Introduction of a trinuclear manganese(iii) catalyst on the surface of magnetic cellulose as an eco-benign, efficient and reusable novel heterogeneous catalyst for the multi-component synthesis of new derivatives of xanthene

Article abstract of DOI:10.1039/d0ra09420j

In this work, the new trinuclear manganese catalyst defined as Fe3O4@NFC@NNSM-Mn(iii) was successfully manufactured and fully characterized by different techniques, including FT-IR, XRD, TEM, SEM, EDX, VSM, and ICP analysis. There have been reports of the use of magnetic catalysts for the synthesis of xanthine derivatives. The critical potential interest in the present method include short reaction time, high yields, recyclability of the catalyst, easy workup, and the ability to sustain a variety of functional groups, which give economical as well as ecological rewards. Also, the synthesized catalyst was used as a recyclable trinuclear catalyst in alcohol oxidation reactions at 40 °C. The magnetic catalyst activity of Fe3O4@NFC@NNSM-Mn(iii) could be attributed to the synergistic effects of the catalyst Fe3O4@NFC@NNS-Mn(iii) with melamine. Employing a sustainable and safe low temperature, using an eco-friendly solvent, no need to use any additive, and long-term stability and magnetic recyclability of the catalyst for at least six successive runs are the advantages of the current protocol towards green chemistry. This protocol is a benign, environmentally friendly method for heterocycle synthesis. This journal is

Full text of DOI:10.1039/d0ra09420j

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Introduction of a trinuclear manganese(III) catalyst
on the surface of magnetic cellulose as an eco-
benign, efficient and reusable novel heterogeneous
catalyst for the multi-component synthesis of new
derivatives of xanthene†
Cite this: RSC Adv., 2021, 11, 4339
a
a
b
*
Ghodsieh Bagherzade and Hossein Eshghi
Pouya Ghamari kargar,
In this work, the new trinuclear manganese catalyst defined as Fe3O4@NFC@NNSM-Mn(III) was successfully
manufactured and fully characterized by different techniques, including FT-IR, XRD, TEM, SEM, EDX, VSM,
and ICP analysis. There have been reports of the use of magnetic catalysts for the synthesis of xanthine
derivatives. The critical potential interest in the present method include short reaction time, high yields,
recyclability of the catalyst, easy workup, and the ability to sustain a variety of functional groups, which
give economical as well as ecological rewards. Also, the synthesized catalyst was used as a recyclable
trinuclear catalyst in alcohol oxidation reactions at 40 ꢀC. The magnetic catalyst activity of
Fe3O4@NFC@NNSM-Mn(III) could be attributed to the synergistic effects of the catalyst
Fe3O4@NFC@NNS-Mn(III) with melamine. Employing a sustainable and safe low temperature, using an
eco-friendly solvent, no need to use any additive, and long-term stability and magnetic recyclability of
the catalyst for at least six successive runs are the advantages of the current protocol towards green
chemistry. This protocol is a benign, environmentally friendly method for heterocycle synthesis.
Received 5th November 2020
Accepted 21st December 2020
DOI: 10.1039/d0ra09420j
rsc.li/rsc-advances
reactions show signicant advantages such as reduced reaction
time, high selectivity, reduction of by-products, and high effi-
ciency.4–6 Among the multi-component reactions referred to as
Introduction
In the last decades, scientists have considered new approaches,
including the development of environmentally friendly chemicals
in terms of academic and industrial processes. The main criteria
for assisting green chemical processes are the use of benign
environmental solvents and the prevention of the formation of by-
products in the synthesis of reactions using heterogeneous cata-
lysts.1,2 A multi-component reaction (MCR) is a process in which
three or more easily accessible components are combined in
a single reaction vessel to produce a nal product displaying all
inputs' features. MCR suggests greater possibilities for molecular
variety per step with minimum synthetic time and endeavor.3
Therefore, organic synthesis through multi-component reactions
(MCR) is now a research area in organic chemistry. MCR reactions
are a powerful tool in drug discovery processes. Multi-component
reactions (MCR) play an important role in chemistry because they
can synthesize drug molecules with structural diversity. These
biologically active heterocycles is called xanthene. The synthesis of
new compounds comprising heterocyclic systems grabs an
important position in the scope of synthetic organic chemistry.7–9
xanthene and its derivatives have become an important class of
organic chemistry in the last few decades because of their wide
range of biological and pharmaceuticals such as anti-inamma-
tory,10 antibacterial,11 anti-plasmodial,12 antidepressants,13 anti-
malarial agent14 and antiviral.15 They also have basic applications
in biodegradable processes such as photodynamic therapy,16
agrochemicals,17 uorescent materials,18 laser technologies,19 and
luminescent sensors.20 To date, several routes and reagents have
been engaged in preparing many of these organic derivatives.
Many catalysts are used for preparing various xanthenes, such as
PVSA,21 [Et3NSO3H]Cl,22 core/shell Fe3O4@GA@isinglass,14 SbCl3/
SiO2,23 amberlyst-15,24 boric acid,25 nano TiO2,26 sulfamic acid,27
acetonitrile28 and etc. However, many of these methods toil from
certain drawbacks, including powerful acidic conditions, long
reaction times, low yields of products and spicy reaction condi-
tions, toxic solvents, and excessive and costly catalysts. Therefore,
it has become important to nd another route for an environment-
friendly preparation of xanthene derivatives. Heterogeneous
catalysis is a signicant accost to environmental remediation
because it decreases the cost and energy provisions of chemical
aDepartment of Chemistry, Faculty of Sciences, University of Birjand, Birjand,
97175-615, Iran. E-mail: gbagherzade@gmail.com; bagherzade@birjand.ac.ir; Fax:
+98 56 32345192; Tel: +98 56 32345192
bDepartment of Chemistry, Faculty of Science, Ferdowsi University of Mashhad,
Mashhad, Iran
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra09420j
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operations. However, catalyst recycling and recovery from the xanthene derivatives using tri-nuclear catalyst manganese is
reaction medium are essential to prevent product contamination introduced. Fe3O4@NFC@NNSM-Mn(III) was synthesized, as
and protect the environment. Recently, magnetic nanoparticles shown in (Fig. 1). The Fe3O4 nanoparticles, obtained by chem-
(Fe3O4) have received scientic attention due to their extraordinary ical purication protocol, were coated with cellulose to obtain
performance, such as high super magnetic properties in the Fe3O4@NFC. The ligand was then placed on a magnetic
presence of an external magnetic eld, etc.29 The surface of substrate. In the next step, manganese nanoparticles were
magnetic nanoparticles has been used for biological and medical immobilized in Fe3O4@NFC@NNSM-Mn(III) by adsorption of
engineering due to its small size, good compatibility, low toxicity Mn(OAC)3 in Fe3O4@NFC@NNS. The catalysts were character-
and good physical, and chemical stability such as magnetic reso- ized by FT-IR, XRD, FE-SEM, EDX, TEM, TGA-DTA, VSM, and
nance imaging, drug delivery, biosensors, cancer treatment with ICP-OES spectroscopy. FT-IR spectra of Fe3O4, Fe3O4@NFC,
magnetic induced hyperthermia.30 Howbeit magnetic nano- Fe3O4@NFC–Cl, Fe3O4@NFC@NN, Fe3O4@NFC@NNS, Fe3-
particles can be separated from the reaction mixture by an external O4@NFC@NNSM-Mn(III) are shown in (Fig. 1). The FT-IR spec-
magnet, the removal of nanoparticles from the reaction mixture trum of Fe3O4 (Fig. 1a), exhibited a wide absorption band at
systems is very challenging. These nanoparticles can easily accu- about 550–600 cmꢁ1, which is related to the vibration modes of
mulate oxidized and agglomerate in aqueous solutions due to their Fe–O bonds in the Fe3O4 crystalline lattice. The characteristic
petite size.31 These small nanoparticles can be distributed over bands that appeared at 1600, and 3400 cmꢁ1 are certied to the
a large area, making them difficult to be collecting. Therefore, to bending and stretching vibrations of the surface hydroxyl
prevent the oxidation of magnetic nanoparticles, a new approach groups and adsorbed water molecules. In addition to Fe3O4
should be considered, such as modifying the nanoparticles' peaks observed in the spectrum that approves the formation of
surface with polymer groups or using a mold to prevent the Fe3O4 nanoparticles, the strong peak at 1097, 2960, 3328 cmꢁ1
nanoparticles from oxidizing for a specic structure, which can be shows the (C–O, C–H, O–H stretching vibrations) of cellulose
useful approaches.32,33 In the recent past, some green plant poly- nanobers (Fig. 1b). The strong absorption bands at about
mers,34 such as nanober cellulose, lignin, and hemicellulose, 1097, 1120, 1410–1520, 2990, and 3120 cmꢁ1 could correspond
polylactic acid (PLA),35,36 chitin37,38 and chitosan,39,40 were consid- to the stretching vibration frequencies of Si–O, C–N, C]C
ered. Among the various materials used as a mold to prevent aromatic, and C–H aliphatic and aromatic bonds.
