A method for preparing α-bromoketone compounds and coupling hydrogen production

Abstract

The present invention discloses a method for preparing α-bromoketone compounds and coupled hydrogen production. The method uses CoS@Ti as an anode electrode and Pt as a cathode electrode. Under the action of current, a NaBr solution in an electrolyte and an olefin compound can undergo a bromoketone reaction at the anode to generate α-bromoketone compounds with high selectivity; the bromoketone compounds include α-bromoketone products of cycloolefins and aromatic olefins. The present invention successfully constructs an efficient electrochemical organic reaction series system and a coupled cathode reduction reaction electrolysis system, which can be used for Br ‑ / Br2-mediated olefin oxidation to prepare α-bromohydrin and α-bromoketone; CoS@Ti has excellent catalytic performance in the bromide ion oxidation process and remains stable after 5 cycles; the selectivities of α-bromohydrin and α-bromoketone can reach above 90% and above 90%, respectively, and the Faradaic efficiency (FE) is as high as 90% for both; the reaction system has good scalability for different olefins, demonstrating its technological application potential.

Description

Technical Field

[0001] The invention relates to a method for preparing α-bromoketone compounds and coupled hydrogen production, and belongs to the field of electrochemical synthesis. Background Art

[0002] Electrosynthesis bridges the gap between traditional electrochemistry and organic chemistry and has become a promising approach for the production of fuels, fertilizers, and pharmaceuticals. α-Bromoketones are widely used synthetic intermediates, typically derived from the bromination of carbonyl compounds, in various organic reactions for the synthesis of agrochemicals, fine chemicals, and pharmaceuticals. Traditional industrial synthesis involves α-substitution of the carbonyl group with elemental bromine in diethyl ether in an ice-water bath. This not only results in expensive substrates and harsh reaction conditions, but also requires bromine, a highly toxic and difficult-to-use reagent. Indeed, the most cost-effective synthetic methods utilize olefins as starting substrates for one-pot synthesis (styrene ≈ 9,600 yuan / ton, acetophenone ≈ 19,200 yuan / ton). However, other reported one-step syntheses of α-bromoketones require the use of excess amounts of strong oxidants, such as H2O2, K2S2O8, and TsNBr2, which still present cost and hazard issues.

[0003] Electrosynthesis uses electricity to directly generate reactants or indirectly generate active intermediates (such as Br· / Br2) for transformation. According to the reaction mechanism between bromine and olefins, active bromine species usually exhibit electrophilicity and form bromonium ions, resulting in multiple reaction pathways and difficulties in selective synthesis. Recently, Qiao Shizhang et al. reported the efficient preparation of 2-chloroethanol by electrocatalytic chlorine evolution in acidic seawater, providing new clues for the halogen-mediated synthesis of α-bromohydrin and α-bromoketone. However, there has never been a direct electrochemical realization of α-bromoketone in order to achieve a one-pot electrosynthesis from olefins to α-bromoketone. Therefore, a comprehensive understanding of this system is crucial to the realization of Br - The electrophilicity and oxidative properties of its active species are key to the electrofunctionalization of olefins.

[0004] Organic researchers usually use platinum, a precious metal, as an electrode to catalyze the redox reaction of bromine electrodes. However, platinum is not only expensive, but also corrodes in halogen electrolytes, which limits its widespread application. Carbon-based materials have a large specific surface area and are inexpensive. They are also often used as bromine electrodes in bromine batteries, but they still have problems such as high overpotential, low energy efficiency and low catalytic activity. Many works have reported the use of cobalt as an active site for bromine oxidation. For example, Zhang Bing et al. used needle-shaped NiCo2O4 as an anode catalyst to achieve a one-pot electrosynthesis of epichlorohydrin mediated by bromine radicals. Cobalt sulfide materials with cobalt as the active center also have special redox activity. Studies have reported that CoS / CoS2@GF has a high redox activity in I - / I2 redox media has better activity than Pt, and its - / Br2 redox medium shows better electrocatalytic activity and stability than other metal sulfides of the first transition series. Compared with carbon substrate, titanium mesh has better conductivity and stability in halogen environment. Therefore, the cobalt sulfide material is loaded on the titanium mesh for Br - / Br2 redox mediator is likely to have good catalytic properties. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing α-bromoketone compounds and coupling hydrogen production in order to solve the above problems. The technical problem to be solved by the present invention is to provide an electrochemical method for synthesizing α-bromoketone compounds with high selectivity and high Faradaic efficiency. CoS@Ti is used as the anode electrode and Pt is used as the cathode electrode. Under the action of current, the NaBr solution in the electrolyte and the olefin compound undergo a bromoketone reaction at the anode to generate α-bromoketone compounds, and platinum undergoes a hydrogen evolution reaction in the cathode solution. This is an electrochemical method for synthesizing α-bromoketone compounds with high selectivity and high Faradaic efficiency, and the system can be coupled with other cathode reactions such as hydrogen production.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing α-bromoketone compounds and coupling hydrogen production therewith, comprising the following steps:

