Peroxyoxalate High-Energy Intermediate is Efficiently Decomposed by the Catalyst Imidazole

Abstract

The peroxyoxalate reaction is a highly efficient chemiluminescence system, its chemiexcitation process involving the intermolecular interaction between an activator (ACT) and the high-energy intermediate (HEI) of the reaction. Typically, the HEI is generated through the reaction of an oxalate ester with H2 O2 , in the presence of a basic/nucleophilic catalyst, such as imidazole (IMI-H). IMI-H, besides catalyzing the formation of the HEI, is also known to decompose this peroxidic intermediate. Despite that, up to now, no rate constant value has been determined for such significant interaction. Through kinetic measurements, we have observed that IMI-H is roughly four times more efficient than 9,10-diphenylanthracene (DPA), a classic ACT, in catalyzing the decomposition of the HEI by a bimolecular electron transfer reaction through a Chemically Initiated Electron Exchange Luminescence-like process. For instance, when IMI-H and DPA are at the same concentration, 78% of the generated HEI is actually consumed by the nonemissive bimolecular interaction with IMI-H. We have obtained an average singlet excited state formation quantum yield, at infinite ACT concentration, of (5.5 ± 0.5) × 10(-2) E mol(-1) , determined at five different IMI-H concentrations. This ultimately suggests that the yield of formation of HEI actually does not depend on the IMI-H concentration.