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The molecular exchange of dimethyl methylphosphonate (DMMP) between the reactive and sorptive components in a mixture of three macroreticular resins (a high surface area carbonaceous adsorbent and strong-base and strong-acid ion-exchange resins) is characterized by 31 P MAS NMR. Data from 31 P MAS magnetization-transfer NMR experiments performed on four samples possessing 2,6,9 and 14% DMMP are analyzed using a modified two-site exchange model which takes into account that only a fraction of DMMP molecules adsorbed on the carbonaceous adsorbent (site B) are able to exchange with those residing on the ion-exchange resins (site A) during the time scale of the experiment. The exchange lifetime determined in this manner for DMMP adsorbed on the carbonaceous adsorbent ( k −1 B ) remains fairly constant at ca. 50 ms for the four samples. The exchange lifetime for DMMP residing on the ion-exchange resins ( k −1 A ) is observed to increase for lower weight-percent loadings: 250 ms (14%), 330 ms (9%), 500 ms (6%) and 670 ms (2%). 31 P MAS 2-D exchange NMR experiments indicate an optimum mixing time (τ m ) of 0.2–0.5 s for the 14% sample, which is consistent with the measured exchange lifetimes.

A powder containing sorptive and reactive resins that was developed for the removal and subsequent catalytic degradation of toxic organophosphorus esters is characterized using dimethyl methylphosphonate (DMMP), p-nitrophenyl diphenylphosphate (PNDP), and 31P MAS NMR. The results for DMMP confirm, spectroscopically, that the adsorbed ester is distributed between the sorptive and reactive resin components. Spectra of the DMMP surface probe adsorbed on the resin are indicative of two different adsorption sites, one possessing a much larger capacity compared with the other. The large-capacity site is identified as the sorptive macroreticular ‘porous’ region of the resin. The smaller-capacity site seems to be associated with the reactive quaternary ammonium hydroxide functional groups of the ion-exchange resin. At each type of site, adsorbed DMMP exhibits ‘liquid-like’ isotropic motion; however, the molecules do not appear to be able to rapidly migrate between the sorptive and reactive regions. Variable-temperature 31P MAS NMR results for DMMP demonstrate that any molecular exchange between these sites must be occurring at a rate of less than 300 s−1, even at 50 °C. PNDP hydrolyzes on the resin powder to yield diphenyl phosphate (DPP) and p-nitrophenoxide. A second 31P MAS NMR resonance is not observed for PNDP adsorbed at the reactive sites; however, the anionic DPP product appears to be tightly bound by the quaternary amine ion-exchange group, which may block further PNDP hydrolysis at the reactive site.

The tertiary amine, N -2-hydroxyethylpiperazine- N '-2-ethanesulfonic acid (HEPES) is a common buffer used in measuring the hydrolysis of neurotoxins such as the phosphonofluoridates soman and sarin. The hydrolysis of soman was monitored in the presence of various concentrations of HEPES at 25 °C and pH= 7. The rate of hydrolysis of soman was linearly related to the concentration of HEPES present as free base in solution. The second-order rate for the HEPES catalysis was 1.6 × 10 −3 M −1 s −1 , in contrast to a value of 10 M −1 s −1 for the hydroxide ion-catalyzed nucleophilic attack on soman.

Transition metal ions, such as manganese(II) or copper(II), catalyze the hydrolysis of O -isopropyl methylphosphonofluoridate (sarin) or O , O' -diisopropyl phosphorofluoridate (DFP). The rate law for the catalyzed path is first order in ester, metal(II) and hydroxide. Thus, the catalytic species could be the hydroxometal complex, or the catalysis could consist of a complex formed between the metal ion and phosphorus substrate which is subsequently attacked by hydroxide. Recently, we measured the solvolysis of sarin in an ethanol-water solution. By means of 31 P nuclear magnetic resonance (NMR), two products were seen to form from parallel attack on sarin by hydroxide and ethoxide. In the presence of zinc(II) chloride, it was shown that both reaction rates were significantly increased. If the increase in reactivity were attributed to a zinc hydroxide complex, then no change would be expected in the rate of attack by ethoxide ion. We further suggest the monitoring of relative rates of reaction in mixed solvents as a way to distinguish whether a metal ion catalyst acts as a Lewis acid or simply supplies a larger concentration of nucleophilic hydroxide ion.