[0008] An H-type electrolytic cell was used with CoS@Ti as the anode electrode and platinum as the cathode electrode. Under the action of current, the NaBr solution in the electrolyte and the olefin compounds in the electrolyte underwent α-bromoketone reaction at the anode to generate α-bromoketone compounds, and platinum underwent hydrogen evolution reaction in the cathode solution.

[0009] Furthermore, the olefin reactant includes one or more of chain olefins, cycloolefins, aromatic olefins, and the like.

[0010] Furthermore, the α-bromoketone compound includes one or more of α-bromoketone products of chain alkenes, α-bromoketone products of cycloalkenes, α-bromoketone products of aromatic alkenes, and the like.

[0011] Furthermore, the NaBr solution includes a solvent and NaBr dissolved in the solvent. The solvent in the NaBr solution includes one or more of acetonitrile (CH3CN), water, n-tetrabutylammonium fluoroborate, sulfuric acid (H2SO4), etc.

[0012] Preferably, the solvent in the NaBr solution is a mixed solution of CH3CN and H2SO4 solution (aqueous solution).

[0013] Further preferably, in the mixed solution of CH3CN and H2SO4 solution (aqueous solution), the volume ratio of CH3CN to H2SO4 is 1:1-1:3, and the concentration of H2SO4 in the H2SO4 solution is 0-0.5 mol / L.

[0014] Wherein, the concentration of the NaBr solution is 0.1-0.3 mol / L.

[0015] Wherein, the molar ratio of the olefin compound to NaBr is 1mmol:2.5-6mmol.

[0016] Preferably, the NaBr is added in two steps, which is conducive to the preparation of α-bromoketone with high selectivity and high Faradaic efficiency.

[0017] Preferably, the molar ratio of the olefin compound to NaBr is 1 mmol:(2.5+2) mmol.

[0018] Furthermore, the chain olefins include one or more of 1-octene, 2-octene, etc.; the cyclic olefins include one or more of cyclohexene, cycloheptene, bornene, α-pinene, β-pinene, etc.; the aromatic olefins include one or more of styrene, various substituted styrenes, allylbenzene, vinylpyridine, etc.

[0019] Furthermore, the current density is 5-20 mA / cm 2 .

[0020] Preferably, the current density is 10 mA / cm 2 .

[0021] Furthermore, the reaction time is 8-12 hours.

[0022] Preferably, the time for preparing the α-bromohydrin compound is 10-12 hours.

[0023] Furthermore, the number of reaction cycles is 1-3 times.

[0024] Furthermore, the concentration of the olefin compound in the solution is 25 mmol / L.

[0025] Furthermore, the electrolyte includes an anolyte and a cathode electrolyte, and a proton exchange membrane is provided between the anolyte and the cathode electrolyte.

[0026] Furthermore, the anode electrolyte includes a NaBr solution and an olefin compound.

[0027] Furthermore, the solvent in the cathode electrolyte includes one or more of acetonitrile, water, sulfuric acid, etc., preferably a mixture of equal volumes of 0.1 mol / L H2SO4 solution and acetonitrile.

[0028] Furthermore, the preparation method of CoS@Ti comprises the following steps:

[0029] (1) Dissolving Co(NO3)2·6H2O, Al(NO3)3·9H2O, and urea in a mixture of water and n-butanol to obtain a precursor solution;

[0030] (2) ultrasonically washing the titanium mesh substrate with acetone, H2O, 1 mol / L HCl, and H2O for 10 min, 5 min, 10 min, and 5 min, respectively, and then transferring the titanium mesh substrate to the precursor solution in step (1) and heating and cooling the resulting solution to obtain a cooling solution;

[0031] (3) Na2S·9H2O was added to the cooled solution obtained in step (2), and the mixture was heated again to generate CoS@Ti. The mixture was cleaned with H2O and anhydrous ethanol, and vacuum dried to obtain the CoS@Ti electrode.

