The ozonation of pyrene: Pathway and product identification

The pathway by which ozone reacts with pyrene, a polycyclic aromatic hydrocarbon (PAH), is proposed in this paper. Pyrene was dissolved in a 90% acetonitrile:water (v/v) mixture. At this ratio, sufficient water is present to participate in the ozonolysis reaction and thereby mimic what occurs in pure water. The initial pyrene concentration was 5 mM. The ozone dosages were varied to obtain different extents of reaction. A stoichiometric ratio of 1.68 mol ozone mol−1 pyrene was required to completely destroy pyrene. The ozonation products were tentatively identified by gas chromatography–mass spectrometry (GC–MS). Fourteen products including aldehyde and carboxylic acid substituted phenanthrene- and biphenyl-type oxidation products were identified. Several ring-cleavage reactions occurred sequentially: (i) ring cleavage of pyrene first occurred at the 4,5 position, with phenanthrene-type products predominating; and (ii) once secondary ring cleavage occurred, the concentration of pyrene and the phenanthrene-type products decreased dramatically, while the concentration of biphenyl-type products increased. The oxidation of pyrene by hydroxyl free radicals was found to be involved in the reaction, even at pH 3.7.