Renewable waste rice husk grafted oxo-vanadium catalyst for oxidation of tertiary amines to N-oxides

Article abstract of DOI:10.1039/c6ra13571d

Low cost renewable waste rice husks (RH) have been used as a support for grafting of an oxo-vanadium Schiff base via covalent attachment for the oxidation of tertiary amines to N-oxide. The synthesis of the desired RH grafted oxo-vanadium complex involves prior functionalization of the RH support with amino-propyltrimethoxysilane (APTMS) followed by its reaction with salicylaldehyde to get an RH-functionalized Schiff base which subsequently reacted with vanadyl sulphate to get the targeted oxo-vanadium catalyst. The synthesized catalyst was found to be an efficient heterogeneous catalyst and afforded an excellent yield of corresponding N-oxides via oxidation of tertiary amines with hydrogen peroxide as an oxidant. Furthermore, the synthesized catalyst was found to be quite stable and showed consistent activity for five runs without any loss in activity.

Full text of DOI:10.1039/c6ra13571d

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: S. L. Jain, V.
Panwar, A. Bansal and S. S. Ray, RSC Adv., 2016, DOI: 10.1039/C6RA13571D.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 7
View Article Online
DOI: 10.1039/C6RA13571D
Journal Name
ARTICLE
Renewable waste rice husk grafted oxo-vanadium catalyst for
oxidation of tertiary amines to N-oxides
Vineeta Panwar,a Ankushi Bansal,a Siddharth S. Raya and Suman L. Jaina*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Low cost renewable waste rice husk (RH) has been used as a support for grafting of oxo-vanadium Schiff base via covalent
attachment for the oxidation of tertiary amines to N-oxide. The synthesis of desired RH grafted oxo-vanadium complex
involves the prior functionalization of RH support with amino-propyltrimethoxysilane (APTMS) followed by its reaction
with salicylaldehyde to get RH-functionalized Schiff base which subsequently reacted with vanadyl sulphate to get the
targeted oxo-vanadium catalyst. The synthesized catalyst was found to be efficient heterogeneous catalyst and afforded
excellent yield of corresponding N-oxides via oxidation of tertiary amines with hydrogen peroxide as oxidant. Furthermore,
the synthesized catalyst was found to be quite stable and showed consistent activity for five runs without any loss in
activity.
www.rsc.org/
layered double hydroxide acid28, tungsten sulphide29,
tungsten-based polyperoxometalates30, selenium31 and
molybdenum oxides32 have been shown to catalyze the N-
Introduction
Owing to the increasing environmental consciousness, there is
a pressing need to develop methodologies for the effective
utilization of biomass waste as it not only creates disposal
problems but also causes environmental pollution1-8. Rice husk
(RH) is one of such a major by-product of the rice-milling
industries and is produced abundantly every year throughout
the globe. RH contains 25–35% cellulose, 8–21%
hemicelluloses, 26–31% lignin, 15–17% amorphous silica and
waxes, and 2–5% of other soluble substances9-12. Moreover,
after it’s burning approximately 20% ash content comprises
over 95% of amorphous silica which has very fine particle size,
very high purity, high surface area, and high porosity13-14. These
properties make the utilization of RH in various areas including
catalysis, a very economically attractive perspective. In this
context, Adam et al. reported the use of RH silica as support
matrix for the grafting of various types of transition metals and
their catalytic potentials in the oxidation, acylation and
oxidation of tertiary amines in the presence of aqueous H2O2.
However, these reported methods suffer from certain
drawbacks such as homogeneous nature, multi-step synthetic
procedures, high cost and non-renewable support matrices. To
the best of our knowledge, heterogenized metal catalyst using
renewable supports has never been realized for this
transformation.
