A process for the synthesis of propionic acid esters by carbonylation of ethylene

Abstract

The present application relates to a method for synthesizing propionic acid ester by ethylene carbonylation. The present application can utilize the combination of phosphine ligand of formula I and palladium catalyst to jointly catalyze the carbonylation reaction of ethylene to synthesize propionic acid ester. The method has the characteristics of high catalytic efficiency, high product yield, high selectivity, simple operation and the like.

Description

Technical Field

[0001] This invention relates to a method for synthesizing propionate by carbonylation of ethylene. Background Technology

[0002] Propionic acid and its esters are important fine chemical products and organic synthesis intermediates, widely used in agriculture, textiles, food, and pharmaceutical industries. Among the three most widely used food preservatives—benzoic acid, propionic acid, and sorbic acid—propionic acid is recognized as the most economical, safe, and effective. As early as the 1930s, the German scientist W. Reppe first proposed a process for the direct synthesis of methyl propionate and ethyl propionate by the carbonylation of ethylene (Liebigs Ann. Chem. 1953, 582, 161). Literature review indicates that catalysts such as ruthenium, nickel, and cobalt also possess certain activity for this reaction; to date, hundreds of catalysts have been reported for this reaction.

[0003] The Shell process uses divalent palladium salts, triphenylphosphine, and acid as catalysts to catalyze the carbonylation of ethylene to synthesize methyl propionate (CN1041517C). Tooze et al. also found that palladium acetate can facilitate the carbonylation of ethylene to synthesize propionate esters under the promotion of acid and phosphine ligands (Chem. Commun. 1999, 1877; WO96 / 19434). The authors found that phosphine ligands are crucial for reactivity and selectivity. Lucite's α-process has been commercially applied, first obtaining methyl propionate from ethylene, carbon monoxide, and methanol, then condensing it with formaldehyde to obtain methyl methacrylate. The ethylene carbonylation process utilizes divalent palladium and phosphine ligands (CN106854221, CN10553496). This catalytic system has attracted widespread attention in both basic research and industrial processes, and there are many related patents in China. For example, Chinese patent CN103319337 provides a process for the carbonylation of ethylene to synthesize methyl propionate, using palladium acetate as the main catalyst, nickel-cobalt-ruthenium transition metal acetates as co-catalysts, and triphenylphosphine as the ligand. However, the catalytic efficiency and selectivity of these systems still need to be improved. In 2017, Beller et al. developed two novel bidentate phosphine ligands and used a Pd(II) / bisphosphine catalytic system with p-toluenesulfonic acid as an additive to achieve the carbonylation of ethylene to synthesize propionic acid. The highest TON reached 1,425,000 (Angew. Chem. Int. Ed. 2017, 56, 5267; Nat. Commun. 2017, 8, 14117; EP3121184; US11028110; CN107628948; US9938310; EP3272759; CN107629092).

[0004] Therefore, the catalysts currently used for the carbonylation of ethylene to synthesize propionate are mainly divalent palladium salts and phosphine ligands. This system has relatively mild conditions, good reaction selectivity and high catalytic conversion number. However, in order to further improve reaction efficiency and selectivity and reduce production costs to meet the industrial application of this process, it is urgent to develop a highly efficient catalytic system for the carbonylation of ethylene to synthesize propionate. Summary of the Invention

[0005] The object of this invention is to provide a method for preparing propionate esters (e.g., methyl propionate, ethyl propionate, butyl propionate, or octyl propionate), the method comprising the steps of:

[0006] a) In a reaction vessel, the palladium catalyst, phosphine ligand, and acid are dissolved in alcohol and optional solvent;

[0007] b) Ethylene is introduced into the reactor, followed by carbon monoxide, to carry out the reaction;

[0008] c) End the reaction and separate the product;

[0009] The phosphine ligands have structures selected from those shown in Formula I:

[0010]

[0011] in,

[0012] R 1 and R 4 Each is independently selected from the following group: substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 3-10 cycloalkyl, substituted or unsubstituted C 6-30 Aryl;

