[Light Emission Process]

In the light emission process of the present embodiment, light is emitted to a colored thiol compound or a composition containing the colored thiol compound. In the process of producing a thiol compound of the present embodiment, the light emission process can be performed once or a plurality of times.

In the light emission process, the wavelength of light emitted can be appropriately determined according to the type of the thiol compound and the formulation of the composition. In the present embodiment, the light emitted preferably includes light with a wavelength of 250 nm to 600 nm. Light with a wavelength of 250 nm or more is preferable because it is less likely to be blocked by absorption of the thiol compound and the organic solvent. In addition, light with a wavelength of 600 nm or less is preferable because it has sufficient energy at which coloring of the thiol compound can be reduced. Since light emitted can effectively reduce coloring of the colored thiol compound, it is more preferable to contain light in a wavelength range of 300 nm to 550 nm, and still more preferable to contain light in a range of 350 to 500 nm.

The type of the light source used in the light emission process is not particularly limited. Specifically, as the light source, sunlight, an incandescent lamp, a fluorescent lamp, a light-emitting diode (LED) lamp or the like can be used. Among these light sources, sunlight can be particularly preferably used because it has a high light emission intensity, includes light in a wide wavelength range, and does not require energy supply from a power source or the like.

The method of evaluating coloring is not particularly limited, but the Hazen color number (APHA) can be preferably used because the color of the colored thiol compound is typically yellow. As a method of determining the Hazen color number, for example, a measurement method using a spectrometer may be used, or a method using a colorimetric tube may be used.

The amount of change in the Hazen color number (APHA) of a measurement target (a colored thiol compound or a composition containing a colored thiol compound) when the light emission process is performed can be adjusted according to the wavelength of light to be emitted, a light emission intensity, and an emission amount (light emission time) with respect to the formulation and amount of the colored thiol compound or the composition containing the same. As the energy of light emitted in the light emission process is stronger and the amount thereof is larger, an effect of reducing coloring of the colored thiol compound is stronger.

For example, when the Hazen color number (APHA) of the thiol compound or the composition containing the same is 100 or more, the light emission process is preferably performed until the Hazen color number becomes less than 100. In this case, the thiol compound after the light emission process can be preferably used for applications as resin raw materials such as optical materials, exterior materials, and paints. Since a thiol compound more suitable for these applications is obtained, the light emission process is more preferably performed until the Hazen color number becomes 80 or less, and still more preferably performed until the Hazen color number becomes 60 or less.

Even if the Hazen color number (APHA) of the thiol compound or the composition containing the same is less than 100, the light emission process may be performed in order to further reduce coloring. For example, when the Hazen color number is 80 or more, the light emission process may be performed until the Hazen color number becomes less than 80, more preferably until the Hazen color number becomes 70 or less, and still more preferably until the Hazen color number becomes 60 or less. When the Hazen color number is 60 or more, the light emission process may be performed until the Hazen color number becomes less than 60, more preferably until the Hazen color number becomes 50 or less, and still more preferably until the Hazen color number becomes 40 or less.

As the container for accommodating the thiol compound or the composition containing the same when the light emission process is performed, for example, a resin container made of polypropylene or the like, a glass container or the like can be used, and the material and the shape are not particularly limited. As the container, when light is emitted from the outside of the container to the thiol compound or the composition containing the same in the container in the light emission process, it is preferable to use a container having favorable permeability of light with a wavelength to be emitted.

The light emission process is preferably performed while stirring the thiol compound or the composition containing the same accommodated in the container. Thereby, it is possible to efficiently reduce coloring of the colored thiol compound without unevenness, and it is possible to efficiently dissipate heat applied from the light source to the thiol compound or the composition containing the same.

The temperature, the pressure, and other conditions when the light emission process is performed are not particularly limited.

