A process for the preparation of 2-propylheptanoic acid

Abstract

The present application relates to the field of fine chemical industry, and particularly to a preparation method of 2-propyl heptanoic acid; the present application uses 2-propyl heptanal, a catalyst, and oxygen to perform an oxidation reaction and vacuum rectification to prepare 2-propyl heptanoic acid; the present application uses AlCl3·6H2O, 2,5-bis(allyloxy)terephthalic acid, N,N-dimethylformamide, 1-methylpyridine-2-thione, mercapto propyl isooctyl cage silsesquioxane, vinyl tributyl ketoxime silane, tetramethyl guanidine, a palladium-containing solution, a silsesquioxane complexing agent, a sodium borohydride solution, and a resin to prepare the catalyst; the catalyst prepared by the present application catalyzes the oxidation reaction of 2-propyl heptanal in a liquid phase, and has mild conditions, is environmentally friendly, and has a long service life; the catalyst prepared by the present application has high yield and high purity of 2-propyl heptanoic acid, and can realize industrial scale production.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals, and in particular to a method for preparing 2-propylheptanoic acid. Background Technology

[0002] 2-N-propylheptanoic acid, also known as 2-propylheptanoic acid, CAS No: 31080-39-4, English name: 2-propylheptanoic acid, molecular formula: C10H20O2, boiling point: 271.6℃, flash point: 142.3℃, refractive index: 1.441, density: 0.913, is a colorless and transparent liquid.

[0003] Currently, phthalate plasticizers, such as dioctyl phthalate (DOP), dimethyl phthalate (DMP), and dibutyl phthalate (DBP), are recognized as harmful to the environment. They are endocrine disruptors that are under close international monitoring and are major culprits in causing male reproductive problems. Cosmetics containing these substances can increase the risk of breast cancer in women and harm the reproductive system of male infants conceived by women. In severe cases, the damage can lead to cell mutations, ultimately resulting in birth defects or cancer.

[0004] Derivatives of 2-propylheptanoic acid can be used to make a variety of excellent new environmentally friendly plasticizers that can replace toxic and harmful phthalate plasticizers.

[0005] CN201210146322.8: Belongs to the field of pharmaceutical synthesis technology, and relates to a new intermediate for the preparation of 2-propylheptanoic acid, a preparation method thereof, and a method for preparing 2-propylheptanoic acid. This invention discloses a new intermediate compound (IX), whose structure is as follows: R is allyl or propynyl, and it is prepared by reacting compound (II), a base, and R-Br in the presence of an iodide, with an excess of base and an excess of R-Br. The iodide is NaI or LiI, and the base is LDA. The molar ratio of compound (II), LDA, and R-Br is 1:≥1.1:≥4. Depending on the different ratios, a special post-treatment method is used to improve the yield of compound (IV). 2-propylheptanoic acid can be obtained from this intermediate. In the preparation of 2-propylheptanoic acid, either the chiral inducing group can be removed first, followed by hydrogenation synthesis, or hydrogenation synthesis can be performed first, followed by removal of the chiral inducing group. Furthermore, hydrogenation synthesis first generates a new intermediate compound (VIII).

[0006] CN201110279165.3: This invention relates to a method for preparing 2-propylheptanic acid, which uses 2-propylheptanol as a raw material and a cost-effective metal oxide as an oxidation catalyst. The oxidation process is completed through heating, pressurizing, and holding. The resulting product is acidified, dehydrated, and distilled to obtain 2-propylheptanic acid, with a high yield. The method recovers sodium sulfate emitted during the dehydration process, which can be used to produce sodium sulfate as a byproduct. There is no discharge of waste gas, wastewater, or solid waste, making it environmentally friendly and pollution-free. The 2-propylheptanic acid obtained by this method is non-toxic and harmless, and can be used to produce a novel environmentally friendly plasticizer to replace phthalate plasticizers, enabling large-scale industrial production.

