Nanostructured Carbon Nitride for Continuous-Flow Trifluoromethylation of (Hetero)arenes

Abstract

Efficient catalytic methods for the trifluoromethylation of (hetero)arenes are of particular importance in organic and pharmaceutical manufacturing. However, many existing protocols rely on toxic reagents and expensive or sterically hindered homogeneous catalysts. One promising alternative to conduct this transformation involves the use of carbon nitride, a non-toxic photocatalyst prepared from inexpensive precursors. Nonetheless, there is still little understanding regarding the interplay between physicochemical features of this photocatalyst and the corresponding effects on the reaction rate. In this work, we elucidate the role of carbon nitride nanostructuring on the catalytic performance, understanding the effect of surface area and band gap tuning via metal insertion. Our findings provide new insights into the structure–function relationships of the catalyst, which we exploit to design a continuous-flow process that maximizes catalyst–light interaction, facilitates catalyst reusability, and enables intensified reaction scale-up. This is particularly significant given that photocatalyzed batch protocols often face challenges during industrial exploitation. Finally, we extrapolate the rapid and simplified continuous-flow method to the synthesis of a variety of functionalized heteroaromatics, which have numerous applications in the pharmaceutical and fine chemical industries.

Multifunctional carbon nitride nanoarchitectures for catalysis

“…245 The abundance of nitrogen in g-CN can offer lone pairs of electrons to form a strong bond with the empty or partially empty orbitals of metal atoms, which significantly stabilises the formed SACs. 231,246–254 Furthermore, their thermal/chemical stability, moderate band gap, extended π conjugation to stabilize the metal centre via charge transfer, and periodicity of active sites make them ideal materials to fabricate SACs. 255–257 These SACs can be loaded at the defect sites on g-CN to obtain single-atom loaded g-CN through a low-cost, facile and eco-friendly top-down mechanochemical abrasion and solvent-free approach, coupled with mild thermal treatment.…”

High-Speed Circulation Flow Platform Facilitating Practical Large-Scale Heterogeneous Photocatalysis

“… Although packed-bed reactors are commonly utilized for heterogeneous catalysis, the opacity of solid photocatalysts restricts their usage to capillary reactors or premodified glass-bead-supported photocatalysts or photocatalysts mechanically mixed with glass beads (Figure S7a). − Other types of flow reactors, including continuous stirred tank reactors (CSTRs), oscillatory flow reactors, , serial microbatch reactors, and rotor–stator spinning disk reactors, may suffer from low production rates with short residence times due to limited reactor volumes or the requirement of specialized equipment investments which are difficult to customize on demand. Therefore, a general, simple, customizable, and easily scalable system that is effective for heterogeneous photocatalysis remains an unmet but highly desirable need.…”

A Guide to Chemical Reactions Design in Carbon Nitride Photocatalysis

“…[109,60] Being an electron acceptor, elemental sulfur in net-oxidative reactions is converted into H 2 S. [110,111] Reduction of perfluoroalkylsulfonyl chlorides by the photogenerated electron yields perfluoroalkyl radical, SO 2 and Cl À . [112,113] On the other hand, oxidation of sodium trifluoromethylsulfinate by the photogenerated hole, gives CF 3 * , and presumably SO 2 . [14] Proton may also be considered as a sacrificial electron acceptor -it is reduced to H 2 , when the photocatalytic reaction, such as dehydrogenation of alcohols or benzylic amines, is performed in the presence of a H 2 -evolution co-catalyst, such as Pt nanoparticles.…”