CN113929885A - Composite catalyst and application thereof in preparation of glycolide - Google Patents

Composite catalyst and application thereof in preparation of glycolide Download PDF

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CN113929885A
CN113929885A CN202111213592.1A CN202111213592A CN113929885A CN 113929885 A CN113929885 A CN 113929885A CN 202111213592 A CN202111213592 A CN 202111213592A CN 113929885 A CN113929885 A CN 113929885A
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glycolide
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methyl glycolate
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methyl
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CN113929885B (en
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翁伟明
吴维果
刘志刚
李国方
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Jiangsu Jinzhihong New Material Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
    • C08G63/08—Lactones or lactides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/82—Preparation processes characterised by the catalyst used
    • C08G63/823—Preparation processes characterised by the catalyst used for the preparation of polylactones or polylactides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Abstract

The invention relates to a composite catalyst and application thereof in preparation of glycolide. The preparation method provided by the invention utilizes the stability and moderate Lewis acidity of 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate and is matched with a cocatalyst to catalyze the dealcoholization polycondensation reaction of methyl glycolate, and then catalyzes the cracking cyclization reaction of the methyl glycolate under the high-temperature high-vacuum environment to prepare glycolide. The glycolide prepared by the catalyst for catalyzing the polycondensation and the cracking cyclization of the methyl glycolate has the characteristics of high purity, high yield, low viscosity of cracking cyclization substrates and no coking.

Description

Composite catalyst and application thereof in preparation of glycolide
Technical Field
The invention belongs to the field of glycolide synthesis catalysts, and particularly relates to a catalyst for catalyzing polycondensation of methyl glycolate and cyclization and cracking of poly methyl glycolate formed by polycondensation to generate glycolide and a method for preparing glycolide by using the catalyst.
Background
Polyglycolide (abbreviated as PGA, also known as polyglycolic acid, polyglycolic acid ester) has a main chain structure as follows:
Figure BDA0003309755850000011
the main chain structure has completely degradable ester chemical groups, the degradation speed is high under the action of hydrolysis and the like, and finally degraded products in nature are carbon dioxide and water, so that the material is considered as an ideal completely biodegradable high polymer material. PGA may be a polymer obtained by ring-opening polymerization of glycolide or by direct polycondensation of glycolic acid (ester). However, since it is relatively difficult to obtain PGA having a relative molecular mass of one hundred thousand or more by the conventional direct polycondensation method, the most mature method for producing PGA is to synthesize glycolide by cyclization of glycolic acid (ester) and then produce polyglycolic acid by ring-opening polymerization of glycolide, as shown in the following formula:
Figure BDA0003309755850000012
the cost of glycolide as a core material for the preparation of PGA and its copolymers has been one of the important factors that restrict the application of PGA. Methyl glycolate can be obtained through a coal chemical industry route, and is a relatively cheap chemical raw material. Therefore, if a highly efficient catalyst can be developed and a suitable process can be used to produce glycolide from methyl glycolate, it is expected that the production cost of PGA can be greatly reduced.
Patent publication No. CN112469704A reports a method for preparing glycolide products from poly (methyl glycolate) or products thereof. The method takes the polyglycolic acid methyl ester as a raw material, adopts an all-metal compound catalyst, firstly hydrolyzes the polyglycolic acid methyl ester, then polymerizes the polyglycolic acid methyl ester, and then carries out pyrolysis (the term "pyrolysis" is the same as the term "cracking cyclization", "cracking" or "depolymerization" in the invention) under high temperature and high vacuum by matching with a viscosity reducer, thereby solving the problems that a depolymerization substrate is easy to carbonize and has high viscosity and the yield of crude glycolide is low in the glycolide generation process. However, this method has a problem that the process flow is long, the addition of a viscosity-reducing agent causes inconvenience in the recovery of the substrate, and the inclusion of free acids in glycolide causes an increase in cost.
Patent publication No. CN 111548339A reports a method for preparing glycolide by polycondensation and depolymerization of glycolates using common tin, antimony and zinc metal compounds as catalysts. However, the method needs complex equipment to solve the problems of low purity of crude glycolide in the preparation process and easy coking in the depolymerization process. And the polycondensation process of the glycolate needs a vacuum environment, and has certain requirements on polycondensation equipment.
