Application of segmented flow technique in catalytic organic syntheses

• Main Author: Omer, Batoul Ahmed
• Published: Cardiff University 2008
• Subjects: 547
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584322

Microflow technology has become an innovative and fashionable tool in synthetic organic chemistry, opening the way to novel challenging interactions between chemistry and other scientific disciplines. The system properties and reaction conditions in microflow chemistry are different to those in flask as a result of higher surface-to- volume ratios and shorter diffusion distances bringing significant advantages over conventional flask method such as improved heat transfer and reduced mixing times. More and more multiphase microflow systems have begun to emerge over the last few years, offering a variety of methodologies. The attention to the various emerging microflow techniques represented the starting point for the development of the present work. The study presented in this thesis focuses on the application of microflow systems using segmented flow technique to various organic transformations by development of a practical and economical system setup in order to provide a basic methodology for synthetic chemists. First, we carried a comparison study between microflow and flask reaction using a simple biphasic hydrolysis under segmented flow. The study was then extended to investigate the effect of parallel vs. segmented flow, in addition to the variation of reaction parameters in the microflow system, such as heating, sonication, and microchannel size. We selected for our study two classes of catalytic organic reactions of particular synthetic relevance, namely palladium-catalysed Heck coupling and ruthenium-catalysed ring-closing metathesis. We carried out biphasic Heck catalysis then moved onto the study of segmented flow application to monophasic reactions both in single step and multistep syntheses. Overall the use of microflow technique, applied to a number of reactions of various types and carried out with many chemical and engineering variables, allowed us to observe overall reaction performances enhancement compared to conventional flask chemistry, on the whole rather agreeably, reproducibly, and displaying very regular trends.