Development of a Process for the Preparation of Chloromethyl Chlorosulfate

A new and efficient synthesis of chloromethyl chlorosulfate (CMCS) from chloroiodomethane and chlorosulfonic acid is described. This process leverages a chlorosulfonic acid-mediated iodide oxidation to drive the equilibrating displacement process to full conversion. The resulting iodine byproduct is further oxidized and removed as iodate, to prevent iodide-induced decomposition of CMCS. This new process provides an efficient and scalable protocol for the preparation of CMCS in 92% solution yield and high purity (>99 GC area %).