Chlorosulfonyl isocyanate

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

Additional recommended knowledge

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Preparation, structure, handling

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

SO₃ + ClCN → ClSO₂NCO

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]

Uses

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.

References

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