A selenium-catalysed synthesis of thiocarbamates from nitroarenes, carbon monoxide and thiols under mild conditions

Article abstract of DOI:10.3184/030823408X360346

An improved method for the selenium-catalysed synthesis of thiocarbamates under mild conditions has been developed. With acetone as solvent, the one-pot selenium-catalysed carbonylation of nitroarenes and thiols with carbon monoxide proceeds smoothly at atmospheric pressure and ambient temperature.

Full text of DOI:10.3184/030823408X360346

JOURNAL OF CHEMICAL RESEARCH 2008
OCTOBER, 589–591
RESEARCH PAPER 589
A selenium-catalysed synthesis of thiocarbamates from nitroarenes,
carbon monoxide and thiols under mild conditions
Xiao-Peng Zhanga,b and Shi-Wei Lub*
aCollege of Chemistry and Environmental Science, Henan Normal University, Xinxiang 453007, P.R. China
bNational Engineering Research Centre for Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian 116023, P.R. China
An improved method for the selenium-catalysed synthesis of thiocarbamates under mild conditions has been
developed. With acetone as solvent, the one-pot selenium-catalysed carbonylation of nitroarenes and thiols with
carbon monoxide proceeds smoothly at atmospheric pressure and ambient temperature.
Keywords: selenium, carbonylation, thiocarbamates, carbon monoxide
Thiocarbamates are frequently employed as bactericides1
and antivirals2 in medicine and as pesticides3 and herbicides4
in agricultural applications. Their biological activities
as bioregulators5 and enzyme inhibitors6 are also well
known. Numerous methods have been developed for the
synthesis of such compounds. Carbonylation of amines
and elemental sulfur with carbon monoxide, followed by
alkylation with alkyl halides, provides an attractive process
for their preparation;7-9 however, multistep approaches are
the primary problem of this method. An alternative approach
to thiocarbamates is intramolecular rearrangements of
various derivatives. However, these methods are extremely
limited in starting materials.10,11 Thiocarbamates can also
be obtained by treating thiols with isocyanates, carbamoyl
chlorides or carbamoylimidazolium salts or by treating
chlorothioformates with amines; unfortunately, the necessary
intermediates are typically prepared directly or indirectly
from phosgene.12,13 Although oxidative coupling of aryl thiols
with amines and carbon monoxide is available, complex
and expensive catalysts are limitations associated with this
method.14 In addition to above approaches, thiocarbamates
synthesis has also been accomplished by selenium-catalysed15
or palladium-catalysed16 carbonylation of amines with
disulfides, by carbonylation of aniline with thiols mediated by
stoichiometric17 or catalytic18 selenium, and by the reaction
of trichloroacetyl chloride with thiols and amines.19 Cyclic
thiocarbamates have been reported to have been formed by
the reaction of amino thiols with carbon monoxide in the
presence of selenium.20
Recently, we demonstrated a novel one-pot approach to
thiocarbamates, i.e., catalysed by selenium, carbonylation of
nitroarenes with thiols proceeded efficiently, affording the
corresponding thiocarbamates mostly in moderate to good
yields.21 However, with an autoclave as reactor, this approach
proceeded at elevated temperature and with pressurised
carbon monoxide, leading to higher cost and inconvenience
for industrial production.
Due to the extensive applications of thiocarbamates,
development of mild synthetic methods is of great importance.
Thus, during the course of our ongoing investigations we made
efforts to explore milder conditions for our above selenium-
catalysed approach to thiocarbamates. We now report our facile
one-pot selenium-catalysed synthesis of thiocarbamates under
atmospheric pressure and ambient temperature conditions.
With acetone as solvent, the facile one-pot selenium-catalysed
carbonylation reaction of nitroarenes and thiols with carbon
monoxide proceeds smoothly under atmospheric pressure and
ambient temperature conditions, affording the corresponding
thiocarbamates mostly in moderate to good yields (Scheme 1).
