Highly sulfonated graphene and graphene oxide nanosheets as heterogeneous nanocatalysts in green synthesis of bisphenolic antioxidants under solvent free conditions

Article abstract of DOI:10.1039/c4ra10177d

Sulfonated functionalized graphene and graphene oxide nanosheets were prepared via chemical approaches and their catalytic activities were investigated in the green synthesis of 6,6′-(arylmethylene) bis(2,4-dialkylphenol) antioxidants. In this research, three types of the catalysts including sulfonated reduced graphene oxide nanosheets (catalyst 1a), sulfonated graphene oxide nanosheets (catalyst 1b), and sulfonated propylsilane graphene oxide nanosheets (catalyst 1c) were synthesized and used in the synthesis of target molecules. The catalysts were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction spectroscopy (XRD), and back acid-base titration. The catalyst 1a showed excellent catalytic activity in the green synthesis of 6,6′-(arylmethylene)bis(2,4-dialkylphenol) antioxidants under solvent free conditions and was reused several times without any appreciable loss of its catalytic activity even after eight consecutive cycles. In addition, the high yield of the products and non-toxicity of the catalysts are other worthwhile advantages of the present methods.

Full text of DOI:10.1039/c4ra10177d

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Highly sulfonated graphene and graphene oxide
nanosheets as heterogeneous nanocatalysts in
green synthesis of bisphenolic antioxidants under
solvent free conditions†
Cite this: RSC Adv., 2014, 4, 56475
Hossein Naeimi* and Mohsen Golestanzadeh
Sulfonated functionalized graphene and graphene oxide nanosheets were prepared via chemical
0
approaches and their catalytic activities were investigated in the green synthesis of 6,6 -(arylmethylene)
bis(2,4-dialkylphenol) antioxidants. In this research, three types of the catalysts including sulfonated
reduced graphene oxide nanosheets (catalyst 1a), sulfonated graphene oxide nanosheets (catalyst 1b),
and sulfonated propylsilane graphene oxide nanosheets (catalyst 1c) were synthesized and used in the
synthesis of target molecules. The catalysts were characterized by field emission scanning electron
microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier
transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction spectroscopy (XRD), and
0
back acid–base titration. The catalyst 1a showed excellent catalytic activity in the green synthesis of 6,6 -
Received 10th September 2014
Accepted 23rd October 2014
(arylmethylene)bis(2,4-dialkylphenol) antioxidants under solvent free conditions and was reused several
times without any appreciable loss of its catalytic activity even after eight consecutive cycles. In addition,
the high yield of the products and non-toxicity of the catalysts are other worthwhile advantages of the
present methods.
DOI: 10.1039/c4ra10177d
www.rsc.org/advances
1
4–16
17
18
catalysts such as
H
2
SO
4
,
HCl,
CF
3
COOH,
hetero-
Introduction
19,20
21
22
23
polyacid,
or AuCl
zeolites, silicasulfuricacid, [Ir(COD)Cl]
2
–SnCl
4
,
,
24
25
26
27
29
Phytochemicals are bioactive non-nutrient compounds found AuCl
in plants. The most important class of phytochemicals in plant AcBr/ZnBr
/AgOTf,
Cu(OTf)
,
FeCl
,
3
Yb(OTf)
3
3
8
2
3
2
/SiO ,
2 2
and multi-walled carbon nanotubes–SO
H.
3
food sources is the group of phenolic compounds. Phenols However, the usages of these homogeneous catalytic systems are
especially polyphenols are very important materials in food and not suitable for practical application because they are toxic,
1
,2
organic chemistry. These materials have been used as dyes,
corrosive, non-reusable, and non-recoverable. Other disadvan-
protecting groups for nucleosides, carbohydrates, anticancer tages of homogeneous catalyst include environmental pollution,
drugs, epoxy resins, and antioxidants.
3
4
5
6
7–12
Phenolic antioxi- difficulty in work-up, and generally they need additional
dants act as efficient free radicals scavengers by donating their neutralization stages. Therefore, the development a novel
alcoholic hydrogen or one of their delocalized electrons. In
addition, the polyphenols have many industrial applications,
for example they may be used as natural colorant, food
13
preservatives, and paints, paper, and cosmetic production.
Bisphenolic antioxidants are an important class of polyphenolic
antioxidants. These antioxidants are usually manufactured by
an acid catalyzed condensation reaction of carbonyl and
aromatic compounds. The chemical structures of some
phenolic antioxidants are shown in Fig. 1.
Thesynthesis ofbisphenolicantioxidants hasbeen performed
in the presence of different homogeneous and heterogeneous
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan,
8
+
†
1
7317-51167, Islamic Republic of Iran. E-mail: naeimi@kashanu.ac.ir; Fax:
983155912397; Tel: +983155912388
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra10177d
Fig. 1 Selected examples of phenolic antioxidants.
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heterogeneous catalyst system with good reusability and appro-
priate catalytic activity is an important challenge in the synthesis
Results and discussion
0
of bisphenolic antioxidants. In spite of their potential applica- The synthesis of 6,6 -(arylmethylene)bis(2,4-dialkylphenol)
tions for the heterogeneous catalysts, many research papers for antioxidants is depicted in Scheme 1. Initially, three types of
synthesis of bisphenolic antioxidants have reported some prob- catalysts according to experimental section were prepared and it
lems such as; long reaction times, excess amount of catalyst, use investigated in the synthesis of target molecules (Scheme 1).
of toxic organic solvent, and non-reusable catalytic systems for
the preparation of bisphenolic antioxidants.
Preparation of the catalysts
Graphene a single two-dimensional (2D) large of carbon
To start our investigation, it was proceeded to prepare three
different solid acids based graphene nanosheets including
RGO–SO H (1a), GO–SO H (1b), and GO–SiPrSO H (1c). Sche-
3 3 3
matic illustrations of prepared catalysts are shown in Scheme 2.
This allowed us to have several solid acid catalysts with different
types of sulfonated groups anchored on graphene support and
various hydrophobic properties for preparation of heteroge-
neous catalysts. The catalysts 1a, 1b, and 1c were achieved in
four, three, and four steps respectively as described in Scheme
30
atoms, has attached much attention in recent years. Graphene
and graphene oxide (GO) have fantastic physical, optical, and
31,32
mechanical properties.
Moreover, graphene and GO have
33
large specic surface area, high surface-to-volume ratio, and
chemical stability. Due to the large specic surface area, and
chemical and thermal stability of GO and graphene, it were
employed in chemical process and organic synthesis as support.
Solid acid have shown great potential to replace traditional
homogeneous liquid acid as environmentally safe acid cata-
2. The GO is the same precursor for the preparation of three
3
4–36
lysts.
useful as solid acid catalysts in organic transformations.
series of sulfonated carbon catalysts was prepared through
Among them, sulfonated based carbon materials are
types of catalysts. First, natural graphite which is commercially
available was converted to graphite oxide using sodium nitrate,
37–41
A
52
2 4
H SO , and potassium permangenante. This step introduced
42,43
direct carbonization of raw materials (sugar, cellulose)
lowed by the sulfonation of resulted carbons. These catalysts
fol-
oxygen containing groups for example epoxy, hydroxyl, and
carboxylic acid groups on the surface of graphite. Aer that, the
graphite oxide was sonicated (75 W) for 15 min to produce GO
nanosheets. For the preparation of catalyst 1a, the GO was
2
ꢁ1
possessed low surface area (ꢀ2 m g ) and do not swell and
37
exhibited much better thermal stability. The sulfonated acti-
vated carbon (AC) has high specic surface area, and low cost.
