过渡金属离子液体[C2mim][FeCl4]的溶解热

在干燥氩气氛下, 用等摩尔的高纯无水FeCl3和氯化1-甲基-3-乙基咪唑(C2mim]Cl])直接搅拌混合, 制备棕色透明的含过渡金属铁的离子液体C2mim]FeCl4]. 在298.15 K下, 利用具有恒温环境的溶解反应热量计测定了这种离子液体的摩尔溶解焓(ΔsHm). 针对C2mim]FeCl4]溶解于水后即分解的特点, 在Pitzer电解质溶液理论基础上, 提出了确定这种离子液体标准摩尔溶解焓的新方法, 得到了C2mim]FeCl4]的标准摩尔溶解焓(ΔsH 0—m=-76.6 kJ/mol), 以及Pitzer焓参数组合: β(0)LFe,Cl+β(0)LC2mim], Cl+ΦLFe,C2mim]=0.072209和β(1)LFe,Cl+β(1)LC2mim], Cl=0.15527. 借助热力学循环和Glasser离子液体晶格能理论, 用Fe3+, Cl-和C2mim]+的离子水化焓数据以及C2mim]FeCl4]标准摩尔溶解焓, 估算得到了配离子FeCl4]-(g)解离成Fe3+(g)和4Cl-(g)的解离焓为5659 kJ/mol. 这个结果揭示了离子液体C2mim]FeCl4]的标准摩尔溶解焓绝对值并不很大的原因, 即很大的离子水化焓被很大的FeCl4]-(g)的解离焓相互抵消.

Studies on the Enthalpy of Solution of Ionic Liquid [C2mim][FeCl4] Based on Transition Metal

A brown and transparent ionic liquid,C2mim]FeCl4], was prepared by mixing anhydrous FeCl3 with 1-methyl-3-ethylimidazolium chloride(C2mim]Cl]), with molar ratio 1∶1 under stirring in a glove box filled with dry argon. The molar enthalpies of solution, ΔsHm, of C2mim]FeCl4] in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. In terms of Pitzer electrolyte solution theory, the standard molar solution enthalpy of C2mim]FeCl4], ΔsH0m, and the sum of Pitzer parameters: (β(0)LFe,Cl+β(0)LC2min],Cl+ΦLFe,C2min]) and (β(1)LFe,Cl+β(1)LC2min],Cl) were obtained, respectively. Using the values of the solution enthalpies and crystal energy of the ionic liquid, the dissociation enthalpy of FeCl4]- anion, ΔHdis≈5659 kJ/mol, for the reaction: FeCl4]-(g)→Fe3+(g)+4Cl-(g), was estimated. It is shown that the enthalpy of solution of theC2mim]FeCl4] is small because the large hydration enthalpies of Fe3+, 4Cl- and C2mim]- was compensated by the large dissociation enthalpy of FeCl4]- anion, ΔdHm, in dissolution process of the IL.