CN119751408A - A method for preparing high-purity vinyl oxalate - Google Patents
A method for preparing high-purity vinyl oxalate Download PDFInfo
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Abstract
The invention discloses a preparation method of high-purity vinyl oxalate. The preparation method comprises the steps of carrying out polycondensation reaction on a mixed reaction system containing reaction monomers, a catalyst and a heat stabilizer to obtain an ethylene oxalate polymer, wherein the reaction monomers comprise ethylene glycol and dimethyl oxalate, the catalyst comprises an MXene material, carrying out high-vacuum depolymerization reaction on the ethylene oxalate polymer, carrying out reduced pressure sublimation to obtain a crude ethylene oxalate product, and purifying to obtain high-purity ethylene oxalate. The preparation method of the high-purity vinyl oxalate provided by the invention uses the high-efficiency catalyst MXene, and can obtain the vinyl oxalate with the yield of more than 80wt% and the purity of more than 99wt% by regulating and controlling the introduction amount, the reaction temperature, the reaction pressure and the type of the purification solvent of the MXene, so that the preparation method has a better industrialized prospect.
Description
Technical Field
The invention belongs to the technical field of oxalate preparation, and particularly relates to a preparation method of high-purity vinyl oxalate.
Background
The polyester plastic provides various convenience for the life of people, but is not easy to degrade in nature, and seriously damages the ecological environment. The lack of microorganisms and environmental temperatures in the ocean and water that degrade the waste degradable plastics makes degradation of the waste plastics in the aqueous phase difficult. However, about 950 ten thousand tons of plastic waste still enter the ocean every year are reported in the literature, and therefore, development of seawater environment-degradable polyesters is needed. The unique structure of oxalic acid carbonyl in the polyoxalate structural unit endows the polyoxalate structural unit with excellent non-enzymatic hydrolysis capability, and the polyoxalate structural unit is a material which can be rapidly degraded in a seawater environment. In addition, the hydrolysis-prone nature of the oxalate-based polyesters imparts the ability to be used in a closed loop under mild conditions.
Vinyl oxalate is a cyclic compound, shows high chemical reactivity, can be applied to the preparation of oxalic acid-based polyester, and has the following molecular structural formula:
The process for producing the ethylene oxalate mainly comprises an esterification reaction route of ethylene glycol and oxalic acid catalyzed by concentrated sulfuric acid, a reaction route of oxalyl chloride and ethylene glycol, and a reaction route of oxalic ester (dimethyl oxalate or diethyl oxalate) and ethylene glycol. The yields of the oxalyl chloride and ethylene glycol reaction routes are 71-87% (chem. Pharm. Bull.1993,41 (2) 408-410), and the yields of other routes are not reported (Journal of Polymer Science：Polymer ChemistryEdition1979,17：2701-2706;Macromolecules 2023,56,3149-3159)., however, the oxalyl chloride has high toxicity and high price, so that the wide application of the vinyl oxalate is severely limited.
The raw materials of the reaction route of oxalic ester (dimethyl oxalate or diethyl oxalate) and ethylene glycol are low in price, and the price of the product can be obviously reduced. In addition, dimethyl oxalate is an intermediate product of the coal-to-ethylene glycol route. Therefore, the preparation of vinyl oxalate from dimethyl oxalate and ethylene glycol is the most preferred route. In this route, dimethyl oxalate and ethylene glycol are first subjected to transesterification and further polycondensation to obtain a hydroxyl-terminated prepolymer, followed by depolymerization under high temperature conditions. However, ethylene oxalate oligomers are susceptible to thermal degradation to ethylene formate compounds above 170 ℃, not only reducing yields but also requiring purification of the product. Therefore, developing efficient polycondensation catalysts and depolymerization catalysts, suitable polymerization and depolymerization routes, and effective purification processes are key technical problems to be solved in the process for obtaining high yield and preparing high-purity vinyl oxalate, and are the direction of long-standing efforts of researchers in the industry.
