Graphene oxide: A promising carbocatalyst for the regioselective thiocyanation of aromatic amines, phenols, anisols and enolizable ketones by hydrogen peroxide/KSCN in water

Article abstract of DOI:10.1039/c5nj02314a

Graphene oxide (GO), as a heterogeneous carbocatalyst, catalyzes the direct thiocyanation of a variety of arenes including aromatic amines, phenols, anisols and carbonyl compounds that possessing α-hydrogen in the presence of hydrogen peroxide and KSCN in water as a green media. This procedure is chemoselective, avoids the use of precious metals and toxic solvents and has a broad substrate scope. Easy removal from the reaction mixture and recyclability with no loss of activity are the key features of graphene oxide in this catalytic system.

Full text of DOI:10.1039/c5nj02314a

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PAPER (or FOCUS or PERSPECTIVE)
Graphene oxide: a promising carbocatalyst for the
regioselective thiocyanation of aromatic amines,
phenols, anisols and enolizable ketones by hydrogen
peroxide/KSCN in water
Cite this: DOI: 10.1039/c3nj00000x
Received 00th XXXXX 2013,
Accepted 00th XXXXX 2013
Dariush Khalilia
DOI: 10.1039/c3nj00000x
Graphene oxide (GO), as a heterogeneous carbocatalyst catalyzes the direct thiocyanation of
a variety of arenes including aromatic amines, phenols, anisols and carbonyl compounds that
possessing α-hydrogen in the presence of hydrogen peroxide and KSCN in water as a green
media. This procedure is chemoselective, avoids the use of precious metals and toxic
solvents and has broad substrate scope. Easy removal from the reaction mixture and
recyclability with no loss of activity are the key features of graphene oxide in this catalytic
system.
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Dedicated to my Doctoral mentor Professor Nasser Iranpoor for celebriting 34 years efforts in organic
chemistry
epoxy, hydroxyl, carbonyl, and carboxyl groups.27 Due to the
introduction of these functional groups, GO tends to have acidic (pH
4.5 at 0.1 mg/mL) and be an oxidant.28, 29 It holds full potentials as a
heterogeneous metalꢀfree catalyst or support for several organic
transformations27, 30ꢀ39 and therefore this carbocatalyst can be ideal
candidate for this purpose. Continuing our studies in developing
novel system reagents for construction of thiocyanates40ꢀ42 it was
interesting to develop a green protocol for the thiocyanation reaction.
Herein an ecoꢀfriendly method for the direct thiocyanation of arenes
and ketones with H2O2/KSCN in water in the presence of graphene
oxide as a catalyst is presented.
Introduction
Sulfurꢀcontaining molecules rank among the most imperative motifs
in natural products and biologically important compounds;1ꢀ3
particularly thiocyanates that play a pivotal role in organic
synthesis.4 This functional group serves as precursor for the
preparation of many valuable heterocycles including agrochemicals,
drugs and dyes.5ꢀ7 Furthermore, thiocyanates could be readily
transformed into a more versatile sulfurꢀbearing groups for the
additional structure modification.8ꢀ11 Therefore, the synthesis of
thiocyanate compounds is attractive in the view of organic and
medicinal chemistry researchers. Arene and αꢀketo thiocyanates are
two main class of thiocyanates which have been more investigated in
recent researches in this area. A number of synthetic methods have
been developed for the thiocyanation of arenes12ꢀ20 and ketones21ꢀ26
using a variety of reagents under different reaction conditions.
