Benzenesulfonyl chloride reacts with Grignard reagent from N-unsubstituted indoles to form oxindoles or substituted indoles. It is the derivatization reagent for the determination of various amines in waste water and surface water at the sub-ppb level by gas chromatography-mass spectrometry.

Benzenesulfonyl chloride is prepared by reaction of benzene and chlorosulfonic acid or from the sodium salt of benzenesulfonic acid and PCl5 or POCl3. It reacts with Grignard reagent from N-unsubstituted indoles to form oxindoles or substituted indoles. Benzenesulfonyl chloride is the derivatization reagent for the determination of various amines in waste water and surface water at the sub-ppb level by gas chromatography-mass spectrometry.