Reactions of Chemical Warfare Agent Simulants in the Common Ion

Ind. Eng. Chem. Res. 2009, 48, 6203–6211

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Reactions of Chemical Warfare Agent Simulants in the Common Ion Binary Ionic Liquid 1,2-Dimethyl-3-propylimidazolium/Copper(II) Bis(trifluoromethylsulfonyl)amide John S. Wilkes, Patrick J. Castle,* Joseph A. Levisky, Adrian Hermosillo, Paul J. Coˆte´, Cynthia A. Corley, Emily A. Montgomery, Donald M. Bird, Ralph R. Hutchinson, and Matthew F. Ditson Department of Chemistry, United States Air Force Academy, 2355 Fairchild DriVe, Suite 2N225, USAF Academy, Colorado 80840

Ionic liquids have the potential for being ideal alternatives for organic solvents in chemical warfare agent reactions and demilitarization processes. They are considered to be an excellent substitute, because of their extraordinarily wide liquid range, low melting points, chemical and thermal stability, high conductivity, and nonvolatility. In addition, many have excellent hydrophobic properties and immiscibility with water and offer the opportunity to isolate the chemical agents and reaction products from the environment. In this report, we describe a two-step process in which chemical warfare simulants are reacted with hydrogen peroxide (H2O2) followed by basic methanol in a common ion binary ionic liquid that consists of 1,2-dimethyl-3propylimidazolium bis(trifluoromethylsulfonyl)amide and copper(II) bis(trifluoromethylsulfonyl)amide. The chemical agent simulants used in this study are diisopropylfluorophosphate, bis(2-ethylhexyl) phosphite, and 2-chloroethylphenyl sulfide, which simulate agents GB, VX, and HD, respectively. Initially, H2O2 is added to the mixture of simulants and ionic liquid to remove 2-chloroethylphenyl sulfide, followed by the addition of methanolic tetramethylammonium hydroxide hydrate (TMAOH · 5H2O) (basic methanol) to eliminate diisopropylfluorophosphate and bis(2-ethylhexyl) phosphite. The reactions were monitored by liquid chromatography/mass spectroscopy time-of-flight (LC/MS-TOF), coupled with ultraviolet (UV) diode array detection. Gas chromatography/mass spectroscopy (GC/MS) was used to aid in product identification. Introduction Currently, a global effort exists to develop chemical reaction systems to destroy a variety of chemical warfare agents (CWAs). Today, especially with the change of leadership in the United States, the threats of a chemical attack remain serious and credible.1 To destroy toxic and lethal chemical agents that most likely would be used in a chemical attack, one needs a reaction system capable of converting chemical agents to nontoxic reaction products that are contained in an environmentally safe medium.2 It is widely accepted that focus should be placed on developing reaction systems to destroy the nerve agents Sarin (GB) and VX and the blister agent sulfur mustard (HD). In developing reaction systems, chemical warfare agent simulants, instead of the actual chemical warfare agents, are used. Simulants are chemical compounds that are similar in chemical composition and physical properties to the chemical agent but are considerably less toxic than the agent itself. In this study, diisopropylfluorophosphate (DFP) (which simulates the nerve agent Sarin), bis(2-ethylhexyl)phosphite (BEHP) (which simulates the nerve agent VX), and 2-chloroethyl phenyl sulfide (CEPS) (which simulates the blister agent sulfur mustard HD) were used. The chemical structures of these compounds are shown in Figure 1. Previously, we reported that a single reaction system that consisted of basic alcohol (i.e., methanol in tetramethyl ammonium hydroxide (TMAOH) in an ionic liquid, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl) amide (DMPITf2N)) was effective in altering the chemical composition of all three simulants.3 In the basic alcohol-DMPITf2N system, * To whom correspondence should be addressed. Fax: 719-333-2947. E-mail address: [email protected].

DFP and BEHP underwent rapid alcoholysis and CEPS was converted to phenylvinyl sulfide via dehydrohalogenation. Ionic liquids were selected as solvents for these reactions, because they offer a reaction matrix that is immiscible with water and possess excellent containment potential. The objectives of studying these reactions in ionic liquids are (1) to identify those chemical compounds that react with simulants in an ionic liquid, (2) to determine the composition of the reaction products, and (3) to conduct these reactions in a medium that remains isolated from the aqueous environment.

