Vapour pressure phosgene

From these data it will be seen that even at ordinary temperatures phosgene has a high vapour pressure which makes it of low persistence as a war gas, although its vapour density is much greater than that of air. 

Logically, the equation illustrates that the toxic area is proportional to the vapour pressure of the substance and the area of the spill, and is inversely proportional to the TLV. For phosgene, the toxicity index (for a 1 m spill) is 1000, compared to a value for dichlorine of 316, and for cyanogen of 100 [1957]. 

VAPOUR PRESSURE DATA FOR A TYPICAL COMMERCIAL SAMPLE OF PHOSGENE [ICI78]... 

In addition, it should be noted that the vapour pressure of commercial samples of phosgene will differ from those recorded for the pure material (see Chapter 6). The vapour pressure corresponding to the sample instanced in Table 4.5 is illustrated in Table 4.6 as a function of temperature [ICI78]. 

Under standard conditions, phosgene is a colourless gas with a density of approximately 3.5 times that of air, in which it is non-flammable. It is easily condensed to a colourless liquid when pure, and in the cylinder it is present as the liquified gas, exerting a vapour pressure of about 157 kPa (1.55 atm) at 20 C. Its relative molecular mass is 98.9158. 

From the published literature [89,744,860,1514,1591] assembled by Stull [1971], the vapour pressure data of phosgene have been processed [1541] in the form of the Antoine equation. Equation (6.3) ... 

Between 0 "C and the critical temperature, the vapour pressure data of phosgene have been summarized by Equation (6.6) (T in K) [744] and, for data above atmospheric pressure, by Equation (6.7) [1843] ... 

In the most recent work [649], between -20 and +20 C, the vapour pressure of phosgene has been represented simply by Equation (6.8), T in K. 

Fig. 6.12 Vapour pressure-composition isotherms for phosgene in organic solvents [1110] (A) aromatic solvents, (B) xylene, (C) chloroaliphatic solvents (facing page), and (D) 1,2-dichloroethane (facing page).

Phosgene and boron(III) chloride are miscible in all proportions [1329], as predicted earlier [738a] and the phase diagram for the COClj-BClj system (Fig. 9.3) reveals a eutectic point at -142.3 C (74.4 mole % COCIj) and no evidence for any complex formation. Moreover, the vapour pressure - composition isotherm (0 C) for this system (Fig. 9.4) shows a positive deviation from Raoult s law (although Henry s law appears to be well obeyed [649]), indicating the presence of unfavourable interactions between phosgene and boron(III) chloride [376]. Thus, the purification of boron(HI) chloride from traces of phosgene will not be complicated by the formation of a thermodynamically stable complex. 

Tetrachloromethane is an important solvent for phosgene, and vapour pressure -composition isotherms for this system are illustrated in Fig. 9.6 [ICI2]. These curves show, as expected, a slight positive deviation from Raoult s law. Earlier, less reliable, data are... 

Paraldehyde (2,4,6-trimethyl-l, 3,5-trioxane) was claimed to behave in a similar way [582], An early German patent, published after Eckenroth s note [582], claimed that no reaction occurs between COClj and aldehydes at normal temperatures [612], and attempts to repeat Eckenroth s preparation [582] have not been successful [1763]. However, by combining the vapours of phosgene and ethanal at atmospheric pressure in a flow system over an activated charcoal catalyst, 1,1 -dichloroethane and carbon dioxide are found to be co-produced, especially in the temperature range of 150-200 "C [1753,ICI98,ICI99]. It was confirmed that no reaction occurs in the absence of a catalyst between 25 and 400 C [1763]. 

Classical CW agents are, in the main, volatile liquids at ordinary temperatures (phosgene is an exception a gas at ordinary temperatures). The degree of volatility varies, of course, from compound to compound. The relationship between the liquid and the vapour phase is particularly important in explaining the effect of temperature on the damage likely to be produced by exposure to an agent and to calculations of the persistency of agents. The relationship between the liquid phase and gas (or vapour) phase of a volatile substance is defined by the vapour pressure of that substance. 

German classification for shells containing compounds with a high vapour pressure and great toxic power on the respiratory tract phosgene, trichloromethyl chloroformate (diphosgene), chloropicrin, etc. 

MDI is one of the monomers more widely used in the polyurethane industry. MDI is preferred over TDI because of its significantly low vapour pressure and the usually higher performance polymers that can be produced. MDI is produced as a variety of isomers and oligomers by phosgenation of the condensation product of formaldehyde and aniline (Fig. 8). 

W. Kireev and coll, have determined the boiling points at ordinary pressure and the composition of the vapour from solutions of phosgene in xylene and in ethylene dichloride containing amounts of phosgene varying from zero to 35% by weight (/. Prikl. Khim., 1935, 949). 

The normal boiling temperature of phosgene has been determined from the vapour equation of Giaque and Jones [751] as 7.56 0.005 C. Earlier values, corrected to standard pressure, are 8.3 [151] 7.69 [1591] 8.4 [1514,89] and 7.64 "C [744]. The most recent work [649] gives a boiling temperature of 7.92 C, corresponding very closely to the average of the earlier values. 

The density of phosgene vapour under standard reference conditions was measured to be 4.526 [742] or 4.525 kg m 3 [1281]. Using the value of the standard molar volume, Vnj j, the density of the gas at 0 C and atmospheric pressure was calculated to be 4.413 kg m 3 Phosgene vapour is thus, unexpectedly, far removed from ideality. An attempt has been made to generalize the Benedict-Wee-Rubin equation of state using three polar parameters as part of a study of a large series of polar substances, which includes COClj as one of the examples [1518]. 

Liquid-vapour equilibria in the phosgene-hydrogen chloride system have also been studied in connection with the problems associated with the separation of these two materials during the production of isocyanates. The system has been examined under atmospheric pressure within the range of the boiling points of the materials, ca. 8 to -85 C. The temperature-composition curve is illustrated in Fig. 6.14 [789] it shows large deviations from ideality. 

---