Fabrication of Ag/γ-Fe2O3@TiO2 hollow magnetic core-shell nanospheres as highly efficient catalysts for the synthesis of β-enaminones

Article abstract of DOI:10.1039/c5ra14878b

Herein, we describe a method to prepare hollow magnetic mesoporous sphere catalysts (Ag/γ-Fe₂O₃@meso-TiO₂). The core-shell strategy efficiently prevents the aggregation of Ag NPs in the high temperature calcination process and the leaching of Ag NPs for the catalytic reaction in the liquid phase. The catalyst is characterized by TEM, XRD and ICP-AES. Moreover, the catalyst exhibited improved activity for the synthesis of β-enaminones, and it could be easily recovered by an external magnet from the reaction mixture and recycled five times without any significant loss in activity.

Full text of DOI:10.1039/c5ra14878b

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Fabrication of Ag/γ-Fe O @TiO hollow magnetic core-shell nanospheres as a highly
2
3
2
efficient catalyst for synthesis of β-enaminones
a
a
a
a
a
a
a
Hongfei Huo , Xinzhe Li , Xingchun Zhou , Lixin Jiao , Shiling Zhao , Le Zhang , Wenzhu Li , Shuwen
a
a
Received 00th January 20xx,
Accepted 00th January 20xx
Li and Rong Li
2 3 2
Herein, we describe a method to prepare hollow magnetic mesoporous spheres catalyst (Ag/γ-Fe O @meso-TiO ) . The
DOI: 10.1039/x0xx00000x
core-shell strategy efficiently prevents the aggregation of Ag NPs in the high temperature calcination process and the
leaching of Ag NPs for the catalytic reaction in a liquid phase. The catalyst is characterized by TEM, XRD, ICP-AES.
Moreover, the catalyst exhibited improved activity for synthesis of β-enaminones, and it could be easily recovered by an
external magnet from the reaction mixture and recycled five times without any significant loss in activity.
www.rsc.org/
6
14
supported
sulfuric
acid,
copper
nanoparticles,
1
. Introduction
1
5
montmorillonite K10 under microwave irradiation
or
The βꢀenaminones and βꢀenamino esters prepared by
6
ultrasound. Although the most of reported homogenous
catalysts are active for this reaction, they always have some
drawbacks such as high cost, and long reaction time. Therefore,
it is significant to develop an economical and easily recyclable
catalyst.
inexpensive raw materials, with very stable structural motifs are
considered as valuable precursors in organic synthesis. As the
enaminones combine three electrophilic and two nucleophilic
sites present within the enaminone functional group, they were
1
2
used as significant intermediates for the preparation of various
heterocyclic compounds e.g. functionalized pyridinꢀ2(1H)ꢀones
which have been used as versatile intermediates in the synthesis
of a wide range of nitrogenꢀcontaining heterocycles, such as
It is well known that noble metal NPs (NMNPs) possess
outstanding catalytic performance due to their versatile,
16
tunable, sizeꢀ, shapeꢀ and composition dependent properties
.
However, the migration, sintering or aggregation of NMNPs
3
pyridine, piperidine, quinolizidine, and indolizidine alkaloids
constantly result in rapid decay of catalytic activity and
4
5
and biologically active compound such as therapeutic agents
which were employed as synthons of different important
17,18
stability.
Hence, it is crucial and challenging to develop
various strategies to effectively synthetize and utilize NMNPs
catalysts with desirable dimensions and improved catalytic
6
6
7
antibacterial, antiꢀinflammatory, antitumor agent , dopamine
autoꢀreceptor agonists, acetylcholinestersase inhibitors,
performance.
Recently,
because
hollow
coreꢀshell
8
oxytocin antagonists and anticonvulsants. They even served as
nanostructures possess desirable shell components, variable
hollow space sizes, and different encapsulated species in the
interior spaces, they have attracted a great deal of interest.
Hollow coreꢀshell structured materials are considered as an
efficient method to inhibit undesirable sintering and
synthons for βꢀaminoacids, γꢀaminoalcohol which are a class of
very stable compounds useful in asymmetric catalysis as a
1
chelating agent . Due to their extensive application, it is very
important to search for a convenient and efficient method for
the synthesis of this type of compounds. A variety of methods
for the synthesis of βꢀenaminones and βꢀenamino esters were
developed. Among the various methods, the condensation of
19, 20, 21, 22, 23, 24
aggregation of the noble metal particles.