Figure 1. Chemical warfare agents and simulants. (From ref 3.)

10.1021/ie801650n CCC: $40.75  2009 American Chemical Society Published on Web 05/26/2009

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Ind. Eng. Chem. Res., Vol. 48, No. 13, 2009

Scheme 1. Two-Step Process of Destroying Chemical Warfare Agent Simulants in an Ionic Liquid

Here, we describe, in the second half of this two-part study, a two-step reaction process to chemically convert all three simulants. Because basic methanol was observed to convert CEPS to phenylvinyl sulfide,3 an alternative process that involves the oxidation of CEPS to 2-chloroethylphenyl sulfoxide was considered to be more desirable. In contrast to our earlier report (i.e., a one-step reaction system), here, we report a two-step oxidation/reduction process that incorporates copper(II) with hydrogen peroxide (H2O2) in a common ion binary ionic liquid, followed by the addition of basic methanol. This two-step process chemically converts all three simulants (see Scheme 1). Note that the second step of this process is the same as the first step in the one-step reaction of DFP and BEHP.3 DFP and BEHP were rapidly and chemically converted. The complexity and number of CEPS pathways that lead to the observed reaction products is unknown and would be too difficult, if not impossible, to describe schematically. The focus of the second of this two-part study is the decomposition/oxidation of mustard agent simulants. The first part of the study was to develop a single agent that would chemically convert all three chemical warfare agent simulants. Basic methanol in an ionic liquid satisfied that requirement, but it chemically converted the HD simulant through dehydrohalogenation to produce phenylvinyl sulfide. We preferred to develop a system that converted the HD simulant via oxidation to 2-chloroethylphenylsulfoxide. Copper(II), as a component of a common ion binary ionic liquid in combination with H2O2, was investigated, and it satisfied that requirement. Unfortunately, the combination of the common ion binary ionic liquid and H2O2 did not remove the other VX and GB. We found that basic methanol, which was the same reagent that was used in the first part of the study, when subsequently added to the reaction mixture, was very effective in removing the other two simulants. The chemistry in Scheme 1 is described as a two-step process; however, it is important to realize that the

Ionic Liquids. Reaction mixture containing three simulants: To 1.00 mmol (419 mg) of DMPITf2N was added 20 mg [Cu(Tf2N)2]. The mixture was heated at 70 °C until all of the Cu(Tf2N)2 dissolved (a light blue homogeneous common ion binary ionic liquid). DFP (0.100 mmol,18.4 mg), BEHP (0.100 mmol, 30.6 mg), and CEPS (0.100 mmol, 17.2 mg) were added to the mixture. The mixture was vortexed for 1 min and allowed to equilibrate for 24 h. To this mixture, a solution of 81 µL (0.6 mmol) of H2O2 was added. Mild effervescence was observed. When the effervescence subsided, the mixture was vortexed for approximately 15 s and a 0.050 mL aliquot was removed and placed in 1.0 mL methanol. The diluted mixture was vortexed and 50 µL aliquot of this dilution was further diluted in 1 mL of methanol. The solution was analyzed by LC/MS-TOF. Following complete reaction of CEPS, 0.4 mmol (72.4 mg) of TMAOH in 0.6 mL methanol was added. A 0.050 mL aliquot was removed and diluted with 1.0 mL of methanol. A 50 µL aliquot of this mixture was further diluted with 1 mL of methanol and analyzed by LC/MS-TOF. Aliquots were removed at timed intervals from the remaining reaction mixture. A. 1,2-Dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPITf2N). 1,2-Dimethyl-3-propylimida-

Figure 2. Total ion chromatogram and the time-of-flight (TOF) mass spectrum of unreacted DFP in the reaction matrix after 24 h.

