Diphosgene

Diphosgene is a chemical compound with the formula ClCO2CCl3. This colorless liquid is a valuable reagent in the synthesis of organic compounds. Diphosgene is related to phosgene and has comparable toxicity, but is more conveniently handled because it is a liquid, whereas phosgene is a gas.

Diphosgene
Names
Preferred IUPAC name
Trichloromethyl carbonochloridate
Other names
Trichloromethyl chloroformate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.242
EC Number
  • 207-965-9
RTECS number
  • LQ7350000
UNII
Properties
C2Cl4O2
Molar mass 197.82 g/mol
Appearance liquid at room temperature
Density 1.65 g/cm3
Melting point −57 °C (−71 °F; 216 K)
Boiling point 128 °C (262 °F; 401 K)
insoluble
Hazards
Main hazards toxic
GHS pictograms
GHS Signal word Danger
H300, H314, H330
P260, P264, P270, P271, P280, P284, P301+310, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P320, P321, P330, P363, P403+233, P405, P501
Flash point 32 °C (90 °F; 305 K)
Related compounds
Related compounds
 COCl2, Cl2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Production and uses

Diphosgene is prepared by radical chlorination of methyl chloroformate under UV light:[1]

Cl-CO-OCH3 + 3 Cl2 —(hv)→ Cl-CO-OCCl3 + 3 HCl

Another method is the radical chlorination of methyl formate:[2]

H-CO-OCH3 + 4 Cl2 —(hv)→ Cl-CO-OCCl3 + 4 HCl

Diphosgene converts to phosgene upon heating or upon catalysis with charcoal. It is thus useful for reactions traditionally relying on phosgene. For example, it convert amines into isocyanates, secondary amines into carbamoyl chlorides, carboxylic acids into acid chlorides, and formamides into isocyanides. Diphosgene serves as a source of two equivalents of phosgene:

2 RNH2 + ClCO2CCl3 → 2 RNCO + 4 HCl

With α-amino acids diphosgene gives the acid chloride-isocyanates, OCNCHRCOCl, or N-carboxy-amino acid anhydrides depending on the conditions.[3]

It hydrolyzes to release HCl in humid air.

Diphosgene is used in some laboratory preparations because it is easier to handle than phosgene.

Role in warfare

Diphosgene was originally developed as a pulmonary agent for chemical warfare, a few months after the first use of phosgene. It was used as a poison gas in artillery shells by Germany during World War I. The first recorded battlefield use was in May 1916.[4] Diphosgene was developed because the vapors could destroy the filters in gas masks in use at the time.

Safety

Diphosgene has a relatively high vapor pressure of 10 mm Hg (1.3 kPa) at 20 °C and decomposes to phosgene around 300 °C. Exposure to diphosgene is similar in hazard to phosgene.

See also

References
  1. Keisuke Kurita and Yoshio Iwakura (1979). "Trichloromethyl Chloroformate as a Phosgene Equivalent: 3-Isocyanatopropanoyl Chloride". Organic Syntheses. 59: 195.; Collective Volume, 6, p. 715
  2. Lohs, K. H.: Synthetische Gifte; Berlin (east), 1974 (German).
  3. Kurita, K. "Trichloromethyl Chloroformate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.
  4. Jones, Simon; Hook, Richard (2007). World War I Gas Warfare Tactics and Equipment. Osprey Publishing. ISBN 1-84603-151-6.
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