Ethyl Methylphosphonothioate Research Articles

Active and Strippable PVA/Borax/NaBO3 Hydrogel for Effective Containment and Decontamination of Chemical Warfare Agents.

Active gels present unique potential for the decontamination of chemical warfare agents (CWAs) as they strongly adhere to surfaces, thus allowing prolonged decontamination time. Herein, we present a decontamination hydrogel based on polyvinyl alcohol/borax, which contains sodium perborate (NaBO3), as an in situ source of the active ingredient hydrogen peroxide. Developed as a binary formulation, this gel instantly forms and effectively sticks when sprayed on various matrices, including porous and vertically positioned matrices. The gel efficiently detoxified the CWAs sarin (GB), O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate (VX), and sulfur mustard (HD) in test tubes (2 μL CWA/0.5 mL gel) to provide nontoxic products with reaction half-lives of <3, 45 and 113 min, respectively. The gel was also shown to efficiently decontaminate surfaces contaminated with VX (5–7 mg, 8–12 mL of gel, i.e., >99%) and to prevent GB evaporation, as proven by laboratory wind tunnel experiments. The universal decontamination abilities of this mild hydrogel, as well as its facile application and removal processes suggest that it holds high potential for future development as a new CWA decontamination tool.

Determination of o-isobutyl-s-[(2-diethylamino)ethyl]-methyl phosphonothioate and the hydrolysis toxic product traces by liquid chromatography-tandem mass-spectrometry

To date, chemical weapons in the Russian Federation have been completely destroyed. Former chemical weapons destruction facilities (CWDFs) are subject to re-profiling. The most important stage of this activity is to assess the safety of engineering elements of the facilities to find out whether they can be involved in national economy. The most toxic and persistent substance processed at the CWDFs was a V-series agent. The certified gas chromatographic methods previously used for control of residual amounts of this substance on the surfaces and in deep layers of materials were based on its conversion to acid fluoride on silver fluoride pads. The latter are no longer produced, and these methods are impossible to use. The use of liquid tandem chromatography-mass spectrometry (HPLC-MS/MS) provided a direct determination of VR in the different matrices at the level of the toxicity threshold. At the same time HPLC-MS/MS method allows to determine the toxic acid formed by the hydrolysis of the P–O bond in the VR molecule. Previously no methods for the determination of this acid were available. A unified procedure for the sensitive target determination of VR (O-isobutyl S- (2-diethylamino)ethyl methylphosphonothioate) and its most toxic hydrolysis product S-[(2-diethylamino)ethyl] methylphosphonothioic acid in surface wipes and in deep layers of various materials is proposed. The method involves the addition of an internal standard (paraoxon) to the sample, extraction with methanol, concentration of the extract, and analysis by HPLC-MS/MS in the multiple reaction monitoring (MRM) mode. The detection limits of the analytes are close to their toxic threshold levels. Special emphasis in the procedure is paid to the reliability of identification of the analytes, which is of key importance in international investigations under the Chemical Weapons Convention.

A flexible self-detoxifying Zr(OH)4-carbon fiber composite for decontamination of chemical warfare agent

Self-detoxifying materials for capturing and destructing chemical warfare agents (CWAs) have attracted intense attention in efficient personal protection and safe handling of contaminated materials. In this study, we reported an approach for synthesis of flexible Zr(OH)4-carbon fiber composite by sol–gel method. Activated carbon fibers serving as substrate carrier and adsorption conveyor could effectively make Zr(OH)4 evenly distributed on the surface, which has excellent sorption properties and wide-ranging reactivity toward CWAs. The results demonstrated that the Zr(OH)4-carbon fiber composite could quickly remove (within 10 s) and 6-h degradation efficiency to 10-mg/mL sulfur mustard (HD) and O-ethyl S-(2-diisopropylamino)-ethyl methylphosphonothioate (VX) could reach 92.2 and 99.99%. In addition, it was found that Zr(OH)4-carbon fiber composite remained intact after adsorption, which could recollect resources and avoid Zr(OH)4 leakage into waters. Therefore, the designed Zr(OH)4-carbon fiber composite will be a good potential application in precision equipment or skin decontamination equipment.

