Baeyer-Villiger oxidation of cyclopentanone over zeolite Y entrapped transition metal-Schiff base complexes

Article abstract of DOI:10.1002/aoc.3910

Transition metal [M?=?VO (IV) and/or Cu (II)] complexes with Schiff base ligand, (Z)-2-((2-hydroxybenzylideneamino)phenol (H₂L) have been entrapped in the super cages of zeolite-Y by Flexible Ligand Method. Synthesized materials have been characterized by preferential physico-chemical techniques such as inductively coupled plasma optical emission spectroscopy (ICP-OES), elemental analyses (CHN), fourier transmission infrared spectroscopy (FTIR), electronic and UV-reflectance spectra, Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron micrographs (SEMs), X-ray diffraction patterns (XRD) and thermogravimetric analysis (TGA). The catalytic competence of zeolite-Y entrapped transition metal complexes was examined in Baeyer-Villiger (BV) oxidation of cyclopentanone using 30% H₂O₂ as an oxidant beside neat complexes to check the aptitude of heterogeneous catalysis over the homogeneous system. The effect of experimental variables such as mole ratio of substrate to an oxidant, amount of catalyst, reaction time, varying oxidants and solvents on the conversion of cyclopentanone was also tested. Under the optimized reaction conditions, one of the zeolite-Y entrapped transition metal complex viz. [VO(L)H₂O]-Y [where L?=?(Z)-2-((2-hydroxybenzylideneamino)phenol] was found to be a potential contender by providing 80.22% conversion of cyclopentanone (TON: 10479.42), and the selectivity towards δ-valerolactone was 83.56%.

Full text of DOI:10.1002/aoc.3910

Received: 28 February 2017
DOI: 10.1002/aoc.3910
Revised: 5 May 2017
Accepted: 10 May 2017
F U L L PA P E R
Baeyer‐Villiger oxidation of cyclopentanone over zeolite Y
entrapped transition metal‐Schiff base complexes
Chetan K. Modi
| Naresh Solanki | Ravi Vithalani | Dikin Patel
Applied Chemistry Department, Faculty of
Technology & Engineering, The Maharaja
Sayajirao University of Baroda, Vadodara
390 001Gujarat, India
Transition metal [M = VO (IV) and/or Cu (II)] complexes with Schiff base ligand,
(Z)‐2‐((2‐hydroxybenzylideneamino)phenol (H2L) have been entrapped in the super
cages of zeolite‐Y by Flexible Ligand Method. Synthesized materials have been
characterized by preferential physico‐chemical techniques such as inductively
coupled plasma optical emission spectroscopy (ICP‐OES), elemental analyses
(CHN), fourier transmission infrared spectroscopy (FTIR), electronic and UV‐
reflectance spectra, Brunauer–Emmett–Teller (BET) surface area measurements,
scanning electron micrographs (SEMs), X‐ray diffraction patterns (XRD) and ther-
mogravimetric analysis (TGA). The catalytic competence of zeolite‐Y entrapped
transition metal complexes was examined in Baeyer‐Villiger (BV) oxidation of
cyclopentanone using 30% H2O2 as an oxidant beside neat complexes to check
the aptitude of heterogeneous catalysis over the homogeneous system. The effect
of experimental variables such as mole ratio of substrate to an oxidant, amount of
catalyst, reaction time, varying oxidants and solvents on the conversion of
cyclopentanone was also tested. Under the optimized reaction conditions, one of
the zeolite‐Y entrapped transition metal complex viz. [VO(L)H2O]‐Y [where
L = (Z)‐2‐((2‐hydroxybenzylideneamino)phenol] was found to be a potential con-
tender by providing 80.22% conversion of cyclopentanone (TON: 10479.42), and
the selectivity towards δ‐valerolactone was 83.56%.
Correspondence
Chetan K. Modi, Applied Chemistry
Department, Faculty of Technology &
Engineering, The Maharaja Sayajirao
University of Baroda, Vadodara,
Gujarat, India.
Email: chetank.modi1@gmail.com
Funding information
University Grants Commission, Grant/Award
Number: 42‐290/2013 (SR) dated‐25th
March, 2013; UGC, New Delhi, Grant/
Award Number: 42‐290/2013
KEYWORDS
Baeyer‐Villiger oxidation of cyclopentanone, flexible ligand method, heterogeneous catalysts, zeolite‐Y
entrapped transition metal complexes
1 | INTRODUCTION
from reaction mixtures. On the other hand, homogeneous
systems are often regarded as imprecise with many restric-
For chemical transformation in both academia and industry,
catalyst technology is nowadays used as a powerful tool
because it plays a vital role in chemical reactions, allowing
faster conversion of a wide variety of starting material to
high‐value products at lower cost with minimum generation
of by‐product. In this day and age, the meadow of heteroge-
neous catalysts has pulled up as eco‐sustainable catalytic
systems transforming various organic substrates into valuable
intermediates for environmentally benign industrial processes
due to its high stability, activity and effortless separation
tions, including the decomposition and deactivation due to
the formation of dimeric μ‐oxo‐ and peroxo‐ bridged species,
and separation problem as well.[1] With added benefits of
flexibility in immobilization of various chemical moieties
and/or nanomaterials into the reaction channels, molecular
sieves have been expanded into an imposing group of inor-
ganic‐crossbreed materials (active heterogeneous catalysts)
with huge number of industrial applications, mainly in the
field of catalysis. It comprises zeolites, mesoporous mate-
rials, and metal–organic frameworks. Predominantly, zeolites
Appl Organometal Chem. 2017;e3910.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3910

