Zinc(II)-catalyzed oxidation of alcohols to carbonyl compounds with chloramine-T

Article abstract of DOI:10.1016/j.tetlet.2012.11.076

Efficient oxidation of primary and secondary alcohols to the corresponding carbonyl compounds can be carried out in acetonitrile, using chloramine-T in the presence of catalytic zinc(II) salts. Primary alcohols are selectively oxidized to aldehydes without carboxylic acid byproduct.

Full text of DOI:10.1016/j.tetlet.2012.11.076

Tetrahedron Letters 54 (2013) 533–535
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Zinc(II)-catalyzed oxidation of alcohols to carbonyl compounds
with chloramine-T
a
b
a
b
a
a
b,
⇑
Peng Wang , Jin Cai , Jiabin Yang , Chunlong Sun , Lushen Li , Huayou Hu , Min Ji
a
School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, China
School of Chemistry & Chemical Engineering, Southeast University, Nanjing 210096, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2012
Revised 12 November 2012
Accepted 20 November 2012
Available online 28 November 2012
Efficient oxidation of primary and secondary alcohols to the corresponding carbonyl compounds can be
carried out in acetonitrile, using chloramine-T in the presence of catalytic zinc(II) salts. Primary alcohols
are selectively oxidized to aldehydes without carboxylic acid byproduct.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Catalytic oxidation
Zinc(II) salt
Chloramine-T
Oxidation of primary and secondary alcohols to the correspond-
ing carbonyl compounds is a frequently used transformation in or-
oxidation product 2 were obtained employing 20 mol % of ZnBr
as the catalyst in acetonitrile (Table 1). Modest yields were ob-
served with ZnCl , ZnSO , and Zn(OAc) . ZnBr showed a remark-
ably high activity even at room temperature, while the
2
1
ganic synthesis. A variety of methods have been documented in the
2
4
2
2
2
3
4
literature, such as Dess–Martin oxidation, Swern oxidation, and
various transition metal reagents. However, the use of a stoichiom-
etric amount of transition metal oxidants and a large quantity of
toxic byproducts was still the disadvantage of conventional meth-
ods. Therefore, there has been a continuous demand to develop
environmentally friendly synthetic methods for this conversion.
Zinc salts have been widely used in organic synthesis especially
taking the place of expensive and toxic metals in some reactions,
transformation cannot proceed in the absence of ZnBr
2
at room
temperature.
In order to elucidate the efficiency of the catalyst, several
amounts of ZnBr were then examined for the oxidation of diphen-
ylcarbinol using chloramine-T in acetonitrile. As indicated in Table
2, it is clear that 20 mol % ZnBr shows exceedingly high catalytic
efficiency compared to 5 mol % ZnBr and there is no significant in-
crease in the yield at a mole rate of 50 mol %. Hence, the required
catalyst to ZnBr is 20 mol %, beyond which no appreciable effect
2
2
2
5
because of their inexpensiveness, abundance, and low toxicity.
At the same time, chloramine-T which was used usually as biocide
and mild disinfectant is an inexpensive, commercially available re-
agent. When used as the oxidant, chloramine-T has an advanta-
geous point that the catalytic oxidation could be performed by a
simple operation without adding any bases and dehydrating
2
on the yield has been observed.
Encouraged by these results, we screened several different sol-
2
vents for the oxidation of 1 using ZnBr and chloramine-T at room
temperature. Excellent yields of benzophenone were observed
after 12 h in dichloromethane and acetonitrile (Table 3, entries 1
and 2) among the solvents examined. However, tetrahydrofuran
(THF), dimethyl sulfoxide (DMSO), toluene, and diethylether were
not suitable for this transformation.
The substrate scope of this method was investigated under stan-
dard reaction conditions, and the results are shown in Table 4.8
A variety of alcohols were efficiently oxidized to their correspond-
ing carbonyl compounds. The para- and meta-substituted benzyl
alcohols were oxidized to the corresponding substituted benzalde-
hydes in good to excellent yields (Table 4, entries 2–9). It seems that
the reaction rates of benzyl alcohols with electron-donating groups
are higher than electron-withdrawing groups. Dimethylamino,
thiomethyl, ester, and cyano groups were tolerated under standard
6
7
agents. Inspired by recent findings, herein we report that a sim-
ple method to oxidized primary and secondary alcohols to corre-
sponding carbonyl compounds under mild conditions by using
chloramine-T as an oxidizing agent and zinc(II) salt as a catalyst.
In the preliminary study, we chose the oxidation of diphenyl-
carbinol 1 as our model system, and several commercial zinc(II)
salts as potential catalysts were used to screen the most efficient
catalyst and the best reaction conditions. The results were shown
in Table 1. It was found that high conversion and good yield of
⇑
Corresponding author. Tel./fax: +86 25 83272078.
E-mail address: jimin@seu.edu.cn (M. Ji).
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.076