Disclosure of Invention
The invention mainly aims to provide a preparation method of high-purity vinyl oxalate, which solves the key technical problems that the reaction route of dimethyl oxalate and ethylene glycol is difficult to obtain high-yield and high-purity vinyl oxalate, thereby overcoming the defects in the prior art.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps:
The embodiment of the invention provides a preparation method of high-purity vinyl oxalate, which comprises the following steps:
performing polycondensation reaction on a mixed reaction system containing reaction monomers, a catalyst and a heat stabilizer at a first reaction temperature and a first reaction pressure to obtain an ethylene glycol oxalate polymer, wherein the reaction monomers comprise ethylene glycol and dimethyl oxalate, and the catalyst comprises an MXene material;
carrying out high-vacuum depolymerization reaction on the ethylene oxalate polymer at a second reaction temperature and a second reaction pressure, and carrying out reduced pressure sublimation to obtain a crude product of ethylene oxalate;
Purifying the coarse product of the vinyl oxalate to obtain the high-purity vinyl oxalate.
In some embodiments, the first reaction temperature is 130-170 ℃, the first reaction pressure is 50-100000 Pa, the polycondensation time is 5.0-13.5 hours, and the second reaction time is 1.5-3.0 hours.
In some embodiments, the second reaction temperature is 200-240 ℃ and the second reaction pressure is 5-100 pa.
Compared with the prior art, the invention has the beneficial effects that:
The preparation method of the high-purity vinyl oxalate provided by the invention can prepare the vinyl oxalate with the yield of more than 80% and the purity of more than 99% by regulating and controlling the introduction amount of the MXene catalyst, the reaction temperature, the reaction pressure and the types of the purification solvents, and is beneficial to the industrial production and the application of the vinyl oxalate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram illustrating the mechanism of the present invention using a Ti-based MXene catalyst;
FIG. 2 is a photograph of a real object and a schematic color of the product prepared in example 1 of the present invention;
FIG. 3 is a diagram showing the nuclear magnetic hydrogen spectrum and the structural composition of the product prepared in example 1 of the present invention.
Detailed Description
In view of the defects of the prior art, the inventor of the present invention has made a long-term study and a great deal of practice to propose the technical proposal of the present invention, because the ethylene oxalate oligomer prepared by the polycondensation reaction of dimethyl oxalate and ethylene glycol is easily thermally degraded into an ethylene formate compound at a temperature higher than 170 ℃, resulting in a reduced yield of ethylene oxalate and requiring further purification. Therefore, the invention creatively introduces the Ti-based MXene catalyst with high activity and environmental protection into a polycondensation reaction system of dimethyl oxalate and ethylene glycol, and achieves the aim of preparing high-yield and high-purity vinyl oxalate by optimizing a reaction route and purifying a crude product by using a low-toxicity solvent.
The present invention will be described in more detail below in order to facilitate understanding of the present invention. It should be understood, however, that the invention may be embodied in many different forms and should not be limited to the implementations or embodiments described herein. Rather, these embodiments or examples are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.
As one aspect of the technical solution of the present invention, it relates to the use of an MXene material for the catalytic depolymerization of ethylene oxalate oligomers to prepare ethylene oxalate, which is formed by the polymerization of ethylene glycol with dimethyl oxalate and the depolymerization of ethylene oxalate oligomers catalyzed by the MXene material as a catalyst.
According to another aspect of the technical scheme, the preparation method of the high-purity vinyl oxalate mainly comprises the steps of firstly converting dimethyl oxalate into ethylene oxalate polymer, then depolymerizing and decompressing to sublimate under high temperature to obtain a crude product vinyl oxalate, and finally purifying the crude product by using a low-toxicity solvent.
In some embodiments, the method for preparing high purity vinyl oxalate specifically comprises:
At a first reaction temperature and a first reaction pressure, carrying out polycondensation reaction on a mixed reaction system at least comprising reaction monomers and a catalyst to obtain an ethylene oxalate polymer, wherein the reaction monomers comprise ethylene glycol and dimethyl oxalate, and the catalyst comprises an MXene material;
Carrying out high-vacuum depolymerization reaction on the ethylene oxalate polymer at a second reaction temperature and a second reaction pressure, and sublimating and depolymerizing a product at a high vacuum degree to obtain a coarse product of ethylene oxalate;
And purifying the coarse product of the vinyl oxalate to obtain the high-purity vinyl oxalate.
In some embodiments, the mixed reaction system further comprises a heat stabilizer.
In some embodiments, the ethylene oxalate polymer has a structure as shown in formula (I):
wherein n=4 to 20.
In some embodiments, the method of preparation comprises purifying the crude vinyl oxalate product using a low toxicity solvent dissolution and recrystallization procedure to obtain a highly pure vinyl oxalate product.
