Photocatalytic deoxygenation of sulfoxides to sulfides over titanium(IV) oxide at room temperature without use of metal co-catalysts

Article abstract of DOI:10.1016/j.catcom.2014.05.028

Deoxygenation of sulfoxides was examined in acetonitrile suspensions of metal-free titanium(IV) oxide (TiO₂) under irradiation of UV light at room temperature. Experimental results indicate that deoxygenation was induced by the TiO₂

Full text of DOI:10.1016/j.catcom.2014.05.028

Photocatalytic deoxygenation of sulfoxides to sulfides over titanium(IV) oxide
at room temperature without use of metal co-catalysts
Hiroshi Kominami, Kosuke Nakanishi, Satoshi Yamamoto, Kazuya Ima-
mura, Keiji Hashimoto
PII:
DOI:
Reference:
S1566-7367(14)00209-X
doi: 10.1016/j.catcom.2014.05.028
CATCOM 3922
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
30 March 2014
27 May 2014
30 May 2014
Please cite this article as: Hiroshi Kominami, Kosuke Nakanishi, Satoshi Yamamoto,
Kazuya Imamura, Keiji Hashimoto, Photocatalytic deoxygenation of sulfoxides to sulfides
over titanium(IV) oxide at room temperature without use of metal co-catalysts, Catalysis
Communications (2014), doi: 10.1016/j.catcom.2014.05.028
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Photocatalytic deoxygenation of sulfoxides to sulfides over
titanium(IV) oxide at room temperature without use of metal
co-catalysts
Hiroshi Kominami*, Kosuke Nakanishi, Satoshi Yamamoto, Kazuya Imamura, Keiji
Hashimoto
Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University,
Kowakae, Higashiosaka, Osaka 577-8502, Japan.
E-mail: hiro@apch.kindai.ac.jp
Abstract
Deoxygenation of sulfoxides was examined in acetonitrile suspensions of
metal-free titanium(IV) oxide (TiO2) under irradiation of UV light at room temperature.
Experimental results indicate that deoxygenation was induced by the TiO2 photocatalyst
and that organic acids such as formic acid and oxalic acid are appropriate as hole
scavengers in the photocatalytic reaction.
Diphenyl sulfoxide was successfully
deoxygenated to diphenyl sulfide with high yields, and the TiO2 photocatalyst could be
repeatedly used for deoxygenation without loss of activity. The present
photocatalytic method could be applied for deoxygenation of various sulfoxides to
corresponding sulfides, and phenyl vinyl sulfoxide was chemoselectively reduced to
phenyl vinyl sulfide without hydrogenation of a C=C double bond.
Keywords: photocatalyst, TiO2, sulfoxide, deoxygenation, sulfide, chemoselective
1. Introduction
Deoxygenation of sulfoxides is an important reaction in both organic synthesis

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and biochemistry [1-3].
However, conventional deoxygenation requires
stoichiometric reagents such as phosphines, halogens, and metal hydrides [4-8] and
yields a large amount of undesirable waste, although many efforts have been devoted to
improve reaction conditions and to minimize the use of toxic reagents by using catalytic
systems [9-11].
Recently, excellent catalysts for deoxygenation of sulfoxides, i.e.,
gold (Au) and ruthenium (Ru) supported on hydroxyapatite (HAP), were
reported[12,13].
temperatures higher than 383 K and dimethylphenylsilane as a reducing agent yielding
by-product residues such as siloxanes. Therefore, a more environmentally friendly
However, even the Au/HAP and Ru/HAP catalysts required
catalytic reaction system for deoxygenation of sulfoxides working at lower temperatures
with “greener” reducing agents giving no residue is keenly desired.
When titanium(IV) oxide (TiO2) is irradiated by UV light, charge separation
occurs and thus-formed electrons in the conduction band and positive holes in the
valence band cause reduction and oxidation, respectively.
Photocatalytic reaction
proceeds at room temperature and under atmospheric pressure, and the TiO2
photocatalyst is easily separated from the reaction mixture after the reaction and can be
used repeatedly without a re-activation or re-generation process.
In addition, TiO2
has been used for a long time as an indispensable inorganic material such as a pigment
and UV absorber because it is inexpensive and not toxic for humans and the
environment.
Since photocatalytic reaction satisfies almost all of the 12 proposed
requirements for green chemistry [14], organic synthesis of various compounds using
photocatalysts has recently been studied by many researchers [15] and the number of
reports on photocatalytic reduction of organic compounds by using photogenerated
electrons has been increasing [16,17].
However, most of the reports deal with
In this study,
reduction (hydrogenation) of nitrobenzenes to aminobenzenes [18-32].
we examined a new photocatalytic reduction system, i.e., deoxygenation of sulfoxides

