SOLID-STATE P-31 MAS NMR-STUDY OF THE DISTRIBUTION AND REACTION OF ORGANOPHOSPHORUS ESTERS ADSORBED ON SYNTHETIC RESIN CATALYSTS

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 P-31 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 P-31 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-degrees-C. PNDP hydrolyzes on the resin powder to yield diphenyl phosphate (DPP) and p-nitrophenoxide. A second P-31 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.