Method for separating and purifying 3-hexene-2, 5-diketone and photoisomerization application

Abstract

The invention provides a method for separating and purifying 3-hexene-2, 5-diketone and photoisomerization application, the method comprises the following steps: step 1, oxidizing 2, 5-dimethylfuran in an oxygen or air atmosphere to obtain an oxidation solution containing 3-hexene-2, 5-diketone; step 2, adding an ether solvent into the oxidation liquid for dissolving, and then standing and crystallizing in a low-temperature environment to obtain a crystallized mixture; step 3, filtering the crystallized mixture, and washing with a precooled ether solvent which is the same as the ether solvent in the step 2 to obtain a crude product 3-hexene-2, 5-diketone; and step 4, adding an aliphatic hydrocarbon solvent into the crude 3-hexene-2, 5-diketone, heating until the crude 3-hexene-2, 5-diketone is dissolved, cooling, recrystallizing, filtering and drying to obtain the trans-3-hexene-2, 5-diketone. According to the method, the DMF oxidation process is converted into a green way for producing high-added-value chemicals, so that the explosion risk caused by peroxide accumulation is fundamentally reduced, and the unification of safety and benefits is realized.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical separation and purification and functional material synthesis technology, and relates to 3-hexene-2,5-dione, specifically to a method for separating and purifying 3-hexene-2,5-dione and its photoisomerization application. Background Technology

[0002] 2,5-Dimethylfuran (DMF) is an important biomass platform molecule and a potential biofuel. Under aerobic conditions, especially during cryogenic storage and transportation, it is prone to auto-oxidation, generating a series of unstable peroxides and ring-opening products, posing a risk of thermal explosion. Among these, 3-hexen-2,5-dione is the most significant ring-opening product of DMF oxidation, containing a conjugated enone system in its molecular structure, exhibiting unique chemical activity and physical properties. Current research on DMF oxidation focuses primarily on reaction mechanisms and hazard assessments, lacking systematic solutions for the high-value utilization of its oxidation products. Efficiently separating high-purity 3-hexen-2,5-dione from complex oxidation mixtures is challenging because, as a thermosensitive conjugated molecule, traditional distillation methods easily lead to its decomposition or polymerization.

[0003] In addition, 3-hexene-2,5-dione exists in two isomers, cis- and trans-. Although its photoisomerization properties are known, this valuable property has never been explored and applied to the construction of functional materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for separating and purifying 3-hexene-2,5-dione and its photoisomerization application, thereby solving the technical problem that the high-value utilization of low-temperature oxidation products of DMF in existing technologies needs to be further improved.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0006] A method for separating and purifying 3-hexene-2,5-dione, the method comprising the following steps: Step 1, Oxidation reaction and pretreatment: 2,5-Dimethylfuran is oxidized in an oxygen or air atmosphere at 40–80 °C for 2–48 h to obtain an oxidized solution containing 3-hexene-2,5-dione.

[0007] Step 2, Solvent dissolution and low-temperature crystallization: Add a low-boiling-point ether solvent to the oxidizing solution obtained in step one to dissolve it, and then let it stand at low temperature for 6 to 24 hours to crystallize, and obtain the crystallized mixture.

[0008] Step 3, Crystal separation and washing: The crystallized mixture obtained in step two was filtered to obtain needle-like or flaky crystals, which were then washed with a pre-cooled ether solvent, the same as that used in step two, to obtain crude 3-hexene-2,5-dione.

[0009] Step 4, recrystallization and refining: Add an aliphatic hydrocarbon solvent to the crude 3-hexene-2,5-dione obtained in step 3, heat until dissolved, cool and recrystallize, then filter and dry to finally obtain trans-3-hexene-2,5-dione.

[0010] The present invention also has the following technical features.

[0011] Specifically, in step two, the low-boiling-point ether solvent is a low-boiling-point ether reagent with a boiling point of less than 100°C, including diethyl ether or methyl tert-butyl ether.

[0012] Specifically, in step two, the low-temperature environment refers to an ambient temperature of -10℃ to 10℃.

[0013] Specifically, in step four, the aliphatic hydrocarbon solvent includes n-hexane, cyclohexane, or petroleum ether.