Herein we report the successful synthesis of rice husk (RH)
grafted oxo-vanadium Schiff base through covalent linkage and
its application for the oxidation of tertiary amines to N-oxides
using hydrogen peroxide as green oxidant (Scheme 1). This is a
simple and clean methodology where compounds formed are
free from any contaminating by-products and the catalyst
shows good activity as well as facile recovery by simple
filtration for recycling runs.
RH-grafted oxo-vanadium
Schiff base, H2O2
R
R
benzylation reactions15-17
.
R
R
R
N
R
N
O
,
,
CH3CN, 80 oC, 4h
N
O
R
N
Oxidation of tertiary amines to N-oxides is an important
transformation as these compounds have found extensive
applications as precursors in the synthesis of bioactive
molecules, offer structural modification and functional group
manipulation possibilities[18]. Apart from the conventional
oxidants such as activated H2O219, a-azo hydroperoxides20,
Caro’s acid (H2SO5)21, dioxirane22 and peracids23, which
generate large amounts of undesirable waste, a number of
metal catalysts such as methyltrioxorhenium24, manganese
porphyrin25, flavin26, TS-127, tungstate-exchanged Mg/Al-
R
Scheme 1: RH-grafted oxo-vanadium Schiff base catalyzed oxidation of tertiary amines
3. Results and discussions
3.1 Synthesis and characterization of catalyst
The schematic representation of the synthesis of RH-grafted
oxo-vanadium Schiff base is shown in Scheme
2. The
preparation of RH-grafted oxo-vanadium Schiff base catalyst
and intermediate steps was examined and monitored using
a.Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun-248005
(India) *Email: suman@iip.res.in; Tel: 91-135-2525788; Fax: 91-135-2660202
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 7
View Article Online
DOI: 10.1039/C6RA13571D
ARTICLE
Journal Name
various techniques XRD, FTIR, TGA, and scanning electron bumps interspaced with small pores which are absent on the
microscopy (SEM).
virgin rice. These buttons like structures or bumps may be
attributed to the obstruction of silica fibre to devolatilization.
Figure 2c shows the SEM image of RH-grafted oxo-vanadium
Schiff base with only difference in the appearance of small
white dots which may be probably due to the presence of
vanadium metal in the synthesized material. Further Figure 2d,
e, and f show the EDX of neat RH, RH-Schiff base and RH-
NH2
OH
CHO
OH
H2N
HO
OH
NH2
APTMS
Toluene
Rice Husk
H2N
H2N
NH2
Rice Husk
OH
HO
HO
OH
OH
Ethanol
NH2
grafted oxo-vanadium Schiff base respectively.
A typical
NH2
composition of the rice husk contains various minerals such as
Fe2O3, MgO, K2O, Al2O3 etc in 0.5 to 2 wt%.35 The EDX of Rice
husk (RH) shows only C, O and N (Fig. 2d) as the area for SEM
micrographs was randomly selected where the EDX analysis
was done. However, in other two Figures (2e-f) appearance of
other elements such as Si, Al, K etc confirmed the presence of
various minerals in the rice husk. The presence of vanadium in
the final catalyst (Fig. 2f), confirmed the successful synthesis of
the desired material.
H
H
O
O
O
HO
OH
N
V
N
N
N
VOSO4.xH2O
Methanol
Rice Husk
Rice Husk
N
N
N
V
O
O
H
N
OH
HO
O
H
Scheme 2: Schematic representation of synthesis of RH-grafted oxo-vanadium
Schiff base
Fig. 1 shows the XRD pattern of bare RH and RH-grafted oxo-
vanadium Schiff base. As shown in Fig. 1a, RH did not show any
sharp diffraction pattern, which indicates that the sample is
amorphous in nature.33 A broad diffraction peak observed at
25∘ is attributed to the amorphous silica. The XRD pattern for
RH-grafted oxo-vanadium Schiff base revealed some sharpness
in the peak which is due to the presence of vanadium which
indicates the semi crystalline nature of the synthesised
material as shown in fig. 1b.
