Iodine monochloride

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Iodine monochloride
Iodine monochloride Iodine monochloride
Systematic name iodine(I) chloride
Other names iodine chloride
Molecular formula ICl
Molar mass 162.35 g/mol
Appearance red to brown liquid
CAS number [7790-99-0]
Density and phase 3.10 g/cm3
Solubility in water hydrolysis
Other solvents carbon disulfide
acetic acid
Melting point 27°C (α-form)
Boiling point 97.4°C (370.6 K)
Crystal structure  ?
Dipole moment  ? D
MSDS External MSDS
Main hazards corrosive
NFPA 704
R/S statement R: ?
S: ?
RTECS number  ?
Supplementary data page
Structure and
n, É√r, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
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, 100 kPa)
Infobox disclaimer and references

Iodine monochloride is the compound with the formula ICl. This red brown compound melts just 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+.”

Preparation of iodine monochloride entails simply combining the halogens in a 1:1 molar ratio, according to this 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


Polymorphy is the phenomenon where a solid exists in two or more different crystalline forms. ICl has two polymorphs, α-ICl which are black needles (red by transmitted light) with a melting point of 27.2 °C and β-ICl which are black platelets (red-brown by transmitted light) with a melting point 13.9 °C.[1]


ICl is a useful reagent in organic synthesis.[1] It is used as a source of electrophilic iodine to synthesise certain aromatic iodides.[2] 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, one obtains the iodo-azide, RCH(I)-CH(N3)R’.[3]


  1. 1.0 1.1 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. Wallingford, V. H.; Krüger, P. A. "5-Iodo-anthranilic Acid" Organic Syntheses, Collected Volume 2, p.349 (1943).
  3. Padwa, A.; Blacklock, T.; Tremper, A. "3-Phenyl-2H-Azirine-2-carboxaldehyde" Organic Syntheses, Collected Volume 6, p.893 (1988).

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