An early experimental result from Hara's group showed that
heating AC in H SO and concentrated H SO only produced AC
treated with NaBH
afford the RGO–SO
from GO nanosheets by treatment of chlorosulfonic acid as a
sulfonating agent to obtain GO–SO H. In continuous, the
4
2 4
as reducing agent and H SO (100%) to
3
H. Also, the catalyst 1b was synthesized
2
4
1
2
4
ꢁ
ꢁ1
with 0.15 mmol g (ref. 44) and 0.44 mmol g (ref. 45 and 46)
SO H groups density respectively. This fact (low density of SO
groups) attributed to the chemical inertness of AC. Recently,
Alamdari, et al. prepared sulfonated single and multi walled
carbon nanotubes via chemical process. But, the high cost, and
hard synthesis of carbon nanotubes are disadvantages of the
3
3
3
H
catalyst 1c was obtained in four steps from the reaction of GO
nanosheets with mercaptopropyl trimethoxysilane (MPTMS) to
afford GO–SiPrSH. Then, the GO–SiPrSH was oxidized to
44
sulfonic acid by H
2 2 3
O (30%) to prepare GO–SiPrSO H.
40,41
reported papers.
Because of prominent properties of graphene and GO such
Characterization of the catalysts
as low cost, easy synthesis, high specic surface area, and The prepared catalysts 1a, 1b, and 1c were characterized by
chemical and thermal stability, they can be enhanced catalytic some microscopic and spectroscopic techniques including FE-
activity and provided an excellent support for the heteroge- SEM, TEM, AFM, FT-IR, Raman spectroscopy, XRD, and back
neous catalysts in organic synthesis. Due to the interesting acid–base titration.
properties of GO and reduced graphene oxide (RGO) as support
3 3
The FE-SEM images of GO, RGO–SO H, GO–SO H, and
for the preparation of heterogeneous catalytic systems, we GO–SiPrSO
3
H are shown in Fig. 2. Different morphologies were
decide to plan three types of catalysts based on GO and RGO observed for pristine GO nanosheets and three types of the
nanosheets with various synthetic routes for anchored prepared catalysts. As shown in Fig. 2a, it was found that GO
sulfonated groups on the surface of GO and RGO nanosheets. nanosheets consists of randomly aggregated, crumpled,
Furthermore, we hope to compare the activities of three types of
prepared catalysts in the synthesis of bisphenolic antioxidants
as the same organic reaction from the view of efficiency of
catalytic activity, turnover frequency (TOF), power of acidity, the
ability of reusability, and time of the reaction performance.
In continuation of our interest towards carbon based mate-
47,48
49–51
rials
and green methodologies,
we report the use of RGO
and GO as support for attachment of sulfonated groups. The
ability of these heterogeneous catalysts were investigated in the
0
synthesis of 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxi-
dants from 2,4-dialkylphenol and aromatic aldehydes in atomic
economic conditions.
Scheme 1 Synthesis of bisphenolic antioxidants.
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the treatment of chlorosulfonic acid as a sulfonated agent with
GO nanosheets. Comparison of the pristine GO with the
GO–SO H images was found that it was covered by a layer
3
foreign matter resulting in thickness GO nanosheets ake-like
sheets and denser network of two-dimensional GO. As can be
shown in Fig. 2d, the structure of catalyst 1c is still ake-like
sheets aer treatment of MPTMS and H
2 2
O . Also, it seems
that the morphology of GO–SiPrSO H is different in compared
3
with the pristine GO nanosheets due to the functionalization
process (Fig. 2, image d vs. a).
Fig. 3 shows the TEM images of GO and RGO nanosheets. It
can be seen that the GO and RGO exhibit a typical exfoliated and
two-dimensional nanostructures with a rather and large at and
smooth ake-like morphology with several layers. Also, this

gure reveals that two-dimensional ake-like of pristine
graphite is still in GO and RGO nanosheets aer Hummer's
method.
As shown in Fig. 4, the AFM analysis reveals that the
measured values of thickness are in the range 0.9–1.5 nm,
indicating that exfoliated mono and dilayer graphene oxide was
obtained in this study. These graphene oxide layers should be
mostly monolayered, although these amount are somewhat
larger than the interlayer spacing (0.78 nm) of the parent GO.
The sheets are a little more ‘bumpy’ than predicted, which is
possibly due to the existence of abundant functional groups,
such as carboxylic, epoxy, and hydroxyl groups, bonded to both
sides of the graphene oxide sheets, which disrupts the original
conjugation and introduces lattice defects to result in folds and
distortions on the sheets.
Scheme 2 Synthetic routes for the preparation of the three types
catalysts.
Fig. 5, shows the FT-IR spectra of pristine graphite, GO, RGO,
RGO–SO H, GO–SO H, GO–SiPrSH, and GO–SiPrSO H. FT-IR is
3 3 3
a tool mainly used to identify the presence or absence of func-
tional groups in chemistry. The high symmetry introduced to
pristine graphite generates very weak infrared peaks due to the
weak difference of charge states and very small induced electric
ꢁ
1
dipole. The peak related to C]C double bonds at 1573 cm is
not sharp in the spectrum of graphite (Fig. 5a). The process of
Hummer's method and sonication breaks the symmetry of
graphite. The FT-IR spectrum of GO was shown in Fig. 5b. The
ꢁ
1
peak at approximately 1580 cm is attributed to C]C double
bonds. This peak is sharper than graphite due to the un-
symmetry of GO. This spectrum shows peaks at 1064, 1719,
ꢁ
1
and 3394 cm which could be assigned to C–O, carbonyl, and
Fig. 2 FE-SEM images of (a) GO nanosheets, (b) RGO–SO
3
H, (c)
hydroxyl stretching mode of functional groups attachment to
GO–SO H, (d) GO–SiPrSO H.
3
3
transparent, and ake-like sheets which also observed with
wrinkles and folds on the surface of GO nanosheets. The shown
morphologies in this gure exhibit that the large two-
dimensional GO nanosheets with layered structures reveal
face to face stacking of sheets. The observed morphology in
Fig. 2b shows signicant difference between GO nanosheets
and RGO–SO
3
H. The RGO–SO
3
H
shows similar two-
dimensional features with foreign matter that it was covered
surface of GO nanosheets aer reduction and sulfonation,
respectively. Fig. 2c, shows FE-SEM image of the GO–SO H from
3
Fig. 3 TEM images of (a) GO nanosheets (b) RGO nanosheets.
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indicate that the functionalization of MPTMS on the GO was
ꢁ
1
happened due to the presence of the peaks at about 2924 cm
3
related to C–H (sp ) stretching mode. Aer oxidation process
with H O (30%), these peaks were still on the surface of GO and
2
2
ꢁ
1
the peak at 3432 cm was clearly appeared related to –OH of
sulfonated groups.