In some more specific preferred embodiments, the method for preparing high purity vinyl oxalate comprises the steps of:
(1) And adding a certain proportion of reaction monomers, a catalyst and a heat stabilizer into a reaction kettle, and performing polycondensation reaction at a set first reaction temperature and a first reaction pressure to obtain a polymer (ethylene oxalate polymer) with a certain molecular weight shown in a formula (I), wherein n=4-20.
(2) And (3) carrying out high-vacuum depolymerization on the polymer at the set second reaction temperature and the set second reaction pressure to obtain a rough product of the vinyl oxalate.
(3) The crude product is subjected to purification operations including dissolution, concentration, filtration and drying using a low-toxicity aprotic solvent.
In some embodiments, in step (1), the reactive monomers are ethylene glycol and dimethyl oxalate.
In some embodiments, in step (1), the first reaction temperature is 130 to 170 ℃ and the first reaction pressure is 50 to 100000pa.
Further, in the step (1), the time of the polycondensation reaction is 5.o-13.5 h.
In some embodiments, in the step (1), the molar ratio of the ethylene glycol to the dimethyl oxalate is 1.1-3.0:1, preferably, the molar ratio is 1.1-2.2:1.
In some embodiments, in step (1), the catalyst may comprise a mixture of any one or more of Ti 3C2Tx、Ti4C3Tx、Ti2CTx, etc., preferably Ti 4C3Tx.
Further, taking the catalyst Ti 3C2Tx as an example, the action mechanism is shown in figure 1, and in the few-layer Ti-MXene planar structure, ti atoms can be uniformly distributed in high density. This promotes efficient coordination of the ethylene glycol and oxalate bonds with the Ti atoms, thereby facilitating the polycondensation reaction. And due to the effect, the OEO has high efficiency of forming the ethylene oxalate under the condition of cyclization temperature and is effectively separated under the condition of high vacuum, so that the probability of oxidative degradation of the ethylene oxalate bonds is obviously reduced, and finally, the preparation of the ethylene oxalate with higher yield and purity is realized.
Accordingly, the present inventors have found that the use of an MXene catalyst can efficiently promote not only the polycondensation reaction of dimethyl oxalate and ethylene glycol, but also the depolymerization of an ethylene oxalate polymer into a vinyl oxalate cyclic compound.
Further, the concentration (i.e., the introduction amount) of the catalyst in the mixed reaction system is 50 to 2000ppm, preferably 500 to 1000ppm.
In some embodiments, in step (1), the heat stabilizer may include, but is not limited to, any one or a combination of two or more of phosphoric acid, triphenyl phosphate, phosphorous acid, trimethyl phosphate, triethyl phosphate, and the like, preferably a combination of triphenyl phosphate, trimethyl phosphate, and triethyl phosphate.
Further, the concentration (i.e., the introduction amount) of the heat stabilizer in the mixed reaction system is 200 to 2000ppm, preferably 200 to 500ppm.
In some embodiments, in step (2), the second reaction temperature is 200 to 240 ℃, and the second reaction pressure is 5 to 100pa.
Further, in the step (2), the second reaction time is 1.5-3.0 h.
In some more preferred embodiments, the second reaction temperature is 220 240 ℃ and the second reaction pressure is 5 to 60pa.
In some embodiments, in step (3), the preparation method comprises purifying the crude product of vinyl oxalate with a low-toxicity aprotic solvent including, but not limited to, at least one of acetone, ethyl acetate, propyl acetate, butyl acetate, dioxane, tetrahydrofuran, cyclohexane, dichloromethane, butanone, cyclohexanone, and the like, preferably at least one of acetone, ethyl acetate, and dichloromethane.
Further, the purification includes the processes of dissolution, concentration, filtration, drying, and the like.
In summary, the preparation method of the invention uses the efficient transesterification catalyst Ti-MXene, and can obtain the vinyl oxalate with the yield of more than 80wt% and the purity of more than 99wt% by regulating and controlling the introduction amount of the MXene catalyst, the reaction temperature, the reaction pressure and the type of the purification solvent, thereby being beneficial to the industrial production and the application of the vinyl oxalate.
In order to facilitate understanding of the present invention, the technical solution of the present invention will be described in further detail with reference to several preferred embodiments and the accompanying drawings, and the embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation procedures are given, but the scope of protection of the present invention is not limited to the following embodiments. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.
