The use of ZnO as a photocatalyst in the preparation of allantoin

Abstract

This invention discloses the use of ZnO as a photocatalyst in the preparation of allantoin. The invention employs ZnO as a photocatalyst to carry out a photocatalytic reaction of uric acid as a substrate under visible light irradiation. Uric acid is oxidized, hydrolyzed, and decarboxylated to convert to allantoin. After 4 hours of reaction, the conversion rate of uric acid to allantoin catalyzed by ZnO reaches 35%. Further extending the reaction time to 6 hours, the conversion rate reaches 85%. This invention uses ZnO as a photocatalyst to photocatalyze the conversion of uric acid to allantoin. Through the directional control of photogenerated electron-hole pairs, selective activation of chemical bonds is achieved, resulting in advantages such as high conversion rate, mild reaction conditions, and low energy consumption.

Description

Technical Field

[0001] This invention relates to novel uses of ZnO, and more particularly to novel uses of ZnO as a photocatalyst in the preparation of allantoin, belonging to the field of allantoin preparation. Background Technology

[0002] Allantoin, also known as 5-ureoylhydantoin, is a natural, safe, and non-toxic imidazole heterocyclic compound widely used in the pharmaceutical, cosmetic, and agricultural fields, with broad development prospects and market potential. In the pharmaceutical field, allantoin can promote cell proliferation, accelerate wound healing, and soften keratin, making it an excellent healing agent for skin wounds. It can also be used to treat ulcers, gastrointestinal inflammation, cirrhosis, and other diseases.

[0003] Allantoin possesses powerful antioxidant capabilities, inhibiting inflammatory responses and protecting cells from free radical damage. Furthermore, research has shown that allantoin also exhibits potential in anti-tumor activity and the prevention of neurodegenerative diseases. It can also be used to treat hypertension, diabetes, and other conditions, regulating blood sugar and lipids. In the cosmetics industry, allantoin is widely used in skincare products such as creams, shampoos, and conditioners due to its moisturizing and anti-inflammatory properties, improving dry and rough skin, leaving it softer and more hydrated. Allantoin is also used in whitening and antioxidant products, possessing free radical scavenging capabilities and helping to delay skin aging. In agriculture, allantoin, as a plant growth regulator, has demonstrated significant effects in increasing yield and efficiency, improving quality, and enhancing stress resistance. It not only stimulates plant growth and promotes crop yield but also enhances crop disease resistance and stress tolerance, improving the overall quality of crops.

[0004] Allantoin has a wide range of sources, including natural extraction from plants such as comfrey, yam, tobacco seeds, plants in the Boraginaceae family, and desert Cistanche. However, natural extraction methods result in low yields, complex processes, and high costs, making it difficult to meet the needs of large-scale production. Therefore, chemical synthesis has become the main production process for allantoin. Among these, the oxalic acid electrolytic glyoxal oxidation method, the calcium acetate hydrochloric acid dissolution method, and the urea dichloroacetic acid heating method are commonly used chemical synthesis methods. The direct condensation method of urea and glyoxylic acid uses urea and glyoxylic acid as raw materials. Glyoxylic acid is generated through catalytic oxidation and then condensed with urea to produce allantoin. This method is currently one of the main processes for producing allantoin. The glyoxal method involves two steps: first, glyoxal is oxidized to glyoxylic acid, and then condensed with urea under the action of a catalyst to produce allantoin. The yield of this method is approximately 40%. The oxalic acid electrolytic glyoxal oxidation method utilizes oxalic acid electrolysis to generate glyoxal, which is then oxidized to glyoxylic acid and finally condensed with urea to produce allantoin. The trichloroacetaldehyde method produces allantoin through the reduction reaction of trichloroacetaldehyde. The calcium acetate hydrochloric acid dissolution method uses urea and calcium acetate hydrochloric acid solution as raw materials, and produces allantoin through a heating reaction. Urea can also react with dichloroacetic acid under heating conditions to produce allantoin. While these traditional chemical synthesis processes can achieve the industrial production of allantoin, they require strong oxidants and high-temperature, high-pressure conditions, resulting in high pollution and high energy consumption. Therefore, in recent years, researchers have been exploring more environmentally friendly and efficient synthesis methods, such as improving reaction conditions to increase yield and reduce wastewater discharge.

