Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2

Article abstract of DOI:10.1007/s10562-019-02710-0

Polymer supported and unsupported oxovanadium(IV) complexes with 2,6-bis(benzimidazolyl)pyridine were synthesized and characterized by elemental analyses, molar conductance, magnetic moment measurements, electronic, IR, ESR spectral studies, LC–MS and thermogravimetric analysis. Based on the results, an octahedral geometry was intended around V(IV) complexes. Polymer-anchored V(IV) complex catalyzed the oxidation of benzyl alcohols in acetonitrile with O₂ as an oxidant. Several parameters were differed to optimize the reaction conditions. Under the optimized reaction conditions, benzyl alcohol oxidation confirmed 96% conversion with 100% selectivity towards benzaldehyde. The developed catalyst revealed excellent benzyl alcohol oxidation at moderate temperature in presence of oxygen making the reaction simpler and environmentally benign. The polymer anchored V(IV) complex showed excellent recyclability as compared to its unsupported analogue. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02710-0

Catalysis Letters
https://doi.org/10.1007/s10562-019-02710-0
Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex
Using O2
M. K. Renuka · V. Gayathri1
1
Received: 29 November 2018 / Accepted: 4 February 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Polymer supported and unsupported oxovanadium(IV) complexes with 2,6-bis(benzimidazolyl)pyridine were synthesized
and characterized by elemental analyses, molar conductance, magnetic moment measurements, electronic, IR, ESR spectral
studies, LC–MS and thermogravimetric analysis. Based on the results, an octahedral geometry was intended around V(IV)
complexes. Polymer-anchored V(IV) complex catalyzed the oxidation of benzyl alcohols in acetonitrile with O as an oxidant.
2
Several parameters were differed to optimize the reaction conditions. Under the optimized reaction conditions, benzyl alcohol
oxidation confirmed 96% conversion with 100% selectivity towards benzaldehyde. The developed catalyst revealed excellent
benzyl alcohol oxidation at moderate temperature in presence of oxygen making the reaction simpler and environmentally
benign. The polymer anchored V(IV) complex showed excellent recyclability as compared to its unsupported analogue.
Graphical Abstract
O
OH
VO(PS-BBP)(H O)(SO )
2
4
H
O , CH CN
2
3
30 mmol
9
6 %
Keywords VO(BBP)(H O)(SO ) · VO(PS–BBP)(H O)(SO ) · Oxygen · Benzyl alcohol · Benzaldehyde
2
4
2
4
1
Introduction
organic reactions using polymer-supported catalysts have
received much attention because of easy workup and recy-
clability [4, 5].
Enormous potentiality of homogeneous transition metal
complex catalysts in chemical transformations has increased
attention in catalyst research, exploring numerous homoge-
neous complex-catalysts in oxidation reactions [1–3]. How-
ever, homogeneous catalysts suffer from several drawbacks
related to the handling of sensitive metal–ligand complexes,
deactivation during reaction and difficulty in recovery and
reuse of expensive reagents, which hinders their practical
applications in industrial processes. On the other hand,
Benzaldehyde is widely used in the pharmaceutical,
dyeing, perfumery, and agrochemical industries [6]. Ben-
zaldehyde is produced mainly via the routes of hydrolysis
of benzyl chloride or oxidation of toluene [7, 8], however
the former approach would face significant chlorine con-
tamination while the latter would result in poor product
selectivity with high temperature and pressure conditions.
Therefore, liquid phase oxidation of benzyl alcohol (BzOH)
to benzaldehyde is preferred and widely accepted [9, 10].
Several works have been carried out using homogeneous
catalysts for BzOH oxidation [11–13], however heterogene-
ous catalysts are easily recovered and reused in BzOH oxi-
dation, which is highly desirable in commercial application.