oxidation of magnetic nanoparticles, cellulose nanober can be
Also, the observed broadband at around 3000–3450 cmꢁ1
mentioned because of its many capabilities, including low cost, could attribute to the stretching vibration frequency of the NH,
easy access, biodegradability, low density, excellent mechanical NH2, and OH groups (Fig. 1c and d). As shown in (Fig. 1e), The
properties, and high level.41–43 Trinuclear catalyst Mn could be FT-IR spectrum of compound 4 (Fig. 1d), indicates the Schiff
better alternatives for greener production of xanthene derivatives base reaction between Fe3O4@NFC@NN and 5-(chloromethyl)-
because they can provide a large surface terrain as the catalytic
patronage for catalyzing organic reactions.44,45 To the best of our
knowledge, no such trinuclear catalyst based on magnetic nano-
ber cellulose has been used so far to prepare these derivatives
making this approach a novel one for such synthesis. In this work,
we synthesized a manganese trinuclear catalyst using a mechan-
ical method using nanober cellulose as a substrate and a ligand
as an anchor.
During our ongoing research into the activity of manganese
trinuclear catalysts nally, aer a successful study of trinuclear
catalysts, their application to the oxidation of primary/
secondary alcohols to produce corresponding carbonyl
compounds with high conversion and good selectivity has been
investigated. Also inspired by these facts as part of our ongoing
efforts to develop new catalytic methods for performing
xanthene multi-component reactions and alcohol oxidation
under more benign environmental conditions, we present here
Fe3O4@NFC@NNSM-Mn(III). We have evaluated this magnetic
ternary catalyst with various techniques and nally used it in
the mentioned reactions.
Result and discussion
Synthesis and characterization of Fe3O4@NFC@NNSM-Mn(III)
Therefore, it is important to use an effective method that
provides the xanthene simply and easily. In this research, an
effective and efficient synthetic method for preparing several NN, (e) Fe3O4@NFC-NNS-Mn(III), (f) Fe3O4@NFC-NNSM-Mn(III).
Fig. 1 (a) Fe3O4, (b) Fe3O4@NFC, (c) Fe3O4@NFC–Cl, (d) Fe3O4@NFC-
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2-hydroxy benzaldehyde, the characteristic peaks at 753 cmꢁ1
(C–Cl stretching), 1670 cmꢁ1 (C]N stretching vibration)
conrms the structure of (Fig. 1e). Complexation of manganese
and melamine to Fe3O4@NFC@NNS causes the adsorption of
chlorine bond to be lost and causes the imine bond (1670 cmꢁ1
)
absorption to lower wavenumbers by about 20 cmꢁ1
(1650 cmꢁ1), indicating the participation of azomethine
nitrogen in bonding with metal ion and conrming the coor-
dination of n(C]N) stretch to the metal via a nitrogen atom.
Also, absorption bands at 1100 and 1600 cmꢁ1 could be
assigned to (C–N and C]N) melamine stretching, respectively
(Fig. 1e). These absorption bonds support the successful prep-
aration of the catalyst. XRD analysis was carried out for Fe3O4
and Fe3O4@NFC@NNSM-Mn(III) to understand the structural
features of the stimulus (Fig. 2). Present tense Fe3O4, Mn2O3
(MnIII), and Fe3O4@NFC@NNSM-Mn(III) X-ray diffraction
patterns in the 2q range between 10ꢀ.
The XRD pattern of Fe3O4 shows six characteristic diffraction
peaks at 2q ¼ 30.3ꢀ, 35.8ꢀ, 43.6ꢀ, 54.8ꢀ, 57.3ꢀ, and 63.2ꢀ corre-
sponding to the (220), (311), (400), (422), (511), and (440) crys-
tallographic phases, respectively, that were entirely in
agreement with the standard structure and the reported XRD
pattern for magnetic (Fig. 2: Fe3O4).46 Besides, diffraction peaks
in Fe3O4 nanoparticles, a broader peak was observed in the XRD
pattern of the Fe3O4@NFC@NNSM-Mn(III) spheres in the 2q
range of 20–30ꢀ, which is the result of the amorphous cellulose.
Thus, the XRD curve of the Fe3O4@cellulose nanoparticles
composites of the same peaks was also observed in the Fe3-
O4@NFC XRD pattern, indicating retention of the crystalline
spinel ferrite core structure during the cellulose coating
process.36 It is the characteristic of diffraction peaks of Mn(III)
nanoparticles observed in the XRD pattern in the catalyst. Weak
and robust peaks at 2q ¼ 32.07ꢀ, 39.47ꢀ, 50.12ꢀ, 60.72ꢀ, 62.17ꢀ,
and 71.02ꢀ corresponding to the (222), (400), (600), (620), (444),
Fig. 3 EDX image of Fe3O4@NFC@NNSM-Mn(III).
and (640) crystallographic phases in XRD pattern are related to
Mn2O3.47
EDX graph conrms the successful connection of Schiff base
manganese(III) complex by the presence of all metallic and non-
metallic elements involved in the catalyst like carbon, nitrogen,
oxygen, silicon, iron, and manganese (Fig. 3). Besides, the best
technique for verication of catalyst preparation incredibly
problematic half, is inductively coupled plasma optical emis-
sion spectroscopy (ICP-OES) analysis. Loading amount of Mn on
the catalyst was measured by inductively coupled plasma
optical emission spectroscopy (ICP-OES) instruments due to
more ensure attainment. The experiment indicated that
1.1 mmol of Mn metal per gram of the catalyst (1.1 mmol 1 g)
was loaded on the catalyst framework VII. Also, the analyses give
the percentage of the heavy metals as: 45.54 w%, 2.33 w%, 7.10
w% for Fe, Si, Mn respectively.
This technique gives the amount of manganese in the fresh
and reuse catalyst. The Mn content of the catalyst was measured
by ICP analysis, which illustrated the attendance of 0.12 mmol
Mn per 1.0 g of the Fe3O4@NFC@NNSM-Mn(III). The surface
morphology of Fe3O4@NFC@NNSM-Mn(III) was further deter-
mined using SEM and TEM images. A comparison of the FE-
SEM images of Fe3O4 with that of Fe3O4@NFC, Fe3O4@-
NFC@NNSM-Mn(III) clearly showed the presence of other
nanoparticles in the SEM images of Fe3O4@NFC@NNSM-
Mn(III), which could be referred to as cellulose or ligand and
Mn. As it is evident in the TEM images, the mean particle sizes
of Fe3O4@NFC@NNSM-Mn(III) were measured to be around 16–
29 nm. The particles of Fe3O4 and NFC can also be recognized
through their indicative crystal lattice fringes (Fig. 4).
