Synthesis, kinetic study, and applications of polyethyleneimine supported nano zirconium chromate in oxidation of furfuryl alcohol to corresponding carbonyl compound

Article abstract of DOI:10.1007/s00706-015-1650-1

The efficiency of highly branched polyethyleneimine has been investigated as a support for nano zirconium chromate and subsequent use as a heterogeneous oxidant for selective oxidation of furfuryl alcohol to furfural. These were synthesized using polyethyleneimine to produce a polymer coordinated nano zirconium, a noble and straightforward method for screening high catalytically active polymer nano composites. The one-step systematic derivatization of the polyethyleneimine scaffold led structurally correlated to the stabilization of zirconium nanoparticles and catalysis. Analysis of this polymeric reagent identified the zirconium chromate nano composite that was able to be effective to oxidation reaction in tetrahydrofuran under mild conditions due to the surface area of the nano zirconium chromate per unit volume. Capacity of the reagent and fixation of nano zirconium chromate is confirmed by ICP and atomic absorption technique. Morphology of this nano composite is investigated by SEM and TEM. The kinetic of oxidation of furfuryl alcohol, over heterogeneous catalyst, nano zirconium chromate in THF, were investigated. Power-law rate model was applied to describe the experimental results and obtain the orders of the reaction with respect to furfuryl alcohol, catalyst, and furfural, which were found to be 0.989, 0.991, and ?0.68, respectively, with the activation energy of 76.78?kJ/mol. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-015-1650-1

Monatsh Chem
DOI 10.1007/s00706-015-1650-1
ORIGINAL PAPER
Synthesis, kinetic study, and applications of polyethyleneimine
supported nano zirconium chromate in oxidation of furfuryl
alcohol to corresponding carbonyl compound
Setareh Sheikh1 Nooredin Goudarzian1
•
Received: 18 June 2015 / Accepted: 29 December 2015
Ó Springer-Verlag Wien 2016
Abstract The efficiency of highly branched poly-
ethyleneimine has been investigated as a support for nano
zirconium chromate and subsequent use as a heterogeneous
oxidant for selective oxidation of furfuryl alcohol to fur-
fural. These were synthesized using polyethyleneimine to
produce a polymer coordinated nano zirconium, a noble
and straightforward method for screening high catalytically
active polymer nano composites. The one-step systematic
derivatization of the polyethyleneimine scaffold led struc-
turally correlated to the stabilization of zirconium
nanoparticles and catalysis. Analysis of this polymeric
reagent identified the zirconium chromate nano composite
that was able to be effective to oxidation reaction in
tetrahydrofuran under mild conditions due to the surface
area of the nano zirconium chromate per unit volume.
Capacity of the reagent and fixation of nano zirconium
chromate is confirmed by ICP and atomic absorption
technique. Morphology of this nano composite is investi-
gated by SEM and TEM. The kinetic of oxidation of
furfuryl alcohol, over heterogeneous catalyst, nano zirco-
nium chromate in THF, were investigated. Power-law rate
model was applied to describe the experimental results and
obtain the orders of the reaction with respect to furfuryl
alcohol, catalyst, and furfural, which were found to be
0.989, 0.991, and -0.68, respectively, with the activation
energy of 76.78 kJ/mol.