5
34
P. Wang et al. / Tetrahedron Letters 54 (2013) 533–535
Table 1
Table 4
Screening of the zinc(II) salts used as the catalyst
Scope of ZnBr
2
-catalyzed the oxidation of alcohols to corresponding carbonylsa
OH
ZnBr2 (0.2 eq)
O
R1 R2
R
1
R
2
chloramine-T (1.0 eq)
CH CN, reflux
3
Entry
1
Alcohols
Time (h)
1.5
Yield (%)
Entry
1
Catalyst (0.2 equiv)
Time (h)
Yielda (%)
OH
—
—
5
12
3
3
3
46
N.R.
80
85
88
95
87
b
95
2
3
4
5
6
ZnCl
ZnSO
Zn(OAc)
2
4
OH
96b
2
3
1.5
3
2
ZnBr
ZnBr
2
1.5
12
OH
b
7
2
85
94
90
N
a
Isolated yield by column chromatography.
At room temperature.
OH
OH
b
4
5
1.5
2
MeO
MeS
Table 2
The amounts of catalyst optimization for the oxidation of diphenylcarbinol
OH
6
7
8
2
3
4
91
83
80
Cl
Entry
ZnBr
2
(equiv)
Time (h)
Yield (%)
OH
1
2
3
4
5
1
1
95
95
95
90
82
MeOOC
NC
0.5
0.2
0.1
0.05
1.5
1.5
3
OH
5
OH
9
2
88
NO2
OH
OH
Table 3
10
11
2
2
4
90
89
78
N
N
Optimization of solvents for the oxidation of diphenylcarbinol
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
CH
CH
2
Cl
CN
2
12
12
24
24
24
24
82
87
60
65
70
30
O
OH
3
12
13
O
THF
DMSO
Toluene
2
Et O
OH
1.5
2
95b
90b
14
OH
OH
91b
15
3
OH
1
1
6
7
4
96b
conditions (Table 4, entries 3, 5, 7, and 8). Moreover, the generality
of the methodology was further confirmed by applying the same
reaction conditions to heterocyclic alcohols. The transformation of
OH
5
5
95
92
2
-hydroxymethylpyridine and 3-hydroxymethylpyridine to the
corresponding aldehydes proceeded smoothly in good yields
Table 4, entries 10 and 11). Piperonyl aldehyde was achieved from
OH
1
1
8
9
(
MeO
Cl
piperonyl alcohol in moderate yield (Table 4, entry 12). Under the
present reaction conditions, simple aliphatic alcohols, such as 1-
butanol, were also oxidized to aliphatic aldehydes in high yields.
With the increase of the carbon chain the reactivity decreased
slightly. For example, the oxidation of 1-hexanol needs 2 h with
OH
5
5
90
93
Cl OH
9
1
0% yield, consuming more time than the transformation of
-butanol. In these reactions, the produced aldehydes were not
20
Cl
F
oxidized further to carboxylic acids, indicating the potential utility
of ZnBr /chloramine-T system as a selective oxidant.
OH
2
2
2
1
2
4.5
1.5
86
94
This method also can be applied to the oxidation of secondary
carbinols under the same reaction conditions. Aliphatic and ben-
zylic secondary alcohols were effectively oxidized to correspond-
ing ketones (Table 4, entries 15–23), but the reaction rate is
slower than primary alcohols. For example, the oxidation of cyclo-
hexanol afforded cyclohexanone taking 4 h in 96% yield. Similarly,
substituted 1-phenylethanols like 1-(2,6-dichloro-3-fluorophenyl)
ethanol were converted into the corresponding acetophenones
slower than 1-phenylethanol, but still in good yields. Both electron
donating and electron withdrawing groups were tolerated in this
transformation, such as methoxy- and halogen-substituted
OH
OH
Me
2
3
2
89
Cl
Cl
a
Unless otherwise stated, reaction was run using alcohol (1 mmol), 20 mol % ZnBr
and 1 equiv chloramine-T in CH
2
,
3
CN at reflux.
b
Determined by GC analysis.

