An electrocatalytic preparation method of an amide

Abstract

The present invention discloses an electrocatalytic preparation method of amide. Using carboxylic acid as a carbon source and nitrogen-containing lye as a nitrogen source, under the action of electrocatalytic co-reduction, through the coupling reaction of free radical intermediates, the product amide is finally obtained. This method uses an inexpensive and readily available transition metal as a catalyst and conducts an electro-synthesis reaction under mild and environmentally friendly conditions of normal temperature and normal pressure, having great application prospects and commercial value.

Description

Technical Field

[0001] The present invention relates to an electrocatalytic synthesis method of amides. More specifically, it relates to the preparation of formamide and its derivatives by the co-reduction process of carboxylic acids and (sub) nitrates. Background Art

[0002] Amides and formamides, as very important chemicals, are widely used in various industries. Specifically, they can be used as industrial solvents in industry, for the production of vitamins and hormones in the pharmaceutical industry, and for manufacturing pesticides in agriculture. In addition, amides are also important intermediates involved in many organic reaction processes. So far, the industrial synthesis of amides requires high-temperature and high-pressure reaction conditions, and a large amount of organic solvents need to be provided, with high costs, high energy consumption, low yields, and a complex separation and purification process in the later stage. Therefore, a large amount of work has been devoted to the green synthesis of amides. CN101970675A discloses a method for preparing amide compounds by biocatalyzing nitrile compounds. A patent of BASF SE (CN102712576A) uses phosphoric acid or a Lewis acidic metal salt as a catalyst to catalyze the conversion of primary amines and formates to prepare aromatic formamides. Additionally, patent CN101684076B uses amino acid ionic liquids as a reaction medium and catalyst to catalyze the Beckmann rearrangement reaction of ketoximes to prepare amides. The preparation methods of amides have become a research hotspot in the world today, but there are still some problems in the current amide synthesis process: low yields, high energy consumption, generation of polluting substances, complex catalyst preparation, and easy deactivation, etc. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art, overcome the problems of high energy consumption, high pollution, and high costs caused in the preparation process of current amide chemicals, and provide an electrocatalytic preparation method of amides, which uses carboxylic acid substances as a carbon source, and nitrate or gas as a nitrogen source, with low costs and being environmentally friendly. In addition, this reaction process is carried out in an aqueous solution, and the later separation and purification are easier.

[0004] The technical purpose of the present invention is achieved through the following technical solutions.

[0005] An electrocatalytic preparation method of amides, in a three-electrode system, a working electrode is selected as a catalyst, a carbon source substance and a nitrogen source substance are uniformly dispersed in an electrolyte solution, and a constant potential is applied to the electrolyte solution for reaction to obtain amides; wherein: the pH of the electrolyte solution is 8 - 13, the carbon source substance is a carboxylic acid, and the nitrogen source substance is a nitrate, nitrite, or nitrogen-containing gas; the molar ratio of the carboxylic acid to the nitrate is (1 - 3):(1 - 8); the molar ratio of the carboxylic acid to the nitrite is (1 - 3):(1 - 8); when the nitrogen source substance is selected as a nitrogen-containing gas, in the constant potential reaction, the nitrogen-containing gas is in a saturated state in the electrolyte solution.

[0006] In the above method, the carboxylic acid is formic acid, acetic acid, propionic acid or benzoic acid.

[0007] In the above method, the nitrate is sodium nitrate or potassium nitrate.

[0008] In the above method, the nitrite is sodium nitrite or potassium nitrite.

[0009] In the above method, the nitrogen-containing gas is nitric oxide.

[0010] In the above method, the molar ratio of the carboxylic acid to the nitrate is (1-2):(1-3).

[0011] In the above method, the molar ratio of the carboxylic acid to the nitrite is (1-2):(1-3).

[0012] In the above method, the working electrode is copper, iron or nickel, such as a copper sheet, copper mesh, copper foam, molybdenum sheet, iron sheet, nickel foam or carbon cloth.

