Tabun properties

The carbamate and OP insecticides and the organophosphorous nerve gases soman, sarin, and tabun all act as anticholinesterases, and most of their toxicity is attributed to this property. The naturally occurring carbamate physostigmine, which has been used in medicine, is also an anticholinesterase. Some OP compounds can cause relatively long-lasting inhibition of the enzyme because of the phenomenon of... 

Ethyl dimethylphosphoramidofluoridate (VIII) was prepared by a similar method and proved to be a very toxic liquid. Its l.d. 50, on intravenous injection into rabbits and also on subcutaneous injection into mice, was 2-5 mg./kg. Toxicity was also determined by inhalation and a Ct ((7 = concentration, <=10 min.) of 200 mg./min./cu.m. killed seven out of a batch of eleven rabbits, guinea-pigs, rats and mice a Ct of 100 mg./min./cu.m. killed four out of eleven. The compound also possessed myotic properties. Other compounds that we made in this series were much more toxic and it will be seen that they bear some resemblance to tabun and sarin now about... 

Irreversible cholinesterases are mostly organophosphorus compounds and combine only with esteratic site of cholinesterase and that site gets phosphorylated. The hydrolysis of phosphorylated site produces irreversible inhibition of cholinesterase. And, because, of this property, the therapeutic usefulness is very limited. Most of the compounds are used as insecticides e.g. parathion, malathion and war gases e.g. tabun, sarin, soman etc. 

ICHO/RES/0045, Properties of Fluoro-tabun An Analysis of Continuing Research (February 1945). 

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). 

The three types of nerve agent known to have been weaponized are typified by sarin (GB), VX and tabun (GA). Soman (GD) and cyclosarin (GF) are less volatile phosphonofluo-ridate analogues of sarin, and RVX or R-33 is a Russian analogue of VX with broadly similar properties. Tabun differs from the other nerve agents in that it does not possess a P-methyl substituent, which has important implications for... 

In the closing days of the war in Europe, the USSR captured a manufacturing facility in eastern Germany and moved the facility and personnel to Russia to continue production (Koelle, 1981). In western Germany, the British and the Americans captured a stockpile of munitions containing an unknown chemical agent. Their initial lack of awareness of the properties of this agent, tabun, was indicated in an early British report ... 

The three German nerve agents, tabun, sarin and soman were coded by the British as G A, GB and GD respectively. Although the Nazis had concentrated upon the manufacture of tabun (GA), tests had shown that sarin (GB) was many times more powerful, and soman more powerful yet. The Russians focused their efforts upon manufacturing soman, but the British decided that the alcohol needed for its production was too difficult to make in quantity. The British began a series of tests to establish the potency and other properties of weapons filled with the medium strength agent, GB. 

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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