VX Evaporation and Degradation from Urban Land Surfaces

Evaporation and degradation of the nerve agent, VX [O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothioate] was explored on common urban or industrial surfaces, including sand, soil, and concrete. Concentration profiles of VX vapor were obtained using a laboratory-sized wind tunnel and thermal desorber in conjunction with gas chromatography. Results show that released VX vapors amounted to <20% of the applied mass and evaporation rates were found to be 0.12 μg/min in sand, 0.088 μg/min in soil, 0.16 μg/min in concrete (water–cement ratio, w/c = 0.50), which are ∼5–10 times slower than in the glass surface. At elevated temperature of 35°C, rates remarkably increased at 0.44 μg/min in sand, 0.12 μg/min in soil, and 0.67 μg/min in concrete. Rates also increased with lower w/c in concrete (0.48 μg/min in concrete [w/c = 0.42] and 0.76 μg/min in concrete [w/c = 0.31]). On the other hand, a drop of neat VX sorbed into the matrices remained for days and degraded following a pseudo first-order rate reaction. Estimated half-lives of VX in these matrices were ∼6 days in sand, 8 days in soil, and 3 days in concrete (w/c = 0.50) at room temperature. Degradation products were the following: ethyl methylphosphonic acid (EMPA), ethyl methylphosphonothioic acid (EMPT), methylphosphonic acid (MPA), 2-(diisopropylamino)ethanethiol (DESH), and bis(2-diisopropylaminoethyl) sulfide [(DES)2]. Parameters, which were quantified and evaluated in this study, will be useful for database establishment in risk assessment of exposure of the general population to highly lethal VX.

Polysaccharide-Thickened Aqueous Fluoride Solutions for Rapid Destruction of the Nerve Agent VX. Introducing the Opportunity for Extensive Decontamination Scenarios

Among the chemical warfare agents, the extremely toxic nerve agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) is a target of high importance in the development of decontamination methods, due to its indefinite persistence on common environmental surfaces. Liquid decontaminants are mostly characterized by high corrosivity, usually offer poor coverage, and tend to flow and accumulate in low areas. Therefore, the development of a noncorrosive decontaminant, sufficiently viscous to resist dripping from the contaminated surface, is necessary. In the present paper we studied different polysaccharides-thickened fluoride aqueous solutions as noncorrosive decontaminants for rapid and efficient VX degradation to the nontoxic product EMPA (ethyl methylphosphonic acid). Polysaccharides are environmentally benign, natural, and inexpensive. Other known decontaminants cannot be thickened by polysaccharides, due to the sensitivity of the latter toward basic or oxidizing agents. We found that the efficiency of VX degradation in these viscous solutions in terms of kinetics and product identity is similar to that of KF aqueous solutions. Guar gum (1.5 wt %) with 4 wt % KF was chosen for further evaluation. The benign nature, rheological properties, adhering capabilities to different surfaces, and decontamination from a porous matrix were examined. This formulation showed promising properties for implementation as a spray decontaminant for common and sensitive environmental surfaces.

Hydrolysis of a VX-like Organophosphorus Compound through Dissociative Chemisorption on the MgO(001) Surface

Organophosporous VX agent O-ethyl S-(2-diisopropylethylamino)ethyl methylphosphonothioate is one of the main nerve agents. For this reason, the search for ways to deactivate it is very important. In this work, hydrolysis and adsorption reactions of a VX-like compound (O,S-dimethyl methylphosphonothioate, DMPT) on the MgO(001) surface were studied by density-functional theory (DFT) using periodic boundary conditions. A degradation reaction mechanism was proposed and theoretically investigated on two types of MgO(001) surfaces: the terrace and the Al-doped. Conformations, free-energy differences, transition states, reaction barriers, and minimum-energy paths were computed. We found that the P–S bond, related to the agent toxicity, breaks via hydrolysis occurring spontaneously throughout the analyzed temperature range, 100–600 K. In the dissociative chemisorption of the DMPT molecule, the formation of the MgO:[PO(CH3)(OCH3)]+[SCH3]− intermediate is catalytically favored from a temperature of about 335 K for ...

