Peroxidative catalytic oxidation of alcohols catalyzed by heterobinuclear vanadium(V) complexes using H2O2 as terminal oxidizing agents

Article abstract of DOI:10.1002/aoc.4299

Here we report the catalytic oxidation of benzylic alcohol, hetero-aryl alcohols and propargylic alcohols to their corresponding carbonyl compound using heterobimetallic sodium-dioxidovanadium(V) complexes. The present catalytic oxidation studies proceed at 70?°C using H₂O₂ as terminal oxidant. During the whole process, the complexes react with hydrogen peroxide to form peroxo-vanadium(V) species. The present study shows the heterogeneity of pre-catalyst which could be easily recovered and moreover isolation of product is very simple.

Full text of DOI:10.1002/aoc.4299

Received: 23 November 2017
DOI: 10.1002/aoc.4299
Revised: 3 January 2018
Accepted: 5 January 2018
F U L L P A P E R
Peroxidative catalytic oxidation of alcohols catalyzed by
heterobinuclear vanadium(V) complexes using H O as
2
2
terminal oxidizing agents
1
2
1
1
Sunshine D. Kurbah
| M. Asthana | Ibanphylla Syiemlieh | Ram A. Lal
1
Centre for Advanced Studies,
Here we report the catalytic oxidation of benzylic alcohol, hetero‐aryl alcohols
and propargylic alcohols to their corresponding carbonyl compound using
heterobimetallic sodium‐dioxidovanadium(V) complexes. The present catalytic
oxidation studies proceed at 70 °C using H O as terminal oxidant. During the
Department of Chemistry, North‐Eastern
Hill University, Shillong ‐793022, India
2
Department of Chemistry, Indian
Institute of Technology Guwahati,
2
2
Guwahati ‐781039, India
whole process, the complexes react with hydrogen peroxide to form peroxo‐
vanadium(V) species. The present study shows the heterogeneity of pre‐catalyst
which could be easily recovered and moreover isolation of product is very
simple.
Correspondence
Ram A. Lal, Centre for Advanced Studies,
Department of Chemistry, North‐Eastern
Hill University, Shillong‐793022, India.
Email: ralal@rediffmail.com
KEYWORDS
bimetallic vanadium (V), catalysis, oxidation, peroxidative
1
| INTRODUCTION
In terms of economy and environmental friendliness,
vanadium complexes catalyzed the aerobic oxidation of
Selective oxidation of alcohols to corresponding aldehydes
and ketones have seen a tremendous growth in the field of
aerobic oxidation catalysis and a wide variety of efficient
methodologies have been developed for this organic trans-
benzylic, allylic, and propargylic alcohols. Vanadium
complex of the composition (HQ) VO(OiPr) (HQ = 8‐
2
quinolinate) reported by Hanson and coworkers,
efficiently catalyzed the oxidation of benzylic, allylic,
and propargylic alcohols in the presence of triethylamine
[1–4]
formations.
Aldehydes and ketones are important
[
16]
starting materials for the preparation of more complex
in air.
heating organic solvents at elevated O
air instead of pure oxygen are more advantageous.
With regard to safety hazard associated with
[5,6]
organic compounds.
Conventionally, there are several
2
pressure using
[12]
methods that have been reported in the literature for the
transformation of alcohols to carbonyl compounds which
Recent studies have focused on the development of
vanadium catalysts for the oxidation of alcohols with air,
few reports are known to exist of an efficient vanadium
catalytic system for aerobic oxidation of alcohols under
atmospheric conditions. Herein, we report the aerobic
oxidation of benzylic, allylic, and propargylic alcohols by
heterobimetallic dioxido‐vanadium(V) complexes.
[7]
include the use of metal like chromium and manga-
[8]
nese. Implementing these methods generate a large
quantity of effluents, such as KMnO , MnO and CrO
3
4
2
which are environmentally toxic and hazardous.
In many cases, the use of noble metal catalysts such as
[9]
[10]
[11]
[12]
ruthenium,
gold,
palladium
and platinum,
shows excellent activities and selectivity's for this chemi-
cal process. However, the use of these novel metals find
many drawbacks and limited services because of their
expensive nature, hence, in order to reduce their usage,
some non‐noble transitional metals are required. In
particular, vanadium complexes are well known as an
2 | RESULTS AND DISCUSSION
Vanadium(V) complexes 1 and 2 were synthesized and
[
17]
characterized in previous reported article.
Molecular
[13–15]
attractive class of catalysts.
structures of the complexes are given in Figure 1. The
Appl Organometal Chem. 2018;e4299.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4299

