A method for preparing benzoic acid by solvent-free room temperature oxidation of toluene

Abstract

This invention discloses a solvent-free, room-temperature oxidation method for preparing benzoic acid from toluene. The method uses toluene as a raw material, a copper-cobalt salt complex as a catalyst, N-hydroxyphthalimide as a co-catalyst, oxygen or air as an oxidant, benzaldehyde as an initiator, and an organic liquid as an auxiliary agent. The reaction is carried out at room temperature with stirring for several hours, achieving efficient conversion of toluene to benzoic acid. Benzaldehyde, as an initiator, generates a certain amount of oxygen-containing free radicals in the initial stage of the reaction system, which is beneficial for breaking the carbon-hydrogen bonds of the abundant toluene in the system. This, combined with the synergistic catalysis of copper and cobalt, enables the preparation of benzoic acid under ambient temperature and pressure. The catalyst used in this invention is widely available, inexpensive, and readily available. It eliminates the need for complex synthetic steps and the reaction does not require an acidic solution. The operation is simple, and the single-pass conversion yield of the target product is high, belonging to the field of fine chemical synthesis.

Description

Technical Field

[0001] This 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 Technology

[0002] Benzoic acid, as an important organic compound, has a wide range of applications in the fine chemical industry. In the pharmaceutical field, it is commonly used as an intermediate in drug synthesis, producing pharmaceutical products such as antibiotics, anti-inflammatory drugs, and analgesics, and exhibits antifungal and antibacterial properties in the treatment of skin diseases. In the plastics industry, benzoic acid is used as a monomer in the production of plastics such as styrene, and is widely used in the manufacture of medical devices, packaging materials, and household goods. Simultaneously, benzoic acid serves as a raw material for resins and coatings, improving the chemical resistance, adhesion, and hardness of coatings. In the fragrance and flavor industry, benzoic acid esters act as fixatives, making fragrances last longer, and play a role in pH regulation and preservation in cosmetics and personal care products. Furthermore, benzoic acid is used in the production of dyes, pesticides, catalysts, and other chemical products, as well as in the preservation and anti-mildew treatment of industrial products such as wood, leather, and textiles. These applications demonstrate the important role of benzoic acid in improving product performance, extending product lifespan, and ensuring product quality.

[0003] In existing technologies, the commonly used synthesis process for benzoic acid involves the reaction of toluene with oxygen. This method typically requires 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 yields in the oxidation of toluene to benzoic acid. Using cobalt acetate (0.5 mol%) and N-hydroxyphthalimide (10 mol%) as catalysts and acetic acid as a solvent, the reaction was carried out at 25°C with stirring, yielding benzoic acid in 81% yield and benzaldehyde in 3% yield. However, while introducing acetic acid as a solvent lowers the reaction temperature, it also reduces the actual reaction volume, increases the separation workload, and the presence of water makes acetic acid corrosive to metals, which is detrimental to long-term industrial applications.

[0004] To avoid using acetic acid as a solvent, a more environmentally friendly and optimized process for the preparation of benzoic acid from toluene has been proposed. This process achieves efficient conversion of benzoic acid under solvent-free and mild conditions and serves as a reserve technology in the field of benzoic acid synthesis, making it a hot research topic in this field. Summary of the Invention

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

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0007] A method for preparing benzoic acid by solvent-free room temperature oxidation of toluene, using toluene as raw material, copper salt combined with cobalt salt as catalyst, N-hydroxyphthalimide as co-catalyst, oxygen or air as oxidant, aldehyde as initiator, and organic liquid as auxiliary agent, and stirring reaction under normal temperature and pressure conditions to obtain benzoic acid product.

[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 solventless 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 copper salt to 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 solventless room temperature oxidation of toluene, the initiator aldehyde compound is one or more of acetaldehyde, n-propionaldehyde, n-butyraldehyde, isobutyraldehyde, trimethylacetaldehyde, 3,5,5-trimethylhexanaldehyde, and benzaldehyde.