Degradation of GD and VX over Oxides Mixing with Bleaching Powder

Nanosize oxides with acidic or basic sites could neutralize the droplets of chemical warfare agents. Refined bleaching powder was added to increase the reactivity of the nanosize oxides for degradation of GD(3,3-dimethyl-2-butyl methylphophonofluoridate or Soman) and VX(O-ehtyl S-2-(diisopropylamino)ethyl methyl-phosphonothioate). It was found that all the studied decontaminant powders exhibited room-temperature reactivity for GD and VX droplets which depends on their surface acid–base property. Decontaminant powders with basicity like nanosize MgO have the best activity towards GD and the degradation rate was improved obviously for N-MgO due to the adding of refined bleaching powder. However, surface acidity was very important for neutralizing VX over the decontaminant powders.

Role of the P–F Bond in Fluoride-Promoted Aqueous VX Hydrolysis: An Experimental and Theoretical Study

Following our ongoing studies on the reactivity of the fluoride ion toward organophosphorus compounds, we established that the extremely toxic and environmentally persistent chemical warfare agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) is exclusively and rapidly degraded to the nontoxic product EMPA (ethyl methylphosphonic acid) even in dilute aqueous solutions of fluoride. The unique role of the P-F bond formation in the reaction mechanism was explored using both experimental and computational mechanistic studies. In most cases, the "G-analogue" (O-ethyl methylphosphonofluoridate, Et-G) was observed as an intermediate. Noteworthy and of practical importance is the fact that the toxic side product desethyl-VX, which is formed in substantial quantities during the slow degradation of VX in unbuffered water, is completely avoided in the presence of fluoride. A computational study on a VX-model, O,S-diethyl methylphosphonothioate (1), clarifies the distinctive tendency of aqueous fluoride ions to react with such organophosphorus compounds. The facility of the degradation process even in dilute fluoride solutions is due to the increased reactivity of fluoride, which is caused by the significant low activation barrier for the P-F bond formation. In addition, the unique nucleophilicity of fluoride versus hydroxide toward VX, in contrast to their relative basicity, is discussed. Although the reaction outcomes were similar, much slower reaction rates were observed experimentally for the VX-model (1) in comparison to VX.

Catalytic Degradation of the Nerve Agent VX by Water-Swelled Polystyrene-Supported Ammonium Fluorides

The catalytic degradation of the nerve agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) by water-swelled polymer-supported ammonium fluorides is described. VX (0.06-0.53 mol/mol F(-)) is rapidly degraded (t(1/2) ∼ 10-30 min) to form the "G-analogue" (O-ethyl methylphosphonofluoridate), which hydrolyzes (t(1/2) ∼ 1-1.5 h) to the nontoxic EMPA (ethyl methylphosphonic acid). The toxic desethyl-VX is not formed. The catalytic effect of fluoride is maintained even when 6 equiv of VX are loaded. GB (O-isopropyl methylphosphonofluoridate) and desethyl-VX agents are also degraded under these conditions.

The reactivity of quaternary ammonium- versus potassium- fluorides supported on metal oxides: paving the way to an instantaneous detoxification of chemical warfare agents

