Iodine‐Catalysed Dissolution of Elemental Gold in Ethanol

Abstract

Gold is a scarce element in the Earth's crust but indispensable in modern electronic devices. New, sustainable methods of gold recycling are essential to meet the growing eco-social demand of gold. Here, we describe a simple, inexpensive, and environmentally benign dissolution of gold under mild conditions. Gold dissolves quantitatively in ethanol using 2-mercaptobenzimidazole as a ligand in the presence of a catalytic amount of iodine. Mechanistically, the dissolution of gold begins when I 2 oxidizes Au 0 and forms a [Au I I 2 ] À species, which undergoes subsequent ligand-exchange reactions and forms a stable bis-ligand Au I complex. H 2 O 2 oxidizes free iodide and regenerated I 2 returns back to the catalytic cycle. Addition of a reductant to the reaction mixture precipitates gold quantitatively and partially regenerates the ligand. We anticipate our work will open a new pathway to more sustainable metal recycling with the utilization of just catalytic amounts of reagents and green solvents.

Quantitative, room‐temperature, solvent-free mechanochemical oxidation of elemental gold into organosoluble gold salts

“…There have been numerous recent attempts to address these problems, e.g., by selective precipitation, 9, 10 chelation of aurate species using macrocyclic hosts, [11][12][13] 3D-printed scavenger filters, 14 direct one-pot conversion of elemental gold to organo-soluble complexes. [15][16][17][18] We have previously shown that mechanochemistry, which encompasses the use of mechanical forces like grinding and shearing to initiate, sustain, and conduct chemical transformations, 19 is a simple, rapid, and environmentally-friendly method to convert noble metals such as Pd, Au, and Pt into water-soluble salts. 20 Specifically, ball milling of these raw precious metals, either alone or in a mixture, with mild oxidants such as potassium peroxymonosulfate (2KHSO5•KHSO4•K2SO4, Oxone ® ), potassium persulfate (K2S2O8), or calcium hypochlorite (Ca(ClO)2) in the presence of simple halide salts results in tetrahaloaurate(III) [AuX4]¯, tetrahalopalladate(II) [PdX4] 2 ¯ or hexahaloplatinate(IV) [PtX6] 4 ¯ derivatives (X = Cl, Br) with a preference for gold oxidization.…”