PHOSGENE

Description

Phosgene is a colourless, reactive, non-flammable gas that is heavier than air with a musty hay odour. Phosgene is commonly stored under high pressure as a liquid. Phosgene reacts with water to form corrosive acids, reacts with most metals in the presence of moisture, liberating hydrogen, an extremely flammable gas, and reacts violently with alkalis. As an industrial and commercially important chemical, phosgene is a precursor material/chemical intermediate, and has extensive application in the manufacture of a wide range of products such as polymers – polyurethanes and polycarbonates – pesticides, medicines, dyestuffs, some insecticides, pharmaceuticals, and in metallurgy.

Description

Phosgene, or carbonyl chloride, is an extremely toxic gas, and it was used for that purpose during World War I. Its name is confusing because the molecule does not contain phosphorus. The manufacture of phosgene from chlorine and carbon monoxide was first patented in 1917. Phosgene has been used in many organic syntheses, notably of isocyanates; but its commercial use has been largely discontinued because of its toxicity.

Chemical properties

Phosgene, COCL2, also known as carbonyl chloride and chlorofonnyl chloride, is a colorless,poisonous gas produced by the action of chlorine and carbon monoxide. It condenses at 0 °C (32 OF) to a fuming liquid. Phosgene was used as a war gas, but is now used in the production of metal chlorides, pharmaceuticals, isocyanate resins,and perfumes.

Chemical properties

Phosgene (CG) is a colorless gas above 8.2C. Fog-like when concentrated. Colorless, fuming liquid below 8.2C. May have the appearance of a white cloud. Light yellow liquid when refrigerated or compressed. It is shipped as a liquefied compressed gas in steel cylinders. At low concentrations CG has a sweet (not pleasant) odor like newly mown hay, green corn, or moldy hay. In higher concentrations, it is poisonous with an odor that is suffocating, irritating, and pungent. The odor is only detectable for a short amount of time when CG is initially released and odor should not be regarded as a reliable indicator of overexposure. A fuming liquid below 8.3C/47F. Shipped as a liquefied compressed gas. The Odor Threshold is between 1.5
6 milligram per cubic meter. A choking agent, phosgene (CG) rapidly decompose in relative humidity over 70%.

Physical properties

Colorless gas at ambient temperature; strong, pungent odor; density of the gas 4.045 g/L at 25°C; density of the liquid 1.392 g/mL at 4°C; liquefies to a light yellow fluid at 8.2°C; freezes at -128°C; critical temperature 182°C, critical pressure 55.96 atm, critical volume 190 cm³/mol; slightly soluble in water with slow hydrolysis; soluble in benzene, toluene and acetic acid.

The Uses of PHOSGENE

PHOSGENE is an intermediate in organic synthesis, especially production of toluene diisocyanate and polymethylene polyphenylisocyanate; in metallurgy to separate ores by chlorination of the oxides and volatilization; occurs as a product of combustion whenever a volatile chlorine compound comes in contact with a flame or very hot metal; originally manufactured as an agent for chemical warfare during World War I.

The Uses of PHOSGENE

COCl2 is a very poisonous gas that was used in combat in the early twentieth century. When not concentrated, it smells like newly cut hay or grass.

The Uses of PHOSGENE

Phosgene is an important commodity and a major industrial chemical used in the production of pesticides and plastics. As a chemical intermediate it is used in the manufacture of dyestuffs, isocyanates and their derivatives, and many other organic chemicals. It was formerly used as a war gas and is also known by itsmilitary designation as “CG.”Much of the clinical information on phosgene poisoning has been developed in the context of its military applications. It is also used in the pharmaceutical industries and in metallurgy. Of the total phosgene produced, 62% is used to manufacture toluene diisocyanate, and varying amounts are used to manufacture related chemicals.

Definition

ChEBI: An acyl chloride obtained by substitution of both hydrogens of formaldehyde by chlorine.

Production Methods

Phosgene is manufactured in many facilities in the United States and in many other countries. Typical production processes involve the reaction of carbon monoxide with nitrosyl chloride, or the reaction of carbon tetrachloride with oleum.