However, many of these methods associated with some
disadvantages including long reaction time, unsatisfactory yield, use
of a large excess of expensive and strong oxidizing agents and toxic
solvents. Although these subjects still represent a real challenge, to
overcome these issues, the concept of heterogeneous systems can be
helpful. Graphene oxide (GO) prepared by exhaustive oxidation of
graphite, consists of a variety of oxygen functional groups, including
Results and discussion
Graphite oxide obtained by oxidation of graphite using the
modified Hummers method.43 Then the graphite oxide aqueous
suspension was ultrasonicated to form graphene oxide. The
prepared GO was characterized using FTꢀIR, UV/Vis and
Raman spectroscopy and also with AFM and XRD study to
establish its authenticity. The FTIR spectrum of GO shows a
broad peak appeared at 3429 cmꢀ1 in the high frequency area
attributed to the stretching mode of OꢀH bond, reveals the
presence of hydroxyl groups in graphene oxide. The band
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observed at 1720 cm−1 was assigned to the carboxyl group. The
sharp peak found at 1615 cm−1 is a resonance peak that can be
assigned to the stretching and bending vibration of OH groups
of water molecules adsorbed on graphene oxide. The peak at
1356 cmꢀ1 arises from CꢀOH group. The peak at 1225 cmꢀ1
denotes CꢀOꢀC stretching and the peak at 1056 cmꢀ1
corresponds to the vibrational mode of the CꢀO group.
large increase in yield of 2a was observed using the graphene
oxide as catalyst (90%, entry 5). To clarify the role of GO, an
experiment was performed. When the model reaction was
carried out in the absence of H2O2 and in the presence of GO at
80 °C, only trace amounts of product 2a was obtained (Table 1,
entry 6). This result clearly highlight the specific role of GO in
this transformation. Decreasing the reaction temperature also
resulted in the yield decline of the desired product (entry 7).
Compared to other screened solvents such as acetonitrile, THF,
ethanol, chloroform and diethyl ether, water appeared to be the
best one (entries 5ꢀ12). The amount of catalyst was also
screened, and 10 mol% loading of GO was found to be optimal;
The UVꢀVis spectrum of graphene oxide has an strong
absorption peak at 233 nm, attributed to
C–C conjugated aromatic domains and weak absorption
(shoulder) at 305 nm due to ꢀ ∗ transition of C=O bond (See
ꢀꢀꢀ∗ transition of the
ꢁ
ꢀ
supporting information). Raman spectroscopy is a standard
nonꢀdestructive technique that is widely used to obtain
structural information about carbonꢀbased materials. Raman
spectra of the graphene oxide shows an intense tangential mode a lower yield was observed when the amount of the catalyst
(G band) at 1587 cmꢀ1, with a disorderedꢀinduced peak (D
was decreased to 5 mol% (entry 13). Increasing the amount of
band) at 1355 cmꢀ1. The G band of graphene oxide broadens
and upꢀshifts in comparison to those observed in graphite
employment of NH4SCN instead of KSCN resulted in a less
(strong G band at 1577 cmꢀ1 due to first order scattering of the
GO did not increase the yield of 2a (entry 14). Notably, the
efficient transformation (entry 15).
E2g mode). A possible explanation of this behavior is the
presence of isolated double bonds which resonate at higher
frequencies. Furthermore, the D band at 1355 cm−1 becomes
prominent, indicating that the oxidation process influences the
Table 1: Optimization of the reaction conditiona
size of the inꢀplane sp2 domains. On the other hand, because of
the breaking of the stacking order which is due to the oxidation
reaction, the intensity of the 2D band is smaller after oxidation.
The surface image and height profiles of AFM for graphene
oxide show the existence of irregularly sheet like morphology
and lateral dimension of a few micrometers with the presence
of mono layers and few layered of graphene oxide. The
presence of a few layers in the sample is due to the aggregation
or self assembly of two or three layers of graphene oxide during
the drying process in the specimen preparation. The height
profiles along the straight line depicted in Figure 4 (supporting
information) show that the height of graphene oxide is about
1.45 nm, compatible well with the reported value.
