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Pentachlorophenol
IUPAC name
2,3,4,5,6-Pentachlorophenol
Identifiers
CAS number
87-86-5
PubChem
992
SMILES
Clc1c(Cl)c(Cl)c(Cl)c(Cl)c1O
ChemSpider ID
967
Properties
Molecular formula
C6HCl5O
Molar mass
266.34 g mol?1
Appearance
White crystalline solid
Density
1.978 g/cm3 at 22
Melting point
190-191
Boiling point
309-310 (dec.)
Solubility in water
0.020 g/L at 30
Except where noted otherwise, data are given formaterials in their standard state(at 25, 100kPa)Infobox references
Pentachlorophenol (PCP) is a synthetic substance that was first produced in the 1930s. It is marketed under the trade names Santophen, Pentachlorol, Chlorophen, Chlon, Dowicide 7, Pentacon, Penwar, Sinituho and Penta among others. It can be found in two forms: PCP itself or as the sodium salt of PCP, which dissolves easily in water. In the past, it has been used as a herbicide, insecticide, fungicide, algaecide, disinfectant and as an ingredient in antifouling paint. Some applications were in agricultural seeds (for nonfood uses), leather, masonry, wood preservation, cooling tower water, rope and paper mill system.
There are two general methods for preserving wood. The pressure process method involves placing wood in a pressure-treating vessel where it is immersed in PCP and then subjected to applied pressure. In the non-pressure process method, PCP is applied by spraying, brushing, dipping, and soaking. Utility companies save millions of dollars in replacement poles, because the life of these poles increases from approximately 7 years for an untreated pole to about 35 years for a preservative-treated pole.
Contents
1 Synthesis
2 Exposure
3 Toxicity
4 Fate in humans and animals
5 Releases to the environment
6 Environmental fate
7 Pentachlorophenol by country
7.1 New Zealand
7.2 United States
8 References
9 External links
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Synthesis
PCP can be produced by the chlorination of phenol in the presence of catalyst (anhydrous aluminium or ferric chloride) and a temperature of up to approximately 191 . However this process is incomplete. As a result, commercial grade PCP is between 84% and 90% pure. During the process several contaminants including other polychlorinated phenols, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are produced too, which can be more toxic than the PCP itself.
Exposure
People may be exposed to PCP in occupational settings through the inhalation of contaminated workplace air and dermal contact or with wood products treated with the chemical. Also, general population exposure may occur through contact with contaminated environment media, particularly in the vicinity of wood treatment facilities and hazardous wastes sites. In addition, some other important routes of exposure seem to be the inhalation of contaminated air, ingestion of contaminated ground water used as a source of drinking water, ingestion of contaminated food, and dermal contact with soils or products treated with the chemical.
Toxicity
Short-term exposure to large amounts of PCP can cause harmful effects on the liver, kidneys, blood, lungs, nervous system, immune system, and gastrointestinal tract. Elevated temperature, profuse sweating, uncoordinated movement, muscle twitching, and coma are additional side effects.
Contact with PCP (particularly in the form of vapor) can irritate the skin, eyes, and mouth. Long-term exposure to low levels such as those that occur in the workplace can cause damage to the liver, kidneys, blood, and nervous system. Finally exposure to PCP is also associated with carcinogenic, renal, and neurological effects. The U.S. Environmental Protection Agency Toxicity Class classifies PCP in group B2 (probable human carcinogen).
Fate in humans and animals
PCP is quickly absorbed through the gastrointestinal tract following ingestion. Accumulation is not common, but if it does occur, the major sites are the liver, kidneys, plasma protein, spleen and fat. Unless kidney and liver functions are impaired, PCP is quickly eliminated from tissues and blood, and is excreted, mainly unchanged or in conjugated form via the urine. Single doses of PCP have half-lives in blood of 30 to 50 hours in humans. Biomagnification of PCP in the food chain is not thought to be significant due to the fairly rapid metabolism of the compound by exposed organisms.
Releases to the environment
PCP has been detected in surface waters and sediments, rainwater, drinking water, aquatic organisms, soil, and food, as well as in human milk, adipose tissue, and urine. As PCP is generally used for its properties as a biocidal agent, there is considerable concern about adverse ecosystem effects in areas of PCP contamination.
Releases to the environment are decreasing as a result of falling consumption and changing use methods. However, PCP is still released to surface waters from the atmosphere by wet deposition, from soil by run off and leaching, and from manufacturing and processing facilities. PCP is released directly into the atmosphere via volatilization from treated wood products and during production. Finally, releases to the soil can be by leaching from treated wood products, atmospheric deposition in precipitation (such as rain and snow), spills at industrial facilities and at hazardous waste sites.
Environmental fate
After PCP is released into the atmosphere it is transformed via photolysis. The main biodegradative pathway for PCP is reductive dehalogenation. In this process, the compound PCP is broken down to tetracholorphenols, tricholorphenols, and dichlorophenols. Another pathway is methylation to pentaclhloroanisole (a more lipid soluble compound). These two methods eventually lead to ring cleavage and complete degradation.
In shallow waters, PCP is also quickly removed by photolysis. In deep or turbid water processes such as sorption and biodegradation take place. In reductive soil and sediments, PCP can be degraded within 14 days to 5 years, depending on the anaerobic soil bacteria that are present. However, adsorption of PCP in soils is pH dependent because it increases under acidic conditions and it decreases in neutral and basic conditions.
Pentachlorophenol by country
New Zealand
PCP was used in New Zealand as a timber preservative and antisapstain treatment and it was no longer used after 1988.
It was also sold as a moss killer to the general public (by Shell, at least) in the form of a 115g/L aqueous solution and labelled as a poison.
United States
Since the early 1980s, the purchase and use of PCP in the U.S has not been available to the general public. Nowadays most of the PCP used in the U.S is restricted to the treatment of utility poles and railroad ties. In the United States, any drinking water supply with a PCP concentration exceeding the MCL, 1ppb, must be notified by the water supplier to the public. Disposal of PCP and PCP contaminated substances are regulated under RCRA as a F-listed hazardous waste.
References
^ a b c d e “Consumer Factsheet on: Pentachlorophenol”. United Stated Environmental Protection Agency. 2006-11-28. http://www.epa.gov/safewater/contaminants/dw_contamfs/pentachl.html. Retrieved on 2008-02-26.
^ “EVALUATION SHEET”. ERMA. 2006. http://www.erma.govt.nz/consultations/ceir/v.pdf. Retrieved on 2009-02-04.
External links
Non-CCA Wood Preservatives: Guide to Selected Resources - National Pesticide Information Center
EPA on Pentachlorophenol
atsdr.cdc.gov/ on Pentachlorophenol
Categories: Fungicides | Organochlorides | Phenols
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