CN114934285A - Method for electrocatalysis of olefin epoxidation by covalent connection of manganoporphyrin electrode - Google Patents

Abstract

The invention discloses a method for electrocatalyzing olefin epoxidation by covalently connecting manganese porphyrin electrodes. The reaction is carried out in an electrolytic cell provided with electrodes to obtain a reaction solution containing the epoxide represented by formula II; the anode sheet of the electrolytic cell is a carbon cloth electrode covalently fixed with manganese porphyrin. The method provided by the invention is simple in experimental operation, high in safety, more economical, environmentally friendly, green and practical, and has high product selectivity. It can effectively overcome the shortcomings of traditional synthesis routes, such as long reaction time, high reaction temperature, unfavorable environmental protection, high pressure, etc., and solves the traditional reaction process with complicated steps, long reaction time, expensive catalysts, excess strong oxidant, high reaction problems such as temperature and low atomic efficiency, and can improve the reaction efficiency, suitable for industrial production.

Description

A method for electrocatalytic epoxidation of olefins by covalently linking manganese porphyrin electrodes

technical field

The invention belongs to the field of organic chemical synthesis, in particular to a method for highly selective electrocatalytic olefin epoxidation by covalently connecting manganese porphyrin electrodes.

Background technique

Epoxy compounds are common intermediates for many chemical products, such as surfactants, epoxy resins, and pharmaceuticals. These epoxy compounds are usually prepared by oxidation of olefins. Most olefin epoxidation reactions employ peroxide-based oxidants such as tert-butyl hydroperoxide (TBHP) or chloroperoxybenzoic acid (mCPBA). Both pathways involve by-products that are not easily separable. In order to solve the above problems, some processes use catalysts to generate hydrogen peroxide in situ as an oxidant, so that epoxy compounds can be synthesized efficiently. However, there are a large number of side reactions in the electrochemical reaction process, such as dimerization of raw materials, which reduces the selectivity of the reaction. Therefore, if an electrocatalyst with the ability to electrocatalyze olefin epoxidation with high selectivity can be rationally designed, it will be of great value in drug R&D and so on. The study of catalyst selectivity can also be extended to other products of olefins on this basis, thereby improving the practicability of catalysts. At present, there are related reports on electrocatalytic epoxidation, but the catalysts used often use organic catalysts soluble in the system, so there are disadvantages such as difficult separation and easy decomposition. Therefore, fixing the catalyst on the electrode can improve this point.

Electrochemical methods have the advantages of high reaction efficiency and mild temperature conditions. The use of heterogeneous catalysts supported on electrodes in the reaction not only facilitates the separation of products and catalysts, but also improves the catalytic efficiency of electrochemical reactions. Combining electrochemistry with a microreactor, the electrochemical reaction in the microreactor can improve the mass transfer of the reaction, so that the efficient catalytic reaction occurs. Photocatalysis can utilize sunlight, a cheap and abundant energy source, which can greatly shorten the steps of traditional chemical synthesis. With the development of society and the exhaustion of resources, the development of green chemistry has become one of the missions of scientists. To this end, the present invention provides a method for highly selective electrocatalytic epoxidation of olefins by covalently linking manganese porphyrin electrodes.

SUMMARY OF THE INVENTION

Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for highly selective electrocatalytic olefin epoxidation by covalently connecting manganese porphyrin electrodes.

In order to solve the above technical problems, the present invention discloses a method for highly selective electrocatalytic olefin epoxidation by covalently connecting manganese porphyrin electrodes. , water, an electrolyte, a mixed homogeneous solution of tetrabutylammonium hydroxide and an organic solvent to carry out an electrolyte reaction in an electrolytic cell provided with an electrode to obtain a reaction solution containing an epoxide shown in formula II; the anode sheet of the electrolytic cell It is a carbon cloth electrode covalently fixed by manganese porphyrin;

Wherein, R ₁ is selected from benzene, 4-methylbenzene, 4-ethylbenzene, 4-chlorobenzene, 4-methoxybenzene, 4-nitrobenzene or naphthalene ring; preferably benzene, 4-methylbenzene , 4-chlorobenzene, 4-methoxybenzene or naphthalene ring; more preferably benzene, 4-methylbenzene, 4-chlorobenzene or 4-methoxybenzene.

