Method for synthesizing butanol from ethanol

Abstract

The invention discloses a method for synthesizing butanol from ethanol through a metal-ligand bifunctional iridium catalyst.Butanol serves as long-chain alcohol, the energy density of the butanol is close to that of gasoline (86%), the butanol is not mixed and dissolved with water, and therefore the butanol is considered to be more ideal biofuel than ethanol, and although the butanol has huge potential, the butanol can be used for preparing the butanol. However, large-scale preparation of butanol is still a challenging problem. So far, the best report of batch synthesis of butanol from raw materials through an ABE fermentation process is only 16% of butanol yield (byproducts include a mixture of acetone, butanol and ethanol). The conventional synthesis method has obvious limitation. In particular they require an inorganic strong base (NaOMe) or a nickel or copper complex as the base. From the perspective of sustainable chemistry, development of a novel catalytic system is very desirable to convert ethanol into n-butanol under a more environment-friendly condition.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic chemistry, and in particular relates to a method for synthesizing butanol from ethanol. Background Art

[0002] Biofuels from renewable biomass have attracted much attention as green alternatives to gasoline. (a) Ragauskas, AJ; Williams, CK; Davison, BH; Britovsek, G.; Cairney, J.; Eckert, CA; Frederick, WJ; Hallett, JP; Leak, DJ; Liotta, CL; Mielenz, JR; Murphy, R.; Templer, R.; Tschaplinski, T. Science 2006, 311, 484-489. (b) Sreekumar, S.; Balakrishnan, M.; Goulas, K.; Gunbas, G.; Gokhale, AA; Louie, L.; Grippo, A.; Scown, CD; Bell, AT; Toste, FD ChemSusChem 2015, 8, 2609-2614. (c) Wu, L.; Moteki, T.; Gokhale, AA; Flaherty, DW; Toste, FD Chem 2016, 1, 32-58. Ethanol is obtained from the fermentation of sugary crops and is widely used as a renewable biofuel. However, Sheehan, J.; Aden, A.; Paustian, K.; Killian, K.; Brenner, J.; Walsh, M.; Nelson, RJ Ind. Ecol. 2003, 7, 117-146. There are several disadvantages to using ethanol instead of gasoline. For example, the energy density of ethanol is only 70% of that of gasoline, and it can corrode the engine. (a) Diirre, P. Biotechnol. J. 2007, 2, 1525-1534. (b) Harvey, BG; Meylemans, HAJ Chem. Technol. Biotechnol. 2011, 86, 2-9. In addition, ethanol easily absorbs water, which easily causes separation, storage and transportation problems. In addition, butanol, as a long-chain alcohol, has an energy density close to gasoline (86%) and is not miscible with water, so it is considered to be a more ideal biofuel than ethanol.(a) Szulczyk, KRInt. J. Energy Environ. 2010, 1, 501-512. (b) Runge, W. Technology entrepreneurship: a treatise on entrepreneurs and entrepreneurship for and in technology ventures; KIT scientific publishing: Mannheim, 2014, Vol. 2, p. 1057. Despite its great potential, large-scale preparation of butanol remains a very challenging problem. So far, the best report on the batch synthesis of butanol from raw materials by ABE fermentation process has only a 16% butanol yield (byproducts include a mixture of acetone, butanol and ethanol). (a) Jin, C.; Yao, M.; Liu, H.; Lee, CF; Ji, J. Renewable Sustainable Energy Rev. 2011, 15, 4080-4106. (b) Anbarasan, P.; Baer, ​​ZC; Sreekumar, S.; Gross, E.; Binder, JB; Blanch, HW; Clark, DS; Toste, FDNature 2012, 491, 235-239.

[0003] Based on the transition metal-catalyzed hydrogen self-transfer process or hydrogen borrowing strategy, the Guerbet reaction has become a promising strategy for the generation of long-chain alcohols from short-chain alcohols. (a) Gabriels, D.; Hernandez, WY; Sels, B.; Van DerVoort, P.; Verberckmoes, Catal. Sci. Technol. 2015, 5, 3876-3902. (b) Dobereiner, GE; Crabtree, RH Chem. Rev. 2010, 110, 681-703. (c) Guillena, G.; Ramon, D.; Yus, M. Chem. Rev. 2010, 110, 1611-1641. (d) C Orma, A.; Navas, J.; Sabater, M. J. Chem. Rev. 2018, 118, 1410-1459. (e) Irrgang, T.; Kempe, R. Chem. Rev. 2019, 119, 2524-2549. In this process, short-chain alcohols are first dehydrogenated to form the corresponding aldehydes, while metal hydrides are generated, followed by base-catalyzed cross-condensation between aldehydes to produce unsaturated aldehydes, which are then subjected to transfer hydrogenation reactions of metal hydrides to form long-chain alcohols. However, the yield of n-butanol prepared by the Guerbet reaction is low and the selectivity is poor, because the thermodynamics of ethanol dehydrogenation during the reaction are unfavorable, the aldol condensation is uncontrolled, and highly reactive acetaldehyde is involved.

