Method for preparing benzoic acid by solvent-free room-temperature oxidation of methylbenzene

Abstract

The invention discloses a method for preparing benzoic acid through solvent-free room-temperature oxidation of toluene, which comprises the following steps: by taking toluene as a raw material, copper salt compounded cobalt salt as a catalyst, N-hydroxyphthalimide as a cocatalyst, oxygen or air as an oxidant and benzaldehyde as an initiator, adding an organic liquid as an auxiliary agent; stirring and reacting for several hours at room temperature, so as to efficiently realize the conversion of preparing benzoic acid from methylbenzene; benzaldehyde serves as an initiator, so that a certain amount of oxygen-containing free radicals are generated in the initial stage of a reaction system, breakage of carbon-hydrogen bonds of methylbenzene existing in a large number in the system is facilitated, and then preparation of benzoic acid under the normal-temperature and normal-pressure conditions is achieved in the copper-cobalt double-metal concerted catalysis process; the catalyst used in the method is wide in source, low in price and easy to obtain, complex synthesis steps are not needed, the reaction does not need to be carried out in an acid solution, operation is easy and convenient, the target product is high in one-way conversion yield, and the method belongs to the field of fine chemical synthesis.

Description

Technical Field

[0001] The invention relates to a method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, belonging to the field of fine chemical synthesis. Background Art

[0002] As an important organic compound, benzoic acid is widely used in the field of fine chemicals. In the pharmaceutical field, it is often used as an intermediate in drug synthesis to produce pharmaceutical products such as antibiotics, anti-inflammatory drugs, and analgesics, and it shows antifungal and antibacterial properties in the treatment of skin diseases. In the plastics industry, benzoic acid is used as a monomer to produce plastics such as styrene, which is widely used in the manufacture of medical devices, packaging materials, and household items. At the same time, benzoic acid, as a raw material for resins and coatings, improves the chemical resistance, adhesion, and hardness of coatings. In the flavor and fragrance industry, benzoate compounds are used as fixatives to make the fragrance last, and play a role in regulating pH and preserving in cosmetics and personal care products. In addition, benzoic acid is also used in the production of chemical products such as dyes, pesticides, and catalysts, as well as in the anti-corrosion and anti-mildew treatment of industrial products such as wood, leather, and textiles. These applications show the important role of benzoic acid in improving product performance, extending product life, and ensuring product quality.

[0003] In the prior art, the common synthesis process of benzoic acid is to obtain benzoic acid from toluene and oxygen, and this method usually needs to be carried out in an acetic acid solution to ensure relatively mild reaction conditions. Japanese scientists Yasutaka Ishii et al. (J.Org.Chem.1997,62,6810) first proposed a conversion process with good yield in the reaction of preparing benzoic acid by oxidation of toluene, which uses cobalt acetate (0.5mol%) and N-hydroxyphthalimide (10mol%) as catalysts, acetic acid as solvent, and stirs the reaction at 25°C to obtain 81% yield of benzoic acid and 3% yield of benzaldehyde product. However, although the introduction of acetic acid solvent reduces the temperature of the reaction, it reduces the actual reaction volume, increases the separation task, and acetic acid is corrosive to metals when water is present, which is not conducive to long-term application in industry.

[0004] In order to avoid using acetic acid as a solvent, a greener and more optimized process for preparing benzoic acid from toluene was proposed, which achieves efficient conversion of benzoic acid under solvent-free and mild conditions. As a reserve technology in the field of benzoic acid synthesis, it is a hot research topic in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing toluene oxidation products without solvent at room temperature and pressure, using toluene as raw material and solvent, oxygen as terminal oxidant, and utilizing cheap and readily available metal copper and metal cobalt salts for synergistic catalysis.

[0006] To achieve the purpose of the present invention, the technical solution adopted is:

[0007] The invention discloses a method for preparing benzoic acid by solvent-free room temperature oxidation of toluene. The method comprises the following steps: using toluene as a raw material, using a copper salt and a cobalt salt as a catalyst, using N-hydroxyphthalimide as a cocatalyst, using oxygen or air as an oxidant, using an aldehyde as an initiator, and using an organic liquid as an auxiliary agent. The benzoic acid product is obtained by stirring and reacting at normal temperature and pressure.

[0008] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the copper salt is copper isooctanoate.

[0009] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the cobalt salt is cobalt chloride.

[0010] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the amount of copper salt added is 0.25% to 0.5% of the molar amount of toluene; and the amount of cobalt salt added is 0.5% to 1.5% of the molar amount of toluene.

[0011] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the ratio of the copper salt to the cobalt salt is 1:1.

