Catalytic system for preparing alpha-phenethyl alcohol through selective hydrogenation of acetophenone as well as preparation method and application of catalytic system

Abstract

The invention provides a catalytic system for preparing alpha-phenethyl alcohol through selective hydrogenation of acetophenone. The catalytic system comprises a Pt nano-catalyst and an L-proline modifier, wherein the Pt nano-catalyst is prepared from quaternary ammonium salt type ionic liquid serving as a stabilizer and a Pt precursor. The invention also provides a preparation method of the catalytic system for preparing alpha-phenethyl alcohol through selective hydrogenation of acetophenone and a method for preparing alpha-phenethyl alcohol through selective hydrogenation of acetophenone catalyzed by the catalytic system for preparing alpha-phenethyl alcohol through selective hydrogenation of acetophenone. The catalytic system for preparing the alpha-phenethyl alcohol through selective hydrogenation of the acetophenone shows high selectivity, only C = O of the acetophenone is hydrogenated, the selectivity of the product alpha-phenethyl alcohol is larger than 99%, the Pt nano catalyst and the modifier L-proline can be recycled for 8 times, and the catalytic system has the advantage of being long in service life. In addition, the catalytic system and the generated product are separated through extraction, and the recycled catalytic system does not need to be treated and can be directly used for next reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of selective hydrogenation catalysis, and particularly relates to a catalytic system for selective hydrogenation of acetophenone modified with L-proline and recyclable to produce alpha-phenylethanol, a preparation method thereof, and application thereof in the selective hydrogenation of acetophenone. Background Art

[0002] α-Phenylethanol is an important organic intermediate and is widely used in the fields of medicine, cosmetics, food, fragrance manufacturing and fine chemicals. Catalytic hydrogenation of acetophenone has been widely studied as an effective method for synthesizing α-phenylethanol. However, since the acetophenone molecule contains two unsaturated groups, a benzene ring and a carbonyl group, benzene ring hydrogenation or full hydrogenation products are easily produced during the hydrogenation process. How to achieve highly selective hydrogenation of acetophenone to obtain α-phenylethanol is still an area worth studying.

[0003] The patent with publication number CN 109939696A discloses a method for preparing a Pt-Fe nanocatalyst. By controlling the reaction conditions, Pt-Fe nanowires with rich high-index surfaces are obtained, and the length of the size is relatively uniform. In the selective hydrogenation of acetophenone, only the carbon-oxygen double bond of acetophenone can be selectively hydrogenated, avoiding hydrogenation or over-hydrogenation of the benzene ring, and a single α-phenylethanol product can be obtained (the selectivity can reach 90%). Yoon et al. loaded the Ru catalyst on a bisphosphine porous organic polymer to achieve highly selective hydrogenation of acetophenone, and the selectivity of the product α-phenylethanol can reach 99% (J. Ind. Eng. Chem. 2021, 94, 361-367).

[0004] In addition, the steric effect produced by the modification of the surface of the nanocatalyst by the modifier is also an effective method to improve the selectivity. For example, Pan et al. encapsulated Pt nanoparticles in an organic metal framework and used them in the asymmetric hydrogenation reaction of α-ketoesters. Under the modification of cinchonidine, the enantioselectivity of the product was significantly improved (J.Mol.Catal.A:Chem.2013,377,108-114), but in the circulation experiment, the modifier cinchonidine needs to be added. The separation and recovery of the modifier still needs further study. Therefore, it is still a big problem to select some specific modifiers to complete their modification on the surface of the nanocatalyst, and to achieve the separation, recovery and recycling of the modifier while achieving the improvement of selectivity (Catal.Sci.Technol.,2015,5,680). Summary of the invention

[0005] Based on the above, the object of the present invention is to provide a catalytic system that can achieve highly selective hydrogenation of acetophenone to produce α-phenylethanol, and can also achieve separation, recovery and recycling of Pt nanocatalysts and modifiers.

[0006] To this end, in a first aspect, the present invention provides a catalytic system for selective hydrogenation of acetophenone to α-phenylethanol, comprising a Pt nanocatalyst prepared with a quaternary ammonium salt ionic liquid as a stabilizer and a Pt precursor, and L-proline and / or its reaction product.

