Reaction Products and Process of 2-Chloroethyl Ethyl Sulfide in Microemulsion Media

Article abstract of DOI:10.1080/10426507.2013.820728

The reaction of 2-chloroethyl ethyl sulfide was investigated in several oil-in-water microemulsions. The reaction products were identified by GC/MS, NMR, and LC/MS, and the reaction process was monitored by measuring peak height of reaction products and 2-chloroethyl ethyl sulfide with time by ¹H NMR spectroscopy. The result showed that 2-chloroethyl ethyl sulfide degraded to 2-hydroxyethyl ethyl sulfide, cyclic sulfonium ion, open chain sulfonium chloro ion and sulfonium hydroxyl ion, and the reaction proceeded via a cyclic sulfonium ion intermediate. Based on the NMR results, a pseudoternary model was established for the reaction process of 2-chloroethyl ethyl sulfide in microemulsion.

Full text of DOI:10.1080/10426507.2013.820728

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Reaction Products and Process
of 2-Chloroethyl Ethyl Sulfide in
Microemulsion Media
Lei Mei-Ling a b , Xi Hai-Ling a b , Shen Ming c , Yuan Ling a b & Han
Shi-Tong a b
a Research Institute of Chemical Defense , P.O. Box 1043, Beijing ,
102205 , China
b State Key Laboratory of NBC Protection for Civilian , P.O. Box 1043,
Beijing , 102205 , China
c College of Chemistry & Chemical Engineering, Yangzhou
University , No. 180 Siwangting Road, Yangzhou , Jiangsu , 225002 ,
China
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Accepted author version posted online: 20 Sep 2013.Published
online: 28 Jan 2014.
To cite this article: Lei Mei-Ling , Xi Hai-Ling , Shen Ming , Yuan Ling & Han Shi-Tong (2014) Reaction
Products and Process of 2-Chloroethyl Ethyl Sulfide in Microemulsion Media, Phosphorus, Sulfur, and
Silicon and the Related Elements, 189:3, 387-393, DOI: 10.1080/10426507.2013.820728
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Phosphorus, Sulfur, and Silicon, 189:387–393, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.820728
REACTION PRODUCTS AND PROCESS
OF 2-CHLOROETHYL ETHYL SULFIDE
IN MICROEMULSION MEDIA
Lei Mei-Ling,1,2 Xi Hai-Ling,1,2 Shen Ming,3 Yuan Ling,1,2
and Han Shi-Tong1,2
1Research Institute of Chemical Defense, P.O. Box 1043, Beijing 102205, China
2State Key Laboratory of NBC Protection for Civilian, P.O. Box 1043, Beijing
102205, China
3College of Chemistry & Chemical Engineering, Yangzhou University, No. 180
Siwangting Road, Yangzhou, Jiangsu 225002, China
GRAPHICAL ABSTRACT
2–HEES
S
2–CEES
Cl
_
+H2O
S
Cl
OH
H
S
S
S
OH
Cl
+H2O
S
S
OH
Cl
S
S
EHT
ECT
Abstract The reaction of 2-chloroethyl ethyl sulfide was investigated in several oil-in-water
microemulsions. The reaction products were identified by GC/MS, NMR, and LC/MS, and the re-
action process was monitored by measuring peak height of reaction products and 2-chloroethyl
ethyl sulfide with time by 1H NMR spectroscopy. The result showed that 2-chloroethyl ethyl
sulfide degraded to 2-hydroxyethyl ethyl sulfide, cyclic sulfonium ion, open chain sulfonium
chloro ion and sulfonium hydroxyl ion, and the reaction proceeded via a cyclic sulfonium
ion intermediate. Based on the NMR results, a pseudoternary model was established for the
reaction process of 2-chloroethyl ethyl sulfide in microemulsion.
Keywords 2-Chloroethyl ethyl sulfide; reaction; microemulsion; sulfonium ions
Received 18 March 2013; accepted 26 June 2013.
We thank Huang Gui-lan of our institute for correcting and improving this paper.
Address correspondence to Xi Hai-Ling, Research Institute of Chemical Defense, P.O. Box 1043 Beijing
102205, China. E-mail: fhlingling@sohu.com
387