[0032] Furthermore, in the mixture of water and n-butanol, the volume ratio of water to n-butanol is 1:1.

[0033] Furthermore, the molar ratio of Co(NO3)2·6H2O and Al(NO3)3·9H2O is 3:1, and the concentrations of Co(NO3)2·6H2O and Al(NO3)3·9H2O are 0.03 mol / L and 0.01 mol / L.

[0034] Furthermore, the molar ratio of Co(NO3)2·6H2O, Al(NO3)3·9H2O, urea, and Na2S·9H2O is 3:1:10:20.

[0035] Furthermore, in step (2), the heating and cooling conditions are as follows: first heating at 120° C. for 6 hours, and then cooling to room temperature.

[0036] Furthermore, in step (3), the vacuum drying conditions are as follows: drying at 40° C. for 6 h.

[0037] Furthermore, in step (3), the heating reaction conditions are as follows: stirring at a rotation speed of 1000 rpm for 0.5 h, and then heating to 120° C. and storing for 6 h.

[0038] Studies have shown that cobalt sulfide heterostructures have better Br resistance than other metal sulfides and even platinum. - / Br2-mediated catalytic performance of olefin dibromination. Therefore, further exploration of the use of cobalt sulfide heterostructures to catalyze Br - The / Br2-mediated electrochemical oxidation of olefins to prepare α-bromohydrins and α-bromoketones is reasonable.

[0039] Working principle: Figure 1 As shown, bromide ions are first oxidized to bromine element at the anode. Under acidic or neutral conditions, the bromo-onium intermediate generated by styrene is attacked by H2O nucleophilically to generate α-bromohydrin product. Under further oxidation, Br2 promotes the oxidation of α-bromohydrin product to α-bromoketone product. Hydrogen evolution reaction (HER) occurs at the cathode, but the use of H-type electrolytic cell avoids the pH change of the anode reaction. - The electrochemical reaction pathway for the conversion of olefins to α-bromoketone products mediated by Br2 redox mediators is as follows:

[0040]

[0041] The reaction equation of hydrogen evolution reaction (HER) at the cathode is: 2H + →H2↑

[0042] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages.

[0043] 1. This invention successfully constructed a highly efficient CoS@Ti self-supporting electrocatalyst for Br - / Br2-mediated electrooxidation of olefins to produce α-bromohydrin and α-bromoketone products, and paired with the cathode hydrogen evolution reaction (HER);

[0044] 2. In this reaction system, the selectivity of α-bromohydrin and α-bromoketone can reach over 90%, and the Faradaic efficiency (FE) can reach over 90%;

[0045] 3. CoS@Ti and the reaction system have good substrate scalability, and the H-type electrolytic cell system can be expanded to a liquid flow system in preliminary attempts and coupled with the hydrogen evolution reaction of other cathodes, proving its technical application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Br - / Br2 redox mediator-mediated electrochemical reaction pathway for the conversion of olefins to α-bromoketone products;

[0047] Figure 2 SEM and XRD patterns of different materials: (a, b) SEM images of CoS@Ti (c) XRD image of CoS@Ti;

[0048] Figure 3 TEM images of CoS@Ti: (a) CoS part in CoS@Ti (b) Ti network part in CoS@Ti;

[0049] Figure 4 Comparative LSV curves of Ti mesh and CoS@Ti;

[0050] Figure 5 CV curves of CoS@Ti at different bromide ion concentrations;

[0051] Figure 6 This is a comparison of photos of the electrodes during actual electrocatalytic process;

[0052] Figure 7 The results of the conversion of α-bromohydrin and α-bromoketone of different substrates are shown;

[0053] Figure 8 SEM images of CoS@Ti after cycling reaction: (a) after the first cycle (b) after the third cycle;

[0054] Figure 9 The XPS results of CoS@Ti after reaction under different conditions: (A) CoS@Ti is newly used to prepare α-bromoketone after α-bromohydrin (B) CoS@Ti is used to prepare α-bromoketone at the beginning of the reaction;

