A preparation method of 2,5-dimethyltetrahydrofuran

Abstract

The present invention discloses a method for highly selectively synthesizing 2,5-dimethyltetrahydrofuran. Using 2,5-hexanedione as a raw material, alcohol as a reaction solvent and reducing agent, and a metal salt as a catalyst, the reaction is carried out in a closed reactor under a certain temperature condition in a non-hydrogen atmosphere for a certain period of time. The present invention uses alcohol as a reducing agent instead of high-pressure hydrogen, with mild reaction conditions, greatly reducing potential hazards. The present invention uses an inexpensive and easily available metal salt instead of a noble metal catalyst, greatly reducing production costs. The catalyst of the present invention is highly efficient, used in small amounts, simple to obtain and easy to recycle, with high product yield and few by-products, and has great application potential.

Description

Technical Field

[0001] The present invention relates to the technical field of high-value utilization of biomass platform chemicals, and particularly relates to a method for preparing 2,5-dimethyltetrahydrofuran. Background Art

[0002] With the continuous progress of the development of human society, the demand for non-renewable fossil resources is increasing day by day, and at the same time, the resulting environmental pollution and energy crisis are becoming increasingly serious. Therefore, it is urgent to develop renewable resources and build sustainable development. Using biomass as a raw material, a variety of platform-based compounds can be obtained through physical, chemical, and biological means; at the same time, these platform-based compounds can be further transformed to obtain a variety of high-value-added chemicals.

[0003] 2,5-Dimethyltetrahydrofuran is a transparent liquid with the molecular formula C6H 12 O. As an important biomass-based chemical, due to its excellent physical and chemical properties, 2,5-dimethyltetrahydrofuran has been widely used in fields such as gasoline additives, organic synthesis, polymer materials, and battery electrolytes.

[0004] In recent years, the research on preparing 2,5-hexanedione from biomass as a raw material has received extensive attention (ACS Sustainable Chem. Eng. 2021, 9, 46, 15394-15405; Appl. Catal. A: Gen. 2015, 504, 664-671). To prepare 2,5-dimethyltetrahydrofuran from 2,5-hexanedione as a raw material, two steps of carbonyl hydrogenation and dehydration need to be experienced. Generally speaking, 2,5-hexanedione first realizes the reduction of the carbonyl group to 2,5-hexanediol in the presence of a noble metal catalyst and a hydrogen atmosphere; the latter realizes intramolecular dehydration conversion to 2,5-dimethyltetrahydrofuran under a protonic acid-type catalyst. For example, the Marcel Schlaf research group used [Ru(triphos)(CH3CN)3](OTf)2 as a catalyst to realize the preparation of 2,5-dimethyltetrahydrofuran from 2,5-hexanedione at 150 o °C under 5.5 MPa H2, with a yield of 66% (Green Chem., 2017, 19, 4666-4679). The same research group also found that [(4’-Ph-terpy)Ru(H2O)3](OTf)2 and [(4’-Ph-terpy)Ir(OTf)3] can also realize the conversion of 2,5-hexanedione to prepare 2,5-dimethyltetrahydrofuran under the above conditions (ACS Catal. 2014, 4, 11, 4116-4128). Pittman et al. used a binary catalyst of Nafion-H and Pd / C, and at 180 o54% of 2,5-dimethyltetrahydrofuran was produced under C and 50 Psi H2 (J. Org. Chem. 1980, 45, 25, 5048–5052). Similarly, Zhou et al. achieved 99% of 2,5-dimethyltetrahydrofuran using Pt / C and Amberlite® IR-120H at 120 o C and 3.0 MPa H2 (Green Chem., 2016, 18, 220-225). Although the current technology can convert 2,5-hexanedione to 2,5-dimethyltetrahydrofuran, improvements are still needed in aspects such as the potential hazards of high-pressure hydrogen and the high cost of noble metal catalysts. Therefore, it is urgent to develop a more economical and effective reaction method to convert 2,5-hexanedione to 2,5-dimethyltetrahydrofuran with high efficiency and low cost, especially to achieve the above conversion process in a non-hydrogen atmosphere. Summary of the Invention