Solvent
Yield
(%)b
<5
Entry
Catalyst (mol%)
Time
(condition)
H2O, 80 °C
H2O, 80 °C
H2O, 80 °C
1c
2
3d
ꢀ
6 h
6 h
6 h
6 h
1 h
1 h
1 h
Graphite (10)
rꢀGO (10)
18
XRD analysis was used to characterize the crystalline nature
and phase purity of the asꢀsynthesized graphene oxide. Pure
graphite has a strong and sharp diffraction peak at 2ꢂ = 26.55°,
corresponds to the (002) plane of hexagonal graphite structure
with the interlayer spacing of 0.34 nm. After the chemical
oxidation and exfoliation into graphene oxide, the 26.55° peak
disappeared and a wide diffraction peak at 11.78° appeared
33
4
Activated carbon (10) H2O, 80 °C
56
5e
6f
GO (10)
GO (10)
GO (10)
GO (10)
GO (10)
GO (10)
GO (10)
GO (10)
GO (5)
H2O, 80 °C
H2O, 80 °C
H2O, r.t.
90
trace
61
7
8
CH3CN, reflux 1 h
85
instead, revealing a
dꢀspacing of 0.83 nm. An increased
9
THF, reflux
EtOH, reflux
CHCl3, reflux
Et2O, reflux
H2O, 80 °C
H2O, 80 °C
H2O, 80 °C
1 h
1 h
1 h
1 h
1 h
1 h
1 h
71
interlayer distance between consecutive carbon basal planes is
attributed to the intercalation of oxygen functional groups and
water molecules into carbon layer structure.
10
11
12
13
14
15g
85
58
36
We then started our study by investigating the electrophilic
thiocyanation of aniline 1a (1 mmol) with H2O2 (3 mmol)/GO
in the presence of KSCN (2.5 mmol) as the model reaction. As
graphene oxide can be easily dispersed in H2O,44 therefore our
initial goal was to use this green media for the thiocyanation
reaction. In fact, the use of water as the solvent has gained
distinctive importance in the past few years due mainly to the
economic and environmental advantages. In the absence of
graphene oxide as a catalyst, when aniline was treated with
hydrogen peroxide and KSCN at 80 °C, no significant
thiocyanation of aniline was observed (Table 1, entry 1). Other
carbon promoters, such as natural flake graphite(Table 1, entry
2), hydrazineꢀreduced graphene oxide45 (Table 1, entry 3) and
activated carbon46 (Table 1, entry 4) were also examined in this
reaction, but the yield of product 2a were lower after 6 h. A
74
GO (15)
GO (15)
89
77
aThe reactions were performed with aniline (1 mmol), H2O2 (35%, 3
mmol), KSCN (2.5 mmol) and carbon promoter ( type indicated),
solvent (3 mL). bIsolated yield. cBlank experiment in H2O without
graphene oxide. drꢀGO = reduced graphene oxide. eBold value signifies
f
g
best reaction conditions. In the absence of H2O2. Reaction performed
using NH4SCN as thiocyanates source.
Comparison of the obtained results confirmed the unique
promoting activity of graphene oxide. Under optimal reaction
conditions, a study on the substrate scope was carried out, and
the results are summarized in Table 2.
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To evaluate the amine scope, the preparation of thiocyanate
products from aniline derivatives was explored using our
standard reaction conditions.
Table 2: Thiocyanation of arenesa
Entry
1
Substrate
Product
Time
3 h
Yield (%)b
90
Aniline (1a)
2a
2b
2
3
2ꢀMethoxyaniline (1b)
3ꢀMethoxyaniline (1c)
2 h
2 h
93
87
11
81
89
85
80
2c
2d
2d'
2e
4
4ꢀMethoxyaniline (1d)
2 h
5
6
7
2ꢀMethylaniline (1e)
3ꢀMethylaniline (1f)
2ꢀChloroaniline (1g)
2 h
2 h
5 h
2f
2g
8
9
Nꢀmethylaniline (1h)
Nꢀethylaniline (1i)
2h
2i
3 h
3 h
5 h
3 h
86
88
83
85
10
11
Nꢀphenylaniline (1j)
N,Nꢀdimethylaniline (1k)
2j
2k
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12
13
Phenol (1l)
2l
8h
79
82
2ꢀMethylphenol (1m)
2m
6 h
14
2,6ꢀdimethylphenol (1n)
2n
6 h
86
15
16
Anisole (1o)
2o
2p
7 h
6 h
78
83
2ꢀMethylanisole (1p)
17
18
Indole (1q)
2q
2r
1 h
90
95
2ꢀMethylindole (1r)
45 min
19
Nꢀmethylindole (1s)
2s
2 h
91
2t
83
9
20c
Pyrrole (1t)
1 h
2t'
aReagents and conditions: arene (1 mmol), GO (10 mol%), H2O2 (35%, 3 mmol), KSCN (2.5 mmol)
, water (3 mL), 80 °C. bIsolated yields after flash column chromatography on silica gel. c After 10
h, 9% yield of the bisꢀadduct was obtained.
