetonitrile, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl acetate, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and water. Among these solvents, acetonitrile and water do not exhibit strong absorption of light in the wavelength range of 200 nm or more, and thus easily transmit the light irradiated in the photoirradiation step. Therefore, acetonitrile and / or water are preferred as the solvent, as they facilitate efficient light irradiation of the thiol compound in the photoirradiation step.

[0032] When the thiol compound is solid at room temperature (25°C), it is preferable to irradiate the thiol compound as a composition dissolved or dispersed in a solvent. When the composition contains a thiol compound that is solid at room temperature and a solvent that dissolves or disperses it, the thiol compound is irradiated with light more uniformly and without unevenness in the light irradiation step than when no solvent is included. As a result, the coloration of the thiol compound can be reduced with less light energy. Even when the thiol compound is a liquid with high viscosity at room temperature (25°C), it is preferable to irradiate the thiol compound as a composition dissolved or dispersed in a solvent. When the composition contains a thiol compound that is a liquid with high viscosity at room temperature and a solvent that dissolves or disperses it, the thiol compound is irradiated with light more uniformly and without unevenness in the light irradiation step than when no solvent is included. As a result, coloration of the thiol compound can be reduced with less light energy.

[0033] Furthermore, even when the thiol compound exhibits significant coloration (e.g., a Hazen color number of 150 or more), the thiol compound may be diluted with a solvent to form a composition before the light irradiation step. This reduces the concentration of the thiol compound in the solution compared to when the light irradiation step is performed on the thiol compound alone, allowing for efficient and uniform light irradiation. As a result, the irradiation time and / or irradiation intensity of the light irradiated in the light irradiation step can be shortened.

[0034] When the composition contains a solvent, the content of the solvent in the composition is not particularly limited and can be, for example, 10 to 90% by mass, preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, and can be appropriately determined depending on the type of thiol compound, etc. When the content of the solvent in the composition is 30% by mass or more, the effect of light reaching the interior by dilution is significant, and the thiol compound can be uniformly and efficiently irradiated with light in the light irradiation step. Furthermore, when the content of the solvent in the composition is 70% by mass or less, the amount of solvent consumed can be reduced, and the light irradiation step can be performed more efficiently using smaller equipment. Furthermore, when the content of the solvent in the composition is 70% by mass or less, the solvent can be easily removed when removing it after the light irradiation step, and the process can be more efficient when the solvent is recovered and reused.

[0035] [Other compounds that are not thiol compounds] The composition containing the thiol compound in this embodiment may contain other compounds that are not thiol compounds or solvents, as needed. Examples of other compounds include by-products produced during the synthesis of the thiol compound, excess raw materials, stabilizers, pH adjusters, etc., and can be determined depending on the use of the thiol compound after the photoirradiation step, and are not particularly limited.

[0036] When the composition contains a compound other than a thiol compound, the content of the other compound in the composition is not particularly limited and can be, for example, 0.1 to 10 mass %, and can be determined appropriately depending on the type of thiol compound.

[0037] The composition preferably does not contain polymers. Here, a polymer refers to a compound in which five or more monomers are bonded, typically ten or more. When a composition contains a polymer, it becomes difficult to achieve a bleaching effect by irradiating it with light. More specifically, polymerized substances have restricted molecular movement and generally have low or no fluidity. For this reason, it is known that chemical reactions are less likely to occur in compositions containing such polymers. Therefore, it is presumed that even if a composition containing a polymer is irradiated with light, unspecified impurities contained in the composition are less likely to be decomposed. The content of polymers in the composition is preferably 10% by mass or less, more preferably 5% by mass or less.