Fig. 2 : SEM images and EDX of a,d) Neat RH; b,e) RH-grafted Schiff base; c,f) RH-
grafted oxo-vanadium Schiff base.
The chemical changes occurred during the immobilization of
oxo-vanadium Schiff base on RH was monitored by FTIR.36-37
Figure 3 shows vibrational assessments of RH, RH-NH2, RH-
grafted Schiff base and RH-grafted oxo-vanadium Schiff base.
The presence of an intense and broad peak in the range 3000-
3700 cm-1 in virgin RH attributed to the stretching mode of
hydrogen bonded Si-OH groups. Other vibrational streching
modes observed at 2915 cm-1 and 2847 cm-1 are due to the
presence of lignin in rice husk containing methyl and
methylene groups. In Fig. 3a, the peaks at 1725 and 1100 cm-1
are related to the aldehydic and the Si-O-Si groups,
respectively in rice husk. The bands between 800 cm-1 and 540
cm-1 suggested the presence of Si-H bonds and deformation of
Si-O bonds. In Figure 3a,b, the band at 1639-1640 cm-1 is
attributed to the presence of water molecules bound to the
silica matrix as well as ketonic groups presented in the hemi-
cellulose of rice husk. In case of Schiff base grafted RH (Fig. 3c),
the peak at 1646 cm-1 is found to be more intense due to the
additional stretching of C=N groups formed due to the
condensation of –NH2 with carbonyl groups. After the reaction
of Schiff base-RH with vanadyl sulphate in figure 3d, the band
Fig 1: XRD Diffractogram of a) neat RH; b) RH grafted oxo-vanadium Schiff base
Surface morphologies of the synthesized materials were
determined by scanning electron microscopy (Fig. 2). Figure 2a
shows the SEM image of virgin rice husk particles, where the
structure resembles to an irregular and highly porous siliceous
structure, which is in well agreement with the other literature
reports.34 Figure 2b shows the SEM image of RH-grafted Schiff
base. Significant change in the morphology is observed with has been shifted to higher wavelength 1652 cm-1 due to the
interaction with metal ions. In addition the appearance of
the presence of a large number of button- like structures or
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 7
View Article Online
DOI: 10.1039/C6RA13571D
Journal Name
ARTICLE
characteristic peak at 613 cm-1 due to V=O, confirmed the
succesful synthesis of the desired material (Fig. 3d).
Fig. 4: TG-DTA curves for a) neat RH b) RH-grafted Schiff base; c) RH-grafted oxo-
vanadium Schiff base
Catalytic activity
The catalytic activity of the prepared RH-grafted oxo-vanadium
Schiff base and its comparison with homogenous analogue was
studied for oxidation of tertiary amines to corresponding N-
oxides using hydrogen peroxide (30 wt% aq.) as oxidant
(Scheme 1). Oxidation of triethylamine was selected as a
model substrate to optimise the reaction conditions by varying
the reaction parameters such as solvent, temperature and
catalyst amount (Table 1). In the absence of any solvent under
neat condition, the reaction was found to be very slow and
only trace amount of the product was obtained even after
prolonged reaction time (Table 1, entry 1). However, among
the various solvents such as water, acetonitrile, methanol, THF
and dichloroethane (Table 1, entry 2-7) studied, acetonitrile
was found to be best solvent and afforded highest product
yield within 4h. The reaction was found to be very slow at
Fig. 3: FTIR Spectra of a) RH b) RH-NH2 c) RH-grafted Schiff base; d) RH-grafted oxo
vanadium Schiff base Catalytic activity
Thermal degradation and corresponding weight loss in RH, RH-
grafted Schiff base and RH-grafted oxo-vanadium Schiff base
was determined by thermogravimetric analysis (TGA) and
differential thermal analyses (DTA) as shown in Figure 4. In
case of RH, initial weight loss below100 oC can be assigned due
to the decomposition of adsorbed water molecules. The major
weight loss in the range of 200-300 oC is mainly due to the
decomposition of other organic moieties38. Further, in case of
RH-grafted Schiff base major weight loss in the range of 300-
o
room temperature; whereas 80 C was found to be optimum
and afforded maximum product yield within 6h (Table 1, entry
8). Furthermore, no reaction occurred in the absence of
catalyst under described reaction conditions (Table 1, entry 9).
