A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates from diethyl dixanthogenate using different oxidants

Article abstract of DOI:10.1007/s00706-010-0328-y

A novel synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates from diethyl dixanthogenate and primary and secondary amines, using three oxidizing systems, has been developed on the laboratory scale, and the method using sodium hypochlorite has been applied on a semi-industrial scale. The effect of the oxidizing agents, sodium hypochlorite, in-situ-generated peracetic acid, and the manganese(II) acetate/oxygen system on product purity and yield was studied. The results obtained by use of these three methods were compared with those obtained by reaction of sodium ethyl xanthogenacetate and amines, and of sodium ethyl xanthate with amines in the presence of sulfated nickel zeolite catalyst. The reaction mechanism of sodium hypochlorite oxidation has been established on the basis of isolation of reaction intermediates and determination of their structure by use of Fourier-transform infrared, ¹H and ¹³C NMR, and mass spectrometric methods. The suggested sodium hypochlorite and manganese(II) acetate/oxygen systems have many advantages in comparison with commercial and catalytically promoted synthetic methods, because they are new ecologically friendly syntheses. Springer-Verlag 2010.

Full text of DOI:10.1007/s00706-010-0328-y

Monatsh Chem (2010) 141:749–755
DOI 10.1007/s00706-010-0328-y
ORIGINAL PAPER
A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
from diethyl dixanthogenate using different oxidants
•
Milutin M. Milosavljevic Milica Sovrlic
•
´
Aleksandar D. Marinkovic Dragan D. Milenkovic
´
•
´
´
Received: 26 January 2010 / Accepted: 11 May 2010 / Published online: 29 May 2010
Ó Springer-Verlag 2010
Abstract A novel synthesis of N-alkyl and N,N-dialkyl
O-ethyl thiocarbamates from diethyl dixanthogenate and
primary and secondary amines, using three oxidizing sys-
tems, has been developed on the laboratory scale, and the
method using sodium hypochlorite has been applied on a
semi-industrial scale. The effect of the oxidizing agents,
sodium hypochlorite, in-situ-generated peracetic acid, and
the manganese(II) acetate/oxygen system on product purity
and yield was studied. The results obtained by use of these
three methods were compared with those obtained by
reaction of sodium ethyl xanthogenacetate and amines, and
of sodium ethyl xanthate with amines in the presence of
sulfated nickel zeolite catalyst. The reaction mechanism of
sodium hypochlorite oxidation has been established on the
basis of isolation of reaction intermediates and determina-
tion of their structure by use of Fourier-transform infrared,
1H and 13C NMR, and mass spectrometric methods. The
suggested sodium hypochlorite and manganese(II) acetate/
oxygen systems have many advantages in comparison with
commercial and catalytically promoted synthetic methods,
because they are new ecologically friendly syntheses.
Keywords Diethyl dixanthogenate ꢀ Thiocarbamates ꢀ
Sodium hypochlorite ꢀ Manganese(II) acetate ꢀ
Peracetic acid ꢀ Sulfated nickel zeolite catalyst
Introduction
The synthesis and properties of N-alkyl and N,N-dialkyl
O-ethyl thiocarbamates have been of interest for many
years because of their structural characteristics, for exam-
ple the direct connection of the thiocarbonyl group to
nitrogen, which contributes to their significant biological
activity [1, 2].
Thiocarbamates are derivatives of thiocarbamic acid,
thus N-alkyl and N,N-dialkyl thiocarbamates are N-alkyl and
N,N-dialkyl O-alkyl esters of thiocarbamic acid (Scheme 1).
Wide application of these selective collectors in flo-
tation of copper and zinc ores is well known [2]. They
are also fungicidal [3], bactericidal [4], herbicidal [5],
pesticidal [6], and pharmaceutically active [7] com-
pounds. A general method for their preparation is the
reaction of dithiocarbonic acid O,S-diesters in aqueous or
alcoholic solution with primary or secondary amines, and
reaction of monothiocarbonic acid O-ester chloride with
the corresponding amines [8]. Thiocarbonic esters are
obtained in a single-stage reaction of an alkaline xan-
thogenate, an amine, and an oxidizing agent [9]. Also,
synthesis of thiocarbamates from thiols and isocyanates
under catalyst-free and solvent-free conditions has been
performed [10].
