Quinolinium Fluorochromate (QFC), C₉H₇NH[CrO₃F]: an improved Cr(VI)-oxidant for organic substrates

Abstract

Yellow-orange crystalline quinolinium fluorochromate (QFC) is easily prepared in a nearly quantitative yield by the interaction of quinoline with CrO₃ and hydrofluoric acid in 1 : 1.5 : 1 molar ratio. The reagent is stable. Compared with pyridinium fluorochromate (PFC), the new reagent is more soluble in organic solvents and less acidic. QFC in CH₂Cl₂ readily oxidizes primary, secondary, and allylic alcohols to the corresponding carbonyls, benzoin to benzil, and anthracene and phenanthrene to anthraquinone and 9,10-phenanthrenequinone, respectively. Oxidations work well also in a variety of sensitive environments, e.g. isopropylidene functionality and trimethylsilyl ethers. Organic sulfides are transformed to sulfoxides at room temperature. The facile oxidation of triphenylphosphine to triphenylphosphine oxide by QFC in CH₂Cl₂ or CH₃CN provides a clear evidence for an oxygen-transfer reaction. The reduced product of QFC, isolated after such reactions, has been ascertained to be C₉H₇NH[CrO₂F], a chromium(IV) species. The advantages of QFC have been highlighted.