Further, to compare the catalytic efficiency of RH-grafted
heterogeneous catalyst with its corresponding homogeneous
analogue, we synthesized oxo-vanadium Schiff base from 2-
hydroxybenzaldehyde and ethylenediamine by following the
literature procedure.39 Thus obtained Schiff base was treated
with vanadyl sulphate hydrate (VOSO4.xH2O) in 1:1 molar ratio
to get homogeneous oxo-vanadium Schiff base.40 The
synthesized homogeneous oxo-vanadium Schiff base was
tested under optimized reaction conditions i.e catalyst amount
o
400 C can be attributed to the decomposition of Schiff base
moieties presented on the RH surface. Fig. 4c shows the TGA-
DTA curves for the RH-grafted oxo-vanadium Schiff base
having first small weight loss below 100 oC is due to
decomposition of water molecules and other major weight loss
o
in the range 250-400 C is due to the decomposition of Schiff
base and other moieties of RH.
o
0.002 mmol, acetonitrile at 80 C. After the 12h reaction time,
the yield of the product was found to be 93% (Table 1, entry
9).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 7
View Article Online
DOI: 10.1039/C6RA13571D
ARTICLE
Journal Name
described reaction conditions (Table 2, entry 14). However, in
case of N,N-dimethylaminopyridine under described reaction
conditions, selective formation of N,N-dimethylaminopyridine
N-oxide obtained without any evidence for the formation of
any by-product which could be obtained due to the oxidation
of nitrogen of N,N-dimethylamino group or both. This is in well
agreement with the existing report.41
Table 1: Results of the optimization experimentsa
Entry
Solvent
oxidant
Temp.
(oC)
Time
(h)
Conv.
(%)
Yield
(%)b
1
2
3
4
5
6
7
8
-
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
80
65
100
40
86
66
110
-
24
6
trace
80
-
Methanol
Water
DCM
80
12
10
7
50
45
85
82
Table 2: RH-grafted oxo-vanadium Schiff base catalyzed oxidation of tertiary aminesa
Yield[b]
tBuOH
THF
70
68
Entry
Substrate
Product
(%)
12
20
6
60
55
N
O
92
1.
N
Toulene
CH3CN
30
25
15c,
78d,94e
-f,95g
60
Trace
72d,92e
-f,93g
55
C2H5
C2H5
O
C2H5
N
C2H5
N
2.
3.
90
9
CH3CN
CH3CN
H2O2
TBHP
O2
80
80
12
10
R
N
R
N
O
85,84,86,
88
R=CH3,Cl, Br, OCH3
10
R=CH3,Cl, Br, OCH3
40
38
4.
5.
65
72
aReaction conditions: triethylamine (2.0 mmol), catalyst (0.1 g, 0.002
mmol), solvent (4 mL) in the presence of H2O2(3.0 mmol); bIsolated yield; at
c25 oC, d60 oC; e80 oC; fIn the absence of catalyst; gusing Homogeneous oxo-
vanadium Schiff base (amount 0.002 mmol, temp. 80 oC, CH3CN solvent in
12 h gave 93 % yield).
N
N
O
CH3
CH3
N
N
The RH-grafted oxo-vanadium Schiff base was found to be
equally efficient as homogeneous analogue. However, the
facile recovery and efficient recycling of the heterogeneous
catalyst make the developed catalyst more effective and
desirable from both environmental and economical
viewpoints. Similarly, the use of aq. TBHP and molecular
oxygen as oxidant in place of hydrogen peroxide afforded poor
product yields (Table 1, entry 10).
O
CH3
CH3
6.
