A method for the oxidation of o-xylene to phthalide

Abstract

This invention provides a method for the oxidation of o-xylene to phthalide, comprising reacting o-xylene with an oxidant in the presence of a catalyst, wherein the catalyst comprises at least two transition metal ions and carbon nanotubes. The method for the oxidation of o-xylene to phthalide provided by this invention utilizes a composite catalyst of at least two transition metal ions and carbon nanotubes, effectively improving the selectivity of phthalide.

Description

Technical Field

[0001] This invention belongs to the field of oxidative preparation of phthalides, and specifically relates to a method for oxidizing o-xylene to prepare phthalides. Background Technology

[0002] Phenylphthalide is an intermediate in fine chemicals. In the pharmaceutical industry, it is used to produce the anticoagulant phenylindanedione and phenylthiazide, the anti-anxiety drug doxepin, and laxatives. In the pesticide industry, it is used to produce the fungicide tetrachlorophthalide. It can also be used in the synthesis of dye intermediates such as 1,4-dichloroanthraquinone and 1-chloroanthraquinone. Currently, phthalide is mainly produced by the hydrogenation of phthalic anhydride. However, this method has poor selectivity, and phthalic anhydride is mainly produced from o-xylene via gas-phase oxidation, which has poor reaction safety, requires a high temperature of around 350℃, is prone to over-oxidation, consumes a large amount of raw materials, and has low product selectivity. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention provides a method for the oxidation of o-xylene to phthalide, which employs a composite catalyst of at least two transition metal ions and carbon nanotubes, effectively improving the selectivity of phthalide.

[0004] The method for oxidizing o-xylene to phthalide provided by this invention includes reacting o-xylene with an oxidant in the presence of a catalyst, wherein the catalyst comprises at least two transition metal ions and carbon nanotubes. This invention employs a composite catalyst of at least two transition metal ions and carbon nanotubes. Carbon nanotubes possess highly graphitized characteristics, and the carbon atoms of their regular six-membered rings can rapidly transfer charges. Combined with transition metal ions, they can rapidly excite free radicals, causing the oxidation reaction to occur immediately. Simultaneously, they can inhibit excessive catalytic oxidation by transition metal ions, ensuring complete oxidation of the substrate to diacids or CO2, thereby improving the selectivity of phthalide.

[0005] In some embodiments, the mass ratio of the carbon nanotubes to the o-xylene is (0.01-0.1):1. When the carbon nanotube content is too low, it is impossible to effectively suppress the catalytic oxidation transition of transition metal ions, thus reducing the selectivity of phthalide. When the carbon nanotube content is too high, the catalytic reaction becomes controlled by the amount of free radicals excited by the carbon nanotubes, resulting in excessively strong transition metal catalytic inhibition, which is also detrimental to improving the selectivity of phthalide.

[0006] In some embodiments, the mass ratio of the carbon nanotubes to the o-xylene is 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.055:1, 0.06:1, 0.065:1, 0.07:1, 0.075:1, 0.08:1, 0.085:1, 0.09:1, 0.095:1, or any value between them. In some embodiments, the mass ratio of the carbon nanotubes to the o-xylene is (0.02-0.07):1.

[0007] In some embodiments, the carbon nanotubes are selected from at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0008] In some embodiments, the carbon nanotubes have an aspect ratio of 125-12500. In some embodiments, the carbon nanotubes have an aspect ratio of 200, 500, 750, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 3750, 4000, 4250, 4500, 4750, 5000, 5250, 5500, 5750, 6000, 7250, 7500, 7750, 8000, 8500, 9000, 9500, 10000, 11000, 12000, or any value between them. In some embodiments, the carbon nanotubes have an aspect ratio of 2000-4000.

[0009] In some embodiments, the outer diameter of the carbon nanotubes is 8 nm-80 nm. When the outer diameter of the carbon nanotubes is too small, the charge transfer process is effective only over a short range, making it difficult to coordinate with metal ions on a macroscopic scale, thus reducing the selectivity of phthalide. When the outer diameter of the carbon nanotubes is too large, metal ions can easily enter the interior of the tube, causing internal diffusion control, which in turn reduces the selectivity of phthalide.

[0010] In some embodiments, the outer diameter of the carbon nanotubes is 9 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 23 nm, 25 nm, 27 nm, 29 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 43 nm, 45 nm, 47 nm, 50 nm, 53 nm, 55 nm, 57 nm, 60 nm, 63 nm, 65 nm, 67 nm, 70 nm, 73 nm, 75 nm, 77 nm, or any value between them. In some embodiments, the outer diameter of the carbon nanotubes is 10 nm to 30 nm.

