Copper(II) acetate


Copper acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu2 where AcO− is acetate. The hydrated derivative, which contains one molecule of water for each Cu atom, is available commercially. Anhydrous Cu2 is a dark green crystalline solid, whereas Cu242 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, copper acetates are used as reagents for the synthesis of various inorganic and organic compounds. Copper acetate, like all copper compounds, emits a blue-green glow in a flame. The mineral hoganite is a naturally occurring form of copper acetate.

Structure

Copper acetate hydrate adopts the paddle wheel structure seen also for related Rh and Cr tetraacetates. One oxygen atom on each acetate is bound to one copper at 1.97 Å. Completing the coordination sphere are two water ligands, with Cu–O distances of 2.20 Å. The two five-coordinate copper atoms are separated by only 2.62 Å, which is close to the Cu–Cu separation in metallic copper. The two copper centers interact resulting in a diminishing of the magnetic moment such that near 90 K, Cu242 is essentially diamagnetic due to cancellation of the two opposing spins. Cu242 was a critical step in the development of modern theories for antiferromagnetic coupling.

Synthesis

Copper acetate is prepared industrially by heating copper hydroxide or copper carbonate with acetic acid.

Related compounds

Heating a mixture of anhydrous copper acetate and copper metal affords copper acetate:
Unlike the copper derivative, copper acetate is colourless and diamagnetic.
"Basic copper acetate" is prepared by neutralizing an aqueous solution of copper acetate. The basic acetate is poorly soluble. This material is a component of verdigris, the blue-green substance that forms on copper during long exposures to atmosphere.

Uses in chemical synthesis

Copper acetate has found some use as an oxidizing agent in organic syntheses. In the Eglinton reaction Cu24 is used to couple terminal alkynes to give a 1,3-diyne:
The reaction proceeds via the intermediacy of copper acetylides, which are then oxidized by the copper acetate, releasing the acetylide radical. A related reaction involving copper acetylides is the synthesis of ynamines, terminal alkynes with amine groups using Cu24. It has been used for hydroamination of acrylonitrile.
It is also an oxidising agent in Barfoed's test.
It combines with arsenic trioxide to form copper acetoarsenite, a powerful insecticide and fungicide called Paris Green or Schweinfurt Green.