Microwave- and ultrasound-accelerated green oxidation of alcohols by potassium permanganate absorbed on copper(II) sulfate pentahydrate

Article abstract of DOI:10.1080/00397910801997819

The solvent-free potassium permanganate (KMnO4)-promoted oxidation of alcohols into the corresponding carbonyl derivatives has been examined in detail with respect to the importance of supporting materials and supporting irradiation. Secondary alcohols are oxidized very efficiently to the corresponding ketones at ambient temperature by KMnO4 absorbed on a fourfold molar amount of copper(II) sulfate pentahydrate. The reaction is accelerated considerably by ultrasonic irradiation and drastically by microwave irradiation. Under the latter conditions, also hydroquinone can be converted 100% into p-benzoquinone within 4.5 min. Benzylic alcohols are oxidized most efficiently to the corresponding benzaldehydes under heterogeneous reaction conditions. Copyright Taylor & Francis Group, LLC.

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Microwave- and Ultrasound-
Accelerated Green Oxidation
of Alcohols by Potassium
Permanganate absorbed on
Copper(II) Sulfate Pentahydrate
Thi Xuan Thi Luu a , Peter Christensen a , Fritz Duus
a & Thach Ngoc Le b
a Department of Science, Systems, and Models,
Roskilde University, Roskilde, Denmark
b Department of Organic Chemistry, University of
Natural Sciences, National University of Hochiminh
City, Hochiminh City, Vietnam
Published online: 12 Jun 2008.
To cite this article: Thi Xuan Thi Luu , Peter Christensen , Fritz Duus & Thach Ngoc
Le (2008) Microwave- and Ultrasound-Accelerated Green Oxidation of Alcohols by
Potassium Permanganate absorbed on Copper(II) Sulfate Pentahydrate, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 38:12, 2011-2024, DOI: 10.1080/00397910801997819
To link to this article: http://dx.doi.org/10.1080/00397910801997819
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Synthetic Communications1, 38: 2011–2024, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801997819
Microwave- and Ultrasound-Accelerated Green
Oxidation of Alcohols by Potassium
Permanganate absorbed on Copper(II)
Sulfate Pentahydrate
Thi Xuan Thi Luu,1 Peter Christensen,1 Fritz Duus,1 and
Thach Ngoc Le2
1Department of Science, Systems, and Models, Roskilde University, Roskilde,
Denmark
2Department of Organic Chemistry, University of Natural Sciences, National
University of Hochiminh City, Hochiminh City, Vietnam
Abstract: The solvent-free potassium permanganate (KMnO4)–promoted oxi-
dation of alcohols into the corresponding carbonyl derivatives has been examined
in detail with respect to the importance of supporting materials and supporting
irradiation. Secondary alcohols are oxidized very efficiently to the corresponding
ketones at ambient temperature by KMnO4 absorbed on a fourfold molar
amount of copper(II) sulfate pentahydrate. The reaction is accelerated consider-
ably by ultrasonic irradiation and drastically by microwave irradiation. Under the
latter conditions, also hydroquinone can be converted 100% into p-benzoquinone
within 4.5 min. Benzylic alcohols are oxidized most efficiently to the correspond-
ing benzaldehydes under heterogeneous reaction conditions.
Keywords: Alcohols; Copper sulfate pentahydrate; Microwave; Oxidation;
Permanganate; Ultrasound
INTRODUCTION
The oxidation of a hydroxy group into the corresponding carbonyl group
is a classic synthetic transformation in organic chemistry, and quite a few
Received in the U.K. August 3, 2007
Address correspondence to Fritz Duus, Department of Science, Systems, and
Models, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark.
E-mail: fd@ruc.dk
2011