The TGA analysis was conducted to determine the uncoated
Fe3O4 NPs, cellulose (NFC), and NFC-coated Fe3O4 NPs, content
in the Fe3O4@NFC@NNSM-Mn(III) nano catalyst. The results
are illustrated in Fig. 5. The TGA analysis was performed to
conrm the coating of organic content on the surface of the
Fe3O4 NPs. TGA spectra of uncoated Fe3O4 NPs show little
weight loss, which is about 10% in the range of 25–800 ꢀC. This
might be due to the loss of residual water in the uncoated Fe3O4
NPs.48 On the other hand, Fig. 5b shows the TGA spectra of
cellulose. The initial step at 125 ꢀC occurs because of the loss of
hydrated and constituent water. The second stage involves
weight reduction that occurs at approximately 225–425 ꢀC. This
Fig. 2 XRD spectra of (black) Fe3O4, (red) Mn2O3 and (blue) Fe3-
O4@NFC-NNSMMn(III).
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Fig. 5 TGA curves for (a) Fe3O4, (b) cellulose, (c) Fe3O4@NFC, and (d)
Fe3O4@NFC@NNSM-Mn(III).
Finally, the thermal stabilities of the Fe3O4@NFC@NNSM-
Mn(III) were examined by TGA (Fig. 5d). As introduced in Fig. 5,
a total weight loss of about 47% was determined from the TGA
curve of the Fe3O4@NFC@NNSM-Mn(III). The reduction in mass
ꢀ
below 160 C can be attributed to the loss of embedded water
molecules. Subsequently, the main weight loss step in the
temperature ranges 160–350 ꢀC (33% reduction) is attributed to
the decomposition of cellulose units through the formation of
levoglucosan and other volatile compounds or another mass
loss, which shows higher thermal stability than Fe3O4@-
NFC@NNSM-Mn(III) has been modied due to a reasonable
reduction in the amount of oxygen-containing functional
groups in cellulose.52a
Moreover, the weight loss of about 6% in the temperature
range between 300 and 700 ꢀC may be due to the thermal crystal
phase alteration from Fe3O4 to g-Fe2O3.52b Other stages of
ꢀ
weight loss up to 800 C may be due to the decomposition of
organic moieties on the surface of the Fe3O4@NFC core–shell
nanoparticles. The magnetic behavior of Fe3O4 and Fe3O4@-
NFC@NNSM-Mn(III) was examined by VSM analysis at room
Fig. 4 SEM image of (a and b) Fe3O4, of (c and d) Fe3O4@NFC, of (e
and f) Fe3O4@NFC@NNSM-Mn(III) and (g and h) TEM image of the
Fe3O4@NFC@NNSM-Mn(III).
is generally associated with the natural carbon of cellulose
ꢀ
under oxidizing conditions. Disintegration past 425 C occurs
because of oxidation of the degraded products of cellulose.49
Comparing with the TGA curves, Fig. 5c illustrates the thermal
decomposition diagrams for Fe3O4@NFC synthesized by the
green method. The rst mass reduction phase occurred at 50–
120 ꢀC, caused by the water's loss absorbed in the nano-
ꢀ
composite surface. The second phase occurred at 150–425 C,
which could have arisen due to the breakdown of the bonds and
destruction of the cellulose structure. The third stage of weight
ꢀ
loss occurs at temperatures above 650 C, which can be due to
the rupture of the bond between nanober cellulose and Fe3O4
nanoparticles,50,51 which were conducted on thermal and
mechanical properties of Fe3O4@NFC.
Fig. 6 VSM pattern Fe3O4 (a), Fe3O4@NFC (b) and (c) Fe3O4@-
NFC@NNSM-Mn(III).
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Table 1 Optimization of reaction conditions for synthesis of 3,3,3,6,6-pentamethyl-9-phenyl-3,4,5,6,7,9-hexahydro -1H-3,5-xanthene-
1,8(2H)-dione
Entry
Solvent
Catalyst (mol%)
Temp. (ꢀC)
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
EtOH : H2O
H2O
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
—
45
45
45
45
45
45
45
45
45
45
45
—
55
65
45
45
45
45
45
45
15
20
10
10
60
75
45
45
10
10
10
60
10
10
20
40
60
60
60
30
90
85
96
85
70
65
85
60
Trace
95
90
55
90
85
96
92
85
0
EtOH
MeOH
CH3CN
EtOAC
CHCl3
Neat
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
9
10
11
12
13
14
15
16
17
18
19
20
1
1.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5b
0.5c
0.5d
0
70
a
Reaction conditions: benzaldehyde (1 mmol) and dimedone (2 mmol). The catalyst was prepared by using 0.5 mol% of catalyst as explained in the
Experimental section. b Reaction was performed in the presence of Fe3O4 as the catalyst. c Reaction was performed in the presence of Fe3O4@NFC as
the catalyst. d Reaction was performed in the presence of Fe3O4@NFC@NNS-Mn(III) as the catalyst.
temperature (Fig. 6). As it could be perceived from the resulting results in Table 1, a premier yield of the desired product was
magnetization curves, the saturation magnetization amount of achieved by using 0.5 mol% of the magnetic catalyst (Table 1,
Fe3O4 and Fe3O4@NFC@NNSM-Mn(III) were 66.50 and 24.30 entry 3). A control experiment lumpish that no product was
emu. gꢁ1, respectively. No discover hysteresis loop in the obtained when the reaction was accomplished in the absence of
magnetization curves of both Fe3O4 and Fe3O4@NFC@NNSM- the catalyst (Table 1, entry 9). The effect of different tempera-
Mn(III) illustrated the superparamagnetic feature of these tures was also examined on the model reaction progress (Table
compounds.
1, entries 12–14) and found that the multi-component reaction
proceeded surprisingly at 45 ꢀC (Table 1, entry 3). It is note-
worthy that the MCR reaction has a small efficiency without
temperature conditions (entry 12). In the next experiment, time
differences were separately used to investigate the effect of time
on the model reaction's progress (Table 1, entries 15–17).
Results indicated that 10 min is the best time for the xanthene
reaction (Table 1, entry 3). To obtain better about the efficiency
of the Fe3O4@NFC@NNSM-Mn(III) catalyst, the magnetic cata-
lytic activity of Fe3O4, Fe3O4@NFC, Fe3O4@NFC@NNS-Mn(III)
(mononuclear), and Fe3O4@NFC@NNSM-Mn(III) (trinuclear)
were separately studied in the model reaction (Table 1, entries
18–20). As can be seen in Table 1, no product was gained by
using Fe3O4 and Fe3O4@NFC species. However, when the
reaction was carried out in the presence of Fe3O4@NFC@NNS-
Mn(III), the result was far from satisfactory (Table 1, entry 20).
These ndings indicated that the enhanced magnetic catalytic
activity of Fe3O4@NFC@NNSM-Mn(III) could be attributed to
The magnetic catalyst activity of Fe3O4@NFC@NNSM-Mn(III)
in the xanthene reaction
To optimize the xanthene reaction parameters, we studied the
effect of catalyst amount, solvent, temperature, and time were
explored towards the reaction progress over the reaction of
benzaldehyde with dimedone as a multi-component reaction.
