Transition metal-free procedure for the synthesis of S-aryl dithiocarbamates using aryl diazonium fluoroborate in water at room temperature

Article abstract of DOI:10.1039/c1gc00001b

A convenient, efficient and green procedure for the synthesis of S-aryl dithiocarbamates has been developed by a simple one-pot condensation of aryl diazonium fluoroborate, carbon disulfide and amine in the absence of any transition metal catalyst in water at room temperature. The reactions of a variety of substituted aryl diazonium fluoroborates, and cyclic and open chain amines, have been addressed. The products are purified by crystallization from ethanol and the process does not involve any hazardous solvent.

Full text of DOI:10.1039/c1gc00001b

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PAPER
Transition metal-free procedure for the synthesis of S-aryl dithiocarbamates
using aryl diazonium fluoroborate in water at room temperature†
Tanmay Chatterjee, Sukalyan Bhadra and Brindaban C. Ranu*
Received 1st January 2011, Accepted 14th April 2011
DOI: 10.1039/c1gc00001b
A convenient, efficient and green procedure for the synthesis of S-aryl dithiocarbamates has been
developed by a simple one-pot condensation of aryl diazonium fluoroborate, carbon disulfide and
amine in the absence of any transition metal catalyst in water at room temperature. The reactions
of a variety of substituted aryl diazonium fluoroborates, and cyclic and open chain amines, have
been addressed. The products are purified by crystallization from ethanol and the process does not
involve any hazardous solvent.
biological properties10 have led to the development of synthetic
1. Introduction
procedures for these compounds.
In recent years, there has been an intense drive towards de-
Conventional methods involve reactions of amines with thio-
veloping green chemical processes using more environmentally
phosgenes, which are not environmentally acceptable.11 Several
acceptable chemicals, reagents, solvents and catalysts.1 A part
one-pot procedures by the reactions of amines with carbon
of this drive is to avoid or minimise the use of metals in
disulfide and alkyl halides/acrylates have been reported.12
chemical reactions, as these are sometimes toxic and difficult to
Although these methods are quite satisfactory for the synthesis
dispose off properly in large quantities. Moreover, the difficulty
of alkyl dithiocarbamates, they are not greatly effective for
of their separation leaves a chance of their contamination of the
aryl dithiocarbamates. Usually, the synthesis of aryl dithio-
product. The presence of a metal, even at the lowest level, in
carbamates involves metal-mediated reactions.13 A couple of
pharmaceutical products is closely regulated. Thus, a metal free
metal-free procedures involving the reaction of the sodium salt
process is desired as a part of the requirements for industry and
of dithiocarbamic acid with diazonium chloride14a and diaryl
a clean environment.
diazonium salts in the presence of hypervalent iodine14b have
The use of large volumes of volatile, hazardous organic
been developed. However, the sodium salt of dithiocarbamic
solvents in chemical processes also poses a serious threat to
acid is difficult to prepare,14a expensive and toxic.15 Nevertheless,
the environment, because these solvents contribute significantly
the multi-component reaction is a useful and attractive tool
to chemical waste.2 Thus, reactions in water have attracted
in organic synthesis as it provides a cost- and energy-effective
considerable interest in recent times because of their envi-
process.16
ronmental acceptability and unique reactivity that cannot be
We report here a one-pot multi-component condensation
attained in conventional organic solvents.3 The development of
of aryl diazonium tetrafluoroborates, carbon disulfide and an
an efficient procedure using water as the reaction medium, and
amine in water at room temperature without using metal or
environmentally benign solvents for isolation and purification
other catalysts (Scheme 1).
of products has received high priority in the design of green
processes.4
Organic dithiocarbamates are receiving attention because of
their potential as useful synthetic intermediates,5 protecting
groups in peptide synthesis6 and linkers in solid phase organic
synthesis.7 Moreover, their occurrence in a variety of biologically
active compounds,8 their pivotal roles in agriculture9 and their
Scheme 1
Department of Organic Chemistry, Indian Association for the Cultivation
2. Results and discussion
of Science, Jadavpur, Kolkata, 700 032, India.
E-mail: ocbcr@iacs.res.in; Fax: +91 3324732805
† Electronic supplementary information (ESI) available: 1H- and 13C-
In a typical experimental procedure, an amine ◦was added to a
NMR spectra of all products in Table 1. See DOI: 10.1039/c1gc00001b
suspension of carbon disulfide in water at 0–5 C, followed by
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Table 1 Transition metal-free coupling of aryl diazonium tetrafluoroborate with dithiocarmate anions
Entry
1
R
H
Amine
Product
Yield (%)a
85
Time/h
3
Ref.