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MODI ET AL.
are crystalline aluminosilicates formed by nanocavities and
channels of strictly regular dimensions in conjunction with
having assorted sizes and shapes as well. Especially, three
dimensional network structure with spacious internal super
cage (~13 Å) and large pore diameter (~7.4 Å) of zeolite‐Y
has been studied here as host lattices. It acquires properties
like high surface area, tunable pore size and functionality,
crystalline open structures, high adsorption capacity, and
partitioning of reactant/products, which allows considering
them as potential supports for entrapment of catalytically
active complexes[2--4] or metal complexes.[5--8] These inor-
ganic‐crossbred porous framework compounds not only
possess heterogeneous catalytic physiognomies, but also
conserve high catalytic efficacy originating in homogeneous
catalysis due to the site sheltered effect.[9]
catalysts using 30% H2O2 as an oxygen donor. The plausible
mechanism of homogeneously catalyzed heterogenized
Baeyer‐Villiger oxidation of cyclopentanone is proposed in
Scheme 1.
2 | EXPERIMENTAL
2.1 | Materials
All the solvents used during the synthesis of catalysts were
purified by standard procedures prior to their use.
Salicylaldehyde, o‐amino phenol, 30% H2O2 as an oxidant,
VOSO4.5H2O and Cu(NO3)2.3H2O were purchased from
Chemdyes Corporation, India. Sodium form of zeolite‐Y
was procured from Hi‐media, India.
In the new born era, oxidation reactions play a vital role
in many fields that benefit the chemical industries for the
manufacture of high tonnage commodities, high‐value fine
chemicals, chemical intermediates and the pharmaceuti-
cals.[10--12] For instance, Baeyer–Villiger (BV) reaction is
a significant oxidation process, providing a straight corridor
to oxidize ketones to lactones or esters by organic
peracids; and they are hefty industrial intermediates, with sig-
nificance on the production of high valuable fine chemicals
(e.g., steroids, antibiotics, antiviral and antiproliferative
agents).[13--20] Consequently, the development of efficient
and sustainable preparative methods to access these related
skeletons are of enormous importance in synthetic organic
chemistry. In these days, the industrial processes engage with
the use of various oxidants including perbenzoic acid,[21] m‐
chloroperbenzoic acid (mCPBA)[22] and trifluoroperacetic
acid,[23] which are expensive, hazardous, and possibly explo-
sive and produces massive amount of the corresponding
carboxylic acids as waste as well, which restricts their
use. Furthermore, the acid by‐product can diminish ester
selectivity by redundant side‐reactions.[24] On the other hand,
catalysts are imposed for an active transfer of oxygen to the
substrate when oxidants akin to hydrogen peroxide (H2O2)
and/or molecular O2 are chosen. In particular, H2O2 is a
beneficial oxidant for this reaction as it produces H2O as
the only by‐product,[25--28] which gratifies the requirements
of environmentally benign approaches.
Presently, the concurrent growth in the field of heteroge-
neous catalysis are mainly centering on the and entrapment of
metal complexes either on the inert supports or in nanovoids
of zeolite Y.[29--32] Especially, Lunsford's and Ben Taarit's
groups[33] have explored this noteworthy field of zeolite Y
encapsulated transition metal complexes way back in
1970's, and is the subject that still motivating us and
remained as a foremost area of catalysis.[29--32] In connection
to our earlier work,[34--36] herein we report the liquid phase
catalytic oxidation of cyclopentanone over VO(IV) and/or
Cu(II) based neat and zeolite Y entrapped complexes as
2.2 | Physical methods and analysis
Numerous physico‐chemical methods have been employed to
characterize the structure of Schiff base ligand as well as their
neat and zeolite‐Y entrapped VO(IV) and/or Cu(II) com-
plexes. The quantitative analysis of Si, Al and transition
metal ions of zeolite‐Y entrapped complexes were carried
out by ICP‐OES using a model Perkin Elmer optima 2000
DV. BET surface area and pore volume of Na‐Y, VO(IV)‐Y,
Cu(II)‐Y and [VO(L)H2O]‐Y and/or [Cu(L)H2O]‐Y were
measured by multipoint BET method using Micromeritics,
ASAP 2010 surface area analyzer. Prior to the BET measure-
ments, the sample was degasified at 125 °C for 2 h to remove
any adsorbed gases. Scanning electron micrographs (SEMs)
of zeolite‐Y entrapped complexes before and after Soxhlet
extraction were carried out using a SEM instrument (model:
JSM‐5610LV), JEOL to analyze the morphology of the sam-
ples. FTIR (4000–400 cm−1) of H2L, neat and entrapped VO
(IV) and/or Cu(II) complexes were recorded with KBr pallets
on the model: FTIR‐8400S Shimadzu. The crystallinity of
compounds was ensured by powder XRD patterns using
Bruker AXS D8 Advance X‐ray powder diffractometer with
a Cu Kα intensity of diffracted radiation within the range of
5°–60° as a function of the angle 2θ between the incident
and diffracted beams. Electronic spectra of Schiff base ligand
and their neat VO(IV) and/or Cu(II) complexes were
recorded on ‘SHIMADZU’ UV‐2450 spectrophotometer
using quartz cell of 1 cm3 optical path in 10−3 M methanol
and DMF solutions, respectively. However, the UV reflec-
tance spectra of zeolite‐Y entrapped complexes were
recorded on UV reflectance spectrometer (Model: LAMDA
19 UV/VIS/NIR) in the solid phase at room temperature.
Thermogravimetric (TG) analysis of ligand, their neat as well
as entrapped complexes were carried out in air atmosphere in
the temperature range 40–700 °C using Shimadzu TGA‐50
Instrument.

