Method for efficiently synthesizing epsilon-caprolactone through photocatalytic Baeyer-Villiger oxidation

Abstract

A method for efficiently synthesizing epsilon-caprolactone through photocatalytic Baeyer-Villiger oxidation comprises the following steps that cyclohexanone, aldehyde, a photocatalyst and a chlorine source are dispersed in a solvent to obtain a preliminary mixture, the molar ratio of the aldehyde to the cyclohexanone is 1: 2-1: 10, the molar ratio of the photocatalyst to the cyclohexanone is 1: 10-1: 100, the molar ratio of the chlorine source to the aldehyde is 1: 2-1: 10, the molar ratio of the aldehyde to the cyclohexanone is 1: 2-1: 10, and the molar ratio of the chlorine source to the cyclohexanone is 1: 1-1: 100; the molar ratio of the chlorine source to the cyclohexanone can be 1: 5-1: 50, the molar ratio of the solvent to the cyclohexanone is (10-40): 1, and the solvent is one or more of acetonitrile, 1, 4-dioxane and tetrahydrofuran; and introducing oxygen into the mixture, and carrying out a reaction under visible light and room temperature conditions to obtain epsilon-caprolactone. The method for efficiently synthesizing epsilon-caprolactone through photocatalytic Baeyer-Villiger oxidation is extremely high in conversion rate and yield, the conversion rate of cyclohexanone is larger than or equal to 99%, the yield of epsilon-caprolactone is larger than or equal to 95%, only a catalytic amount of aldehyde needs to be added, the production cost can be effectively reduced, generation of by-products is reduced, the product separation and purification difficulty is reduced, and reaction conditions are mild and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and particularly to a method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation. Background Art

[0002] Poly ε -caprolactone (PCL) is a chemically synthesized polymer with excellent biodegradability, biocompatibility, and permeability. It can be easily decomposed into carbon dioxide and water by microorganisms or enzymes in nature. With its unique material properties and low-temperature processing advantages, PCL shows significant application potential in the fields of medical devices and high-value-added packaging materials. As a key raw material of PCL, ε -caprolactone synthesis has attracted much attention.

[0003] Currently, industrially, ε-caprolactone is mainly synthesized by the Baeyer-Villiger oxidation reaction of cyclohexanone using peroxyacids as oxidants. However, this method has high process requirements and explosion risks, and is currently only mastered by a few foreign companies. Researchers have also developed the Baeyer-Villiger oxidation reaction using hydrogen peroxide as an oxidant. Although this method is safe and environmentally friendly, the by-product water will reduce the lactone yield. Currently, the method of using oxygen (O2) as an oxidant to produce ε -caprolactone is becoming a research hotspot. However, due to the limited oxidation ability of molecular oxygen, not only catalysts (such as SnO2, Fe3O4, Cu(OAc)2, zeolite molecular sieves, NHPI, Cu-MCM-41, InOx / TUD-1, metal porphyrins / carbazoles, etc.) need to be added, but also an equivalent amount of aldehydes (such as benzaldehyde) needs to be added as a co-oxidant to increase the ε -caprolactone yield. ε -caprolactone yield.

[0004] In recent years, with the improvement of scientific research level, ε -caprolactone has been increasingly widely used, and the market demand has been continuously growing. Therefore, it is particularly important to develop a clean, safe, and environmentally friendly ε -caprolactone production technology. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation, with extremely high conversion rate and yield: the conversion rate of cyclohexanone ≥ 99%, ε -caprolactone yield ≥ 95%, and only a catalytic amount of aldehyde needs to be added, which can effectively reduce the production cost, reduce the generation of by-products, reduce the difficulty of product separation and purification, and the reaction conditions are mild and green and environmentally friendly.

[0006] The present invention provides a method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation, comprising the following steps: Disperse cyclohexanone, aldehyde, photocatalyst and chlorine source into a solvent to obtain a preliminary mixture, wherein the molar ratio of the aldehyde to cyclohexanone is 1:2 - 1:10, the molar ratio of the photocatalyst to cyclohexanone is 1:10 - 1:100, the molar ratio of the chlorine source to cyclohexanone can be 1:5 - 1:50, the molar ratio of the solvent to the cyclohexanone is (10 - 40):1, and the solvent is one or more of acetonitrile, 1,4-dioxane, and tetrahydrofuran; Introduce oxygen into the mixture and carry out the reaction under visible light and room temperature conditions to obtain ε -caprolactone.

[0007] In one embodiment, the aldehyde is an aryl aldehyde or an alkyl aldehyde.

[0008] In one embodiment, the aryl aldehyde is one or more of benzaldehyde, o-fluorobenzaldehyde, o-chlorobenzaldehyde, o-trifluoromethylbenzaldehyde, m-fluorobenzaldehyde, m-chlorobenzaldehyde, m-trifluoromethylbenzaldehyde, p-fluorobenzaldehyde, p-chlorobenzaldehyde, and p-trifluoromethylbenzaldehyde.

[0009] In one embodiment, the alkyl aldehyde is one or more of pivalaldehyde, 2-methyldecanal, and 2-methylundecanal.

