Cu (II) Schiff base complex grafted guar gum: Catalyst for benzophenone derivatives synthesis

Article abstract of DOI:10.1016/j.apcata.2020.117529

In this study Guar gum based Cu(II) Schiff's base complex (GG-Cu) has been synthesized and characterized by FT-IR, PXRD, UV–vis, TGA, XPS, FESEM, TEM, EDAX, solid-state NMR, Elemental mapping, CHNS and AAS analysis. This moiety has been found to be an efficient heterogeneous catalyst for selective oxidation reactions. Fifteen model reactions have been carried to establish the catalytic behavior of GG-Cu, and five of these yield novel products. The ease of separation of catalyst from the reaction mixture simply by filtration is an added advantage; furthermore the catalyst can be reused up to five times without significant loss of catalytic activity. The overall concept of developing newer, efficient and environmental benign catalysts with ease of separation and recycling ability has been successfully demonstrated. All of the isolated products were fully characterized on the basis of their physical and spectral data.

Full text of DOI:10.1016/j.apcata.2020.117529

Applied Catalysis A, General 601 (2020) 117529
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Cu (II) Schiff base complex grafted guar gum: Catalyst for benzophenone
derivatives synthesis
Krishna , Shweta Kumari , Deepak Yadava,b, Sunil K. Sharmaa,*
a,1
a,1
a
Department of Chemistry, University of Delhi, Delhi, 110007, India
b
Department of Chemistry, Central University of Haryana, Mahendergarh, 123031, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study Guar gum based Cu(II) Schiff's base complex (GG-Cu) has been synthesized and characterized by FT-
IR, PXRD, UV–vis, TGA, XPS, FESEM, TEM, EDAX, solid-state NMR, Elemental mapping, CHNS and AAS analysis.
This moiety has been found to be an efficient heterogeneous catalyst for selective oxidation reactions. Fifteen
model reactions have been carried to establish the catalytic behavior of GG-Cu, and five of these yield novel
products. The ease of separation of catalyst from the reaction mixture simply by filtration is an added advantage;
furthermore the catalyst can be reused up to five times without significant loss of catalytic activity. The overall
concept of developing newer, efficient and environmental benign catalysts with ease of separation and recycling
ability has been successfully demonstrated. All of the isolated products were fully characterized on the basis of
their physical and spectral data.
Guar gum
Benzophenone derivatives
Cu complex
1
. Introduction
The use of catalysts in organic synthesis is becoming increasingly
organic synthesis beside the huge potential in this area. Some studies
have demonstrated that nanocomposites of GG act as efficient catalystin
most of these reports, GG has been described as an excellent supporting
and stabilizing material [17–22]. Our objective is to modify the struc-
ture of guar gum using a simple procedure in order to develop new,
efficient and environmental benign heterogenous catalysts. Guar-gum
based copper nanoparticulates have been used as a catalyst for the
Huisgen [3 + 2] cycloaddition reaction of azides and alkynes [23].
Palladium nanoparticles decorated on gaur gum based hybrid material
are known to be used for electrocatalytic hydrazine determination [24].
common to improve the overall conversion, product purity, and save
energy. However the catalyst’s toxicity, difficulty in separation from the
reaction mixture, and lack of reusability are some of the challenges that
still need to be addressed. Designing polymer based material for cata-
lytic activity in organic synthesis has attracted great interest in recent
years [1,2]. The use of naturally occurring polymers over the synthetic
one holds promise due to their abundant availability, low cost and non-
toxic nature [3–5]. Guar-gum (GG) is a naturally occurring, edible
biodegradable and nonionic galactomannan polymer extracted from the
seeds of Cyamopsis tetragonolobus [6]. It has rod like polymeric structure
wherein galactose side chains are linked on the mannose backbone with
an average molecular ratio of 1:2. The presence of large number of
hydroxyl groups not only confers hydrophilicity but also facilitate it to
be readily functionalized with various functional groups, surfactants,
gelling agents, and dyes, so as to allow the resultant products to be
explored for various pharmaceutical/biomedical/industrial applica-
tions [7–16]. GG is insoluble in most of the organic solvents and thus
may be used to develop heterogeneous catalysts for organic reactions.
Despite being economical, eco-friendly and easily available, GG has not
been fully explored for the development of heterogeneous catalysts in
Sivasankar et al. reported Fe
3
O -guar-gum nanocomposites for the re-
4
duction of p-nitroaniline [25].
Our focus is on benzophenone motifs as these are of considerable
interest to chemists due to their importance as building blocks in the
synthesis of natural products and pharmacological compounds [26].
Furthermore, benzophenone derivatives are known to induce apoptosis
in cancerous cells by generating reactive oxygen species and therefore,
have immense potential for the development of new chemotherapeutic
agents [27]. Benzophenone derivatives have been synthesized in nu-
merous ways, one of the most effective and significant method is the
oxidation of benzylic methylenes [28]. A variety of catalysts have been
used to accomplish such oxidation reaction e.g. Ag/SiO
2
-CeO
2
, Cu/
SBA-15 N-doped graphene, Rh, Bi, Au, Re, PdO/SBA-15, CuNi/Co
⁎
Corresponding author.
E-mail addresses: yadav.krishna.sep@gmail.com (Krishna), shwetasingh.ism@gmail.com (S. Kumari), deepakrao2510@gmail.com (D. Yadav),
sk.sharma90@gmail.com (S.K. Sharma).
1
Both authors contributed equally to this manuscript.
https://doi.org/10.1016/j.apcata.2020.117529
Received 10 October 2019; Received in revised form 11 March 2020; Accepted 16 March 2020
Available online 05 May 2020
0926-860X/ © 2020 Elsevier B.V. All rights reserved.