[0007] CN201080033483.5: A method for preparing a mixture of isomeric decanoic acid, comprising the following steps: a) using a rhodium-containing catalyst system to perform a hydroformylation reaction on a mixture of hydrocarbons containing straight-chain C4-olefins; b) performing an aldol condensation reaction on a mixture of C5 aliphatic aldehydes obtained from step a); c) performing a selective hydrogenation reaction on a mixture of C10 unsaturated aldehydes from step b) to generate C10 aliphatic aldehydes; d) performing a non-catalytic oxidation reaction on a mixture of C10 aliphatic aldehydes from step c) to obtain a mixture of 2-propylheptanoic acid comprising at least 70% by mass relative to the total content of isomeric decanoic acid.

[0008] The above-mentioned patents and existing technologies have drawbacks such as low conversion and yield of 2-propylheptanoic acid, complex reaction process, and high equipment requirements. Summary of the Invention

[0009] To address the above problems, this invention provides a method for preparing 2-propylheptanoic acid, the steps of which are as follows:

[0010] S1: By weight, 22-30 parts of 2-propylheptanal and 0.2-1 parts of catalyst are added to an oxidation reactor, stirred, heated and pressurized, and under the protection of nitrogen, 40-60 parts of oxygen are slowly introduced to carry out the oxidation reaction to obtain crude 2-propylheptanic acid.

[0011] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0012] The reaction pressure is 2.8-3.0 MPa.

[0013] The reaction temperature is 260-300℃, and the reaction time is 2-6 hours.

[0014] The pressure of the vacuum distillation is -0.7 to 0.9 MPa, and the temperature is 210 to 220℃.

[0015] The catalyst preparation method is as follows:

[0016] S1: By weight, select 3-10 parts of AlCl3·6H2O and 10-15 parts of 2,5-bis(allyloxy)terephthalic acid and add them to the reaction vessel. Then add 100-150 parts of N,N-dimethylformamide. Stir at room temperature for 30-120 minutes and then place in an oven for reaction. After heating, filter and dry to obtain an organoframe metal containing bis(allyloxy).

[0017] S2: Weigh 6-12 parts of an organoframe metal containing bis(allyloxy) and add it to a reaction vessel. Measure 80-100 parts of 1-methylpyridine-2-thione and add it to the reaction vessel. Mix and stir for 30-60 minutes. Then add 15-22 parts of mercaptopropyl isooctylated cage-like silsesquioxane, 2-5 parts of vinyltributylone oxime silane, and 2-5 parts of tetramethylguanidine. Stir at 65-75℃ for 50-120 minutes. Filter, wash, and dry to obtain a silsesquioxane complexing agent.

[0018] S3: Add 5-10 parts palladium-containing solution, 0.002-0.05 parts sesquioxane complexing agent, and 100-200 parts water. Start stirring and add 6-12 parts sodium borohydride solution cooled with ice water dropwise. Continue stirring for 10-20 hours.

[0019] S4: Add 50-100 parts of resin and continue stirring at room temperature for 10-20 hours; remove water by distillation, dry, and obtain the catalyst.

[0020] The palladium-containing solution is one or more of palladium acetate or palladium chloride.

[0021] The concentration of palladium ions in the palladium solution ranges from 0.2 wt% to 2 wt%.

[0022] The resin is a styrene-based strong acid cation resin or a styrene-based strong base anion resin, such as styrene-based strong acid cation resins with model numbers D001, D006, D008, and D61.

[0023] The reaction temperature of S1 is 180-210℃, and the reaction time is 8-12h.

[0024] The sodium borohydride solution has a mass percentage concentration of 10-20%.

[0025] Reaction mechanism: Attached image description:

[0026] Figure 1 The chromatogram is of 2-propylheptanoic acid prepared in Comparative Example 3.

[0027] Technical effects:

[0028] The present invention provides a method for preparing 2-propylheptanoic acid, which, compared with the prior art, has the following significant advantages:

[0029] 1. The catalyst prepared in this invention provides a mild and environmentally friendly liquid-phase catalytic oxidation reaction of 2-propylheptanal, and the catalyst has a long service life.

