A feature article describing the fundamental characteristics and emerging applications of micro technology in the field of synthetic chemistry.

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The synthesis of stilbene esters using Wittig chemistry has been used to illustrate the generic diversity micro reactors offer in terms of chemical control and rapid method development. The micro reactor consisted of a 'T' design based on channel geometries 200 microns wide and 100 microns deep, etched into borosilicate glass and sealed with a borosilicate top plate using a thermal bonding technique. The movement of the reagent and products was achieved using electroosmotic flow (EOF), assisted by the incorporation of micro porous silica frits within the micro-channels to allow accurate solution control. To optimise the operating conditions methyl 4-formylbenzoate, premixed with sodium methoxide, was reacted with 2-nitrobenzyl-triphenylphosphonium bromide in dry degassed MeOH using flow conditions for both reagents of 0.40 microL min-1 for 20 min. A product yield of 70% (2:1 reaction stoichiometry with the aldehyde in excess) was obtained representing a 10% increase compared with the traditional batch synthesis. To demonstrate the capability of micro reactors to perform atom efficient synthesis a series of experiments based on an injection methodology (optimised to 30 s) were performed in the micro reactor at 1:1 stoichiometry resulting in a yield of 59%. Finally, the capability of micro reactors to perform a series of analogue reactions was investigated. The yields for a further three aldehydes indicated that the technology will be suitable for the development of automated device to support the generation of combinatorial libraries and rapid high throughput synthetic methods.

The formation of porous silica microstructures (frits) in capillaries with an internal diameter of 500 mm has been examined for inducing electroosmotic flow (EOF). Capillaries with this internal diameter are normally considered too large to support efficient EOF, but the discrete pumping devices reported here are able to overcome this limitation. The formation of these structures in the capillaries has been examined, with particular emphasis on identifying parameters within the preparation stage that might give rise to variation in the porosity of the frit. The initial results showed that the induced electroosmotic flow rate increased with frit length (to an optimum of 50 mm) with an applied potential of 700 V. The work offers an opportunity to extend electroosmotic pumping to capillaries of larger internal diameter than was previously thought ideal. It offers a number of potential advantages in the area of fluid propulsion, including the electric control of flow rates, the plug like nature of the flow, and the absence of moving parts. When this technology is applied to micro-reactors, the silica structures offer the dual advantages of providing a pumping mechanism while also retaining the catalyst in the micro-reactor.