Methyl glycolate can generate polymerization reaction under the catalysis of certain Lewis acid to generate poly-methyl glycolate, but few related reports exist about special catalysts which are specially used for preparing glycolide by firstly polymerizing methyl glycolate and then depolymerizing (cracking cyclization).
Carbocations are ions of a positively charged carbon atom that are generally unstable and highly reactive because they do not have 8 electrons to satisfy the octagon rule. The carbonium ion is an sp2 hybridized plane in the carbon center of the carbonium ion, and has an empty P orbital with positive charge for accepting electrons. Thus, carbenium is a potential Lewis acid organic molecular catalyst. However, triphenylcarbenium ion has unusual stability and strong Lewis acidity due to its unique structure. And the Lewis acidity of the triphenylcarbenium ion can be adjusted by changing the electron cloud density on the aromatic ring. For carbenium ions, the more electron donating groups on the aromatic ring, the more Lewis acidic the compound is. Compared with the conventional metal Lewis acid catalyst, the adjustability of Lewis acidity of the carbenium ion is a remarkable advantage, so that the carbenium ion has obvious advantages in certain synthesis fields which are sensitive to the Lewis acidity of the catalyst.
The invention content is as follows:
aiming at the defects of the prior art, the invention aims to provide a catalyst, a preparation method of the catalyst and catalytic application of the catalyst in a glycolide preparation method, so as to solve the problems of more side reactions, easy coking and carbonization of a substrate, low product purity and complex process equipment in the conventional preparation of glycolide from methyl glycolate.
Technical scheme
The invention provides a catalyst which takes triphenyl carbonium ions as a main catalyst, and the catalyst is used for the catalytic application of preparing glycolide from methyl glycolate, and a method for synthesizing glycolide by applying the catalyst.
A method for preparing a composite catalyst, comprising the steps of:
adding metered ethyl benzoate and p-methyl phenyl magnesium bromide into anhydrous tetrahydrofuran, refluxing for 3 hours at 70-80 ℃, and providing for a second step.
② dropping ammonium chloride aqueous solution under ice bath to quench reaction, then separating liquid to obtain organic phase.
And thirdly, evaporating the organic phase obtained in the second step to dryness at 120-160 ℃ by using a rotary evaporator to obtain a viscous yellow oily substance, namely 4, 4' -dimethyl triphenyl carbinol.
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the mass percent of the total amount of the sodium tetrafluoroborate, generating yellow precipitates, and drying the precipitates to obtain the 4, 4' -ditolyl phenyl methyl carbonium ion tetrafluoroborate.
Fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step IV with zinc oxide serving as a cocatalyst according to a certain proportion to obtain the composite catalyst.
In the step I, the mol ratio of the ethyl benzoate to the p-methylphenyl magnesium bromide is 1: 2-1: 4.
in the second step, the ratio of the mol amount of ammonium chloride contained in the dropwise added ammonium chloride aqueous solution to the mol amount of methyl phenyl magnesium bromide is 1: 1-2: 1
In the step (iii), the molar amount of tetrafluoroboric acid contained in the dropwise added tetrafluoroboric acid diethyl ether solution is 1-2 times of the molar amount of 4, 4' -dimethyltriphenylmethanol.
In the fifth step, the mass ratio of the 4, 4' -xylyl phenyl methyl carbonium tetrafluoroborate to the zinc oxide is 1: 1-4: 1.
in the fifth step, the 4, 4' -ditolyl phenyl methyl carbonium ion tetrafluoroborate has a structural formula shown as the following figure
Figure BDA0003309755850000031
A composite catalyst prepared by the method of any one of claims 1 to 5.
The use of the catalyst in the preparation of glycolide from methyl glycolate is characterized in that: firstly, stirring and mixing methyl glycolate and the catalyst in a reaction kettle, reacting for a period of time at 140-230 ℃ under normal pressure environment to obtain methyl glycolate oligomer, and then cracking and cyclizing the methyl glycolate oligomer at 230-245 ℃ under vacuum 50-500 Pa (absolute pressure) environment to generate glycolide.