[0015] Furthermore, in the above-mentioned method for preparing benzoic acid by solventless 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. This invention provides a solvent-free, room-temperature oxidation method for preparing benzoic acid from toluene. Toluene is used as a raw material, a copper-cobalt salt complex as a catalyst, N-hydroxyphthalimide as a co-catalyst, oxygen as an oxidant, benzaldehyde as an initiator, and an organic liquid as an auxiliary agent. The reaction is carried out at room temperature with stirring for several hours to achieve the conversion of toluene to benzoic acid. Benzaldehyde, acting as an initiator, generates a certain amount of oxygen-containing free radicals in the initial stage of the reaction system, which is beneficial for breaking the carbon-hydrogen bonds of the abundant toluene in the system. This, combined with the synergistic catalysis of copper and cobalt, enables the preparation of benzoic acid under ambient temperature and pressure conditions.

[0019] 2. The catalysts used in the technical solution provided by this invention are widely available, inexpensive and readily available, and do not require complex synthesis steps.

[0020] 3. The technical solution provided by the present invention has superior process conditions, does not contain halogens, 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 this invention has a high single-pass yield and simple subsequent separation. When recovering unreacted toluene, the product can be separated by simple distillation without the need to spend a lot of money to recover the unreacted solvent. This invention can serve as a process reference for the continuous flow production of oxidized products from toluene. Attached Figure Description

[0022] Figure 1 This is a gas chromatographic detection chromatogram provided in Embodiment 1 of the present invention.

[0023] Figure 2 This is a gas chromatographic detection diagram provided in Embodiment 2 of the present invention.

[0024] Figure 3 This is a gas chromatographic detection chromatogram provided in Embodiment 7 of the present invention.

[0025] Figure 4 This is a gas chromatographic detection diagram provided in Embodiment 8 of the present invention.

[0026] Figure 5 This is a gas chromatographic detection chromatogram provided in Embodiment 9 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0028] Example 1

[0029] In a 10 mL reaction tube, add 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0195 g (0.15 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, 0.153 mL (1.5 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene. Using oxygen as the oxygen source, attach the tube to the reaction vessel and stir for 20 h at room temperature and 1200 rpm with a magnetic stirrer. After the reaction is complete, remove the oxygen, collect the reaction solution through a syringe, filter the solids from the syringe using a filter membrane, and then inject the filtered reaction solution into a chromatographic vial. Filter the components in the reaction solution and perform quantitative analysis using a gas chromatograph. (See also...) Figure 1 The toluene conversion rate was calculated to be 14.10%, and the benzoic acid yield was 16.59%.

[0030] Example 2

[0031] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 21.82%, and the yield of benzoic acid was 24.39%.

[0032] Example 3

[0033] In a 10 mL reaction tube, add 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 3.0 mL of acetone, 0.153 mL (1.5 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene. Use oxygen as the oxygen source for the reaction, attach the tube, and stir with a magnetic stirrer at 1200 rpm for 20 h at room temperature. After the reaction is complete, remove the oxygen, collect the reaction solution through a syringe, filter the solids in the syringe using a filter membrane, and then inject the filtered reaction solution into a chromatographic vial. Filter the components in the reaction solution and perform quantitative analysis using a gas chromatograph. (See also...) Figure 2 The toluene conversion rate was calculated to be 17.87%, and the benzoic acid yield was 20.42%.

[0034] Example 4

[0035] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, 0.230 mL (2.25 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene were added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred for 20 h at room temperature and 1200 rpm using a magnetic stirrer. After the reaction was complete, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane, and the filtered reaction solution was injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 17.97%, and the yield of benzoic acid was 20.87%.

[0036] Example 5

[0037] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.383 mL (3.75 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 17.72%, and the yield of benzoic acid was 17.72%.

[0038] Example 6

[0039] In a 10 mL reaction tube, 0.7339 g (4.5 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 16.77%, and the yield of benzoic acid was 19.41%.

[0040] Example 7

[0041] In a 10 mL reaction tube, add 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0292 g (0.225 mmol) of cobalt chloride, 0.028 mL (0.075 mmol) of copper isooctanoate, 1.0 mL of acetone, 0.153 mL (1.5 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene. Using oxygen as the oxygen source, attach the tube to the reaction vessel and stir with a magnetic stirrer at 1200 rpm for 20 h at room temperature. After the reaction is complete, remove the oxygen, drain the reaction solution using a syringe, filter the solids from the syringe using a filter membrane, and then inject the filtered reaction solution into a chromatographic vial. Filter the components in the reaction solution and perform quantitative analysis using a gas chromatograph. (See [reference needed]). Figure 3 The calculated conversion rate of toluene was 20.07%, and the yield of benzoic acid was 22.82%.