[0005] Compared to traditional chemical synthesis methods, photocatalysis has attracted much attention in energy conversion and organic synthesis due to its green and low-energy characteristics. Photocatalysis offers milder reaction conditions and significantly reduces energy consumption. Traditional chemical synthesis often relies on harsh conditions such as high temperature and high pressure, while photocatalytic reactions can be completed under ambient temperature and pressure driven by light energy, greatly reducing energy consumption. Furthermore, photocatalysis can improve atom economy and selectivity. Through the directional control of photogenerated electron-hole pairs, photocatalysis can achieve selective activation of chemical bonds. However, the prerequisite or key to achieving the photocatalytic synthesis of allantoin is the selection of a suitable photocatalyst to convert uric acid into allantoin via photocatalytic reaction. Summary of the Invention

[0006] The main objective of this invention is to provide the use of ZnO as a photocatalyst in the preparation of allantoin;

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] This invention provides the use of ZnO as a photocatalyst to catalyze the conversion of uric acid into allantoin, comprising: using ZnO as a photocatalyst, and carrying out a photocatalytic reaction with uric acid as a substrate under visible light irradiation to oxidize, hydrolyze, and decarboxylate uric acid into allantoin.

[0009] In a preferred embodiment of the present invention, the mass ratio of ZnO to uric acid is in the range of (0.1-1):1; preferably, the optimal mass ratio of ZnO to uric acid is 0.1:1.

[0010] In a preferred embodiment of the present invention, the wavelength of the visible light is ≥420nm; preferably, the wavelength range of the visible light is 420-780 nm.

[0011] In a preferred embodiment of the present invention, the reaction temperature of the photocatalytic reaction is in the range of 15-30°C; preferably, the reaction temperature is 25°C.

[0012] In a preferred embodiment of the present invention, the reaction pH value of the photocatalytic reaction is in the range of 5-9; preferably, the pH value is 7.0.

[0013] In a preferred embodiment of the present invention, the light intensity of the photocatalytic reaction is in the range of 50-300 mW / cm². 2 Preferably, the optimal light intensity is 100 mW / cm². 2 .

[0014] In a preferred embodiment of the present invention, the reaction time of the photocatalytic reaction is in the range of 4-8 hours; preferably, the reaction time is 5 hours.

[0015] The ZnO described in this invention can be purchased commercially, and any commercially available ZnO is applicable to this invention.

[0016] Alternatively, those skilled in the art can also prepare ZnO themselves, and the ZnO prepared in this invention is applicable to this invention. For reference, this invention provides a method for preparing ZnO, comprising: adding Zn(CH3COO)2•2H2O to ultrapure water and stirring thoroughly, then adding 4M NaOH and stirring thoroughly to obtain a mixture; transferring the above mixture to a polytetrafluoroethylene liner and placing it in a stainless steel autoclave for heating and reaction at 200°C for 4 h; after the reaction is completed, washing the prepared catalyst with ultrapure water and anhydrous ethanol, collecting it by centrifugation, and drying it at 60°C to obtain the final product.

[0017] This invention uses ZnO as a photocatalyst to catalyze the conversion of uric acid to allantoin. After 4 hours of reaction, the conversion rate of uric acid to allantoin catalyzed by ZnO can reach 35%. After extending the reaction time to 6 hours, the conversion rate of uric acid to allantoin catalyzed by ZnO can reach 85%. Compared with traditional chemical synthesis methods, this invention uses a photocatalytic reaction to convert uric acid to allantoin. Through the directional control of photogenerated electron-hole pairs, selective activation of chemical bonds can be achieved, which has the advantages of mild reaction conditions and low energy consumption. Attached Figure Description

[0018] Figure 1 High-performance liquid chromatography (HPLC) results of the conversion of uric acid to allantoin using CdS as a photocatalyst; Allantoin: allantoin standard; CdS: detection of allantoin in the CdS-catalyzed reaction system; Control: control system without catalyst.

