Oxidation of Alcohols by (NH4)2Cr2O7 in Solution and under Solvent-Free Conditions

Article abstract of DOI:10.1071/CH01104

Ammonium dichromate in the presence of Mg(HSO₄)₂ and wet SiO₂ was used as an effective oxidizing agent for the oxidation of alcohols in solution and under solvent-free conditions.

Full text of DOI:10.1071/CH01104

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Aust. J. Chem. 2001, 54, 405–406
Oxidation of Alcohols by (NH ) Cr O in Solution
4
2
2
7
and Under Solvent-Free Conditions
F. Shirini,A,B M. A. Zolfigol, B. Mallakpour, S. E. Mallakpour and A. R. Hajipour
C
A
D
D
A
Department of Chemistry, College of Science, Guilan University, Rasht, Iran.
Author to whom correspondence should be addressed (e-mail: shirini@cd.gu.ac.ir).
Department of Chemistry, College of Science, Bu-Ali Sina University, Hamadan, Iran.
Organic Polymer Chemistry Research Laboratory, College of Chemistry,
B
C
D
Isfahan University of Technology, Isfahan, Iran.
Ammonium dichromate in the presence of Mg(HSO ) and wet SiO was used as an effective oxidizing agent for
4
2
2
the oxidation of alcohols in solution and under solvent-free conditions.
Manuscript received: 16 August 2001.
Final Version: 2 October 2001.
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Introduction
The omission of the solvent not only eases the workup,
but reduces the reaction time. This method is not suitable for
the oxidation of allylic alcohols (Table 1, entry 13).
The oxidation of alcohols to carbonyl compounds is one of
the fundamental reactions in synthetic organic chemistry.
VI
It should be noted that oxidation did not proceed using
any of Mg(HSO ) , ammonium dichromate or wet SiO
There are many useful Cr based oxidants for this pur-
pose,[ of which Jones’ reagent, CrO /NBu HSO , n-
1]
[2]
[3]
4
2
2
3
4
4
[
4]
alone (Table 1, entries 14–16). These results could be
butylphenylphosphonium dichromate, pyridinium chloro-
chromate,[5,6]
[7]
[8]
attributed to the in situ generation of H CrO4 in low
2
pyrazinium dichromate, ferric dichromate,
[9]
concentration at the surface of wet SiO2 by the solid
inorganic acidic salts (Mg(HSO ) and (NH ) Cr O ).
polyvinylpyridine-supported ferric dichromate, polyethyl-
eneimine-supported silver dichromate
[
10]
4
2
4 2
2
7
and Dowex 1X8
–
(
on which Cl is replaced by dichromate and bisulfate
[11]
Conclusions
ions ) are examples.
VI
However, the utility of Cr reagents in the oxidative
transformation is compromised due to their power,
instability, low selectivity, long reaction time, strong protic
and aqueous conditions and tedious workup. Thus, a milder,
more selective and inexpensive reagent is still desirable.
In this paper we report a convenient and simple method
for the conversion of alcohols into their corresponding
aldehydes or ketones in solution and under solvent-free
conditions.
The ready availability and low cost of the reagents, the
simple and clean workup, the high product yields and the
mild reaction conditions all make this method a useful
addition to the present methodologies for the oxidation of
alcohols. In addition, these properties render this method
attractive for use in large-scale operations.
Experimental
Oxidation of Benzyl Alcohol to Benzaldehyde Under Solvent-Free
Conditions: a Typical Procedure
Results and Discussion
To a mixture of Mg(HSO ) (0.654 g, 3 mmol), wet SiO (50% w/w, 0.1
4
2
2
g) and (NH ) Cr O (0.126 g, 0.5 mmol), was added benzyl alcohol
The oxidation of various alcohols was investigated using
4 2
2
7
(0.108 g, 1 mmol). The resultant mixture was shaken at room
(
(
NH ) Cr O in the presence of Mg(HSO ) and wet SiO
Scheme 1), at room temperature. Yields and reaction times
4 2 2 7 4 2 2
temperature for 3 min. The progress of the reaction was monitored by
thin-layer chromatography (TLC). The reaction mixture was triturated
with CH Cl (10 mL) and then filtered. Anhydrous MgSO was added
are given in Table 1. Over-oxidation of the products, using
this method, was not observed.
2
2
4
to the filtrate and the mixture filtered after 10 min. Evaporation of the
solvent followed by column chromatography on silica gel gave the
benzaldehyde in 92% yield.
Oxidation of 2-Bromobenzyl Alcohol to 2-Bromobenzaldehyde in
n-Hexane: a Typical Procedure
Scheme 1. (i) (NH ) Cr O /Mg(HSO ) /wet SiO , solvent-free,
4
2
2
7
4 2
2
To a suspension of Mg(HSO ) (0.654 g, 3 mmol), wet SiO (50% w/w,
4
2
2
room temperature; (ii) (NH ) Cr O /Mg(HSO ) /wet SiO , n-hexane,
0.1 g) and (NH ) Cr O (0.126 g, 0.5 mmol) in n-hexane (5 mL) was
4
2
2
7
4 2
2
4 2 2 7
room temperature.
added 2-bromobenzyl alcohol (0.187 g, 1 mmol) and the resultant
CSIRO 2001 10.1071/CH01104 0004-9425/01/060405
©

