I2O5: mild and efficient reagents for the oxidation of alcohols in water

Article abstract of DOI:10.1016/j.tetlet.2007.02.123

The mild and efficient nature of HIO₃ and I₂O₅ as environmentally benign, commercially available, atom efficient, and safe reagents for the oxidation of alcohols has been demonstrated. Additionally, these oxidants are highly chemoselective, and effect smooth room temperature oxidation of various electron-rich alcohols with catalytic amounts of KBr in water.

Full text of DOI:10.1016/j.tetlet.2007.02.123

Tetrahedron Letters 48 (2007) 3017–3019
I O : mild and efficient reagents for the oxidation
2
5
of alcohols in water
*
Zhong-Quan Liu, Yankai Zhao, Haiqing Luo, Lingzhi Chai and Qiuju Sheng
Institute of Organic Chemistry, Gannan Normal University, Ganzhou, Jiangxi 341000, PR China
Received 24 January 2007; revised 19 February 2007; accepted 26 February 2007
Available online 1 March 2007
Abstract—The mild and efficient nature of HIO and I O as environmentally benign, commercially available, atom efficient, and
3
2
5
safe reagents for the oxidation of alcohols has been demonstrated. Additionally, these oxidants are highly chemoselective, and effect
smooth room temperature oxidation of various electron-rich alcohols with catalytic amounts of KBr in water.
Ó 2007 Elsevier Ltd. All rights reserved.
The oxidation of alcohols into the corresponding alde-
hydes or ketones is one of the most important functional
group transformations in organic synthesis. Although
numerous methods using a variety of reagents and condi-
tions have been explored, the development of selective
oxidation using safe, economic, and environmentally
benign agents remains a critical challenge in organic syn-
oxidants and catalysts (Miller’s system: 2 equiv I2/
10 mol % TEMPO/Toluene; Kita’s system: 2.2 equiv
PhIO/10 mol % KBr or 1.1 equiv PhIO/1.0 equiv KBr)
in spite of their high efficiency. Recently, we found the
aromatization of 1,3,5-trisubstituted pyrazolines could
not be carried out smoothly by IA and IP unless a cata-
8
lytic amount of bromide salts were added. The addition
1
thesis. Hypervalent iodine reagents have been exten-
of bromide salts such as NaBr, KBr, and CuBr was
found to active IA and IP remarkably. Then, we began
to question that a bromide salt-catalyzed alcohol oxida-
tion with more atom-efficient stoichiometric IA and IP
could be established. Fortunately, we successfully
accomplished an efficient KBr-catalyzed alcohol oxida-
tion at room temperature with a number of economic,
commercially available, atom-efficient, environmental
friendly, and safe iodine (V) agents in water (Table 1).
sively explored in organic chemistry as a result of their
high efficiency, commercial availability, easy handling,
2
and low toxicity. For example, 1-hydroxy-1,2-benzio-
doxol-3(1H)-one-1-oxide (IBX) and Dess–Martin peri-
odinane (DMP) have been successfully used for the
oxidation of alcohols to the corresponding carbonyl
3
compounds. However, most of these procedures were
conducted in organic solvents such as DMSO, CH Cl ,
2
2
and acetone. Herein, we wish to report an efficient selec-
tive catalytic oxidation of primary and secondary alco-
hols to the corresponding aldehydes and ketones in
Although almost equally efficient, we favored the use of
IP in these reactions over its diploid dosage oxidant IA.
Initial investigation of stoichiometric oxidation of
alcohols using IP catalyzed by KBr was carried out
utilizing of 1-phenylethanol as substrate at room
temperature in water. Theoretically, the mole ratio of
I O /alcohol may be about 1/5 as iodine was produced
water by using iodic acid (IA, HIO ) or its anhydride io-
3
dine pentoxide (IP, I O ) as the stoichiometric oxidants.
2
5
Although IA and IP are widely utilized in industry, these
convenient inorganic hypervalent iodines have rarely
4
been used in organic procedures. According to the
2
5
5
investigation of Nicolaou et al., alcohols are inert to
in the oxidation. As a matter of fact, the quantitative
oxidation of 1-phenylethanol cannot be achieved unless
more than 20 mol % of I O or 40 mol % of HIO is
IA and IP in DMSO which is believed to form complex.
Our research was inspired by the results of the TEMPO–
2
5
3
6
Br /I system by Miller and Hoerrner and the PhIO–
present regardless of the dosage of KBr. In addition,
the appropriate quantity of the catalyst was then inves-
tigated in the oxidation of 1-phenylethanol using
2
2
7
KBr system by Kita and co-workers. However, both
suffered from overloading of the stoichiometric terminal
2
5 mol % of I O catalyzed by KBr with quantity vary-
2 5
ing from 1 mol % to 15 mol %. It is seen from Figure 1
that 5 mol % of KBr was found to be superior to others.
*
0
Corresponding author. E-mail: liu_z_q@sina.com
040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.02.123