The starting materials or reagents used in the examples were commercially available unless otherwise indicated. The main raw materials used in the following examples were analytically pure, ethylene glycol, dimethyl oxalate purchased from Allatin, and Ti-MXene catalyst was self-made.
Example 1
Preparation of ethylene oxalate oligomer (OEO 1).
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 12mg,100 ppm) and trimethyl phosphate (60 mg,500 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 4 hours, 150 ℃ for 4 hours and 165 ℃ for 3 hours, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 150 ℃ and the pressure to 50N100 Pa, reacting for 1.5 hours, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO1. The nuclear magnetic resonance hydrogen spectrum calculation shows that the oxalic acid unit content of OEO1 is 8.0mol/kg, the polymerization degree is about 6, and the yield is about 95% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO1 is gradually increased to 170 ℃, the pressure is gradually reduced to 60Pa, the temperature is set to 200 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 3 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 80.3% with a purity >99wt%.
The structural characterization is that a AvIII type nuclear magnetic resonance spectrometer (400 MHz) is adopted, deuterated acetone is used as a solvent, and TMS is used as an internal standard. The nuclear magnetic resonance hydrogen spectrum 1 H NMR and the structural composition of the vinyl oxalate prepared in example 1 of the present invention are shown in FIG. 3.
Color difference measurement the hue of the sample was measured using a WSC-S color difference meter. FIG. 2 shows a physical image and hue values of the vinyl oxalate sample obtained in example 1.
Example 2
Preparation of ethylene glycol oxalate oligomer (OEO 1) was as in example 1.
The temperature of the reaction raw material OEO1 is gradually increased to 170 ℃, the pressure is gradually reduced to 60Pa, the set temperature is 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 3 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 81.5% with a purity >99wt%.
Example 3
Preparation of ethylene glycol oxalate oligomer (OEO 1) was as in example 1.
The temperature of the reaction raw material OEO1 is gradually increased to 170 ℃, the pressure is gradually reduced to 20Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 2 hours until no obvious material exists in the reaction kettle. The sublimate crude ethylene oxalate was collected and recrystallized using a mixed solution of acetone and methylene chloride in a volume ratio of 1:1 to obtain the preparation of refined ethylene oxalate oligomer (OEO 1).
Example 4
Preparation of ethylene glycol oxalate oligomer (OEO 2)
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 24mg,200 ppm) and trimethyl phosphate (60 mg,500 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 4 hours, 150 ℃ for 2 hours, about 95% of crude byproduct methanol is generated, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 150 ℃ and the pressure to 50-100 Pa, reacting 1.0 h, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO2. The nuclear magnetic resonance hydrogen spectrum calculation shows that the oxalic acid unit content of OEO2 is 8.0mol/kg, the polymerization degree is about 6, and the yield is 95% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO2 is gradually increased to 170 ℃, the pressure is gradually reduced to 40Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 2 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 88.0% with a purity >99wt%.
Example 5
Preparation of ethylene glycol oxalate oligomer (OEO 3)
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 120mg,1000 ppm) and trimethyl phosphate (60 mg,500 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 2 hours, 150 ℃ for 2 hours, about 95% of crude byproduct methanol is generated, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 170 ℃ and the pressure to 50-100 Pa, reacting for 1.0h, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO3. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO3 was 8.4mol/kg, the degree of polymerization was about 19, and the yield was 93% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO3 is gradually increased to 170 ℃, the pressure is gradually reduced to 40Pa, the temperature is set to 240 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 2 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 80.0% with a purity >99wt%.
Example 6
Preparation of ethylene glycol oxalate oligomer (OEO 4)
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 240mg,2000 ppm) and trimethyl phosphate (60 mg,500 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 2 hours, 150 ℃ for 2 hours, about 95% of crude byproduct methanol is generated, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 130 ℃ and the pressure to 50-100 Pa, reacting for 1.5h, discharging under nitrogen protection, and cooling to room temperature to obtain the product OEO4. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO4 was 7.6mol/kg, the degree of polymerization was about 4, and the yield was 97% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 93.0% with a purity >99wt%.
Example 7
Preparation of ethylene oxalate oligomer (OEO 5).
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 6mg,50 ppm) and trimethyl phosphate (60 mg,500 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 6 hours, 150 ℃ for 4 hours and 165 ℃ for 2 hours, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 150 ℃ and the pressure to 50-100 Pa, reacting for 1.5h, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO5. The nuclear magnetic resonance hydrogen spectrum calculation shows that the oxalic acid unit content of OEO5 is 8.0mol/kg, the polymerization degree is about 6, and the yield is about 95% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO5 is gradually increased to 170 ℃, the pressure is gradually reduced to 20Pa, the set temperature is 220 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 3 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 86.6% with a purity >99wt%.
