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Copper(II) acetate
Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu2(OAc)4 where AcO- is acetate (CH3CO2-). The hydrated derivative, which contains one molecule of water for each Cu atom, is available commercially. Cu2(OAc)4 is a dark green crystalline solid, whereas Cu2(OAc)4(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, Cu2(OAc)4 is used as a source of copper(II) in inorganic synthesis and as a catalyst or an oxidizing agent in organic synthesis. Copper acetate, like all copper compounds, emits a blue-green glow in a flame. Additional recommended knowledge
HistoryCopper(II) acetate is the primary component of verdigris,[citation needed] the blue-green substance that forms on copper during long exposures to atmosphere. It was historically prepared in vineyards, since acetic acid is a byproduct of fermentation. Copper sheets were alternately layered with fermented grape skins and dregs left over from wine production and exposed to air. This would leave a blue substance on the outside of the sheet. This was then scraped off and dissolved in water. The resulting solid was used as a pigment, or combined with arsenic trioxide to form copper acetoarsenite, a powerful insecticide and fungicide called Paris or Schweinfurt green. Uses in chemical synthesisThe uses for copper(II) acetate are more plentiful as a catalyst or oxidizing agent in organic syntheses. For example, Cu2(OAc)4 is used to couple two terminal alkynes to make a 1,3-diyne:[1]
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 ynamines, terminal alkynes with amine groups using Cu2(OAc)4.[2] StructureCu2(OAc)4(H2O)2 adopts the "Chinese lantern" structure seen also for related Rh(II) and Cr(II) tetraacetates.[2][3] One oxygen atom on each acetate is bound to one copper at 1.97 Å (197 pm. Completing the coordination sphere are two water ligands, with Cu-O distances of 2.20 Å (220 pm). The two five-coordinate copper atoms are separated by only 2.65 Å (265 pm), which is close to the Cu--Cu separation in metallic copper.[5]. The two copper centers interact resulting in a diminishing of the magnetic moment such that near 90 K, Cu2(OAc)4(H2O)2 is essentially diamagnetic due to cancellation of the two opposing spins. Cu2(OAc)4(H2O)2 was a critical step in the development of modern theories for antiferromagnetic coupling.[4] SynthesisCopper(II) acetate has been synthesized for centuries by the method described in the history section. This method, however, leads to an impure copper(II) acetate. In a laboratory, a much purer form can be synthesized in a simple three-step procedure. The overall reaction is as follows:[6]
The hydrate form can be dehydrated by heating at 100 °C in a vacuum:[5]
Heating a mixture of anhydrous Cu2(OAc)4 and copper metal affords colorless, volatile cuprous acetate:[6]
References
Categories: Copper compounds | Acetates | Oxidizing agents | Catalysts |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Copper(II)_acetate". A list of authors is available in Wikipedia. |