Our initial studies began with an investigation of selenium-
catalysed carbonylation of nitrobenzene with propane-1-
thiol at atmospheric pressure of carbon monoxide under
various conditions. The results are summarised in Table 1. As
shown in entries 1 and 2 (Table 1), no reaction occurred in
the absence of either selenium or base, indicating that both
selenium and base were necessary for the carbonylation. The
carbonylation of nitrobenzene (5 mmol) with thiol (10 mmol)
in the presence of 5 mol% or 10 mol% of the catalyst gave
the product with similar yields (entries 3 and 4). This result
showed that 5 mol% of catalyst was sufficient. Thus, further
investigations were carried out in the presence of 5 mol% of
selenium to explore the optimised reaction conditions. The
effect of different bases, such as Et3N, KOH, NaOH, NaOAc,
and pyridine, on the selenium-catalysed carbonylation was
first examined and Et3N was shown to be superior to the
others (entries 3, 5 and 8). When one equivalent of thiol
with respect to nitrobenzene was used, only 53% yield of the
desired thiocarbamate was obtained (entry 9), whereas two
or three equivalents of propane-1-thiol afforded the product
in yields of 79% and 80%, respectively (entries 3 and 10).
The effects of solvents were also tested (entries 3, 11 and
14) and acetone was shown to be the best choice because
of the very good yield (entry 3). Furthermore, the effect of
reaction temperature was studied. The reaction was carried
out in ambient temperature to provide a good yield (entry
3), while at 50°C and at 70°C, the yields were decreased to
42% and 29%, respectively (entries 15 and 16). The results
obtained showed that the optimised reaction of nitrobenzene
was carried out with 2 equiv. of thiol in acetone and Et3N at
ambient temperature in the presence of 5 mol% of selenium
catalyst. After the reaction was completed, selenium could
be easily separated from reaction mixture by simple filtration
after its precipitation. The desired thiocarbamate was then
purified by column chromatography or by recrystallisation
from light petroleum ether.
Using the optimised reaction conditions, selenium-catalysed
carbonylations of nitrobenzene with a series of thiols and aryl
thiols were performed and the results are listed in Table 2.
Cat.Se / Et3N
NO2
+
+
+ 2 CO2
NHCOSR'
3 CO R'SH
Ambient P. Ambient T.
R
R
Scheme 1
* Correspondent. E-mail:lusw@dicp.ac.cn

590 JOURNAL OF CHEMICAL RESEARCH 2008
Table 1 Carbonylation of nitrobenzene with propane-1-thiol under various conditionsa
Entry
Se (mmol)
Base (2.5 mmol)
Thiol/mmol
Solvent (2 ml)
Reaction temperature
Yield/%b
1
2
0
Et3N
None
Et3N
10
10
10
10
10
10
10
10
5
15
10
10
10
10
10
10
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
None
Hexane
THF
DMF
Acetone
Acetone
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
Ambient temperature
50°C
0
0
0.25
0.25
0.50
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
3
79
4
Et3N
80
5c
6c
7c
8
KOH
0
NaOH
NaOAc
Pyridine
Et3N
0
0
31
9
53
10
11
12
13
14
15
16
Et3N
80
Et3N
14
Et3N
23
Et3N
32
Et3N
22
Et3N
42(15)d
29(23)d
Et3N
70°C
c
aReaction conditions: nitrobenzene, 5 mmol; atmosphere pressure of CO; ambient temperature; 15 h. bIsolated yield. Additional
0.1 ml H2O. dDiphenylurea.
The reaction proceeded smoothly under atmospheric pressure
and ambient temperature. The structures of thiols evidently
affected the reaction. Good yields were obtained when linear
chain thiols were used (Table 2, entries 1, 2, 4, 6 and 7); and
bulky thiols gave lower yields (Table 2, entries 3, 8, 9). No
reaction took place when tert-butanethiol was used due to its
steric bulkiness (Table 2, entry 5). When aryl thiols were used,
much lower yields of the corresponding thiocarbamates were
obtained due to their weak nucleophilicity. The aryl thiols
with electron-donating groups such as 4-methoxybenzenethiol
were more reactive than those with electron-withdrawing
groups such as 4-chlorobenzenethiol (Table 2, entries 11, 13).