Because the coreꢀshell structures have the possibilities for new
physical and chemical characteristics, often different and
improved from those of the constituent components, and it
opens new opportunities for their successfully application in
various fields like catalysis, optoelectronics, separation
1
,3ꢀdicarbonyl compounds with amines in aromatic solvents
was the most simple and straightforward route for their
synthesis. However, what is tedious is that it usually required
the azeotropic removal of water. A few modified procedures
25
technology, coatings, and additives. There are some reports
9
3
have been reported using various catalysts such as Sc(OTf) ,
on noble metal related coreꢀshell materials (e.g. Pt@C,
1
0
8
11
12
CoCl
2
•6H
2
O, ZrOCl
2
•8H
2
O, Zn(OAc)
2
•2H
2
O, NaAuCl
4
,
Pt@SiO
2 2
, Pd@SiO ) which showed superior catalytic activity
1
3
6
SnCl
4
,
silicaꢀsupported antimony (III) chloride, silicaꢀ
in hydrogenation, oxidation, reforming and coupling
2
0, 22, 26, 27
reactions.
If replacing the unreactive silica or carbon
shells which only play a dispersion role of the active
component, and the synergistic effect between the NMNPs and
the shells was quite weak, with oxides, such as CeO and
2
2
8, 29
TiO2,
to enhance the synergistic effect between the NMNPs
and the shells may further improve the catalytic ability. TiO is
2
attractive because of its fascinating features, such as good
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chemical and thermal stability, low toxicity, low cost, various.
3 4
1 g Fe O /Ps was dispersed in 80 mL distilled water and then
polymorphs, excellent electronic and optical properties the mixture was homogenized by ultrasonication for 30 min as
3
0
Moreover, TiO
been recognized as an excellent support for heterogeneous solution and then the mixture solution was homogenized by
catalysis. TiO hollow nanostructures have many characteristics ultrasonication for 30 min as part B. Parts A and B were mixed
2 2
possess advantageous properties and has long part A, 0.5 g SnCl was introduced to 100 mL 0.02 M HCl
2
like reduced diffusion resistance, improved accessibility and together under ultrasonicating for 1 h. Subsequently, the
high active surface area, which provide many new opportunities particles were separated with the help of magnetic force and
for the design of a highly active hollow core/TiO
materials. To our best knowledge, magnetic hollow TiO
encapsulated Ag has not been reported to date.
2
2
ꢀshell quickly washed three times with deionized water. Then, the
shell particles were reꢀdispersed in 75 mL of fresh aqueous solution
of ammoniacal silver nitrate (0.225 M) and sonicated for 1 h.
Herein, we report a method to stabilize Ag (0) on the surface At last, the precipitate was separated by magnetic force, washed
of hollow magnetic mesoporous spheres with Ag, γꢀFe three times with deionized water and then dried at 323 K for 12
2
O
3
nanoparticles embedded in the mesoporous shell, by using Ps h.
spheres as the templates. The fabrication procedure mainly
2
.5 Production of Ag/Fe
Fe @mesoꢀTiO
Typically, 100 mg Ag/Fe
3
O
4
@mesoꢀTiO
2
NPs (Ag/γꢀ
involves six steps as shown in Fig.1. The hollow magnetic
mesoporous spheres performed enhanced synergistic effect, and
decreased leaching of noble metals. The catalyst was used for
synthesis of βꢀenaminones and photoreaction.
