Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates

Abstract

Styrene-based peroxotungstate-modified polymer immobilized ionic liquid phase catalysts [PO4{WO(O2)2}4]@ImPIILP (Im = imidazolium) are remarkably efficient systems for the selective oxidation of sulfides under mild conditions both in batch and as a segmented or continuous flow process using either ethanol or acetonitrile as solvent or mobile phase, respectively. The performance of these styrene-based systems has been compared against their Ring Opening Metathesis Polymerisation derived counterparts to assess their relative merits. A comparative survey revealed catalyst supported on N-benzyl imidazolium decorated polymer immobilised ionic liquid to be the most efficient and a cartridge packed with a mixture of [PO4{WO(O2)2}4]@ImPIILP and silica operated as a segmented or continuous flow system giving good conversions and high selectivity for sulfoxide. The immobilised catalyst remained highly active for the sulfoxidation of thioanisole in ethanol with a stable conversion-selectivity profile for up to 8 h under continuous flow operation; for comparison conversions with a mixture of [NBu4]3[PO4{WO(O2)2}4] and silica dropped dramatically after only 15 min as a result of rapid leaching while [PO4{WO(O2)2}4]@ImPIILP prepared from commercially available Merrifield resin also gave consistently lower conversions; these benchmark comparisons serve to underpin the potential benefits of preparing the polymer immobilized ionic liquid supports.

Poly(ionic liquid) composites

“…These comparisons underpin the potential benefits of preparing a PIL support for robust POM catalysts in reactions. 130 Wang and coworkers systematically investigated PIL-POM composites in heterogeneous catalysis. They developed hierarchically nanoporous PILs as supports for immobilizing POMs.…”

Polymeric ionic liquid material‐anchored Mn–porphyrin anion: Heterogeneous catalyst for aerobic oxidation of olefins

“…Besides, it seems that polar solvents have a significant effect on the activation of intermediate species in manganese–porphyrin compounds and increase their catalytic activity . In fact, organic polar solvents, such as CH 3 CN, could affect access of substrate to active sites by increasing the solubility and diffusion of reactants in ILs …”

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

“…In this area Doherty et al have published widely on the application of peroxotungstates being immobilised on ionic resins that allow for selective oxidisation along with a low catalyst leaching. The application in flow enabled a lower catalyst loading and reduced residence times (Scheme 94) [366,367]. Along with the sulfoxides, thiosulfinates have been synthesised in flow using a packed-bed reactor filled with oxone as described by Wirth et al (Scheme 95) [368].…”