The Reaction of Ozone with Bisulfide (HS−) in Aqueous Solution – Mechanistic Aspects

The ozone demand to oxidize HS−/H2S [pKa(H2S) = 6.9, k(HS− + O3) = 3 × 109 M−1 s−1, k(H2S + O3) = 3 × 104 M−1 s−1] to SO4 2− is only 2.4 mol ozone per mol SO4 2− formed, much lower than stoichiometric 4.0 mol/mol if a series of O-transfer reactions would occur. As primary step, the formation of an ozone adduct to HS−, HSOOO–, is suggested that decomposes into HSO– and singlet oxygen (16%) or rearranges into peroxysulfinate ion, HS(O)OO– (84%). Potential reactions of the above intermediates are discussed. Some of these can account for the low ozone demand.