The relative significance of multiple pathways in peroxyoxalate chemiluminescence reactions

Chemiluminescence (CL) from fluorophores generated by the reaction of bis(2,4-dinitrophenyl)oxalate (DNPO), H2O2, and several bases have been examined for the identification of multiple pathways. When the intensity of PO-CL (peroxyoxalate chemiluminescence) vs. time was measured under low base concentration in acetonitrile, two distinctive emission maxima, a fast decaying peak and a slowly decaying peak, were observed. The fast decaying first peak was predominant over the slowly varying peak at high concentration of DNPO and H2O2 and at low base concentration, and might be formed by the direct reaction of hydroperoxy oxalate ester (X) and fluorophore. When another set of the intensity vs. time was measured at high base concentration in ethylacetate containing 5% tert-butylalcohol, there also appeared two different peaks, a slowly decaying peak and a sharply decaying peak. The slowly decaying peaks in both sets of experiments were produced by base-catalyzed nucleophilic reaction of DNPO with X. The sharply decaying peak in the latter experiment could be dependent on the relative basicity of the donor, X, and acceptor, base. Based on the those observations a scheme is suggested that describes three reaction pathways.