离子液体[C2mim][GaCl4]的溶解热研究

在干燥氩气氛下, 用等摩尔的高纯无水GaCl3和C2mim]Cl](氯化1-甲基-3-乙基咪唑)直接搅拌混合, 制备了淡黄色透明的的离子液体C2mim]GaCl4] (1-ethyl-3-methylimidazolium chlorogallate) . 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不同浓度摩尔溶解焓 . 针对C2mim]GaCl4]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]GaCl4]在水中的标准摩尔溶解焓, ＝－132 kJ•mol－1, 以及Pitzer焓参数组合: ＝－0.1373076和 ＝0.3484209. 借助热力学循环和Glasser离子液体晶格能理论, 用Ga3＋, Cl－和C2mim]—的离子水化焓数据以及本文得到的C2mim]GaCl4]标准摩尔溶解焓, 估算了配离子4Cl－(g)解离成Ga3＋(g)和4Cl－(g)的解离焓ΔHdis(GaCl4]-)≈5855 kJ•mol－1. 这个结果揭示了离子液体C2mim]GaCl4]的标准摩尔溶解焓绝对值并不很大的原因, 即是很大的离子水化焓被很大的GaCl4]－(g)的解离焓相互抵消了.

Molal Enthalpy of Solution of Ionic Liquid [C2mim][GaCl4]

An ionic liquid (IL), C₂mim]GaCl₄] (1‐ethyl‐3‐methylimidazolium chlorogallate), was prepared by directly mixing 1‐ethyl‐3‐methylimidazolium chloride (C₂mim]Cl]) and anhydrous GaCl₃ with a molar ratio of 1/1 under dry argon. The molal enthalpies of solution, Δ_sH_m, of C₂mim]GaCl₄], were measured over a molality range of about 0.008–0.1 mol·kg^?1 by a solution reaction isoperibol calorimeter at 298.15 K. Considering the hydrolization of anion GaCl₄]^? in dissolution process of the IL, a new method of determining the standard molal enthalpy of solution, Δ_sH_m^?, was put forward on the basis of Pitzer's mixed electrolyte solution theory so that Δ_sH_m^?=?132 kJ·mol^?1 and the sum of Pitzer's parameters: 4β_Ga,Cl⁽⁰⁾+4β_C2mim],Cl⁽⁰⁾+4_Ca,C2mim]=?0.1373076, β_Ga,Cl^(1)L+β^(1)L=0.3484209 were obtained. In terms of thermodynamic cycle and Glasser's theory of lattice energy for IL, the dissociation enthalpy of GaCl₄]^?(g), ΔH_dis(GaCl₄]^?)≈5855 kJ·mol^?1, that is enthalpy change for the reaction: GaCl₄]^?(g)→Ga³⁺(g)+4Cl^?(g), was estimated.