Among the various solvents examined for the xanthine
reaction (Table 1, entries 1–8), the ethanol solvent performed
best (Table 1, entry 3). Aer that, the effects of different factors
on the reaction progress were perused in EtOH (Table 1, entries
9–13). The result lumpish that the best yield of the product was
obtained in the presence of a stimulus (Table 1, entry 3).
However, the reaction did not proceed without employing any
factors. The effect of the magnetic catalyst amount was next
studied (Table 1, entries 9–11). As clearly understood from the
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Table 2 One-pot three-component synthesis of various xanthene derivatives catalysed by Fe3O4@NFC@NNSM-Mn(III)a
MP (ꢀC)
Time (min) Yieldb (%) Found
Entry
Aldehyde
R1
Product
Reported
1 (ref. 53)
H
10
15
98
95
203–204 203–205
2 (ref. 53)
H
H
229–230 228–230
3 (ref. 54)
15
92
205–206 206–207
4 (ref. 53)
5 (ref. 55)
6 (ref. 56)
H
10
10
10
95
97
96
259–261 260–261
205–206 205–206
203–204 202–204
H
Me
7 (ref. 57)
Me
10
95
169–170 168–170
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Table 2 (Contd.)
MP (ꢀC)
Entry
Aldehyde
R1
Product
Time (min) Yieldb (%) Found
Reported
8 (ref. 58)
Me
10
20
96
93
200–201 201–202
9 (ref. 59)
Me
295–297 >300
10 (ref. 60)
11 (ref. 61)
H
30
25
80
85
267–269 268–269
Me
155–157
—
12
H
15
90
168–170 New
13
14
Me
15
15
92
92
200–202 New
H
220–222 New
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Table 2 (Contd.)
MP (ꢀC)
Time (min) Yieldb (%) Found
Entry
Aldehyde
R1
Product
Reported
15
Me
20
95
250–252 New
a
Reaction conditions: benzaldehyde (1.0 mmol), dimedone (2.0 mmol) and catalyst (0.5 mol%) and EtOH (3 ml), 45 ꢀC. b Isolated yield.
the synergistic effect of melamine and Fe3O4@NFC@NNS- synthesis part for more details). With these interpretations, it
Mn(III) towards the xanthene reaction as a high-efficiency tri- can be inferred that the proper reaction of melamine and Fe3-
nuclear catalyst (see the magnetic catalytic mechanism O4@NFC@NNS-Mn(III) in the synthesis of magnetic catalyst not
Table 3 Screening reaction conditionsa
Entry
Solvent
Catalyst (mol%)
Temp. (ꢀC)
TBHP (mmol)
Yieldb (%)
1
2
3
4
5
6
7
8
Water
EtOH
CH3CN
1
1
1
1
—
0.5
1.5
2
1
1
40
40
40
40
40
40
40
40
r.t,
50
60
70
40
40
2
2
2
2
2
2
2
2
2
2
2
2
1
3
40
85
60
97
25
65
97
90
50
97
75
65
75
85
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
9
10
11
12
13
14
1
1
1
1
a
b
Reaction conditions: benzyl alcohol (1 mmol), 20 min. Yields of product isolated.
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Table 4 Oxidation of alcohols to corresponding aldehydes or ketones
only increases the power of the catalyst but also multiplies the
activity of the magnetic catalyst. This property expedites and
facilitates the reaction process in terms of time and other
reaction conditions. These observations well proved the signif-
icant inuence of the trinuclear catalyst to advance the
xanthene MCR reaction.
in the present of Fe3O4@NFC@NNSM-Mn(III) catalysta
The magnetic catalytic activity of Fe3O4@NFC@NNSM-Mn(III)
in the alcohol oxidation reaction
Entry Substrate
1
Product
Time (min) Yieldb (%)
Encouraged by the promising results obtained from the
xanthene reaction, the magnetic catalytic activity of Fe3O4@-
NFC@NNSM-Mn(III) was next explored towards the alcohol
oxidation reaction under solvent-free conditions (Table 3). As
shown in Table 3, this magnetic catalytic method was very
efficient for the oxidation reaction of different alcohol. Inter-
estingly, it was found that the oxidation reactions for the readily
available and low-cost benzyl alcohol as the highly challenging
substrates, with various derivatives, were also companion with
satisfactory results (Table 4, entries 1–16). One of the most
powerful and useful tools for the production of aldehydes and
ketones is the oxidation of alcohols, which are signicant
mediators in the synthesis of drugs and chemicals. To develop
the application of the trinuclear catalysts, Fe3O4@NFC@NNSM-
Mn(III) magnetic catalyst was employed for the oxidation of
a series of primary and secondary alcohols. To evaluate the
reaction conditions of alcohol oxidation and compare the
performance of manganese catalyst, benzyl alcohol was selected
as a model reaction for alcohol oxidation and the results of this
reaction are summarized in Table 3. Firstly, TBHP was chosen
as the oxidant, as it introduced the highest oxidative activity
among all the oxidants. Noticeably, the additive also has
a strong effect. On the catalytic performance in the selective
oxidation of alcohols.
20
20
97
92
2
3
4
5
6
7
15
15
30
35
45
90
92
88
82
80
8
45
85
9
35
35
95
85
10
Additive and organic/inorganic mixed solvent can promote
ꢀ
the smooth oxidation of alcohol at 40 C temperature. Low to
11
12
30
60
90
80
moderate yields were obtained when using Fe3O4, Fe3O4@NFC,
Fe3O4@NFC@NNS-Mn(III), Fe3O4@NFC@NNSM-Mn(III) as an
additive (20–97%, Fig. 7 respectively). Fe3O4@NFC@NNSM-
Mn(III) (trinuclear) and Fe3O4@NFC@NNS-Mn(III) (mono-
nuclear) catalysts only exhibited 97% and 80% yield of the
product. Whereas with the same conditions Fe3O4@-
NFC@NNSM-Mn(III) catalyst, indicating that the optimization
of parameters and active sites can indeed improve the overall
catalytic performance of the oxidation reactions (Table 3).
Finally, the Fe3O4@NFC@NNSM-Mn(III) catalyst improves the
oxidation reaction of alcohol. Finally, the product was obtained
13
14
30
20
95
75
ꢀ
with 97% yield at 40 C in a solvent-free condition for 30 min.
Furthermore, in the next step, solvents were optimized, which 15
increased the yield overall. The highest yield (97%) was ob-
15
97
tained at solvent-free conditions (Table 3, entries 1–4), which is
in line with the green chemistry. Control experiments were also
a
Reaction conditions: alcohols (1 mmol), TBHP (2 mmol), catalyst
(0.5 mol%), S. F., 40 ꢀC. b Yields of product isolated.
performed in the absence of Mn catalyst in alcohol oxidation. In
this case, the product is difficult to identify (Table 3, entries 5).
Increasing the amount of the catalyst up to 0.5 mol% led to
improved yields, but the more increasing it had no signicant
effect on the product yield (entries 9–12). Then, the model
reaction was carried out under solvent-free conditions at room
temperature and also 40–70 ꢀC (entries 9–12). The product yield
was increased up to 40 ꢀC and was decreased signicantly to
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contrast, the Fe3O4@NFC@NNS-Mn(III) catalyst with a larger
size in the support material exhibited better activity under the
same reaction conditions (80%).
Moreover, the Fe3O4@NFC@NNSM-Mn(III) catalyst as a tri-
nuclear catalyst with a larger surface area exhibited better
activity than the Fe3O4@NFC@NNS-Mn(III) catalyst, indicating
that the larger surface, the site can contribute to improved
catalytic performance. Aer the optimized conditions were
established, this catalytic system was applied to oxidate a wide
variety of primary and secondary alcohols to the corresponding
carbonyl compounds. As shown in Table 4, good to excellent
yields were accomplished in both primary and secondary alco-
hols. The electron nature of the substituents on the aromatic
ring of primary alcohols displayed no apparent effect on this
transformation, because the products were obtained in high
yields. Secondary alcohols to the corresponding carbonyl
compounds. As shown in Table 4, good to excellent results were
accomplished in both primary and secondary alcohols.
