The economic synthesis of pyridinium fluorochromate(VI), C₅H₅NH[CrO₃F] (PFC), and solvent-free oxidation of organic substrates with PFC

Abstract

A 1:1:1 stoichiometric reaction among CrO₃, aqueous HF and pyridine affords orange crystalline pyridinium fluorochromate(VI), C₅H₅NH[CrO₃F] (PFC), in 99.2% isolated yield. The reagent under solvent-free conditions readily converts benzylic, secondary, and allylic alcohols to the corresponding carbonyls and selectively oxidizes secondary alcohols in the presence of primary alcohols, polycyclic hydrocarbons to cyclic ketones, benzoin to benzil, PPh₃ to O=PPh₃, methylphenyl sulfide to sulfoxide, cyclohexanone oxime to cyclohexanone, an allylic Δ⁵-steroid to the corresponding α,β-unsaturated ketone and deprotects dioxolanes and dithiolanes to aldehydes; the economic synthesis of PFC, its ease of reaction without solvent, versatility, and high isolated yields of the products are the significant features of the protocol.