A method for photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones

Abstract

The present invention discloses a method for photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones. The method uses water-soluble cadmium sulfide quantum dots doped with proline as a photocatalyst, and biomass platform small molecule furfural and its derivatives and aldehydes / ketones as substrates, aiming to achieve photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones in an aqueous phase system. The photocatalyst of the present invention is synthesized using cheap and easily available raw materials by a simple and easy-to-operate experimental method. This photocatalytic reaction does not require the use of noble metal materials as co-catalysts, and can achieve dehydration condensation to construct C═C under mild conditions. The products can be applied in fields such as spices and aviation fuel.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic organic synthesis, and particularly relates to a method for realizing the aldol condensation reaction of biomass platform small molecules furfural and its derivatives with aldehydes / ketones by using quantum dots as photocatalysts. Background Art

[0002] In recent years, with the continuous development of the economy, fossil energy has been consumed in large quantities, bringing with it the problems of energy shortage and environmental pollution. To solve this problem, people have turned their attention to various renewable clean energies to replace fossil energy. Among them, biomass energy, as the only non-fossil renewable carbon resource, has received extensive attention. Biomass energy is an environmentally friendly and rich in reserves renewable resource that can be converted into many biomass platform small molecules. The upgrading of biomass is an important means for the future production of fuels and chemicals using renewable resources. As the main component of plant biomass, selectively activating specific chemical bonds in lignocellulose and its platform molecules under mild conditions to prepare high-value chemicals is the key to the efficient conversion and utilization of biomass. However, the macromolecular compounds obtained by the pyrolysis reaction of lignin generally have a high oxygen content, while the small molecular compounds with a low carbon number cannot meet the requirements for a high carbon number in production applications. How to achieve carbon chain growth of biomass platform small molecules under mild conditions is a hot topic of concern. As an important C-C coupling process capable of growing carbon chains, the aldol condensation reaction can increase the carbon chain of some intermediate products that can undergo aldol condensation reactions, such as carbonyl products, through C-C coupling, so that the biomass platform small molecules can meet the carbon number requirements for bio-aviation fuel, spices, etc.

[0003] The aldol condensation reaction generally can proceed under base catalysis or acid catalysis. Yang et al. first demonstrated the synthesis of alkanes in the aviation fuel range from furfural, 2-pentanone, and 2-heptanone obtained from lignocellulose. Through the aldol condensation of furfural with 2-pentanone (or a mixture of 2-pentanone and 2-heptanone) on the basic catalyst CaO, and then further hydrodeoxygenation on a palladium catalyst, alkanes with C9 - C (Green Chem. 2014, 16, 4879 - 4884) can be obtained at a relatively high total carbon yield (about 80%). However, the previous condensation step requires reaction at a high temperature of 403K for 6h in the presence of a basic metal catalyst, and the specific surface area of the solid base is small and it is relatively easy to precipitate. To solve this problem, people have begun to study catalysts with unique shape selectivity and containing acid-base sites. For example, Fang et al. applied zirconium-doped aluminophosphate (ZrAPO-5) to the effective synthesis of diesel and jet fuel series C 12 from biomass-derived furfural (FF) and cyclohexanone (CH). 11 C 12 and C 16Intermediate. Introducing Zr into the APO-5 framework promoted the adsorption of the substrate to the C=O double bond group and generated more and stronger acidic and basic sites, which jointly catalyzed the aldol condensation reaction and promoted the product yield (Appl. Catal. B Environ. 2023, 320, 121936). However, disadvantages such as difficult adjustment of surface acid-base properties, low catalytic efficiency, and harsh reaction conditions seem to greatly limit their practical applications. All these research reports require the condensation conversion of biomass platform small molecule furfural and ketone to be achieved through noble metals or metals and high-temperature thermal reactions.

