The Unexpected Role of SeVI Species in Epoxidations with Benzeneseleninic Acid and Hydrogen Peroxide

Article abstract of DOI:10.1002/anie.201913566

Benzeneperoxyseleninic acid has been proposed as the key intermediate in the widely used epoxidation of alkenes with benzeneseleninic acid and hydrogen peroxide. However, it reacts sluggishly with cyclooctene and instead rapidly decomposes in solution to

Full text of DOI:10.1002/anie.201913566

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Accepted Article
Title: The Unexpected Role of Se(VI) Species in Epoxidations with
Benzeneseleninic Acid and Hydrogen Peroxide
Authors: Thomas George Back, Kai N Sands, Emerita Mendoza
Rengifo, Graham N George, Ingrid J Pickering, and Benjamin
S Gelfand
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Angewandte Chemie International Edition
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COMMUNICATION
The Unexpected Role of Se(VI) Species in Epoxidations with
Benzeneseleninic Acid and Hydrogen Peroxide
[a]
[b]
[b]
[b]
Kai N. Sands, Emerita Mendoza Rengifo, Graham N. George, Ingrid J. Pickering, Benjamin S.
[a]
[a]
Gelfand and Thomas G. Back*
Abstract: Benzeneperoxyseleninic acid has been proposed as the
key intermediate in the widely used epoxidation of alkenes with
benzeneseleninic acid and hydrogen peroxide. However, it reacts
sluggishly with cyclooctene and instead rapidly decomposes in
solution to a mixed selenonium-selenonate salt that was identified by
In 1987, Syper and Młochowski[7] reported that dissolution of
benzeneseleninic acid 1 in 30% hydrogen peroxide resulted in the
precipitation of the corresponding peroxyseleninic acid 3, which
hydrolyzed back to the original seleninic acid when dissolved in
water. When 3 was heated in acetonitrile solution at 80 ºC,
isomerization to 4 was reported, via the proposed selenadioxirane
5, which had been previously suggested as a potential alternative
intermediate in the epoxidation of cyclooctene by Hori and
Sharpless[3b] (Scheme 1). More recently, Orian et al.[8] employed
NMR and computational methods to study the hydrogen peroxide
oxidation of diphenyl diselenide to 1 and then to the peroxy acid
3, but did not address the possible formation of the selenonic acid
4. In contrast to seleninic acids, selenonic acids have been
relatively little studied.[9] We now present evidence that, contrary
to previous assumptions, 3 plays only a secondary role in a
representative epoxidation of cyclooctene conducted with 1 and
hydrogen peroxide, while a selenium (VI) species is the principal
oxidant.
77
x-ray absorption and Se NMR spectroscopy, as well as by single
crystal x-ray diffraction. This process includes selenoxide
a
elimination of the peroxyseleninic acid with liberation of oxygen and
additional redox steps. The salt is relatively stable in the solid state,
but generates the corresponding selenonic acid in the presence of
hydrogen peroxide. The selenonic acid is inert towards cyclooctene
on its own; however, rapid epoxidation occurs when hydrogen
peroxide is added. This shows that the selenonic acid must first be
activated through further oxidation, presumably to the heretofore
unknown benzeneperoxyselenonic acid. The latter is the principal
oxidant in this epoxidation.
Benzeneseleninic acid (1) and anhydride (2), as well as their
congeners, are widely utilized oxidants in a variety of synthetic
transformations.[
1,2]
O
Of special interest are reactions that are
O
conducted with stoichiometric or catalytic seleninic acids, or their
precursor diselenides, in the presence of hydrogen peroxide.
+
H
+ H O
PhSe-OOH
2
PhSe-OH
2O2
1
3
These include epoxidations and dihydroxylations[3a,4] of alkenes,
[
3]
Baeyer-Villiger reactions,[5] dehydrogenations of alcohols and
∆, MeCN
ketones[6] and numerous other processes.[1,2] It has been widely
accepted that peroxyseleninic acids, such as 3, are the active
oxidants, although there is little evidence to support this
assumption or to exclude the possibility that selenonic acid 4 or
other Se(VI) species are involved.
OH
O
O
Se
PhSe-OH
Ph
O
O
4
5
O
O
O
O
O
Scheme 1. Syper and Mlochowski’s preparation and proposed isomerization of
3.
PhSe-OH
PhSe-O-SePh
PhSe-OOH PhSe-OH
1
2
3
O
4
Figure 1. Structures of benzeneseleninic acid (1) and several of its congeners.
