An efficient and reusable vanadium based catalytic system for room temperature oxidation of alcohols to aldehydes and ketones

Article abstract of DOI:10.1016/j.tetlet.2014.07.047

A simple and efficient vanadium based catalyst system for the oxidation of primary and secondary alcohols to aldehydes or ketones is reported using tert-butyl hydroperoxide as oxidizing agent and vanadyl sulfate as catalyst at room temperature. The versatility of the catalytic protocol is studied with wide variety of substrates.

Full text of DOI:10.1016/j.tetlet.2014.07.047

Tetrahedron Letters 55 (2014) 5029–5032
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An efficient and reusable vanadium based catalytic system for
room temperature oxidation of alcohols to aldehydes and ketones
Gayatri Sarmah a, Saitanya K. Bharadwaj a,b, Anindita Dewan a,c, Ankur Gogoi a, Utpal Bora a,c,
⇑
a Department of Chemistry, Dibrugarh University, Dibrugarh 786004, Assam, India
b Department of Chemistry, Pragjyotish College, Guwahati 781009, Assam, India
c Department of Chemical Sciences, Tezpur University, Tezpur 784028, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 April 2014
Revised 9 July 2014
Accepted 12 July 2014
Available online 18 July 2014
A simple and efficient vanadium based catalyst system for the oxidation of primary and secondary
alcohols to aldehydes or ketones is reported using tert-butyl hydroperoxide as oxidizing agent and
vanadyl sulfate as catalyst at room temperature. The versatility of the catalytic protocol is studied with
wide variety of substrates.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Vanadyl sulfate
Peroxovanadium complex
tert-Butyl hydroperoxide
Oxidation
Alcohols
In spite of its notable usefulness, homogeneous catalysis suffers
from a number of drawbacks which lie in the removal and the
reuse of the catalyst. Therefore development of catalytic system
combining high catalytic efficiency with easy recovery and reuse
of the catalytic species is a topic of great interest. Among the var-
ious organic transformations commonly encountered in contem-
porary organic synthesis, the controlled oxidation of alcohols to
aldehydes and ketones, without forming over-oxidized product is
one of the fundamental transformations with immense impor-
tance.1 Conventionally, alcohol oxidation have been performed
with stoichiometric amount of metal oxidants, notably permanga-
nate,2 bromate3 or chromium4 based reagents. These processes
usually generate large amount of environmentally ill-disposed
heavy-metal waste, and therefore they are not always favorable.
Consequently various transition metals, for instance, Fe,5 Mo,6
Ru,7 Pt,8 Pd,9 Ni,10 Cu,11 Au,12 polyoxometalates,13 Mn,14 Rh,15
Se,16 Os17 etc., catalyzed oxidation reactions using molecular
oxygen,18 H2O219 and tert-butyl hydroperoxide (TBHP)20 as oxidiz-
ing agent are well explored. Various vanadium based catalytic sys-
tems such as, VO(acac)2/MS 3 Å,22a,b V-Cu/DABCO,22c VOCl3,22d
V2O5/K2CO3,22e VOSO4/TEMPO,22f VOSO4/NaNO2,22g WO3-VPO,22h
VO(acac)2,22i Silica supported oxo-vanadium Schiff base,22j V2O2–
H2O2,22k V-polyoxometalate13b etc., are effectively used for
oxidation reactions. While considering cheaper and waste-free
oxidant, H2O2 is found to be most suitable, as it produces water
as the only byproduct. However, due to low stability and selectiv-
ity, most of the H2O2-mediated reactions rely on the use of inert
condition and stoichiometric amount of oxidant. Conversely, TBHP
was reported to be an effective oxidant for the selective oxidation
of alcohols,23–25 in presence of vanadium metal. Kaneda et al.
