A method for brominating toluene into p-bromotoluene using a phosphorus-vanadium catalyst

Abstract

The invention relates to a method for brominating toluene into para-bromotoluene using a phosphorus-vanadium catalyst. First, ammonium metavanadate and a phosphoric acid aqueous solution are mixed, then poured into a prepared dicyandiamide aqueous solution, and activated carbon is added. After drying, the mixture is calcined at high temperature under a protective atmosphere to obtain a phosphorus-vanadium catalyst. Then, using the phosphorus-vanadium catalyst, toluene, hydrobromic acid, and hydrogen peroxide are added into a Shrek tube, and the product para-bromotoluene is reacted at a certain reaction temperature. The catalyst has a simple preparation method, catalyzes the highly selective bromination of toluene to prepare para-bromotoluene, has a good catalytic effect, is easy to recycle and reuse, and has a good industrial application prospect.

Description

Technical Field

[0001] The invention relates to a method for brominating toluene into p-bromotoluene using a phosphorus-vanadium catalyst. Background Art

[0002] Previous studies on vanadium-based catalysts, such as Shaanxi University of Science and Technology, disclosed a supported vanadium-based catalyst and its preparation method. First, ammonium metavanadate and sucrose were mixed in a mass ratio of 1:28 to 1:108 and added to distilled water, stirred to completely dissolve to obtain solution A, and then phosphoric acid solution was added to solution A to obtain solution B; then solution B was placed in a hydrothermal kettle and heated to produce a hydrothermal reaction to obtain a carbide; finally, the carbide was washed with ethanol and distilled water in turn until the filtrate was colorless and transparent and then dried to obtain a supported vanadium-based catalyst. The defect of this phosphorus-vanadium catalyst is that it needs to be completed by a hydrothermal method, and the production process is complicated. In addition, Nanjing University also disclosed a supported vanadium-phosphorus-oxygen catalyst for the condensation of acetic acid and formaldehyde to prepare acrylic acid and methyl acrylate, and its preparation method and application. It is by using ammonium metavanadate as a vanadium source, phosphoric acid as a phosphorus source, and water as a solvent medium, and loading it on a silicon-based carrier material (MCM-41, SBA-15, gas-phase SiO2 and multi-level porous SiO2 microspheres) by a simple deposition method, and then calcining in an air atmosphere to obtain the final catalyst. The drawbacks of this phosphorus-vanadium catalyst preparation are high production costs and a long catalyst production cycle.

[0003] p-Bromotoluene is mainly used as an important raw material for the synthesis of pharmaceutical intermediates such as p-bromobenzyl bromide, p-bromophenylacetonitrile, p-bromotrifluorotoluene, p-bromocinnamic acid, p-bromobenzaldehyde, and p-bromobenzoic acid. It is widely used in many organic syntheses in China. p-Bromotoluene is an important organic synthesis raw material used in dye and pharmaceutical synthesis industries. High-purity p-Bromotoluene is an intermediate of Losantan, an important best-selling drug and an antihypertensive drug. The synthesis of p-Bromotoluene mainly includes two routes: toluene bromination and the Sandmeyer reaction of p-toluidine. There are many literature reports on the toluene bromination pathway, most of which are catalytic bromination, with harsh conditions, resulting in isomeric mixtures that are difficult to separate. Using the Sandmeyer reaction as the reaction path, Gao Chunxiang, Yang Xiyue and others selected a scheme using copper sulfate pentahydrate, sodium bromide, sodium sulfite, and sulfuric acid as raw materials to prepare CuBr-2HBr solution. The total yield of the obtained product was 66.4%, the production cycle was 4h, and the product purity was >99.5%. This experiment shortened the production cycle, reduced production costs, and improved product quality.

[0004] Li Jiguo, Hu Weihua and others used p-toluidine as raw material and adopted a two-step reaction method to prepare high-purity p-bromotoluene. This process uses a unique process method based on the traditional process to change the reaction conditions and inhibit the formation of o-bromotoluene and m-bromotoluene. The product yield is 76% and the product content is ≥99 9%. The disadvantage of this method of obtaining p-bromotoluene is that the product yield is relatively low.

