NaBrO3/NaHSO4 · H2O as a versatile reagent system for the oxidation of benzylic alcohols and aldehydes

Article abstract of DOI:10.1080/00397910600770664

The oxidation of benzylic alcohols and aldehydes by NaBrO₃ is efficiently promoted in the presence of NaHSO₄ · H ₂O. All reactions were performed under mild and completely heterogeneous conditions in good to high yields. Copyright Taylor & Francis Group, LLC.

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NaBrO3/NaHSO4 · H2O as a Versatile Reagent
System for the Oxidation of Benzylic Alcohols
and Aldehydes
Farhad Shirini a , Mohammad Ali Zolfigol b & Shayesteh Torabi a
a Department of Chemistry, College of Science, Guilan University, Rasht,
Iran
b Department of Chemistry, College of Science, Bu‐Ali Sina University,
Hamadan, Iran
Version of record first published: 16 Feb 2007.
To cite this article: Farhad Shirini, Mohammad Ali Zolfigol & Shayesteh Torabi (2006): NaBrO3/
NaHSO4 · H2O as a Versatile Reagent System for the Oxidation of Benzylic Alcohols and Aldehydes, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:19,
2833-2840
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Synthetic Communicationsw, 36: 2833–2840, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600770664
.
NaBrO3/NaHSO4 H2O as a Versatile
Reagent System for the Oxidation of
Benzylic Alcohols and Aldehydes
Farhad Shirini
Department of Chemistry, College of Science, Guilan University,
Rasht, Iran
Mohammad Ali Zolfigol
Department of Chemistry, College of Science, Bu-Ali Sina University,
Hamadan, Iran
Shayesteh Torabi
Department of Chemistry, College of Science, Guilan University,
Rasht, Iran
Abstract: The oxidation of benzylic alcohols and aldehydes by NaBrO3 is efficiently
.
promoted in the presence of NaHSO4 H2O. All reactions were performed under mild
and completely heterogeneous conditions in good to high yields.
.
Keywords: Alcohols, aldehydes, NaBrO3, NaHSO4 H2O, oxidation
Because of the important role of the oxidation reactions in functional group
transformations, a huge number of methods and reagents have been
reported for this purpose.[1–5]
Because of its capability in multielectrion transfer, sodium bromate, a
commercially available reagent, is thermodynamically considered to be a
strong oxidant. However, a literature search shows that sodium bromate
Received in the U.K. November 23, 2005
Address correspondence to Farhad Shirini, Department of Chemistry, College of
Science, Guilan University, Rasht 41335-1914, Iran. E-mail: shirini@guilan.ac.ir or
fshirini@yahoo.com
2833

2834
F. Shirini, M. A. Zolfigol, and S. Torabi
individually is not able to oxidize organic compounds, and it is usually used in
aqueous media in the presence of coreactants such as NH4Cl,[6] H2SO4,[7]
AlCl3,[8] HClO4,[9] KHSO4,[10] and CAN.[11] Most of the reported methods
suffer from disadvanges such as tedious workup, long reaction times,
undesirable side reactions, and the need for an excess amount of the reagent.
In continuation of our ongoing research program on the application of
hydrogen sulfate salts in functional group transformations,[12–15] we have
found that the benzylic alcohols and aldehydes are efficiently oxidized
.
using NaBrO3 in the presence of NaHSO4 H2O (Table 1, Scheme 1).
The oxidation of benzylic alcohols to their corresponding carbonyl
compounds is achieved in refluxing n-hexane and under completely hetero-
geneous reaction conditions in good to high yields (Table 1, entries 1–10).
Overoxidation of the products under this condition was not observed.
As shown in Table 1, when the reactions are carried out in refluxing
CH3CN, primary benzylic alcohols are converted to their corresponding
carboxylic acids quantitatively (entries 11–21).
Also, this reagent system is capable of oxidizing benzylic aldehydes to
corresponding acids in refluxing CH3CN. All reactions were performed
under completely heterogeneous reaction conditions in good to high yields
(Table 1, entries 22–35).
It should be noted that the progress of the reaction strongly depends on the
.
presence of H2O in the structure of NaHSO4 H2O; the reaction in the
presence of NaHSO4 does not proceed under the same reaction conditions
(Table 1, entry 36).
To show the efficiency of the selected method, Table 2 compares some of
the results with some of those reported in the literature.[5,16]
In conclusion, we have demonstrated an efficient method for the
oxidation of benzylic alcohols and aldehydes using NaBrO3 in the presence
.
of NaHSO4 H2O. The ready availability and low cost of the reagents, good
to high yields of the products, simple and convenient procedure, and hetero-
geneous nature of the reaction conditions are among the other advantages of
the present method.
EXPERIMENTAL
All of the products were characterized by comparison of their physical and
spectral data with those of known samples. All yields refer to isolated products.
General Procedure for the Oxidation of Benzylic Alcohols to Their
Corresponding Aldehydes and Ketones
The substrate (1 mmol) was added to a suspension of NaBrO3 (0.47 g, 3 mmol)
.
and NaHSO4 H2O (0.14 4, 1 mmol) in n-hexane (5 mL). The mixture was

