Enhanced thermal degradation of 2,2′-dichlorodiethyl sulfide (sulfur mustard, HD) with the presence of metal oxides

Article abstract of DOI:10.1080/10426507.2016.1146277

Thermal degradation of sulfur mustard (2,2′-dichlorodiethyl sulfide, HD) in the presence of metal oxide adsorbents was investigated by thermal desorption in conjunction with gas chromatography–mass spectrometry (GC-MS). Zr(OH)₄, Al₂O₃, Al₂CoO₄, MgO, CeO₂, and V₂O₅were used as metal oxide adsorbents. Neat HD was spiked onto the metal oxides packed in glass tubes, which were kept at room temperature and then heated at moderately elevated temperatures of 100°C by a thermal desorption system. The products of thermal degradation were directly transferred and analyzed by GC-MS. 1,4-Dithiane and 1,4-oxathiane were characterized as the major products of the thermal degradation of HD in the presence of Zr(OH)₄, Al₂O₃, Al₂CoO₄, and CeO₂adsorbents. No effective degradation was observed with MgO and V₂O₅. Of particular note is Zr(OH)₄, which extremely enhanced the thermal degradation of HD.

Full text of DOI:10.1080/10426507.2016.1146277

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Enhanced Thermal Degradation Of 2,2′-
Dichlorodiethyl Sulfide (Sulfur Mustard, Hd) with
the Presence of Metal Oxides
Hyunsook Jung, Hae Wan Lee & Eun Ah Jeong
To cite this article: Hyunsook Jung, Hae Wan Lee & Eun Ah Jeong (2016): Enhanced
Thermal Degradation Of 2,2′-Dichlorodiethyl Sulfide (Sulfur Mustard, Hd) with the
Presence of Metal Oxides, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2016.1146277
To link to this article: http://dx.doi.org/10.1080/10426507.2016.1146277
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Feb 2016.
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Date: 09 April 2016, At: 06:40

ENHANCED THERMAL DEGRADATION OF 2,2′-DICHLORODIETHYL SULFIDE
(SULFUR MUSTARD, HD) WITH THE PRESENCE OF METAL OXIDES
Hyunsook Jung*, Hae Wan Lee, and Eun Ah Jeong
Agency for Defense Development, Yuseong-Gu, Daejeon 305-600, South Korea
Address correspondence to Hyunsook Jung, Agency for Defense Development, Yuseong-Gu,
Daejeon 305-600, South Korea. E-mail: junghs@add.re.kr
GRAPHICAL ABSTRACT
Abstract
Thermal degradation of sulfur mustard (2,2′-dichlorodiethyl sulfide, HD) in
the presence of metal oxide adsorbents was investigated by thermal desorption (TD) in
conjunction with gas chromatography/mass spectrometry (GC-MS). Zr(OH)4, Al2O3, Al2CoO4,
MgO, CeO2, and V2O5 were used as metal oxide adsorbents. Neat HD was spiked onto the
metal oxides packed in glass tubes which were kept at room temperature and then heated at
moderately elevated temperatures of 100 °C by a thermal desorption system. The products of
thermal degradation were directly transferred and analyzed by GC-MS. 1,4-Dithiane and
1,4-oxathiane were characterized as the major products of the thermal degradation of HD in
the presence of Zr(OH)4, Al2O3, Al2CoO4, and CeO2 adsorbents. No effective degradation was
observed with MgO and V2O5. Of particular note is Zr(OH)4 which extremely enhanced the
thermal degradation of HD.
Keywords
Sulfur mustard; metal oxide; thermal degradation; 1,4-dithiane; 1,4-
oxathiane
1