388
L. MEI-LING ET AL.
INTRODUCTION
Microemulsions contain both a polar component (water) and a nonpolar component
(oil); they are capable of solubilizing a wide spectrum of substances.1, 2 A microemulsion
is one of the reaction media that make water and water-soluble components react with
water-insoluble organic chemicals. Mustard (ClCH2CH2SCH2CH2Cl) and its analog, 2-
chloroethyl ethyl sulfide (2-CEES) (CH3CH2SCH2CH2Cl), are extreme insoluble in the
water. The solubility of these compounds is increased when water is mixed with acetone
or ethanol. Usually, 2-CEES was utilized as a simulant for mustard in research because of
their similar structures and the less toxicity of 2-CEES. The reactions of 2-CEES in water,
water/acetone, and water/ethanol mixtures have been investigated.3–8 These studies indicate
that the reaction mechanism is the same as shown in Figure 1. The first step is the formation
of a cyclic sulfonium cation via the intramolecular assistance of the neighboring sulfur; the
cyclic sulfonium cation then reacts quickly with water to form 2-hydroethyl ethyl sulfide
(2-HEES), or reacts with 2-CEES to form (CH3CH2)(CH2CH2Cl)S+(CH2CH2SCH2CH3)
product (ECT), or continue to react with the initial product 2-HEES to form (CH3CH2)
(CH2CH2OH)S+(CH2CH2SCH2CH3) product (EHT). In the reactions, the formation of the
cyclic sulfonium ion is the predominant step that controls the rate of reaction.
Microemulsions have been used to decontaminate classical warfare agents including
mustard; however, no publication indicated the reaction of 2-CEES in a microemulsion
media until now. A clear reaction mechanism is helpful for designing and using a mi-
croemulsion system. This paper investigates the mechanism and the reaction process of
2-CEES in the O/W (oil-in-water) microemulsion media by GC/MS, NMR, and LC/MS.
RESULTS AND DISCUSSION
Identification of Degradation Products
The dichloromethane extract and silylation sample were analyzed by GC/MS. The
structures, retention time, and principal EI ions of the reaction products of 2-CEES are
illustrated in Table 1. Six related compounds were identified and the major product was
2-HEES, based on the chromatogram peak area. Being 2-CEES and 2-HEES were co-eluted
on a DB-5MS column, 2-HEES was identified by TMS derivatization.
The peaks of interest overlap strongly with the peaks of microemulsion compositions
in H NMR spectra. ECT, EHT, and 2-HEES were identified by comparing the spectrum
1
Figure 1 Hydrolysis mechanism of 2-CEES.4

REACTION PRODUCTS AND PROCESS OF 2-CEES IN ME
389
Table 1 Related information for reaction products of 2-CEES identified by GC–MS
No.
1
Compound
Retention time (min)
Principal EI ions (m/z)
60,73,89,103,163,178
TMS derivative of 2-hydroethyl ethyl
sulfide
RT = 7.63
2
3
Vinyl ethyl sulfide
TMS derivative of 2-hydroethyl vinyl
sulfide
RT = 2.55
RT = 7.52
27,45,59,60,76,88
45,73,103,116,161,176
4
5
6
2-bromoethyl ethyl sulfide
1,2-diethylthioethane
(2-ethylthio)ethylene butyl ether
RT = 6.85
RT = 9.55
RT = 9.22
61,75,89,107,168
47,60,61,75,89,121,150
41,57,61,75,89,106,162
of a microemulsion sample with the spectra of 50% acetone/50% water sample9 or the
spectrum of 100% water sample.3 The 1H NMR spectra obtained from the reaction process
(8 min) of 2-CEES in microemulsion are shown in Figure 2. 1H chemical shifts of related
compounds are assigned. The characteristic resonances for the open chain sulfonium ion
are observed at δ4.19, δ4.01 (for ECT), and δ4.17 (for EHT). The –SCH2– triplet from
CH3CH2SCH2CH2OH (2-HEES) is at δ2.82.
The sulfonium ions are detected specifically by high-resolution LC/ESI-MS. LC/MS
data at m/z 213.0529, m/z 195.0882, and m/z 89.0499 ions correspond with the formulas
C8H18S2Cl, C8H19OS2, and C4H9S, respectively. These formulas are consistent with the
ECT, EHT, and cyclic sulfonium ion. These results are also supported by the literature.10, 11
In summary, 2-HEES was identified by GC/MS and NMR. Sulfonium ions can
be identified by NMR spectroscopy, while LC/ESI-MS confirmed ECT, EHT, and cyclic
Figure 2 1H NMR spectra obtained from the reaction of 2-CEES in the microemulsion.