MODI ET AL.
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SCHEME 1 The plausible mechanism for
BV oxidation of cyclopentanone using [VO
(L)H2O]‐Y catalyst
2.3 | Synthesis of Schiff base ligand (H2L)
2.5 | Synthesis of metal exchanged zeolites
[VO(IV)‐Y or cu(II)‐Y]
A methanolic solution (50 ml) of o‐amino phenol (6.0 g,
0.055 M) and salicylaldehyde (6.71 g, 0.055 M) in 1:1 molar
ratio was mixed with constant stirring. Refluxing was carried
out for 4 h. The solution was cooled overnight at room tem-
perature. The formed orange‐yellow colored crystals were
collected and dried in air. Yield: 70%. Anal. Calcd. (%), C
(73.23%), H(5.16%), N(6.57%); found (%) C(73.58%), H
(5.07%), N(6.92%); 1H NMR (400 MHz, DMSO‐d6):
δ(ppm) = 5.85 (1H, s, C‐H of the lateral chain); 7.15–7.48
(m, for aromatic protons); 6.97–7.07 (4H, m, phenolic ring
protons); 8.8 [1H, s, −OH‐‐‐N (intra‐molecular hydrogen
bonding)]; 12.3 (1H, s, −OH); FTIR (KBr, cm−1): (C = O)
1690, 1631 (C = N), 3045 (O–H) of phenolic ring, 1369
Metal exchanged zeolite was synthesized by heating neat
zeolite (Na‐Y) for 24 h at 250 °C to eradicate the impurities.
2 g of Na‐Y was suspended in a round‐bottom flask with
50 ml of 0.01 M aqueous solution of VOSO4·5H2O and/or
Cu(NO3)2.3H2O, and the resultant mixture was refluxed with
continuous stirring for 24 h at 90 °C. To prevent metal
hydroxide preparation, the pH of the solution was maintained
between 3 and 5. After 24 h, the solutions were filtered and
washed thoroughly with warm deionized water to remove
all dissolved ions or free from any metal ion content. The
metal exchanged zeolite was then dried for 10 h in an oven
at 120 °C for further use.
ν
(C–O); UV–vis (λmax, nm) (transition): 290 (ILCT), 370
(π ! π*), 422 (n ! π*).
2.6 | Synthesis of zeolite‐Y entrapped
transition metal‐Schiff base complexes
Zeolite‐Y entrapped metal transition complexes were synthe-
sized following the “Flexible ligand” method.[37,38] In a gen-
eral procedure, 1 g of activated metal substituted zeolite‐Y
[VO(IV)‐Y and/or Cu(II)‐Y] was successively mixed with
methanolic solution of ligand (H2L, 25 mL) and refluxed
with continuous stirring at 60 °C for 24 h under nitrogen
atmosphere. The resulting solid powders so obtained were
subjected to Soxhlet extraction for several hours using
chloroform, acetonitrile, methanol and acetone as solvents.
The color of the compounds did not alter after Soxhlet extrac-
tion and prolonged exposure to air, indicating the formation
2.4 | Synthesis of transition metal complexes
with Schiff base ligand (neat complexes)
To a solution of Schiff base ligand prepared in 10 mL of
methanol, an equimolar methanolic solution of
VOSO4.5H2O and/or Cu(NO3)2.3H2O was added drop‐wise
in it. The pH of the clear solution was adjusted to 5–6 by
drop‐wise addition of CH3COONa. The resultant mixture
was refluxed for 4–5 h with constant stirring and was left
for recrystallization. The solid product was separated by fil-
tration and dried in vacuum.

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MODI ET AL.
of metal complexes inside zeolite‐Y. The powders were then
dried under vacuum and kept in a desiccator for further
characterization.
zeolite‐Y. This observation not only confirms the presence of
metal complexes within the nanovoids but also refutes the
obliteration possibility of the zeolite‐Y framework upon such
modifications viz. ion exchange and the entrapment.
2.7 | Catalytic BV oxidation of
Cyclopentanone
3.3 | SEM analysis
The BVoxidation of cyclopentanone was tested to observe the
effect of heterogeneous catalysts over homogeneous stuff. The
catalytic reactions were carried out in a two‐necked 50 ml
round‐bottom flask. Reaction conditions for the liquid‐phase
oxidation of cyclopentanone were as follows: cyclopentanone
(3.54 ml, 0.04 mol), 30% H2O2 (2.34 ml, 0.1 mol) and catalyst
(80 mg) were mixed in methanol (4 ml). The resulting mixture
was then refluxed at 70 °C in an oil‐bath for 6 h with
continuous stirring. After filtration and washing with a sol-
vent, the filtrate was subjected to gas chromatograph to
analyze and identify the reaction products.
During the course of preparation of zeolite‐Y entrapped metal
complexes, an excessive amount of Schiff base ligand (H2L)
reacts with VO(IV)‐Y and/or Cu(II)‐Y (Section 2.6), the pos-
sibility of clumsy ligand and the formation of metal complex
on the exterior surface of zeolite‐Y cannot be debarred with
the concurrent metal complex formation within the nanovoids
of zeolite‐Y. These peripheral particles can be easily seen in
the SEM image of [VO(L)H2O]‐Y catalyst taken before
[Figure 1(A)] the Soxhlet extraction. To circumvent the
escaping of such superfluous particle from the exterior sur-
face of zeolite‐Y during the catalytic study, both the
entrapped complexes of VO(IV) and/or Cu(II) are purified
by Soxhlet extractor using assorted solvents like chloroform,
acetonitrile, methanol and acetone until the filtrate becomes
colorless and free from any metal ions. The SEM image of
[VO(L)H2O]‐Y taken after the Soxhlet extraction [Figure 1
(B)] implies the existence of well‐defined zeolite‐Y crystals
without any silhouette of the exterior redundant metal ions
or the complexes. This corroborates that the morphology
and surface crystallinity of zeolite‐Y leavings undamaged
upon the entrapment of the complexes.[39]
3 | RESULTS AND DISCUSSION
3.1 | Elemental analysis
The metal ion contents after entrapment can be assigned the
presence of Schiff base complexes in the nanocavities of
zeolite‐Y. The chemical analysis data of neat and entrapped
VO(IV) and/or Cu(II) based complexes are given in Table 1.
The chemical analysis of the samples viz. [VO(L)H2O]‐Y
and/or [Cu(L)H2O]‐Y revealed the presence of organic
matter with a C/N ratio almost comparable with that of neat
complexes. The analogous Si/Al ratio in all zeolite‐Y based
samples (Table 1).suggested the absence of dealumination
process and the fortification of the zeolite‐Y framework
during the modification.
3.4 | FTIR spectral analysis
FTIR spectra of Schiff base ligand (H2L), VO(IV)‐Y, Cu(II)‐
Y and their neat and entrapped complexes are illustrated in
Figure 2 and are discussed here. FTIR spectra of VO(IV)‐Y
and Cu(II)‐Y (Figure 2d, e) show a strong broad band at
~1070 cm−1 due to the asymmetric stretching vibration of
(Si/Al)O4 units.[40,41] Metal exchanged zeolites also show
characteristic bands at ~457, ~831 and ~1174 cm−1
(Figure 2d, e) and these bands were not modified on entrap-
ment of the Schiff base metal complexes, indicating
entrapment has not affected the zeolite framework (Figure 2
f, g). FTIR spectra of neat and entrapped complexes were
harmonized with that of Schiff base ligand (H2L) to define
3.2 | BET surface area analysis
As presented in Table 2, a reduction in the BET surface area
and pore volume of [VO(L)H2O]‐Y and/or [Cu(L)H2O]‐Y
entrapped complexes observed upon the entrapment of com-
plexes inside the nanovoids of pure zeolite‐Y. This decreasing
in BET surface area and pore volume clearly specifies the
entrapment of metal complexes inside the supercages of
TABLE 1 Chemical composition data of synthesized compounds
Compound
Na‐Y
VO(IV)‐Y
Cu(II)‐Y
[VO(L)H2O]
[VO(L)H2O]‐Y
[Cu(L)H2O]‐Y
C (%)
H (%)
N (%)
M (%)
C/N
Si (%)
31.16
31.06
31.11
‐
Al (%)
6.45
6.43
6.44
‐
Si/Al
4.83
4.83
4.83
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
1.97
1.68
48.76 (48.65)
1.98
3.21 (3.15)
0.74
9.63 (9.46)
0.37
11.78 (11.47)
1.95
5.06 (5.14)
5.35
30.97
30.89
6.41
6.40
4.83
4.83
1.65
0.77
0.32
1.66
5.15

