Method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol by cobalt catalysis

Abstract

The present invention provides a method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol by cobalt catalysis, belonging to the technical field of fine chemicals. This method uses 2,3,6-trimethylphenol as the raw material, molecular oxygen as the oxidant, and a cobalt-based material as the heterogeneous catalyst to prepare 2,3,5-trimethylbenzoquinone through a high-performance liquid-phase oxidation reaction. The preparation method of the used cobalt-based material is simple. First, a precursor is obtained by mixing a certain proportion of cobalt salt and a nitrogen-containing organic ligand, and then the precursor is heat-treated in an inert atmosphere at 300-450 °C to obtain the cobalt-based catalyst. The oxidation reaction process of the present invention has mild conditions, is safe, environmentally friendly, the catalyst and the product are easy to separate from the reaction system, and has remarkable practicability and broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic synthesis of fine chemicals, and relates to a new method for preparing 2,3,5-trimethylbenzoquinone by catalytic oxidation using 2,3,6-trimethylphenol as a raw material, molecular oxygen as an oxidant, and a cobalt-based catalyst. Background Art

[0002] 2,3,5-Trimethylhydroquinone is a key intermediate for the industrial synthesis of vitamin E. Among them, using 2,3,6-trimethylphenol as a raw material, first selectively oxidizing it to 2,3,5-trimethylbenzoquinone, and then selectively hydrogenating it is an important way to obtain 2,3,5-trimethylhydroquinone. Therefore, the efficient selective oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone has important application value.

[0003] Currently, the routes for oxidizing 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone mainly include (1) sulfonation oxidation method; (2) catalytic oxidation method. In the process of preparing 2,3,5-trimethylbenzoquinone by the sulfonation oxidation method, 2,3,6-trimethylphenol is sulfonated to the corresponding 4-sulfonic acid group-2,3,6-trimethylphenol using concentrated sulfuric acid, and then oxidized to 2,3,5-trimethylbenzoquinone using manganese dioxide. This method will produce a large amount of waste and cause serious pollution, and has been gradually phased out. The catalytic oxidation method using molecular oxygen or hydrogen peroxide as an oxide has good development prospects. Chinese invention patent (CN 1024188C) oxidizes 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone using oxygen in the presence of a catalyst composed of copper chloride and lithium chloride. Chinese invention patent (CN101260030B) catalyzes the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone by an ionic liquid-supported acetylacetone metal. However, the above methods use homogeneous catalysts and have problems such as difficult product separation and catalyst wastewater.

[0004] From the perspectives of practicality and environment, etc., it is of great significance to develop heterogeneous catalysts for the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. Ruthenium-based complexes supported on nano-silica can efficiently oxidize 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone (RSC Advances., 2019, 9, 28078-28088). Although this catalyst has high activity, the use of precious metals leads to a high cost of the catalytic reaction. Chinese invention patent (CN107185571A) uses a metal cobalt compound coated with alkaline earth metal carbonate supported on activated carbon to catalyze the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. This catalyst has a low cost, but the catalytic efficiency is not high. Chinese invention patent (CN109675635B) discloses a polymer catalyst prepared from Co(Salphen) and dipyridyl compounds, which uses oxygen to oxidize 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. This catalyst has excellent activity, but the preparation process is complex. Therefore, developing a new method for preparing 2,3,5-trimethylbenzoquinone that is environmentally friendly, inexpensive and highly efficient has an application background.

[0005] In the present invention, molecular oxygen is used as the oxygen source, and a cobalt-based material is used as the catalyst to efficiently oxidize 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. The reaction conditions are mild, safe and environmentally friendly, and the separation of the catalyst from the product is simple. Summary of the Invention

[0006] The purpose of the present invention is to provide a new method for catalytic oxidation of 2,3,6-trimethylphenol to prepare 2,3,5-trimethylbenzoquinone. This method is a new method for oxidizing 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone using a cobalt-based material as the catalyst and molecular oxygen as the oxygen source.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for cobalt-catalyzed synthesis of 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol. This method uses a cobalt-based material as the catalyst to oxidize 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. The oxidation reaction steps are as follows:

[0009] The first step is to prepare the catalyst

[0010] Add cobalt salt and nitrogen-containing organic ligand to a solvent, heat and stir for 1-10 h, then cool to room temperature, rotary evaporate to remove the solvent, dry in vacuum, and then heat-treat this mixture in an inert atmosphere at 300-450 °C for 0.5-20 h and then cool to obtain a cobalt-based catalyst.