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(reduction of sulfoxides to sulfides) in a suspension of metal-free TiO2 in the presence
of hole scavengers such as oxalic acid and formic acid. In this reaction, these organic
acids also work as stoichiometric reagents for deoxygenation. However, oxalic acid
and formic acid are recently used as green hole scavengers for photocatalytic reduction
and hydrogenation because these oxalic acids are converted to carbon dioxide, which is
easily separated from the solvent under acidic conditions [33, 34].
Here we report
that corresponding sulfides were successfully produced at room temperature without the
use of toxic or undesirable reagents.
2. Experimental
All of the reagents were commercial materials of reagent grade and used
without further purification.
photocatalyst in this study.
Ishihara ST-01 was mainly used as the TiO2
In a typical run, TiO2 (50 mg) was suspended in 5 cm3 of
acetonitrile containing diphenyl sulfoxide (DPSO) and oxalic acid in a test tube, sealed
with a rubber septum under argon, and then photoirradiated at > 300 nm by a 400-W
high-pressure mercury arc (Eiko-sha, Osaka) with magnetic stirring in a water bath
continuously kept at 298 K.
The amounts of DPSO unreacted and diphenyl sulfide
(DPSI) formed were determined with an FID-type gas chromatograph (GC-2014,
Shimadzu, Kyoto) equipped with a DB-1 column.
The example of the gas
chromatogram output is shown in Figure S1. The amount of hydrogen gas (H2) as the
reduction product of protons (H+) was determined with a TCD-type gas chromatograph
(GC-8A, Shimadzu, Kyoto) equipped with an MS-5A column. To obtain an action
spectrum, the full arc from a xenon (Xe) lamp (Optiplex, Ushio, Tokyo) was
monochromated with light width of ±10 nm using SM-100 (Bunkoukeiki, Tokyo).
The light was used for photocatalytic reaction instead of the mercury arc. Spectra and
intensity of the monochromated light from the Xe lamp were determined using a

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spectroradiometer (USR-45D, Ushio, Tokyo).
3.1. Photocatalytic deoxygenation of diphenyl sulfoxide
Figure 1 shows time courses of DPSO remaining and DPSI formed in an
acetonitrile suspension of TiO2 in the presence of oxalic acid under deaerated conditions.
Just after photoirradiation, DPSO monotonously decreased, while DPSI was formed as
the deoxygenation (reduction) product of DPSO.
After 120 min, DPSO was almost
The results
completely consumed and DPSI was obtained in a high yield (98%).
shown in Figure 1 were expressed as first-order kinetic and the rate constant was
determined to be 2.15 × 10-2 min-1.
Other reduced products such as H2 were not
formed, indicating that photogenerated electrons (in other words, oxalic acid) were
selectively used for reduction of DPSO. No H2 formation in the present reaction
system is attributed to the use of bare (metal-free) TiO2.
This H2-free system is
To
attractive because there is no need to remove H2 from the reaction system.
evaluate stoichiometry and selectivity of the reaction and side-reactions occurring under
the present conditions, a new indicator, i.e., material balance (MB), was calculated by
Equation (1):
n(DPSO)  n(DPSI)
…(1),
MB 
,
n (DPSO)
0
where n(DPSO) and n(DPSI) are the amounts of DPSO and DPSI during the
photocatalytic reaction, respectively, and n0(DPSO) is the amount of DPSO before the
photocatalytic reaction.
As shown in Figure 1, the values of MB were almost unity
during the reaction, indicating that no other intermediates were produced under the
present conditions. We noted that 1) the amount of DPSI was unchanged, 2) the color
of TiO2 became blue (Ti3+ species formed), and 3) no H2 was evolved, under excessive

