13478-10-9

light green or blue-green crystals

Iron(II) chloride tetrahydrate is used as a reducing agent in metallurgy, in pharmaceutical preparations, as a mordant in dyeing and in sewage treatment. Ferrous chloride has a kind of niche application. During the laboratory synthesis of iron complexes, ferrous chloride acts as a reducing flocculating agent in waste water treatment, particularly for wastes containing chromate. It is the precursor to hydrated iron(III) oxides that are magnetic pigments. Ferrous chloride is employed as a reducing agent in many organic synthesis reactions.

ChEBI: A hydrate that is the tetrahydrate form of iron dichloride.

A 550mL round-bottomed Pyrex flask is connected, via a glass tube fitted with a medium porosity sintered-glass disc, to a similar flask. To 240g of FeCl2.4H2O in the first flask is added conductivity water (200mL), 38% HCl (10mL), and pure electrolytic iron (8-10g). A stream of purified N2 gas is passed through the assembly, escaping through a mercury trap. The salt is dissolved by heating which is continued until complete reduction has occurred. By inverting the apparatus and filtering (under N2 pressure) through the sintered glass disc, unreacted iron is removed. After cooling and crystallisation, the unit is again inverted, and the crystals of ferrous chloride are filtered free from mother liquor by applied N2 pressure. Partial drying by overnight evacuation at room temperature gives a mixed hydrate which, on further evacuation on a water bath at 80o, loses water of hydration and absorbed HCl (with vigorous effervescence) to give a white powder of FeCl2.2H2O (see below). [Gayer & Wootner J Am Chem Soc 78 3944 1956, (2H2O) Gayer & Woontner Inorg Synth V 179 1957.]