showed that VO(acac)2–TBHP system selectively catalyzed hydro-
xyl functional to carbonyl compounds.23 Similarly, the selectivity
of V(O-iPr)3–TBHP was monitored by varying the amount of ligand,
and cinnamaldehyde was achieved selectively (50% yield) with
45 mol % of N-hydroxy-N-methylbenzamide.24 Later, vanadium
supported on silica with TBHP was also reported as efficient cata-
lytic system for alcohol oxidation.25 Albeit of selectivity, use of
hazardous solvents like benzene, CCl4 etc.,23 expensive ligand24
and support25 are some of the disadvantages of prime concern. In
the contemporary chemistry, use of recoverable and reusable cat-
alytic system is of main importance. Considering the above, herein,
we report a new catalytic system for the oxidation of alcohols to
aldehydes and ketones, employing VOSO4 as catalyst and TBHP
as oxidizing agent, at room temperature.
Initially, to investigate the effectiveness of the VOSO4 in oxida-
tion reaction, 1-phenylethanol (1 mmol) was chosen as a model
substrate and the reaction was carried out using tert-butyl hydro-
peroxide (TBHP) as oxidant in presence of 10 mol % VOSO4 at room
temperature. The results are summarized in Table 1. The reaction
was found to be very sluggish in water (Table 1, entry 1). However,
⇑
Corresponding author. Tel.: +91 275059; fax: +91 (3712) 267005/6.
E-mail addresses: utbora@yahoo.co.in, ubora@tezu.ernet.in (U. Bora).
http://dx.doi.org/10.1016/j.tetlet.2014.07.047
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

5030
G. Sarmah et al. / Tetrahedron Letters 55 (2014) 5029–5032
Table 1
Once the optimum reaction condition was achieved, various
electronically diverse aromatic and aliphatic alcohols were sub-
jected to oxidation with this present protocol26 and the results
are summarized in Table 3. Both secondary alcohols (Table 3,
entries 1–6) and primary alcohols (Table 3, entries 7–11) gave
the corresponding ketone and aldehydes, respectively, in excellent
yield. No variation in yield was observed while changing the
substituent. Most importantly, this protocol also worked well in
case of aliphatic alcohol (Table 3, entries 12 and 13). Moreover aro-
matic alcohols can also be oxidized to the corresponding aldehydes
with this catalytic system (Table 3, entry 14). Cyclic alcohol was
converted to ketone efficiently (Table 3, entry 15). The newly
developed catalytic system was effective for both 1,2-diols and
1,4-diols to give corresponding ketones in good yields (Table 3,
entries 18–20). However, the protocol failed to selectively oxidize
cinnamyl and propargyl alcohols, which resulted in a complex
mixture of products (Table 3, entries 23 and 24). GCMS analysis
indicated the epoxidation of alkene with cinnamyl alcohol. The
new catalyst system was also effective for hex-5-en-1-ol (Table 3,
entry 24).
Optimization of reaction condition for oxidation of 1-phenyl ethanol
O
OH
10 mol %VOSO4, 2 eqiv TBHP
Solvent (2 mL), RT
Entry
Solvent
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
H2O
MeOH
CH2Cl2
THF
DMF
DMSO
AcOH
CH3CN
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
24
24
24
24
24
20
10
8
47
63
60
45
53
81
84
90
96
57
70
9b
10c
11d
5
20
20
a
b
c
Isolated yield.
2 ml (1:1) solvent was used.
1 equiv TBHP was used.
