Transition-Metal-Free C-S Bond Formation: Aqueous Synthesis of S-Aryl Dithiocarbamates by the use of Stable Arenediazonium Salts Mediated by Nano-Magnetic Supported Silica Sulfonic Acid

Article abstract of DOI:10.1080/10426507.2015.1024311

A convenient and transition-metal-free method for the synthesis of S-aryl dithiocarbamates based on the reaction of stable arenediazonium nano-magneto silica sulfates (ArN₂^+-OSO₃-SiO₂@Fe₃O₄) with dithiocarbamic acid at room temperature was studied. Avoiding the use of any hazardous transition metal, simple procedure, low cast, and short reaction time are noteworthy advantages of this methodology.

Full text of DOI:10.1080/10426507.2015.1024311

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Phosphorus, Sulfur, and Silicon and the Related
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Transition-Metal-Free C-S Bond Formation. Aqueous
Synthesis of s-Aryl Dithiocarbamates by Use of Stable
Arenediazonium Salts Mediated by Nano-Magnetic
Supported Silica Sulfonic Acid
Firouzeh Nematia, Ali Elhampoura & Soghra Zulfagharia
a Department of Chemistry, Semnan University, Semnan, Iran, Zip Code: 35131-19111, Tel.:
+98 09122057819, Fax: +98 (23) 33384057
Accepted author version posted online: 16 Mar 2015.
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To cite this article: Firouzeh Nemati, Ali Elhampour & Soghra Zulfaghari (2015): Transition-Metal-Free C-S Bond Formation.
Aqueous Synthesis of s-Aryl Dithiocarbamates by Use of Stable Arenediazonium Salts Mediated by Nano-Magnetic Supported
Silica Sulfonic Acid, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2015.1024311
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1024311
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Green synthesis of S-aryl dithiocarbamates
TRANSITION-METAL-FREE C-S BOND FORMATION. AQUEOUS SYNTHESIS OF S-
ARYL DITHIOCARBAMATES BY USE OF STABLE ARENEDIAZONIUM SALTS
MEDIATED BY NANO-MAGNETIC SUPPORTED SILICA SULFONIC ACID
Firouzeh Nematia,*, Ali Elhampoura, Soghra Zulfagharia
aDepartment of Chemistry, Semnan University, Semnan, Iran, Zip Code: 35131-19111, Tel.: +98
09122057819, Fax: +98 (23) 33384057
*E-mail: fnemati_1350@yahoo.com; fnemati@semnan.ac.ir
Abstract
A convenient and transition-metal-free method for the synthesis of S-aryl dithiocarbamates based
+
on the reaction of stable arenediazonium nano-magneto silica sulfates (ArN2 −OSO3-
SiO2@Fe3O4) with dithiocarbamic acid at room temperature was studied. Avoiding the use of
any hazardous transition metal, simple procedure, low cast and short reaction time are
noteworthy advantages of this methodology.
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Keywords
Diazotization; Magnetic Nanoparticles; S-Aryl Dithiocarbamates, Diazonium salts; Transition-
metal-free.