Production Methods

Phosgene is produced commercially by the reaction of CO and chlorine gas catalyzed by activated carbon. Estimated worldwide production exceeds 5 billion pounds. Although a gas at atmospheric temperature and pressure, phosgene is often supplied to industry in liquid form in pressurized steel cylinders or in limited quantities as a solid triphosgene. It is used in the manufacture of a variety of organic chemicals, including dyestuffs, isocyanates, carbonic acid esters (polycarbonates), acid chlorides, insecticides, and pharmaceuticals (293). In metallurgy, it is used to refine ores by chlorination of metal oxides.
Suspected sources of atmospheric phosgene are fugitive emissions. Phosgene can be generated by thermal decomposition of chlorinated hydrocarbons (including carbon tetrachloride, methylene chloride, trichloroethylene, or butyl chloroformate) and photooxidation of chloroethylenes in the ambient air. Occupational exposures have resulted from heating paint removers, degreasers, and welding on freshly degreased parts. Phosgene levels have been measured in ambient air with an ambient concentration median of 80 ng/m³. Chlorinated hydrocarbons, such as chloroform, can also degrade spontaneously. One example involved laboratory personnel who became ill when working with 3-year-old chloroform. Subsequent analysis found 15,000 ppm phosgene in the headspace of the bottle and a 1.1% phosgene concentration in the bulk solution (299, 300). Decomposition of chlorinated hydrocarbons can produce other toxic chemicals, including hydrogen chloride, chlorine, and dichloroacetyl chloride.

Preparation

Phosgene is prepared by the reaction of carbon monoxide and chlorine. The mixture of these gases is passed over activated carbon:
CO + Cl2 → COCl2
Alternatively, phosgene can be made by reacting carbon monoxide with nitrosyl chloride, or by treating carbon tetrachloride with oleum.

Air & Water Reactions

Decomposes slowly in water or moist air (or when inhaled) to form very corrosive hydrogen chloride gas (hydrochloric acid) and carbon monoxide.

Reactivity Profile

PHOSGENE is water reactive. Incompatible with strong oxidizing agents, alcohols, amines, alkali. May react violently with aluminum, alkali metals (lithium, potassium, sodium), alcohols (isopropyl alcohol, 2,4-hexadiyn-1,6-diol), sodium azide [Bretherick, 5th ed., 1995, p. 134]. May react vigorously or explosively if mixed with diisopropyl ether or other ethers in the presence of trace amounts of metal salts [J. Haz. Mat., 1981, 4, 291]. PHOSGENE reacts with phosphate or silicate salts, yielding water-reactive and toxic POCl3 with phosphates (Dunlap, K.L. 2005. PHOSGENE. In Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc.).

Hazard

Phosgene is a strong irritant to the eyes, is highly toxic by inhalation, and may be fatal if inhaled. The TLV is 0.1 ppm, and the IDLH is 2 ppm in air. The boiling point is 46°F, and it is noncombustible. When carbon tetrachloride comes in contact with a hot surface, phosgene gas is evolved, which is one of the main reasons that carbon tetrachloride fire extinguishers are no longer approved. The four-digit UN identification number is 1076. The NFPA 704 designation is health 4, flammability 0, and reactivity 1. It is shipped in steel cylinders, special tank cars, and tank trucks.

Health Hazard

PHOSGENE is a lung toxicant that causes damage to the capillaries, bronchioles and alveoli of the lungs, by decomposition to hydrochloric acid. There is little immediate irritant effect upon the respiratory tract, and the warning properties of the gas are therefore very slight. Pulmonary edema, bronchopneumonia and occasionally lung abscesses develop. Degenerative changes in the nerves have been reported as later developments. A concentration of 25 ppm is dangerous for exposures lasting 30-60 minutes and 50 ppm is rapidly fatal after even short exposure.

Health Hazard

Phosgene is severely irritating and corrosive to all body tissues. Irritation of the throat occurs immediately at 3 ppm, while 4 ppm causes immediate eye irritation. Exposure to 20 to 30 ppm for as little as 1 min may cause severe irritation of the upper and lower respiratory tract, with symptoms including burning throat, nausea, vomiting, chest pain, coughing, shortness of breath, and headache. Brief exposure to 50 ppm can be fatal within a few hours. Severe respiratory distress may not develop for 4 to 72 hours after exposure, at which point pulmonary edema progressing to pneumonia and cardiac failure may occur. Phosgene vapor is irritating to the eyes, and the liquid can cause severe burns to the eyes and skin. Phosgene is not regarded as a substance with adequate warning properties.
Phosgene has not been found to be carcinogenic or to show reproductive or developmental toxicity in humans.