[0012] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the organic liquid is one or more of acetone, dimethyl carbonate, ethyl acetate, acetonitrile, N,N-dimethylacetamide, and tetrahydrofuran.

[0013] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the molar ratio of the organic liquid to toluene is 13.6 to 40.85:30.

[0014] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the initiator aldehyde compound is one or more of acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, trimethylacetaldehyde, 3,5,5-trimethylhexanal, and benzaldehyde.

[0015] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the molar ratio of the initiator aldehyde compound to toluene is 1.5 to 3.75:30.

[0016] Furthermore, in the above-mentioned method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, the reaction time is 16-24 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. A method for preparing benzoic acid by solvent-free room temperature oxidation of toluene provided by the present invention, using toluene as a raw material, copper salt compounded cobalt salt as a catalyst, N-hydroxyphthalimide as a cocatalyst, oxygen as an oxidant, benzaldehyde as an initiator, adding an organic liquid as an auxiliary agent, stirring the reaction at room temperature for several hours, and realizing the conversion of toluene to benzoic acid. Among them, benzaldehyde as an initiator makes the reaction system produce a certain amount of oxygen-containing free radicals in the early stage, which is conducive to the breaking of the carbon-hydrogen bonds of toluene present in large quantities in the system, and then in the process of copper-cobalt bimetallic synergistic catalysis, the preparation of benzoic acid under normal temperature and pressure conditions is realized.

[0019] 2. The catalyst used in the technical solution provided by the present invention is widely available, cheap and easy to obtain, and does not require complicated synthesis steps.

[0020] 3. The technical solution provided by the present invention has excellent process conditions, does not contain halogen, does not require the addition of acid as a solvent, and can be achieved by stirring at room temperature.

[0021] 4. The target product of the present invention has a high single-pass yield and is simple to separate subsequently. When unreacted toluene is recycled, the product can be separated by simple distillation without consuming a large amount of cost to recover the unreacted solvent. It can be used as a process reference for the continuous flow production of toluene oxidation products. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a gas chromatography detection diagram provided in Example 1 of the present invention.

[0023] Figure 2 This is a gas chromatography detection diagram provided for Example 2 of the present invention.

[0024] Figure 3 This is a gas chromatography detection diagram provided for Example 7 of the present invention.

[0025] Figure 4 This is a gas chromatography detection diagram provided for Example 8 of the present invention.

[0026] Figure 5 This is a gas chromatography detection diagram provided for Example 9 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with embodiments, but the protection scope of the present invention is not limited to the scope represented by the embodiments.

[0028] Example 1

[0029] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0195g (0.15mmol) of cobalt chloride, 0.057mL (0.15mmol) of copper octanoate, 1.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene. Use oxygen as the oxygen source for the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe. Then inject the filtered reaction solution into a chromatographic bottle, and filter the components in the reaction solution and conduct quantitative analysis by gas chromatography. Figure 1 , it was calculated that the toluene conversion rate was 14.10% and the benzoic acid yield was 16.59%.

[0030] Example 2

[0031] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the toluene conversion rate is 21.82%, and the benzoic acid yield is 24.39%.

[0032] Example 3

[0033] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0584g (0.45mmol) of cobalt chloride, 0.057mL (0.15mmol) of copper octanoate, 3.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene. Use oxygen as the oxygen source for the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe. Then inject the filtered reaction solution into a chromatographic bottle, and filter the components in the reaction solution and conduct quantitative analysis by gas chromatography. Figure 2 , it was calculated that the toluene conversion rate was 17.87% and the benzoic acid yield was 20.42%.

[0034] Example 4

[0035] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.230mL (2.25mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and filter the components in the reaction solution and perform quantitative analysis by gas chromatograph. It is calculated that the toluene conversion rate is 17.97%, and the benzoic acid yield is 20.87%.

[0036] Example 5

[0037] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.383mL (3.75mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 17.72%, and the benzoic acid yield is 17.72%.

[0038] Example 6

[0039] In a 10mL reaction tube, add N-hydroxyphthalimide 0.7339g (4.5mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 16.77%, and the benzoic acid yield is 19.41%.

[0040] Example 7

[0041] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0292g (0.225mmol) of cobalt chloride, 0.028mL (0.075mmol) of copper octanoate, 1.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene. Use oxygen as the oxygen source for the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take out the reaction liquid through a syringe, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction liquid into a chromatographic bottle, filter the components in the reaction liquid and conduct quantitative analysis by gas chromatograph, refer to Figure 3 The toluene conversion rate was calculated to be 20.07%, and the benzoic acid yield was 22.82%.

