Wuttke Stefan, Coman Simona M, Scholz Gudrun, Kirmse Holm, Vimont Alexandré, Daturi Maro, Schroeder Sven L M, Kemnitz Erhard
Humboldt University Berlin, Institute of Chemistry, Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
Chemistry. 2008;14(36):11488-99. doi: 10.1002/chem.200801702.
Novel magnesium fluorides have been prepared by a new fluorolytic sol-gel synthesis for fluoride materials based on aqueous HF. By changing the amount of water at constant stoichiometric amount of HF, it is possible to tune the surface acidity of the resulting partly hydroxylated magnesium fluorides. These materials possess medium-strength Lewis acid sites and, by increasing the amount of water, Brønsted acid sites as well. Magnesium hydroxyl groups normally have a basic nature and only with this new synthetic route is it possible to create Brønsted acidic magnesium hydroxyl groups. XRD, MAS NMR, TEM, thermal analysis, and elemental analysis have been applied to study the structure, composition, and thermal behaviour of the bulk materials. XPS measurements, FTIR with probe molecules, and the determination of N(2)/Ar adsorption-desorption isotherms have been carried out to investigate the surface properties. Furthermore, activity data have indicated that the tuning of the acidic properties makes these materials versatile catalysts for different classes of reactions, such as the synthesis of (all-rac)-[alpha]-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP).
基于氢氟酸水溶液，通过一种新的氟解溶胶 - 凝胶合成法制备了新型氟化镁，用于氟化物材料。在氢氟酸化学计量比恒定的情况下，通过改变水量，可以调节所得部分羟基化氟化镁的表面酸度。这些材料具有中等强度的路易斯酸位点，并且通过增加水量还会产生布朗斯特酸位点。镁羟基通常具有碱性，只有通过这种新的合成路线才有可能产生布朗斯特酸性的镁羟基。X射线衍射（XRD）、魔角旋转核磁共振（MAS NMR）、透射电子显微镜（TEM）、热分析和元素分析已被用于研究块状材料的结构、组成和热行为。进行了X射线光电子能谱（XPS）测量、使用探针分子的傅里叶变换红外光谱（FTIR）以及N₂/Ar吸附 - 脱附等温线的测定，以研究表面性质。此外，活性数据表明，酸性性质的调节使这些材料成为适用于不同类型反应的通用催化剂，例如通过2,3,6 - 三甲基对苯二酚（TMHQ）与异植物醇（IP）缩合合成（全消旋） - α - 生育酚。