[0019] Figure 2 High-performance liquid chromatography (HPLC) results of the conversion of uric acid to allantoin using ZnO as a photocatalyst; Allantoin: allantoin standard; ZnO: detection of allantoin in the ZnO-catalyzed reaction system; Control: control system without catalyst.

[0020] Figure 3 High-performance liquid chromatography (HPLC) results of the conversion of uric acid to allantoin using g-C3N4(Bulk) as a photocatalyst; Allantoin: allantoin standard; g-C3N4(Bulk): detection of allantoin in the g-C3N4(Bulk) catalyzed reaction system; Control: control system without catalyst.

[0021] Figure 4 High-performance liquid chromatography (HPLC) results of the conversion of uric acid to allantoin using TiO2 as a photocatalyst; Allantoin: allantoin standard; TiO2: detection of allantoin in the TiO2-catalyzed reaction system; Control: control system without catalyst. Detailed Implementation

[0022] The present invention will be further described below with reference to specific preliminary embodiments or test examples, and the advantages and features of the present invention will become clearer with the description. However, it should be understood that the preliminary embodiments or test examples are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but such modifications or substitutions all fall within the protection scope of the present invention.

[0023] Preliminary Example 1: Preparation of photocatalyst g-C3N4(Bulk)

[0024] Place 10 g of urea in an agate mortar, grind it thoroughly and evenly, then transfer it to a crucible and heat it to 550 °C in air atmosphere and keep it at that temperature for 2 h to obtain a yellow agglomerate, which is the final product.

[0025] Preliminary Example 2: Preparation of CdS Photocatalyst

[0026] 10 mmol Cd(NO3)2•4H2O was added to 30 mL of ethylenediamine solution and stirred for 30 min. Then, 30 mmol thiourea was added and stirred thoroughly to obtain a mixture. The mixture was transferred to a 50 mL polytetrafluoroethylene liner and placed in a stainless steel autoclave. The mixture was heated at 160 °C for 24 h. After the reaction was completed, the catalyst was washed with ultrapure water and anhydrous ethanol, collected by centrifugation, and dried at 60 °C.

[0027] Preliminary Example 3: Preparation of the photocatalyst TiO2

[0028] 2 mL of TiCl4 was added to 30 mL of ethylene glycol and stirred thoroughly. Then, 2 mL of H2O was added to obtain a mixture. The mixture was transferred to a 50 mL polytetrafluoroethylene liner and placed in a stainless steel autoclave. The mixture was heated at 150 °C for 4 h. After the reaction was completed, the product was washed with ultrapure water and anhydrous ethanol, collected by centrifugation, and dried at 60 °C.

[0029] Preliminary Example 4: Preparation of Photocatalyst ZnO

[0030] Add 5 mmol Zn(CH3COO)2•2H2O to 30 mL of ultrapure water and stir for 30 min. Then add 4 M NaOH and stir thoroughly to obtain a mixture. Transfer the mixture to a 50 mL polytetrafluoroethylene liner and place it in a stainless steel autoclave. Heat the mixture at 200 °C for 4 h. After the reaction is complete, wash the prepared product with ultrapure water and anhydrous ethanol, collect it by centrifugation, and dry it at 60 °C.

[0031] Experimental Example 1: Screening experiment to convert uric acid into allantoin using CdS, ZnO, g-C3N4 (Bulk), and TiO2 as photocatalysts.

[0032] 1. Experimental Methods

[0033] 1.1 Photocatalytic reaction catalyzes the synthesis of allantoin from uric acid.

[0034] The photocatalytic reactions of uric acid oxidation, hydrolysis, and decarboxylation to synthesize allantoin were evaluated using CdS, ZnO, g-C3N4 (Bulk), and TiO2 as photocatalysts, respectively.