[0042] Example 8

[0043] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0584g (0.45mmol) of cobalt chloride, 0.057mL (0.15mmol) of copper octanoate, 1.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene. Use oxygen as the oxygen source for the reaction, put it on the reaction tube, and stir it for 16 hours at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, filter the components in the reaction solution and conduct quantitative analysis by gas chromatograph, see Figure 4 The toluene conversion rate was calculated to be 17.82%, and the benzoic acid yield was 19.76%.

[0044] Example 9

[0045] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0584g (0.45mmol) of cobalt chloride, 0.057mL (0.15mmol) of copper octanoate, 1.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene. Use oxygen as the oxygen source for the reaction, put it on the reaction tube, and stir it for 24h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take the reaction solution through a syringe, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, filter the components in the reaction solution and conduct quantitative analysis by gas chromatograph, see Figure 5 The toluene conversion rate was calculated to be 19.94%, and the benzoic acid yield was 22.62%.

[0046] Comparative Example 1: No acetone added

[0047] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, inject it into a chromatographic bottle, and filter the components in the reaction solution. After filtering, the components are quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 11.93%, and the benzoic acid yield is 13.09%. It can be seen from Example 2 and Comparative Example 1 that in an acid-free system, toluene as the main body of the reaction can be carried out at room temperature and pressure, and acetone as an organic auxiliary agent is helpful for this new type of toluene aerobic conversion reaction.

[0048] Comparative Example 2: No N-hydroxyphthalimide added

[0049] In 10mL reaction tubes, cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol) are added, and toluene 3.0mL (30mmol) is added at last, and oxygen is used as the oxygen source of reaction, and is enclosed in the reaction tube, and stirred for 20h under the magnetic stirrer of room temperature and 1200rpm speed. After the reaction is finished, oxygen is removed, and the reaction solution is exhausted by needle tube, and the solid in the syringe is filtered using a membrane, and injected into a chromatographic bottle, and the component in the reaction solution is quantitatively analyzed by gas chromatograph after filtration. It is calculated that toluene is almost unconverted, and the yield of benzoic acid is 0.74%. By Example 2, it can be seen from Comparative Example 2 that in an acid-free system, toluene can be carried out at normal temperature and pressure as the body of reaction, and N-hydroxyphthalimide is used as a cocatalyst, which is conducive to the main condition that aerobic conversion reaction of toluene can occur.

[0050] Comparative Example 3: No copper octanoate added

[0051] In a 10mL reaction tube, add 0.4893g (3mmol) of N-hydroxyphthalimide, 0.0584g (0.45mmol) of cobalt chloride, 1.0mL of acetone, 0.153mL (1.5mmol) of benzaldehyde, and finally add 3.0mL (30mmol) of toluene, use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, inject it into a chromatographic bottle, and filter the components in the reaction solution and perform quantitative analysis by gas chromatograph. It is calculated that the toluene conversion rate is 9.42% and the benzoic acid yield is 11.62%. It can be seen from Example 2 and Comparative Example 3 that in an acid-free system, toluene as the main body of the reaction can be carried out at room temperature and pressure, and copper isooctanoate as a metal catalyst can activate NHPI to form free radicals, and realize catalytic cycle through charge transfer and change of copper ion valence state, which is conducive to this new type of toluene aerobic conversion reaction.

[0052] Comparative Example 4: No cobalt chloride added

[0053] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), pyridine 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, inject it into a chromatographic bottle, and filter the components in the reaction solution. After filtering, the components are quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 12.43%, and the benzoic acid yield is 14.85%. It can be seen from Example 2 and Comparative Example 4 that in an acid-free system, toluene as the main body of the reaction can be carried out at room temperature and pressure, and cobalt chloride as a metal catalyst can activate NHPI to form free radicals, and realize catalytic cycle through charge transfer and change of cobalt ion valence state, which is conducive to this new type of toluene aerobic conversion reaction.

[0054] Comparative Example 5: No benzaldehyde added

[0055] In a 10mL reaction tube, N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, and finally toluene 3.0mL (30mmol) are added, oxygen is used as the oxygen source of the reaction, and is sleeved on the reaction tube, and stirred for 20h under a magnetic stirrer at room temperature and 1200rpm. After the reaction is completed, oxygen is removed, the reaction solution is exhausted through a syringe, and the solid in the syringe is filtered using a membrane, injected into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 10.57%, and the benzoic acid yield is 12.95%. By Example 2, it can be seen from Comparative Example 5 that in an acid-free system, toluene can be carried out at normal temperature and pressure as the body of the reaction, and benzaldehyde, as an initiator, contributes to this novel toluene aerobic conversion reaction.

[0056] Comparative Example 6: Cobalt acetate is used as catalyst

[0057] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt acetate 0.797g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove the oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that toluene is almost unconverted, and the yield of benzoic acid is 2.13%.