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photoirradiation after complete consumption of DPSO. These results indicate that
DPSI was not consumed by successive reactions such as re-oxidation and degradation
under the present conditions and that oxalic acid remaining was not consumed any more
due to rapid recombination between photogenerated electrons and positive holes over
Ti3+ species.
From these results, the reaction, i.e., deoxygenation of DPSO to DPSI,
would be shown in Scheme 1, although we did not determine the amount of CO2.
Scheme 1 Photocatalytic deoxygenation of DPSO to DPSI in the presence of oxalic
acid as a hole scavenger
Figure 2 shows the effect of the kind and amount of hole scavenger on yield
and selectivity of DPSI produced in photocatalytic deoxygenation of DPSO in
acetonitrile suspensions of TiO2 for 15 min.
Use of a typical alcoholic hole scavenger,
On the other hand,
2-propanol, resulted in a low yield due to the small reaction rate.
large yields were obtained with sufficient selectivities when organic acids (formic acid
and oxalic acid) were used. These organic acids, especially oxalic acid, have been
shown to be efficient hole scavengers for chemoselective reduction of 3-nitrostyrene to
3-aminostyrene over a TiO2 photocatalyst [9]. When the amount of oxalic acid was
decreased, both the yield and selectivity of DPSI decreased.
Decrease in the
selectivity suggests that DPSI was converted to some oxidized species other than DPSO
because re-oxidation of DPSI to DPSO only decreases the yield of DPSI (the selectivity
being preserved).
These results indicate that twice the amount of a hole scavenger is
necessary to avoid consumption of DPSI due to oxidation by positive holes.
An action spectrum is a strong tool for determining whether a reaction

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observed occurs via a photoinduced process or a thermocatalytic process.
To obtain
an action spectrum in this reaction system, deoxygenation of DPSO in acetonitrile
suspensions of TiO2 (ST-01, Ishihara) was carried out at 298 K under irradiation of
monochromated light from a Xe lamp with light width of ±10 nm.
Apparent quantum
efficiency (AQE) at each centered wavelength of light was calculated from the ratio of
twice the amount of DPSI formed and the amount of photons irradiated using the
following Equation (2):
2× the amount of DPSI formed
…(2).
AQE =
×100.
amount of incident photones
As shown in Figure 3, AQE was in agreement with the absorption spectrum of TiO2.
Therefore, it can be concluded that deoxygenation of DPSO in an acetonitrile
suspension was induced by photoabsorption of TiO2.
As also shown in Figure 3,
AQE reached 35% at 350 nm, indicating that photocatalytic deoxygenation of DPSO
proceeded with high efficiency of photon utilization as well as chemical aspects such as
selectivity and MB.
The expected reaction process of photocatalytic deoxygenation of DPSO to
DPSI over TiO2 is shown in Figure 4: 1) By irradiation of UV light, photogenerated
electrons (e-) and positive holes (h+) are formed in the conduction and valence bands of
TiO2, and oxalic acid (or oxalate) is oxidized by h+, and 2) DPSO is reduced by e-,
resulting in the formation of DPSI.
However, H2 formation by reduction of H+ does
not occur under a metal-free condition because H2 evolution generally requires loading
of co-catalysts such as platinum and Pd.
3.2. Applicability of photocatalytic deoxygenation of sulfoxide
The applicability of photocatalytic deoxygenation of sulfoxide to sulfide was
investigated, and the results are summarized in Table 1.
Results of entries 1-3

