Methanesulfonate

Methanesulfonate, also known as mesylate, designates the methanesulfonate anion CH3SO3− or the related esters and salts derived from methanesulfonic acid (CH3SO3H). In common usage, mesylate refers to sulfonate esters formed when an alcohol is treated with methanesulfonyl chloride (MsCl) in the presence of a base, yielding a compound of the form R‑O‑SO2CH3 and a chloride salt byproduct. The methanesulfonate anion also forms salts with metal cations such as sodium and potassium (e.g., sodium methanesulfonate NaCH3SO3). These salts are typically highly soluble in water.

Chemically, the methanesulfonate group is a sulfonate with a strongly withdrawing sulfonyl moiety. Methanesulfonic acid is a strong, non-volatile acid. Mesylate esters are among the best leaving groups available for nucleophilic substitution, which makes them widely used to convert alcohols into reactive mesylates, enabling SN2 reactions with halides, cyanide, thiolates, amines, and other nucleophiles. Mesylates can also serve as protecting-group strategies and as intermediates in the synthesis of pharmaceuticals.

Safety and handling: Methanesulfonyl chloride, the typical reagent for preparing mesylates, is corrosive and lachrymatory. Methanesulfonate salts are generally stable solids but should be handled with standard chemical-safety practices to avoid irritation. The term mesylate is often used interchangeably to describe the anion, the esters, or the salts derived from methanesulfonic acid.

See also: tosylate, triflate, sulfonate esters.