Thiocyanation of aromatic and heteroaromatic compounds using polymer-supported thiocyanate ion as the versatile reagent and ceric ammonium nitrate as the versatile single-electron oxidant

Article abstract of DOI:10.1080/17415993.2015.1137919

ABSTRACT: Indoles, pyrrole aniline derivatives and aromatic amino compounds undergo smooth thiocyanation with cross-linked poly (4-vinylpyridine) supported thiocyanate ion, [P₄-VP]SCN in the presence of ceric ammonium nitrate (CAN) as a versati

Full text of DOI:10.1080/17415993.2015.1137919

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Thiocyanation of aromatic and heteroaromatic
compounds using polymer-supported thiocyanate
ion as the versatile reagent and ceric ammonium
nitrate as the versatile single-electron oxidant
Mohammad Ali Karimi Zarchi & Reza Banihashemi
To cite this article: Mohammad Ali Karimi Zarchi & Reza Banihashemi (2016): Thiocyanation
of aromatic and heteroaromatic compounds using polymer-supported thiocyanate ion as the
versatile reagent and ceric ammonium nitrate as the versatile single-electron oxidant, Journal
of Sulfur Chemistry, DOI: 10.1080/17415993.2015.1137919
To link to this article: http://dx.doi.org/10.1080/17415993.2015.1137919
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Date: 01 April 2016, At: 10:07

JOURNAL OF SULFUR CHEMISTRY, 2016
http://dx.doi.org/10.1080/17415993.2015.1137919
Thiocyanation of aromatic and heteroaromatic compounds
using polymer-supported thiocyanate ion as the versatile
reagent and ceric ammonium nitrate as the versatile
single-electron oxidant
Mohammad Ali Karimi Zarchi and Reza Banihashemi
Department of chemistry, College of Science, Yazd University, Yazd, Iran
ABSTRACT
ARTICLE HISTORY
Received 5 September 2015
Accepted 30 December 2015
Indoles, pyrrole aniline derivatives and aromatic amino com-
pounds undergo smooth thiocyanation with cross-linked poly (4-
vinylpyridine)supportedthiocyanateion, [P4-VP]SCNinthepresence
of ceric ammonium nitrate (CAN) as a versatile single-electron oxi-
dant in ethanol at room temperature to afford the corresponding
3-indolyl 2-pyroyl and 4-aryl thiocyanates, respectively, in high to
excellent yields with excellent selectivity in a short reaction time.
The use of [P4-VP]SCN/CAN makes it quite simple, more convenient,
and practical. The present procedure offers advantages such as short
reaction time, simple reaction work-up, and the polymeric reagents
can be regenerated and reused for several times without significant
loss of their activity.
KEYWORDS
Thiocyanation; ceric
ammonium nitrate;
regioselectivity; polymeric
reagent; aryl thiocyanate
CONTACT Mohammad Ali Karimi Zarchi
makarimi@yazd.ac.ir, makarimi@yazduni.ac.ir
© 2016 Informa UK Limited, trading as Taylor & Francis Group