Example 8
Preparation of ethylene glycol oxalate oligomer (OEO 4) was as in example 6.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product of crude vinyl oxalate was collected and recrystallized using a cyclohexane solution to obtain refined vinyl oxalate. The yield was 91.0% with a purity of >99wt%.
Example 9
Preparation of ethylene glycol oxalate oligomer (OEO 4) was as in example 6.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate crude vinyl oxalate was collected and recrystallized using dioxane solution to obtain refined vinyl oxalate. The yield was 86.0% with a purity >99wt%.
Example 10
Preparation of ethylene glycol oxalate oligomer (OEO 4) was as in example 6.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product of coarse vinyl oxalate is collected and recrystallized by using tetrahydrofuran solution to obtain refined vinyl oxalate. The yield was 82.0% with a purity >99wt%.
Example 11
Preparation of ethylene glycol oxalate oligomer (OEO 4) was as in example 6.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product, crude vinyl oxalate, was collected and recrystallized using an ethyl acetate solution to obtain refined vinyl oxalate. The yield was 88.6% with a purity >99wt%.
Example 12
Preparation of ethylene glycol oxalate oligomer (OEO 4) was as in example 6.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using cyclohexanone solution to obtain refined vinyl oxalate. The yield was 81.5% with a purity >99wt%.
Example 13
Preparation of ethylene glycol oxalate oligomer (OEO 6).
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (68.2 g,1.100 mol), ti 2 CTx (MXene, 240mg,2000 ppm) and trimethyl phosphate (240 mg,2000 ppm) were charged into the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 1h,150 ℃ for 2h and 170 ℃ for 0.5h, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. And (3) reacting for 1.5 hours at 170 ℃ and 50-100 Pa, discharging under nitrogen protection, and cooling to room temperature to obtain the product OEO6. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO6 was 8.4mol/kg, the degree of polymerization was about 20, and the yield was about 91% after subtracting unreacted dimethyl oxalate.
Gradually increasing the temperature of the reaction raw material OEO6 to 220 ℃, increasing the temperature rate to about 2 ℃ per minute, gradually reducing the pressure to 20Pa, and reacting for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product of coarse vinyl oxalate is collected and recrystallized by using acetone solution to obtain refined vinyl oxalate. The yield was 83.5% with a purity >99wt%.
Example 14
Preparation of ethylene glycol oxalate oligomer (OEO 7).
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (136.4 g,2.200 mol), ti 4C3 Tx (MXene, 12mg,100 ppm) and trimethyl phosphate (24 mg,200 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for reaction for 1h,145 ℃ for reaction for 3h and 150 ℃ for reaction for 1h, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 135 ℃ and the pressure to 50-100 Pa, reacting for 1.5h, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO7. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO7 was 7.7mol/kg, the degree of polymerization was about 4, and the yield was about 95% after subtracting unreacted dimethyl oxalate.
Gradually raising the temperature of the reaction raw material OEO7 to 235 ℃, wherein the temperature raising rate is about 2 ℃ per minute, gradually reducing the pressure to 20Pa, and reacting for 2.0h until no obvious material exists in the reaction kettle. The sublimate product of crude vinyl oxalate was collected and recrystallized using methylene chloride solution to obtain refined vinyl oxalate. The yield was 88.6% with a purity >99wt%.
Example 15
Preparation of ethylene glycol oxalate oligomer (OEO 8).
The reaction materials dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (186.2 g,3.000 mol), ti 4C3 Tx (MXene, 12mg,100 ppm) and trimethyl phosphate (24 mg,200 ppm) were added to the reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for reaction for 1h,145 ℃ for reaction for 3h and 150 ℃ for reaction for 1h, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 135 ℃ and the pressure to 50-100 Pa, reacting for 2.0h, discharging under nitrogen protection, and cooling to room temperature to obtain the product OEO8. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO8 was 7.7mol/kg, the degree of polymerization was about 4, and the yield was about 95% after subtracting unreacted dimethyl oxalate.
