Green oxidations. The use of potassium permanganate supported on manganese dioxide

Article abstract of DOI:10.1016/j.tet.2004.09.087

Permanganate supported on active manganese dioxide can be used effectively for the oxidation of organic compounds under heterogeneous or solvent-free conditions. The residue that remains after extraction of the organic products, manganese dioxide, can be recycled, making the process infinitely sustainable, in theory. The use of this approach for the oxidation of arenes, alcohols and sulfides is described. Graphical Abstract.

Full text of DOI:10.1016/j.tet.2004.09.087

Tetrahedron 60 (2004) 11415–11420
Green oxidations. The use of potassium permanganate supported
on manganese dioxide
a
a
b
Ahmad Shaabani,a, Peiman Mirzaei, Soheila Naderi and Donald G. Lee
*
aDepartment of Chemistry, Shahid Beheshti University, PO Box 19839-4716, Tehran, Iran
bDepartment of Chemistry and Biochemistry, University of Regina, SK, Canada S4S 0A2
Received 23 May 2004; revised 1 September 2004; accepted 23 September 2004
Available online 12 October 2004
Abstract—Permanganate supported on active manganese dioxide can be used effectively for the oxidation of organic compounds under
heterogeneous or solvent-free conditions. The residue that remains after extraction of the organic products, manganese dioxide, can be
recycled, making the process infinitely sustainable, in theory. The use of this approach for the oxidation of arenes, alcohols and sulfides is
described.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
from the spent oxidant; however, the amount of solvent
required is reduced and it usually contains fewer
contaminants.)
During the past few decades, alternative experimental
methods with reduced environmental impact have been
developed for many reactions. However, similar progress
has not been made on the modification of organic oxidations
since the removal of electrons from stable molecules is
relatively difficult, requiring vigorous reagents and/or
forcing conditions. There is, therefore, little likelihood
that it will ever be possible to use mild reagents and
conditions for most oxidation reactions.
Homogeneous permanganate oxidations must be carried out
in acidic or basic aqueous solutions,2 and the corresponding
heterogeneous reactions require the use of chemically inert
solvents such as methylene chloride.3–5 However, under
solvent-free conditions, oxidations are done in the absence
of solvent by using a reagent that consists of potassium
permanganate and an approximately equal amount of a solid
support such as alumina or silica. A minimum amount of
organic solvent is then required to extract the products from
the spent oxidant. In addition, solvents such as diethyl ether
can be employed to extract the products, thus reducing the
need to use chlorinated hydrocarbons.
As an alternative to seeking gentle reactions that have low
environmental impact, we have been searching for reactions
that are easily insulated from the environment and which
consume less material. For example, previously reported
work from our laboratories and others has indicated that
carrying out oxidation reactions under solvent-free con-
ditions decreases environmental impact by reducing the
need to deal with contaminated solvents.1 When oxidation
reactions are carried out under homogeneous conditions in
polar solvents, such as aqueous acetone, the solvents must
be cleaned up and disposed of or, preferably, recycled at
the conclusion of the reactions. However, when the
reactions are conducted under solvent-free conditions, no
solvents are contaminated during the reaction. (Some
solvent is usually required to separate the organic products
It has recently been reported that the co-product obtained
when organic compounds are oxidized, manganese dioxide,
can be recycled under industrial conditions to regenerate
permanganate.6 Manganese dioxide is regenerated in a two-
stage process that involves air oxidation to potassium
manganate(VI) in a concentrated potassium hydroxide
solution, followed by electrochemical oxidation to
potassium permanganate.7
In previous descriptions of solvent-free permanganate
reactions, procedures for separating manganese dioxide
from solid supports, such as alumina or silica, have not been
reported. Our experience with these reactions suggests that
such a separation will not be easily achieved and we have,
consequently, begun to investigate other approaches. The
Keywords: Manganese dioxide; Potassium permanganate; Solid support;
Arenes.
* Corresponding author. Tel.: C98 21 2990 2800; fax: C98 21 2403041;
e-mail: a-shaabani@cc.sbu.ac.ir
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.09.087

