Chemical Properties
Nitrogen dioxide (and nitrogen tetroxide, the
solid dimer) is a dark brown gas (above 21 C) or a yellow,
fuming liquid or colorless solid with a pungent, acrid odor.
The solid form is colorless below about 11 C; it is found
structurally as N2O4.
Chemical Properties
Red to brown gas above 21.1C, brown
liquid below 21.1C; colorless solid approximately
?11C.The pressurized liquid is nitrogen tetroxide (dinitrogen tetroxide) because of admixture of
N
2O4 with NO2,Noncombustible but supports combustion.
Uses
Nitrogen dioxide is an intermediate in producing nitric acid. It also is used in the lead chamber process for making sulfuric acid. It is used as a nitrating and oxidizing agent, in rocket fuels, in the manufacture of hemostatic cotton and other oxidized cellulose compounds, and in bleaching flour. Nitrogen dioxide occurs in trace concentrations in the atmosphere due to oxidation of nitric oxide in air. It also is found in exhaust gases of internal combustion engines, in industrial waste gases from plants using nitric acid, and in cigarette smoke. Brown color of smog in many industrial urban areas is attributed to nitrogen dioxide.
General Description
A reddish brown gas or yellowish-brown liquid when cooled or compressed. Shipped as a liquefied gas under own vapor pressure. Vapors are heavier than air. Toxic by inhalation (vapor) and skin absorption. Noncombustible, but accelerates the burning of combustible materials. Cylinders and ton containers may not be equipped with a safety relief device.
Reactivity Profile
Nitrogen Dioxide (nitrogen peroxide) is a strong oxidizing agent. Powdered aluminum burns in the vapor of carbon disulfide, sulfur dioxide, sulfur dichloride, nitrous oxide, nitric oxide, or nitrogen peroxide [Mellor 5:209-212. 1946-47]. Boron trichloride reacts energetically with nitrogen peroxide, phosphine, or fat and grease [Mellor 5:132. 1946-47]. Nitrogen peroxide and acetic anhydride reacted to form tetranitromethane, but resulted in an explosion [Van Dolah 1967]. Nitrogen peroxide forms explosive mixtures with incompletely halogenated hydrocarbons [Chem. Eng. News 42(47):53. 1964]. During an experiment to produce lactic acid by oxidizing propylene with nitrogen peroxide, a violent explosion occurred. These mixtures (olefins and nitrogen peroxide) form extremely unstable nitrosates or nitrosites [Comp. Rend. 116:756. 1893]. Contact of very cold liquefied gas with water may result in vigorous or violent boiling of the product and extremely rapid vaporization due to the large temperature differences involved. If the water is hot, there is the possibility that a liquid "superheat" explosion may occur. Pressures may build to dangerous levels if liquid gas contacts water in a closed container [Handling Chemicals Safely 1980]. Corrosive to steel when wet, but may be stored in steel cylinders when moisture content is 0.1% or less.
Fire Hazard
Nitrogen dioxide is not combustible (NFPA rating = 0) but is a strong oxidizing
agent and will support combustion. Cylinders of NO2 gas exposed to fire or intense
heat may vent rapidly or explode.
Air & Water Reactions
Combines with oxygen to form NITROGEN DIOXIDE(10102-44-0), a brown gas that is deadly poisonous [Merck 11th ed. (1989]. Decomposes in water to form nitric acid and nitric oxide, reacts with alkalis to form nitrate and nitrites [Merck 11th ed. 1989]. The liquid nitrogen oxide is very sensitive to detonation, in the presence of water.
Hazard
Inhalation may be fatal. Can react strongly
with reducing materials. Lower respiratory tract
irritant. Questionable carcinogen.
Health Hazard
Severe exposures may be fatal. Contact may cause burns to skin and eyes. Contact with liquid may cause frostbite. This compound was reported to react with blood to form methemoglobin. The lowest lethal human inhalation dose has been reported at 200 ppm/1 min.
