Decomposition phosgene

Fig. 3. Schematic of toluene diamine phosgenation process A, cold phosgenator B, hot phosgenator C, wash column D, solvent distillation E, preflasher F, evaporator G, TDI distillation H, phosgene removal I, HCl absorber and K, phosgene decomposition.

Waste Gas Streams. Several methods of decomposing phosgene in waste gas streams are used. The outlet gas from the phosgene decomposition equipment is continuously monitored for residual phosgene content to ensure complete decomposition. 

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). 

Caustic coupling process, 10 356-357 Caustic flooding, 15 629-630 Caustic fusion, of zircon, 26 628 Causticiation, 15 63 in Bayer process, 2 352 slaked lime in, 15 45, 63 Caustic scrubbing, phosgene decomposition by, 15 807... 

CI2CO Phosgene, decomposition product in purified CHCI3... 

Other acetyl chloride preparations include the reaction of acetic acid and chlorinated ethylenes in the presence of ferric chloride [7705-08-0] (29) a combination of ben2yl chloride [100-44-7] and acetic acid at 85% yield (30) conversion of ethyUdene dichloride, in 91% yield (31) and decomposition of ethyl acetate [141-78-6] by the action of phosgene [75-44-5] producing also ethyl chloride [75-00-3] (32). The expense of raw material and capital cost of plant probably make this last route prohibitive. Chlorination of acetic acid to monochloroacetic acid [79-11-8] also generates acetyl chloride as a by-product (33). Because acetyl chloride is cosdy to recover, it is usually recycled to be converted into monochloroacetic acid. A salvage method in which the mixture of HCl and acetyl chloride is scmbbed with H2SO4 to form acetyl sulfate has been patented (33). 

Low boiling isocyanates, such as methyl isocyanate [624-83-9] are difficult to prepare via conventional phosgenation due to the fact that the A/-alkyl carbamoyl chlorides are volatile below their decomposition poiat. Interestingly, A/-ethyl carbamoyl chloride decomposes at its boiling poiat whereas the A/-propyl carbamoyl chloride is thermoly2ed cleanly into isocyanate and hydrogen chloride. 

Waste Disposal. Because of its low Boiling poiat and high, toxicity, measures must be taken to prevent the entrance of phosgene iato drains or sewers. If recycle of phosgene is not feasible, phosgene waste can be handled by one of the decomposition methods mentioned above, ie, caustic scmbbiag, moist activated carbon towers, or combustion. 

Unreacted phosgene is removed from the cmde chloroformates by vacuum stripping or gas purging. Chloroformates of lower primary alcohols are distillable however, heavy-metal contamination should be avoided. As stated earlier, chloroformates generating a stable carbonium ion on decomposition, ie, secondary or tertiary chloroformates or henzylic chloroformates, are especially unstable in the presence of heavy metals and more specifically Lewis acids and, hence, should be distilled at as low a temperature and high vacuum as possible. 

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). 

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... 

Aryl isothiocyanates can be prepared by the action of thio-phosgene on the arylamine (this reaction fails with naphthyl compounds), by fission of a 5ym-diaryIthiourea with acidic reagents (this reaction involves the loss of half the amine used), and by the decomposition of an ammonium aryldithiocar-bamate (low yields are reported for naphthyl and other compounds).The procedure described here is that of Baxter, Cymerman-Craig, Moyle, and White. ... 

To this acid was then added 1 g of 4-ethyl-2,3-dioxo-1-piperazinocarbonyl chloride (from the reaction of N-ethylethylenediamine and diethyl oxalate to give 2,3-dioxo-4-ethyl-piperazine which Is then reacted with phosgene) and the resulting mixture was reacted at 15°C to 20°C for 2 hours. After the reaction, a deposited triethylamine hydrochloride was separated by filtration, and the filtrate was incorporated with 0.4 g of n-butanol to deposit crystals. The deposited crystals were collected by filtration to obtain 1.25 g of white crystals of 6-[ D(—l-Ct-(4-ethyl-2,3-dioxo-1 -piperazinocarbonylaminolphenylacetamido] penicillanic acid. Into a solution of these crystals in 30 ml of tetrahydrofuran was dropped a solution of 0.38 g of a sodium salt of 2-ethyl-hexanoic acid in 10 ml of tetrahydrofuran, upon which white crystals were deposited. The deposited crystals were collected by filtration, sufficiently washed with tetrahydrofuran and then dried to obtain 1.25 g of sodium salt of 6-[D(—)-a-(4-ethyl-2,3-di-0X0-1-piperazinocarbonylaminolphenylacetamido] penicillanic acid, melting point 183°C to 185°C (decomposition), yield 90%. 

Respiratory Effects. A worker developed labored breathing and respiratory edema after welding stainless steel that had been washed in trichloroethylene (Sjogren et al. 1991). The effects were attributed to inhalation of the trichloroethylene decomposition products phosgene and diehloroacetyl chloride, although a history of cigarette smoking may have predisposed the subjeet to these respiratory effects. 

Highly toxic perfluoroisobutylene (PFIB) poses a serious health hazard to the human respiratory tract. PFIB is a thermal decomposition of polytetrafluo-roethylene (PTFE), e.g., Teflon. PFIB is approximately lOx as toxic as phosgene. Inhalation of this gas can cause pulmonary edema, which can lead to death. PFIB is included in Schedule 2 of the Chemical Weapons Convention (CWC), the aim of the inclusion of chemicals such as PFIB was to cover those chemicals, which would pose a high risk to the CWC. 

Moist phosgene is very corrosive it decomposes in the presence of moisture to form hydrochloric acid and carbon monoxide thermal decomposition may release toxic and/or hazardous gases. 

Decomposition Toxic gases and vapors (such as oxides of nitrogen, phosgene, nitrosyl chloride, chlorine, and carbon monoxide) may be released when chloropicrin decomposes. 

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