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.
Structure of anhydrous ferrous chloride (Fe, Cl)
3D model (JSmol)
CompTox Dashboard (EPA)
|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|
|Octahedral at Fe|
|NFPA 704 (fire diamond)|
|NIOSH (US health exposure limits):|
|TWA 1 mg/m3|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 spent acid requires treatment if it is disposed. Ferrous chloride is used in the manufacturing of ferric chloride. Ferrous chloride can also be used to regenerate hydrochloric acid. It is also a byproduct from titanium production, since some titanium ores contain iron.
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. The net reaction is shown:
- Fe + 2 HCl → FeCl2 + H2
FeBr2 and FeI2 can be prepared analogously.
- 2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl
In one of two classic syntheses of ferrocene, Wilkinson generated FeCl2 in situ by comproportionation of FeCl3 with iron powder in THF. Ferric chloride decomposes to ferrous chloride at high temperatures.
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].
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. 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. FeCl2 finds some use as a reagent in organic synthesis.
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