The Autoxidation of Triaryl Trithioarsenites, (ArS)3As: Evidence for Binding and Activation of Triplet Dioxygen by Arsenic(III)

Triaryl trithioarsenites, (ArS)₃As, are oxidized by air to As ₂ O ₃ and ArSSAr. In two cases the parent “thiol” (pyrid-2-thione and 1-hydroxypyrid-2-thione) is coproduced. The oxidation, in nonprotic solvents, is favored by electron-withdrawing groups at the para position of the phenyl group. The products obtained in nonprotic solvents were rationalized by assuming that the binding of the triplet dioxygen to arsenic(III) gives a triplet diradical, (ArS) ₃ A?─O─?, or an arsenadioxirane, (ArS) ₃ As(O ₂ ), intermediate, which decomposes after nucleophilic attack by another (ArS) ₃ As molecule. In protic solvents a zwitterion, (ArS) ₃ As⁺─O─O^?, and in the presence of moisture a hydroperoxy arsenic(V) compound, (ArS)₃As(OH)─O─OH, may be intermediates in the air oxidation of some aromatic trithioarsenites. These data tend to indicate that arsenic(III) bound to suitable groups can directly bind dioxygen, a property which may have implications in chemotherapy and carcinogenesis.