Transition-metal-free, chemoselective aerobic oxidations of sulfides and alcohols with potassium nitrate and pyridinium tribromide or bromine

Article abstract of DOI:10.1055/s-0030-1259516

An efficient oxidation of sulfides with air catalyzed by the combination of potassium nitrate with pyridinium tribromide under transition-metal-free conditions was reported. By replacing pyridinium tribromide with bromine, the reaction system was also useful in the oxidation of alcohols. All reactions afforded the corresponding products in good to excellent yields with high chemoselectivities. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0030-1259516

LETTER
559
Transition-Metal-Free, Chemoselective Aerobic Oxidations of Sulfides and
Alcohols with Potassium Nitrate and Pyridinium Tribromide or Bromine
T
Y
ransition-Metal-F
u
ree, Chemoselectiv
Y
e
A
erobic
O
xidat
u
ions of Sulfid
a
es andAlc
n
ohols ,* Xiao Shi, Wei Liu
College of Chemistry & Chemical Engineering, Yangzhou University, Jiangsu Province 225002, P. R. of China
Fax +86(514)7975244; E-mail: yyuan@yzu.edu.cn
Received 7 November 2010
bromide is an alternative reagent to bromine in many re-
actions. The reactivity of pyridinium tribromide is lower
than bromine due to the ‘slow release’ of bromine. When
Abstract: An efficient oxidation of sulfides with air catalyzed by
the combination of potassium nitrate with pyridinium tribromide
under transition-metal-free conditions was reported. By replacing
7
pyridinium tribromide with bromine, the reaction system was also the combination of KNO –Br was replaced by KNO –
3 2 3
useful in the oxidation of alcohols. All reactions afforded the corre- PyHBr , methyl phenyl sulfide was completely converted
3
sponding products in good to excellent yields with high chemose-
lectivities.
to the corresponding sulfoxide and sulfone with a high
chemoselectivity (99:1) within seven hours (Table 1, en-
Key words: aerobic oxidation, sulfide, alcohol, chemoselectivity, try 2). It was found that both KNO and PyHBr (Br )
3
3
2
transition-metal-free
were necessary for the oxidation. Control experiments in-
dicated that, when each of them was employed in catalytic
amount, no oxidation reaction occurred under the same
The selective oxidation of sulfides or alcohols is one of conditions (Table 1, entries 3–5). While the oxidation re-
the most important and fundamental transformations in action was carried out in argon, sulfoxide was only ob-
1
organic synthesis. As one aspect of the ideology of green tained in 10% yield (Table 1, entry 6). It was shown that
chemistry, catalyzed oxidations with ‘clean’ oxidants are the reaction could proceed smoothly with good conver-
2
extremely valuable. Many kinds of catalytic systems sions and high chemoselectivities in various solvents, ex-
3
have been reported on the selective oxidations of sulfides
cept water and methanol (Table 1, entries 7–12). The
4
and alcohols with hydrogen peroxide. However, the low reaction in a mixed solvent of water and acetonitrile failed
concentration (ca. 30%) of hydrogen peroxide limited its to give a good conversion (Table 1, entry 12).
utilization in some industrial processes. Recently, some
With the good results in hand, various sulfides were tested
transition-metal- and acid-catalyzed selective oxidation
under the optimal conditions. As shown in Table 2, most
reactions with air or oxygen as the oxidant have been de-
of the reactions proceeded smoothly and afforded the cor-
responding sulfoxides in good to excellent yields and high
5
veloped. Among these research, the binary system FeBr /
3
Fe(NO ) is a very efficient catalyst for the selective air
3
3
chemoselectivities. A moderate electronic substrate effect
was observed. While sulfides with an electron-donating
group at the aromatic ring were good substrates, the reac-
tions of those with an electron-withdrawing group afford-
ed the corresponding products in moderate yields
5
a
5k
oxidation of sulfides and alcohols and the correspond-
ing desired products could be obtained in high yields.5
However, transition metals and acids are somehow toxic,
unstable, and expensive. For this reason, a variety of stud-
ies on transition-metal-free catalyst system for aerobic
sulfides and alcohols oxidations have been reported which
employed molecular oxygen as terminal oxidant for both
l
(
Table 2, entries 2–7). It was supposed that pyridinium
hydrobromide would decrease the reactivity of PyHBr in
3
the oxidation since there is a rapid equilibrium between
6
economical and environmental benefits. Herein, we re-
8
pyridinium hydrobromide and bromine. With the re-
port an efficient oxidation of sulfides and alcohols with air
at room temperature with a transition-metal-free binary
catalyst system (potassium nitrate/pyridinium tribromide
or potassium nitrate/bromine).
