Method for preparing methyl o-chlorobenzoate from o-chlorotoluene

Abstract

The invention relates to the technical field of organic synthesis processes, and provides a method for preparing methyl o-chlorobenzoate from o-chlorotoluene, which comprises the following steps: adding o-chlorotoluene, acetic acid and a supported catalyst into a mixing kettle, heating to 60-120 DEG C, and stirring to obtain a mixed solution; pouring the mixed solution into a reaction kettle, introducing air to pressurize, heating to 130-180 DEG C, reacting for 2-4 hours, discharging, cooling, filtering, washing and distilling to obtain o-chlorobenzoic acid; the method comprises the following steps: mixing o-chlorobenzoic acid and methanol, stirring, adding a catalyst, heating to 70-90 DEG C, reacting for 2-4 hours, cooling, extracting, washing, standing and layering to obtain an upper phase, namely methyl o-chlorobenzoate. The preparation method has the advantages of low production cost, less waste gas and waste water, and realization of the coordinated development of economic benefits and environmental benefits, and the methyl o-chlorobenzoate prepared from o-chlorotoluene has the advantages of high yield, high purity, and good application value.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis technology, and particularly relates to a method for preparing methyl o-chlorobenzoate by using o-chlorotoluene. Background Art

[0002] Methyl o-chlorobenzoate is an important organic intermediate, widely used in the synthesis of medicines, pesticides, spices and chemical materials. Traditional synthesis methods have problems such as cumbersome steps, low yield, low purity or environmental pollution. As a relatively cheap and easily available raw material, the process of converting o-chlorotoluene into methyl o-chlorobenzoate has important industrial value.

[0003] At present, the oxidation of o-chlorotoluene usually adopts synthesis methods such as diazotization, oxidation and chlorination hydrolysis. The reaction conditions of diazotization are relatively mild, but the process route is long, the cost is high, and there are more three wastes; chlorination is a commonly used method at present, but the reaction time is long, and there are more waste gas and waste water, and the yield is low; oxidation has the advantages of short process route, less waste gas and waste water, and low cost, but there is a defect of long production cycle. In addition, in the subsequent esterification reaction step, how to improve the yield and purity of the product and reduce the occurrence of side reactions is also a problem that the prior art needs to solve.

[0004] Chinese patent CN 113198531 A discloses a composite catalyst and a method for preparing o-chlorobenzoic acid. The composite catalyst is composed of o-chlorotoluene as a raw material, acetic acid as a solvent, and air as an oxidant. A compound composed of cobalt acetate: manganese acetate: zirconium acetate: tetrabromoethane in a mass ratio of 1: (0.5-3): (0.5-3): (0.5-3) is used as a composite catalyst. The materials are first mixed, and then transferred to an oxidation kettle, and air is introduced to pressurize and react at a high temperature to obtain an o-chlorobenzoic acid mixed solution; then the mixture is transferred to a deacidification kettle to distill out acetic acid and water; the temperature is increased in the deacidification kettle to obtain a crude o-chlorobenzoic acid product, and finally distilled. This invention solves the problems of high energy consumption, long production time and low yield in high temperature reaction in traditional production methods; however, the use of this preparation method may result in a relatively short service life of the composite catalyst, which is not conducive to the recycling of the catalyst.

[0005] Therefore, it is urgent to develop a method for preparing methyl o-chlorobenzoate from o-chlorotoluene so that the yield and purity are higher and environmental pollution can be reduced. Summary of the invention

[0006] In view of the existing technical problems, the object of the present invention is to provide a method for preparing methyl o-chlorobenzoate from o-chlorotoluene. The preparation method of the present invention has low production cost, less waste gas and waste water, and the supported catalyst can be recycled and reused, thus achieving the coordinated development of economic benefits and environmental benefits. In addition, the yield and purity of preparing methyl o-chlorobenzoate from o-chlorotoluene are high, and the method has good application value.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for preparing methyl o-chlorobenzoate by using o-chlorotoluene, comprising the following steps:

[0009] S1. Add o-chlorotoluene, acetic acid and supported catalyst into a mixing kettle, heat to 60-120 ° C, stir to obtain a mixed solution;

[0010] S2. Pour the mixed solution obtained in step S1 into a reactor, introduce air to pressurize, heat to 130-180°C, react for 2-4h, discharge, cool, filter, wash, and distill to obtain o-chlorobenzoic acid;

[0011] S3. The o-chlorobenzoic acid and methanol obtained in step S2 are mixed, stirred, a catalyst is added, heated to 70-90° C., reacted for 2-4 hours, cooled, extracted, washed, and the upper phase after standing and stratification is methyl o-chlorobenzoate.

