Study On The Structure Of Hydrophobic Binary/ternary Deep Eutectic Solvents Based On Vibrational Spectroscop

In recent years,people’s concept of green chemistry and green development has increasing.So finding low-toxicity,sustainable green solvents has become one of the most important topics in the field of scientific research.Deep eutectic solvents,as analogues of ionic liquids in green solvents,have many excellent characteristics comparable to ionic liquids,such as low saturated vapor pressure,good solubility,low flammability,good thermal stability,and can be used according to actual conditions.These advantage of deep eutectic solvents has gained more and more attention in the chemical community.Moreover,the preparation of the deep eutectic solvent is simple,low in cost,and the utilization rate of atoms is as high as 100 %,which makes up for the shortcomings of complex preparation,high cost,and difficult purification of ionic liquids,and has the advantages of being environmentally friendly and low economic cost.Therefore,it has a good application prospect in replacing highcost ionic liquids and volatile organic solvents.However,current research mainly focuses on the preparation and application of hydrophilic deep eutectic solvents.The hydrogen bonds in hydrophilic deep eutectic solvents are easily affected by hydrogen bonds in water,which will destroy the structure of DES,and the phase separation cannot be stabilized in water,which limits the application of DES in aqueous phase.In order to overcome this limitation and expand the application range of deep eutectic solvents,hydrophobic deep eutectic solvents have emerged,and hydrophobic deep eutectic solvents have the potential to replace traditional organic solvents and extractants.However,at present,there are few studies on the interaction between components of deep eutectic solvents,and there is still a lack of systematic research on the physical and chemical properties of this new type of green solvent,especially in structural analysis,spectral prediction and formation mechanism.It limits and hinders the design and development of deep eutectic solvent.Therefore,it is of great significance to study the interaction between deep eutectic solvent components.Based on this,in the Part I,Iinvestigates hydrogen bond donors and hydrogen bond acceptors for four common hydrophobic low eutectic solvents.These four substances are thymol,menthol,benzyltriethylammonium chloride,and capric acid,and their infrared and Raman spectra were studied respectively,and a comprehensive and systematic analysis was carried out using the method of density functional theory(DFT).The structure,vibration frequency and belonging of the four pure components of the prepared deep eutectic solvent were studied,and the belonging of their vibration peaks was determined.According to the calculation results,the experimental characteristic peaks of infrared and Raman were almost determined,and it was found that the characteristic peaks had a redshift phenomenon,which could be attributed to the role of hydrogen bonding.Through the comparison of experimental and theoretical calculation results,we can gain insight into the formation mechanism of DES.In the part II,eight kinds of hydrophobic deep eutectic solvents were designed and successfully synthesized by oil bath magnetic stirring method,namely thymol/benzyltriethylammonium chloride(2:1),capric acid/benzyltriethylammonium chloride(1:1),capric acid/thymol(1:1),menthol/thymol(1:1),benzyltriethylammonium chloride/menthol/thymol(1:1:1 and 1:1:2),benzyltriethylammonium chloride/capric acid/thymol(1:1:1 and 1:1:2).These hydrophobic deep eutectic solvents were synthesized by heating and stirring with a magnetic stirrer.After depositing at room temperature for 24 hours,they were still transparent liquids without crystal precipitation.Subsequently,I characterized these hydrophobic deep eutectic solvents by infrared spectroscopy and Raman spectroscopy to study intermolecular hydrogen bonding.In order to further understand the physical and chemical properties and formation mechanism of these HDES.In addition,this paper also made a mixed system of two kinds of DES,mixing thymol/capric acid(1:1)and thymol/benzyltriethylammonium chloride(4:1)in proportion,and studied the characteristic Raman peaks of the mixture confirmed that some peaks surely shifted,which indicated that the hydrogen bonds in the two DESs changed after mixing.