placement of the binary catalyst KNO –PyHBr3 by
3
KNO –Br , the yields of those products with the electron-
3
2
withdrawing groups increased to 90% (Table 2, entries
1–14). It was supposed that the electron-withdrawing
1
Initially, methyl phenyl sulfide was treated with a catalyt- groups deactivated the aryl ring and prevented bromine to
ic amount of potassium nitrate (10 mol%) and bromine react with organosulfur compounds. When the alkyl group
(
15 mol%) in acetonitrile in an air open system at room in sulfide was altered, the reaction results did not change
temperature. After three hours, a moderate yield of methyl significantly in yields and chemoselectivities (Table 2,
1
3
phenyl sulfoxide was obtained, and the ratio of sulfoxide entries 8–10). While chlorine atom existing in alkyl group
and sulfone was 94:6 (Table 1, entry 1). Some unexpected resulted in the low yield with KNO –PyHBr as the cata-
3
3
bromination products were isolated because of the high lyst, the reaction with KNO –Br gave rise to a good yield
3
2
reactivity of bromine. It is well known that pyridinium tri- and was obtained albeit in a lower chemoselectivity
Table 2, entry 15).
(
SYNLETT 2011, No. 4, pp 0559–0564
x
x.
x
x.
2
0
1
1
Advanced online publication: 27.01.2011
DOI: 10.1055/s-0030-1259516; Art ID: W17710ST
©
Georg Thieme Verlag Stuttgart · New York

5
60
Y. Yuan et al.
Table 1 Air Oxidation of Methyl Phenyl Sulfide Catalyzed by KNO –PyHBr /Br
2
LETTER
a
3
3
O
S
S
Me
KNO3–PyHBr3/Br2
MeCN, r.t., air
Me
Entry
Catalyst
KNO –Br
Solvent
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeOH
Time (h)
Conditions
Conversion (%)b SO/SO2b
1
2
3
4
5
6
7
8
9
3
7
air
air
air
air
air
Ard
air
air
air
air
air
air
65
98
5
94:6
99:1
3
2
KNO –PyHBr
3
3
Br2
24
24
24
7
–
–
–
–
–
–
PyHBr3
KNO3
5
n.r.c
10
8
KNO –PyHBr
3
3
3
3
3
3
3
3
KNO –PyHBr
24
24
7
3
KNO –PyHBr
H O
9
3
2
KNO –PyHBr
THF
85
90
73
10
98:2
96:4
3
1
1
1
0
1
2
KNO –PyHBr
1,4-dioxane
EtOAc
7
3
KNO –PyHBr
7
100:0
–
3
e
KNO –PyHBr
MeCN–H O
24
3
2
a
b
c
d
e
Reactions were carried out in an air open system at r.t., with a molar ratio of substrates/KNO /PyHBr /Br = 1:0.1:0.15 mmol in MeCN (2 mL).
Determined by GC.
n.r.: reaction did not occur.
Under an Ar atmosphere (1 atm).
3
3
2
Ratio of 9:1 for MeCN–H O.