[0038] Furthermore, it is preferable that the composition does not contain a photopolymerized material. This is because the molecular motion of the photopolymerized material is restricted, and because the decolorization effect of light irradiation is difficult to achieve for the following reasons: Photopolymerized materials typically contain compounds such as photopolymerization initiators and their decomposition products. Many of these compounds become discolored when exposed to excessive light. Therefore, it is presumed that irradiating a composition containing a photopolymerized material with light not only decomposes unspecified impurities contained in the composition, but also may discolor these compounds, making it difficult to achieve the decolorization effect. The content of the photopolymerized material in the composition is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0039] [Light irradiation process] In the light irradiation step of this embodiment, a colored thiol compound or a composition containing a colored thiol compound is irradiated with light. In the process for producing a thiol compound of this embodiment, the light irradiation step can be performed once or multiple times.

[0040] In the light irradiation step, the wavelength of the irradiated light can be appropriately determined depending on the type of thiol compound and the composition of the composition. In this embodiment, the irradiated light preferably includes light with a wavelength of 250 nm to 600 nm. Light with a wavelength of 250 nm or more is preferred because it is less likely to be blocked by absorption by the thiol compound and organic solvent. Light with a wavelength of 600 nm or less is also preferred because it has sufficient energy to reduce the coloration of the thiol compound. The irradiated light more preferably includes light with a wavelength in the range of 300 nm to 550 nm, and even more preferably includes light in the range of 350 to 500 nm, because this can effectively reduce the coloration of a colored thiol compound.

[0041] The type of light source used in the light irradiation step is not particularly limited. Specifically, sunlight, incandescent lamps, fluorescent lamps, light-emitting diode (LED) lamps, etc. can be used as the light source. Among these light sources, sunlight is particularly preferred because it has a high light irradiation intensity, contains light of a wide range of wavelengths, and does not require the supply of energy from a power source, etc.

[0042] The method for evaluating the coloration is not particularly limited, but since the color of a colored thiol compound is typically yellow, the Hazen color number (APHA) can be preferably used. The Hazen color number can be determined, for example, by measuring with a spectrometer or by using a colorimetric tube.

[0043] The change in the Hazen color number (APHA) of the measurement object (a colored thiol compound or a composition containing a colored thiol compound) due to the light irradiation step can be adjusted by adjusting the wavelength, irradiation intensity, and irradiation amount (light irradiation time) of the irradiated light relative to the composition and amount of the colored thiol compound or the composition containing it. The stronger and more the energy of the light irradiated in the light irradiation step, the greater the effect of reducing the coloration of the colored thiol compound.

[0044] For example, when the Hazen color number (APHA) of the thiol compound or a composition containing the thiol compound is 100 or more, the light irradiation step is preferably carried out until the Hazen color number becomes less than 100. In this case, the thiol compound after the light irradiation step can be preferably used as a resin raw material for optical materials, exterior materials, paints, etc. In order to obtain a thiol compound that is more suitable for these applications, the light irradiation step is more preferably carried out until the Hazen color number becomes 80 or less, and even more preferably until the Hazen color number becomes 60 or less.

[0045] Even when the Hazen color number (APHA) of a thiol compound or a composition containing the same is less than 100, a light irradiation step may be carried out to further reduce coloration. For example, when the Hazen color number is 80 or more, the light irradiation step may be carried out until the Hazen color number becomes less than 80, more preferably until the Hazen color number becomes 70 or less, and even more preferably until the Hazen color number becomes 60 or less. When the Hazen color number is 60 or more, the light irradiation step may be carried out until the Hazen color number becomes less than 60, more preferably until the Hazen color number becomes 50 or less, and even more preferably until the Hazen color number becomes 40 or less.

[0046] The container for containing the thiol compound or the composition containing it when performing the light irradiation step can be, for example, a resin container made of polypropylene or the like, a glass container, etc., and the material and shape are not particularly limited. When irradiating the thiol compound or the composition containing it from the outside of the container in the light irradiation step with light, it is preferable to use a container that has good transmittance of light of the irradiated wavelength.

[0047] The light irradiation step is preferably carried out while stirring the thiol compound or the composition containing the thiol compound contained in the container, which allows the coloration of the colored thiol compound to be uniformly and efficiently reduced and allows the heat imparted from the light source to the thiol compound or the composition containing the thiol compound to be efficiently dissipated. The temperature, pressure and other conditions when carrying out the light irradiation step are not particularly limited.