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A. Shaabani et al. / Tetrahedron 60 (2004) 11415–11420
most successful of our attempts, to date, has been realized
by substituting manganese dioxide as the solid support.
oxidation of arenes, alcohols and sulfides. For comparison
purposes, the results obtained for oxidation of the
corresponding compounds under heterogeneous conditions
is included.
The combination of potassium permanganate and active
manganese dioxide produces a reagent that can be used
effectively for the oxidation of a variety of organic
compounds. When organic compounds are oxidized by
this reagent under solvent-free conditions, the solid
coproduct remaining after the organic products have been
separated is manganese dioxide containing residual amounts
of potassium permanganate. This coproduct can then be
recycled, making the process infinitely sustainable, in
theory.
2. Results and discussion
As can be seen from results reported in Table 1, alkyl arenes
are converted into the corresponding a-ketones in good
yields at room temperature. The products obtained under
solvent-free conditions are identical to those obtained from
heterogeneous reactions where the oxidant is dispersed in
methylene chloride. In addition, the reaction times are
reduced from a day or more to a few hours for many of the
reactions, as summarized in Scheme 1.
While recognizing that this approach may require further
refining before it can be used commercially, we wish, at this
time, to report the results that have been obtained for the
Table 1. Oxidation of arenes to the corresponding carbonyl compounds by KMnO4/MnO2 under heterogeneous conditions (A), under conventional solvent-
free conditions (B) and under solvent-free conditions assisted by ultrasonic irradiation (C)
Entry
Reactant
Product
Yield (%)
(B) (time, h)
(A) (time, h)
25 (48)
(C) (time, min)
0 (42)
1
2
21 (30)
56 (5.5)
89 (23)
85 (24)
92 (27)
62 (50)
65 (58)
78 (85)
3
4
62 (6)
70 (8)
5
6
7
93 (22)
76 (28)
96 (22)
85 (5)
92 (5)
85 (6)
85 (38)
68 (150)
82 (75)
8
93 (16)
94 (6)
80 (75)
9
81 (16)
0 (24)
80 (4)
0 (8)
70 (68)
0 (45)
10
11
No reaction
96 (24)
80 (4)
89 (30)

A. Shaabani et al. / Tetrahedron 60 (2004) 11415–11420
11417
As indicated in Scheme 2, the reactions display a selectivity
similar to that previously observed when oxygen is part of
the bicyclic system. When oxygen is in the b-position,
lactones are obtained in good yields; when it is in the
a-position the reaction is completely inhibited.4,5
Application of ultrasonic irradiation in these reactions
decreases the time required to obtain good yields by a factor
of about 10. As a consequence, it is possible to select the
most appropriate conditions for a particular application. If
time is of little importance, the reaction can be completed
without expenditure of additional energy; however, if time
is an important factor, energy can be applied in the form of
ultrasonic irradiation.
Scheme 1.
As can be seen from Table 2, aryl and alkyl sulfides are
converted into the corresponding sulfones in good yields by
KMnO4 supported on MnO2, with slightly shorter times
being required when the reaction is subjected to ultrasonic
irradiation.
This is a highly useful reaction for the preparation of
sulfones which are important intermediates in the synthesis
of many organic compounds.8 The observation that benzyl
phenyl sulfide (entry 3) is oxidized to the corresponding
sulfone suggests that the reaction likely proceeds by way of
an oxygen transfer mechanism. If the reaction involved
electron transfer instead of oxygen transfer, substantial
Scheme 2.
Table 2. Oxidation of sulfides to the corresponding sulfones by KMnO4/MnO2 under heterogeneous conditions (A), under conventional solvent-free conditions
(B) and under solvent-free conditions with the assistance of ultrasonic irradiation (C)
Entry
Reactant
Product
Yield (%)
(A) (time, h)
93 (3)
(B) (time, min)
(C) (time, min)
91 (24)
1
83 (25)
90 (60)
2
3
4
94 (8)
81 (45)
86 (85)
93 (25)
72 (29)
90 (4.5)
82 (240)
83 (25)
5
6
90 (3.5)
92 (4)
84 (20)
90 (45)
90 (16)
86 (38)
7
8
86 (4.5)
89 (4)
79 (30)
85 (30)
83 (27)
93 (28)
[C8H17]2 S
[C8H17]2 SO2

