Vapor Pressure of Organophosphorus Nerve Agent Simulant Compounds

The vapor pressures of four lower alkyl phosphonate compounds, dimethyl phosphonate (DMHP, CAS 868-85-9), dimethyl methylphosphonate (DMMP, CAS 756-79-6), diethyl methylphosphonate (DEMP, CAS 683-08-9), and diisopropyl methylphosphonate (DIMP, CAS 1445-75-6), have been measured by complementary methods that allow data collection at ambient and high temperatures by use of gas saturation and differential scanning calorimetry, respectively. Kosolapoff (J. Chem. Soc. 1955, 2964-2965) reported vapor pressure data above 200 Pa for several of these compounds measured by use of isoteniscope, although the lowest data points were deemed to be not trustworthy by the author. Our report extends the low end of the measured data range by 2 to 3 orders of magnitude in pressure. Antoine correlations, normal boiling temperatures, temperature-dependent enthalpies of vaporization, and volatility have been derived based on the measured data reported herein. The advantages of using complementary methodology and measuring, as opposed to extrapolating, data have been demonstrated in this work.