Potential Exposure
Nitrogen dioxide is found in automotive
and diesel emissions. Nitrogen dioxide is an industrial
chemical used as an intermediate in nitric and sulfuric acid
manufacture; it is used in the nitration of organic compounds;
it is used as an oxidizer in liquid propellant rocket
fuel combinations. It is also used in firefighting, welding
and brazing.
First aid
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the
skin, remove contaminated clothing and wash immediately
with soap and water. Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,
begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and
CPR if heart action has stopped. Transfer promptly to a
medical facility. When this chemical has been swallowed,
get medical attention. Give large quantities of water and do
not induce vomiting. Do not make an unconscious person
vomit. Medical observation is recommended for
24 48 hours after breathing overexposure, as pulmonary
edema may be delayed. As first aid for pulmonary edema,
a doctor or authorized paramedic may consider administering
a drug or other inhalation therapy. If frostbite has
occurred, seek medical attention immediately; do NOT rub
the affected areas or flush them with water. In order to prevent
further tissue damage, do NOT attempt to remove frozen
clothing from frostbitten areas. If frostbite has NOT
occurred, immediately and thoroughly wash contaminated
skin with soap and water.
Shipping
UN1067/124 Dinitrogen tetroxide, Hazard Class:
2.3; Labels: 2.3-Poisonous gas, 5.1-Oxidizer, 8-Corrosive
material, Inhalation Hazard Zone A. UN1975 Nitric oxide
and dinitrogen tetroxide mixtures or Nitric oxide and
nitrogen dioxide mixtures, Hazard Class: 2.3; Labels:
2.3-Poisonous gas, 5.1-Oxidizer, 8-Corrosive material,
Inhalation Hazard Zone A. Cylinders must be transported
in a secure upright position, in a well-ventilated truck.
Protect cylinder and labels from physical damage. The
owner of the compressed gas cylinder is the only entity
allowed by federal law (49CFR) to transport and refill
them. It is a violation of transportation regulations to refill
compressed gas cylinders without the express written permission
of the owner.
Incompatibilities
A strong oxidizer. Reacts violently with
combustible matter, chlorinated hydrocarbons; ammonia,
carbon disulfide; reducing materials. Reacts with water,
forming nitric acid and nitric oxide. Attacks steel in the
presence of moisture.
Description
nitrogen dioxide is a reddish-brown
gas (or yellow liquid) with a strong, acrid odor. Nitrogen dioxide readily dimerizes to produce
N2O4.nitrogen dioxide are nonfl ammable, toxic gases.The federal government has established air quality standards for nitrogen dioxide
at 0.053 partsper million (ppm), which equals 100μg (micrograms) per cubic meter.Nitrogen dioxide is highly soluble in water and forms nitric acid (HNO3), and nitric oxide
is slightly soluble and forms nitrous acid (HNO2).
Nitrogen dioxide is
a strong oxidizing agent and causes corrosion.Nitrogen dioxide is used as an oxidizing agent, a catalyst in oxidation reactions, an inhibitor,
as a nitrating agent for organic reactions, as a flour bleaching agent, and in increasing the
wet strength of paper.
Waste Disposal
Destroy by incineration with
the addition of hydrocarbon fuel, controlled in such a way
that combustion products are elemental nitrogen, CO2, and
water. Consult with environmental regulatory agencies for
guidance on acceptable disposal practices. Generators of
waste containing this contaminant (≥100 kg/mo) must conform
with EPA regulations governing storage, transportation,
treatment, and waste disposal.
Physical properties
Reddish-brown gas; pungent irritating odor; liquefies to a yellow liquid at 21.2°C; liquefies under pressure to a brown fuming liquid, commercially known as nitrogen tetroxide which actually is an equilibrium mixture of nitrogen dioxide and dinitrogen tetroxide, N2O4; converts to a colorless crystalline solid at -11.2°C; refractive index 1.40 at 20°C; density of gas in air 1.58 (air=1); density of liquid 1.449 g/mL at 20°C; critical temperature 158.2°C; critical pressure 99.96 atm; decomposes in water forming nitric acid; reacts with alkalies; soluble in concentrated nitric and sulfuric acids; soluble in chloroform and carbon disulfide.
