A method for preparing methyl propionate by ethylene hydroesterification

Abstract

The present invention discloses a method for preparing methyl propionate by ethylene hydroesterification. A composite catalyst of a Pd-based compound / bidentate phosphine ligand / acidic promoter is used. With methyl propionate as the solvent, after adding the catalyst components of the Pd-based compound, bidentate phosphine ligand, and acidic promoter and dissolving them, ethylene, carbon monoxide, and methanol are added, wherein the molar ratio of C2H4 / CO is 0.3 - 10:1, and the molar ratio of methanol / methyl propionate is 0.2 - 10:1; the temperature is raised, and methyl propionate is prepared by the hydroesterification reaction of ethylene, carbon monoxide, and methanol. The method of the present invention has a low reaction temperature and reaction pressure, a short reaction time, good catalytic activity and selectivity, can improve the reaction efficiency and inhibit by-products, and the yield of methyl propionate is greater than 95%, and has broad industrial application prospects.

Description

Technical Field

[0001] The present invention relates to a method for preparing methyl propionate, and particularly to a method for preparing methyl propionate by ethylene hydroesterification. Background Art

[0002] Organic carboxylic acid esters, as an important class of oxygen-containing compounds, are widely used. Among them, methyl propionate (PM) has important uses in medicine, chemical industry, fuel, etc., and is an important pharmaceutical intermediate and organic synthesis intermediate. Methyl propionate can be used to synthesize methyl methacrylate (MMA), and MMA is a monomer for synthesizing polymethyl methacrylate (PMMA), which is widely used in fields such as glass and medical equipment.

[0003] The synthesis methods of methyl propionate have been widely reported in the literature and patents. Relevant literature has reported a method for synthesizing methyl propionate using ethylene, CO, and methanol as raw materials under the catalytic action of palladium, organic phosphine ligands, and acid additives (Angew. Chem. Int Ed. 2007, 46, 2273, Green Chem. 2014, 16, 161). Patents CN 103319337 A and CN111253258 A disclose a method for preparing methyl propionate by catalytic ethylene hydroesterification using a bimetallic catalyst system, which uses a composite catalyst system with palladium as the main catalyst and cobalt, nickel, ruthenium, etc. as co-catalysts. Patent CN 107497494 B discloses a method for preparing methyl propionate by catalytic ethylene using a combination catalyst system of non-noble metal / phosphine ligand / acid additive. Patent CN114685276A realizes the preparation of methyl propionate by ethylene hydroesterification by using a homogeneous catalyst system and a polymer dispersant. In addition, Patent CN 114618519 A also discloses the application of a bimetallic supported catalyst different from the homogeneous catalytic system in the preparation of methyl propionate by ethylene hydroesterification. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing methyl propionate by ethylene hydroesterification. By using a homogeneous metal / ligand / auxiliary combination catalyst and through the selection of reaction solvents and the combination of process conditions, the method of the present invention can reduce the reaction temperature and reaction pressure of ethylene hydroesterification, shorten the reaction time, inhibit the generation of by-products, and has high selectivity and yield of the target product methyl propionate, showing good industrial application prospects.

[0005] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing methyl propionate by ethylene hydroesterification, characterized in that a Pd-based compound / bidentate phosphine ligand / acidic promoter composite catalyst is used. Using methyl propionate (PM) as a solvent, after adding the catalyst components Pd-based compound, bidentate phosphine ligand, and acidic promoter and dissolving them, ethylene (C2H4), carbon monoxide (CO), and methanol (MeOH) are added, where the molar ratio of C2H4 / CO is 0.3-10:1, and the molar ratio of methanol / methyl propionate is 0.2-10:1; the temperature is raised, and methyl propionate is prepared by the hydroesterification reaction of ethylene, carbon monoxide, and methanol.

[0007] Furthermore, the molar ratio of each component Pd / bidentate phosphine ligand / acidic promoter in the composite catalyst is 1:(3-20):(1-20).

