Synthesis and dielectric properties of the eco-friendly insulating gas thiazyl trifluoride

Article abstract of DOI:10.1039/c9ra09256k

Sulfur hexafluoride (SF₆), which is known as a superior electrically insulating and arc-quenching medium, plays a decisive role in the modern transmission and distribution network of electric energy, especially in high-voltage power networks. However, the ever-increasing usage of SF₆ also leads to the continuous escalation of atmospheric SF₆ levels, which is considered to be the main cause of the greenhouse effect. To decrease this environmental impact, eco-friendly alternatives to SF₆ have been researched for decades. To date, no significant success has been made regarding replacement gases for transmission networks. Some potential alternatives have comparatively lower global warming potential (GWP) but involve technical trade-offs. Thiazyl trifluoride, which has some excellent chemical and electric properties, is a novel substitution candidate for SF₆. In this article, an efficient synthetic route starting from sulfur monochloride and followed by ammonization and fluorination was proposed. The structures of the intermediates and the target products were determined by X-ray diffraction (XRD), infrared spectroscopy (IR), and gas chromatography-mass spectrometry (GC-MS). The effects of some determining factors on the yield and purity, including the molar ratio of the reactants, recrystallization conditions and condensation temperature, were also investigated. The results showed that the overall yield of thiazyl trifluoride was approximately 25%, while the purity could be up to 90.6% under optimal conditions.

Full text of DOI:10.1039/c9ra09256k

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Synthesis and dielectric properties of the eco-
friendly insulating gas thiazyl trifluoride†
Cite this: RSC Adv., 2020, 10, 2740
a
a
a
a
a
Jiayan Deng,
Min Peng,
Zhanyang Gao,
Yi Wang,
Baoshan Wang,
b
a
a
Wenjun Zhou, Ruichao Peng * and Yunbai Luo
*
Sulfur hexafluoride (SF
plays a decisive role in the modern transmission and distribution network of electric energy, especially in
high-voltage power networks. However, the ever-increasing usage of SF also leads to the continuous
escalation of atmospheric SF levels, which is considered to be the main cause of the greenhouse effect.
To decrease this environmental impact, eco-friendly alternatives to SF have been researched for
6
), which is known as a superior electrically insulating and arc-quenching medium,
6
6
6
decades. To date, no significant success has been made regarding replacement gases for transmission
networks. Some potential alternatives have comparatively lower global warming potential (GWP) but
involve technical trade-offs. Thiazyl trifluoride, which has some excellent chemical and electric
6
properties, is a novel substitution candidate for SF . In this article, an efficient synthetic route starting
from sulfur monochloride and followed by ammonization and fluorination was proposed. The structures
of the intermediates and the target products were determined by X-ray diffraction (XRD), infrared
spectroscopy (IR), and gas chromatography-mass spectrometry (GC-MS). The effects of some
determining factors on the yield and purity, including the molar ratio of the reactants, recrystallization
conditions and condensation temperature, were also investigated. The results showed that the overall
yield of thiazyl trifluoride was approximately 25%, while the purity could be up to 90.6% under optimal
conditions.
Received 7th November 2019
Accepted 8th January 2020
DOI: 10.1039/c9ra09256k
rsc.li/rsc-advances
5,6
boiling point. Signicant efforts have been made to study
insulation gases, and many researchers have made great progress
Introduction
SF
transmission and distribution equipment, such as gas- 7)), hydrouorocarbons, CF
insulated switchgears (GISs) and gas-insulated lines (GILs), These alternatives have higher insulation strength and lower
due to its remarkable dielectric insulation and arc-quenching GWP than SF , but they also have different shortcomings in
performance. According to the report of The Intergovern- terms of boiling point, toxicity, stability, and other aspects. For
mental Panel on Climate Change (IPCC) in 2013, the global example, although the insulation strength of c-C is approxi-
warming potential (GWP) of SF is approximately 23 000 times mately 1.25 times higher than that of SF and the GWP is far
, the liquidus temperature of c-C
is high (ꢀ8
C), and carbon deposition will occur aer discharge, which will
6
is instrumental in achieving space-saving electrical energy using substitutes such as peruorocarbons (e.g. c-C
4
F
8
, C
F N.