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Scheme 1. Schematic representation for the synthesis of GG-Cu.
homogeneous and heterogeneous catalysis, such as high activity and
selectivity together with ease of separation and reusability of the cat-
alyst [44–47]. Polymers are known to have high affinity for complexes.
They can bind to metal complexes through covalent bonding due to the
presence of highly reactive groups such as hydroxyl, carboxyl, amino
etc [2,48]. Larionov et al. reported the immobilization of an iridium
complex on polystyrene as a catalyst for the Friedel-Crafts alkylation
[
49]. Chitosan anchored copper(II) Schiff base complexes are reported
as heterogeneous catalysts for N-arylation of amines [50]. Chromium
(
VI) grafted on mesoporous polyaniline is reported as a reusable het-
erogeneous catalyst for oxidation reactions [51].
Herein, we report the guar-gum anchored copper(II) Schiff base
complex as heterogeneous catalyst for the synthesis of benzophenone
derivatives under mild reaction conditions. To the best of our knowl-
edge, this is the first report of guar-gum linked Schiff base metal
complex used as a catalyst.
2
. Results and discussion
Fig. 1. FT-IR spectra of (a) GG, (b) APTMS-GG, (c) L-APTMS-GG and (d) GG-Cu.
Guar gum in its native form has very high molecular weight and its
extremely high viscosity and gel-forming property limits its use.
Therefore, it needs to be depolymerized in order to be used further.
Also, physiological properties of guar gum can be improved by the
controlled partial hydrolysis (PHGG). A partially hydrolyzed GG with
average molecular weight of 31,776 g/mol measured by GPC (Fig. S1)
composites [29–42]. However, most of these methods suffer from
drawbacks such as lack of reusability and selectivity, cumbersome
synthesis of the catalyst and lower yield of the products. In order to
address these issues, the development of new effective, low-cost and
reusable catalysts for the oxidation of benzylic methylene is highly
desirable and one of the major goals of this study [43].
1
and G/M value of 1:1.87 calculated by H NMR (Fig. S2) was provided
by Lucid Colloids Ltd., Mumbai and used as such. GG anchored Cu(II)
Schiff base complex (GG-Cu) was synthesized by following Scheme 1.
The GG was first treated with (3-aminopropyl)trimethoxysilane
The catalytically active complexes are known to be either im-
mobilized or grafted on a support harvesting advantages of both
(
APTMS) to incorporate aminopropyl moieties on the GG surface
2