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indicate that the TiO2 photocatalyst can be used repeatedly for deoxygenation of DPSO
to DPSI without deactivation. The reusability of TiO2 is attributable to its stability.
Since the TiO2 photocatalyst is used without modification with a metal co-catalyst, the
present reaction system is free from changes in states such as size, dispersion and
oxidation states of the co-catalyst during the photocatalytic reaction.
Almost
quantitative deoxygenation of DPSO occurred under a ten-times concentrated condition
(entry 4) as shown in Figure 1.
deoxygenated to methyl phenyl sulfide (entry 5).
sulfoxide was chemoselectively reduced to phenyl vinyl sulfide without hydrogenation
Methyl phenyl sulfoxide was more easily
We found that phenyl vinyl
of a C=C double bond (entry 6).
Our research group have reported that 3-nitrostyrene
was chemoselectively reduced to 3-aminostyrene without reduction of a C=C double
bond to 3-ethylaniline in a suspension of a TiO2 photocatalyst in the presence of oxalic
acid as hole scavengers at room temperature [32].
The high reduction potential of
vinyl group accounts for the chemoselective reduction of 3-nitrostyrene and phenyl
vinyl sulfoxide. The use of TiO2 without a metal co-catalyst strongly contributed to
the chemoselectivity. If TiO2 modified with a metal co-catalyst is used,
hydrogenation of a C=C double bond [35] would occur as well as deoxygenation.
Photocatalytic deoxygenation was also applicable for sulfoxide of an acyclic compound
(entry 7), though a longer reaction time was required.
3.3. Effects of physical properties of TiO2
To evaluate the effects of physical properties of TiO2, representative
commercial TiO2 samples, which were registered at the Catalysis Society of Japan as
Japan Reference Catalysts (JRC-TIO series), were used for photocatalytic
deoxygenation of DPSO under the same conditions.
Phase of TiO2 and specific
Figure 5 shows the
surface area of the TiO2 samples are summarized in Table S1.

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effect of specific surface area of TiO2 samples on yields of DPSI produced.
A clear
correlation was observed for most of the TiO2 samples between specific surface area
and DPSI yield, though there were some exceptions. These results also mean that
TiO2 structure (anatase or rutile) had little effect on the photocatalytic deoxygenation of
DPSO; however, bi-phase of anatase and rutile in the TiO2 sample may be effective.
We are now investigating adsorption properties of these TiO2 samples toward DPSO,
DPSI and oxalic acid.
4. Conclusions
Photocatalytic deoxygenation of sulfoxides to corresponding sulfides was
examined in acetonitrile suspensions of bare TiO2 particles at room temperature without
the use of a metal co-catalyst and toxic reagents.
Organic acids, especially oxalic
acid, worked efficiently as hole scavengers. The use of an excess of organic acids
was effective for achieving high yields of sulfide and for avoiding fruitless degradation
of sulfides. The present photocatalytic method can be applied for deoxygenation of
various sulfoxides to corresponding sulfides.
Chemoselective reduction of phenyl
vinyl sulfoxide to phenyl vinyl sulfide was also achieved because the metal-free TiO2
photocatalyst had no ability for hydrogenation of the C=C double bond.
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific Research (No.
26630415) from the Ministry of Education, Culture, Sports, Science, and Technology
(MEXT) of Japan.
One of the authors (H. K.) is grateful for financial support from
the Faculty of Science and Engineering, Kinki University, and another author (K. I.) is
grateful to the Japan Society for the Promotion of Science (JSPS) for a Research
Fellowship for young scientists.