[0012] The reaction mechanism and effects of the present invention are as follows:

[0013] 1. The present invention loads cobalt and palladium ions together on a pseudo-boehmite carrier modified by a porogen, thereby promoting the formation of o-chlorobenzoic acid and avoiding the problem of low yield during high temperature reaction.

[0014] When o-chlorotoluene reacts under oxidative conditions to generate o-chlorobenzoic acid, a catalyst is often required for synergistic action. Cobalt can achieve the synthesis of o-chlorobenzoic acid from o-chlorotoluene with high selectivity under mild conditions, thereby increasing the yield of o-chlorobenzoic acid, the precursor of methyl o-chlorobenzoate. However, due to the intensity of the catalytic reaction and the influence of environmental factors, cobalt-based catalysts have a relatively short service life, and are easily affected by external factors such as oxidation, resulting in reduced catalytic activity and selectivity.

[0015] The present invention uses pseudo-boehmite modified by a porogen as a carrier, and uses an impregnation method to fix metal cobalt and palladium on the carrier to obtain a supported catalyst with excellent stability and high catalytic activity. On the one hand, the porogen prepared by the applicant using N-allylimidazole and 1,9-dibromononane as raw materials has a larger steric hindrance, which can make the pseudo-boehmite have a larger pore size, and further make the transition metal palladium and cobalt better loaded in the carrier; on the other hand, the surface of pseudo-boehmite contains abundant hydroxyl groups, which can form coordination with cobalt and palladium ions, and then make cobalt and palladium stably loaded in the carrier; in addition, the imidazole group in the porogen remaining in the carrier and the cobalt and palladium ions may also form coordination, further improving the stability of the metal ions, so that the catalyst as a whole has better stability, prolongs its service life, and then improves the catalytic activity and selectivity.

[0016] Furthermore, supported catalysts are easier to separate and recover after the reaction due to the stability of their carriers, which helps to reduce costs and environmental impact, and achieve coordinated development of economic and environmental benefits.

[0017] 2. The present invention regulates the mass ratio of o-chlorotoluene, acetic acid and supported catalyst to improve the yield and purity of the reaction.

[0018] 3. The present invention selects air as the oxidant, and further regulates the air introduction rate and the pressure of the reactor, shortens the production time, and thus improves the yield and purity of the reaction.

[0019] 4. The present invention uses phosphotungstic acid and activated carbon to prepare a catalyst, which promotes the esterification reaction of o-chlorobenzoic acid to form methyl o-chlorobenzoate. Phosphotungstic acid is a strong acidic substance, which can be used as a catalyst for esterification reaction to increase the reaction rate; activated carbon has a high specific surface area and a pore structure, which can increase the contact area of ​​the catalyst, thereby improving the contact efficiency between the reactant and the catalyst. Loading phosphotungstic acid on activated carbon can play a stabilizing role, prevent the loss or aggregation of phosphotungstic acid during the reaction process, and further improve the stability and life of the catalyst; and the catalyst loaded on activated carbon is easier to separate from the reaction system, which is convenient for the recovery and reuse of the catalyst, and has less impact on the environment, which meets the requirements of modern industry for environmental protection.

[0020] In some embodiments, the mass ratio of o-chlorotoluene, acetic acid and supported catalyst in step S1 is 1:(1.5-3.5):(0.02-0.08).