4 7
F (ref.
3 8
8
9,10
11,12
I, C F10O,
3 5
C F12O and C
6
6
1,2
4 8
F
6
6
higher than that of CO
global warming owing to its extreme chemical stability. The
Kyoto protocol has identied SF
as one of the six emission- affect equipment safety and insulation strength.
limiting gases. Therefore, there is an urgent need to nd
N has to be mixed with CO due to its high boiling point,
which limits its insulation and arc-extinguishing performance.
Thiazyl triuoride (NSF ) is commonly known as a chemi-
2
, and SF
6
has a cumulative effect on below that of SF
6
F
4 8
3
ꢁ
1
3,14
Similarly,
6
C F
4 7
2
4
15
a new environmentally friendly gas to replace SF
6
.
In recent years, researchers have been committed to nding
3
environmentally friendly alternatives to replace SF ; these alter- cally stable, colorless gas that is used as an important precursor
6
natives should have low GWP, high dielectric strength and low for the preparation of various sulfur–nitrogen–uorine
compounds. Recently, the results of a quantum chemical
calculation based on a structure-activity relationship model
a
Engineering Research Center of Organosilicon Compounds & Materials, Ministry of
show that NSF is most likely to be an insulating gas with a low
3
Education, College of Chemistry & Molecular Sciences, Wuhan University, Wuhan
16
greenhouse effect. Baoshan Wang et al. suggested that NSF
has excellent performance parameters: the insulation strength
at the same pressure, and the GWP
3
4
30072, P. R. China. E-mail: prc@whu.edu.cn; ybai@whu.edu.cn; Fax: +86-27-6875-
511; Tel: +86-27-6875-2511
2
b
School of Electrical Engineering and Automation, Wuhan University, Wuhan 430072, is 1.35 times that of SF
6
P. R. China
6
value is 916, which is approximately one-twentieth that of SF ,
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra09256k
while the boiling point is ꢀ27 ꢁC. Therefore, NSF
3
has been
1
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theoretically proven to be a promising alternative gas consid- equipped with a 30 m and 0.250 mm, 0.25 mm df, VF-5 column.
ering its liquidus temperature, insulation performance, and Photoelectron spectra and X-ray diffraction patterns were
greenhouse effect. Research on the synthetic route of this gas is recorded on an X-ray photoelectron spectrometer (ESCA-
a
necessary precondition for testing the comprehensive LAB250Xi, Thermo Fisher Scientic, United States) and an X-ray
performance of NSF in actual electrical equipment. diffractometer (XRD-6100, Shimadzu Corporation, Japan) with
Few reports have described the synthesis of NSF
, and these Cu-Ka radiation (l ¼ 0.154 nm).
studies have seldom focused on its electrical performance.
3
3
17
William H. Kirchhoff reported the general protocol for the
synthesis of NSF by using S and AgF
4 4
. However, Oskar Synthesis of tetrasulfur tetranitride (S N )
3
4
N
4
2
18
Glemser argued that the numerous side products were diffi-
cult to separate; he also reported a synthesis method involving
sulfur, ammonia and silver diuoride, with carbon tetrachlo-
ride as a solvent. Moreover, he suggested that the molar ratio
CCl
4
(250 mL) and S
2
Cl
2
(40 mL, 0.5 mol) were added to
ꢁ
a 500 mL three-necked ask at 0 C with stirring. Aerwards, dry
NH
3
was introduced into the three-necked ask at a ow rate of
ꢀ1
1200 mL min . The whole reaction was carried out in an ice
between the reaction materials was 1 : 1 : 6 (NH
However, the byproducts of the reaction contained hydrogen
uoride gas, which is extremely corrosive and harmful to the
3 2
: S : AgF ).
bath for 1 hour, resulting in the appearance of an orange
precipitate in a red solution. The precipitate was washed with
pure water with stirring for approximately 3 hours, isolated by
Soxhlet extraction with dry dioxane, and then recrystallized

19
20
3
environment. Clifford proposed a method in which NSF was
prepared by SF NCOF oxidation with silver diuoride. Gener-
2
4 4 4 4
from benzene to obtain pure S N crystals. To generate S N
ally, most related studies are more suitable for minor or trace
synthesis rather than large-scale production.