[0014] Specifically, in step four, the process of recrystallization by cooling is as follows: first cool to room temperature, and then further cool to 0-5°C for recrystallization.

[0015] The present invention also protects the use of trans-3-hexene-2,5-dione obtained by the method described above for separation and purification of 3-hexene-2,5-dione in photoisomerization reactions.

[0016] Specifically, the application process involves dissolving trans-3-hexen-2,5-dione in an inert organic solvent and then irradiating it under ultraviolet light to partially or completely convert trans-3-hexen-2,5-dione into cis-3-hexen-2,5-dione, thereby obtaining cis-3-hexen-2,5-dione or a mixture of cis / trans-3-hexen-2,5-dione.

[0017] Specifically, the wavelength of the ultraviolet light is 200–300 nm.

[0018] Specifically, the inert organic solvent includes ethyl acetate or acetonitrile.

[0019] Compared with the prior art, the present invention has the following technical effects.

[0020] (I) The method in this invention transforms the DMF oxidation process into a green pathway for producing high-value-added chemicals, fundamentally reducing the risk of explosion caused by the accumulation of peroxides, achieving a balance between safety and efficiency, and turning waste into treasure.

[0021] (II) The method in this invention uses a combination of low-temperature crystallization and recrystallization, which is mild and efficient. It is particularly suitable for the purification of heat-sensitive conjugated enone compounds. The purified product has a high yield, which can reach more than 50%, and a high purity, which can be greater than 99%.

[0022] (III) This invention is the first to systematically develop and utilize the photoisomerism property, providing a novel photoresponse unit that is simple in structure, widely available and easy to prepare for the synthesis of new photofunctional materials; the significant differences in polarity, spatial structure and ultraviolet absorption between the cis-trans isomers of 3-hexene-2,5-dione lay the foundation for the construction of advanced functional materials such as photo-controlled switches, molecular motors and optical information storage media.

[0023] (IV) The separation and purification method in this invention uses conventional reagents and equipment, is inexpensive, and has a simple process flow, and has good potential for industrial scale-up.

[0024] (V) This invention provides a mild and efficient separation and purification process, and further creatively develops and utilizes the photoisomerism of the obtained trans-3-hexene-2,5-dione. Under ultraviolet light irradiation of a specific wavelength, it can be controllably converted into the corresponding cis isomer, thereby achieving the adjustment of the cis-trans structure. Based on this characteristic, this invention expands the application of trans-3-hexene-2,5-dione or cis / trans-3-hexene-2,5-dione in the preparation of photoresponsive smart materials such as optical switch molecular devices and optical information storage materials. Attached Figure Description

[0025] Figure 1 The 1H NMR spectrum of trans-3-hexene-2,5-dione obtained by separation and purification in Example 1 of this invention ( 1 (HNMR) image.

[0026] Figure 2 The Fourier transform infrared (FTIR) spectrum of trans-3-hexene-2,5-dione obtained by separation and purification in Example 1 of this invention is shown.

[0027] Figure 3 The 1H NMR spectra of the oxidized solution containing 3-hexene-2,5-dione obtained in step one of Example 1 of this invention, after being irradiated with ultraviolet light (wavelength 254 nm) for different times, are shown in Example 2 of this invention. 1 The graph shows the changes in H NMR; (a) after irradiation at 300K for 24 hours, and (b) after irradiation at 300K for 48 hours.

[0028] The specific content of the present invention will be further described in detail below with reference to the embodiments. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, all methods, conditions and raw materials in this invention adopt methods, conditions and raw materials commonly known in the art in the prior art. For example, the vacuum drying method adopts a known method, the oxygen or air atmosphere adopts a known oxygen or air atmosphere, the diethyl ether adopts a known diethyl ether, the methyl tert-butyl ether adopts a known methyl tert-butyl ether, the n-hexane adopts a known n-hexane, the cyclohexane adopts a known cyclohexane, the petroleum ether adopts a known petroleum ether, the ethyl acetate adopts a known ethyl acetate, the acetonitrile adopts a known acetonitrile, and the 200-300 nm ultraviolet light adopts a known ultraviolet light.

[0030] In this invention, room temperature refers to the ambient temperature during the production process, which is typically within the range of 20±10℃.