The thiol compound or the composition containing the same after the light emission process can be directly used as the resin raw material such as optical materials, exterior materials, and paints. When the composition after the light emission process contains a solvent, as necessary, the solvent may be removed using a known method. In addition, when the composition after the light emission process contains compounds other than the thiol compound, as necessary, the other compounds may be removed using a known method.

The thiol compound after the light emission process may be used as an intermediate product.

For example, the thiol compound after the light emission process may be 3-mercaptocarboxylic acid synthesized as an intermediate product in the process of synthesizing 3-mercaptocarboxylic acid ester such as 3-mercaptobutanoic acid ester. When 3-mercaptocarboxylic acid ester is produced by a method of esterifying 3-mercaptocarboxylic acid after the light emission process, a less colored product is obtained.

The method for producing a thiol compound of the present embodiment includes a light emission process in which light is emitted to the colored thiol compound or the composition containing the same. Therefore, according to the method for producing a thiol compound of the present embodiment, it is possible to reduce coloring of the thiol compound.

The method for producing a thiol compound of the present embodiment can be easily performed by adding the light emission process to the conventional method for producing a thiol compound without changing the conventional method for producing a thiol compound.

In addition, the light emission process in the method for producing a thiol compound of the present embodiment can be easily performed without requiring a special facility and using sunlight as a light source.

In addition, the method for producing a thiol compound of the present embodiment can be performed without using compounds such as a decoloring agent and an adsorbing agent. Therefore, for example, this is preferable because there are no contamination of impurities and foreign substances caused by newly added compounds compared to when compounds such as a decoloring agent and/or an adsorbing agent are added to the colored thiol compound or the composition containing the same.

EXAMPLES

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. Here, the following examples are intended to facilitate understanding of the content of the present invention, and the present invention is not limited only to these examples.

The following examples and comparative examples were performed at room temperature (25° C.) unless otherwise specified.

In the following examples and comparative examples, the Hazen color number (APHA) was determined using a spectrophotometer SD6000 (commercially available from Nippon Denshoku Industries Co., Ltd.). The Hazen color number was corrected using solutions obtained by diluting a chromatility standard solution (1,000 degrees) (for chromaticity test, commercially available from Kanto Chemical Co., Inc.) with pure water and having an APHA of 500, 200, 100, 50, 20, 10, and 5 and pure water (with an APHA of 0).

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 obtained. As a result, the APHA was 160.

A light emission process of emitting light was performed on the compound having an APHA of 160 and represented by Formula (9) by the following method.

That is, 50 mL (60 g) of the compound having an APHA of 160 and represented by Formula (9) was put into a semitransparent polypropylene container (Iboy (registered trademark), 50 mL wide-mouth bottle, commercially available from As One Corporation) and sealed. Then, the container was placed under a light source (white LED; LED base light TENQOO (product name); commercially available from Toshiba Lighting & Technology Corporation), and light was emitted to the compound represented by Formula (9) through the container.

As shown in Table 1, the Hazen color number (APHA) of the compound represented by Formula (9) decreased over time after light emission started and the APHA became 72 after 30 days. Then, the container was left in a dark place for 12 days, but the Hazen color number of the compound represented by Formula (9) did not change. Accordingly, it was confirmed that the compound represented by Formula (9) was less colored when light was emitted using a white LED and was not colored even after being stored in a dark place.

TABLE 1

Time

[days]
0
2
7
12
16
22
30

Example 1
APHA
160
114
94
85
80
75
72

Example 2

160
76
54
41
33
26
23

Comparative

160
160
160
161
160
159
158

Example 1

Example 2

50 mL (60 g) of the same compound having an APHA of 160 and represented by Formula (9) as in Example 1 was put into the same container as in Example 1 and sealed. Then, the container was left on a south-facing window exposed to sunlight, and light was emitted to the compound represented by Formula (9) through the container.

