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.

Coupling photocatalytic overall water splitting with hydrogenation of organic molecules: a strategy for using water as a hydrogen source and an electron donor to enable hydrogenation

“…As shown in Scheme 2, the present method allowed various aryl bromides to be smoothly converted to the hydrogenation product in moderate to high yields. Major byproducts were from aryl-aryl couplings of aryl bromides, 58,59 and small amounts of Br/Cl exchange byproducts were sometimes observed. 58,59 Owing to the mild reaction conditions, the present reactions were compatible with various groups such as alkoxy, alkylthiol, cyano, phenolic hydroxyl, ketone carbonyl and ester carboxyl groups (1a-p), even the highly reactive formyl group was also tolerated (1i).…”

“…Major byproducts were from aryl-aryl couplings of aryl bromides, 58,59 and small amounts of Br/Cl exchange byproducts were sometimes observed. 58,59 Owing to the mild reaction conditions, the present reactions were compatible with various groups such as alkoxy, alkylthiol, cyano, phenolic hydroxyl, ketone carbonyl and ester carboxyl groups (1a-p), even the highly reactive formyl group was also tolerated (1i). Larger steric hindrance could decrease the reactivity of the substrates.…”

Rapid Dissolution of Noble Metals in Organic Solvents

“…[19] Recently, this same group achieved the dissolution of gold in ethanol using 2-mercaptobenzimidazole as a ligand in the presence of catalytic quantities of iodine, taking around 13 h to dissolve gold quantitatively. [20] Yang and co-workers exploited N-bromosuccinimide as an oxidant in pyridine to dissolve gold in water at pH 8. [2] Recently, Chen et al described the dissolution of NMs under photocatalytic conditions using TiO 2 and ZnO photocatalysts.…”

“…Repo and co‐workers developed the use of pyridine thiols and H 2 O 2 in ethanol solutions to dissolve gold [19] . Recently, this same group achieved the dissolution of gold in ethanol using 2‐mercaptobenzimidazole as a ligand in the presence of catalytic quantities of iodine, taking around 13 h to dissolve gold quantitatively [20] . Yang and co‐workers exploited N ‐bromosuccinimide as an oxidant in pyridine to dissolve gold in water at pH 8 [2] .…”

Bidentate Ru(II)-NC Complex as a Catalyst for Semihydrogenation of Azoarenes to Hydrazoarenes with Ethanol

“…Among several transfer hydrogen sources, alcohols have been regarded as the best ideal hydrogen source because of their low price and toxicity. Moreover, alcohols are regarded as the best green solvents in organic synthesis, although some visible-light photocatalytic transfer hydrogenations of azoarenes to hydrazoarenes have been established . However, transition metal-based catalysts for the semihydrogenation of azoarenes to hydrazoarenes with alcohols are still challenging.…”