A new type of light-responsive deep eutectic solvent and a preparation method thereof

Abstract

The application belongs to the technical field of eutectic solvent, and discloses a new type of photoresponsive eutectic solvent and a preparation method thereof. The new type of photoresponsive eutectic solvent is composed of azobenzene compounds and quaternary ammonium salt compounds, wherein the molar ratio of the azobenzene compounds to the quaternary ammonium salt compounds is 1:0.5-10. The preparation method comprises the following steps: S1, taking the azobenzene compounds and the quaternary ammonium salt compounds, grinding and crushing, mixing, heating, cooling after forming a homogeneous liquid, and obtaining a viscous liquid; S2, vacuum drying the viscous liquid obtained in S1 to obtain the new type of photoresponsive eutectic solvent. The preparation method of the new type of photoresponsive eutectic solvent is simple, the reaction condition is mild, raw materials are easy to obtain, the new type of photoresponsive eutectic solvent can be recycled, the problem that an additional substance needs to be introduced to drive the responsiveness of the eutectic solvent is solved, and the new type of photoresponsive eutectic solvent is beneficial to the development needs of modern green chemical industry.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of deep eutectic solvents, in particular to a novel light-responsive deep eutectic solvent and a preparation method thereof. BACKGROUND

[0002] Deep eutectic solvents (DES) are generally DESs formed by combining a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD, such as amine, carboxylic acid and polyol compounds) in a certain stoichiometric ratio. In recent years, with the gradual deepening of research, various new DESs have emerged. Different deep eutectic solvents can be obtained by adjusting the R group in the quaternary ammonium salt and X - and the type of hydrogen bond donor, and DESs can be roughly divided into four types: type I DES (metal halide and choline chloride), type II DES (water and metal halide and choline chloride), type III DES (choline chloride and hydrogen bond donor) and type IV DES (transition metal and urea). Since the raw materials for synthesizing DESs are very common compounds, which are abundant in source and low in price, DESs are expected to realize large-scale industrial production and be conducive to the development of modern green chemical industry.

[0003] In addition, as a kind of ionic liquid-like compound, deep eutectic solvents have some advantages of ionic liquids, such as low vapor pressure, good chemical stability and thermal stability, strong solubility and strong modifiability. However, compared with ionic liquids, deep eutectic solvents are mainly formed by hydrogen bonds between hydrogen bond donors and hydrogen bond acceptors to form a homogeneous system, and the preparation process is simple, the atomic utilization rate is high, the raw material price is low, it is non-toxic and harmless and biodegradable, which is conducive to large-scale production. Responsive deep eutectic solvents are a kind of deep eutectic solvents with specific functional groups. These functional groups can undergo reversible changes under external stimuli (such as temperature and pH changes), thereby changing their physical and chemical properties. This responsiveness makes different stimuli-responsive deep eutectic solvents have potential application value in the fields of intelligent materials and drug delivery systems. For example, by adjusting the functional groups therein, the control of the drug release process can be realized, thereby improving the bioavailability and therapeutic effect of the drug. The emergence of responsive DESs expands and optimizes the application of DESs in sample preparation. With its efficient extraction and separation effect, green extraction principle and multi-functional advantage, responsive DESs have become one of the most potential and valuable research topics in the sample pretreatment process.

[0004] Currently, the research of responsive DES mainly focuses on three aspects: (1) CO2 / N2 adsorption. CO2 / N2 has become a recognized trigger for switchable solvents, CO2 / N2 can significantly change the properties of some switchable materials, including solvents, surfactants, catalysts, polymers, gels, etc., the most attractive advantage of CO2 / N2 driven responsive DES is that it can be recycled. (2) pH responsiveness. By adding appropriate proton donors and deprotonation reagents in the solution system containing analytes, the pH value of the system is adjusted, and the switching of DES is completed, without additional equipment, the extraction and separation of target analytes in the solution system can be continuously completed. (3) Temperature responsiveness. In the hydrophobic DES system, water is added to form a mixed two-phase system, and the temperature of the system is changed to drive the formation of a homogeneous system, which is called temperature responsive DES.

[0005] However, although the addition of water, the change of the pH value of the system or the alternate bubbling of CO2 / N2 can respond to the properties of DES, the three response routes all need to introduce additional substances to complete the phase change, which may have a negative impact on some specific analysis. SUMMARY

[0006] The present application aims to provide a new type of light-responsive deep eutectic solvent and a preparation method thereof, which is simple, mild reaction conditions, raw materials are easy to obtain, and the product can be recycled, and solves the problem of introducing additional substances for temperature-responsive, CO2 / N2 adsorption and pH-responsive deep eutectic solvents, which is conducive to the development needs of modern green chemical industry.

