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Studies on Residue-Free Decontaminants for Chemical Warfare Agents George W. Wagner Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 24 Feb 2015 Downloaded from http://pubs.acs.org on February 24, 2015
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Environmental Science & Technology
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Studies on Residue-Free Decontaminants for Chemical Warfare Agents
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George W. Wagner
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U.S. Army Edgewood Chemical Biological Center
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Attn: RDCB-DRP-F
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Aberdeen Proving Ground, MD 21010-5424
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Keywords: Decontamination; VX; GD; HD; Concrete; Hydrogen Peroxide; Ammonia; Carbon Dioxide; No Residue
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[email protected] 21
(410) 436-8468
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Notes
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The author (G.W.W.) declares a patent, “Generation of Residue-Free Decontaminant Using Hydrogen Peroxide, Ammonia, and Carbon Dioxide”, U.S. Patent 7,838,476, 2010, held by him but assigned to The United States as represented by the Secretary of the Army (Washington, DC).
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Abstract Residue-free decontaminants based on hydrogen peroxide, which decomposes to water
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and oxygen in the environment, are examined as decontaminants for chemical warfare agents
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(CWA). For the apparent special case of CWA on concrete, H2O2 alone, without any additives,
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effectively decontaminates S-2-(diisopropylamino)ethyl O-ethyl methylphosphonothioate (VX),
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pinacolyl methylphosphorofluoridate (GD), and bis(2-choroethyl) sulfide (HD) in a process
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thought to involve H2O2-activation by surface-bound carbonates/bicarbonates (known H2O2-
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activators for CWA decontamination). A plethora of products are formed during the H2O2-
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decontamination of HD on concrete, and these are characterized by comparison to synthesized
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authentic compounds. As a potential residue-free decontaminant for surfaces other than
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concrete (or those lacking adsorbed carbonate/bicarbonate) H2O2-activation for CWA
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decontamination is feasible using residue-free NH3 and CO2 as demonstrated by reaction
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studies for VX, GD, and HD in homogeneous solution. Although H2O2/NH3/CO2 (“HPAC”)
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decontaminants are active for CWA decontamination in solution, they require testing on actual
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surfaces of interest to assess their true efficacy for surface decontamination.
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Introduction The remediation of urban, civilian infrastructure and buildings following the release of
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chemical warfare agents (CWA) has been an increasing concern,1 perhaps starting with the
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1995 Tokyo subway sarin attack2 but further underscored by recent events in Syria.3 Although
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sarin (or “GB”, isopropyl methylphosphonofluoridate) was actually deployed in these instances,
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Syria also presumably possesses VX [S-2-(diisopropylamino)ethyl O-ethyl
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methylphosphonothioate) and HD [mustard, bis(2-choroethyl) sulfide].4,5 Churchill et al.6 have
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recently reviewed the destruction and detection of these compounds, in addition to other
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CWAs.
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The persistence and fate of GD (soman, pinacolyl methylphosphorofluoridate – another
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“G-agent”), VX and HD on concrete has been well-documented.7-15 Love et al.1 recently studied
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various decontaminants to remediate these agents on concrete, in addition to other surfaces.
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However, each decontaminant examined would ultimately leave a residue behind, either salts
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and/or surfactants, requiring further cleanup. Such commercial decontaminants would also be
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quite costly for use in large-scale decontamination operations.
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Although modern decontaminants such as DF-20016 and Decon Green17 are based on
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hydrogen peroxide (H2O2) – a substance that merely decomposes to water and oxygen in the
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environment – they require additional activators and additives such as bicarbonates18 and
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surfactants. Bicarbonates function both as a buffer for pH control and as an oxidation catalyst
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for HD.18 Surfactants are typically employed to assist in dissolution of CWA, especially oily,
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water-insoluble HD. Thus salt and/or surfactant residues would typically result following the
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use of current H2O2-based decontaminants. 3 ACS Paragon Plus Environment
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As a potential surface of concern for decontamination, concrete is perhaps unique in
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that it becomes carbonated as it ages.19 Therefore, ample surface-bound carbonate is
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apparently already present. As shown in this paper, this surface carbonate evidently precludes
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the need for externally-added bicarbonate for H2O2-activation and buffering. Furthermore,
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even water-insoluble HD is decontaminated, perhaps owing to its sorption and spreading-out
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over the concrete surface into a relatively thin layer. Such a mechanism has been previously
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observed to enable sorbed-HD to be decontaminated by H2O2 vapor on glass wool substrate.20
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Thus, H2O2 by itself, without any additional additives such as buffers, co-solvents, or
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surfactants, is sufficient for the residue-free decontamination of VX, GD, and HD on concrete.
