Iron(II) chloride

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Iron(II) chloride
Iron(II)-chloride-xtal-sheet-3D-balls-A.png
Structure of anhydrous ferrous chloride (     Fe,      Cl)
FeCl2.png
hydrated ferrous chloride
Trans-FeCl2(H2O)4.png
structure of tetrahydrate
Names
IUPAC names
Iron(II) chloride
Iron dichloride
Other names
Ferrous chloride
Rokühnite
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.949
EC Number 231-843-4
RTECS number NO5400000
UNII
Properties
FeCl2
Molar mass 126.751 g/mol (anhydrous)
198.8102 g/mol (tetrahydrate)
Appearance Tan solid (anhydrous)
Pale green solid (di-tetrahydrate)
Density 3.16 g/cm3 (anhydrous)
2.39 g/cm3 (dihydrate)
1.93 g/cm3 (tetrahydrate)
Melting point 677 °C (1,251 °F; 950 K) (anhydrous)
120 °C (dihydrate)
105 °C (tetrahydrate)
Boiling point 1,023 °C (1,873 °F; 1,296 K) (anhydrous)
64.4 g/100 mL (10 °C),
68.5 g/100 mL (20 °C),
105.7 g/100 mL (100 °C)
Solubility in THF Soluble
log P −0.15
+14750·10−6 cm3/mol
Structure
Monoclinic
Octahedral at Fe
Pharmacology
B03AA05 (WHO)
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
3
0
US health exposure limits (NIOSH):
REL (Recommended)
TWA 1 mg/m3[1]
Related compounds
Other anions
Iron(II) fluoride
Iron(II) bromide
Iron(II) iodide
Other cations
Cobalt(II) chloride
Manganese(II) chloride
Copper(II) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

Production[edit]

Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated "spent acid," especially when the hydrochloric acid is not completely consumed:

Fe + 2 HCl → FeCl2 + H2

The spent acid requires treatment before its disposal. It is also a byproduct from titanium production, since some titanium ores contain iron.[2]

Laboratory preparation[edit]

Structure of "FeCl2(thf)x", Fe4Cl8(thf)6, illustrating both tetrahedral and octahedral coordination geometries.[3]

Anhydrous FeCl2[edit]

Ferrous chloride is prepared by addition of iron powder to a solution of hydrochloric acid in methanol. This reaction gives the methanol solvate of the dichloride, which upon heating in a vacuum at about 160 °C converts to anhydrous FeCl2.[4] The net reaction is shown:

Fe + 2 HCl → FeCl2 + H2

FeBr2 and FeI2 can be prepared analogously.

An alternative synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene:[5]

2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl

In one of two classic syntheses of ferrocene, Wilkinson generated FeCl2 in situ by conproportionation of FeCl3 with iron powder in THF.[6] Ferric chloride decomposes to ferrous chloride at high temperatures.

Hydrates[edit]

The dihydrate, FeCl2(H2O)2, crystallizes from concentrated hydrochloric acid.[7] The dihydrate is a coordination polymer. Each Fe center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands.[8]

Subunit of FeCl2(H2O)2 lattice.

Reactions[edit]

FeCl2 and its hydrates form complexes with many ligands. For example, solutions of the hydrates react with two molar equivalents of [(C2H5)4N]Cl to give the salt [(C2H5)4N]2[FeCl4].[9]

The anhydrous FeCl2, which is soluble in tetrahydrofuran (THF),[3] is a standard precursor in organometallic synthesis. FeCl2. FeCl2 is used to generate NHC complexes in situ for cross coupling reactions.[10]

Applications[edit]

Unlike the related ferrous sulfate and ferric chloride, ferrous chloride has few commercial applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a coagulation and flocculation agent in wastewater treatment, especially for wastes containing chromate or sulfides.[11] It is the precursor to hydrated iron(III) oxides that are magnetic pigments.[2] FeCl2 finds some use as a reagent in organic synthesis.[12]

References[edit]

  1. ^ "NIOSH Pocket Guide to Chemical Hazards #0346". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ a b Egon Wildermuth, Hans Stark, Gabriele Friedrich, Franz Ludwig Ebenhöch, Brigitte Kühborth, Jack Silver, Rafael Rituper “Iron Compounds” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Wienheim, 2005.
  3. ^ a b Cotton, F. A.; Luck, R. L.; Son, K.-A. (1991). "New polynuclear compounds of iron(II) chloride with oxygen donor ligands Part I. Fe4Cl8(THF)6: synthesis and a single crystal X-ray structure determination". Inorganica Chimica Acta. 179: 11–15. doi:10.1016/S0020-1693(00)85366-9. 
  4. ^ G. Winter; Thompson, D. W.; Loehe, J. R. (1973). "Iron(II) Halides". Inorg. Synth. Inorganic Syntheses. 14: 99–104. doi:10.1002/9780470132456.ch20. ISBN 9780470132456. 
  5. ^ P. Kovacic and N. O. Brace (1960). "Iron(II) Chloride". Inorg. Synth. Inorganic Syntheses. 6: 172–173. doi:10.1002/9780470132371.ch54. ISBN 9780470132371. 
  6. ^ G. Wilkinson (1963). "Ferrocene". Organic Syntheses. ; Collective Volume, 4, p. 473 
  7. ^ K. H.. Gayer; L. Woontner (1957). "Iron(II) Chloride 2-Hydrate". Inorg. Synth. Inorganic Syntheses. 5: 179–181. doi:10.1002/9780470132364.ch48. ISBN 9780470132364. 
  8. ^ Morosin, B.; Graeber, E. J. (1965). "Crystal structures of manganese(II) and iron(II) chloride dihydrate". Journal of Chemical Physics. 42 (3): 898–901. doi:10.1063/1.1696078. 
  9. ^ N. S. Gill, F. B. Taylor (1967). "Tetrahalo Complexes of Dipositive Metals in the First Transition Series". Inorg. Synth. Inorganic Syntheses. 9: 136–142. doi:10.1002/9780470132401.ch37. ISBN 9780470132401. 
  10. ^ Bi-Jie Li, Xi-Sha Zhang, Zhang-Jie Shi (2014). "Cross-Coupling of Alkenyl/Aryl Carboxylates with Grignard Reagents via Fe-Catalyzed C-O Bond Activation". Org. Synth. 91: 83–92. doi:10.15227/orgsyn.091.0083. 
  11. ^ Jameel, Pervez (1989). "The Use of Ferrous Chloride to Control Dissolved Sulfides in Interceptor Sewers". Journal (Water Pollution Control Federation). 61 (2): 230–236. JSTOR 25046917. 
  12. ^ Andrew D. White, David G. Hilmey (2009). "Iron(II) Chloride". Encyclopedia of Reagents for Organic Synthesis. Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.ri055.pub2. ISBN 978-0471936237. 

See also[edit]