Selective synthesis of organic sulfides or disulfides by solvent exchange from aryl halides and KSCN catalyzed by NiCl2·6H2O

Article abstract of DOI:10.1016/j.jorganchem.2016.08.026

A method for selective synthesis of symmetric sulfides or disulfides from the reaction of aryl halides with KSCN by solvent exchange is introduced. Aryl halides were selectively converted to the symmetric disulfides or sulfides in high yields when they are treated with KSCN in the presence of NiCl₂·6H₂O and DMAP at 140?°C in DMF or poly ethylene glycol (PEG-200) respectively.

Full text of DOI:10.1016/j.jorganchem.2016.08.026

Journal of Organometallic Chemistry 822 (2016) 112e117
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Selective synthesis of organic sulfides or disulfides by solvent
exchange from aryl halides and KSCN catalyzed by NiCl2$6H2O
Mohammad Abbasi*, Najmeh Nowrouzi, Hadis Latifi
Department of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr, 75169, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A method for selective synthesis of symmetric sulfides or disulfides from the reaction of aryl halides with
KSCN by solvent exchange is introduced. Aryl halides were selectively converted to the symmetric
disulfides or sulfides in high yields when they are treated with KSCN in the presence of NiCl2$6H2O and
DMAP at 140 ꢀC in DMF or poly ethylene glycol (PEG-200) respectively.
Received 23 June 2016
Received in revised form
19 August 2016
Accepted 24 August 2016
Available online 26 August 2016
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Sulfides
Disulfides
Aryl halides
KSCN
NiCl2$6H2O
1. Introduction
2-thiolate/CuCl in DMF [50], Potassium 5-Methyl-1,3,4-oxadiazole-
2-thiolate/NiCl2 in DMF-H2O [50], morpholin-4-iummorpholine-4-
Aryl thioethers are important organosulfur compounds and
widely exist in natural products, functional materials and phar-
maceuticals [1,2]. In the polymer industry, aryl disulfides are
necessary monomers for preparing high-performance engineering
plastics [3]. In biological studies, some aryl disulfide molecules
have shown herbicidal activity in some resistant types of plants [4].
The CeS bond formation between an aryl carbon and a sulfur-
transfer reagent using transition metal catalysts [5e21] specially
Cu and Ni is a powerful tool to synthesize aryl-sulfides and disul-
fides. In this line, aryl thioethers have been synthesized by treat-
ment of aryl halides with thiols/CuI [22e24], thiols/NiCl2 [25,26],
thioacetamide/CuI [27e30], thiourea/CuFe2O4 [31], KSCN/CuI [32],
Na2S$9H2O/CuI [33,34], thiourea/CuO [35], thiourea/CuI [36],
ethanethiolic acid/CuCl2 [37], dithiooxamide/CuI [38], KSCN/CuO
[40e43], S/CuI [44,45] and KSCN/CuCl2 [39]. Similarly, symmetric
aryl disulfides have been prepared by treatment of the corre-
sponding aryl halides with thioacetamide/CuCl/KF/Al2O3 in DMF
[46], Na2S/S/CuI in DMSO [34], S/CuO/in DMSO [47], With sulfur,
potassium hydroxide in water [48], S/Mg or Al/CuI in DMF [30], S/
CuCl2/(n-Bu)4NF in H2O [49], potassium 5-methyl-1,3,4-oxadiazole-
carbo-dithioate/CuCl in DMF-H2O [51], and morpholin-4-ium
morpholine-4-carbo-dithioate/NiCl2 in DMF [52].
2. Results and discussion
The synthesis of organosulfur derivatives using alkane thiols, in
situ generated from the reaction of a sulfur transfer reagent and
alkyl halides, has been the subject of our investigations in recent
years [53e66]. In continuation, we were interested to develop our
studies to synthesize of thiophenol derivatives using aryl halides. In
this regard, our attention was focused on the reaction of aryl halides
with KSCN and finally we succeeded to develop a method for se-
lective synthesis of symmetric aryl-sulfides or disulfides using
NiCl2$5H2O and DMAP by solvent exchange. At first, the model
reaction of iodobenzene with KSCN in the presence of NiCl2$6H2O
and DMAP was studied under various conditions. The results are
presented in Table 1.