Gradually raising the temperature of the reaction raw material OEO8 to 235 ℃, wherein the temperature raising rate is about 2 ℃ per minute, gradually reducing the pressure to 20Pa, and reacting for 2.0h until no obvious material exists in the reaction kettle. The sublimate product of crude vinyl oxalate was collected and recrystallized using methylene chloride solution to obtain refined vinyl oxalate. The yield was 88.6% with a purity >99wt%.
Example 16
Preparation of ethylene glycol oxalate oligomer (OEO 8) was as in example 15.
The temperature of the reaction raw material OEO8 is gradually increased to 170 ℃, the pressure is gradually reduced to 5Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product, crude vinyl oxalate, was collected and recrystallized using an ethyl acetate solution to obtain refined vinyl oxalate. The yield was 89.5% with a purity > 99% by weight.
Example 17
Preparation of ethylene glycol oxalate oligomer (OEO 8) was as in example 15.
The temperature of the reaction raw material OEO8 is gradually increased to 170 ℃, the pressure is gradually reduced to 100Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 2.0h until no obvious material exists in the reaction kettle. The sublimate product, crude vinyl oxalate, was collected and recrystallized using an ethyl acetate solution to obtain refined vinyl oxalate. The yield was 82.6% with a purity of >99wt%.
Comparative example 1
The comparative example is different from example 1 in that the temperature of the reaction raw material OEO1 is gradually increased to 170 ℃ and the pressure is gradually reduced to 20Pa, the temperature is set to 190 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 8 hours until no obvious material exists in the reaction kettle. The sublimate crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and methylene chloride in a volume ratio of 1:1 to obtain refined vinyl oxalate with a yield of 70.3% and a purity of >99wt%.
Comparative example 2
The comparative example is different from example 1 in that the temperature of the reaction raw material OEO1 is gradually increased to 170 ℃ and the pressure is gradually reduced to 60Pa, the temperature is set to 190 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 10 hours until no obvious material exists in the reaction kettle. The sublimate crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and methylene chloride in a volume ratio of 1:1 to obtain refined vinyl oxalate with a yield of 60.1% and a purity of >99wt%.
The results show that the preparation of the ethylene oxalate oligomer with proper polymerization degree can obviously increase the yield of the ethylene oxalate by increasing the depolymerization temperature, the introduction amount of the catalyst Mxene and the vacuum degree.
Comparative example 3
This comparative example was different from example 1 in that dimethyl oxalate (118.1 g,1.000 mol), ethylene glycol (118.1 g,1.903 mol), ti 3C2 Tx (MXene, 3mg,25 ppm) and trimethyl phosphate (60 mg,500 ppm) as reaction materials were charged into a reaction vessel. Under the protection of nitrogen, the temperature of the material is gradually increased to 130 ℃ for 6 hours, 150 ℃ for 6 hours and 165 ℃ for 4 hours, about 95% of crude byproduct methanol is produced, and 10-30 g of unreacted dimethyl oxalate is collected from the byproduct methanol. Setting the temperature to 150 ℃ and the pressure to 50-100 Pa, reacting for 1.5h, discharging under the protection of nitrogen, and cooling to room temperature to obtain the product OEO9. The nuclear magnetic resonance hydrogen spectrum calculation showed that the oxalic acid unit content of OEO9 was 8.0mol/kg, the degree of polymerization was about 6, and the yield was about 86% after subtracting unreacted dimethyl oxalate.
The temperature of the reaction raw material OEO9 is gradually increased to 170 ℃, the pressure is gradually reduced to 60Pa, the temperature is set to 200 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 3 hours until no obvious material exists in the reaction kettle. And collecting sublimate coarse vinyl oxalate, and recrystallizing by using a mixed solution of acetone and methylene dichloride in a volume ratio of 1:1 to obtain refined vinyl oxalate. The yield was 72.3% with a purity >99wt%. This is because the very low amount of MXene introduced does not perform as effectively.
The results show that the preparation of the ethylene oxalate oligomer with proper polymerization degree can obviously increase the yield of the ethylene oxalate by increasing the depolymerization temperature, the introduction amount of the catalyst Mxene and the vacuum degree.
