Microwave-assisted oxidation of alcohols with N,N,N′,N′- tetrabromobenzene-1,3-disulfonamide and poly(N-bromobenzene-1,3-disulfonamide) under solvent-free conditions

Article abstract of DOI:10.1002/jccs.200700177

An efficient and mild methodology for the oxidation of primary and secondary alcohols to the corresponding carbonyl functions is described with N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide and poly(N-bromobenzene-1,3-disulfonamide) using microwave irradiation under solvent-free conditions. Aliphatic, benzylic and allylic alcohols are rapidly oxidized without over-oxidation to carboxylic acids. Secondary carbinols are slowly oxidized so that the reaction is highly chemoselective.

Full text of DOI:10.1002/jccs.200700177

Journal of the Chinese Chemical Society, 2007, 54, 1257-1260
1257
Microwave-assisted Oxidation of Alcohols with
N,N,N¢,N¢-Tetrabromobenzene-1,3-disulfonamide and
Poly(N-bromobenzene-1,3-disulfonamide) under Solvent-free Conditions
Ramin Ghorbani-Vaghei,* Hojat Veisi and Mostafa Amiri
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamadan, Iran
An efficient and mild methodology for the oxidation of primary and secondary alcohols to the corre-
sponding carbonyl functions is described with N,N,N¢,N¢-tetrabromobenzene-1,3-disulfonamide and
poly(N-bromobenzene-1,3-disulfonamide) using microwave irradiation under solvent-free conditions.
Aliphatic, benzylic and allylic alcohols are rapidly oxidized without over-oxidation to carboxylic acids.
Secondary carbinols are slowly oxidized so that the reaction is highly chemoselective.
Keywords: Oxidation; Alcohols; Solid state; Microwave; TBBDA; PBBS.
INTRODUCTION
The oxidation of the hydroxyl group to a carbonyl
are the enhanced selectivity, much improved reaction rates,
milder reaction conditions and formation of cleaner prod-
ucts. These reactions are especially appealing as they can
be carried out in open vessels, thus avoiding the risk of de-
velopment of high pressures in addition to the associated
ease of manipulation.
functionality is an important transformation in organic syn-
thesis and several methods are available to accomplish this
1
-4
conversion under a variety of reaction conditions. Be-
cause of its significant role in synthetic chemistry, this re-
action continues to receive attention from chemists in
5
search of newer and selective oxidation protocols. There-
RESULTS AND DISCUSSION
fore, selective methods allowing for oxidation of primary
alcohols to aldehydes without over-oxidation to carboxylic
acids remains challenging. In recent years organic reac-
tions assisted by microwave irradiation have gained special
In continuation of our ongoing work on development
of highly efficient oxidation protocols, we observed the ox-
idation of neat alcohols (Scheme I) with N,N,N¢,N¢-tetra-
bromobenzene-1,3-disulfonamide [TBBDA] and poly(N-
6-13
attention. The chief features of the microwave reactions
Scheme I
R1
R1
TBBDA or PBBS
MW(solvent-free)
OH
O
R2
R2
R = aryl, alkyl
1
R2= H, alkyl
Br
Br
N
Br
Br
)
N S
Br
N
S
N
S
Br
CH2
CH2 )n
S
O O
O O
O O
O O
PBBS
TBBDA
*
Corresponding author. Fax: (+98) 811 8272404; E-mail: ghorbani@basu.ac.ir

1
258 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Ghorbani-Vaghei et al.
OH
CHO
(85%)
(1mmol)
TBBDA (0.1g) or PBBS (0.2g)
MW (solvent-free)
+
+
OH
O
(10%)
(1mmol)
1
4-21
bromobenzene-1,3-disulfonamide) [PBBS]
using mi-
The method was found to be highly selective for pri-
mary aromatic alcohols. In a mixture of benzyl alcohol and
benzohydrol, we obtained 85% of benzaldehyde and 10%
of benzophenone.
crowave irradiation under solvent-free conditions can be
carried out very fast.
The formation of carbonyl compounds from alcohols
+
most likely involves a Br transfer from reagent to sub-
It is noteworthy that a,b-unsaturated alcohols such
as cinamyl alcohol underwent oxidation with high chemo-
selectivity without addition of reagent to the C=C bond.
Furthermore, functional groups such as p-nitro, p-methyl,
p-methoxy (Entries 2, 3, 4) were also inert to this reagent
and no by-product formation was observed.
strate. The presented results prove TBBDA and PBBS to be
efficient reagents for the oxidation of alcohols. The pre-
sented oxidation method has the additional advantage of
not requiring highly specialized equipment and expensive
reagents. The reaction is fast and easy to perform under
mild reaction conditions, no side product formation, very
low reaction time, and a wide range of aliphatic and benzilic
alcohols can be converted to their corresponding aromatic
aldehydes and ketones.
7
b
In contrast to our previous reports, halogenation of
aromatic rings did not occur and only hydroxyl group oxi-
dation was observed.
The results of the conversion of various alcohols to
aldehydes and ketones are presented in Table 1.
Since reagents contain bromine atoms which are at-
tached to nitrogen atoms it is very possible that this reagent
Benzyl alcohol, 2,4-dicholorobenzyl alcohol and p-
nitro benzyl alcohol (Entries 1, 6, 2) reacted very fast,
whereas other benzylic alcohols required a longer reaction
time. It appeared that substituents on the aromatic ring af-
fected the rate of the reaction; the introduction of elec-
tron-withdrawing substituents into the aromatic ring in-
creases the yield compared to electron-donating substitu-
ents (Entries 3, 4).
+
releases Br in situ which can act as a Lewis acid and oxi-
2
dizing agent in the reaction medium. Therefore the fol-
2
lowing mechanism can be suggested for the conversion of
2
alcohols to aldehydes and ketones (Scheme II).
3
We found that in the reaction, aliphatic alcohols (En-
tries 9, 10) were slower and less reactive than aromatic al-
cohols. Also, in this reaction, secondary alcohols were
slower and the yield lower than with primary alcohols. Pri-
mary and secondary alcohols were found to be oxidized to
aldehydes and ketones without over-oxidation to carbox-
ylic acids (Scheme I).
CONCLUSION
In conclusion we have extended successfully the ap-
plication of TBBDA and PBBS using microwave irradia-
tion and under solvent free conditions. Meanwhile this
method offers some advantages in terms of simplicity of
OH
CHO
CH OH
2
CH2OH
TBBDA (0.1g) or PBBS (0.2g)
MW(solvent-free)
+
Br
80-85%
0%

