L-Gel formulation and decontamination reaction of its active ingredient (oxone) against mustard and VX nerve agent simulants

Article abstract of DOI:10.1080/10426507.2011.590170

L-Gel is an effective decontamination reagent against chemical and biological warfare agents. To achieve optimized formulation of L-Gel, several formulations with different proportional amounts of oxone (oxidizer) and Cab-O-Sil (gelling agent) were prepared and their viscosities and densities were measured. Final optimized formulation of gel was obtained as a 0.25 M aqueous solution of oxone gelled with 13%W/W of Cab-O-Sil EH-5. The L-Gel active ingredient (oxone) was tested against O,O,S-triethyl phosphorothioate (TEPT) as VX simulant and methyl phenyl sulfide (MPS) and chloroethyl phenyl sulfide (CEPS) as HD simulants. Decontamination of TEPT by a 10-fold excess amount of oxone was completed within 7.5 min with a kinetic rate constant of 0.097 S ^-1. In the presence of oxone, MPS was converted to methyl phenyl sulfoxide and methyl phenyl sulfone with a higher reaction rate than CEPS, decontaminated product of which was chloroethyl phenyl sulfone. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2011.590170

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Phosphorus, Sulfur, and Silicon and the
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L-Gel Formulation and Decontamination
Reaction of Its Active Ingredient (Oxone)
Against Mustard and VX Nerve Agent
Simulants
a
a
a
Mahdi Farahipour , Hossein Fakhraian , Akbar Mirzaei & Morteza
a
Ali Hosseini
a
Department of Chemistry, Imam Hossein University, Tehran, Iran
Version of record first published: 31 Oct 2011.
To cite this article: Mahdi Farahipour , Hossein Fakhraian , Akbar Mirzaei & Morteza Ali Hosseini
(
2011): L-Gel Formulation and Decontamination Reaction of Its Active Ingredient (Oxone) Against
Mustard and VX Nerve Agent Simulants, Phosphorus, Sulfur, and Silicon and the Related Elements,
86:12, 2303-2310
1
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Phosphorus, Sulfur, and Silicon, 186:2303–2310, 2011
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.590170
L-GEL FORMULATION AND DECONTAMINATION
REACTION OF ITS ACTIVE INGREDIENT (OXONE)
AGAINST MUSTARD AND VX NERVE
AGENT SIMULANTS
Mahdi Farahipour, Hossein Fakhraian, Akbar Mirzaei,
and Morteza Ali Hosseini
Department of Chemistry, Imam Hossein University, Tehran, Iran
GRAPHICAL ABSTRACT
O
O
Oxone
P
1000 mol%
P
S
CH3
3
H C
O
OH
H
3
C
O
+
3 2 3
CH CH SO H
O
O
7
.5 min
CH
3
CH
3
O
S
O
S
Oxone
5
1
00 mol%
S
CH
3
CH
3
+
CH3
3
min
O
O
S
Oxone
000 mol%
S
CH
2
CH
2
Cl
2 2
CH CH Cl
2
h
O
Abstract L-Gel is an effective decontamination reagent against chemical and biological war-
fare agents. To achieve optimized formulation of L-Gel, several formulations with different
proportional amounts of oxone (oxidizer) and Cab-O-Sil (gelling agent) were prepared and
their viscosities and densities were measured. Final optimized formulation of gel was obtained
as a 0.25 M aqueous solution of oxone gelled with 13%W/W of Cab-O-Sil EH-5. The L-Gel
active ingredient (oxone) was tested against O,O,S-triethyl phosphorothioate (TEPT) as VX
simulant and methyl phenyl sulfide (MPS) and chloroethyl phenyl sulfide (CEPS) as HD sim-
ulants. Decontamination of TEPT by a 10-fold excess amount of oxone was completed within
−
1
7
.5 min with a kinetic rate constant of 0.097 S . In the presence of oxone, MPS was converted
to methyl phenyl sulfoxide and methyl phenyl sulfone with a higher reaction rate than CEPS,
decontaminated product of which was chloroethyl phenyl sulfone.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords L-Gel; oxone; Cab-O-Sil EH-5 fumed silica; decontamination; VX nerve agent
simulant; mustard simulant
Received 11 April 2011; accepted 17 May 2011.
Address correspondence to Hossein Fakhraian, Department of Chemistry, Imam Hossein University, 16987-
5861, Tehran, Iran. E-mail: fakhraian@yahoo.com
1
2
303

