Iron(II) chloride

Anhydrous

Tetrahydrate

Structure of anhydrous ferrous chloride ( Fe, Cl)

structure of tetrahydrate

Names

IUPAC names

Iron(II) chloride
Iron dichloride

Other names

Ferrous chloride
Rokühnite

Identifiers

CAS Number

7758-94-3^Y
16399-77-2 (dihydrate)^N
13478-10-9 (tetrahydrate)^N

3D model (JSmol)

Interactive image

ChEBI

CHEBI:30812^Y

ChemSpider

22866^Y

ECHA InfoCard

100.028.949

EC Number

231-843-4

PubChem CID

24458

RTECS number

NO5400000

UNII

S3Y25PHP1W^Y

CompTox Dashboard (EPA)

DTXSID9029695

InChI

InChI=1S/2ClH.Fe/h2*1H;/q;;+2/p-2^Y
Key: NMCUIPGRVMDVDB-UHFFFAOYSA-L^Y
InChI=1/2ClH.Fe/h2*1H;/q;;+2/p-2
Key: NMCUIPGRVMDVDB-NUQVWONBAL

SMILES

Cl[Fe]Cl

Properties

Chemical formula

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)

Solubility in water

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

Magnetic susceptibility (χ)

+14750·10⁻⁶ cm³/mol

Structure

Crystal structure

Monoclinic

Coordination geometry

Octahedral at Fe

Pharmacology

ATC code

B03AA05 (WHO)

Hazards

NFPA 704 (fire diamond)

NIOSH (US health exposure limits):

REL (Recommended)

TWA 1 mg/m³^[1]

Safety data sheet (SDS)

Iron (II) chloride MSDS

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).

N verify (what is ^YN ?)

Infobox references

Chemical compound

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

Structure of "FeCl₂(thf)_x", Fe₄Cl₈(thf)₆, illustrating both tetrahedral and octahedral coordination geometries.^[2]

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

Fe + 2 HCl → FeCl₂ + H₂

The production of ferric chloride involves the use of ferrous chloride. Ferrous chloride is also a byproduct from the production of titanium, since some titanium ores contain iron.^[3]

Anhydrous FeCl₂

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

For the preparation of ferrocene ferrous chloride is generated in situ by comproportionation of FeCl₃ with iron powder in tetrahydrofuran (THF).^[6] Ferric chloride decomposes to ferrous chloride at high temperatures.

Hydrates

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]

Reactions

Tetra(pyridine)iron dichloride is prepared by treating ferrous chloride with pyridine.^[9]

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].^[10]

The anhydrous FeCl₂, which is soluble in THF,^[2] is a standard precursor in organometallic synthesis. FeCl₂ is used to generate NHC complexes in situ for cross coupling reactions.^[11]

Applications

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.^[12] It is used for odor control in wastewater treatment. It is used as a precursor to make various grades of hematite that can be used in a variety of pigments. It is the precursor to hydrated iron(III) oxides that are magnetic pigments.^[3] FeCl₂ finds some use as a reagent in organic synthesis.^[13]

Natural occurrence

Lawrencite, (Fe,Ni)Cl₂, is the natural counterpart, and a typically (though rarely occurring) meteoritic mineral.^[14] The natural form of the dihydrate is rokühnite - a very rare mineral.^[15] Related, but more complex (in particular, basic or hydrated) minerals are hibbingite, droninoite and kuliginite.

References

^ NIOSH Pocket Guide to Chemical Hazards. "#0346". National Institute for Occupational Safety and Health (NIOSH).
^ ^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.
^ ^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.
^ G. Winter; Thompson, D. W.; Loehe, J. R. (1973). "Iron(II) Halides". Inorganic Syntheses. Vol. 14. pp. 99–104. doi:10.1002/9780470132456.ch20. ISBN 978-0-470-13245-6. {{cite book}}: |journal= ignored (help)
^ P. Kovacic and N. O. Brace (1960). "Iron(II) Chloride". Inorganic Syntheses. Vol. 6. pp. 172–173. doi:10.1002/9780470132371.ch54. ISBN 978-0-470-13237-1. {{cite book}}: |journal= ignored (help)
^ Wilkinson, G. (1956). "Ferrocene". Organic Syntheses. 36: 31. doi:10.15227/orgsyn.036.0031.
^ K. H.. Gayer; L. Woontner (1957). "Iron(II) Chloride 2‐Hydrate". Inorganic Syntheses. Vol. 5. pp. 179–181. doi:10.1002/9780470132364.ch48. ISBN 978-0-470-13236-4. {{cite book}}: |journal= ignored (help)
^ Morosin, B.; Graeber, E. J. (1965). "Crystal structures of manganese(II) and iron(II) chloride dihydrate". Journal of Chemical Physics. 42 (3): 898–901. Bibcode:1965JChPh..42..898M. doi:10.1063/1.1696078.
^ Baudisch, Oskar; Hartung, Walter H. (1939). "Tetrapyridino-Ferrous Chloride (Yellow Salt)". Inorganic Syntheses. Vol. 1. pp. 184–185. doi:10.1002/9780470132326.ch64. ISBN 978-0-470-13232-6.
^ N. S. Gill, F. B. Taylor (1967). "Tetrahalo Complexes of Dipositive Metals in the First Transition Series". Inorganic Syntheses. Vol. 9. pp. 136–142. doi:10.1002/9780470132401.ch37. ISBN 978-0-470-13240-1. {{cite book}}: |journal= ignored (help)
^ 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.
^ 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.
^ Andrew D. White; David G. Hilmey (2009). "Iron(II) Chloride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.ri055.pub2. ISBN 978-0-471-93623-7.
^ "Lawrencite".
^ "Rokühnite".