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INTRODUCTION
Sulfur-containing compounds are found in many biological, pharmaceutical, and material
products.1-6 The formation of a carbon–sulfur (C–S) bond is a fundamental approach to introduce
sulfur into organic compounds. Traditionally, various metal-based catalysts in combination with
different ligands are generally used for the C–S bond formation by cross coupling of their
halides.7-12 But most of these synthetic methods involve designed ligands or catalysts, which may
increase the cost and limit the scope of their applications. Thus, the investigation of new
protocols for C(aryl)–S bond generation, especially under “green” conditions, which can lead to
the discovery of less expensive and more efficient synthetic methods for the preparation of
organo-sulfur compounds has attracted much attention in recent years.13-15
Dithiocarbamates are vital structural motifs occurring in numerous natural products16,
pharmaceuticals and agrochemicals.17 They are also used as linkers in solid phase organic
synthesis,18 protecting groups in peptide synthesis19 and in the synthesis of ionic liquids.20 Thus
the development of novel protocols for the synthesis of dithiocarbamates, which are practical,
cheap and environmentally benign, is highly desirable. The synthetic methods for the formation
of S-aryl dithiocarbamates are somewhat limited. The most commonly used conventional method
is the reaction of amines with thiophosgene or isothiocyanates.21 However, these methods have
limited application because costly and toxic reagents are used. Other methods applied for the
synthesis of S-aryl dithiocarbamates are the reaction of hypervalent iodine compounds with
sodium salts of dithiocarbamic acids,22 the reaction of certain organometallic reagents with
tetramethyllitium disulfide,23 coupling of sodium dithiocarbamates with aryl iodides catalyzed by
CuI in the presence of a ligand in DMF(dimethyl formamide).24 These methods suffer from one
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or more disadvantages such as the use of expensive and toxic reagents or difficulty in preparing
the reagent. Ranu et al. previously described the synthesis of S-aryl dithiocarbamates via two
green routes: the condensation of arenediazonium fluoroborate, carbon disulfide and an amine in
water,25 and coupling of aryl iodides with carbon disulfide and an amine catalyzed by Cu
nanoparticles.26 Even though they are considered as highly useful synthetic method, their only
disadvantage is the need for expensive starting materials such as arenediazonium fluoroborate, or
aryl iodide. Despite these advances, the above drawbacks need to be overcome, and the
development of a convenient and efficient method using cheap and benign reagents for the
synthesis of S-aryl dithiocarbamates is attracting considerable attention. We have recently
reported the synthesis of nano-Fe3O4@SiO2-SO3H and its application in green protocols.27,29 It
has been identified as the ideal heterogeneous solid acid due to its excellent stability as well as
its great accessibility and low cost.30 It can be directly separated from the reaction mixture using
an external magnet and be reused several times without a significant decrease of activity.
RESULTS AND DISCUSSION
In light of the above facts and in continuation of our studies on the application of stable
arenediazonium salts for organic transformations31,32 and as a part of our recent endeavors in the
use of nano-Fe3O4@SiO2-SO3H, we developed an efficient and metal-free reaction for the
synthesis of S-aryl dithiocarbamates. Nano-Fe3O4@SiO2-SO3H can be used as acid source for the
generation of stable diazonium salts from the corresponding anilines that are widely available
commercially or generated by the reduction of the corresponding nitroarene, which may serve as
a protected amine in a synthetic route.33 It is well-known that arenediazonium salts with the
bulky sulfate anion are stable and non-explosive.34-36 So, because of environmental issues, the
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protocol was carried out using the reaction of stable arenediazonium nano-magneto silica sulfates
(ArN2+ −OSO3-SiO2@Fe3O4) with carbon disulfide and a secondary aliphatic amine without the
need of any transition metal in water at room temperature in a short reaction time (Scheme 1).
Fe3O4@SiO2-SO3H was prepared according to our previously reported procedure with
some modification.27 The X-ray diffraction (XRD) pattern of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2-SO3H are depicted in Fig. 1. The XRD pattern of Fe3O4 clearly matches well with
the literature data.29 Six peaks at 30.24, 35.60, 43.24, 53.7, 57.6 and 62.8 can be assigned to the
(220), (311), (400), (422), (511) and (440) planes of Fe3O4 that indexed to the crystalline cubic
inverse spinal structure of MNPs. The crystallite size of the nanoparticles was calculated to be
around 10 nm from the XRD results using the Debye-Scherrer equation.
In the XRD pattern of Fe3O4@SiO2 the same peaks were also observed, and in addition the
broad peak at 2θ = 12.5 is referred to amorphous silica. Notably, the same peaks were also
revealed in XRD spectra of Fe3O4@SiO2-SO3H, which indicate the structural stability of MNPs
after modification with chlorosulfonic acid.
The morphology and structure of the prepared samples were characterized by FE-SEM.
