Cu/Ni-doped sulfated zirconium oxide immobilized on CdFe2O4 NPs: a cheap, sustainable and magnetically recyclable inorgano-catalyst for the efficient preparation of α-aminonitriles in aqueous media

Article abstract of DOI:10.1007/s11164-020-04203-x

Abstract: A new multifunctional bimetallic nanocatalyst was prepared by immobilization of Cu/Ni-doped sulfated zirconium oxide on magnetic cadmium ferrite (CdFe₂O₄@SiO₂@ZrO₂/SO₄^2?/Cu/Ni) and used as an efficient recyclable catalyst for one-pot as well as stepwise preparation of α-aminonitriles under mild conditions. The magnetic nanocatalyst was characterized by FTIR, TGA, VSM, XRD, EDX, FE-SEM, and TEM analyses. Also, the surface acidity of the catalyst was measured by pyridine adsorption assay. The catalyst possesses various active sites which could catalyst a variety of aromatic and aliphatic aldehydes to the corresponding α-amionitriles under moderate to high yields in the presence of aniline. Furthermore, transformation of ketones to the desired α-amionitriles and some bis-aminonitriles was also performed by this method. The catalyst could be readily recovered from the reaction mixture and reused for several times without significant loss of activity. Graphic abstract: A general and efficient method has been developed for transformation of a variety of aliphatic, aromatic aldehydes and ketones to the corresponding α-aminonitriles using a multifunctional recyclable CdFe₂O₄@SiO₂@ZrO₂/SO₄^2?/Cu/Ni nanocatalyst.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-020-04203-x

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04203-x
Cu/Ni‑doped sulfated zirconium oxide immobilized
on CdFe2O4 NPs: a cheap, sustainable and magnetically
recyclable inorgano‑catalyst for the efcient preparation
of α‑aminonitriles in aqueous media
Mohammad Ali Nasseri1 · Simin Ramezani‑Moghadam1 · Milad Kazemnejadi1 ·
Ali Allahresani1
Received: 28 March 2020 / Accepted: 23 June 2020
© Springer Nature B.V. 2020
Abstract
A new multifunctional bimetallic nanocatalyst was prepared by immobilization of
Cu/Ni-doped sulfated zirconium oxide on magnetic cadmium ferrite (CdFe2O4@
SiO2@ZrO2/SO42−/Cu/Ni) and used as an efcient recyclable catalyst for one-pot as
well as stepwise preparation of α-aminonitriles under mild conditions. The magnetic
nanocatalyst was characterized by FTIR, TGA, VSM, XRD, EDX, FE-SEM, and
TEM analyses. Also, the surface acidity of the catalyst was measured by pyridine
adsorption assay. The catalyst possesses various active sites which could catalyst
a variety of aromatic and aliphatic aldehydes to the corresponding α-amionitriles
under moderate to high yields in the presence of aniline. Furthermore, transforma-
tion of ketones to the desired α-amionitriles and some bis-aminonitriles was also
performed by this method. The catalyst could be readily recovered from the reaction
mixture and reused for several times without signifcant loss of activity.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04203-x) contains supplementary material, which is available to authorized users.
*
Mohammad Ali Nasseri
manaseri@birjand.ac.ir
1
Department of Chemistry, Faculty of Science, University of Birjand, P.O. Box 97175-615,
Birjand, Iran
Vol.:(0123456789)
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M. A. Nasseri et al.
Graphic abstract
A general and efcient method has been developed for transformation of a variety of
aliphatic, aromatic aldehydes and ketones to the corresponding α-aminonitriles using
a multifunctional recyclable CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni nanocatalyst.
Keywords Sulfated zirconium oxide · α-Aminonitrile · Strecker synthesis · Ketone ·
Cu/Ni bimetallic
Introduction
Multicomponent reactions have been recognized as a powerful strategy for the
preparation of biomolecules that have the advantages of one-pot bond formation
under simplifed, environmentally friendly and mild conditions, higher efciency,
and high atom economy [1]. One of these reactions is the three-component
Strecker reaction, which even after more than centuries of its discovery, is one
of the most reliable methods for the preparation of α-amino acids and aminoni-
triles and is widely used in laboratory as well as industrial scales [2]. Strecker
synthesis involves a three-component reaction of the accessible and inexpensive
aldehyde, amine, and cyanide source (alkali cyanide salt or hydrogen cyanide),
which results in a one-pot α-aminonitrile product [3]. Preparation of benzo-
furan derivatives via Strecker synthesis are other applications in the preparation
of pharmaceutical compounds [4]. Nitrile functionality (Nitrile compounds) is
very important in organic synthesis, because they are one of the most widely
used and useful synthetic intermediates for the synthesis of organic compounds
that can easily be converted into acid and amide functional groups [2, 5]. Subse-
quently, α-aminonitrile compounds are valuable building blocks for the prepara-
tion of biologically active compounds such as α-amino alcohols, 1,2-diamines,
and heterocyclic nitrogen-containing compounds (such as imidazole and thia-
diazole), amides and α-amino-aldehydes, α-amino acids, etc., which prepared
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
by a nucleophilic amine attack on nitrile functional group. The α-aminonitrile
functional group is found in the structure of various alkaloids [6]. In addition,
the α-aminonitriles prepared by the Strecker synthesis can be easily converted to
their corresponding α-amino acids (synthetic α-amino acids) by means of com-
plete hydrolysis of the nitrile group, since they lack another hydrolysable site.
Optical and mechano-chemical methods are also methods that have recently been
considered for the preparation of α-amino acids [7, 8]. There are generally three
major methods for the preparation of α-amino acids, including: α-halogenation
of carboxylic acid, alkylation of an acetamidomalonate, and Strecker synthesis
(Scheme 1) [9].