[0030] 2. The reaction process of this invention is simple and does not require sophisticated equipment;

[0031] 3. The catalyst prepared using this invention has a high yield and high purity of 2-propylheptanoic acid, and can be used for industrial-scale production. Detailed Implementation

[0032] The invention will be further illustrated below through specific embodiments:

[0033] 1. Purity: Purity of 2-propylheptanic acid = Mass of 2-propylheptanic acid in the mixture ÷ Mass of the mixture × 100%;

[0034] 2. Yield: Yield of 2-propylheptanic acid = Actual amount of 2-propylheptanic acid produced / Theoretical amount of 2-propylheptanic acid produced × 100%.

[0035] Example 1

[0036] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0037] S1: 22g of 2-propylheptanal and 0.2g of catalyst were added to an oxidation reactor, stirred, heated and pressurized, and 40g of oxygen was slowly introduced under the protection of nitrogen to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0038] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0039] The reaction pressure is 2.8 MPa.

[0040] The reaction temperature is 260℃ and the reaction time is 2 hours.

[0041] The pressure of the vacuum distillation is -0.7 MPa and the temperature is 210℃.

[0042] The catalyst preparation method is as follows:

[0043] S1: 3g of AlCl3·6H2O and 10g of 2,5-bis(allyloxy)terephthalic acid were added to the reaction vessel, and then 100g of N,N-dimethylformamide was added. After stirring at room temperature for 30min, the mixture was placed in an oven for reaction. After heating, the reaction was completed, filtered, and dried to obtain an organoframe metal containing bis(allyloxy).

[0044] S2: Weigh 6g of an organoframe metal containing bis(allyloxy) and add it to the reaction vessel. Measure 80g of 1-methylpyridine-2-thione and add it to the reaction vessel. Mix and stir for 30min. Then add 15g of mercaptopropyl isooctylated cage-like silsesquioxane, 2g of vinyltributylone oxime silane, and 2g of tetramethylguanidine. Stir at 65℃ for 50min. Filter, wash, and dry to obtain a silsesquioxane complexing agent.

[0045] S3: Add 5g of palladium-containing solution, 0.002g of sesquioxane complexing agent, and 100g of water. Start stirring and add 6g of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 10 hours.

[0046] S4: Add 50g of resin and continue stirring at room temperature for 10h; remove water by distillation, dry, and obtain the catalyst.

[0047] The palladium-containing solution is palladium acetate, wherein the concentration of palladium ions is 0.2 wt%.

[0048] The resin is a D001 styrene-based strong acid cation exchange resin.

[0049] The reaction temperature of S1 is 180℃ and the reaction time is 8h.

[0050] The sodium borohydride solution has a mass percentage concentration of 10%.

[0051] Example 2

[0052] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0053] S1: Add 25g of 2-propylheptanal and 0.5g of catalyst to an oxidation reactor, stir, heat and pressurize, and slowly introduce 45g of oxygen under nitrogen protection to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0054] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0055] The reaction pressure is 2.9 MPa.

[0056] The reaction temperature is 270℃ and the reaction time is 2-6 hours.

[0057] The pressure of the vacuum distillation is -0.8 MPa and the temperature is 215℃.

[0058] The catalyst preparation method is as follows:

[0059] S1: 5g of AlCl3·6H2O and 12g of 2,5-bis(allyloxy)terephthalic acid were added to the reaction vessel, and then 110g of N,N-dimethylformamide was added. After stirring at room temperature for 60min, the mixture was placed in an oven for reaction. After heating, the reaction was completed, filtered, and dried to obtain an organoframe metal containing bis(allyloxy).

[0060] S2: Weigh 8g of an organoframe metal containing bis(allyloxy) and add it to the reactor. Measure 85g of 1-methylpyridine-2-thione and add it to the reactor. Mix and stir for 40min. Then add 18g of mercaptopropyl isooctylated cage-like silsesquioxane, 3g of vinyltributylone oxime silane, and 3g of tetramethylguanidine. Stir at 70℃ for 70min. Filter, wash, and dry to obtain a silsesquioxane complexing agent.