[0004] Solar energy, as an inexhaustible and clean energy source, has received extensive attention. By using a suitable photocatalyst, the separation and transmission of photoinduced carriers can be achieved, thereby catalyzing the occurrence of chemical reactions. Moreover, photocatalytic reactions are cleaner and milder than thermal catalysis. By regulating the bandgap of the photocatalyst, different types of reactions can be selectively catalyzed to achieve effects that cannot be achieved by thermal catalysis. Currently, there are research reports that under the condition of the presence of light, the condensation reactions of aromatic aldehydes and ketones, and aldehydes and alcohols can be catalyzed. For example: In 2014, the Kang Zhenhui research group synthesized carbon quantum dots by electrochemical etching method. Under visible light irradiation, the hydrogen bond catalytic activity of CDs can be significantly enhanced and C=O can be activated, showing excellent photo-enhanced catalytic aldol condensation reaction between acetone and aromatic aldehydes. After reacting for 24 h at room temperature in a pure organic solvent, the yield can reach 89.4% (ACS Catal. 2014, 4, 781 - 787); In 2018, the Vijai K. Rai research group, under visible light conditions, used methanol as the carbon source substrate and solvent, and in the presence of the catalyst Cu@g-C3N4, methanol was in-situ oxidized to formaldehyde and reacted with aryl ketones at room temperature. α-β unsaturated carbonyl compounds could be formed in 4 - 8 h, and the yield was as high as 84% - 97% (Adv. Synth. Catal. 2019, 361, 1247 - 1252); In 2022, the Jon R. Parquette research group demonstrated that Pro-Lys dipeptide self-assembled into catalytic nanosheets promoting the Aldol reaction in a dissipative manner in the presence of visible light. Under light irradiation, due to the photoisomerization of the o-protonated (1-MCH+) form to the spiropyran (1-SP) state and rapid assembly into nanosheets capable of promoting proline-catalyzed aldol reactions in water (Nanoscale, 2022, 14, 14711 - 14716). These reports only achieved the catalysis of aromatic aldehydes and ketones or aldehydes and alcohols under light irradiation. Some of them require a long reaction time, some need to be in a pure organic system, and the catalyst also contains metals, and there is still room for improvement in terms of environmental friendliness and efficiency; However, there is no relevant report on the high-efficiency conversion of biomass platform small molecule furfural and its derivatives with aldehydes / ketones in the aqueous phase to obtain products with practical applications in production and life. SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a method for photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones without high temperature and high pressure conditions by using cheap and easily available quantum dots as catalysts.

[0006] For the above object, the technical solution adopted by the present invention is: adding water-soluble cadmium sulfide quantum dots doped with proline, a base, an electron sacrificial agent, furfural or its derivative shown in Formula I into a transparent reactor containing water, and adding an aldehyde or ketone shown in Formula II, or adding a ketone shown in Formula IV, mixing evenly, under the protection of an inert gas or in a vacuum condition, irradiating the reactor with visible light having a wavelength of 380 - 780 nm to achieve the dehydration condensation reaction of furfural or its derivative with an aldehyde or ketone. After the reaction is complete, through purification, the condensation products shown in Formula III and V are obtained correspondingly;

[0007]

[0008] In the formula, R1 represents any one of hydrogen, hydroxymethyl, C1 - C4 alkyl, C1 - C4 alkoxy, halogen, trifluoromethyl, acetoxy, nitro, and phenoxy; Formulas II and IV represent aliphatic or aromatic aldehydes / ketones having at least two α-H on at least one side, wherein R2, R3, R4, R5, R6, R7, R8, and R9 each independently represent any one of hydrogen, C1 - C8 alkyl, phenyl, halogen, C1 - C4 alkoxy, nitro, and trifluoromethyl.

[0009] In the above method, preferably, the molar ratio of furfural or its derivative to the aldehyde or ketone is 1:15 - 1:60.

[0010] In the above method, the water-soluble cadmium sulfide quantum dots doped with proline are cadmium sulfide quantum dots modified with 11-mercaptoundecanoic acid doped with proline, wherein the doping amount of proline is 5 to 15 times the molar amount of cadmium sulfide. The average particle size of the water-soluble cadmium sulfide quantum dots doped with proline is 2 to 7 nm, and the ratio of the added mass thereof to the molar amount of furfural or its derivative is 5 to 15 mg: 1 mmol. The preparation method of the water-soluble cadmium sulfide quantum dots doped with proline refers to the synthesis method of 11-mercaptoundecanoic acid modified cadmium sulfide quantum dots (MUA-CdS QDs) reported in "Catal. Sci. Technol., 2020, 10, 2821-2829", and only proline needs to be added to the reaction system. The specific preparation method is as follows: In an N2 atmosphere, CdCl2 is dissolved in distilled water, then proline and 11-mercaptoundecanoic acid are added, and the pH is adjusted to 7 with 1 mol / L aqueous NaOH solution. After the solution changes from colorless to a white turbid liquid and then to a colorless transparent solution, a 0.1 mol / L aqueous Na2S solution is added to the system, and the mixture is refluxed at 100 °C for 4 to 6 hours. After the reaction is completed, a clear orange-yellow solution is obtained. The excess water is removed by rotary evaporation, and the product is repeatedly centrifuged and washed with isopropanol 2 to 3 times to obtain an orange-yellow solid, that is, the water-soluble cadmium sulfide quantum dots doped with proline; wherein the added amount of 11-mercaptoundecanoic acid is 0.5 to 2 times the molar amount of CdCl2, the added amount of Na2S is 0.8 to 1.2 times the molar amount of CdCl2, and the added amount of proline is 5 to 15 times the molar amount of CdCl2.

