Oxygen uptake after electron transfer from donors to the triplet state of nitronaphthalenes and dinitroaromatic compounds

The effects of oxygen in the photolysis of nitroaromatic compounds, such as 1-nitronaphthalene (1NN), 1,4-dinitronaphthalene, 4,4'-dinitrobiphenyl and mono- or di-nitrofluorenone, were studied in air-saturated aqueous acetonitrile solution in the presence of donors, such as aliphatic amines, e.g. triethylamine (TEA), aromatic amino acids or ascorbic acid. The overall reaction is conversion of oxygen via the HO2 center dot/O-2(center dot-) radical into hydrogen peroxide. The quantum yield of oxygen uptake (Phi(-O2)) increases with the donor concentration. The maximum values are Phi(-O2)= 0.3, e.g. for 1NN and 3-30 mM ascorbic acid or TEA. The photoinduced formation of H2O2 is initiated by triplet quenching and subsequent reaction of the donor and acceptor radicals with oxygen. The rate constant of scavenging of the nitroaromatic radical anion by oxygen is (0.6-1) x 10(7) M-1 s(-1). Some specific properties of oxygen and nitroarene compounds, including the radicals involved and the pH and donor concentration dependences, were discussed. (C) 2007 Elsevier B.V. All rights reserved.