Wherein, the electrolyte is any one or a combination of tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate and tetrabutylammonium perchlorate, preferably tetrabutylammonium hexafluorophosphate.

Wherein, the organic solvent is any one or a combination of acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate, preferably propylene carbonate.

Wherein, in the mixed homogeneous solution, the concentration of the olefin compound represented by formula I is 5-15 mM, preferably 7-13 mM, more preferably 10 mM.

Wherein, in the mixed homogeneous solution, the concentration of the electrolyte is 0.05-0.15M, preferably 0.07-0.13M, and more preferably 0.1M.

Wherein, in the mixed homogeneous solution, in the tetrabutylammonium hydroxide aqueous solution composed of tetrabutylammonium hydroxide and water, the mass fraction of tetrabutylammonium hydroxide is 10-50%wt, preferably 20-45%wt, more preferably 35-45% wt, more preferably 40% wt.

Wherein, in the mixed homogeneous solution, the volume ratio of the tetrabutylammonium hydroxide aqueous solution to the organic solvent is 1:14-24, preferably 1:16-22, and more preferably 1:19.

Wherein, the electrolytic cell provided with electrodes includes an unsealed electrolytic cell, a cathode sheet, an anode sheet and a DC power supply; the volume of the unsealed electrolytic cell is preferably 25 mL; the distance between the cathode sheet and the anode in the electrolytic cell is about 1 cm; The anode sheet is a carbon cloth electrode covalently fixed with a manganese porphyrin catalyst; the cathode sheet is a graphite carbon electrode or a platinum sheet electrode, preferably a platinum sheet electrode.

Wherein, the temperature of the reaction is 20-30°C, preferably room temperature.

Wherein, the current intensity of the reaction is 1-5 mA, preferably 2-4 mA, more preferably 3 mA.

Wherein, the residence time of the reaction is 6-12h, preferably 7-11h, more preferably 8h.

Wherein, after the reaction is finished, the liquid in the electrolytic cell is collected, the reaction solution containing the epoxide shown in formula II is diluted five times with ethyl acetate, washed with water, dried and filtered, and then washed with ethyl acetate and petroleum The mixed solvent of ether is rinsed and separated to obtain the epoxide represented by formula II.

Wherein, the volume ratio of the mixed solvent of ethyl acetate and petroleum ether is 1:10-30.

Beneficial effect: Compared with the prior art, the present invention has the following advantages:

The method provided by the invention is simple to operate, high in safety, more economical, environmentally friendly, green and practical. It can effectively overcome the shortcomings of the traditional synthesis route, such as long reaction time, high reaction temperature, low atomic efficiency, high cost, unfavorable environmental protection, etc., and solves the traditional reaction process with complicated steps, long reaction time, excess strong oxidant, high reaction temperature, etc. And low atomic efficiency and other problems, and can improve the reaction efficiency, suitable for industrial production.

Description of drawings

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the above-mentioned and/or other aspects of the present invention will become clearer.

Fig. 1 is the preparation diagram of the catalytic electrode of the present invention.

Fig. 2 is a reaction route diagram of the present invention.

Detailed ways

The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

The electrochemical reaction device described in the following examples includes a DC power supply, a 25mL electrolytic cell, a cathode sheet and an anode sheet; wherein, the electrolytic cell is respectively provided with a cathode sheet (platinum sheet) and an anode sheet (covalently fixed manganese porphyrin). The carbon cloth electrode of the phosphonium catalyst); the distance between the cathode sheet and the anode in the electrolytic cell is about 1 cm.

Among them, the production of the anode sheet adopts a special method: a two-step method is used to connect the manganese porphyrin to the electrode surface (see Figure 1), specifically: (1) The tetraphenyl porphyrin core is co-coated with the carbon cloth through a phenylene linker. The hydrogen on the para position of one of the benzenes of the tetraphenylporphyrin is replaced by a diazo group, and then the diazo group is covalently linked to the carbon cloth electrode; (2) The porphyrin modified electrode is placed in 30 mL, 0.05M Mn(OAc)2 was soaked in DMF:CH3COOH (9:1) solution for 45 minutes, then rinsed with water and dried to obtain a manganese porphyrin modified electrode (for the preparation method of this electrode, please refer to the prior art ACS SustainableChem.Eng.2019 , 7, 3838-3848).