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References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
G. Solladie, Synthesis 3 (1981) 185-196.
M. C. Carreno, Chem. Rev. 95 (1995) 1717-1760.
J. R. Debaun, J. J. Menn, Science 191 (1976) 187-188.
K. Bahrami, M. M. Khodaei, M. S. Arabi, J. Org. Chem. 75 (2010) 6208-6213.
G. S. Bhatia, P. P. Graczyk, Tetrahedron Lett. 45 (2004) 5193-5195.
K. Bahrami, M. M. Khodaei, A. Karimi, Synthesis 16 (2008) 2543-2546.
J. Drabowjcz, M. Mikolajczyk, Synthesis (1976) 527-528.
J. Zhang, X. Gao, C. Zhang, C. Zhang, J. Luan, D. Zhao, Synth. Commun. 40
(2010) 1794-1801.
[9]
K. Ogura, M. Yamashita, G. Tsuchihashi, Synthesis (1975) 385-387.
[10]
[11]
P. Geneste, M. Bonnet, C. Frouin, D. Levache, J. Catal. 61 (1980) 277-278.
N. Garcia, P. G-Garcia, M. R. Pedrosa, F. J. Arnaiz, R. Sanz, Green Chem. 15
(2013) 999-1005.
[12]
Y. Mikami, A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa, K. Kaneda,
Chem. Eur. J. 17 (2011) 1768-1772.
[13]
Y. Takahashi, T. Mitsudome, T. Mizugaki, K. Jitsukawa, K. Kaneda, Chem.
Lett. 43 (2014) 420-422.
[14]
P. T. Anastas, J. C. Warner, Green Chemistry: Theory and Practice, Oxford
University Press, 1998.
[15]
[16]
M. A. Fox, M. T. Dulay, Chem. Rev. 93 (1993) 341-357.
G. Palmisano, V. Augugliaro, M. Pagliarob, L. Palmisano, Chem. Commun.
(2007) 3425-3437.
[17]
G. Palmisano, E. Garcia-Lopez, G. Marci, V. Loddo, S. Yurdakal, V.
Augugliaro, L. Palmisano, Chem. Commun. 46 (2010) 7074-7089.

ACCEPTED MANUSCRIPT
10/20
[18]
[19]
F. Mahdavi, T. C. Bruton, Y. Li, J. Org. Chem. 58 (1993) 744-746.
ˇ
ˇ
V. Brezova, A. Blazkova, I. Surina, B. Havlinova, J. Photochem. Photobio. A
107 (1997) 233-237.
[20]
[21]
[22]
J. L. Ferry, W. H. Glaze, Langmuir 14 (1998) 3551-3555.
J. L. Ferry, W. H. Glaze, J. Phys. Chem. B 102 (1998) 2239-2244.
O. V. Makarova, T. Rajh, M. C. Thurnauer, A. Martin, P. A. Kemme, D. Cropek,
Environ. Sci. Tech. 34 (2000) 4797-4803.
[23] V. Brezova, P. Tarabek, D. Dvoranova, A. Staˇsko, S. Biskupiˇc, J. Photochem.
Photobio. A: Chem. 155 (2003) 179-198.
[24]
[25]
H. Tada, T. Ishida, A. Takao, S. Ito, Langmuir 20 (2004) 7898-7900.
H. Tada, T. Ishida, A. Takao, S. Ito, S. Mukhopadhyay, T. Akita, K. Tanaka, H.
Kobayashi, ChemPhysChem 6 (2005) 1537-1543.
[26]
[27]
T. Zhang, L. You, Y. Zhang, Dyes and Pigments 68 (2006) 95-100.
S. O. Flores, O. R.-Bernij, M. A. Valenzuela, I. Cordova, R. Gomez, R.
Gutierrez, Top. Catal. 44 (2007) 507-511.
[28]
S. Chen, H. Zhang, X. Yu, W. Liu, Chinese Journal of Chemistry 28 (2010)
21-26.
[29]
H. Kominami, S. Iwasaki, T. Maeda, K. Imamura, K. Hashimoto, Y. Kera, B.
Ohtani, Chem. Lett. 15 (2009) 410-411.
[30] K. Imamura, S. Iwasaki, T. Maeda, K. Hashimoto, B. Ohtani, H. Kominami,
Phys. Chem. Chem. Phys. 13 (2011) 5114-5119.
[31]
K. Imamura, T. Yoshikawa, K. Hashimoto, H. Kominami, Appl. Catal. B,
Environ. 134–135 (2013) 193-197.
[32]
K. Imamura, K. Hashimoto, H. Kominami, Chem. Commun. 48 (2012)
4356-4358.
[33]
H. Kominami, A. Furusho, S.-y. Murakami, H. Inoue, Y. Kera and B. Ohtani,

ACCEPTED MANUSCRIPT
11/20
Catal. Lett. 76 (2001) 31-34.
[34]
Y. Kera and B. Ohtani, Chem. Commun. (2005) 2933-2935.
[35] K. Imamura, Y. Okubo, T. Ito, A. Tanaka, K. Hashimoto, H. Kominami, RSC
H. Kominami, T. Nakaseko, Y. Shimada, A. Furusho, H. Inoue, S.-y. Murakami,
Adv. 4 (2014) 19883-19886.

