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

Abstract

The invention provides a method for preparing a 2-alkoxy-2-methyl tetrahydrofuran compound by using 2-methyl furan. The method comprises the following steps of: preparing 2-alkoxy-2-methyl tetrahydrofuran; according to the preparation method disclosed by the invention, the metal hydroxide and zero-valent nickel compounded catalyst is prepared, and the 2-alkoxy-2-methyltetrahydrofuran is generated by directly hydrogenating 2-methylfuran under the conditions of an alcohol solvent and hydrogen. According to the method disclosed by the invention, the use of a homogeneous acid catalyst is avoided, so that the product separation is more convenient, the catalyst can be recycled, meanwhile, the burden on the environment is reduced, a new technical scheme is provided for realizing efficient and green synthesis of the 2-alkoxy-2-methyltetrahydrofuran, and the production of biomass-based fuels, chemicals and green solvents is broadened.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical product preparation, and particularly relates to a catalyst for preparing 2-alkoxy-2-methyltetrahydrofuran from 2-methylfuran, a preparation method and an application thereof. This method involves the efficient conversion of 2-methylfuran to 2-alkoxy-2-methyltetrahydrofuran through hydrogenation and alkoxylation reactions of alcohols catalyzed by a nickel-based catalyst. Background Art

[0002] With the increasing development of the chemical industry towards sustainability and greenness, the production of high-value-added organic compounds from biomass-derived compounds has become an important research field in chemical research. 2-Methylfuran (2-MF), as a typical biomass-derived platform compound, exhibits good reactivity due to its active furan ring structure and methyl substituent, making it one of the ideal raw materials in the hydrogenation conversion process. The conversion of 2-methylfuran provides rich research prospects for high-value-added furan derivatives.

[0003] 2-Alkoxy-2-methyltetrahydrofuran has special chemical properties due to its cyclic structure and alkoxy substituent. It can be used as a solvent and a structural unit in organic synthesis, showing good chemical stability and solubility, and is particularly suitable for the fields of pharmaceutical chemistry and organic chemical synthesis. In addition, as a deep processing product of biomass platform compounds, 2-alkoxy-2-methyltetrahydrofuran also has the potential to be developed into a solvent and a catalytic reaction intermediate, enabling green conversion from raw materials to products. In addition to its application in synthetic chemistry, 2-alkoxy-2-methyltetrahydrofuran also has the potential to be used as a fuel or a fuel additive. Compared with alcohols and 2-methyltetrahydrofuran, 2-alkoxy-2-methyltetrahydrofuran has a higher boiling point, is oxygen-containing and is easily mixed with gasoline and diesel, which can promote the complete combustion of gasoline and diesel. In addition, the calorific value of 2-alkoxy-2-methyltetrahydrofuran is higher than that of methyltetrahydrofuran (MTHF), and this characteristic makes 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, in the prior art, an industrial process and a suitable catalyst for directly preparing 2-alkoxy-2-methyltetrahydrofuran from 2-methylfuran have not been developed. According to the literature report (J. Org. Chem, 1972, 6, 385 - 406), there are studies on indirectly preparing 2-ethoxy-2-methyltetrahydrofuran through 2,5-dihydro-2-methyltetrahydrofuran or other intermediates in organic synthesis. However, this method has several limitations: this process uses p-toluenesulfonic acid (TsOH) as a homogeneous acid catalyst and requires subsequent neutralization treatment with pyridine. Not only is the process complex and the separation difficult, but it is also environmentally unfriendly. In addition, the cost of 2,5-dihydro-2-methyltetrahydrofuran is relatively high, increasing the production cost of this route and limiting its practical application. The literature report (J. Org. Chem, 1951, 476 - 479) reported that 2-methylfuran reacted with methanol and butanol solvents respectively in a hydrogen atmosphere at 160 °C for 150 min to obtain 2-methoxy-2-methyltetrahydrofuran and 2-butoxy-2-methyltetrahydrofuran with yields of 11.4% and 10.2% respectively. What was used in this process was nickel / diatomaceous earth and it was necessary to additionally add a formic acid solution. After the reaction, it was necessary to neutralize with a NaOH solution, with complex operations and a large amount of waste liquid discharge. Summary of the Invention