α-Amino acids are basic building blocks for proteins and play a vital and
essential role in life, which widely used in food and food supplements, as a pre-
cursor to pharmaceutical compounds and biodegradable plastics, and so on. For
application of Strecker synthesis in the pharmaceutical industry can be point to
the preparation of saframycin A [10], saxagliptin [11], ( )-phthalascidin 622
[12], ecteinascidin 743 [13], and hepatitis C virus NS3 serine protease inhibi-
tors [14]. However, the traditional method, Strecker synthesis, is harsh, limiting
its application to a wide extent, especially in industry. To this end, various cat-
alytic systems were developed to improve the conditions for the preparation of
α-aminonitriles. Homogenous Lewis acids, heterogeneous Lewis acids, heteroge-
neous Brønsted acids, organocatalysts, polymeric materials and resins, ionic liq-
uids, and metals and metal complexes are some developed catalytic systems for
the Strecker reaction, which also refects the importance of this reaction [4]. Cho-
line chloride/urea (as a deep eutectic solvent) [15], Galic acid@Magnetic nano-
particles (GA@MNPs) [3], PEG-OSO3H [16], MCM-41-SO3H [17], PVP-SO2
complex [18], Fe3O4@cellulose-OSO3H [5], and K5CoW12O40 [19], are among
Scheme 1 Three main approaches for the preparation of α-amino acids
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M. A. Nasseri et al.
the latest developments in this feld. Also Kouznetsov, et al. [6] have reviewed
recent advances in Strecker synthesis and their biological properties.
Despite all these advances, given the growing importance of environmental
and economic issues, the need to fnd and replace greener, more environmentally
friendly, and cost-efective catalytic systems feel more than ever [20, 21]. Zirconia
has for many years been one of the high acidic solid substrates in the petroleum
refning and petrochemical industries for hydrocarbon conversion, alkylation, crack-
ing, Friedel–Crafts acylation, esterifcation and isomerization are used. Zirconium
oxide (ZrO2) based compounds have high thermal and mechanical resistance. Modi-
fcation of their surfaces with sulfate groups (ZrO2/SO42−) promotes acidic prop-
erties and subsequently increases catalytic properties, especially in acid-catalyzed
reactions [22, 23]. On the other hand, combining/immobilization these materials
with magnetic nanoparticles will not only facilitate the recovery from the reaction
mixture, but also increase the surface area due to their deposition on the nanopar-
ticles, increase the surface area available for catalytic reaction and subsequently
increase the reaction efciency. Signifcant catalytic activities have been reported in
cross-coupling reactions [24], multipartite reactions, benzylation, dioxane synthe-
sis of heterocyclic compounds, etc. [25, 26]. In our recent research work, we incor-
2−
porated copper ions in the framework of ZrO2/SO4 as an efective and recover-
able catalyst in the Sonogashira coupling reaction [24]. Considering the importance
of α-aminonitriles in the feld of medicine and pharmaceuticals, in the light of our
ongoing research on these catalytic systems and on the stunning catalytic activity of
ZrO2/SO42−, zirconium oxide as a solid support with high thermal and mechanical
stability, modifed by sulfate groups and further catalytically active sites were cre-
ated by incorporating copper and nickel ions. The resulting compound was deco-
rated on CdFe2O4 magnetic nanoparticles and was used as an efective catalyst to
prepare α-aminonitriles under mild green conditions. The reaction was conducted
efciently in one-pot as well as stepwise routes. The advantage of this catalyst is that
it utilizes multi-functional catalytic sites such as Lewis acid, Brønsted acid, coor-
dinated transition metals (Cu and Ni), and magnetic CdFe2O4 nanoparticles, which
together have its unique catalytic activity for Strecker reaction (Scheme 2).
Experimental
Instrumentation and materials
All chemicals used in the experiments were purchased from Merck and Fluka and
used as received without further purifcation. All the solvents and reagents were
of analytical grade. Progress of the reactions was monitored by thin layer chro-
matography (TLC) using silica gel impregnated with UV indicator (SIL G/UV
254). Fourier transformation infrared (FTIR) spectra were recorded on a JASCO
FT/IR 4600 spectrophotometer using compressed KBr disk. Known compounds
1
were identifed by matching HNMR and 13CNMR data with pure and authen-
1
tic samples. The HNMR (300 MHz) and 13CNMR (75 MHz) were recorded on a
Bruker AVANCE3 3–300 MHz in pure deuterated chloroform (CDCl3) or dimethyl
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Scheme 2 Catalytic activity of metal incorporated into sulfated zirconium oxide for Sonogashira and
Strecker synthesis
sulfoxide (DMSO-d6) and TMS as an internal standard. Scanning electron micros-
copy images (FE-SEM) were performed using a TESCAN MIRA3 instrument.
Energy-dispersive X-ray spectroscopy (EDX) analyses were done on a FESEM,
JEOL 7600F apparatus equipped with a spectrometer of energy dispersion of X-ray
from Oxford instruments. Transmission electron microscopy (TEM) images were
taken by a Philips EM208 microscope operated at 100 kV. The powder X-ray dif-
fraction (XRD) patterns were obtained on a XRD Philips PW1730 apparatus with
Cu LFF λ=1.540598, voltage and current of 40 kV and 30 mA, respectively, in the
range of 20°–80° (2θ) with a scan speed of 0.05°/s. Electronic spectra (UV–Vis)
were recorded on a SPECORD 210 PLUS Analytik Jena AG spectrophotometer.
Thermogravimetric analyses (TGA) of the samples were performed on a Q600 -TA
company under N2 atmosphere with a heating rate of 10 °C/min. Vibrating Sample
Magnetometer (VSM) analyses of the samples were conducted on a Lake Shore Cry-
otronics 7407 at room temperature. ICP experiments were performed by a VARIAN
VISTA-PRO CCD simultaneous ICP-OES instrument. The acidity of the catalyst
surface was measured using the pyridine adsorption assay in accordance with the
procedure presented in [27, 28].
Preparation of ZrO2/SO42−/Cu/Ni
ZrO2/SO42−/Cu was prepared according to previously reported procedure [23, 24].
