Stopped-Flow Kinetic Investigation of Manganese-based Chemiluminescence Oxidation Reactions

In order to better understand the mechanism of solution manganese-based chemilumines-cence, the kinetics of a number of chemiluminescent oxidations by manganese species were studied using stopped-flow spectrophotometry. Both the kinetics of the decay of the oxi-dant and the chemiluminescence emission were followed for oxidations by permanganate, manganese dioxide sol and Mn3+(aq) of a range of organic compounds.

The most detailed studies were carried out on the oxidation of the relatively simple compounds including glyoxylic acid and glyoxal under pseudo first order conditions and an acidic medium at 25oC. For permanganate under these conditions, the decay is sigmoidal consistent with autocatalysis and for managanese dioxide sol and Mn3+ pseudo first order. Simple mechanisms are suggested and compared with the experimental kinetic data. For per-manganate CL system, the following chemical kinetic model was considered:

MnO4- + xsR  MnO2 (k1)
MnO2 + xsR  Mn3+ (k2)
MnO4- + 3Mn3+  4MnO2 (k3)
Mn3+ + xsR  (Mn2+)*