Figure 2a shows that the Fe3O4 MNPs are spherical in shape, and it has a marked tendency to
form large clusters. Fig. 2b shows that the Fe3O4@SiO2 nanoparticles are spherical with larger
particle size and smoother surface. The SEM images of Fe3O4@SiO2-SO3H demonstrate that
there is no change in the shape of MNPs after being functionalized with sulfonic acid and also
the surface morphology being retained (Fig. 2c).
In order to optimize the reaction condition, as a model reaction, aniline (1 mmol) was
homogenized by mixing 0.8 g of Fe3O4@SiO2-SO3H and 0.2 mL water into a mortar with a
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pestle until the aniline had disappeared as monitored by TLC. Then sodium nitrite (2 mmol) was
added with continues grinding; the diazotation proceeded in few minutes and stable
phenyldiazonium nano-magneto silica sulfate was prepared (Scheme 1, step 1). Next, the stable
phenyl nano-magneto silica sulfate was added to a suspension of piperidine (1.2 mmol) and
carbon disulfide (2.5 mmol) in 3 mL water. The mixture was then stirred at room temperature for
10 min. After the completion of the reaction, the crude product was extracted with ethyl acetate
and Fe3O4@SiO2-SO3H simply separated with an external magnet. The solvent was evaporated
and the raw product was purified by flash chromatography.
Further studies revealed that 0.8 g Fe3O4@SiO2-SO3H that equals to 0.25 mmol H+ loading
was sufficient to generate ArN2+ −OSO3-SiO2@Fe3O4 in high yield. The usage of lower amounts
of nano-magnetic reagent reduced the yield of arenediazonium salts.
The scope of this convenient procedure was investigated using diversely substituted
aromatic amines. The results are summarized in Table 1. The stable arenediazonium nano-
magneto silica sulfates were formed in short reaction times of 5-10 min. Then, they underwent
reactions with carbon disulfide and a secondary aliphatic amine to produce the corresponding
products. A broad range of S-aryl dithiocarbamates was thus synthesized in good to excellent
yields. Both electron-donating (Table 1, entries 4-11) and electron-withdrawing (Table 1, entries
12-16) substrates gave similar high yields. The ortho- and meta-substituents also provided good
results (Table 1, entries 12, 13).
Based on the literature reports,25,37 and considering the substituent effect, we can outline a
SN2Ar reaction pathway for the preparation of S-aryl dithiocarbamates (Scheme 2). In the first
step, I could be formed from the diazotization of aniline derivatives in the presence of wet
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Fe3O4@SiO2-SO3H and NaNO2. Nano-magneto silica sulfate as a bulky counter ion with high
surface not only increases the stability of the diazonium salts but also increases the reaction rate,
so that these salts can be used under mild conditions.34-37 Then, it is thought that the in situ-
generated dithiocarbamate unit (II) attacks C-1 of the aryldiazonium magneto silica sulfate to
form the transient intermediate III, which through elimination of N2 forms the S-aryl
dithiocarbamates.
In an attempt to study the stability of arenediazonium silica sulfate salts, the reaction
condition was investigated for the model reaction after the time specified in Table 2. As shown
in Table 2, the addition of dithiocarbamate to the stored diazonium sulfate salts (stored in a
desiccator at room temperature) provided almost the same yield of the product as that from
freshly prepared salt. Obviously, because of the instability of aryl cations, the arenediazonium
salts with electron-withdrawing groups are more stable than those with electron-donating
groups.38
To demonstrate the efficiency of the present protocol for the synthesis of S-aryl
dithiocarbamates, we compared it with the previously published procedures. The results
summarized in Table 3 show that this methodology is superior to others in terms of reaction
time, readily available starting materials, avoidance of the use of toxic solvent, and simple
procedure.
CONCLUSION
In summary, a new methodology for the synthesis of synthetically important S-aryl
thiocarbamates in a green protocol has been developed. For the first time, nano-Fe3O4@SiO2-
SO3H was employed as a nanomagnetic heterogeneous Brønsted acid, in the synthesis of stable
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diazonium salts and afterwards, the transition-metal-free C-S bond formation. The promising
points for the presented protocols are simple procedure, short reaction time at ambient
temperature, use of stable and readily available starting material without requirement of any
metal, ligand or organic solvent, which makes this procedure better alternative to existing ones.
