A furyl Schiff base and preparation method thereof

Abstract

The present invention discloses a furanyl Schiff base and a preparation method thereof, belonging to the technical field of Schiff base compounds. The structural formula of the furanyl Schiff base is shown below. The prepared furanyl Schiff base contains three benzene rings and two furan ring structures. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of Schiff base compounds, and more particularly to a furyl Schiff base and a preparation method thereof. Background Art

[0002] Schiff bases, also known as Schiff's bases, are organic compounds containing an imine or azomethine group (-RC=N-). Schiff bases are typically formed by the condensation of an amine and a reactive carbonyl group. Schiff bases and their metal complexes have important applications in medicine, catalysis, analytical chemistry, corrosion, and photochromism.

[0003] In medicine, Schiff bases exhibit antibacterial, bactericidal, anti-tumor, and antiviral biological activities. In catalysis, Schiff base complexes with cobalt, nickel, and palladium have been used as catalysts. In analytical chemistry, Schiff bases, as excellent ligands, can be used to identify and characterize metal ions and quantitatively analyze their content. In corrosion, certain aromatic Schiff bases are often used as copper corrosion inhibitors. In the field of photochromism, certain Schiff bases containing characteristic groups also have unique applications. Consequently, Schiff base compounds have garnered widespread attention from chemists and materials scientists.

[0004] Currently, the most studied Schiff bases in the literature are salicylaldehyde Schiff bases, which play an important role in antibacterial, antimicrobial and antiviral activities, but their photoelectric properties are poor. Summary of the Invention

[0005] To address these issues, the present invention uses 5-hydroxymethylfurfural and aniline as raw materials and phosphotungstic acid as a catalyst to prepare a furanyl Schiff base containing three benzene rings and two furan rings. The furanyl Schiff base prepared in this invention exhibits certain photochromic and electrochromic properties.

[0006] The first object of the present invention is to provide a furanyl Schiff base having the structural formula:

[0007]

[0008] A second object of the present invention is to provide a method for preparing the above-mentioned furanyl Schiff base, which is prepared according to the following steps:

[0009] Water is used as a solvent and 5-hydroxymethylfurfural is added to prepare a 5-hydroxymethylfurfural aqueous solution; water is used as a solvent and a heteropoly acid is added to prepare a heteropoly acid aqueous solution; the 5-hydroxymethylfurfural aqueous solution is added to the heteropoly acid aqueous solution, aniline is added under stirring, the reaction is stirred, and the obtained product is separated to obtain a furanyl Schiff base.

[0010] In a preferred embodiment, the concentration of 5-hydroxymethylfurfural in the 5-hydroxymethylfurfural aqueous solution is 0.001-0.1 g / ml, the concentration of heteropolyacid in the heteropolyacid aqueous solution is 0.001-0.005 g / ml, and the volume ratio of the 5-hydroxymethylfurfural aqueous solution to the heteropolyacid aqueous solution is 1:1.

[0011] In a preferred embodiment, the heteropolyacid is phosphotungstic acid.

[0012] In a preferred embodiment, the mass ratio of 5-hydroxymethylfurfural to aniline is 0.4-1:1.

[0013] In a preferred embodiment, the reaction temperature is 0°C-50°C, and the stirring speed is 250 r / min.

[0014] In a preferred embodiment, the reaction time of the condensation reaction and the substitution reaction is 0.5 h to 5 h.

[0015] In a preferred embodiment, the separation method is as follows: the product is centrifuged, the aqueous phase is discarded, the obtained oil phase is washed with deionized water and centrifuged again, and the process is repeated three times to remove the water-soluble matter in the oil phase; the obtained oil phase is dissolved in ethanol to obtain an ethanol solution of the product; and the product is separated by column chromatography to obtain a furanyl Schiff base.

[0016] In a preferred embodiment, the centrifugal separation speed is 10000 r / min; the aqueous phase obtained by centrifugal separation is unreacted raw materials and water-soluble by-products, and the oil phase obtained by centrifugal separation is the target product and oil-soluble by-products.

[0017] In a preferred embodiment, the column chromatography separation uses a stationary phase of grade II activated silica gel with a packing height of 15 cm;

[0018] The mobile phase used in column chromatography separation is petroleum ether, ethyl acetate or a mixture of petroleum ether and ethyl acetate; in the mixture of petroleum ether and ethyl acetate, the volume ratio of petroleum ether to ethyl acetate is 1:9-9:1.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention connects a furan group having excellent hole transport performance, photochromic or electrochromic performance with a -C=N- structure, and can design a multifunctional Schiff base.

