A method for preparing p-bromotoluene by using toluene catalyzed by niobium

Abstract

The present invention relates to a method for preparing p-bromotoluene by using toluene catalyzed by niobium. A supported niobium oxide catalyst is used, toluene, hydrobromic acid and hydrogen peroxide are added into a reactor, and the product p-bromotoluene is obtained by reaction at a certain reaction temperature. The process is simple to operate, has a high utilization rate of bromine atoms and little pollution. The niobium catalyst used has a simple preparation method, is stable in strong acid, can be recycled multiple times without deactivation, has high product selectivity, good catalytic effect, and has good industrial application prospects.

Description

Technical Field

[0001] The invention relates to a method for preparing p-bromotoluene, in particular to a method for oxidative bromination of toluene catalyzed by niobium to produce p-bromotoluene. Background Art

[0002] Niobic acid and niobium oxide can be used as active components, additives or carriers of catalysts, and have achieved good results in a variety of reactions, especially in reactions involving or generating water molecules, showing excellent stability. 2+ Preparation and Photocatalytic Performance of Doped C / Nb2O5 Nanocatalysts[J]" (Journal of Chemistry in Higher Education, 2018, 39(2):319-326) discloses a Zn-doped C / Nb2O5 nanocatalyst prepared by hydrothermal technology. First, niobium chloride is dissolved in a mixture of ethanol and acetic acid, and then zinc acetate is added. After the solution becomes clear and transparent, it is transferred to a polytetrafluoroethylene reactor, and then crystallized at high temperature for 48 hours. After drying, it is calcined in air for 2 hours to obtain Zn-doped Nb2O5 / C material. The disadvantage of this catalyst preparation is that it needs to be completed by high-temperature hydrothermal method, and the preparation process is complicated. Yuanzhi Hong et al. in "Efficient and stable Nb2O5 modified g-C3N4 photocatalyst for removal ofantibiotic pollutant[J]"

[0003] (Chemical Engineering Journal, 2016, 29974-84) synthesized Nb2O5 / g-C3N4 photocatalyst by one-step method. Melamine and Nb2O5 were put into an agate mortar and ground together for 5 minutes. After that, the ground powder was transferred to an alumina crucible and then calcined at 550°C for 4 hours in an air atmosphere. The preparation defects of this catalyst are that the catalyst has a small specific surface area, a narrow absorption range, and a low yield after high-temperature calcination of melamine, which is not suitable for mass production.

[0004] Organic bromides are important intermediates for the synthesis of fine chemicals such as pharmaceuticals, pesticides and dyes. High-purity p-bromotoluene is an intermediate for the important best-selling drug, the antihypertensive drug Losantan. However, traditional bromination reagents such as bromine and N-bromosuccinimide (NBS) produce hydrogen bromide in the bromination reaction, which not only has low atom economy and poor reaction selectivity, but also causes environmental pollution.

[0005] Guo Jianguo et al. introduced a green bromination method in invention patent CN105669364: using hydrobromic acid and sodium hypochlorite as bromine sources and ferric chloride as catalyst, para-bromotoluene can be prepared with high selectivity. However, the use of metal catalysts increases the cost and the post-processing recovery is cumbersome.

[0006] In the article "Study on the Oxidative Bromination of Toluene" (Journal of Zhejiang University of Technology, 2011, 39(4): 369-371, 398), Ju Jie et al. used toluene as raw material, hydrogen peroxide as oxidant, hydrobromic acid as bromination reagent, and reacted at room temperature under 60W incandescent light. The yield of the main product benzyl bromide was 69.9%, and the oxidized product benzaldehyde was 1.3%. This method has the characteristics of high bromine atom utilization and low pollution. This method uses photocatalysis and has a low product yield.

[0007] According to the previous method of the same research group, Huang Jun, Xu Dandan and others provided a method for preparing bromoanisole by oxidation bromination in the invention patent CN114751809A, in which hydrobromic acid was oxidized under the action of a catalyst and hydrogen peroxide to bromoanisole to obtain p-bromoanisole. The phosphotungstic acid catalyst used can be reused and has a good industrial application prospect. However, phosphotungstic acid is unstable in strong acid and easily decomposed. And the catalyst preparation cost is high.

