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Bacon and Stewart 4953 912. Metal Ions and Complexes in Organic Reactions. Part I V.l Copper-promoted Preparations of Diaryl Ethers and Competing Hydrogen-transfer Processes By R. G. R. BACON and 0. J. STEWART Diaryl ethers have been prepared, e.g. in collidine or dimethylacetamide solution at -170", by the reaction: 2ArHal-t 2Ar'OH + Cu,Oin which a suspension of copper(1) oxide functions as reagent and catalyst; copper or copper(I1) oxide may also be used. The process has preparative value and may be superior to the conventional Ullmann condensation. With an alkali-metal phenoxide the copper oxide is not consumed and reaction may be faster than with the phenol, particularly in dimethylacetamide. Pronounced solvent effects were observed. Halide reactivity was in the order ArI > ArBr > ArCl. Substituent effects were studied.Copper-catalysed substitutive reduction, &Hal --+ ArH, was a common competing reaction] and was sometimes a major effect with an efficient hydrogen acceptor, e.g., o-bromonitrobenzene, or with an efficient hydrogen donor, e.g., o-nitrophenol. Sources of transferred hydrogen may be a substituent group, e.g., OH or NH,, or an aromatic or heterocyclic nucleus. Other side-reactions included decarboxylation, halogen exchange] coupling of the halide to a biaryl, and substitution of the halide by a nucleophile other than the phenol.ULLMANN and his co-workers discovered2 that small amounts of copper catalyse the formation of diary1 ethers in the reaction:

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