Photosensitive surfactant and application thereof in Knoevenagel reaction

Abstract

The invention discloses a photosensitive surfactant, a preparation method of the photosensitive surfactant, and an application of the photosensitive surfactant in a Knoevenagel condensation reaction. The preparation method comprises the following steps: reacting 2-aminothiazole with 2-fluorophenol to obtain thiazole azophenol, then reacting the thiazole azophenol with dibromoalkane with different chain lengths to generate an intermediate, carrying out an addition reaction on the obtained intermediate and trimethylamine, and purifying to obtain the photosensitive surfactant. Compared with a traditional photosensitive surfactant, the photosensitive surfactant prepared by the invention can realize reversible conversion between cis-isomer and trans-isomer under irradiation of visible light with different wavelengths, and is applied to a Knoevenagel condensation reaction; the problems that in the Knoevenagel condensation reaction, a catalyst needs to be added, a large amount of organic solvent is used, and product separation is tedious can be solved.

Description

Technical Field

[0001] The present invention belongs to the field of surfactant applications, and particularly relates to a photosensitive surfactant and its preparation, and its application in the Knoevenagel condensation reaction. Background Art

[0002] The Knoevenagel condensation reaction is a reaction that occurs between an aldehyde or ketone and a compound containing an active methylene group (such as malonic ester or ethyl acetoacetate) in the presence of a basic catalyst. Through this process, α,β-unsaturated carbonyl compounds are formed. Traditional Knoevenagel condensation reactions are carried out under homogeneous conditions using, for example, primary amines, secondary amines, piperidine, pyridine, ammonium salts, and ionic liquids. However, these homogeneous catalytic systems usually require relatively high temperature conditions to function, and there are problems with difficult separation, which limits the recycling of the catalyst and may contaminate the product. Although the use of heterogeneous catalysts solves this part of the problem, a large amount of toxic organic solvents still need to be used. Summary of the Invention

[0003] To solve the problems that traditional Knoevenagel condensation reactions require the use of catalysts and a large amount of organic solvents, the present invention uses an emulsion system and starts from surfactants to provide a photosensitive surfactant and its preparation method.

[0004] To achieve the above object, the present invention adopts the following technical solutions: One object of the present invention is to protect a photosensitive surfactant, which is composed of a quaternary ammonium ion as the hydrophilic group and an azobenzene molecule as the hydrophobic group, and its structural formula is as follows: , where n = 2, 4, 6, 8, and preferably n = 6.

[0005] Another object of the present invention is to protect the preparation method of the photosensitive surfactant, which includes the following steps: (1) Mix 2-aminothiazole, hydrochloric acid, water, and sodium nitrite, and stir and react in an ice-water bath for 3 - 5 h. After the reaction is completed, add the reaction solution to an aqueous solution containing 2-fluorophenol, sodium hydroxide, and sodium bicarbonate, and continue to stir and react in an ice-water bath for 6 - 12 h. After the reaction is completed, filter and wash with deionized water to obtain thiazole azophenol; (2) Mix the thiazole azophenol obtained in step (1) with dibromoalkane and potassium hydroxide in solvent A in sequence, stir and reflux at 80 - 130 °C for 12 - 18 h. After the reaction is completed, cool, extract, and purify by chromatography to obtain thiazole azobenzene alkane; (3) Add the thiazole azobenzene alkane obtained in step (2) and trimethylamine into solvent B in sequence, stir and react at 15 - 30 °C for 24 - 36 h. After removing the solvent by rotary evaporation, dissolve the obtained crude product in hot ethanol, and slowly add anhydrous ether dropwise to precipitate white solid. Then perform reprecipitation in an ice bath for 30 minutes. Finally, filter and wash with anhydrous ether to obtain the photosensitive surfactant.

[0006] Further, the molar ratio of 2 - aminothiazole, hydrochloric acid, sodium nitrite, and 2 - fluorophenol used in step (1) is 1:(8 - 10):(3 - 5):(1 - 3).

