Determination of the Enthalpies of Vaporization of Cyclic Organic Peroxides by Correlation of Changes in Gas Chromatographic Retention Times

A. CAÑIZO; N. EYLER; G. BARRETO

CHROMATOGRAPHIA

Vieweg & Sohn

Lugar: Wiesbaden – Alemania; Año: 2007 vol. 65 p. 31 - 34

0009-5893

Liquids and solids peroxides investigated in this work are explosive materials, which vaporization enthalpies, and other thermodynamic or condensed phase properties, cannot be measured directly. Correlation gas chromatography affords the vaporization enthalpy of a solid or liquids at 298.15 K by simply using retention time measurements of knowns and unknowns. This method was used to estimate vaporization enthalpies of volatile cyclic organic peroxides derived from aliphatic ketones. The adjusted retention time (t’R) is obtained subtracting the retention time (tM) of the solvent (diethyl ether), which is an unretained compound. A first plot of ln t’R vs. 1/T for each compound (references and cyclic peroxides) results in a straight line (r2 higher than 0.99 in all cases) that gives enthalpies of transfer from solution to vapor(DgsolHm) when the slopes is multiplied by the gas constant R. A second plot correlates the enthalpies of transfer from solution to vapor(DgsolHm) as measured by GC and the vaporization enthalpies (DvapHm at 298.15 K) obtained from literature of primary reference materials used as standards (in this work a mixture of fatty acid methyl esters C9  to C15 and a mixture of hydrocarbons are used as reference series). The vaporization enthalpies of the cyclic organic peroxides are calculated from the equation of the line obtained in this second correlation where the slope is DvapHm (at 298.15 K) / DgsolHm.  The experiments were carried out under isothermal conditions in a capillary column (DB-5) with FID detection and nitrogen as carrier gas. The column temperature was varied over a range of at least 30 K to 70 K between 403 and 473 K, with chromatograms being acquired at every 10 K. In view of the absence of experimental data of vaporization enthalpies of cyclic organic peroxides calculated from the vapor pressure or gas chromatography-calorimetry or obtained by calorimetric determinations, these results obtained by correlation gas chromatography constitute the first available data reported.