[0048] The thiol compound or a composition containing the thiol compound after the light irradiation step can be used as a resin raw material for optical materials, exterior materials, paints, etc. If the composition after the light irradiation step contains a solvent, the solvent may be removed using a known method as needed. Furthermore, if the composition after the light irradiation step contains a compound other than a thiol compound, the other compound may be removed using a known method as needed.

[0049] The thiol compound after the photoirradiation step may be used as an intermediate product. For example, the thiol compound after the photoirradiation step may be 3-mercaptocarboxylic acid synthesized as an intermediate product in a step of synthesizing a 3-mercaptocarboxylic acid ester such as 3-mercaptobutanoic acid ester. By producing a 3-mercaptocarboxylic acid ester by a method of esterifying the 3-mercaptocarboxylic acid after the photoirradiation step, a product with little coloring can be obtained.

[0050] The method for producing a thiol compound of the present embodiment includes a light irradiation step of irradiating a colored thiol compound or a composition containing the same with light, thereby reducing the coloration of the thiol compound. The method for producing a thiol compound of the present embodiment can be easily carried out by adding a light irradiation step to a conventional method for producing a thiol compound, without changing the conventional method for producing a thiol compound.

[0051] Furthermore, the light irradiation step in the method for producing a thiol compound of this embodiment does not require special equipment, can use sunlight as a light source, and can be easily carried out. Furthermore, the method for producing a thiol compound of the present embodiment can be carried out without using compounds such as a decolorizing agent and an adsorbent, etc. Therefore, compared to, for example, adding a compound such as a decolorizing agent and / or an adsorbent to a colored thiol compound or a composition containing the same, it is preferable because impurities and foreign matter caused by the newly added compound are not mixed in. [Example]

[0052] The present invention will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are intended to facilitate understanding of the present invention, and the present invention is not limited to these examples alone.

[0053] The following examples and comparative examples were carried out at room temperature (25° C.) unless otherwise specified. In all of the following examples and comparative examples, the Hazen color number (APHA) was determined using a spectrophotometer SD6000 manufactured by Nippon Denshoku Industries Co., Ltd. Calibration of the Hazen color number was performed using solutions prepared by diluting a chromaticity standard solution (1000 degrees) (Kanto Chemical, for chromaticity testing) with pure water to give APHA 500, 200, 100, 50, 20, 10, and 5, respectively, and pure water (APHA0).

[0054] [ Reference example 1) A compound represented by formula (9) was synthesized according to the method described in Patent Document 8. The Hazen color number (APHA) of the synthesized compound represented by formula (9) was determined. The result was APHA 160. The compound APHA160 represented by formula (9) was subjected to a light irradiation step in which light was irradiated by the method described below.

[0055] That is, 50 mL (60 g) of the compound represented by formula (9) of APHA160 was placed in a translucent polypropylene container (Eye-Boy (registered trademark), 50 mL wide-mouth bottle, manufactured by AS ONE Corporation) and sealed. The container was then placed under a light source (white LED; LED base light TENQOO (trade name); manufactured by Toshiba Lighting & Technology Corporation), and light was irradiated onto the compound represented by formula (9) through the container.

[0056] As shown in Table 1, the Hazen color number (APHA) of the compound represented by formula (9) decreased over time after the start of light irradiation, reaching APHA 72 after 30 days. The container was then left in a dark place for 12 days, but the Hazen color number of the compound represented by formula (9) did not change. This confirmed that the coloration of the compound represented by formula (9) was reduced by irradiation with light using a white LED, and that it did not become colored even when stored in a dark place thereafter.

[0057] [Table 1]

[0058] [ Reference example 2) Reference example 50 mL (60 g) of the compound represented by formula (9) of APHA160, the same as in 1, Reference example The compound was placed in the same container as 1 and sealed. The container was then placed near a south-facing window where sunlight was shining, and the compound represented by formula (9) was irradiated with light through the container.

