PURPOSE: To obtain the titled compound in high yield economically and advantageously without troublesome operation, by reacting a tertiary alcohol with an amine adduct with sulfur trioxide as a sulfating agent under heating, cooling the reaction mixture, and adding a slightly soluble solvent to isolate the titled compound.

CONSTITUTION: All the tertiary alcohols not only tertiary butanol are heated with an adduct of an amine, e.g. methylamine, cyclopropylamine, aniline or pyridine, of the formula R1R2R3N(R1, R2R3 are H, 1W10C alkyl or cycloalkyl; however, except when any one of R1, R2 and R3 is H) with sulfur trioxide, in an amount of equimolar with the tertiary alcohols at 0W120°C, and cooled to 0°C or below, and then a slightly soluble solvent, e.g. methanol or petroleum ether is added to deposit and isolate the aimed substance. The tertiary alcohols may be used in a large excess.