Method for synthesizing 2, 5-furandicarboxylic acid based on catalytic oxidation of 5-hydroxymethylfurfural by iridium nano-enzyme

Abstract

The invention belongs to the field of enzyme catalysis, and provides a method for synthesizing 2, 5-furandicarboxylic acid (FDCA) based on catalytic oxidation of 5-hydroxymethylfurfural (HMF) by iridium nano-enzyme. The iridium nano-enzyme is synthesized by taking an organic small molecule containing hydroxyl and / or carboxyl and having a carbon chain length of C3-C6 as a ligand, taking iridium trichloride (IrCl3) as a precursor and taking sodium borohydride (NaBH4) as a reducing agent. Under the conditions of weak acidity and hydrogen peroxide (H2O2) as an oxidizing agent, the iridium nano-enzyme can catalyze HMF to oxidize and synthesize FDCA, the substrate conversion rate is up to 100%, and the product yield is about 90%. According to the method, the iridium nano-enzyme with excellent catalytic activity is synthesized by taking the small organic molecules containing hydroxyl and / or carboxyl and with the carbon chain length of C3-C6 as the ligand, the FDCA is synthesized by selectively oxidizing molar-level HMF under a weak acid condition, the substrate conversion rate reaches 100%, the product yield is about 90%, and the method is suitable for industrial production. The method has the advantages of simple catalyst synthesis, stable catalytic performance, high substrate conversion rate and high product selectivity.

Description

Technical Field

[0001] The present invention belongs to the field of enzyme catalysis. It is characterized in that under weakly acidic conditions, iridium nanozyme with peroxidase activity is used to catalyze the oxidation of H2O2 to selectively synthesize 2,5-furandicarboxylic acid (FDCA) from molar 5-hydroxymethylfurfural (HMF). Background Art

[0002] FDCA is an ideal substitute for terephthalic acid (a petroleum derivative and a precursor for producing plastics) for producing degradable plastics, reducing the dependence on petroleum resources in the polyester field and reducing plastic pollution to the environment. Therefore, the synthesis of FDCA has high value and significance. Among them, the synthesis of FDCA by oxidizing HMF is considered a simple and effective route because it only involves the conversion of functional groups. However, the process of synthesizing FDCA by oxidizing HMF involves multiple intermediates, and its selective oxidation has become a difficult point. Although many methods already have high selectivity, most studies usually use a substrate amount of 10 mmol or even less, and high-concentration alkali is also required, while an alkaline environment will produce highly colored humins and other by-products. Therefore, it is a task of great significance to catalytically oxidize molar HMF to selectively synthesize FDCA using a catalyst in a base-free medium.

[0003] Although James A. Dumesic et al. synthesized FDCA by catalytically oxidizing HMF with metal salts in a base-free medium, in order to promote the mass transfer rate of O2 in the reaction, it is necessary to increase the pressure, which may pose a safety hazard. In addition, they did not make corresponding descriptions about the recyclability of the catalyst. Using H2O2 as the oxidant can avoid the safety hazard brought by pressurization. However, most metal catalysts have poor catalytic performance in catalytically oxidizing HMF under base-free conditions and are difficult to meet the requirements of actual production. Summary of the Invention

[0004] Based on the above problems, the present application uses iridium nanozyme with peroxidase activity as the catalyst and hydrogen peroxide as the oxidant to catalytically convert molar 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA). This method has the advantages of an HMF conversion rate of about 100%, an FDCA yield of about 90%, and strong catalyst cycle stability. A method for catalytically oxidizing 5-hydroxymethylfurfural with iridium nanozyme to synthesize 2,5-furandicarboxylic acid, the method comprising: dispersing iridium nanozyme in an aqueous solution of 5-hydroxymethylfurfural, adjusting the pH to 2-10, heating to 30-100 °C; adding 0.025 mmol - 0.25 mmol of H2O2 every half hour; after the reaction ends for 24 h, adding an alkali solution to the reaction solution, centrifuging to separate the catalyst; adjusting the reaction solution to be acidic, and collecting the reaction product;

[0005] The synthesis method of the iridium nanozyme comprises the following steps:

[0006] Step S11, dissolving an organic small molecule containing a hydroxyl group and / or a carboxyl group and having a carbon chain length of C3-C6 in deionized water; the organic small molecule containing a hydroxyl group and / or a carboxyl group and having a carbon chain length of C3-C6 is lactic acid, succinic acid, malic acid, tartaric acid, tetrahydrofurfural, citric acid, or ascorbic acid;

[0007] Step S12, adding IrCl3 to adjust the pH of the solution;

[0008] Step S13, heating the solution to a desired temperature;

[0009] Step S14, add NaBH4, stir evenly, turn off heating and stirring, and let it stand and cool to room temperature;

[0010] Step S15: washing by centrifugation, collecting the precipitate, and drying to obtain the iridium nanozyme.

