Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The vapor pressures of 46 compounds including n-alkanes and their monofunctionalized derivatives, some monoterpenes, as well as chloro- and alkyl benzenes were determined exploring the Kovats retention indices (KI) technique primarily in its basic form using two alkane references (GLC-RTKI). The obvious advantage of GLC-RTKI method is that it guarantees proper choice of alkane reference compounds. Typical relative errors in vapor pressures accompanying this method were below 30 percent for compounds of low polarity, while for polar compounds (nitriles, alcohols) the errors can reach hundreds of percent. In contrast, vapor pressures obtained from the modified Kovats method relying on reference standards whose functional group matches that of the test compound (GLC-RTmKI) were found mostly within 5 % of directly measured values. The success of this method depends, however, on the availability of reliable vapor pressure data for compounds to serve as reference standards. Since our methodology eliminates possible secondary error sources (such as data extrapolation or recalculation from supercooled liquid to solid phase or vice versa), we assume our results to be of maximum GLC- RTKI and GLC- RTmKI attainable accuracy. This study also yielded new directly measured (static method) data on the vapor pressures of C7-C9 alkylnitriles.