[0008] Ali Pourjavadi et al. reported in "Gold-Decorated 3D 2,6-Diaminopyridine Network: A Robust Catalyst for the Bromination of Aromatic Compounds[J]" (INDUSTRIAL&ENGINEERING CHEMISTRY RESEARCH, 2018, 57(37): 12314-12322) that a magnetic heterogeneous catalyst was synthesized by modifying gold ions onto a cross-linked polymer nanocomposite prepared from 2,6-diaminopyridine. The aromatic compound was then brominated using N-bromosuccinimide as a bromine source. The reaction lasted for 7 hours and the yield of p-bromotoluene could reach 87%. The catalyst has the advantages of high yield, high gold loading, good stability, and easy recycling. However, the bromination reaction will generate excessive hydrogen bromide, which pollutes the environment.

[0009] M. Ghiaci et al. in "Regioselective bromination of organic substrates by LDH-CO3 2--Br-promoted by V2O5-H2O2[J]" (APPLIED CATALYSIS A-GENERAL, 2010, 384(1-2):18-26) designed a new heterogeneous catalytic system to generate LDH-CO3 in situ 2– -Br3 - , used for para-selective bromination of aromatic compounds. 2- -Br(LDH-CO3 2- -Br) is a bromide source, V2O5 is a promoter, and hydrogen peroxide is an oxidant to prepare a catalytic system. The phase transfer catalyst reacts at room temperature for 3 hours, and the yield of toluene to form para-bromotoluene can reach 90%. And the loss of catalytic effect after four times of recycling is not obvious. The preparation method of the layered double hydroxide bromine source in this method is cumbersome, and the in-situ generation takes a long time. Summary of the invention

[0010] The purpose of the present invention is to improve the problem that the phosphotungstic acid and phosphorus vanadium supported carbon and nitrogen material catalysts prepared by the prior art (including the previous technology of the research group) are unstable in strong acid and have high preparation costs, and a process method for niobium catalyzed oxidative bromination of toluene to para-bromotoluene is invented. The present invention uses a simple method to immobilize niobium oxalate on the carbon and nitrogen material, solves the shortcomings of the traditional niobium oxide catalyst, such as complex production process, low yield, small specific surface area, and narrow light absorption range, and realizes a catalyst with high yield and high specific surface area. The catalyst can be stable in strong acid for multiple times without deactivation. It is applied to the preparation process of para-bromotoluene, with simple reaction operation, high product yield, high bromine atom utilization rate, green environmental protection and low pollution.

[0011] The technical scheme of the present invention is: a method for preparing para-bromotoluene by using niobium to catalyze toluene, and the specific steps are as follows: a) preparing a niobium oxide-supported carbon-nitrogen material catalyst: preparing a niobium oxide-supported carbon-nitrogen material catalyst by loading and calcining niobium oxalate and a nitrogen source solution, wherein niobium pentoxide accounts for 16% to 25% of the total mass of the catalyst; b) preparing para-bromotoluene: adding toluene, hydrobromic acid, hydrogen peroxide and the niobium oxide-supported carbon-nitrogen material catalyst prepared in step a) into a reactor, and reacting at a certain temperature to obtain para-bromotoluene.

[0012] The specific steps for preparing the niobium oxide-supported carbon-nitrogen material catalyst in the preferred step a) are: adding a nitrogen source to deionized water, heating until dissolved, and then adding activated carbon to the solution to prepare solution A; adding niobium oxalate to the aqueous solution, then adding nitric acid to adjust the pH to 2-3, and heating to dissolve to form solution B; adding solution B to solution A under stirring; stirring for 4-5 hours, drying, and calcining at high temperature to obtain a niobium oxide-supported carbon-nitrogen material catalyst, wherein niobium pentoxide accounts for 16% to 25% of the total mass of the catalyst.

[0013] Preferably, the mass ratio of the nitrogen source to the activated carbon is (0.168-0.5):1; the molar ratio of niobium oxalate to the nitrogen source reagent is 1:(0.9-2.5).

[0014] Preferably, the high temperature calcination temperature is 500-700° C. and the calcination time is 1-2 hours.

[0015] Preferably, the nitrogen source in step a) is dicyandiamide, adenine or diaminomaleonitrile.

[0016] Preferably, in step b), the amount of hydrobromic acid added is 0.8-1.2 times the molar amount of toluene, and the amount of hydrogen peroxide added is 0.9-1.2 times the molar amount of toluene; the added mass of the niobium oxide-supported carbonitride material catalyst is 8.6% to 12% of the mass of toluene.

[0017] Preferably, the reaction temperature in step b) is 20-30° C. and the reaction time is 3-5 h.

