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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)
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