*
V. Gayathri
gayathritvr@yahoo.co.in
1
Department of Chemistry, Central College Campus,
Bangalore University, Bangalore, Karnataka 560001, India
Vol.:(0
1
123456789)
3

M. K. Renuka, V. Gayathri
Numerous supported metal catalyst systems involving Mn,
Ru, Au and Pd have been used for the selective oxidation
of BzOH [14–20] using oxidants such as TBHP, H O , O
in the polymer support (PS) was found to be 9.6% by Vol-
hard’s method. 2,6-Bis(benzimidazolyl)pyridine (BBP)
and functionalized polymer were synthesized as described
earlier [32, 33]. Equimolar quantities (1 mmol) of 0.18 g
VOSO ·XH O and 0.31 g BBP (1 mmol) were dissolved sep-
2
2
2
[
21–23] along with weak and strong bases [24, 25]. Con-
versely, these additives and conditions will affect purifica-
tion and cause pollution [26, 27]. Thus, use of molecular
oxygen as oxidant at lower temperatures has drawn much
attention and widely accepted as a “greener” process for the
production of benzaldehyde [28–30].
4
2
arately in ethanol (10 mL), mixed and refluxed on water bath
for 4–6 h. After cooling to room temperature, a grey colored
complex was formed and filtered, washed with ethanol, and
finally dried over calcium chloride. Yield: 93%. The result-
ing unsupported vanadium complex VO(BBP)(H O)(SO )
In the present work, we report the oxidation of BzOH
using VO(PS–BBP)(H O)(SO ) catalyst using cost effective
2
4
(Scheme 1a) is grey colored solid, air stable and insoluble
in water and common organic solvents, but soluble in DMF
and DMSO.
2
4
and clean oxidant molecular oxygen at moderate temperature
in acetonitrile. Operating parameters were varied; to under-
stand catalyst behavior and improving its performance. The
polymer supported vanadium complex showed better cata-
lytic activity compared to its unsupported analogue towards
oxidation of BzOH.
10 mL ethanol was added to 1 g of functionalized poly-
mer (PS–BBP) at RT and kept for 1 h. To it, VOSO ·XH O
4
2
(1 mmol; 0.17 g) in 10 mL of ethanol was added and stirred
at reflux condition for 48 h. The resulting turkish blue
colored polymer supported complex VO(PS–BBP)(H O)
2
(
SO ) (1.5 g) (Scheme 1b) was filtered, Soxhlet extracted
4
2
Experimental
with ethanol and dried for 24 h at 100 °C.
2.1 Materials and Methods
2.3 Procedure for Benzyl Alcohol Oxidation
All the chemicals used were of AR grade and purified by the
standard methods [31]. The synthesized vanadium(IV) com-
plexes were characterized by FT–IR, UV–Vis, ESR, LC–MS
techniques, magnetic moment, and molar conductivity meas-
urements, elemental and thermogravimetric analyses. The
elemental analyses (carbon, hydrogen, oxygen and nitrogen)
of the complexes VO(BBP)(H O)(SO ) and VO(PS–BBP)
A typical VO(PS–BBP)(H O)(SO ) catalyzed oxidation was
2
4
performed. BzOH (30 mmol), VO(PS–BBP)(H O)(SO )
2
4
(50 mg, 0.0995 mmol) and CH CN (5 mL) were placed in
3
100 mL three-neck round bottom flask fitted with a con-
denser, oxygen was bubbled through the reaction mixture
at 60 °C for 4 h (Scheme 2). An aliquot of the reaction mix-
ture was taken at various time intervals and analyzed by a
Shimadzu GC-2010 gas chromatograph with flame ioniza-
tion detector. The recovered VO(PS–BBP)(H O)(SO ) was
2
4
(
H O)(SO ) was obtained from Elementar Vario Micro Cube
2 4
CHNS analyzer. Diffuse reflectance spectra were recorded
2
4
on BaSO disks in Shimadzu UV–Vis–NIR model-3101P
washed, dried in vacuo and reused.
