Magnetic spent coffee ground as an efficient and green catalyst for aerobic oxidation of alcohols and tandem oxidative Groebke–Blackburn–Bienaymé reaction

Article abstract of DOI:10.1007/s13738-020-02102-x

Abstract: In this work, magnetic spent coffee ground as a green, inexpensive, and abundant material was synthesized and characterized by a variety of techniques, including X-ray diffraction pattern, thermal gravimetric analysis, scanning electron microscopy, energy-dispersive spectroscopy, inductively coupled plasma optical emission spectrometry, and Fourier transform infrared spectroscopy. The magnetic spent coffee ground was successfully utilized as a catalyst in aerobic oxidation of primary and secondary benzylic alcohols and tandem oxidative Groebke–Blackburn–Bienaymé reaction. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-020-02102-x

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-02102-x
ORIGINAL PAPER
Magnetic spent cofee ground as an eꢀcient and green
catalyst ꢁor aerobic oxidation oꢁ alcohols and tandem oxidative
Groebke–Blackburn–Bienaymé reaction
Hassan Farhid · Ahmad Shaabani1
1
Received: 21 August 2020 / Accepted: 14 October 2020
©
Iranian Chemical Society 2020
Abstract
In this work, magnetic spent cofee ground as a green, inexpensive, and abundant material was synthesized and characterized
by a variety oꢀ techniques, including X-ray difraction pattern, thermal gravimetric analysis, scanning electron microscopy,
energy-dispersive spectroscopy, inductively coupled plasma optical emission spectrometry, and Fourier transꢀorm inꢀrared
spectroscopy. The magnetic spent cofee ground was successꢀully utilized as a catalyst in aerobic oxidation oꢀ primary and
secondary benzylic alcohols and tandem oxidative Groebke–Blackburn–Bienaymé reaction.
Graphic abstract
Keywords Spent cofee grounds · Aerobic oxidation · Tandem oxidation process · Magnetic materials · GBB reaction ·
Lignocellulose
Electronic supplementary material The online version oꢀ this
article (https://doi.org/10.1007/s13738-020-02102-x) contains
supplementary material, which is available to authorized users.
Extended author inꢀormation available on the last page oꢀ the article
Vol.:(0
1
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Journal of the Iranian Chemical Society
Introduction
Cofee is one oꢀ the most popular beverages in the world and
one oꢀ the superlative vital ingredients in daily human liꢀe.
This has caused cofee comes second as the world’s most
important commodity aꢀter ꢀossil ꢀuel [1]. According to the
International Cofee Organization (ICO), about 9.1 million
tons oꢀ cofee production was consumed in 2016 and is esti-
mated that 1.6 billion cups oꢀ cofee were spent every day by
people around the world [2, 3]. Spent cofee ground (SCG)
reꢀers to the waste material generated aꢀter preparation oꢀ
the cofee beverage or manuꢀacturing oꢀ instant cofee. Uni-
versally, 550–670 kg oꢀ SCG is produced ꢀrom 1 ton oꢀ coꢀ-
ꢀ
ee bean; thus, over 5.8 million tons oꢀ SCG has generated
annually [4]. This enormous waste directly discards in land-
lls and causing environmental problems due to the pres-
Fig. 1 XRD patterns oꢀ SCG and SCG@Fe O
4
ꢁ
3
ence oꢀ various organic compounds like cafeine, tannins,
and polyphenols [5]. The re-use oꢀ these wastes rather than
simple disposal is important ꢀrom both environmental and
commercial aspects [6]. Thereꢀore, researchers have ꢀound
various applications to utilize these wastes such as biodiesel
Materials and methods
Materials
[
7], and bioethanol [8] production, catalyst [9], composting
10], activated carbon synthesis [11], sugar production [12],
[
SCG used was provided by local cofee shops. All reagents
were purchased ꢀrom Sigma-Aldrich and used without ꢀur-
ther puriꢁcation. The FT-IR spectra were recorded on a
Thermo Nicolet NEXUS 470 FT-IR spectrometer. The
amounts oꢀ metals were measured using an inductively
coupled plasma optical emission spectrometer (ICP-OES;
Varian Vista PRO Radial). Products oꢀ oxidation oꢀ alco-
hols were analyzed using a Varian 3900 GC. The X-ray
powder difraction (XRD) patterns were recorded on an
STOE difractometer with Cu-Kα radiation (λ = 1.5418
Å). Thermogravimetric analysis (TGA) was carried out
using STA 1500 instrument at a heating rate oꢀ 10 °C
min- in the air. Scanning electron microscopy (SEM)
mushroom growth [13], and heavy metals adsorbent [14].