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A. Shaabani et al. / Tetrahedron 60 (2004) 11415–11420
Consequently, the observation that only sulfones are
obtained in these reactions, as summarized in Scheme 3,
suggests that the products are produced from the reaction of
sulfides with KMnO4, and not by a reaction of sulfides with
MnO2.
As indicated from the results reported in Table 3, secondary
alcohols are efficiently converted into the corresponding
ketones in good yields and aldehydes are selectively
obtained from the oxidation of primary alcohols. The
preparation of both aliphatic and aromatic aldehydes from
the corresponding primary alcohols has not previously been
easily achieved using permanganate or other strong oxidants
because aldehydes are readily converted to carboxylic acids
under oxidizing conditions. In addition, it was found that
both primary and secondary a,b-unsaturated alcohols were
oxidized to the corresponding carbonyl compounds without
disruption of the double bond (entries 8–10). These results
are summarized in Scheme 4.
Scheme 3.
amounts of benzaldehyde would have been formed.9,10 Most
standard oxidations of sulfides under solvent-free conditions
result in the formation of sulfoxides;11–13 however,
sulfoxides were not produced in these reactions.
Both manganese dioxide and potassium permanganate will
oxidize sulfides. However, the reaction of active manganese
dioxide with sulfides is known to give only sulfoxides.
Table 3. Oxidation of alcohols to the corresponding carbonyl compounds by KMnO4/MnO2 under heterogeneous conditions (A), under conventional solvent-
free conditions (B) and under solvent-free conditions assisted by ultrasonic irradiation (C)
Entry
Reactant
Product
Yield (%)
(B) (time)
(A) (time, h)
83 (4)
(C) (time, min)
90 (43)
1
94 (50 min)
91 (35 min)
2
3
92 (5)
74 (5)
86 (30)
94 (63)
78 (60 min)
4
52 (14)
67 (3 h)
46 (150)
5
6
86 (2)
86 (45 min)
88 (45)
93 (24)
90 (6 h)
68 (120)
8
9
82 (17)
87 (8)
79 (4 h)
64 (150)
72 (45)
90 (2.5 h)
10
93 (5)
90 (2 h)
95 (105)

