Vapor Pressure of Triethyl and Tri‑n‑Propyl Phosphates and Diethyl Malonate

Triethyl phosphate (TEPO, CAS No. 78-40-0), tri-n-propyl phosphate (TPPO, CAS No. 513-08-6), and diethyl malonate (DEM, CAS No. 105-53-3) are of considerable interest to the chemical defense community as nontoxic simulants for toxic chemical warfare agents. Vapor pressure data have been measured for TEPO at T = (271.25 to 480.15) K, for TPPO at T = (263.15 to 527.61) K, and for DEM at T = (265.15 to 471.25) K using a variety of standard methods that have been modified as necessary. The new data extend the range of vapor pressure data previously reported in the literature for each of the title compounds to subambient temperatures and to lower pressures by approximately 3 orders of magnitude for TEPO, 5 orders of magnitude for TPPO, and 1 order of magnitude for DEM. Vapor pressure data and derived properties, including volatility and temperature-dependent heats of vaporization are reported for TEPO, TPPO, and DEM along with comparisons to chemical warfare agent materials.