2
M. A. KARIMI ZARCHI AND R. BANIHASHEMI
1. Introduction
The most extensively used cerium (IV) reagent in organic chemistry is ceric ammonium
nitrate (CAN). The reasons for its general acceptance as a one-electron oxidant may be
attributed to its large reduction potential value of + 1.61 V (vs. normal hydrogen elec-
trode), low toxicity, and ease of handling, experimental simplicity, and solubility in a
number of organic solvents. The enormous growth in the use of this reagent is evidenced
by the publication of a large number of research papers and several reviews concerning
CAN-mediated reactions.[1–8]
Sulfur-containing compounds have become increasingly useful and important in
organic synthesis. Thiocyanates are well known in organosulfur chemistry.[9] Arylth-
iocyanates are well known in the area of organosulfur chemistry [10] and have found
widespread applications such as insecticides, biocidal, antiasthmatic, vulcanization acceler-
ators, and starting materials for the preparation of heterocycles.[11–14] The thiocyanation
of aromatics and heteroaromatics is an important carbon-heteroatom bond formation
in organic synthesis and constitutes an interesting group, which could be readily trans-
formed into other sulfur-bearing functionalities,[15,16] especially for producing drugs and
pharmaceuticals.[17,18] Also, thiocyanate is a versatile synthon which can be readily trans-
ferred to other functional groups such as sulfide,[19–22] nitrile,[23] thiocarbamate, [24,25]
thionitrile,[26] and aryl thioesters.[27] Therefore, it is important to find new methods for
the thiocyanation systems.
Several methods for the thiocyanation of aromatic systems using a variety of reagents
such as bromine/potassium thiocyanate (only for indoles),[28] N-thiocyanatosuccinimide
(only for 5-methoxy-2-methylindole and accompanied by two bisthiocyanates),[29]
trichloroisocyanuric acid/NH4SCN/wet SiO2,[30] CAN/NH4SCN,[5] acidic montmo-
rillonite K10 clay/NH4SCN,[31] iodine/methanol/NH4SCN,[32] silica boron sulfonic
acid/H2O2/NH4SCN,[33] sodium pertborate/NH4SCN,[34] oxone/NH4SCN,[35] diethyl
azodicarboxylate,[36] diphenylphosphinite ionic liquid,[37] potassium peroxydisulfate-
copper(II),[38] ferric(III) chloride/NH4SCN,[39] acidic alumina/NH4SCN, [40]
Mn(OAc)3/NH4SCN,[41] DDQ/NH4SCN,[42] I2O5/NH4SCN,[43] and para-toluene sul-
furic acid/NH4SCN [44] extensively studied. However, these methodologies suffer from
one or more drawbacks such as the less availability or hard preparation of starting mate-
rials, [28,29] the low yields for some compounds,[5,35] and performances under certain
special conditions.[31]
The recent developments in polymer-supported reactions have led to the propaga-
tion of combinatorial chemistry as a method for the rapid and efficient preparation of
novel functionalized molecules.[45] An interesting and fast growing branch of this area is
polymer-supported reagents.[46] Although polymeric reagents and scavengers have been
used in organic synthesis for decades, development of combinatorial and parallel high-
throughput synthesis techniques brought this class of reagents to a wider attention. The
first compound collections were based on peptides and oligonucleotides, which were step-
wise assembled on a solid support,[47] following the concept developed by Merrifield.[48]
In recent years, the polymeric reagents, especially anion exchange resins, have been widely
applied in organic transformations.[49–66] The advantages of this technique over con-
ventional classical methods are: mild reaction conditions, safe handling, rapid, and very
simple work-up. On the other hand, usually the spent polymeric reagents can be regener-
ated and reused for several times without significant loss of their activity. In addition, many