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T. X. T. Luu et al.
oxidation agents and procedures have been reported.[1–5] However,
contemporary considerations for the environmental aspects of organic
synthesis have led to abandonment of the otherwise very efficient chro-
mium-based oxidation agents in favor of less harmful counterparts,
among which potassium permanganate, KMnO4, has gained attention
as a particularly versatile oxidant.[6] The KMnO4-promoted oxidation
process is recognized as friendly to the environment because manganese
dioxide, MnO2, the coproduct formed by the reduction of KMnO4, can
be recycled.[7]
In 1977, Regen and Koteel communicated their discovery that mole-
cular sieves impregnated with KMnO4 oxidize alcohols efficiently in ben-
zene at 70 ꢀC.[8] Two years later, Menger and Lee reported that secondary
alcohols in particular can be converted, even more efficiently, into the
corresponding ketones upon treatment with KMnO4 absorbed on solid
copper(II) sulfate pentahydrate (CuSO4ꢁ5H2O) in refluxing benzene.[9]
Since then, a variety of papers have appeared, presenting KMnO4 as a
green oxidant toward alcohols, if dispersed in or absorbed on solid sup-
ports such as silica gel,[10] alumina,[11] graphite,[12] zeolite,[13] polymeric
material,[14] montmorillonite K10,[15] manganese dioxide,[16] and, not
least, inorganic salts,[17–20] in particular copper(II) sulfate pentahy-
drate.[11,17,20] Very recently, two thought-provoking papers have
appeared, the first reporting that the KMnO4-promoted oxidation of
benzylic alcohols into the corresponding aromatic aldehyde can take
place without solid support, if performed in an ionic liquid (i.e., 1-
butyl-3-methylimidazolium tetrafluoroborate).[21] The second paper[22]
proclaims that KMnO4 alone (i.e., without any further solid support) is
an efficient heterogeneous oxidant, especially toward benzylic alcohols,
if the oxidation reaction is carried out in acetonitrile solution at
room temperature. Finally, a proper state-of-the-art review on green
manganese-based oxidation of alcohols should comprise also a very
recent paper by Manyar and his coworkers[23] reporting the green oxi-
dation of a variety of alcohols by means of ammonium peroxydisulfate
supported by manganosilicate molecular sieves in aqueous surroundings.
Several of these oxidants were launched as generally applicable to oxi-
dation of not only alcohols, but also alkylarenes and benzocycloalk-
anes,[11,13,15,16,22] cyclic ethers,[11,16] amines,[11,13,17,18] thiols,[11,15,22] and
sulfides.[11,15,16,18,22]
Solvent-free reactions are of importance in green chemistry.[24–26]
Among the oxidation reactions referred to previously, solvent-free reac-
tion conditions have been tested in four cases.[11,15,16,20] Another
aspect of contemporary green chemistry is the support of ultrasonic
irradiation,[27] which among the oxidation reactions referred to
previously has been utilized only in one single case.[16] Likewise, the

Green Oxidation of Alcohols
2013
assistance of microwave irradiation[28] in solvent-free KMnO4=CuSO4ꢁ
5H2O–promoted oxidation of alcohols has also been rather sparsely stud-
ied.[11] Our intentions with this work were to study specifically the
oxidation of alcohols by means of KMnO4 absorbed on copper(II) sul-
fate pentahydrate (CuSO4ꢁ5H2O) under solvent-free conditions and
under the assistance of ultrasonic or microwave irradiation to achieve
maximum yield of the desired product most efficiently with respect also
to the reaction time.
RESULTS AND DISCUSSION
Our choice of CuSO4ꢁ5H2O as supporting material was made on the basis
of the work of Noureldin and Bellegarde,[17] who found that 2-decanol
was most efficiently oxidized into 2-decanone by KMnO4 (under reflux
for 24 h in dichloromethane), if supported by CuSO4ꢁ5H2O (among 10
tested inorganic supporting materials). To justify our choice, a series of
experiments were carried out, in which the oxidation of 2-heptanol
(our arbitrarily chosen model substance) into 2-heptanone by means of
KMnO4 under solvent-free reaction conditions was variously supported
by eight different inorganic salt hydrates. The results (Table 1) substan-
tiate our choice of CuSO4ꢁ5H2O as the most efficient supporting agent,
also under solvent-free reaction conditions. As seen in Table 1, the
efficiency of the inorganic salt–supported KMnO4 oxidant depends on
not only on the nature of the inorganic salt but also on the molar ratio
between KMnO4 and the supporting salt. Further experiments demon-
strated that the KMnO4=CuSO4ꢁ5H2O–promoted solvent-free oxidation
of 2-heptanol into 2-heptanone takes place most efficiently when the
molar ratio between KMnO4 and CuSO4ꢁ5H2O is 1 : 4 (Fig. 1).
In these experiments, the oxidants (i.e., KMnO4 þ the pertinent inor-
ganic salt hydrate) were prepared by dissolving both of the ingredients
(in the appropriate relative molar amounts) in deionized water to
form a homogeneous solution, from which water was subsequently
removed by rotational evaporation to leave the oxidant as a solid mass
(Experimental).
The most efficient of the oxidants investigated, prepared by the sol-
ution method described previously, appeared to be KMnO4 absorbed on
a fourfold molar amount of CuSO4ꢁ5H2O. This oxidant, in the following
referred to as PP=4CSP (potassium permanganate absorbed on a fourfold
molar amount of copper sulfate pentahydrate), was chosen as the stan-
dard oxidant in our subsequent experiments. It should be stressed that
PP=4CSP must be prepared as described (Experimental). If PP=4CSP is
dried under forced conditions, (e.g., by heating for 1 h at 100 ꢀC) and