´
M. M. Milosavljevic
Economics Institute, Kralja Milana 16, 11000 Belgrade, Serbia
´
M. Sovrlic
Institute Kirilo Savic, Vojvode Stepe 5, 11000, Belgrade, Serbia
´
´
A. D. Marinkovic
Faculty of Technology and Metallurgy, University of Belgrade,
Karnegijeva 4, P.O. Box 3503, 11120 Belgrade, Serbia
Besides other procedures reported in the literature [11–
15], alkyl thiocarbamates can be obtained by reaction of
sodium or potassium alkyl xanthates in aqueous solution
with primary or secondary aliphatic amines and elemental
sulfur [16]. Thiocarbamates can also be prepared by
´
D. D. Milenkovic (&)
ˇ ´
High Chemical Technological School, Kosanciceva 36,
ˇ
37000 Krusevac, Serbia
e-mail: milenkovic_dragan@yahoo.com
123

´
M. M. Milosavljevic et al.
750
presence of oxidizing agents. Synthesis of N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates from diethyl dixan-
thogenates and amines without an oxidizing agent gave
only a minor quantity of product which was difficult to
isolate from the crude reaction product. That result indi-
cates that oxidizing species are crucially important in
successful thiocarbamate synthesis. Three oxidizing
agents were used: sodium hypochlorite, in-situ-generated
peracetic acid, and the manganese(II) acetate/oxygen sys-
tem [18].
S
S
H
R1
N
H
OH
N
OR3
R2(H)
N-Alkyl or N,N-dialkyl
Thiocarbamic acid
Scheme 1
thiocarbamates
reaction of xanthogenates and amines in the presence of
nickel(II) sulfate hexahydrate as catalyst [17].
The alkyl amines used were: methylamine, dimethyl-
amine, ethylamine, diethylamine, n-propylamine, di-n-
propylamine, isopropylamine, and diisopropylamine. Study
of the reaction mechanism indicates nucleophilic attack of
the amine on the S–S bond, assisted by the oxidizing
species present, probably causes heterolytic cleavage of
that bond, producing O-ethyl thiocarbamic acid methy-
lammonium salt (3), elemental sulfur (4), and N-methyl
O-ethyl thiocarbamate (5). In addition, the oxidizing spe-
cies in the reaction media oxidizes the intermediate product
3 to the starting diethyl dixanthogenate (1) (Scheme 2).
Moreover, the results of the innovative synthesis have
been compared with those obtained by reaction of sodium
ethyl xanthogenacetate and mono and dialkyl amines [19],
an industrial method widely used for thiocarbamate pro-
duction. Catalytically promoted synthesis of N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates using sulfated nickel
zeolite catalyst [20] was performed for evaluation of the
success of the developed innovative methods.
However, reported methods for thiocarbamate synthesis
have specific disadvantages which necessitate development
of a more efficient and convenient method applicable on an
industrial scale. Nowadays, the most striking criterion for
choice of a production process is environmental friendli-
ness. Development of a process which could use raw
materials either from a commercial source or waste mate-
rial could be an optimum alternative for selection of new
production technology. One such idea is developed in this
work focused on the possibility of using the waste material
diethyl dixanthogenate (3,8-dioxa-5,6-dithiadecane-4,7-
dithione) for synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates. Diethyl dixanthogenate is an inevitably
generated oxidizing by-product from xanthate flotation
collector production plants, or it could be available as
commercial material. The main objective of this study was
to develop a novel optimum synthesis of N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates from waste diethyl
dixanthogenate using different oxidizing agents.
According to the established optimum synthetic meth-
ods 1, 2, and 3 described in the Experimental section, a
series of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
were obtained; the results are given in Table 1.