[0005] In view of the above problems, the present invention proposes an innovative catalytic method. By using a catalyst composed of a metal hydroxide and zero-valent nickel, under the conditions of an alcohol solvent and hydrogen, the direct one-step hydrogenation of 2-methylfuran to produce 2-alkoxy-2-methyltetrahydrofuran is achieved. The method of the present invention avoids the use of a homogeneous acid catalyst, making the product separation more convenient, the catalyst recyclable, and at the same time reducing the environmental burden, providing a new technical solution for the efficient and green synthesis of 2-alkoxy-2-methyltetrahydrofuran.

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

[0007] A method for preparing a catalyst for the one-step preparation of 2-alkoxy-2-methyltetrahydrofuran compounds from 2-methylfuran:

[0008] In a hydrogen atmosphere, using 2-methylfuran as a raw material and an alcohol as a solvent, a composite catalyst containing a metal hydroxide and metallic nickel is employed, and under a certain reaction temperature and reaction pressure, a hydrogenation and alkoxylation reaction of the alcohol are carried out to prepare 2-alkoxy-2-methyltetrahydrofuran compounds by a one-step method.

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

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

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

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

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

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

[0015] Add zero - valent nickel metal into a mixed solution of ethanol, water, and ethylene glycol diethyl ether containing metal ions (nickel ions, cobalt ions, tungsten ions) and adjusted to a certain pH, and place it at a temperature of 80 - 200 °C for 0 - 8 hours (preferably at 120 - 160 °C for 2 - 4 hours); after completion, wash and dry the obtained product to obtain a catalyst in which metal hydroxide is combined with zero - valent nickel.

[0016] The source of the nickel ions includes at least one of nickel chloride, nickel nitrate, or nickel sulfate.

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

[0018] In the 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. And adjust the pH of the mixed solution of ethanol, water, and ethylene glycol diethyl ether to 1 - 5.

[0019] The present invention uses a nickel - based catalyst modified with nickel hydroxide, and under the conditions of an alcohol solvent and hydrogen, realizes the direct hydrogenation of 2 - methylfuran to produce 2 - alkoxy - 2 - methyltetrahydrofuran. The method of the present invention avoids the use of homogeneous acid catalysts, makes the product separation more convenient, the catalyst can be recycled, and at the same time reduces the environmental burden, providing a new technical solution for the efficient and green synthesis of 2 - alkoxy - 2 - methyltetrahydrofuran. The process of the present invention is simple. For the first time, without adding additional protonic acid, 2 - alkoxy - 2 - methyltetrahydrofuran is obtained by using the hydrogenation of 2 - methylfuran and the alcohol - alkoxide oxidation reaction, which can be used as fuel, chemicals, and green solvents.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: Using the biomass-based platform compound 2-methylfuran as a raw material, through a heterogeneous nickel-based catalyst, the one-step preparation of 2-alkoxy-2-methyltetrahydrofuran is realized. The operation and process of the present invention are simple, the catalytic system is single, no additional strong acid needs to be added, and no neutralization step is required, which is conducive to large-scale production and is environmentally friendly. Description of the Drawings

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

[0022] Figure 2 SEM morphology diagram and corresponding element distribution diagram of the nickel-based catalyst modified with nickel hydroxide (Ni(OH) x / Ni) prepared in Example 1. Among them, a) SEM image of the catalyst, b) SEM image of the catalyst and corresponding c) EDS spectra of Ni element and d) O element. Detailed Description of the Invention

[0023] Taking 2-methylfuran as the reactant, using methanol, ethanol and propanol as solvents respectively, and taking the prepared nickel-based catalyst modified with nickel hydroxide as an example, the hydrogenation of 2-methylfuran and the alcohol alkoxylation to prepare 2-alkoxy-2-methyltetrahydrofuran are catalyzed. The protection scope of this patent is not limited by the specific implementation manners, but is limited by the claims.