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KURBAH ET AL.
FIGURE 1 Molecular structure of the complexes 1 and 2 (only one asymmetric unit are shown)
heterobimetallic complexes 1 and 2, are of interest as a pre‐
catalyst for oxidation of organic substrates (Scheme 1).
In order to achieve the optimum condition, we carried
out the oxidation of benzyl alcohol leading to the forma-
tion of benzaldehyde as a model reaction. Using complex
different sources of vanadium V O , VOSO , Vanadyl ace-
2 5 4
tylacetonate and NaVO , but it was found that the com-
3
plex gave better yield compare to these vanadium
sources. The catalytic activity of the complex 2 were also
tested using the same reaction condition and it was found
that complex 2 can be used as catalyst for oxidation of
benzylic, allylic and propargylic alcohols but its yield is
slightly less (<5) compared to complex 1. When the reac-
tion was carried out under dinitrogen atmosphere, the
percentage conversion of benzyl alcohol to benzaldehyde
was unchanged. This proved that air does not participate
in oxidation. Using the above standardized method, we
carried out the catalytic oxidation of various benzylic,
allylic and propargylic alcohols (Table 1).
1
, the reaction was carried out using different amount of
catalyst and found that 0.01 mmol of complex gave the
best yield (Figure 2) at 70 °C (Figure 3). The reaction
was also tested using different organic solvents, but it
was found that acetonitrile gave the best yield
(
(
Figure 4). Using the catalytic amount of catalyst
0.01 mmol), temperature (70 °C) and acetonitrile as
solvent, we studied the effect of additive/base for the
oxidation of benzyl alcohol and it was found that the
use of base reduces the rate of oxidation. We also
performed the oxidation of benzyl alcohol by using
Primary benzyl alcohols bearing electron donating
groups such as, p‐methoxy benzyl alcohol gave 91%
SCHEME 1 Plausible mechanism for
the catalytic oxidation alcohols (only one
unit of complex is shown)

KURBAH ET AL.
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FIGURE 2 Effect of concentration of
catalyst on oxidation of benzyl alcohol
FIGURE 3 Effect of temperature on
oxidation of benzyl alcohol
FIGURE 4 Effect of solvent on
oxidation of benzyl alcohol

4
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KURBAH ET AL.
TABLE 1 Catalytic oxidation of alcohols by heterobimetallic vanadium(V) complexes
Yield (%)
Yield (%)
Sl. No Alcohol
Product
Time (h) (isolated) R‐CHO TON TOF (h‐1) (GC %) R‐CHO
b
c
1
3.4
89
91
80
445
455
400
130.88
113.75
93.02
93
94
87
2
3
4
4.3
4
7.5
88
440
58.67
76
5
6
3
6
No reaction
No reaction
‐
‐
‐
‐
‐
‐
7
7.2
4.5
No reaction
74
‐
‐
‐
8
9
370
82.22
79
4.5
5
88
86
400
430
97.78
86
90
88
1
0
1
1
1
2
5
4
84
86
420
430
84
86
88
107.5
1
3
4
3
3
No reaction
85
‐
‐
‐
1
425
141.67
89
1
5
4
89
445
111.25
92
1
1
6
7
2.3
3.5
78
94
390
470
169.57
134.29
82
96
(Continues)