Graphical abstract
Keywords Furfuryl alcohol Á Nano zirconium chromate Á
Oxidation Á Reaction rate Á Activation energy
Introduction
In recent years, the effective use of more selective sup-
ported and non-toxic solid heterogeneous catalyst or
polymer supported catalysts same as poly(4-vinylpyridine)
supported sodium azide [1], polyethyleneimine supported
silver nanoparticle [2], pyridinium chlorochromate [3],
bipyridinium chlorochromate [4], tetrakis(pyridine)silver
dichromate [5], and zinc borohydride supported charcoal
[6] has been under more attention in various fields of
organic synthesis due to their simple operation, reusability,
environmental compatibility, simple isolation of the prod-
ucts, and high selectivity [7–12]. Most of these reagents
have their deficiencies and drawbacks, e.g. need to use
excess reagent [13], acidity of the reagent [14], need to use
the wet reagent [15], and being expensive [16]. Polymer-
supported catalysts make reaction methods more econom-
ical, convenient, and environmentally safe and benign due
to their ability to be used as recyclable and heterogeneous
& Setareh Sheikh
sheikh@iaushiraz.ac.ir;
sheikh_set@yahoo.com
1
Department of Applied Chemistry, Shiraz Branch, Islamic
Azad University, Shiraz, Iran
123

S. Sheikh, N. Goudarzian
catalysts in organic transformation. Mild conditions can be
considered for the reactions and insoluble polymer support
can be separated easily from the reaction medium, so
simplicity of product purification is resulting. Accordingly,
for oxidation reactions, application of zirconium based
catalysts has also been proven [17]. Formation of zirco-
nium bulk and zirconium agglomeration that has caused
catalyst deactivation in several cases are major problems,
even though there has been a significant progress in
improving substrate scope, selectivity, and catalyst activity.
Although there are many different reagents described in the
literature for transforming alcohol to aldehyde, we need to
either enhance the existing redox procedure or to find new
reagents in order to have better efficiency under milder
conditions [18].
with no loss of activity and capacity. The oxidation reac-
tion stops only at the aldehyde production step and the side
reaction decreases by using the polymer supported oxi-
dizing agent.
Power-law rate model is one of the proper methods for
kinetic study. Reaction rate of oxidation of furfuryl alcohol
(FurOH) depends on some factors. These factors are
amount of catalyst (cat.), concentration of FurOH and
furfural (FurH), and also temperature. Here the oxidation
rate (mol dm-3 min-1) is expressed in terms of the power
law model as:
a
b
c
r ¼ ÀðdCFurOH=dtÞ ¼ k½FurOHŠ ½cat:Š ½FurHŠ
ð1Þ
where k is the rate constant, and a, b, c, are the reaction
orders with respect to the concentration of FurOH
(mol/dm3), catalyst (mol/dm3), and FurH (mol/dm3),
respectively. As it is known the rate constant is a
temperature dependent constant and by using Arrhenius
equation, it can be expressed as:
However, in mechanistic and kinetic studies, using
polymer supported oxidizing agents are limited, neverthe-
less the application of oxidation under phase transfer
catalysis in synthetic organic chemistry are common [18,
19]. The polymer supported oxidizing agent has the ability
to be used and reused without losing its capacity and in
addition it can be used easily and safely which are the main
factors of interest in the current study. The side reaction
will reduce and the process of oxidation stops just at the
product aldehyde step by using polymer supported oxi-
dizing agent. As a part of our study to develop the
application of polymer supported reagents in organic syn-
ꢀ
ꢁ
ÀEa
k ¼ A exp
ð2Þ
RT
In this equation, A and Ea are the pre-exponential factor
and the activation energy (kJ mol-1), respectively. R is the
ideal gas law constant (kJ mol-1 K-1), and T is the
reaction temperature (K).
thesis
[18–20],
application
and
synthesis
of
Results and discussion
polyethyleneimine (PEI, Scheme 1), which is supported by
nano zirconium chromate, is reported.
[PEI-NZrCrO=4] found as a stable, clean and green
polymer bond zirconium chromate for oxidation of alco-
hols to relative aldehydes. Many problems related to metal
chromate oxidizing agent, such as the need to have an
acidic solution and inconsistency of metal chromate [21]
have been resolved by using polymeric oxidizing reagent.
Recently, oxidation under phase transfer catalysis
spreads in a large extent in synthetic organic chemistry, but
mechanistic and kinetic studies of the application of
polymer supported oxidizing agents are limited [22]. Safety
and easy work up of the polymer supported oxidizing agent
are the main factors of interest for the new study, and
moreover this oxidizing agent can be used and be reused
Complexation of highly branched polyethyleneimine with
nano zirconium chloride prepared the highly branched
polyethyleneimine-supported nano zirconium chromate by
replacing the chloride anions with chromates. THF was the
selected solvent, and this medium is applied for all the
oxidation reactions. Polyethyleneimine-supported nano
zirconium chromate is a preferable reagent to many
monomeric reagents because after the oxidation reactions,
the chromium ions and nano zirconium are tightly bound to
the heterogonous polymer support. Evaporation of the
solvent, filtration of the reaction mixture and if further
separation is required, unreacted initial compounds can be
separated by column or plate chromatography in order to
isolate and purify the product.
