A polyethylene glycol-based amphiphilic polymer catalyst, a preparation method thereof, a high internal phase emulsion and application thereof

Abstract

This invention discloses a polyethylene glycol-based amphiphilic polymer catalyst, its preparation method, a high internal phase emulsion, and its applications. The catalyst is copolymerized from polyethylene glycol-based acrylate and a vinylimidazole-functionalized Schiff base transition metal complex. In an oil-water two-phase system, the polymer self-assembles through intramolecular hydrophobic interactions to form an oil-in-water high internal phase emulsion. The polyethylene glycol units stabilize the emulsion through hydrogen bonding, and the Schiff base transition metal complex serves as the catalytically active center. This catalyst solves the problem of mass transfer difficulties between the oil and water phases in aqueous catalytic systems, exhibiting excellent conversion and selectivity. Furthermore, the oil-in-water high internal phase emulsion has extremely high oil loading (>74% by volume), enabling high-throughput catalytic synthesis of fine chemicals in the aqueous phase. The catalyst is simple to prepare, low in cost, and suitable for industrial production. Moreover, the aqueous catalytic process does not require the use of any organic solvents or additives, meeting the requirements of green chemistry.

Description

Technical Field

[0001] This invention relates to a catalyst, specifically to a polyethylene glycol-based amphiphilic polymer catalyst, its preparation method, high internal phase emulsion, and its applications, belonging to the field of catalyst technology. Background Technology

[0002] In recent years, with the increasing prominence of environmental issues, water has become a favorite among chemists as a green solvent. However, organic substrates are insoluble in the aqueous phase, often leading to difficulties in mass transfer. Emulsion catalysis systems can solve the mass transfer problem in the aqueous phase, but the low oil loading (<20%) of traditional emulsions limits the efficiency of aqueous phase catalytic synthesis. Therefore, it is necessary to prepare emulsions with higher oil loading to achieve high-throughput synthesis of fine chemicals in the aqueous phase. High-internal-phase emulsions (HIPEs) are a class of emulsions with high oil loading, typically exceeding 74% by volume. Compared with traditional oil-in-water emulsions, HIPEs have higher oil content, smaller emulsion droplet size, and better stability. The concept of HIPEs was first proposed by Lissant in the 1960s. Subsequently, researchers at home and abroad have conducted extensive research on the formation mechanism, droplet geometry mathematical model, thermodynamic properties, and material preparation of HIPEs. Traditional small-molecule surfactants, such as sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB), can stabilize high-internal-phase emulsions (HIPEs), but require large amounts of emulsifiers and exhibit poor emulsion stability. Biomass-based surfactants can stabilize high-internal-phase emulsions through electrostatic interactions and / or hydrogen bonding, requiring small amounts of emulsifiers, but their structures are difficult to functionalize, limiting their application in catalysis. Amphiphilic polymers can self-assemble and stabilize emulsions in oil-water two-phase systems, and by adjusting their composition, structure, and functional group distribution, they can be applied to aqueous-phase catalysis. However, their application in the preparation and catalytic use of high-internal-phase emulsions is rarely reported.

[0003] Therefore, it is of great significance to develop a polyethylene glycol-based amphiphilic polymer catalyst, its preparation method, high internal phase emulsion, and its applications. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the first objective of the present invention is to provide a polyethylene glycol-based amphiphilic polymer catalyst with high stability and excellent catalytic activity.

[0005] A second objective of this invention is to provide a method for preparing a polyethylene glycol-based amphiphilic polymer catalyst. This method is simple, inexpensive, and suitable for industrial production.

[0006] A third objective of this invention is to provide an oil-in-water emulsion with high internal phase stability. This emulsion exhibits high stability and is suitable for aqueous phase catalytic applications.

[0007] The fourth objective of this invention is to provide a method for preparing an oil-in-water emulsion with a high internal phase. This method is simple and easy to operate.

[0008] A fifth objective of this invention is to provide an application of an oil-in-water emulsion with a high internal phase. This emulsion is suitable for aqueous-phase catalytic oxidation of sulfides and Michael addition reactions of sulfanilamides, enabling high-throughput production of chiral sulfoxides and chiral sulfides with excellent selectivity.