[0021] 5-Hydroxymethylfurfural is an important platform compound formed by biomass resource conversion. Using it as a raw material in this invention improves the economic efficiency of the reaction preparation process and meets the requirements of green and sustainable development. The 5-Hydroxymethylfurfural molecule contains a furan ring, an aldehyde group, and a hydroxymethyl group, all of which have high reactivity, with the aldehyde group being more reactive than the hydroxymethyl group. When 5-Hydroxymethylfurfural reacts with aniline, the aldehyde group and the amine group undergo condensation to form an imine structure. The hydroxymethyl group, under the action of a catalyst, undergoes a substitution reaction with the amine, ultimately forming a furanyl Schiff base.

[0022] The furanyl Schiff base prepared by the invention can be used to have certain photochromic and electrochromic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a mechanism diagram of the present invention;

[0024] Figure 2 It is the ultraviolet spectra of the products of Example and Comparative Example;

[0025] Figure 3 IR spectra of the products of Examples and Comparative Examples;

[0026] Figure 4 The product of the reaction of 5-HMF and aniline in Example 1 is the furyl Schiff base 1 H-NMR;

[0027] Figure 5 The photochromic property of the product of Example 1 is shown below:

[0028] Figure 6 This is the electrochromic effect of the product of Example 1. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] The present invention uses heteropoly acid as a catalyst and 5-hydroxymethylfurfural and aniline as raw materials to prepare a furanyl Schiff base. The preparation method is as follows:

[0031] Using water as solvent, adding 5-hydroxymethylfurfural to prepare a 5-hydroxymethylfurfural aqueous solution;

[0032] Using water as solvent, adding heteropoly acid to prepare heteropoly acid aqueous solution;

[0033] The 5-hydroxymethylfurfural aqueous solution is added to the heteropoly acid aqueous solution, and aniline is added under stirring, and the reaction is stirred, and the obtained product is separated to obtain a furanyl Schiff base.

[0034] The present invention uses water as a reaction system, a heteropoly acid as a catalyst, and a biomass-based platform compound 5-hydroxymethylfurfural as a raw material to react with aniline to prepare a multifunctional Schiff base, thereby broadening the application market of biomass resources and improving the reaction system.

[0035] 5-Hydroxymethylfurfural is an important biomass-based platform compound. Its molecule contains a furan ring, an aldehyde group, and a hydroxymethyl group, all of which are highly reactive. Both the aldehyde group and the hydroxymethyl group are highly reactive, but the aldehyde group is more reactive than the hydroxymethyl group. When 5-Hydroxymethylfurfural is reacted with aniline, the aldehyde group first undergoes an aldolamine condensation reaction, which is a fast reaction. The hydroxymethyl group reacts more slowly with aniline, forming a furanyl Schiff base structure through the strong acidic catalysis of a heteropolyacid.

[0036] In some preferred embodiments, the volume ratio of the 5-hydroxymethylfurfural aqueous solution to the heteropolyacid aqueous solution is 1:1.

[0037] In the aqueous solution of 5-hydroxymethylfurfural, the concentration of 5-hydroxymethylfurfural is 0.001-0.1 g / ml;

[0038] In the heteropoly acid aqueous solution, the concentration of the heteropoly acid is 0.001-0.005 g / ml;

[0039] The product yield can be controlled and the occurrence of side reactions can be reduced by adjusting the concentration of 5-hydroxymethylfurfural in the 5-hydroxymethylfurfural aqueous solution and the concentration of the heteropoly acid in the heteropoly acid aqueous solution.

[0040] Preferably, the heteropolyacid is phosphotungstic acid or phosphomolybdic acid.

[0041] In some preferred embodiments, the heteropoly acid is phosphotungstic acid, and phosphotungstic acid acts as a catalyst in the reaction.

[0042] The separation method of the present invention comprises the following steps: firstly centrifugally separating the product after the reaction is completed, discarding the aqueous phase (the aqueous phase is unreacted raw materials and water-soluble by-products) to obtain an oil phase (target product and oil-soluble by-products); dissolving the obtained oil phase with ethanol; and further separating the obtained oil phase with column chromatography, eluting with petroleum ether and (or) ethyl acetate as mobile phase to obtain the target product, furanyl Schiff base.