13a
2
3
H
H
90
78
3
13a
13a
3.5
4
5
H
82
88
3
3
13a
14b
4-CH3
6
4-CH3
91
2.8
7
8
4-CH3
4-CH3
85
80
3.5
3
14b
14b
9
4-OCH3
4-OCH3
90
94
2.8
2.5
14b
10
11
12
4-OCH3
4-OCH3
81
82
3.5
3
13a
14c
13
2-NO2
79
2.5
14
15
16
2-NO2
74
80
80
3
4-NO2
2.8
3
3-COCH3
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Table 1 (Contd.)
Entry
17
R
Amine
Product
Yield (%)a
84
Time/h
3
Ref.
3-COCH3
18
3-COCH3
3.5
76
19
20
4-I
4-I
3
84
91
2.8
21
22
4-I
3
3
83
92
4-CI
a Isolated yields of pure products (by 1H- and 13C-NMR).
aryl diazonium tetrafluoroborate. The mixture was then stirred
at room temperature for the required period of time (TLC).
The solid product was isolated by filtration and purified by
recrystallization from ethanol.
acid,15 our procedure is more user-friendly, using stable diazo-
nium tetrafluoroborates,17 and commercially available and cheap
carbon disulfide in place of the difficult to access and expensive
sodium salt of dithiocarbamic acid. Moreover, the present
procedure provides a much simpler operation, higher yields
of products and a wide scope for the synthesis of a library of
dithiocarbamates by the manipulation of diversely-substituted
aryl amines as precursors of diazonium fluoroborates, and cyclic
and acyclic amines, whereas the earlier method14a was restricted
to only a few substrates.
A wide range of substituted phenyl diazonium tetrafluorob-
orates underwent reactions with carbon disulfide, and cyclic
and open chain amines, by this procedure to produce the corre-
sponding dithiocarbamates. The results are summarized in Table
1. A variety of electron-donating and electron-withdrawing
substituents, such as OMe, CH3, I, NO2 and COMe, are com-
patible in this reaction, although electron withdrawing group-
substituted phenyl diazonium fluoroborates provide marginally
lower yields compared to those having electron donating groups
(Table 1, entries 5–12 vs. entries 13–19). The o, m and p-
substituents also provide equally good results. Cyclic and open
chain amines provide uniformly good yields of products. The
reactions of several cyclic amines, such as piperidine, morpholine
and thiomorpholine, were addressed.
The reactions are, in general, very clean and high yielding, and
no side product was isolated. The products are obtained in high
purity (by NMR) following a single crystallization. Reactions
scaled up to multigram quantities provided uniform results.
The starting diazonium fluoroborates were prepared easily
from the corresponding anilines by diazotization, followed by
quenching with sodium tetrafluoroborate. These are stable solid
compounds. In comparison to the earlier procedure14a using
toxic diazonium chloride and the sodium salt of dithiocarbamic
To understand the reaction pathway, we carried out two
separate experiments. It was found that CS2 underwent a
very fast (5 min) reaction with piperidine in water at 0–
5
◦C to produce piperidine-1-dithiocarbamic acid (1), which
was isolated and characterized fully by its spectroscopic (1H-
NMR, 13C-NMR and HRMS) data. This solid product upon
reaction (3 h) with phenyl diazonium fluoroborate provided the
corresponding dithiocarbamate in 86% yield. Thus, we propose
that the reaction proceeds via an SN2Ar pathway, which is
favoured over the unimolecular SN1 reaction in water; the ideal
SN1 pathway is more likely in non-nucleophilic solvents.18 The
argument for SN2Ar attack by the dithiocarbamate moiety at C-
+
1 of ArN2 gains support from the Hammett correlation plot19
of log I (where I represents the ratio of the peak intensity
of the disappearance of the starting material after 15 min
with that of the starting material at 0 min by UV analysis)
vs. s (substituent constant) for the reaction of piperidine
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with differently-substituted aryl diazonium salts under identical
reaction conditions (with the same reaction concentration)
(Fig. 1). This shows a linear correlation with a small positive
slope (r = 0.035), which strongly suggests the SN2 reaction
path, considering S–C bond formation as the rate-determining
step. It is speculated that the in situ-generated dithiocarbamate
unit attacks C-1 of the aryl diazonium salt to form transient
intermediate 2, which through N2 elimination forms the S-
aryl dithiocarbamate (Scheme 2). Water being a much weaker
nucleophile than the dithiocarbamate moiety, the possibility of
phenol formation was minimized during the process.
