Method for preparing 2-alkoxy-2-methyl tetrahydrofuran compound from 2-methyl furan

Abstract

Provided in the present invention is a method for preparing a 2-alkoxy-2-methyl tetrahydrofuran compound from 2-methyl furan. In the present invention, a metal hydroxide and zero-valent nickel compounded catalyst is prepared, and a 2-alkoxy-2-methyltetrahydrofuran is generated by directly hydrogenating 2-methylfuran under the conditions of an alcohol solvent and hydrogen. By means of the method of the present invention, the use of a homogeneous acid catalyst is avoided, such that the product separation is more convenient, and the catalyst can be recycled, thereby also reducing the burden on the environment, providing a new technical solution for achieving efficient and green synthesis of a 2-alkoxy-2-methyltetrahydrofuran, and broadening the production of biomass-based fuels, chemicals and green solvents.

Description

A method for preparing 2-alkoxy-2-methyltetrahydrofuran compounds from 2-methylfuran Technical Field

[0001] This invention belongs to the field of chemical product preparation technology, specifically relating to a catalyst, preparation method, and application for preparing 2-alkoxy-2-methyltetrahydrofuran from 2-methylfuran. The method involves the efficient conversion of 2-methylfuran to 2-alkoxy-2-methyltetrahydrofuran via hydrogenation and alkanoic oxidation of an alcohol under the catalysis of a nickel-based catalyst. Background Technology

[0002] With the chemical industry increasingly moving towards sustainability and green development, the production of high-value-added organic compounds from biomass-derived compounds has become an important research area in chemical research. 2-Methylfuran (2-MF), as a typical biomass-derived platform compound, exhibits excellent reactivity due to its reactive furan ring structure and methyl substituents, making it one of the ideal feedstocks for hydrogenation conversion. The conversion of 2-methylfuran into high-value-added furan derivatives offers rich research prospects.

[0003] 2-Alkoxy-2-methyltetrahydrofuran possesses unique chemical properties due to its cyclic structure and alkoxy substituents. It serves as a solvent and structural unit in organic synthesis, exhibiting excellent chemical stability and solubility, making it particularly suitable for medicinal chemistry and organic chemical synthesis. Furthermore, as a deep-processed product of biomass platform compounds, 2-alkoxy-2-methyltetrahydrofuran has the potential to be developed as a solvent and catalytic reaction intermediate, enabling green conversion from raw materials to finished products. Besides its applications in synthetic chemistry, 2-alkoxy-2-methyltetrahydrofuran also shows potential as a fuel or fuel additive. Compared to alcohols and 2-methyltetrahydrofuran, 2-alkoxy-2-methyltetrahydrofuran has a higher boiling point, contains oxygen, and is easily miscible with gasoline and diesel fuel, promoting complete combustion. In addition, the calorific value of 2-alkoxy-2-methyltetrahydrofuran is higher than that of methyltetrahydrofuran (MTHF), making it an ideal choice for high-efficiency fuels. As a fuel additive, it can not only improve the energy release efficiency during combustion, but also effectively improve combustion stability and help reduce harmful emissions.