Figure 3. Reaction of DFP with methanolic tetramethylammonium hydroxide (TMAOH) (step 2 of the reaction sequence).3

reactions are a “one-pot” process. That is, the reactants for the second step are added to the mixture of reagents, reactants, and products from the second step, without any separations. In this report, we describe the two-step process to effectively and chemically convert multiple chemical warfare agent simulants, and we repeat the basic methanol reactions to chemically convert the VX and GB simulants in ionic liquids. Particular attention is given to the analysis of the reaction products. A detailed description of the time-of-flight (TOF) mass spectral data of many of the products is presented. Materials and Methods


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Figure 4. Step 1: Total ion chromatogram and LC/MS-TOF mass spectrum of BEHP after the addition of H2O2.3

Figure 6. Total ion chromatogram, total wavelength chromatogram, and the UV spectrum of CEPS.3

Figure 5. Step 2: Bis(2-ethylhexyl) phosphate resulting from the hydrolysis of BEHP.

zolium bis(trifluoromethylsulfonyl)amide (DMPITf2N). 1,2Dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPITf2N) was prepared according to the procedure described by Sutto et al.4 and previously described in other literature. B. DMPITf2N/Cu(Tf2N)2 Common Ion Binary Ionic Liquid. Cu(Tf2N)2 (0.06 mmol (40 mg)) was added to 1.00 mmol (419 mg) of DMPITf2N. The mixture was heated at 70 °C until all of the Cu(Tf2N)2 dissolved, resulting in a light blue homogeneous liquid. C. Copper(II) Bis(trifluoromethylsulfonyl)amide (Cu(Tf2N)2). Copper(II) bis(trifluoromethylsulfonyl)amide (Cu(Tf2N)2) was prepared according to the procedure of Earle et al.5 Briefly, 200 mg of CuCO3 (54%-56% Cu, from Acros Organics, CAS No. 12069-69-1) were mixed with 840 mg of bis-trifluormethanesulfonimide (Rhodia, CAS No. 82113-653) in 5 mL of 18 mΩ H2O. The solution was stirred for 1 h, until the release of CO2 ceased (the solution turned to a blue/ green color). The mixture was vacuum-filtered through No. 4

Figure 7. CEPS in DMPITf2N/Cu(Tf2N)2 after 24 h.

filter paper, to remove unreacted CuCO3. The filtered solution was transferred to a round-bottom flask and attached to a Welch Model 2027 rotary evaporator at 75 °C that was set to maximum vacuum, to remove excess H2O. After ∼3 h, a blue powder

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Figure 8. Isotopic distribution pattern of the cluster of ions around the m/z ) 309 ion.

Figure 10. Total ion chromatogram and mass spectrum of the mass 307 peak.

Figure 9. Total ion chromatogram and mass spectra of CEPS reaction products in DMPITf2N/Cu(Tf2N)2 after 72 h.

was recovered. The flask and blue powder was placed in an oil bath at 100 °C under vacuum overnight. The blue powder was transferred to a sublimation apparatus that was heated under vacuum at 180 °C and then cooled with dry ice/acetone. After sublimation, a light blue powder was recovered. Atomic absorption spectrophotometry (AAS) was used to determine the purity. The copper content was 95% of the calculated value. D. Tetramethylammonium Hydroxides (CH3)4N+OH-). Tetramethylammonium hydroxide pentahydrate, (Sigma, T7505), was used as purchased. E. Chemical Warfare Agent Simulants and Reaction Products. Diisopropylfluorophosphate (Sigma, Product No. D0879), bis(2-ethylhexyl) phosphate (Aldrich, Product No. 248959), 2-chloroethylphenyl sulfide (Aldrich, Product No. 417602), and chloroethylphenyl sulfone (Aldrich, Product No. 417645) were used as purchased. F. Reaction Mixture Containing a Single Simulant. A 10:1 molar ratio of DMPITf2N/Cu(Tf2N)2:simulant was used throughout this study. In separate experiments, 18.4 mg of diisopropyl fluorophosphate (0.100 mmol) (or 30.6 mg bis(2-ethylhexyl)phosphite (0.100 mmol), or 18.1 mg (0.100 mmol) 2-chloroethylphenyl sulfide) was added to the ionic liquid, which