To verify the insulation properties of NSF and obtain further
3
insight for commercial production, a comparatively economical
crystals, the red solution was transferred to a vacuum aer
evaporation treatment with dichloromethane and recrystallized
with benzene.
The yield was 43%, and the crystal phase of S N was further
4
4
and efficient two-step route (Fig. 1) was proposed. Ammonia
conrmed by XRD (as shown in Fig. 2). According to XPS, the
percentage of S in the sample was above 99%. (N: 30.15%; S:
9.50%; C: 0.13%; O: 0.22%).
and sulfur monochloride (S
2
Cl
2
) were used as raw materials and
. In addition, some
4 4
N
were uorinated by AgF to prepare NSF
2
3
6
decisive factors were studied to maximize the yield and purity.
Experimental methods
General remarks
Synthesis of thiazyl triuoride
(3.7 g, 0.02 mol) and CCl
reactor equipped with a copper reux condenser under N
protection. The mixture was dissolved under magnetic stirring
and heated to stable reux. Then, AgF (45.7 g, 0.32 mol) was
S
4
N
4
4
(80 mL) were added to a copper
2
Some of the chemicals used in this work are potentially
dangerous due to their toxicity. Thus, the detailed information
on the MSDS of the materials used in this experiment were
determined according to the Chemical Book, and all toxic
properties are described in Table S1 in the ESI.†
2
quickly added to the reux. The whole reaction was carried out
ꢁ
at 78 C for 2 hours. The outlet of the condenser was connected
by a conduit, and the gas product was successively dried by
potassium permanganate solution and anhydrous calcium
Material and methods
chloride and nally condensed to obtain crude NSF
product. The purity of NSF
while the structure was conrmed by IR and GC-MS.
3
as the
All solvents used were anhydrous and analytical grade. Sulfur
monochloride (greater than or equal to 98%) was purchased
from Shanghai Aladdin Bio-Chem Technology Company. Sil-
ver(II) uoride was obtained from Sinopharm Chemical Reagent
Co. Ltd. NH3 and nearly 99.99% pure nitrogen gas were ob-
tained from Wuhan Xiangyun Industry and Trade Co. Ltd. The
copper reactor and condenser were obtained from Shanghai
Yanzheng Experimental Instrument Co., Ltd.
3
was 90.6%, as determined by GC,
ꢀ
+
+
GC/EI/MS (70 eV) m/z: 102.8 [M] , 32 [S] , 46.8 [NS] , 65
+
+
+
+
[
NSF] , 69.9 [SF ] , 83.9 [NSF ] , 88.9 [SF ] .
2 2 3
ꢀ
1
ꢀ1
IR: 815 cm (S–F), 945 cm (N^S).
IR spectra were recorded on a Thermo FT-IR 5700 IR spec-
trometer (KBr), and Thermo Fisher DXR was used to record
Raman spectra. GC-MS was carried out on a Varian-450 gas
chromatograph coupled to a Varian-320 m selective detector
equipped with EI detectors. The gas chromatograph was
3 4 4
Fig. 1 Two-step synthesis of NSF starting from sulfur monochloride. Fig. 2 X-ray diffraction spectrum of S N .
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3 6
Table 2 The dielectric strength of NSF and SF
a
b
Gas
SF
Pressure /MPa
Purity /%
Breakdown voltage/kV
6
0.3
0.3
100
87
35.23
45.08
NSF
3
a
b
Isolated pressure. The impurities of NSF
3 6 3 2
were SF , CCl F, and SO ,
as determined by GC-MS.
the concentration of the reactants. Therefore, the reaction of
ammonia to sulfur monochloride in a molar ratio from 6 : 1 to
Fig. 3 Configuration of the high-voltage analysis platform.