[0011] In some embodiments, the length of the carbon nanotubes is 1 μm-100 μm. If the carbon nanotubes are too short, the charge transfer process becomes short-range effective, making it difficult to synergize with metal ions on a macroscopic scale, thus reducing the selectivity of phthalide. If the carbon nanotubes are too long, transition metal ions easily adsorb onto the surface of the carbon nanotubes to form supported catalysts, altering the homogeneous reaction mechanism of the transition metal ions and further reducing the selectivity of phthalide.

[0012] In some embodiments, the length of the carbon nanotubes is 5 μm, 10 μm, 15 μm, 20 μm, 23 μm, 25 μm, 27 μm, 29 μm, 30 μm, 33 μm, 35 μm, 37 μm, 39 μm, 40 μm, 43 μm, 45 μm, 47 μm, 49 μm, 50 μm, 53 μm, 55 μm, 57 μm, 59 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, or any value between them. In some embodiments, the length of the carbon nanotubes is 20 μm-40 μm.

[0013] In some embodiments, the transition metal ion includes at least two of iron ions, cobalt ions, and manganese ions. In some embodiments, the transition metal ion is selected from Fe. 2+ / Fe 3+ Fe 2+ / Co 2+ Co 2+ / Mn 2+ and Fe 2+ / Mn 2+ At least one of them.

[0014] In some embodiments, the molar ratio of the transition metal ion to the o-xylene is (0.01-0.1):1, for example, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, or 0.09:1. In some embodiments, the molar ratio of the transition metal ion to the o-xylene is (0.02-0.06):1.

[0015] In some embodiments, the transition metal ions include a first transition metal ion and a second transition metal ion, wherein the molar ratio of the first transition metal ion to the second transition metal ion is (0.1-10):1. In some embodiments, the molar ratio of the first transition metal ion to the second transition metal ion is 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1.

[0016] In some embodiments, the first transition metal ion is selected from Fe. 2+ Fe 3+ Co 2+ or Mn 2+ One of them. In some embodiments, the second transition metal ion is selected from Fe. 2+ Fe 3+ Co 2+ or Mn 2+ One of them.

[0017] In some implementations, the method includes the following steps:

[0018] S1: After mixing o-xylene, carbon nanotubes and solvent, pretreatment is performed to obtain a pretreated mixture;

[0019] S2: In the presence of an oxidant, the mixture of S1 is mixed with a soluble salt of transition metal ions and then subjected to an oxidation reaction.

[0020] In some embodiments, the pretreatment described in S1 is carried out in an inert atmosphere, such as a nitrogen atmosphere. In some embodiments, the temperature of the pretreatment described in S1 is 100°C-150°C, for example, 120°C, 130°C, or 140°C. In some embodiments, the pressure of the pretreatment described in S1 is 5 bar-15 bar, for example, 7 bar, 10 bar, or 12 bar. In some embodiments, the time of the pretreatment described in S1 is 10 min-100 min, for example, 30 min, 50 min, or 70 min. Pretreatment in an inert atmosphere allows the reaction initiation temperature to be within a precise range, avoiding premature oxidation of the reaction system, which would lead to an increase in byproducts and consequently a decrease in phthalide selectivity.

[0021] In some embodiments, the oxidation reaction in S2 is carried out at a temperature of 100°C-200°C. In some embodiments, the oxidation reaction is carried out at a temperature of 140°C-180°C.

[0022] In some embodiments, the oxidation reaction in S2 is carried out at a pressure of 1 bar to 20 bar. In some embodiments, the oxidation reaction in S2 is carried out at a pressure of 5 bar to 15 bar.

[0023] In some embodiments, the oxidation reaction in S2 takes 60-150 minutes, for example, 90 minutes or 120 minutes.

[0024] In some embodiments, the method further includes: S3: filtering the oxidation reaction product to obtain a filtrate, and crystallizing and drying the filtrate to obtain the phthalide.

[0025] In some embodiments, the filtration is performed at a temperature of 100°C-170°C, for example, 120°C, 140°C, or 160°C. In some embodiments, the crystallization is performed at a temperature of 10°C-40°C.

[0026] In some embodiments, the solvent is selected from acetic acid and / or ethyl acetate. Acetic acid and / or ethyl acetate are easily separated and do not readily generate impurities that would affect separation during the reaction. In some embodiments, the transition metal ion soluble salt is selected from acetates of transition metal ions.

[0027] In some embodiments, the oxidant is selected from air.