[0061] S3: Add 7g of palladium-containing solution, 0.02g of sesquioxane complexing agent, and 140g of water. Start stirring and add 8g of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 14 hours.

[0062] S4: Add 60g of resin and continue stirring at room temperature for 14h; remove water by distillation, dry, and obtain the catalyst.

[0063] The palladium-containing solution is palladium acetate, wherein the concentration of palladium ions is 2 wt%.

[0064] The resin is D006 styrene-based strong acid cation exchange resin.

[0065] The reaction temperature of S1 is 190℃ and the reaction time is 9h.

[0066] The sodium borohydride solution has a mass percentage concentration of 15%.

[0067] Example 3

[0068] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0069] S1: 28g of 2-propylheptanal and 0.8g of catalyst were added to an oxidation reactor, stirred, heated and pressurized, and 55g of oxygen was slowly introduced under the protection of nitrogen to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0070] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0071] The reaction pressure is 2.9 MPa.

[0072] The reaction temperature is 290℃ and the reaction time is 5 hours.

[0073] The pressure of the vacuum distillation is -0.8 MPa and the temperature is 215℃.

[0074] The catalyst preparation method is as follows:

[0075] S1: 9g of AlCl3·6H2O and 14g of 2,5-bis(allyloxy)terephthalic acid were added to the reaction vessel, and then 140g of N,N-dimethylformamide was added. After stirring at room temperature for 90min, the mixture was placed in an oven for reaction. After the reaction was heated, the mixture was filtered and dried to obtain an organoframe metal containing bis(allyloxy).

[0076] S2: Weigh 10g of an organoframe metal containing bis(allyloxy) and add it to the reaction vessel. Measure 95g of 1-methylpyridine-2-thione and add it to the reaction vessel. Mix and stir for 50min. Then add 20g of mercaptopropyl isooctylated cage-like silsesquioxane, 4g of vinyltributylone oxime silane, and 4g of tetramethylguanidine. Stir at 70℃ for 100min. Filter, wash, and dry to obtain a silsesquioxane complexing agent.

[0077] S3: Add 9g of palladium-containing solution, 0.04g of sesquioxane complexing agent, and 180g of water. Start stirring and add 10g of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 18 hours.

[0078] S4: Add 90g of resin and continue stirring at room temperature for 18h; remove water by distillation, dry, and obtain the catalyst.

[0079] The palladium-containing solution is palladium chloride, wherein the concentration of palladium ions is 0.2 wt%.

[0080] The resin is D008 styrene-based strong acid cation exchange resin.

[0081] The reaction temperature of S1 is 200℃ and the reaction time is 11h.

[0082] The sodium borohydride solution has a mass percentage concentration of 15%.

[0083] Example 4

[0084] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0085] S1: Add 30g of 2-propylheptanal and 1g of catalyst to an oxidation reactor, stir, heat and pressurize, and slowly introduce 60g of oxygen under nitrogen protection to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0086] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0087] The reaction pressure is 3.0 MPa.

[0088] The reaction temperature is 300℃ and the reaction time is 6 hours.

[0089] The pressure of the vacuum distillation is -0.9 MPa and the temperature is 220℃.

[0090] The catalyst preparation method is as follows:

[0091] S1: 10g of AlCl3·6H2O and 15g of 2,5-bis(allyloxy)terephthalic acid were added to a reaction vessel, and then 150g of N,N-dimethylformamide was added. After stirring at room temperature for 120min, the mixture was placed in an oven for reaction. After the reaction was heated, the mixture was filtered and dried to obtain an organoframe metal containing bis(allyloxy).

[0092] S2: Weigh 12g of an organoframe metal containing bis(allyloxy) and add it to the reactor. Measure 100g of 1-methylpyridine-2-thione and add it to the reactor. Mix and stir for 60min. Then add 22g of mercaptopropyl isooctylated cage-like silsesquioxane, 5g of vinyltributylone oxime silane, and 5g of tetramethylguanidine. Stir at 75℃ for 120min. Filter, wash, and dry to obtain a silsesquioxane complexing agent.