According to the following steps in the following examples: (1) adding the mixed homogeneous solution prepared in proportion to the electrolytic cell; (2) adjusting the required current; (4) collecting the outflow reaction solution and weighing it by passing through the column The product yield was calculated by the method; the product yield was measured by high performance liquid phase, and then the target product was obtained by column chromatography.

In the following examples, unless otherwise specified, the reaction temperature is room temperature.

Among them, the olefin compounds in the present invention are shown in Table 1.

Table 1

Among them, the epoxides shown in Table 2 are all products synthesized by the method of the present invention.

Table 2

Synthesis of Example 1 Compound 2a:

(1) 0.1 mmol of compound 1a styrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of 40% wt tetrabutylammonium hydroxide aqueous solution were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, which was added to Before the reaction, the distance between the two electrodes was adjusted to 1cm, and the applied current was 1mA; the reaction time was 8h; after the reaction, the reaction liquid was collected, and the product yield was 79% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

(2) 0.1 mmol (0.02403 g) of compound 1a styrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of a 40% wt tetrabutylammonium hydroxide aqueous solution were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution , added to the electrolytic cell; before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 92% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

(3) Dissolve 0.1 mmol of compound 1a styrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of 40%wt tetrabutylammonium hydroxide aqueous solution in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, add Before the reaction, the distance between the two electrodes was adjusted to 1cm, and the applied current was 5mA; the reaction time was 8h; after the reaction, the reaction liquid was collected, and the product yield was 86% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

(4) 0.1 mmol of compound 1a styrene, 1 mmol of tetrabutylammonium hexatetrafluoroborate and 0.5 mL of 40%wt tetrabutylammonium hydroxide aqueous solution were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, Before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 71% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

(5) Dissolve 0.1 mmol of compound 1a styrene, 1 mmol of tetrabutylammonium perchlorate and 0.5 mL of 40%wt tetrabutylammonium hydroxide aqueous solution in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, add Before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 73% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

(6) 0.1 mmol of compound 1a styrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of a 40% wt tetrabutylammonium hydroxide aqueous solution were dissolved in N,N-dimethylformamide (9.5 mL) solvent, A homogeneous solution was obtained and added to the electrolytic cell; before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 69% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

Synthesis of Example 2 Compound 2b:

0.1 mmol of compound 1b 4-chlorostyrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of 40% wt aqueous solution of tetrabutylammonium hydroxide were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, which was added Before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 81% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2b.

Synthesis of Example 3 Compound 2c:

0.1 mmol of compound 1c 4-methylstyrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of 40% wt aqueous solution of tetrabutylammonium hydroxide were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, added Before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected, and the product yield was 89% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2c.

Synthesis of Example 4 Compound 2d:

0.1 mmol of compound 1d 4-methoxystyrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of 40% wt aqueous solution of tetrabutylammonium hydroxide were dissolved in propylene carbonate (9.5 mL) solvent to obtain a homogeneous solution, Before the reaction, the distance between the two electrodes was adjusted to 1cm, and the applied current was 3mA; the reaction time was 8h; after the reaction, the reaction liquid was collected, and the product yield was 94% calculated by HPLC. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to isolate the product 2d.

In the following Comparative Examples 1 to 4, the electrolytic cells are respectively provided with a cathode sheet (platinum sheet) and an anode sheet (carbon cloth electrode without catalyst).

In the following comparative examples 1 to 3, the catalyst used is a homogeneous catalyst Fe ^III -bTAML, which is dispersed in the system.

Comparative Example 1: Non-covalently immobilized electrocatalyst catalyzed the oxidation of styrene to styrene oxide 2a

15 mM styrene, 0.75 mM Fe ^III -bTAML, 0.1 M tetrabutylammonium hexafluorophosphate were dissolved in a mixed solution of acetonitrile and phosphate buffer (v/v 4:1, pH=8) and placed in an electrolytic cell The distance between the two electrodes was set to 1 cm, and the reaction was carried out at a current of 3 mA for 10 h; after the reaction was completed, the reaction liquid was collected, and the yield calculated by HPLC was 66%.