[0008] Furthermore, the bidentate phosphine ligand is a semi-rigid bidentate phosphine ligand, selected from bis(2-(diphenylphosphino)phenyl)methane, or its derivatives, and has the following structural formula:

[0009]

[0010] Among them, R1 and R2 are one or more of hydrogen, C1-C4 alkyl, methoxy, halogen, trifluoromethyl, phenyl, phenoxy, cyano, nitro. Preferably, R1 and R2 are one or two of hydrogen, methyl, methoxy, or tert-butyl.

[0011] Furthermore, the active metal Pd of the composite catalyst is selected from one of palladium acetylacetonate, palladium chloride, palladium acetate, bis(triphenylphosphine)palladium dichloride, bis(acetonitrile)palladium dichloride, (1,5-cyclooctadiene)palladium dichloride, allyl palladium chloride, tetrakis(triphenylphosphine)palladium, palladium acetylacetonate, bis(dibenzylideneacetone)palladium, or tris(dibenzylideneacetone)dipalladium. Preferably palladium chloride, palladium acetylacetonate, or palladium acetate.

[0012] Furthermore, the acidic promoter in the composite catalyst is selected from one of hydrochloric acid, sulfuric acid, perchloric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid, p-toluenesulfonic acid, 2-hydroxypropane-2-sulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, dodecylsulfonic acid, and aluminum trifluoromethanesulfonate. Preferably p-toluenesulfonic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid, or dodecylsulfonic acid.

[0013] Regarding the bidentate phosphine ligand and its synthesis, as well as optional Pd-based compounds and acidic promoters, see CN111087306A.

[0014] Furthermore, in the reaction for preparing methyl propionate by ethylene hydroesterification, the molar ratio of C2H4 / CO is 0.3-10:1, preferably 0.3-3:1, more preferably 0.5-2:1.

[0015] Further, in the reaction of preparing methyl propionate by ethylene hydroesterification, the molar ratio of methanol to the limiting reactant in C2H4 or CO is 1.1 - 2:1.

[0016] Further, in the reaction of preparing methyl propionate by ethylene hydroesterification, the molar ratio of MeOH / MP is 0.2 - 10:1, preferably 0.3 - 4:1.

[0017] Further, in the reaction of preparing methyl propionate by ethylene hydroesterification, the temperature range is 90 - 150 °C, preferably 100 - 120 °C.

[0018] Further, in the reaction of preparing methyl propionate by ethylene hydroesterification, the maximum pressure is ≤6 MPa, preferably ≤4 MPa, more preferably ≤3.5 MPa.

[0019] Further, the reaction time in the reaction of preparing methyl propionate by ethylene hydroesterification is 0.1 - 2 h, preferably 0.5 - 1 h.

[0020] Further, the concentration range of Pd in the catalyst is 60 - 300 ppm, preferably 120 - 260 ppm.

[0021] Advantages of the present invention: According to the method for synthesizing methyl propionate by ethylene carbonylation of the present invention, under the action of a composite catalyst system of Pd-based compound / bidentate phosphine ligand / acidic promoter, ethylene, carbon monoxide and methanol are subjected to hydroesterification to prepare methyl propionate; using methyl propionate as a solvent, adjusting the molar ratio of ethylene, carbon monoxide and methanol can greatly reduce the excess of carbon monoxide, improve the reaction efficiency, inhibit by-products, and increase the yield of the target product methyl propionate. The aryl bidentate phosphine ligand has high stability, and the synthesis method is simple, which can efficiently catalyze the hydroesterification of ethylene to synthesize methyl propionate. The method reduces the reaction temperature and pressure of the ethylene hydroesterification reaction, shortens the reaction time, and can complete the reaction at 100 °C within as short as 0.5 - 1 h, with the maximum pressure not exceeding 4 MPa and the yield of methyl propionate being greater than 95%. The method has good commercial value. Description of the Drawings

[0022] Figure 1 Gas chromatogram of the reaction solution in Example 1 (molar ratio of methyl propionate / methanol is 0.55);

[0023] Figure 2 Gas chromatogram of the reaction solution in Comparative Example 3 (molar ratio of methyl propionate / methanol is 10.38). Detailed Embodiments

[0024] To describe the technical solution of the present invention more clearly, the present invention will be described in detail below in conjunction with specific embodiments. It should be noted that the content recorded below and the preferred embodiments do not constitute a limitation on the present invention, and the method for implementing the present invention is not limited to the method recorded in the following embodiments. The protection scope of the present invention is not limited by the specific implementation manner, but is defined by the claims.

