Iodine catalysis was developed for aliphatic fluorination through light‐promoted homolytic C−H bond cleavage. The intermediary formation of amidyl radicals enables selective C−H functionalization via carbon‐centered radicals. For the subsequent C−F bond formation, previous methods have typically been limited by a requirement for electrophilic fluorine reagents. We here demonstrate that the intermediary instalment of a carbon–iodine bond sets the stage for an umpolung, thereby establishing an unprecedented nucleophilic fluorination pathway.
Iodine catalysis was developed for aliphatic fluorination through light‐promoted homolytic C−H bond cleavage. The intermediary formation of amidyl radicals enables selective C−H functionalization via carbon‐centered radicals. For the subsequent C−F bond formation, previous methods have typically been limited by a requirement for electrophilic fluorine reagents. We here demonstrate that the intermediary instalment of a carbon–iodine bond sets the stage for an umpolung, thereby establishing an unprecedented nucleophilic fluorination pathway.
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ABSTRACT. Optimum conditions for flotation-spectrophotometric determination of iron with 4-(2-pyridylazo)resorcinol (PAR) based on a 1:2 Fe II -PAR complex were found to be as follows: flotation solvent (chloroform), shaking time (2 min), pH (4.50.5), concentration of PAR (2.0×10-4 mol L -1), reducing agent (hydroxylamine hydrochloride), solvent for the floated compound (dimethylsulphoxide, DMSO), wavelength for spectrophotometric measurements (718 nm), and volumes of the organic solvents (5 mL of chloroform and 3 mL of DMSO). Calibration graphs were compared for different volumes of the aqueous phase -10 mL and 40 mL; the corresponding linear ranges were 0.30-1.3 g mL -1 and 0.25-1.0 g mL -1. The iron content was successfully determined in soil samples, reference standard materials (PS-1, COOMET No. 0001-1999 BG, SОD No. 310а-98; PS-2, COOMET No. 0002-1999 BG, SOD No. 311а-98; and PS-3, COOMET No. 0003-1999 BG, SOD No. 312а-98) and zinc sulfide concentrates.
The complex formation and solvent extraction were studied in a system containing iron(II), 4nitrocatechol (4NC), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water, and chloroform. Under the optimum conditions, the extracted complex has a composition of 1 : 1 : 2 (Fe-4NC-TTC) and could be represented with the formula (TT + ) 2 [Fe II (4NC 2-)(OH) 2 ]. Theoretical calculations were performed at the HF/3-21G* level in order to elucidate the geometric structure of the complex and electron distribution according to the crystal field theory. The results showed that the most stable configuration is tetrahedral low-spin structure. Some equilibrium constants (association, distribution, and extraction) and characteristics (absorption maximum, molar absorption coefficient, recovery factor, Beer's law limits, etc.) concerning the application potential of the studied extraction-chromogenic system were determined.
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