[0007] In order to achieve the above purpose, the present application provides the following technical scheme:

[0008] A new type of light-responsive deep eutectic solvent is composed of azobenzene compounds and quaternary ammonium salt compounds, wherein the molar ratio of the azobenzene compounds to the quaternary ammonium salt compounds is 1:0.5-10.

[0009] Further, the azobenzene compounds have one or more of H, hydroxyl, carboxyl, sulfonic acid group and amino on both benzene rings; the quaternary ammonium salt compounds are one or more of monoquaternary ammonium salt, diquaternary ammonium salt, triquaternary ammonium salt and polyquaternary ammonium salt.

[0010] Further, the azobenzene compound is 4-((4-hydroxyphenyl) diazenyl) benzoic acid, and the quaternary ammonium salt compound is tetraethylammonium chloride.

[0011] Further, the azobenzene compound is 4-((4-hydroxyphenyl) diazenyl) benzoic acid, and the quaternary ammonium salt compound is tetraethylammonium chloride.

[0012] Further, the azobenzene compound is 4-((4-hydroxyphenyl)diazenyl)benzoic acid, and the quaternary ammonium salt compound is tetrabutylammonium bromide.

[0013] The preparation method of the novel photoresponsive deep eutectic solvent according to any one of the above, comprising the following steps:

[0014] S1, grinding and crushing the azobenzene compound and the quaternary ammonium salt compound according to the molar ratio, mixing them, gradually heating, and cooling after forming a homogeneous liquid to obtain a viscous liquid;

[0015] S2, vacuum drying the viscous liquid obtained in S1 to obtain a novel photoresponsive deep eutectic solvent.

[0016] Further, in S1, the heating time is 30-120 min, and the heating temperature is 50-120 DEG C.

[0017] Further, in S2, the vacuum drying pressure is 10-20 kPa, the vacuum drying temperature is 50-100 DEG C, and the vacuum drying time is 60-300 min.

[0018] The beneficial effects of the technical solution are:

[0019] 1. The azobenzene compound with different substituents on the benzene ring in the present application is used as a hydrogen bond donor to form a novel photoresponsive deep eutectic solvent with a quaternary ammonium salt compound, and the azobenzene compound can respond to the hydrogen bond effect of the deep eutectic solvent more strongly under ultraviolet irradiation, compared with the traditional three types of responsive deep eutectic solvents, without the need to introduce additional substances to drive the DES, solving the problem of the negative impact of the introduction of additional substances on the solvent in the temperature-responsive, CO2 / N2 adsorption and pH-responsive deep eutectic solvents.

[0020] 2. The raw materials of the present application are widely available, low in cost, simple in preparation method, and mild in reaction conditions, without the need for inorganic acids and bases, and can be recycled and used, without causing a large amount of waste in the post-processing process, thus greatly reducing the cost and environmental pollution, and being conducive to the development of green chemistry. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The photoisomerization schematic diagram of the azobenzene compound with different substituents on the benzene ring and the quaternary ammonium salt compound in the present application to form a DES;

[0022] Figure 2 The structural formula of 4-((4-hydroxyphenyl)diazenyl)benzoic acid (HBD) in the present application;

[0023] Figure 3 The structural formula of tetraethylammonium chloride, tetrabutylammonium chloride and tetrabutylammonium bromide in the present application;

[0024] In the figure, (a) is the structural formula of tetraethylammonium chloride (TEAC) in Examples 1 and 3, (b) is the structural formula of tetrabutylammonium chloride (TBAC) in Example 2, and (c) is the structural formula of tetrabutylammonium bromide (TBAB) in Example 3;

[0025] Figure 4 In Embodiment 1 of the present invention, HBD 1 HNMR spectrum;

[0026] Figure 5 In Embodiment 1 of the present invention, HBD and TEAC-DES 1 HNMR comparison spectrum;

[0027] Figure 6 In Embodiment 2 of the present invention, HBD and TBAC-DES 1 HNMR comparison spectrum;

[0028] Figure 7 In Embodiment 3 of the present invention, HBD and TBAB-DES 1 HNMR comparison spectrum;

[0029] Figure 8 In Embodiment 2 of the present invention, TBAC-DES was subjected to 365nm ultraviolet light irradiation for 6 hours before and after treatment. 1 HNMR comparison spectrum;

[0030] Figure 9 In Embodiment 3 of the present invention, TBAB-DES was subjected to 365nm ultraviolet light irradiation for 6 hours before and after treatment. 1 HNMR comparison spectrum;

[0031] Figure 10 The results of refractive index change detection of TBAC-DES from Example 2 and TBAB-DES from Example 3 under 365nm ultraviolet irradiation are shown in the figure.