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Figure Captions
Figure 1
Time courses of DPSO remaining, DPSI formed and material balance of
DPSO and DPSI in an acetonitrile suspension of TiO2 in the presence of oxalic acid (1
mmol) under irradiation of UV light.
Figure 2
Effects of the kind and amount of hole scavengers on yield and selectivity
of DPSI produced in photocatalytic deoxygenation of DPSO (50 µmol) in acetonitrile
suspensions of TiO2 for 15 min. The values in parentheses are the amounts of hole
scavengers in µmol.
Figure 3
Absorption spectrum (right axis) and action spectrum of TiO2 in the
DPSO: 50 µmol, oxalic acid: 100 µmol.
deoxygenation of DPSO (left axis).
Figure 4
Expected reaction process of photocatalytic deoxygenation of DPSO to
DPSI over metal-free TiO2 in the presence of oxalic acid (OA).
Figure 5
Effect of specific surface area of TiO2 samples on yields of DPSI produced
in photocatalytic deoxygenation of DPSO (50 µmol) for 10 min in acetonitrile solutions
containing oxalic acid (100 µmol). Minor form in bi-phase samples is shown in
parenthesis.

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600
400
200
0
2.0
DPSO
DPSI 1.5
1.0
MB
0.5
0.0
0
50
100
150
Time / min
Figure 1
Time courses of DPSO remaining, DPSI formed and material balance of
DPSO and DPSI in an acetonitrile suspension of TiO2 in the presence of oxalic acid (1
mmol) under irradiation of UV light.

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100
80
60
40
20
0
Figure 2
Effects of the kind and amount of hole scavengers on yield and selectivity
of DPSI produced in photocatalytic deoxygenation of DPSO (50 µmol) in acetonitrile
suspensions of TiO2 for 15 min. The values in parentheses are the amounts of hole
scavengers in µmol.

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40
30
20
10
0
1
0.8
0.6
0.4
0.2
0
300 350 400 450 500
Wavelength
Figure 3
Absorption spectrum (right axis) and action spectrum of TiO2 in the
DPSO: 50 µmol, oxalic acid: 100 µmol.
deoxygenation of DPSO (left axis).

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Figure 4
Expected reaction process of photocatalytic deoxygenation of DPSO to
DPSI over metal-free TiO2 in the presence of oxalic acid (OA).

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50
40
30
20
Anatase(A)
Rutile(R)
A, (R)
10
R, (A)
0
0
100
200
300
400
Surface area / m2 g-1
Figure 5
Effect of specific surface area of TiO2 samples on yields of DPSI produced
in photocatalytic deoxygenation of DPSO (50 µmol) for 10 min in acetonitrile solutions
containing oxalic acid (100 µmol).
parenthesis.
Minor form in bi-phase samples is shown in

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Table 1 Photocatalytic deoxygenation of sulfoxides to
corresponding sulfides over TiO2 at 298 K.[a]
t /
Yield Sel.
Entry Sulfoxides
Sulfides
min / %[b] /%[b]
1
20 93
20 98
20 >99
120 98
15 99
15 82
30 91
95
98
>99
98
99
82
91
2[c]
3[d]
4[e]
5
6
7
[a] Reaction conditions: TiO2 (50 mg), substrate (50 µmol),
acetonitrile (5 cm3), oxalic acid (100 µmol), room
temperature, under Ar.
[b] Determined by GC using an
[c] Second use. [d] Third use.
internal standard.
[e] Diphenyl sulfoxide (500 µmol), oxalic acid (1 mmol).

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Graphical abstract

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Highlights
Photocatalytic deoxygenation of sulfoxides was examined over metal-free TiO2.
Sulfoxides were successfully deoxygenated to corresponding sulfides with high yields.
Formic acid and oxalic acid were appropriate as hole scavengers.
The TiO2 photocatalyst could be repeatedly used without loss of activity.
Phenyl vinyl sulfoxide was reduced to sulfide without hydrogenation of a C=C bond.