Multiple effects of the presence of water on the nucleophilic substitution reactions of NaX Faujasite zeolite with dimethyl methylphosphonate (DMMP)

Abstract

This study examines the dependence of the nucleophilic chemistry of dimethyl methylphosphonate (DMMP) adsorbed in NaX zeolite on adsorbed H 2O content and on DMMP solution concentration. Primarily solid state and solution 1H and 31P NMR and GC–MS methods were employed. Experiments with H 2 18O demonstrate that the nucleophilic attack in the zeolite is at the C atom of the ester group and not at the phosphonate P atom. Water is shown to play a complicated role in the chemistry at low water content by (1) facilitating DMMP adsorption to the supercage reaction sites and (2) hydrolyzing the ionic and framework-bound products of NaX nucleophilic attack on DMMP, but at higher water content (3) by inhibiting the chemistry, presumably through H-bonding to framework and ester O atoms and coordination of the stabilizing Na ions and (4) by exclusion of DMMP from the zeolite supercage volume at very high water adsorption. Evidence is presented for a deviation from an ideal DMMP adsorption dependence on DMMP concentration, when the presence of sufficient water for hydrolysis leads to a greater DMMP adsorption capacity in the zeolite. This is attributed to the release of DMMP binding sites in the zeolite supercage, when the strongly zeolite interacting framework-bound and ionic species are hydrolyzed.