Chromium(V) coordination chemistry

Isotopic 13C NMR spectrometry to assess counterfeiting of active pharmaceutical ingredients: Site-specific 13C content of aspirin and paracetamol

Oxochromium(VI) reagents are some of the most extensively used oxidants for introducing oxygen into organic molecules.1–16 These versatile, sometimes selective, and synthetically useful oxidants react with almost all types of oxidizable groups. This chapter will discuss mechanisms, scope and limitations, and experimental procedures for chromic acid (1), chromyl acetate (2), 17–19 chromyl chloride (3), 13, 15, 20–22 tert-butyl chromate (4), 23, 24 chromium trioxide-pyridine complex (Sarett reagent, 5), 23, 25–28 dipyridine chromium(VI) oxide (Collins reagent, 6), 29–31 pyridinium chlorochromate (PCC, 7), 32 pyridinium dichromate (PDC, 8), 33–35 2, 2′-bipyridinium chlorochromate (BiPy · HCrO3Cl, 9), 36, 37 tetraalkylammonium chromates, 38 supported chromium(VI) oxidants, 39–41 and other chromium(VI) oxidants. A short background review, which describes in general terms the characteristics of some of the more commenly used oxochromium(VI) oxidants, is given below.

Oxidation by Oxochromium(VI) Compounds

Two mechanisms are proposed for the cooxidation of oxalic acid and isopropyl alcohol by chromium(VI). The results of the /sup 13/C-isotope effect studies on the mechanism demonstrate the presence of a significant carbon isotope effect. This /sup 13/C-isotope effect together with a previously established deuterium isotope effect is taken as providing compelling evidence for the synchronous C--H and C--C bond breaking and thus for a three electron mechanism in the cooxidation reaction. (BLM)

Swaminathan Ramesh

Papers

Three-electron oxidation. 14. Carbon-13 isotope effect in the three-electron cooxidation of isopropyl alcohol and oxalic acid