Fig. 6 shows XRD patterns of graphite, GO, RGO, and
RGO–SO
3
H. The XRD pattern of graphite (Fig. 6a) shows a strong
ꢂ
peak at approximately 2q ¼ 26.5 corresponding to the feature of
graphite. Aer to do Hummer's method, the peak at about 2q ¼
ꢂ
ꢂ
2
6.5 was broad peak and the peak at 2q ¼ 12 was appeared. The
interlayer spacing (d-spacing) of GO was calculated 0.78 nm
which revealed the introduction of oxygen species on the gra-
53
phene network sheets (Fig. 6b). Aer chemical reduction of
ꢂ
exfoliated GO with NaBH
4
, the diffraction peak of GO at 2q ¼ 12
ꢂ
was disappeared and a broad peak at centered 2q ¼ 24 was
observed, indicating the fully reduction and exfoliation of GO
54
and the production of RGO nanosheets. As shown in Fig. 6c, in
the RGO nanosheets was rather broad peak and signicantly
different from that observed for pristine graphite. Fig. 6d shows
Fig. 4 AFM image of GO nanosheets.
3
XRD pattern of RGO–SO H aer hydrothermal sulfonation. The
XRD pattern (Fig. 6d) has very similar peaks to RGO suggesting
their similar crystal structure of the graphene layers.
Typical Raman spectrum of GO nanosheet is shown in Fig. 7.
ꢁ1
The D and G band were appeared at about 1347 cm and 1593
ꢁ
1
cm respectively. The G-band arises from the stretching of the
2
C–C bond in graphitic materials, and is related to sp carbon
systems. The D-band is caused by disordered structure of gra-
2
phene. The presence of disorder in sp -hybridized carbon
systems results in resonance Raman spectra. The other Raman
3
Fig. 5 FT-IR spectra of (a) graphite (b) GO (c) RGO (d) RGO–SO H (e)
GO–SO H (f) GO–SiPrSH (g) GO–SiPrSO H.
3 3
GO respectively. The chemical reduction of GO with NaBH4
produce RGO that the spectrum of RGO is shown in Fig. 5c. This
spectrum shows that the peaks of the hydroxyl and carbonyl
groups were disappeared due to the used NaBH
agent. The peak at 3423 cm is related to presence of water on
4
as reducing
ꢁ1
ꢁ
1
KBr pellets. Also, the presence of the peak at 1566 cm show
ꢂ
that aer chemical reduction at 100 C for 24 h, the RGO is still

ake-like sheets. Fig. 5d and e show the FT-IR spectra of
RGO–SO H and GO–SO H. These spectra show peaks related to
3
3
C–O, carbonyl, and hydroxyl groups at about 1020, 1725, and
ꢁ
1
3
400 cm
functionalization of GO with H
occurred to afford RGO–SO H and GO–SO
FT-IR spectra of GO–SiPrSH and GO–SiPrSO
Fig. 5f and g respectively. The FT-IR spectra in Fig. 5f and g
respectively. The FT-IR data conrmed that the
SO and chlorosulfonic acids
H. In addition, the
H are shown in
2
4
3
3
3
3
Fig. 6 XRD patterns of (a) graphite (b) GO (c) RGO (d) RGO–SO H.
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a
Table 1 Optimizing the reaction conditions
ꢂ
b
Entry Catalyst (mg) Solvent
T ( C) Time (min) Yield (%)
Fig. 7 Raman spectrum of GO.
1
2
3
4
5
6
7
8
9
1
1
1
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (40)
1a (50)
1a (30)
1b (40)
1b (40)
1b (60)
1b (80)
1b (75)
1b (75)
1b (75)
1c (40)
1c (40)
1c (70)
1c (90)
1c (100)
1c (110)
1c (100)
1c (100)
1c (100)
EtOH
H O
2
Reux
Reux
Reux
Reux 120
Reux 120
70
55
90
60
70
55
25
35
20
55
75
92
92
92
87
65
65
72
75
75
65
55
50
55
65
65
68
65
60
60
40
CH
n-Hexane
CHCl
3
CN
ꢁ
1
ꢁ1
bands were observed at 2717 cm (2D band), and 2931 cm
55
(
D + G-band). Combined with the G-band, this spectrum is a
3
2
Solvent free 60
Solvent free 80
Solvent free 90
Solvent free 100
Solvent free 110
Solvent free 100
Solvent free 100
Solvent free 100
Solvent free 120
Solvent free 100
Solvent free 100
Solvent free 100
150
60
50
40
40
40
50
60
60
60
60
60
90
90
80
80
75
70
70
75
Raman signature of graphitic sp materials, and 2D-band is a
second-order two-phonon process and exhibits a strong
frequency dependence on the excitation energy.
0
1
2
Acidity of the catalysts (1a, 1b, 1c)
The total amount of the sulfonated groups was measured in the 13
14
15
16
17
18
19
20
21
22
23
24
25
26
three types of the catalysts using back acid–base titration. The
back acid–base titration showed that the density of sulfonated
groups anchored on graphene layers for catalysts 1a, 1b, and 1c
ꢁ
1
were 2.15, 1.2, and 0.85 mmol g , respectively.
EtOH
CH CN
Reux
Reux
3
Solvent free 100
Solvent free 120
Solvent free 100
Solvent free 100
Solvent free 100
Solvent free 100
Catalytic activity of prepared catalysts in the synthesis of
bisphenolic antioxidants under solvent free conditions
The prepared three types of the catalysts were employed in the
0
synthesis of 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxi-
dants. Initially, the reaction parameters were optimized in the
reaction of 2,4-dimethylphenol (1) and 4-nitrobenzaldehyde (2a) 27
in the presence of catalytic amounts of catalysts 1a, 1b, and 1c
H
2
O
Reux 100
Reux 120
Reux 150
EtOH
CHCl
3
28
as the model reaction. The results are shown in Table 1. The
a
General reaction conditions: 2,4-dimethylphenol (1) (6 mmol), 4-
b
model reaction was optimized in the presence of catalyst 1a nitrobenzaldehyde (2a) (2 mmol), solvent (2 mL). Isolated yields.
Table 1, entries 1–12). To choose the medium of the reaction,
the model reaction was performed in various solvents such as
(
EtOH, H
2
O, CH
3
CN, n-hexane, and CHCl
3
and without any reaction was investigated for catalyst 1b and 1c (Table 1, entries
ꢂ
solvent (Table 1, entries 1–10). As can be seen, entry 9 gave the 13, 14 and 20, 21). For catalyst 1b and 1c, the 100 C was the best
best result. Therefore, the solvent free conditions were chosen temperature of the model reaction. Also, the catalytic amounts
as the reaction medium. For optimization of temperature of the of catalysts were studied and the best results were 75 and 100
reaction, an increase in temperature of the reaction (60 to mg for the catalysts 1b and 1c respectively (Table 1, entries 15–