It was found that, the reaction of iodobenzene with KSCN in
DMF in the presence of NiCl2$6H2O and DMAP gives the corre-
sponding symmetric disulfide as the sole product. Considering both
reaction time and yield, the best result was obtained by using
30 mol% of NiCl2$6H2O and 40 mol% of DMAP at 140 ꢀC which gave
the desired disulfide in 89% yield within 12 h (Table 1, entry 3). The
similar reactions in the presence of lower amounts of DMAP or
* Corresponding author.
E-mail addresses: abbassi@pgu.ac.ir, pgu.chem@gmail.com (M. Abbasi).
http://dx.doi.org/10.1016/j.jorganchem.2016.08.026
0022-328X/© 2016 Elsevier B.V. All rights reserved.

M. Abbasi et al. / Journal of Organometallic Chemistry 822 (2016) 112e117
113
Table 1
Optimization of the reaction conditions for conversion of iodobenzene into the corresponding symmetric sulfide and disulfide.a
Entry
NiCl2$6H2O (mol%)
DMAP (mol%)
Solvent
T (ꢀC)
t (h)
I (%)
II (%)
1
10
20
30
40
30
30
e
40
40
40
40
40
30
40
e
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
PEG-200
PEG-200
PEG-200
PEG-200
PEG-200
PEG-200
PEG-200
140
140
140
140
120
140
140
140
140
140
120
140
140
140
140
24
24
12
12
24
24
24
24
24
24
24
24
24
24
24
50
70
89
91
88
77
e
e
e
-
e
e
e
e
e
2
3b
4
5
6
7
8
30
30
20
30
30
40
e
trace
-
9b
10
11
12
13
14
15
40
40
40
30
40
40
e
70 (88)c
55
51
57
73
e
e
e
e
e
e
30
e
27
a
Reaction conditions: Ph-I (2.0 mmol), KSCN (2.2 mmol), solvent (2 mL).
The best reaction conditions.
The reaction was carried out using 4.0 mmol of KSCN.
b
c
NiCl2$6H2O were uncompleted during 24 h and gave the desired
product in lower yields (Table 1, entries 1, 2, 6). Also, the similar
reaction conducted at 120 ꢀC proceeded to completion within 24 h
to produce disulfide in 88% yield (Table 1, entry 5). The increasing
amount of NiCl2$6H2O to 40 mol% did not result the better reaction
time or yield (Table 1, entry 4). The reaction in the absence of NiCl2
(Table 1, entry 7) or DMAP (Table 1, entry 8) did not proceed
efficiently.
Next, the reaction of iodobenzene (2.0 mmol) with KSCN
(2.2 mmol) in the presence of NiCl2 and DMAP in polyethylene
glycol (PEG-200) was studied. Under these conditions, diphenyl
sulfide was produced solely. As the best result, diphenyl sulfide was
produced in 70% yield when a mixture of iodobenzene and KSCN in
PEG-200 was treated with 30 mol% of NiCl2$6H2O and 40 mol% of
DMAP at 140 ꢀC for 24 h (Table 1, entry 9). A little amount of the
starting iodobenzene was also recovered unaltered after this
period. Increasing the quantity of KSCN to 4.0 mmol led to an
improvement in yield from 70% to 88% (Table 1, entry 9).
presence of Ni2þ and symmetric disulfide in the presence of Ni(0)
catalyst. In order to evaluate this hypothesis, a reaction between
iodobenzene and KSCN in PEG in the presence of NiCl2$6H2O and a
ligand which can reduce Ni2þ to Ni(0) could be helpful. In this line, a
mixture of NiCl2$6H2O (30 mol%) and PPh3 (2.0 mmol) as a
reducing ligand in PEG (2 mL) was prepared and stirred for 5 min at
140 ꢀC and subjected to UV spectroscopy. No absorbance peaks for
NiCl2$6H2O were found in UV spectrum indicating complete
reduction of starting Ni2þ to Ni(0) (curve VI of Fig. 1). Next, other
reactants including iodobenzene (2.0 mmol) and KSCN (4 mmol)
were added to the mixture and the stirring was resumed at 140 ꢀC.
The reaction proceeded to completion within 24 h and gave
diphenyl disulfide (not diphenyl sulfide) in 82% yield, confirming
the dependence of reaction product with oxidation state of the Ni
catalyst. Now, with more certainty, it could be claimed that the
reaction of iodobenzene with KSCN gives sulfide and disulfide in
the presence of Ni(II) and Ni(0), respectively.
With these results in hand, the conversion of other aryl halides
to the corresponding sulfides and disulfides under best reaction
conditions based on the reaction time and yield was studied. The
results are presented in Table 2.
As the results show, aryl iodides and bromides have been con-
verted to the symmetric sulfides and disulfides successfully. The
conversion of p-chlorobenzonitrile as an aryl chloride to the cor-
responding sulfide or disulfide under reaction conditions was
completely failed and unreacted chloride was recovered from the
reaction mixture in near quantitative yield after 24 h. Also, o-iodo
toluene as a more sterically hindered substrate remained intact
under reaction conditions within 24 h.
To study the reaction in more detail and specially to understand
the effect of solvent on the kind of reaction product, the interaction
between NiCl2$6H2O catalyst and two solvents was separately
studied by UV spectroscopy (Fig. 1).
Two absorbance peaks for an aqueous solution of NiCl2 at
around 400 and 700 nm were found at room temperature (I). When
a solution of NiCl2$6H2O in DMF was heated at 140 ꢀC for 5 min, the
starting clear solution became turbid and no absorbance peaks
were found in its UV spectrum (II). Addition of KSCN to the mixture,
did not cause any change in the UV spectrum (V), clearness and
color of mixture. It can be concluded that, DMF plays an important
role in reaction by formation of Ni(0) catalyst from Ni2þ solution. It
should be noted that, the reduction of metal ions by DMF is well-
known and has been reported earlier [67e73]. However, when a
clear solution of NiCl2$6H2O in PEG-200 was heated at 140 ꢀC for
5 min or 24 h and then subjected to UV spectroscopy, it showed the
absorbance peaks of Ni2þ as shown in curve (III) of Fig 1. Its light
green color was changed to dark green by adding KSCN to solution
perhaps due to the formation of Ni(SCN)2 (curve IV).
The actual mechanism of the protocol and the precise role of Ni
catalyst are not clear at this stage. Nickel is found in one of several
oxidation states, ranging from ꢁ1 to þ4 [75]. A handful of Ni(IV)
complexes were synthesized, isolated or characterized in situ [76].
However, conversion of Ni(II) to Ni(IV) intermediate via oxidative
addition and vice versa (a Ni(II)/Ni(IV) catalytic cycle) for many Ni
catalyzed cross-coupling reactions has been previously proposed
[77e91]. On the basis of those precedents, we hypothesized that a
high-valent Ni(IV) intermediate might be involved in these Ni-
catalyzed protocols (Schemes 1 and 2).
Now, it can be concluded that, the reaction output depends on
the Ni catalyst oxidation state. It will be symmetric sulfide in the

114
M. Abbasi et al. / Journal of Organometallic Chemistry 822 (2016) 112e117
Fig. 1. UV spectra of NiCl2$6H2O I) in H2O, (II) in DMF; (III) in PEG; (IV) in PEG in the presence of KSCN; (V) in DMF in the presence of KSCN; (VI) and in PEG in the presence of PPh3.
As it is proposed in Scheme 1, Ni(SCN)2 is formed in the reaction
mixture from the reaction of NiCl2 with KSCN which subsequently
undergoes oxidative addition by insertion to aryl CeX bond to
produce Ni(IV) intermediate (1). This step is followed by reductive
elimination to give AreSCN and the Ni(II) catalyst as XeNieSCN
(cycle A). The starting Ni(SCN)2 catalyst, is regenerated by reacting
XeNieSCN with KSCN (cycle A). The in situ generated aryl mer-
captane (from the Ni2þ catalyzed hydrolysis of ArSCN) (path B)
undergoes arylation by second molecule of AreX to produce sym-
metric sulfide (cycle C). This process occurs through replacement of
halide anion of intermediate (1) by thiolate followed by reductive
elimination (cycle C). According to proposed mechanism presented
in Scheme 2, Ni(0) inserts itself into CeX bond of aryl halide to
produce AreNi(II)eX (cycle D). This intermediate is then converted
to AreNi(II)eSCN by replacement of halide by thiocyanate ion.
