Diphosgene

DIPHOSGENE, trichloromethyl ester of chloroformic acid, ClCO₂CCl₃ (German name Perstoff; French surpalite; English diphosgen; American superpalit), with a molecular weight of 197.8; it is a colorless, oily liquid with a specific gravity of 1.653 at 15°, and a boiling point of 128°. Diphosgene received its name because, in its elementary composition, it appears as if it were a doubled molecule of phosgene, although in its structural formula it is a completely different substance (the formulas of both substances are not chemically related). However, the conversion of a significant part of diphosgene in the organism into phosgene according to the formula: ClCO₂CCl₃ = 2COCl₂ is highly probable (Jul. Meyer). Diphosgene, like phosgene, in the presence of water undergoes hydrolysis with the formation of HCl and carbonic acid: ClCO₂CCl₃ + 2H₂O = 4HCl + 2CO₂. However, this hydrolysis process proceeds slower than that of phosgene. At the same time, diphosgene possesses lower chemical activity compared to phosgene. On the other hand, compared to the latter, diphosgene has a higher vapor specific gravity and lower volatility. Thus, both in chemical and physical properties, diphosgene possesses greater persistence (see Chemical warfare agents). Therefore, terrain contaminated with diphosgene can be a source of poisoning for several hours (after phosgene, this danger disappears very quickly). Like phosgene, diphosgene is capable of cumulative action. The toxicity of diphosgene is very high, namely, the value of the Haber formula constant (see Chemical warfare agents) causing lethal poisoning, according to German data, should not be lower than 500 for diphosgene (for phosgene, not lower than 450). Although according to American and Russian (Likhachev) data, the lethal concentration of diphosgene for short-term experiments was determined somewhat higher (which can be explained by a different setup of experiments than that used by the Germans) and turned out to be close to 0.1 mg per 1 liter during a cat's stay for 15 minutes in the poisoned atmosphere, nevertheless, this substance appears to be an extremely active poisonous substance, surpassing, according to Likhachev's and American data, all other poisonous substances. The pharmacodynamics of diphosgene is generally the same as that of other substances of the phosgene group, i.e., those suffocating agents that particularly affect the deep respiratory tracts, and is based on the formation of pulmonary edema with simultaneous hemoconcentration. Compared to phosgene, the process proceeds somewhat slower. Most fatally poisoned animals die at the end of the first or on the second day. As with other suffocating agents, autopsy reveals hyperemia in the lungs alongside edema, as well as emphysematous and atelectatic foci. The epithelium of the bronchioles is often necrotic and mixed with exudate, in which fibrin and leukocytes are also encountered. In non-fatal poisonings, during the subsequent course with a decrease in edema, lobular pneumonia develops. The change in metabolism during diphosgene poisoning is the same as with phosgene: an increase in nitrogen and creatinine excretion, with this increase being most strongly expressed on the second day of poisoning. As some difference in the action of diphosgene from phosgene, a more pronounced lachrymatory effect of diphosgene can be noted. Therapeutic measures for poisoning are the same as for other suffocating agents: 1) change of clothing and undergarments, 2) rest, 3) inhalation of O₂, 4) early phlebotomy, 5) introduction of calcium into the blood, and 6) glucose, 7) in the later period physiological NaCl solution, 8) expectorants, 9) cardiacs, 10) sedatives (see Chemical warfare agents). For literature, see the literature to the article Chemical warfare agents.