[0007] Specifically, L-proline is an industrial catalyst and also an organic small molecule, which has the characteristics of strong activity, good stereospecificity, wide sources, easy preparation, low price, easy operation, environmental friendliness, etc. In the present invention, L-proline is used as a modifier of the Pt nanocatalyst and used in the selective hydrogenation of acetophenone, not only the product selectivity is significantly improved, but also because L-proline is more easily soluble in ionic liquids, the system simultaneously realizes the separation, recovery and recycling of L-proline and the Pt nanocatalyst.

[0008] As a specific embodiment of the present invention, preferably, the structure of the quaternary ammonium salt ionic liquid is as shown in formula (1):

[0009] CH3(OCH2CH2) n N + Et3SO3 - CH3 (1)

[0010] In formula (1), n ​​is selected from 12-22, preferably, n is 16.

[0011] Specifically, the structure of the quaternary ammonium salt ionic liquid is preferably as shown in formula (2):

[0012] CH3(OCH2CH2) 16 N + Et3SO3 - CH3 (2).

[0013] As a specific embodiment of the present invention, preferably, the Pt precursor is a water-soluble platinum source, and further preferably, the water-soluble platinum source is selected from at least one of PtCl4 and H2PtCl6.

[0014] As a specific embodiment of the present invention, preferably, based on 1 part by weight of the Pt precursor, the amount of L-proline is 20-50 parts by weight and the amount of the quaternary ammonium salt ionic liquid is 200-300 parts by weight; and / or, the particle size of the Pt nanocatalyst is 2.0-3.0 nm, more preferably 2.0-2.4 nm.

[0015] To this end, in a second aspect, the present invention provides a method for preparing the above-mentioned catalytic system for selective hydrogenation of acetophenone to α-phenylethanol, comprising the following steps:

[0016] a) dissolving a water-soluble platinum source in a solvent, adding a quaternary ammonium salt type ionic liquid, stirring evenly, dispersing to remove water, and then reducing to obtain a Pt nanocatalyst;

[0017] b) adding an aqueous solution of L-proline to the Pt nanocatalyst for modification.

[0018] As a specific embodiment of the present invention, preferably, the solvent is deionized water; and / or the Pt precursor is a water-soluble platinum source, preferably, the water-soluble platinum source is selected from at least one of PtCl4 and H2PtCl6; and / or the structure of the quaternary ammonium salt ionic liquid is as shown in formula (1):

[0019] CH3(OCH2CH2) n N + Et3SO3 - CH3 (1)

[0020] In formula (1), n ​​is selected from 12-22, preferably, n is 16.

[0021] As a specific embodiment of the present invention, preferably, the mass ratio of the Pt precursor to the quaternary ammonium salt ionic liquid is 1:200-1:300.

[0022] As a specific embodiment of the present invention, preferably, the mass ratio of the Pt precursor to the L-proline is 1:20-1:50.

[0023] As a specific embodiment of the present invention, preferably, in step a), the dispersion conditions are: temperature 60-80°C, time 2-4h; and / or the reduction conditions are: temperature 70-90°C, time 3-6h; and / or in step b), the modification conditions are: temperature 60-80°C, time 1-3h.

[0024] To this end, in a third aspect, the present invention provides a method for selectively hydrogenating acetophenone to produce α-phenylethanol, comprising the following steps:

[0025] The above catalyst system or the catalyst system prepared by the above method is added to an organic solvent, and then acetophenone is added and hydrogen is introduced to carry out a selective hydrogenation reaction; after the reaction is completed, an extraction solvent is added to extract and obtain a product.

[0026] As a specific embodiment of the present invention, preferably, the organic solvent is at least one of toluene, cyclohexane and n-heptane; and / or the conditions of the selective hydrogenation reaction are: hydrogen partial pressure 2-4MPa, temperature 30-40°C, time 3-6h; and / or the mass ratio of the Pt nanocatalyst to the acetophenone is 1:120-1:310, preferably 1:122-1:307; and / or the extraction solvent is cyclohexane or n-heptane.

[0027] Specifically, while adding the extraction solvent to extract and obtain the product, the present invention also completes the separation and recovery of the catalyst system. The recovered catalyst system does not need to be treated and can be directly used for the next reaction.