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T. X. T. Luu et al.
Table 1. Efficiency of various supporting inorganic salts in the KMnO4-
promoted solvent-free oxidation of 2-heptanol into 2-heptanonea
Inorganic salt (mmol)
KMnO4 (mmol)
Yield (%)b
None
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
0
100
96
0
3
11
4
CuSO4ꢁ5H2O (12)
CuSO4ꢁ5H2O (6)
BaCl2ꢁ2H2O (12)
BaCl2ꢁ2H2O (6)
CaSO4ꢁ2H2O (12)
CaSO4ꢁ2H2O (6)
MgSO4ꢁ7H2O (12)
MgSO4ꢁ7H2O (6)
ZnSO4ꢁ7H2O (12)
ZnSO4ꢁ7H2O (6)
NiSO4ꢁ6H2O (12)
NiSO4ꢁ6H2O (6)
CoSO4ꢁ7H2O (12)
CoSO4ꢁ7H2O (12)c
CoSO4ꢁ7H2O (6)c
FeSO4ꢁ7H2O (12)c
FeSO4ꢁ7H2O (6)c
12
7
74
66
90
86
41
18
50
14
18
a2-Heptanol (0.348 g, 3 mmol) was shaken with the oxidant (KMnO4 absorbed
on the pertiment inorganic salt) together with small glass balls for 1 h.
bYields are based on GC=MS analysis.
cThe crystalline inorganic salt was mixed directly with crystalline KMnO4 to
avoid oxidation of the inorganic salt by aqueous KMnO4.
subsequently used as oxidant toward 2-heptanol under standard con-
ditions (Table 1), the yield of the product (2-heptanone) was reduced
drastically (to 4%). Thus, as already observed in 1979 by Menger and
Lee,[9] considerable content of (crystal) water apparently is a precondi-
tion for the efficiency of the KMnO4=CuSO4ꢁ5H2O oxidants in general.
In this context, it should be noted that attempts to oxidize 2-heptanol,
under solvent-free conditions, by KMnO4 alone (i.e., in the absence of
the support of an inorganic salt hydrate) were absolutely unsuccessful
(Table 1).
The support of microwave irradiation in solvent-free organic
synthesis often gives rise to dramatically shortened reaction times.[28]
To check the influence of the molar ratio between KMnO4 and
CuSO4ꢁ5H2O in the oxidant KMnO4=CuSO4ꢁ5H2O on the efficiency of
the oxidation of 2-heptanol into 2-heptanone under solvent-free con-
ditions and under microwave irradiation, a series of experiments were

Green Oxidation of Alcohols
2015
Figure 1. Influence of the molar ratio between KMnO4 and CuSO4ꢁ5H2O in the
oxidation agent KMnO4=CuSO4ꢁ5H2O on the efficiency of the oxidation of
2-heptanol into 2-heptanone under solvent-free reaction conditions (2-heptanol:
3 mmol, KMnO4: 3 mmol).
performed under short reaction time conditions (3 min). The results,
depicted in Fig. 2, demonstrate that (1) the support of microwave
irradiation dramatically reduces the reaction time, (2) a 100% yield of
2-heptanone can be obtained with an oxidant based on a molar ratio
of 1 : 2 between KMnO4 and CuSO4ꢁ5H2O, and (3) PP=4CSP, our chosen
standard oxidant, is still 100% efficient.
Altogether 10 secondary alcohols were subjected to oxidation by
PP=4CSP under solvent-free reaction conditions, using four different
methods. In the first series of oxidation reactions, where the mixture of
reactants were simply shaken together at 33–34 ꢀC (method A, Table 2),
fair to excellent yields were obtained in all cases in, by way of compari-
son,[11] relatively short reaction times. The next series of oxidation reac-
tions were performed as described before but under the assistance of
ultrasound irradiation (method B, Table 2). Although the yields of the
products were only slightly improved, the reaction times were shortened
considerably. The third series of solvent-free reactions was performed
under the assistance of microwave irradiation (method C, Table 2).
The yields of the products were comparable to those of the two former
series of experiments, but the reaction times appeared shortened
drastically, with all oxidation reactions being executed within 2.5 to
12 min (Table 2). Microwave irradiation inevitably effects a rise of the

