Mechanistic Insight into the Molecular TiO₂-Mediated Gas Phase Detoxication of DMMP: A Theoretical Approach

The detoxication of DMMP (dimethyl methylphosphonate) mediated by molecular TiO₂ has been investigated computationally using density functional theory (DFT). From our previous studies, it is evident that the unimolecular detoxication of OPCs (organophosphorus compounds) is kinetically unfeasible at room temperature due to the significantly high activation barrier. Thus, the aim of our work is to find out whether molecular TiO₂ can make any significant impact on the kinetic feasibility of the detoxication processes or not. Here, we have identified a total of three detoxication pathways, where in the first step the detoxication occurs through H-abstraction with the assistance of TiO₂, and in the second step, the titanium complex is separated from the respective phospho-titanium complexes. The outcomes reveal that the TiO₂-mediated detoxication pathways are at least 20.0 kcal/mol more favorable than their respective unimolecular pathways and that among them, the α-H-mediated isomerization is found to be the most feasible pathway. When the separation of a titanium complex is under consideration, the double H₂O-assisted mechanism is found to be the favored pathway. Overall, the entire work provides a widespread idea about the efficiency of molecular TiO₂-assisted detoxication of DMMP, which can be well applicable to other OPCs also.