A method for electrochemically preparing unsaturated alcohols

Abstract

The present invention provides a method for electrochemically preparing unsaturated alcohols. Using a cobalt electrode as the working electrode, Ag / AgCl as the reference electrode, and an inert electrode as the counter electrode, with an aqueous sodium sulfate solution as the electrolyte and an unsaturated aldehyde as the reactant, constant potential electrolysis is carried out to obtain unsaturated alcohols. The cobalt electrode is a foam cobalt electrode, a thermally treated foam cobalt electrode, a Co-a / CP electrode prepared by coating cobalt particles on carbon paper, or a Co-b / CP electrode prepared by coating amorphous cobalt on carbon paper. The present invention has the advantages of simple preparation of electrode materials, high reaction conversion rate, high selectivity for unsaturated alcohols, green solvent, mild reaction conditions, and simple operation, etc.

Description

Technical Field

[0001] The invention relates to a method for electrochemically preparing unsaturated alcohol, and belongs to the field of organic synthesis. Background Art

[0002] Unsaturated alcohols are important components of many high value-added fine chemicals, such as perfumes, flavors, and medicines. Selective hydrogenation of unsaturated aldehydes to prepare unsaturated alcohols is the most atom-economical route, and unsaturated aldehydes are widely derived from biomass. However, conventional hydrogenation methods require higher temperatures and pressures, and C=C bonds are more likely to react than C=O bonds, and the products are more likely to be saturated alcohols. Therefore, it is of great significance to achieve highly selective hydrogenation of unsaturated aldehydes to prepare unsaturated alcohols under mild conditions.

[0003] Electricity is a clean energy source, and electrochemistry can break the thermodynamic limitations of the reaction and achieve catalytic conversion under mild conditions. Although electrochemistry can convert unsaturated aldehydes under mild conditions, the selectivity of the product still needs to be solved. Therefore, finding suitable electrode materials to achieve highly selective electrochemical hydrogenation of unsaturated aldehydes to prepare unsaturated alcohols has great scientific and practical production significance.

[0004] Water is the greenest solvent, and electrochemical organic synthesis using aqueous solution as electrolyte is an important development direction of green sustainable chemistry. The selective hydrogenation of unsaturated aldehydes to prepare unsaturated alcohols in aqueous solution is of even greater significance. Summary of the invention

[0005] The object of the present invention is to provide a method for electrochemically preparing unsaturated alcohols.

[0006] The electrochemical method for preparing unsaturated alcohol provided by the present invention comprises: using unsaturated aldehyde as raw material in aqueous solution, and performing electrochemical hydrogenation reduction to prepare unsaturated alcohol.

[0007] Specifically, the method for electrochemically preparing unsaturated alcohols provided by the present invention comprises the following steps:

[0008] Using a cobalt electrode as a working electrode, Ag / AgCl as a reference electrode, an inert electrode as a counter electrode, an aqueous sodium sulfate solution as an electrolyte, and an unsaturated aldehyde as a reactant, constant potential electrolysis is performed to obtain an unsaturated alcohol.

[0009] In the above method, the cobalt electrode can be zero-valent cobalt of any crystal form, including cubic, hexagonal, amorphous, etc.;

[0010] The cobalt electrode can be cobalt foil, foamed cobalt, or can be prepared by coating the cobalt electrode material on a substrate such as carbon paper or glassy carbon electrode;

[0011] The cobalt electrode can specifically be a cobalt foam electrode, a thermally treated cobalt foam electrode, a Co-a / CP electrode prepared by coating cobalt particles (Co-a) on carbon paper (CP), or a Co-b / CP electrode prepared by coating amorphous cobalt (Co-b) on carbon paper (CP);

[0012] Among them, the cobalt foam electrode is prepared by a method including the following steps: ultrasonic treatment of cobalt foam in acetone followed by drying to obtain it;