Results and discussion
From the results presented in Table 1 it is apparent that
satisfactory yields and purities of the N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates were achieved by use
of the optimum methods 1–3 developed in this work. The
best results were obtained by use of the manganese(II)
acetate/oxygen system, somewhat lower with sodium
In this work, a novel synthesis of eight N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates was developed, start-
ing from diethyl dixanthogenates and primary and
secondary mono and disubstituted alkyl amines in the
Me
S
EtO
S
H3NMe
EtO
S
EtO
N
+
2 MeNH2
+
S
+
S
OEt
H
+
S
S
S
1
2
3
4
5
S
EtO
S
H3NMe
EtO
S
+
+
2 MeNH2 +
2
2 NaOCl
2 NaCl
H2O
S
OEt
S
S
3
1
Scheme 2
123

A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
751
Table 1 Yields and purities of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates obtained according to methods 1, 2, and 3
No.
Compound
Method 1
Yield (%)
Method 2
Yield (%)
Method 3
Yield (%)
GCa (%)
GC (%)
GC (%)
5
EtOC(S)NHMe
EtOC(S)NMe2
EtOC(S)NHEt
EtOC(S)NEt2
87.2
87.0
86.0
86.8
86.2
82.5
80.1
74.0
97.9
97.8
97.0
97.6
98.0
98.4
99.6
98.9
82.8
81.3
80.0
79.4
77.7
75.3
73.1
64.9
98.6
97.4
97.5
97.8
98.3
98.0
99.1
98.6
95.8
94.6
94.6
93.0
94.8
94.7
92.0
90.2
98.7
97.6
97.9
98.2
98.4
98.8
99.0
98.6
6
7
8
9
EtOC(S)NHPr
EtOC(S)NPr2
10
11
12
a
EtOC(S)NH(i-Pr)
EtOC(S)N(i-Pr)2
GC purity
Table 2 Yields and GC purities of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates obtained by use of methods 4 and 5
hypochlorite, and lowest using in-situ-generated peracetic
acid oxidant.
Product yield is highly dependent on the structure of the
amine. Somewhat lower yields were achieved in the syn-
thesis of N,N-di-n-propyl O-ethyl thiocarbamate (82.5% by
method 1 and 75.3% by method 2), N-isopropyl O-ethyl
thiocarbamate (80.1% by method 1 and 73.1% method 2),
and the lowest yield was achieved with N,N-diisopropyl
O-ethyl thiocarbamate (74.0% by method 1 and 64.9% by
method 2). Satisfactory yields of both N,N-di-n-propyl
O-ethyl and N,N-diisopropyl O-ethyl thiocarbamates were
obtained by use of method 3. The voluminous di-n-propyl,
isopropyl, and diisopropyl groups contribute to significant
steric repulsion with diethyl dixanthogenate, which pre-
vents approach of the amine to effect nucleophilic
heterolysis of the S–S bond in the first reaction step. The
structures of amines is of vital importance in their nucle-
ophilic reactivity [21], and further kinetic studies could
provide more information about the reaction mechanism
and the rate-determining step.
No.
Method 4
Yield (%)
Method 5
Yield (%)
GCa (%)
GC (%)
5
82.4
80.9
79.6
78.2
76.8
73.9
72.0
62.8
98.4
97.2
97.2
97.8
98.1
98.0
99.2
98.8
86.0
85.4
84.6
84.9
85.7
82.0
79.5
73.6
98.6
97.4
97.5
77.8
98.3
98.0
99.1
98.6
6
7
8
9
10
11
12
a
GC purity
in agreement with literature data and undoubtedly corrob-
orate the structures of all the N-alkyl and N,N-dialkyl
O-ethyl thiocarbamates synthesized by use of methods 1–5.
Also, considering method 1, definite experimental data
have been presented for establishment of the proposed
reaction mechanism. A mechanistic study of the synthesis
of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates by use
of different oxidizing agents is of utmost significance for
optimization of laboratory synthesis and technological
development and application.