The reactions of the chemical warfare agents (CWAs) 2,2'-dichloroethyl sulfide (HD), O-ethyl S-2-(diisopropylamino)-ethyl methylphosphonothioate (VX) and isopropyl methylphosphonofluoridate (GB) with various metal oxide-supported quaternary ammonium fluorides (QAF) and/or potassium fluoride (KF) reagents are described. These active sorbents, which were prepared by a modified procedure, include alumina, silica and titania, enriched with "available" (not bound to the surface) fluoride ions. Alumina-based fluoride reagents were found to be more active than their silica or titania counterparts. QAF/Al(2)O(3) reagents, compared to KF/Al(2)O(3), exhibit an exceptional reactivity toward HD, as demonstrated both in reaction rates and product identity. For example, with TBAF, t(1/2) is 15 min for the formation of the elimination product divinyl sulfide (DVS), while with KF, t(1/2) is 10 h for the formation of the hydrolysis product thiodiglycol (TDG). On the other hand, both sorbents reacted similarly against the nerve agents GB or VX. In order to increase the "available" fluoride content on the solid surface, the mixed active sorbent TBAF/KF/Al(2)O(3) (20/20/60) was developed. On this powder, all three CWAs were degraded instantaneously at the low loading of 1 wt% (t(1/2) < 2 min) and rapidly at the higher loadings of 5-10 wt% (t(1/2) of minutes scale). We assume that the relatively large amount of inorganic fluoride (KF) acts synergistically as a reservoir for the more reactive organic fluorides (TBAF). Moreover, the alumina surface hydroxyl groups may also operate as a water reservoir for the hydrolysis of VX or GB. Therefore, TBAF/KF/Al(2)O(3) might be considered as a promising destructive sorbent for CWAs.

Gas-chromatographic determination of O-isobutyl-S-2-(N,N-diethylamino)ethyl methylphosphonothioate (VX-like compound) and O-isopropyl methylphosphonofluoridate (Sarin) traces in slag

Procedures for the determination of 04sobutyl- S-2-(N,N-diethylamino)ethyl methylphosphonothioate (VX-like compound) and sarin traces in slag at levels of 5 × 10-5 and 1 × 10-2 mg/kg, respectively, were developed. The procedures are based on the extraction of organophosphorus chemical warfare agents from slag, the preconcentration of the extract, and the conversion of the analytes into dialkyl methylphos-phonates with the use of optically active alcohols. In this case, a solution of AgNO3 in 4-methyl-2-pentanol or a sodium alcoholate solution was used for the derivatization of VX or sarin, respectively. The resulting dias-tereomers were determined by gas chromatography with the use of a flame-photometric detector. The analysis time was no longer than 1.2 or 1 h for the VX-like compound or sarin, respectively.

Facile Hydrolysis-Based Chemical Destruction of the Warfare Agents VX, GB, and HD by Alumina-Supported Fluoride Reagents

A facile solvent-free hydrolysis (chemical destruction) of the warfare agents VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate), GB (O-isopropyl methylphosphonofluoridate or sarin), and HD (2,2'-dichloroethyl sulfide or sulfur mustard) upon reaction with various solid-supported fluoride reagents is described. These solid reagents include different alumina-based powders such as KF/Al(2)O(3), AgF/KF/Al(2)O(3), and KF/Al(2)O(3) enriched by so-called coordinatively unsaturated fluoride ions (termed by us as ECUF-KF/Al(2)O(3)). When adsorbed on these sorbents, the nerve agent VX quickly hydrolyzed (t(1/2) range between 0.1-6.3 h) to the corresponding nontoxic phosphonic acid EMPA as a major product (>90%) and to the relatively toxic desethyl-VX (<10%). The latter byproduct was further hydrolyzed to the nontoxic MPA product (t(1/2) range between 2.2-161 h). The reaction rates and the product distribution were found to be strongly dependent on the nature of the fluoride ions in the KF/Al(2)O(3) matrix and on its water content. All variations of the alumina-supported fluoride reagents studied caused an immediate hydrolysis of the highly toxic GB (t(1/2) < 10 min) to form the corresponding nontoxic phosphonic acid IMPA. A preliminary study of the detoxification of HD on these catalyst supports showed the formation of the nontoxic 1,4-thioxane as a major product together with minor amounts of TDG and vinylic compounds within a few days. The mechanisms and the efficiency of these processes were successfully studied by solid-state (31)P, (13)C, and (19)F MAS NMR.