[0007] Further, the molar ratio of 2 - fluorophenol, sodium hydroxide, and sodium bicarbonate in the aqueous solution in step (1) is 1:(2 - 5):(3 - 5).

[0008] Further, the molar ratio of thiazole azophenol, dibromoalkane, and potassium hydroxide used in step (2) is 1:(3 - 5):(2 - 4).

[0009] Further, the solvent A in step (2) is any one of N,N - dimethylformamide, N,N - dimethylacetamide, chloroform, and acetonitrile.

[0010] Further, the chromatographic purification in step (2) uses a mixed solution of petroleum ether and ethyl acetate with a volume ratio of 4:1 as the eluent.

[0011] Further, the molar ratio of thiazole azobenzene alkane and trimethylamine used in step (3) is 1:(4 - 6).

[0012] Further, the solvent B in step (3) is any one of dichloromethane, acetonitrile, and ethanol.

[0013] Further, the volume ratio of hot ethanol to anhydrous ether used in the reprecipitation in step (3) is 1:5.

[0014] The third object of the present invention is to protect the application of the photosensitive surfactant in the Knoevenagel condensation reaction.

[0015] Specifically, the application method is to add the photosensitive surfactant into a mixed solution containing an aldehyde - or ketone - group compound and an active methylene compound. After reacting at room temperature for 12 h, irradiate the obtained emulsion under visible light to cause demulsification, and then obtain the target product by suction filtration.

[0016] Further, the active methylene compound includes any one or several of malononitrile, ethyl cyanoacetate, ethyl acetoacetate, diethyl malonate, etc.

[0017] Furthermore, the molar ratio of the photosensitive surfactant to the aldehyde or ketone compound and the active methylene compound is 1:10:12.

[0018] Furthermore, the irradiation time is 1 - 2 hours.

[0019] The present invention first proposes to apply a photosensitive surfactant to the Knoevenagel reaction. By designing a photo-responsive surfactant containing an azobenzene structure, a novel light-controlled emulsion reaction system is constructed. Compared with the traditional homogeneous / heterogeneous systems that rely on catalysts and organic solvents, the present invention utilizes the dual functions of the surfactant (emulsifying medium and photo-responsive property) to achieve reversible switching between emulsification and demulsification under visible light irradiation, thus significantly simplifying the reaction process and product separation steps. This innovation not only solves the problems of difficult catalyst recovery and large consumption of organic solvents in the traditional Knoevenagel reaction, but also endows the surfactant with unique light-controlled properties through molecular structure design, combining the photo-responsive property with the surfactant function, beyond the simple functional expansion of existing surfactants, providing a brand-new green solution for the Knoevenagel reaction.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The photosensitive surfactant prepared by the present invention can undergo reversible cis-trans isomerization under visible light irradiation, solving the defect that traditional photosensitive surfactants require ultraviolet light irradiation to convert from the trans isomer to the cis isomer.

[0021] (2) The photosensitive surfactant prepared by the present invention can cause reversible switching between emulsification and demulsification of the emulsion under visible light of different wavelengths (emulsification at 405 nm / demulsification at 525 nm), which can solve the problem that traditional emulsions need to add demulsifiers.

[0022] (3) The emulsion stabilized by the photosensitive surfactant prepared by the present invention can solve the problems of the traditional Knoevenagel condensation reaction that requires adding catalysts and using a large amount of organic solvents, and a reaction yield of over 92% can be obtained without adding an external catalyst. Description of the Drawings

[0023] Figure 1 1H NMR spectrum of the photosensitive surfactant prepared in Example 1.

[0024] Figure 2 Graph of the surface tension change of the photosensitive surfactant prepared in Example 1. [[ID=?]]

[0025] Figure 3 Graph of the photo-responsive ability of the photosensitive surfactant prepared in Example 1.