[0031] In this invention, 2,5-dimethylfuran, abbreviated as DMF, is used. The 2,5-dimethylfuran used is a commonly known 2,5-dimethylfuran in the art.

[0032] Following the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of the present invention fall within the protection scope of the present invention.

[0033] Example 1: (Isolation and purification of 3-hexene-2,5-dione) This embodiment provides a method for separating and purifying 3-hexene-2,5-dione, which includes the following steps: Step 1, Oxidation reaction and pretreatment: 10.0 g of 2,5-dimethylfuran was oxidized at 60 °C and 1.0 MPa in an oxygen atmosphere for 24 h to obtain a dark brown oxidized solution containing 3-hexene-2,5-dione.

[0034] Step 2, Solvent dissolution and low-temperature crystallization: Take all the oxidizing solution obtained in step one and add 20 mL of diethyl ether to dissolve it. Transfer the resulting solution to a crystallizing dish and let it stand in a freezer at 0°C for 12 hours to crystallize, and obtain the crystallized mixture.

[0035] In this embodiment, the crystallizing dish is a crystallizing dish commonly known in the art, and the freezer is a freezer commonly known in the art.

[0036] Step 3, Crystal separation and washing: The mixture of all crystals obtained in step two was filtered to obtain light yellow needle-like crystals, which were then washed twice with ether pre-cooled to 0°C, with 2 mL of ether used each time, to obtain crude 3-hexene-2,5-dione.

[0037] Step 4, recrystallization and refining: Take all the crude 3-hexen-2,5-dione obtained in step three, and add 15 mL of n-hexane preheated to 40°C. After completely dissolving all the crude 3-hexen-2,5-dione, allow it to cool naturally to room temperature, then place it in an ice-water bath at 0°C for recrystallization for 2 hours. Filter and vacuum dry to obtain 2.95 g of light yellow needle-like crystals. Figure 1 neutralization Figure 2 The result identified it as trans-3-hexene-2,5-dione, with a yield of 29.5% and a GC-MS purity of 99.2%.

[0038] In this embodiment, the 0°C ice water bath is a commonly used 0°C ice water bath known in the art.

[0039] In this embodiment, GC-MS is a gas chromatography-mass spectrometry system, and the testing equipment and purity testing methods of GC-MS adopt commonly used testing equipment and methods known in the art.

[0040] In this embodiment, the testing equipment and methods for the proton nuclear magnetic resonance spectrum are those commonly known in the art; the testing equipment and methods for the Fourier transform infrared spectrum are those commonly known in the art.

[0041] Example 2: (Photoisomerization of 3-hexene-2,5-dione) This embodiment describes the application of 3-hexen-2,5-dione in a photoisomerization reaction. 10 mg of trans-3-hexen-2,5-dione was dissolved in 100 mL of acetonitrile to prepare a 0.1 mg / mL solution. The trans-3-hexen-2,5-dione was prepared using the method described in Example 1. The prepared solution was placed in a quartz cuvette and irradiated at a distance of 10 cm using a 254 nm UV lamp. Samples were taken at 0, 1, 5, 10, and 30 min of irradiation, and UV-Vis absorption spectroscopy was immediately performed. The UV-Vis absorption spectroscopy results showed that, under the condition of varying only the irradiation time while keeping all other test conditions the same, the intensity of the characteristic absorption peak at 218 nm in the UV-Vis absorption spectrum gradually decreased and showed a slight red shift as the UV lamp irradiation time increased. This indicates that trans-3-hexen-2,5-dione gradually converted to cis-3-hexen-2,5-dione until a steady-state photoequilibrium was reached.

[0042] The oxidized solution containing 3-hexene-2,5-dione obtained in step one of Example 1 was irradiated at a distance of 10 cm using a 254 nm ultraviolet lamp at a temperature of 300 K. Samples of the same mass were taken at 24 h and 48 h of irradiation, and 1H NMR spectroscopy was immediately performed. 1 H NMR) test, results are as follows Figure 3 As shown. (Comparison) Figure 3 (a) and Figure 3 As shown in (b), with the extension of irradiation time, the content of trans-3-hexen-2,5-dione (E-DAE) gradually decreases, while the content of cis-3-hexen-2,5-dione (Z-DAE) gradually increases, which proves that trans-3-hexen-2,5-dione gradually transforms into cis-3-hexen-2,5-dione.