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Fig. 2. Powder XRD pattern of (a) GG, (b) APTMS-GG, (c) L-APTMS-GG and (d) GG-Cu.
(
APTMS-GG). This was followed by the addition of salicylaldehyde so as
Fig. 2 demonstrate the XRD patterns of GG, APTMS-GG, L-APTMS-
GG, and GG-Cu. In the diffraction pattern of GG, the characteristic peak
appeared at 2Ѳ = 20.1° [56]. In the diffraction spectrum of APTMS-GG
the characteristic peak of GG is retained, however a new broad peak
was observed at 12.67° which corroborate with the existence of an
amorphous nature [57]. No obvious change was observed in XRD pat-
tern of L-APTMS-GG when compared with APTMS-GG. Furthermore,
the XRD pattern of GG-Cu exhibit a new peak at 2θ = 26.9°, 32.28° and
38.43° attributing to plane (002), (110) and (111) of CuO, respectively
[58].
to allow amino groups of APTMS moiety and salicylaldehyde to form
the Schiff base (L-APTMS-GG). The resulting compound, then com-
plexes with Cu(II) acetate to yield GG based Cu(II) Schiff's base complex
GG-Cu (more detail of GG-Cu preparation is given in the ESI).
Synthesis of the GG based copper(II) Schiff base complex and the
intermediate steps were examined by FT-IR, XRD, UV–vis, TGA, XPS,
solid-state NMR, FESEM, EDX, Elemental mapping, TEM and AAS
analysis. The structural changes during the anchoring of copper(II)
Schiff base complex on GG analyzed by FT-IR is shown in Fig. 1. The FT-
−1
IR spectrum of GG exhibited a broad intense peak at 3413 cm , at-
tributed to OeH (Str), accounting for the presence of several hydroxyl
groups which are the linking sites for APTMS [52]. In addition, strong
UV–vis spectra of GG, APTMS-GG, L-APTMS-GG and GG-Cu are
shown in Fig. 3. The UV–vis spectrum of GG shows an absorption peak
at 262 nm, due to the presence of non-bonding electrons on the hy-
droxyl group [59]. However, the UV–vis spectra of APTMS-GG shows a
weak absorption peak at 302 nm, due to the presence of an amine group
of APTMS. Fig. 3c shows a strong absorption peak at 261, 332 nm due
to the n/π* transition of the imine bond in L-APTMS-GG. The UV–vis
spectrum of the GG-Cu showed a characteristic absorption peak at
328 nm, due to the charge transfer between copper ion and the hy-
droxyl group of ligand [60].
−
1
characteristic peaks at 2905, 1076 and 1006 cm
were observed due
to the stretching vibration of CeH, CeOeC and CeO groups, respec-
tively in GG [53]. APTMS-GG in turn shows a correspondingly modified
−
1
FT-IR spectrum. In particular, peaks at 1130 and 1099 cm
were at-
tributed to Si-O-Si and Si-O-C linkages respectively [54]. The bands at
−
1
3
427 and 1599 cm , due to the presence of -NH groups, confirms the
2
successful functionalization of GG through silyl ether formation. The
−1
FT-IR spectrum of L-APTMS-GG depicted a new peak at 1629 cm due
to v C]N bond, thus indicating the condensation reaction between the
carbonyl group of salicylaldehyde (L) and the amino group of GG-
The TGA thermogram of GG and GG-Cu are presented in Fig. 4. The
TGA of GG showed a 10 % weight loss in the range of 50−150 °C, due
to the loss of adsorbed water molecules. The second weight loss around
63 % at 200−420 °C may be due to the polymer decomposition [61].
However, in GG-Cu, 5 % weight loss is observed in the range
30−120 °C, due to the evaporation of water and second loss approxi-
mately of 36 % was observed at 340 °C, due to the degradation of
secondary alcohol in guar gum [62]. After this it degrades slowly and a
total weight loss of 59 % was observed until 600 °C. Thus, it may be
concluded that GG-Cu thermally stable up to 600 °C. Quantitative
-
APTMS. Fig. 1d shows the FT-IR spectrum of GG-Cu, a band at 1604 cm
1
was observed, and blue shift in wavenumber compared with L-
APTMS-GG confirmed the coordination of copper ion to azomethine
−1
nitrogen of Schiff base. Moreover, new peaks at 675 and 560 cm were
observed, which accounts for the stretching mode of CueN and CueO
bonds, respectively [55]. The above data supports the successful for-
mation of copper(II) Schiff base complex on GG by covalent interaction.
3