[0026] Figure 4 1H NMR spectrum of the product obtained by Knoevenagel condensation reaction in Application Example 1. Detailed implementation manners

[0027] A photosensitive surfactant, and its preparation method includes the following steps: (1) Add 2-aminothiazole, hydrochloric acid, water and sodium nitrite into a flask, stir and react in an ice-water bath for 3 - 5 h. After the reaction is completed, add the reaction solution into an aqueous solution containing 2-fluorophenol, sodium hydroxide and sodium bicarbonate, and continue to stir and react in an ice-water bath for 6 - 12 h. After the reaction is completed, filter and wash with deionized water to obtain thiazole azophenol; wherein, the molar ratio of 2-aminothiazole, hydrochloric acid, sodium nitrite and 2-fluorophenol used is 1:(8 - 10):(3 - 5):(1 - 3); the molar ratio of 2-fluorophenol, sodium hydroxide and sodium bicarbonate used is 1:(2 - 5):(3 - 5); (2) Add the thiazole azophenol obtained in step (1), dibromoalkane, potassium hydroxide and solvent A into a flask in sequence, stir and reflux at 80 - 130 °C for 12 - 18 h. After the reaction is completed, cool, extract and purify by chromatography to obtain thiazole azobenzene alkane; wherein, the molar ratio of thiazole azophenol, dibromoalkane and potassium hydroxide used is 1:(3 - 5):(2 - 4); the chromatography purification uses a mixed solution of petroleum ether and ethyl acetate with a volume ratio of 4:1 as the eluent; (3) Add the thiazole azobenzene alkane obtained in step (2), trimethylamine and solvent B into a flask in sequence, stir and react at 15 - 30 °C for 24 - 36 h. After removing the solvent by rotary evaporation, dissolve the obtained crude product in hot ethanol (heat ethanol to slightly boiling and then cool slightly, keep the temperature at 60 - 70 °C for use), and dropwise add anhydrous ether with a volume 5 times that of it to precipitate a white solid. Then perform reprecipitation in an ice bath for 30 minutes, and finally filter and wash with anhydrous ether to obtain the photosensitive surfactant; wherein, the molar ratio of thiazole azobenzene alkane and trimethylamine used is 1:(4 - 6).

[0028] Wherein, the solvent A in step (2) is any one of N,N-dimethylformamide, N,N-dimethylacetamide, chloroform and acetonitrile.

[0029] The solvent B in step (3) is any one of dichloromethane, acetonitrile and ethanol.

[0030] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0031] Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0032] Example 1 (1) 1 g of 2-aminothiazole (0.01 mol) and 16 mL of hydrochloric acid aqueous solution (18% wt) were successively added to a flask. Then, 2.07 g of sodium nitrite (0.03 mol) was dissolved in 15 mL of deionized water, and it was slowly added dropwise into the flask under an ice-water bath condition. After stirring and reacting for 3 h, the reaction solution was added to an aqueous solution containing 1.12 g of 2-fluorophenol (0.01 mol), 0.8 g of sodium hydroxide (0.02 mol), and 3.36 g of sodium bicarbonate (0.04 mol). The reaction was continued with stirring in an ice-water bath for 7 h, and then it was filtered and washed with deionized water to obtain thiazole azophenol; (2) 1.11 g of the thiazole azophenol obtained in step (1) (0.005 mol), 3.66 g of 1,6-dibromohexane (0.015 mol), and 0.56 g of potassium hydroxide (0.01 mol) were successively added to a flask, and 15 mL of N,N-dimethylformamide was added. After stirring and refluxing at 120 °C for 12 h, after cooling, the target product was extracted with dichloromethane (30 mL × 3). The organic phases were combined and dried over anhydrous sodium sulfate, and then the crude product was obtained by rotary evaporation. Further purification was carried out by silica gel column chromatography using a mixed solution of petroleum ether and ethyl acetate (4:1, v / v) as the eluent to obtain thiazole azobenzene hexane; (3) 1.93 g of the thiazole azobenzene hexane obtained in step (2) (0.005 mol) and 4 g of trimethylamine ethanol solution (30% wt) were successively added to a flask, and 10 mL of ethanol was added. After stirring and reacting at 15 °C for 36 h, after removing ethanol by rotary evaporation, the obtained crude product was dissolved in 5 mL of hot ethanol, and 25 mL of anhydrous ether was added dropwise to precipitate a white solid. Then, it was reprecipitated in an ice bath for 30 minutes, and finally, it was filtered and washed with anhydrous ether to obtain a photosensitive cationic surfactant. Its yield reached 75%, and its purity exceeded 98%. The Figure 1 .

