1178
Langmuir 2007, 23, 1178-1186
Decontamination of VX, GD, and HD on a Surface Using Modified Vaporized Hydrogen Peroxide George W. Wagner,*,† David C. Sorrick,† Lawrence R. Procell,† Mark D. Brickhouse,† Iain F. Mcvey,‡ and Lewis I. Schwartz‡ U.S. Army Edgewood Chemical Biological Center, Aberdeen ProVing Ground, Maryland 21010, and Strategic Technologies Enterprises, Inc., 5960 Heisley Road, Mentor, Ohio 44060 ReceiVed September 15, 2006. In Final Form: October 17, 2006 Vaporized hydrogen peroxide (VHP) has proven efficacy for biological decontamination and is a common gaseous sterilant widely used by industry. Regarding chemical warfare agent decontamination, VHP is also effective against HD and VX, but not GD. Simple addition of ammonia gas to VHP affords reactivity toward GD, while maintaining efficacy for HD (and bioagents) and further enhancing efficacy for VX. Thus, modified VHP is a broad-spectrum CB decontaminant suitable for fumigant-type decontamination scenarios, i.e., building, aircraft, and vehicle interiors and sensitive equipment. Finally, as an interesting aside to the current study, commercial ammonia-containing cleaners are also shown to be effective surface decontaminants for GD, but not for VX or HD.
1. Introduction Vaporized hydrogen peroxide (VHP) has been utilized for more than a decade to sterilize clean rooms and pharmaceutical processing equipment. Thus, VHP is a general-purpose fumigant that is safe for delicate equipment and has been widely used by industry for many years. Recently, VHP was also successfully employed to decontaminate buildings affected by the infamous anthrax-containing letters posted in the fall of 2001.1 The decontamination of sensitive equipment, vehicle interiors, and even buildings is of current concern to the military. Given the benign nature of VHP experienced in the industrial/civilian applications previously mentioned, the technology is at first glance an obvious choice for these particular military applications. However, for military purposes, and perhaps, inevitably, even homeland defense (recall the 1995 sarin nerve gas Tokyo subway attack on civilians2), chemical agents must be destroyed in addition to biological agents. Although VHP is quite efficacious for the latter, it was found3 to not possess the broad-spectrum efficacy required for the myriad of the former.4 The activation of hydrogen peroxide to facilitate its reaction with chemical agents has been studied for many years, resulting in the development of liquid decontaminants such as Decon Green.5 Thus, it is well-known how to activate aqueous hydrogen peroxide using benign ingredients. For example, bicarbonate5 (HCO3-) can be used to simultaneously generate peroxyanion (OOH-), a species particularly reactive with nerve agents such as O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate (VX) and pinacolyl methylphosphonofluoridate (GD), and * To whom correspondence should be addressed. Phone: (410) 4368468. E-mail:
[email protected]. † U.S. Army Edgewood Chemical Biological Center. ‡ Strategic Technologies Enterprises, Inc. (1) STERIS Corp. literature; see www.steris.com. (2) Zurer, P. Chem. Eng. News 1998, 76 (Aug 31), 7. (3) (a) Wagner, G. W.; Sorrick, D. C.; Procell, L. R.; Hess, Z. A.; Brickhouse, M. D.; McVey, I. F.; Schwartz, L. I. Vaporized Hydrogen Peroxide (VHP®) Decontamination of VX, GD, and HD. Proceedings of the 2003 Joint SerVice Scientific Conference on Chemical and Biological Defense Research; ECBCSP-018; U.S. Army Edgewood Chemical Biological Center: Aberdeen Proving Ground, MD, Sept 2004. (b) McVey, I. F.; Schwartz, L. I.; Centanni, M. A.; Wagner, G. W. Activated Vapor Treatment for Neutralizing Chemical Warfare Agents. U.S. Patent 7,102,052. (4) Yang, Y.-C.; Baker, J. A.; Ward, J. R. Chem. ReV. 1992, 92, 1729-1743. (5) Wagner, G. W.; Yang, Y.-C. Ind. Eng. Chem. Res. 2002, 41, 1925-1928.