Figure 11. Reaction mixture of CEPS in DMPITf2N/Cu(Tf2N)2 1 h after the addition of H2O2.

consisted of a homogeneous mixture of 419 mg of DMPITf2N (1.00 mmol) and 40 mg of Cu(Tf2N)2. Each mixture was vortexed for 1 min and allowed to equilibrate for 1 h. To each of the mixtures, 27 µL (0.2 mmol) of 50% H2O2 in water was added. Initially, a heterogeneous mixture and mild effervescence with the H2O2 occurred. The mixture was vortexed for ∼15 s and allowed to sit until the effervescence subsided, and a 0.050 mL aliquot was removed and placed in 1.0 mL methanol. The diluted mixture was vortexed and a 50-µL aliquot of this mixture was further diluted in 1 mL of methanol. This solution was analyzed by liquid chromatography/mass spectroscopy timeof-flight (LC/MS-TOF) analysis. The remaining reaction mixtures were sampled later at known timed intervals, and each of the reactions was monitored. Only CEPS was determined to


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LC/MS-TOF Analysis. The mass spectral analyses were performed with an Agilent 1100 series liquid chromatograph that was interfaced to a TOF mass spectrometer (6210 series) by an electrospray ionization source. A polar and aromatic reversed-phase selectivity ether-linked phenyl with a polar endcapping (Synergi Polar-RP) liquid chromatography column was used. A mobile phase that consisted of methanol and 5 mM ammonium formate, using gradient elution from 30% methanol to 90% methanol with a run time of 12 min and a flow rate of 0.3 mL/min, provided good retention and resolution. The electrospray drying gas temperature and pressure were 350 °C and 9.5 L/min, respectively. A capillary voltage of 3000 V and fragmentor voltages of 125-175 V were used. Autotune values for the pusher, puller, puller offset, and other parameters were accepted as default values. Electrospray ionization (ESI) in both positive and negative modes was used. Results and Discussion

Figure 12. Reaction mixture of CEPS in DMPITf2N/Cu(Tf2N)2 24 h after the addition of H2O2.

Figure 13. Total ion chromatogram and extracted ion profiles for 2-chlorothylphenyl sulfoxide and 2-chloroethylphenyl sulfone.

react. Following the complete reaction of CEPS, as evidenced by the absence of its characteristic UV absorption spectrum, 0.3 mL of methanol (7.4 mmol) containing 36.2 mg of TMAOH · 5H2O (0.200 mmol TMAOH and 1.0 mmol H2O) was added. The mixtures were vortexed for ∼15 s and 0.050 mL aliquots were removed and placed in 1.0 mL of methanol. The diluted mixtures were vortexed and 50-µL aliquots of this mixture were further diluted in 1 mL of methanol. Each solution was analyzed via LC/MS-TOF.

