Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the chemical formula where is acetate (). The hydrated derivative, , which contains one molecule of water for each copper atom, is available commercially. Anhydrous copper(II) acetate is a dark green crystalline solid, whereas is more bluish-green. Since ancient times, copper acetates of some form have been used as and green . Today, copper acetates are used as for the synthesis of various inorganic and organic compounds.
Structure
Copper acetate hydrate adopts the paddle wheel structure seen also for related Rh(II) and Cr(II) tetraacetates.
One oxygen atom on each acetate is bound to one copper atom at . Completing the coordination sphere are two water
, with distances of . The two copper atoms are separated by only , which is close to the separation in metallic copper.
The two copper centers interact resulting in a diminishing of the magnetic moment such that at temperatures below , is essentially diamagnetic. was a critical step in the development of modern theories for antiferromagnetic exchange coupling, which ascribe its low-temperature diamagnetic behavior to cancellation of the two opposing spins on the adjacent copper atoms.
Synthesis
Copper(II) acetate is prepared industrially by heating copper(II) hydroxide or basic copper(II) carbonate with
acetic acid.
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Uses in chemical synthesis
Copper(II) acetate has found some use as an oxidizing agent in organic syntheses. In the Eglinton reaction is used to couple terminal alkynes to give a 1,3-diyne:
The reaction proceeds via the intermediacy of copper(I) acetylides, which are then oxidized by the copper(II) acetate, releasing the acetylide radical. A related reaction involving copper acetylides is the synthesis of , terminal alkynes with amine groups using Cu2(OAc)4.[.] It has been used for hydroamination of acrylonitrile.
In chemical analysis, it serves as an oxidizing agent in both the Barfoed's test for presence of monosaccharides and as a precursor to a copper-fatty acid complex in the colorimetric copper soap assay to test for free fatty acids.
It reacts with arsenic trioxide to form copper acetoarsenite, a powerful insecticide and fungicide called Paris Green.
Related compounds
Heating a mixture of anhydrous copper(II) acetate and copper metal affords copper(I) acetate:
Unlike the copper(II) derivative, copper(I) acetate is colourless and diamagnetic.
"Basic copper acetate" is prepared by neutralizing an aqueous solution of copper(II) 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.
Other uses
A mixture of copper acetate and ammonium chloride is used to chemically color copper with a bronze patina.
Mineralogy
The mineral hoganite is a naturally occurring form of copper(II) acetate.
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