[0011] In one embodiment, the pH of the solution in step S12 is adjusted to a range of 6 to 11.

[0012] In one embodiment, the reaction temperature in step S13 is in the range of 50-100°C.

[0013] In one embodiment, the drying temperature in step S15 is 60°C.

[0014] In one embodiment, in the method for synthesizing 2,5-furandicarboxylic acid based on the catalytic oxidation of 5-hydroxymethylfurfural by iridium nanozyme, the pH is adjusted to 4; the heating temperature is 100° C.; and 0.25 mmol H2O2 is added every half hour.

[0015] Beneficial effects:

[0016] This method uses iridium nanozymes to catalyze the oxidation of HMF to synthesize FDCA. Its innovation lies in the use of nanozymes as catalysts to achieve molar-scale selective oxidation of HMF to synthesize FDCA under weak acidity. The substrate conversion rate and product yield of the reaction reached ~100% and ~90%, respectively. This not only expands the application of nanozymes in organic synthesis, but also provides a new idea for the synthesis of FDCA under acidic conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 (a) TEM image, (b) size distribution, (c) XRD pattern, and (d) FT-IR pattern of iridium nanozymes.

[0018] Figure 2 (a) pH optimization and (bd) kinetic characterization of the POD-like activity of iridium nanozymes.

[0019] Figure 3 (a) Influence of temperature on the activity of iridium nanozyme; (b) Storage stability test of iridium nanozyme.

[0020] Figure 4 (a - b) Initial pH of the reaction, (c - d) Dosage of H2O2, and (e - f) Reaction temperature on the oxidation of HMF catalyzed by iridium nanozyme.

[0021] Figure 5 (a) 1 1H NMR (400 MHz, DMSO - d6) δ 7.28; (b) 13 13C NMR (400 MHz, DMSO - d6) δ 158.9, 147.1, 118.3.

[0022] Figure 6 Cyclic stability test of iridium nanozyme. Specific implementation mode

[0023] To make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation mode of the present invention will be described in detail below in combination with the embodiments of the specification.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0025] Secondly, the so - called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that can be included in at least one implementation mode of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selectively exclusive embodiments from other embodiments.

[0026] Example 1: Synthesis of FDCA catalyzed by iridium enzyme

[0027] (1) Synthesis of enzyme catalyst: Aqueous solutions of tartaric acid (TA, 400 mM, 500 μL) and IrCl3 (2 mM, 10 mL) were separately added to 37 mL of deionized water, and the pH was adjusted to about 6.0 with NaOH solution. After the reaction solution was heated to 100 °C, a newly prepared solution of NaBH4 (200 mM, 2 mL) was added to the mixture and stirred evenly (~2 min), then heating and stirring were stopped. After the mixture was cooled to room temperature, an appropriate amount of isopropanol was added as a precipitant, and it was centrifuged and washed at ~8500 r·min-1, and the precipitate was collected and dried at 60 °C to obtain TA-coated iridium nanozyme. TA was replaced with malic acid, succinic acid, ascorbic acid, etc., and the corresponding iridium nanozymes (TA-Ir) were synthesized according to the same steps.

[0028] (2) Oxidation of HMF: 4 mg of the iridium nanozyme obtained in (1) was dispersed in a 10 mL vial containing 4 mL of 0.5 M HMF solution, and the pH was adjusted to ~4 with H2SO4. The vial was placed in an oil bath at 100 °C, and 25 μl of 30% H2O2 was added every half hour, and the reaction was carried out for 24 h. The pH, temperature and H2O2 dosage of the reaction were optimized according to the same steps.

