Synthesis And Evaporation Enthalpy Of Paramagnetic Pyrrolidine Cobalt Ionic Liquids

Paramagnetic metal compounds have unique structures and properties.Paramag-netic metal ionic liquids with different kinds and properties are designed and synthe-sized by changing the structure of cation and anion ions.Their application prospects are very wide.In this paper,a new class of paramagnetic metal ionic liquids were synthesized by two-step method,which are N-ethyl-N-methylpyrrolidine tetraisothio-cyanate cobalt,N-propyl-N-methylpyrrolidine tetraisothiocyanate cobalt,N-butyl-N-methylpyrrolidine tetraisothiocyanate cobalt,N-amyl-N-methylpyrrolidine tetrai-sothiocyanate cobalt,N-hexyl-N-methylpyrrolidine tetraisothiocyanate cobalt（[C_npyrr]₂[Co（SCN）₄]（n=2,3,4,5,6））.The intermediates were characterized by ~1H NMR and ¹³C NMR.Then,the target ionic liquids were characterized by Fourier in-frared spectroscopy（FT-IR）,Raman spectroscopy,Karl Fischer moisture determina-tion,Melting point,EA organic element analysis,X-ray electron spectroscopy and thermogravimetric analysis,so as to determine the structure of the product.Finally,the paramagnetism of this kind of ionic liquid was determined by vibrating sample magnetometer（VSM）,and its magnetism came from anions.The initial decomposition temperature of the target products N-alkyl-N-methylpyrrolidene cobalt tetraisothiocyanate[C_npyrr]₂[Co（SCN）₄]（n=2,3,4,5,6）were determined by thermogravimetric analysis method,and then the constant tem-perature range of the thermogravimetric experiment was determined.The relationship between the mass loss and temperature of this kind of paramagnetic metal ionic liquid was determined by thermogravimetric method.It was proved that the mass loss of the tested ionic liquid was not caused by the decomposition of impurities or degradation products,but by the thermal evaporation of the ionic liquid itself.Secondly,Langmuir equation and isotherm mass analysis were used to measure the enthalpy of evapora-tion of the target ionic liquid[C_npyrr]₂[Co（SCN）₄]（n=2,3,4,5,6）,and then the val-ue of evaporation enthalpy of the ionic liquid at the average temperature T_av was ob-tained.Then according to the Verevkin methods as?_l^gH_m^θ（Tav）into the evaporation enthalpy below 298.15 K;Then the comparison of evaporation enthalpy between common imidazole ionic liquids and magnetic cobalt ionic liquids is discussed.It can be found that the evaporation enthalpy of magnetic cobalt ionic liquids were much greater than that of other ionic liquids in the same alkyl chain,mainly because the evaporation parameters of ionic liquids are strongly and systematically affected by their chemical structure,charge balance of cation and anion,molecular weight,mag-netism and higher ordered structures including polar and non-polar regions;Finally,the uncertainty of evaporation enthalpy at the average temperature of the ionic liquid is calculated.The enthalpy of evaporation measured by thermogravimetric method is reasonable and its accuracy is within a reasonable range.