A method for preparing benzotriazole ultraviolet absorber by electrocatalysis

Abstract

The invention discloses a method for synthesizing a benzotriazole ultraviolet absorber having a structure as shown in formula (III). The method comprises the following steps: in an undivided electrolytic cell equipped with a cathode and an anode, under constant voltage electrolysis conditions, in a solvent, under N2 protection, in the presence of a base, in the presence of an additive, and at room temperature, using benzotriazole represented by formula (I) and a substituted phenol represented by formula (II) as raw materials, adopting an anodic oxidation method under electrocatalytic conditions to obtain a free radical intermediate, and obtaining the benzotriazole ultraviolet absorber (III) through free radical coupling of the intermediate. The technology of the invention is easy to operate, has a high yield, reduces the amount of three wastes, and is convenient for post-processing.

Description

Technical Field

[0001] The invention relates to the field of polymer material additives, and in particular to a method for preparing a benzotriazole ultraviolet absorber. Background Art

[0002] Benzotriazole UV absorbers are an important class of light stabilizers, widely used in polymer materials, coatings, photosensitive materials, and other fields to protect these materials from UV damage. Benzotriazole UV absorbers absorb UV rays and convert them into harmless heat, thereby protecting materials from the adverse effects of UV radiation, such as photoaging, fading, and degradation. These absorbers typically exhibit excellent UV absorption properties, good thermal and chemical stability, and compatibility with a variety of resins.

[0003] The current method for preparing benzotriazole ultraviolet absorbers is to first prepare azobenzene as an intermediate product, and then reduce and cyclize the azobenzene to obtain the corresponding product. Among them, the azobenzene preparation process requires the synthesis of a diazonium salt, which is explosive and has a high risk factor. The reduction methods of the intermediate product azobenzene mainly include: zinc powder reduction method, hydrazine hydrate reduction method, sulfide reduction method, sulfide-zinc powder method, hydrazine hydrate-zinc powder method, hydrazine hydrate-hydrogenation reduction method, hydrazine hydrate-sodium dithionite method, glucose-zinc powder method, and catalytic hydrogenation reduction method. These reduction processes inevitably produce a large amount of alkaline wastewater containing organic matter and difficult-to-treat waste residue. The drawbacks in the above synthesis process have seriously hindered the development of my country's benzotriazole ultraviolet absorber industry.

[0004]

[0005] Electrochemical synthesis is a method that utilizes electrochemical reactions to produce chemical syntheses. The electrochemical cathode and anode continuously provide clean electrons as green redox agents, avoiding excessive reliance on or use of hazardous or toxic oxidants and reductants. This method meets the standards of "green chemistry," is minimally polluting, and atom-efficient. Electrochemical synthesis is typically performed at room temperature and pressure, offering simple reaction operations and the ability to selectively oxidize (or reduce) functional groups. The current and potential can be randomly controlled, resulting in rapid reaction rates and high product purity and selectivity. Electrochemical synthesis technology has applications in a variety of fields, including organic synthesis, materials science, and energy storage.

[0006] In order to address the shortcomings of the preparation method of benzotriazole ultraviolet absorbers, the present invention adopts anodization of phenolic compounds and triazole compounds under electrocatalytic conditions to form corresponding free radical intermediates, and finally obtains the product through free radical coupling. Summary of the Invention

[0007] The present invention aims to provide a method for preparing a benzotriazole ultraviolet absorber having a structure shown in formula (III) using a benzotriazole represented by formula (I) and a substituted phenol represented by formula (II) as raw materials. The method involves electrooxidizing the benzotriazole represented by formula (I) and the substituted phenol represented by formula (II) to obtain corresponding free radical intermediates. The two free radical intermediates undergo free radical coupling to obtain the benzotriazole ultraviolet absorber represented by formula (III).

[0008] The present invention offers two improvements: 1) It utilizes a method of generating free radicals through anodic oxidation under electrocatalytic conditions and then coupling free radicals to efficiently prepare the target compound in a single step; 2) it avoids the preparation of diazo compounds, the synthesis of azo compounds, and the reduction of azo compounds, making the process safer and more environmentally friendly. The present invention overcomes the shortcomings of prior art methods, including long routes, harsh reaction conditions, high risks, high raw material costs, and the production of excessive waste.

[0009]

[0010] In formula (I), formula (II) and formula (III), R is hydrogen or chlorine, R 1 、R 2 Each is independently selected from H, C1-C12 alkyl, phenyl, C1-C4 alkyl.