[0059] As shown in Table 1, the Hazen color number (APHA) of the compound represented by formula (9) decreased over time after the start of light irradiation, reaching APHA 23 after 30 days. The container was then left to stand in a dark place for 12 days. As a result, the compound represented by formula (9) reached APHA 22, showing almost no change. This confirmed that the coloration of the compound represented by formula (9) was reduced by exposure to sunlight and did not change even when stored in a dark place thereafter.

[0060] Comparative Example 1 Reference example 50 mL (60 g) of the compound represented by formula (9) of APHA160, the same as in 1, Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 1, the Hazen color number (APHA) of the compound represented by formula (9) hardly changed even after light irradiation, and after 30 days it was APHA 158. The container was then left in a dark place for 12 days. As a result, the compound represented by formula (9) was APHA 160.

[0061] [ Reference example 3) Reference example A solution was prepared by mixing the compound represented by formula (9) of APHA160, the same as in 1, with toluene (Junsei Chemical, special grade) in a volume ratio of 1:1. The Hazen color number (APHA) of the resulting mixture was determined to be APHA67. 50 mL of this mixture was measured out, Reference example The container was then sealed in the same container as 1. Reference example The mixture was placed under the same light source (white LED) as in 1, and light was irradiated onto the mixture through the container. As shown in Table 2, the Hazen color number (APHA) of the mixed solution decreased with time after the start of light irradiation, and reached APHA 37 after 12 days.

[0062] [Table 2]

[0063] [ Reference example 4) Except for using acetonitrile (Fujifilm Wako Pure Chemical Industries, special grade reagent) instead of toluene, Reference example A mixed solution was prepared in the same manner as in 3. The Hazen color number (APHA) of the obtained mixed solution was determined to be APHA 100. 50 mL of this mixed solution was measured out, Reference example The container was then sealed in the same container as 1. Reference example The mixture was placed under the same light source (white LED) as in 1, and light was irradiated onto the mixture through the container. As shown in Table 2, the Hazen color number (APHA) of the mixed solution decreased with time after the start of light irradiation, and reached APHA 37 after 12 days.

[0064] [ Reference example 5) The Hazen color number (APHA) of the compound represented by formula (6) (Karenz MT (registered trademark) BD1 (manufactured by Showa Denko K.K.)) was determined. As a result, it was APHA57. 30 mL (33 g) of the compound represented by formula (6) of APHA57 was added to Reference example The container was then sealed in the same container as 1. Reference example The container was placed under the same light source (white LED) as in 1, and the compound represented by formula (6) was irradiated with light through the container. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (6) decreased with time after the start of light irradiation, and reached APHA 38 after 8 days.

[0065] [Table 3]

[0066] Comparative Example 2 Reference example 30 mL (33 g) of the compound represented by formula (6) of APHA57, the same as in 5, Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (6) hardly changed even when irradiated with light, and after 8 days, the APHA was 58.

[0067] [ Reference example 6) The Hazen color number (APHA) of the compound represented by formula (7) (Karenz MT (registered trademark) NR1 (manufactured by Showa Denko K.K.)) was determined. As a result, it was APHA45. 30 mL (38 g) of the compound represented by formula (7) of APHA45 was added to Reference example The container was then sealed in the same container as 1. Reference example The container was placed under the same light source (white LED) as in 1, and the compound represented by formula (7) was irradiated with light through the container. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (7) decreased with time after the start of light irradiation, and reached APHA 36 after 8 days.

[0068] Comparative Example 3 Reference example 30 mL (38 g) of the compound represented by formula (7) of APHA45, the same as in 6, Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (7) hardly changed even when irradiated with light, and was APHA 46 after 8 days.

[0069] [ Reference example 7) The Hazen color number (APHA) of the compound represented by formula (8) (Karenz MT (registered trademark) TPMB (manufactured by Showa Denko K.K.)) was determined. As a result, it was APHA42. 30 mL (34 g) of the compound represented by formula (8) of APHA42 was added to Reference example The container was then sealed in the same container as 1. Reference example The container was placed under the same light source (white LED) as in 1, and the compound represented by formula (8) was irradiated with light through the container. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (8) decreased with time after the start of light irradiation, and reached APHA 31 after 8 days.

