Characteristics of Phosgene - Essay Example

Phosgene Phosgene is a colorless, non flammable and highly poisonous liquid. It is the most dangerous among the group of lung damaging agents. Phosgene is known by many other names. Some of these are: Carbonic acid dichloride, Carbonic dichloride, carbon oxychloride, Carbonyl chloride, Choloroformyl chloride. The UN Number of phosgene is UN1076, EINECS Number is 200-870-3, DOT Label (U.S.A.) is PG, and DOT hazard Class (U.S.A.) is Poison A. Its CAS Number is 75-44-5. (Air Liquide SA, 2006) Structure Phosgene is represented as COCl2, or CCl2O. The molecular structure of phosgene is as shown below: Molecular Structure of Phosgene Chemical and Physical Properties Phosgene is a colorless gas at normal temperatures of 21oC or 70oF (bin.pdf). At temperatures above 250oC, phosgene decomposes to mixtures of carbon monoxide (CO), chlorine gas (Cl2), carbon dioxide (CO2), and carbon tetrachloride (CCl4). Owing to its low boiling point of 7.56oC, it is very volatile and non persistent. "It may remain for long periods of time in trenches and other low lying areas" (Federation of American Scientists, 2007). Phosgene smells of newly mown hay, at room temperature. It is soluble in fatty oils and organic solvents. Its odor threshold is 0.12-5.7 ppm. And its Permissible Exposure Limit Threshold Limit value (by volume in air) is 0.1 ppm (American Chemistry Council, 2002). Physical properties of Phosgene are given below: Physical Properties of Phosgene (Source: American Chemistry Council, phosgenepanel.org) Property Value Metric Units Molecular weight Critical Temperature Critical Pressure Critical Volume 98.9158 181.85 5.67E+07 190 g/mol C Dyne/cm2 cm3/mol Critical Compressibility Factor Melting Point Triple Point Temperature Triple Point Pressure 0.285 -127.78 -127.78 9.20651 C C Dyne/cm2 Normal Boiling Point Liquid Molar Volume 7.56 70.5389 C cm3/mol Ideal Gas Heat of Formation Ideal Gas Gibbs of Formation -2.19E+12 -2.05E+12 erg/mol erg/mol Ideal Gas Absolute Entropy Standard Absolute Entropy Standard Heat of Formation Standard Gibbs of Formation 2.84E+09 2.84E+09 -2.19E+12 -2.05E+12 erg/mol-K erg/mol-K erg/mol erg/mol Enthalpy of fusion at M.P. Heat of Combustion Acentric Factor Radius of Gyration 5.74E+10 -1.75E+12 0.201309 2.88E-08 erg/mol erg/mol cm Solubility Parameter Dipole Moment Van der Waals Volume Van der Waals Area 5.64E+04 1.16919 34.9 5.20E+09 (erg/cm3)A1/2 Debye (D) cm3/mol cm2/mol Refractive Index Flash Point Upper Flammability Limit Lower Flammability 1.35609 Unknown Unknown Unknown C vol% in air vol% in air Upper Flammability Temperature Lower Flammability Temperature Auto-Ignition Temperature Unknown Unknown Unknown C C C Density Vapor Density Vapor Pressure 1.38 (20oC) 3.4 365 (-10oC) 555 (0oC) 1173 (20oC) g/cm3 mmhg LC50 5 ppm/1h Phosgene hydrolyses slowly in water and releases hydrochloric acid and carbon dioxide. Phosgene reacts easily with caustic solution and even more so with ammonia and ammonia water. Phosgene produces hazardous chemical reactions with certain substances. Powdered aluminum burns in the presence of the vapor of phosgene. Phosgene also reacts with alcohols. For example, with 2,4-Hexadiyne-1,6-diol, phosgene produces a shock sensitive compound 2,4-hexadiyne-1,6-bischloroformate. It also produces hazardous products on reaction with secondary amines. When phosgene is mixed with potassium and subjected to shock, it explodes (American Chemistry Council, 2002). Mechanism of Injury Phosgene is a highly dangerous pulmonary toxicant. Its exposure may not produce any symptoms for a long time, and by the time symptoms are detected it usually results in fatalities. Its exposure produces massive pulmonary edema. The routes of exposure to phosgene are inhalation, and skin/eye contact. Inhalation: This is the major route of phosgene exposure. Since it is hard to detect the odor, there may be prolonged asymptomatic exposures. Phosgene also causes asphyxiation in poorly ventilated places, since it is heavier than air at temperatures above 8oC (American Chemistry Council, 2006) Skin/Eye Contact: Phosgene will cause irritation and reddening of eyes and wet skin on contact. Liquid Phosgene can cause severe chemical burns of skin and cornea (American