The dissolution of noble metals is important for metallurgy, catalysis, organometallic chemistry, syntheses and applications of noble-metal nanoparticles, and recycling of noble metals. Aqua regia ("royal water") has been used for centuries as a powerful etchant to dissolve noble metals. The beauty of aqua regia is that the simple 1:3 mixture of concentrated nitric and hydrochloric acids can dissolve noble metals such as gold, palladium, and platinum, although these metals are not soluble in either of the acids alone. We show that simple mixtures of thionyl chloride (SOCl 2 ) and some organic solvents/reagents (pyridine, N,N-dimethylformamide, and imidazole) can also dissolve noble metals with high dissolution rates under mild conditions. We name these mixtures "organicus liquor regius".[1] The discovery of this solvent system is of unprecedented scientific significance and engineering value: Compared with inorganic chemistry, organic chemistry provides precise control over chemical reactivity, and the ability to tailor organic reactions enables the selective dissolution of noble metals. By varying the composition of organicus liquor regius we have for the first time realized the selective dissolution of noble metals, namely, the dissolution of Au and Pd from a Pt/Au/Pd mixture and of Au from an Au/Pd mixture. Selective dissolution is important for many applications, especially for recycling noble metals. The global energy crisis demands green energy technologies, which will undoubtedly require increased resources of noble metals. However, noble metals are scarce on earth; thus, the ability to recover high-purity noble metals by recycling processes will be paramount. Among the noble metals, Pt is used most widely as a catalyst in many green technologies, in particular, proton-exchange membrane (PEM) fuel cells. [2][3][4] The recycling of Pt, however, has long been a challenging issue: Current recycling technologies are complicated, and rely on the dissolution of Pt in strong inorganic acids and the subsequent separation of the dissolved Pt from solution. [5][6][7] The nonselectivity of the inorganic acids results in the dissolution of other noble metals such as Ag, Au, and Pd at the same time as Pt. This lack of selectivity limits the quality of the recycled Pt. Therefore, an improved route for Pt recycling-both in terms of quality and efficiency-requires a selective dissolution process, which would remove the noble metal impurities (Ag, Au, Pd, etc.) before the final dissolution of Pt. Preliminary investigations on a few non-aqueous solutions for dissolving noble metals have been carried out, [8][9][10][11] but they showed unsatisfactory solubility, [9][10][11][12] selectivity, [9][10][11][12] efficiency, [8,10] stability, [11] and simplicity.[8-10] These etchants are not ideal because of the intrinsic inorganic chemistry associated with conventional oxidizers of noble metals (halogens and oxygen). [8,9,11] Organicus liquor regius oxidizes noble metals by a different mechanism. Figure 1 shows a graph of the diss...

We are grateful to Zhong-Lin Wang for his valuable advice, Bo Xu for collecting NMR data and helpful discussions, Meilin Liu and Min-Kyu Song for their help with CV experiments, and Anselm Griffin for his helpful discussions on the chemistry of thionyl chloride and pyridine. We acknowledge Josh Agar for his help in preparing the manuscript, and Ziyin Lin for his discussions.Supporting information for this article is available on the WWW under http://dx.

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A new synthetic method for dimethyl 2,3-dihydrobenzo[b]oxepine-2,4-dicarboxylates and methyl 2-(2-carbomethoxybenzo[b]furan-3-yl)propanoates by an intramolecular conjugate displacement reaction or an S N 2 reaction of acetates of Morita-Baylis-Hillman adducts of methyl (2-formylphenoxy)acetates has been described.