ꢂ
1
10 C) led to decreased time of the reaction and increased 17 and 22–25).
ꢂ
yields of the desired product. At temperature of 100 C, the yield
Aer optimization of the reaction conditions, synthesis of
ꢂ
0
of the reaction was 92% and it similar at 110 C (Table 1, entries 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxidants were
9
and 10). The model reaction was performed in the different performed from the condensation reaction of 2,4-dialkylphenol
amount of catalyst 1a (Table 1, entries 10–12). The best result (1) and different aldehydes (2a–q) utilizing catalysts 1a, 1b, and
ꢂ
was observed with 40 mg of the catalyst 1a. The best conditions 1c under solvent free conditions at 100 C. As shown in Table 2,
ꢂ
for catalyst 1a was resulted; T ¼ 100 C, solvent free, and 40 mg all of the products were synthesized using RGO–SO H,
3
of the catalyst. Furthermore, we examined the model reaction in GO–SO H, and GO–SiPrSO H. As shown in Table 2, aromatic
3
3
the presence of different of the catalyst (catalyst 1b, 1c) (Table 1, aldehydes with electron-withdrawing groups on ortho or para
entries 13–28). For two types of the catalysts, solvent free position accelerate the time of the reaction and improved yield
conditions were the best medium of the model reaction (Table of desired products compared with the electron-donating
1, entries 17–19 and 25–28). In addition, the temperature of the
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Table 2 Synthesis of 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxidants
Paper
0
a
Catalyst 1a (RGO–SO
3
H)
Catalyst 1b (GO–SO
3
H)
3
Catalyst 1c (GO–SiPrSO H)
b
b
b
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
ꢁ
1
ꢁ1
ꢁ1
Entry
R
X
Product
)
)
)
1
CH
3
4-NO
2
40
92
16.2
60
75
8.3
70
68
6.9
2
3
4
5
CH
CH
CH
CH
3
3-NO
4-Cl
2-Cl
2
45
93
14.4
75
81
7.2
90
74
5.8
3
3
3
30
30
25
90
94
89
20.9
21.8
24.6
35
45
30
88
76
85
16.8
18.7
18.9
60
80
35
82
73
85
9.6
6.4
2,4-Cl
17.2
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Table 2 (Contd.)
Catalyst 1a (RGO–SO
3
H)
Catalyst 1b (GO–SO
3
H)
3
Catalyst 1c (GO–SiPrSO H)
b
b
b
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
ꢁ
1
ꢁ1
ꢁ1
Entry
R
X
Product
)
)
)
6
CH
3
2-F
40
82
14.4
50
76
10.2
90
65
5.1
7
8
9
CH
3
3-F
30
90
20.9
45
75
11.1
70
65
6.6
CH
3
4-Br
20
95
33.5
25
80
21.2
40
80
14.3
CH
3
3-Br
30
88
20.5
40
76
12.8
60
58
6.8
1
0
CH
3
2-Br
15
89
41.4
25
86
22.8
25
82
23.0
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Table 2 (Contd.)
Catalyst 1a (RGO–SO
3
H)
Catalyst 1b (GO–SO
3
H)
3
Catalyst 1c (GO–SiPrSO H)
b
b
b
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
ꢁ
1
ꢁ1
ꢁ1
Entry
R
X
Product
)
)
)
1
1
CH
3
H
60
80
9.3
100
76
5.1
120
79
4.6
1
2
CH
3
4-CH
3
60
81
9.4
120
79
4.4
150
68
3.2
1
3
CH
3
3-OCH
3
50
78
10.9
100
80
5.3
130
67
3.6
c
1
4
CH
3
4-CHO
30
82
19.1
35
79
15.1
40
79
14.1
tert-
Butyl
1
5
4-NO
2
60
89
10.3
75
85
7.5
100
68
4.8
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Table 2 (Contd.)
Catalyst 1a (RGO–SO
3
H)
Catalyst 1b (GO–SO
3
H)
3
Catalyst 1c (GO–SiPrSO H)
b
b
b
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
Time
(min)
Yield
(%)
TOF
(h
ꢁ
1
ꢁ1
ꢁ1
Entry
R
X
Product
)
)
)
tert-
Butyl
1
6
7
3-NO
2
50
10
90
96
12.6
69.7
80
15
80
91
6.7
110
71
79
4.6
d
1
CH
3
CH
2
O
40.4
30
18.6
a
ꢂ
General reaction conditions: 2,4-dialkylphenol (1) (6 mmol), aldehyde (2a–q) (2 mmol), solvent free, T ¼ 100 C, catalysts 1a ¼ 40 mg, 1b ¼ 75 mg,
b
c
d
1
c ¼ 100 mg. Isolated yields. Reaction conditions: 2,4-dimethylphenol (12 mmol), terephthaldehyde (2n) (2 mmol). Reaction conditions: 2,4-
dimethylphenol (4 mmol), formaldehyde (2q) (2 mmol).
3
groups on ortho or para position. Also, it was observed that the RGO–SO H. The reusability of the catalyst 1a was studied in the
catalyst 1a was better than other catalysts. In the catalyst 1a, the multiple sequential reaction of 2,4-dimethhylphenol (1) and
total density of SO H groups is higher than other catalysts. 4-bromobenzaldehyde (2h). The catalyst was consecutively
3
The proposed reaction mechanism for solid acid catalysts
0
based on graphene nanosheets catalyzed synthesis of 6,6 -
(arylmethylene)bis(2,4-dialkylphenol) antioxidants using 2,4-
dialkylphenol and aromatic aldehydes are shown in Scheme 3.
The reaction proceeds via a series of protonic shis from solid
acid catalysts to the substrates. First, the aromatic aldehydes are
activated by protonation with solid acid catalysts to give species
(I). Nucleophilic attack of 2,4-dialkylphenol on (I) affords
species (II) and (III) which in turn is activated by solid acid
catalysts to afford species (IV). Nucleophilic attack of second
molecule of 2,4-dialkylphenol to species (IV), gives (V)
0
which is subsequently converted to 6,6 -(arylmethylene)bis(2,4-
dialkylphenol) antioxidants and releases solid acid catalysts
for the next catalytic runs.
The reusability and stability of the catalyst 1a
For practical application of solid acid catalysts in industrial, the
life time and stability of the RGO–SO H are very important
3
factors. The homogeneous acidic catalysts cannot recover even
one time, in contrast with the solid acid catalysts such as Scheme 3 The proposed reaction mechanism.
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catalysts was taken on a FE-SEM Hitachi S4160 instrument.
TEM images was recorded with a Zeiss-EM10C with an accel-
eration voltage of 80 kV. The AFM of GO nanosheets was
measured using a scanning probe microscope (SPM-9600, Shi-
madzu). Melting points was obtained with a Yanagimoto micro
melting point apparatus and are uncorrected. The purity
determination of the substrates and reaction monitoring were
accomplished by TLC on silica-gel polygram SILG/UV 254 plates
(from Merck Company).
Typical procedure for the preparation of GO nanosheets
Fig. 8 The reusability of the catalyst 1a in the synthesis of (3h).
GO nanosheets were synthesized using graphite powders by a
52
modied Hummer's method. Typically, 5.0 g of natural
recovered for eight cycles without signicant loss of its catalytic graphite powder and 2.5 g of sodium nitrate were mixed with
activity (Fig. 8). At the end of each reaction, the solid acid 115 mL of sulfuric acid (98%) in a 1000 mL round-bottom ask
catalyst was isolated by simple ltration under reduced pres- equipped with a magnetic stirrer and condenser place in an ice
sure, washed exhaustively with acetone, n-hexane, and ethanol, bath. The obtained solution was stirred and slowly added 15.0 g
ꢂ
and dried at 100 C for 24 h before being used with fresh of potassium permanganate, the stirring was continued for 2 h.