2016
T. X. T. Luu et al.
Figure 2. Influence of the molar ratio between KMnO4 and CuSO4ꢁ5H2O in the
oxidation agent KMnO4=CuSO4ꢁ5H2O on the efficiency of the oxidation of
2-heptanol into 2-heptanone under solvent-free conditions and under microwave
irradiation during 3 min (2-heptanol: 3 mmol, KMnO4: 3 mmol).
temperature of the reaction mixture,[28] and it would therefore be of
interest to check whether the drastically shortened reaction times could
be effected simply by the higher reaction temperatures. Thus a fourth
series of experiments were performed, in which the secondary alcohols
were oxidized by PP=4CSP under solvent-free conditions in the absence
of microwave irradiation but at reaction times and temperatures corre-
sponding exactly to those found optimum in the microwave-assisted
syntheses (method D, Table 2). The results of the latter series of
experiments (Table 2) clearly demonstrate that a conveniently increased
reaction temperature can shorten drastically the reaction time of the
oxidation reaction. However, the yields, although still acceptable, are
generally lower than those obtained by the assistance of microwave
irradiation. As a curio, produced by our curiosity, we can report that
hydroquinone can be oxidized into p-benzoquinone very efficiently by
PP=4CSP under solvent-free reaction conditions, whether assisted by
microwave irradiation or by conventional heating (Table 2).
In 2004, Shaabani et al.[16] reported that 1-heptanol can be oxidized
into 1-heptanal by KMnO4 supported on MnO2 under solvent-free reac-
tion conditions within 6 h in the yield of 90%. Our attempts to oxidize
primary aliphatic alcohols into the corresponding aldehydes by means
of PP=4CSP under any of the described solvent-free reaction conditions

2017

2018
T. X. T. Luu et al.
were not very successful. In general, the yields of the aldehydes were low
(ꢂ20%), and forced reaction conditions inevitably led only to overoxida-
tion into the corresponding carboxylic acids. Our rather disappointing
results are, however, comparable to those obtained by Regen and
Koteel[8] and Lou et al.[12] under heterogeneous oxidation conditions,
(i.e., promoted by KMnO4 in an appropriate solvent).
Although the KMnO4 oxidation of primary aliphatic alcohols has
been rather sparsely studied,[8,12,16] the same oxidation reaction of
benzylic alcohols has been studied quite extensively,[10,12,15,16,21,22] a fact
probably connected with the comparatively higher stability of the
(desired) products, aromatic aldehydes. Thus, fair to excellent yields have
been reported for the oxidation of benzylic alcohols into the correspond-
ing aromatic aldehydes by means of KMnO4 supported on MnO2 under
solvent-free reaction conditions,[16] as well as by KMnO4 with or without
further support under heterogeneous conditions.[10,12,15,21,22] Our
attempts to oxidize benzyl alcohol into benzaldehyde by means of
PP=4CSP under solvent-free reaction conditions (Experimental, method
A) were rather disappointing. For example, on treatment with PP=4CSP
for 30 min benzyl alcohol was converted into both benzaldehyde (68%)
and benzoic acid (4%). Longer reaction times did not increase the yield
of benzaldehyde but rather that of benzoic acid. Therefore, to achieve
a better yield of benzaldehyde, we turned our attention to the use of het-
erogeneous reaction conditions, that is to perform the oxidation as before
(at room temperature) but in the presence of an appropriate solvent. Sev-
eral solvents were checked. More polar solvents appeared to be less
usable because of their tendency to promote overoxidation into benzoic
acid (Table 3), for which reason we finally selected dichloromethane to
Table 3. Yields of benzaldehyde by oxidation of benzyl alcohol by means of
PP=4CSP in various solvents at room temperature
Solvent
Reaction timea
Yield (%)b
CH3CN
Acetone
THF
2
2
30
120
30
65c
69c
49
85c
10
CH2Cl2
300
95
aThe reaction time (in minutes) was fixed by TLC monitoring.
bAbsolute yield of benzaldehyde (determined by GLC).
cAll starting material was consumed by the reaction.

