A method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using Pickering emulsion

Abstract

The present invention discloses a method for synthesizing organic nitrile compounds by electrocatalytic dehydration of aldoxime in a Pickering emulsion, comprising the following steps: ultrasonically dispersing carbon nanotubes in water, dissolving an aldoxime organic substance in cyclohexane, mixing the aqueous solution with the cyclohexane solution, and forming a Pickering emulsion under the action of a homogenizer with a speed of 1500 rpm or more; then injecting a certain amount of nitrogen dioxide gas at a temperature of -0.3 to -1.2 V. RHE The electrolysis was continued within the voltage range for 12 h, and the homogenizer was used for homogenization for 5 seconds every 5 minutes. The present invention relates to the field of organic electrosynthesis technology. The method for synthesizing organic nitrile compounds by electrocatalytic dehydration of aldoxime in a Pickering emulsion is a method for directly preparing organic nitrile in a reactor from the reactants aldoxime and nitrogen dioxide under electrical drive. This method avoids the traditional synthesis technology route of organic nitrile and synthesizes nitrile compounds in one step. It is a new, green and safe synthesis method with low harm to human body and environment.

Description

Technical Field

[0001] The invention relates to the technical field of organic electrosynthesis, in particular to a method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion. Background Art

[0002] Nitriles are a versatile synthetic intermediate used in pharmaceuticals, pesticides, and dyes. Nucleophilic substitution of alkyl halides with stoichiometric amounts of inorganic cyanide is a common method for synthesizing alkyl nitriles, often accompanied by elimination of hydrogen halide, particularly with bulky alkyl halides. Aromatic nitriles (benzonitrile) can be synthesized via the Sandmeyer reaction and ammoxidation. While unsaturated nitriles can be synthesized via the Wittig reaction of the corresponding aldehyde with a cyanoalkyl phosphate, this method typically produces a mixture of E- and Z-isomeric nitriles. Consequently, many of these conventional nitrile synthesis methods require hazardous reagents, such as inorganic cyanide, and can be nonselective.

[0003] Compared to classic nitrile preparation methods, particularly those using highly toxic cyanide, the dehydration of aldoximes is an attractive approach due to their readily available availability, simplicity, and the production of water as a byproduct. Although various methods have been developed for the dehydration of aldoximes, drawbacks remain. For example, some methods require harsh reaction conditions, utilize specialized reagents or large amounts of dehydrating agents, or suffer from low functional group tolerance, waste generation, and difficulty in product purification. Transition-metal-catalyzed methods using Ru, Re, Pt, Pd, W, Sn, Ni, Cu, Zn, Ga, and Fe catalysts have also garnered considerable attention in recent years. However, these methods are subject to inert atmosphere protection, high catalyst loadings, high reaction temperatures (>100°C), and the need for a wide range of ligands. Therefore, the development of strategies for the dehydration of aldoximes to nitriles under milder conditions and using inexpensive catalysts is crucial.

[0004] Compared to traditional chemical catalysis, electrocatalysis can be used at lower temperatures and pressures, with higher reaction rates and synergistic effects. Furthermore, due to the demands of green chemistry and the chemical industry, the introduction of water as a solvent in reactions instead of organic compounds is advantageous because water obtained from natural sources is non-toxic and compatible with life, with a moderate environmental impact. However, the low solubility of organic reactants in water leads to incompatibility in the reaction system, resulting in unsatisfactory catalytic efficiency and hindering its widespread application in electrochemistry.

[0005] Organic-aqueous two-phase catalytic reactions are widely used in biorefining, fine chemical production, and enzymatic reactions due to their improved solubility of reactants. However, the limited reaction interface resulting from uneven oil-water mixing restricts liquid-liquid contact, thereby inhibiting catalytic efficiency. To overcome this insurmountable limitation and improve its practicality, surfactants are often required to promote liquid-liquid contact in the two-phase system and improve mass transfer through emulsion formation. However, the additional addition of surfactants inevitably increases the complexity of the reaction system, especially in terms of recovering the final product and emulsifier, which raises environmental concerns. Therefore, the use of recyclable solid emulsifiers is necessary to address the recycling issue and mitigate the impact of environmental pollution and energy consumption.

[0006] To address these challenges, the development of recyclable solid catalysts at the liquid-liquid interface is highly desirable. Pickering interfacial catalysis refers to a system in which solid particles act as both a solid stabilizer and a catalyst at the liquid / liquid interface of a Pickering emulsion. In the presence of a large number of colloid-stabilized emulsions, the catalyst can reside in the liquid phase (continuous / dispersed phase) or at the liquid / liquid interface. The large reaction interface and unique two-phase environment provided by Pickering emulsions offer irreplaceable advantages: excellent solid catalyst recovery; large interfacial area promotes reaction kinetics; selective catalysis of different substrates distributed between two immiscible reagents; spontaneous separation of key products through a "phase transfer" process, inhibiting unnecessary secondary reactions; and facilitating substrate / product transfer between the phases. To date, Pickering emulsion catalysis has been widely applied in a variety of reaction systems, including hydrogenation / reduction, oxidation / epoxidation, enzymatic reactions, acid-base catalysis, and cascade reactions.