[0013] R 2 and R 3 Each is independently selected from the group consisting of substituted or unsubstituted 5-20 heteroaryl groups;

[0014] R 5 R 6 Each is an independent substituent located on the corresponding ring and selected from the following groups: H, C 1-10 Alkyl, C 1-10 Alkoxy, C 2-10 Ester group, cyano group, COOH group, benzenesulfonyl group, trialkylsilyl group (wherein the alkyl group is C 1-4 alkyl), nitro, C 6-30 aryl, 5-30 membered heteroaryl; or two R atoms located on adjacent ring atoms 5 R 6The ring atoms connected to it together form a 5-7 membered carbon ring or heterocycle, wherein the heterocycle may have 1-3 heteroatoms selected from the group consisting of N, O or S;

[0015] Unless otherwise specified, the substitution refers to the substitution of one or more hydrogen atoms on the group by a substituent selected from the group consisting of: C 1-10 Alkyl, C 1-10 Alkoxy, C 2-10 Ester group, cyano group, COOH group, benzenesulfonyl group, trialkylsilyl group (wherein the alkyl group is C10). 1-4 alkyl), nitro, C 6-30 Aryl, 5-30 heteroaryl.

[0016] In another preferred embodiment, the ligand,

[0017] R 1 and R 4 Each is independently selected from the following group: substituted or unsubstituted C 1-4 Alkyl, substituted or unsubstituted C 3-6 cycloalkyl, substituted or unsubstituted C 6-14 Aryl;

[0018] R 2 and R 3 Each is independently selected from the following group: substituted or unsubstituted 5-20 heteroaryl groups;

[0019] Wherein, the R 1 R 2 R 3 and R 4 Each is independently unsubstituted or substituted by 1-2 substituents selected from the group consisting of: methyl, methoxy, cyano, COOH, benzenesulfonyl, and trimethylsilyl.

[0020] In another preferred embodiment, the ligand,

[0021] R 1 and R 4 Each of the following is independently selected: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl or adamantyl;

[0022] R 2 and R 3 Each of the following groups is selected independently: pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyrroleyl, imidazolyl, pyrazolyl, thiophenyl, furanyl, thiazolyl, and triazolyl.

[0023] In another preferred embodiment, the ligands are selected from the group consisting of:

[0024]

[0025]

[0026] In another preferred embodiment, the reactor is a high-pressure reactor.

[0027] In another preferred embodiment, the amount of the phosphine ligand is 0.00001 to 10% molar equivalent of the ethylene, more preferably 0.0001 to 1% molar equivalent.

[0028] In another preferred embodiment, the reaction temperature is 0–200°C, preferably 60–150°C.

[0029] In another preferred embodiment, the reaction is carried out under the protection of an inert gas; preferably, the inert gas is nitrogen and / or argon.

[0030] In another preferred embodiment, the reaction is carried out at 1-10 MPa; more preferably, the reaction is carried out at 2-8 MPa.

[0031] In another preferred embodiment, the reaction time is 0.2 to 72 hours, preferably 0.2 to 24 hours.

[0032] In another preferred embodiment, the alcohol is C 1-12 Alkyl alcohols; preferably, the alcohols are selected from the group consisting of methanol, ethanol, propanol, butanol, octanol, or combinations thereof.

[0033] In another preferred embodiment, the amount of alcohol used in the reaction is 1-100 molar equivalents of the ethylene, preferably 1-10 molar equivalents.

[0034] In another preferred embodiment, the palladium catalyst is selected from the group consisting of palladium acetate, palladium trifluoroacetate, palladium pentavalerate, palladium tetrafluoroborate tetraacetonitrile, palladium hexafluoroacetylacetonate, bis(acetylacetonate)palladium, palladium tetraacetonitrile trifluoromethanesulfonate, palladium neopentanoate, bis(dibenzylacetonate)palladium, tri(dibenzylacetonate)palladium, palladium chloride, palladium diacetonitrile dichloride, palladium dibenzonitrile dichloride, or combinations thereof.