Briefy, ZrCl4 (2.3 g, 10 mmol) was dissolved in water (10 mL) followed by drop-
wise addition of 1 N NH3 solution (10 mL). The ammonia solution was added dur-
ing 30 min until the pH of the solution reached to 11. The resulting solution was
1 3

M. A. Nasseri et al.
aside for 24 h at room temperature. Zr(OH)2 as a powder was obtained by centrifu-
gation of the solution and washing with deionized water (5×20 mL, pH 7) followed
by drying at 100 °C for 24 h. Zr(OH)4 was impregnated by a (NH4)2SO4 solution
(2.5 g in 50 mL distilled water; mixing ratio of Zr: S, 1:3). Sulfated zirconium oxide
(ZrO2/SO42−) was obtained after dying at 100 °C (24 h) and calcination at 650 °C
2−
for 3 h (10 °C.min−1). In order to incorporation of Cu ions to ZrO2/SO4 (0.1 g)
was impregnated in a solution of Cu2+ (0.1 g Cu(OAc)2.H2O in 50 mL water). The
resulting mixture was dried at 100 °C for 12 h followed by calcination at 400 °C
for 3 h (10 °C.min−1). This process was repeated for incorporation of Ni ions to
2−
ZrO2/SO4 framework. The obtained ZrO2/SO42−/Cu/Ni was washed with deion-
ized water, then dried at 80 °C.
Preparation of CdFe2O4@SiO2 MNPs
CdFe2O4 MNPs were prepared using a co-precipitation method. FeCl3·6H2O (1.3 g,
4.8 mmol), FeCl2·4H2O (0.9 g, 4.5 mmol), and Cd(NO3)2·4H2O (1.3 g, 4.2 mmol)
were dissolved in a 600 mL distilled water. Cetyltrimethylammonium bromide
(CTAB, 4.2 mmol) was added to the mixture. The mixture was heated to 65 °C.
Then, 25 mL NaOH 10%wt was added dropwise to the mixture during 60 min until
the pH of the solution reached to 11.0. The resulting dark gray magnetic powder was
separated magnetically using an external magnetic feld, washed with ethanol and
deionized water three times (each 3×10 mL), then dried into oven (50 °C) for 12 h.
Preparation of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
ZrO2/SO42−/Cu/Ni was immobilized on magnetic CdFe2O4@SiO2 NPs by a same
previously reported method [24]. Scheme 3 shows a general schematic for the prepa-
ration of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni.
General procedure for the preparation of α‑aminonitriles catalyzed by CdFe2O4@
SiO2@ZrO2/SO42−/Cu/Ni
One-pot method: In a 10-mL round bottom fask, aldehyde (1.0 mmol), amine
(1.0 mmol), and the catalyst (0.005 g, 0.01 mol % Ni, 0.014 mol % Cu, 2.12 mol %
Zr) were added to 2.0 mL distilled water. Then, KCN (1.5 mmol), and NH4Cl
(1.5 mmol) were added in turn to the mixture. The progress of the reaction was
monitored by TLC: TLCs were performed with extraction of 20 μL of the mixture to
20 μL of ethyl acetate, then the TLC analysis was taken from organic phase. Upon
reaction completion, the catalyst was removed by an external magnetic feld and
the product was extracted by ethyl acetate (3×7 mL). The combined organic layers
were dried over Na2SO4. The pure α-aminonitrile products were obtained by column
chromatography (EtOAc: n-hexane; 17:3; v/v). The recovered catalyst was washed
by hot ethanol (2×10 mL), then dried in oven (50 °C) and reused in next run.
Stepwise method Firstly, imine compounds were simply prepared from condensa-
tion of a variety of aldehydes (1.0 mmol) with amine (1.0 mmol) in ethanol at room
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Scheme 3 A schematic view for the preparation of bimetallic CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
temperature in the presence of the catalyst (0.005 g, 0.01 mol % Ni, 0.014 mol %
Cu, 2.12 mol % Zr). After reaction completion (TLC), the product was fltered,
dried and recrystallized with hot ethanol. For the preparation of α-aminonitriles, in
a 10-ml round bottom fask, imine (1.0 mmol), KCN (1.5 mmol), NH4Cl (1.5 mmol)
were added/dissolved to 2.0 mL water. The reaction progress was monitored as same
as one-pot method based on consumption of imine. After completion of the reaction,
the product was extracted to ethyl acetate (3×7 mL). The combined organic layers
were dried over Na2SO4. The pure α-aminonitrile products were obtained by column
chromatography (EtOAc: n-hexane; 17:3; v/v). The recovered catalyst was washed
by hot ethanol (2×10 mL), then dried in oven (50 °C) and reused in next run.
2,2′‑(1,2‑Phenylenebis(azanediyl))bis(2‑(2‑hydroxyphenyl)acetonitrile) (15a)
1HNMR (300 MHz, CDCl3): δ (ppm)=4.33 (s, 2H), 5.42 (s, 2H), 6.58–6.63
(m, 2H), 6.7–6.78 (m, 2H), 7.04–7.07 (m, 4H), 0.37–7.43 (m, 4H), 9.87 (s, 1H).
13CNMR (75 MHz, CDCl3): δ (ppm)=49.7, 115.2, 115.9, 116.2, 117.5, 119.1,
120.8, 128.5, 131.3, 132.0, 156.3. Anal. Calcd. (%) for C22H18N4: C, 71.34; H, 4.90;
N, 15.13. Found (%): C, 71.36; H, 4.88; N, 15.12.
2,2′‑((4‑Methyl‑1,2‑phenylene)bis(azanediyl))bis(2‑(2‑hydroxyphenyl)acetonitrile)
(15b)
1HNMR (300 MHz, CDCl3): δ (ppm)=2.10 (s, 3H), 4.37 (s, 2H), 4.94 (s, 2H),
6.63 (s, 1H), 6.73 (d, J=7.5 Hz, 1H), 7.00 (d, J=7.5 Hz, 1H), 7.52–7.55 (m, 4H),
1.80–7.83 (m, 4H). 13CNMR (75 MHz, CDCl3): δ (ppm)=20.4, 51.1, 114.0, 116.0,
116.7, 117.2, 119.4, 120.4, 127.7, 129.5, 130.0, 131.3, 155.4. Anal. Calcd. (%) for
C23H20N4: C, 71.86; H, 5.24; N, 14.57. Found (%): C, 71.90; H, 5.20; N, 14.55.
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M. A. Nasseri et al.
