Cyclic Peroxidic Carbon Dioxide Dimer Fuels Peroxyoxalate Chemiluminescence.

Peroxyoxalate chemiluminescence is used in self-contained light sources, such as glow sticks, where oxidation of aromatic oxalate esters produces a high-energy intermediate (HEI) that excites fluorescence dyes via electron transfer chemistry, mimicking bioluminescence for efficient chemical energy-to-light conversion. The identity of the HEI and reasons for the efficiency of the peroxyoxalate reaction remain elusive. We present here unequivocal proof that the HEI of the peroxyoxalate system is a cyclic peroxidic carbon dioxide dimer, namely, 1,2-dioxetanedione. Oxalic peracids bearing a substituted phenyl group were unable to directly excite fluorescent dyes; hence, they could be ruled out as the HEI. However, base-catalyzed cyclization of these species results in bright chemiluminescence, with decay rates and chemiexcitation quantum yields that are influenced by the electronic phenylic substituent properties. Hammett (ρ = +2.2 ± 0.1) and Brønsted (ß = -1.1 ± 0.1) constants for the cyclization step preceding chemiexcitation imply that the loss of the phenolate-leaving group and intramolecular nucleophilic attack of the percarboxylate anion occur in a concerted manner, generating 1,2-dioxetanedione as the unique outcome. The presence of better leaving groups influences the reaction mechanism, favoring the chemiluminescent reaction pathway over the nonemissive formation of aryl-1,2-dioxetanones.

Mechanistic Studies on the Peroxyoxalate Chemiluminescence Using Sodium Salicylate as Base Catalyst.

Mechanistic studies on the peroxyoxalate chemiluminescence are often conducted with imidazole as base and nucleophilic catalyst. However, it is also known that this compound, at high concentrations, leads to a drastic reduction in the chemiluminescence quantum yields, apparently due to the destruction of the high-energy intermediate. Consequently, the search for new catalysts for this transformation is of importance for mechanistic studies as well as analytical application. Therefore, we report here a study on the mechanism of the peroxyoxalate reaction with sodium salicylate as base catalyst, which has already been utilized in this reaction; however, no detailed mechanistic investigation is known. In this work, a kinetic study on the sodium salicylate-catalyzed reaction of bis(2,4,6-trichlorophenyl) oxalate with hydrogen peroxide using 9,10-diphenylanthracene as activator is reported, where observed rate constants, singlet quantum yields and activation parameters are determined in different reaction conditions, leading to the formulation of a general mechanistic reaction scheme.