[0055] Figure 10 Br - Schematic diagram of the liquid flow system for the Br2-mediated electrochemical oxidation of olefins to prepare α-bromohydrins and α-bromoketones after pairing with HER or nitrobenzene reduction;

[0056] Figure 11 This is a real-life diagram of the liquid flow reaction system. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described below with reference to specific embodiments and accompanying drawings, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0058] Materials and Methods: Unless otherwise specified, reagents and materials were obtained from suppliers without further purification. The following chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. with a purity of 99%: NaBr, Co(NH₂)₂ (urea), n-butanol, concentrated sulfuric acid, Co(NO₃)₂·6H₂O, Al(NO₃)₃·9H₂O, Na₂S·9H₂O, and acetone. Shanghai Aladdin Biochemical Technology Co., Ltd. and Shanghai Bid Pharmaceutical Co., Ltd. provided all olefin compounds used in this study. Gaoshi Ruilian Optoelectronics Technology Co., Ltd. provided electrodes (platinum sheet electrodes, platinum electrode clips, and reference electrodes). Titanium mesh was purchased from Anping Hongyun Metal Co., Ltd.

[0059] SEM images were obtained using a FEI Nova Nano SEM 450, XRD patterns were obtained using a Shimadzu XRD-6100, and TEM images were obtained using a FEI Talos F200X. Substrate and product conversions and selectivities were analyzed using a GC-MS-QP 2010SE. Electrochemical tests were performed using a CHI760E electrochemical workstation from Shanghai Chenhua Instrument Co., Ltd.

[0060] Example

[0061] This embodiment provides a method for the electrosynthesis of α-bromoketone compounds and coupled hydrogen production therewith.

[0062] Step 1: In-situ generation of metal sulfide catalyst on Ti mesh and electrode preparation

[0063] CoS@Ti electrocatalyst was synthesized by in situ topological sulfurization microemulsion solvothermal method for electrocatalytic oxidation of bromide ions. 2 ) was soaked in acetone, H2O, 1 mol / L HCl, and H2O, and ultrasonically washed for 10 min, 5 min, 10 min, and 5 min, respectively. 1.2 mmol Co(NO3)2·6H2O, 0.4 mmol Al(NO3)3·9H2O, and 4 mmol urea were dissolved in 15 mL H2O and 15 mL n-butanol to obtain a precursor solution. The precursor solution was stirred for 0.5 h and then poured into a 50 mL polytetrafluoroethylene liner. The cleaned titanium mesh was also placed in the polytetrafluoroethylene liner, which was then placed in the outer liner of an autoclave and heated to 120°C for 6 h. After cooling to room temperature, a cooled solution was obtained. 8 mmol Na2S·9H2O was then added to the solution, stirred at 1000 rpm for 0.5 h, and heated again to 120°C for 6 h. After cooling, the CoS-loaded titanium mesh was washed several times with water and ethanol, and then dried in vacuum at 40°C for 6 hours to obtain the final CoS@Ti electrode. The loading of Co active sites on the Ti mesh was 11.1 mg / cm 2 First, the morphology of the synthesized CoS@Ti electrode was characterized by scanning electron microscopy (SEM). Figure 2 As shown in a and b, it is found that CoS is uniformly grown on the surface of the Ti mesh in a nano-sponge-like morphology. Secondly, the CoS@Ti electrode was characterized by X-ray diffraction (XRD). Figure 2As shown in Figure c, the CoS@Ti electrode is indeed loaded with CoS. The peak position is marked with Δ, and the corresponding PDF card is PDF#00-019-0366. The other peaks are marked with * and #, corresponding to the Ti mesh substrate (PDF#00-044-1294) and the residual CoAl LDH (PDF#00-051-0045). Finally, the film was sliced ​​by focused ion beam technology (FIB) and observed under a transmission electron microscope (TEM). Figure 3 As shown in a, the CoS part presents a porous structure of sheet-like stacking growth, while 3b shows a complex distribution of CoS with short-range order and long-range disorder.

