Preparation method of alpha, beta-unsaturated ester

Abstract

The invention discloses a preparation method of alpha, beta-unsaturated ester, and relates to the technical field of catalyst.The preparation method comprises the following steps that S1, alcohol, phosphine ylide, mesoporous g-C3N4 and a solvent are sequentially added into a container, a mixture is continuously stirred and reacted at the room temperature, and a blue LED is used for irradiation in the stirring reaction process; the solvent is toluene, acetonitrile or dioxane; s2, after the reaction is completed, a reaction product is purified through column chromatography, eluent is petroleum ether / ethyl acetate, and the use amount ratio of petroleum ether to ethyl acetate is 5: 1. According to the invention, mesoporous g-C3N4 is adopted as a catalyst to realize an alcohol oxidation-Wittig cascade reaction catalytic system, so that the use of noble metals and toxic oxidants is avoided, the reaction system is easy to carry out post-treatment, and the separation and purification process is simple; visible light is used as energy, so that utilization of non-renewable energy such as fossil energy is avoided; the used catalyst mesoporous g-C3N4 can be recycled through simple centrifugation and washing, so that the cost is saved.

Description

Technical Field

[0001] The invention relates to the technical field of catalysis, and in particular to a method for preparing α,β-unsaturated ester. Background Art

[0002] The synthesis of α,β-unsaturated ester compounds usually adopts the Wittig reaction. The Wittig reaction involves the condensation of phosphine ylides with aldehydes or ketones. It is an important reaction for constructing carbon-carbon double bonds. However, due to the instability and volatility of aldehydes, their use in the Wittig reaction is limited to a certain extent. Traditionally, the oxidants used for alcohol oxidation-Wittig tandem reactions are stoichiometric or even excess MnO2, Dess-Martin reagent, IBX, PCC, etc. However, the use of excess oxidants may produce unpredictable by-products, and these oxidants are difficult to remove from the reaction system. In recent years, alcohol oxidation-Wittig tandem reactions catalyzed by metals such as Cu, Pd, and Ru have been widely studied. However, metal catalysts are usually expensive, toxic, and difficult to handle.

[0003] In order to solve the above problems, the use of green semiconductor photocatalytic technology can effectively solve the pollution problem. However, when the photocatalyst is involved, the catalytic reaction mainly occurs on the surface of the catalyst. The existing commonly used photocatalyst g-C3N4 is usually blocky, limited by a small specific surface area and a wide band gap (about 2.7eV), which hinders its catalytic performance. Therefore, it is of great research value to adjust the structure of g-C3N4 by designing synthetic strategies to improve its catalytic performance and then explore its application in organic synthesis. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides an α,β-unsaturated ester capable of recovering an alcohol oxidation-Wittig tandem reaction catalyst and a preparation method thereof.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] Provided is a method for preparing an α,β-unsaturated ester, comprising the following steps:

[0007] S1: alcohol, phosphine ylide, mesoporous g-C3N4 and solvent are added into the container in sequence, the mixture is continuously stirred and reacted at room temperature, and a blue LED is used for irradiation during the stirring reaction; the solvent is toluene, acetonitrile or dioxane;

[0008] S2: After the reaction is completed, the reaction product is purified by column chromatography, and the eluent is petroleum ether / ethyl acetate, and the ratio of petroleum ether to ethyl acetate is 5:1.

[0009] Furthermore, the usage ratio of alcohol, phosphine ylide, mesoporous g-C3N4 and toluene is 1mmol:2mmol:50mg:5ml.

[0010] Furthermore, mesoporous g-C3N4 was prepared using melamine as a precursor, and the preparation method was as follows:

[0011] A1: Dissolve the soft template in water, then add melamine and stir at room temperature until the soft template is completely dissolved;

[0012] A2: After sulfuric acid is added dropwise to the mixture obtained in A1, the mixture is heated in a water bath and refluxed. After the reflux is completed, a white solid is obtained by centrifugation;

[0013] A3: The white solid was repeatedly washed with deionized water and ethanol until the pH value of the supernatant during washing reached 7;

[0014] A4: The washed white solid in A3 is calcined in a muffle furnace, taken out after calcination and naturally cooled to room temperature to obtain mesoporous g-C3N4.

