Chemistry of GD (Soman) 

Soman (GD) has the chemical name methylphosphonofluoridic acid 1,2,2-trimethylpropyl ester has the molecular formula C ₇H ₁₆FO ₂P and formula weight 182.18. Its Chemical Abstracts Service registry number is 96-64-0.

General Information

Discovered in Germany in 1944, laboratory testing of Soman was in progress in Germany at the end of World War II. ¹A short history of nerve gas describes the research and development of the nerve agents in Germany prior to and during World War II. Soman has never been used in combat, but was produced and stockpiled by the Soviet Union. Soman is a colorless liquid when pure; the industrial product is yellow-brown. The pure compound has a fruity odor and the industrial product contains impurities with a camphor-like odor. ² One of the unusual aspects of GD is that it has two chiral centers, one at phosphorus and one at carbon. GD therefore exists as four stereoisomers, known as C ₍₊₎P ₍₊₎, C _(-)P ₍₊₎, C ₍₊₎P _(-), and C _(-)P _(-), ³ shown below with their associated absolute configurations. These constitute two sets of diastereomers, which have different physical and chemical properties and undergo degradation at different rates. For this reason, discrepancies in literature values for GD may be due to differential stereoisomer composition.

Four Stereoisomers of GD; absolute configurations are based on reference 4.

References:

1. Schmaltz, F., Neurosciences and Research on Chemical Weapons of Mass Destruction in Nazi Germany, J. Hist. Neurosci., 2006, 15 (3), 186-209.
2. Edgewood Arsenal, Chemical Agent Data Sheets Volume I, Edgewood Arsenal Special Report EO-SR-74001, DTIC accession no. AD-B028222, 1974.
3. Benschop, H. P.; De Jong, L. P. A., Nerve Agent Stereoisomers: Analysis, Isolation, and Toxicology, Acc. Chem. Res., 1988, 21 (10), 368-374.
4. Ordentlich, A.; Barak, D.; Kronman, C.; Benschop, H. P.; De Jong, L. P. A.; Ariel, N.; Barak, R.; Segall, Y.; Velan, B.; Shafferman, A., Exploring the Active Center of Human Acetylcholinesterase with Stereomers of an Organophosphorus Inhibitor with Two Chiral Centers, Biochemistry, 1999, 38 (10), 3055-3066.

Physical Properties of Soman

melting point 1	<-80 deg C
vapor pressure 2
density 1	D (g/ml) = 1.045549 - 0.00093 T (C)
aqueous solubility (20 deg C) 3	21 g L -1
aqueous solubility (0 deg C) 3	34 g L -1
log Kow4	1.78
log Kow5	1.824
KH(25 deg C) 6	4.6 × 10 6 atm m 3/mole

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

References:

1. Zeffert, B. M.; Coulter, P. B., Physical Constants of G-Series Compounds: Compounds EA 1210, EA 1211, EA 1212, EA 1213, EA 1214, TDMR-1292, Chemical Corps Technical Command, DTIC accession no. AD-B964904, 1947.
2. Savage, J. J.; Fielder, D., The Vapor Pressure of Chemical Agents GD, VX, EA2223, EA 3547, EA 3580, EA 5365, and EA 5533, EC-TR-76058, DTIC accession no. AD-B013164, 1976.
3. Edgewood Arsenal, Chemical Agent Data Sheets Volume I, Edgewood Arsenal Special Report EO-SR-74001, DTIC accession no. AD-B028222, 1974.
4. Benschop, H. P.; Wesselman, H. C., Pharmacokinetics of the Soman Simulant 1,2,2-Trimethylpropyl Dimethylphosphinate (PDP) in Rats, Arch. Toxicol., 1989, 63 (3), 238-243.
5. Czerwinski, S. E.; Maxwell, D. M.; Lenz, D. E., A Method for Measuring Octanol-Water Partition Coefficients of Highly Toxic Organophosphorus Compounds, Toxicol. Methods, 1998, 8, 139-149.
6. Munro, N. B.; Talmage, S. S.; Griffin, G. D.; Waters, L. C.; Watson, A. P.; King, J. F.; Hauschild, V., The Sources, Fate, and Toxicity of Chemical Warfare Agent Degradation Products, Environ. Health Perspect., 1999, 107 (12), 933-974.

Hydrolysis

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

 

GD Hydrolysis Products
Compound	MW	Solubility, g L-1	Estimated log Kow1
Fluoride (as HF)	20.01	"very" 2	-
Methylphosphonic acid, 1,2,2Çtrimethylpropyl ester	180.18	-	1.63
3,3-Dimethyl-2-butanol	102.18	-	1.48 3
Methylphosphonic acid	96.02	"very" 4	-0.70

pH	T (ºC)	t 1/2 (hr)	Reference
10	10	0.6	5
2	20	2.4	6
3	20	25	6
4	20	144	6
5	20	144	6
6	20	144	6
7	20	82.5	5
7	20	80	6
7.6	20	21.8	5
7.6	20	6.6	6
9	20	0.5	6
10	20	0.2	5
10	20	0.4	6
7.4	25	2.3	7
9	25	1.4	7
9	25	2.1	8
9.6	25	0.4	8
9.8	25	0.3	8
10.3	25	0.1	8
10.6	25	0.05	8
10.7	25	0.04	8
10.8	25	0.03	8
7.4	27	6.6	9
8	27	3.2	9
8.6	27	2.2	9
2	30	6.4	5
4	30	251.1	5
7	30	41.3	5
7.6	30	9.6	5
7.4	37	1.75	10
7.4	37	4.8	9
8	37	1.6	9
8.6	37	1.2	9

