Method for preparing organic nitrile compound through electrocatalytic aldoxime dehydration realized by Pickering emulsion

Abstract

The invention discloses a method for synthesizing an organic nitrile compound by using Pickering emulsion to electrocatalyze aldoxime dehydration, which comprises the following steps: ultrasonically dispersing carbon nanotubes in water, dissolving aldoxime organic matters in cyclohexane, mixing an aqueous solution with a cyclohexane solution, and forming the Pickering emulsion under the action of a homogenizer with the rotating speed of more than 1500rpm; then injecting a certain amount of nitrogen dioxide gas, continuously electrolyzing for 12 hours within the voltage range of-0.3 VRHE to-1.2 VRHE, and homogenizing for 5 seconds by the homogenizer every 5 minutes; the invention relates to the technical field of organic electro-synthesis, in particular to a method for synthesizing an organic nitrile compound by using Pickering emulsion to electrocatalyze aldoxime dehydration, which is a method for directly preparing organic nitrile from reactants aldoxime and nitrogen dioxide in a reactor under electric drive. According to the method, the traditional synthetic technical route of organic nitrile is avoided, the nitrile compound is synthesized in one step, and the method is a novel synthetic method which is brand-new, green, safe and low in harm to a human body and the 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 through 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 cyanides is a general method for the synthesis of alkyl nitriles, which is often accompanied by the elimination of hydrogen halide, especially with bulky alkyl halides. Aromatic nitriles (benzonitrile) can be synthesized via the Sandmeyer reaction and ammoxidation. Although unsaturated nitriles can be synthesized via the Wittig reaction of the corresponding aldehyde with a cyanoalkyl phosphate, this method generally produces a mixture of E- and Z-isomeric nitriles. Therefore, many of these conventional nitrile synthesis methods require hazardous reagents, such as inorganic cyanides, and may be non-selective.

[0003] Compared with classical nitrile preparation methods, especially those using highly toxic cyanide, the dehydration of aldoxime is an attractive method because aldoxime is easily available, the process is simple, and water is produced as a byproduct. Although various methods have been developed for the dehydration of aldoxime, disadvantages still exist. For example, some methods require harsh reaction conditions, use special reagents or large amounts of dehydrating agents, or suffer from low functional group tolerance, waste generation, and difficult product purification. In recent years, transition metal-catalyzed methods using Ru, Re, Pt, Pd, W, Sn, Ni, Cu, Zn, Ga, and Fe catalysts have also received much attention, but inert atmosphere protection, high catalyst loading, high reaction temperature (>100 °C), and the need for variable ligands are inevitable. Therefore, it is crucial to develop strategies that can catalyze the dehydration of aldoxime to nitriles under milder conditions using inexpensive catalysts.

[0004] Compared with traditional chemical catalysis, electrocatalysis can be used at lower temperatures and pressures, with higher reaction rates and synergistic effects. In addition, due to the requirements of green chemistry and the chemical industry, it is advantageous to introduce water instead of organic matter as a solvent in the reaction, 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 the reaction in water leads to incompatibility in the reaction system, resulting in unsatisfactory catalytic efficiency, hindering its widespread application in electrochemistry.

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

[0006] In order to solve the above problems, it is very necessary to develop recyclable solid catalysts at the liquid-liquid interface. Pickering interfacial catalysis refers to a system in which solid particles can act as both solid stabilizers and catalysts at the liquid / liquid interface of Pickering emulsions. In the presence of a large amount of colloid-stabilized emulsions, the catalyst can be located in the liquid phase (continuous phase / dispersed phase) or the liquid / liquid interface. Due to the large reaction interface and unique two-phase environment provided by Pickering emulsions, irreplaceable advantages are shown: good recovery rate of solid catalysts; large interfacial area promotes reaction kinetics; selective catalysis of different reaction substrates distributed in two immiscible reagents; spontaneous separation of key products based on the "phase transfer" process, and prohibition of meaningless secondary reactions; promotion of substrate / product transfer between phases. So far, Pickering emulsion catalysis has been widely used in multiple reaction systems such as hydrogenation / reduction, oxidation / epoxidation, enzymatic reactions, acid-base catalytic reactions, cascade reactions, etc.

[0007] Combining electrochemistry with Pickering emulsion catalysis, Pickering emulsion electrocatalysis has begun to develop. In electrocatalytic hydrogenation, the huge interface generated in the Pickering emulsion, which includes an aqueous electrolyte and an organic phase containing the substrate, allows protons to be integrated from water into the organic phase in the other phase, while eliminating post-processing steps such as substrate separation and related limitations. Summary of the invention

[0008] To achieve the above object, the present invention is implemented by the following technical scheme: a method for synthesizing organic nitrile compounds by electrocatalytic dehydration of aldoxime in a Pickering emulsion, comprising the following steps: 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, and then a certain amount of nitrogen dioxide gas was injected at -0.3~-1.2V. 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.