Health Hazard

Phosgeneisahighlypoisonousgas.Itseffectscan be treacherously dangerous, as there maynot be any immediate irritation even at lethalconcentrations. The initial symptoms aremild. However, severe congestion of lungsor pneumonia occurs 6–24 hours after exposure. The toxic symptoms include coughing, dry burning of throat, choking, chestpain, vomiting, foamy sputum (often containing blood), labored breathing, and cyanosis.Death results from anoxia. It hydrolyzes toHCl and CO2 in the lungs. A 30-minute exposure to about 100 ppm of phosgene in aircan be fatal to humans, causing death withina few hours of exposure. A concentrationof 15–20 ppm, however, exhibits only mildeffects. Chronic exposure may result in bron-chitis and fibrosis. Exposure to the gas cancause eye irritation. Contact with the liquidcan cause skin burns.

Fire Hazard

When heated to decomposition or on contact with water or steam, PHOSGENE will react to produce toxic and corrosive fumes. Reacts violently with aluminum; tert-butyl azido formate; 2,4-hexadiyn-1,6-diol; isopropyl alcohol; potassium; sodium; hexafluoro isopropylidene; amino lithium; lithium. Stable in steel containers if dry. Avoid moisture.

Fire Hazard

Noncombustible

Flammability and Explosibility

Noncombustible.

Industrial uses

The common name for carbonyl chloride, COCl₂, a colorless, poisonous gas made by the action of chlorine on carbon monoxide. It was used as a poison war gas. But it is now used in the manufacture of metal chlorides and anhydrides, pharmaceuticals, perfumes, isocyanate resins, and for blending in synthetic rubbers.
Because of its toxicity, most phosgene is produced and employed immediately in captive applications. The biggest use of the material is for toluene diisocyanate (TDI), which is then reacted into polyurethane resins for foams, elastomers, and coatings. Polycarbonate is used for making breakresistant housings, signs, glazings, and electrical tools. Phosgene also is a reactant for the isocyanates that are used in pesticides, and the di- and polyisocyanates are adhesives, coatings, and elastomers.

Materials Uses

Anhydrous phosgene in the liquid state is compatible with a variety of common metals, including aluminum (of 99.5 percent purity), copper, pure iron or cast iron, steel (including cast steel and chrome-nickel steels), lead (up to 250°F or 121°q, nickel, and silver; it is also compatible with platinum and platinum alloys in instruments. Nonmetallic materials with which liquid anhydrous phosgene is also compatible include acid resistant linings (ceramic plates and carbon blocks), enamel on cast iron or glass-lined steel, Pyrex or Kimax, porcelain, quartzware, granite or basalt natural stone, stoneware, and Teflon.
In the presence of moisture, phosgene is not compatible with copper, steel, or pure or cast iron. Detailed data on the corrosion resistance of various materials to phosgene under a range of conditions are given in Corrosion Data Survey-Metals Section of the National Association ofCorrosion Engineers.
For commercial (nonlaboratory) applications, steel piping with seamless fittings is recommended for handling phosgene, and pipe no smaller than 4-inch (l0.2-cm) nominal size should be used to ensure rigidity and minimize possible leaks. For pipe size up to 4 inches (10.2 cm), Schedule 80 seamless (or alloy steel to ASTM A333 GR3) piping is recommended; 6-inch (15.2-cm) diameter Schedule 40 seamless may be used as a larger pipe size. Screwed or flanged joints should be kept to a minimum, and cast iron or malleable iron fittings and valves should not be used; nonarmored porcelain valves must not be used, regardless of the pressure with either liquid or gaseous phosgene. Only outside yoke or rising stem valves are recommended to reduce the possibility of accident; nonindicating valves should not be used. Monel is the material generally used in manually operated valves for the disk, seat, and stem components.
A pipe joint compound of Teflon-based type dope is usually used. Detailed recommendations on these and other materials for various purposes in phosgene service may be obtained from phosgene suppliers.