There is a difference between chromium(VI)-based
polymeric oxidants used for oxidation of alcohols [3, 23–
27] and the discussed reagent, in which the reagent can be
used in similar amounts according to the reactant. Essential
recorded fact in the use of some polymeric reagents [16,
28–32] indicates that the reagent is suitable and non-acidic
for oxidation of acid-sensitive materials. Additional
reagent can be used, product separation is simple and fil-
tration and evaporation of the solvent is a simple method to
123

Synthesis, kinetic study, and applications of polyethyleneimine supported nano zirconium…
obtain pure product with no by-products and waste, and
this is a useful procedure to execute for selective oxidation.
As a result of this study, it is proved that the polymeric
reagent is a stable material and also storable for months
with its initial activity. To evaluate the polymeric reagent
stability [PEI-NZrCrO=4], which was stored 6 months in the
laboratory, is used and the same results as with freshly
prepared [PEI-NZrCrO=4] are achieved. To confirm the
oxidation capability of [PEI-NZrCrO=4] on different types
of alcohols, we used fresh and regenerate catalyst to
oxidize benzyl alcohol, p-chlorobenzyl alcohol,
2-chlorobenzyl alcohol, and 2-nitrobenzyl alcohol under
similar conditions as for oxidation of furfuryl alcohol. The
Fig. 2 Transmission electron microscopy images of [PEI-NZrCrO=4]
results revealed that [PEI-NZrCrO=4] can be used to oxidize
the foregoing alcohols successfully.
[PEI-NZrCrO=4] is a nontoxic, non-pollutant, and non-
volatile oxidizing reagent and does not irritate skin and
mucous membrane. Scanning electron microscopy (SEM)
and transmission electron microcopy (TEM) are used to
assess the morphology of the polymeric reagent. Repre-
sented results about particles morphology in Fig. 1 are
obtained from SEM images. A good dispersion and dis-
sociation of the particles in the polymer bed is shown in the
same image. TEM image clearly shows that spherical
particles of Zr nanoparticles were formed and dispersed
homogenously into the polymer matrix (Fig. 2). In com-
parison with the same available compounds [1–6, 13–16],
the achieved products showed the same results of structure
was studied in the coexistence of catalysts (0.073 g/dm3) at
66 °C. The results are illustrated in Fig. 3a, b. It can be
observed that in Fig. 3b, the plot of ln (initial oxidation
rate) versus ln (concentration of FurOH) shows a good
linear relationship (R2 = 0.995) and the slope of this linear
1
and properties based on melting point, boiling point, H
NMR spectra, and FT-IR.
Using power-law rate model, which is a proper model
[33–36], orders of reaction are determined. By fitting the
model to the experimental data, the kinetic parameters can
be determined. The orders of reaction can be obtained by
changing the concentrations of FurOH, FurH, and the
amount of catalyst, respectively, while other factors should
be maintained constant. The change in the initial reaction
rates as a function of the initial concentration of FurOH
Fig. 3 a Plot of FurOH concentration versus reaction time with
different initial concentration of FurOH, (filled diamond) 2.98 9 10-4
mol/dm3, (filled square) 6.24 9 10-4 mol/dm3, (filled triangle)
7.02 9 10-4 mol/dm3, at 66 °C. b The plot of ln(initial oxidation rate)
vs ln(concentration of FurOH) to obtain the reaction order with respect
to FurOH. Reaction condition: initial [FurH] = 0 mol/dm3, amount of
catalyst = 0.073 g/dm3, at 66 °C
Fig. 1 Scanning electron microscopy images of [PEI-NZrCrO=4]
123

S. Sheikh, N. Goudarzian
equation is 0.989, which is the reaction order with respect
to concentration of FurOH.