[0011] Step 2: Prepare 2,3,5-trimethylbenzoquinone

[0012] Add 2,3,6-trimethylphenol, a catalyst, and a solvent into a reaction kettle, then introduce molecular oxygen as the oxygen source. After sealing the reaction kettle, stir and heat to raise the temperature to 40 - 140 °C. After a reaction time of 1 - 48 h, cool to room temperature and separate to obtain 2,3,5-trimethylbenzoquinone. The dosage of the catalyst in the oxidation reaction step is 1 - 40 wt% of the feeding amount of the raw material 2,3,6-trimethylphenol.

[0013] Furthermore, the molar ratio of the cobalt salt to the nitrogen-containing organic ligand is 1:1 - 1:6; the solvent dosage is 1 - 20 times the mass of the nitrogen-containing organic ligand.

[0014] Furthermore, the molecular oxygen is air, oxygen, or a gas containing oxygen, and the oxygen partial pressure is 0.1 - 5 MPa.

[0015] Furthermore, the solvent in the oxidation reaction step is one or more of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and tert-amyl alcohol.

[0016] Furthermore, the solvent dosage in the oxidation reaction step is 1 - 50 times the mass of the raw material 2,3,6-trimethylphenol.

[0017] Furthermore, the cobalt salt in the catalyst preparation step is one or more of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt carbonate, and the nitrogen-containing organic ligand is one or more of 1,10-phenanthroline, 2,2'-bipyridine, polyaniline, diethylenediamine, melamine, and dicyandiamide.

[0018] Furthermore, the inert atmosphere in the catalyst preparation step is one or a mixture of more of nitrogen, argon, and helium. The solvent in the catalyst preparation step is one or a mixture of more of methanol, ethanol, n-propanol, and isopropanol; the heating temperature in the catalyst preparation step is from room temperature to the reflux temperature of the used solvent.

[0019] The present invention provides a new method for preparing 2,3,5-trimethylbenzoquinone by oxidizing 2,3,6-trimethylphenol. This method has the following beneficial effects:

[0020] (1) Using molecular oxygen as the oxidant and a cobalt-based material as the catalyst, it efficiently catalyzes the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone. The selectivity of 2,3,5-trimethylbenzoquinone is high, the reaction conditions are mild, safe, environmentally friendly, and it has broad application prospects.

[0021] (2) The preparation method of the cobalt-based catalyst used is simple, but it has good reaction activity only when heat-treated in a narrow temperature range of 300 - 450 °C. When the temperature is higher than 450 °C, the catalyst activity decreases significantly, and when the temperature is lower than 300 °C, a heterogeneous catalyst cannot be obtained. The separation of the catalyst from the product is simple, and it can be recycled multiple times, with strong practicability. Description of the Drawings

[0022] Figure 1 XRD pattern of catalyst A prepared under the condition of 400 °C in Example 1.

[0023] Figure 2 XRD pattern of catalyst B prepared under the condition of 800 °C in Example 2.

[0024] Figure 3 GC spectrum of the selective oxidation product of 2,3,6-trimethylphenol in Example 1. Detailed Description of the Invention

[0025] The technical solutions of the present invention are described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0026] The present invention is further described below in conjunction with the drawings and specific examples.

[0027] Example 1: Preparation and reaction results of catalyst A

[0028] The cobalt-based material was prepared by using cobalt acetate and 1,10-phenanthroline in a molar ratio of 1:2: 3 mmol of cobalt acetate and 6 mmol of 1,10-phenanthroline were mixed, 150 mL of ethanol was added, and the mixture was heated to 110 °C and stirred for 4 h. Then it was cooled to room temperature, the ethanol was removed by rotary evaporation, and vacuum dried for 12 h. Then this mixture was heat-treated in a nitrogen atmosphere at 400 °C for 1.5 h and then cooled to obtain a cobalt-based catalyst, denoted as catalyst A.