[0024] Example 1

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

[0026] Add a mixed solution of 38 ml of ethanol, water and ethylene glycol diethyl ether to the polytetrafluoroethylene inner lining of the hydrothermal reactor. The volume ratio of the three is 4.5:1:4.5, and the pH is adjusted to 1 with a 3 mmol / L HCl solution. Take 20.25 mg of NiCl 2 6H 2 O and add it to the above solution. After fully dissolving, add 500 mg of nickel powder (Aladdin, 20 - 100 nm). After tightening the hydrothermal reaction kettle, put it into the oven and keep it at 160 °C for 4 h. Then wash it with ethanol and water and dry it in vacuum at 60 °C for 2 h.

[0027] Example a

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

[0029] Example b

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

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

[0032] Weigh 80 mg of the Ni(OH) / Ni catalyst prepared in Example 1 x 820 mg of 2-methylfuran and 10 ml of anhydrous methanol were successively added into the inner liner of a 25 ml reaction kettle and mixed evenly. After sealing the reaction kettle, nitrogen was first introduced to displace the air in the reaction kettle, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reaction kettle was placed in a heating jacket and heated to 140 °C to start timing. At 2 h of the reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 72%, and the yield of the target product 2-methoxy-2-methyltetrahydrofuran was 30%. The structural formula is

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

[0034] Weigh 80 mg of the Ni(OH) / Ni catalyst prepared in Example 1 respectively x 820 mg of 2-methylfuran and 10 ml of anhydrous ethanol were successively added into the inner liner of a 25 ml reaction kettle and mixed evenly. After sealing the reaction kettle, nitrogen was first introduced to displace the air in the reaction kettle, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reaction kettle was placed in a heating jacket and heated to 140 °C to start timing. At 1 h of the reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 68%, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 27%. The structural formula is

[0035] Example 3-1

[0036] Weigh 80 mg of the Ni(OH) prepared in Example a respectively x820 mg of 2-methylfuran and 10 ml of absolute ethanol were successively added to the inner lining of a 25-ml reactor and mixed evenly. After sealing the reactor, nitrogen was first introduced to displace the air in the reactor, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reactor was placed in a heating jacket and heated to 140 °C to start timing. At the 1 h of reaction, by gas chromatography analysis, 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] Weighed 80 mg of Ni(OH) prepared in Example b x 820 mg of 2-methylfuran and 10 ml of absolute ethanol were successively added to the inner lining of a 25-ml reactor and mixed evenly. After sealing the reactor, nitrogen was first introduced to displace the air in the reactor, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reactor was placed in a heating jacket and heated to 140 °C to start timing. At the 1 h of reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 74%, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 30%.

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

[0040] Weighed 80 mg of Ni(OH) prepared in Example 1 x 820 mg of 2-methylfuran and 10 ml of anhydrous propanol were successively added to the inner lining of a 25-ml reactor and mixed evenly. After sealing the reactor, nitrogen was first introduced to displace the air in the reactor, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reactor was placed in a heating jacket and heated to 140 °C to start timing. At the 4 h of reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 69%, and the yield of the target product 2-propoxy-2-methyltetrahydrofuran was 12%, and the structural formula is

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

[0042] Weighed 80 mg of Ni(OH) prepared in Example 1 x / Ni catalyst, 820 mg of 2-methylfuran and 10 ml of absolute ethanol were successively added into a 25-ml reactor liner and mixed evenly. After sealing the reactor, nitrogen was first introduced to displace the air in the reactor, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reactor was placed in a heating jacket and heated to 120 °C to start timing. At 1 h of reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 36%, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 16%.

[0043] If heated to 120 °C to start timing. At 2 h of reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 53%, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 24%.

[0044] Example 6 (Effect of reaction time)

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

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

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

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

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

[0050] The effect of the reaction time is that as the reaction time progresses, the conversion rate of 2-methylfuran gradually increases, the yield of 2-ethoxy-2-methyltetrahydrofuran shows a trend of first increasing and then decreasing, and 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 other operations are the same as those in Example 3.

[0053] When the catalyst dosage was reduced to 40 mg and the reaction was carried out for 1 h, the conversion rate of 2-methylfuran was 42%, and the maximum yield of 2-ethoxy-2-methyltetrahydrofuran was 19%.