Aniline (1a), anilines having electronꢀdonating (1b
withdrawing groups (1g) can be successfully used in this normally thiocyanated product (2d) as a minor product along
system reagent (Table 2, entries 1ꢀ7). Generally, electronꢀrich with cyclization product of 2d 2d') in a 1:8 ratio (entry 4).
anilines such as 2ꢀmethoxyꢀ (1b) or 2ꢀmethylꢀ (1e) aniline are This observation is not unprecedented.47,
more prone to electrophilic thiocyanation than electronꢀ substituted anilines such as ꢀmethylꢀ (1h),
deficient substrates such as 2ꢀchloroaniline (1g). Utilizing para phenylꢀ (1j) and
ꢀf) or Methoxyaniline (1d) led to the formation of two products, the
(
48
A range of
Nꢀethylꢀ (1i),
N
N
ꢀ
ꢀ
N
ꢀ
N,Nꢀdimethyl (1k) anilines also underwent
substituted anilines which contains a blocked 4ꢀposition, ortho thiocyanation efficiently (Table 2, entries 8ꢀ11). These
thiocyanation occurred. For example thiocyanation of 4ꢀ substrates thiocyanated exclusively at their para position
4 | J. Name., 2012, 00, 1-3
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indicating that this method provides regioselective was also examined by increasing the reaction temperature to
monothiocyanation. However, treatment of phenols and anisols refluxing point of H2O. At this temperature, product 2t' was
such as phenol (1l), 2ꢀmethylꢀ (1m), 2,6ꢀdimethylphenol (1n), obtained in 37% yield even after a 72 h reaction time.
anisol (1o) and 2ꢀmethylanisole (1p) with KSCN in the Generally, the possibility of performing the reactions in water,
presence of H2O2/GO resulted in the formation of thiocyanated the simple filtration for recycling of the catalyst and using H2O2
phenols and anisols (Table 2, entries 12ꢀ16). Furthermore, the as an oxidant make this protocol a valid candidate towards the
reactions of indole derivatives (1qꢀs) with this reagent system goal of green chemistry.
After establishing the activity of the methodology for
thiocyanation of arenes, we attemp ted to further apply this
protocol to the thiocyanation of enolizable ketones. The
procedure for synthesizing thiocynated arenes that was
described above was expanded to the thiocyanation of ketones
(Table 3). Initially, we have attempted the thiocyanation of
acetophenone (3a) with potassium thiocyanate using H2O2 as a
green oxidant and graphene oxide as a catalyst in water at 80
°C. The reaction proceeded smoothly to afford the 1ꢀphenylꢀ2ꢀ
thiocyanatoethanone (4a) in 80% yield (Table 3, entry 1).
Similarly, cyclic ketones such as cyclopentanone (3b) and
cyclohexanone (3c) underwent smooth thiocyanation to furnish
proceeded efficiently and generated the desired products 2qꢀs in
90, 95 and 91% yields, respectively. Pyrrole was also easily
transformed into 2ꢀthiocyanato pyrrole 2t in 1 h (entry 20). In
this case a minor amount of 2,5ꢀdithiocyanatopyrrole 2t' was
obtained along with the 2ꢀthiocyanato derivative. We also
checked the possibility of the selective synthesis of 2,5ꢀ
dithiocyanatopyrrole 2t' under the optimal reaction conditions.