[0013] The thermally treated cobalt foam electrode is prepared by a method including the following steps: calcining cobalt foam in a mixed atmosphere of nitrogen and air to obtain calcined cobalt foam (Co-foam-1), using the calcined cobalt foam (Co-foam-1) as the working electrode, a Pt electrode as the counter electrode, Ag / AgCl as the reference electrode, and a Na2SO4 solution as the electrolyte, and reducing the calcined cobalt foam (Co-foam-1) at a potential of -0.7 to -2.0 V vs. RHE to obtain the thermally treated cobalt foam electrode Co-foam-2,

[0014] Among them, in the mixed atmosphere of nitrogen and air, the volume of N2 is 99% and the volume of air is 1%;

[0015] The calcination time can be 10 - 50 hours, specifically 20 hours;

[0016] The concentration of the Na2SO4 solution is 0.1 - 0.5 M;

[0017] The reduction time can be 10 - 120 minutes, specifically 30 minutes;

[0018] The Co-a / CP electrode is prepared by a method including the following steps: ultrasonically mixing cobalt particles, Nafion D-521 solution, and isopropanol, applying the resulting mixture to the surface of carbon paper (CP), and drying to obtain it;

[0019] Among them, the size of the cobalt particles is about 2 μm;

[0020] The ratio of Co-a, Nafion D-521 solution, and isopropanol can be in sequence: 5 mg: 25 μL: 0.5 mL;

[0021] The drying temperature can be 60 °C.

[0022] The Co-b / CP electrode is prepared by a method including the following steps: Dissolve Co(NO3)2 and NaBH4 in water respectively. Under vigorous stirring, drop the Co(NO3)2 aqueous solution into the NaBH4 aqueous solution, separate the obtained solid, and vacuum dry to obtain amorphous cobalt (Co-b); ultrasonically mix amorphous cobalt (Co-b), Nafion D-521 solution, and isopropanol, coat it on the surface of carbon paper (CP), and dry it to obtain the Co-b / CP electrode.

[0023] Among them, the ratio of Co-b, Nafion D-521 solution, and isopropanol can be in turn: 5 mg: 25 μL: 0.5 mL;

[0024] The drying temperature can be 60 °C.

[0025] The inert electrode mentioned above is a platinum electrode, a palladium electrode, a glassy carbon electrode, etc.;

[0026] The concentration of the sodium sulfate aqueous solution can be 0.1 - 0.5 M;

[0027] The unsaturated aldehyde is an aldehyde containing at least one C=C, including but not limited to cinnamaldehyde, furfural, crotonaldehyde, citronellal, etc.;

[0028] In the system, the concentration of the unsaturated aldehyde is lower than its saturated solubility in the aqueous solution;

[0029] The potentiostatic electrolysis can be carried out in an H-type electrolytic cell,

[0030] The potentiostatic electrolysis is carried out at a potential of -0.10 V to -1.5 V vs. RHE, specifically it can be -0.15 to -0.4 V vs. RHE, -0.15 to -0.3 V vs. RHE, -0.15 to -0.25 V vs. RHE, -0.15 to -0.2 V vs. RHE, -0.2 - to -0.5 vs. RHE, -0.2 - to -0.4 vs. RHE, -0.2 - to -0.6 s.RHE, -0.2 - to -0.7 s.RHE;

[0031] The time of the potentiostatic electrolysis can be 1 - 48 h, specifically it can be 2 - 46 h, 4 - 46 h, 8 - 45 h, 16 - 45 h, more specifically it can be 1.5 h, 2 h, 3 h, 2.5 h, 4 h, 8 h, 10 h, 16 h, 45 h, 46 h.

[0032] The present invention has the following advantages: This invention has the advantages of simple preparation of electrode materials, high reaction conversion rate, high selectivity for unsaturated alcohols, green solvent, mild reaction conditions, and simple operation. Specific embodiments

[0033] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0034] Unless otherwise specified, the materials, reagents, etc. used in the following examples are all commercially available.