Fig. 7 Comparison of the performance of catalysts with each other.
Reaction conditions: alcohols (1 mmol), TBHP (2 mmol), catalyst
(0.5 mol%), S. F., 40 ꢀC.
The stability and reusability of Fe3O4@NFC@NNSM-Mn(III) as
a tri-nuclear catalyst manganese in the xanthene and alcohol–
oxidation reactions
Recovery and reusability of the catalyst are very substantial
factors, exclusively for commercial and industrial applications.
These abilities, clearly contend a heterogeneous catalyst as
a suitable troth towards more sustainable and green chemical
developments. In this line, to investigate the catalyst recycla-
bility, experiments were performed for the model xanthene and
alcohol–oxidation reactions, under the optimized reaction
conditions. To do this, aer each investigation, the catalyst was
separated from the reaction mixture with a magnet. Then, the
isolated catalyst was washed with water and EtOH, vacuum-
ꢀ
dried at 60 C for 2 h, and directly used in the next run of the
reaction. Residual activation was analyzed by ICP for measure-
ment. The amount of manganese that goes from the catalyst to
the solution. As shown in Fig. 9, the catalyst was recovered and
reused for at least 6 consecutive runs without notable loss of
activity. The xanthene and alcohol–oxidation reactions yield
Fig. 8 Reaction conditions: benzyl alcohol (1 mmol), oxidant (2
mmol), catalyst (0.5 mol%), S. F., 40 ꢀC for 20 min.
ꢀ
60 C. The reduction in the product yield could be due to the
decomposition of TBHP to molecular water and tert-butanol in
the presence of Fe3O4@NFC@NNSM-Mn(III) at evaluated
ꢀ
temperatures. As a result, 40 C was selected as the optimum
reaction temperature. Further investigation disclosed that the
number of oxidizing agents is crucial to the product yield
(entries 13–14). When the oxidation of the model reaction was
carried out using 1, 2, and 3 mmol of tert-butyl hydroperoxide,
the product's yield increased as the concentration of tert-butyl
hydroperoxide increased. However, employing more than
three mmol oxidizing agents had the opposite effect on the
product yield that it could be due to over-oxidation. When H2O2,
oxone, and NaIO4 were used instead of TBHP as the oxidant, the
catalyst activity was less than the original, indicating that the
choice of oxidant also has a signicant impact on the oxidation
of alcohol (Fig. 8). The results showed that TBHP is the best
oxygen source because of its good oxidation conversion. By
Fig.
9 Recyclability of Fe3O4@NFC@NNSM-Mn(III) in the model
alcohol oxidation and xanthene multi-component reaction, under the
optimized reaction conditions; Reaction times: 10 min (xanthene
multi-component reaction) and 30 min (alcohol oxidation).
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percentages of the heavy metals and conrm the durability of
the catalyst during recycling.
To show the durability and structure of the catalyst, the
recovered catalyst aer the 6th run was subjected to some
analyses. The FT-IR spectrum of the recovered catalyst aer ve
runs (Fig. 10), revealed the entire preservation of the shape,
position, and relative intensity of the characteristic absorption
bands. This result proved that no substantial changes occurred
in the chemical structure of the present catalyst.
Furthermore, the VSM and FESEM analysis of the catalyst
aer six times of reuse showed that the design and morphology
of the catalyst maintained unchanged during the recycling
process (Fig. 10). These ndings well suggested the commend-
able stability and durability of the tri-nuclear catalyst Mn(III).
Experimental
Materials and measurement
Chemicals and solvents used by Merck company have been
prepared. Product identication is made by their physical and
spectral properties. The FT-IR spectra are recorded by the Per-
kin Elmer 780. The 13C NMR and 1H NMR spectra are recorded
by the Bruker Avance DPX-250 in CDCl3 solvent at room
temperature and the use of TMS as an internal standard. The
Electrothermal 9100 was used to measure melting temperature.
The transmitting electron microscope (TEM) of the Philips
CM10 model and imaging was performed with 100 kV voltage.
The elements in the samples were probed by energy-dispersive
X-ray (EDX) spectroscopy accessory to the Philips scanning
electron microscopy, eld emission scanning electron micros-
copy (FE-SEM) images were obtained on a Tescan MIRA3
Powder X-ray diffraction (PXRD) was conducted using an X'Pert
˚
Pro MPD diffractometer equipped with a Cu-Ka (l ¼ 1.54060 A)
radiation source between 2y ¼ 21 and 2y ¼ 50.01. Magnetic
isotherms were obtained at room temperature using the VSM
magnetic meter, the LakeShore Cryotronics 7407 model.
Synthesis of Fe3O4@NFC–Cl (I–II)
Core–shell (I) Fe3O4@NFC nanospheres were prepared accord-
ing to the formerly described method (Scheme 1).52 Initially,
Fe3O4@NFC (1.5 g) was sonicated in dry toluene (15 ml) for
30 min, and then 3-chloropropyl-trimethoxy silane (1 ml) was
added slowly to the mixture. The mixture was then stirred for
24 h under N2 gas at reux conditions. Aer completion of the
reaction, the reaction mixture was washed with toluene and
diethyl ether and separated using an external magnet, and dried
Fig. 10 (I) FT-IR; (II) VSM ((a) before recycling and (b) after recycling);
(III) Fe-SEM analysis of Fe3O4@NFC@NNSM-Mn(III) after six times.
reached to 85% and 87% for the 6th run. To show durability and
structure of the catalyst, the recovered catalyst aer 6th run was
subjected to some analyses. Also, metal leaching of the catalyst
was measured in each cycle. As shown in Fig. 9, a few leaching
was observed for Fe3O4@NFC@NNSM-Mn(III), whereas only
3.6% for xanthene reaction and 3.2% for alcohol oxidation
reaction metal leaching was observed aer the 6th run. More-
over, ICP analysis of the catalyst for each heavy metal demon-
strated an insignicant change in their weight percentage than
the corresponding fresh values: Fe 45.58, Si 2.35, Mn 6.9 w%.
These results demonstrated insignicant changes in the
ꢀ
at 75 C for 8 h in an oven under vacuum.
Synthesis of 5-(chloromethyl)-2-hydroxybenz aldehyde (IV)
We prepared 1 according to a procedure described62,63 that
involved addition (0.125 mol) of salicylaldehyde, in small
portions with stirring, to 75 ml of concentrated hydrochloric
acid containing (0.225 mol) of paraformaldehyde. This reaction
mixture was maintained at 70 ꢀC with stirring for 24 h and then
water (20 ml) was added to the mix, and the product was
extracted into CH2Cl2 (20 ml). Then the reliable product was
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Scheme 1 Overall flowchart for the fabrication of Fe3O4@NFC@NNSM-Mn(III).
ꢀ
collected by suction ltration and anhydrous MgSO4 was used MP 85–87 C, yield: 95% of pale purple crystals. Its purity was
for drying the organic phase. The CH2Cl2 was removed with checked using TLC with silica-gel plates.
a rotary evaporator and thick yellow oil was set aside overnight.
FT-IR (KBr): nꢀ ¼ 3151 (O–H), 3033, 2975, 2865 (C–H alde-
Then a pale purple reliable product III was isolated (Scheme 1). hyde), 1665 (C]O), 1434 (C]C), 673 (CH2–Cl) cmꢁ1
.
