A method for the synthesis of 2-bromoethanol by selective electrooxidation of ethylene mediated by a sodium bromide solution as a bromine source

Abstract

The application provides a method for synthesizing 2-bromoethanol by using a sodium bromide solution as a bromine source to mediate selective electro-oxidation of ethylene, using ethylene gas as a raw material and a hydrophobic carbon paper as a reaction system of a working electrode, and obtaining corresponding alcohol compounds by constant potential electrochemical selective oxidation, and the reaction potential is 0.5-1.3V. In a wide potential range, efficient and high-selectivity synthesis of 2-bromoethanol can be realized, and the application uses cheap and easily available, efficient carbon materials as electrodes, is green, safe, uses sodium bromide as a bromine source, uses water as a hydrogen source, does not need an additional hydrogen source, has mild reaction conditions, does not need heating, is easy to operate, and a catalyst is easy to recover.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic synthesis of 2-bromoethanol, and more specifically to a method for the selective electrooxidation of ethylene to synthesize 2-bromoethanol using sodium bromide solution as a bromine source. Background Technology

[0002] 2-Bromoethanol, with its unique combination of bromine atoms and hydroxyl groups, possesses excellent reactivity and can be used to introduce different functional groups. Therefore, 2-Bromoethanol is an important synthetic intermediate for many compounds in fields such as pharmaceuticals, pesticides, and dyes. To date, most researchers still use traditional methods to prepare 2-Bromoethanol, specifically as follows: (1) 2-Bromoethanol is synthesized by reacting ethylene glycol with hydrobromic acid. This reaction is usually carried out under heating and acidic conditions. HO-CH2-CH2-OH+HBr→Br-CH2-CH2-OH+H2O

[0003] (2) 2-Bromoethanol is obtained by reacting ethanol with hydrogen bromide (HBr) and sulfuric acid (H2SO4). The reaction involves mixing ethanol with concentrated sulfuric acid and hydrobromic acid, and requires heating. CH3CH2OH + HBr → Br-CH2-CH2-OH

[0004] All of the above methods require acidic conditions and heating, making the conditions relatively harsh. Traditional chemical reagent methods for synthesizing 2-bromoethanol have several drawbacks. The reactions mostly need to be carried out in strongly acidic systems, and high-temperature heating may lead to product decomposition or the generation of more byproducts. Furthermore, hydrobromic acid and bromine gas are highly corrosive, significantly corroding reaction equipment (such as glass and metal). Especially in large-scale industrial production, the cost of corrosion protection for equipment is high, and improper operation may lead to bromine gas leakage, which is harmful to operators and the environment.

[0005] In recent years, electrocatalytic organic synthesis has emerged as a method for organic synthesis driven by electrical energy. It achieves oxidation or reduction reactions by directly or indirectly involving electrodes in the reaction, replacing chemical reagents in traditional chemical reactions. Its core principle is to excite electron transfer between molecules under mild conditions by controlling the electrode potential, thereby achieving the formation or breaking of specific chemical bonds. Therefore, electrocatalytic or promoted organic transformations have gradually become one of the hot research directions in synthetic chemistry. Given the shortcomings of the above synthetic methods, the timely utilization of elemental bromine generated by the oxidation of bromide ions in the electrooxidation of ethylene to 2-bromoethanol using an aqueous electrolyte medium is extremely important. Therefore, finding a cheap and efficient electrocatalyst that achieves high conversion and selectivity in electrocatalytic synthesis is essential. Some researchers have used metal-based materials such as Ir, Co₂O₃, and NiO as catalysts in their research on the electrocatalytic oxidation of ethylene to 2-bromoethanol, but these are expensive and difficult to recycle. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a method for the selective electro-oxidation synthesis of 2-bromoethanol mediated by sodium bromide solution as a bromine source. This method can achieve efficient and highly selective synthesis of 2-bromoethanol over a wide potential range. Furthermore, this invention uses inexpensive, readily available, and efficient carbon materials as electrodes, and green, safe, and abundant water as a solvent and hydrogen source. The reaction conditions are mild, no heating is required, the operation is simple, and the catalyst is easy to recover.

[0007] The technical objective of this invention is achieved through the following technical solution.

[0008] A method for selective electrooxidation of ethylene to synthesize 2-bromoethanol mediated by sodium bromide solution as a bromine source is disclosed. The method involves a constant-potential electrochemical selective oxidation in a three-electrode system with carbon paper as the working electrode. The cathode and anode chambers are separated by a proton exchange membrane. An aqueous sodium bromide solution is introduced into both electrode chambers. Ethylene passes through the gas chamber, permeates the carbon paper, and forms a gas-liquid-solid interface on the surface of the carbon paper. 2-bromoethanol is obtained from the liquid product at the anode through constant-potential electrochemical selective oxidation.

[0009] In the technical solution of this invention, the reaction potential is 0.5-1.3V (Hg / Hg2Cl2).

[0010] In the technical solution of this invention, a peristaltic pump is used to pump an aqueous sodium bromide solution into the bipolar chamber and control its flow rate, such as 10-30 rpm.

[0011] In the technical solution of this invention, a flow meter is used to control the flow rate of ethylene, such as 10-30 sccm.

[0012] In the technical solution of this invention, the concentration of sodium bromide solution is 0.25-1M.

[0013] In the technical solution of this invention, nickel foam or platinum sheet is used as counter electrode, and Hg / Hg2Cl2 (1.0M NaBr aqueous solution) is used as reference electrode.