[0032] Figure 11 The graph shows the conductivity change detection results of TBAC-DES from Example 2 and TBAB-DES from Example 3 under 365nm ultraviolet irradiation.

[0033] Figure 12 The graph shows the results of the light response change of azobenzene (HBD).

[0034] Figure (A) shows the light response change of HBD under illumination at 365nm, and (B) shows the light response change of HBD under illumination at 440nm.

[0035] Figure 13Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light;

[0036] Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light;

[0037] Figure 14 Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light;

[0038] Figure 15 Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light;

[0039] Figure 16 Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light;

[0040] Figure 17 Figure (C) is the result of the change of the light response of TBAB-DES under 365nm light, and (D) is the result of the change of the light response of TBAB-DES under 440nm light. DETAILED DESCRIPTION

[0041] The application will be further described in detail below in combination with the drawings and embodiments:

[0042] Embodiment 1

[0043] A new type of light-responsive deep eutectic solvent is composed of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetraethylammonium chloride, wherein the optimal molar ratio of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetraethylammonium chloride forming the DES is 1:2.

[0044] A preparation method of the new type of light-responsive deep eutectic solvent described above, comprising the following steps:

[0045] S1, according to the molar ratio of 1:1, the obtained 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetraethylammonium chloride are respectively weighed, ground and crushed, and then mixed in a round-bottom flask, heated gradually under stirring, and then cooled to observe the change in the properties of the mixture. If a stable DES cannot be formed, continue to add tetraethylammonium chloride to the round-bottom flask according to the molar ratio, repeat the heating under stirring until a stable DES is formed. It is found that when the molar ratio is 1:1, the HBD and HBA become unstable yellow liquid, and the amount of quaternary ammonium salt is gradually increased until the molar ratio is 1:2. The orange-red viscous liquid obtained by maintaining the heating temperature at 60℃ and continuously heating for 90min can remain stable;

[0046] S2, the orange-red viscous liquid obtained in S1 is dried in a vacuum drying oven at a vacuum pressure of 15kPa for 120min at 60℃ to obtain a new type of light-responsive deep eutectic solvent, i.e. TEAC-DES light-responsive deep eutectic solvent.

[0047] Example 2

[0048] The difference between this embodiment and Example 1 is:

[0049] A new type of light-responsive deep eutectic solvent, which is composed of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetrabutylammonium chloride, wherein the optimal molar ratio of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetrabutylammonium chloride DES is 1:3.

[0050] The preparation method of the new type of light-responsive deep eutectic solvent as described above, comprising the following steps:

[0051] S1, according to the molar ratio of 1:1, the obtained 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetrabutylammonium chloride are respectively weighed, ground and crushed, and then mixed in a round-bottom flask. Gradually heated under stirring, after obtaining the mixture liquid, cool, observe the change of the properties of the mixture, if it can not form a stable DES, then continue to add tetrabutylammonium chloride to the round-bottom flask according to the molar ratio, repeat the stirring and heating until a stable DES is formed. Among them, it is found that when the molar ratio is 1:2, the HBD and HBA become unstable yellow liquid, gradually increase the amount of quaternary ammonium salt, until the molar ratio is 1:3, keep the heating temperature at 60℃ and continue to heat for 90min to obtain an orange-red viscous liquid which can keep stable;

[0052] S2, the orange-red viscous liquid obtained in S1 is dried in a vacuum drying oven with a vacuum pressure of 15kPa at 60℃ for 120min, to obtain a new type of light-responsive deep eutectic solvent, namely TBAC-DES light-responsive deep eutectic solvent.

[0053] Example 3

[0054] The difference between this embodiment and Example 1 is:

[0055] A new type of light-responsive deep eutectic solvent, which is composed of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetrabutylammonium bromide, wherein the optimal molar ratio of 4-((4-hydroxyphenyl) diazenyl) benzoic acid and tetrabutylammonium bromide DES is 1:3.

[0056] The preparation method of the new type of light-responsive deep eutectic solvent as described above, comprising the following steps:

[0057] S1. Weigh out 4-((4-hydroxyphenyl)diazepine)benzoic acid and tetrabutylammonium bromide at a molar ratio of 1:1, grind and crush them, and mix them in a round-bottom flask. Gradually heat the mixture with stirring until a liquid mixture is obtained. After cooling, observe the changes in the properties of the mixture. If a stable DES cannot be formed, continue to add tetrabutylammonium bromide to the round-bottom flask according to the molar ratio, and repeat the heating with stirring until a stable DES is formed. It was found that at a molar ratio of 1:2, HBD and HBA become an unstable yellow liquid. Gradually increase the amount of quaternary ammonium salt until the molar ratio is 1:3. Only by maintaining the heating temperature at 60℃ and heating continuously for 90 minutes can the orange-red viscous liquid remain stable.