[0015] Furthermore, step A2 is specifically as follows: after adding 98% sulfuric acid dropwise to the mixture, heating to 100° C. in a water bath, and reflux for 5 hours; the ratio of sulfuric acid to melamine is 2 mL: 2 g.

[0016] Furthermore, the soft film plate agent is polyether F127.

[0017] Furthermore, the mass ratio of the soft template, water and melamine is 2:1:100.

[0018] Furthermore, the calcination process of step A4 is specifically as follows: setting a heating rate of 2°C / min, heating to 500°C, and keeping warm for 2 hours; then raising the temperature to 550°C at the same heating rate, and keeping warm for another 2 hours to complete the calcination.

[0019] An α,β-unsaturated ester prepared by the above-mentioned preparation method is characterized in that its structure is as follows:

[0020]

[0021] Wherein, R is phenyl, p-nitrophenyl, p-methylphenyl, p-methoxyphenyl, p-bromophenyl, p-fluorophenyl, m-methoxyphenyl, m-fluorophenyl, o-methylphenyl or o-methoxyphenyl.

[0022] The beneficial effects of the present invention are:

[0023] The present invention uses mesoporous g-C3N4 as a catalyst to realize an alcohol oxidation-Wittig tandem reaction catalytic system, thereby avoiding the use of precious metals and toxic oxidants, making the reaction system easy to post-process and the separation and purification process simple; using visible light as energy, avoiding the use of non-renewable energy such as fossil energy; the used catalyst mesoporous g-C3N4 can be recycled by simple centrifugation and washing, saving costs;

[0024] When preparing mesoporous g-C3N4, the present invention selects polyether F127 as a soft template, the reaction process is simple to operate, and the template can be directly removed by calcination after the reaction is completed, so as to form a porous structure in the material, and the obtained mesoporous g-C3N4 has no obvious agglomeration phenomenon, and exhibits excellent performance in the alcohol oxidation-Wittig tandem reaction. When toluene is used as a solvent, oxygen is used as an oxidant, a blue LED lamp is used as a light source, and benzyl alcohol is used as a raw material, α,β-unsaturated esters can be prepared with a yield of 87% within 24 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction pattern of the mesoporous g-C3N4 prepared in Example 1.

[0026] Figure 2 This is the infrared spectrum of the mesoporous g-C3N4 prepared in Example 1.

[0027] Figure 3 This is the fluorescence spectrum of the mesoporous g-C3N4 prepared in Example 1.

[0028] Figure 4 This is the UV-visible absorption spectrum of the mesoporous g-C3N4 prepared in Example 1.

[0029] Figure 5 This is a scanning electron microscope image of the mesoporous g-C3N4 prepared in Example 1.

[0030] Figure 6 This is the transmission electron microscopy image of the mesoporous g-C3N4 prepared in Example 1.

[0031] Figure 7 This is the photocurrent response diagram of the mesoporous g-C3N4 prepared in Example 1.

[0032] Figure 8 This is the hydrogen nuclear magnetic resonance spectrum of the α,β-unsaturated ester prepared in Example 2.

[0033] Fig. 9 This is the carbon NMR spectrum of the α,β-unsaturated ester prepared in Example 2. DETAILED DESCRIPTION

[0034] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0035] Example 1 Preparation of mesoporous g-C3N4 catalyst

[0036] 2g of melamine, 1g of polyether F127 and 100mL of deionized water were added to a three-necked flask equipped with a stirring bar. Then, it was stirred vigorously at room temperature until the polyether F127 was completely dissolved. The resulting mixture was refluxed at 100°C under continuous stirring. Then 2mL of 98% sulfuric acid was added dropwise, and reflux was continued for 5 hours. After the heating process was completed, the mixture was allowed to cool naturally to room temperature. Subsequently, the white solid was collected by centrifugation and washed with deionized water and ethanol several times in sequence until the pH value of the supernatant reached 7. After that, the solid was transferred to a vacuum oven and set to 60°C for drying for 12 hours. A white solid was obtained, and the white solid was placed in a muffle furnace for calcination, heated to 500°C at a rate of 2°C / min, and kept at this temperature for 2 hours. Subsequently, the temperature was raised to 550°C at the same heating rate and kept for another 2 hours. After cooling to room temperature, a yellow-brown powder was obtained.

