(113a) The Use of Immobilised Catalysts for Organic Synthesis in Flow Reactors

Synthetic chemists are continually searching for new ideas that make the construction of organic compounds easier. While solid-supported reagents, scavengers and catalysts have been used to great effect speeding up the purification of product mixtures, reactions are generally slower and employ laborious filtration techniques to remove the supported reagent post reaction. Furthermore, literature president dictates that the efficiency of supported reagents deteriorates over time as a result of mechanical degradation. In comparison, supported reagents are ideally suited for use in flow reactors where compounds are conveniently synthesized by the flow of substrates over the immobilized reagent or catalyst. In such systems, the rate of reaction is enhanced as a result of the high surface to volume ratio and as the catalyst is held within the reactor, it is not necessary to filter the reaction products to remove the supported reagent, enabling several of the traditional disadvantages to be overcome with ease.

Very few publications have reported organic synthesis in micro reactors incorporating supported reagents or catalysts; this is attributed largely to the difficulties associated with the fabrication of such devices. The Hull group has recently overcome these problems using a variety of approaches; the most successful being the incorporation of supported reagents between porous silica frits after the micro reactor has been fabricated. In such systems the group has demonstrated that a wide variety of reaction types may be conducted in near quantitative yield obtaining products in high purity, straight from the reactor, without the need for any form of purification. As the immobilized reagent suffers less physical damage in flow reactors compared with conventional stirred reactions, the result being that the reagents last longer and reactions are more reproducible.

The Hull group has also investigated the feasibility of incorporating supported reagents in series within continuous flow reactors in order to perform multi-step syntheses. In this presentation a series of other reactions will be presented including the use of immobilised enzymes in such systems.