[0029] 2 mmol of 2,3,6-trimethylphenol, 5 wt% of catalyst A, and 3 mL of methanol were added to a reaction kettle, 0.5 MPa of oxygen was charged, and the temperature was raised to 60 °C with stirring and run for 6 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was quantitatively analyzed for the product by gas chromatography. The conversion rate of 2,3,6-trimethylphenol was 99%, and the selectivity of 2,3,5-trimethylbenzoquinone was 82%. The main by-product was dimer ( Figure 3 ). The reaction results are shown in Table 1.

[0030] Example 2: Preparation and reaction results of catalyst B

[0031] The cobalt-based material was prepared with a molar ratio of cobalt acetate and 1,10-phenanthroline (1:2): 3 mmol of cobalt acetate was mixed with 6 mmol of 1,10-phenanthroline, and 150 mL of ethanol was added. After heating to 110 °C and stirring for 4 h, it was cooled to room temperature, the ethanol was removed by rotary evaporation, and it was dried under vacuum for 12 h. Then, this mixture was heat-treated in a nitrogen atmosphere at 800 °C for 1.5 h and then cooled to obtain a cobalt-based catalyst, denoted as Catalyst B.

[0032] 2 mmol of 2,3,6-trimethylphenol, 5 wt% of Catalyst B, and 3 mL of methanol were added to a reaction kettle, 0.5 MPa of oxygen was charged, and the temperature was raised to 60 °C with stirring and run for 6 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was taken for quantitative analysis of the products by gas chromatography, and the conversion rate of 2,3,6-trimethylphenol was 2%. The reaction results are shown in Table 1.

[0033] Example 3: Preparation and reaction results of Catalyst C

[0034] The cobalt-based material was prepared with a molar ratio of cobalt sulfate and dicyandiamide (1:3): 2 mmol of cobalt sulfate was mixed with 6 mmol of dicyandiamide, and 200 mL of methanol was added. After heating to 100 °C and stirring for 8 h, it was cooled to room temperature, the methanol was removed by rotary evaporation, and it was dried under vacuum for 20 h. Then, this mixture was heat-treated in an argon atmosphere at 300 °C for 5.0 h and then cooled to obtain a cobalt-based catalyst, denoted as Catalyst C.

[0035] 2 mmol of 2,3,6-trimethylphenol, 10 wt% of Catalyst C, and 5 mL of ethanol were added to a reaction kettle, 0.1 MPa of oxygen was charged, and the temperature was raised to 140 °C with stirring and run for 48 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was taken for quantitative analysis of the products by gas chromatography, the conversion rate of 2,3,6-trimethylphenol was 89%, and the selectivity of 2,3,5-trimethylbenzoquinone was 88%. The reaction results are shown in Table 1.

[0036] Example 4: Preparation and reaction results of Catalyst D

[0037] The cobalt-based material was prepared with a molar ratio of cobalt carbonate and melamine (1:4): 1 mmol of cobalt carbonate was mixed with 4 mmol of melamine, and 200 mL of n-propanol was added. After heating to 120 °C and stirring for 1 h. Then it was cooled to room temperature, the n-propanol was removed by rotary evaporation, and it was dried under vacuum for 18 h. Then, this mixture was heat-treated in a helium atmosphere at 350 °C for 20.0 h and then cooled to obtain a cobalt-based catalyst, denoted as Catalyst D.

[0038] 2 mmol of 2,3,6 - trimethylphenol, 1 wt% of catalyst D and 13 mL of n - propanol were added to a reaction kettle. 1.0 MPa of oxygen was charged, and the temperature was raised to 100 °C with stirring and the reaction was run for 18 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was taken for quantitative analysis of the products by gas chromatography. The conversion rate of 2,3,6 - trimethylphenol was 89%, and the selectivity of 2,3,5 - trimethylbenzoquinone was 84%. The reaction results are shown in Table 1.

[0039] Example 5: Preparation and reaction results of catalyst E

[0040] The cobalt - based material was prepared by using a molar ratio of cobalt nitrate and polyaniline (1:1): 5 mmol of cobalt nitrate and 5 mmol of polyaniline were mixed, and 300 mL of isopropanol was added. After heating to 130 °C and stirring for 10 h, it was cooled to room temperature, the isopropanol was removed by rotary evaporation, and then vacuum - dried for 24 h. Then this mixture was heat - treated in a nitrogen atmosphere at 400 °C for 5.0 h and then cooled to obtain a cobalt - based material catalyst in the form of black powder, denoted as catalyst E.