[0064] Step 2: Evaluation of the electrocatalytic oxidation reaction of bromide ions using linear sweep voltammetry

[0065] CoS@Ti was directly clamped on a platinum electrode as a self-supporting electrocatalyst, and the platinum electrode and Hg / HgO reference electrode were used as the counter electrode and reference electrode, respectively. - The electrolyte composition of the / Br2 redox reaction was a mixed aqueous solution of 0.05mol / L NaBr and 0.1mol / L NaNO3, and the scan rate was 10mV / s. The electrocatalytic oxidation performance of CoS@Ti and Ti mesh for bromide ions was compared by linear sweep voltammetry (LSV). Figure 4 As shown in the figure, CoS@Ti has a significantly lower peak current potential (E p =1.450V, vs RHE) and a larger peak current density (i p =17.28mA / cm 2 ). Figure 5 It shows that when the bromide ion concentration increases, the current density of CoS@Ti increases significantly, reflecting its high Faradaic efficiency. Figure 6 It can also be seen in the photo that at 1.8V RHE Under the conditions of 100 nm, CoS@Ti produced more Br2 than the washed Ti mesh and produced no oxygen bubbles at all, indicating that CoS@Ti has a high Faradaic efficiency. The prepared CoS@Ti was then directly used as a Br - A self-supporting working electrode (anode) for olefin functionalization mediated by Br / Br2 redox reaction.

[0066] Step 3: Study the effect of different experimental parameters on the selectivity of α-bromohydrin and α-bromoketone

[0067] Since α-bromoketone derived from styrene as a template is of the most practical value, electrochemical experiments were conducted using styrene as a model substrate. In this reaction, dibromo and epoxy products are the most common by-products during the electrochemical preparation process. The reaction pathway is as follows: Figure 1Therefore, by using CoS@Ti as the anode and Pt as the cathode, the effects of different experimental parameters on the selectivity of α-bromohydrin and α-bromoketone were studied.

[0068] 1. Investigate the effects of solvent and pH on the formation of α-bromohydrin.

[0069] From the perspective of the reaction path, the reaction environment should be neutral to acidic. Figure 10 Br shown - Schematic diagram of Br2-mediated organic electrosynthesis coupled with HER: Styrene (118 μL, 1 mmol), sodium bromide (309 mg, 3 mmol), and n-tetrabutylammonium tetrafluoroborate (n-Bu4NBF4, 65.9 mg, 0.2 mmol) were added to a 20 mL 0.2 mol / L mixture of potassium dihydrogen phosphate and dipotassium hydrogen phosphate (PBS, pH ≈ 6.9) in 20 mL acetonitrile. The mixture was placed in the anode of an H-type electrolytic cell, with CoS@Ti (2 cm × 1 cm) as the anode electrode and a 1 cm × 1 cm area of ​​the catalyst actually immersed in the solution. The cathode contained 40 mL PBS and a Pt (1 cm × 1 cm) electrode. Under the action of current, the anode undergoes electrocatalytic oxidation of bromide ions, which further mediates the formation of α-bromohydrin. The current density at room temperature was 10 mA / cm 2 The set time was the value for 100% Faraday efficiency (5.3 hours), but the actual reaction time was only 4 hours. This is because the phosphate ions present in the anode, under potential polarization, cause Co3(PO4)2 precipitation to form on the CoS surface, destroying the Co active sites and hindering the oxidation of bromide ions, causing the voltage to exceed the upper limit of the workstation. Therefore, the applicant reduced the amount or concentration of PBS solution used. The results showed that: although electrolysis could be completed and the substrate conversion rate increased, the selectivity of α-bromohydrin was greatly reduced, resulting in a decrease in the actual Faraday efficiency. Therefore, it was decided to carry out the reaction in an acidic environment. When the solution was changed to 0.1 mol / L H2SO4 solution, both the conversion rate and selectivity were greatly improved. Further increasing the concentration of sulfuric acid did not help the conversion rate and had little effect on the selectivity. Therefore, a systematic screening of solvents showed that a mixed solution of 0.1 mol / L H2SO4 and acetonitrile (1:1) in the anode reaction chamber was the ideal solvent composition for the selective generation of α-bromohydrin.

[0070] Table 1. Solvent and pH screening.

[0071]

[0072] The initial conditions were an H-type reaction cell, the anode solution was MeCN:PBS=20 mL:20 mL, 1 mmol styrene, 3 mmol NaBr, 0.2 mmol n-Bu4NBF4; the cathode solution was 40 mL 0.2 mol / L PBS (pH≈6.9), room temperature (rt), I=10 mA, and the set time t=20000 s.

[0073] a: The reaction ended before the set time due to voltage exceeding the range (4h).

[0074] 2. Follow the above steps to investigate the effect of NaBr content on α-bromohydrin.