First, geometry optimizations (see the Supporting
Information for details) indicated that the selenonic acid 4 is more
-1
stable than its peroxyseleninic acid isomer 3 by 28.8 kcal mol .
Thus, we attribute the preparation of the less stable 3 from 1 and
aqueous hydrogen peroxide to its equilibration and precipitation
from the reaction medium. Attempts at geometry optimization of
the highly strained intermediate 5 failed because it reverted to its
valence bond isomer 4, but single point energy calculations on
[
a]
b]
K. N. Sands, Dr. B. S. Gelfand and Prof. Dr. Thomas G. Back
Department of Chemistry
University of Calgary
2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4
E-mail: tgback@ucalgary.ca
-1
several trial conformations produced energies >100 kcal mol
higher than those of 4. We therefore propose the
peroxyselenurane 6 as a possible alternative, dehydration of
which could lead to either 3 or 4, thereby providing a means for
their interconversion (Scheme 2), favouring the more stable 4 in
solution.
[
E. Mendoza Rengifo, Prof. Dr. G. N. George and Prof. Dr. Ingrid J.
Pickering
Department of Geological Sciences
University of Saskatchewan
114 Science Place
Saskatoon, Saskatchewan, Canada, S7N 5E2
ORCID No. for T.G. Back: https://orcid.org/0000-0002-3790-1422
Supporting information for this article is given via a link at the end of
the document.
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COMMUNICATION
O
and product 7 was obtained in 63% yield (Scheme 3). The same
product was obtained within 40 min at room temperature.
Moreover, the melting point attributed to the selenonic acid 4 (144
ºC) reported by Syper and Młochowski,[7] is almost identical to that
PhSe-OOH
-
H
2O
3
H
O
OH
Se
O
H O
2
2
of
7 (142-144 ºC). These experiments indicate that the
PhSe-OH
Ph
O OH
peroxyseleninic acid 3 is relatively stable in the solid state, but
labile in solution, rapidly affording salt 7 and not the selenonic
acid 4 as previously reported.[7]
1
[14]
6
-
HOH
O
PhSe-OH
O
4
Scheme 2. Alternative formation and isomerization of 4 from 3.
In further investigations, seleninic acid 1 was dissolved in
:CD OD (95:5) and treated with a slight excess (1.15 equiv)
CDCl
3
3
of 30% hydrogen peroxide at room temperature. A rapid reaction
accompanied by gentle gas evolution occurred and the 77Se NMR
spectrum (recorded over ca. 40 min) revealed a new signal at
[10]
1026 ppm, compared to 1173 ppm (CDCl
3
)
for 1. Furthermore,
Figure 2. ORTEP diagram of 7. The disorder in the selenonate anion portion is
due to rotational freedom of the aryl ring, resulting in nonparallel alignment of
the aryl rings in alternating molecules in the unit cell.
when the NMR experiment was repeated at higher concentration
with the UDEFT protocol,[11] an additional weaker peak appeared
at 1218 ppm. Thus, while a new product(s) was clearly produced,
the paucity of existing Se NMR data for peroxyseleninic and
selenonic acids precluded unequivocal assignment of these
peaks to 3, 4 or other oxidized species.
Since the isomeric peroxyseleninic and selenonic acids 3
and 4, respectively, have different oxidation states, a sample of
the product was prepared from the treatment of benzeneseleninic
acid (1) with hydrogen peroxide. It was evaporated under vacuum
and the residue was subjected to x-ray absorption spectroscopy
7
7
O
O
3
0% H O
2
2
PhSeOH
1
PhSe-OOH
H
O
2
3
path a
path b
0
.5 equiv H O
2 2
MeCN
CHCl -MeOH
3
(
XAS) at the Stanford Synchrotron Radiation Lightsource (SSRL)
2.2 equiv
O
O
HO
HO
H
in order to obtain additional structural information (for details and
an illustrative Figure, see the Supporting Information). Thus, the
selenium K-edge x-ray absorption near-edge spectrum of the
above sample was compared with the spectrum of unreacted 1.
The latter displayed a peak energy of 12663.4 eV which is
characteristic of Se (IV), while two peaks were observed in the
sample that was reacted with hydrogen peroxide. The lower
energy peak was seen at 12662.7 eV, while the higher energy
peak appeared at 12666.4 eV. The 12662.7 eV peak is consistent
with an Se (IV) species like peroxyseleninic acid 3, while the
2O2
PhSe-O
O
SePh
PhSe-OH
MeCN
7
O
4
Scheme 3. Formation and further oxidation of selenonium-selenonate salt 7.