[0018]

[0019] The niobium oxide-supported carbon-nitrogen material catalyst prepared by the present invention can also be applied to the bromination of benzene and naphthalene, and the method is as follows:

[0020] (1) Add a certain amount of substrate benzene into the reactor, add hydrobromic acid and hydrogen peroxide in sequence, add the above-mentioned niobium catalyst, and react at 50-60° C. for 5 hours to obtain the corresponding oxidative bromination product bromobenzene with a yield of 67-84%.

[0021] (2) A certain amount of substrate naphthalene was added to the reactor, followed by hydrobromic acid and hydrogen peroxide, and the above-mentioned niobium catalyst. The reaction was carried out at 40° C. for 5 hours to obtain the corresponding oxidative bromination product 1-bromonaphthalene with a yield of 92%.

[0022]

[0023] Beneficial effects:

[0024] The present invention provides a process for preparing para-bromotoluene by oxidative bromination of toluene, which has the advantages of simple reaction operation, high product yield, high bromine atom utilization rate, green environmental protection and low pollution, etc. The niobium oxide catalyst used is a heterogeneous catalyst, which has a simple preparation method, high specific surface area, stability in strong acid, easy recycling and easy large-scale production. DETAILED DESCRIPTION

[0025] Implementation Case 1: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0026] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0027] Implementation Case 2-4:

[0028] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 113g (1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred and reacted at room temperature (25°C) for 3h, 4h and 5h, respectively. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined and the solvent was evaporated under reduced pressure to obtain 115g (0.672mol) of p-bromotoluene with a yield of 84%, 126g (0.736mol) with a yield of 92% and 128.6g (0.752mol) with a yield of 94%.

[0029] Implementation Case 5-7:

[0030] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 100g (0.9mol); 124g (1.1mol); 136g (1.2mol) hydrogen peroxide, and 10g of the catalyst prepared in Example 1. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 119g (0.696mol) of p-bromotoluene, with a yield of 87%; 131g (0.768mol), with a yield of 96%; and 131g (0.768mol), with a yield of 96%. The catalyst after centrifugation was washed with ethyl acetate several times, dried and set aside.

[0031] Implementation Case 8:

[0032] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 6. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0033] Implementation Case 9:

[0034] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst in Example 8. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0035] Implementation Case 10:

[0036] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst in Example 9. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 128.6g (0.752mol) of p-bromotoluene with a yield of 94%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0037] Implementation Case 11:

[0038] 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added to a 5L round-bottom flask, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 10. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 128.6g (0.752mol) of p-bromotoluene with a yield of 94%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0039] Implementation Case 12:

[0040] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added respectively, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 11. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined and the solvent was evaporated under reduced pressure to obtain 128.6g (0.752mol) of p-bromotoluene with a yield of 94%.

[0041] Implementation Cases 13-15:

[0042] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide, and 8g, 9g, and 11g of the catalyst prepared in Example 1 were added, respectively. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined and the solvent was evaporated under reduced pressure to obtain 123g (0.72mol) of p-bromotoluene with a yield of 90%, 126g (0.736mol) with a yield of 92%, and 131g (0.768mol) with a yield of 96%.

[0043] Implementation Cases 16-18:

[0044] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred and reacted at 20°C, 23°C and 30°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined and the solvent was evaporated under reduced pressure to obtain 113g (0.664mol) of p-bromotoluene with a yield of 83%, 120g (0.704mol) with a yield of 88% and 131g (0.768mol) with a yield of 96%.

[0045] Implementation Case 19: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0046] 50 g (0.6 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60°C, and 100 g of activated carbon was added to obtain a mixed solution A. 140 g (0.26 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, and the mixture was heated to 60°C and stirred until completely dissolved to obtain a yellow-green transparent solution B. The solution B was added dropwise to the mixed solution A, and stirring was continued for 5 hours. The mixture was dried in a vacuum oven and calcined at 600°C in a muffle furnace for 2 hours to obtain 156 g of niobium oxide catalyst, in which niobium pentoxide accounted for 22% of the total mass of the catalyst.

[0047] Implementation Case 20:

[0048] 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added to a 5L round-bottom flask, followed by 124g (1.1mol) hydrogen peroxide and 10g of the catalyst prepared in Example 19. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0049] Implementation Case 21:

[0050] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 20. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0051] Implementation Case 22:

[0052] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 21. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0053] Implementation Case 23:

[0054] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 22. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0055] Implementation Case 24:

[0056] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 23. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 128g (0.748mol) of p-bromotoluene with a yield of 93.5%. The centrifuged catalyst was washed with 5ml ethyl acetate several times, dried and set aside.