[0035] Experimental group (1): The photocatalyst CdS (prepared in Preliminary Example 2) was dispersed in a solution containing 2 g / L uric acid. The final concentration of the photocatalyst CdS was 0.2 g / L. The reaction was carried out under visible light irradiation at a wavelength of 480 nm. The reaction conditions were: temperature 25℃, pH 7.0, light intensity 100 mW / cm², and reaction time 8 hours.

[0036] Experimental group (2): The photocatalyst ZnO (prepared in Preliminary Example 4) was dispersed in a solution containing 2 g / L uric acid. The final concentration of the photocatalyst ZnO was 0.2 g / L. The reaction was carried out under visible light irradiation at a wavelength of 480 nm. The reaction conditions were: temperature 25℃, pH 7.0, light intensity 100 mW / cm², and reaction time 8 hours.

[0037] Experimental group (3): The catalyst g-C3N4(Bulk) (prepared in Preliminary Example 1) was dispersed in a solution containing 2 g / L uric acid. The final concentration of the photocatalyst g-C3N4(Bulk) was 0.2 g / L. The reaction was carried out under visible light irradiation at a wavelength of 480 nm. The reaction conditions were: temperature 25℃, pH 7.0, light intensity 100 mW / cm², and reaction time 8 hours.

[0038] Experimental group (4): The catalyst TiO2 (prepared in Preliminary Example 3) was dispersed in a solution containing 2 g / L uric acid, and the final concentration of the photocatalyst TiO2 was 0.2 g / L. The reaction was carried out under visible light wavelength of 480 nm. The reaction conditions were: temperature 25℃, pH 7.0, light intensity 100mW / cm², and reaction time 8 hours.

[0039] 1.2 Allantoin Detection Method

[0040] High-performance liquid chromatography (HPLC) was used to analyze standards and samples equipped with a reversed-phase Diamonsil C18 column (5 μm, 250 × 4.6 mm) and a UV-Vis detector. Mobile phase A was 80 mM ammonium phosphate buffer (pH adjusted to 4.1 by adding phosphate), and mobile phase B was mobile phase A containing 30% methanol. The gradient elution program was set as follows: 0–15 min, 5% B; 15–25 min, 5% B → 25% B; 25–30 min, 25% B → 95% B; 30–35 min, 95% B; 35–40 min, 95% B → 5% B; 40–45 min, maintain 5% B equilibration. Allantoin was detected at a wavelength of 212 nm.

[0041] 2. Experimental Results

[0042] The test results are shown in Figures 1-4The experimental results show that CdS, ZnO, and g-C3N4 (Bulk) can all catalyze the synthesis of allantoin from uric acid. Allantoin formation was detected in the reaction system after 4 hours of light irradiation. Figures 1-3 TiO2 cannot catalyze the synthesis of allantoin. Figure 4 Among them, CdS exhibited the highest catalytic efficiency, achieving a 95% conversion rate of uric acid to allantoin after 4 hours of reaction. Extending the reaction time to 6 hours further resulted in complete conversion of uric acid to allantoin. ZnO showed the second highest catalytic efficiency, achieving a 35% conversion rate after 4 hours of reaction. Extending the reaction time to 6 hours further increased the conversion rate to 85%. After 4 hours of reaction, g-C3N4 (Bulk) achieved a 26% conversion rate of uric acid to allantoin. Extending the reaction time to 6 hours further increased the conversion rate to 38%.

[0043] Experimental Example 2: Using ZnO as a photocatalyst to catalyze the conversion of uric acid to allantoin.

[0044] 1. Experimental Methods

[0045] 1.1 Photocatalytic reaction catalyzes the synthesis of allantoin from uric acid.

[0046] The catalyst ZnO (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) was dispersed in a solution containing 2 g / L uric acid, with a final concentration of 2 g / L. The reaction was carried out under visible light irradiation at a wavelength of 720 nm. The reaction conditions were: temperature 15℃, pH 9.0, light intensity 50 mW / cm², and reaction time 8 hours.

