Method for preparing benzoic acid by oxidizing methylbenzene at room temperature

Abstract

The invention discloses a method for preparing benzoic acid by oxidizing toluene at room temperature, which comprises the following steps of: reacting toluene serving as a raw material, acetic acid serving as a solvent, cobalt salt and a nitrogen-containing compound serving as catalysts, imine serving as a cocatalyst and oxygen serving as an oxidant at normal temperature and normal pressure to prepare benzoic acid; according to the technical scheme, reaction conditions are mild, a catalytic system is homogeneous and soluble, corrosion hazard of the catalyst to process equipment under high-temperature reaction is avoided, and the method belongs to the technical field of fine chemical engineering.

Description

Technical Field

[0001] The invention relates to a method for preparing benzoic acid by oxidizing toluene at room temperature, belonging to the technical field of fine chemicals. Background Art

[0002] Benzoic acid (also known as benzoic acid) is a white crystalline solid with a slightly acidic odor. It is the simplest aromatic carboxylic acid and often exists in the form of free acid, ester or its derivatives. Benzoic acid has multiple industrial applications. It can not only be used as a rust inhibitor for steel equipment to protect metals from corrosion, but also as a mordant in dyeing and printing processes to enhance the effect of dyes. In addition, benzoic acid plays a role in the improvement of alkyd resins, enhancing the performance of the resin. In the pharmaceutical and dye manufacturing industries, benzoic acid, as a key intermediate, is crucial for the synthesis of compounds such as caprolactam and phenol. Benzoic acid and its sodium salt are still one of the widely used preservatives in my country as food preservatives due to their high safety and long history of use.

[0003] The report of benzoic acid oxidation by air in toluene liquid phase is quite extensive. The most primitive production processes are SNIA method and Mid-century (MC) method. Among them, SNIA method is more common. It uses Co(OAc)2 as catalyst, the reaction temperature is 140℃~155℃, the reaction pressure is 0.6MPa~0.8MPa, and the selectivity of the main product benzoic acid is 90%~90.5%. However, the conversion rate of this process is less than 20%, and cobalt acetate easily forms cobalt oxalate precipitate during the oxidation process, which leads to reactor fouling.

[0004] The MC method uses a Co-Mn-Br ternary catalytic system as a catalyst, acetic acid as a solvent, a reaction temperature of 150°C to 250°C, a reaction pressure of 0.5MPa to 3.0MPa, and a high yield of benzoic acid. However, the introduction of halogen Br as a reaction initiator is not conducive to the long-term operation of the equipment.

[0005] Patent CN102115353 discloses a method for selective oxidation of aromatic hydrocarbons, which uses green and sustainable ionic liquids as catalysts and solvents to achieve the goal of selective oxidation of toluene to obtain compounds such as benzoic acid, benzyl alcohol, and benzyl benzoate.

[0006] Patent CN101613269 discloses a method for preparing benzoic acid by liquid phase oxidation of toluene, which avoids the adverse factors caused by the use of halogen Br and obtains benzoic acid with a high yield.

[0007] However, the above reactions all need to be carried out in a high-pressure reactor at high temperature (160°C to 180°C). The focus of attention has been on the process of preparing benzoic acid by toluene air conversion with milder reaction conditions, high activity and environmental friendliness. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing benzoic acid by oxidizing toluene at room temperature, using toluene as a raw material, oxygen as an oxidant, and utilizing commercial cobalt salt and nitrate catalysts for a synergistic catalytic reaction. The catalyst is cheap and readily available, the reaction is easy to achieve, the conversion rate and yield are excellent, and the selectivity is high.

[0009] To achieve the purpose of the present invention, the technical solution adopted is:

[0010] A method for preparing benzoic acid by oxidizing toluene at room temperature, wherein toluene is used as a raw material, acetic acid is used as a solvent, a cobalt salt and a nitrogen-containing compound are used as catalysts, imines are used as a co-catalyst, and oxygen is used as an oxidant, and benzoic acid is prepared by reaction at normal temperature and pressure;

[0011] The molar ratio of toluene, cobalt salt and nitrogen-containing compound is 10:0.2-0.3:0.05-0.3.

[0012] Preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the cobalt salt is anhydrous cobalt acetate; and the nitrogen-containing compound is a nitrite or a nitrate or a nitrite ester compound.

