Seki Tsunetake, Andanson Jean-Michel, Jutz Fabian, Baiker Alfons
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Hönggerberg, HCI, CH-8093 Zurich, Switzerland.
Appl Spectrosc. 2009 Sep;63(9):1008-14. doi: 10.1366/000370209789379312.
The CO(2)-catalyzed acetalization is regarded as a promising alternative to the conventional acid-catalyzed method from a viewpoint of green chemistry (C. A. Eckert et al., Ind. Eng. Chem. Res. 43, 2605 (2004)). We have applied in situ attenuated total reflection infrared (ATR-IR) spectroscopy for elucidating and monitoring the acetalization of cyclohexanone in CO(2)-expanded ethylene glycol and methanol at 50 degrees C and 3 MPa. The ATR-IR spectra of the reaction mixtures periodically recorded with a ZnSe crystal demonstrate that ATR-IR spectroscopy is a practical tool for tracing the kinetics of acetalizations in situ. In addition, the rate of CO(2) dissolution as well as CO(2) solubility into the cyclohexanone-alcohol mixtures could be evaluated from the CO(2)-nu(3)-antisymmetric stretching band. The ZnSe ATR crystal, however, was corroded during longer use under the acidic conditions realized by the dissolution of CO(2) in the alcohols. In contrast, the corrosion did not occur when a Ge crystal was used instead of a ZnSe crystal, and therefore the application of a Ge ATR crystal is recommended for continuous long-term experiments with these media.
从绿色化学的角度来看，CO₂催化的缩醛化反应被视为传统酸催化方法的一种有前景的替代方法（C. A. Eckert等人，《工业与工程化学研究》43，2605（2004））。我们应用原位衰减全反射红外（ATR-IR）光谱法来阐明和监测50℃及3MPa下CO₂膨胀的乙二醇和甲醇中环己酮的缩醛化反应。用ZnSe晶体定期记录的反应混合物的ATR-IR光谱表明，ATR-IR光谱法是一种原位追踪缩醛化反应动力学的实用工具。此外，可从CO₂的ν₃反对称伸缩振动带评估CO₂的溶解速率以及CO₂在环己酮-醇混合物中的溶解度。然而，在CO₂溶解于醇类所实现的酸性条件下长时间使用时，ZnSe ATR晶体被腐蚀。相比之下，当使用Ge晶体代替ZnSe晶体时，未发生腐蚀，因此建议在这些介质的连续长期实验中应用Ge ATR晶体。