[0043] In this embodiment, the cis / trans 3-hexen-2,5-dione mixture refers to a mixture of cis-3-hexen-2,5-dione and trans-3-hexen-2,5-dione during the cis-trans structural conversion process. Cis-3-hexen-2,5-dione is a commonly known cis-3-hexen-2,5-dione in the art, and trans-3-hexen-2,5-dione is a commonly known trans-3-hexen-2,5-dione in the art.

[0044] In this embodiment, the quartz cuvette is a commonly known quartz cuvette in the art; the ultraviolet lamp is a commonly known ultraviolet lamp in the art; the ultraviolet-visible absorption spectroscopy testing equipment and methods are commonly known testing equipment and methods in the art; and the nuclear magnetic resonance hydrogen spectroscopy testing equipment and methods are commonly known testing equipment and methods in the art.

[0045] In this embodiment, by controlling the irradiation time of the ultraviolet lamp, the controllable conversion of trans-3-hexene-2,5-dione to cis-3-hexene-2,5-dione can be achieved, forming a dynamically balanced mixture of cis / trans-3-hexene-2,5-dione.

[0046] In this embodiment, irradiation with an ultraviolet lamp can convert trans-3-hexen-2,5-dione into cis-3-hexen-2,5-dione, which can then be converted back into trans-3-hexen-2,5-dione under heating conditions.

Claims

1. A method for isolating and purifying 3-hexene-2,5-dione, characterized by, The method includes the following steps: Step 1, Oxidation reaction and pretreatment: 2,5-Dimethylfuran is oxidized in an oxygen or air atmosphere at 40–80 °C for 2–48 h to obtain an oxidized liquid containing 3-hexene-2,5-dione. Step 2, Solvent dissolution and low-temperature crystallization: Add a low-boiling-point ether solvent to the oxidizing solution obtained in step one to dissolve it, and then let it stand at low temperature for 6 to 24 hours to crystallize, to obtain a crystallized mixture. Step 3, Crystal separation and washing: The crystallized mixture obtained in step two was filtered to obtain needle-like or flaky crystals, which were then washed with a pre-cooled ether solvent, the same as that used in step two, to obtain crude 3-hexene-2,5-dione. Step 4, recrystallization and refining: Add an aliphatic hydrocarbon solvent to the crude 3-hexene-2,5-dione obtained in step 3, heat until dissolved, cool and recrystallize, then filter and dry to finally obtain trans-3-hexene-2,5-dione.

2. The method of isolating and purifying 3-hexene-2,5-dione according to claim 1, wherein, In step two, the low-boiling-point ether solvent is a low-boiling-point ether reagent with a boiling point of less than 100°C, including diethyl ether or methyl tert-butyl ether.

3. The method of purifying 3-hexene-2,5-dione according to claim 1, wherein In step two, the low-temperature environment refers to an ambient temperature of -10℃ to 10℃.

4. The method of isolating and purifying 3-hexene-2,5-dione according to claim 1, wherein, In step four, the aliphatic hydrocarbon solvent includes n-hexane, cyclohexane, or petroleum ether.

5. The method of isolating and purifying 3-hexene-2,5-dione according to claim 1, wherein, In step four, the specific process of recrystallization by cooling is as follows: first cool to room temperature, and then further cool to 0-5°C for recrystallization.

6. The application of the trans-3-hexene-2,5-dione obtained by the method for separating and purifying 3-hexene-2,5-dione as described in any one of claims 1 to 5 in photoisomerization reactions.

7. The application as described in claim 6, characterized in that, The specific process of the application is as follows: trans-3-hexen-2,5-dione is dissolved in an inert organic solvent and then irradiated under ultraviolet light to partially or completely convert trans-3-hexen-2,5-dione into cis-3-hexen-2,5-dione, thereby obtaining cis-3-hexen-2,5-dione or a mixture of cis / trans-3-hexen-2,5-dione.

8. The application as described in claim 7, characterized in that, The wavelength of the ultraviolet light is 200–300 nm.

9. The use according to claim 7, wherein the compound is ###00003### 8 or ###00004### 9. The inert organic solvent includes ethyl acetate or acetonitrile.

Images