The success of the optimum innovative synthetic
methods 1–3 was compared with results obtained by use of
the well known literature method [19] (method 4), and
sulfated nickel zeolite catalyst-promoted synthesis (method
5) (Table 2).
It is apparent from Tables 1 and 2 that somewhat lower
yields of the N-alkyl and N,N-dialkyl O-ethyl thiocarba-
mates were obtained by use of methods 4 and 5. The results
indicate that all synthetic methods using an amine for
heterolytic S–S cleavage in the presence of different oxi-
dizing agents are the methods of choice for synthesis of
N-alkyl and N,N-dialkyl O-ethyl thiocarbamates. On that
basis, future studies will be focused on synthetic and
mechanistic studies of thiocarbamate synthesis in the
presence of new oxidants or new oxygen/catalyst system
combinations. Results from MS and from Fourier-trans-
form infrared (FT-IR), and 1H, and 13C NMR spectroscopy
of the N-alkyl and N,N-dialkyl O-ethyl thiocarbamates are
It was stated that the reaction mechanism of the thio-
carbamate synthesis, according to method 1, probably
proceeds via nucleophilic heterolysis of the S–S bond of
diethyl dixanthogenate (1) by an amine (2), producing ethyl
xanthic acid methylammonium salt (3), elemental sulfur
(4) finely suspended in the reaction media, and N-methyl
O-ethyl thiocarbamate (5). Subsequent oxidation of amine
salt 3 by hypochlorite ion produces diethyl dixanthogenate
(1). The proposed reaction steps are consecutively repe-
ated, i.e., the amine present performs heterolysis of the S–S
bond of the oxidatively obtained diethyl dixanthogenate
(Scheme 2).
123

´
M. M. Milosavljevic et al.
752
The quantity of sulfur obtained after filtration of the
and the highest yields (90.2–95.8%) were obtained by
using the manganese(II) acetate/oxygen system. Method 1
using sodium hypochlorite oxidant has been developed on
the laboratory scale and applied on a semi-industrial scale.
Techno-economic aspects of innovative method 1 are
extraordinary whereas, despite the high yield, method 3
does not offer the possibility of commercial application
because it requires use of high-cost equipment. Results
from the synthesis applying the commercially well known
method 4, and synthesis performed in the presence of
sulfated nickel zeolite catalyst do not offer comparable
alternatives to methods 1 and 3. In conclusion, the inno-
vative method presented is a powerful and versatile method
for preparation of N-alkyl and N,N-dialkyl O-ethyl thioc-
arbamates. This method has several unique merits, namely
simple operation, mild reaction conditions, avoidance of
hazardous organic solvents, use of moderately toxic and
inexpensive reagents, short reaction times, and high prod-
uct yields. This new environmentally benign process is a
suitable alternative to existing methods, and a significant
contribution to protection of the human environment.
reaction mixture is almost equal to the stoichiometric
quantity expected according to calculation on the basis of
the reaction yield obtained.
In the second reaction step, oxidation of the ammonium
salt of ethyl xanthic acid by hypochlorite ion gives solely
diethyl dixanthogenate, even in reactions with different
amines. It is also proved that in the reaction of diisopropyl
dixanthogenate with ethylamine and isopropylamine
according to method 1 only diisopropyl dixanthogenate is
isolated, which is a crucial proof of the second reaction
step.
Study of the reaction mechanism of thiocarbamate
synthesis performed according to method 3 was not pos-
sible by these experimental techniques. The catalytic
activity of manganese(II) ion is high enough to promote the
oxidizing power of oxygen, and the reaction probably
follows a radical mechanism, which is confirmed by
scavenging of the generated oxygen radical using 1,1-
diphenyl-2-picrylhydrazyl (DPPH).
Satisfactory reaction yields obtained by method 1 and
simple work-up on synthesis of the thiocarbamate enabled
implementation of the optimized laboratory technique on a
semi-industrial scale. Before the start of production based
on the invented procedure, the method has been the object
of a patent application [22]. Techno-economical aspects of
the implemented innovative method 1 indicate extraordi-
nary economic benefit. It was confirmed that the reaction
product was not present in water, and concentrations of
dixanthogenates have been determined to be under the
maximum contamination limit [23]. The necessary waste
water purification process is also very simple. Innovative
method 1 could be widely used for thiocarbamate synthesis
starting from different raw materials: ammonium salt [24]
and alkaline salt of O-alkyl xanthic acid [9], and waste or
commercial diethyl dixanthogenate.