A liquid chromatography/mass spectrometry time-of-flight (LC/MS-TOF) apparatus that was equipped with an electrospray ionization (ESI) chamber was used in the analysis. Methanol and ammonium formate (5 mM) comprised the mobile phase. Gradient elution from 30% to 90% methanol effectively separated the components of the reaction mixture, including the ionic liquid. This method was selected over other analytical methods, because the pretreatment of the reaction mixture involved simple dilutions, rather than more-complex extraction schemes, to remove the ionic liquid prior to analysis. Because of their hydrophobic nature, many ionic liquids present obstacles to GC systems but not so with LC systems. In separate experiments, each of the simulants was subjected to the two-step reaction sequence. Diisopropylfluorophosphate (DFP). A. Step 1: DFP Reaction with H2O2 in DMPITf2N/Cu(Tf2N)2. No reaction occurred after 24 h. The LC/MS-TOF total ion chromatogram and the mass spectrum of an aliquot of the reaction mixture after exposure to H2O2 for 24 h is displayed in Figure 2. Only unreacted diisopropylfluorophosphate (DFP) is detected. Because a large portion of this manuscript involves LC/MSTOF electrospray ionization, it is important to place a significant amount of attention on the interpretation of the mass spectral analytical data. DFP is identified by its ESI-TOF exact mass and the exact masses of its fragment ions. The observed H+ and ammonium (NH4)+ ion adducts at m/z ) 185.0741 and 202.1007, respectively (compared to their calculated masses of 185.0742 and 202.1008, respectively) represent the molecular species. [Note! In this report, the molecular species is defined as the hydrogen or ammonium adduct, i.e., M + 1 or M + 18.] The base peak and fragment ion with m/z ) 100.9800 (H3PO3F)+, compared to its calculated mass of 100.9803, is due to the (H3PO3F)+ species. In addition, the m/z ) 143.0270 fragment ion represents (C3H9PO3F)+ (with a calculated value of 143.0273), which arises from loss of the C3H6 neutral molecule from the (M + 1) molecular species. The total ion chromatogram and the TOF mass spectrum of DFP in the ionic liquid are presented in Figure 2. The large peak at ∼1.2 min is due to the 1,2-dimethyl-3propylimmidazolium cation of the ionic liquid. B. Step 2: The Addition of Methanolic Tetramethylammonium Hydroxide (TMAOH · 5H2O) to the Reaction Mixture Containing DFP and H2O2 in DMPITf2N/Cu(Tf2N)2. After allowing the reaction mixture that contained DFP and H2O2 in DMPITf2N/Cu(Tf2N)2 to sit for 24 h and not observing a reaction (Figure 2), a methanolic solution of TMAOH (0.2 mmol

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TMAOH in 0.3 mL methanol) was added. An aliquot was removed 5 min after the addition and analyzed. The DFP was completely gone and only diisopropylmethyl phosphate, resulting from the -OCH3 displacement of fluoride, was present (see Figure 3). The group of peaks appearing at 0.5-1.5 min in the total ion chromatogram includes the tetramethylammonium cation and the organic cation of the ionic liquid. Routinely, a fragment at ∼10% intensity appears at mass 331.1378. This mass usually appears at the beginning of the oxidation reaction and disappears at the end of the reaction. Attempts to identify this ion have not been successful. Bis(2-ethylhexyl)phosphite. A. Step 1. Bis(2-ethylhexyl)phosphite reaction with H2O2 in DMPITf2N/Cu(Tf2N)2. The LC/ MS-TOF total ion chromatogram obtained from an aliquot of the reaction mixture after exposure to hydrogen peroxide for 24 h is displayed in Figure 4. The mass spectrum indicates that only unreacted BEHP is present. The MS-TOF identification of BEHP in the reaction mixture was based on the observation of a peak in the total ion chromatogram that exhibited a mass spectrum with a base peak of 613.4833 Da (an observed exact mass). The protonated dimer of BEHP has a calculated exact mass of 613.4726. The dimer arises during the electrospray ionization (ESI) process. The sodium adduct of the dimer is also detected (observed mass of 635.4526 compared to the calculated mass of 635.4545). Other positive ions detected in the mass spectrum include [BEHP + H+] with a mass of 307.2407 (calculated mass ) 307.2402), the ammonium ion adduct [BEHP + NH4+], with an observed mass of 324.26657 versus a calculated mass of 324.2668 (see Figure 4). Although BEHP produces a fragment ion at a mass of 82.9898 (H3PO3)+, it is not shown in the mass spectrum because the range of ions monitored for this run was between m/z ) 100 and m/z ) 1000. B. Step 2: The Addition of Methanolic TMAOH · 5H2O to the Reaction Mixture Containing BEHP and H2O2 in DMPITf2N/Cu(Tf2N)2. After allowing the reaction mixture to sit for 24 h after the addition of H2O2 and not observing a reaction, a methanolic solution of TMAOH (0.2 mmol TMAOH in 0.3 mL methanol) was added. An aliquot was removed 5 min after the addition and analyzed. The reaction of BEHP was complete, and only bis(2-ethylhexyl) phosphate, (C16H36PO4)+, which was a result of the hydrolysis, was present (see Figure 5). We noted that, upon standing in contact with methanol, a methanolysis product of BEHP forms, which we discuss later in the context of Figure 15. Reaction of CEPS with DMPITf2N/Cu(Tf2N)2. The neutralization of the HD simulants, 2-chloroethylethyl sulfide (CEES) and 2-chloroethylphenyl sulfide (CEPS), have been studied in numerous systems under a variety of conditions.6-10 Degradation of the CEPS on concrete surfaces under mildly aqueous alkaline conditions has been reported.11 The oxidation of HD with O3, UV, and H2O2 or some combination of the three was reported by Popiel et al.12 In addition, metal-catalyzed oxidation of HD and HD simulants with H2O2 has been investigated.13 The reaction between CEPS and methanolic TMAOH in the ionic liquid DMPITf2N via dehydrohalogenation has also been reported and occurs easily.3 Earlier studies in our laboratory indicated that copper(II), in the form of CuCl2, in combination with H2O2 in DMPITf2N does, in fact, react to neutralize mustard simulants. However, the reaction was heterogeneous, proceeded very rapidly (almost in an uncontrollable manner), and made this process of questionable value. To mediate the severity of the oxidation reaction and produce a more manageable reaction system and