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Recently, Columbus et al.21 reported that H2O2 alone was effective for the
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decontamination of VX and HD on activated carbon, similarly concluding that basic sites on the
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carbon enabled perhydrolysis to occur. Also they observed that the adsorption of HD into
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microenvironments within the carbon apparently facilitated its reaction with the H2O2, being
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devoid of usual co-solvents and surfactants typically required to dissolve/disperse HD for
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efficient reaction. Thus, these results are consistent with those reported below for concrete.
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Regarding other surfaces – where salt and/or residue-free decontamination is desired
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but adventitious carbonation is lacking – modified vaporized hydrogen peroxide (mVHP)
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utilizing ammonia (NH3) gas additive has been shown to possess broad-spectrum reactivity as a
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fumigant for VX, GD and HD on glass wool substrate.20 More recent studies22 have found that
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besides NH3, carbon dioxide (CO2) is also a suitable, volatile additive for formulating H2O2-based
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CWA decontaminants. The efficacy of such a solution – H2O2 activated with NH3 and CO2
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(“HPAC” decontaminant) – is demonstrated for VX, GD, and HD in solution. Thus, these
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preliminary results suggest that residue-free decontamination of CWA surfaces other than
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concrete, which lack H2O2-activating carbonates, may also be possible using only low-cost,
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residue-free ingredients (H2O2, NH3 and CO2); however, decontamination studies on various
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surfaces of interest are required to prove this expectation.
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Experimental Section Materials. Thiodyglycol (TG), thiodiglycol sulfone (TGSO2), 1,4-thioxane (TX),
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1,4,7,10,13,16-hexaoxacyclooctadecane (18-Crown-6 ether), 35 % and 50 % H2O2, NH3, Triton X-
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100, propylene carbonate, and propylene glycol were obtained from Aldrich. VX, GD, HD and
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13
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described.23
C-labeled HD (HD*) were obtained locally. Concrete coupons were prepared as previously
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NMR. 1H, 31P and 13C NMR spectra were obtained using Varian INOVA 400 NMR
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spectrometers. Spectra were referenced to external 85 % H3PO4 (31P, 0 ppm); external sodium
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3-(trimethylsilyl)propionate-2,2,3,3-d4 (TSP) in D2O (1H, 0 ppm; 13C, H2O and tBuOH solvent, 0
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ppm); and internal CH3CN (13C, CH3CN solvent, 0.3 ppm).
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Synthesis of Authentic Compounds. Caution: Syntheses involving Chemical Warfare
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Agents should only be performed by trained personnel utilizing applicable safety procedures.
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HD Sulfoxide (HDO). 25 µL HD was added to 0.55 mL tBuOH in a 5 mm NMR tube, followed by 0.15 mL 50 % H2O2.
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C NMR was used to observe the conversion of HD (peaks 5
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observed at 46.4 and 37.4 ppm) to the sulfoxide, HDO.
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ppm.
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followed by 0.1 mL 50 % H2O2 and 5 mg K2MoO4.
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of HD to HDO and the sulfone, HDO2.
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(63.3, 36.3 ppm) to the sulfoxide, TGO.
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13
13
C NMR was used to observe the conversion of TG
C NMR (H2O, 400 MHz) : 57.6, 56.9 ppm.
Thiodiglycol Sulfone (TGO2). 50 µL authentic thiodiglycol sulfone (TGO2) was added to 0.7 mL H2O in a 5 mm NMR tube.
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C NMR (H2O, 400 MHz) : 59.0, 57.8 ppm.
2-Chloroethyl Vinyl Sulfide (CEVS). 50 µL HD was added to 5 mL tBuOH and 49 mg KOH
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in a capped 20 mL vial and stirred overnight .
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36.6 ppm.
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C NMR was used to observe the conversion
Thiodiglycol Sulfoxide (TGO). 25 µL thiodiglycol (TG) was added to 0.7 mL H2O in a 5 mm NMR tube, followed by 50 µL 50 % H2O2.
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13
C NMR (tBuOH, 400 MHz) : 59.2, 38.5 ppm.