MODI ET AL.
5 of 13
TABLE 2 Specific surface area measurement dataa
Compound
Na‐Y
VO(IV)‐Y
Cu(II)‐Y
[VO(L)H2O]‐Y
[Cu(L)H2O]‐Y
Specific surface area (m2/g)
Specific pore volume (cm3/g)
600
544
531
434
419
0.32
0.29
0.28
0.22
0.21
aCalculated by the BJH‐method.
the coordination sites which involved in chelation. The FTIR
spectrum of Schiff base ligand (H2L) exhibits a sharp band at
1631 cm−1; which can be recognized by the vibration band of
the azomethine group. Whilst in the spectra of neat and
entrapped complexes, this band was shifted towards lower
wave number and appears at 1610–1618 cm−1, indicating
that the coordination takes place through azomethine nitro-
gen. The FTIR spectra of neat complexes shown in
Figure 2b, c exhibited the characteristic C = C, and C–O
stretching vibrations at ~1460, and ~1380 cm−1, respectively.
The presence of these bands, characteristic of ligand, duly
confirms the formation of the metal Schiff base complexes,
viz. [VO(L)H2O], and [Cu(L)H2O]. A broad band in the
region ~3450 cm−1, and two weaker bands at ~760 and
~560 cm−1 in all neat and entrapped complexes are attributed
FIGURE 1 SEM images of [VO(L)H2O]‐Y catalyst (a) before
Soxhlet extraction (b) after Soxhlet extraction
FIGURE 2 FTIR spectra of (a) H2L (b) [VO(L)H2O] (c) [Cu(L)H2O]
(d) VO(IV)‐Y (e) cu(II)‐Y (f) [VO(L)H2O]‐Y (g) [Cu(L)H2O]‐Y

6 of 13
MODI ET AL.
to –OH stretching, rocking and wagging vibrations, respec-
tively, which indicate the presence of coordinated water mol-
ecule.[42] The thermal data confirms the nature of water
molecule to be lattice or coordinated. The thermal study will
be discussed in detailed manner later (Section 3.7). Neat VO
(IV) complex exhibits a sharp band at 989 cm−1 due to
ν(V = O) stretching,[43] while the position of such ν(V = O)
band in VO(IV)‐Y and their entrapped complex was not
possible may be due to the appearance of a strong and broad
band in this region due to zeolitic frame work. Conclusive
evidence regarding the bonding of protonated oxygens and
azomethine nitrogen to the metal ion is provided by the
occurrence of two new bands at ~525 and ~450 cm−1 in the
neat complexes, assigned to ν(M–O) and ν(M–N) modes,
respectively. These data confirm the fact that Schiff base
ligand behaves as a dinegative tridentate ligand forming a
conjugated chelate ring, with the ligand existing in the com-
plexes in the enolized form.
became upturned (Figure 3d). In the case of Na‐Y and VO
(IV)‐Y the intensity of the 220 plane was greater than that of
the 311 plane; that is, I220 > I311. Reversal of the intensities
of the 220 and 311 planes, i.e. I220 < I311, utterly divulges
the formation of VO(IV)‐Schiff base complex inside zeolite‐
Y.[44,45] Such observations of the turnaround of the peak
intensities in the zeolite‐Y entrapped complexes were also
made previously by various other researchers.[29,46] We also
observed such alterations in case of Cu(II) Schiff base com-
plex incorporated inside zeolite‐Y.
3.6 | Electronic spectra
Electronic spectra of Schiff base ligand (H2L) and their VO
(IV) and Cu(II) neat complexes were recorded in DMF solu-
tion and are shown in Figure 4, whereas zeolite‐Y entrapped
VO(IV) and/or Cu(II) complexes were recorded in the solid
phase at room temperature and are illustrated in Figure 5.
The electronic spectra of H2L demonstrates three bands at
292, 352 and 430 nm owing to ILCT (intra ligand charge
transfer transition), π ! π* and n ! π* transitions, respec-
tively. In the spectra of neat VO(IV) and Cu(II) complexes,
the value of the first band (ILCT transition) has undergone
hypsochromic shift and appeared at shorter wavelength viz.,
286 and 272 nm, respectively, resulting from the chelation
of the ligand with the transition metal ions. However, the later
two bands (π ! π* and n ! π* transitions) are as good as to
the values for the discrete neat VO(IV) complex and are
observed at 350 and 430 nm, respectively. Furthermore,
π ! π* transition is remarkably akin to the values for the
entrapped complexes observed at ∼360 nm (Figure 5). This
may indicate the immobilization of complexes within the
nanopores of zeolite‐Y.[47]
3.5 | X‐ray powder diffraction studies
The powder X‐ray diffraction patterns of Na‐Y, VO(IV)‐Y, Cu
(II)‐Y and their entrapped complexes are shown in figure. 3.
The PXRD patterns of the Na‐Y and VO(IV)‐Y were almost
comparable (Figure 3a and b, respectively). However, in the
case of [VO(L)H2O]‐Y entrapped complex, the intensities of
the I220 and I311 planes observed at 10° and 12° 2θ values
The UV‐reflectance spectra of VO(IV) entrapped com-
plex shows two additional absorption bands at 585 and
FIGURE 3 XRD patterns of (a) Na‐Y (b) VO(IV)‐Y (c) Cu(II)‐Y (d)
[VO(L)H2O]‐Y (e) [cu(L)H2O]‐Y
FIGURE 4 Electronic spectra of Schiff base ligand (H2L) and their
VO(IV) and Cu(II) neat complexes

