1-methyl-3-(2-(Sulfooxy)Ethyl)-1H-imidazol-3-ium thiocyanate as a novel, green, and efficient bronsted acidic ionic liquid-promoted regioselective thiocyanation of aromatic and heteroaromatic compounds at room temperature

Article abstract of DOI:10.1080/10426507.2013.818996

An efficient and simple method for the preparation of 1-methyl-3-(2- (sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate ([Msei]SCN) as a Bronsted acidic ionic liquid (BAIL) is described, and it is used in the highly efficient regioselective thiocyanation of aromatic and heteroaromatic compounds via a green and simple protocol. [Msei]SCN as a novel IL and thiocyanation agent, H₂O₂ as a mild and environmentally friendly oxidant, and H₂O:ethanol(1:4) as a solvent were used. This procedure provided the target thiocyanates in high yield and very short reaction time. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional figures.]

Full text of DOI:10.1080/10426507.2013.818996

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1-Methyl-3-(2-(Sulfooxy)Ethyl)-1H-
Imidazol-3-Ium Thiocyanate as A Novel,
Green, and Efficient BrØNsted Acidic
Ionic Liquid-Promoted Regioselective
Thiocyanation of Aromatic and
Heteroaromatic Compounds at Room
Temperature
Sami Sajjadifar a , Hossein Hosseinzadeh a , Saied Ahmadaghaee a
Eshagh Rezaee Nezhad a & Saaid Karimian a
,
a Department of Chemistry, Payame Noor University , Tehran , Iran
Accepted author version posted online: 20 Aug 2013.Published
online: 28 Jan 2014.
To cite this article: Sami Sajjadifar , Hossein Hosseinzadeh , Saied Ahmadaghaee , Eshagh Rezaee
Nezhad & Saaid Karimian (2014) 1-Methyl-3-(2-(Sulfooxy)Ethyl)-1H-Imidazol-3-Ium Thiocyanate as A
Novel, Green, and Efficient BrØNsted Acidic Ionic Liquid-Promoted Regioselective Thiocyanation of
Aromatic and Heteroaromatic Compounds at Room Temperature, Phosphorus, Sulfur, and Silicon and
the Related Elements, 189:3, 333-342, DOI: 10.1080/10426507.2013.818996
To link to this article: http://dx.doi.org/10.1080/10426507.2013.818996
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Phosphorus, Sulfur, and Silicon, 189:333–342, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.818996
1-METHYL-3-(2-(SULFOOXY)ETHYL)-1H-IMIDAZOL-3-IUM
THIOCYANATE AS A NOVEL, GREEN, AND EFFICIENT
BRØNSTED ACIDIC IONIC LIQUID-PROMOTED
REGIOSELECTIVE THIOCYANATION OF AROMATIC
AND HETEROAROMATIC COMPOUNDS AT ROOM
TEMPERATURE
Sami Sajjadifar, Hossein Hosseinzadeh, Saied Ahmadaghaee,
Eshagh Rezaee Nezhad, and Saaid Karimian
Department of Chemistry, Payame Noor University, Tehran, Iran
GRAPHICAL ABSTRACT
Abstract An efficient and simple method for the preparation of 1-methyl-3-(2-(sulfooxy)ethyl)-
1H-imidazol-3-ium thiocyanate ([Msei]SCN) as a Brønsted acidic ionic liquid (BAIL) is de-
scribed, and it is used in the highly efficient regioselective thiocyanation of aromatic and
heteroaromatic compounds via a green and simple protocol. [Msei]SCN as a novel IL and thio-
cyanation agent, H2O2 as a mild and environmentally friendly oxidant, and H2O:ethanol(1:4)
as a solvent were used. This procedure provided the target thiocyanates in high yield and very
short reaction time.
[Supplementary materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental
files: Additional figures.]
Keywords 1-Methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate; [Msei]SCN;
Brønsted acidic ionic liquid (BAIL); thiocyanation
Received 15 March 2013; accepted 20 June 2013.
The authors would like to thank the partial support of this work by Payame Noor University (PNU) of Ilam,
Iran.
Address correspondence to Dr. Sami Sajjadifar, Department of Chemistry, Payame Noor University, PO Box
19395-4697, Tehran, Iran. E-mail: ss sajjadifar@yahoo.com
333

