Copper(I) chloride

Copper(I) chloride
IUPAC name Copper(I) chloride
Other names Cuprous chloride
Identifiers
CAS number	7758-89-6
RTECS number	GL6990000
Properties
Molecular formula	CuCl
Molar mass	98.99 g/mol
Appearance	white powder, slightly green from oxidized impurities
Density	4.140 g/cm3, solid
Melting point	430 °C (703 K)
Boiling point	1490 °C (1760 K), decomposes
Solubility in water	0.0062 g/100 mL (20 °C)
Structure
Crystal structure	Tetrahedral close packed ( Zinc blende structure)
Hazards
MSDS	ScienceLab.com
R/S statement	R: 22, 50, 53 S: 22, 60/61
Main hazards	Irritant
NFPA 704	0 3 0
Related compounds
Other anions	Copper(I) bromide Copper(I) iodide
Other cations	Copper(II) chloride Silver(I) chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. This colorless solid is a versatile precursor to other copper compounds, including some of commercial significance. It occurs naturally as the rare mineral nantokite. Unlike other first-row transition metal halides, it forma a stable complexes with carbon monoxide. It crystallizes in a diamondoid motif, reflecting the tendency of copper(I) to form tetrahedral complexes.

Preparation

Copper(I) chloride is produced industrially by the direct chlorination of copper:

2 Cu + Cl₂ → 2 CuCl

In the laboratory, copper(I) chloride can be prepared by the reduction of copper(II) salts such as CuSO₄ using sulfur dioxide, sodium bisulfite (NaHSO₃), sodium metabisulfite, or copper metal.

2 CuCl₂ + H₂O + SO₃^2- → 2 CuCl + SO₄^2- + 2 Cl^-

The white solid precipitates from the solution. Upon standing in moist air, samples of CuCl become green due to the formation of copper(II) chlorides.

Chemical properties

CuCl is more affordable and less toxic than other soft Lewis acids. In addition, copper can exist in multiple redox states, including I, II, and III. This combination of properties define some of the useful features of copper(I) chloride. It is a soft Lewis acid, classified as soft according to the Hard-Soft Acid-Base concept. Thus, it tends to form stable complexes with soft Lewis bases such as triphenylphosphine:

CuCl + P(C₆H₅)₃ → [CuCl(P(C₆H₅)₃)]₄

Although CuCl is insoluble in water, it dissolves in aqueous solutions containing suitable donor molecules. It forms complexes with halide ions, for example forming H₃O⁺ CuCl₂^- with concentrated hydrochloric acid. It also dissolves in solutions containing CN^-, S₂O₃^2-, and NH₃ to give complexes.

Solutions of CuCl in HCl or NH₃ absorb carbon monoxide to form colourless complexes such as the chloride-bridged dimer [CuCl(CO)]₂. The same hydrochloric acid solutions also react with acetylene gas to form [CuCl(C₂H₂)]. ammoniacal solutions of CuCl react with acetylenes to form the explosive copper(I) acetylide. Complexes of CuCl with alkenes can be prepared by reduction of CuCl₂ by sulfur dioxide in the presence of the alkene in alcohol solution. Complexes with dienes such as 1,5-cyclooctadiene are particularly stable:

Although only poorly soluble in water, its aqueous solution are unstable with respect to disproportionation into Cu and CuCl₂. In part for this reason samples assume a green coloration (see photograph in upper right).

Uses

The main use of copper(i) chloride is as a precursor to the fungicide copper oxychloride. For this purpose aqueous copper(I) chloride is generated by comproportionation and then air-oxidized:

Cu + CuCl₂ → 2 CuCl

6 CuCl + 3/2 O₂ + 3 H₂O → 2 Cu₃Cl₂(OH)₄ + CuCl₂

Copper(I) chloride catalyzes a variety of organic reactions, as discussed above. Its affinity for carbon monoxide in the presence of aluminium chloride is exploited in the COPure^SM process.

In organic synthesis

In the Sandmeyer reaction. Treatment of an arenediazonium salt with CuCl leads to an aryl chloride, for example:

The reaction has wide scope and usually gives good yields.

Early investigators observed that copper(I) halides catalyse 1,4-addition of Grignard reagents to alpha,beta-unsaturated ketones led to the development of organocuprate reagents that are widely used today in organic synthesis:

This finding led to the development of organocopper chemistry. For example, CuCl reacts with methyllithium (CH₃Li) to form " Gilman reagents" such as (CH₃)₂CuLi, which find extensive use in organic synthesis. Grignard reagents react similarly. Although other copper(I) compounds such as copper(I) iodide are now more often used for these types of reactions, copper(I) chloride is still recommended in some case:

Here, Bu indicates an n- butyl group. Without CuCl, the Grignard reagent alone gives a mixture of 1,2- and 1,4-addition products (i.e., the butyl adds at the closer to the C=O).

In polymer chemistry

Copper(I) chloride is also an intermediate formed from copper(II) chloride in the Wacker process. CuCl is used as a catalyst in Atom Transfer Radical Polymerization (ATRP).