[0011] Specifically, the present invention provides a method for preparing a benzotriazole ultraviolet absorber of formula (III), which comprises the following steps:

[0012] In an undivided electrolytic cell equipped with a cathode and an anode, under constant voltage electrolysis conditions, in a solvent, under N2 protection, in the presence of a base, in the presence of an additive, at room temperature, a benzotriazole represented by formula (I) and a substituted phenol represented by formula (II) are used as raw materials, and a free radical intermediate is obtained by an anodic oxidation method under electrocatalytic conditions. The intermediate is then coupled with a benzotriazole ultraviolet absorber (III).

[0013] In the method of the present invention, the anode is one of a platinum electrode, a graphite electrode, an RVC electrode, a PtO2 electrode, etc.; the cathode is one of a graphite electrode, a platinum electrode, a nickel electrode, a silver electrode, etc.; the voltage is 2 to 5V; the additive is one of lithium perchlorate, tetrabutylammonium bromide, tetrabutylammonium iodide, tetrabutylammonium hexafluorophosphate, etc.; and the base is one of 1,8-diazabicyclo[5.4.0]undec-7-ene, lithium hexamethyldisilazide, 4-dimethylaminopyridine, 2,6-lutidine, etc.

[0014] The molar ratio of benzotriazole (I), substituted phenol (II) and additive is 1:1-3:0.1-1.

[0015] The solvent is one of dichloromethane, methanol, trifluoroethanol, hexafluoroisopropanol, or a mixed solvent composed of any two of the solvents. The amount of the solvent is such that the volume ratio of the mole number of benzotriazole (I) to the solvent is 1:5-50 (mmol / mL).

[0016] The volume ratio of the mixed solvent of any two solvents is 1:1 to 1:5. DETAILED DESCRIPTION

[0017] The following non-limiting examples will further illustrate the present invention, but the content of the claims of the present invention is not limited to the enumerated embodiments.

[0018] Example 1:

[0019] p-Cresol (1.78 g, 16.5 mmol, 1.1 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium hexafluorophosphate (1.45 g, 3.75 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (3.42 g, 22.5 mmol, 1.5 eq), and hexafluoroisopropanol / dichloromethane (75.0 mL) were stirred in a sealed electrolytic cell equipped with platinum electrodes as the anode and cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 2.9 g of the desired product in an 85% yield. Melting point: 131-133°C. 1 H NMR (400MHz, CDCl3): δ = 2.34 (s, 3H), 6.92–7.18 (m, 2H), 7.28–7.54 (m, 2H), 7.82–8.06 (m, 2H), 8.22 (d, 1H, J = 2.0Hz), 11.21 (s, 1H). HRMS(ESI-TOF)(m / z):calcd for C 13 H 10 N3O - ([MH] - ),224.0829,found,224.0821.

[0020] Example 2:

[0021] 2-tert-Butyl-4-methylphenol (3.69 g, 22.5 mmol, 1.5 eq), 5-chlorobenzotriazole (2.30 g, 15.0 mmol, 1 eq), lithium perchlorate (0.80 g, 7.5 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (3.42 g, 22.5 mmol, 1.5 eq), and hexafluoroisopropanol (150.0 mL) were stirred in a sealed electrolytic cell equipped with a graphite anode and a platinum cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.0 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 4.3 g of the desired product in a 90% yield. Melting point: 136-137°C. 1 H NMR (400MHz, CDCl3): δ = 1.38 (s, 9H), 2.30 (s, 3H), 7.45 (d, 1H), 7.47 (d, 1H), 7.85–7.92 (m, 2H), 8.34 (d, 1H), 11.50 (s, 1H). HRMS(ESI-TOF)(m / z):calcdfor C 17 H 17 ClN3O - ([MH] - ),314.1066,found,314.1071.

[0022] Example 3:

[0023] 2,4-di-tert-butylphenol (6.18 g, 30.0 mmol, 2 eq), 5-chlorobenzotriazole (2.30 g, 15.0 mmol, 1 eq), tetrabutylammonium bromide (4.83 g, 15.0 mmol), 2,6-lutidine (3.66 g, 30.0 mmol, 2 eq), and trifluoroethanol / dichloromethane (300.0 mL) were stirred in a sealed electrolytic cell equipped with an RVC electrode at the anode and a nickel electrode at the cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 3.0 V until 5-chlorobenzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 4.8 g of the desired product in an 89% yield. Melting point: 147-149°C. 1 H NMR (400MHz, CDCl3): δ = 1.39 (s, 9H), 1.50 (s, 9H), 7.45 (d, 1H), 7.47 (d, 1H), 7.85–7.95 (m, 2H), 8.36 (d, 1H), 11.52 (s, 1H). HRMS(ESI-TOF)(m / z):calcd for C 20 H 23 ClN3O- ([MH] - ),356.1535,found,356.1540.