[0075] After the electrolysis reaction, the electrolyte (50 μL) was extracted with dichloromethane (500 μL). The extracted lower organic phase was removed with a dropper and dried over anhydrous sodium sulfate. After drying, it was injected into a gas chromatography sample bottle vial with a syringe equipped with a filter, and dichloromethane was further added to make the volume 1.4 mL. Gas chromatography-mass spectrometry (GC-MS) was used to identify the product and quantify the conversion and selectivity. The results showed that when 2.5 mmol NaBr was used in a 0.1 mol / L H2SO4 solution, the reaction selectivity increased significantly from 81.6% to 93.5%, indicating that the dibromo product is the main byproduct in an acidic environment, and therefore reducing the amount of bromine source can promote further increase in selectivity. However, when the bromide ion concentration was further reduced to 2 mmol, the conversion rate dropped to 83.3% due to its low concentration, and the selectivity was almost improved (93.0%). This may be due to insufficient bromine generation, resulting in a mismatch between the electrolysis rate and the bromide ion recycling rate. Therefore, the appropriate amount of NaBr is 2.5 mmol.

[0076] The conversion rate and selectivity are calculated by the following formula:

[0077] Conversion rate = sum of peak areas of all products / sum of peak areas of reactants and all products × 100%

[0078] Selectivity = GC-MS peak area of ​​target product / sum of peak areas of all products × 100%

[0079] The formula for calculating Faraday efficiency (FE) is as follows:

[0080]

[0081] The unit of the amount of reactant (n) is mol, the Faraday constant F=96485 C / mol, the unit of current (I) is A, and the unit of time (t) is s.

[0082] 4. A key experimental parameter affecting yield is current density.

[0083] Keeping the total amount of electricity in the electrolysis process constant, the results were studied at 5, 10, 15 and 20 mA / cm 2 Effect of current density on the reaction. As shown in Table 2, when 5 mA / cm 2 When the conversion rate and selectivity are 10mA / cm 2 So from the perspective of time efficiency (time cost), 10mA / cm 2 When the current density increases to 15mA / cm 2 When 20 mA / cm 2 The selectivity is further reduced.

[0084] Table 2 Current density screening

[0085]

[0086] The initial conditions were an H-type reaction cell, the anode solution was MeCN: 0.1 mol / L H2SO4 = 20 mL: 20 mL, 1 mmol styrene, 2.5 mmol NaBr, 0.2 mmol n-Bu4NBF4; the cathode solution was 40 mL 0.1 mol / L H2SO4, room temperature (rt), t = 20000 s.

[0087] 5. Investigate the effect of time on the reaction products α-bromohydrin and α-bromoketone.

[0088] Table 3 Effect of time on the yield of α-bromohydrin and α-bromoketone

[0089]

[0090]

[0091] The initial conditions were an H-type reaction cell with anode solution of MeCN: 0.1 mol / L H2SO4 = 20 mL: 20 mL, 1 mmol styrene, 2.5 mmol NaBr, 0.2 mmol n-Bu4NBF4; cathode solution of 40 mL 0.1 mol / L H2SO4, room temperature (rt), I = 10 mA / cm 2 , t=20000s.

[0092] As shown in Table 3, the conversion and selectivity increased with time within the set reaction time. At 5.56 h, the conversion was 100%, the selectivity was 92.6%, and the FE was 92.6%. Further increases in reaction time significantly increased the α-bromoketone product, with the selectivity shown in the parentheses in Table 3. When the target reaction time for α-bromoketone production was reached, the yield was 56.3%.

[0093] 6. Optimization of reaction conditions for α-bromoketone.

[0094] Table 4 Optimization of reaction conditions for α-bromoketone

[0095]

[0096] The initial conditions were an H-type reaction cell, under air atmosphere, the anode solution was MeCN:0.1 mol / L H2SO4=20 mL:20 mL, 1 mmol styrene, 3 mmol NaBr, 0.01 mol / L n-Bu4NBF4; the cathode solution was 40 mL 0.1 mol / L H2SO4, room temperature (rt), I=10 mA, and the set time t=40000 s.