Occurrence
Nitrogen dioxide is an intermediate in producing nitric acid. It also is used in the lead chamber process for making sulfuric acid. It is used as a nitrating and oxidizing agent, in rocket fuels, in the manufacture of hemostatic cotton and other oxidized cellulose compounds, and in bleaching flour. Nitrogen dioxide occurs in trace concentrations in the atmosphere due to oxidation of nitric oxide in air. It also is found in exhaust gases of internal combustion engines, in industrial waste gases from plants using nitric acid, and in cigarette smoke. Brown color of smog in many industrial urban areas is attributed to nitrogen dioxide.
History
nitrogen dioxide was prepared in 1772 by Joseph Priestley
(1733–1804) and described in his volumes Experiments and Observations of Different Kinds
of Air published between 1774 and 1786. Priestley called nitric oxide nitrous air, nitrogen
dioxide nitrous acid vapor, and nitrous oxide phlogisticated nitrous air, but also referred to the
dioxide. Priestley prepared nitric oxide by reacting nitric acid with a metal such as copper:
3Cu(s) + 8HNO3(aq) → 2NO(g) + 3Cu(NO3)2(aq) + 4H2O(l).
Definition
A brown gas produced by the dissociation
of dinitrogen tetroxide (with which it is in
equilibrium), the dissociation being complete
at 140°C. Further heating causes dissociation
to colorless nitrogen monoxide
and oxygen:
2NO2(g) = 2NO(g) + O2(g)
Nitrogen dioxide can also be made by
the action of heat on metal nitrates (not the
nitrates of the alkali metals or some of the
alkaline-earth metals).
Production Methods
Nitric oxide (nitrogen monoxide, mononitrogen monoxide;
NO) and nitrogen dioxide [nitrogen peroxide, nitrogen
tetroxide (NTO); NO2] are often found in dynamic equilibrium.
Historically, these compounds sometimes have been
erroneously described as “nitrous fumes.” In air, NO is
readily oxidized to NO2, and liquefied NO2 (existing principally
as its dimer nitrogen tetroxide, N2O4) releases NO2 at
room temperature. Thus, these compounds are often
grouped as nitrogen oxides (NOx). Other nitrogen oxides
include nitrogen trioxide (NO3), dinitrogen trioxide (N2O3),
and dinitrogen pentoxide (N2O5). Of all the oxides of nitrogen,
NO2 is the most acutely toxic and has been most
extensively studied. Accordingly, much of this section
focuses on the toxicity of this compound.
Discoveries on the role forNOin biology and medicine led
to a 1998 Nobel Prize for Robert Furchgott, Louis J. Ignarro,
and Ferid Murad. Nitric oxide and NO2 occur
naturally by bacterial degradation of nitrogenous compounds
and to a lesser extent from fires, volcanic action, and fixation
by lightning. NO has been the subject of intense and extensive
research in a vast array of fields including chemistry,
molecular biology, pharmaceuticals, and gene therapy.
Formed endogenously, NO has a physiological role in
blood flow regulation, thrombosis, and neurotransmission,
and a pathophysiological role in inflammation, oxidative
stress, and host defense. NO is derived from the amino
acid L-arginine by five-electron oxidation catalyzed by NO
synthase (requiring reduced pyridine nucleotides, reduced
biopteridines, and calmodulin). The by-product, citrulline,
is recycled back to L-arginine. In the bloodstream,
NO binds primarily hemoglobin, is converted to NO3, and is
eliminated in the urine with a half-life of 5–8 h.
Nitric oxide is manufactured by passing air through an
electric arc or by oxidation of ammonia over platinum gauze.
Flammability and Explosibility
Nitrogen dioxide is not combustible (NFPA rating = 0) but is a strong oxidizing
agent and will support combustion. Cylinders of NO2 gas exposed to fire or intense
heat may vent rapidly or explode.