[0011] In the above method, the base is any one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate. Preferably, the added amount of the base is 2 to 6 times the molar amount of furfural or its derivative.

[0012] In the above method, the electron sacrificial agent is any one of methanol, isopropanol, triethylamine, triethanolamine, and Hans ester. Preferably, the volume ratio of the electron sacrificial agent to water is 1:3 to 2:1.

[0013] In the above method, it is preferable that the reactor is irradiated with visible light having a wavelength of 380 to 780 nm for 1.5 to 2 hours.

[0014] The beneficial effects of the present invention are as follows:

[0015] The present invention uses water-soluble cadmium sulfide quantum dots doped with proline as a photocatalyst, adjusts the alkalinity of the system using potassium hydroxide or sodium hydroxide, etc., and uses triethylamine, triethanolamine, methanol, isopropanol or Hantzsch ester, etc. to provide the electrons required by the system, and conducts visible light-driven aldol condensation reactions of biomass platform small molecule furfural and its derivatives with aldehydes / ketones in an aqueous phase system. The present invention realizes the Aldol dehydration condensation reaction of furfural and its derivatives with aldehydes / ketones under photocatalytic conditions, uses solar energy, a clean energy source, to replace thermal reactions, has simple and easy-to-operate reaction conditions, is environmentally friendly, and can achieve good yields after 1.5 to 2 hours of light irradiation. Each component used in the photocatalytic organic small molecule system of the present invention is cheap and easily available. The selected aldehydes / ketones also act as organic solvents in the system while serving as reactants, eliminating the need for additional organic solvents, complex synthesis and purification, and having high photocatalytic conversion efficiency. At the same time, no noble metals such as platinum and rhodium are required as cocatalysts, and it can be applied to actual production, providing a new method for the conversion and utilization of biomass platform molecules. Description of the Drawings

[0016] Figure 1 is the 1H NMR spectrum of 4-(2-furyl)-3-buten-2-one in Example 1.

[0017] Figure 2 is the 13C NMR spectrum of 4-(2-furyl)-3-buten-2-one in Example 1.

[0018] Figure 3 is the 1H NMR spectrum of 4-[5-(hydroxymethyl)-2-furyl]-3-buten-2-one in Example 2.

[0019] Figure 4 is the 13C NMR spectrum of 4-[5-(hydroxymethyl)-2-furyl]-3-buten-2-one in Example 2.

[0020] Figure 5 is the 1H NMR spectrum of 2-furylacrolein in Example 3.

[0021] Figure 6 is the 13C NMR spectrum of 2-furylacrolein in Example 3.

[0022] Figure 7 is the 1H NMR spectrum of 1-(2-furyl)-1-hexen-3-one in Example 4.

[0023] Figure 8 is the 13C NMR spectrum of 1-(2-furyl)-1-hexen-3-one in Example 4.

[0024] Figure 9 is the 1H NMR spectrum of 6-(2-furylmethylene)-3,5,5-trimethyl-2-cyclohexen-1-one in Example 5.

[0025] Figure 10 It is the carbon-13 NMR spectrum of 6-(2-furfurylidene)-3,5,5-trimethyl-2-cyclohexen-1-one in Example 5. Detailed implementation manners

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments only.

[0027] The preparation method of the water-soluble cadmium sulfide quantum dots doped with proline used in the following examples is as follows: In an N2 atmosphere, CdCl2·H2O (114.7 mg, 0.57 mmol) is dissolved in 100 mL of distilled water. Proline (575 mg, 5 mmol) is added to the above solution, and then 11-mercaptoundecanoic acid (67.5 mg, 0.3 mmol) is added. Subsequently, the pH is adjusted to 7 with 1 mol / L aqueous NaOH solution. After the solution changes from colorless to a white turbid liquid and then to a colorless transparent solution, 5 mL of 0.1 mol / L aqueous Na2S solution is added to the system, and the mixture is refluxed at 100 °C for 4 h. After the reaction is completed, a clear orange-yellow solution is obtained. The excess water is removed by rotary evaporation, a large amount of isopropanol is added, and the mixture is centrifuged and washed twice to obtain an orange-yellow solid, namely the water-soluble cadmium sulfide quantum dots doped with proline.

