Iron(II) chloride, also known as ferrous chloride, is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

of formula FeCl₂. It is a

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl₂

crystallizes Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely de ...

from water as the greenish

tetrahydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was unders ...

, 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

Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

. 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.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.

Anhydrous FeCl₂

Ferrous chloride is prepared by addition of iron powder to a solution of

in methanol. This reaction gives the methanol solvate of the dichloride, which upon heating in a vacuum at about 160 °C converts to

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achi ...

FeCl₂. 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 Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

: :2 FeCl₃ + C₆H₅Cl → 2 FeCl₂ + C₆H₄Cl₂ + HCl In one of two classic syntheses of

ferrocene Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, ...

, Wilkinson generated FeCl₂ ''in situ'' by comproportionation of FeCl₃ with iron powder in

tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

(THF). Ferric chloride decomposes to ferrous chloride at high temperatures.

Hydrates

The dihydrate, FeCl₂(H₂O)₂, crystallizes from concentrated hydrochloric acid. The dihydrate is a

coordination polymer A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2 ...

. Each Fe center is coordinated to four doubly

bridging chloride ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually ...

s. The octahedron is completed by a pair of mutually trans

aquo ligand In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perch ...

Reactions

left, Tetra(pyridine)iron dichloride is prepared by treating ferrous chloride with pyridine. FeCl₂ and its hydrates form complexes with many ligands. For example, solutions of the hydrates react with two molar equivalents of Tetraethylammonium chloride, [(C₂H₅)₄N]Cl to give the salt C₂H₅)₄Nsub>2 eCl₄ The anhydrous FeCl₂, which is soluble in THF, is a standard precursor in organometallic synthesis. FeCl₂ is used to generate

NHC complex A transition metal carbene complex is an organometallic compound featuring a divalent organic ligand. The divalent organic ligand coordinated to the metal center is called a carbene. Carbene complexes for almost all transition metals have been rep ...

es in situ for

cross coupling reaction In organic chemistry, a cross-coupling reaction is a reaction where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = organic fragment, M ...

Applications

Unlike the related

ferrous sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hepta hydrate (''x'' = 7) but several values for x are kn ...

and

ferric chloride Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...

, ferrous chloride has few commercial applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a coagulation and

flocculation Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from ...

agent in

wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environm ...

, especially for wastes containing chromate or

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...

s. 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 chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

Natural occurrence

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

Production

Anhydrous FeCl₂

Hydrates

Reactions

Applications

Natural occurrence

References

See also

Production

Anhydrous FeCl2

Hydrates

Reactions

Applications

Natural occurrence

References

See also

Anhydrous FeCl₂