[0058] Comparative Example 7

[0059] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper acetylacetonate 0.0394g (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 9.44% and the benzoic acid yield is 12.02%.

[0060] The yield of toluic acid in Comparative Examples 6 and 7 is significantly lower than that in Example 1, indicating that the synergistic catalytic performance of the composite of cobalt chloride and copper isooctanoate is significantly higher than that of the composite of cobalt acetate and copper isooctanoate, and that of cobalt chloride and copper acetylacetonate.

[0061] Comparative Example 8

[0062] In a 10mL reaction tube, add N-hydroxyphthalimide 0.0816g (0.5mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 3.28%, and the benzoic acid yield is 6.31%.

[0063] It can be seen from Example 1 and Comparative Example 8 that sufficient NHPI needs to be activated to form free radicals during the toluene conversion process. If the amount of NHPI is too small, the reaction yield will be affected.

[0064] Comparative Example 9

[0065] In 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), acetone 1.0mL, benzaldehyde 0.077mL (0.75mmol), finally add toluene 3.0mL (30mmol), with oxygen as the oxygen source of reaction, sleeve on reaction tube, stir 20h under the magnetic stirrer of room temperature and 1200rpm speed. After the reaction is completed, remove oxygen, take the reaction solution through needle tube, and use filter membrane to filter the solid in syringe, then inject the filtered reaction solution into chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that toluene conversion is 3.93%, and benzoic acid yield is 6.93%. It can be seen from Example 1 and Comparative Example 9 that if the initiator is too little, the reaction rate slows down, resulting in a lower final reaction yield.

[0066] Comparative Example 10

[0067] In a 10mL reaction tube, add N-hydroxyphthalimide 0.4893g (3mmol), cobalt chloride 0.0584g (0.45mmol), copper isooctanoate 0.057mL (0.15mmol), pyridine 1.0mL, benzaldehyde 0.153mL (1.5mmol), and finally add toluene 3.0mL (30mmol), use oxygen as the oxygen source of the reaction, put it on the reaction tube, and stir it for 20h at room temperature and 1200rpm under a magnetic stirrer. After the reaction is completed, remove oxygen, take out the reaction solution through a needle tube, and use a filter membrane to filter the solid in the syringe, then inject the filtered reaction solution into a chromatographic bottle, and the components in the reaction solution are filtered and quantitatively analyzed by a gas chromatograph. It is calculated that the toluene conversion rate is 11.55%, and the benzoic acid yield is 14.74%. Since acetone can better dissolve NHPI, metal catalyst, and toluene, the reaction system is in the same phase and in contact with each other, and pyridine has a greater polarity than acetone, it is difficult to dissolve the more polar NHPI in the less polar toluene under anhydrous conditions, so the yield of toluic acid is relatively low.

[0068] It should be noted that, although only toluene is mentioned as a raw material in the above embodiments, the present invention is also applicable to other aromatic hydrocarbon compounds with similar structures, such as xylene, ethylbenzene, etc. The above embodiments are only used to illustrate the principle of the present invention and do not limit the scope of protection of the present invention. The scope of protection of the present invention should include but is not limited to the technical solutions described in the above embodiments.

Claims

1. A method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, characterized in that: Toluene is used as a raw material, a copper salt and a cobalt salt are used as a catalyst, N-hydroxyphthalimide is used as a co-catalyst, oxygen or air is used as an oxidant, aldehyde is used as an initiator, and an organic liquid is used as an auxiliary agent. Benzoic acid product is obtained by stirring and reacting at normal temperature and pressure.

2. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The copper salt is copper isooctanoate.

3. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The cobalt salt is cobalt chloride.

4. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The copper salt is added in an amount of 0.25% to 0.5% of the molar amount of toluene; and the cobalt salt is added in an amount of 0.5% to 1.5% of the molar amount of toluene.

5. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1 or 4, characterized in that: The ratio of the copper salt to the cobalt salt is 1:

1.

6. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The organic liquid is one or more of acetone, dimethyl carbonate, ethyl acetate, acetonitrile, N,N-dimethylacetamide, and tetrahydrofuran.

7. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The molar ratio of the organic liquid to toluene is 13.6-40.85:

30.

8. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The initiator aldehyde compound is one or more of acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, trimethylacetaldehyde, 3,5,5-trimethylhexanal and benzaldehyde.

9. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The molar ratio of the initiator aldehyde compound to toluene is 1.5-3.75:

30.

10. The method for preparing benzoic acid by solvent-free room temperature oxidation of toluene according to claim 1, characterized in that: The reaction time is 16-24 hours.

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