(190 mg, 2.5 mmol) in water (2 mL) was added piperidine
(102 mg, 1.2 mmol) drop-wise at 0–5 ◦C. After stirring for
5 min, phenyl diazonium tetrafluoroborate (192 mg, 1 mmol)
was added and the reaction mixture stirred at room temperature
(25 ◦C) for 3 h (TLC). The water layer was decanted and the
organic product purified by simple crystallization from ethanol
to provide the corresponding dithiocarbamate, piperidine-1-
carbodithioic acid phenyl ester, as a white solid (201.77 mg,
85%), mp 113–116 ◦C, IR (KBr) 2945, 2852, 1577, 1471, 1427,
1278, 1242, 1130, 1008, 976, 896, 854, 750, 684 cm-1; 1H-NMR
(500 MHz, CDCl3) d 1.73 (s, 6H), 3.99 (br, 2H), 4.28 (br, 2H),
7.41–7.48 (m, 5H); 13C-NMR (125 MHz, CDCl3) d 24.2, 25.4,
26.2, 52.0, 53.2, 129.2 (2C), 129.9, 131.7, 137.1 (2C), 195.9.
This procedure was followed for all the reactions in Table 1.
A few of these products are known compounds (see the
references in Table 1) and were easily identified by comparison
of their spectroscopic data with those previously reported. The
unknown compounds were fully characterized by their IR, 1H-
NMR, 13C-NMR and HRMS spectra, and C, H, N-analyses.
These data are given below in order of their entry in Table 1.
Morpholine-4-carbodithioic acid p-tolyl ester (Table 1, entry
6). Yellow solid (mp 131–133 ◦C); IR (KBr) 2972, 2920, 2856,
1591, 1487, 1462, 1425, 1265, 1230, 1111, 1030, 983, 804, 538,
503 cm-1; 1H-NMR (300 MHz, CDCl3) d 2.41 (s, 3H), 3.77–3.82
(m, 4H), 4.19 (br, 4H), 7.26 (d, J = 8 Hz, 2H), 7.35 (d, J = 8
Hz, 2H); 13C-NMR (75 MHz, CDCl3) d 21.6, 51.4 (2C), 66.3
(2C), 127.5, 130.1 (2C), 136.9 (2C), 140.6, 198.6; anal calc. for
C12H15NOS2: C 56.88, H 5.97, N 5.53; found: C 56.71, H 5.82,
N 5.78%.
Fig. 1 Hammett plot.
Morpholine-4-carbodithioic acid 4-methoxy-phenyl ester
(Table 1, entry 10). Yellowish solid (mp 133–135 ◦C); IR (KBr)
2970, 2926, 2948, 1589, 1570, 1491, 1456, 1415, 1249, 1166, 1111,
1028, 991, 825, 540, 524, 503 cm-1; 1H-NMR (500 MHz, CDCl3)
d 3.77–3.81 (m, 4H), 3.84 (s, 3H), 4.06 (br, 2H), 4.30 (br, 2H), 6.96
(d, J = 9 Hz, 2H), 7.37 (d, J = 9 Hz, 2H); 13C-NMR (125 MHz,
CDCl3) d 51.1 (2C), 55.4, 66.3 (2C), 114.8 (2C), 121.6, 138.6
(2C), 161.3, 199.2; HRMS calc. for C12H15NO2S2 [M + H]+:
270.0625; found: 270.0617.
Piperidine-1-carbodithioic acid 2-nitro-phenyl ester (Table 1,
entry 13). Dark grey solid (mp 92–93 ◦C); IR (KBr) 2941, 2856,
1589, 1568, 1531, 1479, 1429,1350, 1303, 1280, 1242, 1226, 1134,
1111, 1006, 972, 852, 736 cm-1; 1H-NMR (300 MHz, CDCl3) d
1.74 (s, 6H), 4.01 (br, 2H), 4.22 (br, 2H), 7.58–7.67 (m, 3H),
7.97–8.00 (m, 1H); 13C-NMR (75 MHz, CDCl3) d 24.2, 25.5,
26.4, 53.3, 125.1, 127.1, 130.8, 132.7, 139.6, 152.5, 192.3; HRMS
calc. for C12H14N2O2S2Na [M + Na]+: 305.0394; found: 305.0392.
