Through-Wall Mass Transport as a Modality for Safe Generation of Singlet Oxygen in Continuous Flows

Abstract

Singlet oxygen, a reactive oxygen species, has been a basic synthetic tool in the laboratory for many years. It can be generated either through a chemical process or most commonly via a photochemical process mediated by a sensitizing dye. The relative paucity of singlet oxygen employment in fine chemical industrial settings can be attributed to many factors, not least the requirement for excessive quantities of oxygenated organic solvents and the dangers that these represent. Microcapillary films (MCFs) are comprised of multiple parallel channels embedded in a plastic film. In this study, MCFs are employed as flow reactor systems for the singlet oxygen mediated synthesis of ascaridole. No gaseous oxygen is supplied directly to the reaction, rather mass transport occurs exclusively through the reactor walls. The rate of production of ascaridole was found to be strongly dependent on the partial pressure of oxygen present within the reaction system. This methodology significantly simplifies reactor design, allows for increased safety of operation, and provides for space−time yields over 20 times larger than the corresponding bulk synthesis.

Photochemical Perfluoroalkylation with Pyridine N -Oxides: Mechanistic Insights and Performance on a Kilogram Scale

“…Currently available commercial flow systems are capable of providing this increased flux; however, limited reactor volumes limit productivity, and a prohibitive economic penalty is associated with scaling out. 88–90 The original design of a continuous flow reactor for UV photochemistry by Berry, Booker-Milburn, and coworkers. 91 has proven general for visible-light irradiation, and there have been several recent examples.…”

Liquid phase oxidation chemistry in continuous-flow microreactors

“…Small differences in pressure drop can lead to large variations and thus to a different performance in each reaction channel. Examples of this principle in oxidation chemistry have been developed, such as the multichannel microreactors, 336 the falling film microreactor, 337 and the multichannel microcapillary films 180 ( Figure 11, b, c, d). External numbering-up is achieved by placing different microreactors and their individual process control units in parallel.…”

Chemical reaction engineering, process design and scale-up issues at the frontier of synthesis: Flow chemistry

“…No mixing problems have been observed for a one-channel system, but oxygen distribution and mixing was not trivial in the case of multichannel reactors. Oxygen flow was regulated by applying increasing external pressure and it represented the kinetically limiting factor [87].…”