![]() The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. The references in this article would be clearer with a different or consistent style of citation, footnoting, or external linking. ![]() 8Īlthough trivalent chromium is far less poisonous than hexavalent, chromium salts are generally considered highly toxic. The reaction is usually performed using two moles of CrCl 3 per mole of lithium aluminium hydride, although if aqueous acidic conditions are appropriate zinc and hydrochloric acid may be sufficient.Ĭhromium(III) chloride has also been used as a Lewis acid in organic reactions, for example to catalyse the nitroso Diels-Alder reaction. The hydrated chloride may be made by dissolving the metal in hydrochloric acid.Ĭhromium(III) chloride is used as the source of chromium for many inorganic compounds of chromium, for example dibenzenechromium(0), an analogue of ferrocene:Ī significant use of CrCl 3 in organic synthesis is for the in situ preparation of chromium(II) chloride, a popular reagent for (A) reduction of alkyl halides and for (B) the synthesis of ( E)-alkenyl halides. It may also be prepared from the hexahydrate, by heating with thionyl chloride which reacts with the water of hydration. With molten alkali metal chlorides such as potassium chloride, CrCl 3 gives octahedral complexes of the type K 3CrCl 6, as well as K 3Cr 2Cl 9 which is also octahedral but where the two chromiums are linked via three chloride bridges.Īnhydrous chromium(III) chloride may be prepared from chromium metal and chlorine directly, or indirectly using chromium(III) oxide with carbon and chlorine at 800 ☌ :Ĭr 2O 3( s) + 3 C( s) + 3 Cl 2( g) → 2 CrCl 3( s) + 3 CO( g) If substitution reactions are performed in the presence of a trace of Cr 2+, then CrCl 3 can undergo substitution with ligands such as water (giving violet 3+) or pyridine: The most common form of CrCl 3 sold commercially is a dark green hexahydrate with the structure Cl.2H 2O, and like the anhydrous form it is also very inert towards substitution. This chromium(II) compound undergoes substitution easily, and it can exchange electrons with CrCl 3 via a chloride bridge, allowing all of the CrCl 3 to react quickly. One way of opening CrCl 3 up to substitution in solution is to reduce even a trace amount to CrCl 2, for example using zinc in hydrochloric acid. The low reactivity of the d 3 Cr 3+ ion can be explained using crystal field theory. However it is also a chloro complex which is quite inert to substitution, so in fact it is ordinarily quite unreactive. It reacts as a Lewis acid, forming stable chloro complexes such as 3-.Ĭhromium(III) chloride is a Lewis acid, classified as "hard" according to the Hard-Soft Acid-Base theory. When it does react it undergoes ligand substitution reactions to form other complexes of chromium(III). This inertness means that CrCl 3 is generally sluggish to react without the presence of a reducing agent. The common commercial form of the hydrate is the dark green complex shown in the picture, Cl.2H 2O, but two other forms are known, viz., pale green Cl 2.H 2O and violet Cl 3. However, in the presence of a trace of a reducing agent capable of reducing Cr 3+ to Cr 2+, the CrCl 3 dissolves rapidly to form soluble complexes containing hydrated Cr 3+ ions. ![]() Molybdenum(III) chloride Tungsten(III) chlorideĬhromium(II) chloride Chromium(IV) chlorideĮxcept where noted otherwise, data are given for materials in their standard state (at 25 ☌, 100 kPa) Infobox disclaimer and referencesĬhromium(III) chloride (also called chromic chloride) is a violet coloured solid with the formula CrCl 3.Īlthough it is ionic, the solid state structure is kinetically inert so that anhydrous CrCl 3 is surprisingly reluctant to dissolve in water. ![]() Chromium(III) chloride Chromium trichlorideĬhromium(III) fluoride Chromium(III) bromide Chromium(III) iodide
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