MODI ET AL.
7 of 13
of weight loss is detected in the range 50–220 °C, due to
the initial breakdown of ligand. In the second phase,
46.88% of weight loss is detected in the range 220–460 °C
due to absolute subtraction of ligand might be due to forma-
tion of gases like CO, CO2, NO, NO2.[1]
As shown in Figure 6(b), the neat [VO(L)H2O] complex
decomposes in two phases. During the first phase, thermal
dehydration of coordinated water molecule from this com-
plex takes place between 50–200 °C, with a mass loss of
5.84% (calc. 6.08%). One mole of coordinated water mole-
cule is removed in this stage of dehydration. In the second
phase, neat complex decomposes within the temperature
range of 200–700 °C with the estimated weight loss of
66.02% (cal. 65.89%), attributed to the elimination of ligand
via complex breakdown and leaving behind VO2 as the final
residue (Table 3).
FIGURE 5 UV reflectance spectra of (a) [VO(L)H2O]‐Y (b) [Cu(L)
H2O]‐Y
As shown in Figure 6 (c) and (d), the thermal decomposi-
tion of [VO(L)H2O]‐Y and [Cu(L)H2O]‐Y mainly occurs in
the temperature range of 50–200 °C with a mass loss of
15.88 and 14.38%, respectively, owing to the exclusion of
physically and chemisorbed water molecules from the zeolite
framework.[50] In the second phase experiences the weight
loss of 25.26% and 14.38%, respectively in the wide range
of 200–700 °C, can be allotted to the loss of the chelating
ligand which signifies the presence of only small amounts
of the metal complex in the nanovoids of the zeolite Y
(Table 3). From the above discussions, a square‐pyramidal
structure for neat [VO(L)H2O] complex and a square‐planar
structure for [Cu(L)H2O] complex can tentatively be assumed
as shown in Figure 7.
718 nm may be attributed to b2 ! b1 and b2 ! e transi-
tions, respectively,[48] suggesting the square pyramidal
(C4v) geometry of this complex. On the other hand, the
reflectance spectrum of zeolite‐Y entrapped Cu(II) complex
2
shows a shoulder at 540 nm, may be allocated to A1g
2
(F) ! B1g(P) d‐d transition, implying a square‐planar
geometry around the Cu(II) ion.[49]
3.7 | TG analysis
TG report of as prepared samples viz., H2L, neat [VO(L)
H2O], [VO(L)H2O]‐Y and [Cu(L)H2O]‐Y) is represented in
Figure 6. The thermogravimetric analysis data in accordance
with the percent weight loss in different phases and their pos-
sible assignments are presented in Table 3.
4 | CATALYTIC STUDIES
The decomposition of ligand (H2L) takes place in two
phases (Figure 6(a)). In the first phase, practically 53.11%
Usually, the BV oxidation of cyclopentanone shows the way
of fabrication of its selective product i.e., δ‐valerolactone.
In this work, reaction conditions were optimized to control
the liquid‐phase BV oxidation of cyclopentanone. To acquire
this, primarily, all the catalysts, including Na‐Y, metal
exchanged zeolitic samples, neat and zeolite Y entrapped
metal complex samples were experienced for this BV
oxidation of cyclopentanone (Table 4). Samples taken at reg-
ular time intervals were analyzed by GC. Based on these
experimentations, [VO(L)H2O]‐Y was taken as representa-
tive catalyst as it shown notable catalytic activity (Table 4).
in the form of conversion of cyclopentanone (80.22%) and
δ‐valerolactone selectivity (83.56%) along with remarkable
TOF (1746.76 h−1) and TON (10479.42) values, and hence,
it was preferred as a representative catalyst to check the
impact of experimental variables such as impact of varying
mole ratio, amount of catalysts, reaction time, varying
oxidants, varying solvents on cyclopentanone oxidation as
described below:
FIGURE 6 TG Curves of (a) H2L (b) [VO(L)H2O] (c) [VO(L)H2O]‐Y
(d) [Cu(L)H2O]‐Y

