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David Bradley ISSUE #67
July-August 2007
Multichannel Microchemical Factory
Klavs Jensen

In the mid-nineties, microchemistry was set to revolutionize the chemical industry. Klavs Jensen of the Massachusetts Institute of Technology, Cambridge (USA), was one of the pioneers and featured in several articles of mine at the time. But, the chemical industry did not respond quickly to the potential and until recently there was very little movement in an area that should represent a sea change in the way chemicals are produced. The microchemical factory approach offers a safer and scaleable approach to producing materials from the very smallest quantities to the largest bulk. Now, Jensen's most recent work suggests that miniaturization is invading the world of chemical syntheses.

Most typical chemical reactions for making new compounds take place in several reaction steps with various separation or purification steps in between, which has always meant that the application of microchemistry was limited because it could only handle single-step reactions or sequences of reactions requiring no purification between steps.

Credit: Jensen Lab

Jensen and his team have now produced an integrated multiple-step microscale production line, which could change all that.

Their process includes three reaction steps and two separation processes (one gas?liquid and one liquid?liquid separation). Because it is arranged in a microscale reaction network, it is even possible to configure this process so that related compounds can be simultaneously produced in parallel.

To demonstrate their system, the researchers chose the synthesis of carbamates, compounds that are used as pesticides, among other things, and are important building blocks and reagents in the chemical syntheses of other compounds. The three-step synthesis used to make carbamates (the Curtius rearrangement) involves intermediate products (azides, isocyanates) that have the potential to be dangerous, since some of these types of compounds pose an explosive or health hazard. The advantage of the microscale reaction system is that these intermediates are formed in situ and are then immediately consumed, so they don't need to be isolated or stored. This significantly reduces any safety concerns that would arise in a conventional large-scale chemical reactor.

After the second separation step, the product stream is divided and fed into multiple microreactors, each with a different reagent; a series of different but related carbamates can be produced in parallel.

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Angew Chem Int Edn, 2007, 46, 5704-5708; http://dx.doi.org/10.1002/anie.200701434