.
NaBrO3/NaHSO4 H2O as Versatile Reagent System
2835
Table 1. Oxidation of benzylic alcohols and aldehydes using NaBrO3 in the presence
a
.
of NaHSO4 H2O
Time Yield
Solvent (min) (%)b
Entry
1
Substrate
Product
n-hexane
n-hexane
2
90
95
2
3
4
10
n-hexane
n-hexane
3
90
70
17
5
6
7
8
n-hexane
n-hexane
n-hexane
n-hexane
18
60
65
10
70
70
60
80
9
n-hexane
n-hexane
7
90
80
10
10
(continued)

2836
F. Shirini, M. A. Zolfigol, and S. Torabi
Table 1. Continued
Time Yield
Solvent (min) (%)b
Entry
11
Substrate
Product
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
20
20
20
20
30
90
80
95
95
90
12
13
14
15
16
17
18
19
CH3CN
CH3CN
CH3CN
CH3CN
30
30
35
35
80
80
70
70
20
21
CH3CN
CH3CN
45
10
80
95
(continued)

.
NaBrO3/NaHSO4 H2O as Versatile Reagent System
2837
Table 1. Continued
Time Yield
Solvent (min) (%)b
Entry
22
Substrate
Product
CH3CN
CH3CN
4
9
90
90
23
24
CH3CN
CH3CN
9
9
90
85
25
26
27
CH3CN
CH3CN
15
5
80
90
28
CH3CN
15
85
29
30
CH3CN
CH3CN
5
5
90
85
31
32
CH3CN
CH3CN
15
5
90
80
(continued)

2838
F. Shirini, M. A. Zolfigol, and S. Torabi
Table 1. Continued
Time Yield
Solvent (min) (%)b
Entry
33
Substrate
Product
CH3CN
CH3CN
5
60
70
34
15
35
36
CH3CN
CH3CN
15
20
70
0c
aIsolated yields.
bProducts were characterized by their physical constants, comparison with authentic
samples, and IR and NMR spectroscopy.
cReaction was performed in the presence of NaHSO4, and the starting material was
recovered at the end of the reaction.
refluxed for the appropriate time (Table 1). The progress of the reaction was
monitored by thin-layer chromatography (TLC) (eluent: CCl4/Et2O, 6:1).
After completion of the reaction, the mixture was coolded to room tempera-
ture and filtered. The solid material was washed with CH2Cl2 (10 mL). The
solvent was evaporated, and the crude product was purified by chromato-
graphy on silica gel using an appropriate eluent. The pure products were
obtained in good to high yields (Table 1).
Scheme 1.

.
NaBrO3/NaHSO4 H2O as Versatile Reagent System
2839
Table 2. Comparison of some of the Results obtained by our method (1), with some
of those reported with H5IO6/pyridinium chlorochromate (2),[16] and hydrogen
peroxide in the presence of a cobalt(II) complex (3)[5]
Yield, % (min)
Entry
1
Product
(1)
(2)
(3)
—
—
90 (2)
89 (120)
71 (120)
2
3
70 (60)
90 (7)
90 (5)
PhCOPh
97 (120)
—
89 (180)
75 (420)
4
5
—
85 (15)
72 (540)
General Procedure for the Oxidation of Benzylic Alcohols and
Aldehydes to Their Corresponding Carboxylic Acids
To a solution of the substrate (1 mmol) in CH3CN (5 mL), NaBrO3 (0.47 g,
.
3 mmol) and NaHSO4 H2O (0.14 4, 1 mmol) were added and refluxed for
the appropriate time (Table 1). The progress of the reaction was
monitored by TLC (eluent: CCl4/Et2O, 6:1). After completion of the
reaction, the mixture was coolded to room temperature and filtered.
The solid material was washed with CH3CN (10 mL). Evaporation of the
solvent followed by column chromatography on silica gel gave the corre-
sponding carboxylic acid in good to high yieds (Table 1).
ACKNOWLEDGMENT
We are thankful to the Guilan University Research Council for partial support
of this work.
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