Schweizer's reagent

Schweizer's reagent is the common name for the complex tetra-aminecopper dihydroxide, [Cu(NH3)4][OH]2. It is prepared by precipitating copper(II) hydroxide from an aqueous solution of copper sulfate using sodium hydroxide, then dissolving the precipitate in a solution of ammonium hydroxide. It forms a deep azure solution. If the solution is evaporated, it leaves blue, needle-like crystals.

Schweizer's reagent finds use in production of cellulose products such as rayon and cellophane, because wood-pulp, cotton fiber, and other natural cellulose sources are soluble in the solution. Dissolved cellulose precipitates when the solution is acidified.