[0035] Example 1

[0036] Thermally treated cobalt foam was used for the electrochemical reduction of cinnamaldehyde to prepare cinnamyl alcohol and the electrochemical reduction of furfural to prepare furfuryl alcohol. (I) Preparation of the electrode: 0.5 cm × 1 cm cobalt foam was calcined in a mixed atmosphere of 99% (volume) N2 and 1% (volume) air (flow rate 60 mL / min) for 20 hours to obtain calcined cobalt foam (Co-foam-1). Then, using Co-foam-1 as the working electrode, a Pt electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a Na2SO4 solution (0.5 M) as the electrolyte, Co-foam-1 was reduced at -0.7 V vs RHE potential in an H-type electrolytic cell for 30 minutes to obtain Co-foam-2.

[0037] (II) Electro-catalysis: Using Co-foam-2 as the working electrode, a Pt electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, cinnamaldehyde or furfural (10 μL) as the reactant, and a Na2SO4 solution (0.5 M) as the electrolyte, electrolysis was carried out in an H-type electrolytic cell at a potential of -0.12 V to -0.5 V vs RHE for a certain time. The products were analyzed by NMR, and the conversion rate of the reactant and the selectivity of the product at different potentials were calculated. The results are shown in Table 1 and Table 2.

[0038] Example 2

[0039] Commercial cobalt foam was used for the electrochemical reduction of cinnamaldehyde to prepare cinnamyl alcohol and the electrochemical reduction of furfural to prepare furfuryl alcohol

[0040] (I) Preparation of the electrode: 0.5 cm × 1 cm cobalt foam (Co-foam) was ultrasonicated in acetone for 30 minutes and then dried.

[0041] (II) Electro-catalysis: Using Co-foam as the working electrode, a Pt electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, cinnamaldehyde or furfural (10 μL) as the reactant, and a Na2SO4 solution (0.5 M) as the electrolyte, electrolysis was carried out in an H-type electrolytic cell at a potential of -0.4 V to -0.5 V vs RHE for a certain time. The products were analyzed by NMR, and the conversion rate of the reactant and the selectivity of the product at different potentials were calculated. The results are shown in Table 1 and Table 2.

[0042] Example 3

[0043] Commercial cobalt particles were used for the electrochemical reduction of cinnamaldehyde to prepare cinnamyl alcohol

[0044] (1) Electrode material: Commercial cobalt particles (Co-a) with a particle size of about 2 μm were selected.

[0045] (2) Preparation of the electrode: After ultrasonically mixing 5 mg of Co-a, 25 μL of Nafion D-521 solution, and 0.5 mL of isopropanol uniformly, 150 μL of the mixture was taken and coated on the surface of a 0.5 cm × 1 cm carbon paper (CP), and then dried at 60 °C to obtain the Co-a / CP electrode.

[0046] (3) Electrocatalysis: Using Co-a / CP as the working electrode, a Pt electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, cinnamaldehyde (10 μL) as the reactant, and a Na2SO4 solution (0.5 M) as the electrolyte, electrolysis was carried out in an H-type electrolytic cell at a potential of -0.4 V to -0.5 V vs RHE for a certain period of time. The products were analyzed by NMR, and the conversion rate of the reactant and the product selectivity at different potentials were calculated. The results are shown in Table 1.

[0047] Example 4

[0048] Amorphous cobalt was used for the electroreduction of cinnamaldehyde to prepare cinnamyl alcohol

[0049] (1) Synthesis of the electrode material: 1 mmol of Co(NO3)2 and 5 mmol of NaBH4 were respectively dissolved in 20 mL of water. Under vigorous stirring, the Co(NO3)2 aqueous solution was slowly added dropwise to the NaBH4 aqueous solution. Then, the obtained solid was separated by centrifugation and washed repeatedly with deionized water 5 times, and then vacuum dried at 60 °C to obtain amorphous cobalt (Co-b).

[0050] (2) Preparation of the electrode: After ultrasonically mixing 5 mg of Co-b, 25 μL of Nafion D-521 solution, and 0.5 mL of isopropanol uniformly, 150 μL of the mixture was taken and coated on the surface of a 0.5 cm × 1 cm carbon paper (CP), and then dried at 60 °C to obtain the Co-b / CP electrode.

