Provided is a convenient method for the synthesis of quaternary ammonium sulfonate compounds which are useful as curing catalysts for one-part thermosetting resin compositions which maintain storage stability at room temperature. The compounds are synthesized by subjecting in one step a benzyl alcohol optionally having on the benzene ring and/or the .alpha.-position one or more substituent groups to reaction with a corresponding tertiary amine and an organic sulfonic acid chloride.