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C NMR (tBuOH, 400 MHz) : 57.4, 40.0
HD Sulfone (HDO2). 17 µL HD was added to 0.6 mL tBuOH in a 5 mm NMR tube,
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13
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C NMR (tBuOH, 400 MHz) : 134.3, 115.1, 44.9,
2-Chloroethyl Vinyl Sulfoxide (CEVSO). 17 µL HD was added to 0.6 mL tBuOH in a 5 mm 13
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NMR tube, followed by 0.1 mL 50 % H2O2.
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to HDO, at which point 67 mg KOH and 0.2 mL H2O was added; 13C NMR observed the
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conversion to 2-chloroethyl vinyl sulfoxide, CEVSO.
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58.0, 39.5 ppm.
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C NMR was used to observe the conversion of HD
13
C NMR (tBuOH, 400 MHz) : 142.5, 126.0,
2-Chloroethyl Vinyl Sulfone (CEVSO2). 17 µ HD was added to 0.6 mL tBuOH in a 5 mm NMR tube, followed by 0.1 mL 50 % H2O2 and 5 mg K2MoO4.
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C NMR was used to observe the
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conversion to HDO2, at which point 25 mg KOH was added.
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conversion of HDO2 to 2-chloroethyl vinyl sulfone, CEVSO2.
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134.5, 59.3, 38.7 ppm.
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Crown-6 ether in a capped 20 mL vial overnight.
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peaks for divinyl sulfide, DVS.
13
13
Divinyl Sulfoxide (DVSO). 50 µL HD was added to 0.7 mL tBuOH in a 5 mm NMR tube, 13
followed by 0.1 mL 50 % H2O2.
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point 75 mg KOH was added.
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NMR (tBuOH, 400 MHz): 141.5, 127.0 ppm.
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C NMR was used to observe the conversion to HDO, at which
C NMR observed conversion to divinyl sulfoxide, DVSO.
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C
Divinyl Sulfone (DVSO2). 17 µL HD was added to 0.6 mL tBuOH in a 5 mm NMR tube,
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followed by 0.1 mL 50 % H2O2 and 5 mg K2MoO4.
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to HDO2, at which point 25 mg KOH was added.
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sulfone, DVSO2.
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C NMR of the reaction mixture observed
C NMR (CH3CN, 400 MHz): 129.3, 113.8 ppm.
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C NMR (tBuOH, 400 MHz): 139.4,
Divinyl Sulfide (DVS). 100 µL HD was stirred in 10 mL CH3CN, 0.2 g KOH, and 0.2 g 18-
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C NMR was used to observe the
13
13
13
C NMR was used to observe the conversion
C NMR observed conversion to divinyl
C NMR (tBuOH, 400 MHz): 139.9, 132.8 ppm.
1,4-Thioxane Sulfoxide (TXO). 25 µL 1,4-thioxane (TX) was added to 0.7 mL H2O in a 5 13
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mm NMR tube.
C NMR found peaks for TX at 71.3 and 29.1 ppm. 25 µL 50 % H2O2 was added
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and 13C NMR observed conversion to 1,4-thioxane sulfoxide, TXO.
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62.0, 47.5 ppm.
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C NMR (H2O, 400 MHz):
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1,4-Thioxane Sulfone (TXO2). To the above TXO sample, 50 µL more 50 % H2O2 and 5 mg
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K2MoO4 was added and 13C NMR observed conversion of TXO to 1,4-thioxane sulfone, TXO2.
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NMR (H2O, 400 MHz): 69.5, 55.6 ppm.
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C
Reaction Procedures. Caution: These experiments should only be performed by trained personnel utilizing applicable safety procedures. Concrete Reactions. Single 5 µL drops of VX, GD, and HD* were added to ca. 0.3 g
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concrete coupons (12 mm×7 mm×2 mm) and placed in 10 mm NMR tubes. Agents were
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allowed to adsorb into the concrete for 0.5 to 1 h before initial NMR spectra (31P for VX, GD; 13C
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for HD) were recorded for the adsorbed agents. Then 0.8 mL 35 % H2O2 was added to the
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tubes, a volume just enough to completely cover the concrete coupons. Over time, NMR was
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used to monitor the evolution of products in situ.
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HPAC Decontaminant. The H2O2/NH3/CO2 (HPAC) decontaminant was produced by first
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generating the NH4HCO3 solution by bubbling NH3 (120 mL/min) and CO2 (from dry ice
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evaporation, 200 mL/min) into 200 mL water contained in a 1-L bottle for 90 min.