[0025] In the following examples, the ethylene hydroesterification reaction was carried out in a 2L autoclave reactor. A certain amount of semi-rigid bidentate phosphine ligand was weighed and dissolved in methyl propionate solution. After complete dissolution, a Pd-based compound was added. After the palladium metal was dissolved, an acidic promoter was added. After complete dissolution, the solution was transferred to a high-pressure reaction kettle, and then a certain amount of methanol was added. After sealing the reaction kettle, it was replaced with N2. After the replacement was completed, a certain amount of ethylene and CO were introduced, and the temperature was raised to carry out the ethylene hydroesterification reaction.

[0026] In the method described above, the components in the catalyst are added in a molar ratio of Pd / bidentate phosphine ligand / acidic promoter of 1:(3 - 20):

[0027] (1 - 20).

[0028] The semi-rigid bidentate phosphine ligand is selected from bis(2-(diphenylphosphino)phenyl)methane, or a product in which the hydrogen on its phenyl group is substituted by one or two methyl groups, methoxy groups or tert-butyl groups, including:

[0029]

[0030] The active metal Pd of the composite catalyst is preferably palladium chloride, palladium acetylacetonate or palladium acetate. The acidic promoter is preferably p-toluenesulfonic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid or dodecylsulfonic acid.

[0031] In the following examples, the active metal Pd of the composite catalyst is selected from palladium acetylacetonate, and the acidic promoter is selected from p-toluenesulfonic acid.

[0032] According to the method of the present invention, under preferred conditions, the molar ratio of C2H4 / CO in the ethylene hydroesterification reaction is 0.3 - 3:1, more preferably 0.5 - 2:1. It avoids a large excess of CO, and can reduce the maximum reaction pressure from above 7 - 8 MPa to below 4 MPa.

[0033] In the method according to the present invention, methyl propionate is used as the solvent in the ethylene hydroesterification reaction, and the molar ratio of MeOH / MP is 0.2 - 10:1, preferably 0.3 - 4:1. In the method of the present invention, methyl propionate is used as the main solvent in the reaction, and within the preferred range, the yield of methyl propionate is greatly increased (from 84% to 99%), while the generation of by-products is reduced. The ethylene hydroesterification reaction is a gas-liquid two-phase reaction. Instead of using a large excess of methanol as the solvent, increasing the amount of methyl propionate is beneficial to the mass transfer process of the whole reaction and promotes the progress of the reaction.

[0034] In the method according to the present invention, in the reaction of preparing methyl propionate by ethylene hydroesterification, the temperature range is 90 - 150 °C, preferably 100 - 120 °C. The maximum pressure is ≤6 MPa, preferably ≤4 MPa, and the reaction pressure is significantly reduced. The reaction time is shortened to 0.1 - 2 h, and the reaction can be completed within as short as 0.5 - 1 h. The conversion rate of C2H4 or CO is close to 100%, and the yield of methyl propionate reaches more than 95%, and reaches 99% under preferred conditions. As the reaction temperature increases, the yield of methyl propionate shows a positive correlation trend. When the reaction temperature rises to 100 °C, the yield of methyl propionate can reach 99%. Continuing to increase the temperature to 120 °C will slightly reduce the yield of methyl propionate but has little impact. Prolonging the reaction time can increase the reaction conversion rate, but the longer the reaction time, the more serious the side reactions.

[0035] Taking into account the process conditions for the reaction to occur, under the above preferred reaction conditions, the yield of methyl propionate can reach more than 95%.

[0036] After the ethylene hydroesterification reaction is completed, it is cooled to room temperature, the reaction solution is collected for chromatographic analysis, and the yield of methyl propionate is calculated.

