Synthetic toolbox: Flow chemistry


One of the major challenges to the efficiency and sustainability of fine chemical and pharmaceutical industrial scale production is that the final product usually involves a multiple step synthesis with numerous work-up and purification steps required at each stage, which impact negatively on the material efficiency of the industry. Thus, approaches that circumvent or simplify these steps can have an enormous environmental impact on multi-step chemical syntheses; even here continuous flow reactors offer a great advantage as they are well suited for telescoping reactions and many methods have been developed to enable this.[1][2] 

Reaction scale-up usually requires costly re-optimisation reactions due to the change in mixing and heating properties, thus reactions that may have worked well on bench-scale batch reactions may require increased times, super-cooling, or may be impossible to carry out on large scale. Good reactions should be easily scaled without requiring re-optimisation, since a green reaction should be scalable by default.  Again flow methods offer an advantage: the basic way to modify the total amount of product prepared in a continuous system is to change the length of time the reaction is run. Ergo, continuous flow processes allow facile alteration of the amount of product output without the need to modify the whole process or by running multiple batches, therefore meeting the green chemical engineering principle of running to meet needs.[1]

  1. S. G. Newman and K. F. Jensen, The role of flow in green chemistry and engineering, Green Chem., 2013, 15, 1456-1472.
  2. D. Webb and T. F. Jamison, Continuous flow multi-step organic synthesis, Chem. Sci., 2010, 1, 675-680.