Figure 4a shows the effect of catalyst loading on the
initial oxidation rates at 66 °C and in the coexistence of
FurOH (6.28 9 10-4 mol/dm3). It is observed in Fig. 4a
that, with the increase in the catalyst amount, the oxidation
rate increases sharply. Figure 4b is similar to Fig. 3b and
illustrates that the slope of the straight line is 0.991 which
is the reaction order with respect to catalyst and the linear
regression is 0.996. This obtained order indicates that this
oxidation reaction can be considered as a first order reac-
tion with respect to the amount of the catalysts. Also a first
order in the catalyst concentration suggests that the sub-
stances in the heterogeneous catalysis system will not
likely poison the active sites [37].
Small amount of FurH is added to the solution at the
beginning of the reaction for obtaining the order of FurH.
Also this part indicates the effect of product on the reaction
rate. Figure 5a shows FurOH concentration as a function of
reaction time with different concentrations of FurH at
66 °C. In this case, the initial concentration of FurOH and
Fig. 5 a Plot of FurOH concentration versus reaction time with
different initial concentration of FurH, (filled circle) 9.41 9 10-5
mol/dm3, (filled square) 2.12 9 10-4 mol/dm3, (filled triangle)
3.14 9 10-4 mol/dm3, at 66 °C. b The plot of ln(initial oxidation rate)
vs ln(initial concentration of FurH) to obtain the reaction order with
respect to FurH. Reaction condition: initial [FurOH] = 12.56 9 10-4
mol/dm3, initial amount of catalyst = 0.146 g/dm3, at 66 °C
catalyst amount are kept constant at 12.56 9 10-4
mol/dm3 and 0.146 g/dm3, respectively. In Fig. 5b, it is
indicated that related data are fitted linearly with a negative
slope of -0.68 and it is the reaction order for FurH. In
kinetics, negative order implies that the product and reac-
tants undergo competitive adsorption on the surface of
catalyst and adding more FurH causes occupying more
adsorption sites on the surface of catalyst. Therefore the
probability of surface reaction on the catalyst decreases and
as a result reaction rate decreases.
Constant concentration of FurOH (6.28 9 10-4
mol/dm3) and amount of catalyst (0.073 g/dm3) are applied
to determine the kinetics of the reaction at different tem-
peratures (50, 55, 60, and 66 °C). In Fig. 6a, it is observed
that reaction rate increases with increasing temperature. By
applying the calculated rate constants, the value of acti-
vation energy and pre-exponential factor (Eq. 2) were
determined from the corresponding Arrhenius plot in
Fig. 6b. The plot of ln k versus 1/T creates a straight line
and R2 is 0.995. From the slope of the straight line acti-
vation energy (Ea) was obtained that it was 76.78 kJ mol-1
Fig. 4 a Plot of FurOH concentration vs reaction time with different
initial concentration of catalyst, (filled diamond) 0.0352 g/dm3, (filled
square) 0.0847 g/dm3, (filled triangle) 0.1089 g/dm3, at 66 °C. b The
plot of ln(initial oxidation rate) vs ln(concentration of catalyst) to
obtain the reaction order with respect to catalyst. Reaction condition:
initial [FurOH] = 6.28 9 10-4 mol/dm3, initial [FurH] = 0 mol/
dm3, at 66 °C
123

Synthesis, kinetic study, and applications of polyethyleneimine supported nano zirconium…
alcohols besides it is not expensive. In addition to these
advantages this reagent has the properties of reported
polymeric reagents such as easy work-up by filtration and
evaporation of the solvent to separate and obtain pure
product. It is also stable and storable for months with its
initial activity. Furthermore it is a nontoxic, nonvolatile, and
nonpolluting oxidation reagent and it is nonirritating to skin.
In consequence, the spent reagent has been regenerated
several times and no remarkable change has been observed in
its activity. This polymeric reagent is economically appro-
priate for medium to large-scale operations because it has
high stability and ability to regenerate the polymeric bed and
it is a functional addition to represent methodologies.
