Oxidation of a mustard gas analogue using an aldehyde/O2 system catalyzed by V-doped mesoporous silica

Article abstract of DOI:10.1021/ja8056166

Vanadium-doped mesoporous silica was shown to be an effective heterogeneous catalyst for the oxidation of a mustard gas analogue, 2-chloroethyl ethyl sulfide (CEES), in the presence of an aldehyde and molecular oxygen. The oxidation was shown to involve a radical mechanism, which was indicated by the appearance of an induction period when the reaction occurred in the presence of a free radical scavenger. The reaction was initially selective for the oxidation of CEES to the sulfoxide, CEESO, although oxidation of the sulfoxide to the sulfone occurred once all the CEES had been oxidized. Chemical analysis indicated that V species did not leach from the silica support when the reaction was performed in the fluorinated solvent HFE-7100. Copyright

Full text of DOI:10.1021/ja8056166

Published on Web 09/10/2008
Oxidation of a Mustard Gas Analogue Using an Aldehyde/O2 System
Catalyzed by V-Doped Mesoporous Silica
Stephanie R. Livingston and Christopher C. Landry*
UniVersity of Vermont, Department of Chemistry, 82 UniVersity Place, Burlington, Vermont 05405
Received July 18, 2008; E-mail: christopher.landry@uvm.edu
Table 1. Oxidation of CEES by 1 in the Presence of Aldehydes/
Oxidation of the chemical warfare agent mustard gas, bis(2-
chloroethyl) sulfide, using strong oxidants is one way in which
mustard gas decontamination can be accomplished.1,2 The desired
product is the partially oxidized, nontoxic sulfoxide rather than the
fully oxidized, toxic sulfone.3 Although many catalysts exist that
can perform sulfide oxidation using hydrogen peroxide or tert-butyl
hydroperoxide, only a few catalytic systems directly use molecular
O2 as the oxidant under ambient conditions.4 Another possibility
that has not been explored extensively for mustard gas oxidation
is the generation of oxidants in situ from O2. For example, aldehydes
are known to undergo autoxidation by a free radical chain
mechanism that involves the oxidation of the aldehyde to the
corresponding acyl radical.5 The acyl radical then reacts with O2
to form the corresponding peracid, which is capable of oxidizing
an additional aldehyde molecule to the corresponding acid. Although
the autoxidation of aldehydes occurs at ambient conditions, the
reaction rate can be increased by the use of metal catalysts.6 Other
species present in the reaction solution can also be oxidized by the
generated peracid, resulting in the oxidation of sulfides to sulfoxides
and sulfones.7
a
O2
equiv of
aldehyde
aldehyde
time (min)b
acetaldehyde
acetaldehyde
acetaldehyde
trimethylacetaldehyde
trimethylacetaldehyde
trimethylacetaldehyde
propionaldehyde
propionaldehyde
propionaldehyde
10
>1440c
50
20
neatd
10
15
>1440c
35
20
neatd
10
15
45
15
10
20
neatd
a Reaction conditions: CEES (42.9 µmol), aldehyde (429 or 858
µmol), 1 (20 mg) in HFE-7100 (3.0 mL), 21 °C. b Time required for
100% conversion of CEES. c An induction period was observed prior to
CEES oxidation. d Reactions performed in neat aldehyde (3.0 mL).
Supported vanadium oxide catalysts are commonly used in the
oxidation of organic substrates.8 We have recently shown that
vanadium oxide supported on acid prepared mesoporous spheres
(V-APMS) is an effective catalyst for the oxidation of the mustard
gas analogue 2-chloroethyl ethyl sulfide (CEES) by tert-butyl
hydroperoxide.9 We now report the use of V-APMS as a catalyst
in the room temperature oxidation of CEES using molecular oxygen
from the air in the presence of aldehydes (eq 1).
Figure 1. Effect of hydroquinone on CEES oxidation in propionaldehyde
(25 equiv)/CH3CN, catalyzed by 1 at 21 °C.
equipment contaminated with mustard gas without causing damage.
The results given in Table 1 show that CEES oxidation occurred
most rapidly with propionaldehyde/O2. Interestingly, the oxidation
rate increased as a function of time, and a long induction period
was observed with 10 equiv of propionaldehyde and trimethylac-
etaldehyde. This behavior has been observed in similar reaction
systems and has been attributed to the ability of sulfides to act as
free radical scavengers, inhibiting the oxidation by forming radical
species with low reactivity.7b To confirm that radicals were also
present in the propionaldehyde/O2 system, we repeated the reaction
in propionaldehyde (25 equiv)/CH3CN in the presence of hydro-
quinone, which would be expected to inhibit a free radical reaction
until it has been consumed.12,13 CH3CN was used for these
experiments due to the insolubility of hydroquinone in HFE-7100.