2,2′‑((4‑Nitro‑1,2‑phenylene)bis(azanediyl))bis(2‑(2‑hydroxyphenyl)acetonitrile)
(15c)
1HNMR (300 MHz, CDCl3): δ (ppm)=4.64 (s, 2H), 5.48 (s, 2H), 6.72–6.93 (m, 5H),
7.12–7.28 (m, 4H), 7.53 (d, J=7.2 Hz, 1H), 8.16 (s, 1H), 10.05 (s, 1H). 13CNMR
(75 MHz, CDCl3): δ (ppm)=53.0, 107.2, 113.3, 115.0, 115.8, 116.3, 117.4, 121.4,
129.6, 130.4, 133.1, 136.4, 139.1, 157.5. Anal. Calcd. (%) for C22H17N3: C, 63.61;
H, 4.13; N, 16.86. Found (%): C, 63.59; H, 4.15; N, 16.85.
2,2′‑(Cyclohexane‑1,2‑diylbis(azanediyl))bis(2‑(2‑hydroxyphenyl)acetonitrile) (15d)
1HNMR (300 MHz, CDCl3): δ (ppm)=0.97–1.20 (m, 10 H), 4.30 (s, 2H), 5.50
(s, 1H), 6.83–6.93 (m, 4H), 7.35–7.37 (m, 4H), 8.51 (s, 1H). 13CNMR (75 MHz,
CDCl3): δ (ppm)=24.8, 29.6, 42.8, 54.3, 115.4, 116.5, 117.1, 120.8, 129.2, 130.4,
156.7. Anal. Calcd. (%) for C22H24N4: C, 70.19; H, 6.43; N, 14.88. Found (%): C,
70.22; H, 6.44; N, 14.89.
Results and discussion
Catalyst characterization
The catalyst was characterized by various instrumental analyses. Figure 1 shows
FTIR spectra of 2, 3, 5, 6, 7, and 8. The presence of the peak at 3403 cm−1 related
to the hydroxyl groups indicates the formation of Zr(OH)4. Also a series of peaks
at~645–750 is related to Zr–O–Zr stretching vibrations (Fig. 1a). The characteris-
tic peaks corresponding to zirconia solid support at 1143,1044, and 944 cm−1 show
symmetric and asymmetric stretching vibrations for S–O and S=O bonds, respec-
tively (Fig. 1b) [29]. Zr–O–Zr vibrations are also seen in the 466–746 cm−1 region.
In addition, the peak appeared at 3420 cm−1 and the moderate intensity peak at
1636 cm−1 were attributed to O–H stretching and bending vibrations, respectively
[30, 31]. Incorporation of copper and nickel ions resulted in the appearance of Cu–O
and Ni–O vibration peaks at 850–450 cm−1 (Fig. 1c). The peak appearing at 500 and
698 cm−1 (strong) was attributed to Cu–O and Ni–O stretching vibrations, respec-
tively (Fig. 1c). According to these results it can be concluded that the metals are
coordinated by sulfate groups on the surface of the zirconia substrate, which is com-
pletely in agreement with the literature [22–24].
However, the metals are likely to be coordinated between zirconia groups. The
strong absorption at region 520 cm−1 shows Cd–O stretching vibrations in CdFe2O3
nanoparticles. In addition, the strong and broad absorption at 3300 cm−1 shows the
stretching vibrations associated with the water molecules embedded in the nanopar-
ticle crystal structure (Fig. 1d). The presence of strong-broad peak at~1100 cm−1
indicates asymmetric Si–O-Si stretching vibrations in CdFe2O4@SiO2, confrming
the successful coating of CdFe2O4 nanoparticles by silica shell. Figure 1f shows
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Fig. 1 FTIR spectra of a 2, b 3, c 5, d 6, e 7, and f 8
the spectrum obtained from the immobilization of zirconia (ZrO2/SO42−/Cu/Ni)
on magnetic nanoparticles, which the peaks around at~450–750 cm−1, shows the
vibrations related to Cu–O, Ni–O, Cd–O and Zr–O–Zr bonds.
Figure 2 shows the XRD patterns for ZrO2/SO42−, 4, 5, 6, and 8 compounds. The
presence of high intensity peaks at 2θ=30.3°, 50.4°, and 60.3° confrmed the tetrag-
2−
onal crystal structure (JCPDS 17-0923) of ZrO2/SO4 in agreement with those
reported in the literature (Fig. 2a) [24, 28, 32]. In fact, a mixture of the tetragonal
and monoclinic phases was found in the pattern, which represented by hexagon and
pentagon symbols in the pattern, respectively (Fig. 2a). The peaks related to mono-
clinic structure were appeared at 2θ=24.1° and 28.3° [24]. This difraction pattern
indicates that impregnation of zirconium oxide with sulfate groups causes a strong
efect on the zirconia phase from a thermodynamically more stable monoclinic to a
metastable tetragonal phase due to the strong interaction of the sulfate groups with
the zirconia [24, 28]. The change in X-ray difraction pattern with the advent of new
peaks after incorporation of the copper and nickel metals confrms their incorpora-
tion into the zirconium oxide structure as the solid support. It will be shown below
(control experiments) that this modifcation of the structure leads to an improvement
in the properties and performance of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni NPs from
a catalytic point of view. The presence of new peaks at 2θ=35.5°, 38.7°, 48.5°,
66.0°, and 68.0° matched well with the indices (002), (111), (202), (311), and (113),
that were perfectly consistent with the presence of the CuO phases (thermodynami-
cally prepared) in the ZrO2/SO42− solid support [33, 34]. As shown in the difraction
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M. A. Nasseri et al.
Fig. 2 XRD pattern of a ZrO2/
SO42−, b 4, c 5, d 6, and e 8
2−
pattern of ZrO2/SO42−/Cu (4) (Fig. 2b), the phases of the ZrO2/SO4 structure are
quite clear confrming the preservation of its crystalline structure. Incorporating
copper, however, has caused some shift at the corresponding peak locations. The
presence of four low intensity peaks at 2θ=38.6°, 43.2°, 63.1°, and 76° well shows
the NiO-related phases corresponding to indices (111), (200), (220) and (311),
respectively (Fig. 2c, marked with four point star) [35].
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Cu/Ni‑doped sulfated zirconium oxide immobilized on…
As-synthesized CdFe2O4 magnetic NPs were characterized by nine characteristic
peaks at 2θ=30.4°, 32.2°, 36.0°, 44.3°, 50.2°, 56.9°, 62.5°, 66.1°, and 68.3° cor-
responds to (311), (222), (400), (331), (422), (511), (440), (533), and (622) indi-
ces. The pattern was completely in agreement with the crystal structure of CdFe2O4
NPs and could be well indexed to the single type of CdFe2O4 (JCPDS File No.
