: Although deviations are common, the effect of humidity on the volatility of materials is predictable using Raoult's law. This report details the measurement of the effect of water vapor partial pressure on the volatility of triethyl phosphate (TEPO), which has been used as a testing surrogate for G-type nerve agents. The results are compared to similar work for dimethyl methylphosphonate, in which its volatility was suppressed beyond what was predicted by Raoult's law. The current work shows that the effect of humidity on TEPO volatility is nearly as predicted by Raoult's law, that is, vapor pressure suppression is proportional to ambient relative humidity. An empirical correlation taking into account nonideal behavior was developed to enable estimation of TEPO volatility at any combination of ambient temperature and humidity and compared to predications based on Raoult's law. These predictions may be used to support testing using TEPO with a variety of applications, including weapons effects and protective equipment.

: This report compares several methods for expressing vapor pressure as a function of temperature (also referred to as correlation in the traditional literature) using the Antoine equation and discusses statistical analyses of the resulting correlations. Vapor pressure varies nonlinearly with temperature and is an important property of materials for applications ranging from estimates of their behavior in the environment to design of test equipment. Vapor pressure and temperature measurements over wide dynamic ranges are difficult to obtain, and prediction of vapor pressure based on limited data may be required in certain cases, necessitating reliable relationships between pressure and temperature. While the integrated form of the Clausius--Clapeyron equation has sound theoretical basis for correlating pressure and temperature, assumptions required for the temperature dependence of enthalpy may not be valid, particularly over wide temperature ranges. To correct for those approximations, a modified correlation equation may be implemented to enable accurate extrapolation. One variation of the Clausius-Clapeyron equation is the Antoine equation, which incorporates a third fit parameter to more accurately describe the nonlinearity of vapor pressure data. The current results support the use of the procedure proposed by Penski and Latour as the best method for correlating vapor pressure data.

: N,N'-diisopropylcarbodiimide, also known as DICDI, is a stabilizer for chemical warfare nerve agents such as VX and GD. The vapor pressure of DICDI was measured using complementary methods that allow data collection at ambient and high temperatures using gas saturation and differential scanning calorimetry, respectively. A three-parameter Antoine correlation equation based on the new data was determined. The resulting calculated values compared favorably to published and unpublished data cited in this report. This report includes derived properties, such as volatility, temperature-dependent heats of vaporization, normal boiling point, and entropy of vaporization.

Thiodiglycol (TDG), also known as bis(2-hydroxyethyl) sulfide and thiodiethanol, is a precursor of the blister agent sulfur mustard (bis(2-chloroethyl) sulfide). It is also a hydrolytic degradation product, and as such, it is of considerable forensic interest to the chemical defense community. Experimental vapor pressure data have been reported previously for TDG at T = (283.15 to 353.15) K, in addition to reduced-pressure boiling points at T = (353.15 to 454.65) K. New data have been measured using two complementary American Society for Testing and Materials International methods at T = (417.75 to 538.58) K by differential scanning calorimetry and in the ambient temperature range using saturator methodology at T = (298.15 to 313.15) K. The new TDG vapor pressure data are in sharp contrast to widely accepted values from previous literature.

The vapor pressures of three 2-dialkyl aminoethanethiol compounds, 2-dimethyl aminoethanethiol (DMA), 2-diethyl aminoethanethiol (DEA), and 2-diisopropyl aminoethanethiol (DIA), have been determined using complementary methods that enable data collection in the ambient and high temperature ranges using vapor saturation and differential scanning calorimetry, respectively. Previously published vapor pressure data for these materials are sparse, conflicting, and limited in the pressure ranges covered. This work greatly expands the experimental range and, owing to the good agreement obtained using complementary methods, significantly enhances confidence in the accuracy of the measured data. In addition to the observed data, this report includes derived properties, that is, temperature-dependent volatility and heats of vaporization.

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.

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.

The vapor pressure of the vesicant chemical warfare agent, bis(2-chloroethyl) sulfide (also known as sulfur mustard or HD), has been measured at T = (−25 to +20) °C using a modified ASTM vapor saturation methodology. This work represents the initial report of the measured vapor pressure of HD below its melting point, +14.45 °C. The data measured for solid-phase HD are consistent with the previously reported enthalpy of fusion and liquid-phase vapor pressure of HD.

A novel experimental apparatus and procedures have been developed and implemented to measure the volatility of a chemical warfare agent simulant as a function of ambient temperature and water vapor partial pressure. Initial data have been measured for dimethyl methylphosphonate (DMMP) to validate the methodology. The results presented herein reveal a significant volatility suppression for DMMP, increasing as the relative humidity increases. Deviation from ideal behavior as described by Raoult’s law has been quantified. The maximum deviation from ideality occurs at water partial pressures near 500 Pa. An empirical model has been developed to enable interpolation and limited extrapolation of the data to higher water partial pressures as might be found in compressed-air regenerative filtration applications.

Matrix isolation infrared spectroscopy has been combined with theoretical calculations for the characterization of the 1:1 hydrogen-bonded complex between H2O and dimethyl methylphosphonate (DMMP). The symmetric O-H stretching mode was observed to shift 203 cm-1 to lower energy upon hydrogen bond formation, while a 32 cm-1 blue shift was noted for the H-O-H bending mode of the H2O subunit in the complex. These values compare extremely well with the (unscaled) shifts of -203 and +32 cm-1, respectively, that were calculated theoretically at the MP2/6-31+G** level. Additional perturbed modes of the DMMP subunit were observed, shifted relative to the parent band position. The greatest perturbation was to the P═O stretching mode near 1270 cm-1, where a shift of -17 cm-1 was observed (-21 cm-1 calculated theoretically). This suggests that the site of hydrogen bonding in the complex is at the P═O group, in agreement with theoretical calculations. The binding energy ΔE° for the 1:1 complex was calculated to be -7.7 kcal/mol.