2
O
3
2
)
3
O /Ps particles were dispersed in
4
the mixture solution of 40 mL of ethanol and 0.25 g of
cetyltrimethyl ammonium bromide (CTAB). Subsequently, the
solution was homogenized by ultrasonication for 0.5 h. Then,
2
. Experimental section
0
.5 mL tetrabutyl titanate (TBOT) was added to the suspension
under vigorous magnetic stirring. After being stirred at room
O
4
NPs were prepared according to a published temperature for 4 h, 15 mL of ethanol and 3 mL of deionized
2
.1 Synthesis of the magnetite nanoparticles (Fe
The Fe
method with a slight modification . First, 2.0 g FeCl
.8 g of FeCl •6H
O were added to 40 mL deionized water and that the reaction proceeded for 8 h at room temperature under
3 4
O NPs)
3
3
1
•4H
2
O, was added dropwise under vigorous stirring to the system. After
2
4
3
2
stirred vigorously. Second, the above solution was purged with stirring, the resultant particles were separated by an external
nitrogen gas. Then the mixture was heated to 313 K. When magnet and washed with distilled water and ethanol,
temperature is stable, 10 mL of ammonium hydroxide (28 wt%) respectively. After then dried in a vacuum at room temperature
was added rapidly to the solution, and it immediately turned overnight. After that the product was calcined at 773 K in air
black. The compound was kept at 363 K for 2.5 h. A black atmosphere for 7 h to remove Ps sphere, CTAB template and
precipitate was separated by magnetic force, and washed with other organic species and Fe
3
O
4
NPs converte into γꢀFe
2
O
3
deionized water until the pH value of the solution was close to NPs. Finally, the collected sample was treated in a 20% H
2
/N
2
3
ꢀ1
ꢀ1
7
. Finally, the products were dried at 323 K overnight for flow (100 cm min ) at 573 K (ramping rate, 5 K min ) for 3 h
3
ꢀ1
further use.
and passivation (0.1% O
temperature for 3 h. The amount of Ag and Fe in the Ag/γꢀ
Fe @mesoꢀTiO NPs was found to be 16.0 wt% and 7.7%,
Ps latex was prepared referring to a reported method with a based on ICP analysis.
2 2
/N , 40 cm min ) at ambient
2
.2 Preparation of Ps
2
O
3
2
3
2
slight alteration. It was prepared by soapꢀfree emulsion
polymerization copolymerization of styrene (20 g) and crylic
acid (2.5 g) using ammonium persulfate (0.1 g) as an initiator.
2
.6 Typical procedure for preparation of βꢀenaminones
For preparation of βꢀenaminones, 1 mmol of the amine, 2
The reaction was carried out in nitrogen atmosphere at 343 K mmol of dicarbonyl compound, 67.4 mg of the catalyst were
under magnetic stirring for 7 h. The Ps product was separated dissolved in 5 mL of the solvent mixed in cylindrical 25 mL
centrifugation and washed with deionized water and ethanol, vessels in a reaction station equipped with magnetic stirrer bars
respectively, then dried in vacuum at 323 K for 24 h.
and cooling condenser using circulation of cold water. The
reaction temperature was kept in an oil bath and measured by
an alcohol thermometer. After completion of the reaction, when
the mixture was cooled to room temperature, the catalyst was
2
.3 Preparation of polystyrene latex with attached Fe
Fe /Ps)
.5 g Ps and 1.5 g Fe
4 mL hydrochloric acid solution (pH = 2.3), respectively. removed by syringe, and the reaction system was analyzed by
3 4
O NPs
(
3 4
O
2
3 4
O
NPs were dispersed in 60 mL and collected by an external magnet. The solution phase was
8
Then the former suspension was added dropwise into the latter GC (P.E. AutoSystem XL) or GC–MS (Agilent
under vigorous stirring at room temperature. After 6 h, the 6,890N/5,973N). Thereafter, the catalyst was washed with
precipitate, i.e. Fe O
3 4
NPs attached on the surface of Ps methanol and deionized water several times, respectively, after
particles, was separated from the solution with the help of an which the catalyst was dried over vacuum at 333 K to remove
external magnet and washed several times with deionized water the remaining organics. The recovered dried solid catalyst was
until the pH of the solution reached close to 7.
weighed and reused in the next run. In every run, the same ratio
of the substrateꢀtoꢀcatalyst and solventꢀtoꢀcatalyst was kept.
Furthermore, Ag (15.9 wt%) content of the recycled Ag/γꢀ
3 4 3 4
2.4 Loading Ag NPs onto the Fe O /Ps (Ag/Fe O /Ps)
2
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Fe
2 3 2
O @mesoꢀTiO catalyst remained just about the same as the These Ps NPs possess functional groups (ꢀOH, C=O) on the
fresh catalyst, indicating that Ag leaching were negligible.
surface, which offer an important chemical environment for
adsorbing metal ionꢀnanoparticles by electrostatic attraction in
2
.7 Characterization of the catalyst
The synthesized catalyst was confirmed by corresponding composite. The Fe
characterization means. Powder Xꢀray diffraction (XRD) to 15 nm are uniformly distributed on the surface of the Ps NPs.