[0097] As shown in Table 4, the selectivity of α-bromoketone also increased after the bromine content was increased. This may be because 1mmol of the 2.5mmol bromine entered the product, and only 1.5mmol of the bromine content remained in the electrocatalytic oxidation. However, the oxidation rate of the bromine active species during subsequent oxidation is inconsistent with the electrochemical reaction rate, making it difficult to ensure high selectivity of the reaction. So we tried to further increase the amount of sodium bromide added. The selectivity of 3mmol NaBr increased, but the selectivity of 5mmol NaBr decreased instead. The results of GC-MS showed that the increase in the amount of bromide ions led to the generation of a larger amount of dibromo product. In combination with the above experiments, the applicant chose to achieve the preparation of α-bromoketone with high selectivity and high Faraday efficiency by adding sodium bromide in two steps, with a yield of 90.7%.

[0098] Step 4: Investigate the conversion and selectivity of different olefin compounds

[0099] Except for replacing different olefin compounds as starting reactants, the α-bromoketone reaction was carried out in the same manner as in this example. The results are shown in FIG. Figure 7 As shown ( Figure 7Pro-1 refers to the formation of α-bromoketone, and Pro-2 refers to the formation of α-bromohydrin. The 90.7% / 90.7% ratio shown in Reactant 1 indicates the conversion rate and selectivity, respectively. Substrate expansion results indicate that the present method can successfully prepare a variety of α-bromohydrin and α-bromoketone compounds. However, the conversion rate and selectivity of olefin compounds are affected by the solubility of the reactants in the solvents specified in the examples. Generally, the introduction of a strong electron-withdrawing group on the benzene ring and an increase in the number of carbon atoms in the alkyl olefin decrease its solubility, while the introduction of an electron-donating group on the benzene ring has little effect on solubility.

[0100] Step 5: Explore the cyclic performance of the catalyst and catalytic system or conduct scale-up experiments

[0101] 1. Investigate the recycling performance of the catalyst in the preparation of α-bromoketone.

[0102] After the reaction of α-bromohydrin, the CoS on the surface tends to be converted into the needle-like CoO reported in the literature. x , and then further generate book-shaped Co3O4, such as Figure 8 The results of X-ray photoelectron spectroscopy (XPS) show that the surface Co-S is increasingly converted into Co-O, such as Figure 9 B. It is noteworthy that the recovered catalyst showed good stability during the three uses, with the applied voltage remaining almost unchanged (approximately 1.8 V RHE ), and the yields are maintained above 80%. If the preparation of α-bromoketone is continued, more cobalt oxide will cover the CoS surface. However, if new CoS@Ti is used to prepare α-bromoketone directly after the formation of α-bromohydrin, due to the strong oxidizing nature of the system, the CoS on the surface will completely disappear after the reaction, making the catalyst ineffective. Figure 9 A. These results indicate that Br2 plays an oxidizing role in the formation of α-bromoketone, while the Co3O4 formed during the reaction helps protect the internal CoS. In order to extend the service life of the catalyst, it is necessary to continuously use the catalyst in the preparation of α-bromoketone.

[0103] 2. Investigate the cyclic performance of the catalytic system in the preparation of α-bromoketone.

[0104] In addition to focusing on the recycling properties of the material, the sustainability of the reaction solution in different systems was also studied in depth, which is often overlooked in traditional organic reactions. However, in the preparation system of α-bromoketone, by reintroducing the same amount of NaBr (2.5mmol+2mmol) and styrene (1mmol) as in the initial reaction conditions and applying current, the reaction can still proceed smoothly, and the selectivity (88.1%) and yield (88.1%) are maintained well. After three cycles, the gram-scale synthesis of α-bromoketone (1.03g) was successfully achieved.

[0105] 3. Experimental investigation of the liquid flow system coupled with the cathode hydrogen evolution reaction and its derivatives.

[0106] Since the preparation system of α-bromoketone is an H-type electrolytic cell, it is considered to couple the reaction system through a liquid flow electrolytic cell device. The liquid flow circulation system can achieve the coupling of α-bromohydrin or α-bromoketone with the cathode hydrogen evolution reaction, and even the coupling of the selective electroreduction reaction of nitrobenzene derived from the hydrogen evolution reaction. 2 At a current density of 1000 nm, the yields of α-bromohydrin and α-bromoketone are both above 90% in both hydrogen evolution reaction and nitrobenzene reduction reaction. The amount of hydrogen evolved is collected by drainage method. The device is shown in the figure below. Figure 11 As shown; the reaction progress of nitrobenzene and the reaction products were detected by GC-MS.