Specifically, the method comprises the following reaction steps:
polycondensation reaction of methyl glycolate: a certain amount of methyl glycolate is taken into a reaction kettle, then the composite catalyst prepared by the invention is added into the reaction kettle, stirring is started, and the dosage of the catalyst is 0.5-1% of the mass of the methyl glycolate. Then, the temperature is raised to 140 ℃ N2Reacting for 2-4 h under the protection of normal pressure, and heating to 180 ℃ to obtain N2Reacting for 4-6 h under the protection of normal pressure, and finally heating to 230 ℃ N2And (3) carrying out reaction for 2-4 h under the protection of normal pressure to finish the polycondensation reaction of the methyl glycolate to obtain the low molecular weight poly (methyl glycolate).
Depolymerization and cyclization reaction: and vacuumizing the reaction kettle, keeping the vacuum of the reaction kettle at 50-500 Pa (absolute pressure) all the time, heating the reaction kettle, and obtaining glycolide through depolymerization and cyclization reaction of the low-molecular-weight poly (methyl glycolate) at high temperature and high vacuum. The temperature control process during the period is as follows: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 1-2 h; heating to 240 ℃ and reacting for 1-2 h; and finally, heating to 245 ℃ for reaction for 0.5-1 h.
Advantageous effects
The catalyst provided by the invention can greatly improve the conversion rate of methyl glycolate into crude glycolide, and the obtained crude glycolide has higher purity. On the one hand, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate has moderate Lewis acidity and can show good compatibility with the auxiliary catalyst zinc oxide; on the other hand, 4, 4' -ditolyl phenylmethyl carbenium as one kind of phenyl carbenium has higher stability than that of common carbenium.
Drawings
FIG. 14-nuclear magnetic hydrogen spectrum of tolylbenzhydryl carbonium tetrafluoroborate
FIG. 24, 4' -ditolyl phenyl methyl carbonium ion tetrafluoroborate nuclear magnetic hydrogen spectrum
FIG. 34 ', 4' -Trimethylphenylmethyl carbonium tetrafluoroborate nuclear magnetic hydrogen spectrum
Detailed Description
The following detailed description is given for the purpose of illustration, but it is to be understood that the invention is not limited to the specific embodiments disclosed, and that various insubstantial changes and modifications can be made by one skilled in the art based on the teachings of the invention described above.
Except where specifically stated, the apparatus and methods used in the present invention are those commonly used in the art. Glycolide purity test method: the obtained crude glycolide was mixed, crushed and mixed uniformly by a crusher, and then sampled, and the melting point of glycolide was measured by a DSC apparatus (hitachi, model DSC 7020). The purity is evaluated by the melting point of glycolide, the higher the melting point the higher the purity. The specific DSC test method comprises the following steps: taking a proper amount of glycolide sample, and heating the glycolide to 90 ℃ from 40 ℃ at the heating rate of 5 ℃/min. The nuclear magnetic test method comprises the following steps: after a sample is dissolved in 0.5-0.6 ml of a deuterated reagent, the sample is transferred into a nuclear magnetic tube, and the synthesized carbenium tetrafluoroborate is characterized by performing nuclear magnetic resonance hydrogen spectrum analysis on a nuclear magnetic resonance instrument (Bruker Avance AV-400 type, Bruker, Switzerland Bruker).
Example 1
1.1 preparation of the catalyst
60ml of anhydrous tetrahydrofuran are charged with metered amounts of ethyl benzoate (30mmol) and p-methylphenylmagnesium bromide (60mmol) and refluxed at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 30mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ evaporating the organic phase obtained in the step (II) to dryness at 120 ℃ by using a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -dimethyl triphenyl carbinol (5.76g, 20 mmol).
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 40mmol HBF4) Yellow precipitate was formed, and the precipitate was washed and dried to obtain 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate (4.92 g).
Fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step (iv) with zinc oxide serving as a cocatalyst according to the mass ratio of 4:1 to obtain the composite catalyst.