[0013] In the above method, the reference electrode is a saturated calomel electrode, a silver / silver chloride electrode (Ag / AgCl), a mercury / mercuric oxide electrode (Hg / HgO), and the counter electrode is a carbon rod or platinum-carbon.

[0014] During the reaction process, the area of each electrode inserted into the electrolyte solution is controlled to be ≥1 cm 2 .

[0015] During the reaction process, magnetic or mechanical stirring is used to achieve uniform and continuous occurrence of the reaction, and the stirring speed is 300 r / min to 1000 r / min).

[0016] During the reaction process, an external circuit supplies power, and a constant potential is selected for the reaction. The voltage is -0.1 V to -1.2 V vs. RHE, preferably -0.4 V to -0.8 V vs. RHE; the reaction time is at least 1 hour, such as 3-5 hours.

[0017] In the above method, the pH of the electrolyte solution is 9-11.

[0018] In the above method, the electrolyte solution is an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of potassium bicarbonate or an aqueous solution of sodium bicarbonate.

[0019] The preparation method of the present invention conducts an electroreductive coupling reaction under normal temperature, normal pressure, environmentally friendly and mild conditions. First, carboxylic acid substances and nitrogen-containing substances are adsorbed on the catalyst surface; next, both of them undergo reduction reactions simultaneously, generating carbon radicals and amino intermediates; through the coupling effect of the intermediates, a C-N bond is finally formed to obtain amides. Compared with the prior art, the technical solution of the present invention has a high yield and a simple separation and purification process; it can be produced in small-scale decentralized production, saving a large amount of transportation costs; it uses H2O molecules as a hydrogen source, which is safe and pollution-free; it can utilize pollutants (alkali solution, nitric oxide or sodium nitrate) in sewage for synthesis reactions, realizing the reuse of waste and turning waste into treasure; it has high universality with various carboxylic acids as carbon sources and can be extended to the synthesis of a series of other amide chemicals, having great application prospects and commercial value. Brief Description of the Drawings

[0020] Figure 1 1H NMR spectrum of the electrolysis product with formic acid and sodium nitrite as reactants in Example 1 of the present invention 1 (1H) spectrum.

[0021] Figure 2 Gas chromatography-mass spectrometry of the ethyl acetate extraction after electrolysis with formic acid and sodium nitrite as reactants in Example 1 of the present invention.

[0022] Figure 3 1H NMR spectrum of the product in Example 2 of the present invention 1 (1H) spectrum.

[0023] Figure 4 1H NMR spectrum of the product in Example 3 of the present invention 1 (1H) spectrum.

[0024] Figure 5 1H NMR spectrum of the product in Example 4 of the present invention 1 (1H) spectrum.

[0025] Figure 6 1H NMR spectrum of the product in Example 5 of the present invention 1 (1H) spectrum.

[0026] Figure 7 1H NMR spectrum of the product in Example 6 of the present invention 1 (1H) spectrum. Detailed Description of the Invention

[0027] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. The present invention uses formic acid and ammonium nitrate / sodium nitrite as raw materials to carry out a co-reduction reaction at the cathode to produce formamide. The reaction process is as follows: A certain proportion of formic acid and sodium nitrite are mixed evenly. In an electrolyte solution with water as the solvent, a constant potential is applied, and the reaction time is greater than 3 h. The solution of this reaction system requires a weakly alkaline condition, otherwise the synthesis of formamide cannot be achieved. The room temperature is 20-30 degrees Celsius.