[0042] Example 8

[0043] In a 10 mL reaction tube, add 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, 0.153 mL (1.5 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene. Using oxygen as the oxygen source, attach the tube to the reaction vessel and stir for 16 h at 1200 rpm using a magnetic stirrer at room temperature. After the reaction is complete, remove the oxygen, collect the reaction solution through a syringe, filter the solids from the syringe using a filter membrane, and then inject the filtered reaction solution into a chromatographic vial. Filter the components in the reaction solution and perform quantitative analysis using a gas chromatograph. (See [reference needed]). Figure 4 The calculated conversion rate of toluene was 17.82%, and the yield of benzoic acid was 19.76%.

[0044] Example 9

[0045] In a 10 mL reaction tube, add 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, 0.153 mL (1.5 mmol) of benzaldehyde, and finally 3.0 mL (30 mmol) of toluene. Using oxygen as the oxygen source, attach the tube to the reaction vessel and stir with a magnetic stirrer at 1200 rpm for 24 h at room temperature. After the reaction is complete, remove the oxygen, collect the reaction solution through a syringe, filter the solids from the syringe using a filter membrane, and then inject the filtered reaction solution into a chromatographic vial. Filter the components in the reaction solution and perform quantitative analysis using a gas chromatograph. (See [reference needed]). Figure 5 The calculated conversion rate of toluene was 19.94%, and the yield of benzoic acid was 22.62%.

[0046] Comparative Example 1: Without acetone

[0047] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred for 20 h at room temperature and 1200 rpm using a magnetic stirrer. After the reaction was complete, the oxygen was removed, and the reaction solution was collected using a syringe. The solid in the syringe was filtered through a filter membrane and injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 11.93%, and the yield of benzoic acid was 13.09%. As can be seen from Example 2 and Comparative Example 1, in an acid-free system, toluene, as the main reactant, can proceed at room temperature and pressure, and acetone, as an organic auxiliary agent, facilitates this novel aerobic conversion reaction of toluene.

[0048] Comparative Example 2: Without N-hydroxyphthalimide

[0049] In a 10 mL reaction tube, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred for 20 h at room temperature and 1200 rpm using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered through a filter membrane and injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. Calculations showed that toluene was almost not converted, and the yield of benzoic acid was 0.74%. Through Example 2 and Comparative Example 2, it can be seen that in an acid-free system, toluene, as the bulk of the reaction, can proceed at room temperature and pressure. N-hydroxyphthalimide, as a co-catalyst, provides the main conditions conducive to the aerobic conversion of toluene.

[0050] Comparative Example 3: Copper isooctanoate not added

[0051] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added, followed by 3.0 mL (30 mmol) of toluene. Oxygen was used as the oxygen source, and the mixture was stirred for 20 h at 1200 rpm using a magnetic stirrer at room temperature. After the reaction was complete, the oxygen was removed, and the reaction solution was collected using a syringe. The solid in the syringe was filtered through a filter membrane and injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 9.42%, and the yield of benzoic acid was 11.62%. As can be seen from Examples 2 and 3, in an acid-free system, toluene, as the bulk of the reaction, can proceed at room temperature and pressure. Copper isooctanoate, as a metal catalyst, activates NHPI to form free radicals, and achieves catalytic cycling through charge transfer and changes in the valence state of copper ions, which is conducive to this novel aerobic conversion reaction of toluene.

[0052] Comparative Example 4: Without cobalt chloride

[0053] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of pyridine, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered through a filter membrane and injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 12.43%, and the yield of benzoic acid was 14.85%. As can be seen from Example 2 and Comparative Example 4, in an acid-free system, toluene, as the bulk of the reaction, can proceed at room temperature and pressure. Cobalt chloride, as a metal catalyst, activates NHPI to form free radicals, and achieves catalytic cycling through charge transfer and changes in the valence state of cobalt ions, which is conducive to this novel aerobic conversion reaction of toluene.

