Liquid Microsystems in Organic Synthesis

Exploitation of liquid-liquid microreactor in organic synthesis offers attractive advantages, including the reduction of diffusion path lengths to maximize the rate of mass transfer and reaction rates. Despite the advantages, interest in liquid-liquid micro reactors did not take off until recently, perhaps because of the complication of flow pattern manipulation combined with the limited numbers of liquid-liquid reactions. Initial interest focused on the control of parameters responsible for variation in flow patterns to engineer microemulsions or droplets. However, it was soon realized that liquid-liquid microdevices are more than just a tool for controlling flow patterns and further interest developed. 

Most examples describe catalyzed biphasic reactions taking the extra advantage of product isolation and catalyst recycling. De Bellefon et al. [211] published one of the first examples of biphasic reactions performed in a microreactor. The isomerization of allylic alcohols to carbonyl compounds was conducted in a liquid-liquid system using a micromixer combined with a microchannel tube. As there are limited examples of biphasic isomerization reactions, the authors were interested on 

Benzylations reaction using TBAB (tetrabutylammonium bromide) as a phase-transfer catalyst in glass microchannel reactors has been investigated as well [215], A dichloromethane/aqueous biphasic system was used in which both the substrate 

The industrially important nitration of aromatic compounds in a microreactor using two immiscible liquid phases was demonstrated in different studies using either parallel [220] or segmented flow [221]. In all studies, a PTFE capillary microchannel, connected to an inlet junction, was used in which either segmented or parallel flow can be created. The use of PTFE tubing is desirable as it is commercially available and no complicated microfabrication methods are involved. 

In the macroscale reaction, the formation of side products such as dinitrobenzene and picric acid is expected as a result of mass transfer limitations. Hence, by using microreactor system, the formation of the side product was reduced and the rate of reaction was increased. 

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