[0028] Example 1

[0029] (1) Prepare the electrolyte: Prepare a 0.1 M NaOH aqueous solution, and add formic acid and sodium nitrite thereto successively so that their concentrations are 100 and 200 mM respectively, and use this as the electrolyte;

[0030] (2) Use a Shanghai Chenhua workstation, adopt a three-electrode system (Ag / AgCl as the reference electrode, a carbon rod as the counter electrode, and a copper mesh as the working electrode). In an H-type electrolytic cell, select the constant potential method, set the stirring speed to 600 revolutions per minute, and set the working voltage to -0.4 V vs. RHE to carry out a constant potential electrolysis reaction for 10800 s;

[0031] (3) After the reaction is completed, collect the electrolyte, use deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, and perform a proton nuclear magnetic resonance spectrum test with water peak suppression. The results show that the product is formamide ( Figure 1 ), proving that formic acid is the carbon source and sodium nitrite is the nitrogen source, and formamide is successfully synthesized; After the electrolyte is extracted with ethyl acetate, gas chromatography-mass spectrometry analysis ( Figure 2 ) is carried out, and the results also show that the product is formamide, proving that formic acid is the carbon source and sodium nitrite is the nitrogen source, and formamide is successfully synthesized.

[0032] Example 2

[0033] (1) Prepare the electrolyte: Prepare a 0.1 M NaOH aqueous solution, and add formic acid and sodium nitrate thereto successively so that their concentrations are 100 and 200 mM respectively, and use this as the electrolyte;

[0034] (2) Use a Shanghai Chenhua workstation, adopt a three-electrode system (Ag / AgCl as the reference electrode, a carbon rod as the counter electrode, and a copper mesh as the working electrode). In an H-type electrolytic cell, select the constant potential method, set the stirring speed to 400 r / min, and set the working voltage to -0.4 V (vs. RHE) to carry out a constant potential electrolysis reaction for 10800 s;

[0035] (3) After the reaction is completed, use deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, and perform a proton nuclear magnetic resonance spectrum test with water peak suppression. The results show that the product is formamide ( Figure 3) It was proved that formic acid was used as the carbon source and sodium nitrate as the nitrogen source, and formamide was successfully synthesized.

[0036] Example 3

[0037] (1) Prepare the electrolyte: Prepare an aqueous solution of 0.5 M KOH, and sequentially add acetic acid and sodium nitrite to make their concentrations 200 mM and 300 mM respectively, and use this as the electrolyte.

[0038] (2) Use the Shanghai Chenhua workstation, adopt a three-electrode system (Ag / AgCl as the reference electrode, carbon rod as the counter electrode, and copper mesh as the working electrode). In an H-type electrolytic cell, select the potentiostatic method, set the stirring speed to 900 r / min, and set the working voltage to -0.6 V (vs. RHE) to carry out a potentiostatic electrolysis reaction for 10800 s.

[0039] (3) After the reaction is completed, collect the electrolyte, use deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, and perform a 1H NMR test with water peak suppression. The results show that the product is formamide ( Figure 4 ) It was proved that acetic acid was used as the carbon source and sodium nitrite as the nitrogen source, and acetamide was successfully synthesized.

[0040] Example 4

[0041] (1) Prepare the electrolyte: Prepare an aqueous solution of 0.1 M Na2SO4 and 0.2 M KOH, and sequentially add propionic acid and sodium nitrite to make their concentrations 100 mM and 300 mM respectively, and use this as the electrolyte.

[0042] (2) Use the Shanghai Chenhua workstation, adopt a three-electrode system (Ag / AgCl as the reference electrode, carbon rod as the counter electrode, and copper mesh as the working electrode). In an H-type electrolytic cell, select the potentiostatic method, set the stirring speed to 800 r / min, and set the working voltage to -0.4 V (vs. RHE) to carry out a potentiostatic electrolysis reaction for 10800 s.

[0043] (3) After the reaction is completed, collect the electrolyte, use deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, and perform a 1H NMR test with water peak suppression. The results show that the product is formamide ( Figure 5 ) It was proved that propionic acid was used as the carbon source and sodium nitrite as the nitrogen source, and propionamide was successfully synthesized.

