260 COPPER(I) CHLORIDE

Basic copper carbonate occurs in nature as minerals, malachite and azurite. While the carbonate to hydroxide molar composition ratio in natural malachite is 1:1, the ratio in azurite [2CuCO3•Cu(OH)2] is 2:1.

Physical Properties

Natural malachite is a dark green crystalline solid; monoclinic crystals; density 4.0 g/cm3; refractive index 1.655; decomposes at 200°C; insoluble in cold water and alcohols; decomposes in hot water; soluble in acids, ammonium hydroxide and potassium cyanide solutions.

Natural azurite is blue monoclinic crystal; density 3.88 g/cm3; refractive index 1.730; decomposes at 220°C; insoluble in cold water; decomposes in hot water; soluble in ammonium hydroxide and hot sodium bicarbonate solutions.

Preparation

Basic carbonate is obtained from its naturally occurring minerals. It also may be prepared by mixing a solution of copper sulfate with sodium carbonate. The precipitate is then filtered and dried.

Analysis

Elemental composition: Cu 57.47%, C 5.43%, H 0.91%, O 36.18%. Both malachite and azurite may be identified by x-ray analysis and analyzed qualitatively using physical properties such as refractive index and density. For quantitative analysis, the compound may be digested in nitric acid and analyzed for copper by various instrumental methods (see Copper.)

COPPER(I) CHLORIDE

[7758-89-6]

Formula: CuCl (dimeric, Cu2Cl2, in vapor state); MW 98.99; zinc blende structure consisting of tetrahedrally coordinated Cu+; Cu–Cl bond length 2.16Å. Synonym: cuprous chloride

Uses

Copper(I) chloride is used as a catalyst in the production of chlorine by oxygenation of hydrogen chloride. Other important applications are in the petroleum industry as a desulfurization and decolorizing agent; as a condensing agent for fats and oils; as a fungicide; and as an absorbent for carbon monoxide in gas analysis. It occurs in nature as mineral nantokite.

Physical Properties

White cubic crystal which turns blue when heated at 178°C; density 4.14 g/cm3; the mineral nantokite (CuCl) has density 4.14 g/cm3, hardness 2.5 (Mohs), refractive index 1.930; melts at 430°C becoming a deep, green liquid; vaporizes around 1,400°C; vapor pressure 5 torr at 645°C and 400 torr at 1,250°C; low solubility in water (decomposes partially); Ksp 1.72x10–7; insoluble in ethanol and acetone; soluble in concentrated HCl and ammonium hydroxide.

COPPER(I) CHLORIDE 261

Thermochemical Properties

Preparation

Copper(I) chloride is prepared by reduction of copper(II) chloride in solution:

2CuCl + H heat 2CuCl + 2HCl

2 2 →

Alternatively, it can be prepared by boiling an acidic solution of copper(II) chloride with copper metal, which on dilution yields white CuCl:

Cu + CuCl acid 2CuCl

2 →

Copper(I) chloride dissolved in concentrated HCl absorbs carbon monoxide under pressure forming an adduct, CuCl(CO). The complex decomposes on heating releasing CO.

Copper(I) chloride is slightly soluble in water. However, in the presence of

Cl– ion, it forms soluble complexes of discrete halogeno anions such as, CuCl2–, CuCl32–, and CuCl43–.

Formation of complexes and organocopper derivatives as outlined below are not confined only to copper(I) chloride, but typify Cu+ in general.

Reaction with ethylenediamine (en) in aqueous potassium chloride solution forms Cu(II)-ethylenediamine complex, while Cu+ ion is reduced to its metallic state:

2CuCl + 2en → [Cuen2]2+ + 2Cl– + Cu°

It dissolves in acetonitrile, CH3CN forming tetrahedral complex ion [Cu(CH3CN)4]+ which can be precipitated with large anions such as ClO4– or

PF6–.