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1H NMR (DMSO, 300 MHz): d ¼ 4.80 (s, 2H, CH2), 7.56–7.60
(d,d, 2H, H–Ar), 7.72 (s, 1H, H–Ar), 10.06 (s, 1H, CH of alde-
hyde), 11.30 (s, 1H, O–H) ppm. 13C NMR (DMSO, 75 MHz): d ¼
47.0, 117.8, 124.8, 131.1, 136.1, 136.4, 148.4, 163.2, 197.7 ppm.
Preparation of the Fe3O4@NFC@NN from o-
phenylenediamine functionalized Fe3O4@NFC–Cl (III, V)
Fe3O4@NFC–Cl (1.00 g) was reuxed with o-phenylenediamine
(1 mmol : 0.108 g) in CH2Cl2 (10.0 ml) for 12 h to replace the
terminal chlorine atoms. Then 5-(chloromethyl)-2-hydroxy
benzaldehyde (1 mmol : 0.17 g) was added and the mixture
was reuxed for 8 h. Finally, Fe3O4@NFC@NNS(V) was ltered
off, washed three times with ethanol, and dried at 70 ꢀC in the
vacuum oven.
Scheme
xanthene reactions.
2
Catalytic activity of the Fe3O4@NFC@NNSM-Mn(III)
via a comparison of their melting points with the reported ones.
The spectral data for the selected compounds are as follows:
9-Phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione
(Table 2, entry 1). 1H NMR (DMSO, 300 MHz): d ¼ 1.63–1.93 (m,
4H, CH2), 2.01–2.20 (m, 4H, CH2), 2.37–2.48 (m, 4H, CH2), 3.97
(s, 1H, CH), 7.13–7.20 (m, 5H, aromatic) ppm. 13C NMR (DMSO,
75 MHz): d ¼ 21.0, 29.1, 36.3, 38.7113.1, 124.7, 127.1, 129.4,
143.9, 155.4, 199.8 ppm. Mp (ꢀC): 203–204.
Loading with Mn (OAc)3$2H2O (VI)
Fe3O4@NFC@NNS (1.00 g) was mixed with Mn(OAc)3$2H2O (1.2
mmol : 0.32 g) in ethanol (5 ml). The mixture was stirred for 12
hours at room temperature. Aer completion of the reaction,
then it was ltered, and the solid obtained was washed with
ethanol and dried at 70 ꢀC overnight to give Fe3O4@NFC@NNS-
Mn. The manganese loading of Fe3O4@NFC@NNS-Mn(III) was
determined by the inductively coupled plasma (ICP) technique.
9-(4-Chlorophenyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8(2H)-dione (Table 2, entry 2). 1H NMR (DMSO, 300 MHz): d ¼
2.11–2.14 (m, 4H, CH2), 2.45–2.48 (m, 4H, CH2), 2.97–3.04 (m,
Synthesis of Fe3O4@NFC@ONSM-Mn magnetic catalyst (VII)
4H, CH2), 3.93 (s, 1H, CH), 6.97–7.09 (m, 4H, aromatic) ppm. 13
C
Immobilized Fe3O4@NFC@NNS-Mn(III) complex (8) along with
a weighted amount of melamine (molar ratio 3 : 1) were trans-
ferred to a 25 ml oven-dried round bottom ask equipped with
a magnet and a condenser. A solution of triethylamine (3.0
mmol : 0.39 ml) in MeOH (10.0 ml) was added to the mentioned
mixture. The mixture was reuxed in N2 atmosphere for 12 h.
The product, Fe3O4@NFC@NNSM-Mn(III) (9) was collected
using an external magnetic eld, washed with water (2 ꢂ 10 ml)
and EtOH (2 ꢂ 10 ml) and dried into a vacuum oven (5 h, 60 ꢀC).
Scheme 1 shows the complete route for the preparation of VII.
NMR (DMSO, 75 MHz): d ¼ 21.5, 29.6, 36.9, 38.9, 113.2, 127.8,
129.7, 131.8, 143.9, 155.6, 199.5 ppm. Mp (ꢀC): 229–230.
9-(4-Methoxyphenyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8(2H)-dione (Table 2, entry 3). 1H NMR (DMSO, 300 MHz): d ¼
1.58–1.70 (m, 4H, CH2), 2.63–2.67 (t, 4H, CH2), 2.99–3.04 (t, 4H,
CH2), 3.67–3.71 (s, 3H, CH3), 4.05 (s, 1H, CH), 6.70–7.13 (s, s,
4H, aromatic) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 20.9, 29.8,
35.4, 36.9, 55.3, 113.2, 113.8, 129.7, 134.6, 153.8, 157.3,
199.9 ppm. Mp (ꢀC): 205–206.
9-(2-Nitrophenyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8(2H)-dione (Table 2, entry 4). 1H NMR (DMSO, 300 MHz): d ¼
0.85–0.96 (m, 4H, CH2), 2.52–2.56 (t, 4H, CH2), 2.73–2.78 (t, 4H,
CH2), 3.99 (s, 1H, CH), 6.68–7.58 (m, 4H, aromatic) ppm. 13C
NMR (DMSO, 75 MHz): d ¼ 22.5, 29.3, 34.2, 36.0, 116.0, 124.5,
127.1, 129.4, 130.4, 134.6, 147.8, 154.5, 199.6 ppm. Mp (ꢀC):
259–261.
9-(2-Hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahy-
dro-1H-xanthene-1,8(2H)-dione (Table 2, entry 5). 1H NMR
(DMSO, 300 MHz): d ¼ 1.35–1.49 (m, 4H, 2CH2), 2.01–2.09 (t,
4H, 2CH2), 2.57–2.63 (t, 4H, 2CH2), 4.59 (s, 1H, CH), 7.02–7.21
(m, 4H, aromatic), 10.51 (s, 1H, OH) ppm. 13C NMR (DMSO, 75
MHz): d ¼ 20.8, 29.8, 32.3, 35.2, 111.0, 115.7, 118.3, 124.5, 127.5,
128.0, 154.7, 156.8, 196.6 ppm. Mp (ꢀC): 259–261.
3,3,6,6-Tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-
xanthene-1,8(2H)-dione (Table 2, entry 6). 1H NMR (DMSO, 300
MHz): d ¼ 1.11 (s, 12H, 4CH3), 1.82 (s, 4H, 2CH2), 2.07 (s, 4H,
2CH2), 4.06 (s, 1H, CH), 7.02–7.09 (m, 5H, aromatic) ppm. 13C
NMR (DMSO, 75 MHz): d ¼ 28.3, 33.8, 37.8, 52.4, 110.3, 125.8,
127.8, 128.4, 144.7, 155.7, 197.7 ppm. Mp (ꢀC): 203–204.
Synthesis of bis-aldehyde derivatives
A mixture of 2-hydroxy benzaldehyde (10 mmol) or 3-hydroxy
benzaldehyde (10 mmol) or 4-hydroxy benzaldehyde (10 mmol)
and 1,4-di-bromobutane (5 mol) or 1,2-di-bromoethane (5
mmol) in NaOH (10 mmol) in ethanol solvent was reuxed for
24 hours. The reaction mixture was cooled to room tempera-
ture, and the product precipitate was separated aer re-
crystallization in ethanol and dried in an oven.