[0005] The purpose of the present invention is to provide a new method for preparing 2,5-dimethyltetrahydrofuran in a non-hydrogen atmosphere. The 2,5-dimethyltetrahydrofuran is catalytically prepared from 2,5-hexanedione.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] Using 2,5-hexanedione as the reaction substrate, mixing it with a reaction solvent and a catalyst in a certain proportion in a reactor, and carrying out a closed reaction for a certain time under certain temperature conditions, 2,5-dimethyltetrahydrofuran is obtained after the reaction ends.

[0008] The reaction solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, cyclohexanol, etc.

[0009] The catalyst is a metal salt, including but not limited to La(OTf)3, In(OTf)3, Y(OTf)3, Lu(OTf)3, Yb(OTf)3, Sc(OTf)3, ScCl3, Sc(NO3)3, etc. The molar ratio between the catalyst and the reactants is 0.025 - 0.1.

[0010] The reactor includes a microwave pressure reactor and a cartridge high-pressure reactor, preferably a microwave pressure reactor.

[0011] The reaction temperature can be 140 - 180 o C, and the reaction time can be 20 - 100 min.

[0012] Compared with the prior art, the present invention has the following outstanding advantages:

[0013] The present invention reports for the first time the preparation of 2,5-dimethyltetrahydrofuran from biomass-based 2,5-hexanedione under a non-hydrogen atmosphere. In the present invention, an alcohol is used as a reducing agent instead of high-pressure hydrogen, and the reaction conditions are mild, greatly reducing the potential danger. In the present invention, a cheap and easily available metal salt is used instead of a noble metal catalyst, greatly reducing the production cost. The catalyst of the present invention is highly efficient, used in small amounts, simple to obtain and easy to recycle, and the product has a high yield and few by-products. Description of the Drawings

[0014] Figure 1 GC-FID diagram of Example 15

[0015] Figure 2 Gas chromatography-mass spectrometry diagram of the 2,5-dimethyltetrahydrofuran product of Example 15

[0016] Figure 3 Gas chromatography-mass spectrometry diagram of the unreacted 2,5-hexanedione raw material of Example 15 Detailed Description of the Invention

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following examples will further illustrate the present invention in conjunction with the accompanying drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. On the contrary, the present invention covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention as defined by the claims. Further, in order to enable the public to have a better understanding of the present invention, in the following detailed description of the present invention, some specific details are described in detail. Those skilled in the art can fully understand the present invention without the description of these details.

[0018] Example 1: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressurized reactor. After sealing, heat it to 170 o °C and react for 20 min. After the reaction is completed, add naphthalene as an internal standard and quantitatively analyze it by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5-hexanedione is 93.9%, and the yield of 2,5-dimethyltetrahydrofuran is 57.0%.

[0019] Example 2: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of La(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressurized reactor. After sealing, heat it to 170 oReact at 170 °C for 20 min. After the reaction is completed, add naphthalene as the internal standard, and quantitatively analyze using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 38.9%, and the yield of 2,5 - dimethyltetrahydrofuran is 7.4%.

[0020] Example 3: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of In(OTf)3, and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat to 170 o React at 170 °C for 20 min. After the reaction is completed, add naphthalene as the internal standard, and quantitatively analyze using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 49.0%, and the yield of 2,5 - dimethyltetrahydrofuran is 10.5%.

[0021] Example 4: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Y(OTf)3, and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat to 170 o React at 170 °C for 20 min. After the reaction is completed, add naphthalene as the internal standard, and quantitatively analyze using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 72.9%, and the yield of 2,5 - dimethyltetrahydrofuran is 19.2%.