[0037] Chromatographic analysis conditions: All samples are quantitatively analyzed for the products using a Shimadzu 7980 gas chromatograph, and the quantitative method is the internal standard method. The chromatographic column uses an Agilent HP-5 chromatographic column (30 m × 0.32 mm × 0.25 um). The chromatographic detection conditions are: the vaporization chamber temperature is 250 °C, the hydrogen flame ionization detector (FID) temperature is 250 °C, high-purity nitrogen is used as the carrier gas, and the constant flow rate is 2 mL·min -1 . In the FID detector, the air and high-purity hydrogen flow rates are 200 mL·min -1 and 30 mL·min -1 . The column oven temperature uses a programmed temperature rise method, maintaining at 45 °C for 2 minutes, and rising to 160 °C at a heating rate of 10 °C·min -1 .

[0038] Yield of methyl propionate: The yields of methyl propionate in the two cases are respectively:

[0039] (1) When ethylene is in excess, CO is used as the basis for calculating the yield of methyl propionate:

[0040] Yield of methyl propionate (MP) = Molar amount of methyl propionate formed / Molar amount of CO charged * 100%

[0041] (2) When CO is in excess, ethylene is used as the basis for calculating the yield of methyl propionate:

[0042] Yield of methyl propionate (MP) = Molar amount of methyl propionate formed / Molar amount of C2H4 charged * 100%

[0043] Example 1

[0044] Weigh 325 ml (290 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 75 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO) = 2:1. The stirring speed is 400 r / min, the reaction temperature is 110 °C, the maximum pressure during the reaction is 3.17 MPa, and the reaction is carried out for 60 minutes. After the reaction is completed, cool it to room temperature and perform chromatographic analysis. The CO conversion rate is more than 99%, and the yield of methyl propionate is 99%.

[0045] Example 2

[0046] Weigh 325 ml (290 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 75 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO) = 3:1. The stirring speed is 400 r / min, the reaction temperature is 110 °C, the maximum pressure during the reaction is 3.62 MPa, and the reaction is carried out for 60 minutes. After the reaction is completed, cool it to room temperature and perform chromatographic analysis. The CO conversion rate is 92%, and the yield of methyl propionate is 88.2%.

[0047] Example 3

[0048] Weigh 180 ml (160 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand c and add it to the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 220 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, fill in ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO)=1:2, the stirring speed is 400 r / min, the reaction temperature is 110 °C, the maximum pressure during the reaction is 4.09 MPa, react for 60 minutes, cool to room temperature after the reaction is completed, and perform chromatographic analysis. The ethylene conversion rate is more than 99%, and the yield of methyl propionate is 99%.

[0049] Example 4

[0050] Weigh 145 ml (130 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand e and add it to the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 255 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, fill in ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO)=2:1, the stirring speed is 400 r / min, the reaction temperature is 100 °C, the maximum pressure during the reaction is 3.52 MPa, react for 60 minutes, cool to room temperature after the reaction is completed, and perform chromatographic analysis. The CO conversion rate is 92%, and the yield of methyl propionate is 87%.

[0051] Example 5

[0052] Weigh 185 ml (166 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand e and add it to the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 215 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, fill in ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO)=2:1, the stirring speed is 400 r / min, the reaction temperature is 90 °C, the maximum pressure during the reaction is 3.34 MPa, react for 60 minutes, cool to room temperature after the reaction is completed, and perform chromatographic analysis. The CO conversion rate is 96%, and the yield of methyl propionate is 92%.

[0053] Example 6

[0054] Weigh 200 ml (179 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand f and pour it into the conical flask. Dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 200 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times. Each time, pressurize to 0.5 MPa and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases with a molar ratio of n(C2H4):n(CO) = 2:1, a stirring speed of 400 r / min, a reaction temperature of 120 °C, a maximum pressure of 3.0 MPa during the reaction, react for 60 minutes. After the reaction is completed, cool it to room temperature and perform chromatographic analysis. The CO conversion rate is 98%, and the yield of methyl propionate is 96.2%.

[0055] Example 7

[0056] Weigh 270 ml (240 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 1.9 g of phosphine ligand a and pour it into the conical flask. Dissolve it with magnetic stirring. After complete dissolution, add 120 mg of palladium acetylacetonate and 0.69 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 130 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times. Each time, pressurize to 0.5 MPa and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases with a molar ratio of n(C2H4):n(CO) = 2:1, a stirring speed of 400 r / min, a reaction temperature of 110 °C, a maximum pressure of 3.28 MPa during the reaction, react for 60 minutes. After the reaction is completed, cool it to room temperature and perform chromatographic analysis. The CO conversion rate is 99%, and the yield of methyl propionate is 99%.

