Chlorobenzenes—Vapor Pressures

The bromodifluorophosphine prepared as outlined above displayed a vapor pressure of 183 mm. at —45.2° (chlorobenzene slush) (190 mm. in reference 2). The infrared spectrum of the vapor shows absorptions at 858.9 (s), 851.0 (vs), 459.3 (s), and 391.3 (m) cm.-1 in the 4000 to 200 cm.-1 range. As with the chloro derivative, bromodifluorophosphine is best prepared just before use and contact with mercury should be minimized. 

The van t Hoff equation also has been used to describe the temperature effect on Henry s law constant over a narrow range for volatile chlorinated organic chemicals (Ashworth et al. 1988) and chlorobenzenes, polychlorinated biphenyls, and polynuclear aromatic hydrocarbons (ten Hulscher et al. 1992, Alaee et al. 1996). Henry s law constant can be expressed as the ratio of vapor pressure to solubility, i.e., pic or plx for dilute solutions. Note that since H is expressed using a volumetric concentration, it is also affected by the effect of temperature on liquid density whereas kH using mole fraction is unaffected by liquid density (Tucker and Christian 1979), thus... 

Harris, K.R., Dunlop, P.J. (1970) Vapor pressures and excess Gibbs energies of mixtures of benzene with chlorobenzene, -hexane and -heptane at 25°C. J. Chem. Thermodyn. 2, 801-811. 

Kalali, H., Kohler, F., and Svejda, P. Vapor pressure, density, refractive index, excess enthalpy, and heat capacity of 2-chloro-2-methylpropane or chlorobenzene + 2,2,4-trimethylpentane, J. Chem. Eng. Data, 37(1) 133-136, 1992. 

Tabun was planned to be used in chem bombs and rockets, but as it proved to be unstable and of high vapor pressure when used alone, chlorobenzene was incorporated, 5% at first (Tobun A) and later 20% (Tabun B) (Refs 1, 2, 3 4)... 

UNIFAC Approach Jensen et al. [16] have employed the UNIFAC group contribution approach to develop an estimation method for pure-component vapor pressures. The model developed applies to hydrocarbons, alcohols, ketones, acids, and chloroalkanes of less than 500 molecular mass and in the vapor pressure region between 10 and 2000 mmHg. Burkhard et al. [8] extended this model to chlorinated aromatic compounds such as chlorobenzenes and PCBs. 

Myrdal, P., and S. H. Yalkowsky, A Simple Scheme for Calculating Aqueous Solubility, Vapor Pressure and Henry s Law Constant Application to the Chlorobenzenes. SAR QSAR Environ. Res., 1994 2, 17-28. 

The heats of vaponzution at the boiling points for bromo-benzene, chlorobenzene and fluorobcnzcnc are available The hem of vapori/iiiion of benzyl chloride at 2VC has hern drier mined Ironi vapor pressure duui 272 The data weie evtended over a wider temperature range by the Khurbaruto nomograph J... 

The critical properties have been experimentally measured for bromobenzcnc, chlorobenzene, and fluorobcn-Mnc s.s.iuj.w Lydcrsen s method wus used U calculate the critical properties of benzyl chloride 1 Literature data arc reported for the vnpnr pressure ot bru-mobenzene, chlorobenzene, and fluorobcn/ertc up to the critical point, -1" 271 Stull has compiled the vapor pressure data on benzyl chloride up to its boiling point J Ashcroft pce cms data from 48T to I I C. 275 The vapor pressure above the boiling point was estimated ... 

When examining data for Henry s law constants, it is useful to compare values with data for structurally similar compounds. For a homologous series such as the chlorobenzenes, the increase in molar volume or area associated with substitution of chlorine for hydrogen causes a decrease in both solubility and vapor pressure thus H may be fairly constant for such a series. The ideal situation is one in which reliable independent experimental data are available for P , C, and H which permit a consistency check of the three determinations. 

