Chemistry of GB (Sarin) 

Sarin (GB) has the chemical name methylphosphonofluoridic acid, (1-methylethyl) ester, and has the molecular formula C ₄H ₁₀FO ₂P and formula weight 140.09. Its Chemical Abstracts Service registry number is 107-44-8.

General Information

Sarin was discovered in Germany in 1938 by a team led by Dr. Gerhard Schrader. A short history of the development of nerve gas describes the research and development of the nerve agents in Germany prior to and during World War II. Large-scale combat use of Sarin has not occurred, although its use is strongly suspected in an Iraqi attack on the village of Birjinni on 25 August 1988 (samples collected from the site four years later showed the expected breakdown products of Sarin). It is not known with certainty whether or not Sarin was used in the Iran-Iraq war. On 20 March 1995, the Aum Shinrikyo released Sarin in the Tokyo subway, killing 12 and injuring 5,500 people in the first documented terrorist use of chemical weapons. After the Tokyo attack, a June 1994 incident in 1994 that killed 7 and injured 200 in central Japan is now also believed to be the work of Aum Shinrikyo. Sarin was produced and stockpiled in large quantities by both the United States and the Soviet Union. Sarin is a colorless and odorless liquid. ¹

GF

Closely related to sarin is a compound referred to as GF, or cyclohexyl sarin. GF is also a colorless and odorless liquid.

Reference:
1. Franke, S., Manual of Military Chemistry, Volume 1. Chemistry of Chemical Warfare Agents, Deutscher Militîrverlag: Berlin (East), 1967. Translated from German by U.S. Department of Commerce, National Bureau of Standards, Institute for Applied Technology, NTIS no. AD-849 866, pp. 247, 252.

Physical Properties of Sarin

Noblis recently published a review of melting point, boiling point, vapor pressure as a function of temperature, density as a function of temperature, water solubility, and partitioning data for Sarin. References to the original data sources are given in the review.

melting point	-56.3 deg C
boiling point	147 deg C, 158 deg C
vapor pressure (20 deg C)	1.55 mm Hg
density (20 deg C)	1.096 g cm -3
aqueous solubility	miscible
log Kow	0.30

Additional data on properties, health hazards, and handling is given in the material safety data sheet(MSDS) for sarin.

Reference:

1. Bizzigotti, G. O.; Castelly, H.; Hafez, A. M.; Smith, W. H. B.; Whitmire, M. T., Parameters for Evaluation of the Fate, Transport, and Environmental Impacts of Chemical Agents in Marine Environments, Chem. Rev., 2009, in press.

Hydrolysis

GB undergoes hydrolysis by acidic, neutral, and basic mechanisms, all of which give fluoride and isopropyl methylphosphonate as the initial products. The neutral reaction is as follows:

 

GB Hydrolysis Products
Compound	MW	Solubility, g L-1	Estimated log Kow1
Fluoride (as HF)	20.01	"very" 2	-
Methylphosphonic acid, 1Çmethylethyl ester	138.10	-	0.27
2-Propanol	60.10	miscible 3	0.28
Methylphosphonic acid	96.02	"very" 4	-0.70

Noblis recently published a review that compiled hydrolysis rate constants, hydrolysis activation energies, and half-lives in sea water for Sarin. References to the original data sources are given in the review.

References:

1. Bizzigotti, G. O.; Castelly, H.; Hafez, A. M.; Smith, W. H. B.; Whitmire, M. T., Parameters for Evaluation of the Fate, Transport, and Environmental Impacts of Chemical Agents in Marine Environments, Chem. Rev., 2009, in press.
2. Estimated using Syracuse Research Corporation, LOGKOW version 1.50; see Meylan, W. M.; Howard, P. H., J. Pharm. Sci. 1995, 84(1): 83-92.
3. The Merck Index, 11 ed., Budavari, S.; O'Niel, M. J.; Smith, A.; Heckelmanm, P. E., Eds., Merck & Co.: Rahway, 1989, p. 760, compound no. 4723.
4. Reference 2, p. 820, compound no. 5093.
5. Weast, R. C., Ed., Handbook of Chemistry and Physics, 56^thed., CRC Press, 1976.

Photolysis

Sarin and its hydrolysis products exhibit no significant phototransformations in sunlight.

Thermolysis

Sarin and its hydrolysis products are thermally stable at temperatures less than 49 deg C.

Decontamination

Sarin and other G agents are rapidly hydrolyzed in basic solutions, e.g., Na ₂CO ₃, NaOH, or KOH; ¹ GB has a half-life of 0.5 minutes at pH 11 at 25 deg C. ² Catalysts for GB hydrolysis include hypochlorite anion (OCl ^-), ³ hydroperoxide anion (HOO ^-), ⁴ several metal ions and their complexes (Cu ⁺², UO ₂⁺², ZrO ⁺², MoO ₂⁺², Th ⁺⁴ ), ^5,6 and iodosobenzoic acid derivatives. ⁷ Current decontamination systems based on this chemistry include: ¹

• solids, powders and solutions containing various types of bleach (NaOCl ^- or Ca(OCl ^-) ₂)
• Foams and gels based on peroxides, e.g., DF-200, L-Gel
• DS2 (2% NaOH, 70% diethylenetriamine, 28% ethylene glycol monomethyl ether)
• towelettes moistened with NaOH dissolved in water, phenol, ethanol, and ammonia

References:

1. Yang, Y.-C.; Baker, J. A.; Ward, J. R., Decontamination of chemical warfare agents, Chem. Rev., 1992, 92, 1729-1743.
2. Gustafson, R. L.; Martell, A. E., A kinetic study of the copper(II) chelate-catalyzed hydrolysis of isopropyl methylphosphonofluoridate (Sarin). J. Am. Chem. Soc., 1962, 84, 2309-2316.
3. Epstein, J.; Bauer, V. E.; Saxe, M.; Demek, M. M., The chlorine-catalyzed hydrolysis of isopropyl methylphosphonofluoridate (Sarin) in aqueous solution, J. Am. Chem. Soc., 1956, 78, 4068-4071.
4. Larsson, L., Reaction of isopropoxymethylphosphoryl fluoride (Sarin) with hydrogen peroxide, Acta Chem. Scand., 1958, 12, 723-730
5. Courtney, R. C.; Gustafson, R. L.; Westerback, S. J.; Hyytiainen, H.; Chaberek, S. C.; Martell, A. E., Metal chelate compounds as catalyts in the hydrolysis of isopropyl methylphosphonofluoridate and diisopropylphosphorofluoridate. J. Am. Chem. Soc., 1957, 79, 3030-3036.
6. Gustafson, R. L.; Martell, A. E., A kinetic study of the copper(II) chelate-catalyzed hydrolysis of isopropyl methylphosphonofluoridate (Sarin). J. Am. Chem. Soc., 1962, 84, 2309-2316.
7. Hammond, P. S.; Forster, J. S.; Lieske, C. N.; Durst, H. D., Hydrolysis of toxic organophosphorus compounds by o-iodosobenzoic acid and its derivatives, J. Am Chem. Soc., 1989, 111, 7860-7866.