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Copper(II) hydroxide is the hydroxide of the metal copper with the chemical formula of Cu(OH)2. Copper hydroxide is a pale blue, gelatinous solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper hydroxide, quite likely a mixture of copper(II) carbonate and hydroxide. These are often greener in colour.
Copper(II) hydroxide has been known since copper smelting began around 5000 BC although the alchemists were probably the first to manufacture it. This was easily done by mixing solutions of lye (sodium or potassium hydroxide) and blue vitriol (copper(II) sulfate), both chemicals which were known in antiquity.
Copper(II) hydroxide occurs naturally as a component of several copper minerals, notably azurite, malachite, antlerite, and brochantite. Azurite (2CuCO3·Cu(OH)2) and malachite (CuCO3·Cu(OH)2) are carbonates while antlerite (CuSO4·2Cu(OH)2) and brochantite (CuSO4·3Cu(OH)2) are sulfates. Copper(II) hydroxide is rarely found as an uncombined mineral because it slowly reacts with carbon dioxide from the atmosphere to form a basic copper(II) carbonate. The mineral of the formula Cu(OH)2 is called spertiniite.
Copper(II) hydroxide can be produced by adding a small amount of sodium hydroxide to a dilute solution of copper(II) sulfate (CuSO4 · 5H2O). The precipitate produced in this manner, however, often contains water molecules and an appreciable amount of sodium hydroxide impurity. A purer product can be attained if ammonium chloride is added to the solution beforehand. Nevertheless, it is impossible to obtain a pure product; processes for eliminating impurities lead to the destruction of the hydroxide, giving rise to the more stable oxide, CuO. Alternatively, copper hydroxide is readily made by electrolysis of water (containing a little electrolyte such as sodium sulfate). A copper anode is used, often made from scrap copper.
"Copper in moist air slowly acquires a dull green coating. The green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3."
- 2 Cu (s) + H2O (g) + CO2 (g) + O2 (g) → Cu(OH)2 (s) + CuCO3 (s)
Copper(II) hydroxide reacts with a solution of ammonia to form a deep blue solution Cupramine a chelated form - consisting of the [Cu(NH3)4]2+ complex ion. Copper(II) hydroxide in ammonia solution, known as Schweizer's reagent, possesses the interesting ability to dissolve cellulose. This property led to it being used in the production of rayon, a cellulose fiber. It is also used widely in the aquarium industry for its ability to destroy external parasites in fish, including flukes, marine ich, brook and marine velvet, without killing the fish. Although other water soluble copper compounds can be effective in this role, they generally result in high fish mortality. Cupramine is also widely used in organic chemical synthesis, discussed below.
Reagent for organic chemistry
Copper(II) hydroxide has a rather specialized role in organic synthesis. Often, when it is utilized for this purpose, it is prepared in situ by mixing a soluble copper(II) salt and potassium hydroxide.
It is sometimes used in the synthesis of aryl amines. For example, copper(II) hydroxide catalyzes the reaction of ethylenediamine with 1-bromoanthraquinone or 1-amino-4-bromoanthraquinone to form 1-((2-aminoethyl)amino)anthraquinone or 1-amino-4-((2-aminoethyl)amino)anthraquinone, respectively:
Copper(II) hydroxide also converts acid hydrazides to carboxylic acids at room temperature. This is especially useful in synthesizing carboxylic acids with other fragile functional groups. The published yields are generally excellent as is the case with the production of benzoic acid and octanoic acid:
Copper(II) hydroxide has been used as an alternative to the Bordeaux mixture, a fungicide and nematicide. Such products include Dupont's Kocide 3000. Copper(II) hydroxide is also occasionally used as ceramic colorant.
Copper(II) hydroxide has been combined with latex paint, making a product designed to control root growth in potted plants. Secondary and lateral roots thrive and expand, resulting in a dense and healthy root system. It was sold under the name Spin Out, which was first introduced by Griffin L.L.C. The rights are now owned by SePRO Corp. It is now sold as Microkote either in a solution you apply yourself, or as treated pots.
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- Blue verditer. Natural Pigments. 2007.
- Y. Cudennec, A. Lecerf (2003). "The transformation of Cu(OH)2 into CuO, revisited". Solid State Sciences 5: 1471–1474. doi:10.1016/j.solidstatesciences.2003.09.009.
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- Copper (II) hydroxide. Ceramic Materials Database. 2003.
- Pauling, Linus (1970). General Chemistry. Dover Publications, Inc. (p 702).
- Bordeaux Mixture. UC IPM online. 2007.
- "SePRO Corporation".
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