Scheme 2
3. Experimental
General comments
Dimethyl-dithiocarbamic acid 2-nitro-phenyl ester (Table 1,
entry 14). Red-ish solid (mp 113–114 ◦C); IR (KBr) 2926,
1699, 1589, 1568, 1519,1348, 1246, 1141, 981, 854, 783, 734;
1H-NMR (500 MHz, CDCl3) d 3.52 (s, 6H), 7.61–7.66 (m,
3H), 7.97 (m, 1H); 13C-NMR (125 MHz, CDCl3) d 42.6, 45.7,
125.0, 126.7, 131.1, 132.7, 139.7, 152.7, 194.0; HRMS calc. for
C9H10N2O2S2Na [M + Na]+: 265.0081; found: 265.0081.
IR spectra were recorded on a Shimadzu 8300 FTIR spectrom-
1
eter. H- and 13C-NMR spectra were run on Bruker DPX-300
and DPX-500 instruments. HRMS were acquired on a Microtek
Qtof Micro YA263 spectrometer. All commercial reagents were
distilled before use. Aryl diazonium tetrafluoroborates were
prepared from the corresponding aniline by diazotization by
following a previously reported protocol.20
Representative experimental procedure for the condensation of
piperidine, CS2 and phenyl diazonium tetrafluoroborate (Table
1, entry 1). To a well stirred suspension of carbon disulfide
Thiomorpholine-4-carbodithioic acid 4-nitro◦-phenyl ester
(Table 1, entry 15). Yellow solid (mp 112–114 C); IR (KBr)
3093, 2914, 1597, 1575, 1516, 1469, 1413, 1342, 1282, 1139,
1840 | Green Chem., 2011, 13, 1837–1842
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1
1107, 949, 852, 740 cm-1; H-NMR (500 MHz, CDCl3) d 2.82
Morpholine-4-carbodithioic acid 4-chloro-phenyl ester (Table
(s, 4H), 4.22–4.37 (m, 2H), 4.50–4.56 (m, 2H), 7.61 (d, J = 8.5
Hz, 2H), 8.18 (d, J = 8.5 Hz, 2H); 13C-NMR (125 MHz, CDCl3)
d 27.5 (2C), 54.7 (2C), 124.5 (2C), 137.9 (2C), 138.9, 148.8,
194.3; HRMS calc. for C11H12N2O2S3 [M + H]+: 301.0134; found:
301.0135.
1, entry 22). Pale yellow solid (mp 95–96 ◦C); IR (KBr) 2968,
2920, 2856, 1572, 1471, 1421, 1386, 1265, 1230, 1112, 1091, 1030,
987, 815, 750 cm-1; 1H-NMR (500 MHz, CDCl3) d 3.80–3.86 (m,
4H), 4.27 (br, 2H), 4.31(br, 2H), 7.40–7.44 (m, 4H); 13C-NMR
(125 MHz, CDCl3) d 51.5 (2C), 66.4 (2C), 129.6 (2C), 131.4
(2C), 134.5, 136.9, 195.9; anal calc. for C11H12ClNOS2: C 48.25,
H 4.42, N 5.12; found: C 48.42, H 4.24, N 5.34%.
Piperidine-1-carbodithioic acid 3-acetyl-phenyl ester (Table 1,
◦
entry 16). Yellow solid (mp 80–81 C); IR (KBr) 2939, 2854,
1681, 1477, 1429, 1356, 1242, 1224, 1132, 1116, 1008, 970, 684
cm-1; 1H-NMR (500 MHz, CDCl3) d 1.75 (s, 6H), 4.00 (br, 2H),
4.24 (br, 2H), 7.53 (t, J = 8 Hz, 1H), 7.66 (d, J = 8 Hz, 1H), 8.03–
8.04 (m, 2H); 13C-NMR (125 MHz, CDCl3) d 24.1, 25.3, 26.2,
26.6, 52.1, 53.4, 129.1, 129.5, 132.6, 137.0, 137.7, 141.6, 194.8,
197.0; HRMS calc. for C14H17NOS2Na [M + Na]+: 302.0649;
found: 302.0648.
4. Conclusions
In conclusion, the present procedure provides a convenient and
efficient transition metal-free synthesis of aryl dithiocarbamates
by a facile reaction of aryl diazonium tetrafluoroborate, carbon
disulfide and an amine in water at room temperature. The signif-
icant advantages offered by this protocol are simple operation,
easy accessibility of reactants, the use of stable and user-friendly
diazonium tetrafluoroborate in place of diazonium chloride,
reaction in water, use of environmentally-friendly ethanol for
purification, the involvement of no materials as catalysts other
than water, reaction at room temperature (energy efficient),
access to a wide range of functionalized dithiocarbamates and
high yields of products. We believe this procedure, endowed with
several green parameters, will be an attractive alternative for the
synthesis of aryl dithiocarbamates.