[0004] However, no industrial-scale process or suitable catalyst has been developed for the direct preparation of 2-alkoxy-2-methyltetrahydrofuran from 2-methylfuran. According to literature reports (J. Org. Chem, 1972, 6, 385-406), there are studies in organic synthesis on the indirect preparation of 2-ethoxy-2-methyltetrahydrofuran via 2,5-dihydro-2-methyltetrahydrofuran or other intermediates. However, this method has several limitations: the process uses p-toluenesulfonic acid (TsOH) as a homogeneous acid catalyst and requires subsequent neutralization with pyridine, making the process complex, difficult to separate, and environmentally unfriendly. Furthermore, the high cost of 2,5-dihydro-2-methyltetrahydrofuran increases the production cost of this route, limiting its practical application. Literature reports (J. Org. Chem., 1951, 476-479) describe the reaction of 2-methylfuran with methanol and butanol solvents, respectively, at 160 °C for 150 min under a hydrogen atmosphere, to obtain 2-methoxy-2-methyltetrahydrofuran and 2-butoxy-2-methyltetrahydrofuran, with yields of 11.4% and 10.2%, respectively. This process uses nickel / diatomaceous earth and requires the addition of formic acid solution. After the reaction, neutralization with NaOH solution is necessary, making the operation complex and resulting in significant waste discharge. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes an innovative catalytic method that utilizes a catalyst composed of a metal hydroxide and zero-valent nickel to achieve the direct one-step hydrogenation of 2-methylfuran to 2-alkoxy-2-methyltetrahydrofuran under alcohol solvent and hydrogen conditions. This method avoids the use of homogeneous acid catalysts, making product separation more convenient, enabling catalytic recovery, and reducing environmental impact. It provides a new technical solution for the efficient and green synthesis of 2-alkoxy-2-methyltetrahydrofuran.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing 2-alkoxy-2-methyltetrahydrofuran compounds from 2-methylfuran in a one-step process:

[0008] In a hydrogen atmosphere, 2-methylfuran is used as a raw material and alcohols as solvents. A composite catalyst containing metal hydroxide and nickel is used to carry out hydrogenation and alkanolysis of alcohols under certain reaction temperature and pressure to prepare 2-alkoxy-2-methyltetrahydrofuran compounds in one step.

[0009] Furthermore, the alcohol solvent is an alkyl alcohol solvent, including but not limited to one or more alcohol compounds such as methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol.

[0010] Furthermore, the reaction conditions are as follows: reaction temperature 50-300℃, preferably 100-180℃; reaction pressure 0.1-10MPa, preferably 2-5MPa; and carried out under anhydrous conditions.

[0011] Furthermore, the reaction time is 0.5-10 hours, preferably 1-6 hours, to ensure the yield of the target product.

[0012] Furthermore, in the reaction, the concentration of 2-methylfuran in the solvent is 1 mmol / ml. The amounts of 2-methylfuran and catalyst used are 10 mmol: 40–100 mg.

[0013] Furthermore, the active components of the catalyst include nickel hydroxide, tungsten hydroxide, lanthanum hydroxide, and zero-valent nickel metal.

[0014] The catalyst is prepared by a hydrothermal or solvothermal method, and the preparation method includes the following steps:

[0015] Zero-valent nickel metal is added to a mixed solution of ethanol, water, and ethylene glycol diethyl ether containing metal ions (nickel ions, cobalt ions, tungsten ions) and after pH adjustment. The solution is placed at 80-200°C for 0-8 hours (preferably at 120-160°C for 2-4 hours). After completion, the resulting product is washed and dried to obtain a catalyst composed of metal hydroxide and zero-valent nickel.

[0016] The sources of nickel ions include at least one of nickel chloride, nitrate, or sulfate.

[0017] The mass ratio of the zero-valent nickel metal to the nickel ion salt is 500:1 to 50.

[0018] In a mixed solution of ethanol, water, and ethylene glycol diethyl ether, the volume ratio of ethanol, water, and ethylene glycol diethyl ether is 4.5:1:4.5. The pH of the mixed solution is then adjusted to 1–5.

[0019] This invention utilizes a nickel-based catalyst modified with nickel hydroxide to achieve the direct hydrogenation of 2-methylfuran to 2-alkoxy-2-methyltetrahydrofuran under alcohol solvent and hydrogen conditions. This method avoids the use of homogeneous acid catalysts, making product separation more convenient, catalytic recovery possible, and reducing environmental impact. It provides a new technical solution for the efficient and green synthesis of 2-alkoxy-2-methyltetrahydrofuran. The process is simple and represents the first time that 2-alkoxy-2-methyltetrahydrofuran has been obtained through the hydrogenation of 2-methylfuran and the oxidation of an alcohol alkane without the addition of an additional protic acid. This 2-alkoxy-2-methyltetrahydrofuran can be used as a fuel, chemical, and green solvent.

