Chlorosulfonyl isocyanate
# Chlorosulfonyl isocyanate

Chlorosulfonyl isocyanate is the chemical compound $ClSO_2NCO,$ 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.

       $SO_3$ + ClCN → $ClSO_2NCO$

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 $(SO_2Cl)$ 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.

## Uses

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

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 $SO_2Cl$ group can be removed simply by hydrolysis, leaving the secondary amide. Other reactions of CSI:

* Cycloaddition to alkynes to give 1,2,3-oxathiazine-2,2-dioxide-6-chlorides.
* Conversion of primary alcohols to carbamates.
* Conversion of carboxylic acids and the acid chlorides into nitriles.
* Preparation of N,N-disubstituted sulfamides, $R_2NSO_2NH_2$
* Preparation of Burgess reagent

## Safety considerations

CSI is toxic, corrosive and reacts violently with water.

