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Chlorosulfonyl isocyanate

Chlorosulfonyl isocyanate
IUPAC name Chlorosulfonyl isocyanate
Other names N-Carbonylsulfamyl chloride
Isocyanic acid, anhydride
chloropyrosulfonyl isocyanate
CAS number 1189-71-5
Molecular formula CNClO3S
Molar mass 141.53 g/mol
Appearance colorless liquid
Density 1.626 g/cm3
Melting point

-44 °C

Boiling point

107 °C

Solubility in water decomp.
Solubility in other solvents Chlorocarbons
Refractive index (nD) 1.447
Molecular shape tetrahedral at S
Main hazards toxic, corrosive
hydrolyzes violently
Related Compounds
Related compounds SOCl2
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Chlorosulfonyl isocyanate is the chemical compound ClSO2NCO, known as CSI. This compound is a versatile reagent in organic synthesis.


Preparation, structure, handling

CSI is prepared by treating cyanogen chloride with sulfur trioxide, the product being distilled directly from the reaction mixture.[1]


In this transformation, both the carbon and the nitrogen termini of CN are functionalized.

The structure of CSI is represented as ClS(O)2-N=C=O. It consists of two electron-withdrawing components, the chlorosulfonyl group (SO2Cl) and the isocyanate group (-N=C=O). Because of its resulting electrophilicity, the use of CSI in chemical synthesis requires relatively inert solvents such as chlorocarbons, acetonitrile, and ethers.[2]


The molecule has two electrophilic sites, the carbon and the S(VI) center.[3]

CSI has been employed for the preparation of β-lactams, some of which are medicinally important. Thus, alkenes undergo a[2+2]-cycloaddition to give the sulfonamide. The SO2Cl group can be removed simply by hydrolysis, leaving the secondary amide.[4] Other reactions of CSI:

  • Cycloaddition to alkynes to give 1,2,3-oxathiazine-2,2-dioxide-6-chlorides.
  • Conversion of primary alcohols to urethanes.[5]
  • Conversion of carboxylic acids and the acid chlorides into nitriles.
  • Preparation of N,N-disubstituted sulfamides, R2NSO2NH2

Safety considerations

CSI is toxic, corrosive and reacts violently with water. It cannot be stored in glass-stoppered flasks, requiring instead polyethylene bottles.


  1. ^ Graf, R. "Chlorosulfonyl Isocyanate" Organic Syntheses, Collected Volume 5, pages 226ff.
  2. ^ Miller, M. J.; Ghosh, M.; Guzzo, P. R.; Vogt, P. F.; Hu, J.; Filzen, G. F.; Geyer, A. G. "Chlorosulfonyl Isocyanate" in "Encyclopedia of Reagents for Organic Synthesis" 2005 John Wiley & Sons: New York.
  3. ^ D. N. Dhar, K. S. K. Murthy "Recent Advances in the Chemistry of Chlorosulfonyl Isocyanate" Synthesis 1986; pages 437-449.
  4. ^ Cremlyn, R. J. “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0-471-95512-4
  5. ^ Burgess, E. M.; Penton, Jr., H. R.; Taylor, E. A.; Williams, W. M. "Conversion of Primary Alcohols to Urethanes via the Inner Salt of Triethylammonium Hydroxide: Methyl (Carboxylsulfamoyl) Triethylammonium Hydroxide Methyl n-Hexylcarbamate" Organic Syntheses, Coll. Vol. 6, p.788
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Chlorosulfonyl_isocyanate". A list of authors is available in Wikipedia.
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