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showed the NH4HCO3 concentration to be 1.6 M. The test decontaminant solution was
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generated by mixing, in order, 10 vol % Triton X-100 surfactant, 10 vol % propylene carbonate,
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10 vol % propylene glycol, 30 vol % 35 % H2O2, and finally the NH4CO3 solution (25 vol %).
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Although not strictly required for thin-layer, surface decon,20 Triton X-100 and propylene
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carbonate were added to assist with dissolution of water-insoluble HD. Propylene glycol was
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added as an anti-freeze. As in previous studies, none of these additives proved detrimental to
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the CWA reactivity of the HPAC decontaminant efficacy. VX, GD, and HD reactions were carried
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C NMR
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out using 1:50 challenges of the agents to 0.75 mL of the decontaminant contained in a 5 mm
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NMR tube. NMR (31P, VX, GD; 1H, HD) was used to monitor the reactions over time.
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Results and Discussion
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VX on Concrete. Figure 1 shows 31P NMR spectra obtained for 5 µL VX on a concrete
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coupon (bottom spectrum) after it had been allowed to adsorb into the concrete for 1 h. The
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upper spectra of Figure 1 were obtained following the addition of 0.8 mL 35 % H2O2 to the
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concrete coupon. Within minutes, conversion of VX to its non-toxic ethyl methylphosphonate
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(EMPA) product occurs (Scheme 1); in the presence of H2O2 the cleaved thiol (RSH) is known to
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oxidize quickly to the disulfide (RSSR) .20 The facile reaction of VX is attributed to the formation
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of peroxyanion (OOH-)24 on the basic concrete surface. The EMPA peak is sharp as it is
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extracted from the concrete coupon into the aqueous medium surrounding the concrete
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coupon. Conversely, the phosphate H2O2-stabilizer is observed to slowly adsorb into the
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concrete, thus broadening its signal. No sharp signal is observed for VX, indicating that it stays
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put on the concrete while it reacts. Further, no signal is observed for toxic EA-2192, consistent
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with the perhydrolysis mechanism24 for VX.
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Previously, it was observed that VX hydrolyzed faster on fresh concrete (pH 10)
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compared to aged concrete (pH 9).23 As concrete becomes carbonated as it ages, the pH of
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water in its pores does indeed decrease from very alkaline, pH >12, to less than 8.19 Thus, the
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reactivity of concrete toward VX hydrolysis should decrease with age. However, perhydrolysis
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of VX remains very effective even at pH 8.18 Therefore, even on aged concrete, H2O2 is still able
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to effectively decontaminate VX via perhydrolysis.
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Figure 1. Select 31P NMR spectra obtained for 5 µL VX added to concrete coupon before
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(bottom spectrum) and after (upper spectra) addition of 0.8 mL 35 % H2O2 at the indicated
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reaction times.
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Scheme 1
O
O P
S
N
OOHO
O P
O-
+ HS
EMPA
VX
N RSH
OHRSH H2O2 or Air
-O
199
O P
S EA-2192
N
+ EtOH
N
SS
N
+ H2O
RSSR
200 201
GD on Concrete. Figure 2 shows 31P NMR spectra obtained for 5 µL GD allowed to
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adsorb into a concrete coupon for 0.5 h (bottom spectrum) before the addition of 0.8 mL 35 %
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H2O2 (upper spectra). GD also reacts within minutes to form non-toxic pinacolyl
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methylphosphonate (PMPA, Scheme 2), remaining sorbed on the concrete as it does so. The
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presence of a small peak at 44.2 ppm in the 10.5-min spectrum is attributed to peroxy-PMPA
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(pPMPA, Scheme 2),18 suggesting that GD is also reacting via OOH-.
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208 209
Figure 2. Select 31P NMR spectra obtained for 5 µL GD added to concrete coupon before
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(bottom spectrum) and after (upper spectra) addition of 0.8 mL 35 % H2O2 at the indicated
211
reaction times.
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Scheme 2
O
O P
OHF
GD
OOH-
H2O2
-HF
O
213
O
-HF
O P
O P
PMPA -O2, H2O
OO-
pPMPA
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HD on Concrete. Figure 3 shows 13C NMR spectra obtained for 5 µL HD* allowed to
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adsorb into a concrete coupon for 1 h (bottom spectrum) before the addition of 0.8 mL 35 %
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H2O2 (upper spectra). Within minutes peaks are observed (56.3, 40.1 ppm) for water soluble,
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non-vesicant HD-sulfoxide (HDO),25,26 which is extracted into the surrounding aqueous medium.
