Method for preparing cinnamyl alcohol through cinnamyl aldehyde hydrogenation

Abstract

According to the method for preparing cinnamyl alcohol through cinnamyl aldehyde hydrogenation, isopropyl alcohol is adopted as a hydrogen source and a solvent of a reaction system, precious metal modified TiO2-CeO2 is adopted as a catalyst, and cinnamyl aldehyde is subjected to selective hydrogenation under visible light and normal temperature and pressure to synthesize cinnamyl alcohol. According to the invention, isopropanol is used as a hydrogen source and a solvent, so that high-pressure hydrogen is avoided, and potential safety hazards in the reaction process are remarkably reduced; the precious metal modified TiO2-CeO2 can be excited under visible light, normal temperature and normal pressure to perform selective hydrogenation on cinnamyl aldehyde to synthesize cinnamyl alcohol; according to the present invention, the use amount of the noble metal in the hydrogenation reaction system is significantly reduced, the conversion rate of the selective hydrogenation is high, the good economy and sustainability are provided, the preparation process is simple, the industrial mass production is easily achieved, and the green chemical development direction is met.

Description

Technical Field

[0001] The invention relates to a method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde, and specifically belongs to the technical field of organic synthesis. Background Art

[0002] In recent years, the selective hydrogenation of α,β-unsaturated aldehydes to produce unsaturated alcohols has attracted considerable attention, as it is a crucial step in the preparation of a variety of fine chemicals. Cinnamaldehyde, a representative example of this class of α,β-unsaturated aldehydes, is often difficult to selectively hydrogenate, particularly under heterogeneous catalytic conditions. This is because the cinnamaldehyde molecule contains both a C=C double bond (olefin bond) and a C=O double bond (carbonyl group). From a kinetic and thermodynamic perspective, hydrogenation of the C=C double bond is more favorable than hydrogenation of the C=O double bond. When cinnamaldehyde adsorbs on a metal surface, the C=C and C=O double bonds compete for adsorption, making catalytic hydrogenation difficult to control.

[0003] According to existing literature on the selective hydrogenation of α,β-unsaturated aldehydes to produce unsaturated alcohols, monometallic catalysts exhibit high catalytic activity in the selective hydrogenation of cinnamaldehyde, but their selectivity for unsaturated alcohols is poor and they typically require high metal loadings, which increases material costs and limits their application. Although homogeneous catalysts have good performance under certain conditions, the difficulties in their recovery and separation significantly increase production costs and do not meet the requirements of contemporary green chemistry. In addition, most catalytic conditions rely on high temperatures and H2 as a hydrogen source, which are easily limited by the flammability of hydrogen and the safety hazards caused by high-pressure operation. These issues collectively hinder the development of efficient, economical, and environmentally friendly processes for the production of cinnamyl alcohol. Summary of the Invention

[0004] In view of the limitations of the selective catalytic hydrogenation technology of cinnamaldehyde, the present invention provides a method for preparing cinnamyl alcohol by selective hydrogenation of cinnamaldehyde.

[0005] The present invention discloses a method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde. The method uses isopropyl alcohol as a hydrogen source and a solvent for the reaction system, and noble metal-modified TiO2-CeO2 as a catalyst. Cinnamyl alcohol is selectively hydrogenated to cinnamyl alcohol under visible light and normal temperature and pressure. The specific process is as follows: Cinnamaldehyde, isopropyl alcohol, and a noble metal-modified TiO2-CeO2 catalyst were added to a Schlenk tube and stirred for 30 minutes under a nitrogen atmosphere. Cinnamyl alcohol was then obtained by selective catalytic hydrogenation under visible light at room temperature and pressure for 3 hours. The preparation process of the noble metal modified TiO2-CeO2 catalyst is as follows: After dissolving cerium carbonate in ultrapure water, it was slowly added to the precursor solution of tetrabutyl titanate, and then ammonia water was added to adjust the pH of the reaction system solution to 10-11. The reaction was then stirred at 700 rpm / min for 60 min. After standing, the TiO2-CeO2 precipitate was centrifuged, washed with ethanol, vacuum-dried at 60°C for 10 h, and calcined at 500-600°C for 3 h to obtain yellow TiO2-CeO2. TiO2-CeO2 was dissolved in methanol solution, ultrasonically treated for 30 minutes, and then slowly added with chloro noble metal acid solution. After ultrasonic treatment for another 60 minutes, it was placed in a photoreactor and ultraviolet light deposited for 4 hours in a nitrogen atmosphere. After that, it was centrifuged, washed with ethanol and vacuum dried at 60°C for 10 hours to obtain noble metal-modified TiO2-CeO2.

