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 O 3 to Ag(I) is suggested, whereby Ag(III) is formed [Ag + + O 3 + 2 H 2 O → 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) + CO 2 + • CH 3 ]. 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 CO 2 ]. This enhances ozone decay but prevents silver sol formation. Quantum chemical calculations have been carried out for substantiating mechanistic suggestions.