Experimental
General method for the purification of diethyl
dixanthogenate on laboratory and semi-industrial
scales
Purification of waste oxidized product from xanthate pro-
duction to obtain diethyl dixanthogenate was achieved by
two successive extractions with hot distilled water and
filtration. The xanthate alkaline salt is extracted into the
aqueous solution which could be used for thiocarbamate
production according to method 1. Two filtration cakes
were collected and dried giving 55% yield of 99% pure
diethyl dixanthogenate.
Semi-industrial application of process 3 is however
strongly determined by the need to introduce oxygen at
increased pressure, use of triethylamine, and, therefore, far
lower financial gain; this does not justify application of this
method on an industrial scale.
Alternatively, for comparison, commercial diethyl dix-
anthogenate was used for synthesis of all the compounds,
and similar yields and purities were obtained (data not
presented). These results strongly indicate the usefulness of
the presented methods for synthesis of N-alkyl and
N,N-dialkyl O-ethyl thiocarbamates from commercial and
purified industrial waste material.
Conclusion
The presented work describes the optimum synthesis of
N-alkyl and N,N-dialkyl O-ethyl thiocarbamates from die-
thyl dixanthogenates and amine in the presence of different
oxidants: sodium hypochlorite, in-situ-generated peracetic
acid, or the manganese(II) acetate/oxygen system. High
conversion of starting materials into products (74.0–87.2%)
was achieved by use of sodium hypochlorite; in-situ-gen-
erated peracetic acid results in lower yields (64.9–82.8%),
Method 1: Optimum reaction conditions for synthesis
of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
using sodium hypochlorite
In a three-necked flask (250 cm3), equipped with magnetic
stirrer, dropping funnel, condenser, and thermometer,
100 cm3 water and 18.5 g (0.075 mol) 98% diethyl dixan-
thogenate were placed. During 1 h 11.4 cm3 (0.15 mol)
123

A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
753
40% methylamine solution was added with vigorous stir-
ring, and an increase of temperature to 30 °C occurred. After
that period 20.5 g (0.075 mol) sodium hypochlorite (130 g
active chlorine/1,000 cm3) was added dropwise. The tem-
perature of the reaction mixture gradually rose to 45 °C
during the course of reaction of 1.5 h, after which the
reaction was complete. In the course of the reaction sulfur
particles precipitated in a quantity corresponding almost
stoichiometrically to the reaction yield.
cake consisting mainly of sulfur (1.9 g determined ana-
lytically, precipitating as barium sulfate). The filtrate was
then transferred to a separation funnel, and the organic
phase separated as upper layer (N-methyl O-ethyl thiocar-
1
bamate, confirmed by FT-IR, H and 13C NMR, GC MS–
MS spectroscopic data; 4.9 g crude product). The aqueous
solution was transferred into a beaker and hydrochloric
acid (1:1) was added with continuous stirring until the pH
of the solution became slightly acidic (pH & 5). At the
bottom of the beaker a light yellow substance insoluble in
water was deposited, which was extracted with diethyl
ether. The solution was dried with sodium sulfate and ether
was removed by distillation. The structure was confirmed
The reaction mixture was filtered on a Bu¨chner fun-
nel, and the precipitated sulfur was separated as
filtration cake from an aqueous emulsion phase of
N-ethyl O-ethyl thiocarbamate. The product was sepa-
rated from the aqueous phase by two ethereal
extractions, the organic phase was dried with sodium
sulfate, and the ether was removed by distillation at
atmospheric pressure. Pure product was obtained by
fractional vacuum distillation at 105 °C/2 kPa (Ref. [25]
93 °C/1 kPa). N-methyl O-ethyl thiocarbamate (15.6 g)
was obtained, representing a yield of 87.2% (gas chro-
matographic (GC) purity 97.9%).
