Rorrer Julie, Pindi Suresh, Toste F Dean, Bell Alexis T
Energy Biosciences Institute, University of California, Berkeley, CA, 94720, USA.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA, 94720, USA.
ChemSusChem. 2018 Sep 21;11(18):3104-3111. doi: 10.1002/cssc.201801067. Epub 2018 Aug 23.
Linear and branched ether molecules have attracted recent interest as diesel additives and lubricants that can be produced from biomass-derived alcohols. In this study, tungstated zirconia was identified as a selective and green solid acid catalyst for the direct etherification of primary alcohols in the liquid phase, achieving ether selectivities of >94 % for C -C linear alcohol coupling at 393 K. The length of linear primary alcohols (C -C ) was shown to have a negligible effect on apparent activation energies for etherification and dehydration, demonstrating the possibility to produce both symmetrical and asymmetrical linear ethers. Reactions over a series of C alcohols with varying methyl branch positions indicated that substituted alcohols (2°, 3°) and alcohols with branches on the β-carbon readily undergo dehydration, but alcohols with branches at least three carbons away from the -OH group are highly selective to ether. A novel model compound, 4-hexyl-1dodecanol, was synthesized and tested to further demonstrate this structure-activity relationship. Trends in the effects of alcohol structure on selectivity were consistent with previously proposed mechanisms for etherification and dehydration, and help to define possible pathways to selectively form ethers from biomass-derived alcohols.
直链和支链醚分子作为可由生物质衍生醇类生产的柴油添加剂和润滑剂，近来引起了人们的关注。在本研究中，钨酸锆被确定为一种选择性的绿色固体酸催化剂，用于液相中伯醇的直接醚化反应，在393 K下，C -C直链醇偶联的醚选择性>94%。结果表明，直链伯醇（C -C ）的长度对醚化和脱水的表观活化能影响可忽略不计，这表明有可能生产对称和不对称直链醚。对一系列具有不同甲基支链位置的C醇进行的反应表明，取代醇（2°、3°）和β-碳上有支链的醇容易发生脱水，但与-OH基团至少相隔三个碳原子有支链的醇对醚具有高度选择性。合成并测试了一种新型模型化合物4-己基-1-十二醇，以进一步证明这种构效关系。醇结构对选择性影响的趋势与先前提出的醚化和脱水机制一致，并有助于确定从生物质衍生醇类中选择性形成醚的可能途径。
