Chemiluminescence of 5-aminophthalazine-1,4-dione in the presence of hydrogen peroxide

Abstract

In aqueous solutions containing luminol, H₂O₂ and ClO^–₂, chlorine dioxide (ClO^.₂) is generated by pulse radiolysis. ClO^.₂ oxidizes luminol to 5-aminophthalazine-1,4-dione (azaquinone). The latter reacts with HO^–₂ to yield an intense chemiluminescence. The results obtained from detailed kinetic study at various pH values and from product analysis are consistent with the following conclusions:

The azaquinone combines with HO^–₂ to form an open carbon-centred peroxide. The latter decomposes via a short-lived endoperoxide in two parallel reactions. The first of these yields oxygen and luminol while the second one generates nitrogen and ultimately excited 3-aminophthalate with an efficiency of 4%. The kinetics of the present system is compared with that of other similar systems reported. Based on observed differences, the presence of several peroxide intermediates is implied. In addition evidence is presented that 3-aminophthalate may not be the sole emitter in every chemiluminescent system based on luminol.