[0044] Example 5

[0045] (1) Prepare the electrolyte: Prepare an aqueous solution of 0.5 M KHCO3, and sequentially add benzoic acid and sodium nitrite to make their concentrations 100 mM and 300 mM respectively, and use this as the electrolyte.

[0046] (2) Using a Shanghai Chenhua workstation, a three-electrode system (Ag / AgCl as the reference electrode, a carbon rod as the counter electrode, and a copper mesh as the working electrode) was adopted. In an H-type electrolytic cell, the potentiostatic method was selected, the stirring speed was set at 800 r / min, and the working voltage was set at -0.4 V (vs. RHE) for a potentiostatic electrolysis reaction lasting for 10800 s;

[0047] (3) After the reaction ended, the electrolyte was collected. Using deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, a proton nuclear magnetic resonance spectrum test with water peak suppression was carried out. The results showed that the product was benzamide ( Figure 6 ), proving that benzoic acid was the carbon source, sodium nitrite was the nitrogen source, and benzamide was successfully synthesized.

[0048] Example 6

[0049] (1) Prepare the electrolyte: Prepare a 0.1 M aqueous NaOH solution, add formic acid to make its concentration 100 mM, and use this as the electrolyte;

[0050] (2) Introduce 20% NO (containing 80% Ar, by volume percentage) as the nitrogen source into the electrolyte, control the flow rate at 20 mL / min, wait until the gas in the electrolyte is saturated and maintained, and then carry out subsequent electro-synthesis operations;

[0051] (3) Using a Shanghai Chenhua workstation, a three-electrode system (Ag / AgCl as the reference electrode, a carbon rod as the counter electrode, and a copper mesh as the working electrode) was adopted. In an H-type electrolytic cell, the potentiostatic method was selected, the stirring speed was set at 600 r / min, and the working voltage was set at -0.4 V (vs. RHE) for a potentiostatic electrolysis reaction lasting for 10800 s;

[0052] (4) After the reaction ended, the electrolyte was collected. Using deuterated N,N-dimethylformamide (DMSO) as the deuterated reagent, a proton nuclear magnetic resonance spectrum test with water peak suppression was carried out. The results showed that the product was formamide ( Figure 7 ), proving that formic acid was the carbon source, NO was the nitrogen source, and formamide was successfully synthesized.

[0053] The product was qualitatively and quantitatively analyzed by the internal standard method of nuclear magnetic resonance hydrogen spectrum (nuclear magnetic resonance quantitative method). Maleic acid was selected as the internal standard substance, and the ratio of the resonance peak areas of the protons of the target group to the protons of the internal standard substance was used. The specific formula is as follows:

[0054]

[0055] Among them, C is the concentration of the analyte, S1 is the peak area of the analyte in the 1H NMR spectrum, S2 is the peak area of the internal standard in the 1H NMR spectrum, n is the concentration of hydrogen atoms in the internal standard (2.0 mM is used in this application), and m is the number of hydrogen atoms in the analyte (1 for formamide, 3 for acetamide, 3 or 2 for propionamide, and 5 for benzamide). See Appendix Figure 1 —7.

[0056] In the test of the product of the present invention, the calculation formula for the Faradaic efficiency (%) of the product is:

[0057]

[0058] Among them, n is the number of electron transfers (using NO2 - as the nitrogen source, n = 6; using NO3 - as the nitrogen source, n = 8; using NO as the nitrogen source, n = 5), m is the amount of substance of formamide in the product, F is the Faraday constant 96485 C / mol, and C is the total charge consumed in the reaction.

[0059] Based on the above examples, while maintaining the stirring speed, working voltage, and time of the potentiostatic method, the types and concentrations of nitrogen-containing salts and the types of electrolytes were changed to prepare amides and conduct the above tests.

[0060] Table 1. Reaction performance of electro-synthesizing formamide using different nitrogen-source compounds at a potential of -0.4 V (vs. RHE) with formic acid as the carbon source.