A. Shaabani et al. / Tetrahedron 60 (2004) 11415–11420
11419
Active manganese dioxide in the absence of permanganate
is able to oxidize primary and secondary alcohols to the
corresponding aldehydes and ketones under solvent-free
conditions.14 However, the time required to complete the
reaction is often a few days instead of 1 h or less as observed
when permanganate is present.
3. Conclusions
1. A mixture of potassium permanganate (1 g) and
activated manganese dioxide (3 g) can be used as an
effective oxidant for arenes, sulfides and alcohols under
both heterogeneous and solvent-free conditions.
Removal of the organic products by extraction leaves a
residue that consists primarily of manganese dioxide
containing small amounts of potassium permanganate.
2. Ultrasound irradiation increases the rate at which
products are formed.
Scheme 4.
Table 4. Characterization of products
Product
1H NMR (ppm)
IR (cmK1
)
Melting points
Benzaldehyde
Acetophenone
Propiophenone
Butyrophenone
Benzophenone
1-Indanone
7.20–7.79 (m, 5H), 9.94 (s, 1H)
2.43 (s, 3H), 7.15–7.80 (m, 5H)
1300, 950
1.18 (t, 3JHHZ5.1 Hz, 3H) 2.94 (q, 3JHHZ5.2 Hz, 2H) 2980, 1690, 1595, 1450, 1215, 950
3030, 2778, 2703, 1695, 1667, 1587, 2,4-DNP derivative 234–236 8C (lit.
1449, 1389, 1299, 1205, 1163, 1075 237 8C)15
3100, 1700, 1600, 1580, 1450, 1360, 2,4-DNP derivative 247–250 8C (lit.
250 8C)16
2,4-DNP derivative 187–188 8C (lit.
7.47–7.92 (m, 5H)
187–189 8C)15
2960, 1700, 1610, 1455, 1220, 1010, 2,4-DNP derivative 198–200 8C (lit.
0.95 (t, 3JHHZ5.1 Hz, 3H) 1.41–1.96 (m, 2H) 2.82 (t,
3JHHZ5.1 Hz, 2H) 7.12–7.87 (m, 5H)
7.20–7.78 (m, 10H)
700
3060, 1655, 1600, 1450, 1270, 800
200 8C)16
2,4-DNP derivative 237–238 8C (lit.
239 8C)16
2.63 (t, 3JHHZ6.1 Hz, 2H) 3.09 (t, 3JHHZ6.1 Hz, 2H) 2925, 1710, 1600, 1450, 1270, 750
7.08–7.80 (m, 4H)
7.10–7.70 (m, 8H)
7.36–8.32 (m, 8H)
2,4-DNP derivative 253–256 8C (lit.
258 8C)16
9-Fluorenone
Xanthone
3050, 1700, 1600, 1440, 1290, 860
81–82 8C (lit. 84 8C)17
1655, 1610, 1480, 1450, 1340, 1140, 172–173 8C (lit. 174 8C)17
760
Phthalide
1-Isochromaone
5.32 (s, 2H) 7.35–7.86 (m, 4H)
1760, 1460, 1440, 1310, 1050, 745
73–74 8C (lit. 75 8C)17
3.10 (t, 3JHHZ8.5 Hz, 2H) 4.56 (t, 3JHHZ8.5 Hz, 2H) 2945, 1716, 1602, 1455, 1389, 1289, 175–176 8C (lit. 176 8C)15
7.20–8.20 (m, 4H)
3.05 (s, 3H) 7.61–7.94 (m, 5H)
1237, 1115
3091, 3066, 2928, 1585, 1480, 1449 85–87 8C (lit. 86 8C)18
Methyl phenyl
sulfone
Diphenyl sulfone
Benzy phenyl
sulfone
7.94 (m, 4H) 7.56–7.41 (m, 6H)
4.32 (s, 2H) 7.08–7.68 (m, 10H)
1450, 1310, 1150, 1110, 1000
3088, 3006, 2969, 1606, 1495
128–129 8C (lit. 128 8C)17
144–145 8C (lit. 146 8C)17
Tetramethylene
sulfone
Diethyl sulfone
2.20 (m, 4H) 3.01 (m, 4H)
3436, 2973, 2882, 1669, 1464, 1309
—
1.42 (t, 3JHHZ7.50 Hz, 4H) 3.00 (q, 3JHHZ7.47 Hz,
6H)
3241, 2996, 1672, 1479, 1378, 1286 73–75 8C (lit. 74 8C)15
2960, 2880, 1460, 1410, 1300, 1130 45–46 8C (lit. 46 8C)17
2960, 2880, 1460, 1410, 1280, 1125 29–30 8C (lit. 30 8C)15
Dibutyl sulfone
Dipropyl sulfone
Dioctyl sulfone
0.97 (t, 3JHHZ6.7 Hz, 6H) 1.17–1.96 (m, 8H) 2.95 (t,
3JHHZ10.1 Hz, 4H)
1.09 (t, 3JHHZ6.5 Hz, 6H) 1.46–2.11 (m, 4H) 2.95 (t,
3JHHZ6.7 Hz, 4H)
0.89 (t, 3JHHZ5.93 Hz, 6H) 1.20–1.92 (m, 24H) 2.88– 2910, 1463, 1313, 1264, 1122, 771
3.00 (m, 4H)
74–76 8C (lit. 74 8C)17
4-Nitrobenzalde-
hyde
8.09–8.39 (m, 4H) 10.18 (s, 1H)
2850, 2720, 1705, 1600, 1540, 1350, 104–105 8C (lit. 106 8C)15
1200
4-Methoxyben-
zaldehyde
Cyclohexanone
3.83 (s, 3H) 6.92–7.72 (m, 2H) 9.80 (s, 1H)
1.79–2.25 (m, 10H)
2850, 2750, 1700, 1610, 1510, 1255 2,4-DNP derivative 190–191 8C (lit.
191 8C)16
2940, 1710, 1450, 1310, 1220, 1120 2,4-DNP derivative 160–161 8C (lit.
162 8C)19
3-Methyl-2-bute-
nal
Acrolein
9.96 (d, 1H) 5.87 (m, 1H) 2.18 (m, 3H) 1.99 (m, 3H)
3360, 3302, 2855, 2722, 1890, 1693
—
6.11–6.68 (m, 3H) 9.54 (m, 1H)
3360, 3060, 2800, 1690, 1420, 1360
—
Cinnamaldehyde
6.29–6.91 (m, 1H) 7.30–7.58 (m, 1H) 9.67 (d, 3JHHZ6. 3025, 2805, 2740, 1680, 1630, 1450 2,4-DNP derivative 252–254 8C (lit.
7 Hz, 1H)
255 8C)16
2,4-DNP derivative 106–107 8C (lit.
Heptanal
0.90 (t, 3JHHZ5.1 Hz, 3H) 1.34–2.50 (m, 8H) 4.60–4. 2950, 2725, 1750, 1460
3
90 (m, 2H) 9.72 (t, JHHZ5.1 Hz, 1H)
108 8C)16