patterns were carried out at room temperature and performed on Fig. 2c is a TEM image of the Ag/Fe /Ps composite. The Ag
a Rigaku D/maxꢀ2400 diffractometer using CuꢀKa radiation as particles with an average size of about 10 to 15 nm are
the Xꢀray source in the 2θ range of 10ꢀ90 °. The conversion was uniformly distributed on the surface of the Fe /Ps NPs. Using
estimated by GC (P.E. AutoSystem XL) or GCꢀMS (Agilent TBOT as the TiO source and CTAB as a soft template, a thin
,890N/5,973N). Ag content was analyzed by inductively layer of mesoporous TiO is coated onto the Ag/Fe /Ps
acidic solution. Fig. 2a is a TEM image of the Fe
3 4
O /Ps
3
O
4
particles with an average size of about 10
3
O
4
3
O
4
2
6
2
3 4
O
coupled plasma (ICP) on IRIS Advantage analyzer after the sphere. From Fig. 2d the thick of the thin layer of mesoporous
sample was dissolved by HF and HNO . And Ti content was TiO can be seen about 30 to 40 nm. The product was collected
3
2
calculated by the removal of Ag and Fe in the sample. The after the calcination to remove the Ps templates and the organic
morphology and microstructure of the catalyst were groups of CTAB. Then, the Ag/γꢀFe O @mesoꢀTiO catalyst
2
3
2
characterized by transmission electron microscopy (TEM). The was obtained by the reduction with a hydrogen atmosphere. As
TEM images were obtained through Tecnai G2 F30 electron shown in Fig. 2e and Fig. 2f, the TEM images show that Ag, γꢀ
microscope operating at 300 kV, and samples were obtained by Fe O particles were evenly coated with a layer of mesoporous
2
3
placing a drop of a colloidal solution onto a copper grid and shells about 30 to 40 nm thick, while the γꢀFe O3 particles
2
evaporating the solvent in air at room temperature. Specific remained initial their cluster morphologies in the Ag/γꢀ
surface areas were calculated by the BrunauerꢀEmmettꢀTeller Fe O @mesoꢀTiO . Fig. 3e and 3f show the TEM image of the
2
3
2
(BET) method and pore sizes by the BarrettꢀJoynerꢀHalenda Ag/γꢀFe O @mesoꢀTiO , in which wellꢀdispersed Ag NPs with
2 3 2
(
3
BJH) methods using BrunauerꢀEmmettꢀTeller (Tristar II diameter about 5 to10 nm could be observed clearly. Fig. 2g is
020). Inductive coupled plasma atomic emission spectrometer an enlarge TEM image of the Ag/Fe O /Ps composite. The
3
4
(
ICPAES) analysis was conducted with Perkin Elmer (Optimaꢀ Fe O and Ag particles with an average size of about 10 to 15
3 4
4
300DV). Magnetic measurement of Ag/γꢀFe O /@mesoꢀTiO
2
nm are uniformly distributed on the surface of the Ps NPs.
2
3
NPs and γꢀFe O @mesoꢀTiO NPs were investigated with a According to the ICP analysis, the Sn contents were below 0.2
2
3
2
Quantum Design vibrating sample magnetometer (VSM) at wt%, and the Sn presence was not considered as significant in
room temperature in an applied magnetic field sweeping from ꢀ the catalytic performance of the catalyst.
1
5 to 15 kOe.
The elemental composition of the Ag/γꢀFe O @mesoꢀTiO
2 3 2
samples was determined by EDX analysis. The result shown in
Fig. 3f reveals that the prepared products contain Ag, Cu, Ti, C,
Sn, Fe and O. Among these elements, Cu, C and O are
generally influenced by the copper network support films and
their degree of oxidation, and Ti, O, Fe and Ag signals result
from the Ag/γꢀFe O @mesoꢀTiO . From the EDX result, the
2
3
2
signal of Sn element was very weak, revealed that the Sn was
almost completely replaced by Ag.