[0007] The development of Pickering emulsion electrocatalysis, which combines electrochemistry with Pickering emulsion catalysis, has begun. In electrocatalytic hydrogenation, the large interface created in the Pickering emulsion, which includes an aqueous electrolyte and an organic phase containing the substrate, allows protons to be integrated from the aqueous phase into the organic phase in the other phase, while eliminating post-processing steps such as substrate separation and their associated limitations. Summary of the Invention

[0008] To achieve the above object, the present invention is implemented by the following technical solution: a method for synthesizing organic nitrile compounds by electrocatalytic dehydration of aldoxime in a Pickering emulsion, comprising the following steps:

[0009] The carbon nanotubes were ultrasonically dispersed in water, and the aldoxime organic matter was dissolved in an equal volume of cyclohexane. The two were mixed and then formed into a Pickering emulsion under the action of a homogenizer. The speed of the homogenizer was above 1500 rpm. Then a certain amount of nitrogen dioxide gas was injected at -0.3~-1.2V. RHE Electrolysis was continued within the voltage range for 12 h, with homogenization for 5 seconds every 5 minutes.

[0010] The reaction route is as follows: Wherein: R is a substituted or unsubstituted phenyl group, an alkyl group or a halogen-containing phenyl group;

[0011] Preferably, the Pickering emulsion is prepared by ultrasonically dispersing carbon nanotubes in a sodium sulfate electrolyte solution as the aqueous phase, with a mass concentration of the carbon nanotubes of 0.2-5 g / L; then dissolving a low-soluble aldoxime organic reaction substrate in cyclohexane as the oil phase, with a substrate concentration of 0.01-10 mol / L. The total volume of the Pickering emulsion oil-water phase is 1 mL-100 L, with an oil-water phase volume ratio of 0.1-10. The oil-water phase and the mixture are then emulsified using a high-speed homogenizer at a speed of 1500 rpm or higher to obtain the Pickering emulsion.

[0012] Preferably, the composition is an electrolyte with water as solvent and sodium sulfate as electrolyte, wherein the electrolyte can be any one of hydrochloric acid, sulfuric acid, nitric acid, sodium chloride, potassium chloride, potassium sulfate, potassium hydroxide, sodium hydroxide, sodium carbonate, and potassium carbonate.

[0013] Preferably, the stabilizer and catalyst of the Pickering emulsion are acidified carbon nanotubes.

[0014] Preferably, the method for preparing acidified carbon nanotubes comprises:

[0015] treating the raw carbon nanotubes with a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:1 to remove metal impurities and generate oxygen-containing functional groups on the surface of the carbon nanotubes, wherein the concentration of the carbon nanotubes in the acid solution is 0.1-50 g / L;

[0016] In a typical procedure, 10 g of pristine carbon nanotubes were suspended in 500 mL of the acid mixture and heated at 60–120 °C for 1–4 h;

[0017] The solid product was then washed several times with ultrapure water and dried in a vacuum oven at 50-100°C to obtain a sample.

[0018] Preferably, the low-soluble aldoxime organic matter is mainly distributed in the cyclohexane organic phase.

[0019] Preferably, the molar ratio of nitrogen dioxide to aldoxime is 0.05 to 0.5.

[0020] Preferably, the molar ratio of nitrogen dioxide to aldoxime is preferably 0.1 to 0.2.

[0021] Preferably, the reaction needs to be at -0.8V RHE Next proceed.

[0022] Preferably, the room temperature is 20-30°C.

[0023] Preferably, the reaction time is 12 hours.

[0024] Preferably, the amount of carbon nanotubes used is 8 mg.

[0025] Preferably, the reaction substrate concentration is 50 mM.

[0026] Preferably, the speed of the homogenizer is 12000 rpm.

