Method for preparing 10-(4-biphenyl)-2-isopropyl thioxanthone sulfonium hexafluorophosphate through electro-catalysis

Abstract

The invention discloses a method for preparing 10-(4-biphenyl)-2-isopropyl thioxanthone sulfonium hexafluorophosphate through electro-catalysis. According to the method, 2-isopropyl thioxanthone is used as a raw material, and the 10-(4-biphenyl)-2-isopropyl thioxanthone sulfonium hexafluorophosphate is prepared through electro-catalysis. According to the method disclosed by the invention, the intermediate sulfoxide is obtained by adopting a method of anodizing under an electro-catalysis condition and taking water as an oxygen source in the oxidation process, so that the use of an additional oxidant is avoided, and the defects that the additional oxidant is needed, the production raw material cost is high, the product quality is poor and the like in the method in the prior art are overcome.

Description

Technical Field

[0001] The invention relates to the technical field of cationic photoinitiator preparation, and in particular to a method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis. Background Art

[0002] Cationic photoinitiators have shown unique advantages in the field of photocurable materials, such as no oxygen inhibition during polymerization, low curing shrinkage, and strong adhesion. These characteristics make them have significant advantages in the cationic polymerization of epoxy resins, vinyl ethers, alicyclic epoxies, and oxetanes. However, despite these advantages, cationic photoinitiators are also limited in their widespread application by their post-curing characteristics, high cost, and application conditions that are sensitive to moisture and alkaline gases.

[0003] In recent years, onium salt cationic photoinitiators have developed rapidly, and new varieties have continuously emerged, greatly broadening the application scope of photocurable materials. From a structural point of view, onium salt cationic photoinitiators are composed of two parts: anions and cations, of which the cation part mainly includes iodonium salts and sulfonium salts. This type of photoinitiator undergoes transition by absorbing radiation energy to produce superacid cations that can initiate polymerization. The weaker the nucleophilicity of the anion, the stronger the acidity of the superacid produced, and thus the higher the initiation efficiency. This characteristic determines the photochemical properties of the photoinitiator, including its maximum absorption wavelength, molar absorption coefficient, quantum yield and thermal stability.

[0004] The traditional method of formulating cationic light-curing coatings widely uses triarylsulfonium salt photoinitiators such as UVI699. However, they produce simple phenyl compounds such as benzene after photodecomposition, which limits their use.

[0005] In order to overcome the above problems, patent application US4882201 uses long-chain substituted phenyl sulfonium salts, and patent application WO03072567 shows biphenyl substituted sulfonium salts in food, namely 10-(4-biphenyl)-2-isopropylthioxanthone sulfonium hexafluorophosphate, the structure of which is shown in formula (I). The preparation method described in patent application WO03072567 is to oxidize 2-isopropylthioxanthone to obtain sulfoxide, and the sulfoxide is salted with biphenyl to obtain hydrogen sulfate sulfonium salt, and then ion exchange is carried out with potassium hexachlorophosphate aqueous solution in acetic acid to obtain the target product.

[0006]

[0007] Patent application WO03072567 uses cerium ammonium nitrate as an oxidant for sulfide oxidation reaction. However, since the amount of cerium ammonium nitrate used in this technology is too large and its price is particularly high, the production cost of the target product is high and has no industrial value.

[0008] Although patent CN101153037B improves the method in patent application WO03072567, it still uses an external oxidant, ammonium cerium nitrate. Japanese patent application JP0240354A uses sodium hypobromite as an oxidant to replace ammonium cerium nitrate to oxidize sulfur to prepare sulfoxide, but the use of an external oxidant is also inevitable.

[0009] Therefore, there is an urgent need to develop a method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate, which can overcome the problems of the existing technical methods such as the need for an external oxidant, high production raw material costs, and poor product quality, so as to expand the application range of onium salt cationic photoinitiators. Summary of the invention

[0010] The object of the present invention is to provide a method for preparing 10-(4-biphenyl)-2-isopropylthioxanthone sulfonium hexafluorophosphate using 2-isopropylthioxanthone as a raw material, wherein the method electro-oxidizes 2-isopropylthioxanthone to obtain an intermediate sulfoxide, the sulfoxide is then salted with biphenyl to obtain trifluoromethanesulfonium salt, and finally ion-exchange is performed with potassium hexafluorophosphate aqueous solution to obtain a target product. The method of the present invention overcomes the disadvantages of the prior art method, such as the need for an external oxidant, high raw material cost, and poor product quality.

