Methanesulfonyl chloride, also known as mesyl chloride or methane sulfonic acid chloride, is an organic compound with the chemical formula CH3SO2Cl. It is a colorless liquid that is commonly used as a reagent in organic synthesis.

Methanesulfonyl chloride is a versatile compound and is often used as a source of the methanesulfonyl group (-SO2CH3) in various chemical reactions. It can react with a variety of nucleophiles, such as alcohols and amines, to form corresponding methanesulfonates.

Some common uses of methanesulfonyl chloride in organic synthesis include:

1. Protection of alcohols: Methanesulfonyl chloride can be used to convert alcohols into their corresponding methanesulfonate esters. This protects the alcohol functionality from undesired reactions while allowing other parts of the molecule to be modified. The protecting group can later be removed under appropriate conditions.

2. Sulfonamide synthesis: Methanesulfonyl chloride can react with primary and secondary amines to form methanesulfonamide derivatives. These sulfonamides are important intermediates in the synthesis of pharmaceuticals and agrochemicals.

3. Dehydration reactions: Methanesulfonyl chloride can be used as a dehydrating agent to convert carboxylic acids into corresponding acid chlorides. The reaction typically involves the formation of an intermediate methanesulfonate ester, followed by elimination of methanesulfonic acid to yield the acid chloride.