Nitrogen tetroxide

Synonyms

Di-nitrogen dioxide; Dinitrogen tetraoxide; Dinitrogen tetroxide; Nitrogen dioxide, di-; Nitrogen oxide (N2O4); Nitrogen tetraoxide; [ChemIDplus] UN1067

Category

Oxidizers

Description

Colorless gas; [HSDB] Red-brown liquid with a sharp unpleasant odor (kept liquid by compression); bp = 21.15 deg C; [CAMEO]

Sources/Uses

Exposure occurs where nitric acid is used, especially in acid baths for metal cleaning. Like NO2, it is also generated during welding operations. [HSDB] Used in rocket fuels; [REPROTOX]

Comments

Highly toxic; [Quick CPC] Like other nitrogen oxides, inhalation of NO4 may induce delayed pulmonary edema. Concentrations of 25-50 ppm cause irritation of the eyes and nose while 50-100 ppm can cause pulmonary edema and death. Cases of irritant-induced asthma have been reported. In animal experiments, methemoglobin level of 55% were produced in one hour after application of NO4 to the skin of rats. [HSDB] Liquid is an equal mixture of nitrogen dioxide and nitrogen tetroxide (evolves toxic vapors); A strong oxidizing agent; Reacts with water producing nitric acid and nitric oxide; [CAMEO] Classifications in the EU: Causes burns; Highly toxic by inhalation; Human exposures most commonly associated with "silo-fillers disease." Three members of Apollo/Soyuz Test Project crew were exposed to an estimated average concentration of 250 ppm in flight; Each member displayed signs and symptoms of chemical pneumonitis and increased methemoglobin levels; "Since N2O4 is in equilibrium with NO2, the toxic properties observed in clinical and toxicological cases have not distinguished between the two." [IUCLID] Causes impaired liver function tests in 30-week intermittent inhalation studies of rabbits; [RTECS] See "Nitrogen dioxide."

Biomedical References

Yes

904 mm Hg

LC50 (rat) = 105 mg/m3

Explanatory Notes

VP from HSDB;

will not burn

Yes

MetHgb is secondary toxic effect

Hepatoxic (a) from occupational exposure (secondary effect) or (b) in animal studies or in humans after ingestion

Skin burns

Diseases

Occupational diseases associated with exposure to this agent:

• Pneumonitis, toxic

Processes

Industrial Processes with risk of exposure:

• Acid and Alkali Cleaning of Metals
• Welding