Green Oxidation of Alcohols
2019
Table 4. Yields of aromatic aldehydes by oxidation of benzylic alcohols by means
of PP=4CSP under heterogeneous conditions (in CH2Cl2) at room temperature
Method Ea Method Fb
yield
(%),c (rt)d
yield
(%),c (rt)d
Starting material
Benzyl alcohol
4-Methoxybenzyl alcohol 4-Methoxybenzaldehyde
4-Nitrobenzyl alcohol 4-Nitrobenzaldehyde
Product
Benzaldehyde
95 (5)
99 (5)
97 (5)
95 (0.5)
97 (0.5)
97 (0.5)
aMagnetic stirring at room temperature.
bUltrasonic cell at room temperature.
cYields were determined on the basis of GC=MS analysis.
drt ¼ reaction time in hours.
be the most convenient solvent for our further oxidation experiments
under heterogeneous conditions.
Three representative benzylic alcohols were subjected to oxidation
by PP=4CSP under heterogeneous conditions for 5 h (Experimental, method
E) to give high yields of the corresponding aldehydes (Table 4). In a further
series of experiments, the same benzylic alcohols were subjected to oxidation
by PP=4CSP, still under heterogeneous reaction conditions, but supported
additionally by ultrasonic irradiation (Experimental, method F). Under
the latter reaction conditions, the high yields were still maintained, although
the reaction time could be reduced to 30min (Table 4).
The identity and purity of all products reported were ensured by
NMR and IR spectroscopy as well as by gas chromatography/mass
spectrometry (GC=MS). Because all products are well known and
spectroscopically well characterized already, a further presentation and
discussion of the spectra is unnecessary.
CONCLUSION
Comprehensive experimental work has made it possible for us to intro-
duce the stoichiometrically well-defined material PP=4CSP as a highly
efficient green oxidant toward secondary alcohols, which under
solvent-free reaction conditions are smoothly converted into the corre-
sponding ketones in high yields. The assistance of ultrasonic or micro-
wave irradiation efficiently shortens the reaction times. The oxidation
of primary alcohols by PP=4CSP under similar reaction conditions was
less successful because of competitive overoxidation of the first formed
aldehydes into the corresponding carboxylic acids. However, PP=4CSP
is still an excellent oxidant toward benzylic alcohols, which are smoothly

2020
T. X. T. Luu et al.
oxidized into the corresponding aromatic aldehydes in high yields under
heterogeneous reaction conditions.
EXPERIMENTAL
Instrumentation
For solvent-free reactions, ultrasound irradiation was performed by
means of a Branson 1210E-MT ultrasonic bath, operating at 47 kHz.
For solvent-supported reactions, ultrasound irradiation was performed
by means of Ultrasonic Processor model GE 130, operating at 20 kHz.
Microwave irradiation was performed by means of a batch microwave
oven CEM MDS 200. GC=MS analyses were performed on a Hewlett
Packard 5890 GC 5971 A MS apparatus equipped with a J&W DB-5MS
capillary column (30 m, 0.25 mm i.d., 0.25 mm film thickness) and a
Hewlett Packard 7673 A autosampler. NMR spectra were recorded on
a Varian Mercury 300 NMR spectrometer. Infrared spectra were
recorded on a Perkin-Elmer FT-IR 2000 spectrometer.
Chemicals
All chemicals used were from Aldrich or Merck. All liquid chemicals were
distilled before use to secure maximum purity (ꢂ100%, checked by
GC=MS).
Preparation of Oxidants (Including PP/4CSP)
The inorganic salt was dissolved completely in deionized water. Then
KMnO4 was added, followed by a sufficient volume of deionized water
to obtain a homogeneous solution. The solution was stirred for 10 min
at 80 ꢀC. Subsequently, water was removed from the solution by rota-
tional evaporation, until the weight of the remaining solid mass was equal
to the sum of the weights of the original ingredients. The obtained solid
mass was ground in a mortar into a fine homogeneous powder.
To prevent oxidation by KMnO4 in aqueous solution, crystalline
CoSO4ꢁ7H2O and FeSO4ꢁ7H2O were mixed directly with solid KMnO4
and ground in a mortar into a fine powder (cf. Table 1).
Oxidation of Secondary Alcohols into Corresponding Ketones by
PP/4CSP under Solvent-Free Reaction Conditions (Method A)
Finely ground oxidant PP=4CSP (3.47 g, 3.00 mmol) was added to a
5-mL round-bottom flask containing the alcohol (3.00 mmol) and six

