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Cadmium chloride is a white crystalline compound of cadmium and chloride, with the formula CdCl2. This salt is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. The crystal structure of cadmium chloride (described below), is a reference for describing other crystal structures. Also known are CdCl2•H2O and the hemipentahydrate CdCl2•2.5H2O.[2]

Structure

Anhydrous

Anhydrous cadmium chloride forms a layered structure consisting of octahedral Cd2+ centers linked with chloride ligands. Cadmium iodide, CdI2, has a similar structure, but the iodide ions are arranged in a HCP lattice, whereas in CdCl2 the chloride ions are arranged in a CCP lattice.[8][9]

Hydrates

Subunit of CdCl2(H2O)2.5. Color code: red = O (of H2O), blue = Cd, green = Cl.

The anhydrous form absorbs moisture from the air to form various hydrates. Three of these hydrates have been examined by X-ray crystallography.

Crystallographic data for the 3 hydrates of cadmium chloride
Compound CdCl2·H2O[10] CdCl2·2.5H2O[11] CdCl2·4H2O[12]
Molar mass (g/mol) 201.33 228.36 255.38
Crystal Structure Orthorhombic Monoclinic Orthorhombic
Space Group Pnma P21/n P212121
Lattice constant a (Å) 9.25 9.21 12.89
Lattice constant b (Å) 3.78 11.88 7.28
Lattice constant c (Å) 11.89 10.08 15.01
β 93.5°
Density (g/cm3) 3.26 2.84 2.41
Comment Interconnected CdCl3(H2O) octahederons Distorted trans-[CdCl2(H2O)4] octahedrons

Chemical properties

Cadmium chloride dissolves well in water and other polar solvents. It is a mild Lewis acid.[8]

CdCl2 + 2 Cl− → [CdCl4]2−

Solutions of equimolar cadmium chloride and potassium chloride give potassium cadmium trichloride.[13] With large cations, it is possible to isolate the trigonal bipyramidal [CdCl5]3− ion.

Cadmium metal is soluble in molten cadmium chloride, produced by heating cadmium chloride above 568 °C. Upon cooling, the metal precipitates.[14]

Preparation

Anhydrous cadmium chloride can be prepared by the reaction of hydrochloric acid and cadmium metal or cadmium oxide.[14]

Cd + 2 HCl → CdCl2 + H2

The anhydrous salt can also be prepared from anhydrous cadmium acetate using hydrogen chloride or acetyl chloride.[15]

Industrially, it is produced by the reaction of molten cadmium and chlorine gas at 600 °C.[14]

The monohydrate, hemipentahydrate, and tetrahydrate can be produced by evaporation of the solution of cadmium chloride at 35, 20, and 0 °C respectively. The hemipentahydrate and tetrahydrate release water in air.[10][11][12]

Uses

Cadmium chloride is used for the preparation of cadmium sulfide, used as "cadmium yellow", a brilliant-yellow stable inorganic pigment.[14]

CdCl
2 + H
2S → CdS + 2 HCl

In the laboratory, anhydrous CdCl2 can be used for the preparation of organocadmium compounds of the type R2Cd, where R is an aryl or a primary alkyl. These were once used in the synthesis of ketones from acyl chlorides:[16]

CdCl
2 + 2 RMgX → R
2Cd + MgCl
2 + MgX
2
R
2Cd + 2R'COCl → 2R'COR + CdCl
2

Such reagents have largely been supplanted by organocopper compounds, which are much less toxic.

Cadmium chloride is also used for photocopying, dyeing and electroplating.

Like all cadmium compounds, CdCl
2 is highly toxic and appropriate safety precautions must be taken when handling it.

References

  1. ^ a b c d e f g Anatolievich, Kiper Ruslan. "cadmium chloride". chemister.ru. Retrieved 2014-06-25.
  2. ^ a b c d e f g h i j k Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  3. ^ a b Seidell, Atherton; Linke, William F. (1919). Solubilities of Inorganic and Organic Compounds (2nd ed.). New York: D. Van Nostrand Company. p. 169.
  4. ^ a b c d "Cadmium Chloride - CdCl2". chem.uwimona.edu.jm. Mona, Jamaica: The University of the West Indies. Retrieved 2014-06-25.
  5. ^ a b c Sigma-Aldrich Co., Cadmium chloride. Retrieved on 2014-05-23.
  6. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0087". National Institute for Occupational Safety and Health (NIOSH).
  7. ^ "Cadmium compounds (as Cd)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  8. ^ a b N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
  9. ^ A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
  10. ^ a b H. Leligny; J. C. Monier (1974). "Structure cristalline de CdCl2.H2O" [Crystal structure of CdCl2.H2O]. Acta Crystallographica B (in French). 30 (2): 305–309. doi:10.1107/S056774087400272X.
  11. ^ a b H. Leligny; J. C. Monier (1975). "Structure de CdCl2.2,5H2O" [Structure of CdCl2.2,5H2O]. Acta Crystallographica B (in French). 31 (3): 728–732. doi:10.1107/S056774087500369X.
  12. ^ a b H. Leligny; J. C. Monier (1979). "Structure de dichlorure de cadmium tétrahydraté" [Structure of cadmium dichloride tetrahydrate]. Acta Crystallographica B (in French). 35 (3): 569–573. doi:10.1107/S0567740879004179.
  13. ^ F. Wagenknecht; R. Juza (1963). "Potassium cadmium chloride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. NY, NY: Academic Press. p. 1095.
  14. ^ a b c d Karl-Heinz Schulte-Schrepping; Magnus Piscator (2000). "Cadmium and Cadmium Compounds". Ullmann's Encyclopedia of Industrial Chemistry (6th ed.). p. 472. doi:10.1002/14356007.a04_499. ISBN 9783527306732.
  15. ^ F. Wagenknecht; R. Juza (1963). "Cadmium chloride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. NY, NY: Academic Press. pp. 1093–4.
  16. ^ J. March, Advanced Organic Chemistry, 4th ed., p. 723, Wiley, New York, 1992.

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