1
as ethyl xanthic acid (7.0 g) by MS, FT-IR, H, and 13C
NMR data, and its purity was determined potentiometri-
cally to be 98%.
In the second experiment, repeated as described above,
the isolated amine salt of ethyl xanthic acid (the lower
aqueous solution) was filtered to remove sulfur, and then
treated with 20.5 g (0.075 mol) sodium hypochlorite
(150 g active chlorine/1,000 cm3). The temperature was
maintained at 45 °C for 1 h. After completion of the
reaction, the reaction mixture was filtered. The filtration
cake contained pure diethyl dixanthogenate (structure
All other N-alkyl and N,N-dialkyl O-ethyl thiocarba-
mates were synthesized in an analogous manner to the
above procedure, using the appropriate amines under
reaction conditions as presented in Table 3; results of the
syntheses are given in Table 1.
1
confirmed by FT-IR, H, and 13C NMR data). A parallel
experiment was performed with diisopropyl dixanthogen-
ate in reaction with ethylamine and isopropylamine, and
analogously with the former experiment, diisopropyl dix-
anthogenate was isolated as reaction product (structure
Experimental procedures for isolation of reaction
intermediates according to method 1
1
confirmed by FT-IR, H, and 13C NMR data).
In a 250 cm3 three-necked flask equipped with magnetic
mixer, dropping funnel, condenser, and thermometer,
100 cm3 water and 18.5 g (0.075 mol) 98% diethyl dix-
anthogenate were placed. Under gentle stirring 5.7 cm3
(0.075 mol) 40% methylamine was added during half an
hour, causing the temperature to increase to 35 °C. After
that period, 20.5 g (0.075 mol) sodium hypochlorite (130 g
active chlorine/1,000 cm3) was added dropwise. After half
an hour, the reaction mixture was filtered, to give filtration
In the third experiment, the aqueous phase containing
the alkyl ammonium salt of ethyl xanthic acid was treated
with zinc(II) sulfate to precipitate the corresponding salt of
ethyl xanthic acid. The dried zinc salt was characterized
1
using FT-IR, H, and 13C NMR techniques, and atomic
absorption spectroscopy. In that way it was proved beyond
doubt that the alkyl ammonium salt of ethyl xanthic acid
was the intermediate product in the proposed reaction
mechanism presented in Scheme 2.
Table 3 Reaction conditions
No.
Diethyl
dixanthogenate
(mol)
Amine
(mol)
Sodium
hypochlorite
(mol)
Reaction
time (h)
Temperature
(°C)
for synthesis of N-alkyl and
N,N-dialkyl O-ethyl
thiocarbamates by method 1
5
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.075
0.075
0.075
0.080
0.075
0.100
0.100
0.130
2.0
2.0
2.0
2.0
2.0
3.0
3.5
4.5
30–45
30–45
30–45
30–45
30–45
40–50
40–55
40–55
6
7
8
9
10
11
12
123

´
M. M. Milosavljevic et al.
754
Method 2: Synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates analogously to method 1 using
in-situ-generated peracetic acid
Method 4: Synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates by reaction of sodium ethyl
xanthogenacetate and mono and dialkyl amines
The synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocar-
bamates using in-situ-generated peracetic acid was
performed analogously to method 1. Ethylenediamine tet-
raacetic acid (EDTA), obtained from tetrasodium EDTA
and hydrochloric acid, was used as source of acetic acid,
and sodium perborate and sodium percarbonate were used
as oxygen sources. Decomposition of sodium perborate and
percarbonate was catalyzed by addition of 100 ppm Fe(III).
The results obtained using these two oxidizing agents were
similar and only the results for the EDTA/perborate system
are presented in Table 1.
For comparison, synthesis of N-alkyl and N,N-dialkyl
O-ethyl thiocarbamates was performed by the well known
literature method [19]; results of the syntheses are pre-
sented in Table 2.
