Selected thermophysical properties are reported for VX (O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothiolate) and its isomer, RVX (O-isobutyl-S-[2(diethylamino)ethyl] methylphosphonothiolate). Several properties have been reported previously for both compounds; the focus of the current work has been the measurement of additional properties and expansion of the experimental ranges for the existing data. This report consolidates and compares physical property data measured in our laboratory for both compounds. It is important to know the physical properties of these supertoxic materials accurately to understand quantitatively the threat posed by them during military conflict, perform testing of defensive equipment, and determine the necessity to perform decontamination procedures. Knowledge of the properties of these toxic materials facilitates the selection of lower-toxicity candidates to simulate their behavior during testing where the use of the toxic agent is inappropriate. The current work has employed standard American Society for Testing and Materials (ASTM) international methods, intact and modified, to measure physical properties of VX and RVX. Properties investigated in the present work include liquid density, viscosity, surface tension, flash point, vapor pressure, heats of vaporization, and volatility. We also report correlations determined from previously available and new data, where appropriate.

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