Date: 16 April 2024 | Category: News
Steve Ley and Marcus Baumann groups’ insightful review
If you haven’t already, we highly recommend that you read a recent publication by the Baumann and Ley groups, reviewing the role flow chemistry can have in new reaction discovery compared to batch chemistry [1]. This review focuses specifically on four types of chemical processes – photochemistry, electrochemistry, high temperature reactions, and reactive intermediate reactions (such as lithiations) – where continuous flow has led to the discovery of many new reactions and reactivity patterns.
For photochemistry, the advantages of continuous flow include uniform irradiation, increased photon transfer, and scalability.
In the case of electrochemistry, the advantages include a large ratio of electrode surface to reactor volume, efficient mass transfer, and scalability. The small distance between electrodes also allows the reduction (and sometimes elimination) in the use of electrolytes, which means improved sustainability and reduced material costs. Furthermore, by changing the electrode material and the applied potential, the selectivity of the reaction can easily be tuned.
Regarding high temperature reactions, the main advantage comes from improved heat transfer and miniaturisation, giving access to safer thermal reactions that might not be viable in batch. The ability to work above the boiling point of common solvents by using back pressure regulators also contributed to accessing new compounds.
When it comes to lithiation reactions, which are very versatile but can be challenging in batch due to the exothermicity and mixing time, flow chemistry has been opening new avenues. With improved heat and mass transfer, continuous flow setups can minimise side reactions which would otherwise require cryogenic conditions. A telescoped flow process with precise control of residence times also enables the trapping of highly reactive lithium species in seconds.
Many other advantages of flow chemistry were repeated throughout this review as they apply to a variety of reactions:
- Increased safety due to reactor miniaturisation
- Enhanced mass transfer
- Safe handling of toxic gases (e.g. carbon monoxide) at elevated pressures
- Improved gas-liquid mixing
- Controlled residence times for good chemoselectivity, minimising by-product formation
- Telescoped approach – unstable / highly reactive intermediates don’t need to be isolated
- Greener conditions
- Accelerated reaction screening
[1] Continuous Flow Synthesis Enabling Reaction Discovery (A. I. Alfano, J. García-Lacuna, O. M. Griffiths, S. V. Ley, M. Baumann, Chem. Sci., 2024, 15, 4618-4630.)