[0011] In order to achieve the above object of the invention, the present invention provides a method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis, comprising the following steps:

[0012] Step (1): adding 2-isopropylthioxanthone and electrolyte into an aqueous alcohol solvent, inserting a cathode and an anode for electrocatalysis, and using water as an oxygen source to oxidize at the anode to obtain an intermediate sulfoxide;

[0013] Step (2): dissolving the intermediate sulfoxide and biphenyl in an organic solvent, and adding trifluoromethanesulfonic acid dropwise into the organic solvent to carry out a salt-forming reaction, thereby obtaining a compound of formula (II) 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium trifluoromethanesulfonate;

[0014] Step (3): dissolving the compound of formula (II) in an alcohol solvent, adding an aqueous solution of potassium hexafluorophosphate dropwise to the alcohol solvent, and collecting the precipitated solid particles to obtain the compound of formula (I);

[0015]

[0016] In step (2) of the present invention, the organic solvent may be an organic solvent such as dichloromethane.

[0017] According to the method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate described in the present invention, preferably, in step (1), the electrolyte is any one or more of lithium perchlorate, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrabutylammonium hexafluorophosphate, etc.

[0018] According to the method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate of the present invention, preferably, in step (1) and step (2), the molar ratio of 2-isopropylthioxanthone, trifluoromethanesulfonic acid and biphenyl is 1:1 to 6:1 to 3.

[0019] According to the method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate of the present invention, preferably, in the step (1), the aqueous alcohol solvent is a trifluoroethanol aqueous solution or a hexafluoroisopropanol aqueous solution, and the mass percentage concentration of the aqueous alcohol solvent is 95%-98%.

[0020] According to the method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate of the present invention, preferably, in the step (1), the weight-to-volume ratio of the 2-isopropylthioxanthone to the aqueous alcohol solvent is 1:50-100 g / mL.

[0021] According to the method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis of the present invention, preferably, in step (1), the anode is a graphite electrode, a PVC electrode, a PtO 2 The cathode is any one of a graphite electrode, a platinum electrode, a nickel electrode, and a silver electrode.

[0022] According to the method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis of the present invention, preferably, in step (1), the current is 10-50 mA, and the current density is 2.0-5.0 mA / cm 2 .

[0023] According to the method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis of the present invention, preferably, in the step (2), the process of dripping trifluoromethanesulfonic acid and the salt-forming reaction are both carried out below 15°C.

[0024] According to the method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis of the present invention, preferably, in the step (3), the alcohol solvent may be methanol or ethanol.

[0025] According to the method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate of the present invention, preferably, in the step (3), the amount of the alcohol solvent used is 30-60% (V / V) of the potassium hexafluorophosphate aqueous solution.

[0026] The beneficial effects of the present invention are:

[0027] The invention provides a method for preparing 10-(4-biphenyl)-2-isopropylthioxanthone sulfonium hexafluorophosphate by taking 2-isopropylthioxanthone as a raw material. In the method, 2-isopropylthioxanthone is subjected to electro-oxidation to obtain an intermediate sulfoxide, the sulfoxide is reacted with biphenyl to form a salt to obtain trifluoromethanesulfonium salt, and finally ion exchange is carried out with a potassium hexafluorophosphate aqueous solution to obtain a target product.

[0028] The method of the present invention adopts a method of anodic oxidation under electrocatalytic conditions and water as an oxygen source to obtain an intermediate sulfoxide during the oxidation process, thereby avoiding the use of an external oxidant; in addition, a method of dripping an aqueous solution of potassium hexafluorophosphate into an alcohol solution of the intermediate is adopted during the ion exchange reaction process; the disadvantages of the prior art method, such as the need for an external oxidant, high production raw material cost, and poor product quality, are overcome. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments.