4
spectrophotometer. FT–IR spectra of solid compounds as
KBr pellets were taken using Shimadzu 8400 s FT–IR spec-
trometer. Thermogravimetric analyses were carried out in
TA instrument, SDT analyzer model Q600. Atomic absorp-
tion spectra (AAS) were recorded using Avanta Pm, GF
3 Results and Discussion
3.1 Catalyst Characterization
3.1.1 CHN Analyses
3
000 instrument. LCMS measurements were recorded on
LC–MSD-Trap-XCT-Plus. Magnetic moments of the com-
plexes were measured by VSM model 7404. Molar conduc-
tivity measurement was carried out by using WTW conduc-
tivity meter. ESR measurements were carried out in solid
state at room temperature in standard X band JES-FA200
spectrometer. Far IR spectrum was recorded on a Perkin-
Elmer 1700-XFT instrument. SEM analysis is carried out
using an ESEM Quanta 200, FEI.
The CHN and vanadium content in the complexes are listed
in Table 1, indicating 1:1 (metal:ligand) stoichiometry.
The molar conductivity of VO(BBP)(H O)(SO ) com-
2
4
−
3
plex in DMF (~10 M) solution at room temperature was
2
−1
19 S cm mol , signifying its non-electrolytic nature.
.1.2 IR Spectral Studies
3
2
.2 Synthesis of VO(BBP)(H O)(SO ) and VO(PS–
2 4
BBP)(H O)(SO )
The IR spectrum of the chloromethylated polystyrene beads
2
4
−
1
exhibited peaks at 1267 and 829 cm due to ν(CH –Cl)
2
The polymer support used is chloromethylated polystyrene
cross-linked with 6.5% divinylbenzene. The chloride content
and ν(C–Cl) respectively. On functionalization, ν(CH –Cl)
2
and ν(C–Cl) decreased in intensity, in consistent with the
1
3

Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2
(
a)
H
N
H
N
H
N
H
N
N
V
O
Ethanol
Reflux
N
+
VOSO .XH O
N
N
4
2
N
N
H O
OSO3
BBP
2
VO BBP H O SO
(
)( )( )
2
4
9
3 % Yield
(
b)
O
H
C
2
H
C
N
N
N
2
H
N
VOSO4
.XH O
2
P
N
OSO3
V
N
P
N
N
Ethanol, reflux
OH2
PS-BBP
N
HN
VO PS-BBP H O SO
4
)( )( )
(
2
Scheme 1 a Synthesis of unsupported vanadium complex VO(BBP)(H O)(SO ). b Synthesis of polymer supported vanadium complex VO(PS–
2
4
BBP)(H O)(SO )
2
4
O
and bonded to polymer support (Fig. 1). The IR spectrum
of VO(BBP)(H O)(SO ) is presented in Fig. 2. The complex
2
4
OH
VO(PS-BBP)(H O)(SO )
2
4
−1
H
revealed peaks at 3290, 3065 and 1319 cm due to ν(O–H),
ν(N–H) and ν(C–N) respectively. The ν(C=N) of BBP at
O
2
,
CH
3
CN
−
1
−1
3
0 mmol
1615 cm was shifted to lower energy by 10 cm in the
complex suggesting the coordination of tertiary nitrogens of
9
6 %
2+
−1
BBP to VO [33]. Peak at 970 cm was due to the presence
Scheme 2 Oxidation of benzyl alcohol catalyzed by VO(PS–BBP)
H O)(SO )
−1
of ν(V=O). The peaks at 1462 and 1108 cm were due to
(
2
4
asymmetric and symmetric sulphate stretch of monoden-
tately coordinated sulphate group in the complex [34].