[0043] The present invention adds phosphotungstic acid acid catalyst to 5-hydroxymethylfurfural solution, and then adds aniline to carry out the reaction. The reaction mechanism is as follows: Figure 1 shown.

[0044] The first step: the aldehyde group on 5-hydroxymethylfurfural reacts with the amino group of aniline to form an intermediate a containing an imine structure;

[0045] Step 2: The hydroxymethyl group on intermediate a undergoes a nucleophilic substitution reaction with the amino group of aniline under the action of a catalyst to generate intermediate b;

[0046] Step 3: The hydroxymethyl group of intermediate a reacts with the secondary amine of intermediate b to form the target product furyl Schiff base.

[0047] The prepared furanyl Schiff base contains three benzene rings and two furan ring structures, and the structural formula of the furanyl Schiff base is:

[0048]

[0049] Unless otherwise specified, all raw materials and reagents used in the following specific examples of the present invention are commercially available reagents and raw materials.

[0050] Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0051] Example 1

[0052] Weigh 0.603g of 5-hydroxymethylfurfural (5-HMF) and dissolve it in 10ml of deionized water to prepare a 5-HMF aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.020g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-HMF aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 30°C and 250rpm. After the addition is complete, continue stirring and react for 2h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 8:2) were collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.532 g of furyl Schiff base.

[0053] Example 2

[0054] Weigh 0.603g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.050g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0050g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 0.706g of aniline and add it dropwise to the mixed solution at 0°C and 250rpm while stirring. After the addition is complete, continue stirring and react for 2h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 8:2) were collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.254 g of furyl Schiff base.

[0055] Example 3

[0056] Weigh 0.706g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0706g / ml. Dissolve 0.020g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 0.706g of aniline and add it dropwise to the mixed solution at 50°C and 250 rpm while stirring. After the addition is complete, continue stirring and react for 2 hours. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000 rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The mixture was further separated by column chromatography, and the elution fractions were collected by a mixture of petroleum ether and ethyl acetate in a ratio of 8:2. The mixture was placed in a dark place for 24 hours, and the solvent was removed to obtain 0.219 g of furyl Schiff base.

[0057] Example 4

[0058] Weigh 0.603g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.010g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0010g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 30°C and 250rpm. After the addition is complete, continue stirring and react for 5h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 8:2) were collected and placed in a dark place for 24 h. The solvent was removed to obtain 0.502 g of furyl Schiff base.

[0059] Example 5

[0060] Weigh 0.603g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.030g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0030g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 0°C and 250rpm while stirring. After the addition is complete, continue stirring and react for 2h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 8:2) were collected and placed in a dark place for 24 h. The solvent was removed to obtain 0.312 g of furyl Schiff base.

[0061] Example 6

[0062] Weigh 1g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 0.01g / ml 5-hydroxymethylfurfural aqueous solution. Dissolve 0.040g of phosphotungstic acid in 10ml of deionized water to prepare a 0.0040g / ml phosphotungstic acid aqueous solution. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 2.000g of aniline and add it dropwise to the mixed solution at 25°C and 250 rpm. After the addition is complete, continue stirring and react for 1 hour. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000 rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the petroleum ether elution fraction was collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.543 g of furyl Schiff base.

[0063] Example 7

[0064] Weigh 0.01g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 0.001g / ml 5-hydroxymethylfurfural aqueous solution. Dissolve 0.050g of phosphotungstic acid in 10ml of deionized water to prepare a 0.0050g / ml phosphotungstic acid aqueous solution. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 0.0125g of aniline and add it dropwise to the mixed solution at 50°C and 250 rpm while stirring. After the addition is complete, continue stirring and react for 0.5h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000 rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the ethyl acetate elution fraction was collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.0071 g of furyl Schiff base.

[0065] Example 8

[0066] Weigh 0.540g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0540g / ml. Dissolve 0.020g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 0.0125g of aniline and add it dropwise to the mixed solution at 30°C and 250rpm. After the addition is complete, continue stirring and react for 1h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 9:1) were collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.0033 g of furyl Schiff base.

[0067] Example 9

[0068] Weigh 0.603g of 5-hydroxymethylfurfural and dissolve it in 10ml of deionized water to prepare a 5-hydroxymethylfurfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.020g of phosphomolybdic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly to obtain an acidic mixed solution. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 30°C and 250 rpm while stirring. After the addition is complete, continue stirring and react for 2 hours. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000 rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. The product was further separated by column chromatography, and the mixed elution fractions of petroleum ether and ethyl acetate (volume ratio of 1:9) were collected and placed in a dark place for 24 hours. The solvent was removed to obtain 0.256 g of furyl Schiff base.

