Peroxyacetyl nitrate
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| Surname | Peroxyacetyl nitrate | ||||||||||||||||||
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| Molecular formula | C 2 H 3 NO 5 | ||||||||||||||||||
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| Molar mass | 121.05 g mol −1 | ||||||||||||||||||
| Physical state |
liquid |
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| boiling point |
105 ° C |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Peroxyacetyl nitrate (PAN) is a trace gas in the atmosphere and at the same time an air pollutant .
Emergence
PAN produced in the atmosphere by the photochemical oxidation of hydrocarbons to peracetic acid radical in the presence of nitrogen dioxide (NO 2 ), that is - there is not discharged directly into the atmosphere - a secondary air pollutant. Along with ozone and hydrogen peroxide (H 2 O 2 ), it is the most important component of photochemical smog and its concentration is closely linked to the course of the ozone concentration.
In addition to PAN, there are peroxypropionyl, butyryl nitrate and benzoyl nitrate (PPN, PBN, PBzN) (generally peroxy acyl nitrate). Chlorinated forms have also been observed. However, PAN is the most important link in this group. PAN and its homologues reach around 5 to 20% of the concentration of ozone in metropolitan areas, typically around 10%. Depending on the temperature, PAN breaks down again into NO 2 and the peroxyacetyl radical. As a result of this stability, however, it can be transported over long distances and functions as a transporter of nitrogen oxides in clean air areas.
The breakdown of PAN in the atmosphere is primarily thermal; Thus, the long-distance transport of PAN takes place through cold zones of the atmosphere, while the degradation takes place in warmer layers. Degradation also takes place through UV photolysis. PAN thus represents both a source and a sink of RO x and NO x radicals and is therefore also referred to as reservoir gas.
synthesis
PAN can be produced from peracetic acid in a lipophilic solvent . For this purpose, degassed n - tridecane and peracetic acid are placed in the round-bottomed flask cooled by an ice bath and 98% sulfuric acid is carefully added. Concentrated nitric acid is then added dropwise . When the reaction is complete, it is washed four times with ice water, the aqueous, strongly acidic phase is discarded and the organic phase is dried with anhydrous sodium sulfate . This procedure results in PAN dissolved in n- tridecane, which can be reused by expelling it with an inert gas (e.g. helium or nitrogen ) and collecting it in cold traps . Great caution and care must be exercised in this synthesis as there is a risk of explosion.
Alternatively, PAN can also be obtained by synthesis in the gas phase. To do this, a gas mixture of acetone and nitrogen dioxide (NO 2 ) is photolyzed using a mercury vapor lamp. Methyl nitrate (CH 3 ONO 2 ) is formed as a by-product .
Readings
The natural concentration of PAN in the atmosphere is below 0.1 µg / m³. Measurements in western German cities showed half-hourly values of up to about 25 µg / m³, known peak values (e.g. measured in Los Angeles in the 2nd half of the 20th century) are sometimes over 200 µg / m³ (for PAN, 1 ppm corresponds to 4370 µg / m³). Because of the complex measurement method used, PAN is usually only available at point measurements, i.e. no series of measurements comparable to ozone.
Harmful effects
PAN has a higher toxicity than ozone. The eye irritation that occurs with photochemical smog is caused less by the poorly water-soluble ozone than by PAN and accompanying trace gases. In addition, PAN is discussed as a factor in the development of skin cancer : chlorinated derivatives in particular, but also PAN itself, are considered mutagenic .
PAN has also been proven to have harmful effects on plants: it particularly damages the spongy tissue of leaves, starting from the stomata. Therefore, symptoms of pure PAN damage are often first observed on the underside of leaves (silver to bronze color with subsequent necrosis ). Certain sensitive plant species can therefore be used for the bioindication of PAN, e.g. B. French beans or the small nettle ( Urtica urens ).
During the thermal and photolytic degradation of peroxyacetyl nitrate, nitrogen oxides are formed, which promote ozone production in the lower troposphere .
PAN acts as a greenhouse gas in the atmosphere .
Acute and chronic toxicity
PAN causes acute eye irritation in humans. In a volunteer study in 1961, a concentration of 4.95 mg / m³ for 10 to 15 minutes was sufficient. A more recent study from 1987 showed the same symptoms at 0.64 mg / m³ (0.13 ppm). People with COPD reported an exacerbation of the symptoms of the disease after exposure to 0.059 mg / m³ PAN. Mice showed a higher susceptibility to infections by Streptococcus pyogenes which resulted in death after being exposed to a dose of 14.8 to 28.4 mg / m³ PAN for three hours. In long-term studies with rats for 4 weeks to 6 months, amounts from 11.8 ppm (4 weeks) or 74 mg / m³ (6 months) resulted in increased mortality and a wide variety of symptoms such as increased platelet count , enlarged lungs, abnormal behavior and stagnation in growth and severe inflammation up to metaplasia and hyperplasia of the airways. PAN was genotoxic in bacteria ( Salmonella typhimurium ) and lymphocytes from mice and cytotoxic at higher concentrations .
Individual evidence
- ^ A b Otto Hutzinger: Air Pollution . Springer, Berlin / Heidelberg 1989, ISBN 978-3-540-46113-5 ( limited preview in the Google book search).
- ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
- ^ Archives of Environmental Health . Vol. 15, Pg. 739, 1967 .
- ↑ Toxicology Vol. 8, Pg. 231, 1977 .
- ↑ JS Gaffney et al .: Peroxyacyl Nitrates . In: The Handbook of Environmental Chemistry. Vol. 4, Part B, pp. 1-38; Ed .: Hutzinger, O., Springer, 1989 .
- ↑ RK Talukdar, JB Burkholder, A.-M. Schmoltner, JM Roberts, RR Wilson, AR Ravishankara: Investigation of the loss processes for peroxyacetyl nitrate in the atmosphere: UV photolysis and reaction with OH . In: Journal of Geophysical Research . Volume 100, No. D7, 1995, pp. 14163-14173, doi: 10.1029 / 95JD00545 .
- ↑ T. Nielsen, AM Hansen, EL Thomsen: A convenient method for preparation of pure standards of peroxyacetyl nitrate for atmospheric analyzes. In: Atmospheric Environment . Volume 16, No. 10, 1982, pp. 2447-2450, doi: 10.1016 / 0004-6981 (82) 90134-2 .
- ↑ JS Gaffney, R. Fajer, GI Senum: An improved procedure for high purity gaseous peroxyacyl nitrate production: Use of heavy lipid solvents. In: Atmospheric Environment. Volume 18, No. 1, 1984, pp. 215-218, doi: 10.1016 / 0004-6981 (84) 90245-2 .
- ↑ JL Fry Spectroscopy and kinetics of atmospheric reservoir species: HOONO, CH 3 C (O) OONO 2 , CH 3 OOH and HOCH 2 OOH . Ph.D. Thesis , 2006.
- ↑ P. Warneck, T. Zerbach: Synthesis of Peroxyacetyl Nitrate in Air by Acetone Photolysis . In: Environmental Science & Technology , 1992, 26, p. 74, doi: 10.1021 / es00025a005 .
- ↑ S. Gilge: Peroxyacetyl nitrate - an important tropospheric trace substance (PDF file; 42 kB), GAW letter No. 34 of the German Weather Service, May 2006 .
- ↑ Draft OEHHA Report On Ethanol in Gasoline: Toxicity Summaries. (PDF; 579 kB) California Office of Environmental Health Hazard Assessment, February 1, 2002, p. A30 , accessed on December 4, 2017 (English).