Physicochemical And Spectral Properties Of Chelate-based Ionic Liquids As Well As Their Application In Catalytic Oxidation

Chelates can also be melted at low temperature(<100?),which are so-called chelate-based ionic liquids(ChILs).The ChILs not only possess the characterizes of general ionic liquids(ILs),but also the properties of metal such as color,magnetism and catalysis,etc.,thus making them enter into the functional ILs and successfully applied to many fields such as gas absorption,catalysis and extraction.The researches on relationship between the structure and physicochemical properties of ILs laid a solid foundation for their rapid development.Metal chelates,however,are mostly solid at room temperature,hence few researches on ChILs are reported so far.This work aims to systematically study the physicochemical properties and microstructure of ChILs by macroscopic thermodynamics and spectroscopy methods,and on the basis above,to expand their applications in catalytic oxidationIn the first part,the density,viscosity and conductivity of the binary mixtures of[C10mim][Cu(hfacac)3]and linear alcohols were measured,and the effects of temperature and the length of carbon chains for alcohols on the physicochemical properties of[C10mim][Cu(hfacac)s]were discussed.Combined with small angle X-ray scattering analysis,it is found that the filling effect is dominate in[C10mim][Cu(hfacac)3]+methanol mixtures due to the special chelating anion cavity.And butanol molecules can break the entanglement of alkyl chains between ChILs,thus reducing the viscosity more effectively.With the concentration of alcohols increase,the conductivity of these four systems all increase firstly and decrease then.It is interesting that the order of the maximum value of the conductivity is consistent with the dielectric constants of alcohols.The Walden curves shows that the ionicities of these four systems are poorer than that of general ILsThe solvents do affect the structure and physicochemical properties of ILs as discussed above In the second part,we tried to explore the interaction between[C10mim][Cu(hfacac)3]and different solvents or general ILs by electron paramagnetic resonance spectroscopy(EPR).As we know,there is an unpaired electron in d9 electronic configuration with a nuclear spin of 3/2 of 63Cu(?)contained in[C10mim][Cu(hfacac)3],which can generate paramagnetic signals.The existence of solvents will affect the crystal field of 63Cu(?),thereby affecting its hyperfine coupling constant(AIL).The results showed that in protic and aprotic solvents,the AIL located at around 115 and 125 Gauss,respectively.And a good linear relationship between AIL and Kamlet-Taft parameters of molecular solvents indicates the solvation is dominate here.For the solvents such as pyridine,which can coordinate with the central metal to cause a distortion of crystal field,thus leading AIL reach 170 Gauss.In general ILs,two groups of EPR signal peaks can be observed,indicating that ion exchange was occurred between[C10mim][Cu(hfacac)3]and general ILs.Meanwhile,according to the good relationship between AIL and dielectric constants of molecular solvents,the reliability of[C10mim][Cu(hfacac)3]as a probe of EPR to study the solute-solvent interaction was verified.According to the studies above,we can learn that there are significantly difference of the excessive properties between the ChILs and molecular solvents compared with that of general ILs.To explore the reason for this difference in depth,the microstructure of the binary mixtures of[C10mim][Cu(hfacac)3]and methanol was studied by infrared spectroscopy(IR)and two-dimensional correlation analysis in the third part.For a better comparison,the general IL([C10mim][hfacac])was also studied.IR results show that with the concentration of methanol increases,the blue shift of v(C-H)in imidazole ring of[C10mim][hfacac]is more signicant than that of[C10mim][Cu(hfacac)3].The wavenumber shift of the v(C=O)in these two systems,however,is completely opposite,indicating that the filling effect is dominant in[C10mim][Cu(hfacac)3]because of the chelating anion cavity.Methanol enters into the chelating cavity and interacts with C=O band,thus resulting in a rearrangement of electron densities on the ligand and little effect on the hydrogen bond between anion and cation,hence v(C=O)yields a red shift.For[C10mim][hfacac],however,methanol can directly weaken the hydrogen bond between anion and cation,causing a blue shift of the v(C=O).However,two-dimensional correlation analysis of FTIR spectra shows that the formation of the chelating cavity has little effect on the sequence of interaction sites between ILs and methanol,which may provide some inspiration for catalytic applications.In the last part,we applied the[C10mim][Cu(hfacac)3]to the catalytic oxidation of?-isophorone(?-IP)to synthesize keto-isophorone(KIP)based on the study of physicochemical properties above.Compared with the traditional metal salt catalysts,the[C10mim][Cu(hfacac)3]also has a good catalytic performance and the effect of temperature,catalyst concentration and solvent were also studied.By changing the ratio of solvents,the influence of the structure and interaction between solvents and[C10mim][Cu(hfacac)3]on catalytic performance was also investigated,thus linking the physicochemical properities of ChILs and application.As the saying goes:"Rome was not built in a day." The structure and physicochemical properties of ChILs are closely related,and both determine their practical application.In this work,the macroscopic physicochemical properties,microstructure and the application in catalytic oxidation for ChILs was systematically studied,which may shed a light on designing multifunctional ILs and widening their applications.