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It should be noted that oxidation of the sorbed HD may be facilitated by CO2-derived
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carbonate/bicarbonate – which concrete acquires as it ages27 – as carbonate/bicarbonate is a
220
known H2O2-oxidation catalyst for HD.18 Another advantage afforded by concrete is its
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porosity: water-insoluble HD will tend to spread thinly into the pores, thus facilitating contact
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with aqueous H2O2. Looking at further product evolution, after an hour, 1,4-oxathiane 4,4-
223
dioxide is observed (TXO2; 72.2, 52.5 ppm) followed by divinyl sulfoxide (DVSO2; 140.5, 127.7
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ppm), thiodiglycol sulfoxide (TGO; ca. 57.3 ppm) and thiodiglycol sulfone (TGO2; ca. 57.3 ppm).
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The inset peaks in Figure 3 show the evolution of the overlapping peaks for HDO, TGO and
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TGO2, the two tallest peaks in the top spectrum belonging to the latter two compounds. Figure
227
4 shows that the closely-spaced peaks for TGO and TGO2 can be separated in solution 13C NMR
228
spectra following the secondary oxidation of authentic TGO to TGO2 (see Experimental).
229
At extended reaction times on concrete, i.e. > 16 h, thiodiglycol (TG; 63.7, 36.7 ppm) 13
230
itself is observed as H2O2 is depleted, allowing normal hydrolysis of HD to proceed.
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shift data for various authentic HD-derived products are collected in Table 1. Various reactions
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yielding the observed products are shown in Scheme 3.
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Table 1.
13
C NMR Shifts for HD Derivatives a
HD HDO HDO2 δ 46.4, 37.4 b δ 57.4, 40.0 b δ 59.2, 38.5 b Thiodiglycol, TG TGO TGO2 δ 63.3, 36.3 c δ 57.6, 56.9 c δ 59.0, 57.8 c Chloroethyl Vinyl Sulfide, CEVS CEVSO CEVSO2 δ 134.3, 115.1, 44.9, 36.6 b δ 142.5, 126.0, 58.0, 39.5 b δ 139.4, 134.5, 59.3, 38.7 b Divinyl Sulfide, DVS DVSO DVSO2 d b δ 129.3, 113.8 δ 141.5, 127.0 δ 139.9, 132.8 b 1,4-Thioxane, TX TXO TXO2 c c δ 71.3, 29.1 δ 62.0, 47.5 δ 69.5, 55.6 c a Products observed on concrete shown in bold. b t-BuOH. c H2O. d CH3CN.
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Figure 3. Select 13C NMR spectra obtained for 5 µL HD* added to concrete coupon before
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(bottom spectrum) and after (upper spectra) addition of 0.8 mL 35 % H2O2 at the indicated
241
reaction times. Inset peaks show fine detail of the large central resonance in the top three
242
spectra, revealing overlapping lines for HDO, TGO and TGO2 (see text).
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Figure 4. Select 13C NMR spectra obtained for 25 µL TG added to 0.75 mL 50 % H2O2 at the
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indicated reaction times showing secondary oxidation of TGO to TGO2 (see text).
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248
249
250
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Scheme 3 O S OHCEVSO -HCl Cl
H2O2 Cl
S
Cl
HD
-H2O
O S
H2O2 Cl
HDO
-H2O
Cl
O S
OH-HCl
DVSO O Cl
O S
Cl
HDO2
H2O -HCl
O HO
HO
S CH
Cl
H2O -HCl
HO
S TG
H2O2 OH
-H2O
HO
O S
O
H2O Cl
CHO2
H2O
-HCl
O S
-HCl
O S
HO
OH
TGO2 H+
OH
O
TGO
O S
HO
+
O H
H
-H3O+ O
O S
O TXO2
253 254 255
VX, GD, and HD in HPAC Decontaminant. As mentioned above concrete is
256
serendipitously complementary with regards to CWA decontamination using H2O2 owing to its
257
adsorbed carbonate/bicarbonate, as these attributes serve as H2O2-activators. However, other
258
surfaces not possessing this quality would require the addition of additives to suitably activate
259
H2O2 for CWA decontamination purposes.18
260
One activator which would not leave a solid residue is ammonium bicarbonate
261
(NH4HCO3), a compound that slowly decomposes to NH3, water and CO2 – a process greatly
262
accelerated by heat. Thus, although NH4HCO3 could be used in conjunction with H2O2 to
263
generate a residue-free decontaminant, this material would not be stable for storage under
264
military conditions.28 However, it is possible to generate NH4HCO3 from NH3 and CO2, simply by
265
bubbling both gases in aqueous solution. A particular advantage to this approach for
266
generating a residue-free liquid decontaminant is that it utilizes NH3 and H2O2, the two
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ingredients used to generate the gaseous chem/bio fumigant mVHP.20 The only additional
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ingredient required would be CO2.