2304
M. FARAHIPOUR ET AL.
INTRODUCTION
Decontamination is an essential process and an important step to be taken in to
account with the chemical and biological agents. Different decontamination methods and
procedures such as liquids, foams, gels, gaseous, and vapor techniques exist to neutralize
1
–15
and detoxify chemical and biological warfare agents.
Foam and gel technologies are
designed to enhance surface removal of biological or chemical contaminants by delivering
the decontamination formulation in a matrix that can be applied on vertical and horizontal
surfaces. This allows the application to walls with sufficient contact time to ensure that
the chemical and biological agents are effectively treated and consist of systems such as
CASCAD and L-Gel.9
,10
Due to its nontoxic, noncorrosive, and high-rate decontamination nature, L-Gel is a
suitable decontamination reagent to be used for military and civilian purposes and it exerts
9
minimal damage to the environment. L-Gel has three important characteristics: it oxidizes
the chemical warfare agents; kills the bacterial spores used as biological warfare agents;
and sticks to vertical and overhead surfaces.
L-Gel consists of two principal ingredients: the oxidizing and the gelling agent. The
oxidizing agent in L-Gel is oxone, a triple salt with the formula 2KHSO5·KHSO4·K2SO4.
Oxone is a nonchlorine alternative used as a decolorizer and disinfectant and has shown
10
effective reaction with chemical warfare agents. The active ingredient in oxone is potas-
sium peroxymonosulfate “KHSO5.” The peroxymonosulfate anion is a moderate strength
oxidizer that contributes an electron to the chemical bonds of the target compound and
disrupts the bonds.
The gelling agent in L-Gel is Cab-O-Sil EH-5 fumed silica (synthetic amorphous
colloidal silica). High purity, aggregated structure, submicron particle size, low bulk density,
2
high surface area (380 m /g), and hydrophilic surface are the advantages of EH-5 over other
Cab-O-Sil grades. Cab-O-Sil EH-5 has an average particle length of 0.2–0.3 µm with very
14
high surface area and can increase the viscosity of liquid system.
L-Gel is packaged as a high-viscosity, gelatin-like semisolid that is liquefied by
9
shaking or stirring. The liquefied product can be applied using paint spraying equipment
that is commercially available. Due to L-Gel’s acidic properties, stainless steel spray nozzles
must be used.
Most of the toxic organophosphorus esters can be detoxified quickly by hydrolysis
in alkaline solution. However, the hydrolysis of phosphonothiolate esters as VX is much
7
slower and ineffective even at very high pH. However, oxidation of the sulfur in VX in
aqueous acid solution is rapidly followed by hydrolysis to nontoxic products. An acidic
solution also causes protonation of the amine nitrogen, increasing the solubility of VX and
enhancing the oxidation of sulfur.7
,9,12
Oxone has shown the ability to oxidize VX to ethyl
1
methanephosphonic acid and diisopropyl taurine.
MePO(OEt)SCH2CH2N(i Pr)2 + 3 KHSO5 + H2O
MePO(OEt)OH + HO3SCH2CH2N(i Pr)2 + 3 KHSO4
→
Dissolution of sulfur mustard into water is slow. Thus hydrolysis is not very effec-
tive against it and sulfur mustard detoxification in aqueous solution must be performed
1
ꢀ
via oxidation. Oxidation of an organosulfide (RR S) by hydrogen peroxide can produce
ꢀ
ꢀ
two oxidation products, the sulfoxide (RR SO) and the sulfone (RR SO2), under differ-
ent reaction conditions.1
5–21
Thus, the decontamination products of HD via oxidation are

