Brönsted酸性离子液体催化酯化反应研究

合成了以2-吡咯烷酮和N-甲基咪唑为阳离子([Hnhp]＋和[Hmim]＋), , 和 为阴离子的一系列Brönsted酸性离子液体. 考察了这些离子液体的热稳定性和酸性. 以乙酸和异戊醇酯化合成乙酸异戊酯的反应考察了不同离子液体分别在不分水与分水条件下的催化效果, 结果表明, 不分水时, 当醇/酸/[Hnhp]HSO4物质的量比为1.2∶1∶0.2, 100 ℃下回流反应2 h, 酯收率可达93.6%, 反应结束后[Hnhp]HSO4体系可以顺利分相, [Hnhp]BF4则不能; 分水时, [Hnhp]BF4可与酯自动分相, 当醇/酸/[Hnhp]BF4物质的量比为1.2∶1∶0.01, 120 ℃下回流反应1.5 h时, 酯收率可达96.8%, 比相同条件下[Hnhp]HSO4的略高. 这两种体系中的离子液体均具有良好的重复使用性能. 实验中还探讨了不同离子液体的酸性和催化酯化反应后与酯产物的分相效果对其催化活性的影响, 结果表明, 离子液体的酸性和与酯的不可混溶性对其在不同体系中酯化反应的催化活性有不同程度的影响. 此外, 在上述不分水酯化条件(醇∶酸∶催化剂物质的量比均为1.2∶1∶0.2, 100 ℃油浴)下回流浸渍6 h比较离子液体[Hnhp]HSO4/BF4, [Hmim]HSO4/BF4和硫酸对奥氏体316不锈钢的腐蚀性, 测得离子液体腐蚀率比硫酸低; 除了[Hnhp]BF4, 离子液体[Hnhp]HSO4, [Hmim]HSO4和[Hmim]BF4的腐蚀性呈现随酸性递减而下降的趋势. 所测离子液体中[Hnhp]BF4腐蚀性最高. [Hnhp]BF4和硫酸中试样的腐蚀率分别为20.1和41.8 g/(m2•h).

Esterification Catalyzed by Brönsted Acidic Ionic Liquids

A series of Brönsted acidic ionic liquids based on 2-pyrrolidonium and 1-methylimidazolium cations ([Hnhp]＋and [Hmim]＋) with anions , and , were synthesized. Their thermal stabilities and acidities were characterized, and the catalytic activity of the acidic ionic liquids for the esterification of acetic acid with iso-pentanol was studied. When n(i-PentOH)∶n(MeCO2H)∶n([Hnhp]HSO4)＝1.2∶1∶0.2, T＝100 ℃ (oil bath) and t＝2 h, the yield of iso-amyl acetate could be 93.6% without removal of water during the esterificaion. After the reaction, the [Hnhp]HSO4 system achieved phase separation successfully, but [Hnhp]BF4 system did not. When using water separator, n(i-PentOH)∶n(MeCO2H)∶n([Hnhp]BF4)＝1.2∶1∶0.01, T＝120 ℃ (oil bath) and t＝1.5 h, the yield of iso-amyl acetate could reach 96.8%, and the [Hnhp]BF4 system could exhibit good biphasic behavior. There is no appreciable decrease of catalyst activity for both the systems after 6 cycle catalyst repetition. The acidity/biphasic behavior-catalytic activity relationships were also investigated. The results showed that the effects produced by acidity and immiscibility of the acidic ionic liquids with the ester on the both esterification systems, whether the resultant water separated or not, were different. In addition, Austenitic stainless steel 316 was immersed in four kinds of ionic liquids (containing and ) and sulfuric acid respectively for corrosion tests under the above conditions of esterificaion without removal of water, i.e., n(i-PentOH)∶n(MeCO2H)∶ n(catalyst)＝1.2∶1∶0.2, oil bath 100 ℃. After 6 h of reflux immersion, it was observed that there was lower corrosion of the steel sample by each ionic liquid solution system than by sulfuric acid. For [Hnhp]HSO4, [Hmim]HSO4 and [Hmim]BF4, there was a decrease of corrosion rate with the decreasing acidity of ionic liquids. [Hnhp]BF4 was more corrosive than other ionic liquids, and the corrosion rates of [Hnhp]BF4 and sulfuric acid were 20.1 and 41.8 g/(m2•h), respectively.