Cu₂O (Aldrich)
Benzene (distilled from K)
trifluoromethanesulphonic anhydride (Aldrich)

A 250 ml round bottomed flask with a sidearm was charged with Cu₂O (3.64 g 25.4 mmol) and a stirrer bar. The round bottomed flask was evacuated and flushed with argon. Benzene (150 ml) was added via cannula and trifluoromethanesulphonic anhydride (10.0 g 35.4 mmol) was syringed into the stirred suspension. The reaction mixture was refluxed for several hours (overnight) with a double surface water condenser attached and argon gently passing across the top of the condenser. The solution gradually changed colour from bright red to a "grey" solution. The hot solution was filtered through a very small amount of dry Celite on a wide frit (we use a 5 cm diameter), to remove any insoluble matter. On cooling a white solid precipitated from the solution. The solvent was removed by filtration and the off-white solid was washed with benzene (2 x 20 ml). The solid was dried in vacuo and stored in an inert atmosphere (argon glovebox). Yield close to quantitative.

It's important to keep the solution hot when filtering. If it starts to precipitate then it will carry on and filtration will become a nightmare. Use hot glassware.

EA for (CuOTf)₂C₆H₆, Calculated % C, 19.09; H, 1.20. Found % C, 17.96; H, 1.08. ICP Calculated % Cu, 25.25. Found % Cu, 24.13.

Salomon, R.G.; Kochi, J.K. J. Am. Chem. Soc. 1973, 3300-3310.

For applications see J. Am. Chem. Soc., 2000, 122, 7132 and refs therein