[0020] Compared with existing technologies, the advantages of this invention are as follows: using the biomass-based platform compound 2-methylfuran as a raw material, and through a heterogeneous nickel-based catalyst, a one-step preparation of 2-alkoxy-2-methyltetrahydrofuran is achieved. The operation and process of this invention are simple, the catalytic system is singular, no additional strong acid is required, and no neutralization step is needed, which is beneficial for scale-up production and is environmentally friendly. Attached Figure Description

[0021] Figure 1 shows the nickel-based catalyst (Ni(OH)) modified with nickel hydroxide prepared in Example 1. x X-ray diffraction (XRD) pattern (Fig. 1a) and Raman spectrum (Fig. 1b) of Ni.

[0022] Figure 2 shows the nickel-based catalyst (Ni(OH)) modified with nickel hydroxide prepared in Example 1. x SEM images and corresponding elemental distribution diagrams of the catalyst (a) and Ni. Specifically, a) is the SEM image of the catalyst, b) is the SEM image of the catalyst, and c) and d) are the corresponding EDS spectra of Ni and O elements. Detailed Implementation

[0023] The following describes the preparation of 2-alkoxy-2-methyltetrahydrofuran by catalyzing the hydrogenation of 2-methylfuran and the oxidation of alcohols to 2-alkoxy-2-methyltetrahydrofuran, using 2-methylfuran as a reactant and methanol, ethanol, and propanol as solvents, respectively, with a nickel catalyst modified with nickel hydroxide as an example. The scope of protection of this patent is not limited to the specific embodiments, but is limited by the claims.

[0024] Example 1

[0025] Nickel hydroxide-modified nickel-based (Ni(OH)) x Preparation of (Ni) catalyst:

[0026] Add 38 ml of a mixed solution of ethanol, water, and ethylene glycol diethyl ether in a volume ratio of 4.5:1:4.5 to the polytetrafluoroethylene liner of the hydrothermal reactor, and adjust the pH to 1 with 3 mmol / L HCl solution. Add 20.25 mg of NiCl₂·6H₂O to the above solution, and after complete dissolution, add 500 mg of nickel powder (Aladdin, 20-100 nm). After sealing the hydrothermal reactor, place it in an oven and maintain it at 160 °C for 4 hours. Then wash with ethanol and water, and vacuum dry at 60 °C for 2 hours.

[0027] Example a

[0028] Nickel hydroxide-modified nickel-based (Ni(OH)) x Preparation of Ni catalyst: Compared with Example 1, the only difference is that the pH of the 3 mmol / L HCl solution was adjusted to 3, and the other operations were the same as in Example 1.

[0029] Example b

[0030] Nickel hydroxide-modified nickel-based (Ni(OH)) x Preparation of Ni catalyst: Compared with Example 1, the difference is that the pH of the 3 mmol / L HCl solution was adjusted to 5, and the other operations were the same as in Example 1.

[0031] Example 2 Catalytic reaction (preparation of 2-methoxy-2-methyltetrahydrofuran)

[0032] Weigh 80 mg of Ni(OH) prepared in Example 1. x Ni catalyst, 820 mg 2-methylfuran, and 10 ml anhydrous methanol were sequentially added to the lining of a 25 ml reactor and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to purge the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was then placed in a heating mantle, and the temperature was raised to 140 °C, at which point the time was started. After 2 hours of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 72%, and the yield of the target product, 2-methoxy-2-methyltetrahydrofuran, was 30%, with the following structural formula:

[0033] Example 3 Catalytic reaction (preparation of 2-ethoxy-2-methyltetrahydrofuran)

[0034] Weigh 80 mg of Ni(OH) prepared in Example 1. x Ni catalyst, 820 mg 2-methylfuran, and 10 ml anhydrous ethanol were sequentially added to the lining of a 25 ml reactor and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to purge the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was then placed in a heating mantle, and the temperature was raised to 140 °C, at which point timing began. After 1 hour of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 68%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 27%, with the following structural formula:

[0035] Example 3-1

[0036] Weigh 80 mg of Ni(OH) prepared in Example a. xNi catalyst, 820 mg of 2-methylfuran, and 10 ml of anhydrous ethanol were sequentially added to the lining of a 25 ml reactor and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to replace the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was placed in a heating mantle, and the temperature was raised to 140 °C, at which point the time was started. After 1 hour of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 68%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 28%.

