Significant Waste Reduction in Liquid Chromatography by a Reusable Large-Volume Monolithic Silica Column

The highly efficient separation of product mixtures in chemical synthesis is increasingly crucial for realizing sustainable chemical processes. Here, we report that large-volume monolithic silica with a well-defined cocontinuous porous structure brings significant benefits to liquid chromatography, satisfying both the enhanced efficiency and remarkable reduction of chromatographic wastes of solvent and solid separation media. Reusability of the monolithic silica column has been demonstrated by regeneration with an acid-flow washing, in which the cocontinuous porous structure of monolithic silica is well retained even in aqua regia in the regeneration process. The resolution of separation is comparable to preparative high-performance liquid chromatography, and the extremely low column back-pressure is suitable for open and flash columns. Moreover, a good correlation of the retention with conventional thin-layer chromatography and the high loading capacity up to 10 wt % are advantageous in overloading purification. Improved productivity with the large-volume monolithic silica has been confirmed in the practical purification of a low-solubility compound, 9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N,N,N ',N '-tetraphenyl-9H-carbazole-3,6-diamine (DACT-II), for a highly efficient organic light-emitting diode. Reduction of solvent and solid consumption by 60 and 90%, respectively, with increased purities in each step of the total synthesis of DACT-II, has been demonstrated in comparison with purification with standard silica particles.