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Table 2 shows reaction data for VX, GD, and HD, at a 1:50 challenge level, in a
270
decontaminant generated from H2O2, NH3, and CO2 – the HPAC decontaminant. For purposes
271
of testing its CWA efficacy in homogeneous solution the solution was comprised of 10 vol %
272
Triton X-100 surfactant, 10 vol % propylene carbonate, 25 vol % propylene glycol, 30 vol % 35 %
273
H2O2, and 25 vol % 1.6 M NH4HCO3 (generated by bubbling NH3 and CO2 into water). It should
274
be noted that while Triton X-100 and propylene carbonate were employed to adequately
275
dissolve water-insoluble HD for this homogeneous reaction study these additives would not be
276
strictly required for treating thin CWA contamination deposits on surfaces, as shown above for
277
concrete (and for glass wool using mVHP20). However, studies need to be carried out for actual
278
surfaces of interest to confirm this expectation. Propylene glycol was added as this volatile
279
additive would be useful to lower the freezing point of the residue-free decontaminant. Thus,
280
residue-free decontaminants can also be formulated for use in sub-zero conditions.
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283
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Table 2. Reactions of 1:50 Challenges of VX, GD, and HD in H2O2/NH3/CO2
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“HPAC” Decontamination Solution VX
289
Time (min) 2 3 4 5 6 7 8 9 15 30 1h 2h a Half-life 3.6 min.
HD a
GD % Time (min) 28.6 2 20.0 15.0 11.7 10.6 8.6 7.2 6.3 2.8 1.4 0.63 N.D. b b Not detected.
% N.D. b
Time (min) 2 4 6 8 10 12 14 16 18 20 22 24
% 72.3 57.3 43.7 32.0 23.3 16.0 10.7 7.3 4.4 2.4 1.5 < 1.0
290 291
VX reacted with the HPAC decontamination solution to form EMPA; no toxic EA 2192
292
formed. The initial reaction is quite rapid, consuming 71.4 % within the first two minutes. After
293
15 min, only 2.8 % VX remained and the concentration fell below the detection limit within 2 h.
294 295
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The GD reaction was so rapid that no remaining agent was detected after 2 min. Only PMPA and pPMPA is observed, again consistent with attack by OOH- (see above). The relatively short half-life observed for HD, 3.6 min, is much less than the half-life of
297
42 min previously observed for HD without bicarbonate activator,18 consistent with the
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expected formation of HCO4- oxidation catalyst.18
299 300
Outlook for Cost-Effective, Residue-Free Decontamination of Concrete and Other Environmental Surfaces. As shown above, VX, GD, and HD are decontaminated on laboratory19 ACS Paragon Plus Environment
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size concrete coupons using only inexpensive, residue-free aqueous H2O2, with no additional
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co-solvents or surfactants required for HD. However, scale-up studies are required to assess
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achievable efficacy for concrete in larger-scale applications/remediation. For surfaces other
304
than concrete, a CWA-active, residue-free decontaminant can also be generated using NH4HCO3
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as the H2O2 activator, perhaps most easily generated on site from NH3 and CO2 as NH4HCO3 is
306
not stable for storage under military conditions. However, lab-scale testing of such HPAC
307
decontaminants on actual surfaces of interest are required, in addition to requisite scale-up
308
studies previously mentioned.
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Acknowledgements Support of this work was provided by the Defense Threat Reduction Agency (DTRA)
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under Project Nos. BA06DEC016 and BA06DEC052. The author would like to thank Messrs.
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Richard J. O’Connor and Morgan G. Hall, ECBC, for assistance with the agent operations.
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