Dissolution of elemental gold in organic solutions is ac ontemporary approach to lower the environmental burden associated with gold recycling.Herein, we describe fundamental studies on ah ighly efficient method for the dissolution of elemental Au that is based on DMF solutions containing pyridine-4-thiol (4-PSH) as ar eactive ligand and hydrogen peroxidea sa no xidant. Dissolution of Au proceeds through several elementary steps:i somerization of 4-PSH to pyridine-4-thione (4-PS), coordination with Au 0 ,and then oxidation of the Au 0 thione species to Au I simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is aA u I complex bearing two 4-PS ligands and SO 4 2À as ac ounterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations.
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 by 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, whereas the role of inexpensive 2‐mercaptobenzimidazole is to stabilize the formed AuI species through a ligand exchange process. Under optimized conditions, the reaction proceeds vigorously and gold dissolves quantitatively in two hours. The demonstrated ligand‐exchange mechanism with two thiols allows to drastically reduce the thiol consumption and may lead to even more effective gold dissolution methods in the future.
Invited for the cover of this issue is the group of Timo Repo at the University of Helsinki. The image depicts a ligand‐exchange reaction as a battle between hummingbirds and golden birds, which represent two different thiol ligands. Read the full text of the article at 10.1002/chem.202101028
Dissolution of elemental gold in organic solutions is ac ontemporary approach to lower the environmental burden associated with gold recycling.Herein, we describe fundamental studies on ah ighly efficient method for the dissolution of elemental Au that is based on DMF solutions containing pyridine-4-thiol (4-PSH) as ar eactive ligand and hydrogen peroxidea sa no xidant. Dissolution of Au proceeds through several elementary steps:i somerization of 4-PSH to pyridine-4-thione (4-PS), coordination with Au 0 ,and then oxidation of the Au 0 thione species to Au I simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is aA u I complex bearing two 4-PS ligands and SO 4 2À as ac ounterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations.
Dissolution of elemental gold occurs promptly with two different thiol ligands that act in a cooperative manner. The reaction benefits from the dynamic coordination sphere of AuI species that enables the dissolution to proceed via ligand‐exchange reactions. The dissolution proceeds from left to right and the birds represent the different Au species that form during the dissolution. Pyridine‐4‐thiol serves as the initiating ligand and 2‐mercaptobenzimidazole ligands stabilize the formed AuI cations in the dissolution. More information can be found in the Communication by T. Repo et al. (DOI: 10.1002/chem.202101028).
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