[0009] To achieve the above-mentioned technical objectives, this invention provides polyethylene glycol-based amphiphilic polymer catalysts Cat-Ti and Cat-Fe, whose structural expressions are as follows:

[0010]

[0011] Its name is Cat-Ti.

[0012] Its name is Cat-Fe.

[0013] The amphiphilic polymer catalyst of the present invention has a structure containing polyethylene glycol acrylate (PEG, hydrophilic end) and a Schiff base transition metal complex (Salen M, hydrophobic end) modified with vinylimidazolium ionic liquid.

[0014] As a preferred embodiment, M includes one of Fe and Ti.

[0015] This invention also provides a polyethylene glycol-based amphiphilic polymer catalyst, its preparation method, a high internal phase emulsion, and its application. The method involves mixing chiral cyclohexanediamine with salicylaldehyde modified with a vinylimidazolium ionic liquid, performing an aldehyde-amine condensation reaction, and then adding 3,5-di-tert-butylsalicylaldehyde to continue the aldehyde-amine condensation reaction to obtain a vinylimidazolium ionic liquid-modified Schiff base ligand. The vinylimidazolium ionic liquid-modified Schiff base ligand is dissolved in an organic solvent, and a transition metal salt is added to perform a coordination reaction to obtain a vinylimidazolium ionic liquid-modified Schiff base transition metal complex. This complex is then subjected to RAFT polymerization with polyethylene glycol-based acrylate to obtain the final product. The vinylimidazolium ionic liquid-modified salicylaldehyde is prepared by an addition reaction between a vinylimidazolium ionic liquid and a halosalicylaldehyde.

[0016] As a preferred embodiment, the structural expression of the vinylimidazolium ionic liquid is as follows: ,

[0017] As a preferred embodiment, the structural expression of the halosalicylic aldehyde is as follows: ,

[0018] As a preferred embodiment, the structural expression of the vinylimidazole is as follows: .

[0019] The nucleophilic substitution reaction principle involved in the preparation process of vinylimidazolium ionic liquid modified salicylaldehyde is shown in equation (1) below:

[0020] (1).

[0021] As a preferred approach, the molar ratio of vinylimidazole to halosalicylaldehyde is 1:1.2–1.5. Toluene is used as the solvent in the nucleophilic substitution reaction system. The reaction temperature is 80–110 °C. o C.

[0022] The reactions involved in the catalyst preparation process are shown in the following equation:

[0023]

[0024] When the metal salt is tetraisopropyl titanate, it is used to synthesize Cat-Ti; when the metal salt is iron acetylacetone, it is used to synthesize Cat-Fe.

[0025] As a preferred embodiment, the molar amount of the vinylimidazolium ionic liquid modifying salicylaldehyde is 1 to 1.2 times that of chiral cyclohexanediamine.

[0026] As a preferred embodiment, the molar amount of 3,5-di-tert-butylsalicylaldehyde is 1 to 1.2 times that of chiral cyclohexanediamine.

[0027] As a preferred embodiment, the conditions for the dehydration condensation reaction are: an argon or nitrogen protective atmosphere, a temperature of 20–35 °C, and a time of 5–8 h. The solvent used in the dehydration condensation reaction system is ethanol or dichloromethane.

[0028] As a preferred embodiment, the molar ratio of the vinylimidazole ionic liquid-modified Schiff base ligand to the transition metal salt is 1:2 to 1.5.

[0029] As a preferred embodiment, the organic solvent includes ethanol or dichloromethane.

[0030] As a preferred embodiment, the conditions for the coordination reaction are: an argon or nitrogen protective atmosphere, room temperature, and a time of 1 to 5 hours.

[0031] As a preferred embodiment, the polymerization conditions are as follows: using azobisisobutyronitrile (AIBN) as an initiator, 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid (DDMAT) as a RAFT chain transfer agent, and copolymerizing polyethylene glycol acrylate units and vinyl imidazole functionalized Schiff base transition metal complex units, under an argon or nitrogen protective atmosphere, at a temperature of 60 °C, for a time of 24 h.