[0027] The present invention provides a method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion. The method has the following beneficial effects:

[0028] The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion is driven by electricity, and the reactants aldoxime and nitrogen dioxide are directly used to prepare organic nitrile in a reactor. This method avoids the traditional technical route of organic nitrile and synthesizes nitrile compounds in one step. It is a new, green and safe synthesis method with low harm to humans and the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an optical microscope image of the carbon nanotube-stabilized Pickering emulsion of the present invention;

[0030] Figure 2 This is the GC-MS spectrum of the benzonitrile compound prepared by the present invention;

[0031] Figure 3 This is the GC-MS spectrum of the p-chlorobenzonitrile compound prepared by the present invention;

[0032] Figure 4 This is the GC-MS spectrum of the p-methylbenzonitrile compound prepared by the present invention;

[0033] Figure 5 This is the GC-MS spectrum of the p-bromobenzonitrile compound prepared by the present invention;

[0034] Figure 6 This is the GC-MS spectrum of the p-methoxynitrile compound prepared by the present invention;

[0035] Figure 7 This is the GC-MS spectrum of the octanonitrile compound prepared by the present invention;

[0036] Figure 8 This is the GC-MS spectrum of the quinonitrile compound prepared by the present invention;

[0037] Figure 9 The figure is the GC-MS spectrum of the 1-naphthonitrile compound prepared by the present invention. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] See also Figures 1-9 The present invention provides a technical solution: a method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion, which is mainly as follows:

[0040] At room temperature, aldoxime and nitrogen dioxide react in emulsion electrocatalysis to produce nitrile compounds, with the catalyst being acidified carbon nanotubes, and the yield is 75%-85%.

[0041] Specifically, the present invention is further described in detail through the following specific experimental examples.

[0042] Example: Preparation of benzonitrile from benzaldehyde oxime, the reaction scheme is as follows: Weigh 8 mg of carbon nanotubes and add them to 8 mL of sodium sulfate electrolyte, and ultrasonically homogenize them; add 121 mg of benzaldehyde oxime to 8 mL of cyclohexane, then add the aqueous phase and the organic phase to the cathode chamber of the electrolytic cell in sequence, and homogenize them at 12000 rpm for 2 minutes to obtain Pickering emulsion. The anode chamber of the electrolytic cell is filled with 70 mL of sodium sulfate electrolyte. Then, nitrogen dioxide gas is introduced into the cathode chamber at -0.8 V. RHE Electrolysis was performed for 12 hours, during which the homogenizer was used to homogenize for 5 seconds every 5 minutes. After the reaction was completed, the organic phase was filtered out, and the resulting solution was concentrated by rotary evaporation to obtain a crude product. The crude product was separated by silica gel chromatography (eluent: petroleum ether) to obtain 87 mg of a transparent oily liquid with a yield of 85%. The product prepared in this example was subjected to GC-MS testing, and the spectra are shown in detail. Figure 2 .

[0043] According to the above synthesis method, the following compounds were synthesized. In the present invention, different substituents and substrate types have little effect on the reactivity of the compounds: The GC-MS spectra of the above products correspond to Figure 3-Figure 9 .

[0044] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without making creative efforts should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention shall be implemented in accordance with conventional means in the field unless otherwise specified or limited.

Claims

1. A method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion, characterized in that: The steps include: at room temperature, in a Pickering emulsion system, low-soluble aldoxime organic matter and nitrogen dioxide are reacted at -0.3 ~ -1.2V RHE The emulsion stabilizer and catalyst are acidified carbon nanotubes. The reaction equation is as follows: ； Wherein: R is a substituted or unsubstituted phenyl or alkyl group; The preparation of the Pickering emulsion requires ultrasonically dispersing acidified carbon nanotubes in a sodium sulfate electrolyte solution as the aqueous phase, with the mass concentration of the acidified carbon nanotubes being 0.2-5 g / L, and then dissolving the low-soluble aldoxime organic reaction substrate in cyclohexane as the oil phase, with the substrate concentration being 0.01-10 mol / L. The total volume of the Pickering emulsion oil-water phase is 1 mL-100 L, and the oil-water phase volume ratio is 0.1-10. After the two are mixed, they are emulsified using a high-speed homogenizer at a speed of 1500 rpm or more to obtain the Pickering emulsion. The method for preparing acidified carbon nanotubes comprises: The raw carbon nanotubes are treated with a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:1 to remove metal impurities and generate oxygen-containing functional groups on the surface of the carbon nanotubes. The concentration of the carbon nanotubes in the acid solution is 0.1-50g / L.

2. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 1, wherein: The composition of the sodium sulfate electrolyte solution is an electrolyte solution with water as a solvent and sodium sulfate as an electrolyte.

3. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 2, wherein: The method for preparing acidified carbon nanotubes further comprises: In a typical procedure, 10 g of pristine carbon nanotubes were suspended in 500 ml of an acid mixture and heated at 60–120 °C for 1–4 h; The solid product was then washed several times with ultrapure water and dried under vacuum at 50–100 °C to obtain a sample.

4. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 3, wherein: The low-soluble aldoxime organic matter is mainly distributed in the cyclohexane organic phase.

5. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 4, characterized in that: The molar ratio of nitrogen dioxide to aldoxime is 0.05 to 0.5.

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