[0010] In one embodiment, the photocatalyst is one or more of nitrile aromatic hydrocarbons, benzophenones and quinones, pyrans and thiopyrans, quinolines, acridines, rhodamines, or thiazinezines.

[0011] In one embodiment, the chlorine source is one or more of hydrogen chloride, sodium chloride, potassium chloride, ammonium chloride, and tetrabutylammonium chloride.

[0012] In one embodiment, the wavelength range of the visible light is 380 - 440 nm.

[0013] The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention has extremely high conversion rate and yield: the conversion rate of cyclohexanone ≥ 99%, ε the yield of -caprolactone ≥ 95%, and only a catalytic amount of aldehyde needs to be added, which can effectively reduce the production cost, reduce the generation of by-products, reduce the difficulty of product separation and purification, and the reaction conditions are mild and environmentally friendly. Description of the Drawings

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a schematic flow chart of the method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention. Specific embodiments

[0016] The following will describe in detail specific embodiments of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the description of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0017] In the description of the present invention, unless otherwise clearly defined and limited, terms such as "set", "installed", "connected", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0018] The orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use. It is only for the convenience of description and simplification of the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0019] Terms such as "first", "second", "third", etc. are only used to distinguish elements with similar attributes, rather than indicating or implying relative importance or a specific order.

[0020] The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion. In addition to the listed elements, it may also include other elements not specifically listed. Embodiment 1

[0021] Please refer to Figure 1, The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention comprises the following steps: Take a 100 mL glass reactor, and successively add cyclohexanone (1.96 g, 20 mmol), benzaldehyde (0.53 g, 5.0 mmol), photocatalyst 10-methyl-9-mesityl acridine perchlorate (0.16 g, 0.4 mmol), 1,4-dioxane solution (1.0 M) of hydrogen chloride (2 mL, 2.0 mmol), and 20 mL of acetonitrile solvent. Connect the reactor to an oxygen balloon, place it under the irradiation of a 32W blue LED light, and stir the reaction at room temperature for 24 hours. After the reaction is completed, detect the conversion rate of cyclohexanone by gas chromatography; distill off the solvent under normal pressure, and distill and separate the target product ε -caprolactone under reduced pressure (100 °C, 10 mm Hg); detect the purity of the target product by gas chromatography, and the experimental results are shown in Table 1.

[0022] Comparative Example 1 Comparative Example 1 also provides a method for synthesizing ε-caprolactone. The reaction conditions are basically the same as those in Example 1, except that: no photocatalyst is added, and the amount of benzaldehyde added is increased to 3.18 g (30 mmol). The experimental results are shown in Table 1.

[0023] Comparative Example 2 Comparative Example 2 also provides a method for synthesizing ε-caprolactone. The reaction conditions are basically the same as those in Example 1, except that: no chlorine source is added, and the amount of benzaldehyde added is increased to 3.18 g (30 mmol). The experimental results are shown in Table 1.

[0024] Comparative Example 3 Comparative Example 3 also provides a method for synthesizing ε-caprolactone. The reaction conditions are basically the same as those in Example 1, except that: the reaction is carried out in the dark, and the amount of benzaldehyde added is increased to 3.18 g (30 mmol). The experimental results are shown in Table 1. Example 2

[0025] Please refer to Figure 1 , The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention comprises the following steps: Take a 100 mL glass reactor and sequentially add cyclohexanone (1.96 g, 20 mmol), p-chlorobenzaldehyde (0.56 g, 4.0 mmol), the photocatalyst 10-methyl-9-mesityl acridine perchlorate (0.16 g, 0.4 mmol), a 1,4-dioxane (1.0 M) solution of hydrogen chloride (2 mL, 2.0 mmol), and 20 mL of acetonitrile solvent. Connect the reactor to an oxygen balloon and place it under irradiation by a 32 W blue LED light, and stir the reaction at room temperature for 24 hours. After the reaction is completed, detect the conversion rate of cyclohexanone by gas chromatography; distill off the solvent under atmospheric pressure and separate the target product by distillation under reduced pressure (100 °C, 10 mm Hg). ε -caprolactone; detect the purity of the target product by gas chromatography. The experimental results are shown in Table 1. Example 3

[0026] Please refer to Figure 1 , the method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention includes the following steps: Take a 100 mL glass reactor and sequentially add cyclohexanone (1.96 g, 20 mmol), benzaldehyde (0.42 g, 4.0 mmol), the photocatalyst 10-methyl-9-mesityl acridine perchlorate (0.16 g, 0.4 mmol), a 1,4-dioxane (1.0 M) solution of hydrogen chloride (2 mL, 2.0 mmol), and 20 mL of acetonitrile solvent. Connect the reactor to an oxygen balloon and place it under irradiation by a 32 W blue LED light, and stir the reaction at room temperature for 24 hours. After the reaction is completed, detect the conversion rate of cyclohexanone by gas chromatography; distill off the solvent under atmospheric pressure and separate the target product by distillation under reduced pressure (100 °C, 10 mm Hg). ε -caprolactone; detect the purity of the target product by gas chromatography. The experimental results are shown in Table 1. Example 4