2
a
Table 2 Air Oxidation of Sulfides to Sulfoxides Catalyzed by KNO –PyHBr /Br
3
3
2
O
S
S
R2
KNO –PyHBr /Br
R2
3
3
2
R1
R1
MeCN, r.t., air
Entry
1
Substrate
Time (h)
7
Catalyst
Yield (%)b
90
SO/SO c
2
S
Me
S
KNO –PyHBr
99:1
98:2
3
3
3
2
3
4
5
Me
3.5
4
KNO –PyHBr
92
95
90
42
3
S
Me
KNO –PyHBr
100:0
3
3
3
3
Me
Br
O
S
Me
24
48
KNO –PyHBr
99:1
3
S
Me
KNO –PyHBr
100:0
3
Br
S
Me
6
48
KNO –PyHBr
60
98:2
3
3
O2N
Synlett 2011, No. 4, 559–564 © Thieme Stuttgart · New York

LETTER
Transition-Metal-Free, Chemoselective Aerobic Oxidations of Sulfides and Alcohols
561
a
Table 2 Air Oxidation of Sulfides to Sulfoxides Catalyzed by KNO –PyHBr /Br (continued)
3
3
2
O
S
S
R2
KNO –PyHBr /Br
R2
3
3
2
R1
R1
MeCN, r.t., air
Entry
7
Substrate
Time (h)
24
Catalyst
Yield (%)b
76
SO/SO c
2
S
Me
KNO –PyHBr
99:1
100:0
98:2
3
3
NC
S
8
9
Et
6
48
8
KNO –PyHBr
92
32
85
91
3
3
3
3
S
S
Cl
KNO –PyHBr
3
1
1
1
1
0
1
2
3
KNO –PyHBr
93:7
3
S
Me
3
KNO –Br
98:2
3
2
2
2
Br
S
Me
7
4
KNO –Br
93
92
95
83
99:1
96:4
96:4
94:6
3
Br
S
Me
KNO –Br
3
NC
S
Me
1
1
4
5
10
7
KNO –Br
3
2
2
O2N
S
Cl
KNO –Br
3
a
b
c
Reactions were carried out in an open system at r.t., with a molar ratio of substrate/KNO /PyHBr /Br = 1:0.1:0.15 mmol in MeCN (2 mL).
Isolated after chromatography.
Determined by GC.
3
3
2
A mechanism for the selective oxidation of sulfides to sul- that the real catalytic species was NO in the binary cata-
2
foxides with air catalyzed by KNO –PyHBr /Br was in- lytic system.
3
3
2
vestigated. Some literature reports have pointed to Br
species as being the real catalyst for the aerobic oxidation
5
k,9
of sulfides in the presence of water. However, bromine
could not catalyze the sulfide oxidation in air alone
(
Table 1, entry 3) and water prevented this oxidation reac-
tion in this binary catalytic system (Table 1, entry 8). In
comparison to the catalytic mechanism by Br species ca-
talysis, it was believed that both KNO and Br were very
3
2
important for the oxidation reaction of sulfide with air at
room temperature.
Kochi reported that NO was a good catalyst in sulfide ox-
2
10
idation reaction with oxygen at low temperature. When
0 mol% NO was used as catalyst in the oxidation of 4-
1
2
(
methylthio)benzonitrile with air in acetonitrile, 92%
yield of product and 99:1 of chemoselectivity were ob-
served, which was similar with the one used KNO –Br as
3
2
Figure 1 IR spectra of NO , PyHBr , and KNO –PyHBr in MeCN
2 3 3 3
the catalyst (Table 2, entry 13). This result was suggested
Synlett 2011, No. 4, 559–564 © Thieme Stuttgart · New York

