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.Graf, R. "Chlorosulfonyl Isocyanate" Organic Syntheses, Collected Volume 5, pages 226ff. SO3 + ClCN → ClSO2NCO In this transformation, both the carbon and the nitrogen termini of CN are functionalized.
The structure of CSI is represented as . It consists of two electron-withdrawing components, the chlorosulfonyl group (SO2Cl) and the isocyanate group (). Because of its resulting electrophilicity, the use of CSI in chemical synthesis requires relatively inert solvents such as chlorocarbons, acetonitrile, and ethers.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.
Uses The molecule has two electrophilic sites, the carbon and the S(VI) center.D. N. Dhar, K. S. K. Murthy "Recent Advances in the Chemistry of Chlorosulfonyl Isocyanate" Synthesis 1986; pages 437-449.
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.Cremlyn, R. J. "An Introduction to Organosulfur Chemistry" John Wiley and Sons: Chichester (1996). Other reactions of CSI: Cycloaddition to alkynes to give 1,2,3-oxathiazine-2,2-dioxide-6-chlorides. Conversion of primary alcohols to carbamates.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 Conversion of carboxylic acids and the acid chlorides into nitriles. Preparation of N,N-disubstituted sulfamides, R2NSO2NH2 Preparation of Burgess reagent
Safety considerations CSI is toxic, corrosive and reacts violently with water.
Chemical properties Chlorosulfonyl isocyanate reacts with sodium monofluoride to form fluorosulfonyl isocyanate:
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