22-1063) [36, 37]. A difraction peak at~19° (designated by star) represents the
presence of α-Fe2O4 phases (Fig. 1d) [38]. The X-ray difraction pattern of the cata-
lyst, CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni (8), well illustrates the phases related
to sulfated ZrO2/SO42−/Cu/Ni and CdFe2O4. Also, the negligible amount of shift
of the peaks related to both phases and the partial reduction of the peaks from the
crystalline state confrmed the immobilization of the sulfated zirconium groups on
CdFe2O4 nanoparticles (Fig. 1e). In addition, from the X-ray difraction pattern of
8, the functionalization of the CdFe2O4 NPs did not lead to the crystalline structure
(phase) change, which the phases corresponding to both remained intact.
The average crystalline size of the samples were calculated by Debye–Scherrer’s
equation: d=0.9λ/βCosβ; where λ is the source wavelength equal to 0.154 nm (Cu
Kα), θ is the Bragg difraction angle, and β is the width of the XRD peak at half
maximum height [39]. Accordingly, the particle sizes of ZrO2/SO42−, 4, 5, 6, and 8
were calculated as 12, 12, 14, 32, and 46 nm, respectively.
Figure 3A shows the thermal behavior of the CdFe2O4, SiO2@ZrO2/SO42−/Cu,
SiO2@ZrO2/SO42−/Cu/Ni, and CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni samples by
TGA analysis. The CdFe2O4 nanoparticles showed only 1.5% weight loss, indicat-
ing high thermal stability. The slight loss in weight at 300 °C was attributed to the
trapped water in the nanoparticle structure (Fig. 3A–a), which is also well known in
the corresponding IR spectra (Fig. 1d).
SiO2@ZrO2/SO42−/Cu and SiO2@ZrO2/SO42−/Cu/Ni have similar thermal
decomposition behavior, but compound 5 exhibited less weight loss and subse-
quently greater stability (Fig. 3A–b, c). The two weight losses at 210 °C and 350 °C,
respectively, indicate the escape of water from the surface and into the crystal-
line structure of the particles. The results are quite consistent with the proposed
structure for sulfated zirconium oxide particles in the literature [22–24], in which
Fig. 3 A TGA spectra of (a) CdFe2O4, (b) ZrO2/SO42−/Cu, (c) ZrO2/SO42−/Cu/Ni, and (d) CdFe2O4@
SiO2@ZrO2/SO42−/Cu/Ni. B VSM curves of (a) CdFe2O4, (b) CdFe2O4@SiO2, and (c) CdFe2O4@
SiO2@ZrO2/SO42−/Cu/Ni
1 3

M. A. Nasseri et al.
water molecules are located at the particle surface and play the role of Brønsted
acid. Further coordination by Ni ions in 5 imposes more rigid structures on ZrO2/
SO42−/Cu and results in greater thermal stability. The third peak can be attributed
2−
to the decomposition and oxidation of coordinated metals in the ZrO2/SO4 struc-
ture. Sulfate groups are separated from the surface at temperatures between 660
and 680 °C (the fourth weight loss in the b and c spectra) and produce a weight
loss of about 4%. The thermal behavior of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
nanoparticles is shown in Fig. 3A—d. The immobilization of ZrO2/SO42−/Cu/Ni
on CdFe2O4@SiO2 magnetic nanoparticles shows a continuous weight loss with a
gentle slope up to~510 °C, indicating the decomposition of diferent groups on the
nanoparticles. Most of the weight loss occurs at~775° C with a~5% weight loss,
which is related to the decomposition of sulfate groups. It is clear from the results
that all compounds have good thermal stability to 900 °C, with less than 10% weight
loss for all compounds up to this temperature, which also refects their potential use
in industrial applications.
Figure 3B illustrates the study of magnetic behavior of CdFe2O4, CdFe2O4@
SiO2, and CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni nanoparticles by VSM analysis.
The saturation magnetization for CdFe2O4 and CdFe2O4@SiO2 catalysts are 25.7,
20.0, and 7.1 emu.g1 respectively (Fig. 3a–c). Zero coercivity for nanoparticles indi-
cates that they have superparamagnetic properties [39]. The magnetization decrease
of 12.85 emu.g−1 clearly indicates the high and successful immobilization of sul-
fated zirconium oxide on CdFe2O4@SiO2 NPs (Fig. 3B–b, c). Despite this remark-
able reduction, the nanoparticles were well and easily separated from the reaction
medium by a simple external magnetic feld.
The presence of elements in the catalyst was identifed by EDX analysis. Figure 4
shows O, Si, Fe, Ni, Cu, Zr, and Cd elements. The Cu and Ni contents were 0.19 and
0.12 wt %, respectively, which were 0.014 mol %Cu and 0.01 mol %Ni according to
the reaction of the catalyst Strecker used in the reaction (Fig. 4, inset table).
Fig. 4 EDX analysis of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
The morphology and particle size of ZrO2/SO42−/Cu and CdFe2O4@SiO2@ZrO2/
SO42−/Cu/Ni particles were studied by FE-SEM and TEM methods. The results of
previous analyzes [23] showed that the ZrO2/SO42−/Cu particles have an irregular
2−
(heterogeneous) shape, which can be due to the agglomeration of ZrO2/SO4 par-
ticles by copper metal ions (Fig. 5a–d) [40]. TEM image in Fig. 5c, d, shows parti-
cle size, size distribution, and morphology of the NPs. According to TEM images,
ZrO2/SO42−/Cu nanoparticles have an average size of 15 nm and are irregular in
shape with homogenous morphology.
Figures 6a, b shows the FE-SEM and TEM images of CdFe2O4@SiO2@ZrO2/
SO42−/Cu/Ni nanoparticles with an average size of 50 nm resulting from the sta-
bilization of ZrO2/SO42−/Cu/Ni nanoparticles on CdFe2O4 magnetic nanoparticles
(Fig. 6a, b). The resulting particles have a more homogeneous and spherical mor-
phology than ZrO2/SO42−/Cu particles, probably due to the spherical structure of
CdFe2O4 nanoparticles. The FE-SEM image also shows this more homogeneous
morphology (Fig. 6b).
