Reaction of Ozone with Ag(I)—Mechanistic Considerations

Abstract

Ozone reacts slowly with Ag+ (circumneutral pH, k = (11 ± 3) × 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 O3 to Ag(I) is suggested, whereby Ag(III) is formed [Ag+ + O3 + 2 H2O → Ag(OH)3 + O2 + 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)+ + O3 → Ag + 2 O2 + H+], where ozone acts as a reducing agent. Thereby, a single silver atom, Ag, is formed that can be oxidized by O2 and O3 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 + O3 → Ag(III)acetate → Ag(II) + CO2 + •CH3]. In the presence of oxalate, the formed complex reacts faster with ozone than Ag+, and Ag(III)oxalate decarboxylates rapidly [Ag(I)oxalate + O3 → 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.