[0013] More preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the nitrate is one or more of cobalt nitrate hexahydrate, manganese nitrate tetrahydrate, iron nitrate nonahydrate, cerium nitrate hexahydrate, and hydrated copper nitrate; the nitrite is sodium nitrite; and the nitrite ester compound is tert-butyl nitrite.

[0014] Preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the imine co-catalyst is an organic small molecule compound having an imide (C(O)-NH-) structure.

[0015] More preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the imine co-catalyst has a structure as shown in the following general formula (I) and general formula (II);

[0016]

[0017] Among them, the value range of n is 0 to 3; X represents an S atom or an O atom, and Y is -H, -CH3, -OCH3, -Cl, -NO2, -NH2, -CN; Y is substituted at any position of the α or β position of the benzene ring.

[0018] More preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the imine co-catalyst is one or more of N-hydroxyphthalimide, N-hydroxy-o-sulfonylbenzoimide, N-hydroxy-2,3-pyridinedicarboximide, N-hydroxyglutarimide, N-hydroxysuccinimide, N-hydroxy-1,8-naphthalimide, 1,3,5-trihydroxyhexahydro-1,3,5-triazine-2,4,6-trione and N,N'-dihydroxypyromellitic acid imide.

[0019] Preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the molar ratio of toluene to imine co-catalyst is 10:0.4-1.

[0020] Preferably, in the above-mentioned method for preparing benzoic acid by oxidation of toluene at room temperature, the reaction time is 20 to 24 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The technical solution provided by the present invention uses commercial cobalt salts and nitrogen-containing compounds as synergistic catalysts, oxygen as an oxidant, imine compounds as co-catalysts, and acetic acid as a solvent. The reaction is carried out at room temperature to prepare the oxidation product benzoic acid in high yield. In particular, manganese metal salts have a synergistic effect on oxidized cobalt, which can effectively promote its reduction to form low-valent cobalt ions. The hydrogen transfer process involving the imine co-catalyst ensures the oxidation of toluene to prepare benzoic acid. The catalysts and co-catalysts used are widely available, cheap and easy to obtain, and do not require complicated synthesis steps.

[0023] 2. The technical solution provided by the present invention has a synergistic effect on cobalt metal salts when manganese metal salts are added. Compared with the traditional SNIA method and MC method, this method eliminates the introduction of halogen bromide ions, has mild reaction conditions, and the catalytic system is homogeneously soluble, thus avoiding the corrosion hazard of the catalyst to the process equipment under high temperature reaction.

[0024] 3. The technical solution provided by the present invention is easy to operate, has a high yield of the target product, low economic cost, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a gas chromatography detection diagram provided in Example 1 of the present invention.

[0026] Figure 2 This is a gas chromatography detection diagram provided for Example 2 of the present invention.

[0027] Figure 3 This is a gas chromatography detection diagram provided for Example 3 of the present invention.

[0028] Figure 4This is a gas chromatography detection diagram provided for Example 4 of the present invention.

[0029] Figure 5 This is a gas chromatography detection diagram provided for Example 5 of the present invention.

[0030] Figure 6 This is a gas chromatography detection diagram provided for Example 6 of the present invention.

[0031] Figure 7 This is a gas chromatography detection diagram provided for Example 7 of the present invention.

[0032] Figure 8 This is a gas chromatography detection diagram provided for Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0033] The present invention is preferably described below in conjunction with embodiments, but the protection scope of the present invention is not limited to the scope represented by the embodiments.

[0034] Example 1

[0035] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0308g (0.188mmol) of N-hydroxyphthalimide, 0.0067g (0.0376mmol) of cobalt acetate, 0.0145g (0.0564mmol) of manganese nitrate, and 4mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatography, see Figure 1 The yield of benzoic acid was calculated to be 87.8%, the yield of benzaldehyde was 1.9%, and the yield of benzyl alcohol was 0.9%.

[0036] At normal temperature and pressure, the reaction equation is as shown in equation 1-3.