[0069] Comparative Example 1

[0070] Weigh 0.603g of furfural and dissolve it in 10ml of deionized water to prepare a furfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.020g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly until the solution is acidic. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 30°C and 250rpm. After the addition is complete, continue stirring and react for 5h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. Column chromatography was further used for separation, and the elution fractions of a mixture of petroleum ether and ethyl acetate in a ratio of 8:2 were collected and placed in a dark place for 24 hours. The solvent was removed, but the target furyl Schiff base was not obtained.

[0071] Comparative Example 2

[0072] Weigh 0.603g of furfuryl alcohol and dissolve it in 10ml of deionized water to prepare a furfural aqueous solution with a concentration of 0.0603g / ml. Dissolve 0.020g of phosphotungstic acid in 10ml of deionized water to prepare a phosphotungstic acid aqueous solution with a concentration of 0.0020g / ml. Add the 5-hydroxymethylfurfural aqueous solution to the phosphotungstic acid aqueous solution and mix thoroughly until the solution is acidic. Weigh 1.512g of aniline and add it dropwise to the mixed solution at 30°C and 250rpm. After the addition is complete, continue stirring and react for 5h. The reaction system is neutral after completion. After the reaction is complete, centrifuge the reaction product at 10,000rpm, discard the aqueous phase, and repeatedly wash the resulting oil phase with deionized water and centrifuge it three times to remove unreacted starting materials and water-soluble byproducts. Dissolve the resulting oil phase in ethanol to obtain an ethanol solution of the product. Column chromatography was further used for separation, and the elution fractions of a mixture of petroleum ether and ethyl acetate in a ratio of 8:2 were collected and placed in a dark place for 24 hours. The solvent was removed, but the target furyl Schiff base was not obtained.

[0073] Here are the results:

[0074] (1) UV analysis

[0075] The products of Examples 1-5 and Comparative Examples 1-2 were analyzed by UV spectrophotometer. The characteristic absorption peaks were as follows: Figure 2 shown.

[0076] Comparing the ultraviolet absorption spectra of the raw materials 5-hydroxymethylfurfural and aniline, the ultraviolet absorption peak of the product at 230nm is the E band of the benzene ring, and the ultraviolet absorption peak at 290nm is the superposition of the B band of the benzene ring and the furan ring absorption peak, which is caused by π-π* electron transition; the strong absorption peak R band appears near 350nm, indicating that there is a relatively large conjugated structure in the product structure, which is caused by n-π* electron transition, and also proves that aniline and 5-HMF condense to generate a furanyl Schiff base with a hyperconjugated structure.

[0077] Comparative Examples 1 and 2 demonstrate that when furfuryl alcohol or furfural is reacted with aniline, i.e., when the furan ring contains only aldehyde or hydroxymethyl groups, the product structure differs significantly from that of the reaction product of 5-HMF and aniline. Within the range of 260 nm to 380 nm, the furfuryl alcohol product exhibits only one absorption peak at 290 nm, indicating that the hydroxymethyl group reacts with the amine group under acid catalysis. The furfural product exhibits two faint broad peaks within the range of 260 nm to 380 nm, one absorption peak at 290 nm, indicating that the amine group reacts with the aldehyde group, and a C=N peak at 350 nm. The absorption intensity is significantly lower than that of the 5-HMF product, indicating that the aldehyde group reacts with the amine group to form an imine structure.

[0078] (2) Infrared analysis

[0079] The products of the examples and comparative examples were characterized and analyzed by infrared spectroscopy. Figure 3 5-HMF at 3400cm -1 A strong OH stretching vibration absorption peak was observed at 1698 cm -1 In the infrared spectrum of the product, there is no strong OH stretching vibration absorption peak and C=O carbonyl stretching vibration absorption peak, and the NH stretching vibration peak in aniline disappears. At the same time, the peak at 1613cm -1 Nearby, a characteristic absorption peak for a C=N imine group appeared. The appearance of this C=N absorption peak demonstrates condensation between the hydroxymethyl and aldehyde groups in the reactants and the amino groups in the aniline, forming a new C=N double bond. The infrared spectra from three repeated experiments were essentially consistent, demonstrating the reproducibility of this invention.

