Drying phosgene

Chemically much more inert than chlorine, phosgene is a very stable compound and is not dissociated by cxplo. bursting charges. When dry, phosgene does not attack iron ami may, therefore, be kept indefinitely in iron and steel containers. It is, however, extremely sensitive to water, in contact with which it quickly breaks down into hydroehlorii acid and carbon dioxide, according to the equation... 

Alkyl chloroformates are generally prepared by reaction of anhydrous alcohols with a stoicheiometric excess of dry phosgene in a corrosion-resistant reactor. For the lower... 

Typical procedures. AOC- and MPC-amino acids. Method A [379] Amyl chloro-formate Dried phosgene (105 g, 1.06 mol) (for a phosgene source, see Chapter 7) was introduced into a solution of t-amyl alcohol (46 g, 0.52 mol) in dry diethyl ether (500 mL), and then the mixture was cooled to 60 °C in an acetone/dry-ice bath. A solution of pyridine (41 g, 0.52 mol) in dry diethyl ether (500 mL) was added dropwise to the cooled mixture with vigorous stirring. Then the reaction mixture was stored overnight in a deep freezer at —20 °C. The formed pyridine hydrochloride was removed by filtration, and the mother liquor was concentrated to a small volume (about 120 mL) in an ice/water bath under reduced pressure. The product thus obtained was used without further purification in the following reactions. Its purity was determined by acylating a known amount of phenylalanine methyl ester as described below it was found that about 4 mL of the product corresponded to 0.01 mol. The yield was about 60%. 

Pure chloroform has b.p. 61°/760 mm. The solvent, when free from alcohol, should be kept in the dark in order to avoid the photochemical formation of phosgene. It must not be dried with sodium as an explosion may occur. 

In another method, phosgene is gradually passed into 1,2-propylene glycol (9). The chloroformate is washed, dried, and distilled at 266 Pa (2 mm Hg) and added slowly to a mixture of aHyl alcohol and pyridine below 15°C. The purified monomer 1,2-propylene glycol bis(aHyl carbonate) (C H O ) heated with lauroyl peroxide at 70°C gives a hard clear, polymer. 

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). 

After the addition of the last of the /)-nitroaniline, the stream of phosgene is continued for five minutes and then shut off. The flame under the flask is then turned up and the ethyl acetate distilled. Care must be taken at the end not to overheat the residue. The brown residue (Note 5) is treated with 800 cc. of hot dry carbon tetrachloride, and the insoluble residue (the di-substituted urea) is removed by filtration. 

Phosgene [75-44-5] M 98.9, b 8.2 /756mm. Dried with Linde 4A molecular sieves, degassed and distilled under vacuum. This should be done in a closed system such as a vacuum line. HIGHLY TOXIC, should not be inhaled. If it is inhaled operator should lie still and made to breath ammonia vapour which reacts with phosgene to give urea. 

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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