[0058] S2. The orange-red viscous liquid obtained in S1 is dried at 60°C for 120 min in a vacuum drying oven with a vacuum pressure of 15 kPa to obtain a novel photoresponsive eutectic solvent, namely TBAB-DES photoresponsive eutectic solvent.

[0059] The schematic diagram of photoisomerization of azobenzene compounds and quaternary ammonium salt compounds with different substituents on the benzene ring after forming DES is shown below. Figure 1 As shown;

[0060] In Examples 1-3, the structural formula of 4-((4-hydroxyphenyl)diazepine)benzoic acid (HBD) is as follows: Figure 2 As shown, the structural formulas of tetraethylammonium chloride, tetrabutylammonium chloride, and tetrabutylammonium bromide are as follows: Figure 3 As shown. The stable eutectic solvents obtained in Examples 1, 2, and 3 were dissolved in deuterated dimethyl sulfoxide and subjected to 1H NMR spectroscopy (NMR spectroscopy). 1 HNMR detection, results are as follows Figures 4-7 As shown, the peak area of ​​the "-OH" in all three DES types decreased. After HBD formed TEAC-DES, the chemical shift of the "-OH" increased from 10.455 ppm to 11.016 ppm; after forming TBAC-DES, the chemical shift of the "-OH" increased from 10.455 ppm to 10.802 ppm; and after forming TBAB-DES, the chemical shift of the "-OH" increased from 10.455 ppm to 10.480 ppm. Furthermore, the TBAC-DES and TBAB-DES photoresponsive eutectic solvents dissolved in deuterated dimethyl sulfoxide were subjected to 365 nm ultraviolet irradiation for 6 hours and then subjected to 1H NMR spectroscopy again. 1 HNMR detection, results are as follows Figures 8-9As shown, it can be seen that the peak area of "-OH" decreases after 365 nm light irradiation for 6 h, and after light irradiation, the chemical shift of "-OH" of TBAC-DES (6 h) increases from 10.802 ppm to 11.233 ppm, and the chemical shift of "-OH" of TBAB-DES (6 h) increases from 10.480 ppm to 10.521 ppm. Through the change of chemical shift and peak area of "-OH" before and after light irradiation, it can be proved that the hydrogen bonding effect of DESs is enhanced after 365 nm light irradiation.

[0061] The TBAC-DES eutectic solvent of Example 2 and the TBAB-DES eutectic solvent of Example 3 were respectively placed under 365 nm ultraviolet irradiation for refractive index change detection, and the results are shown in Figure 10 As shown, after 365 nm light irradiation, the hydrogen bonding effect of DESs is stronger, the refractive index of TBAC-DES decreases from 1.4781 to 1.3949, and the refractive index of TBAB-DES decreases from 1.4541 to 1.3813. Under 365 nm irradiation, the refractive index of DESs gradually decreases.

[0062] The TBAC-DES eutectic solvent of Example 2 and the TBAB-DES eutectic solvent of Example 3 were respectively placed under 365 nm ultraviolet irradiation for conductivity change detection, and the results are shown in Figure 11 As shown, after 365 nm light irradiation, the hydrogen bonding effect of DES mixture is stronger, the refractive index of TBAC-DES decreases from 4.95 μS / cm to 4.31 μS / cm, and the refractive index of TBAB-DES decreases from 2.38 μS / cm to 1.71 μS / cm. The conductivity of DESs gradually decreases with the irradiation of 365 nm light.

[0063] The HBD and the TBAB-DES eutectic solvent of Example 3 were respectively dissolved in tetrahydrofuran, and the change of photoisomerization rate of azobenzene (HBD) before and after forming DES was investigated, and the photoresponse change results are shown in Figures 12-13 As shown, by comparing the photoisomerization rate of azobenzene before and after forming DESs, it is found that: under 365 nm light irradiation: the photoisomerization rate of HBD decreases from 5.03 × 10 -2 s to 2.32 × 10 -2 s, and under 440 nm light irradiation: the photoisomerization rate of HBD increases from 5.24 × 10 -2 s to 6.4 × 10 -2 s, which proves that the hydrogen bonding effect of DES has a great influence on the photoisomerization rate of azobenzene, and the DES photoisomerization process can be recycled many times;