Safety Profile

A human poison by inhalation, A severe eye, skin, and mucous membrane irritant. In the presence of moisture, phosgene decomposes to form hydrochloric acid and carbon monoxide. This occurs in the bronchioles and alveoli of the lungs, resulting in pulmonary edema followed by bronchopneumonia and occasionally lung abscess. There is little immediate irritating effect upon the respiratory tract, and the warning properties of the gas are therefore very slight. There may be no immedate warning that dangerous concentrations are being inhaled. After a latent period of 2 to 24 hours, the patient complains of burning in the throat and chest, shortness of breath, and increasing dyspnea. Where the exposure has been severe, the development of pulmonary edema may be so rapid that the patient dies within 36 hours after exposure. In cases where the exposure has been less, pneumonia may develop several days after the occurrence of the accident. In patients who recover, no permanent residual disability is thought to occur. A common air contaminant. Under the appropriate conditions it undergoes hazardous reactions with Al, tertbutyl azido formate, 2,4-hexadiyn-l,6-diol, isopropyl alcohol, K, Na, sodium azide, hexafluoroisopropylideneamino lithium, lithium. When heated to decomposition or on contact with water or steam it will react to produce toxic and corrosive fumes of CO and Cl-. Caution: Arrangements should be made for monitoring its use

Potential Exposure

Phosgene can be deadly at a concentration as low as 2 ppm. Phosgene is used as an intermediate in the manufacture of many industrial chemicals, including dyes and plastics; in the making of dyestuffs based on triphenylmethane, coal tar, and urea. It is also used in the organic synthesis of isocyanates and their derivatives, carbonic acid esters (polycarbonates); and acid chlorides. Other applications include its utilization in metallurgy; and in the manufacture of some insecticides and pharmaceuticals. Exposure to phosgene may occur during arc welding and in fires involving vinyl chloride; released from household paint removers and degreasers when they are used in the presence of heat. Phosgene (CG) has been used as a military choking, pulmonary agent since WW I, and has become a staple of chemical arsenals in many countries

Physiological effects

Phosgene is a strong lung irritant and also attacks other parts of the respiratory system. Low concentrations in air cause watering of the eyes and coughing, which may result in a thin, frothy expectoration. It will also result in upper respiratory tract irritation and bronchitis. High concentrations cause greater distress such as shortness of breath, choking, coughing, chest tightness, and painful breathing.
ACGIH recommends a Threshold Limit Value-Time-Weighted Average (TLV-TWA) of 0.1 ppm (0.40 mg/m3) for phosgene. The TLV- TWA is the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. In addition, ACGIH recommends a Threshold Limit Value-Ceiling (TLVq of 0.1 ppm (0.4 mg/m3) for phosgene. The TLV-C is the concentration that should not be exceeded during any part of the working exposure.
One serious difficulty with the treatment of persons exposed to phosgene is that more serious symptoms may not appear until 2 to 24 hours after the exposure. These include bloody sputum, increasing shortness of breath, pulmonary edema, and respiratory failure. The delayed action of phosgene can be particularly injurious if the victim performs heavy exercise after having been exposed. Persistent effects after acute lung injury from phosgene can include bronchiolitis obliterans.
Phosgene is hydrolyzed to hydrogen chloride and chlorine in the alveoli ofthe lungs, which in turn causes irritation and results in pulmonary edema and subsequently leads to respiratory and cardiac failure.
All persons who have been exposed to phosgene must be examined by a physician as soon as possible because serious symptoms may develop subsequently.

Environmental Fate

Phosgene’s widespread use may result in its release to the environment through a variety of means. Historical publicized releases of phosgene into the environment have been primarily large scale, where storage tanks containing the gas have ruptured. Effects have been varied, though largely temporary. Phosgene is only slightly soluble in water; however, it rapidly hydrolyzes to form carbon dioxide (CO2) and hydrochloric acid (HCl); phosgene’s half-life when dissolved in aqueous media is approximately 0.026 s.
In the air, phosgene is expected to degrade in much the same way as in water – via hydrolysis to form carbon dioxide and hydrochloric acid. Potential sources of atmospheric phosgene follow from thermal decomposition of chlorinated hydrocarbons, photooxidation of chloroethylenes, and other emission sources. Phosgene exists as a gas in the ambient atmosphere, and volatilization from contaminated soils is expected to occur readily; the Henry’s Law constant of phosgene is 1.7 × 10^-2 atmm3 mol^-1.
If deposited into the soil, phosgene is expected to maintain high mobility with an estimated Koc of 2.2, although its tendency to rapidly hydrolyze and volatilize likely prevents it from persisting in soil or water for long. In the atmosphere, phosgene is expected to degrade either by gas-phase hydrolysis or by reaction with hydroxyl radicals that are produced photochemically. The half-life for phosgene’s reaction with hydroxyl radicals in air, however, is estimated at 44 years, and the hydrolysis pathway in air is sluggish, resulting in the potential for phosgene to persist in the atmosphere. Due to its persistence in the air, it is possible for long-range transport to be an issue until degradation or some form of deposition allows phosgene to become degraded by a more expedient route.
Although it is capable of persisting in the air, phosgene is not expected to bioaccumulate due to its hydrolytic lability in aqueous environments.