334
S. SAJJADIFAR ET AL.
INTRODUCTION
Thiocyanation of aromatic and heteroaromatic compounds is one of the most im-
portant reactions in organic synthesis compounds.1 Thiocyanate is a versatile synthon,2
which can be easily transferred to other functional groups such as sulfide,3 aryl ni-
trile,4 thiocarbamate,5 and thionitrile.6 It is worth mentioning that the above groups are
greatly useful for producing drugs and pharmaceuticals.7 Several methods have been de-
veloped for the electrophilic thiocyanation of aromatic and heteroaromatic compounds8
such as bromine/potassium thiocyanate,9 N-thiocyanatosuccinimide,10 ceric ammonium
nitrate (CAN),11 acidic montmorillonite K10 clay,12 I2/MeOH,7 Oxone,13 pentavalent io-
dine,14 IBX,15 potassium peroxydisulfate/copper (II) sulfate,16 H2O2, HCl,17 BSA/H2O2,2
Mn(OAc)3,18 which have been applied to the thiocyanation of aromatic and heteroaromatic
system. However, these methodologies suffer from one or more drawbacks such as the low
availability or hard preparation of starting materials,9–10 the requirement of large excess
of strong oxidizing reagents, low yield for some compounds,11 and performance under
certain special conditions.12 Hence, a requirement for developing alternative synthesis rou-
tines accessible to the thiocyanation of aromatic and heteroaromatic compounds is in high
demand.
In the present work, we describe an efficient protocol for the selective thiocyanation
of aromatic and heteroaromatic using 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium
thiocyanate as a novel ionic liquid (IL) and thiocyanation agent. This method has some
advantages including the use of an inexpensive and reusable IL, easy handling, short reaction
times, high yield, and simplicity of the product isolation.
RESULTS AND DISCUSSION
In this study, an acidic IL was prepared in three steps. 1-Methyl-3-(2-(sulfooxy)ethyl)-
1H-imidazol-3-ium chloride ([Msei]Cl) was represented according to the literature.19,20 A
schematic representation of the synthesis of [Msei]SCN IL is shown in Scheme 1.
In recent years, researchers have become more and more interested to apply the ILs in
organic reactions.21 They demonstrated the specific catalytic role of the ILs, which are also
solvents with unique properties such as tunable polarity, high thermal stability, immiscibility
with a number of organic solvents, insignificant vapor pressure, and ease of recyclability. It
must be noted that the IL 4 has been used for the synthesis of dihydropyrimidinones under
solvent-free conditions.21
We easily prepared IL 5 by adding KSCN(aq) to IL 4 then KCl(s) was filtered and
solvent was evaporated (Scheme 1). For easy handling, we add silica gel to IL 5. The IR
spectrum of IL 4,22 and 5 are compared. The peak at 2060 cm−1 is related to group SCN,
and it was shown that novel IL containing thiocyanate ion has been formed (Figure 1).
There are rare thiocyanation agents in which both the catalyst and the thio-
cyanate group source are present and are simultaneously employed, but 1-methyl-3-(2-
(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate in addition to the catalyst property also
plays the role of thiocyanation agent, and in addition, the value of this technique is com-
pared with the other methods. For choosing appropriate values of the H2O2 and catalyst,
we tested different values of H2O2 and IL (the results are summarized in Tables 1 and 2).
According to the yield and reaction time, the mole ratio of 1:3:4 (indole:H2O2:IL)
was found to be the most suitable. When the catalyst was less than 4 mmol, reaction time
had also a lower yield. Also, when we used a larger amount of IL, yield and time did not

[MSEI]SCN AS NOVEL, GREEN, EFFICIENT BAIL-PROMOTED REGIOSELECTIVE
335
Scheme 1 Preparation steps of 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate. (Color figure
available online).
Figure 1 IR spectrum comparison of ILs 4 and 5. (Color figure available online).
Table 1 Optimized IL for thiocyanation of aromatic and heteroaromatic
Entry
Catalyst (mmol)
Time (min)
Yield (%)
1
2
3
4
5
1
2
3
4
5
15
13
10
5
78
80
84
91
85
10

336
S. SAJJADIFAR ET AL.
Table 2 Optimized H2O2 for thiocyanation of aromatic and heteroaromatic
Entry
H2O2 (mmol)
Time (min)
Yied (%)
1
2
3
4
1
2
3
4
20
15
7
76
80
92
82
17
Scheme 2 Synthesis of thiocyanato aromatic and heteroaromatic by Bronsted acidic ionic liquid (BAIL). (Color
figure available online).
significantly change. Also, to select a suitable solvent, we carried out the reaction with the
same concentration of the reactants in H2O, EtOH, MeOH, CH3CN, CH2Cl2, THF, AcOEt,
and different ratios of H2O/EtOH (Table 3).
According to yield and the reaction time, it was specified that H2O:EtOH (1:4) was
the best and most suitable solvent for the thiocyanation of aromatic and heteroaromatic in
the presence of 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate (1.0612 g,
4 mmol) (Scheme 2).
Table 3 Optimized solvent for thiocyanation of aromatic and heteroaromatic
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
MeOH
CH3CN
CH2Cl2
THF
AcOEt
H2O (5 mL)
EtOH (5 mL)
H2O (2 mL)
30
45
35
30
40
20
25
15
20
4
70
58
64
75
55
80
75
86
83
94
90
84
80
EtOH(2 mL)
H2O: EtOH(4:1, 2 mL)
H2O: EtOH(3:2, 2 mL)
H2O: EtOH(2:3, 2 mL)
H2O: EtOH(1:4, 2 mL)
8
12
15