[0024] Embodiment 4:

[0025] 4-(1',1',3',3'-tetramethylbutyl)phenol (9.27 g, 45.0 mmol, 3 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium iodide (0.55 g, 1.5 mmol), 4-dimethylaminopyridine (5.49 g, 45.0 mmol, 3 eq), and trifluoroethanol (100.0 mL) were stirred in a sealed electrolytic cell equipped with a PtO2 anode and a silver cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 4.0 g of the desired product in an 82% yield. Melting point: 105-106°C. 1 H NMR (400MHz, CDCl3): δ = 0.77 (s, 9H), 1.45 (s, 6H), 1.80 (s, 2H), 7.18 (m, 1H), 7.46(m,1H),7.48(m,2H),7.94(m,2H),8.39(d,1H,J=2.0Hz),11.18(s,1H). HRMS(ESI-TOF)(m / z):calcd for C 20 H 24 N3O - ([MH] - ),322.1925,found,322.1920.

[0026] Example 5:

[0027] 2,4-di-tert-butylphenol (4.63 g, 22.5 mmol, 1.5 eq), benzotriazole (15.0 mmol, 1 eq), tetrabutylammonium hexafluorophosphate (7.5 mmol), 2,6-lutidine (30.0 mmol, 2 eq), and hexafluoroisopropanol (150.0 mL) were stirred in a sealed electrolytic cell equipped with a graphite anode and a platinum cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 4.0 g of the desired product in an 83% yield. Melting point: 148-149°C. 1H NMR (400MHz, CDCl3): δ = 1.33 (s, 9H), 1.45 (s, 9H), 7.36 (d, J = 2.4Hz, 1H), 7.37-7.44 (m, 2H), 7.84–7.91 (m, 2H), 8.24 (d, J = 2.4Hz, 1H), 11.76 (s, 1H). HRMS(ESI-TOF)(m / z):calcd for C 20 H 24 N3O - ([MH] - ),322.1925,found,322.1918.

[0028] Example 6:

[0029] 2,4-Bis(1′,1′-dimethylpropyl)phenol (3.86 g, 16.5 mmol, 1.3 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium hexafluorophosphate (1.45 g, 3.75 mmol), 2,6-lutidine (3.21 g, 30.0 mmol, 2 eq), and hexafluoroisopropanol / dichloromethane (75.0 mL) were stirred in a sealed electrolytic cell equipped with platinum electrodes as the anode and cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 4.6 g of the desired product in an 88% yield. Melting point: 78-79°C. 1 H NMR (400MHz, CDCl3): δ=0.63-0.74(m,6H),1.34(s,6H),1.44(s,6H),1.67(q,2H,J=7.6Hz),1.98(q,2H,J= 7.6Hz), 7.26 (d, 1H, J = 2.4Hz), 7.42-7.49 (m, 2H), 7.88-7.95 (m, 2H), 8.23 ​​(d, 1H, J = 2.4Hz), 11.74 (s, IH). HRMS(ESI-TOF)(m / z):calcdfor C 22 H 28 N3O - ([MH] - ),350.2238,found,350.2225.

[0030] Example 7:

[0031] 2,4-bis(1′,1′-dimethylpropyl)phenol (3.86 g, 16.5 mmol, 1.2 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium hexafluorophosphate (2.90 g, 7.5 mmol), 2,6-lutidine (3.21 g, 30.0 mmol, 2 eq), hexafluoroisopropanol / dichloromethane = 5 / 2 (100.0 mL) were stirred in a sealed electrolytic cell equipped with graphite electrodes as anode and cathode under a N2 atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin layer chromatography. The reaction mixture was then concentrated under reduced pressure to obtain 4.2 g of the target product with a yield of 80%.