[0037] Formula 1: Co 3+ +Mn 2+ →Co 2+ +Mn 3+

[0038] Formula 2:

[0039] Formula 3:

[0040] Example 2

[0041] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0308g (0.188mmol) of N-hydroxyphthalimide, 0.0067g (0.0376mmol) of cobalt acetate, 0.0024g (0.0094mmol) of manganese nitrate, and 4mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and conduct quantitative analysis by gas chromatography, see Figure 2 The calculated yield of benzoic acid was 76.9%, the yield of benzaldehyde was 2.4%, and no benzyl alcohol product was detected.

[0042] Example 3

[0043] In a 10 mL reaction tube, add 0.2 mL (1.88 mmol) of toluene, 0.0308 g (0.188 mmol) of N-hydroxyphthalimide, 0.0101 g (0.0566 mmol) of cobalt acetate, 0.0097 g (0.0379 mmol) of manganese nitrate, and 4 mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20 hours at room temperature and 1000 rpm with a magnetic stirrer. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatography, see Figure 3 The yield of benzoic acid, benzaldehyde and benzyl alcohol was calculated to be 79.3%, 2.9% and 1.3%, respectively.

[0044] Example 4

[0045] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0123g (0.075mmol) of N-hydroxyphthalimide, 0.0067g (0.0376mmol) of cobalt acetate, 0.0145g (0.0564mmol) of manganese nitrate, and 4mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and conduct quantitative analysis by gas chromatography, see Figure 4 The yield of benzoic acid, benzaldehyde and benzyl alcohol was calculated to be 74.2%, 2.9% and 3.1%, respectively.

[0046] Example 5

[0047] In a 10 mL reaction tube, add 0.2 mL (1.88 mmol) of toluene, 0.0308 g (0.188 mmol) of N-hydroxyphthalimide, 0.0067 g (0.0376 mmol) of cobalt acetate, 0.0145 g (0.0564 mmol) of manganese nitrate, and 4 mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir at room temperature and 1000 rpm with a magnetic stirrer for 24 hours. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatography, see Figure 5 The calculated yield of benzoic acid was 90.4%, the yield of benzaldehyde was 1.6%, and no benzyl alcohol product was detected.

[0048] Example 6

[0049] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0308g (0.188mmol) of N-hydroxyphthalimide, 0.0067g (0.0376mmol) of cobalt acetate, 0.0145g (0.0564mmol) of ferric nitrate, and 4mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatography, see Figure 6 The yield of benzoic acid, benzaldehyde and benzyl alcohol was calculated to be 28.4%, 3.3% and 0.9%, respectively.

[0050] Example 7

[0051] In a 10 mL reaction tube, add 0.2 mL (1.88 mmol) of toluene, 0.0308 g (0.188 mmol) of N-hydroxyphthalimide, 0.0067 g (0.0376 mmol) of cobalt acetate, 0.0245 g (0.0564 mmol) of cerium nitrate, and 4 mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir at room temperature and 1000 rpm with a magnetic stirrer for 24 hours. After stirring, filter the components in the reaction solution and conduct quantitative analysis by gas chromatography. See Figure 7 The yield of benzoic acid, benzaldehyde and benzyl alcohol was calculated to be 33.7%, 3.1% and 1.1%, respectively.

[0052] Example 8

[0053] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0469g (0.188mmol) of 1,3,5-trihydroxyhexahydro-1,3,5-triazine-2,4,6-trione, 0.0067g (0.0376mmol) of cobalt acetate, 0.0145g (0.0564mmol) of manganese nitrate, and 4mL of acetic acid. Pass enough oxygen through the balloon and seal the reaction tube with it. Stir for 24h at room temperature and 1000rpm under a magnetic stirrer. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 73.8%, the yield of benzaldehyde is 20.1%, and no benzyl alcohol product is detected.

[0054] Example 9

[0055] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0401g (0.245mmol) of N-hydroxy-1,8-naphthalene dicarboximide, 0.0067g (0.0376mmol) of cobalt acetate, 0.0145g (0.0564mmol) of manganese nitrate, and 4mL of acetic acid. Pass enough oxygen through the balloon and seal the reaction tube with it. Stir for 24h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatograph. It is calculated that the yield of benzoic acid is 31.1%, the yield of benzaldehyde is 4.3%, and the yield of benzyl alcohol is 1.2%.