5
62
Y. Yuan et al.
LETTER
In order to confirm the mechanism of the sulfide oxidation To further explore the oxidative reaction with this binary
catalyzed by in situ NO , IR spectrum was used to detect catalyst of KNO –PyHBr (KNO –Br ), the selective aer-
2
3
3
3
2
NO in the reaction system. It was found that NO did ex- obic oxidation of alcohols was also studied. It was found
2
2
ist in the system when pyridinium tribromide (bromine) that the combination of KNO –PyHBr did not work well
3
3
and potassium nitrate were mixed in acetonitrile (Figure 1 (17% yield), but KNO –Br was very effective for the se-
3
2
1
1
and Figure 2). Meanwhile, orange-brown gas was re- lective oxidation of benzylic alcohol under similar condi-
leased from the mixture of pyridinium tribromide (bro- tions. The results of solvent screening are shown in
mine) and potassium nitrate when the mixture was heated. Table 3. Acetonitrile was still the best solvent. When the
NO was identified from the gas because when the gas dis- temperature was increased to 50 °C, benzaldehyde was
2
–
solved in water, NO could be detected by normal analyt- formed in 94% yield.
3
ical methods. However, if the solvent acetonitrile was
changed to water or a mixture of acetonitrile and water,
Table 3 Solvent Screening for the Oxidation of Benzaldehyde with
a
KNO –Br in Air
3
2
NO would react with water immediately to form nitric
2
1
2
acid and lost the catalytic activity.
CH2OH
CHO
KNO3–Br2
MeCN, r.t, air
Entry
Solvent
Temp (°C)
Conversion (%)b
1
2
3
4
5
6
7
8
MeCN
MeOH
25
25
25
25
25
25
25
25
50
86
20
23
17
27
77
59
32
94
H O
2
THF
1,4-dioxane
CH Cl
2
2
EtOAc
MeCN–H Oc
2
9
MeCN
Figure 2 IR spectra of NO , Br , and KNO –Br in MeCN
2
2
3
2
a
Reactions were carried out in an open system at r.t., with a molar ra-
1
0
tio of substrates/KNO /Br =1:0.2:0.3 mmol in MeCN (2 mL).
On the basis of the literature mentioned above and our
experimental results, we suggest the mechanism present-
ed in Scheme 1. The mixture of KNO and Br was easily
3
2
b
c
Determined by GC.
Ratio of 9:1 for MeCN–H O.
2
3
2
generated NO at room temperature in acetonitrile. The in
2
situ NO reacted with sulfide immediately to form the cor- A variety of benzylic alcohols were tested (Table 4). Most
2
responding sulfoxide and NO. Nitrogen dioxide was re- reactions proceeded smoothly and afforded the corre-
generated by transfer from NO in air readily to complete sponding aldehydes or ketones in good to excellent yields.
the catalytic cycle.
Chloro-, bromo-, or methyl-substituted benzylic alcohols
were better substrates to those with a nitro or methoxy
substitution. Meanwhile, secondary alcohols could be
easily converted into ketones with high yields.
KNO3–PyHBr3/Br2
In conclusion, we have developed a selective oxidation of
sulfides and alcohols with air with the combination of
potassium nitrate with pyridinium tribromide or bromine
under the transition-metal-free conditions. Besides opti-
mization for a ‘greener’ procedure, currently dedication
has also been made to extend its scope and to explore its
reaction mechanism and possible synthetic applications.
R2S
NO2
O2
NO + NO2
+
–
[R2S, NO ] NO3
O
S
[
R2S ,NO] NO3–
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
R
R
Scheme 1 Proposed mechanism for the aerobic oxidation of sulfide
with binary catalyst KNO –PyHBr /Br
3
3
2
Synlett 2011, No. 4, 559–564 © Thieme Stuttgart · New York

LETTER
Transition-Metal-Free, Chemoselective Aerobic Oxidations of Sulfides and Alcohols
563
Table 4 Oxidation of Benzaldehydes and Acetophenones Using
References and Notes
a
KNO –Br /PyHBr as Catalyst
3
2
3
(
1) (a) Drabowicz, J.; Kielbasinski, P.; Mikolajczyk, M. In The
Chemistry of Sulfones and Sulfoxides; Patai, S.; Rappoport,
Z.; Stirling, C., Eds.; Wiley: Chichester, 1988, 233–278.
