Tabun physical properties

Physical Properties. Tabun is a colorless compound, which is said to have a somewhat fmity odor. The odor changes with decomposition so that with lesser amounts of decomposition the odor of cyanide (like bitter almonds) is apparent, whereas with greater amounts the odor of dimethyl-amine (like fish) is apparent. Tabun s vapor pressure is the lowest of all the G agents (approximately 0.04 mm Hg at 20°C). This suggests that tabun could be a relatively persistent threat at lower temperatures. Tabun has a vapor density of 5.6 relative to air and a liquid density of 1.08 g/mL (25°C). Its mp is —50°C, and its bp is approximately 240°C. It is three times as water soluble (approximately 10% at 20°C) as is VX, and also soluble in typical organic solvents (e.g., ethanol, diethyl ether, and chloroform). As with other nerve agents, dissolution in inert solvents (e.g., diethyl ether) enhances tabun s stability. 

Physical Properties. Pure soman is a colorless liquid with a somewhat fruity odor. It has density 1.01 g/mL (20°C), vapor pressure of 0.27 mm/Hg (20°C), mp of —80°C, and bp of 190°C (85°C at 15 mm/Hg). Distillation is accompanied by decomposition that begins near 130°C. Soman s solubility in water is about 20% at 25°C. It is only about 20% as soluble in water as is tabun. With two different chiral centers, it exists as four stereoisomers (Benschop et al., 1985), each with a different toxicity. The lethal concentration (inhalation) in humans is estimated at approximately 25-50 mg min/m (Somani et al., 1992). 

Molecular models of the nerve agents tabun, sarin, soman, and VX are shown in Figure 5-3. Table 5-3 summarizes the chemical, physical, environmental and biological properties of these compounds. 

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