[0057] Implementation Case 25:

[0058] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 24. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined and the solvent was evaporated under reduced pressure to obtain 128g (0.748mol) of p-bromotoluene with a yield of 93.5%.

[0059] Implementation Case 26: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0060] 16.8 g (0.2 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 115 g (0.214 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 130 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0061] Implementation Case 27:

[0062] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 26. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 117.6g (0.688mol) of p-bromotoluene with a yield of 86%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0063] Implementation Case 28: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0064] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 90 g (0.167 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 138 g of niobium oxide catalyst, with niobium pentoxide accounting for 16% of the total mass of the catalyst.

[0065] Implementation Case 29:

[0066] 92g (1 mol) toluene and 162g (0.8 mol) hydrobromic acid were added to a 5L round-bottom flask, followed by 124g (1.1 mol) hydrogen peroxide and 10g of the dried catalyst of Example 28. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 113g (0.664 mol) of p-bromotoluene with a yield of 83%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0067] Implementation Case 30: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0068] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 107.6 g (0.2 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 140 g of niobium oxide catalyst, with niobium pentoxide accounting for 19% of the total mass of the catalyst.

[0069] Implementation Case 31:

[0070] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 30. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 123g (0.72mol) of p-bromotoluene with a yield of 90%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0071] Implementation Case 32: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0072] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 161.4 g (0.3 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 160 g of niobium oxide catalyst, with niobium pentoxide accounting for 25% of the total mass of the catalyst.

[0073] Implementation Case 33:

[0074] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 32. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0075] Implementation Case 34: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0076] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined in a muffle furnace at 500° C. for 2 hours to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0077] Implementation Case 35:

[0078] 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added to a 5L round-bottom flask, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 34. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 124g (0.725mol) of p-bromotoluene with a yield of 90.6%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0079] Implementation Case 36: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0080] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined in a muffle furnace at 700° C. for 1 hour to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0081] Implementation Case 37:

[0082] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 36. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0083] Implementation Case 38: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0084] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined in a muffle furnace at 600° C. for 1 hour to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0085] Implementation Case 39:

[0086] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 38. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 116g (0.68mol) of p-bromotoluene with a yield of 85%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0087] Implementation Case 40: Preparation of niobium oxide catalyst using adenine as a nitrogen source.

[0088] 33.8 g (0.25 mmol) of adenine was dissolved in 200 ml of DMF, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, and then the mixed solution was transferred to a 1 L polytetrafluoroethylene-lined hydrothermal autoclave and hydrothermally stirred at 150° C. for 5 hours, the reaction solution was rotary evaporated, and placed in a muffle furnace and calcined at 600° C. for 2 hours to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0089] Implementation Case 41:

[0090] In a 5L round-bottom flask, 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 40. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131g (0.768mol) of p-bromotoluene with a yield of 96%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0091] Implementation Case 42: Preparation of niobium oxide catalyst using diaminomaleic acid dinitrile as nitrogen source.

[0092] Dissolve 32.4g (0.33mol) of diaminomaleic dinitrile in 300ml of ethanol, heat to 60°C, add 100g of activated carbon to obtain a mixed solution A, add 134g (0.25mol) of niobium oxalate to 400ml of water, add nitric acid dropwise to make the pH = 2, heat to 60°C and stir until completely dissolved to obtain a yellow-green transparent solution B, add all of the solution B dropwise to the mixed solution A, continue stirring for 5 hours, dry in a vacuum oven, and calcine in a muffle furnace at 600°C for 2 hours to obtain 1.5g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst. Implementation Case 43:

[0093] In a 5L round-bottom flask, 92g (1mol) of toluene and 162g (0.8mol) of hydrobromic acid were added, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the dried catalyst of Example 42. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 127g (0.744mol) of p-bromotoluene with a yield of 93%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0094] Implementation Case 44: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0095] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 2, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 4 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0096] Implementation Case 45:

[0097] 92g (1mol) toluene and 162g (0.8mol) hydrobromic acid were added to a 5L round-bottom flask, followed by 124g (1.1mol) hydrogen peroxide and 10g of the dried catalyst of Example 44. The mixture was stirred at room temperature of 25°C for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 127g (0.744mol) of p-bromotoluene with a yield of 93%. The centrifuged catalyst was washed with ethyl acetate several times and dried for later use.

[0098] Implementation Case 46: Preparation of niobium oxide catalyst using dicyandiamide as nitrogen source.

