Dinitrogen tetroxide

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General
Dinitrogen tetroxide
IUPAC name Nitrogen Tetroxide (Dinitrogen Tetroxide)
Chemical formula	N₂O₄
Molecular weight	92.011 u
Appearance	Yellow-brown liquid; vapor is reddish-brown (the color comes from NO₂)
CAS number	10544-72-6
MSDS link	N2O4_MSDS_pdf
Physical properties
Density	1443 kg/m³ (liquid at 1.013 bar, boiling point)
Solubility	reacts with water
Thermal decomposition	maintains equilibrium with NO₂ at room temperature
Phase behavior
Melting point	261.9 K (-11.2 °C)
Boiling point	294.3 K (21.1 °C)
Triple point	? K (? °C) ? kPa
Critical point	430.9 K (157.8 °C) 10.132 MPa
Vapor pressure	96 kPa (20 °C) [1] (?)
Heat of fusion (Δ_fusH)	14.67 kJ/mol [2] (?)
Entropy of fusion (Δ_fusS)	? J/mol·K
Heat of vaporization (Δ_vapH)	39.60 kJ/mol [3] (?)
Safety
Ingestion	?
Inhalation	Corrosive & toxic
Skin	Corrosive
Eyes	Corrosive
OSHA Permissible Exposure Limit (PEL)	5 ppm
NIOSH Immediate Danger to Life and Health (IDLH)	20 ppm
Precautions
Hazards: ? Personal protection: Skin: Prevent skin contact Eyes: Prevent eye contact Wash skin: When contaminated Remove: When wet or contaminated Change: No recommendation Provide: Eyewash, Quick drench Reacts with: Combustible material, water, chlorinated hydrocarbons, carbon disulfide, ammonia [Note: Reacts with water to form nitric acid.] Storage: ?
Solid properties
Standard enthalpy change of formation (Δ_fH⁰_solid)	? kJ/mol
Standard molar entropy (S⁰_solid)	? J/(mol·K)
Heat capacity (C_p)	? J/(mol·K)
Density	? g/cm³
Liquid properties
Δ_fH⁰_liquid	-19.5 kJ/mol
S⁰_liquid	209.2 J/(mol·K)
C_p	142.7 J/(mol·K)
Density	1.44 g/cm³
Gas properties
Δ_fH⁰_gas	11.1 kJ/mol
S⁰_gas	304.4 J/(mol·K)
C_p	79.2 J/(mol·K)
Except where noted, all data was produced under conditions of standard temperature and pressure.

Nitrogen tetroxide (or dinitrogen tetroxide) (N₂O₄) is a hypergolic propellant often used in combination with a hydrazine-based rocket fuel. The combination was used to fuel the Titan rockets used in the Gemini missions, and is still used today in the second stage engines of Delta II rockets. By the late 1950s it became the storable oxidizer of choice for rockets in both the USA and USSR. [4]

Nitrogen dioxide is made by the catalytic oxidation of ammonia: steam is used as a diluent to reduce the combustion temperature. Most of the water is condensed out, and the gases are further cooled; the nitric oxide which was produced is oxidised to nitrogen dioxide, and the remainder of the water is removed as nitric acid. The gas is essentially pure nitrogen tetroxide, which is condensed in a brine-cooled liquefier.

Nitrogen tetroxide is a brownish yellow liquid which is easily vaporized. It is a powerful oxidizer, and is highly toxic and corrosive. However, it is not affected by mechanical shock and does not react with air. Nitrogen tetroxide is always in equilibrium with nitrogen dioxide (NO₂) and some nitrogen dioxide will be present in any quantity of nitrogen tetroxide (higher temperatures push the equilibrium towards nitrogen dioxide).

Nitrogen tetroxide is sometimes a component of smog.

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