[0041] 2 mmol of 2,3,6 - trimethylphenol, 20 wt% of catalyst E and 10 mL of tert - butanol were added to a reaction kettle. 2.0 MPa of oxygen was charged, and the temperature was raised to 110 °C with stirring and the reaction was run for 12 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was taken for quantitative analysis of the products by gas chromatography. The conversion rate of 2,3,6 - trimethylphenol was 94%, and the selectivity of 2,3,5 - trimethylbenzoquinone was 81%. The reaction results are shown in Table 1.

[0042] Example 6: Preparation and reaction results of catalyst F

[0043] The cobalt - based material was prepared by using a molar ratio of cobalt chloride and 2,2'-bipyridine (1:6): 2 mmol of cobalt chloride and 12 mmol of 2,2'-bipyridine were mixed, and 250 mL of ethanol was added. After heating to 60 °C and stirring for 7 h, it was cooled to room temperature, the ethanol was removed by rotary evaporation, and then vacuum - dried for 36 h. Then this mixture was heat - treated in a helium atmosphere at 300 °C for 0.5 h and then cooled to obtain a cobalt - based catalyst, denoted as catalyst F.

[0044] 20 mmol of 2,3,6 - trimethylphenol, 25 wt% of catalyst F and 30 mL of tert - amyl alcohol were added to a reaction kettle. 2.5 MPa of oxygen was charged, and the temperature was raised to 40 °C with stirring and the reaction was run for 20 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was taken for quantitative analysis of the products by gas chromatography. The conversion rate of 2,3,6 - trimethylphenol was 86%, and the selectivity of 2,3,5 - trimethylbenzoquinone was 84%. The reaction results are shown in Table 1.

[0045] Example 7: Preparation and reaction results of catalyst G

[0046] The cobalt-based material was prepared by using cobalt acetate, dicyandiamide and 2,2'-bipyridine in a molar ratio of (1:1:1): 3 mmol of cobalt acetate, 3 mmol of dicyandiamide and 3 mmol of 2,2'-bipyridine were mixed, and 300 mL of methanol was added. After heating to 90 °C and stirring for 2 h, it was cooled to room temperature, the methanol was removed by rotary evaporation, and it was dried under vacuum for 48 h. Then this mixture was heat-treated in a nitrogen atmosphere at 400 °C for 20.0 h and then cooled to obtain a cobalt-based catalyst, denoted as catalyst G.

[0047] 50 mmol of 2,3,6-trimethylphenol, 20 wt% of catalyst G and 60 mL of isopropanol were added to a reaction kettle, 5.0 MPa of oxygen was charged, and the temperature was raised to 60 °C with stirring and run for 10 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was quantitatively analyzed for products by gas chromatography. The conversion rate of 2,3,6-trimethylphenol was 90%, and the selectivity of 2,3,5-trimethylbenzoquinone was 88%. The reaction results are shown in Table 1.

[0048] Example 8: Preparation and reaction results of catalyst H

[0049] The cobalt-based material was prepared by using cobalt acetate and diethylenediamine in a molar ratio of (1:4): 3 mmol of cobalt acetate and 12 mmol of diethylenediamine were mixed, and 350 mL of n-propanol was added. After heating to 100 °C and stirring for 5 h, it was cooled to room temperature, the n-propanol was removed by rotary evaporation, and it was dried under vacuum for 16 h. Then this mixture was heat-treated in a nitrogen atmosphere at 330 °C for 8.0 h and then cooled to obtain a cobalt-based catalyst, denoted as catalyst H.

[0050] 2 mmol of 2,3,6-trimethylphenol, 20 wt% of catalyst H and 10 mL of n-propanol were added to a reaction kettle, 2.0 MPa of oxygen was charged, and the temperature was raised to 130 °C with stirring and run for 24 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was quantitatively analyzed for products by gas chromatography. The conversion rate of 2,3,6-trimethylphenol was 97%, and the selectivity of 2,3,5-trimethylbenzoquinone was 81%. The reaction results are shown in Table 1.