[0056] Example 10

[0057] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), cobalt acetate 0.0067g (0.0376mmol), cobalt nitrate 0.0164g (0.0564mmol), acetic acid 4mL. Pass enough oxygen in the balloon and seal the reaction tube with it. Stir for 24h at room temperature and 1000rpm speed of magnetic stirrer. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 92%, and almost no benzaldehyde and benzyl alcohol are detected.

[0058] Embodiment 11

[0059] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), cobalt acetate 0.0067g (0.0376mmol), sodium nitrite 0.0039g (0.0564mmol), acetic acid 4mL. A sufficient amount of oxygen is passed through the balloon, and the reaction tube is sealed with it. Stir for 24h under a magnetic stirrer at room temperature and 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 90%, the yield of benzaldehyde is 3.7%, and the yield of benzyl alcohol is 1.2%.

[0060] Example 12

[0061] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), cobalt acetate 0.0067g (0.0376mmol), tert-butyl nitrite 0.0069mL (0.0564mmol), acetic acid 4mL. A sufficient amount of oxygen is passed through the balloon, and the reaction tube is sealed with it. Stir for 24h under a magnetic stirrer at room temperature and 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 90%, the yield of benzaldehyde is 3.3%, and the yield of benzyl alcohol is 0.8%.

[0062] Comparative Example 1: No nitrate is added, taking manganese as an example

[0063] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0308g (0.188mmol) of N-hydroxyphthalimide, 0.0067g (0.0376mmol) of cobalt acetate, and 4mL of acetic acid. Pass enough oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and a magnetic stirrer at a speed of 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. The benzoic acid yield is calculated to be 6.8%, and no benzaldehyde or benzyl alcohol products are detected.

[0064] Comparative Example 2: No acetate is added, taking cobalt as an example

[0065] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), manganese nitrate 0.0145g (0.0564mmol), acetic acid 4mL. Pass enough oxygen in a balloon and use it to seal the reaction tube. Stir for 20h at room temperature and 1000rpm speed of magnetic stirrer. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 7.7%, the yield of benzaldehyde is 3.5%, and the yield of benzyl alcohol is 1.3%.

[0066] Comparative Example 3: No addition of N-hydroxyphthalimide

[0067] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), cobalt acetate 0.0067g (0.0376mmol), manganese nitrate 0.0145g (0.0564mmol), acetic acid 4mL. A sufficient amount of oxygen is passed through the balloon, and the reaction tube is sealed with it. Stir for 20h at room temperature and a magnetic stirrer at a speed of 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 16.7%, the yield of benzaldehyde is 1.7%, and the yield of benzyl alcohol is 0.6%.

[0068] Comparative Example 4

[0069] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), cobalt acetate 0.0067g (0.0376mmol), manganese nitrate 0.0145g (0.0564mmol), acetic acid 4mL. A sufficient amount of oxygen is passed through the balloon, and the reaction tube is sealed with it. Stir for 15h at room temperature and a magnetic stirrer at a speed of 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 12.0%, the yield of benzaldehyde is 6.5%, and the yield of benzyl alcohol is 1.8%.

[0070] Comparative Example 5

[0071] In a 10mL reaction tube, add toluene 0.2mL (1.88mmol), N-hydroxyphthalimide 0.0308g (0.188mmol), cupric acetate 0.0075g (0.0376mmol), manganese nitrate 0.0145g (0.0564mmol), acetic acid 4mL. A sufficient amount of oxygen is passed through the balloon, and the reaction tube is sealed with it. Stir for 24h under a magnetic stirrer at room temperature and 1000rpm. After stirring, the components in the reaction solution are filtered and quantitatively analyzed by gas chromatograph. It is calculated that the yield of benzoic acid is 26.6%, the yield of benzaldehyde is 4.2%, and the yield of benzyl alcohol is 1.1%.

[0072] Comparative Example 6

[0073] In a 10mL reaction tube, add 0.2mL (1.88mmol) of toluene, 0.0308g (0.188mmol) of N-hydroxyphthalimide, 0.0017g (0.0094mmol) of cobalt acetate, 0.0097g (0.0379mmol) of manganese nitrate, and 4mL of acetic acid. Pass sufficient oxygen through a balloon and seal the reaction tube with it. Stir for 20h at room temperature and 1000rpm under a magnetic stirrer. After stirring, filter the components in the reaction solution and perform quantitative analysis by gas chromatography, see Figure 8 The yield of benzoic acid, benzaldehyde and benzyl alcohol was calculated to be 21.4%, 5.4% and 1.7%, respectively.

