Copper(I) iodide is the
chemical compoundA 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 CuI; it is also known as
cuprous iodide. It is useful in a variety of applications ranging from
organic synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
to
cloud seedingCloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...
.
Copper(I) iodide is white, but samples are often tan or even, when found in nature as rare mineral marshite, reddish brown, but such color is due to impurities. It is common for iodides to become discolored because of the easy oxidation of the iodide anion to iodine.
Copper(I) iodide, like most "binary" (containing only two elements) metal halides, is an inorganic polymer.
Copper(I) iodide is the
chemical compoundA 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 CuI; it is also known as
cuprous iodide. It is useful in a variety of applications ranging from
organic synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
to
cloud seedingCloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...
.
Copper(I) iodide is white, but samples are often tan or even, when found in nature as rare mineral marshite, reddish brown, but such color is due to impurities. It is common for iodides to become discolored because of the easy oxidation of the iodide anion to iodine.
Structure
Copper(I) iodide, like most "binary" (containing only two elements) metal halides, is an inorganic polymer. It has a rich
phase diagramA phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions at which thermodynamically-distinct phases can occur at equilibrium...
, meaning that it exists in several crystalline forms. It adopts a zinc blende structure below 390 °C (ɣ-CuI), a
wurtziteWurtzite is a zinc iron sulfide mineral a less frequently encountered mineral form of sphalerite.Its crystal structure is called the wurtzite crystal structure, to which it lends its name...
structure between 390 and 440 °C (β-CuI), and a rock salt structure above 440 °C (α-CuI). The ions are tetrahedrally coordinated when in the zinc blende or the
wurtziteWurtzite is a zinc iron sulfide mineral a less frequently encountered mineral form of sphalerite.Its crystal structure is called the wurtzite crystal structure, to which it lends its name...
structure, with a Cu-I distance of 2.338 Å.
Copper(I) bromideCopper bromide is the chemical compound with the formula CuBr. This diamagnetic solid adopts a polymeric structure akin to that for zinc sulfide. The compound is widely used in the synthesis of organic compounds....
and
copper(I) chlorideCopper chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl.This colorless solid is a versatile precursor to other copper compounds, including some of commercial significance. It occurs naturally as the rare mineral nantokite. Unlike other first-row...
also transform from the zinc blende structure to the wurtzite structure at 405 and 435 °C, respectively. Therefore, the longer the copper - halide bond length, the lower the temperature needs to be to change the structure from the zinc blende structure to the wurtzite structure. The interatomic distances in copper(I) bromide and copper(I) chloride are 2.173 and 2.051 Å, respectively.
Preparation
In the laboratory, copper(I) iodide is prepared by simply mixing an aqueous solutions of sodium or potassium iodide and a soluble copper(II) salt such copper sulfate.
- 2Cu2+ + 4I− → 2CuI2
The CuI
2 immediately decomposes to iodine and insoluble copper(I) iodide, releasing I
2.
- 2 CuI2 → 2 CuI + I2
This reaction has been employed as a means of assaying copper(II) samples, since the evolved I
2 can be analyzed by redox titration. Copper(I) iodide can also be prepared by heating iodine and copper in concentrated hydriodic acid, HI.
CuI is poorly soluble in water (0.00042 g/L at 25 °C), but it dissolves in the presence of NaI or KI to give the linear anion [CuI
2]
−. Dilution of such solutions with water reprecipitates CuI. This dissolution-precipitation process is employed to purify CuI, affording colorless samples.
Uses
CuI has several uses:
- CuI is used as a reagent in organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. In combination with 1,2- or 1,3 diamine ligands, CuI catalyzes the conversion of aryl, heteroaryl, and vinyl bromides into the corresponding iodides. NaI is the typical iodide source and dioxane is a typical solvent. Aryl halides are used to form carbon-carbon and carbon-heteroatom bonds in process such as the HeckThe Heck reaction is the chemical reaction of an unsaturated halide with an alkene and a strong base and palladium catalyst to form a substituted alkene. It is named after the American chemist Richard F. Heck.The reaction is performed in the presence of an organopalladium catalyst...
, StilleThe Stille reaction is a chemical reaction coupling an organotin compound with an sp
2-hybridized organic halide catalyzed by palladium. The reaction is widely used in organic synthesis....
, SuzukiThe Suzuki reaction is the organic reaction of an aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium complex. It is widely used to synthesize poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl bromides...
, and UllmanThe Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides with copper. The reaction is named after Fritz Ullmann....
type coupling reactions. Aryl iodides, however, are more reactive than the corresponding aryl bromides or aryl chlorides. 2-Bromo-1-octen-3-ol and 1-nonyne are coupled when combined with dichlorobis(triphenylphosphine)palladium(II), CuI, and diethylamineDiethylamine is a secondary amine with the molecular structure CH3CH2NHCH2CH3. It is a flammable, strongly alkaline liquid. It is miscible with water and ethanol. As a liquid it has a dark brown color due to impurities, however when distilled it is...
to form 7-methylene-8-hexadecyn-6-ol.
- CuI is used in cloud seeding
Cloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...
, altering the amount or type of precipitation of a cloud, or their structure by dispersing substances into the atmosphere which increase water's ability to form droplets or crystals. CuI provides a sphere for moisture in the cloud to condense around, causing precipitation to increase and cloud density to decrease.
- The structural properties of CuI allow CuI to stabilize heat in nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides and first produced on February 28, 1935 by Wallace Carothers at DuPont...
in commercial and residential carpet industries, automotive engine accessories, and other markets where durability and weight are a factor.
- CuI is used as a source of dietary iodine in table salt and animal feed.
Sources
- Macintyre, J. Dictionary of Inorganic Compounds. Chapman and Hall, London, (1992). Vol. 3, p.3103.
External links