ClSOOH is used to prepare alkyl sulfates, which are useful as detergents and as chemical intermediates:
:ROH + ClSOH → ROSOH + HCl
An early synthesis of saccharin begins with the reaction of toluene with ClSOOH to give the ortho- and para-toluenesulfonyl chloride derivatives:
:CHCH + 2 ClSOOH → CHCHSOCl + HSO + HCl
Oxidation of the ortho isomer gives the benzoic acid derivative that then is cyclized with ammonia and neutralized with base to afford saccharin.
Reaction with hydrogen peroxide is used to produce peroxydisulfuric acid ("persulfuric acid") and peroxydisulfates. These are used as oxidizing agents and for initiating free radical polymerization, for example to produce polytetrafluoroethylene (Teflon).
Chlorosulfonic acid has been used as an anti-contrail agent in Ryan Model 147 reconnaissance drones, and to produce smoke screens.