[0064] Five mg of the stable eutectic solvents obtained in Examples 2 and 3 were weighed out and subjected to infrared spectroscopy analysis (IR). The results are as follows: Figures 14-15 As shown, the stretching vibration of "-OH" after HBD forms TBAC-DES, from 3240 cm⁻¹ -1 Increased to 3394cm -1 The "-COOH" stretching vibration occurs at 2661 cm⁻¹. -1 2542cm -1 The two smaller peaks decreased to 2561 cm. -1 2432cm -1 The "C=O" in "-COOH" is from 1685cm -1 Increased to 1705cm -1 The bending vibration of the HBD fingerprint region “CH” was measured at 1141 cm. -1 Reduced to 1134cm -1 The stretching vibration of the "-OH" after HBD forms TBAB-DES, from 3240 cm⁻¹ -1 Increased to 3396cm -1 The "-COOH" stretching vibration occurs at 2661 cm⁻¹. -1 2542cm -1 The two smaller peaks decreased to 2569 cm. -1 2441cm -1 The "C=O" in "-COOH" is from 1685cm -1 Increased to 1710cm -1 The bending vibration of the HBD fingerprint region “CH” was measured at 1141 cm. -1 Reduced to 1136cm -1 This proves that a hydrogen bond network exists in DESs.

[0065] 10 mg of the stable eutectic solvents obtained in Examples 2 and 3 were weighed out and subjected to thermogravimetric analysis (TG). The heating rate was set at 10 °C / min, and the maximum temperature was 600 °C. The results are as follows: Figures 16-17 As shown, the first stage of DESs is the breaking of hydrogen bonds, the second stage is the decomposition of HBA, and the third stage is the decomposition of HBD. Hydrogen bonds are a weak intermolecular force, and they will break when the temperature rises to a certain level.

[0066] From the above proton NMR spectrum ( 1 Results from ¹H NMR, infrared spectroscopy (IR), and thermogravimetric analysis (TG) can reveal changes in the hydrogen bonding effect of the solvent driven by ultraviolet irradiation, thus avoiding the negative impacts caused by the introduction of additional substances.

[0067] In summary, the azobenzene compound with different substituents on the benzene ring is used as a hydrogen bond donor to form a new light-responsive deep eutectic solvent with a quaternary ammonium salt compound. Under ultraviolet irradiation, the azobenzene compound can respond to the hydrogen bond effect of the deep eutectic solvent, and compared with the traditional three types of responsive deep eutectic solvents, the azobenzene compound does not need to introduce additional additional substances to drive the DES, and solves the problem that the temperature-responsive, CO2 / N2 adsorption and pH-responsive deep eutectic solvents need to introduce additional substances, which may have a negative impact on the solvent. The raw materials of the present application are widely available, low in cost, simple in preparation method, and the reaction method is mild, does not need to use inorganic acid and alkali, can be recycled and used repeatedly, and will not cause a large amount of three wastes in the post-processing process, so as to greatly reduce the cost and reduce the pollution to the environment, which is conducive to the development of green chemistry.

[0068] The above is only an embodiment of the present application, and the specific technical solutions or characteristics known in the scheme are not described in detail. It should be pointed out that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A class of photoresponsive eutectic solvents, characterized in that, It is composed of an azobenzene compound and a quaternary ammonium salt compound, wherein the molar ratio of the azobenzene compound to the quaternary ammonium salt compound is 1:0.5 to 10; the azobenzene compound is 4-((4-hydroxyphenyl)diazepine)benzoic acid, and the quaternary ammonium salt compound is any one of tetraethylammonium chloride, tetrabutylammonium chloride, or tetrabutylammonium bromide.

2. The method for preparing the photoresponsive eutectic solvent as described in claim 1, characterized in that, Includes the following steps: S1. Take azobenzene compounds and quaternary ammonium salt compounds by molar ratio, grind and crush them separately, mix them, heat them gradually to form a homogeneous liquid, and then cool them to obtain a viscous liquid; S2. The viscous liquid obtained in S1 is dried under vacuum to obtain a novel photoresponsive eutectic solvent.

3. The method for preparing the photoresponsive eutectic solvent according to claim 2, characterized in that: In S1, the heating time is 30–120 min and the heating temperature is 50–120 ℃.

4. The method for preparing the photoresponsive eutectic solvent according to claim 2, characterized in that: In S2, the vacuum drying pressure is 10-20 kPa, the vacuum drying temperature is 50-100 ℃, and the vacuum drying time is 60-300 min.

Images