[0028] In some embodiments, the method for producing phthalide by oxidation of o-xylene according to the present invention includes the following specific steps:

[0029] S1: Add o-xylene, carbon nanotubes and solvent into the reaction apparatus, introduce nitrogen into the reaction apparatus and heat to 100℃-150℃, for example 140℃, and maintain the pressure at 5bar-15bar, for example 10bar.

[0030] S2: Switch the gas, introduce air into the reaction apparatus, and then add a soluble salt of transition metal ions while raising the temperature to 100℃-200℃, for example, 170℃ to carry out the reaction.

[0031] S3: The oxidation reaction product is filtered at a temperature of 100℃-170℃ to obtain a filtrate. The filtrate is then crystallized and dried to obtain the phthalide.

[0032] In some embodiments, the crystallization time is 2-8 hours. The filtrate is then crystallized at 10°C-40°C for 2-8 hours.

[0033] In some embodiments, the drying temperature is 80℃-150℃ and the drying time is 2h-8h.

[0034] Beneficial technical effects of the present invention:

[0035] This invention employs a composite catalyst of at least two transition metal ions and carbon nanotubes, exhibiting high catalytic activity and high selectivity for the target product phthalide in the oxidation of o-xylene to phthalide. The selectivity for phthalide is as high as 75% or more, demonstrating promising prospects for industrial application. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] The present invention will be described in detail below through embodiments.

[0039] Unless otherwise specified, all operations in the examples and comparative examples are performed at room temperature.

[0040] Example 1

[0041] 100 g of o-xylene (99.9 wt.%) and 5 g of carbon nanotubes (TNGM2, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences; specifically, the average outer diameter of the carbon nanotubes was 11 nm, the average length was 30 μm, and the aspect ratio was 2727) were added to 400 g of acetic acid solvent. The mixture was gradually heated to 140 °C in a stirred reactor over 50 min while nitrogen gas was introduced, maintaining a pressure of 10 bar. Air was then introduced at a rate of 0.18 mol / min, followed by the pumping of 0.02 mol Mn over 60 min. 2+ and 0.02 mol Co 2+ (Acetate) The temperature was raised to 170°C and the reaction was carried out for 120 minutes.

[0042] After the reaction was complete, the carbon nanotube solid was filtered off from the reaction solution at 150°C. The filtrate was cooled and crystallized at 15°C for 4 hours, and then the crystallized solid was dried in an oven at 100°C for 6 hours to obtain phthalide product. The conversion rate of o-xylene was 100.0 mol.%, and the selectivity of phthalide was 92.1 mol.%, as detailed in Table 1.

[0043] Example 2

[0044] 100 g of o-xylene (99.9 wt.%) and 5 g of carbon nanotubes (same as in Example 1) were added to 400 g of acetic acid solvent. The mixture was gradually heated to 140 °C in a stirred tank over 50 min while nitrogen gas was introduced, maintaining a pressure of 10 bar inside the tank. Air was then introduced at a rate of 0.18 mol / min, followed by the pumping of 0.02 mol Fe over 60 min. 2+ and 0.02 mol Fe 3+ (Acetate) The temperature was raised to 170°C and the reaction was carried out for 120 minutes.

[0045] After the reaction was completed, the carbon nanotube solid was filtered off from the reaction solution at 150°C. The filtrate was cooled and crystallized at 15°C for 4 hours, and then the crystallized solid was dried in an oven at 100°C for 6 hours to obtain phthalide product. The conversion rate of o-xylene was 100 mol.%, and the selectivity of phthalide was 80.3 mol.%. For comparison, see Table 1.

[0046] Examples 3 to 6

[0047] Except for the lengths of the carbon nanotubes used, which were 8μm, 15μm, 50μm and 70μm respectively, everything else was the same as in Example 1.

[0048] Examples 7 to 10

[0049] Except for the outer diameters of the carbon nanotubes used, which were 9nm, 30nm, 50nm and 70nm respectively, all other aspects were the same as in Example 1.

[0050] Examples 11 to 14

[0051] Except for the carbon nanotubes used, which were 1g, 3g, 7g and 9g respectively, all other aspects were the same as in Example 1.

[0052] Comparative Example 1

[0053] 100 g of o-xylene (99.9 wt.%) was added to 400 g of acetic acid solvent. The mixture was gradually heated to 140 °C in a stirred tank over 50 min while nitrogen gas was introduced, maintaining a pressure of 10 bar inside the tank. Air was then introduced at a rate of 0.18 mol / min, followed by the pumping of 0.02 mol of Mn over 60 min. 2+ and 0.02 mol Co 2+ (Acetate) The temperature was raised to 170°C and the reaction was carried out for 120 minutes.