Fig. 3 shows the XRD patterns between 10 and 90 ° of the
samples. The XRD pattern of Fe O /Ps (Fig. 3a) shows
3
4
characteristic peaks of magnetite NPs, and the sharp and strong
peaks confirm the products are well crystallized. In comparison
with Fe O /Ps, Ag/ Fe O /Ps (Fig. 3b) exhibits four different
3
4
3
4
peaks at 2θ=38.2 °, 44.3 °, 64.6 ° and 77.6 °, corresponding to
the reflections of (111), (200), (220) and (311) crystal planes of
silver, respectively. The XRD pattern of Ag/γꢀFe
TiO (Fig. 3c) shows characteristic peaks of magnetite and TiO
NPs, and the sharp and strong peaks confirm Fe
the products were transformed into γꢀFe
2 3
O @mesoꢀ
2
2
2 3 2
Fig.1 Scheme of the synthetic procedure for preparation of Ag/γFe O @meso-TiO
3
O
4
and TiO
2
in
2
O
3
and rutile,
respectively. Unambiguous evidence of sliver particles in
HMMS is provided via XRD. Meanwhile, the result indicating
the crystalline structure of the support was well maintained in
the Ag samples.
3
. Results and discussion
3
.1 Catalyst preparation and characterization
The morphologies and structures of the products at different
In addition, the surface area and porosity of the Ag/γꢀ
synthetic steps were observed by TEM. Fig. 2a shows the TEM
image of Ps NPs, in which wellꢀdispersed particles with
average diameter about 300 nm could be observed clearly.
Fe
2
O
3
@mesoꢀTiO
2
hollow coreꢀshell nanocomposites have
adsorptionꢀ
been characterized. Fig. 5 displayed the N
2
desorption isotherms and the corresponding poreꢀsize
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Fig. 2 TEM of PS NPs, (b) TEM of Fe
Ag/Fe /Ps@TiO NPs, (e) TEM of Ag/γ-Fe
composite Ag/γ-Fe @meso-TiO
3
O
4
/Ps NPs, (c) TEM of Ag/Fe
3 4
O /Ps, (d) TEM of
2 3 2
distribution curve for Ag/γꢀFe O @mesoꢀTiO . The pore size
was calculated by using the BJH method, as shown in the inset
of Fig. 4. As a result, average pore size was about 9 nm for
O
3 4
2
2 3
O
/Ps@meso-TiO , (f) TEM of final
2
O
2 3
2
.
Ag/γꢀFe
2
O
3
@mesoꢀTiO
2
. The BET surface areas and the
@mesoꢀTiO were 42
cumulative pore volumes of Ag/γꢀFe
2
O
3
2
2
ꢀ1
3
ꢀ1
m g and 0.08 cm g , respectively.
Magnetization curves revealed the superparamagnetic behavior
of the magnetic NPs. The hysteresis loops of Fe /Ps and
Ag/γꢀFe @mesoꢀTiO are shown in Fig. 5. It can be seen that
the magnetic saturation values of these are 25.1 and 6.1 emu g
3
O
4
2
O
3
2
ꢀ
1
,
respectively. The decrease of the saturation magnetization
suggests the presence of the mesoporous TiO shell and some
2
silver particles inside the uniformly pore of hollow mesoporous
sphere.
3
.2 Catalyst testing for synthesis of βꢀenaminones
Acetylacetone and aniline as the representative substrate was
3 4 3 4 2 3 2
Fig. 3 XRD patterns of (a) Fe O /Ps, (b) Ag/Fe O /Ps and (c) Ag/γ-Fe O @meso-TiO .
used for the early exploration of synthesis of βꢀenaminones. To
investigate the effect of time on product distribution, reaction
times of 20, 40, 60, 80, 100, and 120 min were examined in the
presence of the catalyst. The results of the influences of the
reaction time on the exploration are presented in Fig. 6. With
increasing the reaction time, the conversion of the reactants was
increased as expected, the optimum reaction time was
determined as 1 h.
Fig. 4 N
2
adsorption/desorption isotherms and pore size distribution of Ag/γ-Fe
2 3
O
@
meso-TiO
2
(a) BJH adsorption dV/dlog (D) pore volume and (b) BJH desorption
dV/dlog (D) pore volume
3 4
Fig. 5 Room temperature magnetization curves of (a) Fe O /Ps and (b) Ag/γ-
2 3 2
Fe O @meso-TiO .