7.
70
68
N
O
N
N
O
CH3
N
CH3
Thus, the optimized reaction conditions for the present
reaction comprises the oxidation of triethylamine (2 mmol)
with hydrogen peroxide (3 mmol) in the presence of RH-
grafted oxo-vanadium Schiff base (0.1g,) in acetonitrile (4 ml)
under refluxing conditions. After completion of the reaction as
analyzed by TLC (SiO2), the catalyst was easily separated by
simple filtration and reused as such for subsequent runs. The
filtrate was subjected to the usual workup to extract the
corresponding N-oxide. Further, the reaction was extended to
a variety of tertiary amines including aromatic, heterocyclic
and aliphatic under the described reaction conditions. The
results of these experiments are summarized in Table 2.
Among the various substrates, amines having aliphatic
substituents were found to be more reactive (Table 2, entry 1-
3) than substituted pyridines (Table 2, entry 4-10). Among the
various pyridines, those substituted with electron donating
groups were found to be more reactive (Table 2, entry 4-7).
Aliphatic amines such as triethylamine, N-methylmorpholine
and triethanolamine also reacted well and afforded moderate
to high product yield (Table 2, entry 11-13). Strically hindered
tertiary amine such as N,N-dimethylbenzylamine also afforded
reasonably good yield of the corresponding product under
8.
9.
62
58
N
O
N
CN
CN
N
O
N
O
O
NH2
10.
52
NH2
N
N
O
O
Et3N
O
Et3N
11.
12.
92
70
O
N
N
O
HO
HO
OH
OH
N
N
13.
90
O
OH
OH
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 7
View Article Online
DOI: 10.1039/C6RA13571D
Journal Name
ARTICLE
O
N
Rice husk is powered on RETSCH Planetary Ball Mill PM 100. FT-IR
spectra were collected on a Nicolet 8700 FT-IR spectrometer in the
region of 4000-400 cm⁻¹. SEM images were obtained on a FEI
Quanta 200 F using tungsten filament doped with lanthanum
hexaboride (LaB6) as an X-ray source, fitted with an ETD (Everhart
Thornley Detector), which preferentially work as a secondary
electron detector. The sample for SEM was prepared by dispersing
the sample on an adhesive coated carbon paper followed by gold
coating. XRD analysis were carried out on Bruker D8 Advance
diffractometer at 40 kV and 40 mA with Cu Kα radiation (λ= 0.15418
nm) in the range 2o-80o. The thermo gravimetric analysis (TGA) was
done using a thermal analyzer TA-SDT Q-600. ICP-AES analysis was
carried out by inductively coupled plasma atomic emission
spectrometer (ICP-AES, DRE, PS-3000UV, Leeman Labs Inc., USA).
Samples for ICP-AES were prepared by leaching out 0.01 g of
sample with HNO3 (conc.), and then heated for 30 min and volume
to 10 mL.1H-NMR and 13C NMR spectra of the products were
recorded at 500 MHz by using Bruker Avance-III 500 MHz
instrument. GCMS was carried out by using HP 5972 MSD couple
with HP 5890 GC, HP (USA) 1998.
N
14.
75
92
N
N
N
15.
N
O
aReaction conditions: substrate (2.0 mmol), catalyst (0.1 g), acetonitrile (4 ml) in the
presence of H2O2 (3.0 mmol) at 80 oC for 4h; bIsolated yield; c 6.0 mmol of H2O2 is used.