5 mol % VOSO4 was used.
d
In addition, the benzyl groups was found to be compatible
under the present reaction condition and 2-(benzyloxy)ethane-1-
ol was successfully oxidized to the corresponding aldehyde
(Table 3, entry 21). This catalytic system is also applicable for the
oxidation of cholesterol to the corresponding carbonyl compound
in good yield (Table 3, entry 25). However this protocol failed to
oxidize N-(2 hydroxyethyl)benzamide (Table 3, entry 22). Interest-
ingly benzyl chloride also yielded corresponding aldehyde
efficiently with this catalytic system (Table 3, entry 26). It is
noteworthy to mention here that no over-oxidized product was
observed in any of the alcohol studied.
we were able to isolate moderate yield of product in methanol
(Table 1, entry 2). Similarly moderate yields were also obtained
in dichloromethane, THF and DMF (Table 1, entries 3–5). However
we were able to isolate 81% and 84% yield of the product in DMSO
and acetic acid, respectively, (Table 1, entries 6 and 7). Interest-
ingly, excellent conversion was observed in CH3CN (Table 1, entry
8) and we were able to isolate 90% yield of the product. To our
delight, use of aqueous acetonitrile (1:1) yielded the expected ace-
tophenone with 96% yield within very short reaction time (Table 1,
entry 9). This observation may be attributed to solubility of VOSO4
in water and organic alcohols in CH3CN. However, decrease in yield
to 57% was observed (Table 1, entry 10) when we reduced the
amount TBHP to 1 equiv. Moreover 5 mol % of VOSO4 is not suffi-
cient for the complete conversion of 1-phenylethanol to acetophe-
none under the present reaction conditions (Table 1, entry 11).
We have also compared the efficiency of VOSO4 with other
vanadium sources and TBHP with hydrogen peroxide and the
results are summarized in Table 2. Under these controlled reac-
tions, 10 mol% of other vanadium sources viz. V2O5, VO(acac)2 were
used as catalyst in presence of 2 equiv of TBHP. It was observed
that neither V2O5 nor VO(acac)2 was as efficient as VOSO4 to yield
the product in shorter time (Table 2, entries 2 and 3). A similar
reaction were carried out with H2O2 as oxidizing agent in presence
of VOSO4 catalyst, and only 35% of isolated product was observed
(Table 2, entry 4). However, the reaction did not proceed in
absence of VOSO4 (Table 2, entry 5). The above experiments were
found to be convincing enough to use VOSO4 as better catalyst
for oxidation of alcohols with TBHP.
Table 3
Oxidation of alcohols with the optimized reaction conditiona
O
OH
Catalyst (10 mol%), 2 equiv TBHP
CH3CN:H2O (2 mL, 1:1), RT
R/
R
R/
R
Entry
R
R0
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
24
25
26
Ph
p-Cl-Ph
p-Br-Ph
p-CH3O-Ph
Ph
CH3
CH3
CH3
CH3
PhCO
Ph
H
H
H
H
H
5
8
7
6
5
6
3
4
4
4
5
8
8
7
6
6
5
8
7
6
5
5
6
6
7
12
7
96
90
89
93
91
95
88
81
90
92
82
73
70
80
94
65
65
85
88
70
79
—
Ph
Ph
p-NO2-Ph
p-Cl-Ph
p-CH3O-Ph
o-OH-Ph
Octyl
H
H
H
Hexyl
Furyl
Cyclohexanol
Propylene glycol
Isoamyl alcohol
Hexane-1,2-diol
Hydrobenzoin
Hexane-1,4-diol
2-(Benzyloxy)ethan-1-ol
N-(2 Hydroxyethyl)benzamide
Cinnamyl alcohol
Propargyl alcohol
Hex-5-en-1-ol
Table 2
Oxidation of alcohol with different vanadium source
OH
O
Catalyst (10 mol%), 2 eqiv TBHP
CH3CN:H2O (2 mL,1:1), RT
—
—
68
85
82
Entry
Catalyst
Time (h)
Yielda (%)
1
2
VOSO4
V2O5
VO(acac)2
VOSO4
—
5
24
24
24
24
96
46
67
35
Cholesterol
Benzylchloride
3
4b
5
a
All the products were characterized by comparing the FTIR spectra, 1H and 13C
Trace
NMR spectra, melting point measurement and high resolution GC–MS with
authentic compounds.
a
Isolated yield.
