Photochemical Oxidation of MnSO4 in Dimethyl Sulfoxide in the Presence of Water

Resumo

A solution of MnSO₄ in dimethyl sulfoxide is obtained at a water concentration of 0.2–0.6 M. Most of the water molecules in this solution belong to the hydration shell of [Mn(OH)(H₂O)₅]⁺ · \({\text{HSO}}_{4}^{ - }\)(H₂O)_x ion pairs. The photooxidation of manganese to Mn^III in the presence of an electron acceptor (oxygen or nitro blue tetrazolium) in the solution proceeds when the solution is irradiated with light at the wavelength corresponding to the absorption bands of Mn^II ions. The solution and its photochemical conversions are studied by means of spectroscopy, chemiluminescence, and conductometry. The photolysate is found to contain neither hydrogen peroxide nor free superoxide radical anions. The quantum yield for the photochemical generation of Mn^III is determined for the light absorbed by Mn^II at the ⁶A₁ → ⁴E, ⁴A₁ band: 0.01 ± 0.002 mol/Einstein.