ꢂ
2
,4-dimethylphenol and 4-bromobenzaldehyde. The catalyst The mixture solution was transferred to a 35 C water bath and
can be reused for eight runs without any treatment in its cata- stirred for 30 min. Aer this step, 230 mL of deionized water
lytic activity.
was slowly added into the solution and the solution tempera-
ture monitored was about 98 C and stirred for 15 min. Then,
ꢂ
7
00 mL of deionized water and 50 mL of H
2 2
O (30%) was
Conclusions
sequentially added to the mixture solution to terminate the
In conclusions, in this study, three types of the solid acid reaction. The resulting materials was ltered and washed with
catalysts based reduced graphene oxide or graphene oxide 5% HCl solution followed by distilled water for several times.
nanosheets were prepared and were investigated in the The solution was ltered under reduced pressure by vacuum
0
synthesis of 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxi- pump over sinter-glass (G4). The graphite oxide powder was
ꢂ
dants under solvent free conditions. The total density of SO H obtained aer drying in vacuum at 60 C for 12 h. The graphite
3
groups on the surface of solid acid catalysts for RGO–SO
GO–SO H, and GO–SiPrSO H were 2.15, 1.20, and 0.85 mmol 0.5 mg mL , and exfoliated by ultrasonication (75 W) for 30
. The RGO–SO H relative to another two types of the min to generate GO nanosheets, followed by centrifugation at
3
H, oxide was dispersed in distilled water to make concentration of
ꢁ
1
3
3
ꢁ1
g
3
prepared catalysts is more reactive and stable in the synthesis of 3500 rpm for 30 min to remove unexfoliated graphite oxide.
bisphenolic antioxidants because of the high acidity. For the

rst time, we disclosed a highly efficient method for the prep-
0
Typical procedure for the preparation of sulfonated reduced
graphene oxide nanosheets (1a)
aration of 6,6 -(arylmethylene)bis(2,4-dialkylphenol) antioxi-
dants from 2,4-dialkylphenol and aldehydes under atomic
economic and solvent free conditions.
For preparation of catalyst 1a, rst, reduced graphene oxide
(
RGO) was synthesized by the chemical reduction of GO using
NaBH as a reducing agent. In a 1000 mL round-bottom ask,
.0 g of the GO dispersion was added into deionized water (700
mL), followed by sonication (40 W) for 15 min. Then, 2.4 g of
4
Experimental
Materials and apparatus
1
The chemicals used in this work were purchased from Fluka NaBH
4
was added into the round-bottom ask, heating at
ꢂ
and Merck chemical companies and used without purication. 100 C for 24 h. Aer this step, the resulted product was washed
IR spectra were obtained as KBr pellets in the range of 400–4000 with water several times and ltered under reduced pressure by
ꢁ
1
cm on a Perkin-Elmer 781 spectrophotometer and on an vacuum pump over sinter glass (G4) and centrifugation at 3500
1
13
impact 400 Nicolet FT-IR spectrophotometer. H NMR and
C
rpm for 15 min to obtain RGO nanosheets. Sulfonated reduced
H) was prepared from the
NMR spectra were recorded in DMSO-(d ) solvent on a Brucker graphene oxide nanosheets (RGO–SO
6
3
DRX-400 MHz spectrometer using tetramethyl silane as an hydrothermal sulfonation of RGO using H
internal standard. XRD patterns were recorded by an X'PertPro 180 C. 1.0 g of RGO was added into 50 mL of H
2
SO
4
(100%) at
SO . Aer
ꢂ
2
4
˚
(
Philips) instrument with 1.54 A wavelengths of X-ray beam and sonication (40 W) for 15 min, the mixture was transferred into a
ꢂ
ꢁ1
ꢂ
Cu anode material, at a scanning speed of 2 min from 10 to round-bottom ask under nitrogen atmosphere and stirring to
ꢂ ꢂ
0 (2q). The elemental analyses (C, H, N) were obtained from a heat at 180 C for 24 h. Then, the prepared catalyst 1a was
8
Carlo ERBA Model EA 1108 analyzer. The Raman spectra were washed with a large amount of deionized water and drying at
ꢂ
recorded with an Almega Thermo Nicolet Dispersive Raman 80 C for 12 h. Finally RGO–SO
3
H was obtained and checked in
spectrometer excited at 532 nm. The SEM images of prepared the synthesis of bisphenolic antioxidants.
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Typical procedure for the preparation of sulfonic acid
graphene oxide nanosheets (1b)
atmosphere to degas CO
added and the mixture stirred for 2 h at room temperature.
2
. Next 10 mL of NaOH 0.098 N was
Subsequently, the mixture was ltered through sintered glass
For preparation of catalyst 1b, in a typical experiment, GO (0.5
g), dichloromethane (4 mL), and chlorosulfonic acid (1.5 mL)
were added to round-bottom ask 25 mL and stirred at room
temperature for 24 h under nitrogen atmosphere. Aer this
step, the resulted catalyst was thoroughly washed with deion-
ized water and ethanol several times and ltered under reduced
(G-4) and washed several times with deionized water. The

ltrate was then titrated with HCl 0.1 N until reaching the
neutral point as monitored by phenolphthalein as indicator.
The volume required to reach the neutral point was subtracted
from the initial volume of NaOH used to obtain the volume of
NaOH which has reacted with sulfonated group on RGO or GO.
The back acid–base titration for GO was carried out and the
results calculated in the acidity of catalyst 1a, 1b and 1c. The
measurement was repeated three times for each catalyst and the
average calculated (eqn (1)).
pressure over sinter glass (G4). The solid acid 1b was dried at
ꢂ
9
0 C for 24 h and nally the GO–SO H was obtained and used
3
in the synthesis of bisphenolic antioxidants.
Typical procedure for the preparation of the sulfonated
propylsilane graphene oxide nanosheets (1c)
NaOH (mmol reacted with SO
3
H) ¼ NaOH (primary mmol) ꢁ
H) (1)
For preparation of catalyst 1c, the GO was functionalized with NaOH (mmol unreacted with SO
mercaptopropyl trimethoxysilane (MPTMS) as the organic
3
precursor for the preparation of sulfonated propylsilane gra-
phene oxide nanosheets (GO–SiPrSO H). Firstly, GO (0.5 g), and
3
3
.0 mL of MPTMS was added to 4.0 mL of toluene as a medium
Regeneration of the catalyst 1a
ꢂ
reaction and stirred at 110 C for 24 h. Then, the mercapto-
propyl groups of the functionalized GO nanosheets were
oxidized to sulfonic acid group using 10 mL of H O (30%) as
2 2
the green oxidizing agent at room temperature for 24 h. The
obtained catalyst 1c was washed with deionized water and
Recovery and reusability of the heterogeneous catalysts are very
important factor in practice and also from economical and
industrial viewpoint. Reusability of the RGO–SO H was studied
3
in the reaction of 2,4-dimethylphenol and 4-bromobenzalde-
hyde. At the end of each run, the catalyst was isolated by
ꢂ
ethanol to remove the residual precursor, then, dried at 60 C

ltration, washed exhaustively with acetone, n-hexane, and
for 24 h. The prepared catalyst 1c was employed in the reaction
of 2,4-dialkylphenol and aromatic aldehydes for the synthesis of
bisphenolic antioxidants.
ꢂ
ethanol, then dried at 100 C for 12 h before being used with
fresh 2,4-dimethylphenol and 4-bromobenzaldehyde. The
catalyst 1a can be reused eight cycles without any reduction in
its catalytic activity.
General procedure for the preparation of bisphenolic
antioxidants catalyzed by catalysts (1a, 1b, 1c) under solvent
free conditions
Spectroscopic and physical data
0
6
,6 -((4-Nitrophenyl)methylene)bis(2,4-dimethylphenol).