As shown in Table 1, the Hazen color number (APHA) of the compound represented by Formula (9) decreased over time after light emission started, and the APHA became 23 after 30 days. Then, the container was left in a dark place for 12 days. As a result, the APHA of the compound represented by Formula (9) became 22 and hardly changed. Accordingly, it was confirmed that the compound represented by Formula (9) was less colored when sunlight was emitted and was not colored even after being stored in a dark place.

Comparative Example 1

50 mL (60 g) of the same compound having an APHA of 160 and represented by Formula (9) as in Example 1 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded, and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 1, the Hazen color number (APHA) of the compound represented by Formula (9) hardly changed even when light was emitted, and the APHA was 158 after 30 days. Then, the container was left in a dark place for 12 days. As a result, the APHA of the compound represented by Formula (9) was 160.

Example 3

A liquid was prepared by mixing the same compound having an APHA of 160 and represented by Formula (9) as in Example 1 and toluene (commercially available from Junsei Chemical Co., Ltd., special grade) at a volume ratio of 1:1. The Hazen color number (APHA) of the obtained mixed solution was obtained, and the result was an APHA of 67. 50 mL of the mixed solution was measured and put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the mixed solution through the container.

As shown in Table 2, the Hazen color number (APHA) of the mixed solution decreased over time after light emission started, and the APHA became 37 after 12 days.

TABLE 2

Time [days]
0
4
7
12

Example 3
APHA
67
43
41
37

Example 4

100
46
44
37

Example 4

A mixed solution was prepared in the same manner as in Example 3 except that acetonitrile (special grade reagent, commercially available from FUJIFILM Wako Pure Chemical Corporation) was used in place of toluene. The Hazen color number (APHA) of the obtained mixed solution was obtained, and the result was an APHA of 100. 50 mL of the mixed solution was measured and put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the mixed solution through the container.

As shown in Table 2, the Hazen color number (APHA) of the mixed solution decreased over time after light emission started, and the APHA became 37 after 12 days.

Example 5

The Hazen color number (APHA) of the compound represented by Formula (6) (Karenz M T (registered trademark) BD1 (commercially available from Showa Denko K. K.)) was obtained. As a result, the APHA was 57. 30 mL (33 g) of the compound having an APHA of 57 and represented by Formula (6) was put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the compound represented by Formula (6) through the container.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (6) decreased over time after light emission started and the APHA became 38 after 8 days.

TABLE 3

Time [days]
0
1
3
8

Example 5
APHA
57
48
43
38

Example 6

45
39
40
36

Example 7

42
38
34
31

Example 8

57
44
36
32

Example 9

25
23
16
14

Comparative

57
56
56
58

Example 2

Comparative

45
46
46
46

Example 3

Comparative

42
42
42
42

Example 4

Comparative

57
57
58
56

Example 5

Comparative

25
25
24
25

Example 6

Comparative Example 2

30 mL (33 g) of the same compound having an APHA of 57 and represented by Formula (6) as in Example 5 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (6) hardly changed even when light was emitted and the APHA was 58 after 8 days.

Example 6

The Hazen color number (APHA) of the compound represented by Formula (7) (Karenz M T (registered trademark) NR1 (commercially available from Showa Denko K. K.)) was obtained. As a result, the APHA was 45. 30 mL (38 g) of the compound having an APHA of 45 and represented by Formula (7) was put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the compound represented by Formula (7) through the container.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (7) decreased over time after light emission started, and the APHA became 36 after 8 days.

Comparative Example 3

30 mL (38 g) of the compound having an APHA of 45 and represented by Formula (7) as in Example 6 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (7) hardly changed even when light was emitted, and the APHA was 46 after 8 days.

Example 7

The Hazen color number (APHA) of the compound represented by Formula (8) (Karenz M T (registered trademark) TPMB (commercially available from Showa Denko K. K.)) was obtained. As a result, the APHA was 42. 30 mL (34 g) of the compound having an APHA of 42 and represented by Formula (8) was put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the compound represented by Formula (8) through the container.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (8) decreased over time after light emission started, and the APHA became 31 after 8 days.