JOURNAL OF SULFUR CHEMISTRY
3
ion-exchange resins, and indeed reagents supported on them, are commercially available
and are relatively inexpensive.
As far as we know there are a few reports in the literature on the application of polymer-
supported thiocyanate ion [49–54] but, to the best of our knowledge, there is no report on
polymer-supported thiocyanate ion for thiocyanation of aromatic or heteroaromatic rings
by using CAN as the oxidant. We have recently reported an efficient method for the prepa-
ration of cross-linked poly (4-vinylpyridine) supported thiocyanate ion, [P4-VP]SCN, and
applied for the synthesis of alkyl thiocyanates [51] and aryl thiocyanates.[51–54]
2. Results and discussion
Cross-linked poly (4-vinylpyridinium) thiocyanate ion, [P4-VP]SCN, was easily prepared
according to our previously reported method [51] via the reaction of quaternized cross-
linked poly (N-methyl-4-vinylpyridinium) iodide, [P4-VP]I, with an aqueous solution of
KSCN.
In this paper, we report the first procedure for facile and rapid thiocyanation of indoles,
pyrrole, carbazole, aniline derivatives, and aromatic amino compounds using [P4-VP]SCN
as the versatile polymeric reagent and CAN as the versatile single-electron oxidant.
In order to be able to carry out such a reaction in a more efficient way, indole was cho-
sen as the model substrate and some experimentation regarding reaction time, reaction
temperature, and possible solvents were run and the results are summarized in Table 1.
According to the data presented in Table 1, ethanol and methanol have been the same
and the best solvents (Entries 3 and 6). Based on green chemistry and environmental-
friendly nature, ethanol was chosen as the solvent for thiocyanation of different aromatic
and heteroaromatic compounds. During our optimization studies, it was found that a
1.0/2.5/2.2 mole ratio of indole/[P4-VP]SCN/CAN in ethanol at room temperature was
the best, for complete conversion in a short reaction time, to achieve the highest yield of
3-indolyl thiocyanate product (Entry 3).
Under optimized reaction conditions, the thiocyanation of different aromatic and het-
eroaromatic compounds such as indoles, pyrrole, carbazole, aromatic amino compounds,
and aniline derivatives was investigated and the results are summarized in Table 2.
Table 1. Optimization of the reaction conditions for thiocyanation of indole (1mmol) in different sol-
vents and different molar ratio of [P4-VP] SCN/CAN at room temperature.
[P4-VP]SCN (mmol
Entry
Solvent
CCl4
H2O
C2H5OH
CH3CN
CH3COCH3
CH3OH
CH2Cl2
CH2H5OH
CH2H5OH
CH2H5OH
CH2H5OH
of SCN ion)
CAN (mmol)
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.80
2.00
2.20
2.20
2.20
2.20
2.20
2.20
2.20
2.50
1.50
2.20
2.00
120
30
5
40
35
5
120
5
5
0.0
40
98
52
65
98
0.0
97
76
96
92
9
10
11
5
5
aIsolated yields.

4
M. A. KARIMI ZARCHI AND R. BANIHASHEMI
The reaction of indole at room temperature yielded the desired product 3-thiocyanato-
1H-indole in 98% yield (Table 2, Entry 1). The same reaction using N-methyl indole as
the starting material gave 3-thiocyanato-N-methyl indole in 96% yield (Table 2, Entry
6). The reaction was further extended to include with other substituted indoles. It was
found that 2-methylindole gave 94% yield of 3-thiocyanato-2-methylindole (Table 2, Entry
7). The lower yield is probably attributed to the steric hindrance of 2-substituted indole.
As Table 2 reveals, using indoles (Entries 1–7) as substrates, the reaction gave unique
Table 2. Thiocyanation of aromatic and heteroaromatic compounds with [P4-VP]SCN/CAN in ethanol at
room temperature.
M.p.
Entry
1
Substrate
Product
Time (min)
5
Yield (%)a
98
Found
75–76
Reported
73–76,[41]
105–106[42]
2b
3b
4b
5b
6
5
6
98
98
98
94
96
75–76
75–76
75–76
75–76
82–84
73–76,[41]
105–106[42]
73–76,[41]
105–106[42]
8
73–76,[41]
105–106[42]
10
10
73–76,[41]
105–106[42]
83–84 [41],
76–78 [33]
7
8
10
25
94
86
100–102
51–52
99–101[42],
104–106[33]
52–53 [41],
96–98 [34]
(continued).

JOURNAL OF SULFUR CHEMISTRY
5
Table 2. continued.
M.p.
Entry
9
Substrate
Product
Time (min) Yield (%)a Found
Reported
15
15
15
84
88
87
45–47 46–47 [43],
Liquid [42]
10
11
51–53 53–54 [67],
52–53 [68]
72–74 71–72[42],
72–73 [33]
12
13
20
15
89
88
Oil
Oil
Liquid [33]
–
14
15
80
60–62 58–60 [43],
62–64 [42]
109–111 110–111 [42]
15
16
8
82
–
Oil
–
Oil [42, 43]
NRd
NRd
120
–
17
18
120
20
–
––
–
–
–
75
19
90
72
Oil
–
(continued).