[0032] Example 8:

[0033] 2,4-Bis(1′-methylbenzyl)phenol (4.98 g, 16.5 mmol, 1.4 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium hexafluorophosphate (2.90 g, 7.5 mmol), 2,6-lutidine (3.21 g, 30.0 mmol, 2 eq), and hexafluoroisopropanol / dichloromethane (5 / 1) (150.0 mL) were stirred in a sealed electrolytic cell equipped with platinum electrodes as the anode and cathode under a nitrogen atmosphere. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to yield 5.6 g of the desired product in an 89% yield. Melting point: 45-46°C. 1 H NMR (400MHz, CDCl3): δ = 1.72 (d, 2H), 3.57-3.46 (m, 1H), 4.42-4.49 (m, 1H), 6.69 (s, 1H), 7.18-7.36 (m, 10H), 7.26 (d, 1H, J = 2.4Hz), 7.42-7.49 (m, 2H), 7.88-7.95 (m, 2H), 8.23 ​​(d, 1H, J = 2.4Hz), 11.64 (s, IH). HRMS(ESI-TOF)(m / z):calcd for C 28 H 24 N3O - ([MH] - ),418.1925,found,418.1923.

[0034] Example 9:

[0035] p-Cresol (1.78 g, 16.5 mmol, 1.1 eq), benzotriazole (1.79 g, 15.0 mmol, 1 eq), tetrabutylammonium bromide (1.20 g, 3.75 mmol), lithium hexamethyldisilazide (5.01 g, 30.0 mmol, 2 eq), hexafluoroisopropanol / dichloromethane = 1 / 1 (75.0 mL) were stirred in a sealed electrolytic cell equipped with electrodes under a N2 atmosphere, with a PtO2 electrode as the anode and a platinum electrode as the cathode. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to obtain 3.0 g of the target product in a 90% yield.

[0036] Example 10:

[0037] 2-tert-Butyl-4-methylphenol (3.69 g, 22.5 mmol, 1.5 eq), 5-chlorobenzotriazole (2.30 g, 15.0 mmol, 1 eq), tetrabutylammonium bromide (1.21 g, 3.75 mmol), 2,6-lutidine (3.21 g, 30.0 mmol, 2 eq), hexafluoroisopropanol / dichloromethane = 1 / 1 (75.0 mL) were stirred in a sealed electrolytic cell equipped with electrodes under a N2 atmosphere, with a PtO2 electrode as the anode and a platinum electrode as the cathode. The reaction mixture was stirred and electrolyzed at a constant potential of 2.5 V until the benzotriazole disappeared as detected by thin-layer chromatography. The reaction mixture was then concentrated under reduced pressure to obtain 3.8 g of the target product in a yield of 81%.

Claims

1. A method for synthesizing a benzotriazole ultraviolet absorber having a structure as shown in formula (III), comprising the following steps: in an undivided electrolytic cell equipped with a cathode and an anode, under constant voltage electrolysis conditions, in a solvent, under nitrogen protection, in the presence of a base, in the presence of an additive, at room temperature, using benzotriazole represented by formula (I) and a substituted phenol represented by formula (II) as raw materials, using an anodic oxidation method under electrocatalytic conditions to obtain a free radical intermediate, and obtaining the benzotriazole ultraviolet absorber (III) through free radical coupling from the intermediate. In formula (I), formula (II) and formula (III), R is hydrogen or chlorine, R 1 、R 2 Each is independently selected from H, C1-C12 alkyl, phenyl-C1-C4 alkyl; The voltage is 2~5V; The additive is one of lithium perchlorate, tetrabutylammonium bromide, tetrabutylammonium iodide, and tetrabutylammonium hexafluorophosphate; The base is one of 1,8-diazabicyclo[5.4.0]undec-7-ene, lithium hexamethyldisilazide, 4-dimethylaminopyridine and 2,6-lutidine.

2. The method for synthesizing a benzotriazole ultraviolet absorber according to claim 1, wherein The anode is one of a platinum electrode, a graphite electrode, an RVC electrode, and a PtO2 electrode.

3. The method for synthesizing the benzotriazole ultraviolet absorber according to claim 1, wherein The cathode is one of a graphite electrode, a platinum electrode, a nickel electrode and a silver electrode.

4. The method for synthesizing a benzotriazole ultraviolet absorber according to claim 1, wherein The molar ratio of the benzotriazole (I), substituted phenol (II) and additive is 1:1-3:0.1-1.

5. The method for synthesizing the benzotriazole ultraviolet absorber according to claim 1, wherein The solvent is one of dichloromethane, methanol, trifluoroethanol, and hexafluoroisopropanol, or a combination of any two thereof.

6. The method for synthesizing the benzotriazole ultraviolet absorber according to claim 1, wherein The volume ratio of the molar number of the benzotriazole (I) to the solvent is 1:5 to 50 in mmol / mL.

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