Postulation of a phenoxyl radical intermediate as the species responsible for the background emission observed with certain peroxyoxalate chemiluminescence reagents

We demonstrate that the characteristic background emission spectra associated with certain substituted diaryl oxalates used for peroxyoxalate chemiluminescence reagents, namely bis(2,4,6-trichlorophenyl)oxalate, (TCPO, 1), bis(2,4-dichlorophenyl)oxalate, (2) and bis(2,6-dichlorophenyl)oxalate, (3), is not observed with either of the two substituted oxamides, 2,2′-oxalyl-bis[(trifIuoromethanesulfonyl)imino] ethylene-bis(N-methylpyridinium) trifluoromethanesulfonate (PETQ) (4), or (4,4′-oxalyl-bis[(trifluoromethylsulfonyl)-imino]ethylene-bis(1-methyl-1- benzylpiperidinium) trifluoromethanesulfonate, (BPTQ) (5) when utilised under identical chemical conditions. The background emission intensity from TCPO (1) can be significantly enhanced by the addition of 2,4,6-trichlorophenol (TCP). Spectrally identical chemiluminescence is generated upon the reaction of TCP with the two oxamides 4 and 5. Fluorescent spectra obtained from solutions of TCP and hydrogen peroxide confirmed the existence of a transient luminescent species. Consequently, a phenoxyl radical has been postulated as the species responsible for the background emission from TCPO.