1.2 preparation method of glycolide:
taking 200g of methyl glycolate into a reaction kettle, then adding 1g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 2h under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 50Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 1 h; heating to 240 ℃ and reacting for 1 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Example 2
2.1 preparation of the catalyst
60ml of anhydrous tetrahydrofuran are charged with metered amounts of ethyl benzoate (30mmol) and p-methylphenylmagnesium bromide (120mmol) and refluxed at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 240mmol of ammonium chloride) under ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ the organic phase obtained in the step (II) is evaporated to dryness at 160 ℃ by a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -dimethyl triphenyl carbinol (7.49g, 26 mmol).
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 26mmol HBF4) Yellow precipitate was formed, and the precipitate was washed and dried to obtain 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate (5.40 g).
Fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step (iv) with zinc oxide serving as a cocatalyst according to the mass ratio of 1:1 to obtain the composite catalyst.
2.2 preparation method of glycolide:
taking 200g of methyl glycolate into a reaction kettle, then adding 2g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 2h under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 6h under the protection of normal pressure, and finally, heating to 230 ℃ N2And (3) carrying out reaction for 2-4 h under the protection of normal pressure to finish the polycondensation reaction of the methyl glycolate to obtain the low molecular weight poly (methyl glycolate). Vacuumizing the reaction kettle to 150Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ and reacting for 1 h; finally, the temperature is raised to 245 ℃ for reaction for 0.5 h.
The measurement and test results of the collected glycolide are shown in Table 1
Example 3
3.1 preparation of the catalyst
60ml of anhydrous tetrahydrofuran are charged with metered amounts of ethyl benzoate (30mmol) and p-methylphenylmagnesium bromide (80mmol) and refluxed at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 120mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ the organic phase obtained in the step (II) is evaporated to dryness at 140 ℃ by a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -dimethyl triphenyl carbinol (7.78g, 27 mmol).
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 30mmol HBF4) Yellow precipitate was formed, and the precipitate was washed and dried to obtain 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate (5.83 g).
Fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step (iv) with zinc oxide serving as a cocatalyst according to the mass ratio of 3:1 to obtain the composite catalyst.
3.2 preparation method of glycolide:
taking 200g of methyl glycolate into a reaction kettle, then adding 2g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 500Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Example 4
4.1 preparation of the catalyst
Same as example 3
4.2 preparation method of glycolide:
taking 200g of methyl glycolate into a reaction kettle, then adding 2g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Example 5
5.1 preparation of the catalyst
Same as example 3
4.2 preparation method of glycolide: (the amount of the composite catalyst is slightly larger)
Taking 200g of methyl glycolate into a reaction kettle, then adding 4g of the composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Example 6
6.1 preparation of the catalyst
60ml of anhydrous tetrahydrofuran are charged with metered amounts of ethyl benzoate (30mmol) and p-methylphenylmagnesium bromide (100mmol) and refluxed at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 150mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ the organic phase obtained in the step (II) is evaporated to dryness at 140 ℃ by a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -dimethyl triphenyl carbinol (7.20g, 25 mmol).
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 40mmol HBF4) Yellow precipitate was formed, and the precipitate was washed and dried to obtain 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate (5.36 g).
Fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step (iv) with zinc oxide serving as a cocatalyst according to the mass ratio of 2:1 to obtain the composite catalyst.
6.2 preparation method of glycolide:
taking 200g of methyl glycolate into a reaction kettle, then adding 1.6g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 2h under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 3h under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 200Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ and reacting for 1 h; finally heating to 245 ℃ for reaction for 0.5h, and pumpingCollecting the output glycolide, and opening a bottom valve of the reaction kettle to discharge the cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Example 7
7.1 preparation of the catalyst
60ml of anhydrous tetrahydrofuran are charged with metered amounts of ethyl benzoate (30mmol) and p-methylphenylmagnesium bromide (80mmol) and refluxed at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 120mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ the organic phase obtained in the step (II) is evaporated to dryness at 140 ℃ by a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -dimethyl triphenyl carbinol (7.78g, 27 mmol).
Fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 30mmol HBF4) Yellow precipitate was formed, and the precipitate was washed and dried to obtain 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate (5.83 g).
Fifthly, directly using the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step (iv) as a catalyst special for preparing glycolide by using methyl glycolate without complex formulation treatment.