[0009] The reaction route is as follows: Wherein: R is a substituted or unsubstituted phenyl, alkyl or halogen-containing phenyl; Preferably, the preparation of the Pickering emulsion requires ultrasonically dispersing carbon nanotubes in a sodium sulfate electrolyte solution as an aqueous phase, with a mass concentration of carbon nanotubes of 0.2-5 g / L; then dissolving a low-soluble aldoxime organic reaction substrate in cyclohexane as an oil phase, with a substrate concentration of 0.01-10 mol / L. The total volume of the oil-water phase of the Pickering emulsion is 1 mL-100 L, and the oil-water phase volume ratio is 0.1-10. After the two are mixed, they are emulsified with a high-speed homogenizer to obtain the Pickering emulsion, and the speed of the homogenizer is above 1500 rpm.

[0010] 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.

[0011] Preferably, the stabilizer and catalyst of the Pickering emulsion are acidified carbon nanotubes.

[0012] Preferably, the method for preparing acidified carbon nanotubes comprises: 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; In a typical procedure, 10 g of pristine CNTs were suspended in 500 mL of the 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.

[0013] Preferably, the low-soluble aldoxime organic matter is mainly distributed in the cyclohexane organic phase.

[0014] Preferably, the molar ratio of nitrogen dioxide to aldoxime is 0.05 to 0.5.

[0015] Preferably, the molar ratio of nitrogen dioxide to aldoxime is preferably 0.1 to 0.2.

[0016] Preferably, the reaction needs to be at -0.8V RHE Next proceed.

[0017] Preferably, the room temperature is 20-30°C.

[0018] Preferably, the reaction time is 12 h.

[0019] Preferably, the amount of carbon nanotubes used is 8 mg.

[0020] Preferably, the reaction substrate concentration is 50 mM.

[0021] Preferably, the speed of the homogenizer is 12000 rpm.

[0022] 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: The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using Pickering emulsion, under electric drive, the reactants aldoxime and nitrogen dioxide directly 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 human body and environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an optical microscope image of the Pickering emulsion stabilized by carbon nanotubes of the present invention; Figure 2 The GC-MS spectrum of the benzonitrile compound prepared by the present invention; Figure 3 This is the GC-MS spectrum of the p-chlorobenzonitrile compound prepared by the present invention; Figure 4 This is the GC-MS spectrum of the p-methylbenzonitrile compound prepared by the present invention; Figure 5 This is the GC-MS spectrum of the p-bromobenzonitrile compound prepared by the present invention; Figure 6 This is the GC-MS spectrum of the p-methoxynitrile compound prepared by the present invention; Figure 7 This is the GC-MS spectrum of the octanonitrile compound prepared by the present invention; Figure 8 This is the GC-MS spectrum of the nitrile compound prepared by the present invention; Fig. 9 The figure is the GC-MS spectrum of the 1-naphthonitrile compound prepared by the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0025] See also Figure 1-Figure 9The 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: At room temperature, aldoxime and nitrogen dioxide are electrocatalyzed in emulsion to obtain nitrile compounds, the catalyst is acidified carbon nanotubes, and the yield is 75%-85%.

[0026] Specifically, the present invention is further described in detail through the following specific experimental examples.

[0027] Embodiment: 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 mix them evenly with ultrasound; 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 turn, and homogenize them at 12000 rpm for 2 minutes to obtain the 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 The electrolysis was carried out 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 column 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 .

[0028] 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 .

[0029] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and 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 group, an alkyl group or a halogen-containing phenyl group.

2. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 1, characterized in that: The preparation of the Pickering emulsion requires ultrasonically dispersing carbon nanotubes in a sodium sulfate electrolyte solution as an aqueous phase, with a mass concentration of the carbon nanotubes of 0.2-5 g / L, and then dissolving a low-soluble aldoxime organic reaction substrate in cyclohexane as an oil phase, with a substrate concentration of 0.01-10 mol / L. The total volume of the oil-water phase of the Pickering emulsion is 1 mL-100 L, and the oil-water phase volume ratio is 0.1-10. After the two are mixed, they are emulsified with a high-speed homogenizer to obtain the Pickering emulsion, and the speed of the homogenizer is above 1500 rpm.

3. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 2, characterized in that: The invention is composed of 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.

4. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 3, characterized in that: The stabilizer and catalyst of the Pickering emulsion are acidified carbon nanotubes.

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 method for preparing acidified carbon nanotubes comprises: 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; In a typical procedure, 10 g of pristine CNTs were suspended in 500 mL of the 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.

6. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 5, characterized in that: The low-soluble aldoxime organic matter is mainly distributed in the cyclohexane organic phase.

7. The method for preparing organic nitrile compounds by electrocatalytic dehydration of aldoxime using a Pickering emulsion according to claim 6, characterized in that: The molar ratio of the nitrogen dioxide to the aldoxime is 0.05 to 0.5.

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