Triphosgene

Toxicity

As a common production raw material for chemical enterprises, Sanguang gas is not listed in the list of hazardous chemicals, and its risk is not familiar and understood by many users, which often leads to decomposition and poisoning accidents. Therefore, it is of great practical significance to study the hazards and safety measures in the use of Triphosgene. Based on the characteristic identification of triphosgene, the hazards in the process of dissolution and reaction are identified and analyzed, and the corresponding safety measures in the use of Triphosgene are put forward according to the results of hazard identification and analysis. Triphosgene has gradually become the raw material for acyl chlorination in many enterprises because it is a non hazardous chemical, relatively stable material properties, easy transportation and easy treatment of tail gas. However, if the safety measures are not appropriate during the transportation, storage and use of triphosgene, it is very easy to cause poisoning accidents.

Description

Triphosgene is also known as solid phosgene. Its chemical name is bis (Trichloromethyl) carbonate, and its English name is bisgriehloromethyl) carbonate or triphosgene, abbreviated as BTC. Triphosgene is a white crystal, similar to the smell of phosgene. It is mainly used to synthesize chloroformate, isocyanate, polycarbonate and acyl chloride. It is widely used as an intermediate in plastics, medicine, herbicides and pesticides.

Chemical Properties

White solid

Uses

Triphosgene can be employed as a reagent to prepare:

• Thiocarbonates from thiols and alcohols by one-pot, three-component reaction.
• Substituted azetidin-2-ones from acids and imines via ketene–imine cycloaddition reaction.
• Methyl (S)-2-isocyanato-3-phenylpropanoate from L-phenylalanine methyl ester hydrochloride in the presence of sodium bicarbonate.
• Acyl azides derivatives from various carboxylic acids and sodium azide.
• Immunosuppressant agent cyclosporin by solid-phase peptide synthesis.
• Allyl azides from allyl alcohols and sodium azide in one pot method.
• Esterification coupling reagent di-2-thienyl carbonate, from 2(5H)-thiophenone.
• 2-Chloronicotinaldehydes via cyclization of the corresponding enamides.

Uses

Triphosgene is used as a carbonylating agent for aza-peptide synthesis. It reacts with several alfa-amino acids to give the corresponding N-carboxyanhydrides. It is involved in the preparation of the esterification coupling reagent, di-2-thienyl carbonate from 2(5H)-thiophenone. Further, it is used as a reagent in organic synthesis and converts an amino group into isocyanate. In addition to this, it is employed in the preparation of 2-chloronicotinaldehydes through cyclization of the corresponding enamides. It is considered as a useful substitute for phosgene.

Uses

An efficient carbonylating agent for liquid and solid-phase aza-peptide synthesis.

Reactions

The Triphosgene reaction is quenched very carefully by dropwise addition of 75 mL of saturated aqueous sodium sulfate solution  (Notes 5 and 6). The resulting white granular precipitate or slurry is  removed by vacuum filtration through Celite, and the filter cake is  washed with three portions of 75 mL of chloroform .

General Description

Triphosgene [Bis(trichloromethyl)carbonate] is a versatile organic reagent used in organic synthesis alternative to phosgene. A catalytic amount of triphosgene is particularly used in chloroformylations, carbonylations, chlorinations, and dehydration reactions.

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 extremely 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.

Synthesis

Triphosgene is synthesized by exhaustive free radical chlorination of dimethyl carbonate:
CH₃OCO₂CH₃ + 6 Cl₂ → CCl₃OCO₂CCl₃ + 6 HCl
Triphosgene can be easily recrystallized from hot hexanes. 

Purification Methods

It is a good solid substitute for phosgene (using a third mol per mol). Crystallise it from pet ether (b 60-80o), wash it with anhydrous cold Et2O, de-gas it at 200mm then dry at 0.1mm (over H2SO4). It has IR: max 900 and 1900 cm-1 . It is a lachrymator, is TOXIC and should be handled with gloves and in an efficient fume hood. [Hales et al. J Chem Soc 620 1957, Eckert & Forster Angew Chem, Int Ed Engl 26 894 1987, Aldrichimica Acta 21 47 1988, Beilstein 3 H 17, 3 I 8, 3 II 16, 3 III 36, 3 IV 33.]