[0028] The beneficial effects of the present invention are as follows:

[0029] The catalytic system for selectively hydrogenating acetophenone to produce α-phenylethanol provided by the present invention exhibits high selectivity, that is, only C=O of acetophenone is hydrogenated, and the selectivity of the product α-phenylethanol is greater than 99%, and both the Pt nanocatalyst and the modifier L-proline can be recycled for 8 times, having the advantage of long service life. In addition, the catalytic system and the generated product are separated by extraction, and the recovered catalytic system does not need to be treated and can be directly used for the next reaction. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0031] The invention provides a catalyst system which can realize high-selective hydrogenation of acetophenone and can obtain a catalyst system which can be recovered and recycled after being separated from a product. The catalyst system comprises a Pt nanocatalyst and an L-proline modifier, and the Pt nanocatalyst is prepared from a Pt precursor and a quaternary ammonium salt type ionic liquid stabilizer. Specifically, according to parts by mass, the catalyst system comprises 1 part of a Pt precursor, 20-50 parts of L-proline and 200-300 parts of a quaternary ammonium salt type ionic liquid. After the reaction is completed, an extraction solvent (cyclohexane or n-heptane) is added to extract, and the system is divided into two phases, the upper layer is an organic phase, and the product alpha-phenylethanol can be obtained after the solvent in the organic phase is evaporated; the black viscous liquid at the bottom is the catalyst system, and the recovered catalyst system does not need to be treated and can be directly used for the next reaction.

[0032] For the sake of clarity, the following examples are used to explain in detail:

[0033] Example 1

[0034] Preparation of Pt Nanocatalysts Stabilized by Ionic Liquids

[0035] The synthesis of ionic liquid (Formula 2) refers to the synthesis steps in the literature Appl. Organomet. Chem. 2008, 22, 620-623. Then, the Pt nanocatalyst is prepared using the ionic liquid (Formula 2) as a stabilizer. The specific operation steps are: 1.00 mg PtCl4 is dissolved in 0.40 g deionized water, and then 0.20 g of ionic liquid (Formula 2) is added, stirred evenly, dispersed at 60°C for 2h to remove moisture, and then filled with 4MPa hydrogen, reduced at 70°C for 3h in an autoclave, and the speed of the magnetic stirrer is 400r / min, and the Pt nanocatalyst can be obtained, and its particle size is 2.4nm measured by transmission electron microscopy.

[0036] Example 2

[0037] Preparation of Pt Nanocatalysts Stabilized by Ionic Liquids

[0038] The Pt nanocatalyst was prepared using the ionic liquid (Formula 2) as a stabilizer. The specific operation steps are as follows: 1.00 mg PtCl4 was dissolved in 0.40 g deionized water, and then 0.30 g of the ionic liquid (Formula 2) was added. The other operations were carried out in accordance with Example 1, and the Pt nanocatalyst was obtained. The particle size was measured by transmission electron microscopy to be 2.0 nm.

[0039] Example 3

[0040] Modification of Pt Nanocatalysts by L-proline

[0041] Weigh 0, 20 mg, 30 mg, 40 mg, and 50 mg of L-proline respectively and place them in a polytetrafluoroethylene liner, add a small amount of deionized water to dissolve, and then add the Pt nanocatalyst prepared in Example 1 to the liner containing the L-proline aqueous solution of each concentration. Place the liner in an autoclave and heat it open, stir at 60 ° C for 2 hours to remove the water to obtain a viscous black liquid, and the modification is completed to obtain a series of modified Pro / Pt nanocatalysts, which are marked as Pro / Pt nanocatalyst-0, Pro / Pt nanocatalyst-20, Pro / Pt nanocatalyst-30, Pro / Pt nanocatalyst-40, and Pro / Pt nanocatalyst-50 respectively. The modification process has no effect on the particle size of the Pt nanocatalyst.

[0042] Example 4

[0043] Application of modified Pro / Pt nanocatalysts in acetophenone hydrogenation

[0044] The modified series of Pro / Pt nanocatalysts in Example 3 were placed in the liner, 2.000g toluene was added to each, and 0.178g acetophenone was added to each after dissolution, and then each liner was placed in an autoclave and tightened, and 2MPa hydrogen was filled to replace the gas 3 times, and then 2MPa hydrogen was filled to react for 6h at 30°C. After the reaction, cyclohexane was added to extract, and the system was divided into two phases. The upper layer was an organic phase, which was taken out and analyzed by gas chromatography, and then the product α-phenylethanol was obtained after the solvent in the organic phase was evaporated; the black viscous liquid at the bottom was the catalytic system, and the recovered catalytic system did not need to be treated and could be directly used for the next reaction. The reaction results are shown in Table 1.

