CHEMILUMINESCENT REACTIONS OF LUCIGENIN .1. REACTIONS OF LUCIGENIN WITH HYDROGEN-PEROXIDE

The chemiluminescent reaction of lucigenin (N, Nʹ-dimethyl-9, 9ʹ-biacridine, 1) at various pH values (solvent H2O, 30 °C, µ= 1.0) with hydrogen peroxide in excess is first order to 6 half-lives. At constant pH the reaction rate was determined to be dependent upon the first power of the concentration of hydrogen peroxide and to be independent of concentrations of 1 and buffers. From the pH dependence of the pseudo-first-order rate constant (kobsd, [H2O2]T » [1]) the rate of disappearance of 1 follows the general expression d[1]/dt = [[HO2 -] + 62[HO2 -][HO-]]. Diminution in light emission with time was shown to follow the same rate law and the quantum yield was established to be independent of [1], total hydrogen peroxide concentration ([H2O2]T), and pH. These results establish that the chemiluminescent reaction of 1 with hydrogen peroxide follows the same rate law as does the overall disappearance of 1 from solution in the presence of varying concentrations of H2O2 and at all pH values. Replacement of H2O with t-BuO2H provides less light than obtained in the absence of any peroxide agent. Lucigenin reacts with H2O2 and t-BuO2H at various pH values to produce N-methylacridone (2) as the major fluorescent product. The chemiluminescent spectrum at any time could be shown to result from emission by excited 2 and subsequent absorption by 1. Competing dioxetane and linear peroxide mechanisms (with H2O2 and t-BuO2H) are proposed and discussed. Evidence is presented which suggests that the 9, 9ʹ-dioxetane of 1 provides 2 + 2* by the two competing pathways of spontaneous fragmentation and le- transfer. © 1979, American Chemical Society. All rights reserved.