storage

In particular, work with phosgene should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Containers of phosgene solutions should be stored in secondary containers, and phosgene cylinders should be stored in a cool, wellventilated area separate from incompatible materials.

Shipping

UN1076 Phosgene, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 8-Corrosive material, Inhalation, Hazard Zone A. Cylinders must be transported in a secure upright position, in a well-ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner. Military driver shall be given full and complete information regarding shipment and conditions in case of emergency.AR 50-6 deals specifically with the shipment of chemical agents. Shipments of agent will be escorted in accordance with AR 740-32

Purification Methods

Dry the gas with Linde 4A molecular sieves, de-gas it and distil it under vacuum at low temperature. This should be done in a closed system such as a vacuum line. It is hydrolysed by H2O but does not fume in moist air. It is available in cylinders and as a ~20% solution in toluene. It is HIGHLY TOXIC and should not be inhaled. If it is inhaled, the operator should lie still and, be made to breathe in ammonia vapour which reacts with phosgene to give urea. [Pope et al. J Chem Soc 117 1410 1920, Beilstein 3 IV 41.]

Toxicity evaluation

Acute irritations of the airway as well as associated mucous membranes (primarily of the nose, throat, and eyes) occur due to the rapid formation of hydrochloric acid upon degradation of phosgene. Irritation or more lasting effects may result from the ability of phosgene to participate in other reactions, including acylation with amino (–NH2), hydroxyl (–OH), and sulfhydryl (–SH) groups. Further, phosgene is capable of reacting with macromolecules such as proteins, enzymes, and phospholipids to form covalent adducts that are not native to cellular environments. Depletion of these nucleophiles, especially glutathione in the lung, is an important component of phosgene’s toxicity, as restoration of glutathione has been shown to protect individuals from additional injury from phosgene.
In the lung, these secondary reactions may result in fluid leakage into the pulmonary interstitium, and potential for fluid levels to reach the alveoli and peripheral airways, leading to dyspnea and pulmonary edema.

Incompatibilities

Moisture, alkalis, ammonia, alcohols, copper. Reacts slowly in water to form corrosive hydrogen chloride and carbon dioxide. Violent reaction with strong oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alcohols, alkaline materials, strong acids, strong bases, alcohols, ammonia, amines, aluminum, alkali metals. Attacks many metals in presence of water. Phosgene (CG) reacts violently with strong oxidants, amines, alkalis, and many metals. Above 300C, phosgene decomposes in the presence of moisture to form hydrochloric acid and carbon dioxide. In the presence of moisture, phosgene attacks plastic, rubber, coatings and many metals.

Waste Disposal

Principles and methods for destruction of chemical weapons: “Destruction of chemical weapons” means a process by which chemicals are converted in an essentially irreversible way to a form unsuitable for production of chemical weapons, and which in an irreversible manner renders munitions and other devices unusable as such. Each nation shall determine how it shall destroy chemical weapons, except that the following processes may not be used: dumping in any body of water, land burial or open-pit burning. It shall destroy chemical weapons only at specifically designated and appropriately designed and equipped facilities. Each nation shall ensure that its chemical weapons destruction facilities are constructed and operated in a manner to ensure the destruction of the chemical weapons; and that the destruction process can be verified under the provisions of this Convention (Organization for the Prohibition of Chemical Weapons; Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and Their Destruction). Return refillable compressed gas cylinders to supplier. Phosgene may be neutralized by covering it with sodium bicarbonate or an equal mixture of soda ash and slaked lime. After mixing, spray carefully with water. Transfer slowly to a larger container of water. Do not use water directly on spill. Pass controlled discharges of phosgene through 10% NaOH solution in a scrubbing tower . Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal.

GRADES AVAILABLE

Phosgene is available for commercial and industrial use from various suppliers at a typical minimum purity of99 mole percent.