Iodine monochloride

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Iodine monochloride
I-Cl bond length = 232.07 pm Space-filling model
A sample of Iodine monochloride reagent
CAS number 7790-99-0 YesY
PubChem 24640
ChemSpider 23042 YesY
EC number 232-236-7
UN number 1792
MeSH Iodine-monochloride
Jmol-3D images Image 1
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
alcohol, ether, HCl
MSDS External MSDS
Main hazards corrosive
Related compounds
Related interhalogen compounds Chlorine monofluoride
Bromine monochloride
Iodine monobromide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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+.

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 is in equilibrium with ICl3


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]


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.


  1. ^ a b Brisbois, R. G.; Wanke, R. A.; Stubbs, K. A.; Stick, R. V. "Iodine Monochloride" Encyclopedia of Reagents for Organic Synthesis, 2004 John Wiley & Sons. doi:10.1002/047084289X.ri014
  2. ^ Carpenter, G. B.; Richards, S. M. (1 April 1962). "The crystal structure of β-iodine monochloride". Acta Crystallographica 15 (4): 360–364. doi:10.1107/S0365110X62000882. 
  3. ^ Wallingford, V. H.; Krüger, P. A. (1943), "5-Iodo-anthranilic Acid", Org. Synth. ; Coll. Vol. 2: 349 
  4. ^ Padwa, A.; Blacklock, T.; Tremper, A., "3-Phenyl-2H-Azirine-2-carboxaldehyde", Org. Synth. ; Coll. Vol. 6: 893