7.2 preparation method of glycolide:
adding 200g of methyl glycolate into a reaction kettle, adding 1g of 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate into the reaction kettle, starting stirring, and heating to 140 ℃ to obtain N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 500Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps:keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Comparative example 1
Preparing a catalyst:
put metered benzophenone (30mmol) and p-methylphenyl magnesium bromide (80mmol) in 60ml of anhydrous tetrahydrofuran and reflux at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 120mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ the organic phase obtained in the step (II) is evaporated to dryness at 140 ℃ by a rotary evaporator to obtain viscous yellow oily matter, namely 4-methyl triphenyl carbinol (5.6g, 20.4 mmol).
Fourthly, dissolving the 4-methyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage content and 30mmol HBF4) A yellow precipitate was formed, and the precipitate was washed and dried to obtain 4-tolyldiphenylmethylcarbapentanium tetrafluoroborate (5.05 g).
Fifthly, compounding the 4-tolyldiphenyl methyl carbonium tetrafluoroborate obtained in the step (iv) with zinc oxide serving as a cocatalyst according to the mass ratio of 3:1 to obtain the composite catalyst.
The preparation method of glycolide comprises the following steps:
taking 200g of methyl glycolate into a reaction kettle, then adding 2g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. Crack (crack)The heating process of the ring-opening reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Comparative example 2
Preparing a catalyst:
put metered ethyl p-benzoate (26mmol) and p-methylphenyl magnesium bromide (66mmol) in 60ml of anhydrous tetrahydrofuran and reflux at 70 ℃ for 3 h.
② dropping ammonium chloride aqueous solution (containing 120mmol of ammonium chloride) in ice bath to quench reaction, and then separating liquid to obtain organic phase.
③ evaporating the organic phase obtained in the step II to dryness at 140 ℃ by using a rotary evaporator to obtain viscous yellow oily matter, namely 4, 4' -trimethyltriphenylmethanol (5.2g, 17.2 mmol).
Fourthly, dissolving the 4, 4' -trimethyl trityl alcohol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the weight percentage of the nano-particles and 17.2mmolHBF4) A yellow precipitate was formed, and the precipitate was washed and dried to obtain 4-tolyldiphenylmethylcarbapentanium tetrafluoroborate (5.82 g).
Fifthly, compounding the 4, 4' -tritolyl carbonium tetrafluoroborate obtained in the step IV with zinc oxide serving as a cocatalyst according to the mass ratio of 3:1 to obtain the composite catalyst.
The preparation method of glycolide comprises the following steps:
taking 200g of methyl glycolate into a reaction kettle, then adding 2g of composite catalyst into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), and heating to make low molecular weight poly (methyl glycolate) undergo cracking cyclization reaction, during which the extracted ethyleneCollecting lactide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Comparative example 3
Adding 200g of methyl glycolate into a reaction kettle, then adding 2g of zinc oxide into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; and finally, heating to 245 ℃ for reaction for 1h, collecting the extracted glycolide, and opening a bottom valve of the reaction kettle to discharge a cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
Comparative example 4
Taking 200g of methyl glycolate into a reaction kettle, then adding 2g of stannous chloride into the reaction kettle, starting stirring, heating to 140 ℃ and raising the temperature to N2Reacting for 4 hours under the protection of normal pressure, and then heating to 180 ℃ N2Reacting for 4 hours under the protection of normal pressure, and finally, heating to 230 ℃ N2The reaction is carried out for 4 hours under the protection of normal pressure, thus completing the polycondensation reaction of the methyl glycolate and obtaining the low molecular weight poly-methyl glycolate. Vacuumizing the reaction kettle to 100Pa (absolute pressure), heating to enable low molecular weight poly (methyl glycolate) to undergo cracking cyclization reaction, collecting the extracted glycolide in the process, and opening a bottom valve of the reaction kettle to discharge a cracking substrate. The heating process of the cracking cyclization reaction comprises the following steps: keeping the temperature in the reaction kettle at 230 ℃ and reacting for 2 hours; heating to 240 ℃ for reaction for 2 h; finally heating to 245 ℃ for reactionThe extracted glycolide is collected for 1 hour, and a bottom valve of the reaction kettle is opened to discharge the cracking substrate.