[0070] Comparative Example 4 Reference example 30 mL (34 g) of the compound represented by formula (8) of APHA42, the same as in 7, Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (8) did not change even when irradiated with light, and was APHA 42 after 8 days.

[0071] [ Reference example 8) The Hazen color number (APHA) of the compound represented by formula (9) (Karenz MT (registered trademark) PE1 (manufactured by Showa Denko K.K.)) was determined. As a result, it was APHA57. 30 mL (36 g) of the compound represented by formula (9) of APHA57 was added to Reference example The container was then sealed in the same container as 1. Reference example The container was placed under the same light source (white LED) as in 1, and the compound represented by formula (9) was irradiated with light through the container. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (9) decreased with time after the start of light irradiation, and reached APHA 32 after 8 days.

[0072] Comparative Example 5 Reference example 30 mL (36 g) of the compound represented by formula (9) of APHA57, the same as in 8, Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 3, the Hazen color number (APHA) of the compound represented by formula (9) hardly changed even when irradiated with light, and was APHA 56 after 8 days.

[0073] [ Reference example 9) 3-mercaptobutanoic acid was synthesized according to the method described in Patent Document 9. The Hazen color number (APHA) of the synthesized 3-mercaptobutanoic acid was determined. The result was APHA25. 30 mL (34 g) of 3-mercaptobutanoic acid of APHA25 was added to Reference example The container was then sealed in the same container as 1. Reference example The container was placed under the same light source (white LED) as in 1, and light was irradiated onto the 3-mercaptobutanoic acid through the container. As shown in Table 3, the Hazen color number (APHA) of 3-mercaptobutanoic acid decreased with time after the start of light irradiation, reaching APHA 14 after 8 days.

[0074] Comparative Example 6 Reference example 30 mL (34 g) of 3-mercaptobutanoic acid (APHA25) (same as in 9) Reference example The mixture was placed in the same container as in step 1 and sealed. The container was then wrapped in aluminum foil to block out light. Reference example The container was placed under the same light source (white LED) as in 1, and the container wrapped in aluminum foil was irradiated with light. As shown in Table 3, the Hazen color number (APHA) of 3-mercaptobutanoic acid hardly changed even when irradiated with light, and was APHA 25 after 8 days.

[0075] Example 10 A compound represented by formula (9) was synthesized according to the method described in Patent Document 8. The Hazen color number (APHA) of the synthesized compound represented by formula (9) was determined. The result was APHA169. The compound represented by formula (9) of APHA169 was subjected to a light irradiation step in which light was irradiated by the method described below.

[0076] Specifically, a light source was inserted into a 50 mL three-neck flask containing 50 mL (60 g) of the compound represented by formula (9) of APHA169 and a stirrer, and the compound represented by formula (9) was irradiated with light while stirring. The light source used was a photochemical reaction LED light source device PER-AMP (wavelength 470 nm, output 610 mW (manufactured by Creative Science Institute Co., Ltd.)) combined with an LED lamp PER-LED-470 and a power supply unit PER-AMP-N4. As shown in Table 4, the Hazen color number (APHA) of the compound represented by formula (9) decreased with time after the start of light irradiation, and reached APHA 43 after 7 hours.

[0077] [Table 4]

[0078] Example 11 The light irradiation process was carried out in the same manner as in Example 10, except that the photochemical reaction LED light source device PER-AMP (wavelength 385 nm, output 605 mW (manufactured by Creative Science Institute Co., Ltd.)) was used in combination with the LED lamp PER-LED-385 and the power supply unit PER-AMP-N4 as the light source. As shown in Table 4, the Hazen color number (APHA) of the compound represented by formula (9) decreased with time after the start of light irradiation, and reached APHA 42 after 7 hours.