4
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a
Table 1 Study of reaction parameters on reaction of aniline with acetylacetone.
b
Entry
Solvent
Acetylaceton
Aniline
(mmol)
Yield
（
mmol）
（%）
1
2
3
4
5
6
7
8
9
DMSO
DMSO
2
1
2
2
2
2
2
2
2
1
2
1
1
1
1
1
1
1
1
1
1
1
94.0
85.7
46.3
60.1
5.6
Cyclohexane
Ethanol
Acetonitrile
Toluene
THF
12.0
5.4
Water
42
Methanol
Methanol
Solvent free
99.9>
99.9>
Traces
Fig. 6 Effect of reaction time on the conversion of the reaction of aniline and
acetylacetone with Ag/γ-Fe @meso-TiO as catalyst. Reaction conditions: aniline 1
c
2 3
O
2
10
11
mmol, acetylacetone 2 mmol, the catalyst 67.4 mg, methanol 5 mL, 333 K Legend:
conversion (%). Determined by GC or GC-MS.
a
Reaction conditions: solvent (5 mL), Ag/γ-Fe
2
O
3
@meso-TiO
2
(67.4 mg), time (1
h), reaction temperature 323 K.
b
Yield is based on GC-MS analysis
.
c
The reaction time (2 h)
a
Table 2 Synthesis of various β-enaminones.
Fig.
temperature on the conversion of the reaction of aniline and acetylacetone with Ag/γ-
Fe @meso-TiO as catalyst. Reaction conditions: aniline 1 mmol, acetylacetone 2
7
Effect of
1
2
c
Entry
R
R
Time (h)
Product
Yield （
%
）
O
2 3
2
1
2
3
CH
3
CH
3
CH
3
C
6
H
5
1
4
1
1a
2b
3c
99.5
mmol the catalyst 67.4 mg, methanol 5 mL, 1 h. Legend: conversion (%) determined by
GC or GC-MS.
p-CH
3
C
6
H
5
>99.9
PhCH
2
>99.9
b
9
9.0
The effects of the reaction temperature were shown in Fig.7.
As we can see, with increasing the temperature, the conversion
of aniline increased. At temperature from 303 to 323 K, the
aniline conversion increased very remarkably. The optimized
4
5
CH
CH
CH
3
3
3
Cyclohexyl
n-C
i-C
C6H5
p-CH
PhCH
Cyclohexyl
n-C
i-C
1.25
0.5
0.75
4
4d
5e
98.5
>99.9
99.7
98.2
80.6
>99.9
97.3
99.6
99.4
99.6
99.4
>99.9
99.5
99.7
96.7
4 9
H
6
4
H
9
6f
7
OCH3
7g
temperature was found at 323 K
.
8
OCH
OCH
OCH
OCH
OCH
3
3
3
3
3
3
C
6
H
5
4
8h
Table 1 presents the influence of solvent on the condensation
reaction for the synthesis of βꢀenaminones over Ag/γꢀ
9
2
1
9i
10
1.25
0.5
0.75
4
10j
11k
12l
13m
14n
15o
16p
17q
18r
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
8
4 9
H
2 3 2
Fe O @mesoꢀTiO at 323 K In order to promote the formation
4 9
H
of the desired product, an excess amount of acetylacetone with
respect to aniline was used (2:1). It was observed that the
reaction provided a good yield with the use of methanol and
DMSO as solvent, employing best results with methanol
OC
OC
OC
OC
OC
OC
2
2
2
2
2
2
H
5
5
5
5
5
5
6 5
C H
H
H
H
H
H
p-CH
PhCH
Cyclohexyl
n-C
i-C
3
C
6
H
5
4
2
1
1.25
0.5
0.75
(99.5% yield) (Table 1, entries 2ꢀ8, 10, 11), which was then
4 9
H
employed for further study. The reaction was also carried out
under solvent free conditions to evolve the influence of the
solvent parameter but traces of the product were detected mmol), Ag/γ-Fe
4 9
H
a
Reaction conditions: methanol (5 mL), dicarbonyl compound (2 mmol), amine (1
@meso-TiO (67.4 mg), and temperature (323 K).
O
2 3
2
(
Table 1, entry 11). The result indicates that solvent plays a
b
Yield after fifth recycle.
Yield based on GC-MS analysis
great role on the condensation
c
.
2 3 2
reaction and the Ag/γꢀFe O @mesoꢀTiO promote the mass
diffusion and transport of reactants. Meanwhile, the molar ratio
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Journal Name
of acetylacetone and aniline also had a significant influence on Table 3 Synthesis of 4-Phenylamino-pent-3-en-2-one (Table 2, entry 1) in the
presence of different catalysts
the enamination of aniline, the acetylacetone/aniline molar ratio
of 1:1 gave the lower yield of desired products (Table 1, entries
Entry
Catalysts
The
amount
of Ag
0.1
Temperature Time
Yield Ref.