The measurement and test results of the collected glycolide are shown in Table 1
TABLE 1 glycolide yield and test results statistics table
Figure BDA0003309755850000101
Figure BDA0003309755850000111
As can be seen by comparing the examples with comparative examples 1 and 2, the Lewis acidity of the catalyst has a large influence on the melting point of the glycolide obtained and the yield of glycolide. The carbenium borate of comparative example 1 has one less methyl group than the carbenium borate of the examples, while the carbenium borate of comparative example 2 has one more methyl group. Methyl as an electron donating group, and a change in the amount will also directly affect the Lewis acidity of the carbenium borate. The carbonium ion borate adopted by the composite catalyst special for preparing glycolide by methyl glycolate is 4, 4' -ditolyl phenyl methyl carbonium ion tetrafluoroborate, has moderate Lewis acidity, and is just suitable for prepolymerization of methyl glycolate and depolymerization reaction of low molecular weight methyl glycolate.
It can be seen from the comprehensive examples and comparative examples that the composite catalyst specially used for preparing glycolide from methyl glycolate has higher melting point and yield in the preparation of glycolide by polycondensation and cracking cyclization of methyl glycolate, and the cracking substrate has low viscosity, no coking, easy residue discharge and industrial production. Meanwhile, the invention also shows that the special composite catalyst for preparing glycolide by using methyl glycolate has higher selectivity and conversion rate, and is a special catalyst with excellent performance.

Claims (8)

1. A method for preparing a composite catalyst, comprising the steps of:
adding metered ethyl benzoate and p-methyl phenyl magnesium bromide into anhydrous tetrahydrofuran, refluxing for 3 hours at 70-80 ℃, and providing for a second step;
dropping ammonium chloride water solution in ice bath to quench reaction, and separating liquid to obtain organic phase;
evaporating the organic phase obtained in the step two to dryness at 120-160 ℃ by using a rotary evaporator to obtain a viscous yellow oily substance, namely 4, 4' -dimethyl triphenyl carbinol;
fourthly, dissolving the 4, 4' -dimethyl triphenyl carbinol obtained in the third step into the ethyl ether, stirring and slowly dripping the tetrafluoroboric acid ethyl ether solution (HBF)450 percent of the mass percent of the total-content of the four-element boron nitride, generating yellow precipitate, and drying the precipitate to obtain 4, 4' -ditolyl phenyl methyl carbonium ion tetrafluoroborate;
fifthly, compounding the 4, 4' -ditolyl phenyl methyl carbonium tetrafluoroborate obtained in the step IV with zinc oxide serving as a cocatalyst according to a certain proportion to obtain the composite catalyst.
2. The method according to claim 1, wherein in step (i), the molar ratio of ethyl benzoate to p-methylphenyl magnesium bromide is 1: 2-1: 4.
3. the method according to claim 1, wherein in step (ii), the ratio of the mol amount of ammonium chloride contained in the dropwise added ammonium chloride aqueous solution to the mol amount of methylphenylmagnesium bromide is 1: 1-2: 1.
4. the method according to claim 1, wherein in the third step, the molar amount of tetrafluoroboric acid contained in the dropwise added tetrafluoroboric acid-diethyl ether solution is 1 to 2 times the molar amount of 4, 4' -dimethyltriphenylmethanol.
5. The method according to claim 1, wherein in the fifth step, the mass ratio of the 4, 4' -ditolyl phenylmethyl carbonium tetrafluoroborate to the zinc oxide is 1: 1-4: 1.
6. the method according to claim 5, wherein in the fifth step, the 4, 4' -ditolyl phenylmethyl carbonium tetrafluoroborate has the following structural formula:
Figure RE-FDA0003416696930000011
7. a composite catalyst prepared by the method of any one of claims 1 to 6.
8. Use of a catalyst according to claim 7 for the preparation of glycolide from methyl glycolate, characterized in that: firstly, stirring and mixing methyl glycolate and the catalyst of claim 7 in a reaction kettle, reacting for a period of time at 140-230 ℃ under normal pressure environment to obtain methyl glycolate oligomer, and then cracking and cyclizing the methyl glycolate oligomer at 230-245 ℃ under vacuum 50-500 Pa (absolute pressure) environment to generate glycolide.
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