In a 25 mL round-bottom ask equipped with a magnetic bar
and condenser, a mixture of 2,4-dialkylphenol (6 mmol),
aromatic aldehyde (2 mmol) and RGO–SO H (1a) (40 mg) was
heated at 100 C under solvent free conditions for the appro-
ꢂ
ꢁ1
1
(Table 2, compound 3a): mp: 136–138 C; IR (KBr): n (cm )
3482, 3249, 2958, 1599, 1522, 1475, 1349, 1292, 1113, 879. H-
3
NMR (400 MHz, DMSO-d
6
) d (ppm): 1.95 (6H, s, Me), 2.47 (6H,
ꢂ
s, Me), 6.22 (1H, s, Ar CH), 6.26 (2H, s, OH), 6.75 (2H, s, 3-H
3
priate time according to Table 2. The progress of the reaction
was monitored by thin layer chromatography (TLC) (n-hexane–
ethyl acetate 10 : 4). At the end of the reaction, the mixture was
cooled to room temperature and 15 mL of acetone (3 ꢃ 5 mL)
DMP), 7.21 (2H, d, J ¼ 8 Hz, 2,6-H aldehyde), 8.09 (2H, s, 5-H
DMP), 8.11 (2H, d, J ¼ 8 Hz, 3,5-H aldehyde). Anal. calcd for
23 4
C H23NO : C, 73.19; H, 6.14; N, 3.71%. Found: C, 73.06; H,
6
.12; N, 3.70%.
3
was added. The RGO–SO H was ltered under reduced pressure
0
6
,6 -((3-Nitrophenyl)methylene)bis(2,4-dimethylphenol).
using vacuum pump over sinter glass (G4). The solution was
recovered by evaporation on a rotary evaporator. Aer that, the
solid materials were washed with n-hexane (5 mL) and deion-
ized water, successively, to afford pure products. The desired
products were kept in an oven at 80 C for 12 h. In addition, the
prepared catalysts 1b, and 1c were investigated in the synthesis
of bisphenolic antioxidants. The amount of the catalyst 1b, and
ꢂ
ꢁ1
1
(Table 2, compound 3b): mp: 141–143 C; IR (KBr): n (cm )
3433, 3082, 2916, 1606, 1525, 1481, 1347, 1217, 1096, 861. H-
NMR (400 MHz, DMSO-d ) d (ppm): 1.91 (6H, s, Me), 2.46 (6H,
6
s, Me), 6.24 (1H, s, Ar CH), 6.28 (2H, s, OH), 6.57 (2H, s, 3-H
ꢂ
3
DMP), 6.75 (1H, d, J ¼ 7.8 Hz, 5-H aldehyde), 7.43 (1H, d, 6-H
aldehyde), 7.53 (2H, d, J ¼ 7.8 Hz, 2,4-H aldehyde), 7.73 (2H, s, 5-
4
H DMP). Anal. calcd for C23H23NO : C, 73.19; H, 6.14; N, 3.71%.
1
c were 75, and 100 mg respectively and appropriate time were
Found: C, 73.21; H, 7.05; N, 3.67%.
added to Table 2.
0
6
,6 -((4-Chlorophenyl)methylene)bis(2,4-dimethylphenol).
ꢂ
ꢁ1
(Table 2, compound 3c): mp: 158–160 C; IR (KBr): n (cm )
Acidity of the prepared catalysts
3
498, 3467, 3018, 2918, 1587, 1472, 1381, 1254, 1183, 1048, 862.
1
The density of sulfonated group on RGO, and GO was calculated
H-NMR (400 MHz, DMSO-d ) d (ppm): 2.03 (6H, s, Me), 2.08
6
by back acid–base titration. First, 100 mg of RGO–SO
3 3
H was (6H, s, Me), 6.10 (1H, s, Ar CH), 6.26 (2H, s, OH), 6.71 (2H, s, 3-H
ultrasonicated in a water bath for 10 min under nitrogen DMP), 6.96 (2H, d, J ¼ 7.9 Hz, 2,6-H aldehyde), 7.28 (2H, s, 5-H
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DMP), 7.97 (2H, d, J ¼ 7.9 Hz, 3,5-H aldehyde). Anal. calcd for 127.57, 128.07, 128.73, 128.98, 129.86, 130.57, 130.94, 131.98,
C H ClO : C, 75.30; H, 6.32%. Found: C, 75.19; H, 6.29%.
148.06, and 150.68. Anal. calcd for C H BrO : C, 67.16; H,
23 23 2
2
3
23
0
2
6
,6 -((2-Chlorophenyl)methylene)bis(2,4-dimethylphenol). 5.64%. Found: C, 67.08; H, 5.51%.
ꢂ
ꢁ1
0
(
Table 2, compound 3d): mp: 191–193 C; IR (KBr): n (cm
482, 2918, 1600, 1598, 1474, 1331, 1291, 1190, 1037, 866. H- (Table 2, compound 3j): mp: 188–190 C; IR (KBr): n (cm
)
6,6 -((2-Bromophenyl)methylene)bis(2,4-dimethylphenol).
1
ꢂ
ꢁ1
3
)
NMR (400 MHz, DMSO-d
s, Me), 6.19 (2H, s, OH), 6.40 (1H, s, Ar
6
) d (ppm): 1.93 (6H, s, Me), 2.08 (6H, 3484, 2917, 1597, 1566, 1474, 1330, 1189, 1140, 1023, 866, 750.
1
3
CH), 6.71 (2H, s, 3-H
H-NMR (400 MHz, DMSO-d
6
) d (ppm): 1.94 (6H, s, Me), 2.09
CH), 6.72 (2H, s, 3-H
DMP), 6.83 (1H, t, J ¼ 8 Hz, 4-H aldehyde), 7.18 (2H, s, 5-H (6H, s, Me), 6.18 (2H, s, OH), 6.35 (1H, s, Ar
3
DMP), 7.35 (1H, d, J ¼ 7.7 Hz, 6-H aldehyde), 7.96 (2H, d, 3,5-H DMP), 6.83 (1H, d, J ¼ 8 Hz, 6-H aldehyde), 7.08 (1H, d, J ¼ 8 Hz,
aldehyde). Anal. calcd for C H ClO : C, 75.30; H, 6.32%. 4-H aldehyde), 7.21 (1H, d, J ¼ 7.7 Hz, 3-H aldehyde), 7.53 (1H, t,
2
3
23
2
Found: C, 75.29; H, 6.34%.
J ¼ 7.7 Hz, 5-H aldehyde), 7.97 (2H, s, 5-H DMP). Anal. calcd for
0
6
,6 -((2,4-Dichlorophenyl)methylene)bis(2,4-dimethylphenol). C H BrO : C, 67.16; H, 5.64%. Found: C, 67.20; H, 5.59%.
