Nitrogen Tetroxide

Description

Nitrogen tetraoxide is primarily known for its use as a rocket propellant and became an oxidizer of choice by the late 1950s. Nitrogen tetraoxide has been used as a propellant for missiles as well as for spacecraft beginning with its use in Titan rockets in the late 1950s.

Description

Highly toxic and corrosive dinitrogen tetroxide is in equilibrium with NO2?in its liquid and vapor states. Its brownish color comes from NO2; N2O4?is colorless. It is used commercially as an intermediate in the manufacture of HNO3?and as a nitrating and oxidizing agent. N2O4?is the oxidizer of choice for storable rocket propellants because it is hypergolic with hydrazine fuels.

Chemical properties

col liquid [CRC10]

Physical properties

Colorless liquid or gas; exists in equilibrium with NO₂; density 1.45 g/mL at 20°C; boils at 21.25°C; freezes at -9.35°C to a colorless diamagnetic solid; critical temperature 157.85°C; critical pressure 99.64 atm; critical volume 167 cm³/mol; reacts with water.

The Uses of Nitrogen Tetroxide

Nitrogen tetroxide is a solvent and a powerful and selective oxidizing agent. It’s adducts with organic solvents are used to synthesize nitrates of noble metals.

The Uses of Nitrogen Tetroxide

Nitrogen tetraoxide is formed by pressurizing liquid nitrogen dioxide. It is a gas at normal temperature and pressure, and is used in the manufacture of explosives and rocket fuels. Nitrogen tetraoxide is used as a catalyst in oxidation reactions and in many other industrial applications. It is also a component of nitric and sulfuric acid.

Definition

A colorless gas that becomes a pale yellow liquid below 21°C and solidifies below –11°C. On heating, the gas dissociates to nitrogen dioxide molecules:
N₂O₄(g) = 2NO₂(g)
This dissociation is complete at 140°C. Liquid dinitrogen tetroxide has good solvent properties and is used as a nitrating agent.

Definition

dinitrogen tetroxide: A colourlessto pale yellow liquid or a brown gas,N₂O₄; r.d. 1.45 (liquid); m.p. –11.2°C;b.p. 21.2°C. It dissolves in water withreaction to give a mixture of nitricacid and nitrous acid. It may be readilyprepared in the laboratory by thereaction of copper with concentratednitric acid; mixed nitrogen oxidescontaining dinitrogen oxide may alsobe produced by heating metal nitrates.The solid compound is whollyN₂O₄ and the liquid is about 99%N₂O₄ at the boiling point; N2O4 is diamagnetic.In the gas phase it dissociatesto give nitrogen dioxideN₂O₄?2NO₂Because of the unpaired electron thisis paramagnetic and brown. LiquidN₂O₄ has been widely studied as anonaqueous solvent system (selfionizesto NO⁺ and NO₃^-). Dinitrogentetroxide, along with other nitrogenoxides, is a product of combustionengines and is thought to be involvedin the depletion of stratosphericozone.

Preparation

Nitrogen tetroxide always is formed along with nitrogen dioxide during preparation of the dioxide (See Nitrogen Dioxide.) Mixed oxides are produced by oxidation of nitric oxide (NO) in air, heating metal nitrates, or by metals reacting with nitric acids or nitrates.

General Description

Red-brown liquid with a sharp, unpleasant chemical odor. Low-boiling (boiling point 21.15°C) and held as a liquid by compression. Density 1.448 g / cm3. Consists of an equilibrium mixture of brown NO2 (nitrogen dioxide) and colorless N2O4 (diNITROGEN DIOXIDE). Evolves poisonous brown vapors. Cylinders and ton containers may not be equipped with a safety relief device. Prolonged exposure of the containers to fire or heat may result in their violent rupturing and rocketing.

Air & Water Reactions

Reacts with water to form nitric acid and nitric oxide.

Reactivity Profile

Liquid NITROGEN DIOXIDE is an oxidizing agent consisting of an equilibrium mixture of colorless dinitrogen tetraoxide (N2O4) and red-brown nitrogen dioxide (NO2). The exact composition of the mixture depends on the temperature with higher temperature favoring conversion to NO2. Vaporizes readily to give NO2, also an oxidizing agent. Noncombustible but can accelerate the burning of combustible materials. Reacts with reducing agents to generate heat and products that may be gaseous (causing pressurization of closed containers). The products may themselves be capable of further reactions (such as combustion in the air). Reacts with alkalis to form nitrates and nitrites [Merck 11th ed. 1989]. Corrodes steel if wet, but can be stored in steel cylinders if dry [Merck]. Reacts explosively with liquid ammonia even at very low temperatures (below its freezing point) [Mellor, 1940, Vol. 8, 54]. Reacts energetically with boron trichloride [Mellor, 1946, Vol. 5, 132]. Mixtures with metal carbonyls are hypergolic (enflame immediately). Mixtures with halocarbons, hydrazine derivatives, heterocyclic bases (pyridine), isopropyl nitrite/propyl nitrite, active metals (magnesium, calcium, etc.), nitroaromatics, nitrogen trichloride, phosphorus, triethylamine, unsaturated hydrocarbons may react explosively. Accidental mixing with hot cyclohexane caused an explosion [MCA Case History 128. 1962]. A mixture with acetonitrile and indium showed no evidence of change for a time and then detonated when shaken (ascribed to the catalyzed oxidation of acetonitrile) [Chem. & Ind., 1958, 1004]. Mixture with alcohols produced a violent explosion [Chem. Eng. News, 1955, 33, 2372]. Vapor reacts with barium oxide incandescently [Mellor, 1940, Vol. 8, 545]. A slow reaction between the vapor and formaldehyde became explosive near 180°C [Trans. Faraday Soc. 45:767-770. 1949]. Manganese and potassium both ignite in the vapor [Ann. Chem. et Phys.(2) 2:317]. The vapor and ozone react with the evolution of light and often explode when mixed [J. Chem. Phys. 18:366. 1920].

Hazard

See Nitrogen Dioxide, Hazard.

Health Hazard

Very concentrated fumes produce coughing, choking, headache, nausea, pain in chest and abdomen; otherwise, few symtoms appear at time of exposure. After symptom-free period of 5-72 hours, pulmonary edema gradually develops, causing fatigue, restlessness, coughing, difficulty in breathing, frothy expectoration, mental confusion, lethargy, bluish skin, and weak, rapid pulse. Since NOX interferes with gas exchange in lungs, unconscious- ness and death by asphyxiation can result, usually within a few hours after onset of pulmonary edema.

Flammability and Explosibility

Non flammable

Safety Profile

A poison. Moderately toxic by inhalation. When heated to decomposition it emits toxic fumes of NOx. See also NITROGEN MONOXIDE.

Environmental Fate

Nitrogen tetroxide is released into the atmosphere where it can undergo reactions, leading to air pollution.

Purification Methods

Purify it by oxidation at 0o in a stream of oxygen until the blue colour changes to red-brown. Alternatively distil it from P2O5, then solidify it by cooling in a deep-freeze (at –78o, giving nearly colourless crystals). Oxygen can be removed by alternate freezing and melting. TOXIC VAPOUR. [Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 488-489 1963.]

Toxicity evaluation

Nitrogen tetraoxide is absorbed through the respiratory system and reacts with blood, reducing fluid levels, inducing massive pulmonary edema and a severe reduction in hemoglobin levels.