[0021] In some embodiments, the method for preparing the supported catalyst in step S1 comprises the following steps:

[0022] (1) adding N-allylimidazole, 1,9-dibromononane and acetonitrile to a first reaction kettle, heating to 60-90° C., stirring and reacting for 18-24 hours, cooling to 0-2° C., filtering and washing the precipitate, drying and grinding to obtain a porogen for later use; preparing a cobalt acetate aqueous solution and a palladium chloride aqueous solution for later use;

[0023] (2) adding the porogen, pseudo-boehmite and deionized water obtained in step (1) into a second reaction kettle, heating to 140-150° C. and stirring for 20-24 hours, cooling, washing and drying to obtain a modified pseudo-boehmite carrier;

[0024] (3) impregnating the modified pseudo-boehmite support obtained in step (2) into the cobalt acetate aqueous solution obtained in step (1), stirring magnetically for 1-2 hours, and drying to obtain a product;

[0025] (4) The product obtained in step (3) is immersed in the aqueous palladium chloride solution obtained in step (1), magnetically stirred for 1-2 hours, dried, and calcined to obtain a supported catalyst.

[0026] In some embodiments, the molar ratio of N-allylimidazole to 1,9-dibromononane in step (1) is (2.1-2.6):1.

[0027] Preferably, the molar ratio of N-allylimidazole to 1,9-dibromononane in step (1) is (2.2-2.4):1.

[0028] In some embodiments, the mass ratio of the modified pseudo-boehmite carrier, the cobalt acetate in the cobalt acetate aqueous solution and the palladium chloride in the palladium chloride aqueous solution in step (3) and step (4) is 1: (0.04-0.06): (0.02-0.04).

[0029] In some embodiments, the mass ratio of the porogen to pseudo-boehmite in step (2) is (0.15-0.3):1.

[0030] In some embodiments, the rate of introducing air in step S2 is 20-30 L / min.

[0031] In some embodiments, the pressure after pressurization in step S2 is 0.7-1.0 MPa.

[0032] In some embodiments, the method for preparing the catalyst in step S3 comprises the following steps:

[0033] Disperse phosphotungstic acid and activated carbon in deionized water, heat to 80-90°C, stir and react for 5-6h, filter and dry to obtain a catalyst.

[0034] In some embodiments, the mass ratio of the activated carbon to phosphotungstic acid is 1:(0.7-1.2).

[0035] Preferably, the mass ratio of the activated carbon to phosphotungstic acid is 1:(1-1.2).

[0036] In some embodiments, the mass ratio of o-chlorobenzoic acid, methanol and catalyst in step S3 is 1:(1.2-1.5):(0.2-0.3).

[0037] In some embodiments, the yield of the prepared methyl o-chlorobenzoate is not less than 96.5%, and the purity is not less than 98%.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The preparation method of the present invention has low production cost, less waste gas and waste water, and the supported catalyst can be recycled and reused, thus achieving the coordinated development of economic benefits and environmental benefits. The yield of preparing methyl o-chlorobenzoate from o-chlorotoluene is not less than 96.5%, and the purity is not less than 98%, thus having good application value.

[0040] 2. The present invention loads cobalt and palladium ions together on a pseudo-boehmite carrier modified by a porogen, promotes the formation of o-chlorobenzoic acid, and obtains a supported catalyst with excellent stability, thereby avoiding the problem of low yield during high-temperature reaction, and the supported catalyst has high catalytic activity and high selectivity.

[0041] 3. The present invention regulates the mass ratio of o-chlorotoluene, acetic acid and supported catalyst to improve the yield and purity of the reaction.

[0042] 4. The present invention uses phosphotungstic acid and activated carbon to prepare a catalyst, which promotes the esterification reaction of o-chlorobenzoic acid to form methyl o-chlorobenzoate. The synthesized catalyst improves the contact efficiency between the reactant and the catalyst, prevents the loss or aggregation of phosphotungstic acid during the reaction, improves the stability and life of the catalyst, and meets the requirements of modern industry for environmental protection. DETAILED DESCRIPTION

[0043] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, rather than to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0044] According to the ratios of the raw materials and the preparation methods specified in the following examples and comparative examples, methyl o-chlorobenzoate was synthesized.

[0045] In order to facilitate those skilled in the art to implement the present invention, the sources of some raw materials in the embodiments and comparative examples are described as follows:

[0046] Activated carbon: purchased from Gongyi Shuizhiyuan Water Purification Materials Co., Ltd.

[0047] Pseudo-boehmite: purchased from Jinan Xiangfeng Weiye Chemical Co., Ltd.

