OH-/silica-mediated one-pot synthesis of dithiocarbamates under solvent-free conditions

Article abstract of DOI:10.1080/10426507.2011.582593

An efficient, versatile, and environmentally benign method for the synthesis of dithiocarbamates under solvent-free conditions is reported. The Michael addition of electron-deficient alkenes with alkyl or aryl amines and CS₂ in the presence of OH^-/silica in a one-pot three-component reaction protocol gave the corresponding dithiocarbamates in good to excellent yields. This method is suitable for a wide range of amines and a variety of Michael acceptors in solvent-free conditions. The results of the present work show the desired products in excellent yields. Copyright Taylor and Francis Group, LLC 2012.

Full text of DOI:10.1080/10426507.2011.582593

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Phosphorus, Sulfur, and Silicon and the
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OH-/Silica-Mediated One-Pot Synthesis
of Dithiocarbamates Under Solvent-Free
Conditions
Ghasem Rezanejade Bardajee a , Hamid Samareh Afsari a , Seyediraj
Sadraei a & Seyedehmaryamdokht Taimoory a
a Department of Chemistry , Payame Noor University , Tehran ,
Islamic Republic of Iran
Published online: 30 May 2012.
To cite this article: Ghasem Rezanejade Bardajee , Hamid Samareh Afsari , Seyediraj Sadraei &
Seyedehmaryamdokht Taimoory (2012) OH-/Silica-Mediated One-Pot Synthesis of Dithiocarbamates
Under Solvent-Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:7,
871-878, DOI: 10.1080/10426507.2011.582593
To link to this article: http://dx.doi.org/10.1080/10426507.2011.582593
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Phosphorus, Sulfur, and Silicon, 187:871–878, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.582593
OH−/SILICA-MEDIATED ONE-POT SYNTHESIS
OF DITHIOCARBAMATES UNDER
SOLVENT-FREE CONDITIONS
Ghasem Rezanejade Bardajee, Hamid Samareh Afsari,
Seyediraj Sadraei, and Seyedehmaryamdokht Taimoory
Department of Chemistry, Payame Noor University, Tehran,
Islamic Republic of Iran
GRAPHICAL ABSTRACT
Abstract An efficient, versatile, and environmentally benign method for the synthesis of
dithiocarbamates under solvent-free conditions is reported. The Michael addition of electron-
deficient alkenes with alkyl or aryl amines and CS2 in the presence of OH−/silica in a one-pot
three-component reaction protocol gave the corresponding dithiocarbamates in good to ex-
cellent yields. This method is suitable for a wide range of amines and a variety of Michael
acceptors in solvent-free conditions. The results of the present work show the desired products
in excellent yields.
Keywords Dithiocarbamates; OH−/silica; amines; solvent-free; electron-deficient alkenes
INTRODUCTION
Carbon–sulfur bond formation is a fundamental approach to bring sulfur into organic
compounds, and this has received much attention due to its occurrence in many molecules
that are of biological and pharmaceutical importance.1,2 Organic dithiocarbamates, ubiq-
uitously found in a variety of biologically active molecules,3 are of high importance in
academia as well as in industry.4 Besides being widely used as fungicides to protect crops
from fungal diseases,5 dithiocarbamic acid esters have a number of other applications such
as in photochemistry,6 as catalyst in the sulfur vulcanization of rubber,7 and numerous
biological and medicinal properties including applications in the treatment of cancer,8 play
pivotal roles in agriculture,9 and act as linkers in solid-phase organic synthesis.10 They are
Received 5 January 2011; accepted 14 April 2011.
The authors thank Prof. M. R. Saidi’s group (Sharif University of Technology, Iran) for their useful sugges-
tions. This research project was supported by the Research Council of the Payame Noor University.
Address correspondence to Ghasem Rezanejade Bardajee, Department of Chemistry, Payame Noor Univer-
sity 19395-4697, Tehran, Islamic Republic of Iran. E-mail: rezanejad@pnu.ac.ir
871