390
L. MEI-LING ET AL.
Figure 3 Hydrolysis of 2-CEES in o/w microemulsion. Identified 2-CEES with left intensity axis, and identified
2-HEES, EHT and ECT with right intensity axis.
sulfonium ion. The hydrolysate 2-HEES, ECT, and EHT are the major products during
2-CEES reaction in microemulsion.
Reaction Process
1H NMR spectra were acquired periodically to monitor reaction progress and hydrol-
ysis products. The plots of peak height of hydrolysis products and 2-CEES versus time are
showed in Figure 3.
Figure 3 shows that 2-HEES, ECT, and EHT are all exist at the start of observation.
This means that the reaction is quick. With the reaction continued, 2-HEES increased in
the period of 0–30 min, after 30 min, it decreased. ECT increased during 0–40 min and the
intensity was stable until 60 min, and then decreased. EHT shows an increasing trend during
the observation period. As listed in Table 1, 2-bromoethyl ethyl sulfide is produced in the
microemulsion (the bromide ion comes from CTAB). Like the bromide ion, chloride ion
is also a strong nucleophile, so it can react with the cyclic sulfonium ion to form 2-CEES.
The hydrolysis of 2-CEES is a reversible process. These results proved the hydrolysis
mechanism of 2-CEES in O/W microemulsion is the same as shown in Figure 1.
The mechanism and the process of hydrolysis of 2-CEES in the O/W microemulsion
can be described with a pseudoternary model shown in Figure 4. Each of the components
has its own residence site in the reaction process.12 2-CEES resides in both the interface
phase and the oil phase of O/W microemulsion during the reaction process. The cyclic
sulfonium ion forms in the interface phase. A subsequent reaction of the cyclic sulfonium
ion with water and 2-CEES proceeds in the interface or water phases to form 2-HEES and
ECT. Water-soluble 2-HEES and ECT are converted to EHT in the water phase.
In summary, the mechanism of the hydrolysis of 2-CEES in O/W microemulsion is
the same as in water, water/acetone, and water/ethanol mixtures. But the hydrolysis process
of 2-CEES in O/W microemulsion is different from them due to the particular structure of

REACTION PRODUCTS AND PROCESS OF 2-CEES IN ME
391
Figure 4 Pseudoternary reaction model of 2-CEES in O/W microemulsion.
the microemulsion. The interface phase made up of CTAB and 1-butanol is the predominant
reaction zone, while the hydrolysis of 2-CEES in water, water/acetone, and water/ethanol
accomplishes on their contact interface.
CONCLUSIONS
This research presented a same hydrolysis mechanism of 2-CEES in the O/W mi-
croemulsion as in water, water/acetone, and water/ethanol mixture, which hydrolysis pro-
ceeds via a cyclic sulfonium ion intermediate. However, the hydrolysis process of 2-CEES
in O/W microemulsion is different from them. Due to the particular structure of the mi-
croemulsion, it offers a huge surface area for water-insoluble 2-CEES contacting with
water to produce cyclic sulfonium ion. Being the formation of cyclic sulfonium ion is the
predominant step that controls the reaction, it suggests that a bigger interface might result
in a faster rate of reaction.
EXPERIMENTAL
Chemicals
CTAB, 1-butanol, n-hexane, dichloromethane for analytical grade were obtained from
Beijing Chemical Reagent Co., Ltd. 2-CEES (98%) and BSTFA (N,O-bis-(trimethylsilyl)