[0048] Other raw materials are not specially specified and can be purchased from the market.

[0049] Preparation Example 1

[0050] The preparation method of supported catalyst A comprises the following steps:

[0051] (1) 86.8 g of N-allylimidazole, 100 g of 1,9-dibromononane, and 400 ml of acetonitrile were added to a first reaction kettle, heated to 75° C., stirred and reacted for 20 h, cooled to 0° C., filtered and washed 3 times with ether, dried at 80° C. for 5 h, and ground to obtain a porogen for later use; a cobalt acetate aqueous solution and a palladium chloride aqueous solution with a concentration of 0.01 g / ml were prepared and used for later use;

[0052] (2) 22.5 g of the porogen obtained in step (1), 100 g of pseudo-boehmite, and 250 ml of deionized water were added to a second reaction kettle, heated to 145° C. and stirred for 22 h, cooled to room temperature, washed with deionized water three times, and dried at 50° C. for 4 h to obtain a modified pseudo-boehmite carrier;

[0053] (3) impregnating 100 g of the modified pseudo-boehmite support obtained in step (2) into 500 ml of the cobalt acetate aqueous solution obtained in step (1), stirring with a magnetic stirrer for 1.5 h, and drying in an oven at 110° C. for 12 h to obtain a product;

[0054] (4) Immerse 100 g of the product obtained in step (3) into 300 ml of the palladium chloride aqueous solution obtained in step (1), stir magnetically for 2 h, dry in an oven at 110° C. for 12 h, and calcine in a muffle furnace at 500° C. for 5 h to obtain supported catalyst A.

[0055] Preparation Example 2

[0056] The preparation method of supported catalyst B is the same as that of Preparation Example 1, except that the amount of N-allylimidazole added is 68 g.

[0057] Preparation Example 3

[0058] The preparation method of supported catalyst C is the same as that of Preparation Example 1, except that the amount of modified pseudo-boehmite carrier added is 70 g.

[0059] Preparation Example 4

[0060] The preparation method of supported catalyst D comprises the following steps:

[0061] (1) preparing 0.01 g / ml aqueous solution of cobalt acetate and 0.01 g / ml aqueous solution of palladium chloride for standby use;

[0062] (2) impregnating 100 g of pseudo-boehmite into 500 ml of the cobalt acetate aqueous solution obtained in step (1), stirring magnetically for 1.5 h, and drying in an oven at 110° C. for 12 h to obtain a product;

[0063] (3) The product obtained in step (2) was immersed in 300 ml of the palladium chloride aqueous solution obtained in step (1), magnetically stirred for 2 h, dried in an oven at 110° C. for 12 h, and calcined in a muffle furnace at 500° C. for 5 h to obtain a supported catalyst D.

[0064] Preparation Example 5

[0065] The preparation method of catalyst A comprises the following steps:

[0066] Disperse 22 g of phosphotungstic acid and 20 g of activated carbon in 210 ml of deionized water, heat to 85°C, stir and react for 6 h, filter, and dry at 145°C for 5 h to obtain a catalyst.

[0067] Preparation Example 6

[0068] The preparation method of catalyst B is the same as that of Preparation Example 5, except that the amount of phosphotungstic acid added is 12 g.

[0069] Example 1

[0070] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene comprises the following steps:

[0071] S1. 1 kg of o-chlorotoluene, 2.5 kg of acetic acid and 50 g of supported catalyst A were added to a mixing kettle, heated to 90 ° C, and stirred for 2 h to obtain a mixed solution;

[0072] S2. Pour the mixed solution obtained in step S1 into a reactor, introduce air at a rate of 25 L / min, pressurize to 0.8 MPa, heat to 155 ° C, react for 3 h, discharge, cool to room temperature, filter, wash with deionized water 3 times, and distill to obtain o-chlorobenzoic acid;

[0073] S3. 0.8 kg of o-chlorobenzoic acid and 1.04 kg of methanol obtained in step S2 were mixed, stirred for 2 h, 0.2 kg of catalyst A was added, heated to 80 ° C, reacted for 3 h, cooled to room temperature, extracted twice with toluene, washed three times with deionized water, and the upper phase after standing and stratification was methyl o-chlorobenzoate.

