Collins reagent is especially useful for oxidations of acid sensitive compounds. Primary and secondary alcohols are oxidized respectively to
aldehydes and
ketones in yields of 87-98%. Like other oxidations by Cr(VI), the stoichiometry of the oxidations is complex because the metal undergoes 3e reduction and the substrate is oxidized by 2 electrons: :3 RCH2OH + 2 CrO3(pyridine)2 → 3 RCHO + 3 H2O + Cr2O3 + 4 pyridine The reagent is typically used in a sixfold excess.
Methylene chloride is the typical solvent, with the solubility of 12.5 g/100 ml. The application of this reagent to oxidations was discovered by G. I. Poos, G. E. Arth, R. E. Beyler and L.H. Sarett in 1953. It was popularized by J. C. Collins several years later.
Other reagents •
Sarett oxidation •
Oxidation with chromium(VI)-amine complexes Collins reagent can be used as an alternative to the
Jones reagent and
pyridinium chlorochromate (PCC) when oxidizing secondary alcohols to
ketones. PCC and
pyridinium dichromate (PDC) oxidations have largely supplanted Collins oxidation. ==Safety and environmental aspects==