[0107] Experiments using the preparation of 1 mmol of α-bromoketone as a benchmark revealed that when coupled to the hydrogen evolution reaction, the maximum voltage applied to the cathode and anode did not exceed 3.0 V, with maximum energy consumption of 600 J (for α-bromohydrin) and 1200 J (for α-bromoketone). The collected H₂ production was approximately 21.5 mL and 45.0 mL, corresponding to the input energy. When coupled to the reduction of nitrobenzene, the cathode solution was a preferred cathode hydrogen evolution solution (acetonitrile and 0.1 mol / L dilute sulfuric acid in a 1:1 volume ratio), with nitrobenzene added. The selective formation of azobenzene oxide yielded selectivities and conversions of 86.4% and 58.2% (for α-bromohydrin with 1 mmol of nitrobenzene added), and 66.9% and 65.6% (for α-bromoketone with 1 mmol of nitrobenzene added), respectively. These results demonstrate the efficient electrosynthesis capability of the H-type electrolytic cell coupled to the cathode reaction in this method, providing further opportunities for improving the comprehensive utilization efficiency of electrons.

[0108] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above-mentioned embodiments. The description of the embodiments is for the convenience of ordinary technicians in this technical field to understand and use the invention. It is obvious that those familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to go through creative work. Therefore, the present invention is not limited to the above-mentioned embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing α-bromoketone compounds and coupled hydrogen production, characterized in that: The following steps are involved: With CoS@Ti as the anode electrode and platinum as the cathode electrode, under the action of current, the NaBr solution in the electrolyte and the olefin compounds in the electrolyte undergo α-bromoketone reaction at the anode to generate α-bromoketone compounds, and the platinum undergoes hydrogen evolution reaction in the cathode solution. The α-bromoketone compound is selected from one or more of the α-bromoketone products of chain alkenes, α-bromoketone products of cycloalkenes, and α-bromoketone products of aromatic alkenes; The electrolyte includes an anolyte and a catholyte; The anolyte comprises a NaBr solution and an olefin compound; The solvent in the NaBr solution is a mixed solution of CH3CN and H2SO4 aqueous solution; The reaction time of α-bromoketoneization is 8-12h; The current density is 5-10 mA / cm 2 ; The NaBr is added in two steps; the molar ratio of the olefin compound to NaBr is 1 mmol:(2.5+2) mmol; The preparation method of CoS@Ti comprises the following steps: (1) Dissolving Co(NO3)2·6H2O, Al(NO3)3·9H2O, and urea in a mixture of water and n-butanol to obtain a precursor solution; (2) ultrasonically washing the titanium mesh substrate and transferring it to the precursor solution obtained in step (1) for hydrothermal treatment, and cooling the solution to obtain a cooled solution and a loaded titanium mesh substrate; (3) Na2S·9H2O is added to the cooled solution obtained in step (2) to obtain a mixed solution, and the loaded titanium mesh substrate is again placed in the mixed solution for hydrothermal reaction to generate CoS@Ti, which is then cleaned and vacuum dried to obtain the CoS@Ti electrode.

2. The method for preparing α-bromoketone compounds and coupled hydrogen production according to claim 1, characterized in that: The NaBr concentration in the anolyte is 0.1-0.3 mol / L, and the sulfuric acid concentration is 0-0.5 mol / L.

3. The method for preparing α-bromoketone compounds and coupled hydrogen production according to claim 1, characterized in that: The solvent in the cathode electrolyte is selected from one or more of acetonitrile and aqueous sulfuric acid solution.

4. The method for preparing α-bromoketone compounds and coupled hydrogen production according to claim 1, characterized in that: The olefin compound is selected from one or more of chain olefins, cycloolefins and aromatic olefins.

5. The method for preparing α-bromoketone compounds and coupled hydrogen production according to claim 4, characterized in that: The olefin is selected from one or more of 1-octene and 2-octene; The cycloolefin is selected from one or more of cyclohexene, cycloheptene, norbornene, α-pinene, and β-pinene; The aromatic olefin is selected from one or more of styrene, substituted styrene, allylbenzene, and vinylpyridine.

6. The method for preparing α-bromoketone compounds and coupled hydrogen production according to claim 1, characterized in that: The number of electrolyte circulations in the α-bromoketone reaction is 1-3 times.

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