The acidity of the catalyst surface was determined by the pyridine adsorption test
[22, 23]. For this purpose, the catalyst was exposed to diferent concentrations of
pyridine (0.0005, 0.001, 0.005, 0.01, 0.05, and 0.1 M) and the amount of adsorption
Fig. 5 a, b FE-SEM, and c, d TEM images of ZrO2/SO42−/Cu [23]
1 3

M. A. Nasseri et al.
Fig. 6 a FE-SEM and b TEM images of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
was measured based on the peak intensities of the pyridine († ESI, Fig. S1). Treating
pyridine with the catalyst resulted in two new peaks in 1603 and 1446 cm−1, respec-
tively. Pyridine adsorption continued at higher concentrations of pyridine where the
peak B/L ratio was constant. Therefore, the concentration of acidic sites on the cata-
lyst was calculated as 0.19 mmol.g−1 (B/L=1.9 (IB/IL)) using the molar coefcient
[41].
Optimization of reaction parameters
In order to fnd the optimum conditions for the preparation of α-aminonitriles, the
reaction parameters including solvent, temperature and catalyst were investigated.
For this purpose, the reaction of benzaldehyde, aniline, KCN, and NH4Cl in the
presence of CdFe2O4@SiO2@ ZrO2/SO42−/Cu/Ni was selected as the model reac-
tion. The solvent efect was frst studied in which a range of solvents with diferent
polarity and properties were tested (Fig. 7a). The water had the best efect by pro-
viding 97% efciency at room temperature, and then solvents such as DMF, DMSO,
Fig. 7 Optimization of a solvent and b catalyst amount for the Strecker reaction of benzaldehyde, ani-
line, KCN, and NH4Cl in the presence of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni. Reaction conditions:
Except noted the reaction was conducted at room temperature for 1 h. Benzaldehyde (1.0 mmol), aniline
(1.0 mmol), Cat., KCN (1.5 mmol), NH4Cl (1.5 mmol), solvent (2.0 mL).* 1:1; v/v (2.0 mL)
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
H2O: EtOH (1: 1 (v/v)) yielded similar efciencies of 85%. On the other hand, non-
polar solvents did not produce signifcant efciencies for this reaction. Remarkably,
the medium to high efciencies were obtained for all solvents at room temperature.
The results are quite consistent with those reported with zirconium oxide based
catalysts [22, 24]. Sulfated zirconium oxide has many sulfated polar groups (along
with various Lewis and Brønsted acid sites [23, 25]) on the surface which provides
a favorable environment for the preparation of α-aminonitrile compounds due to the
presence of NH4Cl and KCN salts in the high dielectric constant water solvent. The
reaction gave 80% efciency in solvent-free conditions. To investigate the efect of
reaction temperature, the reaction was studied at 50 °C and refux in water solvent.
As shown in Fig. 7a, no change in efciency was achieved at 50 °C, while refux
resulted in a slight decrease in efciency (90%). Diferent amounts of catalyst from
0.001 to 0.02 g were studied for model reaction in water at room temperature (1 h).
The results, as shown in the diagram in Fig. 7b, show the optimum value of the cata-
lyst is 0.005 g. Efciency declined sharply at lower values and at higher values no
positive or negative efects on efciency were observed (Fig. 7b).
Catalytic activity
The catalytic activity of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni was evaluated by a
variety of diferent aldehydes with aniline under the obtained optimum conditions.
As shown in Table 1, high to excellent efciencies (98–75%) for all aldehydes,
whether bearing electron donor or withdrawing substituents, were obtained within
1–3 h. However, aldehydes containing the electron donor group produced higher
efciencies than those containing the electron withdrawing groups (compare 12b
with 12c). Remarkably, no cyanohydrin product is formed (due to the presence of
water in the compound) and the catalyst selectively results in the α-aminonitrile
product.
Satisfactory results for the preparation of α-aminonitriles from aldehydes encour-
aged us to apply the catalyst capability to convert ketones to the corresponding
α-aminonitriles. For this purpose, several derivatives of the ketones were converted
to the corresponding α-aminonitriles by the catalyst under obtained optimized con-
ditions. The results are summarized in Table 2, where signifcant efciencies were
observed only for compounds 14f and 14c. Given the earlier observations and the
mechanism that will be proposed in the future, it seems that the iminium intermedi-
ate here is the rate determining step.
For this purpose, the ketimine derivatives shown in Table 2 were prepared sepa-
rately and then converted to corresponding α-aminonitriles (stepwise method). Ef-
ciency was improved under stepwise conditions, which showed that the formation of
the iminium intermediate would limit the rate.
Finally, the possibility of the preparation of α-aminonitriles from aliphatic
aldehydes/ketones was also studied. As shown in Table 2, the preparation of
α-aminonitriles by aliphatic aldehydes/ketones cyclohexanone and heptane-2-one,
pentanal, and isobutyraldehyde was performed with aniline in the presence of the
catalyst under optimum conditions. Similar results were obtained for ketones for
1 3

M. A. Nasseri et al.
Table 1 One-pot as well as stepwise preparation of α-aminonitriles catalyzed by CdFe2O4@SiO2@
ZrO2/SO42−/Cu/Nia
Entry
R1
Product 12
Efciency
One-pot
Stepwiseb
Time (h)
Time (h)
Yield (%)c
Yield (%)c
1
2
3
4
H
12a
12b
12c
12d
12e
12f
12g
12h
12i
1
2.5
2
2
2
1
1
3
1
97
75
85
80
89
98
98
75
96
94
70
4
5
4.5
4
6
2.5
3.5
7
3
5
95
70
85
70
80
95
95
80
88
90
70
2-NO2
2-OMe
4-CN
4-Cl
2-OH
Cynnamyl
4-OH
2-furyl
4-Me
5
6d
7d
8
9
10
11
12j
12k
1.5
3
4-Br-2-OH
8
aReaction conditions: Aldehyde (1.0 mmol), Aryl amine (1.0 mmol), Cat. (0.005 g, 0.01 mol %Ni,
0.014 mol %Cu, 2.12 mol % Zr), KCN (1.5 mmol), NH4Cl (1.5 mmol), H2O (2.0 mL), R.T. For stepwise
method, 1.0 mmol of pure imine compound was used as the starting material
bThe reaction was performed with isolated imine compounds prepared by condensation of an aldehyde
with an amine in EtOH at 50 °C. Recrystallization from hot EtOH as used for purifcation
cIsolated yield
dQuantitative yield
one-pot and stepwise methods for aliphatic derivatives. As shown in Table 2, the
compounds 14i–14l produced better performance under stepwise conditions.