In order to assign the 77Se NMR signals at 1026 and 1217
ppm of 7 unequivocally to its two respective selenium atoms, 1
was treated with trifluoroacetic acid and the 77Se NMR spectrum
of the resulting selenonium ion 8 produced a signal at 1215 ppm.
This closely correlates with the signal at 1218 ppm in 7 and
permits its assignment to the selenonium moiety, while the peak
at 1026 ppm is therefore attributed to the selenonate anion
1
2666.4 eV peak indicates an Se(VI) species such as selenonic
acid 4.[
12]
Thus, unexpectedly, these results indicated that both
Se(IV) and Se(VI) oxidation states were present in the oxidized
sample subjected to XAS analysis.
Crystals of the product obtained by the similar oxidation of
1) with hydrogen peroxide proved suitable for x-ray diffraction
(
Figure 3).
The formation of the stable salt 7 from 1 and hydrogen
(
(
see Figure 2 and the Supporting Information). To our surprise,
the x-ray structure[ showed that the product was neither 3 nor 4,
13]
peroxide, as shown in path a of Scheme 3, is easily rationalized.
As selenonic acid 4 is produced via isomerization of the initially
formed peroxyseleninic acid 3, as shown in Scheme 2, it
protonates the remaining amphoteric[15] starting material 1,
resulting in the formation of salt 7. This reaction is complete when
but instead the selenonium-selenonate salt 7, formed by
protonation of 1 by an equimolar amount of the selenonic acid 4.
The presence of two selenium atoms in different oxidation states
was clearly evident and consistent with the 77Se NMR and XAS
results. Furthermore, 7 was isolated in 74% yield when only 0.5
equiv of hydrogen peroxide was employed in the oxidation of 1.
When the peroxyseleninic acid 3 was heated in acetonitrile in the
absence of hydrogen peroxide, gas evolution was again observed
5
0% of 1 is oxidized, thus requiring only 0.5 equiv of hydrogen
peroxide. On the other hand, the transformation of 3 directly to 7
in the absence of hydrogen peroxide (path b of Scheme 3), is less
obvious, as both the selenonic acid 4 and seleninic acid 1 are
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COMMUNICATION
(
10) in the absence of hydrogen peroxide at room temperature in
O
O
PhSe-O
O
HO
HO
dichloromethane in separate control experiments. GC analysis
revealed no detectable conversion to the corresponding epoxide
1
PhSe-OOH
SePh
7
1, even after several hours. When the reaction was similarly
Reference Compound
repeated with 3, epoxidation reached only 19% conversion in 1 h
and did not proceed further. Salt 7 was produced simultaneously
in 62% isolated yield and was identified by comparison of its m.p.
and 77Se NMR spectrum with those of an authentic sample. The
relative amounts of the epoxide and the salt indicate that the
pathway to 7 proceeds at least 3.3 times faster than the
epoxidation and explains why direct epoxidation with 3 is relatively
ineffective. Furthermore, when the epoxidation was repeated with
seleninic acid 1 in the presence of one equiv of hydrogen peroxide,
a more rapid reaction ensued, but afforded only 50% of the
epoxide. When 7 was employed under similar conditions, epoxide
formation was rapid, requiring 3.5 h to reach ca. 82% conversion,
after which no further reaction was observed (Scheme 5 and
Figure 4a). The even more striking behaviour of 4 is illustrated in
Figure 4b, where no reaction was observed after 2 h, but upon
addition of 1 equiv of hydrogen peroxide, the epoxide 11 was
formed in 86% yield after only one additional hour.
HO
CF CO
SePh
3
2
HO
214.5 ppm
1
8
1
300 1250 1200 1150 1100 1050 1000 950 90
f1 (ppm)
Figure 3. UDEFT 77Se NMR spectra of the salt 7 and the selenonium
trifluoroacetate 8 in CDCl
3
required for the formation of 7. We propose that the observed
instability of 3 in solution, accompanied by observable gas
evolution, is due to its facile formal selenoxide elimination that
produces benzeneselenenic acid (9) and dioxygen. The oxidation
of 9 by a second molecule of 3 then generates the seleninic acid
(Scheme 4). If this process proceeds at a comparable rate to
the isomerization of 3 to 4, then both components required for the
formation of 7 are produced simultaneously.