Morpholine-4-carbodithioic acid 3-acetyl-phenyl ester (Table
1, entry 17). Light red solid (mp 133–135 ◦C); IR (KBr) 2856,
1683, 1421, 1406, 1357, 1232, 1111, 1030, 985, 862, 810, 538
cm-1; 1H-NMR (500 MHz, CDCl3) d 2.62 (s, 3H), 3.82–3.85 (m,
4H), 4.11 (br, 2H), 4.30 (br, 2H), 7.55 (t, J = 7.5 Hz, 1H), 7.67 (d,
J = 7.5 Hz, 1H), 8.06 (d, J = 10 Hz, 2H); 13C-NMR (125 MHz,
CDCl3) d 26.7, 51.6 (2C), 66.3 (2C), 129.4, 129.9, 131.9, 137.1,
138.0, 141.6, 196.9, 197.0; anal calc. for C13H15NO2S2: C 55.49,
H 5.37, N 4.98; found: C 55.31, H 5.65, N 4.76%.
Dimethyl-dithiocarbamic acid 3-acetyl-phenyl ester (Table 1,
entry 18). Yellow solid (mp 79 ◦C); IR (KBr) 3010, 2928, 1683,
1568, 1504, 1377, 1253, 1149, 983, 755, 684 cm-1; 1H-NMR (500
MHz, CDCl3) d 2.59 (s, 3H), 3.49 (s, 3H), 3.54 (s, 3H), 7.52 (t,
J = 8 Hz, 1H), 7.63–7.65 (m, 1H), 8.03 (d, J = 8 Hz, 2H); 13C-
NMR (125 MHz, CDCl3) d 26.7, 42.1, 45.8, 129.3, 129.7, 132.7,
137.0, 137.9, 141.5, 196.6, 197.1; HRMS calc. for C11H13NOS2
[M + H]+: 240.0547; found: 240.0511.
Acknowledgements
We are pleased to acknowledge financial support from CSIR,
New Delhi by Grant no. 01(2365)/10/EMR-II. T. C. and S. B.
are thankful to CSIR for their fellowships.
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Piperidine-1-carbodithioic acid 4-iodo-phenyl ester (Table 1,
entry 19). White solid (mp 121–122 ◦C); IR (KBr) 2937, 2854,
1562, 1469, 1427, 1379, 1242, 1226, 1132, 1112, 1006, 972, 808,
723 cm-1; 1H-NMR (500 MHz, CDCl3) d 1.74 (s, 6H), 3.97 (br,
2H), 4.26 (br, 2H), 7.18 (d, J = 8 Hz, 2H), 7.75 (d, J = 8 Hz, 2H);
13C-NMR (125 MHz, CDCl3) d 24.3, 25.5, 26.3, 52.2, 53.4, 97.0,
131.6, 138.4 (2C), 138.7 (2C), 195.0; HRMS calc. for C12H14INS2
[M + H]+: 363.9688; found: 363.9685.
Morpholine-4-carbodithioic acid 4-iodo-phenyl ester (Table 1,
entry 20). Dirty white solid (mp 148–150 ◦C); IR (KBr) 2924,
2860, 1460, 1423, 1381, 1263, 1228, 1112, 1028, 985, 804 cm-1;
1H-NMR (500 MHz, CDCl3) d 3.80 (t, J = 5 Hz, 4H), 4.11 (br,
2H), 4.30 (br, 2H), 7.18 (d, J = 8 Hz, 2H), 7.77 (d, J = 8 Hz,
2H); 13C-NMR (125 MHz, CDCl3) d 51.4 (2C), 66.3 (2C), 97.3,
130.7, 138.4 (2C), 138.6 (2C), 196.8; anal calc. for C11H12INOS2:
C 36.17, H 3.31, N 3.83; found: C 36.30, H 3.42, N 3.61%.
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1
1498, 1465, 1373, 1244, 1147, 1004, 970, 808 cm-1; H-NMR
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2H), 7.81 (d, J = 8 Hz, 2H); 13C-NMR (75 MHz, CDCl3) d 42.1,
45.7, 97.2, 131.6, 138.3 (2C), 138.5 (2C), 196.5; HRMS calc. for
C9H10INS2 [M + H]+: 323.9375; found: 323.9372.
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1842 | Green Chem., 2011, 13, 1837–1842
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