[0028] Example 1

[0029]

[0030] 5 mg of water-soluble cadmium sulfide quantum dots doped with proline with an average particle size of 5 nm, 43 μL (0.5 mmol) of furfural, 1.5 mL (20.4 mmol) of acetone, 160 mg (4 mmol) of sodium hydroxide, 0.5 mL of triethylamine, and 0.5 mL of deionized water are added to a pyrex test tube and mixed evenly. The system is placed in a sealed nitrogen atmosphere and irradiated with a 420 nm LED lamp for 1.5 h. After the reaction is complete, the reaction mixture is extracted and layered with dichloromethane. The organic layer mixture is concentrated under vacuum to remove dichloromethane, and the residue is purified by column chromatography using ethyl acetate / dichloromethane = 1:1 (volume ratio) as the eluent to obtain 4-(2-furyl)-3-buten-2-one with a yield of 98%. The structure characterization data are as follows: 1 H NMR (600 MHz, CDCl3): δ 7.77 - 6.26 (m, 5H), 2.32 (d, J = 1.5 Hz, 3H), see Figure 1 ; 1313C NMR (600 MHz, CDCl3): δ 197.74, 150.87, 145.01, 129.39, 124.28, 115.62, 112.53, 27.78, see Figure 2 。

[0031] Example 2

[0032]

[0033] In this example, 51 μL (0.5 mmol) of 5-hydroxymethylfurfural was used to replace furfural in Example 1, and other steps were the same as those in Example 1, obtaining 4-[5-(hydroxymethyl)-2-furyl]-3-buten-2-one with a yield of 99%. The structure characterization data are as follows: 1 1H NMR (400 MHz, CDCl3): δ 7.41 (d, J = 15.6 Hz, 1H), 6.88 (d, J = 15.6 Hz, 1H), 6.62 (d, J = 3.4 Hz, 1H), 6.39 (d, J = 3.4 Hz, 1H), 4.76 - 3.82 (m, 3H), 2.09 (d, J = 50.9 Hz, 3H), see Figure 3 ; 13 13C NMR (400 MHz, CDCl3): δ 188.26, 156.90, 151.48, 129.27, 123.22, 117.12, 110.73, 57.74, 29.79, see Figure 4 。

[0034] Example 3

[0035]

[0036] In this example, 1.5 mL (26.8 mmol) of acetaldehyde was used to replace acetone in Example 1, and other steps were the same as those in Example 1, obtaining 2-furylacrolein with a yield of 74%. The structure characterization data are as follows: 1 1H NMR (400 MHz, CDCl3): δ 9.62 (d, J = 7.9 Hz, 1H), 7.69 - 7.14 (m, 2H), 6.89 - 6.44 (m, 3H), see Figure 5 ; 13 13C NMR (400 MHz, CDCl3): δ 192.90, 150.60, 145.93, 137.83, 126.00, 116.75, 112.89, see Figure 6 。

[0037] Example 4

[0038]

[0039] In this example, 1.5 mL (14.1 mmol) of 2-pentanone was used to replace acetone in Example 1, and the other steps were the same as those in Example 1, to obtain 1-(2-furyl)-1-hexen-3-one with a yield of 65%. The structural characterization data are as follows: 1 H NMR (300 MHz, CDCl3): δ 7.55 - 7.35 (m, 1H), 6.81 (d, J = 6.5 Hz, 1H), 6.48 - 6.45 (m, 1H), 6.06 (s, 1H), 5.30 (s, 1H), 2.35 (d, J = 32.2 Hz, 5H), 1.09 (s, 6H), see Figure 7 ; 13 C NMR (400 MHz, CDCl3): δ 200.26, 154.54, 152.40, 143.83, 127.77, 126.98, 122.19, 112.27, 112.03, 51.45, 38.83, 33.40, 28.57, see Figure 8 .

[0040] Example 5

[0041]

[0042] In this example, 1.5 mL (10.0 mmol) of isophorone was used to replace acetone in Example 1, and the other steps were the same as those in Example 1, to obtain 6-(2-furylmethylene)-3,5,5-trimethyl-2-cyclohexen-1-one with a yield of 81%. The structural characterization data are as follows: 1 H NMR (600 MHz, CDCl3): δ 7.79 - 7.09 (m, 2H), 6.74 - 5.11 (m, 3H), 2.58 (t, J = 7.4 Hz, 2H), 1.69 (d, J = 14.8 Hz, 2H), 0.96 (t, J = 7.4 Hz, 3H), see Figure 9 ; 13 C NMR (400 MHz, CDCl3): δ 199.99, 151.13, 144.78, 128.43, 123.44, 115.45, 112.47, 43.24, 17.80, 13.79, see Figure 10 .

