Triphosgene

Triphosgene (bis(trichloromethyl) carbonate (BTC) is a chemical compound with the formula OC(OCCl3)2. It is used as a solid substitute for phosgene, which is a gas and diphosgene, which is a liquid. Triphosgene is stable up to 200 °C. Triphosgene is used in a variety of halogenation reactions.

Preparation
This compound is commercially available. It is prepared by exhaustive free radical chlorination of dimethyl carbonate:
 * CH3OCO2CH3 + 6 Cl2 → CCl3OCO2CCl3 + 6 HCl

Triphosgene can be easily recrystallized from hot hexanes.

Uses
Triphosgene is used as a reagent in organic synthesis as a source of CO2+. It behaves like phosgene, to which it cracks thermally:
 * OC(OCCl3)2 <-> 3 OCCl2

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.

Safety
The vapor pressure of Triphosgene is sufficiently high for it to reach concentrations that are considered toxicologically unsafe. While several properties of triphosgene are not yet readily available, it is known that it is very toxic if inhaled. A toxic gas is emitted if it comes in contact with water. There is a lack of information and variability regarding the proper handling of triphosgene. It is assumed to have the same risks as phosgene.