CH2OH
CHO
KNO3–Br2
R
R
MeCN, air, 50 °C
(
b) Sulfur Reagents in Organic Synthesis; Metzner, P.;
Thuillier, A., Eds.; Academic Press: London, 1994.
c) Hudlicky, M. Oxidations in Organic Chemistry;
American Chemical Society: Washington DC, 1990.
d) Fernandez, M.; Tojo, G. In Oxidation of Alcohols to
Entry Substrate
Product
Time Yield
(
b
(
h)
(%)
(
CH2OH
CHO
Aldehydes and Ketones: A Guide to Current Common
Practice; Tojo, G., Ed.; Springer: New York, 2006.
2) (a) Shi, Z.-Z.; Zhang, C.; Li, S.; Pan, D.-L.; Ding, S.-T.; Cui,
Y.-X.; Jiao, N. Angew. Chem. Int. Ed. 2009, 48, 4572.
1
2
3
24
24
48
90
(
(
CH2OH
CHO
92
91
(b) Zhang, C.; Jiao, N. J. Am. Chem. Soc. 2010, 132, 28.
(
c) He, X.-J.; Shen, Z.-L.; Mo, W.-M.; Sun, N.; Hu, B.-X.;
Hu, X.-Q. Adv. Synth. Catal. 2009, 351, 89. (d) Miao,
C.-X.; He, L.-N.; Wang, J.-L.; Wu, F. J. Org. Chem. 2010,
CH2OH
CH2OH
CHO
75, 257.
Cl
Cl
3) (a) Legros, J.; Bolm, C. Angew. Chem. Int. Ed. 2003, 42,
5487. (b) Hosseinpoor, F.; Golchoubian, H. Tetrahedron
Lett. 2006, 47, 5195. (c) Liu, R.; Wu, L.-Z.; Feng, X.-M.;
Zhang, Z.; Li, Y.-Z.; Wang, Z.-L. Inorg. Chim. Acta 2007,
CHO
4
48
24
70
62
O2N
Me
O2N
3
60, 656. (d) Rosa, M. D.; Lamberti, M.; Pellecchia, C.;
Scettri, A.; Villano, R.; Soriente, A. Tetrahedron Lett. 2006,
7, 7233. (e) Bolm, C.; Bienewald, F. Angew. Chem., Int.
CH2OH
CHO
5c
4
Me
O
O
Ed. Engl. 1995, 34, 2883. (f) Karimi, B.; Nezhad, M. G.;
Clark, J. H. Org. Lett. 2005, 7, 625. (g) Scarso, A.; Strukul,
G. Adv. Synth. Catal. 2005, 347, 1227. (h) Yuan, Y.; Bian,
Y.-B. Tetrahedron Lett. 2007, 48, 8518. (i) Shi, F.; Tse,
M. K.; Kaiserand, H. M.; Beller, M. Adv. Synth. Catal. 2007,
349, 2425. (j) Wang, X.-S.; Wang, X.-W.; Guo, H.-C.;
Wang, Z.; Ding, K.-L. Chem. Eur. J. 2005, 11, 4078.
4) (a) Martin, S. E.; Garrone, A. Tetrahedron Lett. 2003, 44,
CH2OH
CHO
CHO
6
48
65
NO2
Br
NO2
Br
CH2OH
(
(
7
8
9
36
24
24
24
82
94
96
75
549. (b) Shulpin, G. B.; Suss-Fink, G.; Shulpina, L. S.
J. Mol. Catal. A: Chem. 2001, 170, 17. (c) Liu, J.-H.;
Wang, F.; Sun, K.-P.; Xu, X.-L. Adv. Synth. Catal. 2007,
3
49, 2439. (d) Kantam, M. L.; Yadav, J.; Laha, S.; Sreedhar,
B.; Bhargava, S. Adv. Synth. Catal. 2008, 350, 2575.
e) Roy, M. N.; Poupon, J. C.; Charette, A. B. J. Org. Chem.
009, 74, 8510.
5) (a) Martin, S. E.; Rossi, L. I. Tetrahedron Lett. 2001, 42,
147. (b) Boring, E.; Geletii, Y. V.; Hill, C. L. J. Am. Chem.