8 of 13
MODI ET AL.
TABLE 3 Thermogravimetric results of H2L, their neat and zeolite‐Y entrapped complexes
Compound
TG range (°C)
Mass loss (%) obs. (calc.)
Assignment
H2L
50–220
220–460
53.11
46.88
Removal of one part of the ligand
Removal of remaining part of the ligand
[VO(L)H2O]
50–200
200–700
5.84 (6.08)
66.02 (65.89)
71.84* (71.97)
Loss of one coordinated water molecule
Removal of Schiff base ligand
Leaving VO2 as residue
[VO(L)H2O]‐Y
[Cu(L)H2O]‐Y
50–200
15.88
25.26
Loss of intrazeolite + coordinated water molecules
Loss of Schiff base ligand
200–700
50–200
200–700
16.03
14.38
Loss of intrazeolite + coordinated water molecules
Loss of Schiff base ligand
in amount of the radical formation, whereby the rate of selec-
tivity decreased. Consequently, the optimum catalyst dosage
considered to be 80 mg to conduct further experimentation.
4.1 | Impact of varying mole ratio on
oxidation of cyclopentanone
Four different mole ratios (1:1, 1:1.5, 1:2, 1:2.5) of
cyclopentanone to 30% H2O2 were taken to determine their
effect on cyclopentanone oxidation by keeping all other reac-
tion parameters fixed. Conversion of cyclopentanone was
improved from 80.22 to 97.99% upon increasing the mole
ratio of cyclopentanone to 30% H2O2 from 1:1 to 1:2.5,
respectively (Table 5). On the other hand, the rate of selectiv-
ity of δ‐valerolactone decreased from 83.56 to 80.99% as the
ratio was increased from 1:1 to 1:2.5. It may be due to
decomposition of H2O2 forming large amount of water,
which will cause the selectivity of δ‐valerolactone via
hydrolysis reaction to form 5‐hydroxypentanoic acid. Conse-
quently, the molar ratio was taken to be 1:1 to conduct further
experimentation.
4.3 | Impact of varying reaction time on
oxidation of cyclopentanone
To regulate the crucial reaction time, catalytic BV oxidation
was examined at varying time i.e. 6, 8, 12 and 24 h. It was
observed that cyclopentanone conversion increased with time
growing and reached the top at 24 h with 11854.93 TONs
(Table 7). However, the selectivity was decreased to some
extent with time, owing to the decomposition of H2O2. With
escalating reaction time from 6 to 24 h, low selectivity of δ‐
valerolactone (from 83.56 to 83.44%) was observed. It might
be due to the further hydrolysis of δ‐valerolactone to
pentanoic acid.[51] It meant that the reaction time was one of
influencing factor for BV oxidation of cyclopentanone, and
consequently the optimum reaction time considered to be 6 h.
4.2 | Impact of varying amount of catalyst on
oxidation of cyclopentanone
The amount of catalyst was crucial to the conversion of the
heterogeneous catalyzed oxidation of cyclopentanone along
with δ‐valerolactone selectivity. Values of cyclopentanone
conversion and δ‐valerolactone selectivity are given in
Table 6 for typical essays. Escalating the amount (from 40
to 80 mg) of [VO(L)H2O]‐Y catalyst results in higher conver-
sion of cyclopentanone along with δ‐valerolactone selectiv-
ity, i.e. conversion and selectivity enhances from 16.42 to
80.22 and 55.87 to 83.56, respectively. While further raising
the catalyst amount (up to 100 mg), the selectivity of δ‐
valerolactone decreased. This change may be due to increase
4.4 | Impact of varying oxidant on oxidation of
cyclopentanone
Two different oxidant systems viz., TBHP and/or H2O2 were
studied over [VO(L)H2O]‐Y catalyst to determine their effect
on cyclopentanone oxidation by keeping all other reaction
parameters fixed. The results obtained over the catalyst at
different oxidant systems are tabulated in Table 8. Though
TBHP is strong oxidant than H2O2, in our case, we found
high conversion of cyclopentanone (80.22%) with H2O2 and
higher selectivity of δ‐valerolactone (83.56%) as well. H2O2
is one of the technologically green oxidant, due to the innoc-
uous nature of its by‐product, water. As stated in Scheme 1,
the activation of the catalyst, [VO(L)H2O]‐Y occurs by the
reaction with H2O2 forming HOOVVOH(L) species.[52] In
this species, the O–O bond is polarized, facilitating the
hydroxyl group labile to attack the nucleophilic ketone
carbonyl group of cyclopentanone and gives the final
product, δ‐valerolactone.
FIGURE 7 The proposed structures of (a) [VO(L)H2O] (b) [Cu(L)
H2O]

MODI ET AL.
9 of 13
TABLE 4 Catalytic performance of synthesized materials over BV oxidation of cyclopentanone
Compound
Na‐Y
VO(IV)‐Y
Cyclopentanone conversion (%)
Selectivity (%) δ‐valerolactone
TOFa (h−1
)
TONb
8.49
42.23
40.92
70.16
44.55
80.22
50.40
80.12
84.11
83.99
83.28
83.18
83.56
83.76
‐
‐
‐
‐
‐
‐
Cu(II)‐Y
[VO(L)H2O]
[Cu(L) H2O]
[VO(L)H2O]‐Y
[Cu(L) H2O]‐Y
252.82
‐
1746.76
1608.42
1516.92
‐
10479.42
9650.52
Reaction condition: 80 mg catalyst, 4 mL methanol, 0.04 mol cyclopentanone, 0.1 mol 30% H2O2, 70 °C, 6 h.
aTOF: moles of phenol converted per mole of metal per hour
bTON: moles of phenol converted per mole of metal
TABLE 5 Impact of varying molar ratio (cyclopentanone/H2O2) on oxidation of cyclopentanone
Compound
Cyclopentanone/ H2O2 (%) Cyclopentanone conversion (%) Selectivity (%) δ‐valerolactone TOF (h−1
)
TON
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
1:1
80.22
89.54
90.12
97.99
83.56
83.13
82.68
80.99
1746.76
1810.13
1962.33
2133.69
10479.42
10860.75
11773.98
12802.18
1:1.5
1:2
1:2.5
Reaction condition: 80 mg [VO(L)H2O]‐Y as a representative catalyst, 4 ml methanol, 0.04 mol cyclopentanone, 70 °C, 6 h.
TABLE 6 Impact of varying amount of catalyst on oxidation of cyclopentanone
Compound
Amount of catalyst (mg)
Cyclopentanone conversion (%)
Selectivity (%) δ‐valerolactone TOF (h−1
)
TON
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
[VO(L)H2O]‐Y
40
60
16.42
18.7
55.87
44.36
83.56
80.21
357.54
2145.23
2443.11
10479.42
10862.06
407.19
80
80.22
83.14
1746.76
1810.34
100
Reaction condition: cyclopentanone (0.04 mol), 30% H2O2 (0.04 mol),70 °C, 6 h, catalyst 80 mg, methanol 4 ml.
TABLE 7 Impact of varying time on oxidation of cyclopentanone
Sr. No.
Time (h)
Cyclopentanone conversion (%)
Selectivity (%) δ‐valerolactone
TOF (h−1
)
TON
1
2
3
4
6
8
80.22
85.36
86.17
90.74
83.56
82.11
83.15
83.44
1746.76
1858.68
1876.32
1975.83
10479.42
11152.09
11257.92
11854.93
12
24
Reaction condition: cyclopentanone (0.04 mol), 30% H2O2 (0.04 mol),70 °C, catalyst 80 mg, methanol 4 ml.
TABLE 8 Impact of varying oxidant on oxidation of cyclopentanone
Sr. No.
Oxidant
H2O2
Cyclopentanone conversion (%)
Selectivity (%) δ‐valerolactone
TOF (h−1
1746.76.
1034.73
)
TON
1
2
80.22
47.52
83.56
10479.42
6208.38
TBHP
79.81
Reaction condition: cyclopentanone (0.04 mol), 70 °C, catalyst 80 mg, methanol 4 ml, 6 h.
oxidation of cyclopentanone (Table 9). The cyclopentanone
conversion obtained with different solvent decreases in the
order, methanol (80.22%) > acetonitrile (25.15%) > 1,4‐diox-
4.5 | Impact of varying solvents on oxidation
of cyclopentanone
ane (12.45%). Methanol shows higher TOF (1746.76 h−1
)
In the present study, three different solvents were used with
[VO(L)H2O]‐Y catalyst to perceive their effect on BV
and TON (10479.42) though it is difficult to describe that