[0037] The obtained yellow-brown powder was subjected to X-ray diffraction detection, infrared spectrum detection, fluorescence spectrum detection and UV-visible absorption spectrum detection. The X-ray diffraction detection results are as follows: Figure 1 As shown, the infrared spectrum detection results are as follows Figure 2 The fluorescence spectrum detection results are shown in Figure 3 As shown, the UV-visible absorption spectrum test results are as follows Figure 4 shown by Figure 1-4 It can be seen that the obtained yellow-brown powder has the characteristic peak of g-C3N4, and it is determined that the obtained yellow-brown powder is g-C3N4.

[0038] The yellow-brown powdered g-C3N4 was subjected to scanning electron microscopy and transmission electron microscopy. The results of the scanning electron microscopy test are as follows: Figure 5 The transmission electron microscopy results are shown in Figure 6 As shown by Figure 5 and Figure 6 It can be seen that the yellow-brown powdered g-C3N4 has uniformly distributed pores and presents a porous structure, which confirms that mesoporous g-C3N4 can be obtained by the above method. The photocurrent response results of the yellow-brown powdered g-C3N4 are as follows: Figure 7 As shown by Figure 7It can be seen that the yellow-brown powdered g-C3N4 prepared has good visible light response performance and strong absorption capacity for visible light.

[0039] Example 2 Preparation of α,β-unsaturated esters

[0040] 0.2 mmol benzyl alcohol, 0.4 mmol phosphine ylide, 10 mg mesoporous g-C3N4 prepared in Example 1 and 1 mL toluene solvent were added to a 10 mL Schlenk flask equipped with a stirring bar. In specific implementation, the alcohol can also be p-nitrobenzyl alcohol, p-methylbenzyl alcohol, p-methoxybenzyl alcohol, p-bromobenzyl alcohol, p-fluorobenzyl alcohol, m-methoxybenzyl alcohol, m-fluorobenzyl alcohol, o-methylbenzyl alcohol or o-methoxybenzyl alcohol; the solvent can also be acetonitrile or dioxane;

[0041] The resulting mixture was stirred at room temperature for 24 h under blue LED irradiation. During stirring, the reaction process was monitored by thin layer chromatography. After the raw materials were completely consumed, the reaction product was eluted by flash chromatography, and the eluent was petroleum ether / ethyl acetate with a dosage ratio of 5:1. The purified material was taken for nuclear magnetic resonance detection. The detection results were as follows: Figure 8-9 As shown, Figure 8 is the H NMR spectrum of the purified substance. Fig. 9 is the carbon NMR spectrum of the purified substance, Figure 8-9 It can be seen that the absorption peaks with chemical shifts at 7.39 and 7.52 ppm are the absorption peaks of hydrogen on the benzene ring, and the absorption peaks with chemical shifts at 6.4 and 7.6 ppm are the absorption peaks of hydrogen on the double bond. The absorption peaks with chemical shifts at 4.27 and 1.34 ppm are the absorption peaks of hydrogen on the ethyl group. In the carbon spectrum, the absorption peak with chemical shift at 167.0 ppm is the absorption produced by the carbonyl carbon. The absorption peaks with chemical shifts between 118-144 ppm are the absorption peaks produced by the benzene ring and the double bond carbon. The absorption peaks with chemical shifts at 60.5 and 14.3 ppm are the absorption peaks produced by the two carbons of the ethyl group. The structure of the purified substance prepared is shown in the following formula:

[0042]

[0043] The mass of the purified product was weighed to be 30.6 mg, with a yield of 87%.

[0044] Example 3

[0045] In order to verify the recycling performance of the catalyst, the remaining material in Example 2 was collected by centrifugation to obtain a precipitate, and the precipitate was washed with water, ethanol and ethyl acetate in turn for a total of three times. After washing, the solid was dried in a vacuum drying oven at 60°C for 6 hours to obtain a recovered catalyst.