[0005] Yizhi Yuan et al. reported a Pd-catalyzed direct ortho-CH bromination method with DMSO as a mild oxidant and HBr as a bromide source to incorporate bromine atoms with different selectivities from previous metal-free electrophilic aromatic halogenation reactions. The CH bromination of 2-phenylpyridine and its derivatives was studied with good to excellent efficiency and high selectivity. Zhuang Ma et al. proposed a tungstate-catalyzed biomimetic oxidative halogenation of (Br, Cl, I) (hetero)arenes, which has the advantages of low price, environmentally friendly and operation-friendly manner, as well as a wide range of substrates, diverse functional group tolerance, and good chemical and regioselectivity.

[0006] As one of the most useful building blocks in organic synthesis, (hetero)aryl halides are widely used for transformations such as cross-coupling (e.g., Suzuki coupling, Buchwald-Hartwig coupling, Ullman coupling) (Johansson et al., 2012). Traditional methods for introducing halides (Br, Cl, I) onto (hetero)arenes rely heavily on the use of various reagents such as chlorine, bromine, iodine, NCS, NBS, tBuOCl, and Palau'chlor4 (Rodriguez et al., 2014). The Sandmeyer reaction (Kumar et al., 2012) is another common method for the preparation of (hetero)aryl halides. However, multiple steps, large amounts of chemical waste, and harsh reaction conditions are necessary.

[0007] Oxidative halogenation is an important alternative approach (Podgorsek et al., 2009), such as transition metal (TM)-catalyzed C-H bond functionalization (Petrone et al., 2016), photo / electrocatalysis (Br, Cl) (Hering et al., 2016; Yuan et al., 2019; Liang et al., 2019) and HX (X = Br, Cl) / oxidant (Fosu et al., 2019; Srivastava et al., 1996; Ross and Burrows, 1987; Ben-Daniel et al., 2003). Despite significant progress, there is still much room for improvement.

[0008] In addition, even under mild conditions, complex molecules can be cleaved with high selectivity by enzymes such as metalloenzymes and flavoenzymes using nucleophilic halides (Latham et al., 2018; Butler and Sandy, 2009; Gkotsi et al., 2018; Vailncourt et al., 2006). However, due to the limited substrate range, the high requirements for maintaining enzyme activity (solvent, temperature, pH, etc.), and the inconvenience of large-scale separation processes, its industrial application still needs to be improved in many aspects. Summary of the invention

[0009] The present invention provides a method for preparing a green, environmentally friendly and highly active phosphorus-vanadium catalyst in order to improve the deficiencies of the prior art, and also provides a method for brominating toluene into para-bromotoluene using the phosphorus-vanadium catalyst.

[0010] The technical scheme of the present invention is: a method for preparing para-bromotoluene by catalyzing toluene, and the specific steps are as follows: a) preparing a phosphorus-vanadium catalyst: using ammonium metavanadate and a phosphoric acid aqueous solution to mix, then pouring into a prepared dicyandiamide aqueous solution, adding activated carbon and stirring; after drying, calcining at high temperature under a protective atmosphere to obtain the phosphorus-vanadium catalyst; b) preparing para-bromotoluene: adding toluene, hydrobromic acid, hydrogen peroxide, and the phosphorus-vanadium catalyst prepared in step a) into a reaction apparatus, reacting at a certain reaction temperature to obtain the product para-bromotoluene.

[0011] Preferably, in step a), the mass of phosphorus in the phosphorus-vanadium catalyst accounts for 9% to 13% of the total mass of the catalyst, and the mass of vanadium accounts for 8% to 10% of the total mass of the catalyst.

[0012] Preferably, in step a), the molar ratio of ammonium metavanadate to dicyandiamide to phosphoric acid is 1:(2-3):(1.5-2), and the mass ratio of dicyandiamide to activated carbon is (1.1-3.4):1.