L-GEL FORMULATION AND DECONTAMINATION REACTION
2305
sulfoxide (HDO) and sulfone (HDO2). The sulfoxide is nonvesicant and quite stable to-
ward hydrolysis, whereas the sulfone still retains appreciable vesicant activity and is prone
to slow hydrolysis. Thus, HD can be rendered nonvesicant via selective oxidation to the
13
sulfoxide. In this study, L-Gel formulation and its decontamination effects on VX and
mustard simulants have been investigated.
RESULTS AND DISCUSSION
Preparation of Optimized L-Gel Formulation
In order to achieve optimized formulations of L-Gel, the effects of various factors such
as presence of air, stirring rate, amount of Cab-O-Sil EH-5 and oxone on the gel properties
were investigated. The rate and time of stirring are important, as a result of which Cab-O-Sil
EH-5 molecules are surrounded by solvent and a three-dimensional lattice gel is formed.
The time required for lattice completion was 30 min. Continuation of stirring beyond
30 min caused the lattice to be disrupted and the viscosity to be decreased. This observation
is related to the thixotropy property of gel. In the absence of air, the viscosity of samples
decreases faster, therefore the presence of air is important in gel formation. If the sample is
left unaltered for several hours, its viscosity increases again.
The Gel quality is influenced and controlled by the amount of Cab-O-Sil. If the
Cab-O-Sil percent is less than 8% w/w, the resulting gel is unstable and diphasic. At over
8% w/w, the resulting gel is stable and mono phase even at high-speed centrifugal action.
By increasing the amount of Cab-O-Sil, the viscosity increases and reaches a maximum
for an amount of 13% w/w. Beyond 13% w/w, the trend of changes is switched and the
viscosity drops down. Stirring the viscose gel at an early stage caused the viscosity to
be reduced dramatically. This issue claims that the lattice gel initially suffered a sudden
collapse but in continuation, the trend became slower (Figure 1).
Decontamination of O,O,S-Triethyl Phosphorothioate
Oxone reacted with O,O,S-triethyl phosphorothioate (TEPT) as an insoluble organic
phase and entirely dissolved it. The reaction was exothermic and a lot of heat was librated.
Comparison of 31P and C NMR spectra of pure TEPT in CDCl3 and reaction mixture of
13
0.001 mol of TEPT and 1000 mol% of oxone in aqueous solution after 7.5 min showed the
Figure 1 The effect of stirring time on the viscosity of L-Gel.

2306
M. FARAHIPOUR ET AL.
Figure 2 13C NMR spectra of TEPT in CDCl3 (a) and of TEPT (0.001 mol) in aqueous solutions of oxone
1000 mol%) after 7.5 min (b).
(
formation of novel compounds. According to the 31P NMR spectra, the reaction of oxone
with TEPT (δ = 28.3 ppm) was completed after 7.5 min and a pentagon peak appeared
at 1.2 ppm which indicates the conversion of TEPT to phosphoric acid diethyl ester (i.e.,
(
EtO)2POOH). Considering the 13C NMR spectra (Figure 2), CH3CH2SO3H is another
product formed by the reaction of oxone with TEPT in aqueous solution (Scheme 1a).
To study the kinetics of TEPT decontamination reaction, three experiments with
different concentrations of oxone were carried out (Table 1). At excess amount of oxone
−1
a linear behavior of ln([TEPT]0/[TEPT]) versus time with a kobs value of 0.097 s was
observed showing a pseudo first-order decontamination of TEPT in the presence of excess
amounts of oxone. At 250 mol% of oxone, the reaction had a suitable rate at the beginning
but as the reaction went on, the progress was not notable because in order to decontaminate
1
mol of TEPT, 3 moles oxone were needed. Therefore, the amount of oxone was reduced
after 15 min and the rate of reaction became slower. After 70 min, all the oxone in the