Particle-gas partitioning can be described by a variation of the Pankow absorption model, in which liquid-phase vapor pressure is replaced by the octanol-air partition coefficient as a fitting parameter (equations (22)-(25)). Section 10.3.4 states the advantages of doing so. Koa has been reported as a function of temperature for several PCB congeners, chlorobenzenes, PAHs, polychloronaphthalenes (PCNs), and p,p -DDT (Harner and Bidleman, 1996, 1998b Harner and Mackay, 1995 Komp and McLachlan, 1997). For others, Koa can be estimated from the ratio of the octanol-water partition coefficient to the Henry s law constant (H = Pa m3/ mol) (Finizio et al., 1997 Harner and Mackay, 1995 Simonich and Hites, 1995). 

Physical constants for chlorobenzene, especially its vapor pressure and water solubility, indicate that the air is an important and perhaps the dominant medium for the transport and transformation of chlorobenzene. As an aromatic molecule with strong UV-absorption, chlorobenzene has a half-life of 20 to 40 hrs under simulated atmospheric conditions (Dilling et al. 1976). This appears to be confirmed by the large difference between chlorobenzene measurements in urban air (3,000 ng/m ) and in rural air (not detected) in 1982 (Brodzinsky and Singh 1983). 

Reported vapor pressures of chlorobenzene at various temperatures and the coefficients for the vapor ... 

FIGURE 6.1.1.1.2 Logarithm of vapor pressure versus reciprocal temperature for chlorobenzene. 

FIGURE 6.2.2 Vapor pressure (liquid or supercooled liquid) versus Le Bas molar volume for chlorobenzenes. 

The system l-chlorobutane(l)/benzene(2)/chlorobenzene(3) conforms closely to Raoult s la The vapor pressures of the pure species are given by the following Antoine equations ... 

Vapor pressure is essentially the solubility of a compound in air. Permanent gases, such as methane, have high vapor pressures in fact, they have a vapor pressure of 1 atmosphere (atm) or 760 Torr. Some pesticides have medium vapor pressures for example, hexa-chlorobenzene has a vapor pressure of about 10 7 atm. Some compounds, such as decachlorobiphenyl, have vapor pressures that are so low that they are essentially nonvolatile (10 1(1 atm). For our purposes, the interesting range is 10 4 to 10 x atm. 

EXAMPLE 22-2 The normal boiling points of chlorobenzene and bromobenzene are 132 and 156°C. Estimate the relative volatility from (22-20) and compare this with the ratio of vapor pressures at 140°C (939.5 to 495.8 mm). 

Gases, Vapors, Liquids, and Solids Chap. 3 Next we convert the two vapor pressures of chlorobenzene into psia,... 

The vapor pressure of chlorobenzene is relatively high (11.8 mmHg) therefore, inhalation is a... 

Example Estimate the vapor pressure of chlorobenzene at 50 K intervals from 300 to 600 K. 

To determine the overall effect on pressure error of normally distributed variation in temperature, the Antoine equation must be employed. Thus, the pressure error is a function of the compound of interest. To focus on typical situations, three compounds representative of the range of application of the isoteniscope were used. These were benzene with a relatively high vapor pressure ("true value" = 95 torr at 25°C) toluene for a medium vapor pressure ("true value" = 28 torr at 25°C) and chlorobenzene for a low vapor pressure ("true value" = 12 torr at 25°C). 

The results of isoteniscope simulations show a slight overprediction for all three compounds with a skewed distribution in each case (Figures 6, 7, and 8). Predictably, the lower the vapor pressure, the larger the relative standard deviation. On the other hand, the absolute standard deviation is relatively unchanged over the range of vapor pressures examined, varying between about 0.72 and 0.77 torr for the extreme cases. The maximum skewedness of the distribution is found for toluene, the medium-vapor pressure case. The standard deviation of 2.7 percent found for toluene corresponds quite well to the 3 percent error estimate made by MacKay et al. (4). The 6 percent standard deviation for the chlorobenzene case shows it to be at the lower end of the range recommended for reliable measurement. 

Figure 8. Distribution of simulated vapor pressure for chlorobenzene using the isoteniscope ("true value = 12.0 mm Hg).

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