Scheme 1
monoperoxocarbonate (HCO4-), which is a selective oxidation catalyst for bis(2-chloroethyl) sulfide (HD), facilitating its conversion to the nonvesicant sulfoxide. Yet such typical activators utilized in solution formulations are not volatile, rendering them useless for gas-phase applications. Initial studies3 examining the reactions of VX, GD, and HD with VHP found that gaseous hydrogen peroxide, as is, works quite well for VX and HD; i.e., no additional activation is necessary. VX is observed to undergo conversion to nontoxic ethyl methylphosphonate (EMPA; Scheme 1). Further, it is particularly noteworthy that no toxic S-[2(diisopropylamino)ethyl]methylphosphonothioc acid (EA-2192, Scheme 1) is observed to form in the presence of VHP (nor mVHP; see below). Similarly, HD is selectively oxidized to the nonvesicant sulfoxide6 (HDO, Scheme 2). Although not detected in the initial studies, the vesicant sulfone6 (HDO2) can form under certain conditions (see below). It should be pointed out that, if formed, HDO2 is more amenable to hydrolysis by ambient moisture than either HD or HDO, owing to both its water solubility (unlike HD) and its relatively fast hydrolysis rate (compared to that of HDO).6a Thus, HDO2, if formed, should be less persistent in the environment than either HDO or HD. (6) (a) Marshall, E. K., Jr.; Williams, J. W. J. Pharmacol. Exp. Ther. 1921, 16, 259-272. (b) Lawson, W. E.; Reid, E. E. J. Am. Chem. Soc. 1925, 47, 28212836.
10.1021/la062708i CCC: $37.00 © 2007 American Chemical Society Published on Web 12/05/2006
Decontamination of VX, GD, and HD on a Surface Scheme 2
Scheme 3
Unlike VX and HD, however, GD is quite stable in the presence of VHP, showing no tendency to react. Thus, although additives are not strictly needed for gaseous hydrogen peroxidesto either boost the oxidation of HD or to effect the desired P-S bond cleavage4 of VXsthere is a clear need for an activator to render VHP reactive toward G agents. It is well-known that G agents are easily and quickly decontaminated by both dilute base4 and basic hydrogen peroxide.7 Ammonia (NH3), a gas, is known to form basic solutions when dissolved in water. Further, it is widely used as a fertilizer in agriculture and as the active ingredient in household cleaning products (see below) and is the active ingredient in smelling salts. In fact, ammonia’s potent, distinct aroma has been experienced by practically everyone and is quite recognizable. Thus, NH3 was the basic gas of choice in the attempt to impart reactivity to VHP for G agents. It should be noted here that the exposure limit for ammonia is 25 ppm (NIOSH TWA8). Considering that the exposure limit for hydrogen peroxide is 1 ppm (NIOSH TWA9) and that typical VHP applications employ hydrogen peroxide levels on the order of hundreds of parts per million, ammonia added in amounts limited to its TWA should not add to the normal hazard associated with traditional VHP use. Thus, operators must still remain outside and clear of buildings, vehicles, and other enclosures containing items being decontaminated with mVHP, but only due to the peroxide vapor since ammonia may be employed at levels below 25 ppm (see below). VHP modified with NH3 (mVHP) at low prescribed levels (i.e., 90% of the HD evaporates within 40 min. The oxidation behavior of HD as revealed by the results in Tables 2 and 3 is consistent with a true reduction of [H2O2] by NH3 (not simply detector interference) and that limited amounts of NH3 (ca. 10 ppm) have a negligible, deleterious impact on HD oxidation/decontamination. With regard to why NH3 decreases [H2O2], it should be noted
that peroxide is more stable under neutral to slightly acidic conditions and less stable under basic conditions. 3.3. HD Drop Size Effects/Higher Contamination Densities. HD in both light contamination density, i.e., 1 g/m2, and cast as a thin-film represents an idealized, least-difficult decontamination challenge. However, discreet drops and higher contamination densities, i.e., 10 g/m2, must also be considered as they are apt to be encountered under real-world conditions. Table 4 shows results for two runs with two 0.2 µL drops and a single 0.5 µL drop, yielding the same ca. 1 g/m2 contamination density of the heretofore-considered 0.35 µL thin films. Table 5 shows results for single 3.5 and 4.5 µL drops and a 3.5 µL thin film, all with ca. 10 g/m2 contamination density. Although, technically, it is the 3.5 µL drop size that yields 10 g/m2 (as the density of HD is 1.27 g/mL), the slightly larger 4.5 µL drop is also examined to provide a drop Volume identical to that of 10 g/m2 4.5 µL VX and GD drops (both densities 1.0 g/mL; see below). Table 4 shows that even though comparable 1 g/m2 contamination densities are being processed, two 0.2 µL HD drops take about 1-2 h to decontaminate, whereas a single 0.5 µL HD drop requires at least 2 hssignificantly longer than the 20-30 min required by 0.35 µL thin films. Similarly, Table 5 reveals that, at a contamination density of 10 g/m2, a 3.5 µL HD thin film takes about 3.5 h and 3.5 and 4.5 µL HD drops persist for at least several hours. Of particular note is the significant formation of vesicant HDO2 within the HD dropssbut not the 3.5 µL thin filmsduring these extended reaction times. This is especially evident for the smaller 0.2 µL drops, where up to 7% conversion of the original HD to HDO2 is observed following prolonged exposure.
