Used as a methylating agent in organic synthesis, particularly for transferring methyl groups to nucleophiles such as amines, thiols, and enolates. It is effective in the preparation of quaternary ammonium compounds and in the synthesis of sulfonium ylides, which are key intermediates in reactions like the Johnson–Corey–Chaykovsky reaction for forming epoxides and cyclopropanes. Its stability and solubility in polar solvents make it suitable for use in a variety of solution-phase reactions. Also employed in the modification of biomolecules and in some pharmaceutical syntheses where controlled methylation is required.