Properties Of Ether-functionalized Rhenium Ionic Liquid And Their Applications In Cyclooctene Epoxidation

In recent years,ionic liquids have attracted great attention of the scholars due to their excellent thermal stability and high electrochemical stability.In particular,ionic liquids are functionally configurable,so that a wider variety of ionic liquids can be synthesized and have been applied to chemical production and many other related fields.The introduction of ethyl ether?2OR?on the imidazole cation can effectively reduce the viscosity of the ionic liquid,and it is the lowest in the case of the ethyl group is at the N position.Rhenium and its compounds have been investigated deeply and showed great potential in catalysis.However,their existence of a solid state generally give rise to the heterogeneous catalytic reactions,which leads to a lower yield and selectivity,and limits their development in catalysis.In order to combine the advantages of ionic liquids and rhenium,two novel ether-functionalized rhenium ionic liquids 1-?2-methoxyethyl?-3-ethylimidazolium perrhenate ?[C₂2O1Im][ReO₄]? and 1-?2-ethoxyethyl?-3-ethylimidazolium perrhenate ?[C₂2O2Im][ReO₄]? were synthesized,and their structure characteristics were verified through proton nuclear magnetic resonance spectrum ?¹H-NMR?,carbon nuclear magnetic resonance spectrum (¹³C-NMR),Raman spectrum?Raman?,mass spectrum?ESI-MS?and differential scanning calorimetry?DSC?.After determining the accuracy of the synthesized target products,their physical and chemical properties were investigated.In the specific temperature range,their density,surface tension,refractive index,electrical conductivity and viscosity were measured at intervals of 5 K,and the volume properties and surface properties of them were estimated by the semi-empirical method.The results well explained the room temperature molten salts properties of the ionic liquid after comparing the calculated lattice energy value with the inorganic molten salts.Besides,the thermal expansion coefficients of the two ionic liquids were estimated by the interstice model theory,which were in well consistent with the experimental values.At the same time,the relationship between the properties of sound velocity W,molar polarization R_m,polarizability?_p,molar conductivity?,viscous flow activation Gibbs free energy?G^?with temperature,and the contribution of methylene group to molecular volume V_m,standard entropy S^? and lattice energy U_POT were also discussed.As a sort of chemically active and easily convertible organic synthesis intermediates,epoxy compounds occupy an extremely important position in various industries of national production.The epoxidation of olefins is an important way to synthesize epoxy compounds.In this paper,two novel ether-based functional rhenium ionic liquids [C₂2O1Im][ReO₄] or [C₂2O2Im][ReO₄] were used as catalyst and solvent in the reaction system of cyclooctene epoxidation to epoxy cyclooctane respectively.The optimum conditions for this catalytic reaction were found by single factor experiments.On this basis,three-factor and three-level response surface optimization experiments were designed to optimize them,and the degree of influence of three main factors was discussed.Under the optimal reaction conditions,the yields of the two rhenium ionic liquids catalyzing the epoxidation of cyclooctene are greater than 90% and the selectivity are greater than 99%.The effect of three factors on the catalytic yield is:oxidant dosage>reaction temperature>ionic liquid dosage.This paper has certain guiding significance for the development of metal chemistry,green chemistry and catalytic chemistry.It enriches the study of types,properties and catalytic applications of ionic liquids and provides important theoretical support for industrial production.