Cooperative Ligands in Dissolution of Gold.

Development of new, environmentally benign dissolution methods for metallic gold is driven by needs in the circular economy. Gold is widely used in consumer electronics, but sustainable and selective dissolution methods for Au are scarce. Herein we describe a quantitative dissolution of gold in organic solution under mild conditions using hydrogen peroxide as an oxidant. In the dissolution reaction, two thiol ligands, pyridine-4-thiol and 2-mercaptobenzimidazole, work in a cooperative manner. The mechanistic investigations suggest that two pyridine-4-thiol molecules form a complex with Au0 that can be oxidized, while the role of inexpensive 2-mercaptobenzimidazole is to stabilize the formed AuI species via a ligand exchange process. Under optimized conditions, the reaction proceeds vigorously and gold dissolves quantitatively in an hour. The demonstrated ligand exchange mechanism with two thiols allows us to drastically reduce the thiol consumption and may lead to even more effective gold dissolution methods in the future.