Nitrogen dioxide
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NO
2 converts to the colorless dinitrogen tetroxide (N 2O 4) at low temperatures and reverts to NO 2 at higher temperatures. | |||
Names | |||
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IUPAC name
Nitrogen dioxide
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Other names
Nitrogen(IV) oxide,[1] deutoxide of nitrogen
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Identifiers | |||
3D model (
JSmol ) |
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard
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100.030.234 | ||
EC Number |
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976 | |||
PubChem CID
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RTECS number
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UNII | |||
UN number | 1067 | ||
CompTox Dashboard (EPA)
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Properties | |||
NO• 2 | |||
Molar mass | 46.005 g·mol−1 | ||
Appearance | Brown gas[2] | ||
Odor | Chlorine-like | ||
Density | 1.880 g/L[2] | ||
Melting point | −9.3 °C (15.3 °F; 263.8 K)[2] | ||
Boiling point | 21.15 °C (70.07 °F; 294.30 K)[2] | ||
Hydrolyses | |||
Solubility | Soluble in CCl 4, nitric acid,[3] chloroform | ||
Vapor pressure | 98.80 kPa (at 20 °C) | ||
+150.0·10−6 cm3/mol[4] | |||
Refractive index (nD)
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1.449 (at 20 °C) | ||
Structure | |||
C2v | |||
Bent | |||
Thermochemistry[5] | |||
Heat capacity (C)
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37.2 J/(mol·K) | ||
Std molar
entropy (S⦵298) |
240.1 J/(mol·K) | ||
Std enthalpy of (ΔfH⦵298)formation |
+33.2 kJ/mol | ||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards
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Poison, oxidizer | ||
GHS labelling: | |||
Danger | |||
H270, H314, H330 | |||
P220, P260, P280, P284, P305+P351+P338, P310 | |||
NFPA 704 (fire diamond) | |||
Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration)
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30 ppm (guinea pig, 1 h) 315 ppm (rabbit, 15 min) 68 ppm (rat, 4 h) 138 ppm (rat, 30 min) 1000 ppm (mouse, 10 min)[7] | ||
LCLo (lowest published)
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64 ppm (dog, 8 h) 64 ppm (monkey, 8 h)[7] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible)
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C 5 ppm (9 mg/m3)[6] | ||
REL (Recommended)
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ST 1 ppm (1.8 mg/m3)[6] | ||
IDLH (Immediate danger) |
13 ppm[6] | ||
Safety data sheet (SDS) | ICSC 0930 | ||
Related compounds | |||
Related nitrogen oxides
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Dinitrogen pentoxide Dinitrogen tetroxide | ||
Related compounds
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Chlorine dioxide Carbon dioxide | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Nitrogen dioxide is a
Nitrogen dioxide is poisonous and can be fatal if inhaled in large quantities.[8] Cooking with a gas stove produces nitrogen dioxide which causes poorer indoor air quality. Combustion of gas can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.[9][10] The LC50 (median lethal dose) for humans has been estimated to be 174 ppm for a 1-hour exposure.[11] It is also included in the NOx family of atmospheric pollutants.
Properties
Nitrogen dioxide is a reddish-brown gas with a pungent, acrid odor above 21.2 °C (70.2 °F; 294.3 K) and becomes a yellowish-brown liquid below 21.2 °C (70.2 °F; 294.3 K). It forms an
The bond length between the nitrogen atom and the oxygen atom is 119.7 pm. This bond length is consistent with a bond order between one and two.
Unlike
The reddish-brown color is a consequence of preferential absorption of light in the blue region of the spectrum (400–500 nm), although the absorption extends throughout the visible (at shorter wavelengths) and into the infrared (at longer wavelengths). Absorption of light at wavelengths shorter than about 400 nm results in photolysis (to form NO + O, atomic oxygen); in the atmosphere the addition of the oxygen atom so formed to O2 results in ozone.
Preparation
Industrially, nitrogen dioxide is produced and transported as its cryogenic liquid dimer,
- 4 NH3 + 7 O2 → 4 NO2 + 6 H2O
It can also be produced by the oxidation of nitrosyl chloride:
- 2 NOCl + O2 → 2NO2 + Cl2
Instead, most laboratory syntheses stabilize and then heat the nitric acid to accelerate the decomposition. For example, the thermal decomposition of some metal nitrates generates NO2:[14]
- Pb(NO3)2 → PbO + 2 NO2 + 1⁄2 O2
Alternatively, dehydration of nitric acid produces nitronium nitrate...