Method 5: Synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates by reaction of sodium ethyl xanthate
and mono and dialkyl amines in the presence of sulfated
nickel zeolite catalyst
Catalyst preparation [20]
Sulfated nickel/Y-zeolite catalyst was prepared by the
impregnation technique. A determined amount of the pre-
pared nickel sulfate aqueous solution was slowly added to a
known amount of Na–Y zeolite support at room tempera-
ture. The concentration of the solution was adjusted to obtain
a catalyst of approximately 7% nickel loading (Ni content
determined by atomic absorption spectroscopy). The cata-
lyst was then dried at 120 °C for 4 h and calcined from 350
to 450 °C with controlled heating rate (5 °/min). The cata-
lyst was activated by heating at 450 °C for 2 h and under a
hydrogen atmosphere at the same conditions. No differences
in catalytic activity were observed, and only results from use
of the heat-activated catalyst are presented.
Method 3: Synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates using manganese(II) acetate/oxygen
system
In a 250 cm3 three-necked flask equipped with magnetic
mixer, dropping funnel, condenser, thermometer, and
oxygen bubbling device 100 cm3 water and 18.5 g
(0.075 mol) 98% diethyl dixanthogenate were placed.
During 1 h, 11.4 cm3 (0.15 mol) of 40% methylamine
solution was added dropwise with vigorous stirring,
causing the temperature to increase to 30 °C. At this
point, 15.2 g (0.15 mol) triethylamine and 30.0 mg
(1.2 9 10-4 mol) manganese(II) acetate tetrahydrate were
added, and oxygen bubbling was started immediately. The
reaction mixture was maintained at constant temperature
of 50 °C while providing an oxygen pressure of
2 9 105 Pa for 1.0 h, after which the reaction was com-
plete. In the course of the reaction sulfur particles
precipitated in a quantity less than expected for the
reaction yield. Some elemental sulfur was probably oxi-
dized to sulfur oxides.
Synthesis of N-alkyl and N,N-dialkyl O-ethyl
thiocarbamates using sulfated nickel zeolite catalyst
To a 250 cm3 round bottom flask containing 120 cm3
deionized water, 60.4 g 81% active commercial sodium
ethyl xanthate (0.34 mol) was added, with stirring. After
the xanthate was completely dissolved, 23.2 g sulfated
nickel/Y-zeolite catalyst was added to the reactor. Sub-
sequent to addition of the catalyst, 28.9 cm3 40%
methylamine solution (0.38 mol) was added. The reactor
was then heated to 80 °C and maintained at this tempera-
ture for 16 h, followed by cooling to room temperature.
Pure N-methyl O-ethyl thiocarbamate (34.8 g, yield 86.0%,
GC purity 98.6%) was obtained by fractional vacuum
distillation at 105 °C/2 kPa. The results of the syntheses of
other N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
according to method 5 are given in Table 2.
The reaction mixture was filtered on a Bu¨chner funnel,
separating sulfur from an aqueous emulsion phase of N-
methyl O-ethyl thiocarbamate. The product was isolated
from the aqueous phase by two ethereal extractions, the
organic phase was dried with sodium sulfate, and ether was
removed by distillation at atmospheric pressure. Pure
product was obtained by fractional vacuum distillation at
105 °C/2 kPa, giving 18.7 g N-methyl O-ethyl thiocarba-
mate (yield 95.8%, GC purity 98.7%).
All other N-alkyl and N,N-dialkyl O-ethyl thiocarba-
mates were synthesized in an analogous manner to the
above procedure, using the appropriate amines; results of
the syntheses are given in Table 1.
For all N-alkyl and N,N-dialkyl-O-ethyl thiocarbamates
synthesized by the methods presented above, boiling point,
MS, FT-IR, 1H, and 13C NMR data agree with the literature
values [25–31].
123

A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates
755
Instrumental techniques used for determination of the
structures of the synthesized compounds and reaction
intermediates
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Acknowledgments This work was supported by the Ministry of
Science and Technological Development of Serbia (Project Number
142063).
123