Rapid destruction of sarin surrogates by gas phase reactions with focus on diisopropyl methylphosphonate (DIMP)

Abstract

Rapid destruction of stockpiles of sarin and other chemical weapon agents (CWA) requires understanding and quantitative description of the relevant chemical reactions. Rapid reactions at elevated temperatures are of particular interest for prompt agent defeat scenarios. Diisopropyl methylphosphonate (DIMP) is a sarin surrogate particularly well suited to model sarin thermal decomposition and is often used in experiments. This article is a review of different experimental methods addressing decomposition of gasified DIMP, respective results and their interpretations. Major early decomposition products are propene, methylphosphonic acid, methyl(oxo)phosphoniumolate, and isopropanol. Early computational work using available kinetic data for fluorine and the phosphorus-fluorine bond predicted the decomposition under incineration conditions. Experiments using an isothermal flow reactor operated at 700–800 K were used to model DIMP decomposition as unimolecular reaction with results that were consistent with the earlier theoretical work. Decomposition in dynamic environments was studied using DIMP supported on rapidly heated substrates. The results showed different decomposition products and product sequences forming at different heating rates, suggesting the need for revised reaction kinetics. However, species quantification in such experiments is difficult because of inherent large temperature gradients. Plasma produced in a corona discharge was also reported to lead to rapid DIMP decomposition at low temperatures. Decomposition products were distinct from those observed at high temperatures. Shock tube experiments may be well suited to study decomposition of organophosphorus compounds like DIMP following their rapid heating in diverse environments. However, presently, only sarin surrogates other than DIMP have been investigated, and no intermediate reaction products, important for developing a validated mechanism, could be detected.