[0013] Preferably, the stirring time in step a) is 4 to 5 hours; the high temperature calcination temperature is 500 to 700° C., and the calcination time is 1 to 2 hours.

[0014] Preferably, the added mass of the phosphorus-vanadium catalyst in step b) is 10% to 11% of the mass of toluene.

[0015] Preferably, in step b), the amount of hydrobromic acid added is 1 to 1.1 times the molar amount of toluene; the amount of hydrogen peroxide added is 2 to 2.5 times the molar amount of toluene; the reaction temperature is 20 to 25° C.; and the reaction time is 0.5 to 1 h.

[0016] The principle of the present invention is as follows:

[0017]

[0018] Beneficial effects:

[0019] The phosphorus-vanadium catalyst provided by the invention has a simple preparation method and a high specific surface area, and when used in the preparation of p-bromotoluene, it has high reaction activity and is easy to recycle and reuse, and is very suitable for industrial production. DETAILED DESCRIPTION

[0020] Implementation case 1: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0021] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined at 600°C in a tubular furnace for 2 hours to obtain 1.21 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 11% of the total mass of the catalyst and vanadium accounted for 8% of the total mass of the catalyst.

[0022] Implementation Case 2:

[0023] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (10 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.46 g of p-bromotoluene with a yield of 85%.

[0024] Implementation Case 3:

[0025] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 2.4 g (20 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.37 g of p-bromotoluene with a yield of 80%.

[0026] Implementation Case 4:

[0027] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 90 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.55 g of p-bromotoluene with a yield of 90%.

[0028] Implementation Case 5:

[0029] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 20 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.4 g of p-bromotoluene with a yield of 82%.

[0030] Implementation Case 6:

[0031] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25 degrees for 0.5 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.37 g of p-bromotoluene with a yield of 80%.

[0032] Implementation Case 7:

[0033] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.7 g of p-bromotoluene with a yield of 99%. The catalyst was washed with ethyl acetate and dried for later use.

[0034] Implementation Case 8:

[0035] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 7. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0036] Implementation Case 9:

[0037] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst in Example 8. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.632 g of p-bromotoluene with a yield of 96%. The catalyst was washed with ethyl acetate and dried for later use.

[0038] Implementation Case 10:

[0039] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst in Example 9. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0040] Implementation Case 11:

[0041] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 10. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.581 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0042] Implementation Case 12:

[0043] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 11. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.547 g of p-bromotoluene with a yield of 91%.

[0044] Implementation Case 13: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0045] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined at 700°C in a tubular furnace for 2 hours to obtain 1.18 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 11% of the total mass of the catalyst and vanadium accounted for 9% of the total mass of the catalyst.

[0046] Implementation Case 14:

[0047] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 13. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%.

[0048] Implementation Case 15:

[0049] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 14. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.581 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0050] Implementation Case 16:

[0051] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 15. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.581 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0052] Implementation Case 17:

[0053] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 16. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.53 g of p-bromotoluene with a yield of 90%. The catalyst was washed with ethyl acetate and dried for later use.

[0054] Implementation Case 18:

[0055] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 17. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.496 g of p-bromotoluene with a yield of 88%. The catalyst was washed with ethyl acetate and dried for later use.

[0056] Implementation Case 19:

[0057] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 18. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.445 g of p-bromotoluene with a yield of 85%.

[0058] Implementation Case 20: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0059] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined in a tubular furnace at 500°C for 2 hours to obtain 1.25 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 10% of the total mass of the catalyst and vanadium accounted for 8% of the total mass of the catalyst.

[0060] Implementation Case 21:

[0061] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 20. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.37 g of p-bromotoluene with a yield of 80%.

[0062] Implementation Case 22: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0063] 0.34 g (4 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined at 600°C in a tubular furnace for 2 hours to obtain 1.07 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 12% of the total mass of the catalyst and vanadium accounted for 9% of the total mass of the catalyst.

[0064] Implementation Case 23:

[0065] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 22. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.59 g of p-bromotoluene with a yield of 94%.