392
L. MEI-LING ET AL.
trifluoroacetamide) (98%) were purchased from ACROS. Methanol for HPLC grade was
obtained from Honeywell. Deuterium oxide (≥99.8%) and DSS were purchased from CIL.
The double-distilled water was obtained from our laboratory.
Instrumentation
Capillary column GC–MS in the EI mode was performed using a Thermo DSQ II
mass spectrometer equipped with a TRACE gas chromatography. A 30 m × 0.25 mm ×
0.25 μm (length × i.d. × film thickness) J&W DB-5MS capillary column was used for
analysis with the following temperature program: 40◦C (1 min), then 10◦C/min to 280◦C
(3 min). The carrier gas was high-purity helium at a constant flow rate of 1 mL/min.
The following parameters were used: injector temperature, 250◦C; interface temperature,
250◦C; source temperature, 200◦C; electron energy, 70 eV; emission current, 100 μA; and
the scanned mass range m/z 27–500.
LC/MS in the ESI mode was performed using a Agilent 6520 Accurate-Mass Q-TOF
equipped with a Waters Model 616 LC pump and a Zorbax 150 × 0.32 mm i.d. C18 SB
(5 μm) packed fused silica capillary column. 50% methanol/50% water (v/v) was used
as the mobile phase with a flow rate of 0.1 mL/min. The scanned mass ranges were m/z
65–550.
1H NMR analyses were performed with a Varian Unity Plus 600 Fourier transform
NMR spectrometer system equipped with a variable temperature controller and autox
dual broadband probes. Chemical shifts were referenced to external DSS. The following
parameters were used: spectrometer frequency, 599.778 MHz; and testing temperature,
25◦C.
Experimental Methods
The different microemulsion media were chosen in accordance with the phase dia-
gram.9 The reactions of 2-CEES in several microemulsion systems were studied. Because
the result is similar, the microemulsion which is comprised of 85% w/w water, 5.2% w/w
CTAB, 7.8% w/w n-butanol, and 2% w/w n-hexane was used in this paper.
2-CEES (10 μL) was dissolved in microemulsion (1 mL) with ultrasonic vibration
for 30 s, and then reacted for 30 min at 25◦C prior to solvent extraction. The microemul-
sion sample was extracted by dichloromethane (3 × 1 mL) with ultrasonic vibration for
30 s. The extract was dried by adding sodium thiosulfate and then concentrated to 1 mL
under a gentle stream of nitrogen. The dichloromethane solution was analyzed by GC/MS.
Trimethylsilyl (TMS) derivatization was performed following solvent extraction of the mi-
croemulsion sample. The pH of the microemulsion fraction was adjusted to 10 with 10%
(w/w) NaOH and evaporated to dryness on a rotary evaporator. The residue was dissolved
in a mixture of BSTFA in acetonitrile (1 mL, 1:9) by ultrasonic vibration for 5 min and
the mixture was heated at 70◦C for 30 min. The derivatized sample was also analyzed by
GC/MS.
2-CEES (10 μL) was dissolved in microemulsion (1 mL, here, D2O was used)
1
by ultrasonic vibration for 30 s. H NMR spectra were acquired periodically to monitor
reaction progress and product formation. The intensities of 2-CEES and reaction products
were expressed with the NMR peak height.

REACTION PRODUCTS AND PROCESS OF 2-CEES IN ME
393
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