Pinacolyl methylphosphonic acid

Water extract None O-Pinacolyl methylphosphonic acid 2.B.4... 

Agent GD may hydrolyze to relatively nontoxic hydroflouric and pinacolyl methylphosphonic acids (MacNaughton and Brewer, 1994 Rosenblatt et al., 1995). The hydrolysis rate is a function of temperature and pH the rate is minimum between pH 4 and 6. The C/2 for GD is approximately 100 hours with 20 x ti/2 being required to attain a 1 x 10 reduction in GD concentration. 

In addition, due to the reversibility of the binding reaction of sarin and soman to CarbE, it appears that CarbEs are involved in metabolic detoxification of these agents to their corresponding nontoxic metabolites isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA) (Jokanovic et al, 1996). 

FIGURE 19.2 Hydrolysis pathway of sarin (GB), soman (GD), and cyclosarin (GIO hydrolysis pathway of nerve agents proceeds through the alkyl methylphosphonic acids, isopropyl methylphosphonic acid (IMPA), pinacolyl methylphosphonic acid (PMPA), and cyclohexyl methylphosphonic acid (CMPA) to methylphos-ponic acid (MPA). Analysis of the alkyl methylphosphonic acids allows identification of the parent agent, while assay of MPA is nonspecific. 

Agent GD pinacolyl methylphosphonic acid methylphosphonic acid... 

N -butylphosphonic acid, phenylphosphonic acid, ethyl methylphosphonic acid, ethyl methylthiophosphonic acid, isopropyl methylphosphonic acid, pinacolyl methylphosphonic acid, dimethyl phenylphosphonate in 16 min Methylphosphonic acid, ethylphosphonic acid, CZE... 

GD dissolves in water but the rate of hydrolysis under neutral conditions is slow (Yang et al. 1992). Qualitatively, the hydrolysis of GD is similar to that of GA however, the reaction rate is fivefold slower than that of GA, and GD has an estimated half-life of about 60 hr at pH 6 and 25 °C (Hambrook et al. 1971). The reaction is both acid- and base catalyzed, resulting in a hydrolysis curve similar to that of GA (Clark 1989). The primary hydrolysis product of GD is pinacolyl methylphosphonic acid, which slowly hydrolyzes, with the release of pinacolyl alcohol, to methyl phosphonic acid (Fig. 6) (Clark 1989 Kingery and Allen 1995). At pH >10, hydrolysis to pinacolyl methylphosphonic acid occurs within a few minutes (Yang et al. 1992). Because an acid is produced, the pH will decrease, lessening the rate of hydrolysis. GD stored at pH 6 for 8 wk had a pinacolyl methylphosphonic acid/methyl phosphonic acid ratio of 250 (Hambrook et al. 1971), which Kingery and Allen (1995) extrapolated to a half-life of 27 yr. The C-P bond is very resistant to hydrolysis. Hydrolysis products are listed in Table 37. 

GD (shaip doublets centered near 29 ppm. Figure 3) readily hydrolyzes (see Scheme 1) to pinacolyl methylphosphonic acid (PMPA, broad peak at 24 ppm) which binds to the oxide surface as shown in Scheme 1. Additionally, on -MgO and AP CaO a second, minor product peak appears near 20 ppm. Based on the results for high-loading GD on AP-AI2O3 (see below) diis second product is assigned to die corresponding metal pinacolyl mediy hosphonates rather than MPA since PMPA is extremely resistant to hydrolysis. 

Fig. 1 HPLC-ESP MS reconstructed (total) ion chromatogram from a standard mixture of alkyl phosphonic acids at a concentration of 1 p-g/ml each 1) methylphosphonic acid (MPA) 2) ethylphosphonic acid (EPA) 3) methyl ethylphosphonic acid (MEPA) 4) ethyl methylphosphonic acid (EMPA) 5) ra-propylphosphonic acid (nPrPA) 6) ethyl ethylphosphonic acid (EEAP) 7) isopropyl methylphosphonic acid (iPrMPA) 8) n-propyl methylphosphonic acid (nPrMPA) 9) isopropyl ethylphosphonic acid (iPrEPA) 10) n-propyl ethylphosphonic acid (nPrEPA) 11) isohutyl methylphosphonic acid (iBuMPA) 12) cyclohexyl methylphosphonic acid (CHMPA) 13) pinacolyl methylphosphonic acid (PinMPA).

Fig. 3 Reversed-phase HPLC-MS/MS chromatogram using formic acid in the mobile phase and an Atlantis dC18 column. The standard mixture of alkyl phosphonic acids with a concentration of 10 p,g/ml each was detected using multiple reaction monitoring (MRM) 1) methylphosphonic acid (MPA, miz 96.8 78.7) 2) ethyl methylphosphonic acid (EMPA, mIz 125 96.8) 3) C>-elhyl A,A-dimethylamidophosphoric add (EDMAPA, miz 154.2—>126) 4) isopropyl methylphosphonic acid (iPrMPA, nJz 139.1 %.8) 5) pinacolyl methylphosphonic acid (PinMPA, miz 181.3- 96.8) 6) diisopropyl methylphosphonic add (DiPrMPA, mk 181.3 139.1). See the text for further chromatogr hic details and the MS/MS conditions used.

FIGURE 22.4 Mass spectra of pinacolyl methylphosphonic acid (PMPA) on soil particles, at a concentration of 0.02 molecular layer. Top MS-1 bottom MS-2, following isolation and fragmentation of the conjugate base at m/z 179. 

Ingram, J.C., Appelhans, A.D., Groenewold, G.S. (1998) Ion-trap SIMS analysis of pinacolyl methylphosphonic acid on soil. Int. J. Mass Spectrom. Ion Process., 175,253. 

Figure 10. El, Methane Cl and Ammonia Cl Mass Spectra of Pinacolyl Methylphosphonic Acid, TMS Derivative.

Figure 10 compares the El, methane Cl and ammonia Cl mass spectra obtained for a representative member of this series, the TMS derivative of pinacolyl methylphosphonic acid. No El molecular ion is observed. The methane Cl [M+H] ion is small, less than 10% of the base peak. As shown previously in Figures 8 and 9, this class of compounds gives very similar El mass spectra, which is excellent for class screening but not for compound identification. Of the three methods of ionization, ammonia Cl is the method of choice for identification and molecular weight confirmation. The [M+H] ion is the base peak. The [M+NH4] adduct ion is also observed (20% of base peak in the above example). 

Sarin is metabolized to isopropyl methylphosphonic acid (IMPA) and excreted by the kidneys (Little et al., 1986). Approximately 50% of soman is converted to free pinacolyl-methylphosphonic acid within 1 min in mice. The half-life of this metabolite is less than 1 h (Reynolds et al., 1985). 

The primary hydrolysis product of GD is pinacolyl methylphosphonic acid (PMPA). Other hydrolysis products include the breakdown of PMPA to MPA and pinacolyl alcohol. Major impurities found in GD consist of dipinacolyl methylphosphonate, methyl pinacolyl methylphosphonate, methyl methylphosphonofluoridate and methyl methacrylate. Toxicological data for MPA was discussed earlier in Section 2.2 and can be found in Table 2.4. There are no current toxicity data available on the major degradation product PMPA, although it is structurally similar to IMPA, which exhibits low toxicity (Tables 2.4 and 2.5). Toxicity reports have found that methyl methacrylate is considered to possess moderately acute effects and is irritating to the eyes... 

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