Comparative example 4
To demonstrate the high efficiency of the Ti-MXene catalyst, 240mg of tetrabutyl titanate (TBT) was substituted for Ti 3C2 Tx and the synthesis procedure of OEO4 was repeated to give OEO10, which was calculated by nuclear magnetic resonance spectroscopy to show that OEO10 had an oxalic acid unit content of 7.5mol/kg and a degree of polymerization of about 4, and a yield of 93% after subtracting unreacted dimethyl oxalate. Then the temperature of the reaction raw material OEO10 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the set temperature is 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate crude vinyl oxalate was collected and recrystallized using a mixed solution of acetone and methylene chloride in a volume ratio of 1:1 to obtain refined vinyl oxalate in a yield of 75.0% with a purity of >99wt%. Experimental results show that Ti 3C2 Tx has better capability of depolymerizing glycol oxalate compared with TBT.
Comparative example 5
To demonstrate the high efficacy of low toxicity aprotic solvents, the present comparative example uses ethanol reported in the literature as the purification solvent.
The temperature of the reaction raw material OEO4 is gradually increased to 170 ℃, the pressure is gradually reduced to 35Pa, the temperature is set to 235 ℃, the temperature rising rate is about 2 ℃ per minute, and the reaction is carried out for 1.5 hours until no obvious material exists in the reaction kettle. The sublimate product of crude vinyl oxalate was collected and recrystallized using ethanol to obtain refined vinyl oxalate. The yield was 86.0% and the purity was about 98% by weight. The results show that the proton solvent is easy to open the ring due to the high reactivity of the vinyl oxalate, and the open-ring product remains in the refined vinyl oxalate, thereby reducing the purity of the product.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent transformation of the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (10)
1. The preparation method of the high-purity vinyl oxalate is characterized by comprising the following steps:
performing polycondensation reaction on a mixed reaction system containing reaction monomers, a catalyst and a heat stabilizer at a first reaction temperature and a first reaction pressure to obtain an ethylene glycol oxalate polymer, wherein the reaction monomers comprise ethylene glycol and dimethyl oxalate, and the catalyst comprises an MXene material;
carrying out high-vacuum depolymerization reaction on the ethylene oxalate polymer at a second reaction temperature and a second reaction pressure, and carrying out reduced pressure sublimation to obtain a crude product of ethylene oxalate;
Purifying the coarse product of the vinyl oxalate to obtain the high-purity vinyl oxalate.
2. The method of claim 1, wherein the first reaction temperature is 130-170 ℃, the first reaction pressure is 50-100000 Pa, the polycondensation time is 5.0-13.5 h, and/or the molar ratio of the ethylene glycol to the dimethyl oxalate is 1.1-3.0:1.
3. The method of claim 2, wherein the molar ratio of ethylene glycol to dimethyl oxalate is 1.1-2.2:1.
4. The method of claim 1, wherein the catalyst comprises one or more of Ti 3C2Tx、Ti4C3Tx、Ti2CTx and/or the concentration of the catalyst in the mixed reaction system is 50-2000 ppm.
5. The method of claim 2, wherein the ethylene oxalate polymer has a structure represented by formula (I):
Wherein n=4 to 20;
and/or the concentration of the catalyst in the mixed reaction system is 500-1000 ppm.
6. The method of claim 1, wherein the heat stabilizer comprises one or a combination of two or more of phosphoric acid, triphenyl phosphate, phosphorous acid, trimethyl phosphate and triethyl phosphate, and/or the concentration of the heat stabilizer in the mixed reaction system is 200-2000 ppm.
7. The method according to claim 6, wherein the heat stabilizer comprises a combination of triphenyl phosphate, trimethyl phosphate and triethyl phosphate, and/or the concentration of the heat stabilizer in the mixed reaction system is 200-500 ppm.
8. The method of claim 1, wherein the second reaction temperature is 200-240 ℃, the second reaction pressure is 5-100 Pa, and the second reaction time is 1.5-3.0 h.
9. The method according to claim 8, wherein the second reaction temperature is 220-240 ℃ and the second reaction pressure is 5-60 Pa;
And/or purifying the crude product of vinyl oxalate by adopting a low-toxicity aprotic solvent, wherein the low-toxicity aprotic solvent comprises at least one of acetone, ethyl acetate, propyl acetate, butyl acetate, dioxane, tetrahydrofuran, cyclohexane, dichloromethane, butanone and cyclohexanone;
and/or, the purification comprises dissolving, concentrating, filtering and drying.
10. The method according to claim 9, wherein the low-toxicity aprotic solvent comprises at least one of acetone, ethyl acetate and dichloromethane;
and/or, the yield of the preparation method is greater than 80wt%;
and/or the purity of the high-purity vinyl oxalate prepared by the preparation method is more than 99wt%.
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