Chemistry Council, 2006). Pathophysiology Two mechanisms of injury have been noted in cases of Phosgene exposure. It may act by Hydrolysis after inhalation, and form HCl in the alveoli. And secondly, it may act through "direct Acylating reactions with nucleophilic structures of cells and their products" (American Chemistry Council, 2006). In the former case, it may cause irritation of the eyes, nose and throat and cough and chest oppression (American Chemistry Council, 2006). In the latter case, the reactions in the respiratory tract may damage the terminal bronchioli and alveoli, leading to hypoxemia and, finally, to pulmonary edema. This stage occurs about 24-30 hours after exposure and may stay for a few days. If a patient survives for more than 48 hours, they would probably recover without sequelae. Rest, warmth, sedation and oxygen are recommended. In some cases, corticosteroids in high doses may also be prescribed (Federation of American Scientists). Manufacture and Commercial Chemistry Phosgene is produced when a mixture of high purity carbon monoxide (CO) and anhydrous chlorine (Cl2) gases are exposed to carbon catalyst, activated charcoal. The reaction is exothermic. The reaction is shown as: Activated CO + Cl2 = COCl2 + Heat Carbon monoxide Chlorine Charcoal (Source: Textbook of Organic Chemistry, C.R. Noller, 1966, as cited in American Chemistry Council 2002) There are many industrial manufacturers of Phosgene, mainly for captive consumption in the production of di- and poly-isocyanates and polycarbonate resins. Bayer Polymers, Baytown, Tex., produces the highest quantity at 1,150 million pounds (2002). The price of phosgene in 2002 was $0.78 per pound. (The Innovation Group, 2002) Disposal and Defense Personal precautions against Phosgene exposure require the use of breathing filters and self contained breathing equipment and chemically resistant protective clothing, adequate air ventilation and evacuation from the area. Phosgene changes the pH balance in aqueous ecosystems. Environmental precautions would include measures to stop its release, and stop its entry to sewers, basements and workpits, and the use of fine water spray to reduce vapor (Air Liquide SA, 2005). Phosgene does not remain for very long in the atmosphere as it vaporizes and disperses, unless trapped in low lying or closed areas. The cleanup process would involve the ventilation of the affected area, and washing down the contaminated equipment or material with copius quantities of water, and hosing down of the affected area. Phosgene should not be disposed into the atmosphere, or in places where it could become accumulated. (Air Liquide SA, 2005) References American Chemistry Council. Properties of Phosgene. 2002. phosgenepanel.org. www.americanchemistry.com/s_acc/bin.aspSID=1&DID=4402&CID=1175&VID=109&DOC=File.PDF. (accessed March 8, 2007) American Chemistry Council. PHOSGENE Information on Options for First Aid and Medical Treatment. 2006. Phosgenepanel.org. www.americanchemistry.com/s_acc/bin.aspCID=1175&DID=4396&DOC=FILE.PDF. (accessed March 8, 2007) AIR LIQUIDE SA, France. Phosgene Safety Data Sheet. Revised edition no: 1, Date: 15/7/2005, AL099. 2005. [Online]encyclopedia.airliquide.com/sds/en/099_AL_EN.pdf. (accessed March 8, 2007) Air Liquide, France. Phosgene. Gas Encyclopedia. 2006. [Online]http://encyclopedia.airliquide.com/encyclopedia.aspGasID=100. (accessed March 8, 2007) Federation of American Scientists. Lung Damaging Agents (Choking Agents). Chapter 4. www.fas.org. [Online]http://www.fas.org/nuke/guide/usa/doctrine/dod/fm8-9/3ch4.htm. (accessed March 8, 2007) International Programme on Chemical Safety and the European Commission. Phosgene. IPCS 2006. ICSC: 0007, August 2002. International Occupational Safety and health Information Center. International Labor Organization. [Online]http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0007.htm. (accessed March 8, 2007) Noltkamper, D., & Burgher, S.W. 2007. Toxicity, Phosgene. Toxicology Profiles. eMedicine from WebMD. January 11, 2007. http://www.emedicine.com/emerg/topic849.htm. (accessed March 8, 2007) The Innovation Group. Phosgene. Chemical Profiles. 2002. [Online]http://www.the-innovation-group.com/ChemProfiles/Phosgene.htm.(accessed March 8, 2007) Read More