take advantage of copper(II)/H2O2 oxidation, an alternative source of copper(II) was sought. Copper(II) in the form of copper(II) bis(trifluoromethylsulfonyl)amide was observed to produce a homogeneous common ion binary ionic liquid when combined with DMPITf2N. This common ion binary ionic liquid became both the reactant and the solvent for our studies. The ionic liquid was prepared by mixing 419 mg (1.0 mmol) of DMPITf2N and 20 mg of (0.03 mmol) Cu(Tf2N)2. Portions (27.2 µL) of H2O2 were added to the reaction mixture sequentially until all of the CEPS starting material was eliminated. Aliquots were taken at timed intervals and analyzed by the in-line diode array UV detector of the HPLC/MS-TOF system. Because CEPS does not ionize readily under ESI, it is not detected by LC/ ESI-MS analysis. However, it does contain a chromophore and can be detected by the diode array UV in the LC system. Figure 6 shows the total ion chromatogram, the total wavelength chromatogram, and the UV spectrum of CEPS (peak at 9.44 min in the total wavelength chromatogram). Note the absence of a peak at 9.44 min in the total ion chromatogram. The assignment of the UV spectrum of CEPS by UV diode array detector was confirmed by an alternative method using a Hewlett-Packard UV spectrophotometer. A sample of CEPS in methanol was prepared and analyzed over the range of 200-400 nm, which matched the UV spectrum obtained by the LC/MSTOF system (see Figure 6). An aliquot was removed and analyzed 24 h after the addition of CEPS to the common ion binary ionic liquid. The TIC indicated that the mixture contained two distinct reaction products: one at 8.08 min and the other at 10.03 min (see Figure 7), both occurring from ESI. The peak at 8.08 min, which exhibits a m/z ion value of 291.0879 is due to the (M+1) molecular species (C16H19S2O)+, and the peak at 10.03 min, which exhibits an m/z ion value of 309.0533, is caused by the (M+1) molecular species (C16H18S2Cl)+. The structure of the (C16H19S2O)+ ion that creates the 291.0879 mass (retention time ) 8.08 min) has not been unequivocally determined; however, there are several different isomeric compounds that can account for that mass:

It is apparent from the fragmentation pattern (m/z ions at 137.04256 and 109.01073) that the molecular ion contains a C6H5SCH2CH2 array. The fragment ion with m/z ) 137.04256 is due to (C6H5SCH2CH2)+, which has a calculated mass of 137.04249, and the m/z ) 109.01073 ion is due to (C6H5S)+, which has a calculated mass of 109.0112. Both of the ions arise


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that the m/z ) 309 peak at 10.03 min (structure 5) disappeared and a new species, m/z ) 307 (C16H16S2Cl)+ with an observed mass of 307.03886, appeared. This peak appears to be the H+ adduct of the dehydrogenated compound described below (structure 6). The calculated mass of structure 6 is 307.03819.