3018
Z.-Q. Liu et al. / Tetrahedron Letters 48 (2007) 3017–3019
a
3 2 5
Table 1. Atom-efficient oxidation of alcohols using HIO and I O in water
OH
O
I O (25mol%)/KBr(5mol%)
2
5
R1
Product
CHO
R2
R1
R2
H2O, RT
Method
b
b
c
Entry
1
Substrate
CH OH
Time (h)
24
Conv. (%)
Select (%)
Yield (%)
2
A
A
A
A
B
87.8
74.8
94.3
90
71.9
100
100
89.5
100
100
100
100
62
70
92
80
86
72
98
98
CH OH
CHO
2
2
3
4
5
6
7
8
9
4.5
4
Cl
Br
Cl
Br
CH OH
CHO
2
CH OH
CHO
2
12
12
12
12
24
CH OH
CHO
2
90.5
75
MeO
MeO
CH OH
CHO
2
A
A
A
CH OH
CHO
2
100
100
CH OH
CHO
2
O N
2
O N
2
OH
O
A
A
3.5
8
100
100
100
100
98
99
OH
O
1
0
Cl
Cl
OH
O
1
1
1
1
2
3
A
A
B
12
5
100
100
100
100
100
100
98
96
96
O N
O N
2
2
OH
O
OH
O
12
MeO
MeO
OH
O
14
A
2.5
100
100
96
15
OH
O
A
24
22.3
100
20
a
Reaction conditions: alcohol (10 mmol), water, room temperature. Method A: I
0.5 mmol).
Conversions and selectivities are determined by GC–MS.
Yield of isolated chromatographically pure compound.
O
2 5
(2.5 mmol), KBr (0.5 mmol); Method B: I
2
O
5
(5 mmol), KBr
(
b
c
Under the following conditions: 10 mmol of alcohol,
5 mol % of I O , 5 mol % of KBr, H O, room temper-
2
100
2
5
2
ature, almost all electron-rich alcohols were converted
into their corresponding aldehydes, and ketones in high
isolated yields (Table 1). It is seen from Table 1 that
80
60
40
20
0
9
substituted benzyl alcohols gave good yields of the cor-
responding benzaldehydes derivatives (entries 1–8). The
25% of benzoic acid and 9% of 4-methylbenzoic acid
were, respectively, obtained during the oxidation of
the corresponding phenylmethanol (entry 1) and p-tolyl-
methanol (entry 4). Aromatic secondary alcohols gave
almost quantitative yields of the corresponding ketones
and no over oxidation by-products were found (entries
1
5
1
1
mol % KBr
mol % KBr
0 mol % KBr
5 mol % KBr
0
1
2
3
4
5
6
Time (h)
9
–14). Cyclohexanone was obtained in 20% yield and
Figure 1. Oxidation of 1-phenylethanol using I
O
2 5
catalyzed by KBr
100% selectivity in the oxidation of cyclohexanol (entry
with varying quantity.
15). Due to the presence of double bond, the a,b-unsat-

