Study of the characteristics of three high-energy intermediates generated in peroxyoxalate chemiluminescence (PO-CL) reactions

Abstract

Perylene emission intensity generated from peroxyoxalate chemiluminescence (PO-CL) reactions was studied as a function of time and order of reagent addition. Based on ¹H-NMR analyses, kinetics of UV absorbance and emission intensity vs. time profiles, we conclude that PO-CL reactions in the presence of imidazole (ImH) can proceed by three distinct reaction pathways depending on how the reagents are mixed together. When bis(2,4,6-trichlorophenyl) oxalate (TCPO) is mixed simultaneously with H₂O₂, ImH and perylene, a slowly decaying emission curve is generated from the interaction between perylene and a high-energy intermediate (i.e., six- or eight-membered cyclic compound) formed by the ImH-catalyzed nucleophilic reaction (TCPO-CL reaction). Upon mixing TCPO simultaneously with ImH and perylene in the absence of H₂O₂, however, distinctly different CL curves of lower intensity are generated from the interaction between perylene and a new, unknown high-energy intermediate formed from the reaction between the aryl oxalate and ImH. Finally, using ¹H-NMR, we observed that 1,1′-oxalyldiimidazole (ODI) is also formed from the reaction between TCPO and ImH. When ODI reacts with excess H₂O₂ in the presence of perylene, a higher intensity and relatively fast decaying emission curve is generated (ODI-CL reaction) from the interaction between perylene and the high-energy intermediate produced, which we propose is imidazolylhydroxydioxetanone or 1,2-dioxetanedione.