[0066] Implementation Case 24:

[0067] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 23. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.411 g of p-bromotoluene with a yield of 83%. The catalyst was washed with ethyl acetate and dried for later use.

[0068] Implementation Case 25:

[0069] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 24. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.408 g of p-bromotoluene with a yield of 83%. The catalyst was washed with ethyl acetate and dried for later use.

[0070] Implementation Case 26:

[0071] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 25. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.39 g of p-bromotoluene with a yield of 82%. The catalyst was washed with ethyl acetate and dried for later use.

[0072] Implementation Case 27:

[0073] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 26. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.34 g of p-bromotoluene with a yield of 79%. The catalyst was washed with ethyl acetate and dried for later use.

[0074] Implementation Case 28:

[0075] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 27. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.29 g of p-bromotoluene with a yield of 76%.

[0076] Implementation Case 29: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0077] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined in a tubular furnace at 600°C for 1 hour to obtain 1.28 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 10% of the total mass of the catalyst and vanadium accounted for 7% of the total mass of the catalyst.

[0078] Implementation Case 30:

[0079] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 29. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.3 g of p-bromotoluene with a yield of 78%.

[0080] Implementation Case 31: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0081] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 4 hours, the mixture was dried in a vacuum oven, and calcined at 600°C in a tubular furnace for 2 hours to obtain 1.21 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 11% of the total mass of the catalyst and vanadium accounted for 8% of the total mass of the catalyst.

[0082] Implementation Case 32:

[0083] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 31. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.6 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0084] Implementation Case 33:

[0085] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 32. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0086] Implementation Case 34:

[0087] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 33. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.58 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0088] Implementation Case 35:

[0089] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 34. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0090] Implementation Case 36:

[0091] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 35. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.581 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0092] Implementation Case 37:

[0093] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 36. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.547 g of p-bromotoluene, with a yield of 91%.

[0094] Implementation Case 38: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0095] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.15 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.4 g (4 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, the mixture was dried in a vacuum oven, and calcined at 600°C in a tubular furnace for 2 hours to obtain 1.1 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 13% of the total mass of the catalyst and vanadium accounted for 10% of the total mass of the catalyst.

[0096] Implementation Case 39:

[0097] 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added to a 50 ml round-bottom flask, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 38. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.58 g of p-bromotoluene with a yield of 93%. The catalyst was washed with ethyl acetate and dried for later use.

[0098] Implementation Case 40:

[0099] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 39. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.598 g of p-bromotoluene with a yield of 94%. The catalyst was washed with ethyl acetate and dried for later use.

[0100] Implementation Case 41:

[0101] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 40. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.54 g of p-bromotoluene with a yield of 91%. The catalyst was washed with ethyl acetate and dried for later use.

[0102] Implementation Case 42:

[0103] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 41. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.5 g of p-bromotoluene with a yield of 88%. The catalyst was washed with ethyl acetate and dried for later use.

[0104] Implementation Case 43:

[0105] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 42. The mixture was stirred at room temperature of 25 degrees for 1 hour. After the reaction, the mixture was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.45 g of p-bromotoluene with a yield of 85%. The catalyst was washed with ethyl acetate and dried for later use.

[0106] Implementation Case 44:

[0107] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the dried catalyst of Example 43. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.44 g of p-bromotoluene with a yield of 85%.

[0108] Implementation Case 45: Preparation of phosphorus-vanadium catalyst using ammonium metavanadate as vanadium source.

[0109] 0.5 g (6 mmol) of dicyandiamide was dissolved in 10 ml of water, heated to 60°C, 0.3 g of activated carbon was added to obtain a mixed solution A, 0.23 g (2 mmol) of ammonium metavanadate was dissolved in 10 ml of water, 0.3 g (3 mmol) of phosphoric acid was added, the mixture was heated to 60°C and stirred for 30 minutes to obtain a solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 4 hours, the mixture was dried in a vacuum oven, and calcined at 600°C in a tubular furnace for 2 hours to obtain 1.21 g of a phosphorus-vanadium catalyst, in which phosphorus accounted for 9% of the total mass of the catalyst and vanadium accounted for 8% of the total mass of the catalyst.