[0093] S3: Add 10g of palladium-containing solution, 0.05g of sesquioxane complexing agent, and 200g of water. Start stirring and add 12g of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 20 hours.

[0094] S4: Add 100g of resin and continue stirring at room temperature for 20h; remove water by distillation, dry, and obtain the catalyst.

[0095] The palladium-containing solution is palladium chloride, wherein the concentration of palladium ions is 2 wt%.

[0096] The resin is a D61 styrene-based strong acid cation exchange resin.

[0097] The reaction temperature of S1 is 210℃ and the reaction time is 12h.

[0098] The sodium borohydride solution has a mass percentage concentration of 20%.

[0099] Comparative Example 1

[0100] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0101] S1: 22g of 2-propylheptanal and 0.2g of catalyst were added to an oxidation reactor, stirred, heated and pressurized, and 40g of oxygen was slowly introduced under the protection of nitrogen to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0102] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0103] The reaction pressure is 2.8 MPa.

[0104] The reaction temperature is 260℃ and the reaction time is 2 hours.

[0105] The pressure of the vacuum distillation is -0.7 MPa and the temperature is 210℃.

[0106] The catalyst preparation method is as follows:

[0107] S1: Add 5g of palladium-containing solution and 100g of water, start stirring, add 6g of sodium borohydride solution cooled with ice water dropwise, and continue stirring for 10 hours;

[0108] S2: Add 50g of resin and continue stirring at room temperature for 10h; remove water by distillation, dry, and obtain the catalyst.

[0109] The palladium-containing solution is palladium acetate, wherein the concentration of palladium ions is in the range of 0.2 wt%.

[0110] The resin is a D001 styrene-based strong acid cation exchange resin.

[0111] The reaction temperature of S1 is 180℃ and the reaction time is 8h.

[0112] The sodium borohydride solution has a mass percentage concentration of 10%.

[0113] Comparative Example 2

[0114] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0115] S1: 22g of 2-propylheptanal and 0.2g of catalyst were added to an oxidation reactor, stirred, heated and pressurized, and 40g of oxygen was slowly introduced under the protection of nitrogen to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0116] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0117] The reaction pressure is 2.8 MPa.

[0118] The reaction temperature is 260℃ and the reaction time is 2 hours.

[0119] The pressure of the vacuum distillation is -0.7 MPa and the temperature is 210℃.

[0120] The catalyst preparation method is as follows:

[0121] S1: Weigh 80g of 1-methylpyridine-2-thione and add it to the mixture. After mixing and stirring for 30 minutes, add 15g of mercaptopropyl isooctylated cage-like silsesquioxane and 2g of vinyltributylone oxime silane. Stir at 65°C for 50 minutes, filter, wash, and dry to obtain silsesquioxane complexing agent.

[0122] S2: Add 5g of palladium-containing solution, 0.002g of sesquioxane complexing agent, and 100g of water. Start stirring and add 6g of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 10 hours.

[0123] S4: Add 50g of resin and continue stirring at room temperature for 10h; remove water by distillation, dry, and obtain the catalyst.

[0124] The palladium-containing solution is palladium acetate, wherein the concentration of palladium ions is in the range of 0.2 wt%.

[0125] The resin is a D001 styrene-based strong acid cation exchange resin.

[0126] The reaction temperature of S1 is 180℃ and the reaction time is 8h.

[0127] The sodium borohydride solution has a mass percentage concentration of 10%.

[0128] Comparative Example 3

[0129] A method for preparing 2-propylheptanoic acid, comprising the following steps:

[0130] S1: 22g of 2-propylheptanal and 0.2g of catalyst were added to an oxidation reactor, stirred, heated and pressurized, and 40g of oxygen was slowly introduced under the protection of nitrogen to carry out the oxidation reaction and obtain crude 2-propylheptanic acid.

[0131] S2: Crude 2-propylheptanoic acid is subjected to vacuum distillation to obtain the finished product, 2-propylheptanoic acid.

[0132] The reaction pressure is 2.8 MPa.

[0133] The reaction temperature is 260℃ and the reaction time is 2 hours.