[0029] We characterized the structure of the iridium nanozyme by transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy. As Figure 1 shown in a-b, the TA-Ir nanozyme is an interconnected nanochain with a particle size of about 1.98±0.39 nm. Figure 1 The XRD pattern in c shows that the crystal planes of the TA-Ir nanozyme contain {111}, {200}, {220} and {311}. Infrared characterization proved the presence of ligands on the surface of the iridium nanozyme ( Figure 1 d). These results proved that we successfully prepared the TA-Ir nanozyme. Figure 2 The enzyme activity test proved that the TA-Ir nanozyme has peroxidase activity. In the reaction system of catalyzing H2O2 and 3,3,5,5-tetramethylbenzidine (TMB), the maximum reaction rate was 35.51×10-5 mM / s, and the affinity for H2O2 was 1.48 mM. In addition, appropriate heating can improve the peroxidase activity of the TA-Ir nanozyme, and the enzyme activity of the TA-Ir nanozyme did not decrease significantly after being stored for 1 month ( Figure 3 ).

[0030] We optimized the catalytic oxidation conditions of HMF using TA-Ir nanozyme as the catalyst and H2O2 as the oxidant. The results showed that under the conditions of pH 4, temperature of 100 °C and 0.25 mM H2O2 added each time, the conversion rate of HMF and the yield of FDCA reached ~100% and ~90% respectively ( Figures 4 - 5 ). Figure 6It shows that TA-Ir nanozyme has good recyclability in the catalytic oxidation of HMF.

[0031] In summary, this application provides a method for synthesizing FDCA by catalytic oxidation of HMF based on iridium nanozyme. This method not only has simple synthesis operation and stable catalytic performance of the catalyst, but also the catalyst can catalyze the oxidation of molar-level HMF by H2O2 to selectively synthesize FDCA under weak acidity. The substrate concentration of the catalytic reaction is as high as molar level, the conversion rate reaches ~100%, and the product yield reaches ~90%.

[0032] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for synthesizing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural based on iridium nanozyme, characterized in that, Using an iridium nanozyme with peroxidase activity as a catalyst and hydrogen peroxide as an oxidant, catalytically convert molar amounts of HMF into FDCA selectively; the specific method is as follows: Disperse the iridium nanozyme in an aqueous solution of 0.5 M 5-hydroxymethylfurfural, adjust the pH to 2-10, and heat to 30-100 °C; add 0.025 mmol to 0.25 mmol of H2O2 every half hour; after the reaction ends after 24 h, add an alkali solution to the reaction solution, and centrifuge to separate the catalyst; adjust the reaction solution to be acidic, and collect the reaction product; the iridium nanozyme is an interconnected nanochain with a diameter of 2.0 nm. [[ID=Y1]]The synthesis method of the iridium nanozyme includes the following steps: [[ID=Y2]]Step S11: Dissolve an organic small molecule containing a hydroxyl group and / or a carboxyl group and having a carbon chain length of C3-C6 in deionized water; the organic small molecule containing a hydroxyl group and / or a carboxyl group and having a carbon chain length of C3-C6 is lactic acid, succinic acid, malic acid, tartaric acid, pentaerythritol, citric acid or ascorbic acid. [[ID=Y3]]Step S12: Add IrCl3 and adjust the pH of the solution. [[ID=Y4]]Step S13: Heat the solution to the required temperature. [[ID=Y5]]Step S14: Add NaBH4, stir evenly, turn off heating and stirring, and let it stand and cool to room temperature. [[ID=Y6]]Step S15: Collect the precipitate by centrifugal washing, and dry to obtain the iridium nanozyme.

2. A method for synthesizing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural based on iridium nanozyme according to claim 1, characterized in that, [[ID=Y7]]The reaction ratio of the ligand, metal ion and reducing agent used is 1:10:

10.

3. A method for synthesizing 2,5-furandicarboxylic acid by catalyzing the oxidation of 5-hydroxymethylfurfural based on iridium nanozyme according to claim 1, characterized in that, [[ID=Y8]]In step S12, the pH of the solution is adjusted in the range of 6-11.

4. A method for synthesizing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural based on iridium nanozyme according to claim 1, wherein [[ID=Y9]]The reaction temperature range in step S13 is 50-100 °C.

5. A method for synthesizing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural based on iridium nanozyme according to claim 1, characterized in that, [[ID=Y10]]In the method for synthesizing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural with an iridium nanozyme, the pH is adjusted to 4; the heating temperature is 100 °C; 0.25 mmol of H2O2 is added every half hour.

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