[0110] Implementation Case 46:

[0111] In a 50 ml round-bottom flask, 0.92 g (10 mmol) of toluene and 2.02 g (11 mmol) of hydrobromic acid were added respectively, followed by 3 g (25 mmol) of hydrogen peroxide and 100 mg of the catalyst prepared in Example 45. The mixture was stirred at room temperature of 25 degrees for 1 h. After the reaction, it was extracted with ethyl acetate, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 1.48 g of p-bromotoluene with a yield of 87%.

[0112] The catalyst washed and dried after the reaction in Implementation Case 2 was reused. The process flow is consistent with the implementation case, and the catalyst recycling and use are shown in the following table:

[0113] Recycling times Yield of p-bromotoluene 1 94％ 2 96％ 3 94％ 4 93％ 5 91％

[0114] The catalyst washed and dried after the reaction in Implementation Case 14 was reused. The process flow is consistent with the implementation case, and the catalyst recovery and use are as shown in the following table:

[0115] Recycling times Yield of p-bromotoluene 1 93％ 2 93％ 3 90％ 4 88％ 5 85％

[0116] The catalyst washed and dried after the reaction in Implementation Case 22 was reused. The process flow is consistent with the implementation case, and the catalyst recovery and use are as shown in the following table:

[0117] Recycling times Yield of p-bromotoluene 1 94％ 2 83％ 3 82％ 4 79％ 5 76％

[0118] The catalyst washed and dried after the reaction in Implementation Case 31 was reused. The process flow is consistent with the implementation case, and the catalyst recycling and use are as follows:

[0119] Recycling times Yield of p-bromotoluene 1 94％ 2 94％ 3 93％ 4 94％ 5 91％

[0120] The catalyst washed and dried after the reaction in Implementation Case 38 was reused. The process flow is consistent with the implementation case, and the catalyst recycling and use are as follows:

[0121] Recycling times Yield of p-bromotoluene 1 93％ 2 94％ 3 91％ 4 88％ 5 88％

Claims

1. A method for preparing p-bromotoluene by catalyzing toluene, the specific steps of which are as follows: a) preparing a phosphorus-vanadium catalyst: using ammonium metavanadate and phosphoric acid aqueous solution to mix, then pouring into a prepared dicyandiamide aqueous solution, adding activated carbon and stirring; after drying, calcining at high temperature under a protective atmosphere to obtain the phosphorus-vanadium catalyst; wherein the molar ratio of ammonium metavanadate to dicyandiamide to phosphoric acid is 1:(2-3):(1.5-2), and the mass ratio of dicyandiamide to activated carbon is (1.1-3.4):1; b) preparing p-bromotoluene: adding toluene, hydrobromic acid, hydrogen peroxide, and the phosphorus-vanadium catalyst prepared in step a) into a reaction apparatus, reacting at a certain reaction temperature to obtain the product p-bromotoluene.

2. The method according to claim 1, characterized in that: In step a), the mass of phosphorus in the phosphorus-vanadium catalyst accounts for 9% to 13% of the total mass of the catalyst, and the mass of vanadium accounts for 8% to 10% of the total mass of the catalyst.

3. The method according to claim 1, characterized in that: In step a), the stirring time is 4 to 5 hours; the high temperature calcination temperature is 500 to 700° C., and the calcination time is 1 to 2 hours.

4. The method according to claim 1, characterized in that: The added mass of the phosphorus-vanadium catalyst in step b) is 10% to 11% of the mass of toluene.

5. The method according to claim 1, characterized in that: In step b), the amount of hydrobromic acid added is 1 to 1.1 times the molar amount of toluene; the amount of hydrogen peroxide added is 2 to 2.5 times the molar amount of toluene; the reaction temperature is 20 to 25° C.; and the reaction time is 0.5 to 1 h.

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