[0037] Example 3-2

[0038] Weigh 80 mg of Ni(OH) prepared in Example b. x Ni catalyst, 820 mg of 2-methylfuran, and 10 ml of anhydrous ethanol were sequentially added to the lining of a 25 ml reactor and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to replace the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was placed in a heating mantle, and the temperature was raised to 140 °C, at which point timing began. After 1 hour of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 74%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 30%.

[0039] Example 4 Catalytic reaction (preparation of 2-propoxy-2-methyltetrahydrofuran)

[0040] Weigh 80 mg of Ni(OH) prepared in Example 1. x Ni catalyst, 820 mg 2-methylfuran, and 10 ml anhydrous propanol were sequentially added to a 25 ml volume reactor liner and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to purge the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was placed in a heating mantle, and the temperature was raised to 140 °C, starting the timer. After 4 hours of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 69%, and the yield of the target product, 2-propoxy-2-methyltetrahydrofuran, was 12%, with the following structural formula:

[0041] Example 5 (catalytic reaction temperature: 120°C)

[0042] Weigh 80 mg of Ni(OH) prepared in Example 1. xNi catalyst, 820 mg of 2-methylfuran, and 10 ml of anhydrous ethanol were sequentially added to the lining of a 25 ml reactor and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to replace the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was placed in a heating mantle, and the temperature was raised to 120 °C, at which point the time was started. After 1 hour of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 36%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 16%.

[0043] If the temperature is raised to 120℃ and the timing begins, after 2 hours of reaction, gas chromatography analysis shows that the conversion rate of 2-methylfuran is 53%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, is 24%.

[0044] Example 6 (Effect of Reaction Time)

[0045] The difference between Example 6 and Example 3 is that the reaction time is different, but the other operations are the same.

[0046] If the reaction time is 0.5 hours, the yield is 21%.

[0047] If the reaction time is 2 hours, the yield is 28%.

[0048] If the reaction time is 4 hours, the yield is 18%.

[0049] If the reaction time is 18 hours, the yield is 5%.

[0050] The effect of reaction time is as follows: as the reaction time proceeds, the conversion rate of 2-methylfuran gradually increases, while the yield of 2-ethoxy-2-methyltetrahydrofuran shows a trend of first increasing and then decreasing. The final product is mainly 2-methyltetrahydrofuran.

[0051] Example 7 (Effect of Catalyst Dosage)

[0052] The difference between Example 7 and Example 3 is that the catalyst dosage is 40 mg, while the other operations are the same as in Example 3.

[0053] When the amount of catalyst was reduced to 40 mg, the conversion rate of 2-methylfuran was 42% after 1 hour of reaction, and the maximum yield of 2-ethoxy-2-methyltetrahydrofuran was 19%.

[0054] Example 8 (Comparative Example)

[0055] 8.1 Preparation of Nickel Reduction Catalyst

[0056] Add 80 mg of nickel powder (Aladdin, 20-100 nm) to a reducing tube furnace. First, purge the air in the tube with nitrogen, then purge with a 10% H2 / Ar mixture while simultaneously raising the temperature to 200 °C and holding for 2 hours at a rate of 10 °C / min.

[0057] 8.2 Catalytic reaction

[0058] 80 mg of the nickel reduction catalyst prepared in Example 8.1, 820 mg of 2-methylfuran, and 10 ml of anhydrous ethanol were weighed and added sequentially to a 25 ml volume reactor liner, and mixed thoroughly. After sealing the reactor, nitrogen gas was first introduced to replace the air inside, followed by hydrogen gas, and finally the hydrogen pressure was adjusted to 3 MPa. The reactor was placed in a heating mantle, and the temperature was raised to 140 °C, at which point timing began. After 2 hours of reaction, gas chromatography analysis showed that the conversion rate of 2-methylfuran was 77%, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 5%.