[0099] 33.6 g (0.4 mol) of dicyandiamide was dissolved in 200 ml of water, heated to 60° C., 100 g of activated carbon was added to obtain a mixed solution A, 134 g (0.25 mol) of niobium oxalate was added to 400 ml of water, nitric acid was added dropwise to make the pH = 3, heated to 60° C. and stirred until completely dissolved to obtain a yellow-green transparent solution B, all of the solution B was added dropwise to the mixed solution A, stirring was continued for 5 hours, dried in a vacuum oven, and calcined at 600° C. in a muffle furnace for 2 hours to obtain 150.7 g of niobium oxide catalyst, with niobium pentoxide accounting for 22% of the total mass of the catalyst.

[0100] Implementation Case 47:

[0101] 92 g (1 mol) of toluene and 162 g (0.8 mol) of hydrobromic acid were added to a 5 L round bottom flask, followed by 124 g (1.1 mol) of hydrogen peroxide and 10 g of the catalyst prepared in Example 46. The mixture was stirred at room temperature of 25° C. for 5 h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 131 g (0.768 mol) of p-bromotoluene with a yield of 96%. The catalyst after centrifugation was washed with ethyl acetate several times and dried for later use.

[0102] Implementation Case 48:

[0103] In a 5L round-bottom flask, 92g (1mol) of toluene and 182g (0.9mol) of hydrobromic acid were added respectively, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 148g (0.864mol) of p-bromotoluene with a yield of 96%.

[0104] Implementation Case 49:

[0105] In a 5L round-bottom flask, 92g (1mol) of toluene and 202g (1mol) of hydrobromic acid were added respectively, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 164g (0.96mol) of p-bromotoluene with a yield of 96%.

[0106] Implementation Case 50:

[0107] In a 5L round-bottom flask, 92g (1mol) of toluene and 223g (1.1mol) of hydrobromic acid were added respectively, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 166g (0.97mol) of p-bromotoluene with a yield of 97%.

[0108] Implementation Case 51:

[0109] In a 5L round-bottom flask, 92g (1mol) of toluene and 243g (1.2mol) of hydrobromic acid were added respectively, followed by 124g (1.1mol) of hydrogen peroxide and 10g of the catalyst prepared in Example 1. The mixture was stirred at room temperature (25°C) for 5h. After the reaction, the unreacted acid was removed with anhydrous potassium carbonate, and ethyl acetate was added for extraction. The organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 166g (0.97mol) of p-bromotoluene with a yield of 97%.

[0110] Table 1:

[0111] The catalyst washed and dried after the reaction in Implementation Case 6 was reused. The process flow is consistent with Implementation Case 6, and the catalyst recovery and use are as follows:

[0112] Recycling times Yield of p-bromotoluene 1 96％ 2 96％ 3 94％ 4 94％ 5 94％ 6 94％ 7 94％ 8 94％ 9 93％ 10 94％

[0113] The catalyst washed and dried after the reaction in Implementation Case 20 was reused. The process flow is consistent with that in Implementation Case 20, and the catalyst recycling and use is as follows:

[0114] Recycling times Yield of p-bromotoluene 1 96％ 2 96％ 3 96％ 4 93.5％ 5 93.5％ 6 93.5％ 7 93.5％ 8 93％ 9 94％ 10 93％

[0115] The catalyst washed and dried after the reaction in Implementation Case 27 was reused. The process flow is consistent with that in Implementation Case 27, and the catalyst recycling and use is as follows:

[0116]

[0117]

[0118] The catalyst washed and dried after the reaction in Implementation Case 29 was reused. The process flow is consistent with that in Implementation Case 29, and the catalyst recycling and use is as follows:

[0119] Recycling times Yield of p-bromotoluene 1 83％ 2 83％ 3 83％ 4 82％ 5 82％ 6 82％ 7 82％ 8 82％

[0120] The catalyst washed and dried after the reaction in Implementation Case 31 was reused. The process flow is consistent with that in Implementation Case 31, and the catalyst recycling and use is as follows:

[0121] Recycling times Yield of p-bromotoluene 1 90％ 2 90％ 3 88％ 4 88％ 5 88％ 6 88％ 7 89％ 8 88％

[0122] The catalyst washed and dried after the reaction in Implementation Case 33 was reused. The process flow is consistent with Implementation Case 33, and the catalyst recovery and use are as shown in the following table:

[0123] Recycling times Yield of p-bromotoluene 1 96％ 2 96％ 3 96％ 4 94％ 5 94％ 6 93％ 7 93％ 8 94％

