Iodine monochloride

Iodine monochloride
Preferred IUPAC name Iodine monochloride Iodine(I) chloride
Systematic name Chloroiodane
Other names Iodine chloride
Identifiers
CAS number	7790-99-0 Y
PubChem	24640
ChemSpider	23042 Y
EC number	232-236-7
UN number	1792
MeSH	Iodine-monochloride
Jmol-3D images	Image 1
SMILES ClI
InChI InChI=1S/ClI/c1-2 Y Key: QZRGKCOWNLSUDK-UHFFFAOYSA-N Y InChI=1S/ClI/c1-2 Key: QZRGKCOWNLSUDK-UHFFFAOYSA-N InChI=1/ClI/c1-2 Key: QZRGKCOWNLSUDK-UHFFFAOYAO
Properties
Molecular formula	ICl
Molar mass	162.35 g/mol
Appearance	red to brown liquid black crystals
Density	3.10 g/cm3
Melting point	27.2°C (α-form) 13.9 °C (β-form)
Boiling point	97.4°C (370.6 K)
Solubility in water	hydrolysis
Solubility	soluble in CS2 acetic acid pyridine alcohol, ether, HCl
Hazards
MSDS	External MSDS
Main hazards	corrosive
Related compounds
Related interhalogen compounds	Chlorine monofluoride Bromine monochloride Iodine monobromide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Iodine monochloride is an interhalogen compound with the formula ICl. It is a red-brown compound that melts near room temperature. Because of the difference in the electronegativity of iodine and chlorine, ICl is highly polar and behaves as a source of I⁺. Owing to the similarity of the properties of the compound with bromine (red-brown liquid at room temperature), its synthesis led early researchers to believe that the reaction between the heaviest and lightest of a 'triad' of elements (three elements with similar chemical properties, now found in the same group of the modern periodic table) would produce the central element of the triad, the so-named 'Law of Averages'.

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

Polymorphs

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.^[1]

In the crystal structures of both polymorphs the molecules are arraigned in zig-zag chains. β-ICl is monoclinic with the space group P2₁/c.^[2]

Uses

ICl is a useful reagent in organic synthesis.^[1] It is used as a source of electrophilic iodine in the synthesis of certain aromatic iodides.^[3] 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.^[4]

This solution, which is iodine monochloride dissolved in acetic acid, is used to determine the iodine value of a substance.

References