(%)a
2, 10).
(℃)
(h)
Various amines were allowed to react with βꢀdicarbonyl
compounds under optimized conditions in the presence of a
catalytic amount of Ag/γꢀFe @mesoꢀTiO (67.4 mg) for a
1
2
Ag/γ-
50
2
>99.9
>99.9
2
O
3
2
Fe
Fe
2
O
3
@meso-
TiO
Ag/γ-
@meso-
TiO
Ag Np
certain period of time required to complete for the reactions.
The results are summarized in Table 2, from which it can be
observed that the reactions of amine derivatives with βꢀenamino
ketones and esters proceeded efficiently (Table 2, entries 1ꢀ18).
2
0.1
60
1
2
O
3
2
3
4
0.1
60
60
8
90
86
1
Acetylacetone was found to give
a good yield with
Zn(OAc)
2
•2H
2
O
0.05
48
11
benzylamine, and pꢀtoluidine (Table 2, entries 1ꢀ3). The yield
of 2b was not obviously increased by the reaction time was
prolonged 2 h after removed the catalyst from reaction system.
The result shows that this reaction did not proceed even in the
same conditions without metallic catalyst. The solution was not
found the element of Fe based on ICP analysis. But the Ag
content in the solution was found to be 0.4 ppm based of ICP
elemental analysis, indicating that a very small amount of Ag
was possibly leached. The reactions of acetylacetone with
aliphatic and alicyclic amines proceeded to give excellent
5
Zn(OAc)
2
•2H
2
O
0.1
0.1
60
60
80
8
100
100
6
6
Ag/HMMS
6
a
Yield based on GC-MS analysis
.
4
. Conclusions
In conclusion, we demonstrated a successful synthesis of
multicomponent Ag/γꢀFe @mesoꢀTiO with wellꢀdefined
coreꢀshell nanostructures. According to the TEM, tiny Ag NPs
were encapsulated within hollow magnetic mesoporous
spheres. The Ag NPs were free of protection ligands and were
wellꢀdispersed in mesoporous spheres with
aggregation. Moreover, the obtained Ag/γꢀFe
catalyst exhibited improved catalytic activity for synthesis of βꢀ
enamino ketones or esters from βꢀdicarbonyl compounds,
especially for synthesis of 4ꢀPhenylaminoꢀpentꢀ3ꢀenꢀ2ꢀone
2
O
3
2
2 3 2
yields in a short period with the Ag/γꢀFe O @mesoꢀTiO as a
catalyst (Table 2, entries 4ꢀ6). The reaction with aliphatic
amines proceeded easily in a shorter time than aromatic amines,
owning to the fact that the higher nucleophilicity of aliphatic
amines as compared to aromatic amines. The addition of
amines to other dicarbonyl compounds like methy acetoacetate
and ethyl lacetoacetate was also studied. Methy acetoacetate
and ethyl acetoacetate were found to give an excellent yield of
desired products with aliphatic, aromatic and alicyclic amines
under optimized reaction conditions (Table 2, entries 7ꢀ18). The
catalyst can be easily recovered in a facile manner from the
reaction solution by using a permanent magnet. Furthermore,
the catalyst revealed a remarkable activity and was reused up to
five consecutive cycles without any significant loss in catalytic
activity (Table 2, entry 3).
a
few of
@mesoꢀTiO
2
O
3
2
(
2 3 2
Table 2, entry 1). Furthermore, the Ag/γꢀFe O @mesoꢀTiO
catalyst had stable catalytic activity, evidenced by being
extensively reused for five times without any substantial loss of
activity which was mainly attributed to the small size of Ag
NPs and the hollow structure of TiO . In addition, the structural
2
stability of this catalyst during reaction is very well.
In order to show the merit of Ag/γꢀFe
comparison with other reported catalysts, we summarized some
2 3 2
O @mesoꢀTiO in
Acknowledgements
of results for preparation of entry 1 in Table 2, which shows This work was supported by the Fundamental Research Funds
that Ag/γꢀFe
previously reported.
2
O
3
@mesoꢀTiO
2
is more efficient catalyst to those for the Central Universities (lzujbkyꢀ2015ꢀ16 and lzujbkyꢀ
2015ꢀ17).
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DOI: 10.1039/C5RA14878B
Journal Name
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