O
O
10
X
H O
2
2
1
11
PhSe-OH
PhSe-OOH
1
3
fast
slow 10
H O
2
2
O
O
1
0
PhSe
H
HO
10
PhSeOH + O2
O
SePh
11
X
PhSe-O
O
O
9
H O
2
2
HO
3
O
O
11
7
H O
2
O
O
2
+
PhSeOH
2
PhSe-OH
PhSe-OOH
3
9
1
10
X
10
H O
O
11
PhSe-OH
O
isomerization
via Scheme 2
O
2
2
O
4
PhSe-OOH
PhSe-OH
11
Scheme 5. Epoxidation of cyclooctene
3
O
4
O
O
O
HO
HO
Although it is possible that seleninic acid 1 can produce 4
via selenurane 6 (Scheme 2) without the intermediacy of
peroxyseleninic acid 3, we have shown that any 3 that might form
would be rapidly converted to the salt 7. The same salt would also
be produced by the reaction of 1 and 4 (Scheme 4). Thus, the
formation of 7 competes effectively with the relatively slow and
limited epoxidation of cyclooctene with 3 in the absence of
hydrogen peroxide (Scheme 6). In addition, the faster
epoxidations observed with 7, and especially with 4, in the
presence of hydrogen peroxide, together with their inertness in its
absence, indicate that downstream intermediates are the principal
oxidants of the alkene. We therefore propose that the selenonium
ion moiety of 7 reacts further with hydrogen peroxide to
regenerate the peroxyseleninic acid, which is then recycled back
+
PhSe-OH
PhSe-OH
PhSe-O
O
SePh
1
4
O
7
Scheme 4. Selenoxide elimination of 3 leading to 7 in the absence of hydrogen
peroxide.
Upon further oxidation of 7 with 2.2 equiv of hydrogen
peroxide in acetonitrile at 60 ºC, it afforded selenonic acid 4
quantitatively (Scheme 3), identical to an authentic sample (see
77
Supporting Information) with a Se NMR signal (CD
ppm.
3
CN) at 1025
Finally, we examined the reactions of stoichiometric
amounts of independently prepared 1, 4 and 7 with cyclooctene
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A
B
Addition of
equiv of
1
H
2O
2
Figure 4. A) Yields of cyclooctene epoxide were obtained by GC analysis with an internal standard. Reactions were performed in dichloromethane with equimolar
amounts of cyclooctene, the selenium compound and, where indicated, hydrogen peroxide. B) Epoxidation was conducted similarly with selenonic acid 4 alone,
followed by addition of one equiv of hydrogen peroxide after 2 h. Rate constants are provided in the Supporting Information.
O
O
spectroscopy. The spectrum showed two peaks of roughly equal
intensity, one at 1026 ppm from unreacted 4 and a second signal
at 1024 ppm attributed to 13.16 When excess hydrogen peroxide
was added, only the upfield signal was observed. This appears to
via
PhSe-OOH
4
PhSe-OH
+
Scheme 4
1
1
-H O
2
3
be the first observation, albeit
peroxyselenonic acid. Unfortunately, 13 proved too unstable for
isolation and further characterization.
In summary, these experiments indicate that the
peroxyselenonic acid 13, and not the peroxyseleninic acid 3, is
the principal oxidant in the epoxidation of cyclooctene. Further
work will be required to determine if this is also true for other
oxidations conducted with seleninic acid 1 or its congeners in the
presence of hydrogen peroxide.17
a
tentative one, of
a
H O
2
2
O
HO
HO OH
Se
PhSe-O
O
SePh
HO
Ph
OOH
7
6
-
H O
2
H O
O
2
2
11
O
PhSe-OH
O
4
Acknowledgements
H O
2
2
10
O
We thank the Natural Sciences and Engineering Research
Council of Canada for financial support. K.N.S. thanks Walpole
Island First Nation and the Province of Alberta for postgraduate
scholarships. G.N.G. and I.J.P. are Canada Research Chairs.
E.M.R. acknowledges a Dean’s Scholarship. Use of SSRL, SLAC
National Accelerator Laboratory, is supported by the U.S. DOE,
Office of Science, OBES under Contract No. DE-AC02-
HO OH
Se
-H
2O
PhSe-OOH
O
Ph
OOH H O
2
O
13
12
Scheme 6. Proposed mechanism of epoxidation of cyclooctene with 1 and
hydrogen peroxide.
