Phosgene detection

Depending on the reagent ratio, oxalyl chloride reacts with fluorobenzene m the presence of aluminum chloride to afford either 4-fluorobenzoyl chloride or 4,4 -difluorobenzophenone [ii] (equation 22). Phosgene, detected by infrared spectroscopy, is an intermediate. 

Composites of PANI-NFs, synthesized using a rapid mixing method, with amines have recently been presented as novel materials for phosgene detection [472]. Chemiresistor sensors with nanofibrous PANI films as a sensitive layer, prepared by chemical oxidative polymerization of aniline on Si substrates, which were surface-modified by amino-silane self-assembled monolayers, showed sensitivity to very low concentration (0.5 ppm) of ammonia gas [297]. Ultrafast sensor responses to ammonia gas of the dispersed PANI-CSA nanorods [303] and patterned PANI nanobowl monolayers containing Au nanoparticles [473] have recently been demonstrated. The gas response of the PANI-NTs to a series of chemical vapors such as ammonia, hydrazine, and triethylamine was studied [319,323]. The results indicated that the PANI-NTs show superior performance as chemical sensors. Electrospun isolated PANI-CSA nanofiber sensors of various aliphatic alcohol vapors have been proven to be comparable to or faster than those prepared from PANI-NF mats [474]. An electrochemical method for the detection of ultratrace amount of 2,4,6-trinitrotoluene with synthetic copolypeptide-doped PANI-NFs has recently been reported [475]. PANI-NFs, prepared through the in situ oxidative polymerization method, were used for the detection of aromatic organic compounds [476]. 

S. Viiji, R. Kojima, J. D. Fowler, J. G. Villanueva, R. B. Kaner, and B. H. Weiller, Polyaniline nanofiber composites with amines Novel materials for phosgene detection, Nano Res., 2, 135-142 (2009). 

Health and Safety. Remover formulas that are nonflammable may be used in any area that provides adequate ventilation. Most manufacturers recommend a use environment of 50—100 parts per million (ppm) time weighted average (TWA). The environment can be monitored with passive detection badges or by active air sampling and charcoal absorption tube analysis. The vapor of methylene chloride produces hydrogen chloride and phosgene gas when burned. Methylene chloride-type removers should not be used in the presence of an open flame or other heat sources such as kerosene heaters (8). 

Phosgene in air and in mixture with other gases can be detected by a variety of methods (35). Trace quantities to a lower limit of 0.05 f-lg/L air can be detected by uv spectroscopy (36). Both in and gas chromatography have been used extensively to measure phosgene in air at 1 ppb—1 ppm (7,37,38). Special... 

Methods and iastmments that are used to monitor phosgene content ia air are well developed and have been reviewed (46—48). One detection iastmment is a porous tape that measures the concentration of phosgene ia air ia quantities as small as 6 ppb (49). Fourier transform ir spectrometry techniques have been developed to permit line and area monitoring ia the area around phosgene plants (50). 

Detection in the field M18A2, odor, and Draeger Tube Phosgene 0.25/b... 

NIOSH (1976) performed two studies to determine the odor threshold of phosgene. In the first, 56 military personnel were exposed to phosgene at increasing concentrations until all subjects could detect odor. The lowest detectable concentration was 0.4 ppm. Thirty-nine percent of subjects could detect odor at 1.2 ppm, and 50% of subjects detected odor at 1.5 ppm. In the other study, four subjects identified 1.0 ppm as the lowest concentration at which the distinctive new-mown hay odor of phosgene could be detected. 

In a phosgene processing factory, phosgene concentrations were measured over an 8-mo period with a device capable of detecting phosgene at 0-0.5 ppm (Henschler 1971). Positive values, of relatively short duration, were recorded on only 32 of 240 d 22 d, 0.05 ppm 6 d, between 0.06 and 0.1 ppm 3 d, between 0.1 and 0.5 ppm 1 d, 0.5 ppm (of short duration). For longer time... 

Photolysis of an aqueous solution containing chloroform (314 pmol) and the catalyst [Pt(cohoid)/Ru(bpy) /MV/EDTA] yielded the following products after 15 h (mol detected) chloride ions (852), methane (265), ethylene (0.05), ethane (0.52), and unreacted chloroform (10.5) (Tan and Wang, 1987). In the troposphere, photolysis of chloroform via OH radicals may yield formyl chloride, carbon monoxide, hydrogen chloride, and phosgene as the principal products (Spence et al., 1976). Phosgene is hydrolyzed readily to hydrogen chloride and carbon dioxide (Morrison and Boyd, 1971). 

About the size of a package of cigarettes, individual sensors are available for H2S, phosgene, N02, HCN, and CO. In the near future, the series will be expanded to include CI2 and hydrazine. When used with the Chronotox microprocessor, the Monitox serves as a personal monitor as well as a gas detection alarm system. 

In this experiment, no carbon tetrachloride was detected but, on the basis of the mechanism proposed, carbon tetrachloride would have been an important reaction product, arising by the combination of chlorine atoms and trichloj-omethyl radicals. Further, the production of octachloropropane by the secondary photolysis of octachlorobutanone would involve the formation of decachlorobutane. In the presence of chlorine, only carbon tetrachloride was formed, whereas by interaction of the postulated CCI3CO- radical with chlorine, substantial amounts of trichloroacetyl chloride should have been observed. In the presence of oxygen, only carbon dioxide and phosgene were found and the yield of the latter was far too small to account for the loss of the radical products. 

Phenyl iso-thiocyanate, 642,643 Phenylthioureas, 422, 655 Phenylurea, 644, 645 Phenylurethanos, 264 Phloroacetophenone, 727, 736 Phosgene, 185 Phosphoric acid, 189, 284 Phosphorus, detection of, 1043 Phosphorus, red, purification of, 193 Phosphorus oxychloride, 367 Phosphorus pentabromide, 489, 492 Phosphorus pentachloride, 799, 822, 974 Phosphorus pentoxide, handling of, 407 Phosphorus tribromide, 189, 492 Phosphorus trichloride, 367 Phosphorus trisulphide," 836 Phthalamide, 983 Phthalein test, 681 ... 

The contaminants in commercial boron trichloride usually are HCI and COCI2, as well as oxychlorides which have some volatility. The oxyhalides are readily removed by one or two trap-to-trap distillations in a clean vacuum system. Most of the HCl can be removed by holding the BCI3 at — 78°C and pumping away the volatiles for a brief period (some BCI3 is sacrificed in the process). Phosgene, which may be detected by its gas-phase infrared absorption at 850 cm"1, is very difficult to remove. Liquid boron tribromide is generally supplied in sealed ampules. If it is straw colored, dibromine is a likely impurity, and this... 

Phosgene was identified as the principal intermediate during the photooxidation of all five compounds. Chloroaldehyde and chloroacetylchloride were also detected in low concentrations (Bhowmick and Semmens, 1994). The concentrations of these intermediates reached a maximum value but subsequently fell with time as the oxidation process continued. The rates of oxidation of the VOCs tested are proportional to UV irradiation intensity. The addition of ozone to UV irradiation improved the kinetics of TCE and PCE oxidation however, no significant change in the oxidation rates of CHL, TCA, and CTC was observed. 

---