17 : 1 was studied, and the synthetic route and results are dis-
played in Table 3. The yield of 2 increased from 30.3% to 73.8%
as the molar ratio increased and then remained constant when
the amount of ammonia reached over 16 equivalents of sulfur
monochloride. Thus, the optimal molar ratio of sulfur mono-
chloride to ammonia should be 1 : 16.
The insulation performance of thiazyl triuoride
A high-voltage analysis platform was applied to evaluate the
21
insulation performance of NSF3. The conguration of the
circuit is shown in Fig. 3, and the parameters are shown in
Table 1. The measurement accuracy was within ꢂ1%.
Two tungsten–copper alloy electrodes with diameters of
Effects of recrystallization conditions on the yield of
tetrasulfur tetranitride
10 mm were employed as the test electrodes and positioned
with a 2.5 mm-long interelectrode gap. The cavity was
composed of a stainless-steel base, a sealed quartz-glass body,
a charging/extracting valve and an electrode spacing adjust-
ment screw. The unit can withstand a maximum pressure of
Sulfur was found to be the main impurity aer removal of
ammonium chloride by distilled water. Recrystallization was
one of the most important steps in the preparation of S N . In
4 4
addition to temperature, diverse types of solvent could also
directly affect the process of crystallization since the solubility
4 4
varies by material. Nevertheless, the solubilities of S N and
sulfur were extremely similar; thus, choosing an appropriate
0.7 MPa.
The gas chamber was evacuated to vacuum and then lled
with inert buffer gas aer stabilization for 20 min. The proce-
dure above was repeated three times to eliminate the effects of
other impurities in the test chamber. The experimental gas was
injected into the chamber until the pressure was equal to the
Table 3 Effects of the various molar ratios of sulfur monochloride to
ꢁ
saturated vapor pressure (absolute pressure at 20 C). An
a
ammonia on the yield of 2
increasing voltage method was applied to the discharge
chamber through a power frequency voltage to determine the
instantaneous breakdown voltage. The tests were conducted at
least 5 times with a gap of 4 min between every two breakdowns.
The breakdown voltages of NSF
conditions are shown in Table 2, which shows that the insu-
lation strength of NSF (whose purity was approximately 87%)
was 1.28 times that of SF
3 6
and SF under the same
b
Entry
S
2
Cl
2
: NH
3
Yield (%)
3
6
.
1
2
3
4
5
6
7
8
1 : 6
1 : 8
30.3
45.6
58.9
73.2
81.8
83.0
83.8
84.3
1 : 10
1 : 12
1 : 14
1 : 16
1 : 17
1 : 18
Results and discussion
Effects of the molar ratio of reactants on the yield of
tetrasulfur tetranitride
According to previous studies, the yield was greatest when
a
ꢀ
1
22
Reaction conditions: S Cl (0.19 mol), CCl (100 mL), NH at a rate of
ammonia was passed through at a rate of 900–1000 mL min
.
2
2
4
3
ꢀ
1
ꢁ
b
1000 mL min , at ꢀ4 C for 1 hour. Isolated yield.
However, the effect of ammonia on the reaction was related to
not only its injection speed but also its total amount by affecting
Table 1 The parameters of the high-voltage test device
Max output
voltage
Protective
resistor
Rated voltage
20 V
Rated capacity
10 kVA
Voltage divider
1000 : 1
2
100 kV
5 kU
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a
Table 4 Effect of cooling temperature on recrystallization yield
ꢁ
Entry
Temperature/ C
Yield (%)
b
1
2
3
4
5
6
7
5
10
15
20
25
30
35
—
b
—
27.1
38.4
50.4
52.2
48.1
a
Reaction conditions: impurity-containing S
4
N
4
was dissolved by
ꢁ
stirring with benzene, and the saturated solution was heated to 80
before cooling. No expected product was obtained.