[0079] Example 12 The light irradiation process was carried out in the same manner as in Example 10, except that the photochemical reaction LED light source device PER-AMP (wavelength 325 nm, output 36 mW (manufactured by Creative Science Institute Co., Ltd.)) was used in combination with the LED lamp PER-LED-325 and the power supply unit PER-AMP-D2 as the light source. As shown in Table 4, the Hazen color number (APHA) of the compound represented by formula (9) decreased with time after the start of light irradiation, reaching APHA 168 after 7 hours and APHA 149 after 24 hours.

[0080] Table 5 shows: Reference example 1~ Reference Example 9, Example 1012. The thiol compounds in the measurement objects (thiol compounds or compositions containing the same) in Comparative Examples 1 to 6, the amount of the measurement object, the light source, the time for which the light irradiation process was carried out (light irradiation time), and the Hazen color number (APHA) before the start of the light irradiation process and after the end of the light irradiation process are summarized.

[0081] [Table 5]

[0082] As shown in Table 5, Reference example 1~ Reference Example 9, Example 10 In Example 12, it was confirmed that the Hazen color number (APHA) of the thiol compound or the composition containing the same was reduced by carrying out the light irradiation step, and coloring was reduced. In contrast, in Comparative Examples 1 to 6, in which the light irradiation step was performed in a dark environment, no decrease in the Hazen color number (APHA) of the thiol compound or the composition containing it due to the light irradiation step was confirmed.

Claims

1. A method for producing a thiol compound with reduced coloration, comprising a light irradiation step of irradiating a colored thiol compound or a composition containing the colored thiol compound with light, the colored thiol compound has a Hazen color number of 10 or more, The method for producing a thiol compound, wherein the thiol compound contains one or both of 3-mercaptocarboxylic acid and a 3-mercaptocarboxylic acid ester, and the light contains light having a wavelength of 250 nm to 600 nm.

2. the colored thiol compound or the composition has a Hazen color number of 100 or more, The method for producing a thiol compound according to claim 1 , wherein the light irradiation step is carried out until the Hazen color number of the colored thiol compound or the composition becomes less than 100.

3. The method for producing a thiol compound according to claim 1 or claim 2, wherein the thiol compound comprises a thiol having at least one secondary mercapto group.

4. The method for producing a thiol compound according to claim 1, wherein the thiol compound includes one or both of 3-mercaptobutanoic acid and a 3-mercaptobutanoic acid ester.

5. The method for producing a thiol compound according to claim 4, wherein the 3-mercaptobutanoic acid ester is any one of compounds represented by the following formulas (1) to (4): 【Chemical 1】 (In formula (1), R １ represents a hydrogen atom or a group represented by formula (5). (In formula (2), R ２ , R ３ each independently represents a hydrogen atom or a group represented by formula (5). (In formula (3), R ４ , R ５ each independently represents a hydrogen atom or a group represented by formula (5). (In formula (4), R ６ , R ７ , R ８ each independently represents a hydrogen atom or a group represented by formula (5). (In formula (5), * indicates the bonding position with the compounds represented by formulas (1) to (4).)

6. The method for producing a thiol compound according to claim 4, wherein the 3-mercaptobutanoic acid ester is any one of compounds represented by the following formulas (6) to (9): 【Chemistry 2】

7. The composition contains the colored thiol compound and at least one solvent selected from the group consisting of toluene, xylene, cyclohexane, methylcyclohexane, acetonitrile, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl acetate, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and water. The method for producing a thiol compound according to any one of claims 1 to 6.

8. A method for producing a thiol compound with reduced coloration, comprising a light irradiation step of irradiating a colored thiol compound or a composition containing the colored thiol compound with light, the colored thiol compound has a Hazen color number of 10 or more, and the thiol compound contains one or both of a 3-mercaptocarboxylic acid and a 3-mercaptocarboxylic acid ester; The method for producing a thiol compound, wherein the light in the light irradiation step is light emitted from a light-emitting diode lamp containing light with a wavelength of 250 nm to 600 nm as a light source.

9. The method for producing a thiol compound according to claim 8, wherein the thiol compound includes one or both of 3-mercaptobutanoic acid and a 3-mercaptobutanoic acid ester.

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