[0124] The catalyst washed and dried after the reaction in Implementation Case 35 was reused. The process flow is consistent with Implementation Case 35, and the catalyst recovery and use are as follows:

[0125] Recycling times Yield of p-bromotoluene 1 90.6％ 2 90％ 3 90％ 4 88％ 5 88％ 6 88％ 7 87％ 8 88％

[0126] The catalyst washed and dried after the reaction in Implementation Case 37 was reused. The process flow is consistent with Implementation Case 37, and the catalyst recovery and use are as follows:

[0127] Recycling times Yield of p-bromotoluene 1 96％ 2 96％ 3 96％ 4 94％ 5 94％ 6 94％ 7 94％ 8 94％

[0128] The catalyst washed and dried after the reaction in Implementation Case 39 was reused. The process flow is consistent with Implementation Case 39, and the catalyst recovery and use are as follows:

[0129] Recycling times Yield of p-bromotoluene 1 85％ 2 85％ 3 83％ 4 83％ 5 83％ 6 84％ 7 84％ 8 83％

[0130] The catalyst washed and dried after the reaction in Implementation Case 41 was reused. The process flow is consistent with Implementation Case 41, and the catalyst recovery and use are as shown in the following table:

[0131]

[0132]

[0133] The catalyst washed and dried after the reaction in Implementation Case 43 was reused. The process flow is consistent with Implementation Case 43, and the catalyst recovery and use are as follows:

[0134] Recycling times Yield of p-bromotoluene 1 93％ 2 94％ 3 94％ 4 93％ 5 93％ 6 93％ 7 93％ 8 93％

[0135] The catalyst washed and dried after the reaction in Implementation Case 45 was reused. The process flow is consistent with Implementation Case 45, and the catalyst recovery and use are as shown in the following table:

[0136] Recycling times Yield of p-bromotoluene 1 93％ 2 93％ 3 93％ 4 91％ 5 92％ 6 92％ 7 92.5％ 8 91％

[0137] The catalyst washed and dried after the reaction in Implementation Case 47 was reused. The process flow is consistent with Implementation Case 47, and the catalyst recovery and use are as follows:

[0138] Recycling times Yield of p-bromotoluene 1 96％ 2 96％ 3 94％ 4 94％ 5 94％ 6 94％ 7 94％ 8 94％

Claims

1. A method for preparing p-bromotoluene by using niobium to catalyze toluene, the specific steps of which are as follows: a) Preparation of niobium oxide-supported carbon-nitrogen material catalyst: niobium oxalate and a nitrogen source solution are subjected to loading and calcining to prepare a niobium oxide-supported carbon-nitrogen material catalyst, wherein niobium pentoxide accounts for 16% to 25% of the total mass of the catalyst; the specific steps are: adding a nitrogen source into deionized water, heating until dissolved, and then adding activated carbon into the solution to prepare solution A; adding niobium oxalate into the aqueous solution, then adding an acid to adjust the pH to 2 to 3, and heating to dissolve into solution B; adding solution B into solution A under stirring; stirring for 4 to 5 hours, drying, and calcining at high temperature to prepare a niobium oxide-supported carbon-nitrogen material catalyst, wherein niobium pentoxide accounts for 16% to 25% of the total mass of the catalyst; wherein the nitrogen source is dicyandiamide, adenine or diaminomaleic dinitrile; b) Preparation of p-bromotoluene: adding toluene, hydrobromic acid, hydrogen peroxide and the niobium oxide-supported carbon-nitrogen material catalyst prepared in step a) into a reactor, and reacting at a certain temperature to obtain p-bromotoluene.

2. The method according to claim 1, characterized in that: The mass ratio of the nitrogen source to the activated carbon is (0.168-0.5):1; the molar ratio of niobium oxalate to the nitrogen source reagent is 1:(0.9-2.5).

3. The method according to claim 1, characterized in that: The high-temperature calcination temperature is 500-700°C, and the calcination time is 1-2h.

4. The method according to claim 1, characterized in that: In step b), the amount of hydrobromic acid added is 0.8-1.2 times the molar amount of toluene, and the amount of hydrogen peroxide added is 0.9-1.2 times the molar amount of toluene; the added mass of the niobium oxide-supported carbon-nitrogen material catalyst is 8.6% to 12% of the mass of toluene.

5. The method according to claim 1, characterized in that: The reaction temperature in step b) is 20-30° C. and the reaction time is 3-5 h.

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