Pyridinethiol‐Assisted Dissolution of Elemental Gold in Organic Solutions

Dissolution of elemental gold in organic solutions is a contemporary approach to lower the environmental burden associated with gold recycling. Herein, we describe fundamental studies on a highly efficient method for the dissolution of elemental Au that is based on DMF solutions containing pyridine‐4‐thiol (4‐PSH) as a reactive ligand and hydrogen peroxide as an oxidant. Dissolution of Au proceeds through several elementary steps: isomerization of 4‐PSH to pyridine‐4‐thione (4‐PS), coordination with Au0, and then oxidation of the Au0 thione species to AuI simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is a AuI complex bearing two 4‐PS ligands and SO42− as a counterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations.