DDQ-promoted thiocyanation of aromatic and heteroaromatic compounds

Article abstract of DOI:10.1139/V07-092

Thiocyanation of various aromatic and heteroaromatic compounds has been achieved using ammonium thiocyanate in the presence of 2,3-dichloro-5,6- dicyanobenzoquinone (DDQ) in methanol solution at room temperature and under reflux condition. The rate of rea

Full text of DOI:10.1139/V07-092

930
DDQ-promoted thiocyanation of aromatic and
heteroaromatic compounds
Hamid R. Memarian, Iraj Mohammadpoor-Baltork, and Kobra Nikoofar
Abstract: Thiocyanation of various aromatic and heteroaromatic compounds has been achieved using ammonium
thiocyanate in the presence of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in methanol solution at room temperature
and under reflux condition. The rate of reaction is influenced by the electron-donor ability of the aromatic nucleus.
Key words: amines, DDQ, indoles, thiocyanation.
Résumé : On a effectué la thiocyanatation de divers composés aromatiques et hétéroaromatiques en utilisant du thio-
cyanate d’ammonium en présence de 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), en solution dans le méthanol, à la
température ambiante ainsi que sous des conditions de reflux du méthanol. La vitesse de la réaction est influencée par
le caractère électrodonneur des substituants sur le noyau aromatique.
Mots-clés : amines, DDQ, indoles, thiocyanatation.
[Traduit par la Rédaction] Memarian et al. 937
Introduction
transformations, e.g., benzylic oxidation of Catechine (12),
oxidation of benzhydrols (13), selective oxidation of allylic
or benzylic hydroxyl groups (14), anodic oxidation of
naphthalenes (15), and oxidation of thioglycosides (16).
DDQ has also been used alone for a wide range of trans-
formations, such as dehydrogenation (17), carbon–carbon
bond cleavage (18), and alcoholysis of epoxides (19); or in
combination with triphenylphosphine for the conversion of
epoxides to halohydrines (20), thiocyanation of α-hydroxy
phosphonates (21), and thiocyanation and isothiocyanation
of some alcohols and ethers (22). DDQ is also a well-known
electron-acceptor species, and its interaction with a variety
of electron donors has been the subject of several investiga-
tions concerning the formation of charge-transfer (CT) com-
plexes (23–28). Herein, we wish to report an effective and
benign method for the thiocyanation of aromatic and
heteroaromatic compounds using ammonium thiocayanate,
as a thiocyanating agent, in the presence of DDQ at room
temperature (Method A) and under reflux conditions
(Method B).
The electrophilic thiocyanation of aromatic and
heteroaromatic compounds is an important process of
carbon–sulfur bond formation in organic synthesis, since the
nucleophilic attack of the thiocyanate ion to the aromatic nu-
cleus by displacement reactions is not the easy way to form
thiocyanated compounds. Thiocyanates constitute an inter-
esting group, which could be readily transformed into other
sulfur-bearing functionalities (1–4), especially for producing
drugs and pharmaceuticals (5). Therefore, it is important to
find new methods for the thiocyanation of aromatic systems.
Several methods have been developed for the thiocyanation
of aromatic systems using bromine/potassium thiocyanate
(6), N-thiocyanatosuccinimide (7), cerric ammonium nitrate
(CAN) (8), montmorillonite K-10 (9), iodine/methanol (4),
oxone (10), and ferric(III) chloride (11). However, some of
these methods suffer from disadvantages, such as low yields,
especially in the case of aromatic amines, the use of strongly
acidic or oxidizing conditions, the use of special conditions
(long reaction time and (or) high temperature), and also the
use of expensive reagents. In this research, we have devel-
oped a new route for the thiocyanation of aromatic and
heteroaromatic systems.
Results and discussion
2,3-Dichloro-5,6-dicyanobenzoquinone (DDQ) is a versa-
tile reagent for organic synthesis. Owing to its oxidizing
ability and also its relative stability under various reaction
conditions, this reagent has been used for various organic
Solvent effect and optimization of the reactants
Since the nature of solvent influences the rate of reaction,
thiocyanation of 2-methylindole as a model substrate was
performed in various solvents at room temperature. Accord-
ing to the data presented in Table 1, methanol has been cho-
sen as the best solvent for this purpose. One reason for the
observed different reaction times could be the solubility of
the starting materials, especially DDQ, in solvents used in
this study. Therefore, we carried out the reaction with the
same concentration of the dissolved reactants in n-hexane
(as non-polar solvent) and methanol (as polar solvent). We
found that methanol is the suitable solvent for our reaction.
The next step is the optimization of NH4SCN:DDQ molar
ratio in thiocyanation reaction under two reaction conditions.
Received 14 May 2007. Accepted 13 July 2007. Published on
the NRC Research Press Web site at canjchem.nrc.ca on
20 September 2007.
H.R. Memarian,1 I. Mohammadpoor-Baltork, and
K. Nikoofar. Catalysis Division, Department of Chemistry,
Faculty of Science, University of Isfahan, 81746–73441,
Isfahan, Iran.
1Corresponding author (e-mail: memarian@sci.ui.ac.ir).
Can. J. Chem. 85: 930–937 (2007)
doi:10.1139/V07-092
© 2007 NRC Canada

Memarian et al.
931
Table1. Solvent effect on the reaction of 2-methylindole with
NH4SCN in the presence of DDQ at room temperature (method A).
Table 2. Optimization of NH4SCN:DDQ molar ratio in the
thiocyanation of 2-methylindole under two different conditions.
Entry
Solvent
Time (min)
Yield (%)
Method Aa
Time (min)
[yield (%)]
Method Bb
Time (min)
[yield (%)]
Molar ratio of
NH4SCN:DDQ
0
1
2
H2O
180
70
Entry
H2O–CH3OH (1:1)
10
1
2
3
4
5
6
7
8
9
3:1.5
3:0.5
3:1
3:1.25
2:1.25
1:1.5
2:1.5
2:1
15 [99]
—
40 [75]
60 [88]
25 [95]
—
15 [99]
—
15 [99]
15 [99]
90 [35]
70 [85]
15 [90]
15 [99]
35 [62]
15 [99]
40 [78]
—
3
4
DMF
CH3CN
75
25
10
99
5
6
CH2Cl2
CHCl3
90
90
85
75
7
8
9
n-hexane
EtOAc
CH3OH
180
40
15
40
93
99
Note: All reactions were performed in the presence of 2 mmol of
2.5:1.5
NH4SCN and 1.5 mmol of DDQ in 5 mL of solvent.
Note: In all cases, methanol (5 mL) was used as solvent.
aRoom temperature conditions.
bUnder reflux conditions.
The results presented in Table 2 showed that the optimized
molar ratio of NH4SCN:DDQ is 2:1.5 for method A and
2:1.25 for method B. These data also show that an increase
of the amount of NH4SCN did not affect the yield or the rate
of the reaction.
C–
DDQ , followed by the proton abstraction, accomplished
the reaction under the formation of the thiocyanated product
+
and DDQH–NH4 . The following experiments support the
involvement of a π complex (path a) in the reaction rather
Thiocyanation of aromatic and heteroaromatic systems
Under optimized reaction conditions, the thiocyanation of
different aromatic and heteroaromatic compounds was inves-
tigated under two conditions, at room temperature (method A)
and under reflux conditions (method B). The results are
summarized in Table 3. Clearly, various compounds were
converted to their corresponding thiocyanation products in
good to excellent yields. The products were identified by IR,
1H NMR, and MS spectra. IR spectra showed the character-
istic peaks of –SCN between 2120–2150 cm–1 and the C–S
stretching between 650–750 cm–1. The regiochemistry of
than the electron-transfer process (path b):
(i) The electronic absorption spectra of 0.001 mol/L solu-
tions of the donor molecule 1b or 1c with the acceptor
molecule DDQ (0.001 mol/L) and also the mixture of
either 1b + DDQ or 1c + DDQ in methanol show the
formation of the weak charge-transfer (CT) complexes
between both donor and acceptor molecules (Figs. 1 and 2).
(ii) Addition of ammonium thiocyanate to the mixture of ei-
ther 1b + DDQ or 1c + DDQ at room temperature
causes a decrease of CT-complex absorption (Figs. 3
and 4).
1
substitution was achieved by the interpretation of H NMR
spectra and their comparison with the spectra and physical
data of authentic samples (see Experimental Section).
According to the results obtained from the control experi-
ment and the results presented in Table 3, we can summarize
the following:
(i) The presence of DDQ is necessary for the reaction be-
cause the reaction of 1b as a test compound with
NH4SCN in methanol in the absence of DDQ did not
proceed at all.
(iii) To obtain more information about the formation of
charge-transfer complexes between DDQ and the aro-
matic and heteroaromatic systems as a key step in the
reaction, conductance measurements, as a much sensi-
tive method, was used. Conductance measurements
were carried out on the solutions of 1b, 1c, DDQ and
their mixtures 1b + DDQ and 1c + DDQ at three molar
ratios (0.5:1, 1:1, and 2:1) at 23 °C and 50 °C. The re-
sults are summarized in Table 4.
(ii) The use of DDQ in a molar ratio of 1.25 and 1.5 to 1 of
the aromatic compound indicates that DDQ does not act
as a catalyst, since it is consumed during the reaction.
(iii) The times and the yields of the reactions are dependent
on the electron-donating ability of the aromatic and
heteroaromatic compounds.
On the basis of the forgoing results, the following mecha-
nism is proposed for the reaction, by taking (1a) as an exam-
ple (Scheme 1).
The results showed that the addition of DDQ to the solu-
tions of 1b and 1c causes a sharp increase in the conductiv-
ity. The conductivities of the mixture of 1b with DDQ or 1c
with DDQ are more than the sum of conductivities of the
separated compounds. The results clearly indicate that the
charge-transfer complexes are more mobile than the individ-
ual compounds (29). The differences between the conductiv-
ities of the mixture of 1b with DDQ and (1c) with DDQ and
the sum of the conductivities of the individual compounds at
the same concentration could be related to the extent of CT
formation, which is directly related to the electron-donor
ability of 1b compared with 1c. This is supported by com-
paring the rate of thiocyanation of 1b (15 min) with 1c
(30 min). These experiments show clearly that by increasing
DDQ ratio from 0.5 to 1 and 2, the difference in conductiv-
ity is increased, but there is no difference between the con-
ductivities of the 1:1 and 1:2 molar ratios. This result
According to the proposed mechanism, either the forma-
tion of a π complex between the aromatic system and DDQ
can occur (path a) or an electron-transfer process leads to
the formation of an ion pair, namely, the radical cation of ar-
C–
omatic system and DDQ (path b). Nucleophilic attack of
one of these intermediates by the thiocyanate ion leads to the
formation of a thiocyanated radical system accompanied by
C–
DDQ . An electron transfer from the radical intermediate to
© 2007 NRC Canada

932
Can. J. Chem. Vol. 85, 2007
Scheme 1.
O
O
-
+
CN
CN
Cl
Cl
path a
SCN NH4
)
(
H
SCN
N
H
O
O
Δ
.
N
H
H
CN
CN
Cl
Cl
+
π - complex
N
H
+
_
path b
(
)
+
NH4
CN
O
-
+
.+
ET
.-
SCN NH4
Cl
Cl
1a
DDQ
+
BET
N
H
CN
O
.
Ion pair
DDQ.-NH4
+
OH
SCN
+
CN
Cl
Cl
1. ET
2. H+-abs
CN
N
H
O
NH4+
DDQH-NH4
+
2a
confirms that a 1:1 complex is formed between the donor
and the acceptor molecules (Figs. 5 and 6).
the reaction. It is expected that the presence of the methyl
group in position 1, should increase the electron-donating
character of the nitrogen; therefore, a reaction-time decrease
should be observed for the thiocyanation of compound 1c
(Table 3, entry 3) compared with compound 1a (Table 3, en-
try 1). The obtained reaction times do not confirm these sug-
gestions. The reason is probably that because of the
rehybridization of the nitrogen atom from sp3 to sp2 for
better participation of the nitrogen lone pair in a conjugative
system, the repulsive effect of the methyl group in position 1
(compound 1c) with the hydrogen in position 7 is increased,
which leads to the aversion of the nitrogen of pushing elec-
tron to the pyrrole ring to increase the HOMO energy. Due
to cross conjugation of the nitrogen to both phenyl rings in
carbazole 1e, compared with indole 1a, the energy of the
HOMO should lay lower; therefore, a longer reaction time is
expected. The most interesting results were obtained for the
thiocyanation of aniline and its N- and ring substituted de-
rivatives. While the presence of the methyl group(s) on the
nitrogen decreases the reaction time, the presence of elec-
tron-withdrawing substituents, such as chlorine, methoxy, or
phenyl groups, increases the reaction time. The data reported
in Table 3 also showed that for pyrrole 1g and diphenyl-
amine 1l, both mono- and dithiocyanated products were
formed.
Concerning the regiochemistry of thiocyanate-ion addi-
tion, especially for indole and its derivatives, two possible
radical intermediates 3 (a donor-substituted radical center)
and 4 (a benzylic radical center) should be considered
(Scheme 2). The stability of these radical intermediates ex-
plains the direction of thiocyanate addition to the hetero-
aromatic ring. The conjugation of a radical center in 4 with
the aromatic ring should disturb the aromaticity of ring,
whereas the interaction of the nitrogen lone pair with the ad-
jacent radical center in 3 should increase the stabilization of
a radical center, while the aromaticity of ring stays intact
(30). For other starting materials (Table 3, entries 5–12), the
Interestigly, conductivity measurements showed that by
increasing the temperature, the conductivities are decreased.
This clearly indicates that the cleavage of a π complex oc-
curs by increasing the temperature and supports the reaction
path a. In path b and formation of the ionic intermediates,
we expected that ion mobility should be increased by in-
creasing temperature. All these observations support the in-
volvement of a π complex in the thiocyanation in our study.
These observations are also supported by the fact that the re-
action of thiophene, furan, pyridine, and their benzo-
condenced derivatives, namely, benzothiophene, benzofuran,
and quinoline, as less electron-donor compounds compared
with the compounds considered in this study, under the same
reaction conditions did not result in changing the color of
solution (indicating the lack of any CT-complex formation)
or in the formation of any product(s) even after stirring the
reaction mixture at room temperature for 6 h.
The results presented in Table 3 showed that various aro-
matic and heteroaromatic compounds are converted to their
corresponding thiocyanated derivatives in good to excellent
yields. A comparison of the times for the maximum progres-
sion of reactions indicates that the electron-donor ability of
compounds is an important factor for this reaction. These re-
sults indicate that the steric and electronic effects (e.g., the
HOMO energy) are responsible for the CT-complex forma-
tion, which supports our suggestion of the involvement of
the π complex in the rate-determining step. In comparison
with the results obtained by the thiocyanation of indolic
compounds (Table 3, entries 1–4), we found that the induc-
tive effect of the methyl group at the 2 position (Table 3, en-
try 2) decreases the time required for the completion of the
reaction, compared with compound 1a (Table 3, entry 1) that
does not have this substituent. Contrary to these observa-
tions, the presence of the methyl group at position 1 (com-
pound 1c) increases the time required for the completion of
© 2007 NRC Canada

Memarian et al.
933
Table 3. Thiocyanation of aromatioc and heteroaromatic compounds with NH4SCN in the presence of
DDQ under different reaction conditions.
aAll products were identified by compariing their physical and spectral data with those of the authentic samples
(See also the Experimental Section).
bRoom temperature, molar ratio of NH4SCN:DDQ = 2:1.5.
cReflux conditions, molar ratio of NH4SCN:DDQ = 2:1.25.
dIsolated yields.
eThe numbers in parentheses show the time and yield of the reaction in the presence of 1.25 mmol of DDQ.
© 2007 NRC Canada

934
Can. J. Chem. Vol. 85, 2007
Fig. 1. Electronic absorption spectra of 1b–DDQ reaction in
CH3OH. (A) [1b] = 0.001 mol/L, (B) [DDQ] = 0.001 mol/L,
(C) 1b–DDQ mixture: [1b] = [DDQ] = 0.001 mol/L.
Fig. 3. Time evolution of the UV–vis spectra for the reaction of
NH4SCN with DDQ and 2-methylindole (1b) CT-complex at
room temperature. The spectra were taken at 2 min intervals.
Fig. 4. Time evolution of the UV–vis spectra for the reaction of
NH4SCN with DDQ and 1-methylindole (1c) CT-complex at
room temperature. The spectra were taken at 2 min intervals.
Fig. 2. Electronic absorption spectra of 1c–DDQ reaction in
CH3OH. (A) [1c] = 0.001 mol/L, (B) [DDQ] = 0.001 mol/L,
(C) 1c–DDQ mixture: [1c] = [DDQ] = 0.001 mol/L.
PF254, prepared by applying the silica gel as a slurry and dy-
ing in air.
resonance effect of the nitrogen lone pair directs the position
of thiocyanate addition after complexation with DDQ.
General procedure for the thiocyanation of aromatic
and heteroaromatic compounds at room temperature
(method A)
Experimental
Melting points were determined using a Stuart Scientific
SMP2 capillary apparatus and are uncorrected. IR spectra
were recorded from KBr discs (unless otherwise mentioned)
To a solution of the aromatic or heteroaromatic compound
(1 mmol) and NH4SCN (2 mmol) in CH3OH (5 mL), was
added DDQ (1.5 mmol) at room temperature. The reaction
mixture was stirred for the appropriate time according to Ta-
ble 3. The progress of the reaction was monitored by TLC.
The solvent was evaporated; the residue was diluted with
water (10 mL) and extracted with chloroform (3 × 10 mL).
The combined organic layers were dried over MgSO4 and
evaporated under reduced pressure. The resulting crude
product was purified by plate chromatography on silica gel
(PLC; eluent: n-hexane–EtOAc, 9:1). Further recrystalliza-
tion from petroleum ether – EtOAc gives the pure product
(Table 3).
1
on Shimadzu IR-435. H NMR spectra were recorded with a
Brucker drx 500 (500 MHz) machine. They are reported as
follows: chemical shifts (multiplicity, number of protons,
coupling constants J (Hz), and assignment). Mass spectra
were obtained on Platform II spectrometer from Micromass;
EI mode at 70 eV. Elemental analysis was run on CHN-O-
RAPID analyzer from Heraeus. Conductance measurements
were carried out with an ORION (1c) Model 180 coductivity
meter. A dip-type cell with a cell constant of 0.723 cm–1 of
platinum blank was used. Stock solutions of 1b and DDQ
were prepared in methanol. Varying concentrations of DDQ
were added to a fixed concentration of 1b and 1c to prepare
the desired DDQ to 1b or 1c molar ratios of 0.5:1, 1:1, and
2:1 for conductance measurements at 23 and 50 °C. Prepara-
tive layer chromatography (PLC) was carried out on 20 ×
20 cm2 plates, coated with a 1 mm layer of Merck silica gel
General procedure for the thiocyanation of aromatic
and heteroaromatic compounds under reflux conditions
(method B)
To a solution of the aromatic or heteroaromatic compound
(1 mmol) and NH4SCN (2 mmol) in CH3OH (5 mL), was
© 2007 NRC Canada

Memarian et al.
935
Table 4. Observed conductances (µs/cm2) of charge-transfer complexes 1b and 1c with DDQ at different molar
ratios at 23 and 50 °C in methanol solution.
Molar ratioa
0:1b
23
0.5:1c
23
1:1c
23
2:1c
23
T °C
50
50
50
50
1b
1c
0.82
0.79
15.35
15.2
48.34
47.77
5.85
5
81.21
68.24
26.05
14.9
90.08
70.71
30.65
21.5
Note: The values refer to the corrected conductances. This means that the conductances of methanol has been subtracted.
aMolar ratio of DDQ:1b or 1c.
bC (1b or 1c) = 0.01 mol/L.
cConductance of DDQ at 23 (50 °C) and 0.005 mol/L, 0.01 mol/L, and 0.02 mol/L was 11.18 (126.41), 23.81 (127.01), and 38.34
(131.41), respectively.
Fig. 5. The plot of conductances vs. DDQ–1b in different molar
ratios at 23 and 50 °C.
Scheme 2.
2-Methyl-3-thiocyanatoindole (2b)
Mp 99–101 °C (Lit. (11) 102–103 °C). IR ν: 3324 (NH),
Fig. 6. The plot of conductances vs. DDQ–1c in different molar
ratios at 23 and 50 °C.
2140 (SCN), 1582, 1540, 1455, 1408, 1228, 738 (N–H), 658
1
(C–S) cm–1. H NMR (CDCl3) δ: 2.58 (s, 3H, CH3), 7.23–
7.28 (m, 2H, 5-, 6-H), 7.34 (d, 1H, J = 7.63 Hz, 4-H), 7.69
(d, 1H, J = 7.52 Hz, 7-H), 8.41 (brd s, 1H, NH). EI-MS m/z
(%): 188 [M+] (100), 173 [M+ – CH3] (5), 161 [M+ – HCN]
(22), 146 [M+ – HCN, – CH3] (6), 117[M+ – SCN, – CH3]
(15).
1-Methyl-3-thiocyanatoindole (2c)
Mp 83–84 °C. IR ν: 2145 (SCN), 1514, 1240, 748 (C–S),
1
661 cm–1. H NMR (CDCl3) δ: 3.82 (s, 3H, CH3), 7.31–7.41
(m, 4H, 4-, 5-, 6-, 7-H), 7.81 (d, 1H, J = 7.56 Hz, 2-H). EI-
MS m/z (%): 188 [M+] (100), 173 [M+ – CH3] (37), 162 [M+ –
CN] (27), 146 [M+ – HCN, – CH3] (40), 130 [M+ – SCN]
(12).
added DDQ (1.25 mmol). The reaction mixture was taken in
pre-heated oil bath for the appropriate time according to Ta-
ble 3. The progress of the reaction was monitored by TLC.
The solvent was evaporated; the residue was diluted with
water (10 mL) and extracted with chloroform (3 × 10 mL).
The combined organic layers were dried over MgSO4 and
evaporated under reduced pressure. The resulting crude
product was purified by plate chromatography on silica gel
(PLC; eluent: n-hexane–EtOAc, 9:1). Further recrystalliza-
tion from petroleum ether – EtOAc gives the pure product
(Table 3).
5-Bromo-3-thiocyanatoindole (2d)
Mp 127–129 °C. IR ν: 3321 (NH), 2122 (SCN), 1452,
1
1408, 1106, 794 (N–H), 654 (C–S), 601 cm–1. H NMR
(CDCl3) δ: 7.31 (d, 1H, J = 8.68 Hz, 7-H), 7.41 (dd, 1H, J =
8.65 Hz, J = 1.71 Hz, 6-H), 7.53 (d, 1H, J = 2.79 Hz, 4-H),
7.93 (s, 1H, 2-H), 8.72 (brd s, 1H, NH). EI-MS m/z (%): 253
[M+] (27), 227 [M+ – CN] (7), 173 [M+ – Br] (100), 146
[M+ – HCN, – Br] (19), 114 [M+ – HSCN, – Br] (8).
3-Thiocyanatocarbazole (2e)
3-Thiocyanatoindole (2a)
Mp 80–81 °C (Lit. (6) 76.5–78 °C). IR ν: 3295 (NH),
Mp 105–106 °C (Lit. (11) 125–127 °C). IR ν: 3334 (NH),
2155 (SCN), 2925, 1721, 1620, 1472, 1208, 1121, 1062, 734
1
2150 (SCN), 1435, 1410, 1232, 1095, 735 (N–H), 658 (C–
(N–H), 702 (C–S) cm–1. H NMR (CDCl3) δ: 7.41–7.47 (m,
1
S) cm–1. H NMR (CDCl3) δ: 7.29–7.42 (m, 4H, 4-, 5-, 6-,
4H, 6-,7-,8-, 9-H), 7.53 (d, 1H, J = 8.55 Hz, 2-H), 7.59 (d,
1H, J = 3.1 Hz, 5-H), 7.68 (dd, 1H, J = 8.53 and 1.86 Hz, 2-
H), 8.31 (brd S, 1H, NH). EI-MS m/z (%): 224 [M+] (2), 191
[M+ – SH] (4), 165 [M+ – SCN, – H] (100).
7-H), 7.81 (d, 1H, J = 8.72 Hz, 2-H), 8.90 (brd s, 1H, NH).
EI-MS m/z (%): 174 [M+] (100), 148 [M+ – CN] (63), 116
[M+ – SCN] (28).
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Can. J. Chem. Vol. 85, 2007
2-Thiocyanatopyrole (2fa)
4-Thiocyanatodiphenylamine (2la)
Liquid (Lit. (4) liquid). IR (film) ν: 3395 (NH), 2902,
2126 (SCN), 1462, 1381, 1115, 735 (N–H), 662 (C–S) cm–1.
1H NMR (CDCl3) δ: 6.29 (dd, 1H, J = 5.91 and 2.91 Hz, 4-
H), 6.66 (s, 1H, 3-H), 6.99 (s, 1H, 5-H), 8.87 (brd s, 1H,
NH). EI-MS m/z (%): 124 [M+] (100), 98 [M+ – CN] (10).
Mp 62–64 °C. IR ν: 3332 (NH), 2132 (SCN), 1602, 1578,
1525, 1488, 1330, 820, 745 (N–H), 692 (C–S) cm–1. H
1
NMR (CDCl3) δ: 5.93 (brd s, 1H, NH), 7.03 (d, 2H, J =
8.65 Hz, 2-,6-H), 7.07 (t, 1H, J = 7.38 Hz, 4′-H), 7.14 (d,
2H, J = 7.82 Hz, 2′-, 6′-H), 7.34 (t, 2H, J = 7.84 Hz, 3′-, 5′-
H), 7.43 (d, 2H, J = 8.67 Hz, 3-,5-H). EI-MS m/z (%): 226
[M+] (100), 200[M+ – CN] (30), 167 [M+ – H, – SCN] (66),
77 [Ph+] (36).
2,5-Dithiocyanatopyrole (2fb)
Mp 97–99 °C (Lit. (10) 99–102 °C). IR ν: 3392 (NH),
2906, 2122 (SCN), 1623, 1381, 1105, 792 (N–H), 683 (C–
1
S) cm–1. H NMR (CDCl3) δ: 6.71 (d, 2H, J = 1.18 Hz, 3-,
4,4′-Dithiocyanatodiphenylamine (2lb)
4-H), 9.38 (brd s, 1H, NH). EI-MS m/z (%): 181 [M+] (92),
154 [M+ – HCN] (77), 123 [M+ – SCN] (99), 96 [M+ –
HCN, – SCN] (100), 64 [M+ – HSCN, – SCN] (27).
Mp 110–111 °C. IR ν: 3342 (NH), 2125 (SCN), 1582,
1516, 1482, 1335, 803 (N–H) cm–1. H NMR (CDCl3) δ:
1
6.09 (brd s, 1H, NH), 7.12 (d, 4H, J = 8.68 Hz, 3-, 5-, 3′-,
5′-H), 7.49 (d, 4H, J = 8.68 Hz, 2-, 6-, 2′-, 6′-H). EI-MS
m/z (%): 283 [M+] (19), 257 [M+ – CN] (4), 225 [M+ –
SCN] (23), 149[M+ – PhSCN] (11), 122 [M+ – PhSCN,
– HCN] (22), 90 [M+ – PhSCN, – HSCN] (4).
4-Thiocyanatoaniline (2g)
Mp 51–52 °C (Lit. (10) 51–52 °C). IR ν: 3375 (NH2),
2144 (SCN), 2902, 1595, 1382, 1095, 795 cm–1. H NMR
1
(CDCl3) δ: 3.95 (brd s, 2H, NH2), 6.68 (d, 2H, J = 8.59 Hz,
2-, 6-H), 7.37 (d, 2H, J = 8.56 Hz, 3-, 5-H). EI-MS m/z (%):
150 [M+] (33), 134 [M+ – NH2] (4), 123 [M+ – HCN] (14),
91[M+ – HSCN] (53).
Acknowledgments
We are thankful to the Center of Excellence (Chemistry)
and Office of Graduate Studies of the University of Isfahan
for their financial support.
4-Thiocyanato-N-methylaniline (2h)
Liquid. IR (film) ν: 3385 (NH), 2908, 2142 (SCN), 1596,
1508, 1305, 1181, 814 (N–H), 745 (C–S) cm–1. H NMR
1
(CDCl3) δ: 2.84 (s, 3H, CH3), 4.12 (brd s, 1H, NH), 6.58 (d,
2H, J = 8.67 Hz, 2-, 6-H), 7.38 (d, 2H,, J = 8.64 Hz, 3-, 5-
H). EI-MS m/z (%): 164 [M+] (100), 149 [M+ – CH3] (820),
138 [M+ – CN] (69), 105 [(M+ – SCN, – H] (60), 90 [M+ –
SCN, – H, – CH3] (21), 77 [M+ – CH3, – NH, – SCN] (38).
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