[MSEI]SCN AS NOVEL, GREEN, EFFICIENT BAIL-PROMOTED REGIOSELECTIVE
337
The substrate scope of this reaction was then examined using various aromatic and
heteroaromatic compounds under the optimized conditions (Table 4). Generally, this reac-
tion provided good-to-excellent yield with all the substrates tested. As shown in Table 4,
indoles and electron-rich indoles gave the desired products in excellent yield (Table 4,
entries 1–3). Moreover, electron-deficient indoles such as 5-bromoindole reacted with 1-
methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate to afford the corresponding
5-bromo-3-thiocyanatoindole in good yield, but it required longer reaction time (Table 4,
entry 4). This observation can be attributed to the lower electron density of such sub-
strates. In the case of indoles, thiocyanato group is selectively added to the 3 position of
indoles ring16 and then various N,N-disubstituted aromatic amines were converted into
the respective 4-thiocyanatoanilines in high to excellent overall yields (Table 4, entries
5–11). Anilines thiocyanato group is selectively added to the para position of the amino
group but in the case of para-substituted anilines, orto–thiocyanation did not occur (Ta-
ble 4, entry 15). When indoline used as a substrate, reaction time is high and yield is low
(Table 4, entry 13). In case of 1,2,3,4- tetrahydroquinoline, the reaction did not complete
(Table 4, entry 14). Under optimized conditions, when N,N,4-trimethylaniline, N-phenyl
acetanilide, anisole, and N,N,N-triphenylamine were used as the substrate, no reaction oc-
curred and the starting materials were recovered after periods of up to 2 days (Table 4, entries
15–18).
We found high ability of IL 5 in comparison with other catalysts in regioselective
thiocyanation reaction under green conditions (Table 5).
Whereas the previously reported methods—such as the uses of refluxing conditions
for some substrates or the assistance of ultrasonic irradiation—needed toxic solvent or
oxidant, our research method has a mild and green reaction condition.
Finally, it should be noted that in this research an efficient, simple, and green-mediated
thiocyanation of aromatic and heteroaromatic compounds with high regioselectivity was
developed. The described method has advantages such as a simple workup, short reaction
times, it can also be mentioned that the uses of mild and metal free reaction conditions can
efficiently produce the desired clean products in high yield.
The proposed reaction mechanism is shown in Scheme 3. In the first step, 1-methyl-
3-(2-(sulfooxy) ethyl)-1H-imidazol-3-ium thiocyanate produced SCN− and H+ ion in the
presence of the solvent. Then, H2O2 reacted with BAIL (H+) to presumably form in
situ hydrogen peroxonium ion (H3O2+).21 Subsequently, reaction of hydrogen peroxo-
nium ion with SCN− generates HOSCN, which in the presence of H+ is able to produce
thiocyanium ion +SCN and H2O. In the last step of the reaction, the electrophilic sub-
stitution of thiocyanium ion +SCN with indole will generate the corresponding indole
thiocyanate.
CONCLUSIONS
In conclusion, we describe a simple, convenient, and highly efficient protocol for
the preparation of aromatic and heteroaromatic compounds thiocyanates through the elec-
trophilic thiocyanation of aromatic and heteroaromatic compounds using 1-methyl-3-(2-
(sulfooxy)ethyl)-1H-imidazol-3-ium thiocyanate ([Msei]SCN) as an IL and thiocyanation
agent. This method has advantages including the use of an inexpensive and reusable IL,
short reaction times, high yield, and simplicity of the product isolation.

338
S. SAJJADIFAR ET AL.
Table 4 Thiocyanation of aromatic and heteroaromatic compounds with 1-methyl-3-(2-(sulfooxy)ethyl)-1H-
imidazol-3-ium thiocyanate. (Color version available online).
Entry Indoles and N,N-dialkyl anilines
Product
Time (min) Yield% [Ref]
1
4
94
89
15
15
2
3
4
13
10
23
88
90
15
13
5
6
10
25
97
80
17
17
7
35
78
17
(Continued on next page)