General experimental procedure for the synthesis of xanthene
In a round-bottomed ask, aldehyde (1 mmol), dimedone (2
mmol) and Fe3O4@NFC@NNSM-Mn(III) (0.5 mol%) were mixed
thoroughly at EtOH (5 ml). The ask was heated at 45 C with
concomitant stirring. Aer completing the reaction conrmed
by TLC (EtOAc : n-hexane), the solid catalyst was separated from
the reaction mixture by an ordinary magnet. The solvent was
evaporated, and the green products were recrystallized from
ethanol, gave the pure products 88–97% yields based on the
starting aldehyde (Scheme 2). The products were characterized
ꢀ
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8H, 4CH2), 3.95–4.13 (m, 4H, 2CH2), 4.78 (s, 1H, CH), 6.75–6.79
(m, 2H, CH aromatic), 4.78 (s, 1H, CH), 6.75–6.79 (m, 2H, Ar),
7.00–7.04 (m, 2H, Ar), 7.20–7.25 (m, 2H, Ar), 7.84–7.88 (m, 2H,
Ar), 9.91 (s, 1H, COH) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 20.3,
25.9, 27.1, 30.8, 37.0, 67.1, 67.9, 114.0, 114.7, 117.0, 117.1, 129.3,
129.8, 132.0, 136.8, 157.4, 163.7, 164.1, 190.9, 196.7 ppm. Mp
(ꢀC): 168–170.
9-(4-Chlorophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahy-
dro-1H-xanthene-1,8(2H)-dione (Table 2, entry 7). 1H NMR
(DMSO, 300 MHz): d ¼ 1.25 (s, 6H, 2 ꢂ 2CH3), 2.19 (s, 2H, 2 ꢂ
CH2), 5.51 (s, 1H, CH), 7.11–7.17 (d, 2H,
2
ꢂ
2CH
aromatic) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 26.9, 30.1, 36.0,
36.5, 52.4, 114.5, 128.4, 133.1, 141.3, 157.1, 198.7 ppm. Mp (ꢀC):
169–171.
4-(2-(4-(3,3,6,6-Tetramethyl-1,8-dioxo-2,3,4,5,6,7,8,9-octahy-
dro-1H-xanthene-9-yl)phenoxy)ethoxy)benzaldehyde (Table 2,
entry 13). H NMR (DMSO, 300 MHz): d ¼ 1.12 (s, 12H, 4CH3),
9-(2-Hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahy-
dro-1H-xanthene-1,8(2H)-dione (Table 2, entry 8). 1H NMR
(DMSO, 300 MHz): d ¼ 1.07 (s, 12H, 4CH3), 1.71 (s, 4H, 2CH2),
2.26 (s, 4H, 2CH2), 1.98–2.00 (m, 2H, CH2), 2.36 (s, 2H, CH2),
2.40 (s, 2H, CH2), 6.66–7.24 (m, 4H, CH-aromatic) 10.51 (s, 1H,
OH) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 20.8, 27.7, 32.5, 34.2,
37.1, 48.5, 112.4, 115.7, 124.7, 126.2, 127.3, 128.8, 155.5, 157.9,
196.4 ppm. Mp (ꢀC): 200–202.
4-(3,3,6,6-Tetramethyl-1,8-dioxo-2,3,4,5,6,7,8,9-octahydro-
1H-xanthene-9-yl) benzaldehyde (Table 2, entry 9). 1H NMR
(DMSO, 300 MHz): d ¼ 1.25 (s, 6H, 2 ꢂ 2CH3), 1.88 (s, 2H, 2ꢂ
CH2), 2.19 (s, 2H, 2ꢂ CH2), 5.51 (s, 1H, CH), 7.11–7.17 (d, 2H, 2
ꢂ 2CH aromatic), 11.88 (s, 1H, COH) ppm. 13C NMR (DMSO, 75
MHz): d ¼ 28.3, 31.7, 37.8, 52.4, 115, 127.8, 130.2, 133.1, 149,
157.1, 195.6, 206.4 ppm. Mp (ꢀC): 295–297.
1
2.21 (s, 4H, 2CH2), 2.29 (s, 4H, 2CH2), 3.97 (s, 1H, CH), 4.29–4.32
(m, 2H, CH2), 4.37–4.40 (m, 2H, CH2), 6.79–6.86 (m, 4H,
aromatic), 7.04–7.07 (d, 2H, aromatic), 7.84–7.88 (m, 2H,
aromatic), 9.91 (s, 1H, COH) ppm. 13C NMR (DMSO, 75 MHz):
d ¼ 27.3, 32.2, 50.7, 66.0, 66.8, 114.1, 114.9, 115.6, 115.7, 127.8,
129.4, 132.0, 137.2, 156.8, 157.0, 162.1, 163.7, 190.8, 196.5 ppm.
Mp (ꢀC): 200–202.
2-(4-(2-(1,8-Dioxo-2,3,4,5,6,7,8,9-octahydro-1H-xanthene-9-
yl)phenoxy)butoxy)benzaldehyde (Table 2, entry 14). 1H NMR
(DMSO, 300 MHz): d ¼ 2.01–2.09 (m, 4H, 2CH2), 2.33–2.65 (m,
8H, 4CH2), 3.06–3.11 (m, 4H, 2CH2), 3.80 (s, 1H, CH), 3.97–4.14
(m, 4H, 2CH2), 6.94–7.04 (m, 3H, aromatic), 7.23–7.25 (d, 1H,
aromatic), 7.42–7.45 (d, 1H, aromatic), 7.57–7.60 (t, 1H,
aromatic), 7.69–7.71 (d, 1H, aromatic), 7.84–7.86 (d, 1H,
aromatic), 9.91 (s, 1H, COH) ppm. 13C NMR (DMSO, 75 MHz):
d ¼ 20.4, 25.9, 27.0, 30.3, 36.9, 67.7, 68.5, 112.5, 114.0, 119.8,
121.0, 124.7, 127.9, 131.0, 132.9, 136.9, 157.7, 158.6, 161.5,
189.5, 196.5. Mp (ꢀC): 220–222.
9,90-((Ethane-1,2-diylbis(oxy))bis(3,1-phenylene))bis(3,3,6,6-
tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione)
(Table 2, entry 15). 1H NMR (DMSO, 300 MHz): d ¼ 1.03 (s, 12H,
2 ꢂ 4CH3), 2.23 (s, 4H, 2 ꢂ 2CH2), 2.49 (s, 4H, 2 ꢂ 2CH2), 4.28
(s, 2H, 2ꢂ CH2), 4.77 (s, 1H, 2ꢂ CH), 6.70–7.18 (m, 4H, 2ꢂ
aromatic) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 27.5, 32.2, 50.7,
112.4, 114.9, 115.5, 121.4, 128.9, 145.7, 158.5, 162.3, 196.4 ppm.
Mp (ꢀC): 250–252.
9-(1H-Indol-3-yl)-3,4,5,6,7,9-hexahydro-1H-xanthene-
1
1,8(2H)-dione (Table 2, entry 10). H NMR (DMSO, 300 MHz):
d ¼ 1.79–1.84 (m, 4H, 2CH2), 1.92–1.96 (m, 4H, 2CH2), 3.45–3.49
(t, 4H, 2CH2), 4.89 (s, 1H, CH), 6.93–6.98 (m, 2H, aromatic), 6.99
(s, 1H, CH indole), 7.04–7.59 (d of d, 2H, aromatic), 10.80 (s, 1H,
NH) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 22.3, 26.9, 34.1, 36.9,
103.9, 111.8, 118.5, 119.4, 120.9, 124.2, 126.1, 136.6, 164.7,
196.8 ppm. Mp (ꢀC): 267–269.
3,3,6,6-Tetramethyl-9-(5-nitrofuran-2-yl)-3,4,5,6,7,9-hexahy-
dro-1H-xanthene-1,8(2H)-dione (Table 2, entry 11). 1H NMR
(DMSO, 300 MHz): d ¼ 1.14 (s, 12H, 4CH3), 1.85 (s, 4H, 2CH2),
2.32 (s, 4H, 2CH2), 5.47 (s, 1H, CH), 6.25 (s, 1H, furane), 7.28 (s,
1H, furane) ppm. 13C NMR (DMSO, 75 MHz): d ¼ 26.2, 28.0,
31.9, 35.5, 50.4, 110.3, 111.9, 115.1, 150.7, 161.5, 162.9,
196.1 ppm. Mp (ꢀC): 155–157.