Reactions of VX, GD, and HD with Nanotubular Titania

Reactions of VX [O-ethyl-S-(2-diisopropylethylamino)ethyl methylphosphonothioate], GD (pinacolyl methylphosphonofluoridate), and HD [bis(2-chloroethyl) sulfide] have been examined with nanotubular titania (NTT) using 31P and 13C MAS NMR. All three agents hydrolyze on NTT with the reaction of VX being notably fast (t1/2 < 30 min), approaching the rate achievable with liquid decontaminants. 31P MAS NMR reveals that VX is adsorbed within the NTT tubules and/or its titania layers, perhaps providing optimum conditions for its hydrolysis by water sandwiched between the layers. Consistent with the availability of copious water on NTT, HD is hydrolyzed to its CH-TG sulfonium ion. GD hydrolysis is similarly efficient, with its products—PMPA and HF—attacking the titania structure to form a titanophosphonate species.

Surface-Enhanced Raman Spectra of VX and its Hydrolysis Products

Detection of chemical agents as poisons in water supplies not only requires microg/L sensitivity, but also requires the ability to distinguish their hydrolysis products. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect chemical agents at these concentrations. Here we expand these studies and present the SERS spectra of the nerve agent VX (ethyl S-2-diisopropylamino ethyl methylphosphonothioate) and its hydrolysis products, ethyl S-2-diisopropylamino methylphosphonothioate, 2(diisopropylamino) ethanethiol, ethyl methylphosphonic acid, and methylphosphonic acid. Vibrational mode assignments for the observed SERS peaks are also provided. Overall, each of these chemicals produces a series of peaks between 450 and 900 cm(-1) that are sufficiently unique to allow identification. SERS measurements were performed in silver-doped sol-gel-filled capillaries that are being developed as part of an extractive point sensor.

Gas Chromatographic Determination of Traces of O-Isobutyl S-2-(N,N-Diethylamino)ethyl Methyl Phosphonothioate (VX-Like Compound) in Working Area and Community Air

A gas-chromatographic procedure is proposed for the determination of O-isobutyl S-2-(N,N-diethylamino)ethyl methyl phosphonothioate (mixed ester) at the maximum permissible level for the working area air (5 × 10–6 mg/m3) and at the safe reference level of impact for the community air (5 × 10–8 mg/m3). The procedure is based on trapping the mixed ester from air by a chemisorbent. Next, the analyte is extracted by hexane; transformed to O-methyl-O-isobutyl methyl phosphonate by silver nitrate in methanol; and, in the case of the working area air, the methanol solution of the derivative is chromatographed. In the determination of the mixed ester in the community air, a solution of O-methyl-O-isobutyl methyl phosphonate (dialkyl methyl phosphonate) in methanol is passed through a column with an adsorbent and transferred to the chromatographic system with a thermal desorption system. The relative error of the determination of the mixed ester in the working area and community air is no more than 28 and 40 rel. %, respectively.

Gas-Chromatographic Determination of Trace Isobutyl S-2-(N,N-Diethylamino)ethyl Methylphosphonothioate (VX-like Compound) in Soil and Construction Materials

Procedures were developed for the determination of trace isobutyl S-2-(N,N-diethylamino)ethyl methylphosphonothioate (IBDAEMP) in soil and construction materials by gas chromatography at a level of 1 × 10–9%. The procedures are based on the extraction of IBDAEMP from test materials using an aqueous solution of monoethanolamine or chloroform saturated with ammonia, the back extraction of IBDAEMP into hexane, the evaporation of the hexane solution (with an addition of HCl) to dryness, the treatment of the residue with a solution of silver nitrate in methanol for obtaining O-isobutyl O-methyl methylphosphonate, and gas-chromatographic separation on an open tubular column with the HP–5MS chemically modified stationary phase with flame-photometric detection.

Analysis of Chemical Neutralization Products of Phosphonothiolates by Gas Chromatography Mass Spectrometry

A series of phosphonothiolates, including the highly toxic O-Ethyl-S-(2-diisopropylamino) ethyl methylphosphonothioate (VX), have been subjected to chemical neutralization reaction with metallic sodium. The phosphonothiolates decompose to their respective phosphonic and phosphonothioic acids and this results in the detoxification of VX. GC/MS technique in both EI and CI mode has been applied for reaction monitoring and final identification of the neutralization products formed in this reaction.