EXPERIMENTAL
Chemical reagents in high purity were purchased from Merck and Aldrich and were used
without further purification. Melting points were determined in open capillaries using an
1
13
Electrothermal 9100 without further corrections. H NMR and C NMR spectra were recorded
using a Bruker DRX-400 spectrometer at 400 and 100 MHz respectively. FT-IR spectra were
obtained with KBr pellets in the range of 400–4000 cm-1 using a Shimadzu 8400s spectrometer.
The elemental analysis (C, H, N) was performed on a Perkin-Elmer CHN analyzer, 2400 series
II. The purity of the compounds synthesized was monitored by TLC on commercial aluminum-
backed plates of silica gel 60 F254, visualizing with ultraviolet light. X-Ray diffraction (XRD)
was detected by Bruker D4 ENDEAVOR X-ray diffractometer using Cu-Kα radiation of
wavelength 1.54Å. Scanning electron Microscopy, SEM, analysis was performed using Tescan
vega II XMU Digital Scanning Microscope. Samples were coated with gold at 10 mA for 2 min
1
prior to analysis. The Supplemental Materials contains sample H NMR spectra for some
products (Figures S 1 – S 6)
Preparation of nano magneto silica sulfuric acid
The Fe3O4@SiO2–SO3H was prepared in accordance to our earlier report.27
Typical procedure for the synthesis of 4-nitro-phenyl piperidine-1-carbodithioate
(14a).
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4-Nitroaniline (0.13 g, 1 mmol) was homogenized by mixing of Fe3O4@SiO2-SO3H (0.8 g)
and water (0.2 mL) into a mortar with a pestle. Next, NaNO2 (0.136 g, 2 mmol) was added and
grinding was continued mildly for 8 min (as monitored by TLC), until the aromatic amine had
disappeared. 4-Nitrophenyl nano-magneto silica sulfate was added to a freshly prepared solution
of dithiocarbamic acid. [The dithiocarbamic acid was prepared in a separate vessel by drop-wise
addition of piperidine (0.102 g, 1.2 mmol) to a suspension of CS2 (0.19 g, 2.5 mmol) in water (3
mL) at 0-5 °C for 5 min]. The mixture was stirred at room temperature for 15 min (Table 1).
After completion of the reaction, EtOAc (10 mL) was added to the reaction mixture. The nano
magnetic reagent was simply separated by an external magnet and the organic layer was dried
over anhydrous Na2SO4. After evaporation of the solvent, the crude product was purified by flash
chromatography (n-hexane: EtOAc, 95:5). 14a was obtained as a yellowish solid (0.25 g, 95%).
1
M.p.: 158-159 °C; IR: ν 2943, 2856, 1582, 1531, 1350 cm−1; H NMR (CDCl3): δ 1.77 (6H, s),
13
4.00 (2H, s, br), 4.28 (2H, s, br), 7.62-7.66 (2H, m), 8.19-8.27 (2H, m); C NMR (CDCl3): δ
25.38, 53.72, 56.87, 123.9, 125.6, 136.5, 137.8, 139.0, 148.8, 193.6; Anal. calcd. for
C12H14N2O2S2: C, 51.06; H, 4.96; N, 9.92; Found: C, 51.21; H, 4.71; N, 10.06.
Reusability of catalyst
After the completion of a reaction, the nano magnetic reagent was removed by use of an external
magnet, washed exhaustively with diethyl ether and methanol and dried at 90º C for 1h. It could
be reused in subsequent reactions after treating it with the appropriate amount of chlorosulfonic
acid.
Acknowledgment
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The authors gratefully acknowledge Semnan University Research Council for financial support
of this work.
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Table 1. Synthesis of S-aryl dithiocarbamates.
Time Diazotization/C-S
bond formation/min
Product
Yield/%a
87
M.p./°C (Lit.)