An induction period was observed for the reactions that contained
hydroquinone (0.02 and 0.05 equiv with respect to CEES) that
lengthened in duration as the hydroquinone concentration increased
(Figure 1). Similar results were obtained in the absence of CEES,
indicating that the oxidation of aldehydes by O2, catalyzed by
V-APMS with a vanadium loading of 0.6 wt% (1) was prepared
via wet impregnation of APMS with NH4VO3 following a previ-
ously described procedure.10 The surface areas of undoped APMS
and 1 were 888 and 794 m2/g; the lack of XRD peaks corresponding
to crystalline V2O5 indicated that isolated VO4 tetrahedra were the
predominant vanadium oxide species.10
Initial studies of the room temperature oxidation of CEES in
neat acetaldehyde, trimethylacetaldehyde, and propionaldehyde
showed that the oxidation of CEES occurred even in the absence
of a catalyst, resulting in 100% conversion of CEES within 75 min.
This oxidation is attributed the autoxidation of acetaldehyde at
ambient temperatures as described above.11,12 In the presence of
1, complete conversion of CEES was observed in less than 15 min,
indicating the catalytic nature of V-APMS.
We also studied the oxidation of CEES catalyzed by 1 in a system
of aldehyde and the fluorinated solvent HFE-7100 (C4F9OCH3).
HFE-7100 is of practical interest because it is nontoxic and
nonflammable and can be used to rinse polymeric and electronic
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13214 J. AM. CHEM. SOC. 2008, 130, 13214–13215
10.1021/ja8056166 CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
determined by chemical analysis as synthesized, after stirring in
pure aldehydes, and after stirring in HFE-7100 containing 10 equiv
of aldehydes. It was found that between 5 and 41 wt% V leached
from the support in the neat aldehydes after 1 h. However, there
was no significant V leaching in HFE-7100, indicating that under
these conditions V-APMS acts as a heterogeneous catalyst, not a
source of solvated V, and it could easily be recovered by filtration
for repeated use.
In summary, we have shown that CEES can be oxidized under
ambient conditions using several aldehydes and O2 from air, with
V-APMS acting as a heterogeneous catalyst for both the in situ
generation of the corresponding peracid and the oxidation of CEES
and CEESO by the peracid. Although this work was limited to the
oxidation of CEES and aldehydes, additional work may reveal other
applications of V-APMS/aldehyde/O2 systems in aerobic oxidations.
Figure 2. Concentration of CEES, CEESO, and CEESO2 for 1 catalyzed
oxidation of CEES by propionaldehyde (10 equiv)/O2 in HFE-7100 at 21
°C.
V-APMS, occurs by a radical mechanism and that radicals are
present in the CEES oxidation reactions.
Acknowledgment. This work was funded by the Army Research
Office under Grant No. W911NF-06-1-0263.
Figure 2 shows the products formed during CEES oxidation with
1 in the propionaldehyde/HFE-7100 system. CEES was initially
exclusively oxidized to the corresponding sulfoxide (CEESO), and
formation of the sulfone (CEESO2) only occurred after CEES had
been completely consumed. This is consistent with a two-step
oxidation process in which CEESO2 is formed from CEESO, not
directly from CEES.1 It also indicates that the oxidation of the
sulfide is faster than the sulfoxide, which is a consequence of the
reduced nucleophilicity of the sulfur atom in the sulfoxide.14
There are two possible capacities in which V-APMS could act
as a catalyst in this reaction: (1) the oxidation of the aldehyde to
the corresponding peracid by O2 and (2) the oxidation of CEES
and CEESO by the peracid. The possibility that V-APMS catalyzed
the oxidation of propionaldehyde was studied by quantifying the
amount of propionic acid formed in the presence and absence of 1
in HFE-7100. After 60 min, the propionic acid concentration was
0.05 M in the presence of 1 and the acid concentration was only
0.002 M when it was absent, showing that V-APMS was catalyzing
the oxidation of propionaldehyde to the acid. The ability of
V-APMS to catalyze the oxidation of CEES by a peracid was also
studied by reacting CEES and peracetic acid in the presence and
absence of 1 in HFE-7100. In either case, when equimolar amounts
of peracetic acid and CEES were used, the reaction was extremely
rapid; however the product distributions were measurably different.
In the absence of 1, the conversion of CEES was 97% after 1 min,
and the product ratio of CEESO to CEESO2 was 24:1. When 1
was present, CEES conversion was only 67% after 1 min, but the
product ratio was now 1.9:1. The increased concentration of
CEESO2 indicates that the role of the catalyst is not exclusively to
form the peracid; it also participates in sulfide and sulfoxide
oxidations. The amount of sulfone in the catalyzed reaction indicated
that the catalyst enhanced the oxidation of both substrates. The
formation of CEESO2 was found to be dependent on the initial
peracid concentration; decreasing the concentration of peracetic acid
increased the selectivity for CEESO. This accounts for the initial
sulfoxide selectivity observed with 1 (Figure 2); the concentration
of peracid remained low, since it was being generated and then
consumed in the oxidation of CEES.