However, due to the high volume oꢀ this waste, there is still
need to ꢁnd a solution to utilize these natural wastes [15].
SCG consists oꢀ 74.2 wt% carbohydrate (that predominantly
is lignocellulose), 13.3 wt% protein, 10.3 wt% oil, and 2.2
wt% ash [16].
Catalytic aerobic oxidation oꢀ alcohols is a signiꢁcant
organic transꢀormation ꢀrom both laboratory and industrial
chemistry points oꢀ view [17–20]. The tandem oxidation
process (TOP) is an inventive and well-organized syn-
thetic protocol, which combines in situ generated aldehyde
or ketone ꢀrom oxidation oꢀ alcohols with nucleophiles
1
[
21–23]. Although the extensive research protocols have
been reported ꢀor the development oꢀ TOP, its applica-
tion in some chemical process, especially multicomponent
reactions (MCRs), is less considered [24]. This is probably
because oꢀ the inherent complexity oꢀ MCRs mechanism
and multiple ꢀunctionalities oꢀ these processes [25, 26].
Fe O nanoparticles (NPs) are prominent and green mate-
3
4
rials and are widely used as a support ꢀor signiꢁcant homo-
geneous catalytically active metals due to easier separation
operation [27, 28]. Moreover, these NPs can eꢂciently cata-
lyze various transꢀormations such as oxidation reactions [29]
or act as a Lewis acid in acid-catalyzed reactions [30].
According to these points and in order to develop an
appropriate utilization ꢀor SCG that has causes environ-
mental problems, herein, we investigate the catalytic activ-
ity oꢀ magnetic SCG in aerobic oxidation oꢀ alcohols and
the tandem oxidative GBB reaction.
Fig. 2 TGA curves oꢀ SCG and SCG@Fe O
3
4
1
3

Journal of the Iranian Chemical Society
Fig. 3 SEM images oꢀ SCG (a,
b) and SCG@Fe O (c, d)
3
4
Fig. 5 FT-IR spectra oꢀ SCG and SCG@Fe O
3
4
Fig. 4 EDS result ꢀor SCG@Fe O
3
4
Preparation of SCG
observations were carried out on an electron microscopy
Philips XL-30 ESEM. All samples were sputtered with
gold beꢀore observation. Melting points were measured
SCG was washed with boiling water several times until the
color oꢀ solvent was remained almost colorless and then
dried at 100 °C ꢀor 8 h. The washed SCG (10 g) is weighed
into a thimble in the Soxhlet extractor and ꢁtted to a coni-
cal ꢃask. Cofee oil is extracted with 250 mL n-hexane
under reꢃux ꢀor 1 h. Then, the sample was washed with
n-hexane several times and dried at 100 °C ꢀor 8 h.
1
with an Electrothermal 9200 apparatus. H NMR spectra
were recorded on a BRUKER DRX-300 AVANCE spec-
trometer at 300.13 MHz. NMR spectra were obtained in
DMSO-d .
6
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Journal of the Iranian Chemical Society
Table 1 Optimization oꢀ reaction conditions ꢀor aerobic oxidation ꢀor
Table 2. The progress oꢀ the reaction was ꢀollowed by
TLC. Upon completion, the reaction mixture was ꢁltered
and the ꢁltrate was analyzed by GC.
benzyl alcohol by SCG@Fe O
3
4
Entry Catalyst
Amount oꢀ Solvent
catalyst (g)
Base
Yield (%)a
1
2
3
4
5
6
7
8
9
1
1
1
1
1
–
SCG
–
0.05
Toluene KOH
Toluene KOH
Toluene KOH
Toluene KOH
22
24
75
94
General procedure for tandem oxidative GBB
reaction using SCG@Fe O
3
4
SCG@Fe O4 0.03
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
SCG@Fe O4 0.05
3
3
An alcohol (1.00 mmol) was added to a two-necked
ꢃask containing SCG@Fe O (0.05 g), KOH (0.028 g,
Toluene K CO 18
3
2 3
3
4
Toluene NaOH 59
3
0
.50 mmol) and toluene (4.00 mL). The reaction was
b
c
Toluene KOH
Toluene KOH
p-xylene KOH
40
33
97
10
Trace
N.R.