[0004] In recent decades, the research groups of Ishii, Wass, Jones, Szymczak, Milsterin, and Liu have independently developed several catalytic systems for converting ethanol to n-butanol using iridium, ruthenium, or manganese complexes. (a) Koda, K.; Matsu-ura, T.; Obora, Y.; Ishii, Y. Chem. Lett. 2009, 38, 838-839. (b) Dowson, GRM; Haddow, MF; Lee, J.; Wingad, RL; Wass, DF; Angew. Chem. Int. Ed. 2013, 52, 9005-9008. (c) Chakraborty, S.; Piszel, PE; Hayes, CE; Baker, RT; Jones, WD; Am. Chem. Soc. 2015, 137, 14264- 14267. (d) Tseng, K.-NT; Lin, S.; Kampf, JW; Szymczak, NK Chem. Commun. 2016, 52, 2901-2904. (e) Xie, Y.; Ben-David, Y.; Shimon, LJW; Milstein, DJ Am. Chem. Soc. 2016, 138, 9077-9080. (f) Fu, S.; Shao, Z.; Wang, Y.; Liu, QJ Am. Chem. Soc. 2017, 139, 11941-11948. However, these methods have obvious limitations. In particular, they require strong inorganic bases (NaOMe) or nickel or copper complexes as bases. From the perspective of sustainable chemistry, it is highly desirable to develop a new catalytic system to convert ethanol to n-butanol under more environmentally friendly conditions. Summary of the invention

[0005] The object of the present invention is to provide a method for synthesizing butanol from ethanol.

[0006] The present invention is achieved by the following technical scheme: a novel method for synthesizing butanol from ethanol by metal-ligand bifunctional iridium catalysis in the presence of carbonate (Formula I)

[0007]

[0008] It is a reaction (Formula II) using ethanol as a raw material

[0009]

[0010] The reaction occurs in the presence of a metal-ligand bifunctional iridium catalyst, and the general reaction formula is:

[0011]

[0012] Ethanol, a metal-ligand bifunctional iridium catalyst and a carbonate are added to a reaction container. After the reaction mixture is allowed to stand for several hours, it is cooled to room temperature to obtain a mixed solution containing butanol.

[0013] Among them, the metal-ligand bifunctional iridium catalyst has the following structure:

[0014]

[0015] The base is selected from sodium carbonate, potassium carbonate, and cesium carbonate; the molar ratio of the catalyst to ethanol is 0.1 mol%; the molar ratio of the base to ethanol is 6 mol%; 400 mg of ethanol; the reaction is carried out in a test tube at 150° C.; and the reaction time is 12 hours.

[0016] The invention discloses a method for synthesizing butanol from ethanol by using a metal-ligand bifunctional iridium complex with the participation of carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the cat.1-product H NMR spectrum;

[0018] Figure 2 It is the cat.1-product NMR carbon spectrum;

[0019] Figure 3 This is the hydrogen NMR spectrum of the product of Example 1. DETAILED DESCRIPTION

[0020] Show examples to illustrate certain embodiments of the present invention, and should not be construed as limiting the scope of the present invention. Many improvements, changes and variations can be made to the disclosed content of the present invention from materials, methods and reaction conditions simultaneously. All these improvements, changes and variations all fall within the spirit and scope of the present invention for sure.

[0021] Synthesis steps of cat.1

[0022]

[0023] 2,2'-Methylenebibenzimidazole

[0024]

[0025] o-phenylenediamine (216 mg, 2 mmol), malonic acid (104 mg, 1 mmol, 0.5 equiv.), polyphosphoric acid (392 mg, 4 mmol, 2 equiv.) and ethylene glycol (8 mL) were added to a 25 mL gram tube. After reacting at 180°C for 24 hours, the mixture was cooled to room temperature. After neutralization with ammonia water, the mixture was filtered and the precipitate was washed three times with water and dried in a vacuum oven to obtain the target compound.

[0026] 2,2'-Carbonylbibenzimidazole

[0027]

[0028] 2,2′-methylenebibenzimidazole (497 mg, 2 mmol), 0.5 mL 30% hydrogen peroxide solution and 10 mL acetic acid were added into a 25 mL glove tube and reacted at room temperature for 48 hours. The mixture was cooled to room temperature and the solid was collected by filtration, washed with water and dried in a vacuum oven to obtain the target compound.

