STUDIES ON THE FORMATION OF H2O2 IN THE OZONOLYSIS OF ALKENES

The formation of H2O2 in the reactions of ozone with alkenes, isoprene and some terpenes has been studied with tunable diode laser absorption spectroscopy. The measured yields of H2O2 were found to be considerably enhanced in the presence of water vapour. H2O2 is thought to be formed in the ozonolysis of the alkene with O3 by direct reaction of an intermediate with water vapour. The yield of H2O2 relative to the reacted alkene in the ozonolysis of trans-2-butene in the presence of water vapour was also studied with long path FTIR spectroscopy. Irrespective of the analytical methods and reaction conditions applied, the H2O2 yields in the reaction of O3 with the different alkenes in the presence of water vapour were found to be in the range of a few per cent or less. Under the assumption that the reactive species forming H2O2 in the ozonolysis is the Criegee biradical, the overall rate constants for the reactions of some biradicals with water vapour were measured relative to the rate constant of the biradical with SO2. For the H2COO biradical a rate constant of (5.8 +/- 2.5) x 10(-17) cm3 s-1 was determined and for the (CH3)2COO biradical (2.9 +/- 1.5) x 10(-17) cm3 s-1; in the latter case with the assumption that (CH3)2COO reacts with SO2 as fast as CH2COO.