N.R.
Trace
3
heated at 80 °C with continuous bubbling oꢀ air with a
3
−1
ꢃow rate oꢀ 15 mL min ꢀor 5 h. Aꢀterward, the reaction
3
mixture was cooled to room temperature and a 2-amino
heterocycle (1.00 mmol) and an isocyanide (1.00 mmol)
were added to the reaction mixture and stirred at 80 °C
0
1
2
3
4
DMF
KOH
3
d
d
d
d
n-hexane KOH
3
EtOH
KOH
KOH
3
ꢀ
or 3 h. Aꢀter completion oꢀ the reaction (monitored by
H O
3
2
TLC), the reaction mixture was cooled to the room tem-
perature and the crude oꢀ the reaction was ꢁltered. The
crude product was separated ꢀrom the catalyst with hot
ethanol and recrystallized with deionized water to aford
the corresponding pure product.
CH CN KOH
3
3
Conditions: benzyl alcohol (1.00 mmol), solvent (4 mL), base
(
0.50 mmol), air oxidant, 80 °C, 5 h
Yield determined by GC analysis
a
b
c
d
5
0 °C
5 °C
Reꢃux
2
Spectral data
N‑(tert‑butyl)‑2‑phenylimidazo[1,2‑a]pyridin‑3‑amine
(
Table 4, Entry 1)
Synthesis of SCG@Fe O
3
4
1
White solid (80%): mp 161 °C. H NMR (300.13 MHz,
DMSO-d ) δ: 8.39 (d, J = 6.9 Hz, 1H, H ), 8.16 (d,
The prepared SCG (1.00 g) was mixed with 25 mL
oꢀ deionized water and was stirred ꢀor 5 min. Then,
FeCl ·4H O (aq)/FeCl ·6H O (aq) (1:2) (0.37 g/1.00 g)
6
arom
J = 7.6 Hz, 2H, H ), 7.47–7.14 (m, 5H, H ), 6.86 (t,
arom
arom
2
2
3
2
J = 6.8 Hz, 1H, H ), 4.62 (br s, 1H, NH), 0.99 (s, 9H,
arom
which was dissolved in 2 mL oꢀ deionized water was
added while the temperature oꢀ the mixture was increased
to 80 °C ꢀor 1 h. Ammonia solution (25 wt%) was added
dropwise to adjust the pH oꢀ the solution to 10 and then
continuously stirred ꢀor 1 h at 80 °C. Subsequently, the
reaction mixture was cooled to room temperature and the
solution was neutralized with 0.5 M hydrochloric acid
solution. Aꢀter 1 h, magnetic SCG was separated using
an external magnet and washed with deionized water and
ethanol several times, and then, it was dried at 100 °C ꢀor
H
). Anal. Calcd ꢀor C H N : C, 76.95; H, 7.22; N,
aliphatic 17 19 3
15.84; ꢀound C, 77.03; H, 7.20; N, 15.75.
N‑cyclohexyl‑2‑phenylimidazo[1,2‑a]pyridin‑3‑amine
(Table 4, Entry 2)
1
White solid (81%): mp 176–178 °C. H NMR (300.13 MHz,
DMSO-d ) δ: 8.30 (d, J = 7.0 Hz, 1H, H
), 8.21 (d,
arom
6
arom
J = 7.7 Hz, 2H, H ), 7.47–7.14 (m, 5H, H ), 6.87 (t,
arom
8
h to aford SCG@Fe O .
J=6.8 Hz, 1H, H ), 4.79 (d, J =5.8 Hz, 1H, NH), 2.82
3
4
arom
(
br s, 1H, HCN), 1.72–1.48 (m, 5H, H
), 1.28–1.08 (m,
aliphatic
General procedure for oxidation of alcohols using
5H, H
). Anal. Calcd ꢀor C H N : C, 78.32; H, 7.26;
aliphatic 19 21 3
SCG@Fe O4
N, 14.42; ꢀound C, 78.64; H, 7.32; N, 14.04.
