Method for preparing methyl propionate palladium complex through free coordination cage effect stable ethylene hydrogen esterification

Abstract

The invention relates to a method for preparing a methyl propionate palladium complex through free coordination cage effect stabilization ethylene hydrogen esterification, which aims at the problem that central metal of the palladium complex for preparing methyl propionate through ethylene methyl esterification is easy to gather and inactivate, and utilizes the cage effect of a stabilizer to construct a cage network around the palladium complex; meanwhile, the free coordination effect is utilized to cooperate with a bidentate phosphine ligand, so that the formation of palladium black inactivation of an active component palladium is effectively slowed down, the stabilization time is maximally prolonged by 360 hours, the TOF value is as high as 20000 h <-1 >, and the selectivity is 100%. The hydrogen esterification reaction system comprises ethylene, CO, methanol, a stabilizer and a palladium complex catalyst; the palladium complex catalyst comprises palladium acetate, 1, 2-bis (di-tert-butylphosphinomethyl) benzene and an acid accelerant. According to the method, the stability of the palladium complex is greatly improved while high catalytic activity and selectivity of the reaction are guaranteed, the reaction condition is mild, the atom utilization rate is high, and the method has a good application prospect in the reaction for synthesizing methyl propionate through ethylene hydrogen esterification.

Description

Technical Field

[0001] The invention belongs to the technical field of homogeneous catalysis for synthesizing organic chemical products by ethylene hydroesterification, and particularly relates to a method for stabilizing a palladium complex for preparing methyl propionate by ethylene hydroesterification through a free coordination cage effect. Background Art

[0002] Methyl methacrylate (MMA) is an important basic raw material in the fields of high-end polymer materials such as aerospace, electronic information, etc. my country's annual demand is about 1.5 million tons, of which 50% depends on imports. It is one of the top ten products with the highest import dependence in my country's fine chemical industry. In the MMA synthesis route, the process of preparing MMA by two-step hydroesterification-hydrogenation with ethylene as raw material has many technical advantages such as a wide source of raw materials, a short reaction route, high atomic utilization, good reaction selectivity, and a clean and non-toxic process. However, the palladium complex catalyst used in the process of preparing methyl propionate by ethylene hydroesterification has long been monopolized by Lucite. Existing research mainly focuses on the development of phosphine ligands to enable the catalyst to have good reaction activity and selectivity during the hydroesterification reaction. However, the precious metal palladium is prone to aggregation and deactivation of the catalyst, which is not conducive to the recovery and reuse of the catalyst. It has become a key problem that is difficult to break through in this process and is also a research focus that needs to be urgently solved in the field of palladium homogeneous catalysis.

[0003] At present, a variety of methods for improving the stability of the catalytic system have been reported in the published patents. CN 116237086A invented a catalyst system for preparing methyl propionate by ethylene hydroesterification based on an antioxidant strategy, and the oxidation of the catalytic system was inhibited by adding trace amounts of antioxidants such as phenol, ascorbic acid, inorganic salt derivatives, etc. CN 114685276 A provides a method for adding a polymer dispersant to keep the catalytic particles stable, preventing the metal palladium from settling and thus facilitating the recovery of lost metals. CN 115957823 A discloses a bidentate phosphine ligand catalyst system using a xanthene skeleton, and the rigid skeleton structure of the ligand facilitates the formation of a spatially favorable coordination mode and a stable complex structure. CN 116328761 B invented a method for improving the aggregation of palladium elements and improving the thermal stability of the catalyst using two active additives.

[0004] However, while the method provided by the above invention patent improves the stability of the catalyst, it also brings new problems such as loss of catalytic activity and liquid product selectivity, or increases the difficulty of system separation, and the reaction is mostly carried out at a temperature above 100°C, which increases the reaction energy consumption. Therefore, while ensuring the excellent reaction activity and selectivity of the catalytic system, developing a simple and efficient palladium catalyst stabilization method is of great strategic significance for establishing a process for preparing methyl propionate by ethylene hydroesterification with independent intellectual property rights. Summary of the invention

[0005] The purpose of the present invention is to provide a method for stabilizing the palladium complex of methyl propionate by ethylene hydroesterification with a free coordination cage effect, so as to improve the thermal stability of the palladium complex catalyst system. The method utilizes the stabilizer cage effect to effectively slow down the aggregation of the palladium complex, and simultaneously utilizes the stabilizer free coordination effect to coordinate the bidentate phosphine ligand to achieve the stability of the palladium catalyst system. The method not only improves the thermal stability of the palladium complex catalyst system through dual effects, but also further ensures the excellent reaction activity and selectivity of the catalyst system, and does not bring about additional outstanding process problems, and has good application prospects.

