COPPER (II) HYDROXIDE: STRUCTURE, PROPERTIES, NOMENCLATURE, USES - CHEMISTRY - 2025

The copper hydroxide (II) or cupric hydroxide is a crystalline solid inorganic greenish blue pale blue or the chemical formula Cu (OH) ₂. It is obtained as a voluminous blue precipitate by adding an alkaline hydroxide to cupric solutions (meaning that they contain Cu ²⁺ ions). It is an unstable compound.

To increase its stability, it is prepared in the presence of ammonia (NH ₃) or phosphates. If it is prepared in the presence of ammonia, a material with good stability and large particle size is produced.

Sample of cupric hydroxide, Cu (OH) ₂. SamZane at Italian Wikipedia Source: Wikipedia Commons

When prepared starting from copper (II) phosphate, Cu ₃ (PO ₄) ₂, a material with finer particle size and greater surface area is obtained. Cupric hydroxide is widely used as a fungicide and bactericide in agriculture and to treat wood, extending its useful life.

It is also used as a food supplement for animals. It is used as a raw material to obtain other copper (II) salts and in electroplating to coat surfaces.

Studies are underway to estimate its potential to combat bacterial and fungal infections in humans.

Structure

Copper (II) hydroxide contains infinite chains of copper ions (Cu ²⁺) linked by bridges of hydroxyl groups (OH ^-).

The chains are so packed together that 2 oxygen atoms from other chains are above and below each copper atom, thus assuming a distorted octahedral configuration, which is common in most copper (II) compounds.

In its structure, four oxygen atoms are at a distance of 1.93 A; two oxygen atoms are at 2.63 A; and the Cu-Cu distance is 2.95 A.

Crystal structure of cupric hydroxide. Aleksandar Kondinski. Source: Wikipedia Commons

Nomenclature

- Copper (II) hydroxide.

- Cupric hydroxide.

- Copper dihydroxide.

Properties

Physical state

Crystalline solid.

Molecular weight

99.58 g / mol.

Melting point

It decomposes before melting. Degradation point 229 ºC.

Density

3.37 g / cm ³

Solubility

It is virtually insoluble in water: 2.9 micrograms / L at 25ºC. Quickly soluble in acids, in concentrated alkaline solutions and in ammonium hydroxide. Insoluble in organic solvents. In hot water, it decomposes generating copper (II) oxide, which is more stable.

Other properties

It is easily soluble in strong acids and also in concentrated alkaline hydroxide solutions, to give deep blue anions, probably of type ^2-.

Its stability depends on the method of preparation.

It can decompose giving black copper (II) oxide (CuO) if it remains at rest for a few days or under heating.

In the presence of an excess of alkali it decomposes over 50 ºC.

Applications

In agriculture

Copper (II) hydroxide has a wide application as a fungicide and antibacterial in agricultural crops. Here are some examples:

- Serves against bacterial stains (Erwinia) on lettuce, applying as a foliar treatment.

- Against bacterial spots (of Xanthomonas pruni) in peaches, for which a latent and foliar treatment is applied.

- It is used against the leaf and stem pest of blueberries through latent applications.

- Against rot during storage of blueberries caused by Monilinia oxycocci, by latent application.

For the application in agriculture, copper (II) hydroxide is used, which is prepared in the presence of phosphates due to its small particle size.

Lettuce cultivation. Source: Pixabay

In the preservation of wood

Wood, being organic in nature, is sensitive to attack by insects and microorganisms. Copper (II) hydroxide is used as a biocide for fungi that attack wood.

It is generally used in conjunction with a quaternary ammonium compound (NH ₄ ⁺). The copper hydroxide acts as a fungicide and the quaternary ammonium compound works as an insecticide.

In this way, the treated wood withstands or resists service conditions, reaching the level of performance required by the user. However, wood treated with these compounds has a high level of copper and is very corrosive to common steel, so a type of stainless steel is required that can withstand the processing of treated wood.

Despite its usefulness, copper (II) hydroxide is considered a slightly hazardous biocide.

For this reason, there is concern that it will be released from treated wood into the environment in amounts that could be harmful to microorganisms naturally present in waters (rivers, lakes, wetlands, and the sea) or soil.

In the manufacture of rayon

Since the 19th century, ammoniacal solutions of copper (II) hydroxide have been used to dissolve cellulose. This is one of the first steps to obtain the fiber called rayon using the technology developed by Bemberg in Germany.

Copper (II) hydroxide dissolves in a solution of ammonia (NH ₃), forming a complex salt.

The refined short cotton fibers are added to the copper ammonia solution containing the copper (II) hydroxide as a precipitated solid.

Cotton cellulose forms a complex with copper tetra-ammonium hydroxide dissolving in solution.

Subsequently, this solution coagulates while being passed through an extrusion device.

Due to its high cost, this technology has already been surpassed by viscose. Bemberg's technology is currently used only in Japan.

In the animal feed industry

It is used as traces in animal feed, as it is one of the substances required as micronutrients for the complete nutrition of animals.

Concentrated feed for livestock. Thamizhpparithi Maari. Source: Wikipedia Commons

This is because in higher living beings copper is an essential element, required for the activity of a variety of copper-containing enzymes.

For example, it is contained in the enzyme that participates in the production of collagen and in the enzyme required for the synthesis of melanin, among others.

It is a compound generally recognized as safe when added at levels consistent with good feeding practice.

Milky cows. Source: Pixabay

In the manufacture of other copper (II) compounds

Active precursor in the production of the following copper (II) compounds: copper (II) naphthenate, copper (II) 2-ethylhexanoate and copper soaps. In these cases, copper (II) hydroxide is used, which is synthesized in the presence of ammonia.

Other uses

It is used in the stabilization of nylon, in battery electrodes; as a color fixer in dyeing operations; as a pigment; in insecticides; in the treatment and staining of paper; in catalysts, as a catalyst in the vulcanization of polysulfide rubber; as an antifouling pigment; and in electrolysis, in electroplating.

Future medical applications

Copper (II) hydroxide is part of the copper compounds that are being studied in the form of nanoparticles for the elimination of bacteria such as E. coli, K. pneumoniae, P. aeruginosa, Salmonella spp., among others, causing diseases in humans.

It has also been found that copper nanoparticles can be effective against Candida albicans, a fungus that is a common cause of human pathologies.

This indicates that copper nanotechnology may play an important role against bacteria and fungi that cause infections in humans, and copper (II) hydroxide could be very useful in these fields.

References

1. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
2. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 7. Fourth Edition. John Wiley & Sons.
3. Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. Volume A7. VCH Verlagsgesellschaft mbH.
4. Dance, JC; Emeléus, HJ; Sir Ronald Nyholm and Trotman-Dickenson, AF (1973). Comprehensive Inorganic Chemistry. Volume 3. Pergamon Press.
5. National Library of Medicine. (2019). Copper (II) Hydroxyde. Recovered from: pubchem.ncbi.nlm.nih.gov
6. Schiopu, N. and Tiruta-Barna, L. (2012). Wood preservatives. In Toxicity of building materials. Chapter 6. Recovered from sciencedirect.com.
7. Mordorski, B. and Friedman, A. (2017). Metal Nanoparticles for Microbial Infection. In Functionalized Nanomaterials for the Management of Microbial Infection. Chapter 4. Recovered from sciencedirect.com.
8. Takashi Tsurumi. (1994). Solution spinning. In Advanced fiber spinning technology. Chapter 3. Recovered from sciencedirect.com.