Studies on singlet oxygen in aqueous solution. Part 1. Formation of singlet oxygen from hydrogen peroxide with two-electron oxidants

Kinetic parameters are reported for the trapping of singlet oxygen by anthracene-9,10-bis(ethanesulphonate)(aes) in water and deuterium oxide solutions. The kinetics of the reactions of N-chloro-succinimide, chloramine T (N-chlorotoluene-p-sulphonamide), N-chloromethanesulphonamide, and N,N-dichloromethanesulphonamide with hydrogen peroxide have been studied. For chloramine T and N-chloromethanesulphonamide the rate-determining step is formation of the corresponding dichloro-compounds, which are the reactive species. Using aes as a trap, it is shown that both chloramine T and N-chlorosuccinimide with H2O2 produce singlet oxygen in essentially quantitative yield. Iodylbenzene reacts with H2O2 to give, in the rate-determining step, iodosylbenzene and oxygen and then iodobenzene and oxygen; 47% of the oxygen produced is in the singlet state. For the corresponding reaction with 4-iodosylbenzene-1-sulphonic acid, the yield of singlet oxygen is 45%, i.e. indistinguishable within experimental error. Periodate and H2O2 give lower yields of singlet oxygen, and it is considered that two concomitant processes are involved. With hypobromite and H2O2 the yield of singlet oxygen is 76%. These variations in yield are briefly discussed.