To expand the scope of reaction substrates, various
substituted nitroarenes were employed under the same mild
conditions. As summarised in Table 3, the reaction can proceed
smoothly with many different nitroarenes, affording the desired
thiocarbamates with yields ranging from 42 to 81% with the
exception of 2-chloronitrobenzene. In addition to nitroarenes,
as an example of nitroheteroaromatics, we have performed a
carbonylation of 2-methoxy-5-nitropyridine with propane-1-
thiol and found that the reaction worked well, affording the
corresponding thiocarbamate in 77% isolated yield in 15 h
(Table 3, entry 13). Both steric hindrance and electron effects
of nitroarenes seemed to influence the reaction. The electron-
rich ones (Table 3, entries 6–13) showed higher reactivity
than the electron-deficient ones (Table 3, entries 1–5). Steric
hindrance seemed to be the reason that the nitroarenes with
substituents in the ortho-position (Table 3, entries 1, 6, 11)
were less reactive than those with substituents in the para-
Table 3 Selenium-catalysed carbonylation of propane-1-thiol
with different nitroarenesa
Entry
R
R'
Product
Yield/%b
1
2
2-Chloro
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
Propyl
2a
2b
2c
2d
2e
2f
2g
2h
2i
0
3-Chloro
57
42
43
52
54
71
73
73
72
74
81
3
4-Chloro
4
4-Bromo
5
4-Acetyl
6
2-Methyl
3-Methyl
4-Methyl
4-Ethyl
7
8
9
10
11
12
13
4-Isopropyl
2-Methoxy
4-Methoxy
2-Methoxy-5-
nitropyridine
2j
2k
2l
Propyl
2m
77
aReaction conditions: nitroarenes, 5 mmol; thiol, 10 mmol;
Se, 0.25 mmol; Et3N, 2.5 mmol; acetone, 2 ml; atmosphere
pressure of CO; ambient temperature; 15 h. bIsolated yield.
position (Table 3, entries 3, 8, 12). The combined effect of
electronic and steric factors was the most probable reason that
2-chloronitrobenzene failed to undergo this reaction (Table 3,
entry 1).
In conclusion, we have developed a facile one-pot method
for the synthesis of thiocarbamates from nitroarenes, carbon
monoxide and thiols through selenium-catalysed carbonylation
reaction at atmospheric pressure and ambient temperature.
This procedure offers many advantages including simple
starting materials, cheap catalyst, one-pot synthesis, very
mild reaction conditions, simple experimental procedures and
simple workup, which make it an attractive strategy for larger
scale production.
Table 2 Selenium-catalysed carbonylation of nitrobenzene
with different thiolsa
Entry
R
R'
Product
Yield/%b
Experimental
1
2
H
H
H
H
H
H
H
H
H
H
H
H
H
Ethyl
1a
1b
1c
1d
1e
1f
77
79
52
76
0
72
70
61
61
21
14
30
42
Propyl
Elemental selenium (99.99%) and carbon monoxide (99.9%) used
as purchased. Nitroarenes, thiols, triethylamine and acetone were
reagent grade and used without further purification. Melting points
were determined on a Taike X-4 apparatus (Beijing, China) and were
3
Isopropyl
Butyl
tert-Butyl
Pentyl
Hexyl
Cyclohexyl
Benzyl
Phenyl
4-Chlorophenyl
4-Methylphenyl
4-Methoxyphenyl
4
5
1
6
uncorrected. H NMR spectra were recorded on a Bruker DRX 400
7
1g
1h
1i
spectrometer at ambient temperature, with CDCl3 as solvent and
Me4Si as internal standard.