Reactions with alkoxides of alkali metals produce yellow copper(I) alkoxides. For example, reaction with sodium ethoxide yield copper(I) ethoxide, a yellow compound that can be sublimed from the product mixture:

CuCl + NaOC2H5 → CuOC2H5 + NaCl

Copper(I) chloride forms complexes with ethylene and other alkenes in solutions that may have compositions such as [Cu(C2H4)(H2O)2]+ or [Cu(C2H4)(bipy)]+. (bipy = bipyridyl)

Reactions with lithium or Grignard reagent yield alkyl or aryl copper(I) derivatives, respectively. Such organocopper compounds containing Cu–Cu bonds are formed only by Cu+ and not Cu2+ ions.

262 COPPER(II) CHLORIDE

Analysis

Elemental composition: Cu 64.18%, Cl 35.82%. Copper(I) chloride is dissolved in nitric acid, diluted appropriately and analyzed for copper by AA or ICP techniques or determined nondestructively by X-ray techniques (see Copper). For chloride analysis, a small amount of powdered material is dissolved in water and the aqueous solution titrated against a standard solution of silver nitrate using potassium chromate indicator. Alternatively, chloride ion in aqueous solution may be analyzed by ion chromatography or chloride ion-selective electrode. Although the compound is only sparingly soluble in water, detection limits in these analyses are in low ppm levels, and, therefore, dissolving 100 mg in a liter of water should be adequate to carry out all analyses.

Toxicity

Copper(I) chloride is moderately toxic by ingestion and possibly other routes of entry into the body. The oral LD50 in mouse is reported to be 347 mg/kg; and subcutaneous LD50 in guinea pigs is 100 mg/kg.

COPPER(II) CHLORIDE

[7447-39-4]

Formula: CuCl2; MW 134.45; forms a dihydrate CuCl2•2H2O [10125-13-0] MW 170.48

Synonyms: cupric chloride; cupric dichloride

Uses

Copper(II) chloride is used as a mordant in dyeing and printing of fabrics; as an ingredient of isomerization and cracking catalysts; and as a desulfurizing and deodorizing agent in petroleum industry. Other important applications are in copper plating of aluminum; in tinting-baths for iron and tin; in pigments for ceramics and glasses; as a fixer and desensitizer reagent in photography; in mercury extraction from ores; in laundry-marking and invisible inks; and in manufacture of several copper salts.

Physical Properties

The anhydrous form constitutes yellow to brown monoclinic crystals. It is hygroscopic; forms dihydrate on exposure to moist air; density 3.40 g/cm3; melts around 630°C with decomposition; soluble in water, ethanol and acetone.

The dihydrate exists as greenish blue orthorhombic crystals; density 2.51 g/cm3; decomposes at 100°C; is very soluble in water and ethanol (solubility greater than anhydrous salt in these solvents); also soluble in acetone; insoluble in ether.

COPPER(II) CHLORIDE 263

Thermochemical Properties

Preparation

Copper(II) chloride may be synthesized by heating elemental copper with chlorine:

Cu + Cl heat CuCl

2 → 2

Alternatively, it may be prepared by treating copper carbonate with hydrochloric acid followed by crystallization:

CuCO3 + 2HCl → CuCl2 + CO2 + H2O

In the above preparation, the hydrate of the salt crystallizes, precipitates, and may be dehydrated by heating under vacuum.

Reactions

When heated above 300°C, copper(II) chloride partially decomposes to copper(I) chloride and chlorine:

2CuCl2 >300o C → 2CuCl + Cl

Also, it is reduced to CuCl and elemental copper when treated with reducing agents.

Fluorination with fluorine produces copper(II) fluoride, CuF2. Adding potassium ferrocyanide to CuCl2 aqueous solution precipitates out reddish brown cupric ferrocyanide. Reaction with caustic soda forms blue cupric hydroxide:

CuCl2 + 2NaOH → Cu(OH)2 + 2NaCl

Black copper(II) sulfide, CuS, is obtained when hydrogen sulfide is passed through dissolved CuCl2.

CuCl2 forms several copper(II) complexes with several types of ligands in aqueous solutions.

Analysis

Elemental composition: Cu 47.26%, Cl 52.74%. Aqueous CuCl2 may be analyzed for copper by various instrumental methods (see Copper) and the chloride anion may be analyzed by ion chromatography, chloride ion-selective electrode, or by titration with a standard solution of silver nitrate.