- 2 HNO3 → N2O5 + H2O
- 6 HNO3 + 1⁄2 P4O10 → 3 N2O5 + 2 H3PO4
...which subsequently undergoes thermal decomposition:
- N2O5 → 2 NO2 + 1⁄2 O2
NO2 is generated by the reduction of concentrated nitric acid with a metal (such as copper):
- 4 HNO3 + Cu → Cu(NO3)2 + 2 NO2 + 2 H2O
Selected reactions
Nitric acid decomposes slowly to nitrogen dioxide by the overall reaction:
- 4 HNO3 → 4 NO2 + 2 H2O + O2
The nitrogen dioxide so formed confers the characteristic yellow color often exhibited by this acid. However, the reaction is too slow to be a practical source of NO2.
Thermal properties
At low temperatures, NO2 reversibly converts to the colourless gas dinitrogen tetroxide (N2O4):
- 2 NO2 ⇌ N2O4
The exothermic equilibrium has
At 150 °C (302 °F; 423 K), NO2 decomposes with release of oxygen via an endothermic process (ΔH = 14 kJ/mol):
- 2 NO2 →2 NO + O2
As an oxidizer
As suggested by the weakness of the N–O bond, NO2 is a good oxidizer. Consequently, it will combust, sometimes explosively, in the presence of hydrocarbons.[16]
Hydrolysis
NO2 reacts with water to give nitric acid and nitrous acid:
- 2 NO2 + H2O → HNO3 + HNO2
This reaction is one of the steps in the
Conversion to nitrates
NO2 is used to generate anhydrous metal nitrates from the oxides:[15]
- MO + 3 NO2 → M(NO3)2 + NO
Alkyl and metal iodides give the corresponding nitrates:[12]
- TiI4 + 8 NO2 → Ti(NO3)4 + 4 NO + 2 I2
With organic compounds
The reactiivity of nitrogen dioxide toward organic compounds has long been known.[18] For example, it reacts with amides to give N-nitroso derivatives.[19] It is used for nitrations under anhydrous conditions.[20]
Uses
NO2 is used as an intermediate in the manufacturing of
Environmental presence
Nitrogen dioxide typically arises via the oxidation of nitric oxide by oxygen in air (e.g. as result of corona discharge):[15]
- 2 NO + O2 → 2 NO2
NO2 is introduced into the environment by natural causes, including entry from the stratosphere, bacterial respiration, volcanos, and lightning. These sources make NO2 a trace gas in the atmosphere of Earth, where it plays a role in absorbing sunlight and regulating the chemistry of the troposphere, especially in determining ozone concentrations.[24]
Anthropogenic sources
Nitrogen dioxide also forms in most combustion processes. At elevated temperatures nitrogen combines with oxygen to form nitrogen dioxide:
- N2 + 2 O2 → 2 NO2
For the general public, the most prominent sources of NO2 are
Outdoors, NO2 can be a result of traffic from motor vehicles.
Toxicity
NO2 diffuses into the epithelial lining fluid (ELF) of the respiratory epithelium and dissolves. There, it chemically reacts with antioxidant and lipid molecules in the ELF. The health effects of NO2 are caused by the reaction products or their metabolites, which are reactive nitrogen species and reactive oxygen species that can drive bronchoconstriction, inflammation, reduced immune response, and may have effects on the heart.[32]
Acute exposure
Acute harm due to NO2 exposure is rare. 100–200 ppm can cause mild irritation of the nose and throat, 250–500 ppm can cause edema, leading to bronchitis or pneumonia, and levels above 1000 ppm can cause death due to asphyxiation from fluid in the lungs. There are often no symptoms at the time of exposure other than transient cough, fatigue or nausea, but over hours inflammation in the lungs causes edema.[33][34]
For skin or eye exposure, the affected area is flushed with saline. For inhalation, oxygen is administered,
It is classified as an
Long-term
Exposure to low levels of NO2 over time can cause changes in lung function.[38] Cooking with a gas stove is associated with poorer indoor air quality. Combustion of gas can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.[9][10] Children exposed to NO2 are more likely to be admitted to hospital with asthma.[39]
Environmental effects
Interaction of NO2 and other NOx with water, oxygen and other chemicals in the atmosphere can form acid rain which harms sensitive ecosystems such as lakes and forests.[40] Elevated levels of NO
2 can also harm vegetation, decreasing growth, and reduce crop yields.[41]
See also
- Dinitrogen tetroxide (N2O4)
- Nitric oxide (NO) – pollutant that is short lived because it converts to NO2 in the presence of ozone
- Nitrite (NO−2)
- Nitrous oxide (N2O) – "laughing gas", a linear molecule, isoelectronic with CO2 but with a nonsymmetric arrangement of atoms (NNO)
- Nitryl
References
- ^ "nitrogen dioxide (CHEBI:33101)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute. 13 January 2008. Main. Archived from the original on 4 March 2016. Retrieved 4 October 2011.