8
9
10
11
12
13
a
1j
General procedure for the selenium-catalysed synthesis of
thiocarbamates (1a–d, 1f–m and 2b–2m)
To a 500-ml three-neck round-bottom flask was added selenium
(0.25 mmol). The flask was sealed, subjected to a vacuum and flushed
with carbon monoxide three times in turn. Carbon monoxide was then
introduced again into the flask and the flask was connected to a bag
containing carbon monoxide. Into the flask the mixture of nitroarene
1k
1l
1m
Reaction conditions: nitrobenzene, 5 mmol; thiol, 10 mmol;
Se, 0.25 mmol; Et3N, 2.5 mmol; acetone, 2 ml; atmosphere
pressure of CO; ambient temperature; 15 h. bIsolated yield.

JOURNAL OF CHEMICAL RESEARCH 2008 591
(5 mmol), thiol (10 mmol), triethylamine (2.5 mmol), and acetone
(2 ml) was injected. The reaction proceeded at ambient temperature
with vigorous stirring for 15 h. After the apparatus was opened,
the reaction mixture was dissolved in THF and stirred for another
30 min to precipitate selenium which could be recovered by filtration.
The filtrate was concentrated and the residue was purified either by
column chromatography or by recrystallisation from light petroleum
ether to give the product thiocarbamate.
(m, 5H), 2.94 (t, J = 8.0 Hz, 2H), 2.30 (s, 3H), 1.67 (m, 2H), 1.00 (t,
J = 4.0 Hz, 3H).
N-(4-ethylphenyl)thiocarbamic acid S-propyl ester (2i): M.p. 60–
61°C(lit.21 60–61°C);1HNMR(400MHz,CDCl3)δ7.31(d,J=8.4Hz,
2H), 7.13 (d, J = 8.4 Hz, 2H), 7.12 (s, 1H), 2.94 (d, J = 7.2 Hz, 2H),
2.60 (q, J = 7.6 Hz, 2H), 1.68 (m, 2H), 1.20 (t, J = 7.6 Hz, 3H), 1.00
(t, J = 7.4 Hz, 3H).
N-(4-isopropylphenyl)thiocarbamic acid S-propyl ester (2j): M.p.
72–73°C (lit.21 72–73°C); 1H NMR (400 MHz, CDCl3) δ 7.32 (d,
J = 8.4 Hz, 2H), 7.16 (d, J = 8.4 Hz, 2H), 7.16 (s, 1H), 2.95 (t, J = 7.2 Hz,
2H), 2.88 (m, 1H), 1.68 (m, 2H), 1.22 (d, J = 7.2 Hz, 6H), 1.00 (t,
J = 7.4 Hz, 3H).
N-Phenylthiocarbamic acid S-ethyl ester (1a): M.p. 67–68°C (lit.18
1
67–68°C); H NMR (400 MHz, CDCl3) δ: 7.43–7.09 (m, 6H), 2.99
(q, J = 7.4 Hz, 2H), 1.35 (t, J = 7.4 Hz, 3H).
N-Phenylthiocarbamic acid S-propyl ester (1b): M.p. 83–84°C
1
(lit.18 83–84°C); H NMR (400 MHz, CDCl3) δ 7.42–7.07 (m, 6H),
N-(2-methoxylphenyl)thiocarbamic acid S-propyl ester (2k):
Colourless oil (lit.21 colourless oil); 1H NMR (400 MHz, CDCl3)
δ 8.16 (d, J = 7.6 Hz, 1H), 7.69 (s, 1H), 7.01–6.82 (m, 3H), 3.81 (s,
3H), 2.94 (t, J = 7.2 Hz, 2H), 1.68 (m, 2H), 1.00 (t, J = 7.4 Hz, 3H).
N-(4-methoxylphenyl)thiocarbamic acid S-propyl ester (2l): M.p.
72–73°C (lit.21 71–72°C); 1H NMR (400 MHz, CDCl3) δ 7.32–7.30
(d, J = 8.8 Hz, 2H), 7.23 (s, 1H), 6.83 (d, J = 8.8 Hz, 2H), 3.78 (s,
3H), 2.94 (t, J = 7.2 Hz, 2H), 1.67 (m, 2H), 0.99 (t, J = 7.4 Hz, 3H).