[0074] Example 2

[0075] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene comprises the following steps:

[0076] S1. 1 kg of o-chlorotoluene, 1.5 kg of acetic acid and 20 g of supported catalyst A were added to a mixing kettle, heated to 60 ° C, and stirred for 4 h to obtain a mixed solution;

[0077] S2. The mixed solution obtained in step S1 was poured into a reactor, air was introduced at a rate of 20 L / min, pressurized to 0.7 MPa, heated to 130 ° C, reacted for 4 h, discharged, cooled to room temperature, filtered, washed with deionized water 3 times, and distilled to obtain o-chlorobenzoic acid;

[0078] S3. 0.8 kg of o-chlorobenzoic acid and 0.96 kg of methanol obtained in step S2 were mixed, stirred for 2.5 h, 0.16 kg of catalyst A was added, heated to 70 ° C, reacted for 4 h, cooled to room temperature, extracted with toluene twice, washed with deionized water three times, and the upper phase after standing and stratification was methyl o-chlorobenzoate.

[0079] Example 3

[0080] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene comprises the following steps:

[0081] S1. 1 kg of o-chlorotoluene, 3.5 kg of acetic acid and 80 g of supported catalyst A were added to a mixing kettle, heated to 120 ° C, and stirred for 1.5 h to obtain a mixed solution;

[0082] S2. The mixed solution obtained in step S1 was poured into a reactor, air was introduced at a rate of 30 L / min, pressurized to 1.0 MPa, heated to 180°C, reacted for 2 h, discharged, cooled to room temperature, filtered, washed with deionized water 3 times, and distilled to obtain o-chlorobenzoic acid;

[0083] S3. 0.8 kg of o-chlorobenzoic acid and 1.2 kg of methanol obtained in step S2 were mixed, stirred for 1.5 h, 0.24 kg of catalyst A was added, heated to 90 ° C, reacted for 2 h, cooled to room temperature, extracted twice with toluene, washed three times with deionized water, and the upper phase after standing and stratification was methyl o-chlorobenzoate.

[0084] Example 4

[0085] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of supported catalyst B is used to replace supported catalyst A.

[0086] Example 5

[0087] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of supported catalyst C is used to replace supported catalyst A.

[0088] Example 6

[0089] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of supported catalyst D is used to replace supported catalyst A.

[0090] Example 7

[0091] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of catalyst B is used to replace catalyst A.

[0092] Example 8

[0093] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that the added amount of supported catalyst A is 15g.

[0094] Example 9

[0095] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation manner is the same as that of Example 1, except that the rate of introducing air in step S2 is 10 L / min.

[0096] Example 10

[0097] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation manner is the same as that of Example 1, except that the pressure after pressurization in step S2 is 0.5 MPa.

[0098] Comparative Example 1

[0099] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of commercially available cobalt acetate is used to replace the supported catalyst A.

[0100] Comparative Example 2

[0101] A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, the specific implementation method is the same as that of Example 1, except that an equal amount of commercially available 20wt% oleum is used to replace catalyst A.

[0102] Effect evaluation:

[0103] The methyl o-chlorobenzoate synthesized in the above Examples 1-10 and Comparative Examples 1-2 was tested and the purity was determined by gas chromatography. The specific results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] From the results in Table 1, it can be seen that the yield and purity of methyl o-chlorobenzoate prepared in Examples 1-3 are high and have good application value.

[0108] Compared with Example 1, in Example 4, the molar ratio of N-allylimidazole and 1,9-dibromononane was changed when preparing the supported catalyst, and the steric hindrance of the formed porogen was reduced. Compared with Example 1, in Example 6, no porogen was introduced when preparing the supported catalyst, and the steric hindrance was reduced; both of them would reduce the stability of the catalyst, affect the formation of o-chlorobenzoic acid, and further affect the yield and purity of methyl o-chlorobenzoate.

[0109] Compared with Example 1, in the preparation of the supported catalyst, the mass ratio of the modified pseudo-boehmite carrier, the cobalt acetate in the cobalt acetate aqueous solution and the palladium chloride in the palladium chloride aqueous solution was changed in Example 5; and compared with Example 1, in the preparation of the catalyst, the mass ratio of the activated carbon and the phosphotungstic acid was changed in Example 7, both of which would deteriorate the stability of the load and cause uneven contact with the reaction solution, thereby affecting the yield and purity.