In this case, by changing the ratio of KSCN to oxidant (H2O2)
no improvement in the yield of 2t' was observed. Prolonged
reaction time may also help to increase the yield of 2,5ꢀ
dithiocyanatopyrrole 2t'. Therefore the effect of this parameter
on the yield of 2t' was investigated. When the reaction time
was extended to 72 h, the yield of the desired product 2t'
reached to 29%. Further increasing the reaction time failed to
improve the outcome. Additionally, the effect of temperature
the corresponding αꢀthiocyanoketones 4bꢀc in good yields
(Table 3, entries 2 and 3).
Table 3: Graphene oxide (GO) catalyzed thiocyanation of carbonyl compoundsa
Entry
1
Substrate
Product
Time (h) Yield (%)b
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
4
4
5
5
5
80
86
83
83
86
2
3
4
5
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c
6
7
3f
4f
4
4
-
-
d
3g
4g
aReaction conditions: carbonyl compound (1 mmol), GO (10 mol%), H2O2
(35%, 3 mmol), KSCN (2.5 mmol), water (3 mL) at 80 °C. bIsolated yields
reported. cThe product readily decomposed. dA mixture of decomposed
products was obtained.
the activation of H2O2 by GO as a solid acid. Then, reaction of
activated H2O2 with KSCN generates HOꢀSCN17, 51, 52 which is
activated again on subsequent reaction with GO and able to
produce thiocyanium ion SCN+. Eventually, this electrophile is
attacked by arene/enolizable ketone to produce the target
product and water as a byproduct.
Other cyclic ketones, such as 2ꢀmethylcyclohexanone (3d) also
participated well in this reaction (entry 4). Similarly, enolizable
acyclic ketones such as 1ꢀphenylpropanꢀ1ꢀone (3e) (Table 1,
entry 5,) also reacted readily with potassium thiocyanate to give
the corresponding αꢀthiocyanated product 4e in good yield. The
good reactivity of H2O2/GO in the thiocyanation of aryl methyl
ketones and cyclic ketones prompted us to extend this
thiocyanation method for βꢀdicarbonyl compounds. Thus,
pentaneꢀ2,4ꢀdione (acetylacetone) (3f), upon treatment with our
system, afforded a complex mixture of products and our efforts
to isolate the product was not successful. This observation is in
accordance with those reported for the thiocyanation of βꢀ
dicarbonyl compounds.49 We ratiocinate that since these
catalytic reactions must be performed at 80 °C, the product 3ꢀ
thiocyanatopentaneꢀ2,4ꢀdione (4f) decomposed readily to a
black semisolid. The possibility of applying this catalytic
system in the reaction of pentaneꢀ2,4ꢀdione (3f) with KSCN at
0 °C (at which product 4f is more stable) was examined.
Unfortunately, it was found that the yield of 3ꢀ
thiocyanatopentaneꢀ2,4ꢀdione (4f) decreased dramatically to
<10% when the reaction temperature was decreased from 80 °C
to 0 °C. Under the same condition (80 °C), the transformation
of ethyl acetoacetate (3g) went to completion at 80 °C in water
(as indicated by TLC and IR of the crude product) but attempts
to isolate product ethyl αꢀthiocyanatoacetoacetate (4g) using
H2O2/GO (even at 0 °C) proved to be unsuccessful, yielding a
viscous oily mixture of several compounds (Table 3, entry 7).
This behavior is due to the rapid decomposition of the product
Scheme 1: Plausible reaction mechanism
To confirm this hypothesis we performed a reaction sample in
the absence of indole and isolated a yellow precipitate after the
removal of GO which could be due to the formation of OHꢀ
SCN (I). IR analysis of this precipitate shows the characteristic
ꢀSCN and ꢀOH bands at 2190 and 3383 cmꢀ1, respectively.
