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Gold is designated as the noblest metal because of its chemical inertness. It is known to dissolve in cyanide solutions in the presence of air or H2O2 or in halogen-containing solutions, aqua regia being the most famous example. Herein, we report a unique thiol, especially 4-pyridinethiol (4-PS), assisted dissolution of Au in alcohol solutions. Although dissolution was found to be very selective for pyridinethiols, such a phenomenon is astonishing since thiols are commonly used as etch resists for Au and even 4-PS is extensively used as a surface modifier for Au. To gain further understanding of the dissolution process, the influence of the reaction conditions was extensively studied. On the basis of the obtained results, a mechanism for the dissolution reaction is proposed. Fascinatingly, by tuning of the reaction conditions, this phenomenon can be applied in selective preparation of self-supporting nanometer-thick Au foils.

Coinage metals Cu, Ag, and Au are essential for modern electronics and their recycling from waste materials is becoming increasingly important to guarantee the security of their supply. Designing new sustainable and selective procedures that would substitute currently used processes is crucial. Here, we describe an unprecedented approach for the sequential dissolution of single metals from Cu, Ag, and Au mixtures using biomass‐derived ionic solvents and green oxidants. First, Cu can be selectively dissolved in the presence of Ag and Au with a choline chloride/urea/H2O2 mixture, followed by the dissolution of Ag in lactic acid/H2O2. Finally, the metallic Au, which is not soluble in either solution above, is dissolved in choline chloride/urea/Oxone. Subsequently, the metals were simply and quantitatively recovered from dissolutions, and the solvents were recycled and reused. The applicability of the developed approach was demonstrated by recovering metals from electronic waste substrates such as printed circuit boards, gold fingers, and solar panels. The dissolution reactions and selectivity were explored with different analytical techniques and DFT calculations. We anticipate our approach will pave a new way for the contemporary and sustainable recycling of multi‐metal waste substrates. [ABSTRACT FROM AUTHOR]

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 I2 oxidizes Au0 and forms a [AuII2]− species, which undergoes subsequent ligand‐exchange reactions and forms a stable bis‐ligand AuI complex. H2O2 oxidizes free iodide and regenerated I2 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. [ABSTRACT FROM AUTHOR]

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 Au0, and then oxidation of the Au0 thione species to AuI simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is a AuI complex bearing two 4‐PS ligands and SO42− as a counterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations. Golden solution: The rapid dissolution of gold is facilitated by a reactive combination of pyridine‐4‐thiol and H2O2 in DMF solution. The ligand assists the dissolution as it stabilizes gold(I) centers and serves as the source of a sulfate counteranion. [ABSTRACT FROM AUTHOR]

The article shows that unsupported bulk gold (Au) itself can catalyze the liquid-phase oxidation of π-activated alcohols, such as benzyl alcohol (BA), cinnamyl alcohol (CA), into the corresponding aldehydes or ketones by oxygen (O2). BA, CA, 1-octanol, and 2-octanol were first selected to be oxidized over unsupported bulk Au foils. It was found that as the conversion increases, the selectivity to ester in BA oxidation in heptane increases.

Catalysis, Gold, Iodine, Recycling, Sustainable Chemistry Keywords: Catalysis; Gold; Iodine; Recycling; Sustainable Chemistry EN Catalysis Gold Iodine Recycling Sustainable Chemistry 1 1 1 03/23/22 20220328 NES 220328 B Gold b is a valuable metal that can be dissolved with common household chemicals as reported by Timo Repo et al. I i in their Research Article (e202117587). Inside Cover: Iodine-Catalysed Dissolution of Elemental Gold in Ethanol (Angew. [Extracted from the article]

Innentitelbild: Iodine-Catalysed Dissolution of Elemental Gold in Ethanol (Angew. Keywords: Catalysis; Gold; Iodine; Recycling; Sustainable Chemistry EN Catalysis Gold Iodine Recycling Sustainable Chemistry 1 1 1 03/23/22 20220328 NES 220328 B Gold b ist ein wertvolles Metall, das mit gewöhnlichen Haushaltschemikalien aufgelöst werden kann, wie Timo Repo et al. in ihrem Forschungsartikel (e202117587) berichten. Catalysis, Gold, Iodine, Recycling, Sustainable Chemistry. [Extracted from the article]

Base-free oxidation of glucose to gluconic acid with supported gold catalysts was studied using microwave heating. High conversion and selectivity were obtained in a remarkably shortened reaction time; in 10 min gluconic acid was obtained with up to 76% yields with 0.09 mol% Au/Al 2 O 3 and hydrogen peroxide as oxidant. Very high turn-over frequencies over 10,000 h − 1 were measured for the microwave assisted oxidation. Moreover, the catalyst activity remained constant in four consecutive runs, even though minor particle growth was observed. [ABSTRACT FROM AUTHOR]

Abstract: The ability of N,N′-ethylene-bis(4-dodecyloxysalicylideneiminato)Co(II) (4) and literature known N,N′-ethylene-bis(3,5-di-t-butylsalicylideneiminato)Co(II) (5) to coordinate molecular oxygen was studied using ultraviolet–visible spectroscopy. For a comparison, the study was complemented with the archetype Co(II) salen (salen= N,N′-ethylene-bis(salicylideneamine)) complex. Especially 4, bearing long alkoxy chain substituents, coordinates dioxygen efficiently and reversibly, and therefore is an attractive candidate for further development of functional surfaces e.g. towards molecular level dioxygen sensors. In this respect, complexes 4 and 5 were attached on two different 4-pyridinethiol pre-treated polycrystalline Au surfaces. The changes in surface morphology after pyridinethiol and the complex treatment were studied with atomic force microscopy (AFM) measurements. Accordingly, with this method fairly smooth surfaces bearing cobalt(II) salen complexes can be prepared. In addition, the AFM results were complemented by X-ray reflection, cyclic voltammetry and wettability studies. [Copyright &y& Elsevier]