[0080] (3) 1 H NMR analysis

[0081] 1 H NMR spectrum ( Figure 4) at δ = 4.68 ppm corresponds to the 1H peak of the methylene structure between the central nitrogen and the furanyl group; δ = 6.43 ppm and 6.69 ppm correspond to the 2H and 3H peaks of the furan ring; δ = 6.87 ppm and 6.88 ppm correspond to the 4H and 5H peaks of the central benzene ring; δ = 7.37 ppm corresponds to the 6H peak of the central benzene ring; δ = 7.22 ppm corresponds to the H peaks of the two benzene rings; and δ = 8.20 ppm corresponds to the characteristic Schiff base structure of the carbon-nitrogen double bond. The 1H-8H integrated area ratios are 4:2:2:2:1:10:4:2, respectively. This confirms that the structure of the reaction product of 5-HMF and aniline is the furanyl Schiff base of interest.

[0082] (4) Photochromism and electrochromism

[0083] Under 365nm UV light ( Figure 5 ) and 1.0V voltage ( Figure 6 ) under the action of a molten salt, the furanyl Schiff bases prepared in Example 1 of the present invention all exhibited color change: from light yellow to pink, and then returned to their original light yellow color after being placed in the dark for 20 hours. By combining the furanyl group, which exhibits excellent hole-transporting photochromic or electrochromic properties, with a -C=N- structure, multifunctional Schiff bases with photochromic and electrochromic properties can be designed.

[0084] It should be noted that Figure 5 In the figure, the arrows point to the UV exposure times of 0 min, 30 s, 1 min, 2 min, 3 min, and 5 min, respectively. Figure 6 In the figure, the arrows point to the power-on time of 0min, 30s, 1min, 2min, 3min and 5min respectively.

[0085] It should be noted that when the claims of the present invention involve numerical ranges, it should be understood that the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. In order to avoid redundancy, the present invention describes preferred embodiments.

[0086] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0087] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A furyl Schiff base, characterized in that The structural formula of the furyl Schiff base is: 。 2. A method for preparing the furyl Schiff base according to claim 1, characterized in that: Follow these steps to prepare: Water is used as a solvent and 5-hydroxymethylfurfural is added to prepare a 5-hydroxymethylfurfural aqueous solution; water is used as a solvent and a heteropoly acid is added to prepare a heteropoly acid aqueous solution; the 5-hydroxymethylfurfural aqueous solution is added to the heteropoly acid aqueous solution, aniline is added under stirring, the reaction is stirred, and the obtained product is separated to obtain a furanyl Schiff base; the heteropoly acid is phosphotungstic acid.

3. The method for preparing a furyl Schiff base according to claim 2, wherein: The concentration of 5-hydroxymethylfurfural in the 5-hydroxymethylfurfural aqueous solution is 0.001-0.1 g / ml, the concentration of heteropoly acid in the heteropoly acid aqueous solution is 0.001-0.005 g / ml, and the volume ratio of the 5-hydroxymethylfurfural aqueous solution to the heteropoly acid aqueous solution is 1:

1.

4. The method for preparing a furyl Schiff base according to claim 2, wherein: The mass ratio of 5-hydroxymethylfurfural to aniline is 0.4-1:

1.

5. The method for preparing a furyl Schiff base according to claim 2, wherein: The reaction temperature is 0 o C-50 o C, stirring speed is 250 r / min.

6. The method for preparing a furyl Schiff base according to claim 2, wherein: The reaction time is 0.5h-5h.

7. The method for preparing a furyl Schiff base according to claim 2, wherein: The separation method comprises the following steps: centrifuging the product, discarding the aqueous phase, washing the obtained oil phase with deionized water and centrifuging again, and repeating the process three times to remove water-soluble matter in the oil phase; dissolving the obtained oil phase with ethanol to obtain an ethanol solution of the product; and separating the product with column chromatography to obtain a furanyl Schiff base.

8. The method for preparing a furyl Schiff base according to claim 7, wherein: The centrifugal separation speed is 10000 r / min; the aqueous phase obtained by centrifugal separation is unreacted raw materials and water-soluble by-products, and the oil phase obtained by centrifugal separation is the target product and oil-soluble by-products.

9. The method for preparing a furyl Schiff base according to claim 7, wherein: The stationary phase used in column chromatography separation was grade II activated silica gel with a packing height of 15 cm; The mobile phase used in column chromatography separation is petroleum ether, ethyl acetate or a mixture of petroleum ether and ethyl acetate; in the mixture of petroleum ether and ethyl acetate, the volume ratio of petroleum ether to ethyl acetate is 1:9-9:1.

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