- ^ a b c d Haynes, 4.79.
- S2CID 97875925.
- ^ Haynes, 4.134.
- ^ Haynes, 5.16.
- ^ a b c d e NIOSH Pocket Guide to Chemical Hazards. "Nitrogen dioxide". National Institute for Occupational Safety and Health (NIOSH).
- ^ a b "Nitrogen dioxide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ a b This article incorporates public domain material from Nitrogen dioxide. United States Environmental Protection Agency. Feb 23, 2016.
- ^ a b "Clearing the Air: Gas Cooking and Pollution in European Homes". CLASP. 8 November 2023. Retrieved 2024-05-05.
- ^ a b Seals, Brady; Krasner, Andee. "Gas Stoves: Health and Air Quality Impacts and Solutions". RMI. Retrieved 2024-05-05.
- ^ "Immediately Dangerous to Life or Health Concentrations (IDLH): Nitrogen dioxide". The National Institute for Occupational Safety and Health (NIOSH). May 1994. Retrieved October 20, 2023.
- ^ ISBN 978-0-08-037941-8.
- ^ ISBN 978-3-527-30673-2.
- ISBN 978-0-08-037941-8.
- ^ ISBN 0-12-352651-5.
- ^ physical chemistry
- doi:10.1039/B208564J.
- .
- .
- ISBN 978-0-471-72091-1
- ISBN 978-0-309-09225-8
- ^ "Mechanism Overview, June 2012" (PDF). noxilizer.com. Noxilizer, Inc. Archived from the original (PDF) on 12 April 2016. Retrieved 2 July 2013.
- ^ Cotton, Simon (21 March 2013) Nitrogen dioxide. RSC Chemistry World.
- ^ WHO Air Quality Guidelines – Second Edition. Chapter 7.1 Nitrogen Dioxide.
- ^ "Air quality guidelines – global update 2005". WHO. Archived from the original on March 9, 2014. Retrieved 2016-10-19.
- ^ US Dept. of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Division of Toxicology. April 2002 ATSDR Nitrous Oxides.
- ^ "The Impact of Unvented Gas Heating Appliances on Indoor Nitrogen Dioxide Levels in 'TIGHT' Homes" (PDF). ahrinet.org. 2013-03-21. Archived from the original (PDF) on 2020-08-05. Retrieved 2018-09-25.
- PMID 9731022.
- ^ This article incorporates public domain material from Nitrogen Dioxide Basic Information. United States Environmental Protection Agency. Retrieved February 23, 2016.
- PMID 348288.
- PMID 1887117.
- ^ a b U.S. EPA. Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (2016 Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/068, 2016. Federal Register Notice Jan 28, 2016 Free download available at Report page at EPA website.
- ^ Toxnet Nitrogen dioxide: Human Health Effects Page accessed March 28, 2016.
- ^ CDC NIOSH International Chemical Safety Cards (ICSC): Nitrogen Dioxide Page last reviewed: July 22, 2015; Page last updated: July 1, 2014.
- ^ Agency for Toxic Substances and Disease Registry via the CDC Medical Management Guidelines for Nitrogen Oxides Page last reviewed: October 21, 2014; Page last updated: October 21, 2014
- ^ University of Kansas Hospital, Poison Control Center Poison Facts: Medium Chemicals: Nitrogen Dioxide Archived 2016-04-11 at the Wayback Machine page accessed March 28, 2016
- ^ "40 C.F.R.: Appendix A to Part 355—The List of Extremely Hazardous Substances and Their Threshold Planning Quantities" (PDF) (July 1, 2008 ed.). Government Printing Office. Archived from the original (PDF) on February 25, 2012. Retrieved October 29, 2011.
- PMID 28615020.
- PMID 38623450.
- ^ US EPA, OAR (2016-07-06). "Basic Information about NO2". US EPA. Retrieved 2020-07-03.
- ^ "Nitrogen oxides". Queensland Government. Retrieved 2020-07-03.
Cited sources
- Haynes, William M., ed. (2011). ISBN 978-1-4398-5511-9.
External links
- International Chemical Safety Card 0930
- National Pollutant Inventory – Oxides of nitrogen fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- WHO-Europe reports: Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
- Nitrogen Dioxide Air Pollution
- Current global map of nitrogen dioxide distribution
- A review of the acute and long term impacts of exposure to nitrogen dioxide in the United Kingdom IOM Research Report TM/04/03
- Reaction of nitrogen dioxide with hydrocarbons and its influence on spontaneous ignition