Oxidative Cleavage of S–S Bond During the Reduction of Tris(pyridine‐2‐carboxylato)manganese(III) by Dithionite in Sodium Picolinate–Picolinic Acid Buffer Medium

The reduction of tris(pyridine‐2‐carboxylato)manganese(III) by dithionite has been investigated within the temperature window 288–303 K and at pH range 5.22–6.10 in sodium picolinate–picolinic acid buffer medium. The reaction obeys the following stoichiometry: The reaction is described in terms of a mechanism that involves an initial complex formation between S₂O₄^2? and [Mn^III(C₅H₄NCO₂)₃] followed by S–S bond cleavage to give 2HSO₃^? and [Mn^II(C₅H₄NCO₂)₂(H₂O)₂] as the products via the formation of SO₂^●? radical anion. Kinetics and spectrophotometric evidences are cited in favor of the suggested mechanism. Thermodynamic parameters associated with the equilibrium step and the activation parameters with the rate‐determining step have been computed.