The kinetic study of FurOH oxidation on the nano cat-
alyst has been investigated. The reaction kinetics was
initially modeled using the power-law rate expression
leading to reaction orders of 0.989, 0.991, and -0.68 with
respect to FurOH, catalyst, and FurH, respectively; with the
activation energy of 76.78 kJ mol-1. It is our suggestion
that this heterogeneous catalyst has suitable capabilities for
more practical applications in industries.
Experimental
All the compounds such as chemical materials were either
synthesized in our laboratory or were purchased from
Fluka, Sigma Aldrich Chemical Co., Merck Chemical Co.
Reaction progression was monitored by TLC using silica
gel Polygram SIL G/UV 254 plates or gas chromatogra-
phy (GC) equipped with flame ionization detector (FID,
SE-30 capillary column) and UV–Visible. Comparison
was performed between all the products according to their
FT-IR, 1H NMR, GC-Mass spectra, TLC, and physical
data with pure compounds and all the materials were
characterized.
Fig. 6 a Plot of FurOH concentration versus reaction time under
different reaction temperature of (filled diamond) 50 °C, (filled
square) 55 °C, (filled triangle) 60 °C, (filled circle) 66 °C. b Arrhe-
nius plot of ln(k) versus 1/T. Reaction condition: initial
[FurOH] = 6.28 9 10-4 mol/dm3, initial amount of cata-
lyst = 0.073 g/dm3, initial [FurH] = 0 mol/dm3
and from the intercept of this line, the pre-exponential
factor (A) was calculated to be 8.18 9 1011 mol-1/3
dm min-1
.
Based on the above results and by applying the values of
reaction orders and activation parameters into Eq. (1),
according to power-law model, the rate expression is:
GC-Mass spectra where run on a GC aglient7890/
Mass 7000 triple quad and FT-IR spectra were run on a
Perkin Elmer RXI spectrophotometer. UV–Visible was
run on a HACH DR5000 Spectrophotometer and 1H
NMR spectra were obtained by Bruker Avance DPX
instrument (250 MHz). The Zr analyses and the leaching
test were analyzed by ICP-OES analyzer (Warian,
Vista—Pro), TEM analyses where preformed on an
EM912 Omega electron microscope with an acceleration
voltage of 120 kV instrument. Scanning electron micro-
graphs where achieved by SEM, Hitachi S-4700
microscope operated at an acceleration voltage of 10 kV.
Melting points where characterized in open capillaries
with an Electro thermal 9100 melting point instrument.
All product yields refer to the isolated yield unless
reported as GC yield. Atomic absorption was run on an
Aurora instruments A11200.
r ¼ 8:18 Â 1011
0:989
0:991
À0:68
 eÀ76:78=RT ½FurOHŠ
½cat:Š
½FurHŠ
ð3Þ
This rate expression can be used for predicting the relative
rate of oxidation of FurOH under different conditions.
Conclusions
Unlike other reported catalysts used to oxidize alcohols,
[PEI-NZrCrO=4] can be used in similar amounts according to
the reagent and there is no need to use excessive amounts
and also there is no need to wet. Since it has no acidic
properties, it is suitable for oxidation of acid-sensitive
123

S. Sheikh, N. Goudarzian
Preparation of polyethyleneimine supported nano
zirconium tetrachloride
and then vacuum was used overnight to dry and produce
reddish, non-hygroscopic and stable powder (Scheme 2).
The FT-IR spectrum showed bonds at 852, 858, 889, 942,
1722 cm-1 characteristics of chromate ion. Capacities of
the reagent measured by titration method, atomic absorption
and ICP technique in terms of mmol CrO=4 per gram reagent
was 2.03 mmol/g. M.p.: 218 °C (decomposed).