[0006] The molar concentration of the chloro noble metal acid solution is 19.3 mmol / L; The volume ratio of cinnamaldehyde to isopropyl alcohol is 1:100; The molar ratio of cerium carbonate to tetrabutyl titanate is 1:4; The precious metal is Au; The tetrabutyl titanate precursor solution is composed of tetrabutyl titanate, ethanol and acetic acid, and the volume ratio of tetrabutyl titanate, ethanol and acetic acid is 5:10:3; The solid-liquid ratio of the cerium carbonate dissolved in ultrapure water is 0.179 g / mL.

[0007] The beneficial effects of the present invention are as follows: the present invention adopts isopropanol as a hydrogen source and solvent, avoids the use of high-pressure hydrogen, and significantly reduces the potential safety hazards in the reaction process; electrons and holes in the noble metal-modified TiO2-CeO2 can be excited under visible light and normal temperature and pressure, driving the selective hydrogenation of the carbonyl group in cinnamaldehyde to synthesize cinnamyl alcohol; the noble metal-modified TiO2-CeO2 is used as a selective catalytic hydrogenation catalyst, which significantly reduces the amount of noble metal used in the hydrogenation reaction system, and the conversion rate of the selective hydrogenation is high, with good economy and sustainability, simple preparation process, easy industrial mass production, and in line with the development direction of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 : Gas chromatography mass spectrometry of the selective hydrogenation reaction of cinnamaldehyde in Example 3 of the present invention; Retention time: cinnamaldehyde 12'17, cinnamyl alcohol 12'55; Figure 2 : Gas chromatography-mass spectrometry of the selective hydrogenation reaction of cinnamaldehyde in Example 4 of the present invention; Retention times: cinnamaldehyde 12'17, cinnamyl alcohol 12'55. Specific implementation plan

[0009] Example 1 The preparation of TiO2-CeO2 adopts the following steps: Dissolve 5 mL of tetrabutyl titanate in 10 mL of ethanol and add 3 mL of acetic acid to obtain a tetrabutyl titanate precursor. Dissolve 1.79 g of cerium carbonate in 10 mL of ultrapure water to obtain a cerium carbonate precursor. Slowly pour the cerium carbonate precursor into the tetrabutyl titanate precursor solution. Add ammonia to adjust the pH of the TiO2-CeO2 solution to 10-11 and stir at 700 rpm / min for 60 minutes. The TiO2-CeO2 precipitate obtained by static precipitation is centrifuged, washed with ethanol, and vacuum-dried at 60°C for 10 hours to obtain a yellow-white solid. The yellow-white solid is then calcined in a muffle furnace at 500-600°C for 3 hours to obtain yellow TiO2-CeO2.

[0010] Example 2 The preparation of precious metal modified TiO2-CeO2 (Au / TiO2-CeO2) catalysts was carried out as follows: 300 mg of yellow TiO2-CeO2 catalyst was dissolved in 20 mL of methanol solution and ultrasonicated for 30 minutes. Then 395 μL of HAuCl4 solution (HAuCl4 molar concentration was 19.3 mmol / L) was slowly added and ultrasonicated for another 60 minutes. The liquid was transferred to a photoreactor and kept in a nitrogen atmosphere. After 4 hours of ultraviolet light deposition, it was centrifuged, washed with ethanol and vacuum dried at 60°C for 10 hours to obtain a 0.5w% Au / TiO2-CeO2 catalyst.