H2O2 was used as oxidizing agent.
b
b
Isolated yield.

G. Sarmah et al. / Tetrahedron Letters 55 (2014) 5029–5032
5031
Table 4
The catalytic system could be reused successfully until the sixth
run without either significant loss of yield or extension of the reac-
tion time. Use of aqueous solvent, no ligands and reusability of cat-
alyst are some major advantages of the present protocol.
Results of recycling experiments27
Runa
1
2
3
5.5
96
4
5
96
5
5
94
6
5
94
Time (h)
5
5
Yieldb (%)
96
95
a
Acknowledgments
1-Phenylethanol was used as substrate.
Isolated yield.
b
We wish to thank UGC, New Delhi for support of this Project (No.
41 254/2012 (SR). G.S. thanks UGC for RFSMS fellowship. A.D. thanks
Department of Science and Technology, New Delhi for support.
O
H2O
V
OH2
OH2
SO4
H2O
Supplementary data
tBuOOH
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.07.
047.
O
O
O
V
OH2
O
+
H2O
H2O
R2
R1
H
O
H
O
tBuOH
(I)
References and notes
R2
H
R1
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The reusability of catalyst is very important for cost reduction
in process chemistry. We examined the reusability of the VOSO4
and tert-butyl hydroperoxide system in oxidation reaction27 and
the results are incorporated in Table 4. In order to study the recy-
clability of the catalyst, after completion, the reaction mixture was
extracted with ethyl acetate (10 mL) for three times to obtain the
product in organic layer. Active catalytic species remained in
aqueous layer, which was used for next run by adding required
amount of fresh acetonitrile, substrate and TBHP. Remarkably,
VOSO4 could be reused successfully until the sixth run without
either significant loss of yield or extension of the reaction time.
This is a significant attribute of the present catalytic system.
Formation of peroxovanadium complex as an intermediate in
oxidation reaction using peroxide is well established.28,21c In the
present study, addition of tert-butyl hydroperoxide to the vanadyl
sulfate gives a red-coloured solution which was assumed to be a
peroxovanadate(V) complex and isolated by evaporating the
solvent. The FTIR (see Supporting information) spectrum of the this
complex shows sharp peaks at 986, 778 and 516 cmꢀ1 which
indicate the presence of V@O, OAO(peroxide) and VAO2, respec-
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of coordinated water. Again the UV–visible spectrum shows a
LMCT band at 372 and 223 nm (see Supporting information). The
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with the oxomonoperoxo vanadate(V) reported earlier.30 Based on
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I which
undergoes nucleophilic substitution of water (ligand) by alcohol
(substrate) to form another intermediate II. Finally intermediate
complex II gives the carbonyl compound.
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stirred at room temperature for the time specified in Table 1. The progress of
the reaction was monitored by TLC. After the completion of the reaction, the
mixture was extracted with ethyl acetate (3 ꢂ 20 mL) three times. The ethyl
acetate layer was dried with anhydrous Na2SO4 and evaporated under reduced
pressure. The crude product was purified by column chromatography using
ethyl acetate–hexane as the eluent. Formation of the product was confirmed by
comparing FTIR spectra, 1H NMR spectra, 13C NMR spectra, melting point
measurement and GC–MS with authentic compounds.
27. Experimental procedure for catalyst reusability study: In
a 100 mL round
bottomed flask 3 mmol 1-phenylethanol was stirred with 10 mol % VOSO4 in
6 mL CH3CN/H2O (1:1). To this mixture, 2 equiv of TBHP was added. After the
completion of the reaction the organic portion was extracted with ethyl
acetate (3 ꢂ 10 mL). The remaining aqueous portion contains the catalyst and
was reused for the next run with further addition of same amount of substrate,
TBHP and acetonitrile. This process was repeated up to six cycles without loss
of catalytic activity.
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a round
bottomed flask. To this mixture 2 equiv 70% TBHP (aqueous) was added and