[0074] It can be seen from Example 1 and Comparative Examples 1-3 that the technical solution provided by the present application has higher conversion activity and milder chemical reaction conditions for the conversion of toluene into benzoic acid. In particular, in the presence of manganese metal salts, the cobalt metal active center can effectively carry out catalytic cycles and promote the reaction to produce benzoic acid.

[0075] It can be seen from the yield of benzoic acid in Example 1 and Comparative Example 4 that the yield of benzoic acid after 15 hours of reaction is significantly lower than the yield of benzoic acid after 24 hours of reaction. This is because in the initial stage of the reaction, the activation of the carbon-hydrogen bond of toluene is a slow process, in which the reaction system needs to form unstable intermediates or active species, and the generation rate of these intermediates determines the rate of the entire reaction. At the same time, as the concentration of the oxidation intermediates of toluene accumulates, they begin to show autocatalytic effects, accelerating the subsequent reaction steps, resulting in a significant increase in the reaction rate in the late 20h, shortening the induction period and increasing the yield of benzoic acid.

[0076] It can be seen from the yields of benzoic acid in Example 1 and Comparative Example 5 that the yield of benzoic acid prepared by using copper acetate and manganese nitrate as synergistic catalysts is significantly lower than the yield of benzoic acid prepared by using cobalt salts and nitrogen-containing compounds as synergistic catalysts, indicating that manganese nitrate and tert-butyl nitrite have a synergistic effect on oxidized cobalt and can effectively promote its reduction to form low-valent cobalt ions, and cooperate with the hydrogen transfer process involving imine co-catalysts to ensure the oxidation of toluene to prepare benzoic acid.

[0077] It can be seen from the yields of benzoic acid in Example 1 and Comparative Example 6 that when the amount of cobalt acetate is reduced, the yield of benzoic acid is also significantly reduced.

Claims

1. A method for preparing benzoic acid by oxidation of toluene at room temperature, characterized in that: Benzoic acid is prepared by reacting toluene as raw material, acetic acid as solvent, cobalt salt and nitrogen-containing compound as catalyst, imine as co-catalyst and oxygen as oxidant at normal temperature and pressure. The molar ratio of toluene, cobalt salt and nitrogen-containing compound is 10:0.2-0.3:0.05-0.

3.

2. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 1, characterized in that: The cobalt salt is anhydrous cobalt acetate.

3. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 1, characterized in that: The nitrogen-containing compound is a nitrite or a nitrate or a nitrite ester compound.

4. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 3, characterized in that: The nitrate is one or more of cobalt nitrate hexahydrate, manganese nitrate tetrahydrate, iron nitrate nonahydrate, cerium nitrate hexahydrate, and hydrated copper nitrate; the nitrite is sodium nitrite.

5. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 3, characterized in that: The nitrite ester compound is tert-butyl nitrite.

6. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 1, characterized in that: The imine co-catalyst is an organic small molecule compound with an imide (C(O)-NH-) structure.

7. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 6, characterized in that: The imine co-catalyst has the following general structural formulas (I) and (II): Among them, the value range of n is 0 to 3; X represents an S atom or an O atom, and Y is -H, -CH3, -OCH3, -Cl, -NO2, -NH2, -CN; Y is substituted at any position of the α or β position of the benzene ring.

8. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 6 or 7, characterized in that: The imine co-catalyst is one or more of N-hydroxyphthalimide, N-hydroxy-o-sulfonylbenzoimide, N-hydroxy-2,3-pyridinedicarboximide, N-hydroxyglutarimide, N-hydroxysuccinimide, N-hydroxy-1,8-naphthalimide, 1,3,5-trihydroxyhexahydro-1,3,5-triazine-2,4,6-trione, and N,N'-dihydroxypyromellitic acid imide.

9. The method for preparing benzoic acid by oxidation of toluene at room temperature according to claim 1, characterized in that: The molar ratio of toluene to imine co-catalyst is 10:0.4-1.

10. The method for preparing benzoic acid by oxidizing toluene at room temperature according to claim 1, characterized in that: The reaction time is 20 to 24 hours.

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