[0022] Example 5: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Lu(OTf)3, and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat to 170 o React at 170 °C for 20 min. After the reaction is completed, add naphthalene as the internal standard, and quantitatively analyze using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 78.4%, and the yield of 2,5 - dimethyltetrahydrofuran is 21.9%.

[0023] Example 6: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Fe(OTf)3, and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat to 170 o React at 170 °C for 20 min. After the reaction is completed, add naphthalene as the internal standard, and quantitatively analyze using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 67.7%, and the yield of 2,5 - dimethyltetrahydrofuran is 5.4%.

[0024] Example 7: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Al(OTf)₃ and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o °C and react for 20 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 31.9%, and the yield of 2,5 - dimethyltetrahydrofuran is 1.4%.

[0025] Example 8: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Sc(OTf)₃ and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o °C and react for 40 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 96.8%, and the yield of 2,5 - dimethyltetrahydrofuran is 71.0%.

[0026] Example 9: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Sc(OTf)₃ and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o °C and react for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 98.8%, and the yield of 2,5 - dimethyltetrahydrofuran is 82.2%.

[0027] Example 10: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Sc(OTf)₃ and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o °C and react for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 99.6%, and the yield of 2,5 - dimethyltetrahydrofuran is 88.3%.

[0028] Example 11: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Sc(OTf)₃ and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 oReact at 100 °C for 100 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5-hexanedione is 99.8%, and the yield of 2,5-dimethyltetrahydrofuran is 91.5%.

[0029] Example 12: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressure reactor. After sealing, heat up to 140 o React at °C for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5-hexanedione is 89.1%, and the yield of 2,5-dimethyltetrahydrofuran is 39.9%.

[0030] Example 13: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressure reactor. After sealing, heat up to 150 o React at °C for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5-hexanedione is 92.8%, and the yield of 2,5-dimethyltetrahydrofuran is 55.9%.

[0031] Example 14: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressure reactor. After sealing, heat up to 160 o React at °C for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5-hexanedione is 96.6%, and the yield of 2,5-dimethyltetrahydrofuran is 69.7%.

[0032] Example 15: Weigh 1.0 mmol of 2,5-hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave pressure reactor. After sealing, heat up to 170 o React at °C for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5-hexanedione is 99.5%, and the yield of 2,5-dimethyltetrahydrofuran is 88.5%.

[0033] Example 16: Weigh 1.0 mmol of 2,5 - hexanedione, 0.1 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 o °C and react for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 99.8%, and the yield of 2,5 - dimethyltetrahydrofuran is 92.5%.

[0034] Example 17: Weigh 1.0 mmol of 2,5 - hexanedione, 0.025 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 o °C and react for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 85.3%, and the yield of 2,5 - dimethyltetrahydrofuran is 38.2%.

[0035] Example 18: Weigh 1.0 mmol of 2,5 - hexanedione, 0.05 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 o °C and react for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 90.5%, and the yield of 2,5 - dimethyltetrahydrofuran is 59.3%.

[0036] Example 19: Weigh 1.0 mmol of 2,5 - hexanedione, 0.075 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 o °C and react for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 95.9%, and the yield of 2,5 - dimethyltetrahydrofuran is 77.2%.

[0037] Example 20: Weigh 1.0 mmol of 2,5 - hexanedione, 0.125 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 oReact at 80 °C for 80 min. After the reaction is completed, add naphthalene as the internal standard and quantitatively analyze it by using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 99.9%, and the yield of 2,5 - dimethyltetrahydrofuran is 93.5%.

[0038] Example 21: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of ethanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o React at °C for 20 min. After the reaction is completed, add naphthalene as the internal standard and quantitatively analyze it by using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 65.2%, and the yield of 2,5 - dimethyltetrahydrofuran is 7.4%.

[0039] Example 22: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of n - propanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 170 o React at °C for 20 min. After the reaction is completed, add naphthalene as the internal standard and quantitatively analyze it by using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 73.3%, and the yield of 2,5 - dimethyltetrahydrofuran is 8.8%.

