Reaction of Ozone with Ag(I)-Mechanistic Considerations

摘要

Ozone reacts slowly with Ag+ (circumneutral pH, k = (11 +/- 3) x 10(-2) M-1 s(-1)). After some time, ozone decay kinetics may suddenly become faster with the concomitant formation of silver sol. As primary process, an O-transfer from O-3 to Ag(I) is suggested, whereby Ag(III) is formed Ag+ + O-3 + 2 H2O Ag(OH)(3) + O-2 + H+. This conproportionates with Ag(I), which is in large excess, leading to Ag(II) Ag+ + Ag(OH)(3) ? 2 Ag(OH)(+) + HO-. Further, Ag(II) reacts with ozone in a high exergonic reaction Ag(OH)(+) + O-3 Ag + 2 O-2 + H+, where ozone acts as a reducing agent. Thereby, a single silver atom, Ag, is formed that can be oxidized by O-2 and O-3 or can aggregate to a silver sol. Aggregation slows down the rate of oxidation. When Ag+ is complexed by acetate ions, ozone decay and silver sol formation are speeded up by enhancing Ag(II) formation Ag(I)acetate + O-3 Ag(III)acetate Ag(II) + CO2 + center dot CH3. In the presence of oxalate, the formed complex reacts faster with ozone than Ag+, and Ag(III)oxalate decarboxylates rapidly Ag(I)oxalate + O-3 Ag(III)oxalate Ag+ + 2 CO2. This enhances ozone decay but prevents silver sol formation. Quantum chemical calculations have been carried out for substantiating mechanistic suggestions.