Figure 14. Total ion chromatogram and extracted ion profiles of m/z 222-223.

during the fragmentation of some species that contain that array. The structure proposed in structure 2 can be eliminated. Structure 1 can result from the hydrolysis of the complex C6H5SCH2CH2C6H5SCH2CH2+/[Cu(Tf2N)2Cl]-. Trace amounts of water are present in the system, most likely from the preparation of the Cu(Tf2N)2. If that species were, in fact, present, one would expect to see a peak with m/z ) 305, following a quenching with methanol. Such was the case. Also, if an aliquot was quenched with ethanol, one would expect to see a peak with m/z ) 319. That also was observed. There is precedence for structure 3; however, that compound (an ether) is reported to occur after the exposure of CEPS on concrete to water.11 Although the ether cannot be eliminated, the reaction system reported here lacks the necessary conditions to produce that compound. The m/z ) 309 peak at a retention time of 10.03 min, due to (C16H18S2Cl)+ (structure 5),

which is also shown in the TIC in Figure 7, most likely arises from a Lewis-acid-catalyzed electrophilic aromatic substitution reaction. The copper(II) species in the common ion binary ionic liquid functions as the Lewis acid and interacts with a CEPS molecule to produce the electrophile (C6H5SCH2CH2)+, which then attacks a second CEPS molecule to produce the product. Para substitution is displayed, but the exact isomer distribution pattern has not been determined. The chlorine isotopic distribution pattern near mass 309 (see Figure 8) indicates that the species contains a single Cl atom and provides further proof in assigning the structure to that m/z ion. After 72 h, following the addition of CEPS to DMPITf2N/ Cu(Tf2N)2, an analysis of an aliquot of the mixture indicated

The chlorine isotopic distribution pattern of the (M+1) molecular species giving rise to structure 6 (see Figure 9) with a characteristic isotopic peak at 309.03656 (i.e., the m/z ) 307 + 37Cl peak) indicates that one, and only one, Cl atom is present in each compound. Note that the (M+1) molecular species of structure 5 and the isotopic peak of structure 6, are distinguishable from each other by their exact masses: 309.05343 for structure 5 and 309.03656 for the 37Cl isotope of structure 6. CEPS, DMPITf2N/Cu(Tf2N)2 and H2O2. CEPS was added to DMPITf2N/Cu(Tf2N)2 and allowed to equilibrate for 24 h. When 50% H2O2 (0.2 mmol) was added to the mixture, a mildly effervescent reaction occurred. An aliquot was removed after 1 h. In addition to the m/z ) 291 ion (present in the reaction mixture before the addition of H2O2), several new products appeared and were identified by their mass spectra (see Figure 10). Relatively large amounts of (C8H10SOCl)+, (C16H19S2O2)+, and (C16H18S2OCl)+ at retention times of 2.9, 2.5, and 4.0 min, respectively, were present. The (C8H10SOCl)+ species was identified as 2-chloroethylphenyl sulfoxide (structure 7), with a calculated mass of 189.0141.

The compound eluting at 2.5 min could be either 8 or 9. Both compounds have a calculated mass of 307.0826. Note that the isotopic distribution pattern about mass 307 (see Figure 10) indicates that chlorine is absent in the structure!

The compound that appears at 4.0 min, with an observed mass of 325.0482, is assigned as 10. The calculated mass of 10 is 325.0488.

Simple hydrolysis of 10 could lead to 8, whereas ether formation could lead to 9. Only a small amount of CEPS remained (see Figure 11). An aliquot was removed 24 h later (following the addition of an additional 0.2 mmol of H2O2) and all of the CEPS reacted, as did the products of the initial interaction of CEPS and the DMPITf2N/Cu(Tf2N)2 (i.e., before the addition of any H2O2