L-GEL FORMULATION AND DECONTAMINATION REACTION
2307
O
O
Oxone
P
1000 mol%
P
S
CH3
3
H C
O
OH
H
3
C
O
+
CH CH SO H
a
O
3
2
3
O
7
.5 min
CH
3
CH
3
O
S
O
S
Oxone
5
1
00 mol%
S
CH
3
CH
3
+
CH3
b
c
3
min
O
O
S
Oxone
000 mol%
S
CH
2
CH
2
Cl
2 2
CH CH Cl
2
h
O
Scheme 1
reaction mixture were consumed and the reaction was halted so the composition of the
reaction mixture remained constant.
Table 1 Decontamination of TEPT in the presence of 250, 500 and 1000 mol% of oxone after different reaction
31
times according to the P NMR spectra
(
CH3CH2O)2PO(SCH2CH3)
(CH3CH2O)2POOH
31
31
Oxone
Reaction
P NMR δ = 28.3 ppm
P NMR δ = 1.2 ppm
(
mol%)
time (min)
(%)
(%)
2
5
50
00
5
58
42
32
19
10
4
42
58
68
81
90
1
5
1
30
7.5
1
2
5
5
96
1
000
5
6
94
7
.5
0
100
Decontamination of Methyl Phenyl Sulfide
Chromatographic comparison of pure methyl phenyl sulfide (MPS) (retention time of
9 min) and the reaction mixture of MPS with oxone (500 mol%) after 3 min showed that
MPS was oxidized and converted to two compounds with retention times of ∼14 and ∼16
min (Scheme 1b). The same compounds were found as the decontamination products of
MPS by activated hydrogen peroxide with the same GC characteristics and were identified
by GC-MS analysis as methyl phenyl sulfoxide [MPSO; retention time: 6.9 min; m/z (%):
∼
4
9
1(17), 43(10), 45(25), 50(36), 51(68), 53(23), 55(12), 65(19), 77(50), 81(11), 94(24),
7(87), 124(20), 125(83), 140(100), 141(24)] and methyl phenyl sulfone [MPSO2; retention
time: 8.1 min; m/z (%): 50(22), 51(47), 65(16), 77(100), 93(12), 94(51), 141(29), 156(31)]
15
as was reported previously for the oxidation of MPS with activated hydrogen peroxide.