Besides, in order to show thiocyanating ability of this
precipitate, the reaction of indole (1q), with 10 mol% of GO
49
into a complex mixture and is known in the literature.26,
Therefore, we made no further endeavors to purify this mixture.
To the best of our knowledge, thiocyanation of a wide range of
substrates including aromatic amines, phenols, anisols and
enolizable ketones have not yet been reported and therefore
effectiveness for thiocyanation of broad range of substrates is
the unique feature of our system. Based on the existing
literature17, 40 and our observations, a plausible mechanism is
outlined in Scheme 1. In the recent years, the acidic nature of
and 2.5 eqiv of this yellow precipitate (I) in water was
examined. The desired product (2q) was obtained in 85% yield
at 80 °C. In addition, to prove that the observed reactivity of
GO in thiocyanation reaction was not mediated by the residual
Mn, which used in the preparation of GO, inductively coupled
plasma atomic emission spectroscopy (ICPꢀAES) was
performed on an aqueous dispersion of GO. In particular,
the manganese content was measured to be <40 ppb
(approximately equivalent to other native metal contaminants
found in the material).53, 54
GO has been ascribed to the presence of surface attached
33, 39, 50
carboxylic functions29,
and also organosulfate group
being originated during the oxidation of graphite using
Hummers method. These active functional groups specially
carboxylic acid groups50 facilitate the proton transfer reactions
due to their acidic properties. The reaction pathway begins with
We also checked the reusability of the catalyst for the
thiocyanation of aniline under optimized conditions (Table 4).
It was found that the catalytic system can be effectively reused
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for up to five cycles without much loss in catalytic activity. It Germany) was used to characterize functional groups and
should be noted that during the recycling experiments, the GO structural information. The analysis system was equipped with
catalyst was filtered off after previous run, washed with diethyl highꢀenergy laser diodes. Melting points were determined in
ether and warm ethanol for several times and dried in vacuum open capillaries with a GalenꢀKamp melting point apparatus
before starting the next test.
and are not corrected.
Synthesis of graphene oxide (GO): natural flake graphite (1g,
particle size: <50µm; from Merck), NaNO3 (fine mesh, 1.0 g)
and H2SO4 (48 ml, 98%) was cooled to 0 °C by stirring in an
ice bath for 15 min. 3.0 g finely meshed KMnO4 powder was
added slowly with vigorous stirring while keeping the
temperature below 20 °C (a dark colored mixture was
obtained). After 1.5 h, the mixture was warmed to 35±3 °C for
30 min. Then 180 ml water was added slowly, the temperature
rose gradually and was kept in 95 °C for another 30 min. Then
400 ml water was added. Finally aqueous solution of hydrogen
peroxide (H2O2, 35%, 10 mL) was added to convert the
unreacted permanganate and manganese dioxide into soluble
sulfates. The vibrant yellow mixture was then filtered and the
precipitate washed with an aqueous HCl solution (5%, 200
mL). The prepared GO was dialyzed in a dialysis bag for 1
week to ensure the complete removal of acid and residual metal
ions. The final precipitate was kept in the dark until further use.
For using in the reactions, the graphite oxide aqueous
suspension was ultrasonicated (200 mL, 10 mg mL−1) for 1 h to
form graphene oxide.
General procedure for the thiocyanation of arenes/enolizable
ketones: To a solution of graphene oxide (10 wt%) in H2O (3
mL), hydrogen peroxide (30%, 3 mmol, 0.26 mL) was added
and stirred for 5 min at 80 °C. Then arene/ketone (1 mmol) and
KSCN (2.5 mmol, 243 mg) were added to the resulting mixture
and stirring was continued at 80 °C until TLC analysis showed
the completion of the reaction. After completion of the reaction,
the stirring was stopped and the graphene oxide was separated
by simple filtration. Then the solution was extracted with ethyl
acetate (3×10 mL). The combined extracts were washed
sequentially with brine, dried over anhydrous Na2SO4 followed
by concentrated in vacuo. The resulting crude was purified with
column chromatography on silica gel to afford the thiocyanato
derivatives. All the products are known compounds and were
characterised by the comparison of their spectral data with
those reported in the literature (see supporting information).