7
6SF00515. The SSRL Structural Molecular Biology Program is
supported by the DOE OBER, and by the NIH, NIGMS
P41GM103393). The contents of this publication are solely the
to 7, while the simultaneous liberation of 4 from 7 accompanies
each cycle of this process (Scheme 6). Moreover, the observation
that the selenonic acid 4 can only effect epoxidation in the
presence of hydrogen peroxide indicates that a new species such
as the peroxyselenonic acid 13, probably produced via 12, must
serve as the principal active oxidant. In order to confirm the
formation of 13, a sample of 4 was treated with 0.5 equiv of
(
responsibility of the authors and do not necessarily represent the
official views of NIGMS or NIH.
Conflicts of Interest
7
7
hydrogen peroxide and subjected to UDEFT
Se NMR
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COMMUNICATION
A. Godfrey, J. W. Morzycki, W. B. Motherwell, S. V. Ley, J. Chem. Soc.,
Perkin Trans. 1 1982, 1947-1952.
The authors declare no conflict of interest.
[
7]
8]
L. Syper, J. Młochowski, Tetrahedron, 1987, 43, 207-213.
[
G. Ribaudo, M. Bellanda, I. Menegazzo, L. P. Wolters, M. Bortoli, G.
Ferrer-Sueta, G. Zagotto, L. Orian, Chem. Eur. J. 2017, 23, 2405-2422.
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Biology, (Eds.: D. L. Klayman, W. H. H. Günther), Wiley, New York, 1973,
Chapter 4; b) J. Drabowicz, W. H. Midura, D. Krasowska in The
Chemistry of Organic Selenium and Tellurium Compounds, Vol. 3, Part
Keywords: benzeneperoxyseleninic acid •
benzeneperoxyselenonic acid • epoxidation • oxidation •
peroxides
[9]
2
(Ed.: Z. Rappoport), J. Wiley and Sons, Chichester, 2012, Chapter 17;
c) R. Boese, A. Haas, S. Herkt. M. Pryka, Chem. Ber. 1995, 128, 423-
28; d) M. Abdo, S. Knapp, J. Am. Chem. Soc. 2008, 130, 9234-9235;
4
[1]
a) T. G. Back in Organoselenium Chemistry – A Practical Approach,
Ed.: T. G. Back), Oxford University Press, Oxford, 1999, Chapter 5; b)
e) K. Satheeshkumar, S. Raju, H. B. Singh, R. J. Butcher, Chem. Eur. J.
(
2018, 24, 17513-17522.
F. V. Singh, T. Wirth in Organoselenium Chemistry–Synthesis and
Reactions, (Ed.: T. Wirth), Wiley-VCH, Weinheim, 2012, Chapter 8.2.12;
c) A. Nomoto, A. Ogawa in The Chemistry of Organic Selenium and
Tellurium Compounds, Vol. 3, Part 1 (Ed.: Z. Rappoport), J. Wiley and
Sons, Chichester, 2012, Chapter 11. d) A. L. Braga, R. S. Schwab, O. E.
D. Rodrigues in Organoselenium Chemistry: Between Synthesis and
Biochemistry, (Ed.: C. Santi), Bentham, Sharjah, 2014, Chapter 8. e) E.
J. Lenardão, C. Santi, L. Sancineto, New Frontiers in Organoselenium
Compounds, Springer, Heidelberg, 2018, pp. 1-97.
[10]
The 77Se NMR chemical shift of seleninic acid 1 was also reported as δ
1152 ppm in an aqueous buffer at pH 8.0: K. L. House, R. B. Dunlap, J.
D. Odom, Z. P. Wu, D. Hilvert, J. Am. Chem. Soc. 1992, 114, 8573-8579.
M. Piotto, M. Bourdonneau, K. Elbayed, J.-M. Wieruszeski, G. Lippens,
Magn. Reson. Chem. 2006, 44, 943 – 947.
[11]
[12]
For a review of XAS of selenium compounds, see: N. V. Dolgova, S.
Nehzati, S. Choudhury, T. C. MacDonald, N. R. Regnier, , A. M.
Crawford, O. Ponomarenko, G. N. George, I. J. Pickering Biochim.
Biophys. Acta 2018, 1862, 2383-2392.
[2]
For reviews of seleninic acids and related compounds as catalysts for
oxidations, see: a) J. Młochowski, M. Brzaszcz, M. Giurg, J. Palus, H.
Wójtowicz, Eur. J. Org. Chem. 2003, 4329-4339; b) J. Młochowski, H.
Wójtowicz-Młochowska, Molecules 2015, 20, 10205-10243; c) T. G.
Back, Curr. Green Chem. 2016, 3, 76-91; (d) D. M. Freudendahl, S.
Santoro, S. A. Shahzad, C. Santi, T. Wirth, Angew. Chem. Int. Ed. 2009,
[13]
[14]
Deposition
number
1958185
contains
the
supplementary
crystallographic data for this paper. These data are provided free of
charge by the joint Cambridge Crystallographic Data Centre and
Fachinformationszentrum Karlsruhe Access Structures Service
(www.ccdc.cam.ac.uk/structures).
More than 100 years ago, Doughty reported the preparation of
48, 8409-8411; Angew. Chem. 2009, 121, 8559-8562.
2 4
benzeneselenonic acid (4) by heating H SeO in benzene in a sealed
[3]
a) P. A. Grieco, Y. Yokoyama, S. Gilman, M. Nishizawa, J. Org. Chem.
tube for 100 h at 110 ºC. In 1964, Paetzold and Lienig repeated the
experiment and used a Bunsen test to show that both Se(IV) and Se(VI)
were present in the product. On that basis, they proposed the
selenonium-selenonate salt 7 as a revised structure for Doughty’s
product. a) H. W. Doughty, Am. Chem. J. 1909, 41, 326-337; b) R.
Paetzold, D. Lienig, Z. Chem. 1964, 4, 186.
1977, 42, 2034-2036; b) T. Hori, K. B. Sharpless, J. Org. Chem. 1978,
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299-301; d) T. Kametani, H. Nemoto, K. Fukumoto, Bioorg. Chem. 1978,
7, 215-220; e) B. Betzemeier, F. Lhermitte, P. A. Knochel, Synlett 1999,
489-491; (f) G.-J. ten Brink, B. C. M. Fernandes, M. C. A. van Vliet, I. W.
C. E. Arends, R. A. Sheldon, J. Chem. Soc., Perkin Trans. 1 2001, 224-
28.
a) C. Santi, R. Di Lorenzo, C. Tidei, L. Bagnoli, T. Wirth, Tetrahedron
012, 68, 10530-10535; b) L. Yu, J. Wang, T. Chen, Y. Wang, Q.Xu, Appl.
[15]
[16]
G. Ayrey, D. Barnard, D. T. Woodbridge, J. Chem. Soc. 1962, 2089-
2099.
2
[4]
The broadened shape of the singlet at 1024 ppm suggests that the
peroxyselenonic acid 13 may be in rapid equilibrium with its hydrate, the
selenurane 12.
2
Organomet. Chem. 2014, 28, 652-656.
[
5]
6]
P. A. Grieco, Y. Yokoyama, S. Gilman, Y. Ohfune, J. Chem. Soc. Chem.
Commun. 1977, 870-871.
[17]
Additional information, including charge densities of 3 and 13, and pK
values of 1 and 4, is provided in the Supporting Information
a
[
In related work, the authors employed benzeneseleninic anhydride (2) as
the catalyst and iodoxybenzene as the cooxidant: D. H. R. Barton, C. R.
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Text for Table of Contents
Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
((Insert TOC Graphic here))
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Kai N. Sands, Emerita
O
O
O
PhSe-O
O
O
O
Mendoza Rengifo, Graham N.
George, Ingrid J. Pickering,
Benjamin S. Gelfand and
Thomas G. Back*
H
2
O
2
HO
HO
H
2
O
2
H
2 2
O
PhSe-OH
benzene-
PhSe-OOH
SePh
PhSe-OH
PhSe-OOH
O
O
benzeneperoxy-
seleninic acid
O
seleninic acid
benzene-
selenonic acid
XAS, X-ray diffraction, 77Se NMR
proposed benzeneperoxy-
selenonic acid
Page No. – Page No.
Peroxyseleninic or peroxyselenonic? What a difference a vowel makes! The main
active intermediate in the epoxidation of cyclooctene with benzeneseleninic acid
and hydrogen peroxide is not benzeneperoxyseleninic acid, but surprisingly, the
corresponding postulated peroxyselenonic acid.
The Unexpected Role of Se(VI)
Species in Epoxidations with
Benzeneseleninic Acid and Hydrogen
Peroxide
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