[0006] In order to achieve the above invention object, the technical solution adopted by the present invention is:

[0007] A method for preparing methyl propionate by stabilizing a palladium complex through free coordination cage effect by ethylene hydroesterification. The palladium complex catalyst system comprises palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene, an acid promoter and a stabilizer.

[0008] The acid promoter is one or a combination of two organic acids such as p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, 1,4-butanesulfonic acid, benzenesulfonic acid, 2-naphthalenesulfonic acid, borosalicylic acid, etc. The stabilizer is one or a combination of toluene, dichloromethane, pyridine, tetrahydrofuran, acetonitrile, etc.

[0009] Furthermore, the molar ratio of palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene and acid promoter is 1:(0.5-10):(5-30); preferably 1:(1-6):(6-20).

[0010] Furthermore, the volume ratio of the stabilizer to methanol is (0.25-15):7.5; preferably (1-5):7.5.

[0011] Another object of the present invention is to protect the use of the palladium complex catalyst system described in one or more schemes, wherein the catalyst system is used to catalyze the process of preparing methyl propionate by hydroesterification of ethylene, CO and methanol.

[0012] Furthermore, the hydroesterification reaction temperature is 60-120° C., the pressure is 1-4 MPa; and the molar ratio of ethylene to CO in the raw gas is 1:1.

[0013] The present invention proposes and invents a new method and strategy for effectively slowing down the aggregation and inactivation of palladium complexes by adding a stabilizer to a palladium complex catalyst system. The principle is: utilizing the cage effect of the stabilizer to confine the palladium complex to the cage network formed by the stabilizer, thereby preventing the aggregation and inactivation of the complexes due to collisions; at the same time, utilizing the nucleophilic effect of the stabilizer, it can freely coordinate to the empty orbit of the palladium complex, and cooperate with the bidentate phosphine ligand to improve the thermal stability of the palladium catalyst system, further preventing the polymerization of the active center metal palladium. When the reactant is inserted, dynamic decoordination can occur due to the weak coordination ability of the stabilizer, thereby providing insertion space for the reactant, without affecting the reaction performance of the palladium complex catalyst, and ensuring excellent TOF (the number of moles of methyl propionate converted per mole of palladium atom per hour, h -1 ) reaction indicators.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention uses a stabilizer and utilizes its cage effect and free coordination to cooperate with the bidentate phosphine chelate ligand to effectively improve the thermal stability of the palladium complex catalyst system.

[0016] 2. The stabilizer used in the present invention has a wide range of sources and low cost. The use of the stabilizer ensures the excellent reaction activity and selectivity of the catalytic system and does not bring about additional outstanding process problems.

[0017] 3. The present invention is a homogeneous reaction process with high atom utilization, mild reaction conditions, good product selectivity and simple process. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is described in detail in conjunction with the following embodiments. It should be understood that the specific embodiments described herein are only illustrative and are not intended to limit the present invention.

[0019] Hydroesterification reaction experiment: a certain amount of palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene, acid promoter, stabilizer and methanol after dehydration and deoxygenation were weighed in a glove box, added into a 25mL high-pressure reactor and sealed, and the gas in the reactor was replaced with ethylene / CO mixed gas 3 times, and then the reactor was heated to 60-120°C, with a stirring rate of 1000r / min. After reaching the set reaction temperature, the raw gas was introduced to 1-4MPa, and the pressure in the reactor was kept constant. After a period of reaction, the activity and selectivity of the catalyst can be evaluated based on the gas phase raw material consumption (flow meter indication change) and the liquid phase product generation (chromatographic analysis).

[0020] Experiment to evaluate thermal stability of palladium complex catalyst: In a glove box, weigh a certain amount of palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene, acid promoter, stabilizer and methanol after dehydration and deoxygenation, add them into a 48mL pressure tube, seal the pressure tube and place it in a 60-120℃ oil bath with stirring at a stirring rate of 1000r / min. Observe the liquid state in the pressure tube and take samples at regular time intervals. After filtering the samples, analyze the palladium content in the solution through ICP test to evaluate the thermal stability of the catalytic system. When the palladium content in the solution begins to decrease, it is determined that the catalyst begins to deactivate.

[0021] Comparative Example 1

[0022] Add 7.5 mL of methanol after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0148 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 20324h -1 , the selectivity of methyl propionate is 100%, and the catalytic system in the pressure tube is stable for about 10 hours.

[0023] Example 1

[0024] Add 7.5 mL of methanol after dehydration and deoxygenation, 3.0 uL of pyridine after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0148 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 20610h -1 , the selectivity of methyl propionate is 100%, and the stable time in the pressure tube is about 24 hours.

[0025] Example 2

[0026] Add 7.5 mL of methanol after dehydration and deoxygenation, 2.5 mL of toluene after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 19787h -1 , the selectivity of methyl propionate is 100%, and the stable time in the pressure tube is about 75h.