[0059] Example 8 with Ni(OH) x Compared to the Ni catalyst, the reduced nickel powder exhibits decreased catalyst activity, and the yield of 2-ethoxy-2-methyltetrahydrofuran is significantly reduced, with 2-methyltetrahydrofuran being the main product.

[0060] Example 9

[0061] Preparation of nickel hydroxide: Compared with Example 1, the difference is that nickel powder was not added, but the other operations are the same as in Example 1.

[0062] When nickel hydroxide catalyst alone was used in the catalytic reaction of Comparative Example 2, the final yield of the target product 2-methoxy-2-methyltetrahydrofuran was 0%.

[0063] Example 10

[0064] Catalyst preparation: NiCl2 6H2O in Example 1 was replaced with CoCl2, and other operations were the same to obtain a nickel catalyst modified with cobalt hydroxide.

[0065] The catalytic reaction was the same as in Example 3, and the yield of the target product, 2-ethoxy-2-methyltetrahydrofuran, was 27%.

[0066] Example 11

[0067] Catalyst preparation: NiCl2 6H2O in Example 1 was replaced with WCl3, and other operations were the same to obtain a nickel catalyst modified with tungsten hydroxide.

[0068] The catalytic reaction was the same as in Example 3, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 33%.

[0069] Example 12

[0070] Catalyst preparation: NiCl2 6H2O in Example 1 was replaced with LaCl3, and other operations were the same to obtain a nickel catalyst modified with lanthanum hydroxide.

[0071] The catalytic reaction was the same as in Example 3, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 33%.

[0072] As demonstrated by the above examples, 2-alkoxy-2-methyltetrahydrofuran can be directly prepared from 2-methylfuran via hydrogenation and alcoholysis under the catalytic action of a nickel catalyst modified with nickel hydroxide. Using methanol, ethanol, and propanol as examples, this invention yielded the corresponding reaction products 2-methoxy-2-methyltetrahydrofuran, 2-ethoxy-2-methyltetrahydrofuran, and 2-propoxy-2-methyltetrahydrofuran, respectively, proving the preparation of the catalyst and the substrate universality of the catalytic reaction of this invention.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for the preparation of a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran, the process comprising the steps of: In a hydrogen atmosphere, 2-methylfuran is used as a raw material, an alcohol solvent is added, and a catalyst containing a metal hydroxide and zero-valent nickel is used to prepare 2-alkoxy-2-methyltetrahydrofuran compound in one step under certain reaction temperature and pressure. The metal hydroxide is a nickel hydroxide, a tungsten hydroxide, or a lanthanum hydroxide; the alcohol is an alkyl alcohol.

2. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 1, wherein, The alcohol solvents mentioned include, but are not limited to, one or more of methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol.

3. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 1, wherein, The reaction is carried out at a temperature of 50-300℃ and a pressure of 0.1-10MPa under anhydrous conditions.

4. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 1, wherein, The reaction time is 0.5-10 hours.

5. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 1, wherein, The specific preparation method of the catalyst is as follows: zero-valent nickel metal is added to a mixed solution of ethanol, water and ethylene glycol diethyl ether containing metal ion salt, the pH is adjusted to 1-6, and the solution is placed at 80-200℃ for 2-8 hours. After completion, the product is washed and dried to obtain a catalyst composed of metal hydroxide and zero-valent nickel. The metal ion is one of nickel ion, cobalt ion and tungsten ion.

6. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 5, wherein, The sources of the metal ions include at least one of metal chlorides, nitrates, or sulfates.

7. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 5, wherein, The mass ratio of zero-valent nickel metal to metal ion salt is 500:1 to 50.

8. The method of preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran according to claim 5, wherein, In a mixed solution of ethanol, water, and ethylene glycol diethyl ether, the volume ratio of ethanol, water, and ethylene glycol diethyl ether is 4.5:1:4.5.

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