[0032] This invention also provides a high internal phase emulsion comprising the aforementioned polyethylene glycol-based amphiphilic polymer catalyst. Because the catalyst in this invention has a long PEG chain as a hydrophilic end, it can stabilize the high internal phase emulsion in water through intermolecular hydrogen bonding, thus significantly improving the stability of the high internal phase emulsion of this invention.

[0033] The present invention also provides a method for preparing a high internal phase emulsion, which involves dissolving a polyethylene glycol-based amphiphilic polymer catalyst in water, then mixing it with oil and stirring to obtain the emulsion.

[0034] As a preferred embodiment, the oil phase has a volume content of 40% to 78%.

[0035] As a preferred option, the oil phase includes phenyl methyl sulfide, toluene or various sulfides, and propanethiol, etc.

[0036] This invention also provides an application of a high internal phase emulsion for the oxidation of thioethers and the Michael addition of sulfonamides. This invention coordinates a transition metal (Ti or Fe) with a Schiff base ligand, thereby endowing polyethylene glycol-based amphiphilic polymers with catalytic activity.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The polyethylene glycol-based amphiphilic polymer catalyst prepared by this invention has high catalytic activity, strong substrate universality, stable performance, and its preparation method is simple and low cost, making it suitable for industrial production.

[0039] (2) The high internal phase emulsion prepared by the present invention has strong stability and good catalytic performance. It has excellent catalytic activity, conversion rate and selectivity for sulfide oxidation reaction and sulfanilamide Michael addition reaction.

[0040] (3) High internal phase emulsions can achieve high-throughput organic synthesis in water, and the product separation and purification are simple, environmentally friendly and low cost. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 The images show the appearance and microscopic observation of the high internal phase emulsion product prepared in Example 1 of this invention.

[0043] Figure 2Microscopic images and laser confocal images (Rhodamine-labeled aqueous phase) of the high internal phase emulsion product prepared in Example 2 of this invention.

[0044] Figure 3 The image shows the appearance of the emulsion obtained in Example 1 of this invention with a catalyst ratio of PEG:Salen Ti=5:1.

[0045] Figure 4 The rheological characterization diagram is obtained for the catalyst prepared in Example 1 of this invention with a ratio of PEG:Salen Ti=5:1.

[0046] Figure 5 The images show the appearance and microscopic observation of the high internal phase emulsion product prepared in Example 4 of this invention.

[0047] Figure 6 The image shows the appearance of the emulsion obtained in Example 5 of this invention, where the catalyst ratio was PEG:Salen Fe = 50:1. Detailed Implementation

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0049] Preparation of the catalyst (Cat-Ti):

[0050] (1) Vinylimidazolium and chlorosalicylaldehyde were mixed in toluene at a molar ratio of 1:1.2 and stirred and heated to 80°C for 48 h. After the reaction was completed, the solvent was removed under vacuum and the mixture was washed five times with toluene. The crude product was purified by silica gel column chromatography to remove impurities, yielding vinylimidazolium ionic liquid-modified salicylaldehyde.

[0051] (2) Chiral cyclohexanediamine was added to dichloromethane, and argon gas was passed through for 35 min to purge the air. Then, 1.5 times the amount of the above-mentioned ionic liquid-modified salicylaldehyde relative to the chiral cyclohexanediamine was added, and the mixture was heated to 30 °C for 4 h under stirring. Then, 1.5 times the amount of 3,5-di-tert-butylsalicylaldehyde relative to the chiral cyclohexanediamine was added, and the reaction was continued for 4 h under the above reaction conditions. After the reaction was completed, the solvent was removed under vacuum. The obtained product was purified by recrystallization using n-hexane or cyclohexane solvent to obtain a vinylimidazolium ionic liquid-modified Schiff base ligand.

[0052] (3) The Schiff base ligand modified with the high-purity vinylimidazolium ionic liquid was dissolved in methanol, and argon gas was passed through for 35 min to remove the air. Then tetraisopropyl titanate was added dropwise, and the reaction was stirred at room temperature for 6 h. After the reaction was completed, the mixture was filtered or centrifuged, and the resulting yellow solid was the Schiff base transition metal complex modified with vinylimidazolium ionic liquid.