3
An alcohol (1.00 mmol) was added to a two-necked
ꢃask containing SCG@Fe O (0.05 g), KOH (0.028 g,
2‑(4‑Bromophenyl)‑N‑cyclohexylimidazo[1,2‑a]
pyridin‑3‑amine (Table 4, Entry 3)
3
4
0
.50 mmol), and toluene (4.00 mL). The reaction was
1
heated at 80 °C with continuous bubbling oꢀ air with a
White solid (73%): mp 175–176 °C. H NMR (300.13 MHz,
ꢃow rate oꢀ 15 mL min− ꢀor indicated times as given in
1
DMSO-d ) δ: 8.31 (d, J = 6.9 Hz, 1H, H
), 8.19 (d,
arom
6
1
3

Journal of the Iranian Chemical Society
Table 2 Aerobic oxidation
oꢀ various alcohols to the
corresponding carbonyl
compounds by SCG@Fe O
3
4
Entry
1
Alcohol
Product
Time (h) Yield (%)a
5
94
2
3
4
5
6
7
5
96
5
5
5
5
5
87
85
95
88
78
8
9
5
83
95
1.5
1
1
0
1
4
94
99
1.5
1
1
2
3
4
4
81
90
1
4
1.5
97
1
1
5
6
4
5
84
83
1
1
7
8
8
8
Trace
Trace
1
3

Journal of the Iranian Chemical Society
Table 2 (continued)
Conditions: alcohol (1.00 mmol), SCG@Fe O (0.05 g), toluene (4 mL), KOH (0.50 mmol), air oxidant,
3
4
8
0 °C, 5 h
a
Yield determined by GC analysis
Table 3 Comparison oꢀ the catalytic eꢂciency oꢀ SCG@Fe O with the reported catalysts ꢀor aerobic oxidation oꢀ benzyl alcohol
3
4
Entry
Catalyst
Solvent
Temperature
Oxidant
Additive
Time (h)
Yield (%)
Reꢀerences
1
2
3
4
5
6
7
8
9
Pd@SBA-15
Toluene
Toluene
Acetonitrile
–
Toluene
Toluene
Toluene
Toluene
Toluene
–
Toluene
o-xylene
p-xylene
p-xylene
Toluene
80 °C
40 °C
60 °C
50 °C
100 °C
105 °C
90 °C
110 °C
100 °C
140 °C
80 °C
r.t.
Air
Air
O2
O2
O2
O2
O2
O2
O2
O2
Air
Air
Air
Air
O2
K CO
–
TEMPO
–
–
–
5.5
24
8
1.5
4
>99
78
>98
85
78
>99
94
91.4
84.3
42.5
93.6
99
90
95
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[29]
[43]
[44]
[45]
[46]
2
3
Au/Hydrotalcite
Fe O /CuBDC/GO
3
4
Fe O /Cys-Pd
3
4
Fe O /C/MnO
2
3
4
Ru(OH) /Fe O
4
1
x
3
SiO @Fe O -Pro-Pd
K CO
10
10
6
5
8
7
0.5
4
2
3
4
2
3
Fe O @SiO @PEI@Ru(OH)
x
–
3
4
2
Fe O @SiO -Au
K CO
3
4
2
2
3
10
11
12
13
14
15
Fe O @C
–
–
3
4
Fe O /C
3
4
MnO /Cellulose
K CO
2
2
3
Porous chitosan–MnO2
Co-natural hydroxyapatite
Fe O @SiO @mTiO -
80 °C
80 °C
80 °C
–
KOH
–
a
0.75
99
3
4
2
2
HN(CH CH NH ) /Pd
2
2
2 2
1
6
SCG@Fe O
Toluene
80 °C
Air
KOH
5
94
This work
3
4
aUnder UV irradiation
J = 8.2 Hz, 2H, H
), 7.63–7.16 (m, 4H, H
), 6.89
Result and discussion
arom
arom
(
t, J = 6.8 Hz, 1H, H
), 4.84 (d, J = 5.9 Hz, 1H, NH),
arom
2
1
6
.82–2.78 (m, 1H, HCN), 1.73–1.50 (m, 5H, Haliphatic),
At ꢀirst, SCG was magnetized through co-precipitation
method and characterized by XRD, TGA, SEM, EDS, ICP-
OES analysis, and FT-IR. The XRD patterns oꢀ SCG and
SCG@Fe O were employed to exhibit the structure oꢀ the
.28–1.09 (m, 5H, H ). Anal. Calcd ꢀor C H BrN : C,
aliphatic
19 20
3
1.63; H, 5.44; N, 11.35; ꢀound C, 61.82; H, 5.21; N, 11.47.
