Chemical and electrochemical oxidation and reduction of dithizone

A non-aqueous electrochemical study of dithizone, H₂Dz, 1, is compared with the chemical oxidation and reduction profile of this versatile ligand. Chemical oxidation of 1 by I₂ initially leads to an isolatable disulfide-bridged species, (HDz)₂, 2₂, but ultimately monomeric dehydrodithizone, Dz, 3, is formed. Electrochemically, in CH₂Cl₂/0.1 mol dm⁻³ N(ⁿBu)₄]B(C₆F₅)₄], two oxidation processes are observed for 1. Evidence of the electrochemical formation of the dimer 2₂ was found, but on a CV timescale the fully oxidized species, 2_2oxidized, did not convert to the chemically stable species 3. Regeneration of 1 during an irreversible electrochemical reduction of the electrochemically generated fully oxidized species, 2_2oxidized, was detected. Two further one-electron electrochemical irreversible reduction steps were also identified to ultimately generate H₃Dz⁻, 8, one of the synthetic precursors to 1. In contrast, resolution and identification of the electron transfer steps of 1 in both dimethylsulfoxide, DMSO, or in CH₂Cl₂/0.1 mol dm⁻³ N(ⁿBu)₄]PF₆] were hampered by solvation and ion paring of PF₆]⁻ especially with the oxidized species of 1. A metathesis of water-soluble potassium dithizonate, KHDz, 4b, led to lipophilic N(ⁿBu)₄]HDz], 4c.