INTRODUCTION
2,2′-Dichlorodiethyl sulfide or HD (mustard gas, the common name) is one of the
most well-known chemical warfare agents (CWAs). It has been used as a chemical weapon
during World War I in 1917 and Iran-Iraq war in 1980s.1, 2 Although the Chemical Weapons
Convention (CWC) specified destruction of the chemical agent stockpiles and outlawed the
use of mustard in 1997, it is still highly possible for terrorists or the military of rogue nations
to weaponize mustard gas.3
HD is also a major component in stockpiles of CWAs due to its environmental
stability. One effective way for destruction of HD and its related agents is incineration at high
temperatures.4 Previous work proposed that HD can be thermally degraded at high
temperatures as shown in Scheme 1.5 The major products are 1,4-dithiane and 1,2-
dichloroethane which are formed via various intermediate sulfonium salts.6 However, thermal
degradation of HD in the absence of catalysis demands operating temperatures as high as
1800K at least.4
Metal oxides (MOx) have been examined as effective and environmentally-friendly
8
10,11
catalysts for the decontamination of CWAs. In particular, Zr(OH)4,7 Al2O3 , CaO,9 TiO2
MgO12 etc. have shown capability of degradation of HD. In general, the agent HD
decomposes on the metal oxides as shown in Scheme 2.8 The major products are
chlorohydrin and thiodiglycol are formed via hydrolysis. Chloroethyl vinyl sulfide is also a
major product resulting from elimination of hydrogen chloride. Although these reactions take
place at room temperature, the half-lives are rather slow.6
Herein, we describe our experiments on the thermal degradation of HD in the
presence of catalytic metal oxides. We employed a thermal desorption (TD) system in
conjunction with GC-MS which directly provides heat and analyzes degraded products of HD
with high selectivity and sensitivity. We also suggest a possible reaction pathway for the
thermal degradation of HD in the presence of metal oxides.
RESULTS AND DISCUSSION
Following our interest in the catalytic effect of metal oxides on thermal degradation
of HD, we used various metal oxide as adsorbents: Zr(OH)4, Al2O3, Al2CoO4, MgO, CeO2,
and V2O5. Each metal oxide (~ 40 mg) was packed in a glass tube as shown in Figure 1. Then,
2

neat HD was spiked onto the metal oxide adsorbent and the glass tube was end-capped to
prevent the evaporation of neat HD. Each sample was then kept at room temperature for 6 h
and then heated for 3 min at 100 °C by the thermal desorption (TD) system.
As shown in Figure 2, Zr(OH)4, Al2O3, Al2CoO4, and CeO2 effectively degraded HD.
However, no effective degradation was observed in the presence of MgO and V2O5. It should
be noted that the amount of desorbed HD was approximately equal to that of the applied HD
while degraded products were merely qualitative. 1,4-Dithiane was formed as one major
decomposition product with the presence of Zr(OH)4 and CeO2. Interestingly, 1,4-oxathiane
was mainly detected in the presence of Al2CoO4, Al2O3, and CeO2. In addition, vinyl species
including 2-hydroxylethyl vinyl sulfide and 2-chloroethyl vinyl sulfide were formed as minor
products. Unfortunately, 1,2-dichloroethane could not be detected in our experiments. Mass
spectra of all products are described in Figure 3. Reportedly, 1,4-dithiane is one of the major
thermal decomposition products of HD.5 It is also known as a common degradation product
of HD remaining in the environment.13 1,4-Dithiane is formed by dehydrochlorination via a
cyclic sulfonium salt as shown in Scheme 1. However, formation of 1,4-dithiane occurs
extremely slowly at ambient temperature.14 Even at higher temperatures, the thermal
degradation of HD in the absence of catalysts is known to be a slow reaction, requiring
temperatures up to 1800K at least.4 Obviously the presence of metal oxide adsorbents
enhanced the thermal reactivity of HD at a relatively low temperature of 100 °C.
1,4-Oxathiane, the other major product formed in the presence of Al2CoO4, Al2O3,
and CeO2, is usually formed by dehydrochlorination of partially hydrolyzed HD (i.e.,
chlorohydrin as shown in Scheme 2).8 In some cases, it may also be formed by rearrangement
of 2-hydroxylethyl vinyl sulfide.13, 17 Interestingly, chlorohydrin was not found in our study.
Instead, only 2-hydroxylethyl vinyl sulfide and 2-chloroethyl vinyl sulfide were observed
(see Figure 3 for their mass spectra). According to previous studies, metal oxides such as
MgO and Al2O3 are so basic that elimination of hydrogen chloride from HD under formation
of vinyl species occurs.7, 8, 12, 18 Therefore, the basic surfaces of Al2CoO4, Al2O3, and CeO2
enable the elimination of hydrogen chloride from HD, resulting in the elimination products 2-
hydroxyethyl vinyl sulfide and 2-chloroethyl vinyl sulfide.
Of particular note is zirconium hydroxide or Zr(OH)4 which extremely enhanced the
thermal reactivity of HD in our study. Zr(OH)4 has been reported as an effective means of
removing various toxic chemicals.7, 15, 16 It is believed that the basic hydroxyl groups of
Zr(OH)4 are related to its catalytic reactivity toward HD. As shown in Figure 4, 1,4-dithiane
3