[0057] Example 8

[0058] Weigh 270 ml (240 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 0.9 g of phosphine ligand a and pour it into the conical flask. Dissolve it with magnetic stirring. After complete dissolution, add 60 mg of palladium acetylacetonate and 0.36 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 130 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times. Each time, pressurize to 0.5 MPa and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases with a molar ratio of n(C2H4):n(CO) = 2:1, a stirring speed of 400 r / min, a reaction temperature of 110 °C, a maximum pressure of 3.30 MPa during the reaction, react for 60 minutes. After the reaction is completed, cool it to room temperature and perform chromatographic analysis. The CO conversion rate is 91%, and the yield of methyl propionate is 89%.

[0059] Example 9

[0060] Weigh 325 ml (290 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand f and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 75 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, fill in ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO)=2:1, the stirring speed is 400 r / min, the reaction temperature is 110 °C, the maximum pressure during the reaction is 3.32 MPa, react for 60 minutes, cool to room temperature after the reaction is completed, and perform chromatographic analysis. The CO conversion rate is more than 99%, and the yield of methyl propionate is 99%.

[0061] Comparative Example 1

[0062] Weigh 75 ml (67 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 325 ml of methanol. After mixing evenly, transfer it to a 2000 mL high-pressure reactor and seal it. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, fill in 2 mol of ethylene, with a pressure of 1.6 MPa, and then fill in carbon monoxide to 6.0 MPa, the stirring speed is 400 r / min, the reaction temperature is 110 °C, the pressure during the reaction is 8.0 MPa, and use CO gas for pressure stabilization. React for 240 minutes, cool to room temperature after the reaction is completed, and perform chromatographic analysis. The ethylene conversion rate is 94%, and the yield of methyl propionate is 84.1%.

[0063] Comparative Example 2

[0064] Weigh 75 ml (67 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 325 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, charge 2 mol of ethylene, and then charge carbon monoxide to 6.0 MPa. The stirring speed is 400 r / min, the reaction temperature is 110 °C, the reaction pressure is 8.0 MPa, and the pressure is stabilized with CO gas. React for 120 minutes. After the reaction is completed, cool it to room temperature and conduct chromatographic analysis. The ethylene conversion rate is 93.5%, and the yield of methyl propionate is 89.8%.

[0065] Comparative Example 3

[0066] Weigh 75 ml (67 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 325 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, charge 2 mol of ethylene, and then charge carbon monoxide to 6.0 MPa. The stirring speed is 400 r / min, the reaction temperature is 110 °C, the reaction pressure is 8.0 MPa, and the pressure is stabilized with CO gas. React for 60 minutes. After the reaction is completed, cool it to room temperature and conduct chromatographic analysis. The ethylene conversion rate is 93.2%, and the yield of methyl propionate is 88.97%.

[0067] Comparative Example 4

[0068] Weigh 75 ml (67 g) of methyl propionate and pour it into a 500 mL conical flask for standby. Weigh 5.0 g of phosphine ligand a and pour it into the conical flask, and dissolve it with magnetic stirring. After complete dissolution, add 240 mg of palladium acetylacetonate and 1.37 g of p-toluenesulfonic acid in sequence. After complete dissolution, add 325 ml of methanol, mix evenly and transfer it to a 2000 mL high-pressure reactor for sealing. Use N2 to displace the air in the reactor 6 times, pressurize to 0.5 MPa each time, and then slowly release the gas. After the displacement is completed, charge ethylene and carbon monoxide gases, and their molar ratio is n(C2H4):n(CO)=1:2. The stirring speed is 400 r / min, the reaction temperature is 110 °C, the maximum reaction pressure is 4.19 MPa, react for 60 minutes. After the reaction is completed, cool it to room temperature and conduct chromatographic analysis. The CO conversion rate is 93%, and the yield of methyl propionate is 89.2%.