3
4
N‑cyclohexyl‑2‑phenylimidazo[1,2‑a]pyrimidin‑3‑amine
Table 4, Entry 4)
synthetic catalyst (Fig. 1). The difraction peaks oꢀ SCG
(
were appeared as two broad peaks at 2θ values oꢀ around
1
6° and 22° that correspond to the XRD pattern oꢀ cellu-
1
Brown solid (70%): mp 161–162 °C. H NMR (300.13 MHz,
lose [31]. In the XRD pattern oꢀ SCG@Fe O , in addition
3 4
DMSO-d ) δ: 8.74 (d, J=6.8 Hz, 1H, H ), 8.47–8.45 (m,
to the difractions mentioned ꢀor SCG, the difractions at
2θ values oꢀ around 30.3, 35.7, 43.4, 53.7, 57.3, and 62.9°
were observed, which are related to the Fe O NPs [29] and
6
arom
1
H, H ), 8.25–8.20 (m, 2H, H ), 7.55–7.28 (m, 3H,
arom
arom arom
), 7.05–6.52 (m, 1H, H ), 4.90 (d, J =6.1 Hz, 1H,
arom
H
3
4
NH), 2.84 (br s, 1H, HCN), 1.82–1.63 (m, 6H, H
),
conꢁrmed the synthesis oꢀ Fe O NPs on SCG.
aliphatic
3 4
1
7
.50–1.10 (m, 4H, H
). Anal. Calcd ꢀor C H N : C,
TGA was perꢀormed ꢀor SCG and SCG@Fe O in the
3 4
aliphatic
18 20
4
3.94; H, 6.89; N, 19.16; ꢀound C, 73.59; H, 7.03; N, 19.40.
air to examine the thermal stability, and the results are
illustrated in Fig. 2. Up to around 170 °C, approximately
14% oꢀ the SCG weight was reduced, which is related to
the moisture content, and this value is less ꢀor SCG@
Fe O . Up to around 600 °C, almost about 51% and 18%
N‑(tert‑butyl)‑2‑(4‑chlorophenyl)imidazo[1,2‑a]
pyridin‑3‑amine (Table 4, Entry 5)
3
4
1
White solid (79%): mp 147 °C. H NMR (300.13 MHz,
weight loss was observed ꢀor SCG and SCG@Fe O ,
3 4
DMSO-d ) δ: 8.40 (d, J = 7.1 Hz, 1H, H
), 8.21 (d,
respectively, due to the decomposition oꢀ the lignocellu-
lose moiety [32]. This 33% diference between residual
weights was attributed to the Fe O NPs. It is noteworthy
6
arom
J = 7.8 Hz, 2H, H ), 7.48–7.17 (m, 4H, H ), 6.89 (t,
arom
arom
J = 7.0 Hz, 1H, H
), 4.69 (br s, 1H, NH), 1.01 (s, 9H,
arom
3
4
H
). Anal. Calcd ꢀor C H ClN : C, 68.11; H, 6.05;
that the thermal stability oꢀ SCG@Fe O is about 275 °C.
aliphatic
17 18
3
3 4
N, 14.02; ꢀound C, 68.37; H, 5.95; N, 14.12.
1
3

Journal of the Iranian Chemical Society
Table 4 Tandem oxidative GBB
reaction by SCG@Fe O
3
4
Entry
Alcohol
2-Amino heterocycle
Isocyanide
Product
Melting point
Reported Found
Yield
a
(
%)
1
160-
62
161
80
81
73
1
[
[
[
47]
2
3
176-
78
176-
178
1
47]
175-
77
175-
176
1
48]
4
162-
63
161-
162
70
1
[47]
5
148-
50
147
79
1
[49]
6
7
75-80
77-
78
[
50]
8
0
201-
200-
205
76
2
10
[51]
8
9
166-
69
166-
167
70
1
[
49]
150-
52
151-
153
68
1
[52]
1
0
207-
08
206
83
2
[53]
1
3

Journal of the Iranian Chemical Society
Table 4 (continued)
Conditions: alcohol (1.00 mmol), 2-Amino heterocycle (1.00 mmol), isocyanide (1.00 mmol), SCG@
Fe O (0.05 g), toluene (4 mL), KOH (0.50 mmol), air oxidant, 80 °C, 8 h
Isolated yield
3
4
a
Table 5 Investigation oꢀ the catalytic activity oꢀ SCG@Fe O in GBB
Also, comparing FT-IR spectra oꢀ SCG and SCG@Fe O
3 4
3
4
reaction
Entry
illustrates the structure oꢀ the SCG did not change aꢀter mag-
netization (Fig. 5).