[0110] Compared with Example 1, Example 8 changes the mass ratio of o-chlorotoluene, acetic acid and supported catalyst, which affects the catalytic activity and further affects the yield and purity of methyl o-chlorobenzoate.

[0111] Compared with Example 1, Example 9 changed the rate of air introduction, and Example 10 changed the pressure after pressurization compared with Example 1. The change in reaction conditions reduced the yield and purity of methyl o-chlorobenzoate.

[0112] Compared with Example 1, Comparative Example 1 uses an equal amount of cobalt acetate to replace supported catalyst A, and Comparative Example 2 uses an equal amount of 20 wt % oleum to replace catalyst A, which not only reduces the activity of different reactions, but also affects the yield and purity of the reaction.

[0113] The above is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present application. Although the present application is disclosed as above in the preferred embodiment, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution.

Claims

1. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene, characterized in that: The following steps are included: S1. Add o-chlorotoluene, acetic acid and supported catalyst into a mixing kettle, heat to 60-120 ° C, stir to obtain a mixed solution; S2. Pour the mixed solution obtained in step S1 into a reactor, introduce air to pressurize, heat to 130-180°C, react for 2-4h, discharge, cool, filter, wash, and distill to obtain o-chlorobenzoic acid; S3. The o-chlorobenzoic acid and methanol obtained in step S2 are mixed, stirred, a catalyst is added, heated to 70-90° C., reacted for 2-4 hours, cooled, extracted, washed, and the upper phase after standing and stratification is methyl o-chlorobenzoate.

2. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 1, characterized in that: The mass ratio of o-chlorotoluene, acetic acid and supported catalyst in step S1 is 1:(1.5-3.5):(0.02-0.08).

3. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 1, characterized in that: The method for preparing the supported catalyst in step S1 comprises the following steps: (1) adding N-allylimidazole, 1,9-dibromononane and acetonitrile to a first reaction kettle, heating to 60-90° C., stirring and reacting for 18-24 hours, cooling to 0-2° C., filtering and washing the precipitate, drying and grinding to obtain a porogen for later use; preparing a cobalt acetate aqueous solution and a palladium chloride aqueous solution for later use; (2) adding the porogen, pseudo-boehmite and deionized water obtained in step (1) into a second reaction kettle, heating to 140-150° C. and stirring for 20-24 hours, cooling, washing and drying to obtain a modified pseudo-boehmite carrier; (3) impregnating the modified pseudo-boehmite support obtained in step (2) into the cobalt acetate aqueous solution obtained in step (1), stirring magnetically for 1-2 hours, and drying to obtain a product; (4) The product obtained in step (3) is immersed in the aqueous palladium chloride solution obtained in step (1), magnetically stirred for 1-2 hours, dried, and calcined to obtain a supported catalyst.

4. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 3, characterized in that: The molar ratio of N-allylimidazole to 1,9-dibromononane in step (1) is (2.1-2.6):

1.

5. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 3, characterized in that: The mass ratio of the modified pseudo-boehmite carrier, the cobalt acetate in the cobalt acetate aqueous solution and the palladium chloride in the palladium chloride aqueous solution in step (3) and step (4) is 1: (0.04-0.06): (0.02-0.04).

6. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 1, characterized in that: The rate of introducing air in step S2 is 20-30 L / min.

7. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 1, characterized in that: The pressure after pressurization in step S2 is 0.7-1.0 MPa.

8. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 1, characterized in that: The method for preparing the catalyst in step S3 comprises the following steps: Disperse phosphotungstic acid and activated carbon in deionized water, heat to 80-90°C, stir and react for 5-6h, filter and dry to obtain a catalyst.

9. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to claim 8, characterized in that: The mass ratio of the activated carbon to phosphotungstic acid is 1:(0.7-1.2).

10. A method for preparing methyl o-chlorobenzoate from o-chlorotoluene according to any one of claims 1 to 9, characterized in that: The yield of the prepared methyl o-chlorobenzoate is not less than 96.5%, and the purity is not less than 98%.

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