Polymer-bound catalysts, used continuous reaction

The use of such an oxazaborolidine system in a continuously operated membrane reactor was demonstrated by Kragl et /. 58] Various oxazaborolidine catalysts were prepared with polystyrene-based soluble supports. The catalysts were tested in a deadend setup (paragraph 4.2.1) for the reduction of ketones. These experiments showed higher ee s than batch experiments in which the ketone was added in one portion. The ee s vary from 84% for the reduction of propiophenone to up to >99% for the reduction of L-tetralone. The catalyst showed only a slight deactivation under the reaction conditions. The TTON could be increased from 10 for the monomeric system to 560 for the polymer-bound catalyst. 

While linear, soluble polymers have seen scattered use in many reactions and have achieved some recognition in certain instances such as peptide synthesis, the use of soluble polymer-bound reagents and catalysts is a promising area which merits further study. While a homogeneous reagent such as a soluble macro-molecular reagent cannot always be used in a continuous process. 

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