OH
OH
O
O
(
2
7
Soc. 2001, 123, 1625. (c) Komatsu, N.; Uda, M.; Suzuki, H.
Chem. Lett. 1997, 1229. (d) Riley, D. P.; Shumate, R. E.
J. Am. Chem. Soc. 1984, 106, 3179. (e) Iwahama, T.;
Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 1998, 39, 9059.
OH
O
(
f) Semmelhack, M. F.; Schmid, C. R.; Cortés, D. A.; Chou,
1
0
C. S. J. Am. Chem. Soc. 1984, 106, 3374. (g) Kaneda, K.;
Fujie, Y.; Ebitani, K. Tetrahedron Lett. 1997, 38, 9023.
Me
Me
O
O
(
h) Iwahama, T.; Yosino, Y.; Keitoku, T.; Sakaguchi, S.;
a
Ishii, Y. J. Org. Chem. 2000, 65, 6502. (i) Jia, C.-G.; Jing,
F.-Y.; Hu, W.-D.; Huang, M.-Y.; Jiang, Y.-Y. J. Mol. Catal.
1994, 91, 139. (j) Chan, W.-L.; Sung, H.-J.; Koo, S.-Y.;
Han, M.-J.; Chi, K.-W. Tetrahedron Lett. 2009, 50, 559.
Reactions were carried out in an open system at r.t., with a molar
ratio of substrate/KNO /Br = 1:0.2: 0.3 mmol in MeCN (2 mL).
3
2
b
c
Isolated after chromatography.
Pyridinium tribromide (0.3 mmol) instead of bromine.
(
k) Minisci, F.; Punta, C.; Recupero, F.; Fontana, F.; Pedulli,
G. F. Chem. Commun. 2002, 688. (l) Martin, S. E.; Suarez,
D. F. Tetrahedron Lett. 2002, 43, 4475. (m) Kinen, C. O.;
Rossi, L. I.; de Rossi, R. H. J. Org. Chem. 2009, 74, 7132.
Acknowledgment
This work was supported by the National Natural Science Founda-
tion of China (20702043) and by the Program for New Century Ex-
cellent Talents in Yangzhou University.
(6) (a) Zhang, H.; Chen, C.-Y.; Liu, R.-H.; Xu, Q.; Zhao, W.-Q.
Molecules 2010, 15, 83. (b) Zhang, H.; Chen, C.-Y.; Liu,
R.-H.; Xu, Q.; Liu, J.-H. Synth. Commun. 2008, 38, 4445.
(c) Xie, Y.; Mo, W.-M.; Xu, D.; Shen, Z.-L.; Sun, N.; Hu,
B.-X.; Hu, X.-Q. J. Org. Chem. 2007, 72, 4288. (d) Liu,
R.-H.; Dong, C.-Y.; Liang, X.-M.; Wang, X.-J.; Hu, X.-Q.
J. Org. Chem. 2005, 70, 729. (e) Liu, R.-H.; Liang, X.-M.;
Dong, C.-Y.; Hu, X.-Q. J. Am. Chem. Soc. 2004, 126, 4112.
(
f) Yang, G.-Y.; Wang, W.; Zhu, W.-M.; An, C.-B.; Gao,
Synlett 2011, No. 4, 559–564 © Thieme Stuttgart · New York

5
64
Y. Yuan et al.
LETTER
X.-Q.; Song, M.-P. Synlett 2010, 437.
phases were separated. The aqueous layer was extracted with
CH Cl . The combined organic layers were washed with
(
(
7) Djerassi, C.; Scholz, C. R. J. Am. Chem. Soc. 1948, 70, 417.
8) Doxsee, K. M.; Hutchison, J. E. In Green Organic
Chemistry; Thompson Brooks/Cole: Pacific Grove CA,
2
2
H O and dried over MgSO . The solvent was removed under
2
4
vacuum, and the residue was purified by chromatography.
Representative Spectral Data of Sulfoxide – Methyl
Phenyl Sulfoxide
2
004, 120–124.