P. Wang et al. / Tetrahedron Letters 54 (2013) 533–535
535
nient for oxidizing both primary and secondary alcohols as other
methods reported in the literature. Additional investigations will
focus on the extension of this catalytic system.
Acknowledgments
This work was supported by the National Basic Research Pro-
gram of China (No. 2011CB933503). H. Hu is grateful to China Post-
doctoral Science Foundation funded project (No. 2012M511645)
and NSFC (No. 21202058) for their financial support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
1
1.076.
Scheme 1. Proposed reaction mechanism of alcohol oxidation by chloramine-T
with ZnBr as catalyst.
2
References and notes
1
.
.
Smith, M. B.; March, J. March’s Advanced Organic Chemistry: Reactions,
Mechanisms, and Structure, 5th ed.; Wiley-Interscience: New York, 2001.
(a) Brink, G.-J. T.; Arends, I. W. C. E.; Sheldon, R. A. Science 2000, 287, 1636–1639;
1
-phenylethanols. We also tested some substituted diphenylc-
2
arbinols (Table 4, entries 22 and 23). In the case of 4-methyl-
benzhydrol, its corresponding ketone was obtained in high
yield.
(
b) Mallat, T.; Baiker, A. Chem. Rev. 2004, 104, 3037–3058; (c) Zhan, B.-Z.;
Thompson, A. Tetrahedron 2004, 60, 2917–2935.
3
.
.
(a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155–4156; (b) Li, P.; Majireck,
M. M.; Korboukh, I.; Weinreb, S. M. Tetrahedron Lett. 2008, 49, 3162–3164.
(a) Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651–1660; (b) McConnell, J. R.;
Hitt, J. E.; Daugs, E. D.; Rey, T. A. Org. Process Res. Dev. 2008, 12, 940–945.
On the basis of the above results and mechanism reported in the
4
9
literature, a plausible reaction mechanism is shown in Scheme 1.
Initially, coordination of alcohols to zinc bromide results in facili-
tating the cleavage of the hydroxyl bond. Then chloramine-T
successively reacts with alcohols to afford the intermediate 3.
Finally, the decomposition of the intermediate 3 into carbonyl
compounds proceeds in a concerted manner. Therefore, complexa-
tion of the oxygen atom of the alcohols with zinc should accelerate
the cleavage of the O–H bond and the hydrogen transfer in the
presence of zinc bromide.
In conclusion, an efficient procedure for the conversion of alco-
2
hols into the corresponding carbonyl compounds using ZnBr /chlo-
ramine-T system has been developed. Primary and secondary
alcohols are rapidly oxidized without overoxidation to carboxylic
acids. This novel method makes use of very easily available and
cheaper reagents under mild conditions. It seems to be as conve-
5. Wu, X.-F. Tetrahedron Lett. 2012, 53, 3397–3399.
6
7
.
.
Campbell, M. M.; Johnson, G. Chem. Rev. 1978, 78, 65–79.
(a) Kitagawa, H.; Mukaiyama, T. Chem. Pharm. Bull. 2002, 50, 1276–1279; (b)
Cao, H. T.; Grée, R. Tetrahedron Lett. 2009, 50, 1493–1494; (c) Li, S.-J.; Wang, Y.-G.
Tetrahedron Lett. 2005, 46, 8013–8015.
8.
General procedure for oxidation of alcohols: A CH
3
CN solution of diphenylcarbinol
1
(1 mmol), ZnBr (45 mg, 0.2 mmol), and chloramine-T (282 mg, 1 mmol) was
2
placed in a three necked flask with a reflux condenser. After the mixture was
stirred under reflux for 1.5 h, it was quenched by adding water and the resulting
mixture was extracted with AcOEt. Removal of the solvent under reduced
pressure gave the crude product, which was purified by column
chromatography on silica gel (n-hexane/AcOEt = 8/1) to give benzophenone 2
(173 mg, 95% yield). 1H NMR (300 MHz, CDCl ) d (ppm) 7.46–7.51 (m, 4H), 7.57–
3
7
1
2
.62 (m, 2H), 7.80–7.82 (m, 4H). 13C NMR (75 MHz, CDCl
32.3, 137.4, 196.5. ESI-MS: calcd [M+Na] for C13
05.0628. All other carbonyl derivatives have spectral data in agreement with
3
) d (ppm) 128.1, 129.9,
H10ONa: 205.0624, found:
+
authentic samples and/or with literature data.
9.
Hassan, Y. I.; Saeed, N. H. M. E-J. Chem. 2012, 9, 642–649.