C
b
However, sulfur crystallized aer some time, resulting in a low
yield. As shown in Table 4, the optimum cooling temperature
ꢁ
was 30 C, and several orange needle-shaped crystals of good
crystal shape were obtained at this time, while the yield was up
to 52.2%. At this point, the cooling rate was moderate, which
contributed to the formation of the S
4 4
N crystal nucleus, thus
making it easier to avoid the precipitation of sulfur. Further
heating accelerated the dissolution of S
a decrease in yield (entry 7).
4 4
N , leading to
Such efforts were made to promote the industrialization of
the route. For instance, unpuried S was reacted with AgF
4 4
Fig. 4 (a) The solubility of S N varies with temperature in three
4
N
4
2
,
solvents. (b) The solubility of sulfur varies with temperature in three which resulted in a substantial amount of NSF and effectively
3
solvents.
avoided environmental pollution by carcinogenic benzene.
However, the purication process of gases remains to be further
explored.
solvent became key to improving the yield. Accordingly,
benzene, 1,4-dioxane, and cyclohexane were selected as alter-
native solvents for recrystallization aer taking polarity and
Effects of uidizer on the yield of thiazyl triuoride
boiling point into account; therefore, the dissolution differ- This reaction was a combination of a S–N compound with
ences in various temperature phases were tested. As shown in a double-wedge cage structure and an active uoride ion
Fig. 4, the solubilities of S N and sulfur in cyclohexane were provided by silver diuoride. The reaction procedure is shown
4 4
relatively low, and the temperature sensitivities showed similar in Fig. 5. Apparently, the reactivity and mass of the active
trends, which indicated that cyclohexane cannot be used as uoride ion played key roles in the yield of NSF . We had already
3
a solvent during the recrystallization process. By contrast, the tried different kinds of uorinating agents, such as KF (with 18-
solubilities of sulfur and S N in 1,4-dioxane were higher than crown-6 as the phase transfer catalyst), CsF and AgF . The target
4
4
2
those of the other compounds. However, the solubility of sulfur product NSF3 could only be obtained by AgF . It was worth
2
was too sensitive to temperature, which resulted in the forma- noting that AgF was highly susceptible to deterioration during
2
tion of a turbid liquid and eutectoid. Both S
be well dissolved by benzene, which has a good thermosensi-
tivity to S . In general, benzene was treated as the optimal
4 4
N and sulfur can
4 4
N
solvent for recrystallization.
Furthermore, the cooling temperature of crystallization was
also a decisive factor; thus, reactions were carried out over
a temperature gradient to verify the optimal temperature.
Table 4 provides the relationship between recrystallization yield
and cooling temperature. The results showed that the solution
cooled rapidly, and the two substances were simultaneously
precipitated by supersaturation at a low temperature (lower
ꢁ
than 10 C, entries 1–2). The yield of S
4
N
4
increased obviously
from 27.1% to 52.2% with the increase in temperature from
ꢁ ꢁ
5 C to 30 C (entries 3–6). S N precipitated rst and separated
4 4
from sulfur when the temperature ranged from 10–20 C. tetranitride.
1
Fig. 5 Pathway for the synthesis of thiazyl trifluoride from tetrasulfur
ꢁ
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a
3
the loading process, which would apparently result in the loss of Table 6 Effects of reaction time on the yield of NSF
a considerable amount of raw material, resulting in a low yield.
b
c
Entry
Time /h
Yield /(%)
Therefore, we investigated the effects of AgF on the yield. As
2
shown in Table 5, the yield of NSF was found to increase from
3
1
2
3
4
5
6
0.5
1
1.5
2
2.5
3
28.12
35.35
43.03
57.15
57.54
57.68
2 4 4
21.32% to 57.38% (entries 1–5) when the AgF : S N molar ratio
increased from 8 : 1 to 16 : 1, owing to the increase in the
ꢀ
concentration of F . Aer that, the yield of NSF
3
approached
a steady state at approximately 58% upon further addition of
AgF (entry 6). Based on our ndings, it could be concluded that
the optimal molar ratio of AgF to S N was 16 : 1, considering
2
a
Reaction conditions: S
4
N
4
2 4
(3 mmol), AgF (48 mmol), and CCl
2
4 4
(waterless, 30 mL). The reaction was carried out under stirring at
economic factors and reaction efficiency.