6
M. A. KARIMI ZARCHI AND R. BANIHASHEMI
Table 2. continued
M.p.
Reported
Entry
20
Substrate
Product
Time (min) Yield (%)a Found
12
86
Oil
–
21
50
45
98–99
–
22
23
40
70
–
44–45
–
–
NRd
120
–
24
NRd
NRd
120
120
–
–
–
–
–
–
25
aIsolated yields.
bThe Entries 2–5, refer to the use of the [P4-VP]SCN that is recycled first, second, third, and fourth time, respectively, under
identical conditions.
cDithiocyanated product was also observed, when thiocyanation reaction of diphenylamine was performed.
dNR: No reaction.
3-thiocyano-substituted indoles in high yields (94–96%), but unique 2-thiocyano substi-
tuted pyrrole was obtained in 82% isolated yield, when thiocyanation of pyrrole was treated
(Entry 15).
We then explored the reactions of aniline and its derivatives. Thiocyanation of
aniline performed under described above conditions afforded the desired product
(4-thiocyanatoanilline) in 86% yield (Table 2, Entry 8). Different mono and di-N-
substituted anilines were also used, and they all gave high yields (84–89%) of the
corresponding products (Table 2, Entries 9–12) except when 1-phenyl piperazine, 4-
aminobiphenyl and aniline derivatives with electron-withdrawing groups such as N-
phenylacetamide, 2-bromoaniline, 2-nitroaniline and 4-nitroaniline (Table 2, Entries
17,25,16,22–24, respectively) were used for the thiocyanation reaction, no product was
observed. As Table 2 reveals, aromatic amino compounds were readily converted to the
mono thiocyanated products with high para-selectivity (Table 2, Entries 8–13 and 20–22)
and the thiocyanato group is selectively substituted to the para position of the amino group.
These observations are also supported by other reported methods.[37,41–43,48–51,53,54]
One exception was observed when diphenylamine was subjected to this approach because

JOURNAL OF SULFUR CHEMISTRY
7
mono and dithiocyanated products could be produced. Thiocyanation occurred on 4-
position of phenyl (59%) and over thiocyanation was followed on 4-position of the second
phenyl ring (21%), (Table 2, Entry 14). The same results has been reported by Nair et al.
when CAN was used for thiocyanation of diphenylamine by ammonium thiocyanate (32%
mono and 6% di thiocyanated products) [5] and by our recent studies when using [P4-
VP]SCN/potassium peroxydisulfate (57% mono and 30% di thiocyanated products) [53]
and by using [[P4-VP]SCN/oxone (60% mono and 25% di thiocyanated products).[54] The
regiochemistry of substitution was achieved by the interpretation of 1H NMR spectra and
their comparison with the spectra and physical data of authentic samples.
The recycling of the polymer was examined. For this purpose, the polymer was recov-
ered from the reaction of indole (in model reaction) and reloaded with KSCN (aq.)
(Scheme 1, step 4) and reused for the conversion of indole to its corresponding thio-
cyanated product without considerable loss of reactivity. Entries 2–5 in Table 2 refer to the
use of the [P4-VP]SCN that is recycled first, second, third, and fourth time, respectively,
under identical conditions. Preparation of the [P4-VP]SCN (steps 1 and 2), regioselective
thiocyanation of aromatic and heteroaromatic compounds (steps 3), and regeneration of
the polymer (step 4) are shown in Scheme 1.
The proposed thiocyanation mechanism of indole with [P4-VP]SCN/CAN is shown in
Scheme 2.
Scheme 1. Preparation of [P4-VP]SCN, thiocyanation of aromatic and heteroaromatic compounds and
regeneration of the polymer.
Scheme 2. The plausible mechanism of thiocyanation of indole.