Functionalized polymer PS–BBP exhibited peak due
bonding of BBP onto the polymer support. The free BBP
−
1
−1
−1
exhibited a peak around 3190 cm due to ν(N–H) and its
to ν(N–H) around 3190 cm and the peak at 1623 cm
−
1
intensity decreased and shifted to 2927 cm in functional-
ized polymer indicating that one or two NH’s groups of the
benzimidazole moiety of the ligand may be deprotonated
was assigned to ν(C=N) of benzimidazole/pyridine moi-
eties in addition to polymer peaks [35]. The IR spectrum
of VO(PS–BBP)(H O)(SO ) showed peaks due to ν(C=N)
2
4
Table 1 Analytical data and
Compound
C %
H %
N %
V %
µeff (BM)
1.75
magnetic moments of supported
and unsupported vanadium
complexes
VO(BBP)(H O)(SO )
45.36
3.43
13.87
10.01
2
4
(
46.35)
(3.07)
(14.22)
(10.35)
VO(PS–BBP)(H O)(SO )
Recycled VO(PS–BBP)(H O)(SO )
76.30
76.30
8.72
8.72
5.09
5.09
5.6
5.0
1.73
–
2
4
2
4
Calculated values are in parentheses
1
3

M. K. Renuka, V. Gayathri
1
00
8
0
0
0
0
6
4
2
3
500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm
)
Fig. 3 IR spectrum of VO(PS–BBP)(H O)(SO )
2
4
Fig. 1 FT–IR spectra of PS, BBP and PS–BBP
Fig. 4 Far IR spectra of (a) VO(PS–BBP)(H O)(SO ) (b) VO(BBP)
2
4
(
H O)(SO )
2 4
−
1
3
500
3000
2500
2000
1500
1000
500
group was at 1135 cm (Fig. 3). The far-IR spectra of
VO(PS–BBP)(H O)(SO ) and VO(BBP)(H O)(SO ) (Fig. 4)
-
1
Wavenumber (cm )
2
4
2
4
−
1
showed 330 and 343 cm respectively due to ν(V–N).
Fig. 2 FT–IR spectrum of VO(BBP)(H O)(SO )
2
4
3
.1.3 Electronic Spectral Studies
and ν(N–H) at 1599 cm−1 and 3074 cm respectively. The
shift of ν(C=N) and ν(N–H) peaks in the supported complex
when compared to PS–BBP, indicated the coordination of
vanadium through N of C=N and N–H moieties of pyri-
−1
The electronic spectra of both unsupported VO(BBP)(H O)
2
(SO ) and supported VO(PS–BBP)(H O)(SO ) complexes
4
2
4
exhibited strong absorption bands from 210 to 334 nm,
which were attributed to π →π* and n →π* transitions of
PS and BBP respectively, and another in the range 340 to
370 nm arising due to ligand to metal charge transfer band
(LMCT) [33]. Spectra of both the complexes exhibited
−
1
dine and benzimidazoles. The peaks at 1322 and 1463 cm
attributed to ν(C–N) and δ(N–H) respectively. The ν(V=O)
peak was observed at 944 cm− and the peak due to sulphate
1
1
3

Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2
5
2000
290
367
1
1
500
000
4
3
2
1
0
334
5
00
0
8
40
-
500
-
1000
600
800
Wavelength (nm)
1000
-1500
-2000
2
00
400
Wavelength (nm)
3
50
Magnetic field (mT)
Fig. 5 Electronic spectrum of VO(BBP)(H O)(SO )
2
4
Fig. 7 EPR spectrum of VO(BBP)(H O)(SO ) at RT
2
4
227
1
1
500
000
210
870
500
600
800
1000
Wavelength (nm)
0
343
-500
-
-
1000
1500
200
400
Wavelength (nm)
2
50
300
350
400
450
Magnetic field (mT)
Fig. 6 Electronic spectrum of VO(PS–BBP)(H O)(SO )
2
4
Fig. 8 EPR spectrum of VO(PS–BBP)(H O)(SO ) at RT
2
4
two weak d–d bands in the visible region ~ 800–900 nm
2
(
dxy → dxz, dyz) and ~ 400–450 nm (dxy → dz ), where
latter is obscured under a strong CT band [36]. On the basis
of electronic spectral data, an octahedral structure has been
proposed for vanadium complexes (Figs. 5, 6).
nuclear spin of I=7/2. This confirms the presence of a single
vanadium(IV) cation as metallic center in the complex. The
EPR spectrum of VO(PS–BBP)(H O)(SO ) in polycrystal-
2
4
line state at RT (Fig. 8) exhibits an isotropic spectrum. The
3
.1.4 ESR Spectral Studies and Magnetic Moment
characteristic g value obtained for both unsupported and
iso
Measurements
supported complexes was 1.93, which is typical value of
V(IV) complexes.
