Empirical Prediction of Heats of Vaporization and Heats of Adsorption of Organic Compounds

Abstract

Partitioning between the gas phase and ambient condensed phases is an important process in determining the transport and fate of organic chemicals in the atmosphere as well as in other environmental compartments exhibiting a vadose zone (e.g., soils). In general, partition processes including the gas phase are strongly temperature dependent and the respective enthalpies of transfer need to be known. Unfortunately, such data are often not available. In this paper, we evaluate the possibilities of estimating both the enthalpies of vaporization from the pure liquid and the enthalpies of gas/surface adsorption of organic compounds from either their (subcooled) liquid vapor pressure or their equilibrium adsorption constant at a particular temperature. Such an approach becomes possible when linear relationships between the enthalpy and entropy, and hence between the enthalpy and the logarithm of the partition constant, exist. Using literature data reported for almost 200 compounds covering a wide range of compound classes we have derived an empirical relationship that can be used to estimate the enthalpy of vaporization, Δvap H i, of a given compound i from its saturated liquid vapor pressure, p iL*, at 25 °C: Δvap H i (kJ/mol) = −3.82(±0.03) ln p iL* (Pa, 25 °C) + 70.0(±0.2); n = 195; r 2 = 0.99. An analogous equation is given for the estimation of the enthalpy of adsorption of organic vapors to mineral surfaces. The application of this equation to other surfaces including liquid and solid organic phases as well as the liquid water surface is discussed. The equations presented are useful practical tools for approximating the temperature dependence of liquid vapor pressure and of vapor/surface adsorption constants of organic chemicals in the ambient temperature range.

A general structure-property relationship to predict the enthalpy of vaporisation at ambient temperatures

“…The empirical relationship between vapour pressure and enthalpy of vaporisation at 298 K, first reported by Goss and Schwarzenbach [50], was confirmed. This relationship can be used to extend the current model to also cover vapour pressure, although the development of a dedicated model would be preferred.…”

“…One outlier (malathion) was removed and 546 compounds with reported enthalpies of vaporisation, vapour pressures, and melting points at or below 298 K were selected for further evaluation. Goss and Schwarzenbach reported the following regression equation [50]: The two equations are in close agreement, figure 4. The minor deviation and slightly lower proportion of explained variance in the current evaluation is probably due to a different coverage of the chemical domain.…”

“…Goss and Schwarzenbach reported on a useful relationship between the enthalpy of vaporisation and the (subcooled) liquid vapour pressure at 298 K [50]. This correlation has the same limitation in requiring experimental data, but since the two properties are often used together it still provides a valuable method to expand the database.…”

Comparison of Atmospheric Travel Distances of Several PAHs Calculated by Two Fate and Transport Models (The Tool and ELPOS) with Experimental Values Derived from a Peat Bog Transect

“…While ELPOS has a built-in routine to adjust these coefficients to a user-supplied temperature, The Tool requires the user to supply temperature-adjusted input information. The K AW values were adjusted using the temperature dependent pp-LFERs from Goss et al [35]; K OA values from Ma et al [24] were adjusted using enthalpies of vaporization, derived as described in Goss and Schwarzenbach [36]. Finally, temperature-adjusted K OW were obtained as the product of K AW and K OA .…”

Thermisch unterstützte Bodenreinigung durch direkte Erwärmung mittels Radiowellen Teil 3: Referenzversuche im Feldmaßstab

“…Die in Abb. 10 dargestellten Verhältnisse entsprechen im Wesentlichen denen, die anhand der Adsorptionsenthalpien von MKW abzuschät-zen sind [18]. Für einige Verbindungen war jedoch bereits eine Abreicherung bzw.…”