A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

Abstract

When conducting a photooxidation reaction, the key question is what is the best amount of photocatalyst to be used in the reaction? This work demonstrates a fast and simple method to calculate a reliable concentration of the photocatalyst that will ensure an efficient reaction. The determination is based on shifting the calculation away from the concentration of the compound to be oxidized to utilizing the limitations on the total light dose that can be delivered to the catalyst. These limitations are defined by the photoflow setup, specifically the channel height and the emission peak of the light source. This method was tested and shown to work well for three catalysts with different absorption properties through using LEDs with emission maxima close to the absorption maximum of each catalyst.

Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry

“…These specific issues can be overcome by using flow technology. − Considering the technological challenges associated with the safe handling of gaseous oxygen, many studies have been reported on the development of efficient biphasic or even triphasic flow regimes. − The photocatalyst concentration is an important variable to be considered as well, not only because it has relevant consequences in an industrial flow setup, not only for economic reasons but also because it could affect downstream purification processes. On this regard, researchers at Corning highlighted the importance of the physical characteristics of the photoreactor and the nature of the light source …”

“…On this regard, researchers at Corning highlighted the importance of the physical characteristics of the photoreactor and the nature of the light source. 465 Up to 2016, several reports about singlet oxygen oxidations in continuous flow were described. 466−469 In particular, various studies reported on the oxidation of sulfides in batch 470 and in flow, 471 reflecting the importance of sulfoxides especially in medicinal chemistry.…”

Performances of Homogeneous and Heterogenized Methylene Blue on Silica Under Red Light in Batch and Continuous Flow Photochemical Reactors

“…We next investigated the performances of the homogeneous and heterogeneous systems, using the same model reaction, in a continuous flow photoreactor consisting of a 2.7 ml transparent plate with narrow channels and a heart-shaped static mixer with optimized mass transfer properties. (Horn and Gremetz, 2020). The plate is irradiated with interchangeable tunable LEDs and connected upstream to an HPLC pump, a mass flow controller (MFC), which is itself connected to an O 2 cylinder, and downstream to a back pressure regulator (Figure 3).…”

Efficient Photooxygenation Process of Biosourced α-Terpinene by Combining Controlled LED-Driven Flow Photochemistry and Rose Bengal-Anchored Polymer Colloids

“…29,30 Most of the literature related to LED-driven flow photochemistry considers a sensitizer solubilized in the reaction medium. [31][32][33][34][35][36] In parallel, the concept of solid-supported sensitizers offers many advantages as it makes it easier to separate the organic sensitizer from the other reactants and products, avoiding expensive downstream separation. [37][38][39][40][41][42][43][44][45][46] It is also a strategy for transposing poorly soluble photosensitizers into green solvents, while simultaneously enhancing their photostability and reusability.…”

“…Most of the literature related to LED-driven flow photochemistry considers a sensitizer solubilized in the reaction medium. − In parallel, the concept of solid-supported sensitizers offers many advantages as it makes it easier to separate the organic sensitizer from the other reactants and products, avoiding expensive downstream separation. − It is also a strategy for transposing poorly soluble photosensitizers into green solvents, while simultaneously enhancing their photostability and reusability. Solid-supported sensitizers in continuous-flow microstructured reactors were first implemented in the form of polymer/silica films cast onto the walls of the reactor. − However, the light that can be delivered per specific surface area of the reactor is significantly reduced in this configuration and the replacement of the substrate film is complex.…”