9) Suarez, A. R.; Baruzzi, A. M.; Rossi, L. I. J. Org. Chem.
998, 63, 5689.
10) (a) Bosch, E.; Kochi, J. K. J. Org. Chem. 1996, 60, 3172.
b) Roy, S.; Baiker, A. Chem. Rev. 2009, 109, 4054.
(
–
1 1
1
IR (KBr): nmax = 3265, 1477, 1038, 749, 692 cm . H NMR
(
(
(600 MHz, CDCl ): d = 2.73 (s, 3 H), 7.48–7.54 (m, 3 H),
3
1
3
(
7.64–7.65 (d, 2 H, J = 7.44 Hz). C NMR (150 MHz,
11) Silverstein, R. M.; Webster, F. X.; Kiemle, D. J. In
Spectrometric Identification of Organic Compounds; John
Wiley and Sons, Inc.: New York, 2005.
CDCl ): d = 44.13, 123.6, 129.5, 131.2, 145.7. MS (EI, 70
3
+
3h
eV): m/z (%) = 140 [M ].
Procedure for Oxidation of Benzaldehydes and
(
(
12) Thiemann, M.; Scheibler, E.; Wiegand, K. W. Nitric Acid,
Nitrous Acid, and Nitrogen Oxides, In Ullmann’s
Encyclopedia of Industrial Chemistry; Wiley-VCH:
Weinheim, 2005.
Acetophenones Using KNO –Br /PyHBr as Catalyst
A typical experiment was carried out in an open reaction
tube. Benzaldehyde or acetophenone (1 mmol) was added to
3
2
3
the mixture of KNO (0.2 mmol) and bromine (0.3 mmol) in
3
13) General Methods
MeCN (2 mL). The reaction mixture was stirred under aerial
conditions at 50 °C. The reaction progress was detected by
GC and TLC. After the starting material had disappeared,
Na S O aq solution was used to quench the reaction.
1H NMR and 13C NMR spectra were obtained with a Bruker
AVANCE 600 spectrometer in CDCl with TMS as an
3
internal standard. Infrared spectra were recorded with a
Bruker Tensor 27 FT-IR spectrometer using KBr pellets.
GC-MS was performed on a FINNIGAN Trace DSQ
chromatograph.
2
2
3
CH Cl was added to the reaction mixture, and the two
2
2
phases were separated. The aqueous layer was extracted with
CH Cl . The combined organic layers were washed with
2
2
Procedure for Oxidation of Sulfide Using KNO3–
PyHBr /Br as Catalyst
A typical experiment was carried out in an open reaction
tube. Sulfide (1 mmol) was added to the mixture of KNO3
H O and dried over MgSO . The solvent was removed under
2
4
vacuum, and the residue was purified by chromatography.
Representative Spectral Data of Aldehyde –
Benzaldehyde
3
2
–
1
(
(
0.1 mmol) and PyHBr (or bromine; 0.15 mmol) in MeCN
2 mL). The reaction mixture was stirred under aerial
IR (KBr): n = 3064, 2819, 1701, 1311, 1203, 746 cm .
3
max
1
H NMR (600 MHz, CDCl ): d = 7.51–7.54 (t, 2 H, J = 7.54
3
conditions at r.t. The reaction progress was detected by
GC and TLC. After the starting material had disappeared,
Na S O aq solution was used to quench the reaction.
Hz), 7.61–7.64 (t, 1 H, J = 7.43 Hz), 7.87–7.88 (d, 2 H,
1
3
J = 7.69 Hz), 10.00 (s, 1 H). C NMR (150 MHz, CDCl ):
3
d = 129.0, 129.7, 134.4, 136.4, 192.4. MS (EI, 70 eV): m/z
2
2
3
+
2c
CH Cl was added to the reaction mixture, and the two
(%) = 106 [M ].
2
2
Synlett 2011, No. 4, 559–564 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not be copied or
emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.
However, users may print, download, or email articles for individual use.