Catalyst
–
SCG@Fe O
Time (h)
Yield (%)a
In the next step, the catalytic activity oꢀ SCG@Fe O
3
4
1
2
3
3
10>
94
was examined in aerobic oxidation oꢀ alcohols. In order
to optimization oꢀ the reaction conditions, aerobic oxida-
tion oꢀ benzyl alcohol was chosen as a model reaction and
the efects oꢀ the solvent, temperature, and the amount oꢀ
catalyst were investigated (Table 1). As shown in Table 1,
nonpolar solvents such as toluene and xylene and alkaline
bases are more efective ꢀor this transꢀormation (Entries 4,
3
4
Conditions:
benzaldehyde
(1.00
mmol),
2-aminopyridine
(
1.00 mmol), cyclohexyl isocyanide (1.00 mmol), catalyst (0.05 g),
toluene (4 mL), 80 °C
a
Isolated yield
6
, and 9). Also, the reaction yield depends on the amount oꢀ
catalyst (Table 1, Entries 3 and 4). The reaction was carried
out in the presence oꢀ 0.05 g oꢀ catalyst in toluene at 80 °C
as the suitable conditions (Entry 4).
Oxidation oꢀ diferent alcohols was examined to inves-
tigate the substrates scope. As indicated in Table 2, the
catalyst eꢂciency ꢀor the aerobic oxidation oꢀ secondary
benzylic alcohols is higher than ꢀor primary benzylic alco-
hols. Various primary benzylic alcohols containing elec-
tron-donating as well as electron-withdrawing groups and
halogen substitutions were used, and in all cases high yields
were achieved. Unꢀortunately, this catalytic system ꢀailed
to transꢀorm the aliphatic alcohols to their corresponding
carbonyl compounds.
Scheme 1 Plausible mechanism ꢀor the ꢀormation oꢀ product 5
A comparison oꢀ the catalytic eꢂciency oꢀ SCG@Fe O
3
4
The SEM analysis was done to represent the structure
and morphology oꢀ the SCG and SCG@Fe O . SCG has
with the reported catalysts ꢀor aerobic oxidation oꢀ benzyl
alcohol is presented in Table 3. In most cases oꢀ magnetic
catalysts that were used ꢀor aerobic oxidation oꢀ alcohols,
iron oxides act as vehicles ꢀor supporting expensive cata-
lytically active transition metals. There are ꢀar ꢀewer reports
which in Fe O NPs operate as a catalytic active site [29].
3
4
porous morphology and did not ꢀundamentally change dur-
ing magnetization (Fig. 3). The EDS analysis was carried
out to determine the chemical composition oꢀ the SCG@
Fe O . The results showed that the iron is present in the
3
4
3
4
catalyst (Fig. 4). Furthermore, to determine the amount oꢀ
Accordingly, utilizing oꢀ Fe O NPs as a catalytic active site
3 4
Fe O NPs, ICP-OES analysis was perꢀormed and results
and SCG as a green support can be signiꢁcant ꢀrom green
chemistry point oꢀ view.
3
4
revealed a 1.43 mmol/g Fe O is loaded in the catalyst.
3
4
Fig. 6 Recyclability oꢀ SCG@
Fe O ꢀor ꢁve cycles using
3
4
aerobic oxidation oꢀ benzyl
alcohol and tandem oxidative
GBB reaction
1
3

Journal of the Iranian Chemical Society
presence oꢀ the catalyst, the reaction proceeded eꢂciently
and the desired product was achieved in 94% yield. These
results revealed that SCG@Fe O is an eꢂcient catalyst ꢀor
3
4
the GBB reaction in addition to oxidation transꢀormation.
According to the control experiments and based on the
literature reports [54], a plausible mechanism ꢀor the GBB
reaction is proposed in Scheme 1. Firstly, 2-amino heterocy-
cle 3 reacts with aldehyde 2 in the presence oꢀ SCG@Fe O
3
4
to generate imine 6. Nucleophilic attack oꢀ isocyanide 4 to
activated imine 6 results in the ꢀormation oꢀ intermediate 7
ꢀ
ollowed by 1, 3-H shiꢀt to aford the desired product.
