Chlorosulfonyl isocyanate

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Chlorosulfonyl isocyanate
Chlorosulfonyl isocyanate
Chlorosulfonyl isocyanate
IUPAC name
Chlorosulfonyl isocyanate
Other names
N-Carbonylsulfamyl chloride
Chloropyrosulfonyl isocyanate
Sulfuryl chloride isocyanate
3D model (JSmol)
ECHA InfoCard 100.013.378
Molar mass 141.53 g/mol
Appearance colorless liquid
Density 1.626 g/cm3
Melting point −44 °C (−47 °F; 229 K)
Boiling point 107 °C (225 °F; 380 K)
Solubility in other solvents Chlorocarbons
tetrahedral at S
Main hazards toxic, corrosive, flammable,
reacts violently with water
Safety data sheet "External MSDS"
R-phrases (outdated) R14 R20 R24/25 R29 R34 R42/43[1]
S-phrases (outdated) (S1/2) S8 S24 S26 S30 S36/37/39 S38 S45 [1]
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Related compounds
Related compounds
Thionyl chloride
Cyanogen bromide
Phosphoryl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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

Preparation, structure, handling[edit]

CSI is prepared by treating cyanogen chloride with sulfur trioxide, the product being distilled directly from the reaction mixture.[2]


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.[3]


The molecule has two electrophilic sites, the carbon and the S(VI) center.[4]

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.[5] Other reactions of CSI:

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

Safety considerations[edit]

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


  1. ^ a b
  2. ^ Graf, R. "Chlorosulfonyl Isocyanate" Organic Syntheses, Collected Volume 5, pages 226ff.
  3. ^ 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.
  4. ^ D. N. Dhar, K. S. K. Murthy "Recent Advances in the Chemistry of Chlorosulfonyl Isocyanate" Synthesis 1986; pages 437-449.
  5. ^ Cremlyn, R. J. “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0-471-95512-4
  6. ^ 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