Superoxometal-catalyzed co-oxidation of alcohols and nitrous acid with molecular oxygen

A superoxochromium(III) ion, CraqOO2+, acts as a catalyst for the co-oxidation of alcohols and nitrous acid with molecular oxygen according to the stoichiometry: CH3OH + HNO2 + O-2 --> CH2O + NO3- + H2O + H+. The kinetics are second order in [HNO2] and independent of the concentrations of the superoxochromium catalyst, substrate, and O-2. The proposed mechanism features the disproportionation of HNO2 to NO and NO2, both of which react rapidly with CraqOO2+. The CraqOO2+/NO reaction generates another equivalent of NO2 and a mole of CraqO2+, the active oxidant. The two-electron oxidation of the alcohol by CraqO2+ produces Cr-aq(2+), which reacts rapidly with O-2 to regenerate the catalyst, CraqOO2+. The NO2/CraqOO2+ reaction yields the peroxynitrato complex, CraqOONO22+' in a dead-end equilibrium process that has no effect on the catalytic reaction. The disproportionation of NO2 yields the final nitrogen-containing product, NO3-, and regenerates an equivalent of HNO2. Under a fixed set of conditions, the relative catalytic efficiency (CE) of CraqOO2+ decreases as its concentration increases owing to the competition between O-2 and CraqOO2+ for the intermediate Craq (C) 2003 Elsevier Science B.V. All rights reserved.