The heterogeneous character oꢀ the catalyst was veriꢁed
using a ꢁltration test and atomic absorption spectroscopy.
A ꢁltration test was accomplished aꢀter~ 50% completion
oꢀ the model oxidation reaction oꢀ benzyl alcohol to control
whether the catalyst is working in a heterogeneous ꢀashion
or catalyst is merely a reservoir ꢀor more active soluble iron
species. The ꢁltrates were then transꢀerred to another ꢃask
under the same initial reaction conditions. Upon ꢀurther stir-
ring oꢀ the catalyst-ꢀree solution ꢀor 5 h, no signiꢁcant pro-
gress was detected. Furthermore, using atomic absorption
spectroscopy oꢀ the same reaction solution at the midpoint
oꢀ completion showed that no signiꢁcant quantities oꢀ iron
are lost.
Fig. 7 XRD patterns oꢀ SCG@Fe O beꢀore (a), aꢀter using (b) ꢀor
3
4
the tandem process
In the ꢀollowing, according to the promising results
obtained ꢀor aerobic oxidation oꢀ primary benzylic alcohols,
the tandem oxidative GBB reaction was investigated in a
one-pot, two-step sequential strategy. The ꢁrst step is the
oxidation oꢀ alcohol in the optimized conditions to aford the
corresponding aldehyde as an intermediate. Then, an isocya-
nide and a 2-amino heterocycle were added to the reaction
mixture and the reaction continued at the same condition
without bubbling oꢀ air. As indicated in Table 4, various
derivatives oꢀ benzyl alcohols, 2-amino heterocycles, and
isocyanides were employed and in all cases the correspond-
ing 3-aminoimidazo-ꢀused heterocycles were synthesized in
good yields.
For reusability examination, SCG@Fe O was sur-
3
4
veyed to ꢁve consecutive cycles ꢀor the model reactions
in the oxidation oꢀ benzyl alcohol and tandem oxidative
GBB reaction using benzyl alcohol, 2-aminopyridine and
cyclohexyl isocyanide. Aꢀter completion oꢀ the reaction,
the catalyst was separated ꢀrom the reaction mixture,
washed with water, ethanol and acetone, dried, and reused
in the next run. The recycled catalyst was employed in
the next ꢀour sequential runs without signiꢁcant loss oꢀ
catalytic potential as shown in Fig. 6.
To clariꢀy the role oꢀ SCG@Fe O in the GBB reaction,
3
4
two control experiments were perꢀormed. The reaction oꢀ
benzaldehyde, cyclohexyl isocyanide, and 2-aminopyri-
dine was examined in the presence and absence oꢀ SCG@
Fe O in toluene at 80 °C. As shown in Table 5, the reaction
XRD pattern oꢀ the recovered catalyst ꢀor the tandem
process was recorded and compared with the XRD pat-
tern oꢀ the ꢀresh catalyst. Result conꢁrmed the stability oꢀ
3
4
yield in the absence oꢀ catalyst was less than 10%, but in the
Table 6 Comparison oꢀ the
Entry
Catalyst
Solvent
Temperature
Time (h)
Yield (%)
Reꢀerences
catalytic eꢂciency oꢀ SCG@
Fe O with the reported Lewis
3
4
1
2
3
4
5
6
7
8
9
AgOAc
Ethylene glycol
EtOH
–
–
1,4-Dioxane
–
MeOH
–
MeOH
Toluene
90 °C
60 °C
40 °C
65 °C
MW
35 °C
Reꢃux
60 °C
r.t.
2
2.5
1
3
1
1.5
3
0.33
3
88
94
89
95
78
96
89
95
[55]
[56]
[51]
[57]
[58]
[59]
[52]
[60]
acid catalysts ꢀor the reaction oꢀ
benzaldehyde, 2-aminopyridine,
and cyclohexyl isocyanide
Fe O @mPMF
3
4
RuCl ·3H O
3
2
NH -MIL-53(Al)
2
ZnCl2
Nano-LaMnO3
Cellulose@Fe O
2
3
LaCl ·7H O
3
2
a
b
Silica sulꢀuric acid
SCG@Fe O
98
[61]
This work
1
0
80 °C
3
94
3
4
a
An example oꢀ heterogeneous Brønsted acid catalyst
b
2
-Amino-6-bromopyridine was used instead oꢀ 2-aminopyridine
1
3

Journal of the Iranian Chemical Society
SCG@Fe O during the process. As indicated in Fig. 7, no
10. R. Hachicha, O. Rekik, S. Hachicha, M. Ferchichi, S. Woodward,
3
4
N. Monceꢀ, J. Cegarra, T. Mechichi, Chemosphere 88, 677 (2012)
signiꢁcant changes are observable and some trivial difer-
ences between the reꢃection intensities can be attributed to
the variation in the orientation oꢀ powder samples during
XRD patterns recording.