[0054] Example 8 (Comparative example)

[0055] 8.1 Preparation of reduced nickel catalyst

[0056] 80 mg of nickel powder (Aladdin, 20 - 100 nm) was added into a reduction tube furnace. Nitrogen was first introduced to displace the air in the pipeline, and then 10% H2 An Ar mixed gas was introduced while heating to 200 °C and maintaining for 2 h at a heating rate of 10 °C / min.

[0057] 8.2 Catalytic reaction

[0058] 80 mg of the reduced nickel catalyst prepared in 8.1 of Example 8, 820 mg of 2-methylfuran, and 10 ml of absolute ethanol were weighed and successively added to the inner lining of a 25-ml reactor and mixed evenly. After sealing the reactor, nitrogen was first introduced to displace the air in the reactor, then hydrogen was introduced for displacement, and finally the pressure of hydrogen was adjusted to 3 MPa. The above reactor was placed in a heating jacket and heated to 140 °C to start timing. At 2 h of the reaction, by gas chromatography analysis, the conversion rate of 2-methylfuran was 77%, and the yield of the target product 2-ethoxy-2-methyltetrahydrofuran was 5%.

[0059] Example 8 compared with Ni(OH) x / Ni catalyst, the reduced nickel powder as a catalyst showed a decrease in activity, and the yield of 2-ethoxy-2-methyltetrahydrofuran decreased significantly, with the main product being 2-methyltetrahydrofuran.

[0060] Example 9

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

[0062] Using the single nickel hydroxide catalyst 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] Preparation of the catalyst: Replace NiCl 2 6H 2 O in Example 1 with CoCl 2 while keeping other operations the same, to obtain a cobalt hydroxide-modified nickel catalyst.

[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] Preparation of the catalyst: Replace NiCl 2 6H 2 O in Example 1 with WCl 3 while keeping other operations the same, to obtain a tungsten hydroxide-modified nickel catalyst.

[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] Preparation of the catalyst: Replace NiCl 2 6H 2 O with LaCl 3 , and perform the same other operations 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 can be seen from the above examples, under the catalysis of the nickel catalyst modified with nickel hydroxide, 2-alkoxy-2-methyltetrahydrofuran can be directly prepared by the hydrogenation and alcoholysis of 2-methylfuran. Taking methanol, ethanol, and propanol as examples respectively, the corresponding reaction products 2-methoxy-2-methyltetrahydrofuran, 2-ethoxy-2-methyltetrahydrofuran, and 2-propoxy-2-methyltetrahydrofuran were obtained, demonstrating the substrate generality of the preparation of the catalyst and the catalytic reaction of the present invention.

[0073] The above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran, the method comprising the following steps: 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 metal is used. At a certain reaction temperature and reaction pressure, a 2-alkoxy-2-methyltetrahydrofuran compound is prepared in one step; wherein the metal hydroxide is nickel hydroxide, tungsten hydroxide or lanthanum hydroxide; and the alcohol is an alkyl alcohol.

2. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 1, characterized in that: The alcohol solvent includes but is not limited to one or more of methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol.

3. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 1, characterized in that: The reaction temperature is 50-300°C, the reaction pressure is 0.1-10MPa, and the reaction is carried out under anhydrous conditions.

4. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 1, characterized in that: The reaction time is 0.5-10 hours.

5. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 1, characterized in that: The specific preparation method of the catalyst is: adding zero-valent nickel metal to a mixed solution of ethanol, water and ethylene glycol diethyl ether containing metal ion salts, adjusting the pH to 1-6, placing it at a temperature of 80-200°C for 2-8 hours, and after completion, washing and drying the resulting product to obtain a catalyst composite of metal hydroxide and zero-valent nickel; the metal ion is one of nickel ion, cobalt ion, and tungsten ion.

6. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 5, characterized in that: The source of the metal ions includes at least one of metal chlorides, nitrates or sulfates.

7. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 5, characterized in that: The mass ratio of the zero-valent nickel metal to the metal ion-containing salt is 500:1-50.

8. The method for preparing a 2-alkoxy-2-methyltetrahydrofuran compound from 2-methylfuran as claimed in claim 5, characterized in that: In the 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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