Chlorinated hydrocarbons phosgene

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

Phosgenes Thermal decomposition of chlorinated hydrocarbons, degreasing, manufacture of dyestuffs, pharmaceuticals, organic chemi- Metal fabrication, heavy chemicals Damage capable of leading to pulmonary edema, often delayed... 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

A fire is reported subsequent to industrial mixing of calcium peroxide and a chlorinated paraffin. Even completely chlorinated hydrocarbons can be oxidised, to phosgene. 

When chloroform is heated to decomposition, phosgene gas is formed (NIOSH, 1997). At temperatures greater than 450 °C, tetrachloroethane, HCl, and various chlorinated hydrocarbons are formed. Heating chloroform in the presence of dilute caustics (e.g., sodium hydroxide) yields formic acid (WHO, 1994). 

Process Economics Program Report SRI International. Menlo Park, CA, Isocyanates IE, Propylene Oxide 2E, Vinyl Chloride 5D, Terephthalic Acid and Dimethyl Terephthalate 9E, Phenol 22C, Xylene Separation 25C, BTX, Aromatics 30A, o-Xylene 34 A, m-Xylene 25 A, p-Xylene 93-3-4, Ethylbenzene/Styrene 33C, Phthalic Anhydride 34B, Glycerine and Intermediates 58, Aniline and Derivatives 76C, Bisphenol A and Phosgene 81, C1 Chlorinated Hydrocarbons 126, Chlorinated Solvent 48, Chlorofluorocarbon Alternatives 201, Reforming for BTX 129, Aromatics Processes 182 A, Propylene Oxide Derivatives 198, Acetaldehyde 24 A2, 91-1-3, Acetic Acid 37 B, Acetylene 16A, Adipic Acid 3 B, Ammonia 44 A, Caprolactam 7 C, Carbon Disulfide 171 A, Cumene 92-3-4, 22 B, 219, MDA 1 D, Ethanol 53 A, 85-2-4, Ethylene Dichloride/Vinyl Chloride 5 C, Formaldehyde 23 A, Hexamethylenediamine (HMDA) 31 B, Hydrogen Cyanide 76-3-4, Maleic Anhydride 46 C, Methane (Natural Gas) 191, Synthesis Gas 146, 148, 191 A, Methanol 148, 43 B, 93-2-2, Methyl Methacrylate 11 D, Nylon 6-41 B, Nylon 6,6-54 B, Ethylene/Propylene 29 A, Urea 56 A, Vinyl Acetate 15 A. 

SAFETY PROFILE Moderately toxic by ingestion. Mutation data reported. A very dangerous fire hazard when exposed to heat or flame. When heated to decomposition it emits highly toxic fumes of CT and phosgene. See also CHLORINATED HYDROCARBONS, ALIPHATIC and PROPYLENE DICHLORIDE. 

DOT CLASSIFICATION 6.1 Label Poison SAFETY PROFILE A poison by ingestion, inhalation, skin contact, intraperitoneal, intravenous, and subcutaneous routes. Moderately toxic to humans by inhalation. It can affect the nervous system, liver, spleen, and lungs. An experimental teratogen. Mutation data reported. A severe eye and mild skin irritant. Flammable liquid when exposed to heat, flame, or oxidizers. To fight fire, use alcohol foam, CO2, dry chemical. Violent reaction with chlorosulfonic acid, ethylene diamine, sodium hydroxide. Reacts with water or steam to produce toxic and corrosive fumes. Potentially violent reaction with oxidizing materials. When heated to decomposition it emits highly toxic fumes of CT and phosgene. See also CHLORINATED HYDROCARBONS, 7M.IPHATIC. 

When heated to decomposition it emits highly toxic fumes of CT and phosgene. See also CHLORINATED HYDROCARBONS, ALIPHATIC. 

Phosgene is widely used as a chemical intermediate. It is used in metallurgy and in the production of pesticides, herbicides, and many other compounds. It is a by-product of chloroform biotransformation and can be generated from some chlorinated hydrocarbon solvents under intense heats. Phosgene has been used as a chemical warfare agent. 

Emissions of phosgene most commonly arise as a result of its release during manufacture and use, its formation from the decomposition of chlorinated hydrocarbons, and its formation from the photochemical oxidation of air-borne chlorinated organic materials, particularly the C, and C chloroalkanes, and chloroethenes. The location and estimation of air emissions from sources of phosgene have been described by the US Environmental Protection Agency [2088b], Catastrophic emissions and accidental spills and leaks are discussed in Section 3.6. 

Chlorinated hydrocarbons, and other halogenated materials containing chlorine, can decompose to more toxic substances when subjected to heat or electromagnetic radiation in the presence of air or moisture [201,586]. The products of decomposition may include chlorine, hydrogen chloride and phosgene, inter alia, and it is clearly important, in view of the widespread commercial uses of the various halogenated hydrocarbons as solvents, refrigerants. 

The oxidation of various chlorinated hydrocarbons, either by air or other means, has been used as a method of synthesizing phosgene this is discussed in detail in Chapter S. 

Owing to their low flammability and excellent degreasing properties, the chlorinated hydrocarbons are commonly used as solvents in the laboratory, office and industrial workplaces. These materials, however, are particularly susceptible to thermal or photochemical decomposition to phosgene in normal environments. 

Chlorinated hydrocarbons mixed with an excess of air. l emperatures corresponding to maximum phosgene production. Measured in mg of COCl per g of chlorinated hydrocarbon. 

Phosgene may be formed when chlorinated hydrocarbons are exposed to ultraviolet radiation in the presence of air [627]. Dichloromethane was found to contain trace quantities of phosgene after storage for a few days in clear glass flasks, despite being protected from exposure to direct sunlight [855]. Trichloromethane decomposes photooxidatively in a similar way to that described for its thermal oxidation (Section 3.3.3), the process differing in the... 

The photochemical oxidation of chlorinated hydrocarbons into phosgene has been the subject of particular concern for the welding workshop [679,2217]. Solvent residues from degreasing procedures may remain on the part to be welded, particularly in cracks and cavities where the solvent may have been drawn by capillary action [627]. Upon exposure to the heat of the welding arc, the residues vaporize and although some thermal oxidation will then... 

Although phosgene is undoubtedly a photolysis product of a number of commodity chlorinated hydrocarbons, the quantity of phosgene formed in the atmosphere, and the relative importance of the various sources, is difficult to assess [2088b]. Phosgene is likely to be... 

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