Water phosgene

Photolytic. Reported photooxidation products via OH radicals include carbon dioxide, carbon monoxide, formyl chloride, and phosgene (Spence et al, 1976). In the presence of water, phosgene hydrolyzes to HCl and carbon dioxide, whereas formyl chloride hydrolyzes to hydrogen chloride and carbon monoxide (Morrison and Boyd, 1971). 

Rona has made some experiments on the decomposition of war gases by water. He has demonstrated experimentally that some substances are rapidly decomposed by water (phosgene,... 

In the absence of water, phosgene reacts quantitatively with sodium iodide in acetone solution according to the equation COCI2 2NaI = CO I2 -j- 2NaCl. 

The water-phosgene system is a particularly difficult one to study, since water is a potentially reactive solvent and true equilibrium may not be established between the gas and liquid phases. The hydrolysis reaction of phosgene has been the subject of many conflicting statements and is dealt with in Section 9.10.3.1. 

Phosgene is responsible for 80% of the gas casualties in World War I Phosgene is a nerve gas used in World War II Phosgene is rapidly destroyed by water Phosgene is an effective chemical warfare agent... 

Chemical Properties. Phosgene is readily soluble in organic solvents and fatty oils. In water, phosgene is rapidly hydrolyzed with the formation of hydrochloric acid and carbon dioxide. 

Phosgene reacts slowly with cold water to give CO2 and HCl and more quickly at higher temperatures (25). In the reaction of gaseous phosgene with water, it is difficult to get the necessary intimate mixing of the gas and water. 

Because phosgene reacts with water, great care must be taken to prevent contamination with traces of water since this could lead to the development of pressure by hydrogen chloride and carbon dioxide. Wet phosgene is very corrosive therefore phosgene should never be stored with any quantity of water (4). 

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

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). 

Chloroform slowly decomposes on prolonged exposure to sunlight in the presence or absence of air and in the dark in the presence of air. The products of oxidative breakdown include phosgene, hydrogen chloride, chlorine, carbon dioxide, and water. At 290°C, chloroform vapor is not attacked by oxygen. In contact with iron and water hydrogen peroxide is also produced, probably by the following reaction sequence (2) ... 

Compound (1) decomposes to form dichloroacetyl chloride, which in the presence of water decomposes to dichloroacetic acid and hydrochloric acid (HCl) with consequent increases in the corrosive action of the solvent on metal surfaces. Compound (2) decomposes to yield phosgene, carbon monoxide, and hydrogen chloride with an increase in the corrosive action on metal surfaces. 

Stabilized tetrachloroethylene, as provided commercially, can be used in the presence of air, water, and light, in contact with common materials of constmction, at temperatures up to about 140°C. It resists hydrolysis at temperatures up to 150°C (2). However, the unstabilized compound, in the presence of water for prolonged periods, slowly hydrolyzes to yield trichloroacetic acid [76-03-9] and hydrochloric acid. In the absence of catalysts, air, or moisture, tetrachloroethylene is stable to about 500°C. Although it does not have a flash point or form flammable mixtures in air or oxygen, thermal decomposition results in the formation of hydrogen chloride and phosgene [75-44-5] (3). 

Phosgenation. Reaction of phosgene with arylamines to form ureas, and with reactive aryl species to form substituted hen zophen ones, are special cases of acylation. They are dealt with separately siace a more specialized plant is required than for other acylations. Urea formation takes place readily with water-soluble arylamines by simply passiag phosgeae through a slightly alkaline solutioa. An important example is carbonyl-J-acid from J-acid. 

Because of its bitter taste and water iasolubiUty, guaiacol has been chemically modified to improve its properties. Sulfonation provides a mixture of guaiacol-4- and 5-sulfonic acids which, as the potassium salts, is water-soluble, comparatively tasteless, but less active than guaiacol. Treatment of the sodium salt of guaiacol with phosgene provides guaiacol carbonate [553-17-1] (3) which also lacks the bitter taste of guaiacol, but is less water-soluble. 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

Use inherently safer chemistry (e.g., when phosgene is cooled in a heat exchanger, consider use of an inert oil as the coolant rather than water as heat exchanger tubes may fail)... 

Acetyl chloride CH3COCI Colourless, fuming, corrosive liquid Flash point 4°C When heated, emits phosgene Decomposes violently with water to produce heat and toxic fumes MCI... 

Benzoyl chloride C6H5COCI Colourless, fuming, corrosive liquid with a strong odour Combustible flash point 72°C Generates phosgene gas when heated Reacts strongly with water or water vapour, producing heat and toxic/corrosive fumes Use of water must be considered carefully... 

Fire Hazards - Flash Point (deg. F) 162 OC Flammable Limits in Air (%) 1.2 - 4.9 Fire Extinguishing Agents Foam, carbon dioxide, dry chemical, water fog Fire Extinguishing Agents Not To Be Used Water spray. Do not allow water to enter containers Special Hazards of Combustion Products Highly poisonous phosgene gas forms during fires Behavior in Fire At fire temperature the... 

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