Z.-Q. Liu et al. / Tetrahedron Letters 48 (2007) 3017–3019
3019
urated aldehydes and ketones were not obtained from
the corresponding alcohols. The alcohols with bromina-
tion of their aryl groups were produced in low yields
from the corresponding primary alkyl substituted alco-
hols. A complex mixture was formed in the oxidation
of some simple alcohols such as ethanol and n-butanol.
The oxidation of aliphatic alcohols cannot be achieved
in the catalytic process, however, the transition metal-
free, cost-low, atom-efficient and the organic solvent-
free features make this procedure very attractive.
Rev. 2002, 102, 2523; (c) Varvoglis, A. Hypervalent Iodine in
Organic Synthesis; Academic Press: San Diego, 1997; (d)
Wirth, T.; Hirt, U. H. Synthesis 1999, 1271; (e) Stang, P. J.
J. Org. Chem. 2003, 68, 2997; (f) Tohma, H.; Kita, Y. Adv.
Synth. Catal. 2004, 346, 111; (g) Wirth, T. Angew. Chem.
2
005, 117, 3722; Angew. Chem., Int. Ed. 2005, 44, 3656.
. (a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155;
b) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113,
277; (c) Wirth, T. Angew. Chem. 2001, 113, 2893; Angew.
3
(
7
Chem., Int. Ed. 2001, 40, 2812; (d) More, J. D.; Finney, N.
S. Org. Lett. 2002, 4, 3001; (e) Liu, Z.; Chen, Z. C.; Zheng,
Q. G. Org. Lett. 2003, 5, 3321; (f) Surendra, K.; Krishna-
veni, N. S.; Reddy, M. A.; Nageswar, Y. V. D.; Rao, K. R.
J. Org. Chem. 2003, 68, 2058; (g) Weik, S.; Nicholson, G.;
Jung, G.; Rademann, J. Angew. Chem. 2001, 113, 1489; .
Angew. Chem., Int. Ed. 2001, 40, 1436.
In summary, this work demonstrates that I O /KBr is a
2
5
very efficient, environmentally benign, commercially
available, safe, atom-efficient, and low-cost system for
the oxidation of alcohols. Additionally, these alternative
reagents to IBX and DMP are chemoselective, and effect
smooth room temperature oxidation of various electron-
rich alcohols with catalytic amounts of KBr in water.
These mild conditions may be helpful for a variety of
other substrates that cannot tolerate strong oxidants.
Extension of this process to expanded functional groups
and further studies on the chemical selectivity are under-
way in this laboratory.
4
. For selected examples, see: (a) Hiroto, U.; Keiji, N.;
Katsumi, O.; Patent No. JP 06040710; Chem. Abstr. 1994,
1
20 326849; (b) Chandrasekhar, S.; Gopalaiah, K. Tetra-
hedron Lett. 2002, 43, 4023; (c) Hashemi, M. M.; Rahimi,
A.; Jaberi, Z. K.; Ahmadibeni, Y. Acta Chim. Slov. 2005,
52, 86.
5. Nicolaou, K. C.; Montagnon, T.; Baran, P. S. Angew.
Chem. 2002, 114, 1444; Angew. Chem., Int. Ed. 2002, 41,
1
386.
6
7
. Miller, R. A.; Hoerrner, R. S. Org. Lett. 2003, 5, 285.
. (a) Tohma, H.; Takizawa, S.; Maegawa, T.; Kita, Y.
Angew. Chem. 2000, 112, 1362; Angew. Chem., Int. Ed.
2000, 39, 1306; (b) Tohma, H.; Maegawa, T.; Takizawa, S.;
Kita, Y. Adv. Synth. Catal. 2002, 344, 328.
Acknowledgment
8
9
. Chai, L. Z.; Zhao, Y. K.; Sheng, Q. J.; Liu, Z. Q.
Tetrahedron Lett. 2006, 47, 9283.
. Typical procedure: An alcohol (10 mmol) was mixed with
iodine pentoxide (2.5 mmol) and KBr (0.5 mmol) in water
The authors thank the Gannan Normal University for
financial support.
(
30 mL). The mixture was stirred at room temperature until
the reaction was completed as monitored by TLC. Extrac-
tion of the reaction mixture with ether, washed by Na SO
dried with anhydrous MgSO , removal of the solvent under
References and notes
2
3
,
1
. Hudlicky, M. Oxidations in Organic Chemistry; American
Chemical Society: Washington, DC, 1990.
4
reduced pressure, and column chromatographic separation
1
2
. For reviews, see: (a) Stang, P. J.; Zhdankin, V. V. Chem.
Rev. 1996, 96, 1123; (b) Zhdankin, V. V.; Stang, P. J. Chem.
gave the pure product which was identified by H NMR.
The conversion and selectivity were determined by GC–MS.