N-(6-methoxypyridine-3-yl)thiocarbamic acid S-propyl ester (2m):
2.95 (t, J = 8.0 Hz, 2H), 1.68 (m, 2H), 0.99 (t, J = 8.0 Hz, 3H).
N-Phenylthiocarbamic acid S-isopropyl ester (1c): M.p. 112–
1
113°C (lit.18 112–113°C); H NMR (400 MHz, CDCl3) δ 7.43–7.09
(m, 6H), 3.72 (m, 1H), 1.39 (d, J = 6.9 Hz, 6H).
N-Phenylthiocarbamic acid S-butyl ester (1d): M.p. 73–74°C (lit.18
1
73–74°C); H NMR (400 MHz, CDCl3) δ7.42–7.08 (m, 6H), 2.98 (t,
J = 8.0 Hz, 2H), 1.64 (m, 2H), 1.42 (m, 2H), 0.93 (t, J = 8.0 Hz, 3H).
N-Phenylthiocarbamic acid S-pentyl ester (1f): M.p. 47–48°C
(lit.18 47–48°C); 1H NMR (400 MHz, CDCl3) δ7.59 (brs, 1H), 7.41–
7.05 (m, 5H), 2.95 (t, J = 8.0 Hz, 2H), 1.64 (m, 2H), 1.33 (m, 4H),
0.87 (t, J = 8.0 Hz, 3H).
1
M.p. 66–67°C (lit.21 66–67°C); H NMR (400 MHz, CDCl3) δ 8.11
(d, J = 2.4 Hz, 1H), 7.79(d, J = 7.6 Hz, 1H), 7.52 (s, 1H), 6.71 (d,
J = 8.8 Hz, 1H), 3.91 (s, 3H), 2.94 (t, J = 7.2 Hz, 2H), 1.67 (m, 2H),
0.99 (t, J = 7.4 Hz, 3H).
N-Phenylthiocarbamic acid S-hexyl ester (1g): M.p. 69°C (lit.18 69°C);
1H NMR (400 MHz, CDCl3) δ7.41–7.08 (m, 6H), 2.96 (t, J = 8.0 Hz,
2H), 1.65 (m, 2H), 1.38 (m, 2H), 1.29 (m, 4H), 0.88 (t, J = 8.0 Hz, 3H).
N-Phenylthiocarbamic acid S-cyclohexyl ester (1h): M.p. 115–
1
116°C (lit.18 115–116°C); H NMR (400 MHz, CDCl3) δ 7.42–7.03
1
Supplementary material such as copies of H NMR spectra
(m, 6H), 3.54 (t, J = 3.6 Hz, 1H), 2.05–1.27 (m, 10H).
N-Phenylthiocarbamic acid S-benzyl ester (1i): M.p. 97–98°C (lit.18 97–
98°C); 1H NMR (400 MHz, CDCl3) δ7.31–6.99 (m, 11H), 4.13 (s, 2H).
N-Phenylthiocarbamic acid S-phenyl ester (1j): M.p. 122–123°C
(lit.18 122–123°C); 1H NMR (400 MHz, CDCl3) δ 7.63–7.08 (m, 11H).
N-Phenylthiocarbamic acid S-4-chlorophenyl ester (1k): M.p.
147–148°C (lit.18 147–148°C); 1H NMR (400 MHz, CDCl3) δ 7.52–
7.10 (m, 10H).
N-Phenylthiocarbamic acid S-4-methylphenyl ester (1l): M.p. 131–
132°C (lit.18 131–132°C); 1H NMR (400 MHz, CDCl3) δ 7.50–7.08
(m, 10H), 2.38 (s, 3H).
N-Phenylthiocarbamic acid S-4-methoxyl-phenyl ester (1m): M.p.
109–110°C (lit.18 109–110°C); 1H NMR (400 MHz, CDCl3) δ 7.52–
6.93 (m, 10H), 3.81 (s, 3H).
of the thiocarbamates can be available by contacting us.
Received 16 May 2008; accepted 6 August 2008
Paper 08/5283 doi: 10.3184/030823408X360346
Published online: 10 October 2008
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