Green Oxidation of Alcohols
2021
glass balls (d ¼ 2 mm). The flask was fitted to a shaking machine to be
shaken at speed 280 rpm for a specific period of time (Table 2). Then the
reaction mixture was extracted with 4 ꢃ 15 mL of ether (or 4 ꢃ 15 mL of
tetrahydrofuran, by the oxidation of hydroquinone). The combined
extracts were filtered through a 1.5- to 2-cm layer of celite 545 and then
dried (anhydrous Na2SO4). After removal of the solvent by rotational
evaporation, the remaining crude product was analyzed by GC=MS,
NMR spectroscopy, and IR spectroscopy. The ketone was isolated by flash
column chromatography (4–7 g silica gel, Davisil, grade 710, 4–20 mm,
60 A, 99%) using as eluent a mixture of hexane and ethyl acetate (9 : 1 v=v).
Oxidation of Secondary Alcohols into Corresponding Ketones by
PP/4CSP under Solvent-Free Reaction Conditions assisted by
Ultrasound Irradiation (Method B)
Finely ground PP=4CSP (3.47 g, 3.00 mmol) was added to a long-necked
10-ml flask containing the alcohol (3.00 mmol). The flask was placed into
an ultrasound bath, where the mixture of reactants was exposed to ultra-
sound irradiation for a specified period of time (Table 2). Subsequently
the reaction mixture was worked up as described in method A.
Oxidation of Secondary Alcohols into Corresponding Ketones by
PP/4CSP under Solvent-Free Reaction Conditions assisted by
Microwave Irradiation (Method C)
Finely ground PP=4CSP (3.47 g, 3.00 mmol) were added to a test tube
(h ¼ 16 cm, d ¼ 1.4 cm) containing the alcohol (3.00 mmol). The test tube
was placed into a beaker, equipped to adhere test tubes, in the CEM
(Matthews, North Carolina, USA) oven. For each of the alcohols, an
irradiation program was applied to determine the most efficient reaction
conditions [with respect to maximum yield of product, most convenient
irradiation energy (Watts), and shortest reaction time (minutes)]; see
Table 2. For every experiment performed, the temperature of the reaction
mixture was measured immediately after the stop of the reaction. Subse-
quently, the reaction mixture was worked up as described in method A.
Oxidation of Secondary Alcohols into Corresponding Ketones by
PP/4CSP under Solvent-Free Reaction Conditions assisted by
Conventional Heating (Method D)
A test tube (h ¼ 16 cm, d ¼ 1.4 cm) containing 3.47 g (3.00 mmol) of
finely ground PP=4CSP and 3.00 mmol of the alcohol was placed in an

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T. X. T. Luu et al.
oil bath heated to the temperature measured by reaction stop of the
parallel reaction run under microwave irradiation. The test tube was kept
in the oil bath for a period of time corresponding exactly to that found
optimum by method C. After cooling, the reaction mixture was worked
up as described in method A.
Oxidation of Benzylic Alcohols into Corresponding Aldehydes by
PP/4CSP under Heterogeneous Reaction Conditions (Method E)
Finely ground PP=4CSP (3.47 g, 3.00 mmol) was added to a 25-mL
round-bottom flask containing the benzylic alcohol (3.00 mmol) dis-
solved in 6 mL of dichloromethane. This reaction mixture was stirred
magnetically at the rate of 500 rpm for 5 h. Subsequently the reaction
mixture was worked up as described in method A.
Oxidation of Benzylic Alcohols into Corresponding Aldehydes by
PP/4CSP under Heterogeneous Reaction Conditions assisted by
Ultrasonic Irradiation (Method F)
Finely ground PP=4CSP (3.47 g, 3.00 mmol) was added to a 50-mL
two-necked pear-shaped flask equipped with an inside ultrasonic probe,
containing also the benzylic alcohol (3.00 mmol) dissolved in 6 mL of
dichloromethane. The reaction mixture was exposed to ultrasonic
irradiation at 50% of maximum level for 30 min. Subsequently, the
reaction mixture was worked up as described in method A.
ACKNOWLEDGMENT
We thank Danish International Aid Programme (DANIDA) for financial
support via the Enhancement of Research Capacity (ENRECA) program.
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Green Oxidation of Alcohols
2023
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