Further, we checked the recycling of the recovered RH-grafted
oxo-vanadium Schiff base catalyst for oxidation of
triethylamine as representative substrate. After completion of
the reaction the catalyst could easily be recovered by filtration,
dried and used for subsequent runs. The recyclability of the
catalyst was checked for five runs. In all experiments the
reaction time and yield of desired product remained almost
similar as shown in Fig 5, establishing the efficient recycling of
the catalyst. Furthermore, to ascertain the leach-proof nature
of the catalyst following reaction was performed: a reaction
mixture containing catalyst and oxidant was refluxed for three
hours. After being cooled at room temperature, the catalyst
was recovered by filtration and the filtrate was charged with
fresh substrate and oxidant and stirred the mixture under
reflux for three hours. The oxidation did not take place,
indicating that there was no leaching during the reaction and
the reaction was truly heterogeneous. This was further
supported by ICP-AES analysis of recovered catalyst, where
percentage of the vanadium in recovered remained almost
similar to fresh one 1.19 wt%.
2.3 Synthesis of amino functionalized rice husk (RH-NH2)
Firstly the rice husk obtained is washed with water and ethanol and
then dried in an oven overnight and then powdered it in a ball mill.
In a typical synthesis, 2.0 g of RH was adequately dispersed in 50 mL
toluene by using an ultrasonic probe. Subsequently, 6.0 mL of
APTMS was added to the RH dispersion and then the reaction vessel
was refluxed for 24
h under a nitrogen atmosphere. After
completion of the reaction, the amino functionalized RH (RH-NH2)
was washed with toluene to remove excess/non-reacted APTMS
followed by its drying at 70 oC under vacuum.
2.4 Synthesis of RH-grafted oxo-vanadium Schiff base
Briefly 1.0 g of amino functionalized RH was dispersed in 50 ml
ethanol using an ultrasonic bath. This is followed by addition of 3mL
of salicylaldehyde. The reaction mixture was refluxed for 8 h under
a nitrogen atmosphere in order to execute the reaction between
amino groups of APTMS moieties and salicylaldehyde. After
completion of the reaction, four consecutive ethanol washings were
performed to remove the non-reacted salicylaldehyde and the
obtained yellow coloured material was dried in an oven at 70 oC
overnight. Further in the final step, 1 g of Schiff base immobilized
Rice Husk was dispersed in methanol and refluxed for 24 h in the
presence of 0.5 g vanadium sulphate hydrate (VOSO4.xH2O) under a
nitrogen atmosphere to obtain the desired RH-grafted oxo-
vanadium Schiff base as shown in Scheme 2. The obtained material
was thoroughly washed with methanol to remove the undigested
vanadium sulphate. Washing of the final product was repeated 3-4
times and then it dried in an oven. This greenish powder, RH-
grafted oxo-vanadium Schiff base, was used as a catalyst for the
oxidation of tertiary amines to N-oxides. Further the loading of
vanadium in the prepared catalyst was found to be 1.2 wt% as
determined by ICP-AES analysis.
Fig. 5: Results of recycling experiment
2. Experimental section
2.1 Materials
All reagents and solvents were obtained from commercial sources
and used without further purification. Rice Husk (RH) was obtained
from sangam rice mill, mehal kalan in Punjab, India. Amino-
propyltrimethoxysilane (>97 %), Vanadyl sulfate and salisaldehyde
(>98 %) were purchased from Sigma-Aldrich and used without
further purification. Hydrogen peroxide (30 wt%), and other
solvents were of analytical grade and were used as received.
Distilled water was used throughout the synthesis.
2.5 General experimental procedure
2.2 Techniques used
Into a stirred mixture of tertiary amine (2.0 mmol) and catalyst (0.1
g, 0.002 mol) in acetonitrile was added aqueous 30 wt % H2O2 (3.0
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 7
View Article Online
DOI: 10.1039/C6RA13571D
ARTICLE
Journal Name
mmol) and the resulting mixture was stirred at 80 oC for 4h. The
progress of the reaction was monitored by TLC (SiO2). At the end of
the reaction, the catalyst was removed by filtration and reused for
subsequent recycling runs. The filtrate was concentrated under
reduced pressure. The residue thus obtained was purified by
column chromatography (SiO2, hexane/ethyl acetate, 6:4). The
yields of the N-oxide and their reaction times are presented in Table
2. The conversion of the reaction product was determined by GC
analysis. The identity of the products was established by comparing
with their physical and spectral data with those of authentic
samples.42,43
9
V. Gerardi, F. Minelli, and D. Viggiano, Biomass Bioenergy, 1998, 14
295.