8
M. A. KARIMI ZARCHI AND R. BANIHASHEMI
Table 3. Comparison of the reaction times and yields of thiocyanation of model
reaction from the present method with other reported classical methods.
Entry
Time (min)
Yield (%)
M.p.
Ref.
1
2
3
4
5
6
7
8
9
10
120
20
15
45
50
43
20
5
83
97
95
88
85
98
93
97
96
98
73–76
105–106
78
[41]
[42]
[34]
[44]
[32]
[35]
[43]
[53]
[54]
Aa
–
–
72–73
70–72
75–76
73–74
74–76
10
5
aA: Present method Table 2 (Entry 1).
In Table 3, the model reaction of the present method is compared with other reported
classical methods.[32,34,35,41–44,53,54] As Table 3 reveals, in this method, the reaction
times are always shorter than the other methods but the yields are compatible. This can
probably be attributed to the local concentration of thiocyanate ion species inside the pores
of the polymer.
The advantages of the present method over conventional classical methods are mild
reaction conditions, safe handling, rapid, and very simple work-up. In addition, there is
current research and general interest in heterogeneous systems because such systems are
important in industry and developing technologies.[69]
3. Conclusions
We have developed an efficient, rapid, experimentally simple method for regioselec-
tive thiocyanation of indoles, pyrrole, carbazole, aniline derivatives, and aromatic amino
compounds via a green and simple protocol using cross-linked poly (4-vinylpyridine)
supported thiocyanate ion as the versatile polymeric reagent and CAN as the versatile
single-electron oxidant. The spent polymeric reagent can be easily separated by filtration
and can be easily regenerated by treating with aqueous solution of KSCN and reused for
several cycles without significant loss of their activity.
4. Experimental
4.1. Materials and instruments
Chemicals were either prepared in our laboratory or were purchased from Fluka
(Buchs, Switzerland), Aldrich (Milwaukee, WI), and Merck chemical companies. Poly (4-
vinylpyridine) cross-linked with 2% divinyl benzene (DVB), (white powder, and 100–200
mesh), [P4-VP] 2% DVB, was purchased from Fluka (Buchs, Switzerland). Cross-linked
poly (N-methyl-4-vinylpyridinium) iodide, [P4-VP]I, and cross-linked Poly (N-methyl-
4-vinylpyridine) thiocyanate, [P4-VP]SCN, were synthesized according to our reported
procedures.[50] Progress of the reaction was monitored by thin layer chromatography
using silica gel Poly Gram SIL G/UV 254 plates (Fluka). Melting points were determined
with a Buchi melting point B-540 B.V. CHI apparatus. The arylthiocyanate products were