[0035] In another preferred embodiment, the palladium catalyst is selected from the group consisting of palladium acetate, palladium trifluoroacetate, palladium pentavalerate, tris(dibenzylideneacetone)palladium, palladium chloride, or combinations thereof.

[0036] In another preferred embodiment, the amount of palladium catalyst used is 0.00001 to 10% molar equivalent of the ethylene, more preferably 0.0001 to 1% molar equivalent.

[0037] In another preferred embodiment, when the phosphine ligand is a bisphosphine ligand (i.e., compound of formula I), the molar ratio of the palladium catalyst to the bisphosphine ligand is 1:1 to 1:30, more preferably 1:1 to 1:5.

[0038] In another preferred embodiment, the acid is selected from the group consisting of: perchloric acid, sulfuric acid, phosphoric acid, sulfonic acid, alkylphosphonic acid, alkylsulfonic acid, alkylcarboxylic acid, perfluoroalkylsulfonic acid, and perfluoroalkylcarboxylic acid (wherein the alkyl group is C). 1-12 Alkyl) or aryl sulfonic acid.

[0039] In another preferred embodiment, the acid is selected from the group consisting of: methanesulfonic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid, p-toluenesulfonic acid (PTSA), 2-hydroxypropane-2-sulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, dodecyl sulfonic acid, sulfuric acid, sulfonic acid, formic acid, and trifluoroacetic acid.

[0040] In another preferred embodiment, the amount of acid used is 0.00004 to 40% molar equivalent of the ethylene, preferably 0.0004 to 4% molar equivalent.

[0041] In another preferred embodiment, the solvent is selected from the group consisting of alkane solvents, substituted aromatic solvents, ether solvents, ketone solvents, nitrile solvents, ester solvents, or combinations thereof.

[0042] In another preferred embodiment, the alkane solvent is selected from the group consisting of n-hexane, cyclohexane, or combinations thereof.

[0043] In another preferred embodiment, the substituted aromatic solvent is selected from the group consisting of chlorobenzene, toluene, xylene, and trifluorotoluene.

[0044] In another preferred embodiment, the ether solvent is selected from the group consisting of tetrahydrofuran, diethyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, anisole, ethylene glycol dimethyl ether, 1,4-dioxane, or combinations thereof.

[0045] In another preferred embodiment, the ketone solvent is selected from the group consisting of acetone.

[0046] In another preferred embodiment, the nitrile solvent is selected from the group consisting of acetonitrile, propionitrile, benzonitrile, or combinations thereof.

[0047] In another preferred embodiment, the ester solvent is selected from the group consisting of ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, octyl propionate, or combinations thereof.

[0048] In another preferred embodiment, the alcohol is methanol, and the reaction is carried out under the following conditions:

[0049] a) Dissolve palladium acetate, phosphine ligand, and acid in methanol and an optional solvent;

[0050] b) Ethylene is introduced into the reactor, followed by carbon monoxide to carry out the reaction, wherein the reaction is carried out at room temperature to 60-100°C;

[0051] c) End the reaction and separate the product.

[0052] In another preferred embodiment, the alcohol is ethanol, and the reaction is carried out under the following conditions:

[0053] a) Dissolve palladium acetate, phosphine ligand, and acid in ethanol and optional solvents;

[0054] b) Ethylene is introduced into the reactor, followed by carbon monoxide to carry out the reaction, wherein the reaction is carried out at room temperature to 60-100°C;

[0055] c) End the reaction and separate the product.

[0056] In another preferred embodiment, the alcohol is butanol, and the reaction is carried out under the following conditions:

[0057] a) Dissolve palladium acetate, phosphine ligand, and acid in butanol and an optional solvent.

[0058] b) Ethylene is introduced into the reactor, followed by carbon monoxide to carry out the reaction, wherein the reaction is carried out at room temperature to 60-100°C;

[0059] c) End the reaction and separate the product.

[0060] In another preferred embodiment, the alcohol is octanol, and the reaction is carried out under the following conditions:

[0061] a) Dissolve palladium acetate, phosphine ligand, and acid in octanol and an optional solvent.