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Fig. 3. UV-vis spectra of (a) GG, (b) APTMS-GG, (c) L-APTMS-GG and (d) GG-Cu.
Fig. 4. TGA thermogram of (a) GG and (b) GG-Cu.
evaluation of grafting of Cu(II) complex on guar gum using TGA data
suggest that approx. 25 % guar gum is grafted [63].
and 941.2 eV, respectively. The deconvoluted C 1s spectrum of the GG-
Cu is shown in Fig. 5c, it exhibits the typical peaks at 286.4, 284.2,
283.0, 282.3 and 281.6 eV that can be assigned to carbon atoms in
CeOH, C]N C–O, CeC and CeH, respectively. Correspondingly, the O
1s peak was observed at energy position 529.4 eV in Fig. 5d. The fitted
peak values for O 1s were 530.7, 529.5 and 528.0 eV which corresponds
to the, OeH, CeO and CueO, respectively. The N 1s XPS spectrum
(Fig. 5e) shows a peak at 397.3 which confirms the presence of N]C
[64–68]. In Fig. 5f a band at 100.1 eV attributed to SieO emerged,
For the chemical state variation and the surface functionalization in
the GG-Cu, X-ray photoelectron (XPS) analysis was carried out Fig. 5.
Fig. 5a shows the presence of Cu, C, O, Si and N species in GG-Cu. The
XPS spectrum of the Cu 2p core level spectrum in Fig. 5b exhibits two
bands located at the binding energies of 951.5 and 931.8 eV which
correspond to the binding energy of Cu 2p1/2 and Cu 2p3/2. Mean-
while, a Cu 2p1/2 and Cu 2p3/2 satellite peaks were observed at 959.7
4

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Fig. 5. X-ray photoelectron (a) survey spectra of GG-Cu, (b) Cu 2p, (c) deconvoluted C 1s, (d) deconvoluted O 1s, (e) N 1s and (f) Si 2p.
Fig. 6. 13C and 29Si solid-state NMR spectra of GG-Cu.
which indicate the silylation of the reaction surface. The XPS results
further supported the formation of Cu(II) complex grafted on the GG.
A deep understanding of the structure and chemical composition of
second region at 132 to 103 ppm due to aromatic carbons of sali-
caldehyde and anomeric carbons for galactose and mannose of guar
gum. Third region at 80 to 60 for guar gum and fourth region come at
1
3
29
GG-Cu, was analyzed by solid-state NMR spectroscopy Fig. 6. The C ss
nmr spectrum have four set of signals. First region at 171 to 165 ppm
due to aromatic carbons attached to hydroxyl group of salicaldehyde,
18 to 10 ppm for APTMS group [69,70]. The Si ss nmr spectrum of
GG-Cu also consist a set of signals at −50 to −65 ppm region due to
silicon attached with eOMe, eCH and GG environment [71]. The ss
2
5

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Fig. 7. (i) FESEM of (a) GG, (b) APTMS-GG, (c) L-APTMS-GG, and (d) GG-Cu; (ii) TEM images of GG-Cu; (iii) EDAX spectra of (a) GG, (b) APTMS-GG, (c) L-APTMS-
GG, and (d) GG-Cu and (iv) elemental mapping of GG-Cu.
NMR spectra results supported the presence of aromatic as well APTMS
and guar gum region in GG-Cu which confirm the formation of Cu(II)
complex grafted on the GG.
Cu are described with the help of FESEM and TEM images. The FESEM
images of GG in Fig. 7(i)a. show the macromolecule with rough surface
topology. FESEM images of APTMS-GG, L-APTMS-GG displays nanos-
tructural features which demonstrated the chemical modification of GG
The surface morphology of GG, APTMS-GG, L-APTMS-GG, and GG-
6