1182 Langmuir, Vol. 23, No. 3, 2007
Wagner et al.
Table 5. Oxidation of an HD 3.5 µL Thin Film and 3.5 and 4.5 µL Drops by VHPa (ca. 10 g/m2 Contamination Density) time (min) 2 2.5 3 3.5 4 4.5 5 6 7 a
3.5 µL thin film, [H2O2] ) 310-400 ppm [HD] [HDO] [HDO2] evapb
single 3.5 µL drop, [H2O2] ) 345-380 ppm [HD] [HDO] [HDO2] evap
single 4.5 µL drop, run 1, [H2O2] ) 380-490 ppm [HD] [HDO] [HDO2] evap
single 4.5 µL drop, run 2, [H2O2] ) 390-455 ppm [HD] [HDO] [HDO2] evap
31.3 24.1 31.3 NDc ND
88.5
80.0
89.2
9.5
ND
1.4
69.6
17.6
ND
12.8
56.1 33.1 33.1 9.5
22.3 29.1 30.5 43.9
ND trace trace 0.7
21.6 37.8 36.5 45.9
15.1 19.3 22.9 17.5 18.7
ND ND ND ND ND
53.6 56.6 45.8 82.5 80.7
6.1
ND
5.5
9.0
ND
11.0
53.3
11.5
0.6
34.5
30.3
23.2
trace
46.5
30.3 ND
19.4 10.9
0.6 0.6
49.7 88.5
ND ND
38.1 40.6
0.7 0.7
61.3 58.7
Expressed as a percentage of the original applied HD. b Includes any HD and/or product lost to evaporation. c Not detected. Table 6. Effect of NH3 on VX Thin Film Reactions with VHPa 0.45 µL VX thin film (1 g/m2), no NH3, [H2O2] ) 390-440 ppm
time
[VX]
[EMPA]b
evapc
10 min 30 min 1h 2h 3h 4h 5h 6h 7h
50.0 51.1 48.9
50.0
0.0
42.1 46.6 39.8
60.2
4.5 µL VX thin film (10 g/m2), no NH3, [H2O2] ) 425-470 ppm
4.5 µL VX thin film (10 g/m2), [NH3] ) 100 ppm, [H2O2] ) 90-100 ppm
[VX]
[EMPA]
[VX-pyro]
evapc
[VX]
[EMPA]
[VX-pyro]
evapc
43.6 42.3 39.9
55.8 55.9 56.4
0.6 1.8 3.7
0.0 0.0 0.0
4.4 ND ND ND
26.7 20.0 17.8 16.3
ND ND ND ND
68.9 80.0 82.2 83.7
33.1
63.8
3.1
0.0
NDd
95.1
4.9
0.0
0.0
a
Expressed as a percentage of the original applied VX. Includes any VX-NO formed. b Includes any VX-pyro formed. c Includes any VX or product lost to evaporation. d Not detected.