2308
M. FARAHIPOUR ET AL.
Decontamination of Chloroethyl Phenyl Sulfide
GC analysis of the reaction mixture of chloroethyl phenyl sulfide (CEPS) with oxone
(
1000 mol%) extracted by CH2Cl2 states that 90% of CEPS (retention time of ∼16 min) is
eliminated after 2 h and a new product with a retention time of ∼18 min is formed (Scheme
1
1
c). The decontamination product shows a H NMR spectrum with two triplets at 3.55
and 3.75 ppm (ꢀδ = 0.20 ppm) attributed to two CH2 groups which are characteristic of
chloroethyl phenyl sulfone conform on the prediction of the Chem Office software which
1
predicts the chemical shift of two triplet in the H NMR spectra as 3.05 and 3.75 for
chloroethyl phenyl sulfoxide (ꢀδ = 0.70 ppm) and as 3.70 and 3.95 for chloroethyl
phenyl sulfone (ꢀδ = 0.25 ppm). GC-MS analysis of the reaction mixture of CEPS
with oxone (1000 mol%) extracted with CH2Cl2 showed a decontamination product with
a retention time of 9.2 min and fragmentation pattern with m/z (%, fragment) of 205
(28, C6H5SO2CH2CH2Cl), 156 (14, C6H5SO2CH2), 141 (100, C6H5SO2), and 125 (27,
C6H5SO) demonstrating the structure of decontamination product as chloroethyl phenyl
sulfone.
CONCLUSION
In conclusion, L-gel containing less than 8% w/w of Cab-O-Sil is unstable and
diphasic but over 8% w/w of Cab-O-Sil it is stable and forms a single phase. The op-
timum amount of Cab-O-Sil to form a stable gel with a suitable viscosity is 13% w/w.
The optimized time of stirring to form a lattice gel is 30 min, after when, leaving the
gel unaltered, it gradually starts to get viscous. The decontamination of TEPT with 1000
mol% of oxone in aqueous solution occurred after 7.5 min following a pseudo first-order
−1
reaction with kobs value of 0.097 s with apparition of diethyl phosphite (EtO)2POOH) and
CH3CH2SO3H as the decontamination products. MPS in the presence of excess amounts
of oxone (500 mol%) after 3 min was oxidized and converted to MPSO and MPSO2. The
reaction rate of CEPS with oxone was slower and decontamination of CEPS in the pres-
ence of 1000 mol% of oxone occurred after 2 h producing chloroethyl phenyl sulfone as
the decontamination product. Additional studies should be done at a facility able to handle
the real VX and HD agent to truly understand the overall effectiveness of such decontami-
nation reagent.
EXPERIMENTAL
Viscometer DV-II + Pro Brookfield was used to determine the viscosities. NMR
1
spectra were obtained on a Bruker ADVANCE DPX-250 instrument (250 MHz for H
NMR, 62.5 MHz for 13C NMR and 100 MHz for P NMR), and CDCl3, and D2O were
31
13
used as solvents; chemical shifts are reported in δ (ppm) from TMS for C and H3PO4
31
for P. Gas chromatograms (GC) spectra were recorded on a Varian STAR 3400CX with a
ꢀ
ꢀ
packed column (10% OV-101 CWHP 80/100, 2 m × 1.8 ) and a He flow rate of 10 mL/min.
Electron ionization GC-MS spectra were recorded on a Varian (SATURN 4D) spectrometer
using an ionization current of 8 µA with a capillary column (DB-5MS, 0.1 µm, 30 m ×
0
.250 mm). Only m/z values having intensities of more than 10% are given. Retention
◦
◦
times for GC and GC-MS were reported using temperature programming (100 C–250 C,
◦
◦
◦
5
C/min for GC and 10 C/min for GC-MS) with Tcol = Tinj = 210 C. MPS, CEPS, and
TEPT were synthesized in our laboratory with a purity of >95%.

L-GEL FORMULATION AND DECONTAMINATION REACTION
2309
Preparation of Optimized L-Gel Formulation
Cab-O-Sil EH-5 (2.6 g, 13% w/w) was gently added to the stirred aqueous solution of
oxone (2.29 g (0.0037 mol) of oxone dissolved in 15 mL of water). Stirring was continued
for 30 min. If we are in a rush to use L-Gel, we should leave the gel to stand for 1 h to be
in contact with air without stirring until the three-dimensional lattice gel is formed and the
viscosity reaches the maximum. Aged gel should be stirred by a mechanical mixer prior to
use, so that it becomes less viscous.
Decontamination Study of O,O,S-Triethyl Phosphorothioate
TEPT and an aqueous solution of oxone were directly mixed in an NMR tube and
P NMR spectrum was studied during the time.
31
Decontamination Study of Methyl Phenyl Sulfide
and Chloroethyl Phenyl Sulfide
A total of 0.0001 mol (0.012 g) MPS was added to 1 mL of 0.5 M oxone solution
(0.08 g, 500 mol%). The mixture was stirred and after 3 min the sample was extracted by
CH2Cl2 and analyzed by GC and GC-MS.
A total of 0.0002 mol (0.034 g) CEPS was added to 1 mL of a 2M solution of oxone
(0.3 g, 1000 mol%). The mixture was stirred and, after 30 min, one-half part of the sample
was extracted with CH2Cl2 and was analyzed by GC. The second part of the mixture
was stirred for 1.5 h and the sample was extracted with CH2Cl2 and analyzed by GC and
GC-MS.
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