Triphosgene (bis(trichloromethyl) carbonate (BTC) is a chemical compound with the formula OC(OCCl₃)₂. It is used as a solid substitute for

phosgene Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, esp ...

, which is a gas. 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 Dimethyl carbonate (DMC) is an organic compound with the formula OC(OCH3)2. It is a colourless, flammable liquid. It is classified as a carbonate ester. This compound has found use as a methylating agent and more recently as a solvent that is e ...

: :CH₃OCO₂CH₃ + 6 Cl₂ → CCl₃OCO₂CCl₃ + 6 HCl Triphosgene can be easily recrystallized from hot hexanes.

Uses

Triphosgene is used as a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

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

isocyanate In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...

s. Triphosgene has been used to synthesize organohalides. The use of triphosgene in these reactions provided a broader class of substrates that could be used for halogenation. Alkyl chlorides are synthesized via an S_N2 reaction with chloride ions using triphosgene and

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with ...

. An alternative reaction uses triphosgene and

sodium hydride Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in co ...

, which results in a carbonyl addition and a ring opening caused by chloride ions. Alkyl dichlorides and trichlorides can similarly be synthesized using triphosgene. Vinyl chlorides are synthesized using triphosgene and DMF to form a

Vilsmeier reagent The Vilsmeier reagent is an organic compound with the formula CH3)2NCHCll. It is a salt consisting of the N,N-dimethyliminium cation ( CH3)2N=CHClsup>+) and chloride anion. Depending on the particular reaction, the anion can vary. In typical POC ...

from a

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...

, followed by a ring opening by chloride ions. Aryl chlorides can also be produced using a Vilsmeier reagent from triphosgene and DMF. Chlorocarbonates can be synthesized by a ketone reacting with triphosgene, which forms a six-membered ring that is then chlorinated. In addition to chlorination reactions, triphosgene can be used in a mixture with

potassium bromide Potassium bromide ( K Br) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion (sodium bromide is equall ...

to create aryl bromides. Triphosgene is capable of converting several

functional groups In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...

, which is useful in the formation of reaction intermediates. Triphosgene is used in the preparation of carbonyl chlorides, the activation of

carboxylic acids In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

, and the addition of carbonyl groups.

Safety

Triphosgene's low vapor pressure makes it possible 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.

References

{{reflist

External links

Bulletin about Triphosgene
Organochlorides Carbonate esters Reagents for organic chemistry Trichloromethyl esters Carbon oxohalides

Preparation

Uses

Safety

See also

References

External links