2
3
23
0
2
ꢂ
ꢁ1
(
Table 2, compound 3e): mp: 183–185 C; IR (KBr): n (cm ) 3500,
6,6 -((Phenyl)methylene)bis(2,4-dimethylphenol). (Table 2,
1
ꢂ
ꢁ1
3466, 3022, 2917, 1602, 1481, 1405, 1252, 1184, 1138, 847. H- compound 3k): mp: 113–115 C; IR (KBr): n (cm ) 3339, 3021,
1
NMR (400 MHz, DMSO-d
s, Me), 6.17 (2H, s, OH), 6.33 (1H, s, Ar
DMP), 7.80 (2H, s, 5-H DMP), 7.29 (1H, d, J ¼ 8 Hz, 6-H aldehyde), s, Me), 6.13 (1H, s, Ar
.50 (1H, d, J ¼ 8 Hz, 5-H aldehyde), 8.01 (1H, s, 2H aldehyde). DMP), 6.97 (2H, t, J ¼ 8 Hz, 3,5-H aldehyde), 7.11 (1H, t, J ¼ 8 Hz,
6
) d (ppm): 1.92 (6H, s, Me), 2.08 (6H, 2920, 1600, 1481, 1447, 1384, 1292, 1186, 1142, 864, 702. H-
CH), 6.73 (2H, s, 3-H NMR (400 MHz, DMSO-d ) d (ppm): 2.06 (6H, s, Me), 2.08 (6H,
CH), 6.29 (2H, s, OH), 6.70 (2H, s, 3-H
3
6
3
7
Anal. calcd for C H Cl O : C, 68.83; H, 5.53%. Found: C, 68.64; 4-H aldehyde), 7.23 (2H, d, J ¼ 8 Hz, 2,6-H aldehyde), 7.93 (2H, s,
2
3
22
2 2
H, 5.49%.
5-H DMP). Anal. calcd for C H O : C, 83.10; H, 7.28%. Found:
23 24 2
0
6
,6 -((2-Fluorophenyl)methylene)bis(2,4-dimethylphenol). C, 83.14; H, 7.24%.
ꢂ
ꢁ1
1
0
(
Table 2, compound 3f): mp: 146–148 C; IR (KBr): n (cm
)
6,6 -((4-Methylphenyl)methylene)bis(2,4-dimethylphenol).
ꢂ
ꢁ1
3484, 3920, 1584, 1482, 1333, 1290, 1223, 1193, 1140, 866. H- (Table 2, compound 3l): mp: 168–170 C; IR (KBr): n (cm )
1
NMR (400 MHz, DMSO-d
s, Me), 6.26 (2H, s, OH), 6.35 (1H, s, Ar
DMP), 6.72 (1H, t, J ¼ 7.8 Hz, 4-H aldehyde), 7.06 (2H, s, 5-H Me), 2.21 (3H, s, CH -aldehyde), 6.06 (1H, s, Ar CH), 6.28 (2H, s,
6
) d (ppm): 1.95 (6H, s, Me), 2.09 (6H, 3501, 2917, 1604, 1476, 1330, 1188, 1139, 1031, 866. H-NMR
3
CH), 6.72 (2H, s, 3-H (400 MHz, DMSO-d ) d (ppm): 2.01 (6H, s, Me), 2.07 (6H, s,
6
3
3
DMP), 7.20 (1H, d, J ¼ 8 Hz, 6-H aldehyde), 7.98 (2H, d, t, 3,5-H OH), 6.68 (2H, s, 3-H DMP), 6.84 (2H, d, J ¼ 8.1 Hz, 3,5-H
1
3
aldehyde). C-NMR (100 MHz, DMSO-d ) d (ppm): 17.18, 20.95, aldehyde), 7.01 (2H, s, 5-H DMP), 7.88 (2H, d, J ¼ 8.1 Hz, 2,6-H
6
1
3
3
1
6.84, 115.28, 115.50, 124.44, 127.42, 128.15, 129.80, 130.88, aldehyde). C-NMR (100 MHz, DMSO-d
31.98, 132.13, 150.64, 159.51, and 161.94. Anal. calcd for 43.26, 124.38, 127.30, 128.18, 128.94, 129.45, 129.58, 131.95,
6
) d (ppm): 17.21, 20.97,
C
23
H
23FO
2
: C, 78.83; H, 6.62%. Found: C, 78.72; H, 6.61%.
134.81, 141.78, and 150.69. Anal. calcd for C24
H
26
O
2
: C, 83.20;
0
6
,6 -((3-Fluorophenyl)methylene)bis(2,4-dimethylphenol). H, 7.56%. Found: C, 83.14; H, 7.49%.
ꢂ
ꢁ1
0
(Table 2, compound 3g): mp: 94–96 C; IR (KBr): n (cm ) 3335,
6,6 -((3-Methoxyphenyl)methylene)bis(2,4-dimethylphenol).
1
ꢂ
ꢁ1
3923, 1611, 1586, 1482, 1442, 1385, 1292, 1189, 1142, 783. H- (Table 2, compound 3m): mp: >270 C; IR (KBr): n (cm ) 3453,
1
NMR (400 MHz, DMSO-d ) d (ppm): 1.95 (6H, s, Me), 2.09 (6H, 2975, 1622, 1505, 1402, 1347, 1230, 1088, 790. H-NMR (400
6
s, Me), 6.14 (1H, s, Ar CH), 6.28 (2H, s, OH), 6.66 (2H, s, 3-H MHz, DMSO-d ) d (ppm): 1.94 (6H, s, Me), 2.08 (6H, s, Me), 3.80
3
6
DMP), 6.72 (2H, d, J ¼ 7.9 Hz, 5,6-H aldehyde), 6.96 (1H, d, J ¼ (3H, s, OCH
3
3
), 6.14 (1H, s, Ar CH), 6.28 (2H, s, OH), 6.68 (2H, s,
7
8
6
.9 Hz, 2-H aldehyde), 7.25 (1H, d, J ¼ 7.9 Hz, 4-H aldehyde), 3-H DMP), 6.84 (1H, s, 2-H aldehyde), 6.94 (1H, d, J ¼ 7.9 Hz, 4-H
.00 (2H, s, 5-H DMP). Anal. calcd for C23
H
23FO
2
: C, 78.83; H, aldehyde), 7.64 (2H, s, 5-H DMP), 8.12 (2H, m, 5,6-H aldehyde).
Anal. calcd for C24 : C, 79.53; H, 7.23%. Found: C, 79.58; H,
.62%. Found: C, 78.79; H, 6.54%.
26 3
H O
0
6
,6 -((4-Bromophenyl)methylene)bis(2,4-dimethylphenol). 7.20%.
ꢂ
ꢁ1
1
0
00
(
2
(
Table 2, compound 3h): mp: >240 C; IR (KBr): n (cm ) 3468,
6,6 ,6 ,6%-(1,4-Phenylenebis(methanetriyl))tetrakis(2,4-dime-
ꢂ
917, 1601, 1480, 1401, 1251, 1184, 1138, 1072, 860. H-NMR thylphenol). (Table 2, compound 3n): mp: 65–67 C; IR (KBr): n
ꢁ
1
400 MHz, DMSO-d ) d (ppm): 2.06 (6H, s, Me), 2.08 (6H, s, (cm ) 3429, 3012, 2918, 1686, 1602, 1479, 1294, 1208, 1016, 861.
6
1
Me), 6.07 (1H, s, Ar
3
CH), 6.25 (2H, s, OH), 6.70 (2H, s, 3-H DMP),
H-NMR (400 MHz, DMSO-d
6
) d (ppm): 1.90 (12H, s, Me), 2.10
6
7
C
.88 (2H, d, J ¼ 7.9 Hz, 2,6-H aldehyde), 7.38 (2H, s, 5-H DMP), (12H, s, Me), 6.07 (2H, s, Ar
3
CH), 6.25 (4H, s, OH), 6.52 (2H, s, 3-
.96 (2H, d, J ¼ 7.9 Hz, 3,5-H aldehyde). Anal. calcd for H DMP), 6.61 (4H, m, 2,6-H aldehyde), 6.72 (4H, s, 5-H DMP),
1
3
23
H
23BrO
2
: C, 67.16; H, 5.64%. Found: C, 67.18; H, 5.61%.