[0045] Table 1 Effect of L-proline dosage on the reaction

[0046]

[0047] As can be seen from Table 1, when L-proline is not used to modify the Pt nanocatalyst, the selectivity of α-phenylethanol is only 58%. As the amount of L-proline increases, the selectivity of α-phenylethanol also increases significantly. When the amount of L-proline increases to 40 mg, the selectivity of α-phenylethanol increases to >99%. However, when the amount of L-proline continues to increase, the conversion rate of acetophenone no longer increases. Therefore, the most preferred amount of L-proline is 40 mg.

[0048] Example 5

[0049] Effects of reaction temperature and hydrogen pressure on the reaction

[0050] The Pt nanocatalyst was prepared by referring to the methods of Examples 1 and 3 and modified with 40 mg of L-proline. Then, the Pro / Pt nanocatalyst was used in the hydrogenation reaction of acetophenone by referring to the method of Example 4. The reaction temperature and hydrogen pressure in Example 4 were adjusted according to Table 2 to investigate the effects of the reaction temperature and hydrogen pressure on the reaction.

[0051] Table 2

[0052]

[0053] As can be seen from Table 2, when the temperature is 25°C, the acetophenone conversion is 91% and the α-phenylethanol selectivity is >99%. When the temperature is raised to 30°C, the substrate conversion and product selectivity are both >99%. When the temperature is further raised, the acetophenone conversion is still >99%, but the product selectivity gradually decreases. The effect of hydrogen pressure was then investigated. When the hydrogen pressure was 1MPa, the acetophenone conversion was 93% and the α-phenylethanol selectivity was >99%. When the hydrogen pressure was raised to 2MPa, the acetophenone conversion and α-phenylethanol selectivity were both >99%. However, when the hydrogen pressure was further raised, the product selectivity decreased.

[0054] Example 6

[0055] Effect of acetophenone dosage and reaction time

[0056] The Pt nanocatalyst was prepared by referring to the methods of Examples 1 and 3 and modified with 40 mg of L-proline. Then, referring to the method of Example 4, the Pro / Pt nanocatalyst was used in the hydrogenation reaction of acetophenone, with a reaction temperature of 30° C. and a hydrogen pressure of 2 MPa. The amount of acetophenone and the reaction time were adjusted according to Table 3 to investigate the effects of the amount of acetophenone and the reaction time on the reaction.

[0057] Table 3

[0058]

[0059]

[0060] As shown in Table 3, when the reaction time is 3h, the conversion rate of acetophenone shows a downward trend as the amount of acetophenone increases. When the amount of acetophenone remains unchanged and the reaction time is extended, the conversion rate of acetophenone increases significantly and can reach more than 99%. During the reaction, the selectivity of the product α-phenylethanol has always been greater than 99%, highlighting the advantage of high selectivity of the catalytic system.

[0061] Example 7

[0062] Effect of catalyst service life

[0063] Pt nanocatalyst was prepared by the method of Examples 2 and 3 and modified by using L-proline (40 mg). Then, Pro / Pt nanocatalyst was used in the hydrogenation reaction of acetophenone by referring to the method of Example 4, and the amount of acetophenone added was 0.071 g. After the reaction was completed, cyclohexane or n-heptane was added, and the system was divided into two phases. The upper organic phase was taken out and analyzed by gas chromatography. After the solvent in the organic phase was evaporated, the product α-phenylethanol was obtained. The black viscous liquid at the bottom was a catalytic system comprising a Pt nanocatalyst and a modifier. The above steps were repeated and recycled 8 times. The reaction results are shown in Table 4.

[0064] Table 4

[0065] Use times Acetophenone conversion rate (%) α-Phenylethanol selectivity (%) 1 ＞99 ＞99 2 ＞99 ＞99 3 ＞99 ＞99 4 ＞99 ＞99 5 ＞99 ＞99 6 ＞99 ＞99 7 ＞99 ＞99 8 ＞99 ＞99 9 92 ＞99

[0066] It can be seen from Table 4 that the conversion rate of acetophenone and the selectivity of the product α-phenylethanol in the first eight reactions were always greater than 99%. In the ninth reaction, the substrate conversion rate dropped to 92%, which may be caused by the loss of the catalyst.