Correlation spectroscopy with diffractive grating synthetic spectra and orthogonal subspace projection filters

We evaluate the feasibility of implementing correlation spec- troscopy for remote sensing with a passive IR sensor that incorporates a diffractive grating on which a synthetic spectrum is imbedded. The spec- tral diffraction reflectances of diffractive gratings are measured and com- pared to the theoretical design spectra and to the library absorbance spectra. Five gratings are evaluated: sulfur hexafluoride (SF6), ((dimethoxyphosphinothioyl)thio)butanedioic acid, diethyl ester (malathion), diisopropyl-methylphosphonate (DIMP), methylphosphono- fluoridic acid,(1-methylethyl) ester (Sarin or GB), and O-ethyl-S-(2- diisopropylamino)ethyl methylphosphonothioate (VX). While the gratings were designed from liquid phase infrared spectra, the measurements and models provide a satisfactory proof of principle for the exploitation of synthetic spectra in correlation spectroscopy. The predicted noise equivalent concentration pathlength (NECL) for detecting GB and VX in a desert environment is computed for distances up to 5 km. The device was found to have high sensitivity in terms of NECL. The selectivity of the grating is found to be poor, but can be improved dramatically with the use of orthogonal subspace projection (OSP) filters that reduce the false alarm (improve selectivity) from misidentifying a GB as VX (and vice versa) at the ''cost'' of a slight increase of the NECL (reduce sensitivity). © 2003 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1531638) Subject terms: correlation spectroscopy; infrared spectroscopy; orthogonal sub- space projection (OSP); vapor detection; false alarm; diffractive optics; synthetic spectra.

Gas-Chromatographic Determination of Sarin, Soman, and O-Isobutyl S-2-(N,N-Diethylamino)ethyl Methylphosphonothioate (a VX-Like Compound) Traces in Water

A gas-chromatographic procedure for the determination of O-isobutyl S-2-(N,N-diethylamino)ethyl methylphosphonothioate (VX), sarin, and soman in water at levels of 2 × 10–6, 5 × 10–5, and 2 × 10–6 mg/L, respectively, was proposed. The procedure includes liquid–liquid extraction with the use of salting-out agents, back extraction, and evaporation. In this case, the VX compound was converted into O-isobutyl O-methyl methylphosphonate (a substance convenient for chromatographic determination) by the reaction with hydrochloric acid, methanol, thriethylamine, and silver nitrate.

Reactions of VX, HD, and Their Simulants with NaY and AgY Zeolites. Desulfurization of VX on AgY

The room-temperature reactions of the chemical warfare agents VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate), HD (2,2‘-dichloroethyl sulfide, or mustard), and their common simulants, O,S-diethyl phenylphosphonothioate (DEPPT) and 2-chloroethyl phenyl sulfide (CEPS), with NaY and silver-exchanged (AgY) zeolites have been studied using solid-state magic angle spinning NMR. VX hydrolyzes via exclusive cleavage of the P−S bond on both NaY and AgY to yield ethyl methylphosphonate (EMPA). The reaction is significantly faster on AgY than on NaY, suggesting catalysis by silver. On AgY, an intermediate silver salt of EMPA is apparently formed which is slowly converted to ethyl 2-(diisopropylamino)ethyl methylphosphonate (QB, the desulfurized analogue of VX) in about a 78% yield. DEPPT similarly hydrolyzes via P−S cleavage on AgY to yield an apparent silver salt of ethyl phenylphosphonate, which does not undergo further reaction to the desulfurized analogue. No reaction is observed for DEPPT on NaY. HD on AgY forms both vinyl sulfide and the cyclic ether 1,4-thioxane. HD reacts faster on NaY to exclusively form the CH-TG sulfonium ion (HOCH2CH2SCH2CH2S+[CH2CH2OH]2). CEPS also reacts faster on NaY, forming 2-hydroxyethyl phenyl sulfide. On AgY, CEPS does not give the vinyl product, but does yield the ether product PhSCH2CH2OCH2CH2SPh. A mechanism is proposed for the silver-catalyzed hydrolysis of VX, the desulfurization of the cleaved thiol, and the formation of QB.