4-(4-(4-(1,8-Dioxo-2,3,4,5,6,7,8,9-octahydro-1H-xanthene-9-
yl)phenoxy)butoxy)benzaldehyde (Table 2, entry 12). 1H NMR
(DMSO, 300 MHz): d ¼ 1.93–2.04 (m, 4H, 2CH2), 2.33–2.67 (m,
The general procedure of oxidation of alcohols
In a typical experiment, Fe3O4@NFC@NNSM-Mn(III) (0.5 mol%)
and TBHP (1 mmol) were placed in a vessel containing benzyl
Table 5 Comparison of the reaction conditions and results for the synthesis of xanthene
Entry
Catalyst
Solvent
Time (min)
Temp. (ꢀC)
Yield (%)
Ref.
1
2
3
4
5
6
7
8
[SO3H–Pyrazine–SO3H]Cl2
Fe3O4 nanoparticles
TCCAa
[Et3N–SO3H]Cl
LUS-Pr-SO3Hb
[Cmmim][BF4]
ICl3/SiO2
NP
Cu(II)/NP
—
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
EtOH
10
20
40
60
15
120
60
6.5 h
120
24 h
10
100
100
110
80
140
80
93
90
78
97
90
94
90
90
98
—
96
56
64
65
22
66
67
68
69
75
Reux
Reux
Reux
45
9
10
11
EtOH
EtOH
EtOH
70
71
Fe3O4@NFC@NNSM-Mn(III)
This work
a
Trichloroisocyanuric acid. b Propyl sulfonic acid functionalized LUS-1 (Laval University silica) (LUS-Pr-SO3H).
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alcohol (1 mmol) without any organic solvents as green condi-
ꢀ
tions were stirred at 40 C for an appropriate time. Upon reac-
tion completion, monitored by TLC, the catalyst was removed
from the mixture of reaction by the magnet. The products were
puried on a silica gel plate to give pure products. For the
identication of the nal products, their physical data were
compared with those of reliable samples, because all of them
have been studied in the past. Also all of these compounds are
already known.
Comparative study
To better clarify the merits of the competency tri-nuclear cata-
lytic system over the reported metal-based other catalytic
systems in the xanthene reactions, the comparing efficacy
results were tabulated in Table 5. It has been observed that the
synthesized catalyst has almost a very good advantage over
other reported catalysts which can be due to suitable reaction
conditions, short reaction time, high reaction efficiency and
Scheme 3 A plausible mechanism for the synthesis of xanthene while
lower catalyst load and on the other hand timely recovery of using the Fe3O4@NFC@NNSM-Mn(III) catalyst.
magnetic catalyst. In addition to the reusability of the catalyst,
most importantly, the use of a non-toxic, benign green solvent
that is environmentally friendly and does not require the use of
any additives or toxic solvents supports the green chemistry
approach well. Chromium derivatives containing aromatic
aldehydes can be synthesized by our catalytic method. These
promising results should be attributed to the co-operation of
three metal verb positions: Lewis acid in Fe3O4@NFC@NNSM-
Mn(III). Finally, a series of green metrics72,73 such as atom
economy (AE), atom efficiency (AEF), carbon efficiency (CE),
reaction mass efficiency (RME), optimum efficiency (OE),
process mass intensity (PMI), E-factor (E), solvent intensity (SI),
and water intensity (WI) were calculated to evaluate the green-
ness of the one-pot three-component reaction of aldehydes,
dimedone (Fig. 11–13, see ESI for detailed calculations† for
detailed calculations). As it is shown in Fig. 11a and 12a, the
high values of the AE, AEF, CE, RME, and OE for the synthesis of
three xanthene derivatives of Table 2 (entries 5–7) and also new
derivatives Table 2 (entries 11–15), illustrate well the greenness
of the process. The lower the PMI, E, and SI, the more favour-
able is the process because of green chemistry. These values are
less than 50 in the synthesis of the xanthene mentioned above's
(Fig. 11b and 12b, see ESI†). Minimal amounts of WI were also
obtained in these processes (Fig. 11b and 12b, see ESI†). The
green organic solvent, which was used in these protocols was
EtOH. Hence, it can be concluded that about the high values of
RME and low values of PMI, E, SI, and WI, this one-pot three-
component process is an efficient and green protocol for
synthesizing xanthene. To stable, the more greenness of the
current catalyst over the reported catalysts in the one-pot three-
component reaction of benzaldehyde, dimedone, the current
catalyst's green metrics was compared with those of two previ-
ously reported catalysts (Table 5, entries 1 and 8).56,70
acknowledged that the Fe3O4@NFC@NNSM-Mn(III) is a greener
and more supportable catalyst for such an Multi-component
reaction (see ESI† for detailed calculations).
Mechanism studies
An acceptable mechanism for the synthesis of xanthine using
the Fe3O4@NFC@NNSM-Mn(III) catalyst has been reported.
Initially, the acid catalyst Fe3O4@NFC@NNSM-Mn(III) activates
the carbonyl aldehyde and dimedone groups, and intermediate
(I) is formed from the densied Knoevenagel densities of
dimedone and aryl aldehyde by the removal of a water molecule.
Then, from the increase of Michael Dimedone's next molecule
to intermediate (I), intermediate (II) is formed, which is
As can be perceived from the results in Fig. 13a and b (see
ESI†), the higher the AEF, CE, and RME factors and the lower
the PMI, E, SI, and WI factors of Fe3O4@NFC@NNSM-Mn(III)
Scheme 4 A plausible mechanism for the synthesis of oxidation
compared with those of NP and [SO3H–Pyrazine–SO3H]Cl2, alcohols while using the Fe3O4@NFC@NNSM-Mn(III) catalyst.
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tautomeric with intermediate (III). In the end, by intramolecular
looping and removal of a water molecule, product (IV) is ob-
tained (Scheme 3).
The proposed reaction mechanism for the oxidation of
benzyl alcohol derivatives using TBHP in the presence of Fe3-
O4@NFC@NNSM-Mn(III) based on the available literature74 is
shown in Scheme 4. Decomposition of t-BuOOH on the surface
of Fe3O4@NFC@NNSM-Mn(III) leads to the formation of t-
BuOOc radical species and also increase of Mn(III) to Mn(IV).
Besides, decomposition of t-BuOOH on the surface of Mn(IV)
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Conclusions
In this work, a novel magnetically trinuclear catalyst denoted as
Fe3O4@NFC@NNSM-Mn(III) was successfully fabricated as an
efficient trinuclear catalyst. To characterize the tri-nuclear
catalyst, various techniques, including FT-IR, XRD, TGA, TEM,
FESEM, EDX, VSM, and ICP analysis have been employed.
Interestingly, Fe3O4@NFC@NNSM-Mn(III) was an excellent tri-
nuclear catalyst to promote the xanthene and alcohol–oxidation
reactions of a broad range of benzaldehyde and most impor-
tantly the highly challenging benzyl alcohol, which are far
extensively available and cheaper. The presented catalytic
system can be magnetically separated and conveniently recycled
at least ve times without a noticeable decrease in its activity.
Moreover, low metal leaching and utilizing an eco-friendly
solvent are other advantages that support the going protocol
towards green chemistry. The use of the presented new trinu-
clear catalyst to promote another Multi-component reaction is
continuing in our lab.
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Conflicts of interest
There are no conicts to declare.
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Acknowledgements
We gratefully acknowledge the nancial support of the research
Council of the University of Birjand and we also thank Univer-
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