[0062] b) Ethylene is introduced into the reactor, followed by carbon monoxide to carry out the reaction, wherein the reaction is carried out at room temperature to 60-100°C;

[0063] c) End the reaction and separate the product.

[0064] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Detailed Implementation

[0065] Based on long-term and in-depth research, the inventors have prepared a series of novel phosphine ligands and a method for synthesizing propionate esters by ethylene carbonylation based on these ligands. This method can improve the catalytic efficiency of the ethylene carbonylation reaction, increase the conversion rate of ethylene and the product selectivity, and the reaction conditions are mild and the operation is simple. Based on the above findings, the inventors have completed this invention.

[0066] definition

[0067] In this invention, "room temperature" refers to 10–30°C.

[0068] In this invention, the term "alkyl" refers to a straight-chain or branched saturated hydrocarbon group, preferably C10. 1-10 Alkyl groups (e.g., C15) 1-8 alkyl, C 1-6 alkyl, C 1-4 Alkyl groups).

[0069] In this invention, the term "cycloalkyl" refers to a saturated monocyclic ring, or a carbocyclic substituent comprising a fused, bridged, or spirocyclic polycyclic system, preferably C14. 3-8 cycloalkyl (e.g., C10) 3-6 (cycloalkyl groups).

[0070] In this invention, the term "alkoxy" refers to a cyclic or acyclic alkyl group connected by an oxygen bridge. The definitions of alkyl and cycloalkyl are as described above, and C10 is preferred. 1-10 alkoxy groups (e.g., C) 1-8 alkoxy, C 1-6 alkoxy, C 1-4 (alkoxy group).

[0071] Unless otherwise specified, in this invention, "aryl" refers to a group having 6-30 (preferably 6-14) ring carbon atoms and zero heteroatoms, a monocyclic or polycyclic (e.g., bicyclic or tricyclic) 4n+2 aromatic ring system (e.g., having 6, 10, or 14 shared p electrons in a cyclic array), preferably C6-C. 14 Aryl, more preferably C6-C 10 Aryl).

[0072] Unless otherwise specified, in this invention, "heteroaryl" refers to a group having 5-30 (preferably 5-20, more preferably 5-14) ring atoms (the ring atoms may be carbon atoms or heteroatoms) of a monocyclic or polycyclic (e.g., bicyclic or tricyclic) 4n+2 aromatic ring system (e.g., having 6, 10, or 14 shared p electrons in a cyclic array), preferably a 5-15 member heteroaryl, more preferably a 5-9 member heteroaryl.

[0073] Without violating common sense in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0074] The reagents and raw materials used in this invention are all commercially available.

[0075] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight.

[0076] Example 1

[0077] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L1 (19.4 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 100 °C and stirred for 2 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a methyl propionate yield of 94% and a selectivity greater than 95%.

[0078] Example 2

[0079] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L₂ (19.6 mg, 0.02 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 6 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 86% and a selectivity greater than 95%.

[0080] Example 3

[0081] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L3 (19.5 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 100 °C and stirred for 2 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 85% and a selectivity greater than 95%.

[0082] Example 4

[0083] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L4 (11.7 mg, 0.02 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 60 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 78% and a selectivity greater than 95%.

[0084] Example 5

[0085] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L5 (19.4 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (20 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 3 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a methyl propionate yield of 90% and a selectivity greater than 95%.

[0086] Example 6

[0087] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L6 (19.4 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 3 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a methyl propionate yield of 90% and a selectivity greater than 95%.

[0088] Example 7

[0089] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L7 (18.4 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 100 °C and stirred for 10 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 84% and a selectivity greater than 95%.

[0090] Example 8

[0091] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L8 (9.9 mg, 0.02 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 100 °C and stirred for 5 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 87% and a selectivity greater than 95%.

[0092] Example 9

[0093] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L9 (18.3 mg, 0.04 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 5 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 88% and a selectivity greater than 95%.