[0030] Example 1

[0031] A method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate in this embodiment comprises the following steps:

[0032] Step (1): 2-isopropylthioxanthone (508 g, 2 mol, 1.0 equivalent), lithium perchlorate (424 g, 4 mol, 2 equivalents), and 2,2,2-trifluoroethanol aqueous solution (30 L, mass percent concentration of 98%) were added to a 50 ml reaction bottle, and a bottle cap with an anode (graphite electrode) and a cathode (platinum electrode) was inserted into the above mixture, and a constant current of 10 mA (j = 2.5 mA / cm 2 ) for 5 hours of electrolysis; after the electrolysis is completed, the anode electrode is rinsed with dichloromethane, the solvent is removed under vacuum, the residue is washed with ether, and vacuum dried to obtain isopropylthioxanthone sulfoxide, 491 grams of light yellow solid, with a yield of 91%. Melting point: 200-201°C.

[0033] 1 H NMR (400 MHz, CDCl 3): δ8.29(d,J=7.6Hz,2H),8.14(d,J=7.60Hz,2H),7.96(t,J=7.6Hz,2H),7.88(t,J=6.8Hz,2H); 13 C NMR (100 MHz, CDCl 3 )δ177.4,139.9,134.2,132.7,129.6,128.0,122.2. HRMS(ESI-TOF)(m / z):calcd for C 15 H 12 O 2 S + ([M + H] + ),256.0553,found,256.0540.

[0034] Step (2): add isopropyl thioxanthone sulfoxide (41 g, 0.15 mol, 1 equivalent), biphenyl (52 g, 0.17 mol, 1.1 equivalent) and 18 mL of dichloromethane into a 500 ml four-necked bottle, stir and dissolve, then place in a low temperature bath and cool to below 15°C, add 50 mL of trifluoromethanesulfonic acid dropwise, and keep the temperature of the reaction solution not higher than 15°C; after the addition is complete, stir and react at 15°C for 2 h, transfer the reaction solution to a 2.5 L reaction bottle, add 1 L of water and 1 L of dichloromethane, stir for 30 min, and then place in a separatory bucket for stratification, collect the lower layer of dichloromethane solution, and evaporate to dryness on a rotary evaporator to obtain 10-(4-biphenyl)-2-isopropyl thioxanthone-10-sulfonium trifluoromethanesulfonate.

[0035] Step (3): dissolving the 10-(4-biphenyl)-2-isopropylthioxanthone-10-sulfonium trifluoromethanesulfonate obtained in step (2) in 300 mL of methanol, and dropping 500 mL of an aqueous solution containing 28 g of potassium hexafluorophosphate (0.152 mol) into the methanol solution. After the dropping is completed, stirring is continued for 5 h. The precipitated powdery solid is collected, filtered, washed with water, and dried to obtain 10-(4-biphenyl)-2-isopropylthioxanthone-10-sulfonium hexafluorophosphate, a yellow solid product of 68 g, a yield of 89%, and a melting point of 183-190°C.

[0036] 1 H NMR (CDCl 3 ): δ8.67-8.65(m,1H),8.51-8.50(d,1H),8.21-8.18(m,1H),8.13-8.11(m,1H ),7.86-7.74(m,6H),7.71-7.42(m,6H),3.19-3.12(m,1H),1.28-1.27(m,6H).

[0037] Example 2

[0038] The method of Example 2 is the same as that of Example 1 except step (1). Step (1) of Example 2 is as follows:

[0039] Step (1): 2-isopropylthioxanthone (508 g, 2 mol, 1.0 equivalent), tetrabutylammonium bromide (1.29 kg, 4 mol, 2 equivalents), and hexafluoroisopropanol (30 L, mass percentage concentration of 97%) were added to a 50 ml reaction bottle, and a bottle cap with an anode (graphite electrode) and a cathode (graphite electrode) was inserted into the above mixture. A constant current of 30 mA (j = 3.3 mA / cm 2 ) for 2h of electrolysis; after the electrolysis is completed, the anode electrode is rinsed with dichloromethane, the solvent is removed under vacuum, the residue is washed with ether, and vacuum dried to obtain isopropylthioxanthone sulfoxide as a light yellow solid (513 g) with a yield of 95%.

