Triphosgene is used as a reagent in organic synthesis as a source of CO.  It behaves like phosgene, to which it cracks thermally:
Alcohols are converted to carbonates.  Primary and secondary amines are converted to ureas and isocyanates.
Triphosgene has been used to synthesize chlorides. Some Alkyl chlorides are prepared by treating alcohols with a mixture of triphosgene and pyridine. Alkyl dichlorides and trichlorides can similarly be synthesized using triphosgene. Vinyl chlorides are synthesized from ketones using triphosgene and DMF to form a Vilsmeier reagent, followed by a ring opening by chloride ions. Aryl chlorides can also be produced using a Vilsmeier reagent from triphosgene and DMF.