3.4. Effect of NH3 on VX Thin Film Reactions. As shown in Table 6, both 0.45 and 4.5 µL thin films of VX, comprising loadings of 1 and 10 g/m2, respectively, require at least several hours to react with VHP. Yet addition of 100 ppm NH3 causes VX in 4.5 µL thin films to react in less than 2 h. It is important to note that no EA-2912 forms, with or without NH3. Further note that NH3 effects substantial evaporation of VX and/or EMPA from the glass wool substrate, whereas a negligible amount is lost in its absence (normal VHP). Evaporation of EMPA and RSH/RSSR following VX degradation on (basic) concrete has been previously observed.13 Regarding the cleaved thiol group (RSH), it is immediately oxidized to the disulfide (RSSR), followed by slower oxidation to the sulfonic acid (RSO3H, Scheme 1). The 1H NMR spectrum obtained for the 4.5 µL VX thin film in a glass wool disk exposed to mVHP (100 ppm NH3) showing the RSSR and RSO3H species is given in Figure 2. Finally, it is important to note that toxic VX-pyro (Scheme 1) does not form in the presence of NH3, whereas it tends to increase and accumulate in the absence of NH3 as the VX reaction proceeds to completion. This important observation affords an important clue as to the VX reaction mechanism operative in the absence of NH3 (see the Discussion). Also, the observations of, in the absence of NH3, the relative persistence of the 0.45 µL VX thin film compared to the 4.5 µL VX thin film and the rather rapid, eventual conversion of VX within the latter (i.e., between 5 and 7 h, VX drops from 33.1% to nondetectable quantities) are also consistent with a different mechanism being operative to provide for the unexpected5 completeness of the reaction of VX with VHP. Table 7 shows results for the effects of various NH3 concentrations on the reaction of 0.45 µL VX thin films. It is clear that NH3 concentrations of 25 ppm and higher are increasingly effective; however, 10 ppm NH3 shows only little (13) Wagner, G. W.; O’Connor, R. J.; Procell, L. R. Langmuir 2001, 17, 4336-4341.
improvement over the background reaction with VHP (refer to Table 6). Mirroring this result is the pronounced jump in evaporation of VX and/or EMPA at 25 ppm NH3 and above, whereas no significant evaporation is evident at 10 ppm NH3. The fact that, in the presence of NH3, no sudden surge in VX conversion at extended reaction times is observed is a further clue that a different mechanism is operative in its absence (see the Discussion). 3.5. Effect of NH3 on GD Thin Film Reactions. Tables 8 and 9 show the reactivity of both 0.45 and 4.5 µL GD thin films with VHP in the absence and presence of various levels of NH3. Also shown is the reaction of a 0.45 µL GD thin film with only NH3 (no H2O2). In Figure 3 are shown typical 1H and 31P NMR spectra showing detection of GD, PMPA, and pPMPA (Scheme 3).14 Starting with the data in Table 8, both the relative lack of reaction of GD with VHP in the absence of NH3 and a quite remarkable reactivity of GD with NH3 alone (no H2O2) are evident. Yet with mVHP, i.e., the combination of H2O2 and NH3, the reaction rate increases with increasing NH3, becoming particularly fast at the upper level of 100 ppm. Note that, at the nominal NH3 concentration of 25 ppm, 0.45 µL thin films of GD (1 g/m2) may be decontaminated within about 30 min, whereas 4.5 µL thin films (10 g/m2) require 1 h or more. 3.6. Reactions of Single 4.5 µL HD, VX, and GD Drops with mVHP under Identical Conditions. Table 10 shows the reactions of single 4.5 µL (10 g/m2) drops of HD, VX, and GD under identical NH3 concentrations. Considering HD, the 4.5 µL drop reacts within 7 h, compared to only 45 min for the 0.35 µL thin film (same conditions, Table 2). Perhaps coincidentally, the 7 h duration is also in the same vicinity for the reaction of 4.5 µL HD drops in the absence of NH3 (Table 5), although in that (14) Both GD and pPMPA yield pairs of peaks in 31P NMR spectra as the result of the presence of two diastereomers.15 That the two diastereomers of pPMPA are resolved indicates that the peroxy groups are not exchanging. The single peak seen for PMPA indicates that the hydroxyl groups on this species are exchanging, albeit at a rate slow enough to cause noticeable broadening.