ꢁ
b
c
7
8
C.
2
Timing began aer AgF was added. Isolated yield,
measured by GC-MS.
Effects of reaction conditions on the preparation of thiazyl
triuoride
gradually approached the boiling point of NSF , owing to the
3
NSF3 was synthesized from S N and AgF2 by ring-opening
4
4
absence of an inert carrier gas, thereby leading to a decrease in
the overall purity of the product. Therefore, it was suggested

uorination; the three S–F single bonds were formed in a step-
wise manner, which meant insufficient reaction time would
result in a low crude yield of the product. Consequently, it was
necessary to keep the reaction stable at a constant temperature
for a period of time. William H. Kirchhoff reported that the
whole process was approximately 3 hours. However, it was
found that the yield increased from 28.12% to 57.15% as the
reaction time was extended to 2 hours (as shown in Table 6).
Further extension of the reaction time had no signicant effect
on yield; thus, the time should be controlled for approximately 2
ꢁ
that the rst-stage condensation temperature should be ꢀ15 C
3
to maximize the purity of NSF .
Hence, NSF
reaction using sulfur monochloride, ammonia and silver(II)
uoride as raw materials. The total yield of NSF was 25% under
3
was successfully synthesized via a two-step

3
the optimal conditions, and the purity was over 90%.
Assessment of the thermal stability of thiazyl triuoride
hours to obtain the highest yield and maximum economic To evaluate the thermal stability of thiazyl triuoride, normal
benet.
vibration mode analysis was performed, and the vibration free
To purify the target gas, GC-MS was used to identify the energy at 298 K was estimated to predict the reaction free energy
impurities in the crude product, and SF , CCl F and SO were of the radical decomposition. The simulation of the gas phase
6
3
2
conrmed to be the main impurities. The multistage conden- radical decomposition reaction was performed with Gaussian
sation method was used for further purication, in conjunction
with a potassium permanganate solution and anhydrous
a
calcium chloride. In consideration of the boiling point of NSF
3
Table 7 Effects of condensing temperature on the purity of NSF3
and other impurity gases, ice-salt baths with different temper-
ature gradients for condensation were set up, and the impacts
on the purity are displayed below. By comparing the results
shown in Table 7, it was found that the purity increased rst and
then decreased as the temperature decreased. Moreover, the
ꢁ
b
Entry
Condensing temperature/ C
Purity /%
1
2
3
4
5
ꢀ5
49
60
90
82
75
ꢀ10
ꢀ15
ꢀ20
ꢀ25
purity of NSF reached 90% when the condensing temperature
3
was ꢀ15 ꢁC. It was speculated that this result was because
a
impurities whose boiling points were higher than that of NSF
3
4 4 2 4
Reaction conditions: S N (3 mmol), AgF (48 mmol), and CCl
(
7
waterless, 30 mL). The reaction was carried out under stirring at
were easier to liquefy and separate during the temperature
reduction process. However, the target gas was also liqueed,
and the gas ow rate decreased as the condensing temperature
ꢁ
8 C for 2 hours, and the gas mixture was condensed at different
b
temperatures. GC purity.
a
2 4 4 3
Table 5 Effects of the AgF : S N molar ratio on the yield of NSF
ꢁ
b
Entry
Molar rate (AgF
2
/S
4
N
4
)
Reaction time/h
Temperature/ C
Yield /(%)
1
2
3
4
5
6
8 : 1
2
2
2
2
2
2
78
78
78
78
78
78
21.32
32.32
44.79
53.44
57.38
58.27
10 : 1
12 : 1
14 : 1
16 : 1
18 : 1
a
b
Reaction conditions: S
4
N
4
(3 mmol), CCl
4
(waterless, 30 mL), and AgF
2
were added in the specied proportions under stirring. Isolated yield.
