Iron(II) chloride

Iron(II) chloride
IUPAC name Iron(II) chloride Iron dichloride
Other names Ferrous chloride, Rokühnite
Identifiers
CAS number	7758-94-3 Y,  16399-77-2 (dihydrate) 13478-10-9 (tetrahydrate)
PubChem	24458
ChemSpider	22866 Y
UNII	S3Y25PHP1W Y
ChEBI	CHEBI:30812 Y
RTECS number	NO5400000
Jmol-3D images	Image 1
SMILES Cl[Fe]Cl
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
Properties
Molecular 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) 2.30 g/cm3 (dihydrate) 1.39 g/cm3 (tetrahydrate)
Melting point	677 °C (anhydrous) 120 °C (dihydrate) 105 °C (tetrahydrate) [1]
Boiling point	1023 °C (anhydrous)
Solubility in water	64.4 g/100 mL (10°C), 68.5 g/100mL (20°C), 105.7 g/100 mL (100°C)
Solubility in THF	soluble
Structure
Crystal structure	Monoclinic
Coordination geometry	octahedral at Fe
Hazards
NFPA 704	0 3 0
Related compounds
Other anions	Iron(II) fluoride Iron(II) bromide Iron(II) iodide
Other cations	Cobalt(II) chloride Manganese(II) chloride Copper(II) chloride
Y chloride (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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, and is usually obtained as an off-white solid. 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 also soluble in water; aqueous solutions of FeCl₂ are yellow.

Production

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 byproduct from titanium production, since some titanium ores contain iron.^[2]

Laboratory preparation

Ferrous chloride is conveniently prepared by addition of iron powder to a solution of methanol and concentrated hydrochloric acid under an inert atmosphere. This reaction gives the methanol solvate, which upon heating in a vacuum at about 160 °C gives anhydrous FeCl₂.^[3] FeBr₂ and FeI₂ can be prepared analogously.

An alternative laboratory synthesis of FeCl₂ entails the reaction of FeCl₃ with chlorobenzene:^[4]

2 FeCl₃ + C₆H₅Cl → 2 FeCl₂ + C₆H₄Cl₂ + HCl

FeCl₂ prepared in this way exhibits convenient solubility in tetrahydrofuran, a common solvent for chemical reactions. In one of two classic syntheses of ferrocene, Wilkinson generated FeCl₂ by heating FeCl₃ with iron powder.^[5] Ferric chloride decomposes to ferrous chloride at high temperatures.

Reactions

FeCl₂ forms complexes with many ligands. It reacts with two molar equivalents of [(C₂H₅)₄N]Cl to give the salt [(C₂H₅)₄N]₂[FeCl₄]. Related compounds that can be prepared similarly include the [MnCl₄]²⁻, [MnBr₄]²⁻, [MnI₄]²⁻, [FeBr₄]²⁻, [CoCl₄]²⁻, [CoBr₄]²⁻, [NiCl₄]²⁻, and [CuCl₄]²⁻ salts.^[6]

Applications

Ferrous chloride has a variety of niche applications, but the related compounds ferrous sulfate and ferric chloride enjoy more applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a reducing flocculating agent in wastewater treatment, especially for wastes containing chromate. It is the precursor to hydrated iron(III) oxides that are magnetic pigments.^[2] Ferrous chloride is employed as a reducing agent in many organic synthesis reactions.

References

1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
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. ^ G. Winter; Thompson, D. W.; Loehe, J. R. (1973). "Iron(II) Halides". Inorg. Synth. 14: 99–104. doi:10.1002/9780470132456.ch20. 
4. ^ P. Kovacic and N. O. Brace (1960). "Iron(II) Chloride". Inorg. Synth. 6: 172. doi:10.1002/9780470132371.ch54. 
5. ^ G. Wilkinson (1963), "Ferrocene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0473 ; Coll. Vol. 4: 473 
6. ^ N. S. Gill, F. B. Taylor (1967). "Tetrahalo Complexes of Dipositive Metals in the First Transition Series". Inorg. Synth. 9: 136–142. doi:10.1002/9780470132401.ch37. 

See also

• Iron(III) chloride
• Iron(II) sulfate