4
06
F. Shirini et al.
Table 1. Oxidation of alcohols by ammonium dichromate in the presence of Mg(HSO ) and wet SiO in n-hexane
4
2
2
or under solvent-free conditions at room temperature
Entry
Substrate
ProductA
Solvent-free oxidation
Oxidation in solvent
B
B
Time
Yield
(%)
Time
(min)
Yield
(%)
(min)
1
2
3
4
5
6
Benzyl alcohol
Benzaldehyde
5
5
5
5
5
92
90
90
89
90
90
5
5
10
5
15
15
95
92
85
85
85
80
4-Bromobenzyl alcohol
2-Bromobenzyl alcohol
2-Chlorobenzyl alcohol
4-Methoxybenzyl alcohol 4-Methoxybenzaldehyde
4-Benzyloxybenzyl
alcohol
4-Bromobenzaldehyde
2-Bromobenzaldehyde
2-Chlorobenzaldehyde
4-Benzyloxybenzaldehyde
15
7
8
9
0
1
2
3
4
5
6
2-Nitrobenzyl alcohol
1-Phenyl ethanol
Diphenylcarbinol
Cyclohexanol
1-Phenylpropan-2-ol
3-Phenylpropan-1-ol
Cinnamyl alcohol
Benzyl alcohol
2-Nitrobenzaldehyde
Acetophenone
5
5
5
30
10
10
5
100
100
110
95
90
92
85
90
87
15
30
75
240
300
60
92
88
90
Benzophenone
Cyclohexanone
Phenylpropan-2-one
3-Phenylpropanal
Cinnamaldehyde
Benzaldehyde
C
1
1
1
1
1
1
1
—
—
—
—
7
0
C
C
C
C
—
5
0
5
D
D
300
180
180
E
E
Benzyl alcohol
Benzyl alcohol
Benzaldehyde
Benzaldehyde
F
F
0
0
A
1
All products were characterized by infrared (IR) and H nuclear magnetic resonance (NMR) spectroscopy and by
B
C
Mixture of products. D In the absence of Mg(HSO ) .
E
comparison with authentic samples.
Isolated yield.
In the
4
2
F
absence of (NH ) Cr O . In the absence of wet SiO .
4
2
2
7
2
mixture was stirred at room temperature for 10 min. The progress of the
reaction was monitored by TLC and the mixture filtered upon
completion. The residue was washed with CH Cl (10 mL). Anhydrous
[3] T. Burnelet, C. Jouitteau, G. Gelbard, J. Org. Chem. 1986, 51,
4016.
[4] I. M. Baltork, M. M. Sadeghi, N. Mahmoodi, B. Kharamesh,
Indian J. Chem. 1997, 368, 438.
2
2
MgSO was added to the filtrate and the mixture filtered after 10 min.
4
Evaporation of the solvent followed by column chromatography on
silica gel gave 2-bromobenzaldehyde in 85% yield.
[5] E. J. Corey, J. W. Suggs, Tetrahedron Lett. 1975, 31, 2647.
[6] J. S. Cha, M. Kim, J. M. Kim, O. O. Kwon, J. H. Chun, S. D. Cho,
Bull. Korean Chem. Soc. 1998, 19, 724.
Acknowledgments
[7] B. Tamami, H. Alinezhad, Iran. J. Sci. Technol. 1997, 21, 375.
[
[
8] H. Firouzabadi, B. Tamami, N. Goudarzian, M. M. Lakouraj, H.
Hatam, Synth. Commun. 1991, 21, 2077.
9] B. Tamami, H. Firouzabadi, M. M. Lakouraj, A. Mahdavian, Iran
J. Polym. Sci. Technol. 1994, 3, 82.
We are thankful to Guilan University Research Council for
the partial support of this work.
References
[
10] N. Goudarzian, P. Ghahramani, S. Hossini, Polym. Int. 1996, 39,
1.
11] F. Shirini, H. Tajik, F. Jalili, Synth. Commun. 2001, 31, 2885.
6
[
[
1] J. Muzart, Chem. Rev. 1992, 92, 113.
2] A. Buners, T. G. Halsall, E. R. H. Jones, A. Lemine, J. Chem.
Soc. 1953, 2548.
[