氯铝酸离子液体酸性的吡啶探针红外光谱研究

Studies on Acidity of Chloroaluminate Ionic Liquids Using Pyridine as Infrared Spectroscopic Probe

利用吡啶探针红外光谱法研究了氯铝酸离子液体的酸性，发现当氯铝酸离子液体AlCl3的摩尔分数χ为0．4—0．5时，离子液体表现出弱Lewis酸的红外特性。对吡啶探针吸附Lewis酸位AlCl7^-、AlCl4^-、Al2Cl6和AlCl3的各振动模式红外特征峰峰位进行了归属，通过红外特征峰峰位置和峰面积可以指示离子液体的酸强度。利用吡啶探针递增吸附法考察了吡啶递增吸附对氯铝酸离子液体酸性位的影响。研究发现，当吡啶量增加到一定程度时，Py—Al2Cl7^-配位络合物容易与吡啶发生反应生成Py—AlCl4^-和Py—AlCl3配位络合物，从而导致离子液体的吡啶吸附红外特征峰发生变化。

Knowledge of the acidity of ionic liquid （ILs） is critically required for utilization of ionic liquid. The acidity of chloroaluminate ionic liquids was investigated by pyridine （Py） as infrared spectroscopic probe. It was found that when the anion molar composition χ of ionic liquid varies within 0.4 - 0.5, ionic liquids exhibits weak Lewis acidity. Infrared （IR） absorption frequencies of ring stretching vibrations for pyridine on Lewis acid Al2Cl7^- , AlCl4^- , Al2Cl6 and AlCl3 were assigned, respectively. The frequency and peak area of IR absorption spectra could be indicative of the acidity strength of ionic liquids. In addition, the evolvement mechanism of the Lewis acid site of ionic liquid was studied on the basis of the method of adsorption incremental of pyridine. The results showed that the highly Lewis acidic adsorption state-Py-Al2Cl7^- complex was converted into Py-AlCl4^- complex and Py-AlCl3 complex with increasing pyridine contents.