10 G. Mansaray and A. E. Ghaly, Biores. Technol., 1998, 65, 13.
,
11 P.M. Stefani, D. Garcia, J. Lopez and A. Jimenez, J. Therm. Anal.
Calorim., 2005,81, 315.
12 S. Chandrasekhar, P. N. Pramada and L. Praveen, J. Mater. Sci., 2005,
40, 6535.
13 F. Adam, K. M. Hello and M. R. Ben Aisha, Journal of the Taiwan
Institute of Chemical Engineers, 2011, 42(5) , 843–851.
14 H. P. Wang, K. S. Lin, Y. J. Huang, M. C. Li, and L. K. Tsaur, Journal of
Hazardous Materials, 1998, 58(1–3), 147–152.
15 F. Adam, P. Retnam, and A. Iqbal, Applied Catalysis A, 2009, 357, 93.
16 A.E. Ahmed and F. Adam, Microporous and Mesoporous Materials,
2009, 118, 35.
17 F. Adam, K. Kandasamy and S. Balakrishnan, Journal of Colloid and
Interface Science, 2006, 304, 137.
18 J. H. Boyer, Chem. Rev., 1980, 80, 495.
19 G. B. Payne, P. H. Deming and P. H. Williams, J. Org.Chem., 1961,
26, 659.
20 A. L. Baumstark, M. Dotrong and P. C. Vasquez, Tetrahedron Lett.,
1987, 28, 1963.
21 J. G. Robhe, E. J. Behrman, J. Chem. Res., 1993, 412.
22 M. Ferrer, F. Sanchez-Baeza and A. Messgure, Tetrahedron, 1997,
53, 15877.
23 H. S. Mosher, L. Turner and A. Carlsmith, Org. Synth. Coll., 1963, 4,
828.
24 Y. Jiao and Y. Hongtao, Synlett, 2001, 73.
25 A. Thellend, P. Battioni, W. Sanderson and D. Mansuy, Synthesis,
1997, 1387.
26 K. Bergstad and J. E. Backvall, J. Org. Chem., 1998, 63, 6650.
27 D. J. Robinson, P. McMom, D. Bethell, P. C. Bulmanpage, C. Sly, F.
King, F. E. Hangcock and G. J. Hutching, Catal. Lett., 2001, 72, 233.
28 B. M. Choudary, B. Bharathi, Ch. V. Reddy, M. L. Kantam and K. V.
Raghavan, Chem. Commun., 2001, 1736.
29 H. Masashi and H. Hirotoshi, Japanese Patent JP 2004307473, 2004
30 A. J. Bailey, W. P. Griffith and B. C. Parkin, J. Chem. Soc. Dalton
Trans., 1995, 1833.
31 L. Franz, L. Andre and D. Paul, European Patent EP 224662, 1986.
32 N. Hirofumi, Japanese Patent JP 09087251, 1995.
33 M. G. A. Vieira, A. F. de Almeida Neto, M. G. Carlos da Silva, C. C.
Nóbrega and A. A. Melo Filho, Brazilian Journal of Chemical
Engineering, 2012, 29(3), 619 – 633.
Conclusion
The present work shows a unique application of bio waste rice husk
as a support material for development of heterogeneous catalyst
for organic transformation by considering the rich –OH
functionalities of the RH support. The APTMS grafted RH support
was prepared by chemical interaction between amino groups of
APTMS and oxygen functionalities available on the RH support.