872
G. R. BARDAJEE ET AL.
used in controlled radical polymerization techniques,11,12 and recently, in the synthesis of
ionic liquids.13 For these reasons, the synthesis of functionalized dithiocarbamates using
different substitution patterns at the thiol chain has become a field of increasing interest in
synthetic organic chemistry during the past few years. In the past, dithiocarbamic acid esters
had been prepared from the reaction of amines with expensive and toxic reagents, such as
thiophosgene and isothiocyanate.14,15 Because of some limitations such as long reaction
times, low product yields, or harsh reaction conditions, researchers are still attempting
to improve the preparation methods of dithiocarbamates. Recently, a one-pot reaction of
amines with carbon disulfide (CS2) and electrophilic reagents has been developed. Much
effort has been focused on the exploration of reaction conditions for one-pot preparation of
these compounds.15–18 Various bases, for instance, NaOC2H5, Et3N, Cs2CO3, and guani-
dine as well as different solvents such as dimethylformamide (DMF), dimethyl sulfoxide
(DMSO), and methanol have been used to catalyze or improve the reaction performance.
However, it is still a challenge to synthesize aryldithiocarbamic acid esters from aryl amines,
because few previous reports used aryl amines as low reactivity substrates to participate in
the synthesis of dithiocarbamates through Michael addition reactions.18
OH−/silica is a basic support, which is simply prepared from easily available, cheap,
and commercial starting materials.19 Owing to the basic nature of this support, it can be
considered as a good replacement for organic bases in various reactions. For example, this
catalyst was applied for the transesterification of refined sunflower oil with methanol at
323 K and atmospheric pressure.19 Herein, we describe an efficient synthesis of aryl and
also alkyl dithiocarbamic acid esters from solvent-free reaction of aryl and alkyl amines,
CS2, and electrophilic alkenes in the presence of OH−/silica as outlined in Scheme 1.
Scheme 1
RESULTS AND DISCUSSION
Herein, our contribution is intended to extend the scope of available methods for the
synthesis of dithiocarbamates via description of the use of OH−/silica as a new support
in their synthesis. Our investigations show that the Michael reaction of benzylamine with
CS2 and acrylonitrile in the presence of OH−/silica under solvent-free conditions affords
the corresponding dithiocarbamates in good yields (Scheme 1). This result developed our
interest in an efficient procedure for the synthesis of alkyl and aryldithiocarbamates.
To test the feasibility of this reaction, we initially investigated the Michael reaction
of benzylamine with CS2 and acrylonitrile under various reaction conditions. To this end,
solvents such as diethylether, DMF, acetonitrile, and dichloromethane as well as a solvent-
free medium were tested as the reaction medium. Because of the high yields and green
protocol, solvent-free conditions were found to be the best for this reaction (Table 1, entries
1–5). In the next step, the amount of OH−/silica was changed in the reaction to find the
optimum amount of support with respect to the yield of the reaction (Table 1, entries 4,
6–8). The overall yield versus a variation in temperature up to 100 ◦C was also investigated.

SOLVENT-FREE SYNTHESIS OF DITHIOCARBAMATES
873
Table 1 Screening of the conditions for the Michael reaction of benzylamine with CS2 and acrylonitrile in the
presence of OH−/silicaa
Entry
Solvent
OH−/silica (g)
Temperature (◦C)
Yield (%)b
1
2
3
4
5
6
7
8
9
Diethylether
DMF
0.1
0.1
0.1
0.1
0.1
0.05
0.15
0.2
0.1
0.1
0.1
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
50
25
48
42
64
25
45
64
64
71
Acetonitrile
Solvent-free
Dichloromethane
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
10
11
70
100
85 (81)c
85
Note: r.t., room temperature.
aAll reactions were run under the following conditions: benzylamine (1 mmol), CS2 (1 mmol), acrylonitrile (1
mmol), and OH-/silica (0.05–0.2 g) in the preferred solvent (2 mL) were heated in a sealed tube at the desired
temperature for 10 h.
bGC yields.
cIsolated yield in parentheses.
The desired product was obtained in 85% GC yield in a solvent-free green reaction medium
at 70 ◦C (81% isolated yield, Table 1, entry 10).
Having established the optimum reaction conditions, we next examined the gen-
erality of these conditions to other substrates using several alkyl or aryl amines and
electron-deficient alkenes. As shown in Table 2, the aliphatic amines including primary
amines and acyclic or cyclic secondary amines could afford the corresponding products
in high yields when reacted with a variety of Michael acceptors such as methyl acrylate,
acrylonitrile, and acrylamide (Table 2, entries 1–19). The reactivity of alkyl amines was
mainly controlled by steric and electronic effects. For example, tert-butylamine showed
lower yields compared with other primary and secondary amines (Table 2, entry 8) due to
its steric effect. The reaction of cyclic secondary amines such as pyrolidine took place in
higher yields compared with the other amines (Table 2, entries 15–18). This higher reac-
tivity can be attributed to the nucleophilicity of cyclic secondary amines versus other steric
factors. Furthermore, the nature of a Michael acceptor can influence the performance of
the reaction. For instance, by using acrylonitrile or methyl acrylate as a Michael acceptor,
all tested alkyl and aryl amines gave the expected products in good to excellent yields
(Table 2, entries 17–25), while the use of acrylamide as a Michael acceptor resulted in
moderate yields (Table 2, entry 16). The dominant mechanism for the production of dithio-
carbamates can be summarized by a nucleophilic addition of amine to CS2 followed by
the Michael addition of the corresponding thiolate anion to electron-deficient alkenes. We
believe that the basic nature of OH−/silica activates nucleophilic amine groups to attack
the desired electrophilic substrates such as CS2 or electron-deficient alkenes.20
We also examined the reusability of OH−/silica. The reusability of supported catalysts
is an important benefit and makes them useful for commercial applications. We found that
the support could be separated and reused after washing with dichloromethane and drying
at 90 ◦C. The results show that the catalyst can be used effectively three times without any
loss of its activity (Table 2, entry 5).

874
G. R. BARDAJEE ET AL.
Table 2 Dithiocarbamates obtained from the Michael reaction of electron-deficient alkenes with alkyl and aryl
amines and CS2 in the presence of OH−/silica
Entry
1
Amine 1
Compound 2
Product
Yield (%)a,b
91
Reference
17
2
3
82
76
17
17
4
5
6
93
81 (75)c
78
17, 18
17, 18
17
8
9
65
92
17
17
10
13
86
86
17
17, 18
14
15
16
83
96
60
17, 18
17, 18
17
17
92
17, 18

SOLVENT-FREE SYNTHESIS OF DITHIOCARBAMATES
875
Table 2 Dithiocarbamates obtained from the Michael reaction of electron-deficient alkenes with alkyl and aryl
amines and CS2 in the presence of OH−/silica (Continued)
Entry
18
Amine 1
Compound 2
Product
Yield (%)a,b
84
Reference
17
19
20
92
81
17
17
21
22
23
24
25
88
82
78
55
84
17
17
18
18
18
26
27
71
66
18
18
28
80
18
aIsolated yields.
bAll reactions were run under the following conditions: benzylamine (1 mmol), CS2 (1 mmol), Michael acceptor
(1 mmol), and OH−/silica (0.1 g) were heated in a sealed tube at 70 ◦C for 10 h.
cIsolated yield after three times recycling.

876
G. R. BARDAJEE ET AL.
Table 3 Comparison of our results with some previously reported data for the synthesis of dithiocarbamate 6
Catalyst
Alkyl/aryl amine applicability Temperature (◦C) Time (h) Yield (%) Reference
No catalyst (in water)
Alkaline Al2O3
OH−/silica
Only alkyl amines
Alkyl/aryl amines
Alkyl/aryl amines
r.t.
r.t.
70
5–18
10–30
0.5–10
80
80
93
17
18
This work
Note: r.t., room temperature.
The results show the wide applicability of the presented method. Some previously
reported data for the synthesis of dithiocarbamate 6 (Table 2, entry 4) were compared with
our results in terms of the applicability to alkyl and aryl amines, temperature, reaction time,
and percentage yields (Table 3). As one can see, our results show a very good comparability
with previously reported data with respect to yields, applicability, and reaction times.
CONCLUSIONS
In summary, we have described a one-pot, efficient, and novel method for the prepa-
ration of dithiocarbamic acid esters by the Michael addition of amines and CS2 to electron-
deficient alkenes in OH−/silica media. OH−/silica is an environmentally friendly and re-
cyclable catalyst, which demonstrated to be an excellent catalyst for the reaction. A wide
range of amines, especially aryl amines, reacted with CS2 and an array of Michael acceptors
to afford the Michael addition products in high yields. Furthermore, the procedure offers
several advantages including cleaner reactions, improved yields, and simple experimental
procedures, which make it a useful and attractive strategy in multicomponent reactions in
combinatorial chemistry.
EXPERIMENTAL
Materials
All amines, Michael acceptors, CS2, and solvents were commercially available and
were purchased from Merck or Sigma-Aldrich and used without further purification. The
solvents were analytical grade and used as received. The course of the syntheses was
followed by thin layer chromatography on silica gel plates (Merck, silica gel 60 F254, ready
to use), using ethyl acetate:n-hexane (1:3) as eluent.
Instrumentation
1H and 13C NMR spectra were recorded at room temperature on a Bruker AC
500 MHz spectrometer using CDCl3 or DMSO-d6 as the NMR solvents. 1H NMR spectra
are referenced to tetramethylsilane (0.00 ppm) and 13C NMR spectra are referenced from
the solvent central peak (e.g., 77.23 ppm for CDCl3). Chemical shifts are given in ppm.
Gas chromatography-mass spectrometry (electron impact) [GC-MS (EI)], 70 eV, and HP
6890 column: HP-5 (30 m × 0.25 mm × 0.2 uml MSD: HP5793) were used to record
the mass spectra. IR spectra were taken as KBr pellets on an ABB Bomem MB-100 FTIR
spectrophotometer. IR is reported as characteristic bands (cm−1) at their maximum intensity.

SOLVENT-FREE SYNTHESIS OF DITHIOCARBAMATES
877
General Procedure for the One-Pot Reaction of Amines, CS2,
and α,β-Unsaturated Olefins
The support OH−/silica was prepared according to a previously reported proce-
dure19 via using commercially available sodium hydroxide and silica gel starting materials
(Table 2, entries 1–25).17,18 The mixture was stirred at room temperature for 20 min, and
then it was concentrated in vacuo and dried in a vacuum oven at 100 ◦C for 2 h. The mixture
◦
of amine (1 mmol), CS2 (1 mmol), and OH−/silica (0.1 g) was heated at 70 C for 1 h.
Then, methyl acrylate as the Michael acceptor (1 mmol) was added, and the entire mixture
was stirred vigorously for 10 h. Finally, the solid mixture thus obtained was washed with
ethyl acetate (10 mL), and OH−/silica was filtered off. The organic solvent was removed
under reduced pressure to give the desired product. The crude product was purified by
recrystallization or column chromatography over silica gel to give the desired product. All
products were characterized by melting point, IR, and NMR, and their physical data were
similar to those reported in the literature.17,18
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