JOURNAL OF SULFUR CHEMISTRY
9
characterized by fourier transform-infrared (FT-IR); and 1H- and 13C-NMR spectroscopy.
IR spectra showed the characteristic peak of –SCN between 2144 and 2160 cm−1 and the
–C–S stretching at 642–749 cm−1. The characteristic spectral data of some arylthiocyanate
products are given below.
4.1.1. 3-Thiocyanatoindole
FT-IR (neat), νmax (cm−1) = 3395 (NH), 2156 (SCN), 1504, 1455, 1410, 1339, 1239, 1097,
1
744 (C–S); H NMR (400 MHz), δ (ppm) = 8.71 (1H, s), 7.68 (1H, t, J = 4.0 Hz), 7.23
(4H, m); 13C NMR (100 MHz), δ (ppm) = 136.1, 131.2, 127.6, 123.8, 121.8, 118.6, 112.4,
112.2, 91.6.
4.1.2. 1-Methyl-3-thiocyanatoIndole
FT-IR (neat), ν
(cm−1) = 2153 (SCN), 1513, 1459, 1422, 1336, 1244, 1157, 1012, 742
max
(C–S), 544;1H NMR (400 MHz), δ (ppm) = 3.81 (3H, s, CH3), 7.37 (4H, m), 7.64 (1H, d,
J = 6.8 Hz), 3.81 (3H, s, CH3); 13C NMR (100 MHz), δ (ppm) = 37.2, 135.1, 128.5, 123.4,
121.6, 118.9, 111.9, 110.2, 89.8, 33.4.
4.1.3. 2-Methyl-3-thiocyanatoIndole
FT-IR (neat), ν
(cm−1) = 3395 (NH), 2149 (SCN), 1406, 1228, 739 (C–S), 644, 595;
max
1H NMR (400 MHz), δ (ppm) = 2.47 (3H, s, CH3), 7.28 (2H, m), 7.71 (1H, d, J = 7.6 Hz),
7.73 (1H, d, J = 7.6 Hz), 8.71 (1H, s, NH);13C NMR (100 MHz), δ (ppm) = 142.3, 135.2,
128.7, 122.9, 121.5, 117.9, 112.5, 111.6, 111.4, 11.9.
4-Thiocyanatoaniline
FT-IR (neat), ν
(cm−1) = 3375 (NH2), 2152 (SCN), 1625, 1595, 1496, 824, 739
max
(C–S);1H NMR (400 MHz), δ (ppm) = 4.00 (2H,s, NH2), 6.68 (2H,d, J = 8.80 Hz), 7.36
(2H, d, J = 8.80 Hz);13C NMR (100 MHz), δ (ppm) = 148.8, 134.5, 116.0, 112.4, 109.5.
4-Thiocyanato-N-methylaniline
FT-IR (neat), ν
(cm−1): 3409 (NH), 2898, 2151 (SCN), 1595, 1513, 1330, 1184, 819,
max
675 (C–S);1H NMR (400 MHz), δ (ppm) = 2.86 (3H, s, CH3), 4.13(s,1H,NH), 6.58 (2H,
d, J = 8.80 Hz), 7.39 (2H, d, J = 8.80 Hz); 13C NMR (100 MHz), δ (ppm) = 151.1, 134.7,
113.3, 112.7, 107.3, 30.2.
4-Thiocyanato-N-ethylaniline
FT-IR (neat), ν
(cm−1) = 3382 (NH), 2974, 2152 (SCN), 1598, 1514, 1335, 1150,
max
815, 748 (C–S);1H NMR (400 MHz), δ (ppm) = 1.24 (3H, t, J = 7.20 Hz), 3.12 (2H, q,
J = 7.20 Hz), 4.09 (1H, s, NH), 6.56 (2H, d, J = 8.80 Hz), 7.35 (2H, d, J = 8.80 Hz);13C
NMR (100 MHz), δ (ppm) = 150.3, 134.8, 113.6, 112.9, 106.8, 38.0, 14.5.
4-Thiocyanato-N,N-dimethylaniline
FT-IR (neat), ν
1074,990, 947, 809, 737 (C–S) 519.
(cm−1) = 2144 (SCN), 1595, 1510, 1444, 1321, 1266, 1231, 1198,
max