[0033] Figure 2 is the surface tension change diagram of the photosensitive surfactant. As can be seen from the figure, its critical micelle concentration is 6.7×10 -5 mol / L, and the critical surface tension is 33.53 mN / m.

[0034] 6.7×10 -5The surfactant solution with a concentration of [[mol / L]] was placed in a quartz cuvette and alternately irradiated with LED light sources at 405 nm (10 mW / cm²) and 525 nm (10 mW / cm²). The change in the characteristic absorption peak of azobenzene at 350 nm was recorded in real-time using a UV-visible spectrophotometer. The results are shown in Figure 3 . It can be seen from Figure 3 that the half-life of the cis-trans isomerization conversion is less than 5 seconds, indicating its fast light response characteristics.

[0035] Example 2 (1) 1 g of 2-aminothiazole (0.01 mol) and 18 mL of hydrochloric acid aqueous solution (18% wt) were successively added to a flask. Then, 2.415 g of sodium nitrite (0.035 mol) was dissolved in 20 mL of deionized water and slowly added dropwise to the flask under an ice-water bath condition. After stirring and reacting for 3.5 h, the reaction solution was added to an aqueous solution containing 1.68 g of 2-fluorophenol (0.015 mol), 1.4 g of sodium hydroxide (0.035 mol), and 4.2 g of sodium bicarbonate (0.05 mol). The mixture was continuously stirred and reacted in an ice-water bath for 8 h, and then filtered and washed with deionized water to obtain thiazole azophenol; (2) 1.11 g of the thiazole azophenol obtained in step (1) (0.005 mol), 4.88 g of 1,6-dibromohexane (0.02 mol), and 0.56 g of potassium hydroxide (0.01 mol) were successively added to a flask, and 15 mL of N,N-dimethylacetamide was added. After stirring and refluxing at 110 °C for 14 h, the mixture was cooled and the target product was extracted with dichloromethane (30 mL × 3). The organic phases were combined, dried with anhydrous sodium sulfate, and then concentrated by rotary evaporation to obtain a crude product. The crude product was further purified by silica gel column chromatography using a mixed solution of petroleum ether and ethyl acetate (4:1, v / v) as the eluent to obtain thiazole azobenzene hexane; (3) 1.93 g of the thiazole azobenzene hexane obtained in step (2) (0.005 mol) and 5 g of trimethylamine ethanol solution (30% wt) were successively added to a flask, and 10 mL of acetonitrile was added. After stirring and reacting at 20 °C for 32 h, ethanol was removed by rotary evaporation. The obtained crude product was dissolved in 5 mL of hot ethanol, and 25 mL of anhydrous ether was added dropwise to precipitate a white solid. The solid was then reprecipitated in an ice bath for 30 minutes, and finally filtered and washed with anhydrous ether to obtain a photosensitive cationic surfactant.