Subsequent reaction with salicylaldehyde to give RH-grafted Schiff
base which further reacted with vanadyl sulphate to give
corresponding RH-grafted oxo-vanadium Schiff base through
covalent attachment. The successful synthesis of the desired
catalyst was confirmed by thorough characterization of the catalyst
by various techniques such as XRD, FTIR, SEM-EDX, TGA and ICP-AES
analysis. The developed catalyst was utilized as a heterogeneous
catalyst for the oxidation of tertiary amines to N-oxides using
hydrogen peroxide as an oxidant. Moreover, the developed catalyst
was found to be easily recoverable and recyclable without
significant loss in the catalytic activity. This work with added
benefits of flexibility in immobilization of various chemical moieties
and on bio-waste rice husk offers new opportunities for designing
highly active heterogeneous catalysts for organic transformations.
Acknowledgements
We acknowledge Director, CSIR-Indian Institute of Petroleum (IIP)
for his kind permission to publish these results. Analytical science
division is highly acknowledged for providing characterisation
results of the material. VP thanks Council of Scientific and Industrial
Research (CSIR) for providing fellowship in the form of Senior
Research Fellowship (SRF).
34 A. Bharadwaj, Y. Wang, S. Sridhar and V. S. Arunachalam
science, 2004, 87(7)
35 K. N. Farooque, M. Zaman, E. Halim, S. Islam, M. Hossain, Y. A.
, current
.
Mollah and A. J. Mahmood, Bangladesh J. Sci. Ind. Res. 2009, 44(2)
157-162.
,
36 W. Nakbanpote, B. A. Goodman, and P. Thiravetyan, Colloids Surf. A.,
2007, 304, 7-13.
37 C. R. T Tarley, S. L. C. Ferreira, and M. A. Z. Arruda, Microchem. J.,
2004, 77, 163-175.
Notes and references
38 C. R. T. Tarley and M. A. Z, Arruda, Chemosphere, 2004, 54(7), 987-
995.
39 R. Radfard and A. Abedi, J. App. Chem. Res. 2015, 9(2), 59-65.
40 I. Correia, J. C. Pessoa, M. T. Duarte, M. F. Minas da Piedade, T.
Jackush, T. Kiss, M. Margarida C. A. Castro, C. F. G. C. Geraldes and F.
Avecilla, Eur. J. Inorg. Chem. 2005, 732–744.
1
2
C. Clasen and W-M. Kulicke, Prog. Polym. Sci., 2001, 26, 1839.
C. D. Granados and R. Venturini, Ind. Eng. Chem. Res., 2008, 47
4754–4757.
,
3
4
M. Rozainee, S. P. Ngo and A. A. Salema, Bioresour. Technol., 2008,
99, 703–713.
S. H. Gheewala, and P. Suthum, International Journal of Mechanical,
Aerospace, Industrial, Mechatronic and Manufacturing Engineering,
41 M. Colladon, A. Scarso and G. Strukul, Green Chem. 2008, 10, 793–
798
42 S. L. Jain, J. K. Joseph, B. Sain, Synlett, 2006, 2661-2663.
43 P. Veerakumar, S. Balakumar, M. Velayudham, K.-L. Luc, S. Rajagopal
Catal. Sci. Technol., 2012, 2, 1140-1145
2009, 3(5)
.
5
6
K. A. Matori and M. M. Haslinawati, JBAS., 2009, 1(3), 512.
E. O. Onche, O. N. Namessan, and G. A. Asikpo, LEJPT., 2006,
178.
9
, 167-
7
8
A. B. Rabah, S. B. Oyeleke, S. B. Manga and L.G. Hassan, IRJM., 2011,
2(8), 253-258.
K. R. Srinivas and S. V. Naidu, Journal of Chemical, Biological and
Physical Sciences, 2013, 2(3), 602-606.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 7
View Article Online
DOI: 10.1039/C6RA13571D
Journal Name
ARTICLE
Renewable waste rice husk grafted oxo-vanadium catalyst for
oxidation of tertiary amines to N-oxides
Vineeta Panwar,a Ankushi Bansal,a Siddharth S. Raya and Suman L. Jaina*
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins