酸功能化-温控型三元杂多酸离子液体的合成、表征及其酯催化性能

采用酸化-乙醚萃取法制备了不同钒取代数目的 Keggin结构的磷钨钒杂多酸,并进一步通过离子交换法合成了磺酸功能化的杂多酸离子液体催化剂,采用核磁、元素分析、红外、紫外、X射线衍射、热重-差示扫描、电位滴定等分析手段对所得样品进行了表征,考察了所得样品对氯乙酸和正戊醇的酯化反应性能和重复使用性能。结果表明,所制备的杂多酸离子液体是一种具有温度响应特性的无定型结构化合物,仍保留Keggin结构和较高的酸强度,该催化剂在反应温度下与反应物形成一相,而反应结束温度降低后,催化剂和产物又形成两相,通过简单的倾倒法就可以快速分离催化剂和反应产物。与杂多酸以及未磺酸化的杂多酸离子液体相比,磺酸功能化的杂多酸离子液体具有更高的酯催化活性。在优化的反应条件下,PyPS]4PW11VO40(PyPS为1-(3-磺酸基)丙基吡啶)对氯乙酸的转化率可达到97.6%,重复使用4次后转化率为91.9%,而催化剂的结构未有明显变化。

Synthesis, Characterization and Esterification Application of Acid-Functionalized Ternary Heteropolyanion-Based Ionic Liquids with Temperature-Responsive Behaviour

A series of vanadium-substituted ternary heteropoly acids with Keggin structure were synthesized by acidification-ether extraction method. Furthermore, the heteropolyanion-based ionic liquids with functional sulfonic acid group,PyPs]_3+nPW_12-nV_nO₄₀ (n=1, 2, 3), were synthesized by an ion exchange method. The products were characterized by nuclear magnetic resonance spectroscopy (NMR), element analysis, Fourier transform infrared spectrophotometry (FT-IR), UV-Vis spectrophotometry, X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC) and potentiometric titration measurements. The catalytic ability and reusability of the ionic liquid catalysts were evaluated in esterification reaction of chloroacetic acid with n-pentyl alcohol. The results show that the ionic liquid catalyst was an amorphous structural compound with temperature responsive characteristics, in which Keggin structure and high acid strength of ionic liquid catalyst remain. The catalyst formed a homogeneous mixture with the reactants at the reaction temperature, but precipitated with biphase separation when the reaction ends and reaction temperature was lowered, and so could be easily separated from the products by a simple filtration. Sulfonic acid functionalized heteropolyanion-based ionic liquids exhibited higher ester catalytic activity than heteropoly acids and unsulfonated heteropolyanion-based ionic liquids. Under the optimized reaction conditions, the conversion rate ofPyPS]₄PW₁₁VO₄₀ (PyPS is 1-(3-sulfonate) propyl pyridine) to chloroacetic acid could reach 97.6%, and the conversion rate was 91.9% after repeated reaction four times, but the structure of the catalyst had no change significantly.