[0036] Example 3 (1) Add 1 g of 2-aminothiazole (0.01 mol) and 20 mL of hydrochloric acid aqueous solution (18% wt) into the flask in sequence. Then dissolve 2.76 g of sodium nitrite (0.04 mol) in 20 mL of deionized water, and slowly add it dropwise into the flask under the condition of an ice-water bath. After stirring and reacting for 4 h, add the reaction solution into the aqueous solution containing 2.24 g of 2-fluorophenol (0.02 mol), 1.6 g of sodium hydroxide (0.04 mol) and 5.46 g of sodium bicarbonate (0.065 mol). Continue to stir and react in the ice-water bath for 9 h, then filter and wash with deionized water to obtain thiazolylazophenol; (2) Add 1.11 g of thiazolylazophenol (0.005 mol) obtained in step (1), 6.1 g of 1,6-dibromohexane (0.025 mol) and 0.84 g of potassium hydroxide (0.015 mol) into the flask in sequence, and add 20 mL of chloroform. After stirring and refluxing at 100 °C for 16 h, cool it and extract the target product with dichloromethane (30 mL × 3). Combine the organic phases, dry them with anhydrous sodium sulfate, then obtain the crude product by rotary evaporation. Then use silica gel column chromatography and purify it with a mixed solution of petroleum ether and ethyl acetate (4:1, v / v) as the eluent to obtain thiazolylazobenzenehexane; (3) Add 1.93 g of thiazolylazobenzenehexane (0.005 mol) obtained in step (2) and 6 g of trimethylamine ethanol solution (30% wt) into the flask in sequence, and add 15 mL of dichloromethane. After stirring and reacting at 25 °C for 28 h, remove ethanol by rotary evaporation. Then dissolve the obtained crude product in 5 mL of hot ethanol, and slowly add 25 mL of anhydrous ether dropwise to precipitate white solid. Then perform reprecipitation in an ice bath for 30 minutes. Finally, filter and wash with anhydrous ether to obtain the photosensitive cationic surfactant.

[0037] Example 4 (1) Add 1 g of 2-aminothiazole (0.01 mol) and 20 mL of hydrochloric acid aqueous solution (18% wt) into the flask in sequence. Then dissolve 2.76 g of sodium nitrite (0.04 mol) in 20 mL of deionized water, and slowly add it dropwise into the flask under the condition of an ice-water bath. After stirring and reacting for 4 h, add the reaction solution into the aqueous solution containing 2.8 g of 2-fluorophenol (0.025 mol), 2.4 g of sodium hydroxide (0.06 mol) and 6.72 g of sodium bicarbonate (0.08 mol). Continue to stir and react in the ice-water bath for 12 h, then filter and wash with deionized water to obtain thiazolylazophenol; (2) 1.11 g of the thiazolyl azophenol obtained in step (1) (0.005 mol), 6.1 g of 1,6-dibromohexane (0.025 mol), and 0.84 g of potassium hydroxide (0.015 mol) were successively added to a flask. Then 25 mL of acetonitrile was added. After stirring and refluxing at 80 °C for 18 h, the target product was extracted with dichloromethane (30 mL × 3) after cooling. The organic phases were combined, dried with anhydrous sodium sulfate, and then the crude product was obtained by rotary evaporation. Then silica gel column chromatography was used, and the mixture of petroleum ether and ethyl acetate (4:1, v / v) was used as the eluent for purification to obtain thiazolyl azobenzene hexane; (3) 1.93 g of the thiazolyl azobenzene hexane obtained in step (2) (0.005 mol) and 7 g of trimethylamine ethanol solution (30% wt) were successively added to a flask. Then 10 mL of acetonitrile was added. After stirring and reacting at 30 °C for 24 h, ethanol was removed by rotary evaporation. The obtained crude product was dissolved in 5 mL of hot ethanol, and 25 mL of anhydrous ether was added dropwise to precipitate white solid. Then it was reprecipitated in an ice bath for 30 minutes, and finally filtered and washed with anhydrous ether to obtain the photosensitive cationic surfactant.

[0038] Application Example 1 5 mL of an aqueous solution of the surfactant obtained in Example 1 at 6.7×10 -5 mol / L was added to a 10 mL glass bottle equipped with a rotor; 0.053 g of benzaldehyde and 0.066 g of malononitrile were weighed and dissolved in 1.25 mL of n-octane, and then added to the above glass bottle. The reaction was carried out at room temperature for 12 h. After the reaction was completed, the emulsion was irradiated with visible light for 1.5 h to cause demulsification, and the final product was obtained by suction filtration. The product yield reached 92%, and the purity was >98% (HPLC).

[0039] Application Comparative Example 1 5 mL of a 5 mol% piperidine ethanol solution was added to a 10 mL glass bottle equipped with a rotor; 0.053 g of benzaldehyde and 0.066 g of malononitrile were weighed and dissolved in 1.25 mL of n-octane, and then added to the above glass bottle. The reaction was carried out at 80 °C for 12 h, and then the final product was obtained by extraction and column chromatography purification. The product yield was 88%, and the purity was 94%. This result was significantly lower than the effect obtained by using the photosensitive surfactant system in Application Example 1.