[MSEI]SCN AS NOVEL, GREEN, EFFICIENT BAIL-PROMOTED REGIOSELECTIVE
339
Table 4 Thiocyanation of aromatic and heteroaromatic compounds with 1-methyl-3-(2-(sulfooxy)ethyl)-1H-
imidazol-3-ium thiocyanate. (Color version available online). (Continued)
Indoles and
N,N-dialkyl
anilines
Yield
%
Entry
Product
Time (min)
12
[Ref]
17
8
93
9
15
90
15
10
11
11
7
93
90
15
13
12
13
50
50
96
68
17
17
14
60
73
17
EXPERIMENTAL
General
Chemicals were purchased from Merck (Frankfurt, Germany). IR spectra of the
compounds were obtained on a Frontier Fourier transform infrared (FT-IR) (Perkin Elmer)
1
spectrometer using a KBr disk. The H NMR spectra were recorded on a Bruker AQS
300 Avance instrument at 300 MHz in dimethyl sulfoxide (DMSO-d6) as solvent and

340
S. SAJJADIFAR ET AL.
Table 5 Ability comparison of IL 5 with different catalyst
Entry
Catalyst
Time (min)
Yield%
[Ref]
1
2
3
4
5
Iodine/MeOH
Oxone/MeOH
Anodic
Citric acid
Microwave-Assisted
50
43
—
20
5
2.5 h
4
15
—
85
98
42
91
85
90
94
90
83
7a
13
23b
24a
25a
25b
6
7
[Msei]SCN
This worka
This workb
18a
Mn(OAc)3/HOAc
aFor entry 1.
bFor entry 9.
Scheme 3 The proposed mechanism for the thiocyanation of indoles. (Color figure available online).
tetramethylsilane (TMS) as an internal standard. The progress of reaction was followed
with by TLC using silica gel SILG/UV 254 and 365 plates. It is worth mentioning that all
products are known compounds and have been characterized by comparing the IR, 1H, and
13C NMR spectroscopic data, and their melting points with the literature values. All yields

[MSEI]SCN AS NOVEL, GREEN, EFFICIENT BAIL-PROMOTED REGIOSELECTIVE
341
refer to isolated products. The Supplemental Materials contains characterization data for
the products and sample 1H and 13C NMR spectra for selected products (Figures S1–S4)
Typical Procedure of Preparation of 3-Thiocyanatoindole. A suspension
of indole (0.117 g, 1 mmol) and 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium thio-
cyanate (1.0612 g, 4 mmol) in H2O:ethanol (1:4) (5 mL) was stirred at room temperature
for 5 min. Then H2O2 (%30) (3 mmol) was added dropwise (2–5 min). The progress of the
reaction was monitored by TLC, using n-hexane/EtOAc (5:1) as eluent. After completion
of the reaction, the reaction mixture was extracted with CHCl3 (3 × 25 mL). Anhydrous
Na2SO4 (3 g) was added to the organic layer and filtered off after 20 min. CHCl3 was re-
moved. The yield was 0.164 g, (94%), mp 70 ◦C –72 ◦C. FT-IR (KBr) νmax/cm−1: 2060, 1H
NMR (FT-300MHz, CDCl3/TMS): δ 8.87 (br s, 1H, NH), 7.83 (d, 1H, J 8.8 Hz), 7.46–7.23
(m, 4H). 13C NMR (75 MHz, CDCl3): 136.06, 131.22, 127.66, 123.83, 121.87, 118.65,
112.24, 91.76.
Preparation of Ionic Liquid 5 (IL). 1-Methylimidazole 1 (4.1 g, 50 mmol)
and 2-chloroethanol 2 (4.02 g, 50 mmol) were added in a flask containing 10 mL of
CHCl3, the mixture was refluxed for 8 h and removed CHCl3 under vacuum. Unreacted
1-methylimidazole or 2-chloroehanol extracted with ether (3 × 10 mL) was used to give
1-methyl-3-(2-hydroxylethyl)-imidazolium chloride (Scheme 1, step 1) (yield 95%).22
A stoichiometric amount of 97% chlorosulfonic acid (3.4 mL, 50 mmol) in CCl4
(10 mL) was added dropwise to compound 3 over a period of 45–60 min at 0 ◦C, afterward,
HCl gas was evolved in an alkali trap immediately. The mixture was washed with CCl4
(3 × 10 mL) to remove the unreacted chlorosulfonic acid and at last the 1-methyl-3-(2-
(sulfooxy)ethyl)-1H-imidazol-3-ium chloride ([Msei]Cl) is formed (yield 92%).
[Msei]Cl (10.89 g, 45 mmol) was dissolved in acetone (35 ml) and stirred at room
temperature for 20 min, KSCN (45 mmol) was also dissolved in acetone (50 ml) and
was added dropwise to [Msei]Cl over a period of 60 min at room temperature. After
completion of the addition, the mixture was filtered for separation of KCl(s). The solvent
was evaporated under low pressure for 15 min until 1-methyl-3-(2-(sulfooxy)ethyl)-1H-
imidazol-3-ium thiocyanate ([Msei]SCN) as a target product will be formed (yield 96%).
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