COPPER (I) CHLORIDE (CUCL): STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2024

The copper chloride (I) is an inorganic compound consisting of copper (Cu) and chlorine (Cl). Its chemical formula is CuCl. The copper in this compound has a valence of +1 and the chlorine -1. It is a white crystalline solid which, when exposed to air for a long time, acquires a greenish color due to the oxidation of copper (I) to copper (II).

It behaves like Lewis acid, requiring electrons from other compounds that are Lewis bases, with which it forms complexes or stable adducts. One of these compounds is carbon monoxide (CO), so the ability to bind between the two is used industrially to extract CO from gas streams.

Purified copper (I) chloride (CuCl). Leiem / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.

It has optical properties that can be used in light emitting semiconductors. Furthermore, CuCl nanocubes have great potential to be used in devices to store energy efficiently.

It is used in the art of pyrotechnics because in contact with a flame it produces a blue-green light.

Structure

CuCl is made up of the cuprous ion Cu ⁺ and the chloride anion Cl ^-. The electron configuration of the Cu ⁺ ion is:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 3d ¹⁰ 4s ⁰

and it is because copper lost the electron from the 4s shell. The chloride ion has the configuration:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶

It can be seen that both ions have their complete electronic shells.

This compound crystallizes with cubic symmetry. The image below shows the arrangement of atoms in a crystalline unit. The pink spheres correspond to copper and the green spheres to chlorine.

Structure of CuCl. Author: Benjah-bmm27. Source: Wikimedia Commons.

Nomenclature

• Copper (I) chloride
• Cuprous chloride
• Copper monochloride

Properties

Physical state

White crystalline solid that in prolonged contact with air oxidizes and turns green.

Molecular weight

98.99 g / mol

Melting point

430 ºC

Boiling point

Approximately 1400 ºC.

Density

4.137 g / cm ³

Solubility

Almost insoluble in water: 0.0047 g / 100 g of water at 20 ° C. Insoluble in ethanol (C ₂ H ₅ OH) and acetone (CH ₃ (C = O) CH ₃).

Chemical properties

It is unstable in air because Cu ⁺ tends to oxidize to Cu ²⁺. Over time, cupric oxide (CuO), cuprous hydroxide (CuOH) or a complex oxychloride is formed and the salt turns green.

Copper (I) chloride that has been exposed to the environment and partially oxidized. May contain CuO, CuOH, and other compounds. Benjah-bmm27 / Public domain. Source: Wikimedia Commons.

In aqueous solution it is also unstable as an oxidation and reduction reaction occurs simultaneously, forming metallic copper and copper (II) ion:

CuCl → Cu ⁰ + CuCl ₂

CuCl as Lewis acid

This compound acts chemically as Lewis acid, which means that it is hungry for electrons, thus forming stable adducts with compounds that can provide them.

It is very soluble in hydrochloric acid (HCl), where Cl ^- ions behave as electron donors and species such as CuCl ₂ ^-, CuCl ₃ ^2- and Cu ₂ Cl ₄ ^{2- are formed}, among others.

This is one of the species that form in solutions of CuCl in HCl. Author: Marilú Stea.

Aqueous CuCl solutions have the ability to absorb carbon monoxide (CO). This absorption can occur when said solutions are both acidic, neutral or with ammonia (NH ₃).

In such solutions it is estimated that various species are formed such as Cu (CO) ⁺, Cu (CO) ₃ ⁺, Cu (CO) ₄ ⁺, CuCl (CO) and ^-, which depends on the medium.

Other properties

It has electro-optic characteristics, low optical loss over a wide range of the light spectrum from visible to infrared, low refractive index and low dielectric constant.

Obtaining

Copper (I) chloride can be obtained by directly reacting copper metal with chlorine gas at a temperature of 450-900 ° C. This reaction is applied industrially.

2 Cu + Cl ₂ → 2 CuCl

A reducing compound such as ascorbic acid or sulfur dioxide can also be used to convert copper (II) chloride to copper (I) chloride. For example, in the case of SO ₂, it is oxidized to sulfuric acid.

2 CuCl ₂ + SO ₂ + 2 H ₂ O → 2 CuCl + H ₂ SO ₄ + 2 HCl

Applications

In CO recovery processes

The ability of CuCl solutions to absorb and desorb carbon monoxide is used industrially to obtain pure CO.

For example, the process called COSORB uses stabilized copper chloride in the form of a complex salt with aluminum (CuAlCl ₄), which dissolves in an aromatic solvent such as toluene.

The solution absorbs CO from a gaseous stream to separate it from other gases such as CO ₂, N _2, and CH ₄. The monoxide-rich solution is then heated under reduced pressure (that is, below atmospheric) and the CO is desorbed. The gas recovered in this way is of high purity.

Structure of carbon monoxide where the electrons available to complex with CuCl are observed. Author: Benjah-bmm27. Source: Wikimedia Commons.

This process allows to obtain pure CO starting from reformed natural gas, gasified coal or gases derived from steel production.

In catalysis

CuCl is used as a catalyst for various chemical reactions.

For example, the reaction of the element germanium (Ge) with hydrogen chloride (HCl) and ethylene (CH ₂ = CH ₂) can be performed using this compound. It is also used for the synthesis of organic silicon compounds and various heterocyclic organic sulfur and nitrogen derivatives.

A polyphenylene ether polymer can be synthesized using a 4-aminopyrine and CuCl catalyst system. This polymer is very useful for its mechanical properties, low moisture absorption, excellent insulation from electricity and resistance to fire.

In obtaining organic copper compounds

Alkenylcuprate compounds can be prepared by reacting a terminal alkyne with an aqueous solution of CuCl and ammonia.

In obtaining polymers bound to metals

Copper (I) chloride can coordinate with polymers, forming complex molecules that serve as catalysts and that combine the simplicity of a heterogeneous catalyst with the regularity of a homogeneous one.

In semiconductors

This compound is used to obtain a material formed by γ-CuCl on silicon, which has photoluminescence properties with a high potential to be used as a photon emitting semiconductor.

These materials are widely used in ultraviolet light emitting diodes, laser diodes, and light detectors.

In supercapacitors

This product, obtained in the form of cubic nanoparticles or nanocubes, makes it possible to manufacture supercapacitors, as it has an outstanding charging speed, high reversibility and a small loss of capacitance.

Supercapacitors are energy storage devices that stand out for their high power density, safe operation, fast charge and discharge cycles, long-term stability, and are environmentally friendly.

CuCl nanocubes could be used in electronics and energy storage applications. Author: Tide He. Source: Pixabay.

Other apps

Since CuCl emits blue-green light when subjected to a flame, it is used to prepare fireworks where it provides that color during the execution of pyrotechnics.

The green color of some fireworks may be due to CuCl. Author: Hans Braxmeier. Source: Pixabay.

References

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