One group has used the data to develop the following expression for hydrolysis rates: ¹¹

Several Cu ⁺² complexes have been shown to catalyze GD hydrolysis. ^12,13

References:

1. Estimated using Syracuse Research Corporation, LOGKOW version 1.50; see Meylan, W. M.; Howard, P. H., J. Pharm. Sci. 1995, 84(1): 83-92.
2. 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.
3. Measured value from Dillingham, E. O.; Mast, R. W.; Bass, G. E.; Autian, J., Toxicity of methyl- and halogen-substituted alcohols in tissue culture relative to structure-activity models and acute toxicity in mice, J. Pharm. Sci., 1973, 2(1), 22.
4. Weast, R. C., Ed., Handbook of Chemistry and Physics, 56th ed., CRC Press, 1976.
5. Grochowski, J. W.; Korecki, J.; Hydrolysis Rate of Soman at Various pH and Temperatures, Biul. Wojskowej Akad. Techn., 1965, 14 (10/158), 177-189.
6. Healy, T.V., Kinetics of the Hydrolysis of Pinacolyl Methane Fluorophosphonate (GD), Porton Technical Paper No. 79, Chemical Defence Research Establishment Porton Down, 1948.
7. Desire, B.; Saint-Andre, S., Interaction of Soman with ß-Cyclodextrin, Fundam. Appl. Toxicol., 1986, 7 (4), 646-657.
8. Ward, J. R.; Yang, Y.-C.; Wilson, R. B.; Burrows, W. D.; Ackerman, L. L., Base-Catalyzed Hydrolysis of 1,2,2-Trimethylpropyl Methylphosphonofluoridate-an Examination of the Saturation Effect., Bioorg. Chem., 1988, 16 (1), 12-16.
9. Broomfield, C. A.; Lenz, D. E.; MacIver, B., The Stability of Soman and its Stereoisomers in Aqueous Solution: Toxicological Considerations, Arch. Toxicol., 1986, 59 (4), 261-265.
10. Buckles, L. C., The Hydrolysis Rate of GD, TCIR No. 373, Chemical Corps Technical Command, DTIC accession no. AD-B966291, 1947.
11. Rádl, Z.; Opluštil, F.; Skoumal, M., Hydrolysis of 1,2,2-Trimethylpropyl Methylphosphonofluoridate [Soman] in Aqueous Medium, Paper presented at: 4th International Symposium on Protection against Chemical Warfare Agents; 8-12 June 1992; Stockholm.
12. Hammond, P. S.; Forster, J. S., A polymeric amine-copper(II) complex as catalyst for the hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) and bis(1-methylethyl)phosphorofluoridate (DFP), J. Appl. Polym. Sci.,1991, 43(10), 1925-1931.
13. Katritzky, A. R.; Offerman, R. J.; Durst, H. D.; Ward, J. R.; Hovanec, J. W.; Albrizo, J. M., Copper chloride-cyanopyridine complexes as catalysts for the decomposition of fluorophosphonate esters, J. Fluorine Chem., 1989, 44(1) 121-131.

Photolysis

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

Thermolysis

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

Decontamination

Soman and other G agents are rapidly hydrolyzed in basic solutions, e.g., Na ₂CO ₃, NaOH, or KOH; ¹ soman has a half-life of approximately 1 minute at pH 11 at 25 deg C. ² Catalysts for soman hydrolysis include copper (II) complexes ^3,4 and iodosobenzoic acid derivatives. ⁵ Based on its chemical similarity to sarin, soman hydrolysis should be catalyzed by hypochlorite anion (OCl ^-) ⁶ and hydroperoxide. Current decontamination systems based on this chemistry include: ¹

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

References:

1. Yang, Y.-C.; Baker, J. A.; Ward, J. R., Decontamination of chemical warfare agents, Chem. Rev., 1992, 92, 1729-1743.
2. Ward, J. R.; Yang, Y. C.; Wilson, R. B.; Burrows, W. D.; Ackerman, L. L., Base-catalyzed hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate - an examination of the saturation effect, Bioorg. Chem., 1988, 16(1), 12-16.
3. Hammond, P. S.; Forster, J. S., A polymeric amine-copper(II) complex as catalyst for the hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) and bis (1-methylethyl)phosphorofluoridate (DFP), J. Appl. Polym. Sci., 1991, 43, 1925-1931.
4. Katritzky, A. R.; Offerman, R. J., Copper chloride-cyanopyridine complexes as catalysts for the decomposition of fluorophosphonate esters, J. Fluorine Chem., 1989, 44, 121-131.
5. 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.
6. 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.