10 of 13
MODI ET AL.
TABLE 9 Impact of varying solvent on oxidation of cyclopentanone
Catalyst
Cyclopentanone conversion (%)
Selectivity (%) δ‐valerolactone
TOF (h−1
547.63
)
TON
Acetonitrile
1,4‐dioxane
Methanol
25.15
12.45
80.22
55.87
44.36
83.56
3285.79
1626.56
10479.42
271.09
1746.76
Reaction condition: cyclopentanone (0.04 mol), 30% H2O2 (0.04 mol), 70 °C, catalyst 80 mg, 6 h.
which goods of the solvent influenced the cyclopentanone
conversion. However, it may be due to inductive effect; the
electron cloud of oxygen atom in methanol can activate the
ketone carbonyl group of the cyclopentanone via transferring
to vacant electron site of vanadium, and thus enhancement of
electophilicity of ketone carbonyl oxygen. Thus, increase of
electrophilicity can favor oxidation reaction.[53,54] On the
other hand, due to the lack of the proton donating group,
the non‐protic solvents, such as acetonitrile and 1,4 dioxane,
cannott increase stability of intermediate and hence they have
lower reaction activity.
was recycled and washed with methanol after each run and
dried at 110 °C for the BV oxidation of cyclopentanone with
a view to establishing the effect of entrapment on thermal sta-
bility, catalytic activity, and reusability. Under the same reac-
tion conditions, the catalytic activity in consecutive runs has
no or minor apparent reduction as compared to the fresh cat-
alyst with 81.72, 75.92, and 74.46% δ‐valerolactone selectiv-
ity for three consecutive runs, respectively (Figure 8). For
this reason, it is impeccable to say that the porous support
prevents the complex from leaching and decomposition dur-
ing the reaction, and makes it recyclable and reusable.
4.6 | Baeyer‐Villiger oxidation of cyclic
4.8 | Catalytic assessment
ketones
X. Peng and his group[55] reported the BV oxidation of
cyclopentanone over silica/A153–SO3H catalyst (Table 12,
entry 2). They observed maximum conversion of
cyclopentanone (53%) and δ‐valerolactone selectivity of
45% with acetonitrile solvent system. Catalyst Sn–
aminomethyl polystyrene was developed by Q. Zhang
et al.[56] and used to check over Baeyer–Villiger oxidation
of cyclopentanone. This catalytic system allowed converting
the substrate 22% only with lactone selectivity of 100% using
fluorobenzene as a solvent system along with low TON value
of 58 (Table 12, entry 3). Y. Wang et al.[57] developed a cat-
alytic system involving polar hydrophilic Fe–Co/SO3H head
group and a hydrophobic PS tail, i.e., Fe–Co/SPS system,
achieving 81% conversion of cyclopentanone with nearly
similar δ‐valerolactone selectivity (80%) in CH2Cl2 as a sol-
vent (Table 12, entry 4). Z. Lei and his co‐workers[58]
focused on cyclic & acyclic ketones and the traditional
Baeyer–Villiger oxidation using Aniline–Sn catalyst in 1,4‐
dioxane solvent system. They observed that this catalytic
system is less promising for Baeyer–Villiger oxidation of
Under the best reaction conditions, various cyclic ketones
(0.04 mol) reacted with representative catalyst, [VO(L)
H2O]‐Y (80 mg), 30% H2O2 (0.04 mol) in methanol (4 ml)
to give corresponding lactone products at 70 °C (Table 10).
The reaction of cyclopentanone and cyclohexanone gave the
corresponding products 84–85% yields with observed TOF
(1746.76 and 1238.99 h−1
, respectively) and TON
(10479.42 and 7433.94, respectively) values.
4.7 | Recyclability test
A series of recyclability tests were performed to check the
efficiency of [VO(L)H2O]‐Y catalyst on BV oxidation of
cyclopentanone (Table 11). Fresh [VO(L)H2O]‐Y catalyst
has shown 80.22% conversion of cyclopentanone with
83.56% selectivity towards δ‐valerolactone. Additionally, it
TABLE 10 Baeyer‐Villiger oxidation of cyclic ketones
Conversion Selectivity TOF
TABLE 11 Recyclability test of the recovered catalyst on the oxida-
tion of cyclopentanone
Substrate Product
(%)
(%)
(h−1
)
TON
80.22
83.56
1746.76 10479.42
Cyclopentanone
conversion (%)
Selectivity (%)
δ‐valerolactone
Catalyst
Fresh
80.22
78.45
72.69
68.73
83.56
81.72
75.92
74.46
56.87
84.67
1238.99 7433.94
1st run
2nd run
3rd run
Reaction condition: Substrate (0.04 mol), 30% H2O2 (0.04 mol), 70 °C, [VO(L)
H2O]‐Y catalyst 80 mg, methanol 4 ml, 6 h.
Reaction condition: cyclopentanone (0.04 mol), 30% H2O2 (0.04 mol), 70 °C, cat-
alyst 80 mg, 6 h.