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
However, oxidant also plays an important role in affecting the reaction
to a large extent. In order to study the effect of oxidant, the reaction was
carried out in the presence of different oxidants such as TBHP, m-CPBA,
O
2
, H
2
O (Table 1, entry 8–11). The optimum yield of 90 % was ob-
2
served while using TBHP as an oxidant. Under these conditions 5 mg of
the catalyst was found to be sufficient for the oxidation reaction of
diarylmethane. A further decrease in the amount of catalyst (2 mg) was
found to significantly hamper the yield (Table 1, entry 13). Therefore,
the use of 5 mg of the GG-Cu catalyst at 70 °C in the presence of solvent
acetonitrile and TBHP as an oxidant was found to be the optimized
reaction condition to afford benzophenone (2a) in excellent yield in a
short reaction time (Table 1, entry 14). The generality of the present
method was established by using different types of diarylmethane
bearing electron withdrawing groups, tosylated group and thiophene
moiety to afford the corresponding benzophenone derivatives with
excellent yields as shown in Fig. 8. A few sulfones were also included in
the study as they too constitute an important functional group due to
their presence in biologically active compounds, e.g. anticancer, anti-
bacterial, antiglaucoma agents [72,73]. It may be noted that the
benzylic oxidation proceeded exclusively at the methylene group and
methyl groups remains unaffected. Amongst the reactions tried, five
newer products (2j, 2k, 2l, 2m and 2n) were formed. All of the known
Scheme 2. Synthesis of benzophenone derivatives via catalytic oxidation.
Table 1
a
Optimization of reaction conditions for the oxidation of diarylmethane.
o
b
Entry Catalyst (mg) Solvent
Oxidant Temp ( C) Time (h) Yield of 2a
(
%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
————
Water
Water
Water
TBHP
TBHP
TBHP
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
24
24
24
24
12
12
12
12
12
12
12
12
12
08
——
——
20
GG (20)
GG-Cu (20)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (10)
GG-Cu (5)
GG-Cu (2)
GG-Cu (5)
Toluene TBHP
Pyridine TBHP
35
48
Ethanol
DMF
TBHP
TBHP
TBHP
38
44
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
90
m-CPBA Reflux
55
0
1
2
3
4
O
2
2
Reflux
Reflux
70
37
H
O
2
60
TBHP
TBHP
TBHP
90
1
13
70
65
and new products are characterized by IR, H & C NMR and Mass
spectroscopy.
70
89
Furthermore, comparison of the catalytic efficiency of the GG-Cu
with previously reported catalysts, for the preparation of benzophenone
derivatives, in terms of the catalyst amount and reaction conditions, is
summarized in Table 2.
a
b
Reaction condition: Diarylmethane (1 mmol) TBHP (10 mol %).
Isolated yield after workup.
through APTMS and salicylaldehyde in Fig. 7(i)b and 7(i)c, respec-
tively. On the other hand, FESEM images of GG-Cu (Fig. 7(i)d) exhibits
different morphologies having twisted nanostructural irregular-shape
and these may serve as an ideal platform for reactant to accomplish the
desired product. The TEM image shown in Fig. 7(ii) reveals the nano-
scopic features of the GG-Cu with a uniform distribution of copper(II)
Schiff base complex without aggregation throughout the GG. The EDAX
analysis provides detailed chemical analysis on the GG, APTMS-GG, L-
APTMS-GG and GG-Cu. The EDAX analysis of GG-Cu in Fig. 7(iii)d
depicts the change in elemental composition with the introduction of
copper, nitrogen and silicon, which are core elements of the complex
apart from carbon and oxygen. Further, EDAX elemental mapping was
achieved to understand the distribution of the Cu-Schiff base complex
on GG. The elemental mapping indicated the uniform distribution of
Cu, N and Si over the GG surface in Fig. 7(iv). Along with the EDAX
analysis, the composition of carbon, nitrogen and hydrogen in the GG-
Cu complex determined by the CHNS analysis was found to be 26.92 %,
The catalyst was evaluated for its recyclability up to six times. It is
apparent from Fig. S3 that the GG-Cu catalyst could be reused up to five
cycles. However, gradual decline in the catalytic activity was noticed
rd
after 3 cycle. The XRD pattern, FTIR and SEM images also showed that
there was no change in the phase and surface morphology in recycled
GG-Cu (Fig. S4). AAS of the used catalyst was found to be 1.39 mg/L
which was almost similar to the amount of Cu in fresh catalyst. Hence,
the catalyst has shown its proficiency for various industrial applica-
tions.
Based on the literature, a plausible mechanism for the reaction is
shown in Scheme 3 [77,80]. It is speculated that first a homolytic
cleavage of TBHP occurs in the presence of heat that produce the alkoxy
(
A) and hydroxyl radicals (equation i) which subsequently reacts with
TBHP and form radical B. On the other hand GG-Cu catalyst which
binds with the reactant gets activated by the free radical A and removal
of acetic acid. In the next step Cu(II) bind with free radical B and
produces a highly reactive Cu(III)-peroxide species (2). The peroxide
species, then quickly rearranges via a radical pathway with an electron
transfer to the catalyst, producing the Cu(II) organoperoxides (3).
Homolytic dissociation of these organoperoxide by removal of radical
hydrogen of the remaining benzylic proton (4) generates the product.
4
.16 % and 2.46 %, respectively. Subsequently, the quantitative esti-
mation of the copper content in GG-Cu was done after digestion using
AAS and the corresponding copper loading was found to be
−
1
1
.48 mg L
.
The catalytic efficiency of GG-Cu was evaluated in the synthesis of
benzophenone derivatives via an oxidation reaction as shown in
Scheme 2 (synthetic details given in the ESI).
3
. Conclusions
In order to optimize the reaction conditions for the synthesis of
benzophenone derivatives, various parameters such as the catalyst
amount, oxidant, reaction time, temperature, and solvent were thor-
oughly investigated and summarized in the Table 1. Diarylmethane was
chosen as a model reactant for the oxidation reaction, in the control
reaction carried out in the absence of a catalyst at reflux, no noticeable
reaction was observed (Table 1 entry 1). Even in the presence of GG in
water under reflux for 24 h no product formation was observed (Table1,
entry 2). However, in the presence of GG-Cu catalyst and in different
solvents, e.g. water, toluene, pyridine, ethanol, DMF and acetonitrile,
the product was found to be formed (Table 1 entry 3–8). Acetonitrile
was observed to be the solvent of choice for the oxidation reaction.
We have successfully used a carbohydrate based natural polymer
obtained from guar gum (GG) to develop a heterogeneous catalyst for
organic reactions. The low cost, nontoxicity, presence of large number
of hydroxyl groups, and limited solubility of guar gum in organic sol-
vents are the favourable factors to employ this natural product for the
synthesis of heterogenous catalyst. Grafting of Cu(II) Schiff base com-
plex on GG via covalent interaction afforded a heterogeneous catalyst
which was characterized by FT-IR, PXRD, UV–vis, TGA, XPS, solid-state
NMR, FESEM, TEM, EDAX, Elemental mapping, CHNS, AAS and ele-
mental analysis. The catalyst reported is convenient to use due to its
ease of separation from the reaction mixture and is stable in ambient
conditions. Furthermore it was found to be highly efficient, selective for
7