Oxidation of Alcohols with Sulfonamides under Microwave
Table 1. Oxidation with TBBDA and PBBS in microwave
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1259
alcohol and p-nitro benzyl alcohol are shown in Table 2. It
is noteworthy that most of these reported reagents require
long times to effect reaction. The procedure is simple and
allows for rapid oxidation of primary alcohols to aldehydes
under mild conditions with a high degree of chemoselectiv-
ity. The benzilic and allylic alcohols were oxidized with
excellent conversion, whereas aliphatic alcohols were slow
and less reactive. It is noteworthy that the aldehydes do not
undergo further oxidation to carboxylic acids.
a
Entry
Substrate
System Time (mine) Yield %
OH
A
B
2
2
96
92
1
OH
A
B
1.5
1.5
96
90
2
3
O2N
Me
OH
A
B
4
4
90
85
OH
A
B
4
4
92
84
4
5
6
7
MeO
EXPERIMENTAL
OH
A
B
3
3
92
90
Br
IR and NMR spectra were run using Perkin-Elmer
FT-IR and Jeol 90 MHZ FT NMR spectrometers, respec-
tively. The source of microwave radiation was the LG do-
mestic microwave oven (model MG-583MC).
OH
A
B
3
3
98
94
Cl
Cl
OH
A
B
4
4
85
80
General method for oxidation of alcohols using
TBBDA and PBBS under solvent-free conditions
Alcohol (1 mmol), PBBS (0.2 g) or TBBDA (0.1 g)
were added to a round-bottomed flask (25 mL). The flask
OH
A
B
6
6
75
60
8
9
A
B
2
2
78
70
CH3(CH2)8CH2OH
CH CH CH CH
2
was placed in a bath containing SiO to enable absorption
3
2
3
A
B
6
6
60
52
of additional microwave irradiation. The flask was irradi-
ated in a microwave oven at a power output of 900 W (LG
Co. microwave, 230 v ~ 50 Hz, RF output 900 W). After
completion of the reaction, [1.5-6 min, Table 1, monitored
1
0
OH
a
Products were characterized from their physical properties,
comparision with authentic samples and by spectroscopic
methods.
2 2
by TLC (5:1, n-Hexan/acetone)], CH Cl (10 mL) was added,
and the reagent was removed by filtration. Evaporation of
the solvent under reduced pressure gave the product. Fur-
ther purification was achieved by column chromatography
(silica-gel, n-hexane/ethylacetate, 9:1).
performance, solvent-free conditions, no side product for-
mation and very low reaction time. The advantages of PBBS
and TBBDA over reported reagents in oxidation of benzyl
Scheme II

1
260 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Ghorbani-Vaghei et al.
Table 2. Comparsion of reaction times and yields of our reagents with previously published methods
Substrate
Conditions
Reaction time
Yield (%)
Benzyl alcohol
TBBDA (MW)
PBBSA (MW)
2 mine
2 mine
15 h
96
92
2
72
5
Benzyl alcohol
TEMPO (5 mol%), CuCl (5 mol%), O2,
(
bmim)(PF ), 65 °C
6
a
(P and P -VPCP) , CH CN, reflux
23
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
01 h
24 h
85-93
2
4
3
2
6
FeBr , CH CN, 25 °C
3
91
90
82
95
3
+
(C H ) N [CrO F] , CH Cl , RT
-
24
30 mine
24 h
4
9 4
3
2
2
2
2
8
7
V O (5 mol%), O , Toluene, 100 °C
5
2
2
Poly[vinyl(pyridinum fluorochromate],
cyclohexane, 80 °C
15 mine
p-Nitrio benzyl alcohol
TBBDA (MW)
1.5 mine
1.5 mine
06 h
96
90
PBBSA (MW)
a
(P and P -VPCP) , CH CN, reflux
23
p-Nitrio benzyl alcohol
p-Nitrio benzyl alcohol
p-Nitrio benzyl alcohol
a
80-89
24
94
2
4
3
+
-
(C H ) N [CrO F] , CH Cl , RT
20 mine
25 h
4
9 4
3
2
2
1
4
V O (5 mol%), O , Toluene, 100 °C
2
79
5
2
Polymer Suported Chromium Peroxide Complexes
1
4. Ghorbani-Vaghei, R.; Zolfigol, M. A.; Chegeny, M.; Veisi,
H. Tetrahedron Let. 2006, 47, 4505.
Received December 26, 2006.
1
5. Ghorbani-Vaghei, R.; Jalili, H. Synthesis 2005, 7, 1099.
6. Ghorbani-Vaghei, R.; Shahbazee, E. J. Braz. Chem. Soc.
1
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