The X-band room temperature ESR spectrum of VO(BBP)
H O)(SO ) complex (Fig. 7) showed eight lines pattern,
The room temperature magnetic moments of unsupported
and polymer supported vanadium complexes were found to
be 1.75 and 1.73 B.M respectively, indicating the presence
of one unpaired electron (Table 1).
(
2
4
which is due to hyperfine splitting arising from the inter-
5
1
action of the unpaired electron with V nucleus having
1
3

M. K. Renuka, V. Gayathri
Fig. 9 LC–MS of VO(BBP)
H O)(SO )
(
2
4
Fig. 11 Thermogram of VO(BBP)(H O)(SO )
2
4
Fig. 10 Thermogram of VO(PS–BBP)(H O)(SO )
2
4
1
10–215 °C. The loss of sulphate ion (28%) took place
3
.1.5 LC–MS Studies
at 215–430 °C. The decomposition of BBP occurred at
higher temperature (> 430 °C) (Fig. 11).
The molecular ion peak of complex VO(BBP)(H O)(SO ) is
All these studies revealed that polymer supported and
unsupported V(IV) complexes were octahedral in geom-
etry (Scheme 1a, b).
2
4
observed at 493 m/z, which is in agreement with molecular
formula C H N O SV. Further fragmentation of the com-
1
9
15
5
6
plex revealed ion peak with m/z 310 due to BBP (Fig. 9).
3
.1.7 SEM and EDS Mapping Analysis
3.1.6 Thermal Analyses
Surface of functionalized bead is smoother than that of
complexed resin. The rough surface of the beads appeared
because of the rearrangement of the polymer chains on
complexation with metal ions.
Thermograms of complexes were recorded in the range of
0–1000 °C at heating rate of 10 °C/min. The TG curve of
VO(PS–BBP)(H O)(SO ) (Fig. 10) indicated 2% first step
2
2
4
weight loss at 122–185 °C due to water molecule. Second
step involved weight loss of 10% at 185–210 °C attributa-
ble to the loss of sulphate ion. Third step weight loss (23%)
at 210–350 °C was due to the loss of two benzimidazole
moieties of BBP ligand. The loss of pyridine moiety of
ligand and polymer occurred after 350 °C. The thermal
decomposition of VO(BBP)(H O)(SO ) showed weight
A good dispersion of V(IV) complex particles on the
polymer support was evidenced by SEM microscopy
(Fig. 12). It was believed that this sustain the immobiliza-
tion of the complexes by coordination interaction between
the vanadium ion and the N atoms of the functionalized
supports. The SEM images showed the change of polymer
supported V(IV) complex morphology after immobiliza-
tion. The morphology of recycled polymer vanadyl com-
plex is almost similar to the fresh catalyst.
2
4
loss of 4% due to loss of coordinated water molecule at
1
3

Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2
3
.2.1 Catalytic Activity of VO(PS–BBP)(H O)(SO )
2 4
To achieve the maximum conversion of BzOH, the param-
eters such as the oxidants, solvents, VO(PS–BBP)(H O)
2
(
SO ) concentration and temperature were varied and their
4
effect on the reaction was investigated. In all these reactions,
it was observed that BzOH was converted to benzaldehyde
with 100% selectivity.
3
.2.2 Effect of Temperature and Time
The reactions were conducted at RT (30 °C) to 70 °C. The
influence of reaction temperature on the catalytic activity of
VO(PS–BBP)(H O)(SO ) under reaction conditions is illus-
2
4
trated in Fig. 14. The BzOH conversion increased as the
reaction proceeded from RT (59%) to 60 °C (96%). When
the temperature increased from 60 to 70 °C BzOH conver-
sion (85%) was decreased which is due to the decomposition
of oxidant at higher temperature. Hence, for BzOH conver-
sion, 60 °C for 4 h was considered as optimum.