[0027] Please refer to Figure 1 , the method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention includes the following steps: Take a 100 mL glass reactor and successively add cyclohexanone (1.96 g, 20 mmol), benzaldehyde (0.53 g, 5.0 mmol), the photocatalyst rhodamine B (0.19 g, 0.4 mmol), a 1,4-dioxane solution of hydrogen chloride (1.0 M) (2 mL, 2.0 mmol), and 20 mL of acetonitrile solvent. Connect the reactor to an oxygen balloon and place it under irradiation by a 32 W blue LED light, and stir the reaction at room temperature for 24 hours. After the reaction is completed, detect the conversion rate of cyclohexanone by gas chromatography; distill off the solvent under normal pressure, and separate the target product by distillation under reduced pressure (100 °C, 10 mm Hg). ε -caprolactone; detect the purity of the target product by gas chromatography. The experimental results are shown in Table 1 below. Example 5

[0028] Please refer to Figure 1 , the method for the efficient synthesis of ε-caprolactone by photocatalytic Baeyer-Villiger oxidation provided by the present invention includes the following steps: Take a 100 mL glass reactor and successively add cyclohexanone (1.96 g, 20 mmol), pivalaldehyde (0.43 g, 5.0 mmol), the photocatalyst 10-methyl-9-mesityl acridine perchlorate (0.21 g, 0.5 mmol), sodium chloride (0.23 g, 4.0 mmol), and 20 mL of tetrahydrofuran solvent. Connect the reactor to an oxygen balloon and place it under irradiation by a 32 W blue LED light, and stir the reaction at room temperature for 24 hours. After the reaction is completed, detect the conversion rate of cyclohexanone by gas chromatography; distill off the solvent under normal pressure, and separate the target product by distillation under reduced pressure (100 °C, 10 mm Hg). ε -caprolactone; detect the purity of the target product by gas chromatography. The experimental results are shown in Table 1 below.

[0029] Table 1. Experimental Results Conversion rate of cyclohexanone Yield of ε-caprolactone Purity of ε-caprolactone Example 1 ≥99% 98% 98% Example 2 ≥99% 99% 99% Example 3 ≥99% 98% 98% Example 4 ≥99% 96% 97% Example 5 ≥99% 95% 97% Comparative Example 1 7% 5% - Comparative Example 2 6% 6% - Comparative Example 3 7% 5% - From the data in Table 1, it can be seen that by using the scheme provided by the present invention for the Baeyer-Villiger oxidation of cyclohexanone, the target product can be obtained with extremely high conversion rates and yields, and ε-caprolactone with a purity ≥ 97% can be separated only by simple distillation under reduced pressure. On the contrary, when no photocatalyst is used, or no chlorine source is used, or no light irradiation is carried out, only a small amount of product can be obtained in this reaction. Therefore, this technology can significantly improve the reaction efficiency and is expected to become the next-generation clean, safe, and environmentally friendly ε-caprolactone production technology.

[0030] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation, characterized in that: The steps include: Dispersing cyclohexanone, aldehyde, photocatalyst and chlorine source in a solvent to obtain a preliminary mixture, wherein the molar ratio of the aldehyde to the cyclohexanone is 1:2-1:10, the molar ratio of the photocatalyst to the cyclohexanone is 1:10-1:100, the molar ratio of the chlorine source to the cyclohexanone may be 1:5-1:50, the molar ratio of the solvent to the cyclohexanone is (10-40):1, and the solvent is one or more of acetonitrile, 1,4-dioxane and tetrahydrofuran; Oxygen is introduced into the mixture, and the reaction is carried out under visible light and room temperature to obtain ε -Caprolactone.

2. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 1, characterized in that: The aldehyde is an aryl aldehyde or an alkyl aldehyde.

3. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 2, characterized in that: The aromatic aldehyde is one or more selected from benzaldehyde, o-fluorobenzaldehyde, o-chlorobenzaldehyde, o-trifluoromethylbenzaldehyde, m-fluorobenzaldehyde, m-chlorobenzaldehyde, m-trifluoromethylbenzaldehyde, p-fluorobenzaldehyde, p-chlorobenzaldehyde and p-trifluoromethylbenzaldehyde.

4. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 2, characterized in that: The alkyl aldehyde is one or more of p-valeraldehyde, 2-methyldecanal, and 2-methylundecanal.

5. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 1, characterized in that: The photocatalyst is selected from nitrile aromatic hydrocarbons, benzophenones and quinones, pyrans and thiopyrans, quinolines, acridines, rhodamines or thiophenazines.

6. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 1, characterized in that: The chlorine source is one or more of hydrogen chloride, sodium chloride, potassium chloride, ammonium chloride, and tetrabutylammonium chloride.

7. The method for efficiently synthesizing ε-caprolactone by photocatalytic Baeyer-Villiger oxidation according to claim 1, characterized in that: The wavelength range of the visible light is 380-440 nm.

Images