Comparative Example 4

30 mL (34 g) of the same compound having an APHA of 42 and represented by Formula (8) as in Example 7 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (8) did not change even when light was emitted, and the APHA was 42 after 8 days.

Example 8

The Hazen color number (APHA) of the compound represented by Formula (9) (Karenz M T (registered trademark) PE1 (commercially available from Showa Denko K. K.)) was obtained. As a result, the APHA was 57. 30 mL (36 g) of the compound having an APHA of 57 and represented by Formula (9) was put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to the compound represented by Formula (9) through the container.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (9) decreased over time after light emission started, and the APHA become 32 after 8 days.

Comparative Example 5

30 mL (36 g) of the same compound having an APHA of 57 and represented by Formula (9) as in Example 8 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 3, the Hazen color number (APHA) of the compound represented by Formula (9) hardly changed even when light was emitted, and the APHA was 56 after 8 days.

Example 9

3-mercaptobutanoic acid was synthesized by the method described in Patent Document 9. The Hazen color number (APHA) of the synthesized 3-mercaptobutanoic acid was obtained. As a result, the APHA was 25. 30 mL (34 g) of 3-mercaptobutanoic acid having an APHA of 25 was put into the same container as in Example 1 and sealed. Then, the container was left under the same light source (white LED) as in Example 1, and light was emitted to 3-mercaptobutanoic acid through the container.

As shown in Table 3, the Hazen color number (APHA) of 3-mercaptobutanoic acid decreased over time after light emission started, and the APHA became 14 after 8 days.

Comparative Example 6

30 mL (34 g) of the same 3-mercaptobutanoic acid having an APHA 25 as in Example 9 was put into the same container as in Example 1 and sealed. Then, the container was wrapped with an aluminum foil and light-shielded and left under a light source (white LED) as in Example 1, and light was emitted to the container wrapped with an aluminum foil.

As shown in Table 3, the Hazen color number (APHA) of 3-mercaptobutanoic acid hardly changed even when light was emitted, and the APHA was 25 after 8 days.

Example 10

A compound represented by Formula (9) was synthesized by the method described in Patent Document 8. The Hazen color number (APHA) of the synthesized compound represented by Formula (9) was obtained. As a result, the APHA was 169. A light emission process of emitting light was performed the compound having an APHA of 169 and represented by Formula (9) by the following method.

That is, a light source was inserted into a 50 mL three-necked flask containing 50 mL (60 g) of the compound having an APHA of 169 and represented by Formula (9) and a stirring bar, and light was emitted to the compound represented by Formula (9) with stirring. As the light source, an LED light source device PER-AMP for a photochemical reaction (a wavelength of 470 nm and an output of 610 mW (commercially available from The Institute of Creative Chemistry Co., Ltd.)) was used in combination 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 over time after light emission started, and the APHA became 43 after 7 hours.

TABLE 4

Time

[days]
0
1
3
7
24

Example 10
APHA
169
75
56
43

Example 11

169
86
62
42

Example 12

169

168
149

Example 11

A light emission process was performed in the same manner as in Example 10 except that, as the light source, an LED light source device PER-AMP for a photochemical reaction (a wavelength of 385 nm and an output of 605 mW (commercially available from The Institute of Creative Chemistry Co., Ltd.)) was used in combination with an LED lamp PER-LED-385 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 over time after light emission started, and the APHA became 42 after 7 hours.

Example 12

A light emission process was performed in the same manner as in Example 10 except that, as the light source, an LED light source device PER-AMP for a photochemical reaction (a wavelength of 325 nm and an output of 36 mW (commercially available from The Institute of Creative Chemistry Co., Ltd.)) was used in combination with an LED lamp PER-LED-325 and a power supply unit PER-AMP-D2.

As shown in Table 4, the Hazen color number (APHA) of the compound represented by Formula (9) decreased over time after light emission started, the APHA became 168 after 7 hours, and the APHA became 149 after 24 hours.