[0040] Example 23: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of 2 - butanol solvent and place them in a microwave - pressurized reactor. After sealing, heat it to 180 o React at °C for 20 min. After the reaction is completed, add naphthalene as the internal standard and quantitatively analyze it by using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 95.6, and the yield of 2,5 - dimethyltetrahydrofuran is 57.0%.

[0041] Example 24: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a cartridge reactor. After sealing, place it in a pre - heated oil bath at 170 o React at °C for 20 min. After the reaction is completed, add naphthalene as the internal standard and quantitatively analyze it by using a Shimadzu 2010 Plus gas chromatograph. The conversion rate of 2,5 - hexanedione is 66.6%, and the yield of 2,5 - dimethyltetrahydrofuran is 26.6%.

[0042] Example 25: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a cartridge reactor. After sealing, react at 170 o °C in a preheated oil bath for 40 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 79.7%, and the yield of 2,5 - dimethyltetrahydrofuran is 35.8%.

[0043] Example 26: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a cartridge reactor. After sealing, react at 170 o °C in a preheated oil bath for 60 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 88.6%, and the yield of 2,5 - dimethyltetrahydrofuran is 42.1%.

[0044] Example 27: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a cartridge reactor. After sealing, react at 170 o °C in a preheated oil bath for 80 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 93.0%, and the yield of 2,5 - dimethyltetrahydrofuran is 48.5%.

[0045] Example 28: Weigh 1.0 mmol of 2,5 - hexanedione, 0.10 mmol of Sc(OTf)3 and 15.0 mL of isopropanol solvent and place them in a cartridge reactor. After sealing, react at 170 o °C in a preheated oil bath for 100 min. After the reaction is completed, add naphthalene as an internal standard and perform quantitative analysis by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5 - hexanedione is 95.0%, and the yield of 2,5 - dimethyltetrahydrofuran is 52.3%.

[0046] Example 29: After removing the liquid from the mixture after the reaction in Example 16 by vacuum distillation, the recovered Sc(OTf)3 catalyst is obtained and placed in 1.0 mmol of 2,5 - hexanedione and 15.0 mL of isopropanol solvent in a cartridge reactor. After sealing, place it in a microwave - pressurized reactor and heat it to 180 oReact at 80 min under C. After the reaction is completed, add naphthalene as an internal standard and quantitatively analyze by Shimadzu 2010 Plus gas chromatography. The conversion rate of 2,5-hexanedione is 99.0%, and the yield of 2,5-dimethyltetrahydrofuran is 92.0%.

[0047] The implementation manners of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the present invention.

Claims

1. A method for preparing 2,5-dimethyltetrahydrofuran, characterized in that: Using 2,5-hexanedione as a raw material, an alcohol as a reaction solvent and a reducing agent, and a metal salt as a catalyst, the reaction was carried out in a closed reactor under a certain temperature condition in a non-hydrogen atmosphere for a certain time, achieving the highly selective synthesis of 2,5-dimethyltetrahydrofuran; The metal salt includes any one of La(OTf)3, In(OTf)3, Y(OTf)3, Lu(OTf)3, Yb(OTf)3, Sc(OTf)3, ScCl3, and Sc(NO3)3.

2. The method according to claim 1, wherein The reactors used include a microwave pressure reactor and a cartridge high-pressure reactor.

3. The method according to claim 2, wherein The reactor used is a microwave pressure reactor.

4. According to the method described in claim 1, the molar ratio between the catalyst and the reactant is 0.025 - 0.

1.

5. The method according to claim 1, characterized in that The solvent used is any one of methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, and cyclohexanol.

6. The method according to claim 1, wherein The temperature used is in the range of 140 - 180 °C.

7. The method according to claim 1, wherein The time used is in the range of 20 - 100 min.

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