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3
09 soware. The geometries of all molecules were optimized by unimolecular decomposition or isomerization of NSF is
B3LYP/6-31G(d,p). The convergence threshold for geometry negligible even at extremely high temperatures (e.g., ꢄ3000 K
16
optimization was tighter than the default value (opt ¼ tight), whenever partial discharge or arc occurs).
and tight grid integration was applied to perform DFT simula-
tion (int ¼ ultrane).
Comparison with other insulating gases
The schematic illustration of radical decomposition is
shown in Fig. 6, and we consider two types of bond cleavage
between N–S and S–F to assess all the decomposition patterns.
All the structures of molecules aer geometry optimization
are listed in Fig. 7. For the rst step of radical decomposition,
one of the F or N atoms is deleted, forming a single radical
A comparison of the physical and environmental properties of
NSF and other mainstream potential substitute gases is shown
3
in Table S3.† Although c-C
ties, the GWP remains high at 8700. Besides, c-C
at high energy may precipitate carbon, which may affect the
4
F
8
has desirable insulating proper-
4 8
F
discharges
insulation capacity. C
5
F
10O and C
4
F
7
N have disadvantages of
ꢃ
ꢃ
molecule, which results in the NSF and SF as shown in Fig. 7B
ꢁ
ꢁ
2
3
their high boiling point (26.5 C and ꢀ4.7 C, respectively), so
and C.
The reaction free energy for the radical decomposition
reaction of the NSF molecule is shown in Table S2.† The bond
cleavage between F and S produces the lowest reaction energy
they need to be mixed with buffer gases to avoid the obstacle of
high boiling point to a certain extent. The gas CF I exhibits high
3
3
dielectric strength, low boiling point and GWP. However, it has
been proven that iodine precipitation can be produced with
high voltage and severe discharge, which may lead to a decline
of dielectric strength. It can be concluded from the comparison
that the performance of NSF in various aspects is relatively
3
excellent and has certain application prospects.
ꢀ1
(
58.22 kcal mol ) and decomposition into molecules B. The
other pathway produces molecules C and nitrogen radical,
resulting in a reaction energy higher than 58.22 kcal mol
Thus, it is difficult to decompose (especially radical nitrogen
atom). The decomposition from SF to SF (as shown in Fig. 7D)
ꢀ1
.
ꢃ
ꢃ
3
2
and F radical has the lowest reaction energy in this system. All
the simulation results listed above suggest the formation of SF2
ꢃ
Conclusions
radical. Furthermore, it has been conrmed that the thermal
In this paper, an efficient and convenient synthesis route of
thiazyl triuoride from sulfur monochloride was developed. It is
worth noting that this compound has the potential to be a novel
eco-friendly insulating gas to replace SF6 in high-voltage
transmission systems. Sulfur monochloride reacted with
ammonia in an ice bath to obtain tetrasulfur tetranitride.
Aerwards, tetrasulfur tetranitride was uorinated by AgF
treated with multistage condensation to produce thiazyl tri-
uoride. The conditions of the relevant reactions were also
2
and

optimized to maximize the yield and purity. The overall yield of
NSF was approximately 25%, and the purity was up to 90.6%,
3
which has not been mentioned in previous research. The
Fig.
a molecule.
6 Schematic illustration of the radical decomposition of
3
dielectric strength of NSF was conrmed to be 1.28 times that
of SF through electrical experiments, indicating that NSF
6
3
6
might be a potential alternative to SF .
Conflicts of interest
There are no conicts to declare.
Acknowledgements
The work was supported by the National Key R&D Program of
China (2017YFB0902500) and State Grid Science & Technology
Project (The Key Technology of Environmentally-Friendly Gas-
Insulated Transmission Lines). In addition, we are thankful
for the technical assistance by Wuhan University Testing Center
and School of Electrical Engineering.
Notes and references
Fig.
31G(d,p). (A) Geometry of NSF
the first step of decomposition (losing a fluorine atom). (C) Geometry
of SF after the first step of decomposition (losing a nitrogen atom). (D)
Geometry of SF resulting from the decomposition of SF
7
Geometry of molecules after optimization with B3LYP/
6
3
molecules. (B) Geometry of NSF after
2
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