[0040] Application Example 2 5 mL of 6.7×10 -5An aqueous solution of the surfactant obtained in Example 1 at a concentration of [mol / L]; Weigh 0.062 g of p-fluorobenzaldehyde and 0.066 g of malononitrile and dissolve them in 1.25 mL of n-octane, then add them to the above glass bottle. React at room temperature for 12 h. After the reaction is completed, irradiate the emulsion under visible light for 1.5 h to cause demulsification, and then filter to obtain the final product, with a product yield of 89% (HPLC purity > 97%).

[0041] Application Comparative Example 2 Add 5 mL of a 5 mol% piperidine ethanol solution in a 10 mL glass bottle equipped with a rotor; Weigh 0.062 g of p-fluorobenzaldehyde and 0.066 g of malononitrile and dissolve them in 1.25 mL of n-octane, then add them to the above glass bottle. React at room temperature for 12 h, and then obtain the final product through extraction and column chromatography purification. The product yield is 78% and the purity is 91%. This result is lower than the effect achieved in Application Example 2 using the photosensitive surfactant system.

[0042] The above results fully prove that the use of the photosensitive surfactant of the present invention can achieve the efficient progress of the Knoevenagel reaction under catalyst-free conditions, with high reaction efficiency (the yield is increased by 4%) and simple operation (column chromatography is avoided).

[0043] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A photosensitive surfactant, characterized in that: The structural formula thereof is as follows: , where n = 2, 4, 6, 8.

2. A preparation method of a photosensitive surfactant as described in claim 1, characterized in that: It includes the following steps: (1) Mix 2-aminothiazole, hydrochloric acid, water and sodium nitrite, and stir and react in an ice-water bath for 3-5 h. After the reaction is completed, add the reaction solution to an aqueous solution containing 2-fluorophenol, sodium hydroxide and sodium bicarbonate, and continue to stir and react in an ice-water bath for 6-12 h. After the reaction is completed, filter and wash with deionized water to obtain thiazolylazophenol; (2) Mix the thiazolylazophenol obtained in step (1) with dibromoalkane and potassium hydroxide in solvent A, stir and reflux at 80-130 °C for 12-18 h. After the reaction is completed, cool, extract and purify by chromatography to obtain thiazolylazobenzane; (3) Add the thiazolylazobenzane obtained in step (2) and trimethylamine to solvent B in sequence, stir and react at 15-30 °C for 24-36 h. After removing the solvent by rotary evaporation, subject the obtained crude product to reprecipitation, filtration, and wash with anhydrous ether to obtain the photosensitive surfactant.

3. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (1), the molar ratio of 2-aminothiazole, hydrochloric acid, sodium nitrite and 2-fluorophenol used is 1:(8-10):(3-5):(1-3); the molar ratio of 2-fluorophenol, sodium hydroxide and sodium bicarbonate in the aqueous solution is 1:(2-5):(3-5).

4. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (2), the molar ratio of thiazolylazophenol, dibromoalkane and potassium hydroxide used is 1:(3-5):(2-4).

5. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (2), the solvent A is any one of N,N-dimethylformamide, N,N-dimethylacetamide, chloroform and acetonitrile.

6. The preparation method of a photosensitive surfactant according to claim 2, wherein: In step (2), the chromatographic purification uses a mixed solution of petroleum ether and ethyl acetate with a volume ratio of 4:1 as the eluent.

7. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (3), the molar ratio of thiazolylazobenzane and trimethylamine used is 1:(4-6).

8. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (3), the solvent B is any one of dichloromethane, acetonitrile and ethanol.

9. The preparation method of a photosensitive surfactant according to claim 2, characterized in that: In step (3), reprecipitation is carried out with hot ethanol and anhydrous ether with a volume ratio of 1:

5.

10. Application of a photosensitive surfactant as described in claim 1 in the Knoevenagel condensation reaction.

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