Sulfur trioxide pyridine complex is the compound with the formula C5H5NSO3.

It is a colourless solid that dissolves in polar organic solvents.

The compound is mainly used as a source of sulfur trioxide, for example in the synthesis of sulfate esters from alcohols:[1] It also is useful for sulfamations: The compound is used for sulfonylation reactions, especially in the sulfonylation of furans.

[2] It is also an activating electrophile in a Parikh-Doering oxidation.

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