Golden Selection

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Science  08 Oct 2010:
Vol. 330, Issue 6001, pp. 153
DOI: 10.1126/science.330.6001.153-a

Gold's widespread use in jewelry design and dentistry is due in large part to its remarkable resistance to chemical oxidation. There is in fact a fairly straightforward means of dissolving the metal—a concentrated combination of nitric and hydrochloric acids that's been in use for hundreds of years—but this solvent mixture is so generally corrosive that rings and fillings wouldn't be the primary worry if some happened to spill onto your fingers and teeth. Of more commercial concern is the acid mixture's failure to discriminate between gold and platinum, which hampers catalyst-recycling protocols. Lin et al. have discovered that a different, nonaqueous solvent mixture—thionyl chloride and pyridine—can also dissolve gold quite effectively but leaves platinum fully intact. The process is clearly oxidative, although the exact product is somewhat uncertain; x-ray photoelectron spectroscopy implicates the formation of trivalent gold species, and a salt of the tetrachloride anion [AuCl4] precipitates after several months. A number of other aromatic amines, as well as dimethyl formamide, can substitute for the pyridine.

Angew. Chem. Int. Ed. 49, 10.1002/anie.201001244 (2010).

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