Reductive-elimination step, gives ArSCN along with regeneration of
Ni(0) catalyst (cycle D). ArSeNi(II)eCN is then generated by inser-
tion of Ni(0) into SeCN bond of in situ generated aryl thiocyanate
(cycle E). The intermediate (3) is subsequently produced via
oxidative addition of Ni (II) to the SeCN bond of the second
molecule of RSeCN. Finally, the reductive elimination of this in-
termediate takes place to give the target symmetric disulfide and
Ni(II) catalyst which in turn, undergoes reduction with DMF to
regenerate Ni(0) catalyst.
Chemical Companies. 1H NMR and 13C NMR spectra were recorded
in CDCl3 using a Bruker Avance DPX instrument (1H NMR 250 MHz,
13C NMR 62.5 MHz). Chemical shifts are reported in ppm (
d)
downfield from TMS. Coupling constants (J) are in Hertz. Elemental
analyses were run on a Thermo Finnigan Flash EA-1112 series. Thin-
layer chromatography was carried out on silica gel 254 analytical
sheets obtained from Fluka. Column chromatography was per-
formed on Merck Kiesel gel (230e270 mesh).
4.2. General procedure for synthesis of disulfides
KSCN (2.2 mmol) was added to a magnetically stirred mixture of
an aryl halide (2 mmol), NiCl2$6H2O (0.6 mmol, 30 mol%, 0.143 g)
and DMAP (0.8 mmol, 40 mol%, 0.098 g) in DMF (2 mL) at 140 ꢀC.
The stirring was continued until the starting halide was completely
consumed. Next, the reaction mixture was diluted with water
(1 mL) and extracted with 1:1 EtOAc/hexane (4 ꢂ 2 mL). The
organic extracts were combined, concentrated and purified by
chromatography on silica gel. The desired disulfides were produced
in 79e92% yields (Table 2).
4.2.1. 1,2-Diphenyldisulfane (Table 2, entry 1)
MP: 57e58 ꢀC (Lit. 59e60 ꢀC) [51]. 1H NMR (250 MHz, CDCl3):
dH ¼ 7.53e7.49 (m, 4H), 7.34e7.23 (m, 6H) ppm. 13C NMR
(62.9 MHz, CDCl3): dC ¼ 137.0, 129.4, 127.5, 127.1 ppm. Anal. Calcd
for (C12H10S2): C, 66.02; H, 4.62; S, 29.37. Found: C, 66.15; H, 4.52; S,
29.33.
3. Conclusion
In summary, the first Ni-catalyzed coupling of aryl halides and
KSCN was developed. Symmetric diaryl-sulfides or disulfides were
synthesized selectively in high yields by treatment of aryl halides
with KSCN in the presence of NiCl2$6H2O and DMAP in PEG-200
and DMF, respectively. A variety of aryl bromides and iodides
bearing the electron donating and withdrawing groups were
screened without difficulty. The method is simple, high yielding
which tolerates a variety of functional groups on the aryl rings.
4.2.2. 1,2-Di-p-tolyldisulfane (Table 2, entry 3)
MP: 43e45 ꢀC (Lit. 41e45 ꢀC) [74]. 1H NMR (250 MHz, CDCl3):
dH ¼ 7.36 (d, J ¼ 8.6 Hz, 4H), 7.07 (d, J ¼ 8.6 Hz, 4H), 2.28 (s, 6H) ppm.
13C NMR (62.9 MHz, CDCl3): dC ¼ 137.4, 134.0, 129.8, 128.6,
21.1 ppm. Anal. Calcd for (C14H14S2): C, 68.25; H, 5.73; S, 26.02.
Found: C, 68.29; H, 5.83; S, 25.88.
4.2.3. 1,2-Bis(4-methoxyphenyl)disulfane (Table 2, entry 2)
MP: 40e43 ꢀC (Lit. 41e43 ꢀC) [51]. 1H NMR (250 MHz, CDCl3):
dH ¼ 7.34 (d, J ¼ 8.8 Hz, 4H), 6.89 (d, J ¼ 8.8 Hz, 4H), 3.83 (s, 6H)
ppm. 13C NMR (62.9 MHz, CDCl3): dC ¼ 159.1, 132.8, 127.5, 114.7,
55.5 ppm. Anal. Calcd for (C14H14O2S2): C, 60.40; H, 5.07; S, 23.03.
Found: C, 60.23; H, 5.17; S, 23.13.
4. Experimental
4.1. General information
Chemicals were purchased from Merck, Fluka and Acros

M. Abbasi et al. / Journal of Organometallic Chemistry 822 (2016) 112e117
115
Table 2
Conversion of aryl halides into symmetric sulfides or disulfides.
Entry
AreX
Product
ArSeSAra
Time (h)
12
AreSeArb
Time (h)
24
Yield (%) [Ref]
89 [30]
Yield (%) [Ref]
1
2
88 [44]
16
16
20
92 [30]
85 [30]
90 [30]
24
24
24
85 [44]
3
4
87 [44]
87 [31]
5
6
15
24
85 [47]
24
24
80 [44]
e
e
7
8
14
18
90 [30]
83 [30]
24
24
86 [44]
84 [44]
9
22
79 [30]
24
86 [31]
10
11
15
15
85 [74]
85 [47]
24
24
81 [44]
79 [44]
12
24
e
24
e
a
Reaction conditions: ArX (2.0 mmol), KSCN (2.2 mmol), NiCl2$6H2O (30 mol%), DMAP (40 mol%), DMF (2 mL), 140 ꢀC.
Reaction conditions: ArX (2.0 mmol), KSCN (4.0 mmol), NiCl2$6H2O (30 mol%), DMAP (40 mol%), PEG-200 (2 mL), 140 ꢀC.
b

116
M. Abbasi et al. / Journal of Organometallic Chemistry 822 (2016) 112e117
NiCl2.6H2O
KSCN
KCl
II
ArX
KX
II
Ni(SCN)2
Ni(SCN)2
KSCN
ArSAr
ArX
Ar
X
IV
NCS
NCS
II
Ni
Ar
X
IV
X
Ni SCN
NCS
IV Ar
Ni
NCS
NCS
Ni
(1)
NCS
SAr
(2)
(1)
HX
cycle A
ArSCN
ArSH
OH2
cycle C
Ni2+
Ni2+
OH2
NH2
S
NH2
Ar
NH
Ni2+
N
Ni2+
O
HOCONH2
Ar
Ar
C
O
S
OH
S
S
Ar
path B
Scheme 1. Proposed reaction pathway for the Ni(II)-catalyzed formation of symmetric sulfides.
4.3.2. Di-p-tolylsulfune (Table 2, entry 8)
1H NMR (250 MHz, CDCl3): dH ¼ 7.20e7.16 (m, 4H), 6.77e6.71
(m, 4H), 2.33 (s, 6H) ppm. Anal. Calcd for (C14H14S): C, 78.46; H,
6.58; S, 14.96. Found: C, 78.61; H, 6.52; S, 14.87.
4.3.3. Bis(4-methoxyphenyl)sulfane (Table 2, entry 2)
1H NMR (250 MHz, CDCl3): dH ¼ 7.38e7.30 (m, 4H), 6.78e6.74
(m, 4H), 3.72 (s, 6H) ppm. Anal. Calcd for (C14H14O2S): C, 68.26; H,
5.73; S, 13.02. Found: C, 68.16; H, 5.70; S, 13.15.
4.3.4. 4,40-Thiodibenzonitrile (Table 2, entry 10)
1H NMR (250 MHz, CDCl3): dH ¼ 7.56e7.52 (m, 4H), 7.36e7.32
(m, 4H) ppm. Anal. Calcd for (C14H8N2S): C, 71.16; H, 3.41; N, 11.86;
S, 13.57. Found: C, 71.28; H, 3.37; N, 11.95; S, 13.40.
Scheme 2. Proposed reaction pathway for the Ni(0)-catalyzed formation of symmetric
disulfides.
Acknowledgments
4.2.4. 1,2-Bis(4-nitrophenyl)disulfane ((Table 2, entry 5)
MP: 174e176 ꢀC (Lit. 173e175 ꢀC) [51]. 1H NMR (250 MHz,
CDCl3): dH ¼ 8.16e8.10 (m, 4H), 7.44e7.40 (m, 4H) ppm. Anal. Calcd
for (C12H8N2O4S2): C, 46.75; H, 2.62; N, 9.09; S, 20.80. Found: C,
46.89; H, 2.73; N, 8.91; S, 20.65.
We are thankful to Persian Gulf University Research Council for
partial support of this work.
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KSCN (4 mmol) was added to a magnetically stirred mixture of
an aryl halide (2 mmol), NiCl2$6H2O (0.6 mmol, 30 mol%, 0.143 g)
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