Decontamination of VX, GD, and HD on a Surface
Langmuir, Vol. 23, No. 3, 2007 1183
Figure 2. 1H NMR spectrum obtained for the CD3CN extract of the 4.5 µL VX thin film exposed to mVHP (100 ppm NH3, Table 6) for 4.0 h. RSSR yields intense peaks at 3.74 (septuplet), 3.37 (triplet), and 2.98 (triplet) ppm. RSO3H yields peaks at 3.97 (septuplet), 3.96 (overlapping triplet), and 3.20 (triplet) ppm. Residual EMPA is also visible as the small septuplet (partially underlying that of RSSR) at 3.79 ppm. Table 7. Effect of Various NH3 Concentrations on 0.45 µL VX Thin Film Reactions with mVHPa [NH3] ) 10 ppm, [H2O2] ) 100-160 ppm time
[VX]
10 min 20 min 30 min 45 min 60 min 75 min 1.5 h 2h 3h 4h 5h 6h 7h
44.4
[EMPA]b
evapc
36.3
[NH3] ) 25 ppm, [H2O2] ) 125-250 ppm [VX]
[EMPA]b
[NH3] ) 50 ppm, [H2O2] ) 50-110 ppm
evapc
37.2
12.0
32.4
10.0 4.0 2.7
24.8 11.7 4.8 2.1
21.0 19.4 18.5 13.7
86.3
[VX]
ND ND 35.4
[EMPA]b
61.0
evapc
[NH3] ) 100 ppm, [H2O2] ) 50-100 ppm [VX]
[EMPA]b
evapc
12.9 7.2 5.0 1.4 NDd ND
46.0
54.0
39.0
62.5
0.0
a Expressed as a percentage of the original applied VX. Includes any VX-NO formed. b Includes any VX-pyro formed. c Includes any VX or product lost to evaporation. d Not detected.
Table 8. Reactions of a 0.45 µL GD Thin Film with VHP, with and without Various Amounts of NH3 and H2O2a time (min) 5 10 15 20 25 30 45
no NH3, [H2O2] ) 195-240 ppm [GD] [PMPA]b evapc
[NH3] ) 25 ppm, no H2O2 [GD] [PMPA]b evapc
[NH3] ) 25 ppm, [H2O2] ) 35-75 ppm [GD] [PMPA]b evapc
[NH3] ) 50 ppm, [H2O2] ) 25-65 ppm [GD] [PMPA]b evapc
90.4 87.3 42.8 3.0 11.4 ND
86.5 76.9 46.8 ND 0.6 ND
89.1 92.7 73.9 50.3
NDd ND 7.3 5.5
10.9 7.3 18.8 44.2
78.9 5.9 0.7 0.7
1.3 3.3 2.0 2.6
19.7 90.8 97.4 96.7
12.7 0.6
4.2 5.5
83.0 93.9
0.7 trace
2.6 2.6
96.7 97.4
ND 1.8 6.0 10.2 9.0 7.2
9.6 10.8 51.2 86.7 79.5 92.8
1.9 5.8 19.2 16.7 17.3 14.1
11.5 17.3 34.0 83.3 82.1 85.9
[NH3] ) 100 ppm, [H2O2] ) 20-40 ppm [GD] [PMPA]b evapc ND ND ND ND ND ND
3.1 2.5 3.1 3.1 3.1 2.5
96.9 97.5 96.9 96.9 96.9 97.5
a Expressed as a percentage of the original applied GD. b Includes any pPMPA formed. c Includes any GD or product lost to evaporation. d Not detected.
case substantially less evaporation (only 46-61%), greater product formation (38-44% HDO), and somewhat greater HDO2 formation (0.7%) occurred. For VX, more than 9 h is required to react with the 4.5 µL drop, compared to 5 h for the 0.45 µL thin film (same conditions, Table 7). Finally, for GD, 6 h is required for the 4.5 µL drop, compared to only 30 min and ca. 1 h for the 0.45 and 4.5 µL thin films, respectively (Tables 8 and
9). Thus, bulk drops of agents on the order of 4.5 µL require a much greater period of time to decontaminate with mVHP than thin films. Although these comparative results were obtained utilizing TWA levels of NH3 (25 ppm) and near saturation levels of H2O2 (0.5 g/min H2O2 feed rate; see the Experimental Section), levels of both NH3 and H2O2 may be individually tailored to optimize
1184 Langmuir, Vol. 23, No. 3, 2007
Wagner et al.