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(see Figure 12)). Note that both 2-chloroethylphenyl sulfoxide (referred to as sulfoxide) and 2-chloroethylphenyl sulfone (referred to as sulfone) were identified in the reaction mixture. The extracted ion profiles for the sulfoxide (m/z ) 189-190; intensity ) 2.84 × 106 cps) and the sulfone (m/z ) 222.0-222.3; intensity ) 1.91 × 105 cps) are shown in Figure 13. Only 6% sulfone, relative to the amount of sulfoxide in the reaction mixture, seems to have been produced. Because the toxicity of the sulfone in the elimination of the actual chemical warfare agent is greater than that of the sulfoxide, any chemical process that leads to extensive sulfone production is regarded as unfavorable, whereas a process that ends in sulfoxide formation is considered somewhat more favorable. The sulfone is identified by ESIsMS-TOF in the reaction mixture as its ammonium adduct, and the sulfoxide is identified as its H+ adduct. The ammonium adduct of the sulfone has a calculated mass of 222.0356, compared to the observed mass of 222.0351. Also, the chlorine isotopic distribution patterns indicate that the species that cause the peaks that are identified as the sulfoxide and the sulfone have a single Cl atom. Two other peaks in the reaction mixture, which also have masses of m/z ) 222 (observed mass ) 222.9751), have been detected and are most likely due to the isomeric (C8H9SOCl2)+ species ions 11 and 12.

The chlorine isotopic distribution pattern of ∼9:6:1 for both peaks indicates that each species has two Cl atoms in the structure. An advantage of exact mass/mass spectrometry lies in its capability to differentiate chemical species of identical unit masses. For example, the m/z 307 species that appears in the CEPS/DMPITf2N/Cu(Tf2N)2 mixture after 72 h has an observed mass of 307.0386, because of (C16H16S2O2)+, and the m/z 307 species that appears 24 h after the addition of H2O2 has an observed mass of 307.08270, because of (C16H16S2Cl)+. The difference of 0.0441 mass units is sufficient to clearly delineate the differences between the two species. Also, the different species that have unit masses of m/z ) 222 (see Figure 14) can be readily identified by their exact masses. The species that causes the peak with an observed mass of 222.9752 is (C8H9SOCl2)+, whereas the species with an observed mass 222.0356 is (C8H9SO2ClNH4)+. The mass difference of 0.8396 between the different species allows for unequivocal identification. Mass spectrometers with unit mass resolution are not capable of making that distinction. Reaction of Three Simulant Mixtures (DFP, BEHP, and CEPS) in DMPITf2N/Cu(Tf2N)2 and H2O2. When all three simulants were added to the DMPITf2N ionic liquid and reacted with three times the amount of H2O2 (DMPI:DFP:BEHP: CEPS:H2O2 ratio ) 10:1:1:1:6), only CEPS (2-chloroethylphenylsulfide) reacted. BEHP and DFP remained intact throughout the exposure to H2O2. After the reaction to destroy CEPS was complete, a methanolic solution that contained 0.4 mmol TMAOH was added. DFP reacted quickly; however, significant amounts of BEHP remained. Following a second addition of the methanolic TMAOH solution (another 0.4 mmol), the remaining BEHP disappeared within several minutes.

Figure 15. Summary of the two-step process leading to major reaction products.

In summary, the overall two-step reaction scheme and products are described in Figure 15.

Conclusions Chemical warfare agent simulants such as diisopropylfluorophosphate (DFP), bis(2-ethylhexyl) phosphite (BEHP), and 2-chloroethylphenyl sulfide (CEPS) are readily neutralized in a two-step reaction process. These reactions were performed in a common ion binary ionic liquid solvent that was composed of 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide and copper(II) bis(trifluoromethylsulfonyl)amide. The first step involved reaction with hydrogen peroxide (H2O2) to remove CEPS, followed by the second step, which used a methanolic solution of tetramethylammonium hydroxide hydrate (TMAOH · 5H2O) to chemically convert BEHP and DFP. The reactions occur at a relatively rapid rate, resulting in oxidation, alcoholysis, and hydrolysis. These results suggest that a combination of H2O2 and alcoholic solutions of tetraalkylammonium hydroxide hydrates in an ionic liquid that contains soluble copper(II) ions may provide a multipurpose chemical warfare agent reaction matrix that is effective and relatively rapid.


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ReceiVed for reView October 30, 2008 ReVised manuscript receiVed April 9, 2009 Accepted May 1, 2009 IE801650N

Reactions of Chemical Warfare Agent Simulants in the Common Ion

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