[0051] (3) Electrocatalysis: Using Co-b / CP as the working electrode, a Pt electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, cinnamaldehyde (10 μL) as the reactant, and a Na2SO4 solution (0.5 M) as the electrolyte, electrolysis was carried out in an H-type electrolytic cell at a potential of -0.4 V to -0.5 V vs RHE for a certain period of time. The products were analyzed by NMR, and the conversion rate of the reactant and the product selectivity at different potentials were calculated. The results are shown in Table 1.

[0052] The reaction results of different cobalt electrodes for the electrocatalytic hydrogenation of cinnamaldehyde to prepare cinnamyl alcohol are shown in Table 1.

[0053] Table 1 Reaction results of electrocatalytic hydrogenation of cinnamaldehyde over different cobalt electrodes. The electrodes include cobalt foam (Co-foam), thermally treated cobalt foam (Co-foam-2), commercial cobalt particles (Co-a / CP), and amorphous cobalt (Co-b / CP).

[0054]

[0055]

[0056]

[0057] Reaction conditions: 10 μL cinnamaldehyde; 30 mL 0.5 M Na2SO4; 25 °C.

[0058] A = cinnamaldehyde; B = cinnamyl alcohol; C = phenylpropanal; D = phenylpropanol.

[0059] The reaction results of electrocatalytic hydrogenation of furfural to furfuryl alcohol over different cobalt electrodes are shown in Table 2.

[0060] Table 2 Reaction results of electrocatalytic hydrogenation of furfural over different cobalt electrodes. The electrodes include cobalt foam (Co-foam), thermally treated cobalt foam (Co-foam-2), commercial cobalt particles (Co-a / CP), and amorphous cobalt (Co-b / CP).

[0061]

[0062]

[0063]

[0064] Reaction conditions: 10 μL furfural; 30 mL 0.5 M Na2SO4; 25 °C.

[0065] A = furfural; B = furfuryl alcohol; C = tetrahydrofurfural; D = tetrahydrofurfuryl alcohol.

Claims

1. A method for electrochemically preparing unsaturated alcohols, which is as follows: in an aqueous solution, using an unsaturated aldehyde as a raw material, electrochemically hydrogenating and reducing to prepare unsaturated alcohols; The method comprises the following steps: Using a cobalt electrode as the working electrode, Ag / AgCl as the reference electrode, an inert electrode as the counter electrode, an aqueous sodium sulfate solution as the electrolyte, and an unsaturated aldehyde as the reactant, performing constant potential electrolysis to obtain unsaturated alcohols; The cobalt electrode is a thermally treated foam cobalt electrode; The thermally treated foam cobalt electrode is prepared by a method comprising the following steps: calcining the foam cobalt in a mixed atmosphere of nitrogen and air to obtain calcined foam cobalt, using the calcined foam cobalt as the working electrode, a Pt electrode as the counter electrode, Ag / AgCl as the reference electrode, and a Na2SO4 solution as the electrolyte, and reducing the calcined foam cobalt at a potential of -0.7 to -2.0 vs RHE to obtain the thermally treated foam cobalt electrode.

2. The method according to claim 1, wherein: The inert electrode is a platinum electrode, a palladium electrode, or a glassy carbon electrode; the concentration of the aqueous sodium sulfate solution is 0.1 to 0.5 M; The unsaturated aldehyde is an aldehyde containing at least one C═C; 3. The method according to claim 2, wherein: The unsaturated aldehyde is cinnamaldehyde, furfural, crotonaldehyde, or citronellal; 4. The method according to claim 1, wherein: The constant potential electrolysis is carried out at a potential of -0.10 V to -1.5 V vs. RHE; 5. The method according to claim 1, characterized in that: The time of the constant potential electrolysis is 1 - 48 h; 6. The method according to claim 1, wherein: The constant potential electrolysis is carried out in an H-type electrolytic cell.

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