[0094] Example 10

[0095] Pd₂(dba)₃ (4.6 mg, 0.005 mmol), bisphosphine ligand L10 (12.8 mg, 0.02 mmol), methanesulfonic acid (6.5 μL, 0.10 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging until the autoclave pressure reached 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 5 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 85% and a selectivity greater than 95%.

[0096] Example 11

[0097] Pd(dba)₂ (5.7 mg, 0.01 mmol), bisphosphine ligand L11 (13.5 mg, 0.02 mmol), trifluoromethanesulfonic acid (14.2 μL, 0.16 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Nitrogen was purged, and the pressure was increased to 2.0 MPa with ethylene gas, followed by carbon monoxide purging to a pressure of 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 5 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 84% and a selectivity greater than 95%.

[0098] Example 12

[0099] PdCl2 (1.8 mg, 0.01 mmol), bisphosphine ligand L12 (29.2 mg, 0.04 mmol), dodecyl sulfonic acid (26.1 mg, 0.08 mmol), methanol (50 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Ethylene gas was then introduced to a pressure of 2.0 MPa, followed by carbon monoxide to a pressure of 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 87% and a selectivity greater than 95%.

[0100] Example 13

[0101] Pd(hfacac)₂ (3.1 mg, 0.01 mmol), bisphosphine ligand L13 (28.1 mg, 0.04 mmol), methanesulfonic acid (10.4 μL, 0.16 mmol), methanol (30 mL), n-hexane (20 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Ethylene gas was then introduced to 2.0 MPa, followed by carbon monoxide to bring the autoclave pressure to 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of methyl propionate of 85% and a selectivity greater than 95%.

[0102] Example 14

[0103] In a 300 mL Parr autoclave under nitrogen protection, Pd(CH3CN)4(BF4)2 (4.4 mg, 0.01 mmol), bisphosphine ligand L14 (15.7 mg, 0.02 mmol), methanesulfonic acid (10.4 μL, 0.16 mmol), propanol (30 mL), acetonitrile (20 mL), and a stir bar were added. Ethylene gas was then introduced to 2.0 MPa, followed by carbon monoxide to bring the autoclave pressure to 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of propyl propionate of 80% and a selectivity greater than 95%.

[0104] Example 15

[0105] Pd(OAc)₂ (11.2 mg, 0.05 mmol), bisphosphine ligand L15 (30.2 mg, 0.04 mmol), methanesulfonic acid (10.4 μL, 0.16 mmol), butanol (30 mL), toluene (20 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Ethylene gas was then introduced to 2.0 MPa, followed by carbon monoxide to bring the autoclave pressure to 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of butyl propionate of 82% with a selectivity greater than 95%.

[0106] Example 16

[0107] Pd(OAc)₂ (0.2 mg, 0.001 mmol), bisphosphine ligand L1 (1.9 mg, 0.004 mmol), p-toluenesulfonic acid (1.8 mg, 0.01 mmol), ethanol (30 mL), tetrahydrofuran (20 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Ethylene gas was then introduced to 2.0 MPa, followed by carbon monoxide to bring the autoclave pressure to 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 8 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of ethyl propionate of 86% and a selectivity greater than 95%.

[0108] Example 17

[0109] Pd(OAc)₂ (2.2 mg, 0.01 mmol), bisphosphine ligand L1 (19.4 mg, 0.04 mmol), trifluoroacetic acid (12 μL, 0.16 mmol), octanol (30 mL), tetrahydrofuran (20 mL), and a stir bar were added to a 300 mL Parr autoclave under nitrogen protection. Ethylene gas was then introduced to a pressure of 2.0 MPa, followed by carbon monoxide to a pressure of 6.0 MPa. The mixture was rapidly heated to 80 °C and stirred for 5 hours. After the reaction was complete, the temperature was lowered, and an internal standard was added. NMR analysis revealed a yield of octyl propionate of 87% with a selectivity greater than 90%.

[0110] The phosphine ligands of the present invention can produce propionate products in high yields (>78%, >90% in the best example) with good selectivity when used for catalytic preparation of propionate, and therefore have potential industrial applications.