[0029] cat.1

[0030]

[0031] [Cp*IrCl 2 ] 2 (159 mg, 0.2 mmol), 2,2′-carbonylbibenzimidazole (105 mg, 0.4 mmol, 2 equiv) and 6 mL of dichloromethane solution were sequentially added into a 25 mL g tube. After reacting at 60° C. for 12 hours, the mixture was cooled to room temperature, the precipitate was filtered, washed with dichloromethane, and dried in a vacuum oven to obtain the target compound.

[0032] 1 H NMR (500 MHz, DMSO-d 6 )7.90 (d, J=8.3Hz, 2H), 7.81 (d, J=8.2Hz, 2H), 7.64 (t, J=7.6Hz, 2H), 7.58 (t, J=7.7Hz, 2H), 1.36 (s, 15H); 13 C NMR (125 MHz, DMSO-d 6 )δ168.08, 143.43, 140.92, 134.25, 127.73, 125.72, 119.90, 114.96, 88.25, 8.29.HRMS(ESI)m / zcalcd for C 25 H 26 N 4 OCl 2 Ir + (M+H) +659.1090, found 659.1086.

[0033] Cat 1 single crystal

[0034]

[0035] Crystal data is shown in the figure

[0036] X-ray structure of[Cp*Ir(2,2'-COBiBzImH 2 )Cl][Cl](thermal ellipsoidsset at 30% probability).Hydrogen atoms have been omitted for clarity.Selectedbond lengths and angles[deg]: Ir1-N1, 2.099(3); Ir1-N3, 2.104(3); Ir1-CI1, 2.3935(10); N1-Ir1-N3, 83.01(10); N1-Ir1-Cl1, 87.53(8); N3-Ir1-Cl1, 88.47(8).

[0037] The reaction principle is shown in the figure:

[0038]

[0039] The initial step of the reaction involves the production of two unsaturated species A by eliminating HCl from two cats. Then, the ligands of the two iridium species A accept the protons of two ethanol molecules to give two alkoxyiridium species B, which undergo β-hydrogen elimination to give two iridium hydride species C and two acetaldehyde molecules. In the presence of a base, a cross-aldol condensation reaction occurs between the two acetaldehyde molecules to give crotonaldehyde as an intermediate. While the ligand promotes the simultaneous transfer of two hydride ions on the iridium and the protons of the two NH groups on the two C ligands to crotonaldehyde, the two catalyzed species A are regenerated and n-butanol is released.

[0040] Embodiment 1:

[0041] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 32%.

[0042] Embodiment 2:

[0043] Ethanol (400 mg, 8.7 mmol), cat 2 (6 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 30%.

[0044] Embodiment 3:

[0045] Ethanol (400 mg, 8.7 mmol), cat 3 (5 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 26%.

[0046] Embodiment 4:

[0047] Ethanol (400 mg, 8.7 mmol), cat 4 (7 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 25%.

[0048] Embodiment 5:

[0049] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 135°C for 12 hours, the mixture was cooled to room temperature. The final yield was 29%.

[0050] Embodiment 6:

[0051] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 165°C for 12 hours, the mixture was cooled to room temperature. The final yield was 35%.

[0052] Embodiment 7:

[0053] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (170 mg, 6 mol%) were added into a 10 mL K-tube in sequence. After reacting at 180°C for 12 hours, the mixture was cooled to room temperature. The final yield was 37%.

[0054] Embodiment 8:

[0055] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (340 mg, 12 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 33%.

[0056] Embodiment 9:

[0057] Ethanol (400 mg, 8.7 mmol), cat 1 (6 mg, 0.1 mol%) and cesium carbonate (510 mg, 18 mol%) were added into a 10 mL K-tube in sequence. After reacting at 150°C for 12 hours, the mixture was cooled to room temperature. The final yield was 34%.

Claims

1. A method for synthesizing butanol from ethanol (Formula I): It is a reaction (Formula II) using ethanol as a raw material The reaction occurs in the presence of a metal-ligand bifunctional iridium catalyst, and the general reaction formula is:

2. The method for synthesizing butanol from ethanol using bifunctional iridium catalyst according to claim 1, characterized in that the catalyst It is a metal-ligand bifunctional iridium catalyst.

3. The method for synthesizing butanol from ethanol using bifunctional iridium catalyst according to claim 1, characterized in that The reaction was carried out in the presence of 6 mol % cesium carbonate.

4. The method for synthesizing butanol from ethanol using bifunctional iridium catalyst according to claim 1, characterized in that The amount of the catalyst used was 0.1 mol % relative to ethanol.

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