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A. Shaabani et al. / Tetrahedron 60 (2004) 11415–11420
reaction was monitored by TLC. When complete, the
reaction mixture was washed with methylene chloride or
diethyl ether (2!20 mL). After filtration to separate spent
oxidant, the solvent was evaporated. Relatively pure
product was obtained and characterized as described below.
3. Since industrial processes for recycling and reoxidizing
manganese dioxide to permanganate are well estab-
lished, the reactions are infinitely sustainable, in theory.
4. Experimental
4.5. Characterization of products
4.1. Preparation of oxidant
The products of these reactions were characterized from
their H NMR and IR spectra and by comparison of their
melting points (or those of their derivatives) with known
compounds, as indicated in Table 4.
1
The oxidant was prepared by grinding potassium permanga-
nate (1.0 g, 6.3 mmol) and active manganese dioxide
(3.00 g, 34.5 mmol) in a mortar until a homogeneous
powder was obtained. This reagent was used for all of the
oxidations described herein. Active manganese dioxide,
obtained commercially, is a reagent that is produced by the
Carus Chemical Company of La Salle, Il, USA.
Acknowledgements
Financial support from the Research Council of Shahid
Beheshti University is acknowledged.
4.2. Procedure A. The oxidation of organic compounds
by KMnO4/MnO2 under heterogeneous conditions
Substrate (2.0 mmol) was dissolved in CH2Cl2 (25 mL) and
placed in a round-bottomed flask fitted with a magnetic
stirrer. The oxidant, finely grounded KMnO4/MnO2 reagent
(4.0 g), was added in small portions over a period of 15 min.
The mixture was stirred vigorously at room temperature
while the progress of the reaction was monitored by TLC.
Upon completion of the reaction, the product was filtered
through a sintered glass funnel to remove spent oxidant. The
residue was then washed successively with CH2Cl2 (2!
20 mL). Evaporation of the solvent gave product that was
characterized by the use of spectroscopy and melting points,
as described below.
References and notes
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7. Reidies, A. H. Ullmann’s Encyclopedia of Industrial
Chemistry; VCH: Weinheim, 1990; pp 123.
4.3. Procedure B. The oxidation of organic compounds
by KMnO4/MnO2 under solvent-free conditions
8. Simpkins, N. A. Sulphones in Organic Synthesis; Pergamon:
Oxford, 1993.
Substrate (2.0 mmol) was added to the oxidant, a mixture of
KMnO4 and MnO2 (4.0 g), in a 25 mL round bottomed
flask. These reactants were then mixed by magnetic stirring
at room temperature. The progress of the reaction was
monitored by TLC. Upon completion of the reaction, the
residue was washed with a minimum amount of methylene
chloride or diethyl ether. After filtration to remove any spent
oxidant, the solvent was evaporated. Product of acceptable
purity for most purposes was obtained. If greater purity is
required, the product can be distilled or recrystallized. The
products were characterized as described below.
9. Baciocchi, E.; Lanzalunga, O.; Maladndrucco, S. J. Am. Chem.
Soc. 1996, 118, 8973.
10. Baciocchi, E.; Lanzalunga, O.; Pirozzi, B. Tetrahedron 1997,
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Systematic Identification of Organic Compounds; Wiley: New
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4.4. Procedure C. The oxidation of organic compounds
by KMnO4/MnO2 under solvent-free conditions and
assisted by ultrasound irradiation
17. Weast, R. C.; Lide, D. R.; Ashe, M. J.; Beyer, W. H. Handbook
of Chemistry and Physics; CRC: Boca Raton, Florida, 1989.
18. Bannard, D. J. Chem. Soc. 1957, 4547.
Substrate (2.0 mmol) and oxidant, a mixture of KMnO4 and
MnO2 (4.0 g), were thoroughly mixed together and the
reaction mixture was irradiated in a 25 mL beaker for an
appropriate period at room temperature. The progress of the
19. Criddle, W. J.; Ellis, G. P. Spectral and Chemical Character-
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