MODI ET AL.
11 of 13
out over [VO(L)H2O]‐Y catalyst, gave very promising results
of 80.22% conversion with 83.56% δ‐valerolactone selectiv-
ity in 6 hours at 70 °C (TOF: 1746.76 h−1 and TON:
10479.42).
4.9 | Proposed Catalytic mechanism of BV
oxidation of cyclopentanone over [VO(L)H2O]‐
Y catalyst:
Generally, inserting oxygen to an organic substrate in a dis-
tinctive Baeyer‐Villiger oxidation reaction on an industrial
scale would prefer a cheaper and eco‐friendly source of
oxidant i.e. H2O2 and/or O2.
The mechanism of homogeneously catalyzed
heterogenized Baeyer‐Villiger oxidation of cyclopentanone
is proposed in Scheme 1. In view of the catalyst being regen-
erated after a cycle of reactions, it should be possible to rep-
resent a catalytic process by a closed loop incorporating
various steps of reactions involved. The mechanism can be
broadly divided into two catalogues, [61] one being activation
of VIV species (catalyst) that takes place through the electro-
philic attack of H2O2 and other being activation of ketone
carbonyl substrate through active intermediate species that
will be discussed thoroughly as follows:
FIGURE
cyclopentanone
8
Recyclability of [VO(L)H2O]‐Y on oxidation of
cyclopentanone with 60% conversion (Table 12, entry 5),
while for other cyclic and acyclic ketones, promising conver-
sion with 100% selectivity were observed. An admirable con-
version of 100% and δ‐valerolactone selectivity of >99%
(Table 12, entry 6) in the BV oxidation of cyclopentanone
was achieved by S. Konera et al.[59] with tin‐salen moiety
immobilized into NaY zeolite matrix, i.e., Sn(salen)‐NaY.
Montmorillonite (MMT) supported Sn catalyst was prepared
by Z. Lei et al.[60] using ion‐exchange technique (Table 12,
entry 7). Cyclopentanone is oxidized by 30% H2O2 in n‐
Butanol solvent system over Sn‐MMT catalyst achieving
45% conversion and 100% lactone selectivity (TON: 75).
While in the present work (Table 12, entry 1), BV oxidation
of cyclopentanone using 30% H2O2 as an oxidant carried
4.10 | Activation of VIV species (catalyst)
through the electrophilic attack of H2O2:
The Gibbs activation barriers for the addition and rearrange-
ment steps in the non‐catalyzed BV oxidation have been
reported to be 39.8 and 41.7 k cal mol−1, respectively, which
makes the reaction difficult to proceed without catalyst.[62,63]
TABLE 12 Comparison between reported heterogeneous catalytic systems and our catalyst for BV oxidation of cyclopentanone
b
Cyclopentanone
conversion (%)
TOF
(h−1
Selectivity (%)
δ‐Valerolactone
Entry
Catalyst
[VO(L)H2O]‐Yc
Silica/A153‐ SO3Hd
PS‐Sne
Solvent
Methanol
TONa
)
Ref.
1
2
3
4
5
6
7
80.22
53
10479.42
1746.76
83.56
This work
[51]
Acetonitrile
Fluorobenzene
CH2Cl2
‐
58
‐
‐
‐
‐
‐
‐
‐
45
[52]
[53]
[54]
[55]
[56]
22
100
80
Fe–Co/SPSf
81
Aniline–Sng
Sn(salen)‐NaYh
Sn–MMTi
60
1,4‐Dioxane
1,4‐Dioxane
n‐Butanol
100
>99
100
100
45
158
‐
75
aTON: Turnover number = moles converted/mol of active site.
bTOF: Turnover frequency = moles converted/ (moles of active site × time).
cCyclopentanone (0.04 mol), 30% H2O2 (0.04 mol), methanol (4 ml), catalyst (80 mg), 70 °C, 6 h.
dCyclopentanone (2.5 mmol), 30% H2O2 (1.5 ml), acetonitrile (3.0 mL), catalyst (10 mg), 10 °C, 20 h.
eCyclopentanone (0.1 mmol), 30% H2O2 (1.5 eq to substrate), catalyst (4 mg), Fluorobenzene (3‐ml) 70 °C, 24 h.
fCyclopentanone (2.5 mmol), H2O2 (2.5 eq), catalyst (15 mg), 10 °C, 20 h.
gCyclopentanone (0.1 mol), 30% H2O2 (1.5 eq), catalyst (2000 mg), 1,4‐dioxane (3 ml), 70 °C, 12 h.
hCyclopentanone (1000 mg), tert‐BuOOH (2 ml), 1,4‐dioxane (5 ml), catalyst (50 mg), 70 °C, 12 h.
iCyclopentanone (0.1 mmol), 30% H2O2 (2.0 eq), catalyst (3 mg), n‐Butanol (3 ml) 90 °C, 24 h.

12 of 13
MODI ET AL.
By employing [VO(L)H2O]‐Y catalyst, the Gibbs activation
barriers for the addition and rearrangement steps presumed
to be reduced may be due to the activation of VIV species
[A] through the electrophilic attack of H2O2 (Step‐I)
followed by the formation of intermediate species,
HOOVVOH(L) [B]. Upon rearrangement of this intermedi-
ate, an active species, ∙OOVIV(L) [C] is formed.
noteworthy for the handling, separation and recycling
abilities from an inexpensive, technological and ecolog-
ical point of view.
ACKNOWLEDGMENTS
We express our gratitude to the Head, Applied Chemistry
Department, Faculty of Technology & Engineering, The
Maharaja Sayajirao University of Baroda, Vadodara, Gujarat
(India) for providing the necessary laboratory facilities. One
of the authors (Chetan K Modi) would like to present his
deep thanks and gratitude to the UGC, New Delhi [Grant
F. No. 42‐290/2013 (SR) dated‐25 March 2013] for Major
Research Project (MRP) financial support.
4.11 | Activation of ketone carbonyl substrate
and BV rearrangement of Criegee's
intermediate to the lactone product:
The electrophilicity enhancement of ketone carbonyl facili-
tates the free radical attack via ∙OOVIV(L) intermediate
species [C]. In this reductive elimination step, this activated
species, ∙OOVIV(L), attacks the substrate reversibly, may
be through interaction between the carbonyl group of the
substrate and the Lewis acid sites (i.e., the metal atom
incorporated in the zeolite lattice) with forming ‘Criegee’
intermediate, [D], which gives the final desired product
(δ‐valerolactone).
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How to cite this article: Modi CK, Solanki N,
Vithalani R, Patel D. Baeyer‐Villiger oxidation of
cyclopentanone over zeolite Y entrapped transition
metal‐Schiff base complexes. Appl Organometal
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