[0011] Example 3 Add 20 μL of cinnamaldehyde, 2 mL of isopropanol and 10 mg of TiO2-CeO2 as a catalyst to a 10 mL schlenk tube. Tighten the schlenk tube, first use a vacuum pump to evacuate the air in the tube at room temperature, then purge with high-purity nitrogen for 5 minutes to eliminate the air in the tube. After stirring at room temperature in the dark for 30 minutes, place the schlenk tube under a visible light source for reaction, start stirring, the stirring speed is 1100prm / min, the temperature is room temperature for 3 hours, take out the product, separate it, dilute it with ethanol and analyze it with a gas mass spectrometer. The conversion rate of cinnamaldehyde is 54.62%, and the selectivity of cinnamyl alcohol is 96.5%. The gas phase mass spectrum of the selective hydrogenation reaction of cinnamaldehyde is shown in Figure 1 , retention time: cinnamaldehyde 12'17, cinnamyl alcohol 12'55.

[0012] Example 4 The TiO2-CeO2 catalyst was replaced with 0.5w% Au / TiO2-CeO2, and the other conditions were the same as in Example 3. The conversion rate of cinnamaldehyde was 95.07%, and the selectivity of cinnamyl alcohol was 97.2%. The gas phase mass spectrum of the selective hydrogenation reaction of cinnamaldehyde is shown in FIG. Figure 2 , retention time: cinnamaldehyde 12'17, cinnamyl alcohol 12'55.

Claims

1. A method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde, characterized in that: The method uses isopropanol as a hydrogen source and a solvent for the reaction system, and noble metal-modified TiO2-CeO2 as a catalyst to selectively hydrogenate cinnamaldehyde to synthesize cinnamyl alcohol under visible light and normal temperature and pressure. The specific process is as follows: Cinnamaldehyde, isopropyl alcohol, and a noble metal-modified TiO2-CeO2 catalyst were added to a Schlenk tube and stirred for 30 minutes under a nitrogen atmosphere. Cinnamyl alcohol was then obtained by selective catalytic hydrogenation under visible light at room temperature and pressure for 3 hours. The preparation process of the noble metal modified TiO2-CeO2 catalyst is as follows: After dissolving cerium carbonate in ultrapure water, it was slowly added to the precursor solution of tetrabutyl titanate, and then ammonia water was added to adjust the pH of the reaction system solution to 10-11. The reaction was then stirred at 700 rpm / min for 60 min. After standing, the TiO2-CeO2 precipitate was centrifuged, washed with ethanol, vacuum-dried at 60°C for 10 h, and calcined at 500-600°C for 3 h to obtain yellow TiO2-CeO2. TiO2-CeO2 was dissolved in methanol solution, ultrasonically treated for 30 minutes, and then slowly added with chloro noble metal acid solution. After ultrasonic treatment for another 60 minutes, it was placed in a photoreactor and ultraviolet light deposited for 4 hours in a nitrogen atmosphere. After that, it was centrifuged, washed with ethanol and vacuum dried at 60°C for 10 hours to obtain noble metal-modified TiO2-CeO2.

2. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The molar concentration of the chloro noble metal acid solution is 19.3 mmol / L.

3. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The volume ratio of the cinnamaldehyde to the isopropyl alcohol is 1:

100.

4. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The molar ratio of the cerium carbonate to tetrabutyl titanate is 1:

4.

5. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The noble metal is Au.

6. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The tetrabutyl titanate precursor solution is composed of tetrabutyl titanate, ethanol and acetic acid, and the volume ratio of tetrabutyl titanate, ethanol and acetic acid is 5:10:

3.

7. The method for preparing cinnamyl alcohol by hydrogenating cinnamaldehyde according to claim 1, wherein: The solid-liquid ratio of the cerium carbonate dissolved in ultrapure water is 0.179 g / mL.

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