[0053] (4) The above-mentioned vinylimidazolium ionic liquid-modified Schiff base Ti(IV) complex and polyethylene glycol acrylate are mixed at different molar ratios. you The product was dissolved in methanol, and azobisisobutyronitrile (AIBN) and 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid (DDMAT) were used as free radical initiators and end-capping agents, respectively. Argon gas was passed through for 35 min to remove air, and the polymerization reaction was carried out at 60 °C for 24 h. The product was purified by precipitation with tetrahydrofuran and cyclohexane.

[0054] Emulsion preparation:

[0055] (4) Dissolve 15 mg of the above catalyst in 0.26 mL of water, then add 0.74 mL of toluene to the system (oil-to-water volume ratio 74:26), stir for 10 min to completely emulsify and form a high internal phase emulsion. After standing for half a year, no significant changes were observed in appearance. The appearance of this high internal phase emulsion is shown in the figure. Figure 1 It is a gel-like substance with excellent stability, and can remain stable for a long time. Example

[0056] Preparation of the catalyst (Cat-Ti):

[0057] (1) Vinyl imidazole and chlorosalicylaldehyde were mixed in toluene at a molar ratio of 1:1.2 and stirred and heated to 80°C for 48 h. After the reaction was completed, the solvent was removed under vacuum and the crude product was washed with toluene 5 times. The crude product was purified by silica gel column chromatography to remove impurities and obtain vinyl imidazole ionic liquid modified salicylaldehyde.

[0058] (2) Add chiral cyclohexanediamine to dichloromethane, purge with argon for 35 min to remove air, then add 1.5 times the amount of the above ionic liquid modified salicylaldehyde relative to the chiral cyclohexanediamine, heat to 30 °C for 4 h under stirring, then add 1.5 times the amount of 3,5-di-tert-butylsalicylaldehyde relative to the chiral cyclohexanediamine and continue the reaction for 4 h under the above reaction conditions. After the reaction is completed, remove the solvent by rotary evaporation, and the obtained product is purified by recrystallization with n-hexane or cyclohexane solvent to obtain the vinylimidazolium ionic liquid modified Schiff base ligand.

[0059] (3) The Schiff base ligand modified with the high-purity vinylimidazolium ionic liquid was dissolved in methanol, and argon gas was passed through for 35 min to remove the air. Then, tetraisopropyl titanate was added dropwise to the methanol solution containing the Schiff base ligand. The reaction was stirred at room temperature for 6 h. After the reaction was completed, the solid and liquid phases were separated. The solid phase was the Schiff base Ti(IV) complex catalyst modified with vinylimidazolium ionic liquid.

[0060] (4) Mix the above metal complex with PEG at different molar ratios. you The product was dissolved and then polymerized using AIBN and DDMAT as free radical initiators and end-capping agents at 60 °C for 24 h. The resulting product was then purified by precipitation with tetrahydrofuran and cyclohexane.

[0061] Emulsion preparation:

[0062] (5) Dissolve 15 mg of the above catalyst and rhodamine in 0.26 mL of water, then add 0.74 mL of toluene to the system and sonicate for 10 min to completely emulsify it into a high internal phase emulsion. Prepare the emulsion on a glass slide and observe it under an optical microscope and a laser confocal microscope, respectively. Figure 2 .from Figure 2 As can be seen from this example, the emulsion droplets prepared are uniform in size and are water-in-oil type emulsion with a high internal phase. Example

[0063] 15 mg (0.2 mol% of substrate amount) of the catalyst (Cat-Ti) prepared in Example 1 was dissolved in 0.13 mL of water. Then, 0.37 mL of phenyl methyl sulfide was added to each system. The mixture was ultrasonically stirred for 10 min to completely emulsify and form a high internal phase emulsion. Then, 0.42 mL of 30 wt% hydrogen peroxide solution (1.2 times the amount of substrate) was added to each emulsion. The mixture was allowed to stand at room temperature for 1 h. After the reaction was completed, the conversion rate and selectivity were calculated. The results are shown in Table 1.

