Methanesulfonyl Chloride
( \newcommand{\kernel}{\mathrm{null}\,}\)
Methanesulfonyl chloride or mesyl chloride (abbreviation: MsCl) is the compound obtained when the hydroxy group in the molecule of methanesulfonic acid is replaced with a chlorine atom.
Methanesulfonyl chloride is the reagent used to convert alcohols into alkyl mesylates.
eg:
see also p-toluenesulfonyl chloride