[0027] Example 3

[0028] Add 7.5 mL of methanol after dehydration and deoxygenation, 2.5 mL of tetrahydrofuran after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 21111h -1 , the selectivity of methyl propionate is 100%, and the stable time in the pressure tube is about 92h.

[0029] Example 4

[0030] Add 7.5 mL of methanol after dehydration and deoxygenation, 2.5 mL of dichloromethane after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. The average TOF is 20216h -1 , the selectivity of methyl propionate is 100%, and the stable time in the pressure tube is about 229 hours.

[0031] Example 5

[0032] Add 7.5 mL of methanol after dehydration and deoxygenation, 0.25 mL of acetonitrile after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 22430h -1 , methyl propionate selectivity 100%, stable time in pressure tube about 120h

[0033] Example 6

[0034] Add 7.5 mL of methanol after dehydration and deoxygenation, 1.5 mL of acetonitrile after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 22112h -1, methyl propionate selectivity 100%, stable time in pressure tube about 248h

[0035] Example 7

[0036] Add 7.5 mL of methanol after dehydration and deoxygenation, 2.5 mL of acetonitrile after dehydration and deoxygenation, 0.0028 g of palladium acetate, 0.0247 g of 1,2-bis(di-tert-butylphosphinomethyl)benzene, and 0.0215 g of p-toluenesulfonic acid to a 25 mL high-pressure reactor. Seal the reactor, replace the atmosphere in the reactor, start stirring and heating, and introduce raw gas when the reactor temperature reaches 80°C. Start timing when the pressure stabilizes at 2 MPa. Stop the experiment after 10 minutes. Average TOF 20610h -1 , the selectivity of methyl propionate is 100%, and the stable time in the pressure tube is about 360 hours.

[0037] Table 1 Effect and stability of catalysts of comparative examples 1-2 and examples 1-7 on ethylene carbonylation reaction

[0038]

[0039]

[0040] Based on the above examples, after adding stabilizer to the system, the TOF value of the catalytic system reaction activity is still as high as 20000h -1 Moreover, due to the cage effect of the stabilizer, a cage network can be constructed around the palladium complex, which slows down the aggregation of the Pd complex. Compared with the system without stabilizer, the stability of the Pd catalytic system is significantly improved. It also reflects the synergistic effect of the free coordination of the stabilizer on the bidentate phosphine ligand, indicating the important significance of the research on such catalysts.

[0041] The embodiments of the aforementioned invention are only for explaining the present invention, and can be freely combined into multiple embodiments, and are not used to limit the present invention, and the words therein are explanatory words rather than restrictive words. Those skilled in the art shall make modifications based on the disclosure of the present invention without departing from the scope of the present invention, and the present invention can be extended to other applications with the same functions.

Claims

1. A method for stabilizing the free coordination cage effect to prepare methyl propionate palladium complex by ethylene hydroesterification, characterized in that: In view of the problem that the palladium complex in the preparation of methyl propionate by ethylene hydroesterification is prone to central metal aggregation and deactivation, a method is proposed that utilizes the cage effect of a stabilizer to effectively slow down the aggregation of the palladium complex, and utilizes the free coordination effect of the stabilizer to cooperate with the bidentate phosphine ligand to achieve the stability of the palladium catalytic system; the palladium complex catalyst system includes palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene, an acid promoter and a stabilizer.

2. The palladium catalyst system according to claim 1, wherein The stabilizer is one or more combinations of toluene, dichloromethane, pyridine, tetrahydrofuran, acetonitrile and the like.

3. The palladium catalyst system as claimed in claim 1, characterized in that: The ratio of the stabilizer to methanol is controlled at (0.25-15):7.5; preferably (1-5):7.

5.

4. The palladium catalyst system according to claim 1, wherein: The acid promoter is one or a combination of two organic acids such as p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, 1,4-butanesulfonic acid, benzenesulfonic acid, 2-naphthalenesulfonic acid, and borosalicylic acid.

5. The palladium catalyst system according to claim 1, wherein The molar ratio of palladium acetate, 1,2-bis(di-tert-butylphosphinomethyl)benzene and acid promoter is: 1:(0.5-10):(5-30); preferably 1:(1-6):(6-20).

6. The palladium catalyst system according to claim 2-5, characterized in that The catalyst system is used for catalyzing the process of preparing methyl propionate through the hydroesterification reaction of ethylene, CO and methanol.

7. The palladium catalyst system according to claim 6, wherein The temperature of the ethylene hydroesterification reaction is 40-150° C., preferably 60-100° C.; the reaction pressure is 0.2-10.0 MPa, preferably 1.0-3.0 MPa; and the molar ratio of ethylene to carbon monoxide is 1:1.

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