[0064] The catalytic oxidation reaction formula for phenyl methyl sulfide is shown below:

[0065]

[0066] Table 1

[0067] 1 40 1:1 99 70 99 2 40 5:1 99 92 99 3 40 10:1 99 85 99 4 40 50:1 30 99 99

[0068] As can be seen from the results in Table 1, the catalyst of this invention achieves a conversion rate of up to 99% and a selectivity of 92% for the catalytic oxidation of phenyl methyl sulfide when PEG: Salen Ti = 5:1, with an enantioselectivity of 99%. Its catalytic performance is significantly higher than that of other comparative catalysts. Example

[0069] Preparation of the catalyst (Cat-Fe):

[0070] (1) Vinyl imidazole and chlorosalicylaldehyde were mixed in toluene at a molar ratio of 1:1.2 and stirred and heated to 80°C for 48 h. After the reaction was completed, the solvent was removed by rotary evaporation and the crude product was washed with toluene 5 times. The crude product was purified by silica gel column chromatography to remove impurities and obtain vinyl imidazole ionic liquid modified salicylaldehyde.

[0071] (2) Add chiral cyclohexanediamine to dichloromethane, purge with argon for 35 min to remove air, then add 1.5 times the amount of the above ionic liquid modified salicylaldehyde relative to the chiral cyclohexanediamine, heat to 30 °C for 4 h under stirring, then add 1.5 times the amount of 3,5-di-tert-butylsalicylaldehyde relative to the chiral cyclohexanediamine and continue the reaction for 4 h under the above reaction conditions. After the reaction is completed, remove the solvent by rotary evaporation, and the product is purified by recrystallization with n-hexane or cyclohexane solvent to obtain the vinylimidazolium ionic liquid modified Schiff ligand.

[0072] (3) The above-mentioned vinylimidazolium ionic liquid-modified Schiff base ligand was dissolved in methanol, and argon gas was passed through for 35 min to remove the air. Then, acetylacetone iron was added dropwise to the methanol solution containing the Schiff base ligand. The reaction was stirred at room temperature for 6 h. After the reaction was completed, the solid and liquid were separated, and the solid phase was the vinylimidazolium ionic liquid-modified Schiff base Fe(Ⅳ) complex catalyst.

[0073] (4) The above metal complex was dissolved with PEG at different molar ratios, and then polymerized at 60 °C for 24 h using AIBN and DDMAT as free radical initiators and end-capping agents. The product was then purified by precipitation with tetrahydrofuran and cyclohexane.

[0074] Emulsion preparation:

[0075] 15 mg of the above catalyst was dissolved in 0.26 mL of water, and then 0.74 mL of toluene was added to the system (oil-to-water volume ratio 74:26). The mixture was ultrasonically stirred for 10 min to completely emulsify and form a high internal phase emulsion. After standing for six months, no changes were observed. The appearance of the high internal phase emulsion is shown below. Figure 5 It is a gel-like substance with excellent stability, and can remain stable for a long time. Example

[0076] Preparation of the catalyst (Cat-Fe):

[0077] (1) Vinyl imidazole and chlorosalicylaldehyde were mixed in toluene at a molar ratio of 1:1.2 and stirred and heated to 80°C for 48 h. After the reaction was completed, the solvent was removed by rotary evaporation and the crude product was washed with toluene 5 times. The crude product was purified by silica gel column chromatography to remove impurities and obtain vinyl imidazole ionic liquid modified salicylaldehyde.

[0078] (2) Add chiral cyclohexanediamine to dichloromethane, purge with argon for 35 min to remove air, then add 1.5 times the amount of the above ionic liquid modified salicylaldehyde relative to the chiral cyclohexanediamine, heat to 30 °C for 4 h under stirring, then add 1.5 times the amount of 3,5-di-tert-butylsalicylaldehyde relative to the chiral cyclohexanediamine and continue the reaction for 4 h under the above reaction conditions. After the reaction is completed, remove the solvent by rotary evaporation, and the obtained product is purified by recrystallization with n-hexane or cyclohexane solvent to obtain the vinylimidazolium ionic liquid modified Schiff base ligand.