Claims

1. A method for photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones, characterized in that: Add the water-soluble cadmium sulfide quantum dots doped with proline, a base, an electron sacrificial agent, furfural or its derivative shown in Formula I, and an aldehyde or ketone shown in Formula II, or a ketone shown in Formula IV into a transparent reactor containing water, and add an aldehyde or ketone shown in Formula II, or a ketone shown in Formula IV. Mix them evenly. Under the protection of an inert gas or in a vacuum condition, irradiate the reactor with visible light having a wavelength of 380 - 780 nm to achieve the dehydration condensation reaction of furfural or its derivative with the aldehyde or ketone. After the reaction is complete, through purification, the condensation products shown in Formula III and V are obtained correspondingly; In the formula, R1 represents any one of hydrogen, hydroxymethyl, C1 - C4 alkyl, C1 - C4 alkoxy, halogen, trifluoromethyl, acetoxy, nitro, and phenoxy; R2, R3, R4, R5, R6, R7, R8, and R9 each independently represent any one of hydrogen, C1 - C8 alkyl, phenyl, halogen, C1 - C4 alkoxy, nitro, and trifluoromethyl; The water-soluble cadmium sulfide quantum dots doped with proline are cadmium sulfide quantum dots modified with 11-mercaptoundecanoic acid doped with proline, wherein the doping amount of proline is 5 - 15 times the molar amount of cadmium sulfide; The water-soluble cadmium sulfide quantum dots doped with proline are prepared by the following method: In an N2 atmosphere, dissolve CdCl2 in distilled water, then add proline and 11-mercaptoundecanoic acid, adjust the pH to 7 with 1 mol / L aqueous NaOH solution. Wait until the solution changes from colorless to a white turbid liquid and then to a colorless transparent solution, and then add 0.1 mol / L aqueous Na2S solution to the system. Reflux at 100 °C for 4 - 6 hours. After the reaction is completed, a clear orange-yellow solution is obtained. Spin out the excess water and repeat centrifugal washing with isopropanol 2 - 3 times to obtain an orange-yellow solid, which is the water-soluble cadmium sulfide quantum dots doped with proline; wherein the addition amount of 11-mercaptoundecanoic acid is 0.5 - 2 times the molar amount of CdCl2, the addition amount of Na2S is 0.8 - 1.2 times the molar amount of CdCl2, and the addition amount of proline is 5 - 15 times the molar amount of CdCl2; The electron sacrificial agent is any one of methanol, isopropanol, triethylamine, triethanolamine, and Hantzsch ester.

2. The method for dehydrative condensation of photocatalytic biomass platform small molecule furfural and its derivatives with aldehyde / ketone according to claim 1, wherein: The molar ratio of the furfural or its derivative to the aldehyde or ketone is 1:15 - 1:

60.

3. The method for photocatalytic dehydration condensation of small molecule furfural and its derivatives with aldehyde / ketone according to claim 1, characterized in that: The average particle size of the water-soluble cadmium sulfide quantum dots doped with proline is 2 - 7 nm, and the ratio of the added mass to the molar amount of the furfural or its derivative is 5 - 15 mg:1 mmol.

4. The method for dehydrative condensation of photocatalytic biomass platform small molecule furfural and its derivatives with aldehyde / ketone according to claim 1, characterized in that: The base is any one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate.

5. The method for dehydration condensation of photocatalytic biomass platform small molecule furfural and its derivatives with aldehyde / ketone according to claim 4, characterized in that: The addition amount of the base is 2 - 8 times the molar amount of the furfural or its derivative.

6. The method for photocatalytic dehydration condensation of biomass platform small molecule furfural and its derivatives with aldehydes / ketones according to claim 1, characterized in that: The volume ratio of the electron sacrificial agent to water is 1:3 - 2:

1.

7. The method for dehydrative condensation of photocatalytic biomass platform small molecule furfural and its derivatives with aldehyde / ketone according to claim 1, characterized in that: Irradiate the reactor with visible light having a wavelength of 380 - 780 nm, and the irradiation time is 1.5 - 2 hours.

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