Supporting Information Available: Experimental details and
characterization. This material is available free of charge via the Internet
at http://pubs.acs.org.
References
(1) Yang, Y.-C.; Baker, J. A.; Ward, J. R. Chem. ReV. 1992, 92, 1729.
(2) Popiel, S.; Witkiewicz, Z.; Szewczuk, A. J. Hazard. Mater. 2005, B123,
94.
(3) (a) Hirade, J.; Ninomiya, A. J. Biochem. 1950, 37, 19. (b) Wagner, G. W.;
Yang, Y.-C. Ind. Eng. Chem. Res. 2002, 41, 1925.
(4) (a) Boring, E.; Geletii, Y. V.; Hill, C. L. J. Mol. Catal. A: Chem. 2001,
176, 49. (b) Okun, N. M.; Anderson, T. M.; Hill, C. L. J. Mol. Catal. A:
Chem. 2003, 197, 283. (c) Okun, N. M.; Tarr, J. C.; Hilleshiem, D. A.;
Zhang, L.; Hardcastel, K. I.; Hill, C. L. J. Mol. Catal. A: Chem. 2006,
246, 11. (d) Roeker, L.; Dobson, J. C.; Vining, W. J.; Meyer, T. J. Inorg.
Chem. 1987, 26, 779. (e) Huynh, M. H. V.; Withan, L. M.; Lasker, J. M.;
Wetzler, M.; Mort, B.; Jameson, D. L.; White, P. S.; Takeuchi, K. J. J. Am.
Chem. Soc. 2003, 125, 308.
(5) McNesby, J. R.; Heller, C. A., Jr. Chem. ReV. 1954, 54, 325.
(6) (a) Chen, L.-C.; Chou, T.-C. Ind. Eng. Chem. Res. 1994, 33, 2523. (b)
Sloboda-Rozner, D.; Neimann, K.; Neumann, R. J. Mol. Catal. A 2007,
262, 109. (c) Kholdeeva, O. A.; Vanina, M. P.; Timofeeva, M. N.;
Maksimovskaya, R. I.; Trubitsina, T. A.; Melgunov, M. S.; Burgina, E. B.;
Mrowiec-Bialon, J.; Jarzebski, A. B.; Hill, C. L. J. Catal. 2004, 226, 363.
(d) Suprun, W. Y.; Kiebling, D.; Machold, T.; Papp, H. Chem. Eng. Technol.
2006, 29, 1376. (e) ten Brink, G.-J.; Arends, I. W. C. E.; Shledon, R. A.
Chem. ReV. 2004, 104, 4105.
(7) (a) Vincent, S.; Lion, C.; Hedayatullah, M.; Challier, A. Phosphorus, Sulfur,
and Silicon 1994, 92, 189–192. (b) Venkateshwar Rao, T.; Sain, B.; Kumar,
K.; Murthy, P. S.; Prasada Rao, T. S. R.; Joshi, G. C. Synth. Commun.
1998, 28, 319–326. (c) Song, G.; Wang, F.; Zhang, H.; Lu, X.; Wang, C.
Synth. Commun. 1998, 28, 2783–2787. (d) Imagawa, K.; Nagata, T.;
Yamada, T.; Mukaiyama, T. Chem. Lett. 1995, 335. (e) Khavrutskii, I. V.;
Maksimov, G. M.; Kholdeeva, O. A. React. Kinet. Catal. Lett. 1999, 66,
325. (f) Murata, S.; Murata, K.; Kidena, K.; Nomura, M. Energy and Fuels
2004, 18, 116.
(8) Weckhuysen, B. M.; Keller, D. E. Catal. Today 2003, 78, 25.
(9) Ringenbach, C. R.; Livingston, S. R.; Kumar, D.; Landry, C. C. Chem.
Mater. 2005, 17, 5580–5586.
(10) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic
Compounds; Academic Press: New York, 1981; pp 359-362.
(11) Stahmann, M. A.; Bergmann, M. J. Org. Chem. 1946, 11, 586.
(12) Emanuel, N. M.; Knorre, D. G. Chemical Kinetics; Halstead Press: New
York, 1873; pp 324-326.
(13) (a) Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Nature 1999, 398,
227. (b) Zhang, W.; Muir, D. M.; Singh, P. Hydrometallurgy 2000, 58,
117.
(14) Lewis, S. N. In Oxidation: Techniques and Applications in Organic
Synthesis; Augustine, R. L., Ed.; Marcell Dekker, Inc.: New York, 1969;
pp 244-247.
(15) Arends, I. W. C. E.; Sheldon, R. A. Appl. Catal. A: General 2001, 212,
175.
Finally, leaching of V from solid substrates has also been a recent
concern.15 To examine this effect, the amount of V in 1 was
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