Table 4: Reusability of GO for the thiocyanation of aniline
with H2O2 and KSCNa
Run
1
2
3
4
5
% Yieldb of 90
89
89
88
87
2a
aConditions: Aniline (1 mmol), GO (10 mol%), H2O2
(35%, 3 mmol), KSCN (2.5 mmol) in water (3 mL) at 80
°C. bIsolated yield.
Conclusions
In summary, we have developed a useful, and simple method
for the regioselective thiocyanation of wide range of substrates
including aromatic amines, phenols, anisols and enolizable
ketones using graphene oxide as a reusable catalyst and H2O2 as
a green oxidant in the presence of KSCN in water. High
stability, easy separation from the reaction mixture, and
reusability of the catalyst with minimal loss of activity are the
major advantages of the catalyst. It can be envisioned that such
a cost effective solid acid catalyst holds great potential for a
wide range of acidꢀcatalyzed reactions.
Experimental
General information
All chemicals used in this study were analytical grade,
commercially available and used without further purification.
Graphite (CAS No. 7782ꢀ42ꢀ5, particle size: <50µm) was
purchased from Merck. Most of the products were purified by
column chromatography from appropriate solvents and were
identified by 1H NMR, 13C NMR and elemental analyses.
Progress of the reactions was monitored by TLC using silica gel
polygrams SIL G/UV 254 plates. FTꢀIR spectra were recorded
on Shimadzu DRꢀ8001 Spectrometer. NMR spectra were
recorded on a Bruker Avance DPX 250 MHz Instrument in
CDCl3 or DMSOꢀd6 solvents using TMS as internal standard.
Chemical shifts were reported in ppm (δ), and coupling
Acknowledgements
Financial support from Shiraz University research council is
greatly appreciated.
Notes and references
a Department of Chemistry, College of Sciences, Shiraz University, Shiraz
71454, Iran. E-mail: khalili@shirazu.ac.ir; Fax: +98-711-6460788; Tel:
+98-711-6460724
constants (J), in Hz. Elemental analyses were determined in our
department using ThermoFinnigan Flash EA 1112 Series. The
surface morphology of graphite and graphene oxide was
†
Electronic Supplementary Information (ESI) available: FTꢀIR, UVꢀ
Vis. Raman spectrum, XRD and AFM image of graphene oxide (GO).
The spectral data of all the products are enclosed. See
analyzed by using
a Field emission scanning electron
microscopy (FESEM, SIGMA, ZEISS, Germany) and Atomic DOI: 10.1039/x0xx00000x
force microscope (AFM, DUALSCOPETM DS 95ꢀ50ꢀE, DME,
Denmark). Xꢀray diffraction (XRD) patterns were recorded on
a XRDꢀD8 (BRUKER, Germany) employing a scanning rate of
1.
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0.05° s−1 from 10° to 90° with CuK
ꢃ
radiation. The absorbance
of graphene oxide solutions was detected by UVꢀVis 2.
Spectrophotometer (Pharmacia Biotech Ultraspec 4000).
Dispersive Raman Microscope (SENTERRA, BRUKER,
M. Artico, R. Silvestri, E. Pagnozzi, B. Bruno, E. Novellino, G.
Greco, S. Massa, A. Ettorre, A. G. Loi, F. Scintu and P. La Colla,
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Page 9 of 9
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ02314A
Graphene oxide: a promising carbocatalyst for the regioselective
thiocyanation of aromatic amines, phenols, anisols and enolizable ketones
by hydrogen peroxide/KSCN in water
Dariush Khalili
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
E-mail: khalili@shirazu.ac.ir
Graphene oxide as a heterogeneous carbocatalyst catalyzes the direct thiocyanation of a
variety of arenes and enolizable carbonyl compounds