10
M. A. KARIMI ZARCHI AND R. BANIHASHEMI
4-Thiocyanato-N,N-diethylaniline
FT-IR (neat), ν
(cm−1) = 2151 (SCN), 1591, 1507, 1274, 749 (C–S);1H NMR
max
(400 MHz), δ (ppm) = 1.17 (6H, t, J = 7.20 Hz), 3.35 (4H, q, J = 7.20 Hz), 6.65 (2H, d,
J = 9.20 Hz), 7.39 (2H, d, J = 9.20 Hz);13C NMR (100 MHz), δ (ppm): 149.3, 135.0, 112.8,
112.6, 104.8, 44.5, 12.3.
4-Thiocyanato-N-phenylaniline
FT-IR (neat), ν
(cm−1): 3360 (NH), 2153 (SCN), 1585, 1493,1322, 750, 697 (C–S);1H
max
NMR (400 MHz), δ (ppm) = 5.98 (1H, s, NH), 6.87 (2H, d, J = 8.80 Hz), 6.92 (1H,
t, J = 7.60 Hz), 7.00 (2H, d, J = 7.60 Hz), 6.92 (2H, t, J = 7.60 Hz), 7.26 (2H, d,
J = 8.80 Hz); 13C NMR (100 MHz), δ (ppm) = 146.2, 141.0, 134.1, 129.6, 123.0, 120.1,
117.1.
4,4ꢀ-Dithiocyanatodiphenylamine
FT-IR (neat), ν
(cm−1) = 3368 (NH), 2150 (SCN), 1573,1740, 1583, 1486, 1340,
max
1215, 806, 642 (C–S);1H NMR (400 MHz), δ (ppm) = 6.15 (1H, s, NH), 7.03 (4H, d,
J = 8.80 Hz), 7.40 (4H, d, J = 8.80 Hz); 13C NMR (100 MHz), δ (ppm) = 143.8, 133.6,
119.2, 114.4, 111.5.
2-Thiocyanatopyrrole
FT-IR (neat), νmax (cm−1) = 3267 (NH), 2160 (SCN), 1523, 1415, 1033, 796, 686 (C–S).
4-Amino-1-naphthyl thiocyanate
FT-IR (neat), νmax (cm−1) = 3425, 3384 (NH2), 2151 (SCN), 1634, 1514, 1442, 1345, 1293,
817, 738 (C–S).
3-Thiocyanatocarbazole
FT-IR (neat), νmax (cm−1) = 3415 (N–H), 2151 (SCN), 1595, 1448, 1318, 1276, 1235, 893,
815, 734 (C–S).
2-Phenyl-4-Thiocyanato aniline
3481, 3378 (NH2), 2153 (SCN), 1619, 1499, 1484, 1445, 1402, 1300, 1155, 895, 818, 774,
704 (C–S).
2-Cyano-4-Thiocyanato aniline
FT-IR (neat), νmax (cm−1) = 3445, 3362, 2923, 2219 (CN), 2156 (SCN), 1632, 1557, 1493,
1458, 1315, 1265, 1185, 1160, 905, 824, 748 (C–S).
2-Bromo-4-Thiocyanato aniline
FT-IR (neat), νmax (cm−1) = 3474, 3370 (NH2), 2924, 2154 (SCN), 1616, 1582, 1485, 1398,
1260, 1156, 813, 750 (C–S), 699.
4.2. Preparation of [P4-VP]SCN
Cross-linked poly (N-methyl-4-vinylpyridinium) thiocyanate, [P4-VP]SCN, was synthe-
sized and its capacity was determined according to our reported procedure (Scheme 1).[51]

JOURNAL OF SULFUR CHEMISTRY
11
The obtained capacity of the polymer was 3.3 mmol of thiocyanate ion per gram of
polymer.
4.3. General procedure for thiocyanation of aromatic or heteroaromatic
compounds using [P4-VP]SCN/CAN
About 1.2 g of CAN (2.2 mmol) that dissolved in ethanol (10 mL) was added dropwise
to a suspension of [P4-VP]SCN (757 mg, 2.50 mmol of SCN ion) and an aromatic or
heteroaromatic compound (1 mmol) in ethanol (5 mL) and the reaction mixture was
stirred at room temperature for the appropriate time according to Table 2. The progress
of the reaction was monitored by TCL [eluent: n-hexane/ethyl acetate (8/2)]. Then the
polymer was separated by filtration and the filtrate was diluted with water (15 mL) and
extracted with dichloromethane (4 × 8 mL). The combined organic layer was dried over
anhydrous Na2SO4 and the solvent was evaporated under reduced pressure. The result-
ing crude product was purified by column chromatography on silica gel (eluted with
n-hexane/ethylacetate: 8/2) to afford the corresponding thiocyanated products.
4.4. Regeneration of [P4-VP]SCN
The spent polymer (1.00 g) was added to an excess aqueous solution of KSCN and was
stirred for 24 h at room temperature. The mixture was filtered and washed several times
with distilled water and ethanol and dried overnight under vacuum in the presence of P2O5
at 40°C (Scheme 1, step 8). The regenerated polymer can be reused several cycles without
losing significantly its activity (Table 2, Entries 2–5).
Disclosure statement
No potential conflict of interest was reported by the authors.
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