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 Au , and then oxidation of the Au thione species to Au simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is a Au complex bearing two 4-PS ligands and SO as a counterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations.