(Photo)Chemical Conversion of Diazonium Salts in Flow Including Online NMR Analysis
Thomas Rehm, Senior Scientist, Fraunhofer IMM
The use of microstructured reactors has become a key technology for
(photo)chemical synthesis. As first example for flow photochemistry we
have applied our falling film microreactor (FFMR) technology for the
blue light mediated C-H arylation of heteroarenes with diazonium salts
using TiO2 as immobilized photocatalyst in the microchannels of the
FFMR. Beside catalyst analysis a broad scope of aryldiazonium salts were
investigated with furan, thiophene and pyridine as heteroarenes
including a long-term run. As second example we used a capillary
photoreactor for the dye-sensitized C-H arylation of furan with a
trifluoromethylated diazonium salt. In this case we adopted a benchtop
NMR spectrometer for the online 19F NMR analysis of the reaction
progress. On-going research now focuses on the non-catalysed C-C
coupling of diazonium salts with arene derivatives in flow reactors
connected to our online NMR analytics. All three processes benefit from
the mild (photo)chemical reaction conditions and the flow capabilities
of microreactors. Additionally, integrated online NMR technology has
proved its efficiency as contact-free analytical method for syntheses in
flow mode.
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