[0079] (3) The above-mentioned vinylimidazolium ionic liquid-modified Schiff base ligand was dissolved in methanol, and argon gas was passed through for 35 min to remove the air. Then, acetylacetone iron was added dropwise to the methanol solution containing the Schiff base ligand. The reaction was stirred at room temperature for 6 h. After the reaction was completed, the solid and liquid were separated, and the solid phase was the vinylimidazolium ionic liquid-modified Schiff base Fe(Ⅳ) complex catalyst.

[0080] (4) The above metal complex was dissolved with PEG at different molar ratios, and then polymerized at 60 °C for 24 h using AIBN and DDMAT as free radical initiators and end-capping agents. The product was then purified by precipitation with tetrahydrofuran and cyclohexane.

[0081] Emulsion preparation:

[0082] (5) Dissolve 15 mg of the above catalyst in 0.26 mL of water, then add 0.74 mL of toluene to the system (oil-to-water volume ratio 74:26). Stir ultrasonically for 10 min to completely emulsify and form a high internal phase emulsion. After standing for six months, no changes were observed. The appearance of this high internal phase emulsion is shown in the image below. Figure 5 It is a gel-like substance with excellent stability, and can remain stable for a long time. Example

[0083] Take 15 mg (0.2% of the substrate amount) of the catalyst prepared in Example 4 and dissolve it in 0.13 mL of water. Then add 0.37 mL of a mixed solution of propanethiol and chalcone to each system. Stir ultrasonically for 10 min to completely emulsify it into a high internal phase emulsion. Let the reaction stand at room temperature for 8 h. After the reaction is completed, the conversion rate and selectivity are calculated. The results are shown in Table 2.

[0084] The Michael addition reaction of sulfonamides is shown below:

[0085]

[0086] Table 2

[0087] 1 8 10: 1 60 99 99 2 8 50: 1 99 99 99 3 8 75: 1 85 99 99

[0088] As can be seen from Table 1, when PEG: Salen Fe = 50: 1 in the catalyst of this invention, the conversion rate of the sulfanilamide Michael addition reaction is as high as 99%, the selectivity is as high as 99%, and the enantioselectivity is 99%, which is significantly higher than that of other comparative catalysts.

Claims

1. A method for preparing a polyethylene glycol-based amphiphilic polymer catalyst, characterized by, Includes the following steps: (1) Vinylimidazolium ionic liquid reacts with halosalicylaldehyde via a nucleophilic substitution reaction to obtain vinylimidazolium ionic liquid-modified salicylaldehyde; (2) Chiral cyclohexanediamine undergoes a first dehydration condensation reaction with the product obtained in step (1), and then 3,5-di-tert-butylsalicylaldehyde is added to undergo a second dehydration condensation reaction to obtain a Schiff base ligand modified with vinylimidazolium ionic liquid. (3) The Schiff base ligand obtained in step (2) undergoes a coordination reaction with a transition metal salt to obtain a Schiff base transition metal complex, wherein the transition metal is one of Fe or Ti; (4) The Schiff base transition metal complex obtained in step (3) is reacted with polyethylene glycol-based acrylate through a reversible addition-fragmentation chain transfer polymerization reaction to obtain the polyethylene glycol-based amphiphilic polymer catalyst.

2. A polyethylene glycol-based amphiphilic polymer catalyst, characterized in that, The polyethylene glycol-based amphiphilic polymer catalyst was prepared according to claim 1.

3. A high internal phase emulsion, characterized in that, The polyethylene glycol-based amphiphilic polymer catalyst of claim 2 is used as an emulsifier and catalyst.

4. A method for preparing the high internal phase emulsion of claim 3, characterized in that, The polyethylene glycol-based amphiphilic polymer catalyst of claim 2 is dissolved in the aqueous phase and then mixed and emulsified with the oil phase.

5. The method for preparing a high internal phase emulsion according to claim 4, characterized in that, The oil phase accounts for 40% to 80% of the total volume of the emulsion.

6. The application of the high internal phase emulsion according to claim 4, characterized in that: It is used in thioether oxidation reactions and sulfonamide Michael addition reactions.

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