KURBAH ET AL.
5 of 7
TABLE 1 (Continued)
Yield (%)
Yield (%)
Sl. No Alcohol
Product
Time (h) (isolated) R‐CHO TON TOF (h‐1) (GC %) R‐CHO
b
c
18
19
20
48
48
24
80
34
17
400
170
85
8.33
3.54
3.54
82.4
37
21
a
b
c
2 2
Reaction condition: catalyst (0.01 mmol); 15% H O (4.85 mmol); alcohol (4.84 mmol). yield; GC Yield.
isolated yield of p‐methoxy benzaldehyde (GC: 94%)
Table 1, entry 2), p‐methyl benzyl alcohol gave 88%
confirmed that during the oxidation process, dissociation
of the ligand from the metal ions doesn't occur.
(
p‐methyl benzaldehyde (Table 1, entry 9), whereas 3,4,5‐
trimethoxy benzyl alcohol gave 94 % of isolated yield
within 3.5 h (GC: 96%) (Table 1, entry 17). Electron donat-
ing group present at the ortho and meta position of the
benzene ring such as o‐methyl benzyl alcohol gave 84%
of o‐methyl benzaldehyde and m‐methyl benzyl alcohol
give 86% of isolated m‐methyl benzaldehyde (Table 1,
entry 10, 11). Benzyl alcohol containing electron
withdrawing group such as p‐nitro benzyl alcohol and
m‐chloro benzyl alcohol gave 80% (Table 1, Entry 3) and
3
| CONCLUSION
In conclusion, we have reported an efficient practical
method for the catalytic oxidation of benzyl alcohol, het-
ero‐aryl alcohols and propargylic alcohols using H O as
terminal oxidant under mild conditions using available
heterobimetallic vanadium(V) complexes and cheap
available starting materials. The process is simple,
efficient and the catalyst can be easily recovered without
any lost during the whole conversion process.
2
2
7
4% (Table 1, Entry 8) of the isolated yield of correspond-
ing aldehyde lower to that of electron donation groups
present in para position of the benzene ring. Benzyl
alcohol containing double bond functional groups, such
as cinnamyl alcohol was oxidized selectively with 88%
conversion without oxidation of double bond and 75%
4
| MATERIALS AND METHODS
.1 | Materials and instruments
4
(
Table 1, entry 4) selectivity for aldehyde. 2‐Hydroxy‐1,2‐
diphenylethan‐1‐one was also oxidized to benzil with
6% yield within 2 h. Secondary benzyl alcohols such as
All alcohols such as benzyl alcohol, aliphatic alcohols,
propargylic alcohols and solvents were reagent grade
and used as received. The H NMR were recorded with a
Bruker Avance II 400 MHz in DMSO solution using
TMS as an internal standard.
8
1
phenyl ethanol (entry 6), phenyl propanol (entry 7),
cyclohexanol (entry 5) and cycloheptanol (entry 13) were
also subjected to oxidation but did not react at all. Fur-
ther, hetero‐aryl alcohols such as furan‐2‐yl‐methanol,
pyridine‐2‐yl methanol and thiophene methanol (entries
4.2 | Procedure for oxidation of alcohols
1
4, 15, 16) gave 85%, 89% and 78% of their corresponding
aldehydes. In case of aliphatic alcohols such as n‐butanol,
and n‐octanol were also oxidized for a period of 48 h, giv-
ing their yield of 80% and 34%. Propargylic alcohols such
as 2‐hexyne‐1‐ol, were also oxidized to 2‐hexyne‐1‐al with
lower yield 12% (entry 19).
At the end of each reaction, the catalyst was separated
out using separating funnel, washed three times with ace-
tonitrile and dried at 60 °C. In the consecutive cycles, the
catalyst was recovered and reused again. The studies
In 50 ml round bottom flask containing benzyl alcohol
(0.05 g, 0.5 mmol), 15% H O2 (0.3 g, 8.83 mmol),
2
complexes 1 and 2 (0.01 mmol) were added. The reaction
mixture was first stirred at ambient temperature for
20 min and then temperature was raised to 70 °C for
2 h. The reaction mixture containing crude product was
extracted and dried over anhydrous sodium sulfate. The
oxidized product was purified by column chromatography
to afford the corresponding aldehyde. The NMR spectra of

6
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KURBAH ET AL.
the oxidized products are given in the supporting
information.
4.3.8 | Pyridine‐2 Cabaldehyde
1
Colourless liquid; yield: 89%: H (400 MHz, CDCl ): 9.66
3
1
3
(
s, 1H), 7.32 (d, J = 3.6 Hz, 1H), 6.64‐6.63 (m, 1H);
C
(
100 MHz, CDCl ): 191.2, 152.7, 151.3, 137., 124.3, 121.8;
4
4
.3 | Characterization data
3
‐
1
IR (KBr): 1680 cm .
.3.1 | Benzaldehyde
1
Colourless liquid; yield, 89%; H (400 MHz, CDCl ): 9.96
3
4.3.9 | Thiophene‐2‐carbaldehyde
13
(
s, 1H), 7.87‐7.4 (m, 5H); C (100 MHz, CDCl3): 192.5,
36.2, 134.4, 129.8, 128.9; IR (KBr): 1702 cm .
1
‐1
Light yellow liquid; yield: 78; H (400 MHz, CDCl ): 9.95
(
1
3
13
s, 1H), 7.72‐7.79 (m, 2H), 7.22 (m, 2H); C (100 MHz,
CDCl ): 183.8, 144.0, 136.8, 135.3, 128.1; IR (KBr):
3
‐
1
4.3.2 | p‐Methoxybenzaldehyde
1676 cm .
1
Colourless liquid; yield: 91%; H (400 MHz, CDCl ): 9.78
3
(s, 1H), 7.75 (d, J = 8.0 Hz, 2H), 3.83 (s, 3H); 13C
ACKNOWLEDGEMENTS
(
5
100 MHz, CDCl ): 190.83, 164.5, 131.9, 129.8, 114.3,
5.4; IR (KBr): 1699 cm .
3
‐
1
Authors are thankful to, SAIF, North‐Eastern Hill
University, Shillong‐793022, India for providing NMR
spectra. Sunshine D. Kurbah would like to thank UGC,
New Delhi for NFST fellowship.
4
.3.3 | p‐Nitrobenzaldehyde
1
Pale yellow solid; yield: 80%; H (400 MHz, CDCl ): 10.17
3
(s, 1H), 8.41 (d, J = 8.0 Hz, 2H), 8.08 (d, J = 8.0 Hz, 2H);
ORCID
1
3C (100 MHz, CDCl3): _ 190.2, 140.0, 130.4, 124.3; IR
Sunshine D. Kurbah http://orcid.org/0000-0001-5029-3815
Ram A. Lal http://orcid.org/0000-0002-4957-0958
‐
1
(KBr): 1677 cm .
4.3.4 | Cinnamaldehyde
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1
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