It is a colorless liquid that is used as a strong methylating agent in organic synthesis.

Because of its extreme toxicity, it has largely been replaced by the related reagent methyl trifluoromethanesulfonate.

It is prepared by distillation of an equimolar mixture of fluorosulfonic acid and dimethyl sulfate.

[2] Similar to phosgene, it is acutely toxic[1] by inhalation, with an LC50 (rat, 1 hour) of about 5 ppm.

Several cases of poisoning resulting in death from pulmonary edema have been reported.