[0040] Example 3

[0041] The method of Example 3 is the same as that of Example 1 except step (1). Step (1) of Example 3 is as follows:

[0042] Step (1): 2-isopropylthioxanthone (508 g, 2 mol, 1.0 equivalent), tetrabutylammonium hexafluorophosphate (1.55 kg, 4 mol, 2 equivalents), and 2,2,2-trifluoroethanol (30 L, mass percentage concentration of 95%) were added to a 50 ml reaction bottle, and a bottle cap with an anode (PVC electrode) and a cathode (nickel electrode) was inserted into the above mixture. A constant current of 50 mA (j = 3.3 mA / cm 2 ) for 2h of electrolysis; after the electrolysis is completed, the anode electrode is rinsed with dichloromethane, the solvent is removed under vacuum, the residue is washed with ether, and vacuum dried to obtain isopropylthioxanthone sulfoxide as a light yellow solid of 502 g with a yield of 93%.

[0043] Comparative Example:

[0044] The method mentioned in Example 1 of patent CN101153037B is as follows:

[0045] In a 1L four-necked bottle, add 60.0g (0.24mol) 2-isopropylthioxanthone, 450mL acetic acid and 100mL water, 18.0g cerium ammonium nitrate (0.0328mol), 10.0g 48% hydrobromic acid solution, stir evenly, keep the temperature at 25-30°C, add 200g (0.24mol) 10% sodium hypochlorite solution from the dropping funnel, stir for 24 hours. Add 400mL water to the reaction solution, stir for 1 hour, filter, wash the filter cake with 100mol water, and dry to obtain 54g of light yellow isopropylthioxanthone sulfoxide, with a yield of 88%.

[0046] By comparison, it can be seen that, by adopting the method of the present invention, without using an external oxidant, the yield of the intermediate isopropylthioxanthone sulfoxide is increased from 88% to more than 91%, even reaching 95%, and the yield is improved. Therefore, the present invention overcomes the shortcomings of the prior art method that an external oxidant is required, the production raw material cost is high, and the product quality is poor, and has significant advantages.

[0047] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate by electrocatalysis, characterized in that: The steps include: Step (1): adding 2-isopropylthioxanthone and electrolyte into an aqueous alcohol solvent, inserting a cathode and an anode for electrocatalysis, and using water as an oxygen source to oxidize at the anode to obtain an intermediate sulfoxide; Step (2): dissolving the intermediate sulfoxide and biphenyl in an organic solvent, and adding trifluoromethanesulfonic acid dropwise into the organic solvent to carry out a salt-forming reaction, thereby obtaining a compound of formula (II) 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium trifluoromethanesulfonate; Step (3): dissolving the compound of formula (II) in an alcohol solvent, adding an aqueous solution of potassium hexafluorophosphate dropwise to the alcohol solvent, and collecting the precipitated solid particles to obtain the compound of formula (I); 2. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 1, characterized in that: In step (1), the electrolyte is any one or more of lithium perchlorate, tetrabutylammonium bromide, tetrabutylammonium iodide, and tetrabutylammonium hexafluorophosphate.

3. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 1, characterized in that: In step (1) and step (2), the molar ratio of 2-isopropylthioxanthone, trifluoromethanesulfonic acid and biphenyl is 1:1-6:1-3.

4. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 3, characterized in that: In the step (1), the aqueous alcohol solvent is a trifluoroethanol aqueous solution or a hexafluoroisopropanol aqueous solution, and the mass percentage concentration of the aqueous alcohol solvent is 95-98%.

5. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 4, characterized in that: In the step (1), the weight-to-volume ratio of the 2-isopropylthioxanthone to the aqueous alcohol solvent is 1:50-100 g / mL.

6. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 3, characterized in that: In the step (1), the anode is any one of a graphite electrode, a PVC electrode, and a PtO2 electrode; the cathode is any one of a graphite electrode, a platinum electrode, a nickel electrode, and a silver electrode.

7. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 6, characterized in that: In the step (1), the current is 10-50 mA, and the current density is 2.0-5.0 mA / cm 2 .

8. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 1, characterized in that: In the step (2), the process of adding trifluoromethanesulfonic acid and the salt-forming reaction are both carried out at a temperature below 15°C.

9. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 1, characterized in that: In the step (3), the alcohol solvent may be methanol or ethanol.

10. The method for electrocatalytically preparing 10-(4-biphenyl)-2-isopropylthioxanthonesulfonium hexafluorophosphate according to claim 9, characterized in that: In the step (3), the amount of the alcohol solvent used is 30-60% (V / V) of the potassium hexafluorophosphate aqueous solution.

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