7.77 (2H, m, 3,5-H aldehyde), 7.94 (2H, m, 3,5-H aldehyde). C-
) d (ppm): 16.41, 17.20, 20.56, 20.95,
43.28, 114.88, 123.88, 124.32, 124.68, 127.30, 127.61, 128.29,
345, 2922, 1591, 1478, 1383, 1325, 1293, 1188, 1143, 1075, 863. 129.19, 129.81, 130.28, 131.58, 132.02, 141.99, 150.66, and
0
6
,6 -((3-Bromophenyl)methylene)bis(2,4-dimethylphenol). NMR (100 MHz, DMSO-d
6
ꢂ
ꢁ1
(Table 2, compound 3i): mp: 124–126 C; IR (KBr): n (cm )
3
1
H-NMR (400 MHz, DMSO-d ) d (ppm): 2.03 (6H, s, Me), 2.08 153.50. Anal. calcd for C H O : C, 81.88; H, 7.21%. Found: C,
6
40 42 4
(
6H, s, Me), 6.10 (1H, s, Ar
3
CH), 6.26 (2H, s, OH), 6.72 (2H, s, 3-H 81.82; H, 7.20%.
0
DMP), 6.96 (1H, d, J ¼ 8 Hz, 6-H aldehyde), 7.19 (1H, d, J ¼ 8 Hz,
6,6 -((4-Nitrophenyl)methylene)bis(2,4-di-tert-butylphenol).
ꢂ
ꢁ1
5
7
-H aldehyde), 7.21 (1H, J ¼ 7.8 Hz, 4-H aldehyde), 7.33 (1H, J ¼ (Table 2, compound 3o): mp: 153–155 C; IR (KBr): n (cm
)
1
3
.8 Hz, 2-H aldehyde), 8.01 (2H, s, 5-H DMP). C-NMR (100 3491, 2959, 1690, 1598, 1522, 1474, 1417, 1350, 1188, 116, 862.
1
MHz, DMSO-d
6
) d (ppm): 17.19, 20.94, 43.50, 121.84, 124.65,
6
H-NMR (400 MHz, DMSO-d ) d (ppm): 1.05 (18H, s, tert-butyl),
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1
7
7
3
.33 (18H, s, tert-butyl), 6.28 (1H, s, Ar CH), 6.47 (2H, s, OH), 16 Y. A. Gurvich, US Pat., 1,475,973, 1977.
.13 (2H, s, 3-H DMP), 7.13 (2H, d, J ¼ 8 Hz, 2,6-H aldehyde), 17 A. R. Davis and F. A. V. Sallivan, US Pat., 2,538,355, 1951.
.70 (2H, s, 5-H DMP), 8.13 (2H, d, J ¼ 8 Hz, 3,5-H aldehyde). 18 S. Saito, T. Ohwada and K. Shudo, J. Am. Chem. Soc., 1995,
1
3
C-NMR (100 MHz, DMSO-d ) d (ppm): 30.35, 31.70, 34.27,
117, 11081–11084.
6
3
1
5.16, 44.12, 121.76, 123.47, 125.08, 130.50, 130.64, 137.52, 19 C. V. Rode, A. C. Garade and R. C. Chikate, Catal. Surv. Asia,
41.46, 146.18, 151.02, and 153.25. Anal. calcd for C35 2009, 13, 205–220.
H47NO :
4
C, 77.03; H, 8.68; N, 2.57%. Found: C, 77.07; H, 8.61; N, 2.59%. 20 K. Shimizu, S. Kontani, S. Yamada, G. Takahashi,
0
6
,6 -((3-Nitrophenyl)methylene)bis(2,4-di-tert-butylphenol).
T. Nishiyama and A. Satsuma, Appl. Catal., A, 2010, 380,
33–39.
ꢂ
ꢁ1
(
3
Table 2, compound 3p): mp: 118–120 C; IR (KBr): n (cm )
1
528, 2959, 1530, 1473, 1350, 1186, 1023, 884. H-NMR (400 21 S. K. Jana, T. Okamoto, T. Kugita and S. Namba, Appl. Catal.,
A, 2005, 288, 80–85.
1H, s, Ar CH), 6.29 (2H, s, OH), 6.93 (2H, s, 3-H DMP), 7.16 (1H, 22 I. Mohammadpoor-Baltork,
MHz, DMSO-d ) d (ppm): 2.01 (6H, s, Me), 2.06 (6H, s, Me), 6.06
6
(
M.
Moghadam,
3
d, J ¼ 8 Hz, 6-H aldehyde), 7.55 (2H, m, 4,5-H aldehyde), 7.64
S. Tangestaninejad, V. Mirkhani, K. Mohammadiannejad-
Abbasabadi and M. A. Zolgol, C. R. Chim., 2011, 14, 934–943.
(
2H, s, 5-H DMP), 8.12 (1H, s, 2-H aldehyde). Anal. calcd for
35 4
C H47NO : C, 77.03; H, 8.68; N, 2.57%. Found: C, 76.97; H, 23 S. Podder, J. Choudhury, U. K. Roy and S. Roy, J. Org. Chem.,
8
.64; N, 2.55%.
2007, 72, 3100–3103.
0
6,6 -Methylenebis(2,4-dimethylphenol). (Table 2, compound 24 V. Nair, K. G. Abhilash and N. Vidya, Org. Lett., 2005, 7, 5857–
ꢂ
ꢁ1
3q): mp: 105–107 C; IR (KBr): n (cm ) 3424, 3299, 2917, 1609,
5859.
1
1
482, 1381, 1286, 1193, 1150, 855. H-NMR (400 MHz, DMSO-d ) 25 J. Esquivias, R. G ´o mez Array ´a s and J. C. Carretero, Angew.
6
d (ppm): 2.00 (6H, s, Me), 2.10 (6H, s, Me), 3.74 (2H, s, CH ), 6.62
Chem., Int. Ed., 2006, 45, 629–633.
2
(2H, s, OH), 6.68 (2H, s, 3-H DMP), 8.25 (2H, s, 5-H DMP). Anal. 26 Z. Li, Z. Duan, J. Kang, H. Wang, L. Yu and Y. Wu,
calcd for C17
.79%.
H
20
O
2
: C, 79.65; H, 7.86%. Found: C, 79.62; H,
Tetrahedron, 2008, 64, 1924–1930.
27 S. Genovese, F. Epifano, C. Pelucchini and M. Curini, Eur. J.
Org. Chem., 2009, 1132–1135.
7
2
8 M. Kodomari, M. Nagamatsu, M. Akaike and T. Aoyama,
Tetrahedron Lett., 2008, 49, 2537–2540.
Acknowledgements
The authors are grateful to University of Kashan for supporting 29 R. Fareghi-Alamdari, M. Golestanzadeh, F. Agend and
this work by Grant no. 159148/43.
N. Zekri, J. Chem. Sci., 2013, 125, 1185–1195.
30 M. J. Allen, V. C. Tung and R. B. Kaner, Chem. Rev., 2009, 110,
1
32–145.
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