Fluoride Action Network

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

Source: Defence Technology [in press] | Authors: Senyurt EI, Schoenitz M, Dreizin EL.
Posted on June 22nd, 2020
Location: International
Industry type: Chemical Weapons

Note from FAN:
The molecular structure of Sarin:

2D chemical structure of 107-44-8


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.


Chemical weapon agent
Agent defeat
Thermal decomposition
Prompt reactions

1. Introduction

1.1. Chemical weapon agents and prompt agent defeat

Chemical warfare is the use of the toxic chemical substances to kill, injure or incapacitate an enemy [1,2]. A chemical substance intended for such use is a chemical weapon agent (CWA). North Atlantic Treaty Organization (NATO) classified CWAs as blister agents, nerve agents, asphyxiants, choking agents and incapacitating/behavior altering agents [[3], [4], [5]].

CWAs pose a threat to humankind and are widely banned [6,7]. Therefore, guidelines for environmentally safe destruction of CWA stockpiles need to be developed [7,8]. Because CWAs are highly toxic, direct experimental studies are limited to those conducted in specially equipped military laboratories, and research on CWAs is often conducted using simulant compounds. An ideal CWA simulant (CWAS) would imitate the pertinent chemical and physical properties of the agent without its associated toxicological properties [3,4].

Efforts focused on safe and effective destruction of CWA stockpiles have been active for decades [1]. Most available CWA decontamination methods require exposure times of minutes or hours. Such methods are useful when decontamination chemicals and equipment can be delivered and operated directly at the location of CWA stockpiles or infected areas [5,9]. Conversely, challenges arise when access is limited, and CWA needs to be destroyed rapidly, without unintended release, or other collateral effects. For such cases, technologies ensuring prompt defeat of CWAs [10], with characteristic times of milliseconds to seconds become crucial.

Means of prompt defeat must be developed for destruction of both chemical and biological agent stockpiles, especially in cases when CWA aerosols or gases can be released due to elevated temperatures [11]. Indeed, high temperatures typically occur in fireballs, generated to neutralize or destroy the agents. The associated blast overpressure risks spreading the CWAs before they are decomposed [10,11]; such effects should be minimized. Therefore, respective munitions should rely on reactive materials generating copious amounts of heat without substantial gas release [12,13]. To develop effective prompt defeat techniques and respective reactive materials, detailed measurements and models need to first focus on laboratory experiments with CWAS. The CWAS must be reproducing the CWA behavior in conditions involving rapid heating and exposure to high temperatures for durations typical of fireballs. This poses constraints on both, the choice of CWAS, and the experimental approach for studying their decomposition reactions.

Reported methods for destroying CWAs can be broadly split into three categories: thermal decomposition [14,15], chemical degradation [16] and catalytic decontamination [4,17]. Thermal decomposition is achieved either by incineration [18] or pyrolysis [15,19]. Chemical degradation reduces the toxicity of CWAs by alkaline solutions and other oxidants [1,16,17,20]. Catalytic decontamination turns CWAs into benign chemicals using catalysts [21,22]. Chemical degradation, commonly involving reactions in liquid phase, is a relatively slow process [20,23]; therefore, it may not be suitable for prompt defeat applications. The other two methods, thermal decomposition and catalytic decontamination can occur in the gas phase and thus are important for understanding and describing various CWA prompt defeat processes depending on the temperature and materials generated by the fireball. Because elevated temperatures always accompany a fireball, thermal decomposition is always expected to be a process important for prompt defeat.

There are several reports in the literature on rapid thermal decomposition of CWAS and CWA. For example, Zegers et al. [15], describe the gas phase pyrolysis of diethyl methylphosphonate (DEMP), which is a surrogate for the nerve agent sarin. More recently, Shan et al. [24], studied the thermal decomposition of sarin. Both studies described a significant reduction of the agent or surrogate amounts after a short, sub-second exposure to elevated temperatures. Data describing intermediate products formed in such reactions are limited, however. Some of such intermediates may remain harmful, and thus it is important to develop a comprehensive mechanism describing their formation and lifetime. In a practical situation associated with expanding and decaying fireballs, reaction times may vary from a fraction to hundreds of ms and the temperature can rapidly change from hundreds to thousands of K. The oxidizing environment may also change, from oxygen starved to fuel-lean. Studies aimed to support prompt defeat methods should thus determine how such dynamically changing environments affect CWA decomposition, what the intermediate products are, and how rapidly they decompose into harmless species…

READ THE FULL ARTICLE AT https://www.sciencedirect.com/science/article/pii/S2214914720303755


This work was supported by the US Defense Threat Reduction Agency, Award HDTRA1-19-1-0023.



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