was already formed from the sample kept at room temperature for 30 min and then heated for
3 min at 100 °C. Along with 1,4-dithiane, 2-chloroethyl vinyl sulfide and 1,4-oxathiane were
already formed. The time required for the complete degradation of HD was approximately 6
h. When we performed the same experiment (HD/Zr(OH)4) at room temperature without
heating (6 h), no effective degradation of HD was observed. Indeed, slightly detectable
amounts of degraded products (i.e., 2-chloroethyl vinyl sulfide and 1,4-oxathiane) were found
only as shown in Figure 5. We, therefore, attribute the extraordinary thermal reactivity of HD
at the relatively low temperature of 100 °C to the catalytic effect of Zr(OH)4, suggesting that
thermal degradation of HD can be extremely enhanced with the presence of appropriate metal
oxides even at a moderate temperature as described herein.
CONCLUSIONS
In summary, we studied thermal degradation of HD with the presence of catalytic
metal oxide adsorbents. The thermal reaction of HD was effectively enhanced with Zr(OH)4,
Al2O3, Al2CoO4, and CeO2. No effective degradation was observed on MgO and V2O5. The
major products of thermal degradation of HD were 1,4-dithiane and 1,4-oxathiane, with a
trace of 2-hydroxylethyl vinyl sulfide and 2-chloroethyl vinyl sulfide. Vinyl species may be
formed due to alkaline metal oxide surface properties. Our results suggest that the presence of
metal oxides promotes a greater extent of thermal degradation of HD, resulting in 1,4-
dithiane, 1,4-oxathiane, and 2-hydroxylethyl vinyl sulfide which are known to have relatively
less toxicity than HD. We hope that these results may be of value to others seeking effective
methods for the mass destruction for HD and related agents.
EXPERIMENTAL
All metal oxides were obtained from Aldrich and used without further purification.
The source of sulfur mustard was distilled sulfur mustard (HD), which was shown to be 98 %
pure by GC and NMR. (Caution: sulfur mustard is a highly toxic vesicant chemical, and an
extreme care must be taken to prevent exposure to liquid or vapor. It should only be handled
by trained personnel with protective ensemble).
Neat HD (1 µL) was spiked onto the metal oxides (~ 40 mg) in glass tubes which
were pre-filled with glass wool, metal oxides, and Teflon. Each sample was kept at room
4

temperature for a certain time and then heated at 100 °C for 3 min for thermal degradation.
The desorption was performed for 5 min at 250 °C using a UNITY/ULTRA thermal
desorption (TD) system (Markes International, UK). The desorbed samples from each tube
were then transferred to GC-MS (Agilent 7890 GC, 5973 MSD) via a heated transfer line
(120 °C) at a flow rate of 20 mL/min. Separation was achieved on a 30m x 0.25mm HP-5MS
GC-MS capillary column. The column oven temperature was programmed from 80 °C (kept
for 3 min) to 260 °C at 15 °/min. The column flow rate was 1.2 mL/min at a constant pressure
of 10.3 psi. The injection port and detector temperature were 250 °C, MSD transfer line
280 °C, MSD quad 150 °C, and MSD source 230 °C. The samples were analyzed in the
electron impact (EI) mode scanning from 30-300 amu with 5.19 scans/s.
ACKNOWLEDGMENTS
We thank Dr. Yonghan Lee, Senior Researcher at Agency for Defense Development,
for assistance with identification of decomposed products of HD observed in this study and
Chemical Analysis Test and Research Lab for the synthesis of HD.
5

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6

Figure 1 Representative picture of a sample constructed for thermal decomposition of HD
with the presence of metal oxide adsorbent in a glass tube
7

Figure 2 Chromatograms of thermally-degraded HD with the presence of various metal oxide
adsorbents: (a) Zr(OH)4, (b) MgO, (c) Al2CoO4, (d) Al2O3, (e) CeO2, and (f) V2O5
8

Figure 3 Mass spectra of (a) 1,4-oxathiane (Rt = 3.4 min), (b) 2-chloroethyl vinyl sulfide (Rt
= 3.7 min), (c) 2-hydroxyethyl vinyl sulfide (Rt = 3.9 min), (d) 1,4-dithiane (Rt = 5.9 min),
and (e) 2,2′-dichlorodiethyl sulfide or HD (Rt = 7.2 min)
9

Figure 4 Thermal degradation profiles of HD with the presence of Zr(OH)4 at different times
10

Figure 5 Chromatogram of HD with the presence of Zr(OH)4 at room temperature without
heating (6 h)
11

12

13