Measurements of Saturated Vapor Pressure above the Liquid Phase for Isomeric Dichlorobenzenes and 1,2,4-Trichlorobenzene Vladislav Roha ´ c ˇ , Vlastimil Ru ˚ z ˇ ic ˇ ka, and Kve ˇ toslav Ru ˚ z ˇ ic ˇ ka Department of Physical Chemistry, Institute of Chemical Technology, 166 28 Prague 6, Czech Republic Karel Aim* E. Ha ´ la Laboratory of Thermodynamics, Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6-Suchdol, Czech Republic Saturated vapor pressures have been measured for liquid 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4- dichlorobenzene, and 1,2,4-trichlorobenzene by precision comparative ebulliometry over an approximate pressure range from 6 to 105 kPa. The relative error in pressure is estimated to be less than or equal to (0.05% of the measured value and the absolute error in temperature is estimated at less than or equal to (0.01 K on ITS-90. The results have been represented by the Antoine and Wagner-type equations within experimental uncertainties and compared with the data so far available in the literature. On the basis of the present and previous measurements, vapor pressure equations for the chlorobenzenes covering the entire range of liquid existence have been constructed and discussed. Introduction Chlorobenzenes are synthetic products that have been introduced into the environment only by human activities; so far they have not been found to occur in nature. Never- theless, their industrial use is wide: liquid chlorobenzenes (chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene) are used as solvents and extrac- tive agents for organic compounds. Chlorobenzene and 1,2,4-trichlorobenzene (and hexachlorobenzene) are used as intermediates in the manufacture of pesticides and herbicides. Furthermore, 1,3-dichlorobenzene and 1,4- dichlorobenzene are used as active components in disin- fectants and deodorants. Chemical waste dump leaching, direct manufacturing effluents, solvent applications, stack effluents from refused- fired steam boilers and power plants are the major sources of chlorobenzenes emissions into the atmosphere. Owing to their low solubility in water and slow rate of biodegrada- tion in water and soil, chlorobenzenes tend to accumulate in fat tissue of living organisms. Since chlorobenzenes have also been widely detected in ambient air, population exposure may generally occur both through oral consump- tion of contaminated drinking water and food (particularly fish) and through inhalation of contaminated air. Even though the effects of chlorobenzenes on humans have not yet been in all aspects satisfactorily determined, they are known to have narcotic effects as well as to cause harm to the nervous system and internal organs. To understand the partitioning and fate of chloroben- zenes in the environment, it is necessary to know the values of several types of basic physical-chemical proper- ties in the temperature range from about -30 to 50 °C. Vapor pressure is certainly one of the most important properties needed, the others being solubility in water, Henry’s law constant, octanol-water partition coefficient, and enthalpy of vaporization. Despite the fact that vapor pressures of all chlorobenzenes are quite low at environ- mentally relevant temperatures, data of high accuracy are still required. Even though some data on vapor pressure are available for each of the chlorobenzenes, they are either of dubious quality or cover only a narrow range of condi- tions (or both). This work has been concerned with experimental deter- mination of accurate vapor pressures of all isomeric dichlo- robenzenes and of 1,2,4-trichlorobenzene over the range of conventional ebulliometric conditions. In future work, recommended data on vapor pressure and heat of vaporiza- tion for all isomeric dichlorobenzenes, trichlorobenzenes, and pentachlorobenzene will be generated by simultaneous correlation of vapor pressures and thermal data using the vapor pressure data measured in this work, data measured by a static method (Polednı ´c ˇek et al., 1996), and data selected from literature. Experimental Section Materials. 1,2-Dichlorobenzene (C 6 H 4 Cl 2 ). Fluka prod- uct of stated purity >99%; original purity determined by GC analysis was 99.58%. The sample was further purified by a duplicate fractional distillation under reduced pres- sure of about 1.5 kPa in a packed column and dried over molecular sieves type 4A. The final purity determined by GC was 99.98%. 1,3-Dichlorobenzene (C 6 H 4 Cl 2 ). Aldrich product of stated purity 98%; original purity determined by GC analysis was 99.38%. The sample was further purified and dried as stated above, reaching the final GC purity of 99.55%. 1,4-Dichlorobenzene (C 6 H 4 Cl 2 ). Aldrich product of stated purity >99%; original purity determined by GC analysis was 99.91%. The sample was further purified by four times repeated zone-refining at ambient temperature between -10 and 5 °C. The final amount of impurities was below the limit of GC detection. 1,2,4-Trichlorobenzene (C 6 H 3 Cl 3 ). Aldrich product of stated purity 98%, original purity 98.65%. The sample was * Corresponding author. E-mail: kaim@icpf.cas.cz, kaim@mbox.cesnet.cz. 770 J. Chem. Eng. Data 1998, 43, 770-775 S0021-9568(97)00144-1 CCC: $15.00 © 1998 American Chemical Society Published on Web 08/19/1998