Phosgene oxime

Preparation and reactions

Phosgene oxime can be prepared by reduction of chloropicrin:

Cl₃CNO₂ + 2 Sn + 5 HCl + H₂O → Cl₂C=N−OH + 2 H₃O[SnCl₃]

The observation of a transient violet color in the reaction suggests intermediate formation of trichloronitrosomethane (Cl₃CNO). Early preparations, using stannous chloride as the reductant, also started with chloropicrin.

The compound is electrophilic and thus sensitive to nucleophiles, including base hydrolysis:

Cl₂CNOH + 2 NaOH → CO₂ + NH₂OH + 2 NaCl + H₂O

Similar processes provide an easy way to destroy this dangerous compound. Hydrazine converts it to HCN and N₂.

Safety

Phosgene oxime is classified as a vesicant even though it does not produce blisters. It is toxic by inhalation, ingestion, or skin contact. The effects of the poisoning occur almost immediately. No antidote for phosgene oxime poisoning is known. Generally, any treatment is supportive. Typical physical symptoms of CX exposure are as follows:

Skin: Blanching surrounded by an erythematous ring can be observed within 30 seconds of exposure. A wheal develops on exposed skin within 30 minutes. The original blanched area acquires a brown pigmentation by 24 hours. An eschar forms in the pigmented area by 1 week and sloughs after approximately 3 weeks. Initially, the effects of CX can easily be misidentified as mustard gas exposure. However, the onset of skin irritation resulting from CX exposure is a great deal faster than mustard gas, which typically takes several hours or more to cause skin irritation.

Eyes: Eye examination typically demonstrates conjunctivitis, lacrimation, lid edema, and blepharospasm after even minute exposures. More severe exposures can result in keratitis, iritis, corneal perforation, and blindness.

Respiratory: Irritation of the mucous membranes may be observed on examination of the oropharynx and nose. Evidence of pulmonary edema, including rales and wheezes, may be noted on auscultation. Pulmonary thromboses are prominent features of severe CX exposure.

Gastrointestinal: Some animal data suggest that CX may cause hemorrhagic inflammatory changes in the GI tract.

Decontamination, treatment, and handling properties

Phosgene oxime is highly soluble in water. It is corrosive to metals and also decomposes on contact with metals. It is rapidly hydrolysed by alkaline solutions. Adsorbent powders such as Fuller's earth or talcum powder can also be used.