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.

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.

The SO2Cl group can be removed simply by hydrolysis, leaving the secondary amide.