[0046] The recovered catalyst was then placed in a 10mL Schlenk flask equipped with a stirring rod, and 0.2mmol benzyl alcohol, 0.4mmol phosphine ylide and 1mL toluene solvent were added in sequence. The resulting mixture was stirred at room temperature for 24h under blue LED irradiation. During stirring, the reaction process was monitored by thin layer chromatography. After the raw materials were completely consumed, the reaction product was eluted by flash chromatography, and the eluent was petroleum ether / ethyl acetate with a dosage ratio of 5:1. The mass of the purified product was weighed to be 30.0mg, and the yield was 85%. Compared with Example 2, it can be seen that the mass difference between the product obtained by using the recovered catalyst and the product obtained in Example 2 is only 0.6mg. It may be that during the recovery process, the catalyst remained on the container wall and was not completely recovered, resulting in a slight decrease in yield, which is a normal error. It can be seen that the catalyst mesoporous g-C3N4 can be recycled by simple centrifugation and washing.

Claims

1. A method for preparing an α,β-unsaturated ester, characterized in that: The steps include: S1: alcohol, phosphine ylide, mesoporous g-C3N4 and solvent are added into the container in sequence, the mixture is continuously stirred and reacted at room temperature, and a blue LED is used for irradiation during the stirring reaction; the solvent is toluene, acetonitrile or dioxane; S2: After the reaction is completed, the reaction product is purified by column chromatography, and the eluent is petroleum ether / ethyl acetate, and the ratio of petroleum ether to ethyl acetate is 5:

1.

2. The method for preparing an α,β-unsaturated ester according to claim 1, characterized in that: The alcohol is benzyl alcohol, p-nitrobenzyl alcohol, p-methylbenzyl alcohol, p-methoxybenzyl alcohol, p-bromobenzyl alcohol, p-fluorobenzyl alcohol, m-methoxybenzyl alcohol, m-fluorobenzyl alcohol, o-methylbenzyl alcohol or o-methoxybenzyl alcohol.

3. The method for preparing an α,β-unsaturated ester according to claim 1, characterized in that: The usage ratio of the alcohol, phosphine ylide, mesoporous g-C3N4 and toluene is 1mmol:2mmol:50mg:5ml.

4. The method for preparing an α,β-unsaturated ester according to claim 1, characterized in that: The mesoporous g-C3N4 is prepared by using melamine as a precursor, and the preparation method is as follows: A1: Dissolve the soft template in water, then add melamine and stir at room temperature until the soft template is completely dissolved; A2: After sulfuric acid is added dropwise to the mixture obtained in A1, the mixture is heated in a water bath and refluxed. After the reflux is completed, a white solid is obtained by centrifugation; A3: The white solid was repeatedly washed with deionized water and ethanol until the pH value of the supernatant during washing reached 7; A4: The washed white solid in A3 is calcined in a muffle furnace, taken out after calcination and naturally cooled to room temperature to obtain mesoporous g-C3N4.

5. The method for preparing an α,β-unsaturated ester according to claim 4, characterized in that: The step A2 specifically comprises: adding 98% sulfuric acid dropwise to the mixture, heating the mixture to 100° C. in a water bath, and refluxing the mixture for 5 hours; the ratio of sulfuric acid to melamine is 2 mL: 2 g.

6. The method for preparing an α,β-unsaturated ester according to claim 4, characterized in that: The soft film plate agent is polyether F127.

7. The method for preparing an α,β-unsaturated ester according to claim 4, characterized in that: The mass ratio of the soft template, water and melamine is 2:1:

100.

8. The method for preparing an α,β-unsaturated ester according to claim 4, characterized in that: The calcination process of step A4 is specifically as follows: setting a heating rate of 2°C / min, heating to 500°C, and keeping warm for 2 hours; then raising the temperature to 550°C at the same heating rate, and keeping warm for another 2 hours to complete the calcination.

9. An α,β-unsaturated ester prepared by the preparation method according to any one of claims 1 to 8, characterized in that: Its structure is as follows: Wherein, R is phenyl, p-nitrophenyl, p-methylphenyl, p-methoxyphenyl, p-bromophenyl, p-fluorophenyl, m-methoxyphenyl, m-fluorophenyl, o-methylphenyl or o-methoxyphenyl.

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