1
1. Y.S. Yun, M.H. Park, S.J. Hong, M.E. Lee, Y.W. Park, H.-J. Jin,
ACS Appl. Mater. 7, 3684 (2015)
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1
3. F. Leiꢀa, A. Pandey, C.R. Soccol, Braz. Arch. Biol. Technol. 44,
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3
4
2
05 (2001)
with the reported Lewis acid catalysts ꢀor the reaction oꢀ
benzaldehyde, 2-aminopyridine, and cyclohexyl isocya-
nide is demonstrated in Table 6. The use oꢀ Fe O sup-
4. N.M.M. Alvarez, J.M. Pastrana, Y. Lagos, J.J. Lozada, Sustain.
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4
1
1
1
1
2
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Mohanty, BioResources 11, 7637 (2016)
ported on SCG, as an inexpensive and abundant material
that has causes environmental problems, in the tandem
oxidation process is the advantages oꢀ this protocol.
7. M. Mahyari, M.S. Laeini, A. Shaabani, Chem. Commun. 50,
7855 (2014)
8. A. Shaabani, S. Keshipour, M. Hamidzad, S. Shaabani, J. Mol.
Catal. A: Chem. 395, 494 (2014)
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Conclusions
0. A. Shaabani, Z. Hezarkhani, Cellulose 22, 3027 (2015)
In summary, SGG as an enormous waste material has been
investigated in the ꢁeld oꢀ catalyst. SCG was magnetized
through co-precipitation method and successꢀully used as
an eꢂcient catalyst in the aerobic oxidation oꢀ alcohols
and tandem oxidative GBB reaction. It is demonstrated
that this green material has dual catalytic role in the tan-
dem process: (i) As a reusable catalyst in the oxidation
transꢀormations and (ii) As an acidic heterogeneous cata-
lyst in the GBB MCR. As well, high yield, reusability oꢀ
the catalyst, simple and cheap starting materials, and mild
reaction conditions are the other advantages oꢀ this work.
21. R.J. Taylor, M. Reid, J. Foot, S.A. Raw, Acc. Chem. Res. 38, 851
(
2005)
2
2
2. A. Shaabani, A. Maleki, Chem. Pharm. Bull. 56, 79 (2008)
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24. A. Shaabani, R. Mohammadian, A. Hashemzadeh, R. Aꢀshari,
M.M. Amini, New J. Chem. 42, 4167 (2018)
2
5. M.T. Nazeri, R. Mohammadian, H. Farhid, A. Shaabani, B.
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26. M.T. Nazeri, H. Farhid, R. Mohammadian, A. Shaabani, ACS
Comb. Sci. 22, 361 (2020)
2
7. M.B. Gawande, P.S. Branco, R.S. Varma, Chem. Soc. Rev. 42,
3
371 (2013)
2
2
8. A. Maleki, V. Eskandarpour, J. Iran. Chem. Soc. 16, 1459 (2019)
9. L. Geng, B. Zheng, X. Wang, W. Zhang, S. Wu, M. Jia, W. Yan,
G. Liu, ChemCatChem 8, 805 (2016)
Acknowledgements We grateꢀully acknowledge ꢁnancial support ꢀrom
the Research Council oꢀ Shahid Beheshti University.
30. Z.-H. Zhang, H.-Y. Lü, S.-H. Yang, J.-W. Gao, J. Comb. Chem.
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2, 643 (2010)
3
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Compliance with ethical standards
2. B. Dang, Y. Chen, X. Shen, C. Jin, Q. Sun, X. Li, Cellulose 26,
Conꢁlict oꢁ interest All authors declare that they have no conꢃict oꢀ
5
455 (2019)
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(
Aꢀliations
Hassan Farhid · Ahmad Shaabani1
1
1
*
Ahmad Shaabani
Faculty oꢀ Chemistry, Shahid Beheshti University, G.C., P.O.
a-shaabani@sbu.ac.ir
Box 19396-4716, Tehran, Iran
1
3