[0069] The reaction process conditions of the above examples and the yields of the target product methyl propionate are shown in Table 1.

[0070] Analyze the main components of the reaction solution. The chromatograms of the reaction solution of Example 1 and the reaction solution obtained in Comparative Example 3 are respectively as Figure 1 and Figure 2 . The peaks in the chromatogram are methanol, methyl propionate and its accompanying peak, dioxane solvent, internal standard, by-product 1 (methyl 4-oxohexanoate) and by-product 2 from left to right. Figure 2 In the chromatogram of Figure 2 , Figure 1 there are obvious by-products 1 (methyl 4-oxoheptanoate, retention time 9.084 min) and by-product 2 (retention time 12.511 min). Comparing the chromatograms

[0071] Table 1

[0072] Name <![CDATA[n(C2H4 / CO)]]> n(MeOH / MP) Reaction temperature Reaction pressure Reaction time Yield of MP Example 1 2 / 1 0.55 110℃ 3.17 MPa 60 min 99％ Example 2 3 / 1 0.55 110℃ 3.62 MPa 60 min 88.2％ Example 3 1 / 2 2.9 110℃ 4.09 MPa 60 min 99％ Example 4 2 / 1 4.1 100℃ 3.52 MPa 60 min 87％ Example 5 2 / 1 2.7 90℃ 3.34 MPa 60 min 92％ Example 6 2 / 1 2.3 120℃ 3.30 MPa 60 min 96.2％ Example 7 2 / 1 1.1 110℃ 3.28 MPa 60 min 99％ Example 8 2 / 1 1.1 110℃ 3.30 MPa 60 min 89％ Example 9 2 / 1 0.55 110℃ 3.32 MPa 60 min 99％ Comparative Example 1 10.38 110℃ 8.0 MPa 240 min 84.1％ Comparative Example 2 10.38 110℃ 8.0 MPa 120 min 89.8％ Comparative Example 3 10.38 110℃ 8.0 MPa 60 min 88.97％ Comparative Example 4 1 / 2 10.38 110℃ 4.19 MPa 60 min 89.2％

Claims

1. A method for preparing methyl propionate by ethylene hydroesterification, characterized in that, Using a composite catalyst of Pd-based compound / bidentate phosphine ligand / acidic promoter, with methyl propionate as the solvent, after adding the catalyst components Pd-based compound, bidentate phosphine ligand, and acidic promoter and dissolving them, ethylene, carbon monoxide, and methanol are added, where the molar ratio of C2H4 / CO is 0.3 - 10:1, and the molar ratio of methanol / methyl propionate is 0.3 - 4:1; the temperature is raised, and methyl propionate is prepared by hydroesterification of ethylene, carbon monoxide, and methanol. The reaction temperature range is 90 - 150 °C, the reaction time is 0.1 - 2 h, and the maximum pressure during the reaction ≤ 4 MPa.

2. The method for preparing methyl propionate by ethylene hydroesterification according to claim 1, wherein The molar ratio of each component Pd / bidentate phosphine ligand / acidic promoter in the composite catalyst is 1:(3 - 20):(1 - 20).

3. The method for preparing methyl propionate by ethylene hydroesterification according to claim 1, wherein The bidentate phosphine ligand selected is bis(2-(diphenylphosphino)phenyl)methane or its derivative, and has the following structural formula: Wherein, R1 and R2 are one or more substituents selected from hydrogen, C1-C4 alkyl, methoxy, halogen, trifluoromethyl, phenyl, phenoxy, cyano, nitro.

4. The method for preparing methyl propionate by ethylene hydroesterification according to claim 1, 2 or 3, characterized in that, The molar ratio of C2H4 / CO is 0.3 - 3:

1.

5. The method for preparing methyl propionate by ethylene hydroesterification according to claim 1, 2 or 3, characterized in that, The molar ratio of the methanol to the limiting reactant in C2H4 or CO is 1.1 - 2:

1.

6. The method for preparing methyl propionate by ethylene hydroesterification according to claim 1, 2 or 3, characterized in that, The concentration range of Pd in the catalyst is 60 - 300 ppm.

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