[0134] The pressure of the vacuum distillation is -0.7 MPa and the temperature is 210℃.

[0135] The catalyst preparation method is as follows:

[0136] S1: 3g of AlCl3·6H2O and 10g of 2,5-bis(allyloxy)terephthalic acid were added to the reaction vessel, and then 100g of N,N-dimethylformamide was added. After stirring at room temperature for 30min, the mixture was placed in an oven for reaction. After heating, the reaction was completed, filtered, and dried to obtain an organoframe metal containing bis(allyloxy).

[0137] S2: Add 5g of palladium-containing solution and 100g of water, start stirring, add 6g of sodium borohydride solution cooled with ice water dropwise, and continue stirring for 10 hours;

[0138] S3: Add 50g of resin and continue stirring at room temperature for 10h; remove water by distillation, dry, and obtain the catalyst.

[0139] The palladium-containing solution is palladium acetate, wherein the concentration of palladium ions is in the range of 0.2 wt%.

[0140] The resin is a D001 styrene-based strong acid cation exchange resin.

[0141] The reaction temperature of S1 is 180℃ and the reaction time is 8h.

[0142] The sodium borohydride solution has a mass percentage concentration of 10%.

[0143]

[0144]

Claims

1. A method for preparing 2-propylheptanoic acid, comprising the following steps: S1: By weight, 22-30 parts of 2-propylheptanal and 0.2-1 parts of catalyst are added to an oxidation reactor, stirred, heated and pressurized, and under the protection of nitrogen, 40-60 parts of oxygen are slowly introduced to carry out the oxidation reaction to obtain crude 2-propylheptanic acid. S2: Crude 2-propylheptanoic acid was subjected to vacuum distillation to obtain the finished product 2-propylheptanoic acid; The catalyst preparation method is as follows: S3: By weight, select 3-10 parts of AlCl3·6H2O and 10-15 parts of 2,5-bis(allyloxy)terephthalic acid and add them to the reaction vessel. Then add 100-150 parts of N,N-dimethylformamide. Stir at room temperature for 30-120 minutes and then place in an oven for reaction. After heating, filter and dry to obtain an organoframe metal containing bis(allyloxy). S4: Weigh 6-12 parts of a bis(allyloxy)-containing organic framework metal and add it to the reaction vessel; then measure 80-100 parts of 1-methylpyridine-2-thione and add it to the reaction vessel. After mixing and stirring for 30-60 minutes, add 15-22 parts of mercaptopropyl isooctylated cage-like silsesquioxane, 2-5 parts of vinyltributylone oxime silane, and 2-5 parts of tetramethylguanidine. Stir at 65-75℃ for 50-120 minutes, filter, wash, and dry to obtain the silsesquioxane complexing agent. S5: Add 5-10 parts of palladium-containing solution, 0.002-0.05 parts of sesquioxane complexing agent, and 100-200 parts of water. Start stirring and add 6-12 parts of sodium borohydride solution cooled with ice water dropwise. Continue stirring for 10-20 hours. S6: Add 50-100 parts of resin, and continue stirring at room temperature for 10-20 hours; remove water by distillation, dry, and obtain the catalyst; The palladium-containing solution is one or more of palladium acetate or palladium chloride; The resin is one of D001, D006, D008, and D61; The reaction pressure in step S1 is 2.8-3.0 MPa; The reaction temperature in step S1 is 260-300℃, and the reaction time is 2-6 hours. The reaction temperature of step S3 is 180-210℃, and the reaction time is 8-12h.

2. The method for preparing 2-propylheptanoic acid according to claim 1, characterized in that: The pressure of the vacuum distillation is -0.7 to 0.9 MPa, and the temperature is 210 to 220℃.

3. The method for preparing 2-propylheptanoic acid according to claim 1, characterized in that: The concentration of palladium ions in the palladium solution ranges from 0.2 wt% to 2 wt%.

4. The method for preparing 2-propylheptanoic acid according to claim 1, characterized in that: The sodium borohydride solution has a mass percentage concentration of 10-20%.

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