[0051] Example 9: Preparation and reaction results of catalyst I

[0052] The cobalt-based material was prepared by using cobalt sulfate and 1,10-phenanthroline in a molar ratio of (1:6): 1 mmol of cobalt sulfate and 6 mmol of 1,10-phenanthroline were mixed, and 230 mL of isopropanol was added. After heating to 140 °C and stirring for 7 h, it was cooled to room temperature, the isopropanol was removed by rotary evaporation, and it was dried under vacuum for 72 h. Then this mixture was heat-treated in an argon atmosphere at 300 °C for 12.0 h and then cooled to obtain a cobalt-based catalyst, denoted as catalyst I.

[0053] 2 mmol of 2,3,6-trimethylphenol, 40 wt% of catalyst I and 10 mL of tert-amyl alcohol were added to a reaction kettle, filled with 0.2 MPa of oxygen, heated to 140 °C with stirring and run for 1 h. Then it was cooled to room temperature and carefully depressurized to atmospheric pressure. The sample was quantitatively analyzed for the product by gas chromatography. The conversion rate of 2,3,6-trimethylphenol was 95%, and the selectivity of 2,3,5-trimethylbenzoquinone was 88%. The reaction results are shown in Table 1.

[0054] Table 1. Different catalyst compositions and their respective reaction results

[0055] Catalyst number Catalyst (mol / mol) Catalyst calcination temperature (°C) Conversion rate (%) Selectivity (%) A Cobalt acetate: 1,10-phenanthroline = 1:2 400 99 82 B Cobalt acetate: 1,10-phenanthroline = 1:2 800 2 - C Cobalt sulfate: dicyandiamide = 1:3 300 89 88 D Cobalt carbonate: melamine = 1:4 350 89 84 E Cobalt nitrate: polyaniline = 1:1 400 94 81 F Cobalt chloride: 2,2'-bipyridine = 1:6 300 86 84 G Cobalt acetate: dicyandiamide: 2,2'-bipyridine = 1:1:1 400 90 88 H Cobalt acetate: diethylenediamine = 1:4 330 97 81 I Cobalt sulfate: 1,10-phenanthroline = 1:6 300 95 88

[0056] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol by cobalt catalysis, characterized in that, It includes the following steps: The first step is to prepare a cobalt-based material catalyst Add cobalt salt and nitrogen-containing organic ligand into a solvent, heat and stir for 1 - 10 h, then cool to room temperature, rotary evaporate to remove the solvent, dry under vacuum, and then heat-treat this mixture in an inert atmosphere at 300 - 450 °C for 0.5 - 20 h and then cool to obtain a cobalt-based catalyst; the cobalt salt is one or more of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt carbonate, and the nitrogen-containing organic ligand is one or more of 1,10-phenanthroline, 2,2'-bipyridine, polyaniline, diethylenediamine, melamine, and dicyandiamide; The second step is to prepare 2,3,5-trimethylbenzoquinone Add 2,3,6-trimethylphenol, a catalyst and a solvent into a reaction kettle, then introduce molecular oxygen as an oxygen source, close the reaction kettle, stir and heat to raise the temperature to 40 - 140 °C for an oxidation reaction, after the reaction time of 1 - 48 h, cool to room temperature, and separate to obtain 2,3,5-trimethylbenzoquinone; the dosage of the catalyst in the oxidation reaction step is 1 - 40 wt% of the feeding amount of the raw material 2,3,6-trimethylphenol.

2. The method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The molar ratio of the cobalt salt to the nitrogen-containing organic ligand is 1:1 - 1:6; the solvent dosage is 1 - 20 times the mass of the nitrogen-containing organic ligand.

3. The method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The molecular oxygen is air, oxygen or a gas containing oxygen, and the oxygen partial pressure is 0.1 - 5 MPa.

4. A method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The solvent in the oxidation reaction step is one or more of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and tert-amyl alcohol.

5. The method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The solvent dosage in the oxidation reaction step is 1 - 50 times the mass of the raw material 2,3,6-trimethylphenol.

6. The method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, wherein, The inert atmosphere in the catalyst preparation step is one or a mixture of more of nitrogen, argon, and helium.

7. A method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The solvent in the catalyst preparation step is one or a mixture of more of methanol, ethanol, n-propanol, and isopropanol.

8. A method for synthesizing 2,3,5-trimethylbenzoquinone from 2,3,6-trimethylphenol catalyzed by cobalt according to claim 1, characterized in that, The heating temperature in the catalyst preparation step is from room temperature to the reflux temperature of the used solvent.

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