Finally, the ability of the catalyst to prepare bis-aminonitrile compounds was
studied. For this purpose, o-phenylenediamine was reacted with various aldehydes
in the presence of the catalyst and under optimum conditions. Moderate efciencies
were obtained for compounds 15a–15d (Scheme 4).
The results showed that the desired α-aminonitrile product was formed in the
presence of copper salt as well as the catalyst 8. However, this only occurs for
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Table 2 One-pot as well as stepwise preparation of α-aminonitriles from ketone and aliphatic aldehyde
catalyzed by CdFe2O4@SiO2@ZrO2/SO42−/Cu/Nia
Entry
13
Product 14
Time (h)
One-pot
Yield (%)
One-pot
Stepwise
Stepwise
1
2
3
4
5
6
7
8
Acetophenone
Benzophenone
14a
14b
14c
14d
14e
14f
14g
14h
14i
4
8
8
12
12
8
8
12
8
8
8
4
6
6
8
8
4.5
6
8
6
96
30
75
13
20
70
50
30
60
80
70
86
96
50
75
40
55
70
65
50
75
80
80
80
Phenyl ethyl ketone
4′-Chloroacetophenone
p-Nitroacetophenone
1-(p-Tolyl)propan-1-one
4′-Methoxyacetophenone
4-Acetylpyridine
Cyclohexanone
Butan-2-one
Decanal
Acetone
9
10
11
12
14j
14k
14l
5
7
7
8
Scheme 4 One-pot preparation of bis-α-aminonitriles catalyzed by CdFe2O4@SiO2@ZrO2/SO42−/Cu/
Ni under optimized conditions. Reaction conditions: salicylaldehyde (2.0 mmol), aryl amine (1.0 mmol),
Cat. (0.005 g, 0.01 mol %Ni, 0.014 mol %Cu, 2.12 mol % Zr), KCN (3.0 mmol), NH4Cl (3.0 mmol),
H2O (2.0 mL), R.T
four-dentate salen-type intermediates (Scheme 4). On the other hand, salen-type
compounds prepared with aldehydes other than salicylaldehyde lead to the product
of α-aminonitrile only in the presence of the catalyst 8, whereas in the presence of
copper salt no reaction occurs. The lack of strong interaction of copper with these
ligands results in the lack of a suitable nucleophilic attack on the iminium interme-
diate and the formation of the α-aminonitrile product.
In another experiment, the copper salen complex 16 was frstly prepared. No
α-aminonitrile products were formed either in the presence of catalyst or in the
presence of copper salt. According to the observations, it can be concluded that
1 3

M. A. Nasseri et al.
the preparation of α-aminonitrile compounds using salicylaldehyde leads to a four-
dentate ligand which, with its partial coordination, weakens the imine bond and
subsequently nucleophilic attack of the cyanide ion give the desired α-aminonitrile
(Scheme 5), a completely diferent mechanism to the catalyst 8 (Scheme 5). Salen
complexes do not transform to α-aminonitrile product, because most of the electron
clouds holds the imine bond.
Control experiments
In order to elucidate the catalytic activity of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
in the preparation of α-aminonitriles, several control experiments were performed
on the model reaction under optimum conditions (Table 3). The results are summa-
rized in Table 3. The results showed that the catalytic activity of CdFe2O4@SiO2@
ZrO2/SO42−/Cu/Ni is unique compared to the other catalyst components alone: (1)
Reaction in the absence of any catalyst showed no detectable efciency (Table 3,
entry 1); (2) the sulfate groups on the zirconium substrate signifcantly increase its
acidity and subsequently increase the efciency, such that the compounds ZrCl4 and
Zr(OH)2 with low efciency (~0–12%, Table 3, entries 2,3) after modifcation with
sulfate groups produced 45% efciency for 12a; (3) Copper and nickel salts pro-
vided similar efciencies of 30% in water (Table 3, entries 6,7); (4) signifcantly,
the remarkable increase in efciency after the incorporation of copper and nickel
ions into the zirconium framework indicates that (i) the metals are in the zirconium
framework in such a way that a suitable and strong catalytic active site is provided
besides sulfate groups, and (ii) the simultaneous presence of copper and nickel in
the catalyst structure increases the efciency by up to 90%, which can be consid-
ered as a synergistic efect (Table 3, entries 8,9); (5) CdFe2O4 and CdFe2O4@SiO2
nanoparticles showed poor efciency, but after the immobilization of 5 on the mag-
netic nanoparticles (7), the reaction proceeded completely (Table 3, entry 12). This
improvement in efciency can probably be attributed to the increased surface area
(or aspect ratio) of the nanoparticles and their small catalytic efect. The results
illustrate well the process of improvement of the catalytic activity of CdFe2O4@
Scheme 5 Proposed reaction pathway for the preparation of bis-α-aminonitriles catalyzed by Cu2+ and
CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Table 3 Control experiments for the preparation of 12a from the one-pot reaction of aniline, benzalde-
hyde, KCN, and NH4Cl catalyzed by CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni (8)
Entry
Catalyst
Yield (%)
1
2
3
4
–
N.R.
Trace
12
Trace
45
ZrCl4
Zr(OH)4 (2)
(NH4)2SO4
2−
5
ZrO2/SO4
6
Cu(OAc)2.H2O
30
7
Ni(OAc)2.4H2O
30
8
9
10
11
12
4
78
90
15
10
5
CdFe2O4
CdFe2O4@SiO2
8
97
SiO2@ZrO2/SO42−/Cu/Ni by modifying various groups to synthesis one of the most
important and most widely used compounds, α-aminonitriles, in organic and medi-
cal chemistry, which ultimately results in quantitative efciency.