[0014] In the technical solution of the present invention, a flow cell electrolytic cell is used as the reaction vessel.

[0015] In the technical solution of this invention, the reaction environment temperature is room temperature, 20-25℃.

[0016] In the technical solution of this invention, carbon paper is used as a catalyst to convert ethylene into 2-bromoethanol under the mediation of sodium bromide solution as bromine source, and the carbon paper (CP) is hydrophobic carbon paper 28BC type.

[0017] This invention uses inexpensive, readily available, and efficient carbon materials as electrodes, and green, safe, and abundant water as a solvent and hydrogen source. The reaction conditions are mild, requiring no heating, and the operation is simple. The products are easy to separate, and the catalyst is easy to recover. This effectively avoids the problems of other synthetic methods, such as the use of precious metal catalysts, complex operation, long reaction time, low yield, poor selectivity, high reagent toxicity, and environmental pollution caused by reaction byproducts. The carbon electrode has good stability and can be recycled multiple times. The Faraday efficiency, yield, and selectivity for generating 2-bromoethanol do not change significantly, exhibiting high conversion rate and selectivity, and avoiding the influence of byproducts. Attached Figure Description

[0018] Figure 1 The images show the nuclear magnetic resonance (NMR) spectra of standard samples of 2-bromoethanol at different concentrations used in this invention.

[0019] Figure 2 The graph shows the linear relationship between the concentration of 2-bromoethanol and the ratio of the NMR peak area of ​​2-bromoethanol to that of DMSO.

[0020] Figure 3 These are the nuclear magnetic resonance line spectra of the products under different constant potentials in the embodiments of this invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0022] A flow cell electrolytic cell was used as the reaction vessel. The cathode and anode chambers of the electrolytic cell were separated by a proton exchange membrane. 20 ml of 1 M sodium bromide solution was placed in an electrolyte bottle, and the liquid was injected into both chambers at 20 rpm using a peristaltic pump. Ethylene was introduced into the gas chamber at 20 sccm. A hydrophobic 28BC carbon paper was placed between the gas chamber and the anode chamber, allowing ethylene gas to pass through while preventing electrolyte penetration in the anode chamber. The carbon paper was used as the working electrode, nickel foam as the counter electrode, and a (Hg / Hg2Cl2) electrode as the reference electrode. The system was connected to an electrochemical workstation, and an isostatic test was performed. After ten minutes of reaction, the anolyte product was collected, and 2-bromoethanol was obtained by NMR detection. Quantitative analysis was then performed using NMR.

[0023] After cleaning the anolyte, add fresh electrolyte to prepare for the next potential test.

[0024] To perform quantitative analysis of the product 2-bromoethanol, 2-bromoethanol standards of different concentrations were purchased for NMR testing. A linear programming algorithm was then applied to the 2-bromoethanol concentration and the ratio of the dibromoethanol to the DMSO NMR peak area, as follows: Figure 1 and Figure 2As shown. Further nuclear magnetic resonance (NMR) analysis of the anolyte products obtained at different constant potentials revealed that the products at all potentials were the target product, 2-bromoethanol. Based on... Figure 2 The linear relationship presented is used to calculate the concentration of the target product. In the testing of the product of this invention, the calculation of the product's charge utilization efficiency (Faradaic efficiency, %) is based on:

[0025]

[0026] Where n is the number of electrons transferred, m is the amount of substance of the product, and F is the Faraday constant 96485 Cmol. -1 C represents the total charge consumed in the reaction.

[0027]

[0028]

[0029] The above analysis shows that the test results are not significantly affected by the potential, and the target product 2-bromoethanol can be prepared in all cases, with a Faraday efficiency of 60%-73%.

[0030] Adjusting the process parameters according to the present invention can achieve the synthesis of 2-bromoethanol, exhibiting performance essentially consistent with that of the present invention. The present invention has been described above as exemplary. It should be noted that any simple modifications, alterations, or other equivalent substitutions that can be made by those skilled in the art without creative effort, without departing from the core of the present invention, fall within the protection scope of the present invention.

Claims

1. A method for the selective electrooxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source, characterized in that, In a three-electrode system with carbon paper as the working electrode, constant potential electrochemical selective oxidation is performed. The cathode chamber and the anode chamber are separated by a proton exchange membrane. Sodium bromide aqueous solution is introduced into the two electrode chambers. Ethylene passes through the gas chamber, permeates through the carbon paper, and forms a gas-liquid-solid three-phase interface on the surface of the carbon paper. 2-bromoethanol is obtained in the liquid product of the anode through constant potential electrochemical selective oxidation. The carbon paper is hydrophobic.

2. The method for selective electrooxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, The reaction potential is 0.5–1.3 V Hg / Hg2Cl2.

3. The method for selective electro-oxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, The flow rate of ethylene is controlled to be 10-30 sccm using a flow meter.

4. The method for selective electro-oxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, A peristaltic pump is used to pump an aqueous sodium bromide solution into the bipolar chamber, and the flow rate is controlled at 10–30 rpm.

5. The method for selective electro-oxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, The concentration of sodium bromide solution is 0.25–1 M.

6. The method for selective electro-oxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, Nickel foam or platinum sheet is used as the counter electrode, and Hg / Hg2Cl2 is used as the reference electrode.

7. The method for selective electrooxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, A flow cell electrolyzer was used as the reaction vessel.

8. The method for selective electro-oxidation of ethylene to 2-bromoethanol mediated by sodium bromide solution as a bromine source according to claim 1, characterized in that, The reaction environment temperature is room temperature, 20-25℃.

Images