Improved Reaction Control
The benefits of flow chemistry over traditional batch techniques are widely known and translate equally to flow photochemistry. Most of these benefits come from the precise control of reaction parameters that flow chemistry offers. By controlling factors such as temperature, mixing, stoichiometry, and reaction times, we can enhance the control of our chemical reactions. In a flow photochemistry reactor, we can increase this control further over traditional batch photochemical techniques.
Flow photochemistry reactors offer:
- Consistent light penetration: this homogeneity allows reproducible reactions
- Controlled reaction exposure times: reducing degradation of products and unwanted side reactions
- The ability to increase photon flux into the reactor: potentially increasing reaction rates
- A simpler route to scale-up: increasing reaction rates can help increase reaction throughput
If we consider the use of monochromatic LED light sources, we can add better reaction selectivity through the control of the wavelength used, enabling higher conversions and yields, and better heat exchange via isolation of the light source temperature and reactor.
Access to Multiphase Chemistry
The design of flow chemistry reactor systems allows chemists to perform reactions in numerous ways. The most common is homogeneous chemistry, where all the reactants and products are in solution. Reactions can also be performed in multiphase environments. We can carry out reactions with liquid-liquid partitions, where the two liquids are immiscible and also in liquid-gas partitions, where one of the components is a gas.
The size of flow reactors is typically small, which enables the ability to easily pressurize the reactor and flow system. This has a multitude of benefits:
- we can increase the temperature of a reaction above its reflux temperature
- we can avoid cavitation of low boiling point and low vapour pressure reactants
- we can introduce gases into the flow reaction
It is the final point that is the most relevant to photochemical applications. Gas insertion type reactions such as continuous oxidations, hydrogenation, halogenations and carbonylations are well documented.1
The use of oxygen in photochemistry for photooxygenation chemistries is an important application. This is highlighted by the synthesis of the anti-malaria drug Artemisinin demonstrated by the Seeberger group.3
Molecular oxygen is an attractive oxidant due to its atom efficiency, reduced cost, and sustainable nature. However, these reactions are prone to over oxidations, which leads to to unwanted by-products.
Flow photochemistry with its ability to control the reaction exposure time can offer an advantage over traditional batch photochemistry techniques.
In these applications, singlet oxygen (1O2) can be produced starting from triplet oxygen (3O2), by light irradiation in the presence of a suitable photosensitizer. Working with large amounts of oxygen gas in batch conditions is extremely hazardous due to its flammable nature. Flow photochemistry can provide easy access to 1O2 in a much safer process, compared with batch procedures. 1O2 exhibits higher electrophilicity compared with 3O2, which allows substrates to be oxidized that are otherwise unreactive to oxygen.3
For more information about flow photochemistry or how you can achieve better results using Syrris products, please contact us.
1. Cambié, D.; Bottecchia, C.; Straathof, N. J. W.; Hessel, V.; Noël, T. Applications of Continuous-Flow Photochemistry in Organic Synthesis, Material Science, and Water Treatment. Chem. Rev., 2016, 116 (17), 10276–10341. https://doi.org/10.1021/acs.chemrev.5b00707
3. Lévesque, F.; Seeberger, P. H. Continuous-Flow Synthesis of the Anti-Malaria Drug Artemisinin. Angew. Chemie Int. Ed., 2012, 51 (7), 1706–1709. https://doi.org/10.1002/anie.201107446.