[0054] Comparative Example 5: Without benzaldehyde

[0055] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, and 1.0 mL of acetone were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred for 20 h at room temperature and 1200 rpm using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered through a filter membrane and injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 10.57%, and the yield of benzoic acid was 12.95%. As can be seen from Example 2 and Comparative Example 5, in an acid-free system, toluene as the bulk of the reaction can proceed at room temperature and pressure, and benzaldehyde as an initiator facilitates this novel aerobic conversion reaction of toluene.

[0056] Comparative Example 6 used cobalt acetate as a catalyst.

[0057] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.797 g (0.45 mmol) of cobalt acetate, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. Calculations showed that toluene was almost completely unconverted, and the yield of benzoic acid was 2.13%.

[0058] Comparative Example 7

[0059] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.0394 g (0.15 mmol) of copper acetylacetonate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 9.44%, and the yield of benzoic acid was 12.02%.

[0060] The yields of toluene in Comparative Examples 6 and 7 were significantly lower than those in Example 1, indicating that the synergistic catalytic performance of cobalt chloride and copper isooctanoate was significantly higher than that of cobalt acetate and copper isooctanoate, as well as the synergistic catalytic performance of cobalt chloride and copper acetylacetonate.

[0061] Comparative Example 8

[0062] In a 10 mL reaction tube, 0.0816 g (0.5 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solids in the syringe were filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 3.28%, and the yield of benzoic acid was 6.31%.

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

[0064] Comparative Example 9

[0065] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of acetone, and 0.077 mL (0.75 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The tube was fitted with the oxygen and stirred for 20 h at room temperature and 1200 rpm using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane, and the filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 3.93%, and the yield of benzoic acid was 6.93%. As can be seen from Example 1 and Comparative Example 9, if the initiator is too small, the reaction rate slows down, resulting in a lower final reaction yield.

[0066] Comparative Example 10

[0067] In a 10 mL reaction tube, 0.4893 g (3 mmol) of N-hydroxyphthalimide, 0.0584 g (0.45 mmol) of cobalt chloride, 0.057 mL (0.15 mmol) of copper isooctanoate, 1.0 mL of pyridine, and 0.153 mL (1.5 mmol) of benzaldehyde were added. Finally, 3.0 mL (30 mmol) of toluene was added. Oxygen was used as the oxygen source for the reaction. The mixture was placed on the reaction tube and stirred at 1200 rpm for 20 h at room temperature using a magnetic stirrer. After the reaction was completed, the oxygen was removed, and the reaction solution was collected through a syringe. The solid in the syringe was filtered using a filter membrane. The filtered reaction solution was then injected into a chromatographic vial. The components in the reaction solution were filtered and quantitatively analyzed by gas chromatography. The calculated conversion rate of toluene was 11.55%, and the yield of benzoic acid was 14.74%. Because acetone can better dissolve NHPI, metal catalysts, and toluene, the reaction system is in contact with each other in the same phase. However, pyridine is more polar than acetone, and it is difficult to dissolve the more polar NHPI in the less polar toluene under anhydrous conditions. Therefore, the yield of toluene acid is relatively low.

[0068] It should be noted that although the above embodiments only mention the use of toluene as a raw material, the present invention is also applicable to other aromatic hydrocarbon compounds with similar structures, such as xylene and ethylbenzene. The above embodiments are only used to illustrate the principles 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, Benzoic acid product is obtained by stirring the reaction of toluene as raw material, copper salt and cobalt salt as catalyst, N-hydroxyphthalimide as co-catalyst, oxygen or air as oxidant, aldehyde as initiator, and organic liquid as auxiliary agent under normal temperature and pressure conditions. The copper salt is copper isooctanoate; the cobalt salt is cobalt chloride; and the organic liquid is acetone.

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

3. 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 to 40.85:

30.

4. 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, n-propionaldehyde, n-butyraldehyde, isobutyraldehyde, trimethylacetaldehyde, 3,5,5-trimethylhexanaldehyde, and benzaldehyde.

5. 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.

6. 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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