You can use acetonitrile. The Cu+1 dissolves in CH3CN with formation of complex with acetonitrile. But of course you should yse inert atmosphere because Cu+1 can be easily oxidized by oxygen in the air.

Dear Hlib Repich,

Thank you very much for your suggestion. Do you have a reference on the reaction of Cu(I) iodide in acetonitrile? I wonder if it produce any gas upon addition of Cu(I) iodide to acetonitrile?

Also if the Cu+1 forms a complex with acetonitrile, shouldn't it be stable as Cu+1? I am confused how the complex can be oxidized to Cu+2 in the presence of oxygen in air?

Thank you very much for your help!

Copper(I) iodide is nicely soluble in acetonitrile (nearly 7-8%) and, in somewhat lesser extent, in other nitriles (butyronitrile, benzonitrile, adiponitrile) and in mixtures of acetonitrile with inert solvents (chloroform, dichloromethane). The solutions are air-stable and may be stored at r.t. They react with different N-donor species (pyridines, pyrazoles, triazoles etc) producing complexes of Cu(I) iodide. CuCl and CuBr work in similar, they are soluble in acetonitrile even much more better (nearly 20% for chloride). However, solutions of CuCl are unstable and eventually deposit green powder of Cu(I,II) oxochlorides.

Dear Konstantin Domasevitch,

Thank you very much for your answers. I really appreciate all of the advice and suggestions.

Soluble in ammonia aq. sol., dilute hydrochloric acid, aq. sol. of alkali salts of cyanide, iodide or thiosulfate; acetonitrile.