Materials Uses
When dry (0.1 percent moisture or less), nitrogen dioxide is not corrosive to mild steel at ordinary temperatures and pressures. Numerous
metals and alloys such as carbon steel, stainless
steel, aluminum, nickel, and Inconel are satisfactory for handling and storage. Under wet
conditions, stainless steels resistant to about 60
percent nitric acid serve best.
Equipment parts, such as valve stems, which
are partly in contact with the atmosphere,
should be stainless steel with sufficient chromium content to resist corrosion caused by
leaks through stuffing boxes. Good quality ceramic bodies and Pyrex are satisfactory for handling wet or dry nitrogen dioxide.
Among the plastics, Teflon and Kel-F films
are most satisfactory. Koroseal and Saran are
useful but have a limited service life. In general,
the vinyl plastics do not hold up well with nitrogen dioxide. Asbestos and asbestos-graphite are
satisfactory for valve stuffing boxes. Koroseal
has given reasonably good service in this use.
For use on pipe threads, graphite-disodium silicate (waterglass) is recommended, and hydrocarbon lubricants should be avoided.
Physiological effects
A major hazard regarding exposure to nitrogen
dioxide is that serious effects are not felt until
several hours after the exposure. Exposure to
nitrogen dioxide at levels of 90 ppm and higher
has resulted in delayed pulmonary edema occurring anywhere from a few hours to 72 hours
after exposure ceases. Symptoms include cyanosis, shortness of breath, restlessness, headache, and the production of a frothy yellow or
brown sputum. With appropriate treatment,
symptoms usually resolve rapidly, but can persist for several weeks.
Exposures to nitrogen dioxide of 10 minutes
or less at a level of about 150 ppm produces
cough, nose and throat irritation, tearing, headache, nausea, and vomiting. Exposures ranging
from 50 ppm to 150 ppm have been associated
with moderate irritation to the eyes and mucous
membranes. Permanent eye damage can occur, however, if exposures at these levels are prolonged.
Delayed pulmonary edema may follow exposure to 100 ppm to 150 ppm for only 30-60
minutes, while a few breaths at a concentration
of 200 ppm to 700 ppm will produce severe
pulmonary damage that may result in fatal pulmonary edema after 5 to 8 hours have elapsed.
Nitrogen dioxide in 10 ppm to 20 ppm concentrations in air is slightly irritating to mucous
membranes and the upper respiratory tract. The
odor is distinct in concentrations of 5 ppm.Concentrations above 100 ppm in air cause immediate distress. Exposure of the skin to liquid
nitrogen dioxide can cause severe bums.
ACGIH recommends the Threshold Limit
Value-Time-Weighted Average (TLV-TWA)
of 3 ppm (5.6 mg/m3) for nitrogen dioxide. The
TLV-TWA is the time-weighted average concentration for a normal 8-hour workday and a
40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without adverse effect. ACGIH also recommends
the Threshold Limit Value-Short Term Exposure Limit (TLV-STEL) of 5 ppm (904 mg/m3) for nitrogen dioxide. The TLV-STEL is the
IS-minute TWA exposure that should not be
exceeded at any time during a workday even if
the 8-hour TWA is within the TLV-TWA. Exposures above the TLV- TWA up to the STEL
should not be longer than 15 minutes and should
not occur more than 4 times per day. There
should be at least 60 minutes between successive exposures in this range.
OSHA lists a Ceiling Value of 5 ppm (9 mg/m3) for nitrogen dioxide. The Ceiling Value
is the exposure limit that shall not be exceeded
at any time during the working day. If instantaneous monitoring is not feasible, then the ceiling shall be assessed as a IS-minute TWA exposure that shall not be exceeded at any time
during the working day.
storage
Cylinders of nitrogen dioxide should be stored and used
in a continuously ventilated gas cabinet or fume hood.
GRADES AVAILABLE
Nitrogen dioxide is available in grades of 99.5
percent or 99.995 percent.
;