Fig. 12 SEM and EDS mapping analysis of PS–BBP and VO(PS–
BBP)(H O)(SO )
2
4
3.2 Catalytic Activity: Benzyl Alcohol Oxidation
3
.2.3 Effect of Solvents
The BzOH oxidation was carried in absence of catalyst at
0 °C in 5 mL CH CN using O as oxidant for 4 h, where
6
To investigate the influence of the solvent nature on the
catalytic oxidation, the reaction was conducted in water,
THF and acetonitrile. It was observed that the conversion
followed the order: 96% in acetonitrile (dielectric constant
ε = 37.5, donor number D = 14.1) > 72% in THF (ε = 7.3,
3
2
conversion was only 15% (Fig. 13). When the reaction
was carried out using supported (50 mg, 0.0995 mmol)
and unsupported (48.96 mg, 0.0995 mmol) complexes of
vanadium, the yield of benzaldehyde was 96% and 39%
respectively. Since polymer supported catalyst showed
higher conversion, it was used to optimize the reaction
conditions.
D = 20) > 36% in H O (ε = 80.4, D = 29.8). Among them,
2
acetonitrile was found to be the most suitable solvent for the
reaction (Fig. 15).
Temperature variation
100
96
100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
8
6
0
0
RT
50 °C
6
7
0 °C
0 °C
3
9
40
2
8
2
0
0
1
5
1
2
3
4
Blank
reaction
Polymer
supported
catalyst
Unsupported
catalyst
PS
Time (h)
Fig. 14 Effect of temperature on the oxidation of BzOH, Reaction
Fig. 13 Benzyl alcohol oxidation catalyzed by VO(BBP)(H O)(SO ),
conditions: VO(PS–BBP)(H O)(SO ) (50 mg), CH CN (5 mL); O
2
4
2
4
3
2
VO(PS–BBP)(H O)(SO ) and without catalyst (blank reaction)
(1 atm)
2
4
1
3

M. K. Renuka, V. Gayathri
Solvents variation
acetonitrile is depicted in Fig. 17. The BzOH conversion was
found to be same (96%) in H O , TBHP and O , although the
1
00
2
2
2
time taken for the conversion was 2, 3, and 4 h respectively.
Though the time taken by O was longer compared to H O
2
8
6
4
2
0
0
0
0
0
2
2
and TBHP, O was chosen as oxidant since it is environ-
2
Acetonitrile
Water
mentally benign.
Using above optimized reaction conditions, activity and
scope of catalyst was explored in the oxidation of primary
and secondary benzyl alcohols (Table 2). Both electron rich
THF
(
entries 1–4) and electron deficient (entries 5, 6) derivatives
of BzOH showed excellent reactivity and afforded the corre-
sponding aldehydes. The effect of substituents on the BzOH
oxidation was studied and conversion was found in the order
NH >OH>CH >OCH >NO . Secondary alcohols, phe-
1
2
3
4
Time (h)
2
3
3
2
nylethanol (70%) and phenylpropanol (68%) conversion was
Fig. 15 Effect of solvents on the oxidation of BzOH, reaction condi-
tions: VO(PS–BBP)(H O)(SO ) (50 mg), solvent (5 mL); O (1 atm);
slightly lower (entries 7 and 8).
2
4
2
Temperature (60 °C) in 4 h
3
.3 Comparison of Catalytic Activity
3.2.4 Effect of Catalyst Amount
with the Literature
Varying concentrations of VO(PS–BBP)(H O)(SO ) cata-
The performance of VO(PS–BBP)(H O)(SO ) is compared
2 4
2
4
lyst (40, 50 and 60 mg), illustrates the conversion in the
with literature work and it is tabulated in Table 3.
order 50 mg (0.0995 mmol, 96%)>60 mg (0.1194 mmol,
7
2%)>40 mg (0.0796 mmol, 62%) (Fig. 16). Hence, 50 mg
3.4 Catalyst Recyclability
VO(PS–BBP)(H O)(SO ) is optimal concentration of the
2
4
catalyst. The yield increases with increase in concentra-
tion up to certain extent, afterwards yield decreases due to
the presence of excess of catalytic sites may results rapid
decomposition of oxidant before oxidizing the substrate.