[0047] 1.2 Allantoin Detection Method

[0048] High-performance liquid chromatography (HPLC) was used to analyze standards and samples equipped with a reversed-phase Diamonsil C18 column (5 μm, 250 × 4.6 mm) and a UV-Vis detector. Mobile phase A was 80 mM ammonium phosphate buffer (pH adjusted to 4.1 by adding phosphate), and mobile phase B was mobile phase A containing 30% methanol. The gradient elution program was set as follows: 0–15 min, 5% B; 15–25 min, 5% B → 25% B; 25–30 min, 25% B → 95% B; 30–35 min, 95% B; 35–40 min, 95% B → 5% B; 40–45 min, maintain 5% B equilibration. Allantoin was detected at a wavelength of 212 nm.

[0049] 2. Experimental Results

[0050] After 4 hours of reaction, the conversion rate of ZnO-catalyzed substrate uric acid to allantoin can reach 32%. After extending the reaction time to 6 hours, the conversion rate of ZnO-catalyzed substrate uric acid to allantoin can reach 83%.

[0051] Experimental Example 3: Using ZnO as a photocatalyst to catalyze the conversion of uric acid to allantoin.

[0052] 1. Experimental Methods

[0053] 1.1 Photocatalytic reaction catalyzes the synthesis of allantoin from uric acid.

[0054] The catalyst ZnO (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) was dispersed in a solution containing 2 g / L uric acid, and the final concentration of the photocatalyst ZnO was 1 g / L. The reaction was carried out under visible light irradiation at a wavelength of 430 nm. The reaction conditions were: temperature 35℃, pH 5.0, light intensity 300 mW / cm², and reaction time 8 hours.

[0055] 1.2 Allantoin Detection Method

[0056] High-performance liquid chromatography (HPLC) was used to analyze standards and samples equipped with a reversed-phase Diamonsil C18 column (5 μm, 250 × 4.6 mm) and a UV-Vis detector. Mobile phase A was 80 mM ammonium phosphate buffer (pH adjusted to 4.1 by adding phosphate), and mobile phase B was mobile phase A containing 30% methanol. The gradient elution program was set as follows: 0–15 min, 5% B; 15–25 min, 5% B → 25% B; 25–30 min, 25% B → 95% B; 30–35 min, 95% B; 35–40 min, 95% B → 5% B; 40–45 min, maintain 5% B equilibration. Allantoin was detected at a wavelength of 212 nm.

[0057] 2. Experimental Results

[0058] After 4 hours of reaction, the conversion rate of ZnO-catalyzed substrate uric acid to allantoin can reach 31%. After extending the reaction time to 6 hours, the conversion rate of ZnO-catalyzed substrate uric acid to allantoin can reach 80%.

Claims

1. Use of ZnO as a photocatalyst for the conversion of uric acid into allantoin, comprising: ZnO is used as a photocatalyst to oxidize and hydrolytic decarboxylate uric acid into allantoin under visible light irradiation.

2. Use according to claim 1, characterized in that, The mass ratio of ZnO to uric acid ranges from 0.1 to 1.

3. Use according to claim 2, characterized in that, The mass ratio of ZnO to uric acid is 0.1:

1.

4. Use according to claim 1, characterized in that, The wavelength of the visible light is greater than or equal to 420 nm.

5. Use according to claim 4, characterized in that, The wavelength of the visible light ranges from 420 nm to 780 nm.

6. Use according to claim 1, characterized in that, The reaction temperature of the photocatalytic reaction ranges from 15 to 30℃, and the reaction pH value of the photocatalytic reaction ranges from 5 to 9.

7. Use according to claim 6, characterized in that, The reaction temperature of the photocatalytic reaction is 25℃, and the reaction pH value of the photocatalytic reaction is 7.

0.

8. Use according to claim 1, characterized in that, The light intensity of the photocatalytic reaction is in the range of 50-300 mW / cm 2 ; the reaction time of the photocatalytic reaction is 4-8 hours.

9. Use according to claim 8, characterized in that, The light intensity of the photocatalytic reaction is 100 mW / cm 2 The reaction time of the photocatalytic reaction is 5 hours.

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