Mechanism studies
The results obtained on the one-pot preparation of α-aminonitriles showed that
it passes through a imine intermediate (based on TLC and isolation characteriza-
tion of imine intermediate). On the other hand, the absence of NH4Cl results in
a severe loss of efciency, which is another evidence of the formation of imine
intermediate. The presence of ammonium salt appears to form the active cyanide
ammonium salt for cyanation of iminium bond (Scheme 6). On the other hand,
due to the multifunctionality of the catalyst and in accordance with the results of
the control experiments, it can be suggested that both amines (via sulfate groups)
and aldehydes (by metal centers) are activated by the catalyst. As shown in the
proposed mechanism (in agreement with the literature [2, 6, 42]) in Scheme 6,
aldehyde and amines are frst activated by groups on the catalyst surface and
facilitate the nucleophilic attack of the amine to aldehyde carbonyl bond. Ami-
nohydrin intermediates are also activated by the catalyst surface groups and by
eliminating a water molecule it creates an imine intermediate. Cyanide salts,
resulting from an ion exchange reaction with ammonium chloride, form NH4CN,
1 3

M. A. Nasseri et al.
Scheme 6 A plausible proposed mechanism for the preparation of α-aminonitriles in aqueous media cat-
alyzed by CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni
which itself forms an active HCN species for the Strecker reaction upon removal
of an ammonia molecule. The nucleophilic attack on the catalytically activated
imine compound produces the desired α-aminonitrile product. The catalyst also
returns to the cycle after this step.
One of the most important characteristics of a catalyst and its superiority over
a homogeneous catalyst is its ability to recover and re-use it without loss its cata-
lytic activity [43]. The recoverability of CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni was
studied on the model reaction. For this purpose, the catalyst was recovered by an
external applied magnetic feld for 8 consecutive runs and reused. The reaction
efciencies were recorded at a fxed time of 1 h (Fig. 8). Also, the amount of
copper, nickel and cadmium leaching was measured at each recovery time of the
residual solution. Separate specifc lamps were used to determine the leaching of
each metal. The results showed no loss for any of the metals until the ninth cycle,
completely consistent with the literature [22–24]. These results not only refect
the stability of the catalyst, but also show that the Cu and Ni ions are strongly
2−
coordinated into the structure of the ZrO2/SO4 and are also responsible for its
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
Fig. 8 Recycling/leaching studies of the recovered catalyst after the ninth runs for the model Strecker
reaction (one-pot method) under optimized conditions for the preparation of 3a
catalytic activity. In addition, the drop in efciency for preparation of 3a and
catalysis yield in consecutive cycles was negligible (Fig. 8).
In order to investigate the stability, morphology and structure of the catalyst dur-
ing successive cycles, the recovered catalyst after the ninth cycle was studied by
FTIR, XRD, FESEM and TEM analyzes. As shown in Fig. 9a, b, the FTIR and XRD
Fig. 9 A FTIR spectra and B the XRD patterns of the fresh (a) and the recovered catalyst after the ninth
runs for the model Strecker reaction (one-pot method) under optimized conditions. C FE-SEM and D
TEM images of the recovered catalyst after 8th run
1 3

M. A. Nasseri et al.
spectra of the recovered catalyst are quite similar to that of the freshly prepared cata-
lyst, refecting confrmation of the structure and high stability of the catalyst under
reaction conditions. No shifts in the peaks as well as the existence of extra peaks in
the recovery spectra are observed, which indicates that the catalyst is heterogene-
ous. In addition, by comparing the FESEM and TEM images of the fresh—with
recovered—catalyst, it can be concluded that the morphology of the catalyst remains
completely intact and no changes in morphology (shape and size) and agglomera-
tion are observed (Fig. 9c, d).
Scalability of the method was also investigated in large quantities (gram scale).
To study the potential of the present method for larger scales, the one-pot reac-
tion of aniline, benzaldehyde, KCN, and NH4Cl was performed in the presence of
CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni in water at room temperature, as a model reac-
tion (Table 4). The reactions were performed with 50, 100, 200, and 500 mmol of
benzaldehyde. As shown in Table 4, the process demonstrated a direct scalability
and didn’t found any considerable loss in efciency of 12a even at larger quantities.
However, a reasonable loss in yield of 12a was observed as the amount of benzalde-
hyde rises [23].
Conclusion
A new, general and efcient method has been developed for transformation of a vari-
ety of aliphatic, aromatic aldehydes and ketones to the corresponding α-aminonitriles
using a multifunctional recyclable CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni nanocata-
lyst. The characteristics of the catalyst were studied by various analyses including
FTIR, TGA, VSM, XRD, EDX, FE-SEM, and TEM. Moderate to high efciencies
was achieved for the α-aminonitrils in water at room temperature in the presence of
CdFe2O4@SiO2@ZrO2/SO42−/Cu/Ni (0.01 mol %Ni, 0.014 mol %Cu, 2.12 mol %
Zr). The activity of the catalyst was evaluated by various control experiments. The
catalyst could be recycled for at least 9 consecutive runs by a simple external magnet
without any considerable loss in catalytic activity. The leaching studies for Ni, Cu,
Table 4 Gram scale production
Entry
mmol of benzalde- Time (h)
hyde
Yield (%)b
of 12a from the one-pot reaction
of aniline, benzaldehyde,
KCN, and NH4Cl catalyzed by
1
2
3
4
5
1
1
1
1
1
1
97
94
90
86
81
2−
CdFe2O4@SiO2@ZrO2/SO4
/
50
Cu/Ni (8)a
100
200
500
aExcept entries 1, 2, the reactions were performed in a 1-L round
bottom fask and the reactions were mechanically stirred. All experi-
ments were performed in water at room temperature. For each entry,
the amounts of water, the catalyst, and reactants were proportional to
the amount of benzaldehyde
bIsolated yield
1 3

Cu/Ni‑doped sulfated zirconium oxide immobilized on…
and Zr didn’t detect any metal leaching. FTIR, XRD, FE-SEM, and TEM analyses
from the recovered catalyst confrmed its stability and structure. Mild reaction con-
ditions, zero metal leaching, various potential active sites, magnetically recyclable,
applicable for a variety of aldehyde and ketones, high mechanical and thermal sta-
bility are some of the advantages of the catalyst that make it as a suitable alternative
methodology for the preparation of α-aminonitriles. This system provides a suitable
platform for incorporation of a variety of transition metals so as to catalyze organic
reactions, which is now being studied in our lab.
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