Recycling study of the VO(PS–BBP)(H O)(SO ) catalyst for
2
4
the oxidation of BzOH under optimized reaction conditions
was investigated (Fig. 18). After the first use, the supported
catalyst was recovered by simple filtration and reused after
washing and drying. The recovered catalyst was successfully
employed in subsequent six cycles revealing excellent con-
version and its activity decreased from seventh run (92%).
Vanadium content of the recycled catalyst (after sixth cycle)
3.2.5 Effect of Oxidant
The effect of different oxidants on the oxidation of
BzOH over VO(PS–BBP)(H O)(SO ) catalyst at 60 °C in
2
4
Oxidants variation
Catalyst concentration variation
100
1
00
8
6
4
2
0
0
0
0
0
8
6
0
0
O2
H2O2
TBHP
4
5
6
0 mg
0 mg
0 mg
40
20
0
1
2
3
4
1
2
3
4
Time (h)
Time (%)
Fig. 16 Effect of VO(PS–BBP)(H O)(SO ) concentration on the oxi-
Fig. 17 Effect of oxidants on the oxidation of BzOH, reaction con-
2
4
dation of BzOH, Reaction conditions: CH CN (5 mL); O (1 atm);
ditions: VO(PS–BBP)(H O)(SO ) (50 mg), CH CN (5 mL); oxidants
3
2
2
4
3
Temperature (60 °C) in 4 h
(H O and TBHP; 30 mmol)/O (1 atm); temperature (60 °C) in 4 h
2 2 2
1
3

Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2
Table 2 VO(PS–BBP)(H O)
2
Entry
Substituted benzyl
alcohol
Aldehyde
%
conversion
97
TON TOF
(
SO ) catalyzed oxidation of
4
-1
benzyl alcohol surrogates
(h )
1
294
74
2
3
90
91
273
275
69
69
4
5
85
80
257
242
64
61
6
75
227
57
7
8
70
68
212
206
50
52
Reaction conditions: VO(PS–BBP)(H O)(SO ) (50 mg), CH CN (5 mL); O (1 atm); Temperature
2
4
3
2
(
60 °C) in 4 h
Table 3 Evaluation of present work with other reported catalysts
Catalyst
Catalyst conc.
Temp. (°C) Oxidant Time (h) Yield
Selectivity Refs.
Poly(S-DVB-EDTA-Cu)
Poly(S-DVB-EDTA-Co)
150 mg
50 mg
50 mg
50
50
50
35
O2
TBHP
O2
6
2
24
1
42
50
74.5
42
100
>99
[37]
[38]
[39]
[40]
Au/Ni Al HT
3
5
−1
Polymer supported Ru(III)salan complex 7.12×10 mol L
O2
Rate of reac-
tion=0.50 mL min−
1
PS–(QBIM) Cu(II) complex
0.02 mmol
50 mg
0.1 mol %
50
60
70
TBHP
H O
3
6
6
98
100
71
96
100
100
[41]
[42]
[43]
2
[
(
PS–Cu–TSC] catalyst
2
2
2
[aqua(4-bromobenzoato) (2,2′dipyri-
H O
2
dylamine)copper(II)](perchlorate))
Present work
50
60
O2
4
96
100
–
[
PS–Cu–TSC], polymer-supported thiosemicarbazone copper(II) complex; QBIM, 2-quinolylbenzimidazole
1
3

M. K. Renuka, V. Gayathri
Recyclability
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Acknowledgements The first author greatly acknowledges the UGC
for providing Junior Research Fellowship. We gratefully acknowledge
Thermax Ltd. India for providing chloromethylated poly(styrene–divi-
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SAIF, IIT Madras for magnetic moment measurements.
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Compliance with Ethical Standard
5
Conflict of interest The authors declare that they have no conflict of
interest.
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