Trichloroisocyanuric acid/KBr as a catalytic system for the chemoselective oxidation of benzylic and secondary alcohols

Article abstract of DOI:10.1055/s-2006-942396

Chemoselective oxidation of benzylic and secondary alcohols were proceeded by using a catalytic amount of KBr in the presence of trichloroisocyanuric acid and wet SiO₂ under mild and heterogeneous conditions with excellent yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942396

PAPER
2043
Trichloroisocyanuric Acid/KBr as a Catalytic System for the Chemoselective
Oxidation of Benzylic and Secondary Alcohols
a
b
a
C
M
hemoselective
O
xida
o
tion of
B
enz
y
h
lic
a
nd Seco
a
ndar
y
A
lc
o
m
hols mad Ali Zolfigol,* Farhad Shirini, Arash Ghorbani Choghamarani
a
Chemistry Department, College of Science, Bu-Ali Sina University, Post Box No 4135, Hamadan 65174, Iran
Fax +98(811)8272404; E-mail: Zolfi@basu.ac.ir
b
Department of Chemistry, College of Science, Guilan University, Rasht, Iran
Received 11 October 2005; revised 8 March 2006
Cl
N
Abstract: Chemoselective oxidation of benzylic and secondary al-
O
O
cohols were proceeded by using a catalytic amount of KBr in the
N
N
OH
Cl
Cl
O
presence of trichloroisocyanuric acid and wet SiO under mild and
2
O
heterogeneous conditions with excellent yields.
R1
R2
R1
R2
KBr, wet SiO2
CH2Cl2, r.t.
Key words: trichloroisocyanuric acid, benzylic and secondary al-
cohols, chemoselective oxidation
1
2
Scheme 1
The oxidation of alcohols into the corresponding alde-
hydes or ketones is one of the most important functional
group transformations in organic synthesis. Many oxidiz-
ing reagents have been traditionally employed in order to
For showing the chemoselectivity of the described system
some competitive reactions were design. A mixture of
equal amounts of primary and secondary alcohols was
subjected to oxidation in the presence of reagents under
the conditions given in Table 1 (Scheme 2). Tetraphenyl-
ethylene glycol was converted into benzophenone with
good yield (Table 1, Entry 9). This observation is in close
1
–19
accomplish this transformation.
From an economic
and environmental viewpoint, catalytic oxidation process-
es are thus valuable, and those employing metal-free cat-
1
3,14,18,20
alysts are particularly attractive.
21
agreement with our previously reported data. When a
The aim of this work was two-fold: (a) to overcome the mixture of cyclohexanol and n-octanol was allowed to re-
limitations and drawbacks of the reported methods such as act under the described conditions, the former oxidized to
over oxidation, tedious work-up, acidic media, transition cyclohexanone in 100% conversion and the latter gave n-
1
5–17
metals and safety problems;
(b) to develop this proce- octanal in trace conversion. A similar result was obtained
dure as a highly useful technique, especially for industry in the oxidation of 1-indanol and 2-phenyl ethanol, afford-
and it has many advantages: reduced pollution, low costs, ing 1-indanone and 2-phenyl ethanal in 100% and trace
chemoselectivity and simplicity in process and handling conversions, respectively. These studies clearly reveal
(
these factors are especially important in industry).
that this method can be applied for the chemoselective ox-
idation of secondary alcohols in the presence of primary
hydroxy groups. Although these results are in contrast to
the data reported by Giacomelli et al. (in that work, the re-
2
1
In continuation of our studies in this regard, we have
2
2
found that trichloroisocyanuric acid, an inexpensive
commercially available reagent primarily used as a disin-
fectant and deodorant, has found little application in or-
1
8
ported catalyst was TEMPO), they are in close agree-
ment with the data reported by Konwar et al.1
2
3
ganic chemistry. On the basis of abovementioned facts
and our interest in the use of heterogeneous systems in or- Also, we observed that the secondary hydroxyl group in 1-
2
4
ganic reactions, herein we report a very mild, simple, phenyl-1,2-ethanediol was selectively oxidized into the
cheap and chemoselective method for the general oxida- corresponding ketone (Scheme 3; Table 1, entry 12).
tion of alcohols to the corresponding carbonyl compounds
using trichloroisocyanuric acid and a catalytic amount of
A plausible mechanism for the oxidation is shown in
Scheme 4 based on literature, our observations and ob-
tained results, catalytic activity of KBr (Scheme 5) and in
25
KBr in the presence of wet SiO in dichloromethane. Dif-
2
ferent types of benzylic and secondary alcohols (1) were
subjected to the oxidation reaction in the presence of
trichloroisocyanuric acid (I), catalytic amount of KBr (II)
situ generation of HOCl by the use of trichloroisocyanuric
22c,26,27
acid in the presence of water.
The oxidation of bro-
mide ion by HOCl would give hypobromous acid25 and
subsequent oxidation of alcohols affords aldehydes and
ketones.
and wet SiO in dichloromethane at room temperature
2
(
Scheme 1, Table 1).
In conclusion, chemoselectivity, the cheapness and avail-
ability of the reagents, easy and clean work-up and high
yields make this method attractive for chemists. We be-
lieve that the present methodology could be an important
addition to the existing methodologies.
SYNTHESIS 2006, No. 12, pp 2043–2046
x
x.
x
x
.
2
0
0
6
Advanced online publication: 11.05.2006
DOI: 10.1055/s-2006-942396; Art ID: Z19605SS
Georg Thieme Verlag Stuttgart · New York
©