[0067] In summary, the catalytic system for selective hydrogenation of acetophenone to α-phenylethanol provided by the present invention exhibits high selectivity, that is, only C=O of acetophenone is hydrogenated, and the selectivity of the product α-phenylethanol is greater than 99%, and the Pt nanocatalyst and the modifier L-proline can be recycled 8 times, which has the advantage of long service life. In addition, the catalytic system and the generated product are separated by extraction, and the recovered catalytic system does not need to be treated and can be directly used for the next reaction.

[0068] Any numerical value mentioned in the present invention, if there is only an interval of two units between any minimum value and any maximum value, includes all values ​​from the minimum value to the maximum value each time increasing by one unit. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0069] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A catalytic system for selective hydrogenation of acetophenone to α-phenylethanol, characterized in that: The invention comprises a Pt nano catalyst prepared by using a quaternary ammonium salt type ionic liquid as a stabilizer and a Pt precursor, and L-proline and / or a reaction product thereof.

2. The catalytic system according to claim 1, characterized in that The structure of the quaternary ammonium salt ionic liquid is shown in formula (1): <h2 style=";text-align:left;direction:ltr">CH3(OCH2CH2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> N<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> Et3SO3-CH3 (1) In formula (1), n ​​is selected from 12-22, preferably, n is 16.

3. The catalytic system according to claim 1 or 2, characterized in that: The Pt precursor is a water-soluble platinum source. Preferably, the water-soluble platinum source is selected from at least one of PtCl4 and H2PtCl6.

4. The catalytic system according to any one of claims 1 to 3, characterized in that Based on 1 part by weight of the Pt precursor, the amount of L-proline is 20-50 parts by weight and the amount of the quaternary ammonium salt ionic liquid is 200-300 parts by weight; and / or the particle size of the Pt nanocatalyst is 2.0-3.0 nm, preferably 2.0-2.4 nm.

5. A method for preparing a catalytic system for selective hydrogenation of acetophenone to α-phenylethanol according to any one of claims 1 to 4, characterized in that: The following steps are involved: a) dissolving a Pt precursor in a solvent, adding a quaternary ammonium salt type ionic liquid, stirring evenly, dispersing to remove water, and then reducing to obtain a Pt nanocatalyst; b) adding an aqueous solution of L-proline to the Pt nanocatalyst for modification.

6. The preparation method according to claim 5, characterized in that: The solvent is deionized water; and / or the Pt precursor is a water-soluble platinum source, preferably, the water-soluble platinum source is selected from at least one of PtCl4 and H2PtCl6; and / or the structure of the quaternary ammonium salt ionic liquid is as shown in formula (1): <h2 style=";text-align:left;direction:ltr">CH3(OCH2CH2)<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> N<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> Et3SO3-CH3 (1) In formula (1), n ​​is selected from 12-22, preferably, n is 16.

7. The preparation method according to claim 5 or 6, characterized in that: The mass ratio of the Pt precursor to the quaternary ammonium salt ionic liquid is 1:200-1:300; and / or the mass ratio of the Pt precursor to the L-proline is 1:20-1:

50.

8. The preparation method according to any one of claims 5 to 7, characterized in that: In step a), the dispersion conditions are: temperature 60-80°C, time 2-4h; and / or the reduction conditions are: temperature 70-90°C, time 3-6h; and / or in step b), the modification conditions are: temperature 60-80°C, time 1-3h.

9. A method for preparing α-phenylethanol by selective hydrogenation of acetophenone, characterized in that: The following steps are involved: The catalyst system according to any one of claims 1 to 4 or the catalyst system prepared by the method according to any one of claims 5 to 8 is added to an organic solvent, and then acetophenone is added and hydrogen is introduced to carry out a selective hydrogenation reaction; after the reaction is completed, an extraction solvent is added to extract and obtain a product.

10. The method according to claim 9, characterized in that The organic solvent is at least one of toluene, ethylbenzene, cyclohexane and n-heptane; and / or the conditions of the selective hydrogenation reaction are: hydrogen partial pressure 2-4MPa, temperature 30-40°C, time 3-6h; and / or the mass ratio of the Pt nanocatalyst to the acetophenone is 1:120-1:310, preferably 1:122-1:307; and / or the extraction solvent is cyclohexane or n-heptane.

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