Phase Behavior Modulation Of Deep Eutectic Solvent-water Systems By CO₂ And Temperature

As a class of novel green solvents,deep eutectic solvents?DESs?have attracted extensive attention in academia and industry,especially in the fields of separation and purification,organic synthesis,gas capture and biocatalysis etc.Deep eutectic solvents not only have some unique characteristics of ionic liquids,but also have the advantages of low cost,easy to prepare,biodegradable and good biocompatibility etc.Therefore,they are considered as a kind of alternative solvents of traditional organic solvents.However,at present there are few types of deep eutectic solvents and they are not readily recyclable,which has greatly limited their practical application.Atmospheric CO₂ and temperature can be used to switch the properties of solvents.Compared with other control measures,CO₂ is cheap,non-toxic and easy to remove from systems.The advantage of using temperature as a stimulant is that it is easy to operate.Based on these features,we have designed and prepared a series of functionalized deep eutectic solvents which are responsive to CO₂ or temperature.By changing the structures of hydrogen bond donors and acceptors,the regulation and control of CO₂ or temperature on the phase behavior of these functionalized deep eutectic solvents-water systems have been systematically investigated.The possible mechanism for such a modulation is studied by NMR spetrascopy and dynamic light scattering.In addition,the application of CO₂ or temperature modulated deep eutectic solvent-water systems have been applied in the recovery of deep eutectic solvent components and extraction of some coumarin compounds.The results obtained here are useful for the design of functionalized deep eutectic solvents and their applications in chemical synthesis,extraction and separation.The main contents are as follows.1.A class of functionalized deep eutectic solvents were designed and synthesized with phenolic compounds as hydrogen bond donors and alkanolamine compounds as hydrogen bond acceptors.CO₂ was used to switch the phase behavior of these alkylamine-functionalized deep eutectic solvent-water systems:deep eutectic solvents were miscible with water at atmospheric temperature and pressure,and the system was phase-separated after the introduction of CO₂.Then,it returned to the initial state by bubbling of N₂.The reversible phase separation mechanism was studied by ¹³C NMR spectroscopy and dynamic light scattering.Then,two components of the deep eutectic solvent were recovered separately by using the CO₂-triggered binary systems,which provides a new strategy to the recovery of deep eutectic solvent components.2.The temperature triggered phase behavior of alkylamine-functionalized deep eutectic solvent-water systems was studied.The mixture of water and deep eutectic solvents was found to have the characteristic of a UCST-type phase separation:at 20?,such deep eutectic solvents were immiscible with water,but when the system temperature was raised to 25?,deep eutectic solvents and water formed a homogeneous solution.The mechanism of phase separation of these deep eutectic solvents-water systems was studied by means of temperature-dependent FTIR and ¹H NMR,and dynamic light scattering.In addition,some coumarin compounds were extracted from aqueous solution by using deep eutectic solvent-water systems,which provides important information for the application of deep eutectic solvent systems contain water in the extraction and separation field.3.A series of functionalized deep eutectic solvents were designed and synthesized with phenolic compounds as hydrogen bond donors and 1,3-propylenediamine compounds as hydrogen bond acceptors.Interestingly,these deep eutectic solvents showed a lower critical solution temperature in water:at 25?,deep eutectic solvents and water are completely miscible,but phase separation was observed when the temperature is raised to 60?.The phase separation mechanism was studied by means of ¹H NMR and dynamic light scattering.These temperature-responsive deep eutectic solvents-water systems are expected to have applications in chemical reactions,extraction and separation.