Method for preparing 2-methyl-1, 4-naphthoquinone through photocatalysis

Abstract

The invention discloses a method for preparing 2-methyl-1, 4-naphthoquinone through photocatalysis, which comprises the following steps: under the catalysis and illumination conditions of elemental iodine, 2-methyl-1, 4-tetrahydronaphthoquinone and oxygen are subjected to oxidation reaction in an organic solvent, and the 2-methyl-1, 4-naphthoquinone is obtained after the reaction is completed. According to the method, the 2-methyl-1, 4-naphthoquinone is prepared by adopting a photocatalytic oxidation method, so that the use of toxic reagents which are difficult to treat is avoided, the post-treatment is simple, the reaction conditions are milder, the reaction can be carried out at room temperature, and the method is more suitable for industrial operation.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and specifically relates to a method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis. Background Art

[0002] Menadione, also known as 2-methyl-1,4-naphthoquinone, is a key raw material for synthesizing vitamin K3, and its appearance is a yellow crystalline powder. Vitamin K3 is a procoagulant in clinical practice and can be used to treat hemorrhagic diseases caused by vitamin K3 deficiency. In addition, it plays an important role in the metabolism and oxidative phosphorylation of high-energy compounds, as well as in the metabolism of other fat-soluble vitamins, and has the function of lowering blood pressure. Environmental pollution and energy shortage are challenges currently faced by mankind. Photocatalysis has the characteristics of low cost and pollution-free, and has great potential in environmental purification and new energy development. The continuous flow chemical process uses a microchannel reactor to replace the traditional chemical reactor for chemical reaction and realizes industrial production. Continuous flow chemistry has the characteristics of high efficiency, flexibility and safety.

[0003] Patent CN111689844A reports the synthesis of 2-methyl-1,4-naphthoquinone using o-methylphenol as raw material through three-step reactions such as oxidation and condensation. The process uses DMSO as a solvent and an oxidant to oxidize 2-methyl-1,4-tetrahydronaphthoquinone under a copper bromide / manganese bromide catalytic system with a yield of 91.3%. The process uses DMSO as an oxidant and solvent, making post-processing difficult; copper bromide / manganese bromide is used as a catalyst, which is prone to heavy metal residues, high production costs, and is not conducive to industrial production.

[0004]

[0005] Patent US5770774 reported that 2-methyl-1,4-naphthoquinone was prepared from m-methylphenol by DA (Diels-Alder) reaction and oxidation reaction. However, the price of m-methylphenol, the raw material of this process, is relatively high, the oxidation reaction risk is high, the yield is only 65%, and the process uses highly toxic SnCl4, which is not conducive to industrial production.

[0006] Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis, which has mild reaction reagents, simple post-treatment and is suitable for industrial production.

[0008] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0009] A method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis comprises the following steps:

[0010] Under the catalytic conditions of elemental iodine and light, 2-methyl-1,4-tetrahydronaphthoquinone reacts with oxygen in an organic solvent to produce 2-methyl-1,4-naphthoquinone.

[0011] The synthetic route of 2-methyl-1,4-naphthoquinone is as follows:

[0012]

[0013] The present invention carries out the reaction under photocatalytic conditions, and the catalytic reagent used is milder, avoiding the use of highly toxic reagents such as SnCl4 or copper bromide / manganese bromide. At the same time, green oxidant oxygen is used for oxidation, and the post-treatment is simple, which is more suitable for industrial operation.

[0014] Preferably, the oxidation reaction is carried out in a pipeline reactor in a continuous flow manner;

[0015] The continuous flow method is as follows:

[0016] The 2-methyl-1,4-tetrahydronaphthoquinone and elemental iodine are added to an organic solvent to form a solution, and then the solution and oxygen are introduced into the pipeline reactor simultaneously for reaction. The reaction efficiency can be further improved by adopting a continuous flow reaction method.

[0017] Preferably, the pipe reactor can be a pipe reactor conventionally used in the art, such as a multi-tube reactor or a microchannel reactor. As a preferred implementation or example, the pipe of the pipe reactor is a transparent hose with a length of 40 to 50 m, an outer diameter of 5 to 7 mm, and an inner diameter of 3 to 5 mm.