Table 9. Reactions of a 4.5 µL GD Thin Film with VHP, with and without Various Amounts of NH3a time (min) 10 20 30 40 50 60
no NH3, [H2O2] ) 355-390 ppm [GD] [PMPA]b evapc
[NH3] ) 10 ppm, [H2O2] ) 290-335 ppm [GD] [PMPA]b evapc
[NH3] ) 25 ppm, [H2O2] ) 120-170 ppm [GD] [PMPA]b evapc
[NH3] ) 50 ppm, [H2O2] ) 35-55 ppm [GD] [PMPA]b evapc
[NH3] ) 100 ppm, [H2O2] ) 35-55 ppm [GD] [PMPA]b rvapc
80.1 67.5 33.1 30.5 23.8 19.2
75.5 67.1 28.0 23.8 21.0 15.4
79.7 21.9 16.1 16.8 0.6 0.6
48.7 16.7 0.7 5.3 1.3 trace
43.5 6.5 NDd ND ND ND
2.0 2.0 1.3 1.3 1.3 2.0
17.9 30.5 65.6 68.2 74.8 78.8
1.4 1.4 1.4 1.4 0.7 1.4
23.1 31.5 70.6 74.8 78.3 83.2
3.2 14.2 11.6 7.8 7.8 7.1
23.2 63.9 72.3 75.5 91.6 92.3
20.0 22.7 15.3 18.7 12.0 11.4
31.3 60.7 84.0 76.0 83.7 88.7
30.4 30.4 2.8 12.3 2.1 0.8
26.1 63.0 97.1 87.7 97.8 99.2
a Expressed as apercentage of the original applied GD. b Includes any pPMPA formed. c Includes any GD or product lost to evaporation. d Not detected.
Figure 3. 1H and 31P NMR spectra obtained for the CD3CN extract of the 4.5 µL GD thin film (Table 9) on a glass wool disk exposed to mVHP (100 ppm NH3) for 20 min. In the 31P spectrum (bottom) GD yields a pair13 of doublets at 31.24 (JPF ) 1037 Hz) and 30.34 (JPF ) 1037 Hz) ppm, PMPA yields a broad singlet at 30.59 ppm, and pPMPA yields a pair13 of peaks at 39.10 and 38.21 ppm. In the 1H spectrum (top) the species are most easily quantitated by the intense singlets due to their -C(CH3)3 groups: GD, 0.914 ppm; pPMPA, pair14 of peaks at 0.911 and 0.905 ppm; PMPA, 0.891 ppm (see the inset). Table 10. Reactions of 4.5 µL Drops of HD, VX, and GD (10 g/m2) with mVHPa HD, [NH3] ) 25 ppm, [H2O2] ) 120-190 ppm
VX, [NH3] ) 25 ppm, [H2O2] ) 120-330 ppm
time (h)
[HD]
[HDO]
[HDO2]
evapb
1 2 3 4 5 6 7 8 9
85.1 96.5 57.4 43.3 24.8
1.4 1.8 2.1 2.8 2.8
ND ND ND ND trace
13.5 1.8 40.4 53.9 72.3
NDe
2.8
trace
97.2
GD, [NH3] ) 25 ppm, [H2O2] ) 50-115 ppm
[VX]
[EMPA]c
evapb
[GD]
[PMPA]d
evapb
47.5
45.5
7.1
48.3 15.2
6.6 4.6
45.0 80.1
25.2 25.3 24.0 18.2 9.1
74.8 69.7 76.0 57.6 45.5
0 5.1 0 24.2 45.5
trace trace ND
3.3 2.7 1.3
96.7 97.4 98.7
a Expressed as a percentage of the original applied agent. b Includes agent or product lost to evaporation. c Includes any VX-pyro formed. d Includes any pPMPA formed. e Not detected.