Polyethyleneimine (PEI, 1 g, 23.2 mmol) in THF was
added drop wise to 1 g nanoZrCl4 (4.8 mmol) solution in
20 cm3 methanol. Precipitation occurred immediately. The
mixture was stirred and kept warm for 30 min and then
stored in refrigerator for 24 h. The precipitate was filtered
and washed several times with methanol, dried in vacuum
overnight. Atomic absorption and gravimetric technique
was used to determine the ratio of polyethyleneimine to the
metal ion, which was about 6:1. M.p.: 223–226 °C (de-
composed); FT-IR (KBr): vꢀ = 3400–3500 (N–H),
Determination of the capacity of [PEI-NZrCrO=4]
The principal methods which were used in determination of
capacities of polymeric reagents were atomic absorption,
ICP, and iodometric titration methods. For atomic
absorption and ICP methods, a series of standard solutions
containing 0.25–2 ppm of zirconium chloride (with respect
to Zr) and potassium dichromate (with respect to Cr) in
concentrated nitric acid were prepared. The catalyst [PEI-
NZrCrO=4], it was treated successively with 25 cm3 mixture
of concentrated H2SO4, HNO3, and HCl, and filtered.
The filtrate was diluted to 30 cm3 with deionized water
and used ICP method and atomic absorption technique.
This solution with respect to Zr and Cr was determined and
the amount of zirconium and chromium was calculated by
using the calibration curve for characterized the amount of
1570–1620 (C–H ben), 1354 (C–N) cm-1
.
Preparation of polyethyleneimine supported nano
zirconium chromate [PEI-NZrCrO=4]
Polyethyleneimine supported nano zirconium tetrachloride
(1 g, 4.00 mmol) was suspended in THF and added to a cold
solution of 2 g chromium trioxide (10 mmol) in water/THF
(10 cm3/20 cm3). The mixture was shaken magnetically at
room temperature for 10 h. The pure product was filtered
and washed several times by deionized water, diethyl ether
123

Synthesis, kinetic study, and applications of polyethyleneimine supported nano zirconium…
zirconium and chromium, the Zr content and Cr content are
equal to 1.97 and 2.03 mmol g-1, respectively. For iodo-
metric titration method, 1.000 g of [PEI-NZrCrO=4] was
suspended in 25 cm3 of sodium hydroxide (5 N). Potas-
sium iodate (100 cm3, 0.25 N) was added immediately,
and the flask stirred vigorously for 10 min. Five grams of
KIO3 were added, followed by 40 cm3 of 4 N sulfuric acid.
The flask was allowed to stand in the dark for 3–5 min
before iodine was titrated with 0.1 N sodium thiosulfate
(starch indicator) until the blue color disappeared. The
capacity was then calculated as milimole CrO=4 per gram
[PEI-NZrCrO=4] was 2 [38].
with known standards. External calibration method was
used for quantitative analysis of the concentrations of
reactants and products generated.
In this study, the initial reaction rate method was
employed to conduct the kinetic investigations [39].
Samples were taken at various time intervals within the
initial 30 min of this oxidation reaction. For finding the
overall kinetic expression, series of experiments were
performed by implementing different reaction conditions
and determining the initial reaction rates. It should be
mentioned that in each set of experiments only one
parameter was varied and the other parameters were kept
constant [33].
Preparation of furfural from furfuryl alcohol:
typical procedure
Acknowledgments Financial support of Shiraz Branch, Islamic
Azad University (Shiraz, Iran) is gratefully acknowledged.
Under reflux condition *0.5 g of [PEI-NZrCrO=4] (equal to
1 mmol CrO=4) was added to a mixture of 98.1 mg furfuryl
alcohol (1 mmol) and 10 cm3 THF in a 25 cm3 round-
bottomed flask, and the mixture was stirred for 135 min.
The progression of the reaction was recorded by using TLC
method (ethyl acetate: n-hexane, 3:1). The mixture was
filtered, and the solvent was volatilized to achieve pure
Furfural (96 mg, 99.9 % yield) to complete the reaction.
B.p.: 161–162 °C (lit. 161 °C); FT-IR and 1H NMR spectra
agree with published data.
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hydrochloric acid (2 N). The obtained suspension was
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