[0018] Preferably, the illumination condition uses an LED light source with a wavelength of 400-650nm and 90-110W. More preferably, the illumination condition uses an LED light source with a wavelength of 400-520nm and 90-100W. The wavelength of the illumination condition has a greater influence on the reaction result. In this case, the reaction can be carried out with a higher conversion rate and yield.

[0019] There are many solvents that can be applied to the present invention. Preferably, the organic solvent is one or more of aromatic hydrocarbon solvents, nitrile solvents, ester solvents, and halogenated hydrocarbon solvents. As a further preference, the organic solvent is one or more of toluene, acetonitrile, ethyl acetate, and dichloromethane, and toluene is further preferred.

[0020] Preferably, the temperature of the oxidation reaction is 20 to 50°C.

[0021] Preferably, the amount of elemental iodine used is 2-4% of 2-methyl-1,4-tetrahydronaphthoquinone on a molar basis, and more preferably 3%.

[0022] The retention time in the pipeline reactor will affect the reaction results. Preferably, the retention time of the reaction solution in the pipeline reactor is 100 to 200 minutes, more preferably 125 minutes.

[0023] Preferably, the mass percentage of the 2-methyl-1,4-tetrahydronaphthoquinone in the solution is 1 to 5%;

[0024] The flow rate of the solution is 2-5 g / min, and the flow rate of the oxygen is 25-64 mL / min.

[0025] Preferably, after the reaction is complete, the solvent and elemental iodine are recovered by distillation and applied to the next batch of reactions, and then crystallized to obtain yellow 2-methyl-1,4-naphthoquinone.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention adopts a photocatalytic oxidation method to prepare 2-methyl-1,4-naphthoquinone, which avoids the use of difficult-to-handle and toxic reagents, has simple post-treatment, milder reaction conditions, and can occur at room temperature, making it more suitable for industrial operation.

[0028] (2) The present invention adopts a reaction mode combining photocatalysis and continuous flow chemistry, which has a faster reaction efficiency and a higher reaction yield, which can be as high as about 95%.

[0029] (3) The catalyst and solvent used in the reaction can be easily recycled and reused, which has the advantages of high efficiency and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 The present invention is a schematic diagram of a method for preparing 2-methyl-1,4-naphthoquinone; in the figure, 1: feed bottle; 2: oxygen tank; 3: liquid flow pump; 4: gas flow meter; 5 and 6: preheater; 7 and 8: temperature display; 9: mixer; 10: light source; 11: pipeline reactor; 12: gas-liquid separator; 13: discharge bottle. DETAILED DESCRIPTION

[0032] In order to facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive, and the specific process is as follows:

[0033] Add organic solvent and elemental iodine to 2-methyl-1,4-tetrahydronaphthoquinone to prepare a 2-methyl-1,4-tetrahydronaphthoquinone and elemental iodine solution with a certain concentration in the feed bottle 1. The oxygen tank 2 is connected to the mixer 9 through a pressure reducing valve, a gas flow meter 4, a preheater 6, a temperature display 8 and a stop valve to control the flow of oxygen. The feed bottle is connected to the mixer 9 through a liquid flow pump 3, a preheater 5, a temperature display 7 and a stop valve to control the liquid flow. The light source 10 is visible light, which is vertically irradiated to the pipe reactor 11 in the form of a coil, wherein the pipe of the pipe reactor is a transparent hose with a length of 45m, an outer diameter of 6mm and an inner diameter of 4mm. The material composition of the receiving liquid is monitored in real time. After the reaction is complete, the solvent and elemental iodine are recovered by distillation and applied to the next batch of reactions, and the kettle liquid is crystallized to obtain yellow 2-methyl-1,4-naphthoquinone.

[0034] Hereinafter, the photocatalytic method for preparing 2-methyl-1,4-naphthoquinone will be further described by the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0035] Example 1

[0036] Weigh 10g of 2-methyl-1,4-tetrahydronaphthoquinone, 0.43g of elemental iodine (3mol%) and 400g of toluene in a 1L feed bottle and shake well. At room temperature (25°C), the flow rate of oxygen is controlled to 50mL / min by a flow meter and the flow rate of liquid is controlled to 3.28g / min by a flow pump. At the same time, the 520nm, 100W LED light source is turned on for irradiation. The retention time is 125min. The outlet liquid is distilled to recover toluene and elemental iodine, which are directly applied to the next batch of reactions. The kettle liquid is crystallized to obtain 9.28g of 2-methyl-1,4-naphthoquinone. The reaction raw material conversion rate is 100%, and the yield of 2-methyl-1,4-naphthoquinone is 95.0%.

[0037] Example 2

[0038] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the amount of elemental iodine used is 0.29 g (2 mol%), and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0039] Example 3

[0040] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the amount of elemental iodine used is 0.58 g (4 mol%), and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0041] Example 4

[0042] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the solvent used is acetonitrile, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0043] Example 5

[0044] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the solvent used is ethyl acetate, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0045] Example 6

[0046] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the solvent used is dichloromethane, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0047] Example 7

[0048] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the visible light used is a 650nm LED light source, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0049] Example 8

[0050] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the visible light used is a 600nm LED light source, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0051] Example 9

[0052] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the visible light used is a 450nm LED light source, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0053] Example 10

[0054] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone, which is compared with Example 1, except that the visible light used is a 400nm LED light source, and the rest is exactly the same as Example 1. The specific results are shown in Table 1. The specific results are shown in Table 1.

[0055] Embodiment 11

[0056] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone, compared with Example 1, except that the retention time is 100 min, the liquid flow rate is 4.1 g / min, the oxygen flow rate is 62.4 mL / min, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0057] Example 12

[0058] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone, which is compared with Example 1, except that the retention time is 200 min, the liquid flow rate is 2.05 g / min, the oxygen flow rate is 25 mL / min, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0059] Example 13

[0060] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the reaction temperature is 50°C, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0061] Comparative Example 1

[0062] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the photocatalyst is benzophenone, and the rest is exactly the same as Example 1. No target product is obtained. The specific results are shown in Table 1.

[0063] Comparative Example 2

[0064] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the photocatalyst is anthracene-9,10-dicarbonitrile, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0065] Comparative Example 3

[0066] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the photocatalyst is 9-fluorenone, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0067] Comparative Example 4

[0068] This example provides a method for synthesizing 2-methyl-1,4-naphthoquinone. Compared with Example 1, the difference is that the reaction temperature is 5°C, and the rest is exactly the same as Example 1. The specific results are shown in Table 1.

[0069] Table 1

[0070]

[0071] a The conversion rate was measured by gas chromatography external standard method.

[0072] b The yield is the crystallization yield.

Claims

1. A method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis, characterized in that: The following steps are involved: Under the catalysis of elemental iodine and light irradiation conditions, 2-methyl-1,4-tetrahydronaphthoquinone and oxygen undergo an oxidation reaction in an organic solvent to obtain the 2-methyl-1,4-naphthoquinone.

2. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 1, characterized in that: The oxidation reaction is carried out in a pipeline reactor in a continuous flow manner; The continuous flow method is as follows: The 2-methyl-1,4-tetrahydronaphthoquinone and elemental iodine are added to an organic solvent to form a solution, and then the solution and oxygen are respectively introduced into the pipeline reactor at the same time to react.

3. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 1 or 2, characterized in that: The wavelength of the illumination condition is 400-650 nm.

4. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 3, characterized in that: The wavelength of the illumination condition is 400-520 nm.

5. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 1 or 2, characterized in that: The organic solvent is one or more of aromatic hydrocarbon solvents, nitrile solvents, ester solvents, and halogenated hydrocarbon solvents.

6. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 5, characterized in that: The organic solvent is one or more of toluene, acetonitrile, ethyl acetate and dichloromethane.

7. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 1 or 2, characterized in that: The temperature of the oxidation reaction is 20-50°C.

8. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 1 or 2, characterized in that: In terms of molar amount, the amount of elemental iodine used is 2-4% of 2-methyl-1,4-tetrahydronaphthoquinone.

9. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 2, characterized in that: The reaction liquid is retained in the pipeline reactor for 100 to 200 minutes.

10. The method for preparing 2-methyl-1,4-naphthoquinone by photocatalysis according to claim 2 or 9, characterized in that: The mass percentage of the 2-methyl-1,4-tetrahydronaphthoquinone in the solution is 1 to 5%; The flow rate of the solution is 2-5 g / min, and the flow rate of the oxygen is 25-64 mL / min.

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