efficacy for agent/surface combinations of interest to both military and homeland defense. Additional studies to probe these more subtle effects are planned. 3.7. Decontamination of GD with Ammonia-Based Household Cleaning Products. The extreme reactivity exhibited by gaseous NH3 for GD during the mVHP studies suggested that NH3, itself, might afford a good, stand-alone, solution-phase decontaminant for GD. Conveniently, NH3-containing household cleaners are readily available, and two brands of window cleaners and one floor cleaner were selected for study. Generally, it is desirable for a decontaminant to decontaminate a 1:50 agent challenge within 15 min; i.e., 50 mL of decontaminant should be able to decontaminate at least 1 mL of agent within this time
frame. Simple NMR experiments5 were employed using 0.75 mL of the cleaners, to which 15 µL of GD was added to follow the reaction kinetics, assess the extent of reaction, and identify the product(s). These results are summarized in Table 11. At the end of 15 min, both window cleaners contained significant amounts of GD. However, the floor cleaner decontaminates GD to below detectable levels within 15 min. The pH of the floor cleaner is 12, significantly higher than that of the window cleaners (both pH 10); thus, its higher pH and perfectly acceptable performance for GD decontamination are consistent with it possessing a higher NH3 concentration. As a simple demonstration of the efficacy of NH3-based cleaners for surface decontamination of GD, single 0.5 µL drops
Decontamination of VX, GD, and HD on a Surface
Langmuir, Vol. 23, No. 3, 2007 1185
Table 11. Reactions of GD with Household NH3-Containing Window and Floor Cleanersa window cleaner 1
window cleaner 2
floor cleaner
time 1:50 1:500 1:50 1:500 1:50 1:500 (min) challenge challenge challenge challenge challenge challenge 2 5 15 b
81.8 81.0 75.6
68.5 45.3 24.0
86.6 70.4 57.9
63.0 33.6 17.4
20.5 1.2 NDb
ND
a Expressed as a percentage of the original applied GD remaining. Not detected.
Table 12. Fifteen Minute Reactions of 0.5 µL GD Drops on 24 mm Glass Wool Disks with Household NH3-Containing Window and Floor Cleanersa floor cleaner
window cleaner 2
0.5 mL 1:1000 challenge
0.5 mL 1:1000 challenge
1.0 mL 1:2000 challenge
NDb
66.7
19.7
a
1.5 mL 1:3000 challenge ND b
Expressed as a percentage of the original applied GD. Not detected.
of GD were deposited on 24 mm glass wool disks, decontaminated with various amounts of floor cleaner or window cleaner 2 for 15 min, immediately extracted with CD3CN, and analyzed by NMR. The results are shown in Table 12. The floor cleaner still possessed superior capacity for GD compared to window cleaner 2, and it was able to decontaminate the disk to below detectable levels within 15 min with as little as 0.5 mL. Yet complete decontamination using the latter was also achievable simply by increasing its amount to 1.5 mL. 3.8. Reactions of Ammonia-Based Cleaning Products with VX and HD. Demonstration of the effectiveness of simple ammonia-based cleaners for the decontamination of GD begs the question as to how effective they might be with VX and HD. VX is soluble in water, and its reaction with the floor cleaner could conveniently be followed by NMR (see above). HD is water-insoluble but can be reacted with water (and aqueous ammonia cleaners) with sufficient agitation. Table 13 shows results for the reactions of VX and HD with the floor cleaner. Similar to the reaction done for GD above, 15 µL of VX was added to 0.75 mL of floor cleaner (1:50) contained in an NMR tube. However, for HD, 40 µL was added to 2 mL of floor cleaner (1:50) or water (used as a control) in a 4 mL vial, which was then stirred for 15 min. A 0.75 mL aliquot of the resulting aqueous layer was withdrawn and placed in an NMR tube for product analysis. The extent of the reaction with HD was judged by the amount of water-soluble product formed; the balance of the HD remained undissolved/reacted in the bottom of the 4 mL vial. A blank sample of 15 µL of HD dissolved in 0.75 mL of CD3CN (1:50) was also prepared to allow comparison of the product peak intensity with that of the original HD challenge. The water was used as a control to determine whether the floor cleaner presented any advantage. The results for VX show that only 75.9% reacted within 15 min, but, more importantly, about 7% of the toxic EA-2192 byproduct formed (Scheme 1)sa typical problem exhibited by basic decontaminants.11 Therefore, unlike the case of GD, substantial toxicity remains following decontamination of VX with ammonia-based cleaners. For HD, 92.9% remained undissolved and unreacted by the floor cleaner after vigorous stirring for 15 min. The product formed is 2-chloroethyl vinyl sulfide, the expected product of a basic decontaminant.4 Yet the water control actually consumed more HD during the 15 min stirring period, leaving only 86.4% remaining undissolved/unreacted. The usual products were found: thiodiglycol (TG; 9.7%) and
the CH-TG sulfonium ion (3.9%).4 Thus, on the basis of this simple experiment, ammonia cleaners afford no advantage for HD decontamination over plain water, both of which are poor decontaminants for HD (when time is of the essence).