[0061]

[0062] Table 2. Reaction performance of electro-synthesizing acetamide using different nitrogen-source compounds at a potential of -0.4 V (vs. RHE) with acetic acid as the carbon source.

[0063]

[0064]

[0065] Table 3. Reaction performance of electro-synthesizing propionamide using different nitrogen-source compounds at a potential of -0.4 V (vs. RHE) with propionic acid as the carbon source.

[0066]

[0067] Table 4. Reaction performance of electro-synthesizing benzamide using different nitrogen-source compounds at a potential of -0.4 V (vs. RHE) with benzoic acid as the carbon source.

[0068]

[0069]

[0070] It can be found from the above embodiments that the method of the present invention uses carboxylic acid as a carbon source, selects a nitrogen-containing salt or gas as a nitrogen source, and under the action of electrocatalytic co-reduction, utilizes the coupling reaction of free radical intermediates to finally obtain the product amide. In this method, a cheap and easily available transition metal Cu is used as a catalyst (i.e., the working electrode as a copper mesh, and iron or nickel or carbon cloth can also be selected), and the electro-synthesis reaction can be carried out under mild conditions of normal temperature and normal pressure. This reaction has low requirements for equipment, low cost, is green and environmentally friendly, and has great application prospects and commercial value.

[0071] By adjusting the process parameters according to the content of the present invention, the preparation of amide can be realized. The above is an exemplary description of the present invention. It should be noted that any simple deformation, modification or equivalent substitution that can be made by those skilled in the art without creative labor falls within the protection scope of the present invention without departing from the core of the present invention.

Claims

1. An electrocatalytic preparation method of an amide, characterized in that, In a three - electrode system, the working electrode is selected as the catalyst. The carbon - source material and the nitrogen - source material are uniformly dispersed in the electrolyte. A constant potential is applied to the electrolyte for the reaction to obtain amide. The constant - potential reaction is carried out at a voltage of - 0.1 V to - 1.2 V vs. RHE; where: the pH of the electrolyte is 8 - 13, the carbon - source material is carboxylic acid, the nitrogen - source material is nitrate, nitrite or nitrogen - containing gas; the molar ratio of carboxylic acid to nitrate is (1 - 3):(1 - 8); the molar ratio of carboxylic acid to nitrite is (1 - 3):(1 - 8); when the nitrogen - source material is a nitrogen - containing gas, in the constant - potential reaction, the nitrogen - containing gas is in a saturated state in the electrolyte.

2. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The carboxylic acid is formic acid, acetic acid, propionic acid or benzoic acid.

3. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The nitrate is sodium nitrate, potassium nitrate; the nitrite is sodium nitrite, potassium nitrite.

4. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The nitrogen - containing gas is nitric oxide.

5. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The reference electrode is a saturated calomel electrode, a silver - silver chloride electrode, a mercury - mercuric oxide electrode, and the counter electrode is a carbon rod or platinum - carbon.

6. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The electrolyte is an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of potassium bicarbonate or an aqueous solution of sodium bicarbonate; the pH of the electrolyte is 9 - 11.

7. The electrocatalytic preparation method of an amide according to claim 1, wherein, The working electrode is copper, iron or nickel.

8. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The molar ratio of carboxylic acid to nitrate is (1 - 2):(1 - 3).

9. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, The molar ratio of carboxylic acid to nitrite is (1 - 2):(1 - 3).

10. The electrocatalytic preparation method of an amide according to claim 1, characterized in that, Select to carry out a constant - potential reaction at a voltage of - 0.4 V to - 0.8 V vs. RHE; the reaction time is at least 1 hour.

11. The electrocatalytic preparation method of an amide according to claim 1, wherein Select to carry out a constant - potential reaction at a voltage of - 0.4 V to - 0.8 V vs. RHE; the reaction time is 3 - 5 hours.

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