Chromium(II) chloride
Encyclopedia
Chromium chloride is the chemical compound
with the formula
Cr
Cl
2. This white, crystalline solid is used for the synthesis of other chromium complexes. CrCl2 is hygroscopic. It dissolves in water to give bright blue solutions that are easily oxidized by air to give Cr(III)-containing products. CrCl2 crystallizes with the calcium chloride
structure, an orthorhombically distorted variant of that of rutile
.
with hydrogen
at 500 °C:
Small scale preparations can use LiAlH4, or related reagents, to reduce CrCl3
Commonly, it is generated by reduction of CrCl3 with zinc.
The reduction potential
for Cr3+ + e– ⇄ Cr2+ is −0.41. The reduction potential for water in acidic conditions is +0.00, making the reaction occur easily. The reaction in basic environments is:
This reaction forms a precipitate of chromium(II) oxide
.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
Cr
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
Cl
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
2. This white, crystalline solid is used for the synthesis of other chromium complexes. CrCl2 is hygroscopic. It dissolves in water to give bright blue solutions that are easily oxidized by air to give Cr(III)-containing products. CrCl2 crystallizes with the calcium chloride
Calcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
structure, an orthorhombically distorted variant of that of rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
.
Synthesis
CrCl2 is produced by reducing chromium(III) chlorideChromium(III) chloride
Chromium chloride is a violet coloured solid with the formula CrCl3. The most common form of CrCl3 sold commercially is a dark green hexahydrate with the formula [CrCl24]Cl.2H2O. Two other hydrates are known, pale green [CrCl5]Cl2.H2O and violet [Cr6]Cl3...
with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
at 500 °C:
- 2 CrCl3 + H2 → 2 CrCl2 + 2 HCl
Small scale preparations can use LiAlH4, or related reagents, to reduce CrCl3
- 4 CrCl3 + LiAlH4 → 4 CrCl2 + LiCl + AlCl3 + 2 H2
Commonly, it is generated by reduction of CrCl3 with zinc.
- 2 CrCl3 + Zn → 2 CrCl2 + ZnCl2
Reactions
Chromium(II) chloride reacts with any small amount of acid in the water to form hydrogen gas:- 3 CrCl2 + H2O → 2 CrCl3 + CrO + H2
The reduction potential
Reduction potential
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts , or millivolts...
for Cr3+ + e– ⇄ Cr2+ is −0.41. The reduction potential for water in acidic conditions is +0.00, making the reaction occur easily. The reaction in basic environments is:
- CrCl2 + 2 OH– → Cr(OH)2 + 2 Cl–
This reaction forms a precipitate of chromium(II) oxide
Chromium(II) oxide
Chromium oxide is an inorganic compound composed of chromium and oxygen. It is a black powder that crystallises in the rock salt structure.Hypophosphites may reduce chromium oxide to chromium oxide:It is readily oxidized by the atmosphere....
.
Uses
Chromium(II) chloride is used as precursor to other inorganic and organometallic chromium complexes. Alkyl halides and nitroaromatics are reduced by CrCl2. The moderate electronegativity of chromium and the range of substrates that CrCl2 can accommodate make organochromium reagents very synthetically versatile. It is a reagent in the Nozaki-Hiyama-Kishi reaction.External links
- http://www.osha.gov/SLTC/healthguidelines/chromium2/recognition.html