2
044
M. A. Zolfigol et al.
PAPER
O
OH
O
Cl
Cl
N
N
O
N
O
CHO
(
0.7 equiv)
Cl
+
+
OH
KBr (0.15 equiv)
wet SiO2 (0.2 g)
CH2Cl2, r.t.
1
00%
trace
O
Cl
Cl
N
N
O
OH
CH2CHO
CH2CHOH
O
N
O
(
0.4 equiv)
Cl
+
+
KBr (0.1 equiv)
wet SiO2 (0.2 g)
CH2Cl2, r.t.
1
00%
trace
Scheme 2
O
O
Cl
Cl
OH
N
N
O
OH
R1
R2
CHCH2OH
O
N
O
CCH2OH
CHCHO
HOCl
Cl
+
_
Br
KBr, wet SiO2
CH2Cl2, r.t.
70%
0%
Scheme 3
Br+
_
_
Oxidation of 4-Bromobenzyl Alcohol to 4-Bromobenzaldehyde:
Typical Procedure
KBr (0.0142 g, 0.12 mmol) was added to a solution of 4-bromoben-
OH
R2
Cl
+
OH
R1
zyl alcohol (0.187 g, 1 mmol) and wet SiO (0.2 g) in CH Cl (10
mL), followed by addition of trichloroisocyanuric acid (0.093 g, 0.4
mmol). The resulting reaction mixture was stirred at r.t. for 75 min
2
2
2
Scheme 5
(
the progress of the reaction was monitored by TLC) and then fil-
Acknowledgment
tered. The residue was washed with CH Cl2 (20 mL). Anhyd
2
Na SO (1 g) was added to the filtrate and filtered off after 20 min.
2
4
Financial support for this work by the Research Council of Bu-Ali
Sina University, Hamadan, Iran, and Guilan University, Rasht, Iran
CH Cl was removed. The yield was 0.173 g (94%).
2
2
(
as a Common project) is gratefully acknowledged.
O
O
Cl
Cl
H
O
H
N
N
N
N
+
H2O (wet SiO2 )
+
HOCl
O
N
O
N
H
O
Cl
_
_
HOCl
+
Br
Cl
+
+
HOBr
_
Br+
OH
HOBr
.
.
OH
Br+
O
H
Br
R2
_
O
–
Br
– H+
R1
R2
R1
R1
R2
– HCl
1
Cl–
2
Scheme 4
Synthesis 2006, No. 12, 2043–2046 © Thieme Stuttgart · New York

PAPER
Chemoselective Oxidation of Benzylic and Secondary Alcohols
2045
Table 1 Oxidation of Alcohols 1 to the Corresponding Carbonyl Compounds 2a
b
Yield (%)c
Entry
Substrate 1
Product 2
Reagent and catalyst/substrate Time (h)
b
(mmol)
I
II
1
2
3
4
5
6
7
8
9
Benzyl alcohol
Benzaldehyde
0.4
0.4
0.6
2
0.1
0.75
1.25
1.25
48
93
94
4-Bromobenzyl alcohol
2,4-Dichlorobenzyl alcohol
4-Nitrobenzyl alcohol
4-Methylbenzyl alcohol
1-Indanol
4-Bromobenzaldehyde
2,4-Dichlorobenzaldehyde
4-Nitrobenzaldehyde
4-Methylbenzaldehyde
1-Indanone
0.12
0.15
0.35
0.1
96
50d
90
0.4
0.4
0.7
0.4
2.7
0.7
0.7
0.6
0.4
0.7
0.4
0.7
0.7
0.5
0.25 (5)e
28
0.1
98
2-Phenyl ethanol
Benzhydrol
2-Phenyl ethanal
Benzophenone
0.15
0.15
0.4
trace
97
2
Tetraphenylethyleneglycol
2-Menthol
Benzophenone
48
80c
96
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
2-Menthon
0.15
0.15
0.15
0.1
3
Cyclododecanol
1-Phenylethan-1,2-diol
1-Cyclohexyl ethanol
Cyclohexanol
Cyclododecanone
1-Phenyl-2-hydroxy ethanone
1-Cyclohexyl ethanone
Cyclohexanone
1.25
3.75
1
98
70d,f
82
0.15
0.15
0.15
0.15
1.5
0.75
4
95d,f
100d,f
trace
trace
2-Pentanol
2-Pentanone
1-Octanol
1-Octanal
1-Pentanol
1-Pentanal
5
a
b
c
d
e
f
Conditions: combination of trichloroisocyanuric acid (I) and wet SiO (50%) in the presence of a catalytic amount of KBr (II) in CH Cl at r.t.
2
2
2
Wet SiO :substrate (0.2 g:1 mmol).
2
Isolated yields.
Conversion.
Without KBr.
GC yields.
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Synthesis 2006, No. 12, 2043–2046 © Thieme Stuttgart · New York