4. Discussion The reactions of HD, VX, and GD with gas-phase H2O2 are remarkably similar to the corresponding solution-phase reactions with two notable exceptions: (1) HD appears to be more readily converted to both the sulfoxide and the sulfone and (2) VX conversion to EMPA readily goes to completion. For example, it was previously found5 that for 0.1 M HD in 15 wt % H2O2 (with t-BuOH as a cosolvent), the half-life for conversion to HDO was 42 min. Furthermore, observed half-lives in activated peroxide solutions showed that the conversion of HDO to HDO2 is typically at least 2 orders of magnitude slower than the conversion of HD to HDO.5,16 Yet thin films of HD in the presence of VHP are completely converted to HDO within 20 min, and for HD drops, substantial amounts of HDO2 are formed within 15 min. For VX, it was found5 that a 0.01 M amount of this agent in 15 wt % H2O2 (with t-BuOH as a cosolvent) reacted about 50% within 1 h, but no further reaction occurred after 16 h of monitoring. This is in stark contrast to the behavior observed earlier3a for single 5 µL VX drops and as noted above for 4.5 µL VX thin films (Table 6) where VX reacts completely with VHP within 24 and 7 h, respectively. However, the behavior of GD with gas-phase H2O2sno substantial observable reactions is entirely consistent with its previously demonstrated behavior in aqueous H2O2: 0.01 M GD in 15 wt % H2O2 (with t-BuOH as a cosolvent) only slowly decomposes with a half-life of 29 days.5 The unusual behaviors exhibited by HD and VX in the presence of VHP allow speculation as to their origins. For HD, the fact that it is oxidized much faster than in solution and that drops exhibit a greater tendency to yield HDO2 than thin films strongly suggests that H2O2 is selectively absorbed and concentrated within HD films/droplets. This is in agreement with a known characteristic of H2O2: it behaves more like an organic solvent than it does water, enabling it to even penetrate and soften paint and plastics.17 Thus, the resultant high local concentration of H2O2 within the HD deposit could not only yield rapid conversion to HDO, but also facilitate secondary oxidation to HDO2. Of course water vapor would be excluded by oily, water-insoluble HD, consistent with the lack of any noticeable HD hydrolysis products. These processes are depicted in Figure 4. For VX, the reactivity of VHP can be partially explained by protonation of the amine group by H2O2 to yield peroxyanion (OOH-) and protonated VX. Thus, similar to the situation envisioned in Figure 4, H2O2 would absorb into VX drops/films to generate OOH-, which would then react with VX to yield EMPA (Scheme 2). Importantly (see below), H2O would also (15) Benschop, H. P.; Konings, C. A. G.; de Jong, L. P. A. J. Am. Chem. Soc. 1981, 103, 4260-4262. (16) Wagner, G. W.; Procell, L. R.; Yang, Y.-C.; Bunton, C. A. Langmuir 2001, 17, 4809-4811. (17) Weres and Pocekay have noted swelling and blistering of painted surfaces following exposure to 50% H2O2.18 Similarly, hydrogen peroxide’s ability to swell plastics as deftly as organic solvents is demonstrated by manufacturer data for HDPE Polystone G: the material is quite resistant to water (defined as swelling of