Comparative Example 2: Non-covalently immobilized electrocatalyst catalyzed the oxidation of 4-chlorostyrene to 4-chlorostyrene oxy2b

15 mM 4-chlorostyrene, 0.75 mM Fe ^III -bTAML, 0.1 M tetrabutylammonium hexafluorophosphate were dissolved in a mixed solution of acetonitrile and phosphate buffer (v/v 4:1, pH=8), juxtaposed In an electrolytic cell; the distance between the two electrodes was set to 1 cm, and the reaction was carried out under a current of 3 mA for 10 h; after the reaction was completed, the reaction liquid was collected, and the yield calculated by HPLC was 57%.

Comparative Example 3: Non-covalently immobilized electrocatalyst catalyzed the oxidation of 4-methoxystyrene to 4-methoxystyrene oxide 2d

15mM 4-methoxystyrene, 0.75mM FeIII- ^bTAML , 0.1M tetrabutylammonium hexafluorophosphate were dissolved in a mixed solution of acetonitrile and phosphate buffer (v/v 4:1, pH=8), and placed in an electrolytic cell; the distance between the two electrodes was set to 1 cm, and the reaction was carried out under a current of 3 mA for 10 h; after the reaction was completed, the reaction liquid was collected, and the yield calculated by HPLC was 51%.

Comparative Example 4: Same as Example 1 (2), the difference is that only the anode sheet of the electrolytic cell is replaced with a carbon cloth electrode without catalyst supported, and the manganese porphyrin catalyst is directly added to the reaction system.

0.1 mmol (0.02403 g) of compound 1a styrene, 1 mmol of tetrabutylammonium hexafluorophosphate and 0.5 mL of a 40% wt aqueous solution of tetrabutylammonium hydroxide were dissolved in propylene carbonate (9.5 mL) solvent, and 0.0075 mmol of catalyst tetra Phenyl porphyrin manganese to obtain a homogeneous solution, which was added to the electrolytic cell; before the reaction, the distance between the two electrodes was adjusted to 1 cm, and the applied current was 3 mA; the reaction time was 8 h; after the reaction, the reaction liquid was collected and calculated by HPLC The product yield was 21%. The reaction liquid was diluted five times with ethyl acetate, washed with water, dried, filtered, and rinsed with a mixed solvent of ethyl acetate/petroleum ether (1:30) to obtain product 2a.

The present invention provides an idea and method for a method for electrocatalyzing olefin epoxidation by covalently connecting manganese porphyrin electrodes. There are many specific methods and approaches for realizing this technical solution. The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims (10)

1. A method for electrocatalytic olefin epoxidation by covalently connecting manganese porphyrin electrodes is characterized in that a mixed homogeneous solution containing an olefin compound shown as a formula I, water, an electrolyte, tetrabutylammonium hydroxide and an organic solvent is reacted in an electrolytic bath provided with electrodes to obtain a reaction solution containing an epoxide shown as a formula II; the anode plate of the electrolytic cell is a carbon cloth electrode covalently fixed by manganese porphyrin;

wherein R is ₁ Selected from benzene, 4-methylbenzene, 4-ethylbenzene, 4-chlorobenzene, 4-methoxybenzene, 4-nitrobenzene or naphthalene rings.

2. The method according to claim 1, wherein the electrolyte is any one or a combination of tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate and tetrabutylammonium perchlorate.

3. The method according to claim 1, wherein the organic solvent is any one or a combination of acetonitrile, methanol, N-dimethylformamide and propylene carbonate.

4. The method of claim 1, wherein the concentration of the olefinic compound of formula I in the mixed homogeneous solution is 5-15 mM.

5. The method of claim 1, wherein the mixed homogeneous solution has an electrolyte concentration of 0.05 to 0.15M.

6. The method according to claim 1, wherein the mixed homogeneous solution contains tetrabutylammonium hydroxide in a mass fraction of 10-50% wt.

7. The method of claim 1, wherein the mixed homogeneous solution has a ratio of water to organic solvent of 0.001-0.010 mol/mL.

8. The method of claim 1, wherein the reaction temperature is 20-30 ℃; the current intensity of the reaction is 1-5 mA.

9. The process according to claim 1, wherein the residence time of the reaction is between 6 and 12 hours.

10. The method according to claim 1, wherein after the reaction is finished, the reaction solution containing the epoxide shown in the formula II is diluted by ethyl acetate, washed by water, dried, filtered, and then leached and separated by a mixed solvent of ethyl acetate and petroleum ether, so that the epoxide shown in the formula II is obtained.

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