Chromyl chloride is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula CrO₂Cl₂. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...

compounds. It is the dichloride of

chromic acid Chromic acid is a chemical compound with the chemical formula . It is also a jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide. The term "chromic ...

Preparation

Chromyl chloride can be prepared by the reaction of

potassium chromate Potassium chromate is the inorganic compound with the formula Potassium, K2Chromate ion, CrO4. This yellow solid is the potassium salt of the Chromate ion, chromate anion. It is a common laboratory chemical, whereas sodium chromate is important ...

or potassium dichromate with

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

in the presence of concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

, followed by

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

. :K₂Cr₂O₇ + 6 HCl → 2 CrO₂Cl₂ + 2 KCl + 3 H₂O The sulfuric acid serves as a dehydration agent. It can also be prepared directly by exposing

chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula . It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid ...

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 achie ...

hydrogen chloride gas. :CrO₃ + 2 HCl ⇌ CrO₂Cl₂ + H₂O

Usage

Test for the presence of chlorides

The chromyl chloride test involves heating a sample suspected to contain chlorides with potassium dichromate and concentrated

. If a chloride is present then chromyl chloride forms which is indicated by the evolution of red smoke. No similar compound is formed in the presence of

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...

, bromide, iodide, or

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

, making this test specific to chlorides.

Reagent for oxidation of alkenes

Chromyl chloride oxidizes internal

alkenes In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

to alpha-chloroketones or related derivatives. It will also attack benzylic

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated a ...

s to give aldehydes via the Étard reaction. Dichloromethane is a suitable solvent for these reactions.

Others

CrO₂Cl₂ can also be used to test for the absence of

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

ions.

Safety considerations

Chromyl chloride is severely corrosive and easily burns the skin and eyes. It is a probable human carcinogen.

References

External links

CDC - NIOSH Pocket Guide to Chemical Hazards - Chromyl Chloride
{{DEFAULTSORT:Chromyl Chloride Chromium(VI) compounds Chromium–halogen compounds Oxychlorides Oxidizing agents Carcinogens Chromium–oxygen compounds