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Fig. 8. Synthesized benzophenone derivatives via catalytic oxidation.
Table 2
Comparative catalytic performance of the GG-Cu with other previously reported catalysts in oxidation reactions.
Entry
Catalyst
Amount of catalyst (mg)
Oxidant
Time (h)/
Solvent/Condition
TON
TOF
Refs.
yield (%)
1
2
3
4
5
6
7
CrO
3
5.9
2.7
3.1
9.5
9.9
30
H
5
IO
6
1/99
CH
3
CN/RT
49.87
45.55
16.90
7.95
49.87
1.89
1.40
0.33
2.44
4.91
11.57
[74]
FeCl
3
.2H
2
O
TBHP
24/91
12/85
24/81
8/98
Pyridine/82 °C
[75]
Fe(III)/THA
CuI
H
2
O
2
O
2
CH
3
3
CN/60 °C
[76]
CH
CN /100 °C
[77]
Cu(OAc)
2
.H
2
O
TBHP
TBHP
TBHP
H
2
2
O/80 °C
19.56
19.66
115.77
[78]
[CuI(aas-TPB)]n
GG-Cu
4/99
H
O/RT
[79]
5.0
10/90
CH
3
CN /70 °C
This work
the oxidation of methylene group using TBHP as an oxidant. The reu-
sability of the catalyst upto five cycles without any significant loss of
activity is an added advantage and allows the catalyst to be considered
superior to other commonly available catalysts.
CRediT authorship contribution statement
Data curation, Formal analysis, Investigation. Shweta Kumari:
Methodology, Writing - original draft, Visualization, Formal analysis.
Deepak Yadav: Formal analysis. Sunil K. Sharma: Supervision.
8

Krishna, et al.
Applied Catalysis A, General 601 (2020) 117529
Scheme 3. Plausible mechanism for benzophenone synthesis using the GG-Cu catalyst.
Declaration of Competing Interest
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There is no conflict of interest to declare.
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also thankful to the SAIF IIT Kanpur, USIC, University of Delhi for
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