[0111] Furthermore, the phosphine ligands of the present invention exhibit good catalytic conversion rates, thus enabling catalytic conversion at low dosages (<10). -4 Equivalent, preferably <10 -5 Equivalent, preferably <10 -6 The catalytic reaction is completed in equivalent quantities.

[0112] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for synthesizing propionate by palladium-catalyzed ethylene carbonylation, characterized in that, The method includes the following steps: a) In a reaction vessel, the palladium catalyst, phosphine ligand, and acid are dissolved in alcohol and optional solvent; b) Introduce ethylene into the reactor, then introduce carbon monoxide to carry out the reaction; c) End the reaction and separate the product; The phosphine ligands have structures selected from the following group of formulas: I, L5, L12: 、 、 in, R 1 and R 4 Each is independently selected from the group consisting of isopropyl, tert-butyl, or adamantyl; R 2 and R 3 Each is independently selected from the group consisting of: substituted or unsubstituted pyridyl, pyrazinyl, pyrimidinyl, pyrroleyl, pyrazolyl, thiophenyl, and furanyl; R 5 R 6 Each is an independent substituent located on the corresponding ring and selected from the following groups: H, C 1-10 Alkyl, C1 alkoxy, trimethylsilyl, C6 aryl; The substitution refers to the substitution of one or more hydrogen atoms on a group by a substituent selected from the group consisting of: C 1-10 alkyl.

2. The method as described in claim 1, characterized in that, In the ligands described, R 1 and R 4 Each is independently selected from the group consisting of isopropyl, tert-butyl, or adamantyl; R 2 and R 3 Each of the following groups is selected independently: pyridyl, pyrazinyl, pyrimidinyl, pyrroleyl, pyrazolyl, thiophenyl, furanyl.

3. The method as described in claim 1, characterized in that, The ligands are selected from the following group: 、 、 、 、 、 、 、 、 、 、 、 、 。 4. The method as described in claim 1, characterized in that, The amount of the phosphine ligand used is 0.00001 to 10% molar equivalent of the ethylene.

5. The method as described in claim 1, characterized in that, The amount of palladium catalyst used is 0.00001~10% molar equivalent of the ethylene.

6. The method of claim 1, wherein when the phosphine ligand is a bisphosphine ligand of formula I, the molar ratio of the palladium catalyst to the bisphosphine ligand is 1:1 to 1:

30.

7. The method as described in claim 1, characterized in that, The alcohol is C 1-12 Alkyl alcohols.

8. The method as described in claim 1, characterized in that, The alcohol is selected from the group consisting of methanol, ethanol, propanol, butanol, octanol, or combinations thereof.

9. The method as described in claim 1, characterized in that, The palladium catalyst is selected from the group consisting of palladium acetate, palladium trifluoroacetate, palladium pentavalerate, palladium tetrafluoroborate tetraacetonitrile, palladium hexafluoroacetylacetonate, bis(acetylacetonate)palladium, palladium tetraacetonitrile trifluoromethanesulfonate, palladium neopentanoate, bis(dibenzylacetonate)palladium, tri(dibenzylacetonate)palladium, palladium chloride, palladium diacetonitrile dichloride, palladium dibenzonitrile dichloride, or combinations thereof.

10. The method as described in claim 1, characterized in that, The acid is selected from the group consisting of: perchloric acid, sulfuric acid, phosphoric acid, sulfonic acid, alkyl carboxylic acids, and perfluoroalkyl carboxylic acids, wherein the alkyl group is C. 1-12 alkyl.

11. The method as described in claim 1, characterized in that, The acid is selected from the group consisting of alkylphosphonic acids, alkyl sulfonic acids, perfluoroalkyl sulfonic acids, and aryl sulfonic acids, wherein the alkyl group is C. 1-12 alkyl.

12. The method as described in claim 1, characterized in that, The solvent is selected from the group consisting of alkane solvents, substituted aromatic solvents, ether solvents, ketone solvents, nitrile solvents, ester solvents, or combinations thereof.

Images