[0054] After the reaction was complete, the carbon nanotube solid was filtered off from the reaction solution at 150°C. The filtrate was cooled and crystallized at 15°C for 4 hours, and then the filtered solid was dried in an oven at 100°C for 6 hours to obtain phthalide product. The conversion rate of o-xylene was 100 mol.%, and the selectivity of phthalide was 13.5 mol.%, as detailed in Table 1.

[0055] Comparative Example 2

[0056] 100 g of o-xylene (99.9 wt.%) and 5 g of SiO2 were added to 400 g of acetic acid solvent. The mixture was gradually heated to 140 °C in a stirred tank over 50 min while nitrogen gas was introduced, maintaining a pressure of 10 bar inside the tank. Air was then introduced at a rate of 0.18 mol / min, followed by the pumping of 0.02 mol of Mn over 60 min. 2+ and 0.02 mol Co 2+ (Acetate) The temperature was raised to 170°C and the reaction was carried out for 120 minutes.

[0057] After the reaction was complete, the reaction solution was filtered to remove the solid at 150°C. The filtrate was cooled at 15°C for 4 hours to crystallize, and then the crystallized solid was dried in an oven at 100°C for 6 hours to obtain phthalide product. The conversion rate of o-xylene was 30.4 mol.%, and the selectivity of phthalide was 11.9 mol.%, as detailed in Table 1.

[0058] Comparative Examples 3 to 4

[0059] In addition to adding 0.04 mol Co 2+ 0.04 mol Mn 2+ Except for the above, everything else is the same as in Example 1.

[0060] Table 1

[0061]

[0062] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for the oxidation of o-xylene to phthalide, comprising reacting o-xylene with an oxidant in the presence of a catalyst, wherein, The catalyst comprises at least two transition metal ions and carbon nanotubes; The carbon nanotube has an aspect ratio of 125-12500, an outer diameter of 8nm-80nm, and a length of 1μm-100μm. The transition metal ions include at least two of iron ions, cobalt ions, and manganese ions; The oxidant is selected from air; The mass ratio of the carbon nanotubes to the o-xylene is (0.01-0.1):1; The molar ratio of the transition metal ion to the o-xylene is (0.02-0.06):1; The transition metal ions include a first transition metal ion and a second transition metal ion, wherein the molar ratio of the first transition metal ion to the second transition metal ion is (0.1-10):

1.

2. The method according to claim 1, characterized in that, The mass ratio of the carbon nanotubes to the o-xylene is (0.02-0.07):

1.

3. The method according to claim 1, characterized in that, The carbon nanotubes are selected from at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; and / or The aspect ratio of the carbon nanotubes is 2000-4000.

4. The method according to claim 1, characterized in that, The outer diameter of the carbon nanotubes is 10nm-30nm; and / or The length of the carbon nanotubes is 20μm-40μm.

5. The method according to claim 1, characterized in that, The transition metal ion is selected from Fe. 2+ / Fe 3+ Fe 2+ / Co 2 + Co 2+ / Mn 2+ and Fe 2+ / Mn 2+ At least one of them.

6. The method according to claim 1, characterized in that, The first transition metal ion is selected from Fe 2+ Fe 3+ Co 2+ or Mn 2+ One of them, wherein the second transition metal ion is selected from Fe 2+ Fe 3+ Co 2+ or Mn 2+ One of them.

7. The method according to claim 1, characterized in that, The method includes the following steps: S1: After mixing o-xylene, carbon nanotubes and solvent, pretreatment is performed to obtain a pretreated mixture; S2: In the presence of an oxidant, the mixture of S1 is mixed with a soluble salt of transition metal ions and then subjected to an oxidation reaction.

8. The method according to claim 7, characterized in that, Also includes: S3: Filter the oxidation reaction product to obtain a filtrate, then crystallize and dry the filtrate to obtain the phthalide.

9. The method according to claim 8, characterized in that, The filtration is carried out at a temperature of 100℃-170℃, and the crystallization is carried out at a temperature of 10℃-40℃.

10. The method according to claim 7, characterized in that, The solvent is selected from acetic acid and / or ethyl acetate; and / or The soluble salts of the transition metal ions are selected from the acetates of the transition metal ions.

11. The method according to claim 7, wherein, The pretreatment is carried out under an inert atmosphere, at a temperature of 100℃-150℃, at a pressure of 5 bar-15 bar, and for a time of 10 min-100 min; and / or The oxidation reaction temperature is 100℃-200℃; the oxidation reaction pressure is 1 bar-20 bar; and the oxidation reaction time is 60 min-150 min.

12. The method according to claim 7, characterized in that, The pretreatment was carried out under a nitrogen atmosphere.

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