113-116
S
N
5/10
1a
(113-116)26
S
S
N
5/12
5/12
5/15
5/15
5/20
80
71
87
82
79
93-95 (93-94)26
44-46 (44-45)26
2a
3a
4a
5a
6a
S
S
N
S
118-120
S
N
(118-119)25
S
H3C
H3C
H3C
O
131-132
S
N
(131-133)25
S
S
N
111-112
(111-112)25
S
S
N
5/17
5/15
5/15
5/12
78
85
88
75
76-78(75-76)25
7a
S
H3C
101-102
S
N
8a
(102-103)25
S
H3CO
O
133-135
S
N
9a
(133-135)25
S
H3CO
H3CO
S
N
91-93(92-93)22
10a
S
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S
N
5/10
82
75
Oil25
11a
12a
S
H3CO
S
N
10/17
92-93(92-93)25
S
NO2
S
N
138-140
10/15
70
13a
(139-141)22
S
NO2
S
N
8/15
5/20
7/22
95
81
79
158-159
14a
15a
16a
S
O2N
120-121
S
N
(121-122)25
S
I
S
N
102-104
(101-103)22
S
Cl
a The yield is based on the aniline starting material
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Table 2. The stability of nano-magnetic arenediazonium silica sulfate salts at room temperature.a
Diazonium salt
Immediately
87
After 12
h(%)
87
After 24 After 48
h(%)
h(%)
69
81
89
78
Fe3O4@SiO2-SO3- +N2
Fe3O4@SiO2-SO3- +N2
Fe3O4@SiO2-SO3- +N2
95
85
95
85
80
63
NO2
OMe
a materials: diazonium salt, piperidine, carbon disulfide.
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Table 3. Comparison of published procedures for synthesis of S-aryl dithiocarbamtes with this
work
Reaction
conditions
Entry
Substrates
Time
Yield (%)
Nano-Cu, H2O,
Reflux
H2O, r.t.
126
225
324
422
539
ArI, CS2, HNR2
ArN2+ −BF4, CS2, HNR2
8-9 h
75-94
74-94
71-95
46-86
77-86
3 h
CuI, Liganda,
K2CO3, DMF, N2
t-BuOH, 70°C
Basic alumina,
ball milling
CuI, liganda,
DMF, 110 °C
Fe3O4@SiO2-
SO3H, NaNO2,
H2O, r.t.
−
ArI, R2NCS2 Na+
22 h
−
R2NCS2 Na+, ArI+ ArX−
4-18 h
15-20 min
ArN2+ −BF4, CS2, HNR2
64
7b
ArI, R2NCS2 Na+
22 h
55-90
75-95
−
ArNH2, CS2, HNR2
15-32 min
a N,N-dimethylglycine
b This work
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Figure 1. XRD patern of (a) Fe3O4 (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
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Figure 2. The FE-SEM images of (a) Fe3O4 (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
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Step 1:
NH2
N
2 O3SO
OSO3H, NaNO2
H2O (0.2 mL)
Grinding (5-10 min)
r.t.
G
G
aryl diazonium nano-magneto silica sulfate
Step 2:
N
2 O3SO
S
NR2
C
S
H2O, r.t.
+ CS2 + HNR2
10-25 min
G
G
95-70%
= Fe3O4@SiO2
G= H, Me, OMe, NO2, Cl, I
Scheme 1. Steps of protocol
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-H2O
Wet Fe3O4@SiO2-SO3H
2NaNO2
2HNO2
N2O3
NH2
NHNO
N=NOH
N2O3
-HNO2
G
G
G
H2O
S
NHR2 + CS2
Fe3O4@SiO2-SO3
N=NOH
Fe3O4@SiO2-SO3H
N2
HS
NH2
(II)
-H2O
G
G
(I)
Fe3O4@SiO2-SO3H
S
NR2
NR2
S
N2
S
S
N2
G
G
(III)
Fe3O4@SiO2-SO3
Scheme 2. A plausible mechanism
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