Iodine monochloride
Chemical compound
Iodine monochloride is an interhalogen compound with the formula ICl. It is a red-brown chemical compound that melts near room temperature. These characteristics are so similar to those of bromine that Justus von Liebig mistook ICl for bromine. Because of the difference in the electronegativity of iodine and chlorine, this molecule is highly polar and behaves as a source of I+. Discovered in 1814 by Gay-Lussac, iodine monochloride is the first interhalogen compound discovered.
01Preparation
Iodine monochloride is produced simply by combining the halogens in a 1:1 molar ratio, according to the equation
- I2 + Cl2 → 2 ICl
When chlorine gas is passed through iodine crystals, one observes the brown vapor of iodine monochloride. Dark brown iodine monochloride liquid is collected. Excess chlorine converts iodine monochloride into iodine trichloride in a reversible reaction:
- ICl + Cl2 ⇌ ICl3
02Polymorphs
ICl has two polymorphs; α-ICl, which exists as black needles (red by transmitted light) with a melting point of 27.2 °C, and β-ICl, which exists as black platelets (red-brown by transmitted light) with a melting point 13.9 °C.
In the crystal structures of both polymorphs the molecules are arranged in zigzag chains. β-ICl is monoclinic with the space group P21/c.
03Reactions and uses
Iodine monochloride is soluble in acids such as HF and HCl but reacts with pure water to form HCl, HI, iodine, and iodic acid:
- 2 ICl + 2 H2O → 2 HCl + 2 HI + O2
- 4 ICl + 2 H2O → 4 HCl + 2 I2 + O2
- 5 ICl + 3 H2O → 5 HCl + HIO3 + 2 I2
ICl is a useful reagent in organic synthesis. It is used as a source of electrophilic iodine in the synthesis of certain aromatic iodides. It also cleaves C-Si bonds.
ICl will also add to the double bond in alkenes to give chloro-iodo alkanes.
- RCH=CHR′ + ICl → RCH(I)-CH(Cl)R′
When such reactions are conducted in the presence of sodium azide, the iodo-azide RCH(I)-CH(N3)R′ is obtained.
The Wijs solution, iodine monochloride dissolved in acetic acid, is used to determine the iodine value of a substance.
It can also be used to prepare iodates, by reaction with a chlorate. Chlorine is released as a byproduct.
Iodine monochloride is a Lewis acid that forms 1:1 adducts with Lewis bases such as dimethylacetamide and benzene.
Sources and credits
This article is adapted from the Wikipedia article “Iodine monochloride”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Iodine monochloride1.jpg by W. Oelen, CC BY-SA 3.0
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