Sulfides and Disulfides of s-Triazine: Potential Thermal Thiyl Radical Generators

Article abstract of DOI:10.1002/chem.201802427

A series of aliphatic and aromatic thioethers and dithioethers of s-triazine were synthesised to study their thermal properties, in particular the thermally induced thiyl radical generation ability. Four symmetric s-triazine sulfides of the type (RS)₃C₃N₃, namely 2,4,6-tris(phenylthio)- (1), 2,4,6-tris(para-tolylthio)- (3), 2,4,6-tris(ethylthio)- (5) and 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7), as well as four symmetric s-triazine disulfides of the type (RSS)₃C₃N₃, namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(ethyldithio)- (6) and 2,4,6-tris(tert-butyldithio)-1,3,5-triazine (8) were synthesised. All compounds were comprehensively characterised by ¹H and ¹³C NMR, infrared and Raman spectroscopy as well as elemental analyses. Single-crystal X-ray diffraction analyses of 1, 2 and 5 are discussed. The thermal behaviour was studied by thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and quantum chemical calculations. Limiting oxygen index (LOI) flammability tests showed that the disulfides are the most promising radical generators, and are most likely suitable flame retardants for selected polymers.

Full text of DOI:10.1002/chem.201802427

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Accepted Article
Title: Sulfides and Disulfides of s-Triazine: Potential Thermal Thiyl
Radical Generators
Authors: Carl-Christoph Höhne, Christian Posern, Uwe Böhme, and
Edwin Kroke
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Chemistry - A European Journal
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Sulfides and Disulfides of s-Triazine: Potential Thermal Thiyl Rad-
ical Generators
Carl-Christoph Höhne*,[a,b], Christian Posern , Uwe Böhme and Edwin Kroke
[a]
[a]
[a]
Abstract: A series of aliphatic and aromatic thioethers and dithio-
ethers of s-triazine were synthesized to study their thermal proper-
ties, in particular the thermally induced thiyl radical generation ability.
we synthesized aryl- and alkyl-substituted thio- and dithio-s-
triazines and studied their thermal properties and capacity for
thermally induced thiyl radical formation.
Four symmetric s-triazine sulfides of the type (RS)
,4,6-tris(phenylthio)- (1), 2,4,6-tris(para-tolylthio)- (3), 2,4,6-
tris(ethylthio)- (5) and 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7), as
well as four symmetric s-triazine disulfides of the type (RSS)
namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4),
,4,6-tris(ethyldithio)- (6) and 2,4,6-tris(tert-butyldithio)-1,3,5-
triazine (8) were synthesized. All compounds were comprehensively
3 3 3
C N , namely
Trithiocyanuric acid is well-known in the literature[11] and
dates back to Hofmann[12] and Klason[13] in 1885. Aryl- and alkyl-
substituted thiocyanurates are also known: in parallel to our
study, Mehrotra and Angamuthu[ studied the synthesis and the
single crystal structure of eight aryl-substituted thiocyanurates.
They showed that arylthiols - even sterically demanding arylthi-
2
14]
3 3 3
C N ,
2
ols - react with cyanuric chloride with high yields in the range of
1
13
[14]
characterized by H and C NMR, infrared and Raman spectroscopy
as well as elemental analyses. Single-crystal X-ray diffraction anal-
yses of 1, 2 and 5 are discussed. The thermal behavior was studied
by thermogravimetric analyses coupled with mass spectrometry
87% to 62%.
The thermal analysis of these compounds
showed thermal stability at 230 °C to 280 °C.[ The main de-
composition step occurs below 400 °C. Most of them decom-
pose or volatilize with one single decomposition step.[ Further
studies with arylthiocyanurates used as anti-cancer agents[ or
synthesized by C-S cross-coupling reactions of thiocyanuric acid
and aryl halides[16] are reported. To the best of our knowledge,
the first reported syntheses of aryl-substituted thiocyanurates
were carried out by Klason[ in 1886. He synthesized phenyl-
thiocyanurate and p-tolylthiocyanurate from cyanuric chloride
14]
14]
15]
(TGA-MS) and quantum chemical calculations. LOI flammability
tests showed that the disulfides were the most promising radical
generators, and were most likely to be suitable flame retardants for
selected polymers.
13]
Introduction
and sodium thiolates.[13] Hofmann[12] and Klason[13] also men-
tioned alkyl-substituted thiocyanurates, with methyl-[
12,13]
, ethyl-
In a previous paper, we presented the first representatives of the
new class of arylthio-substituted s-heptazines.[1] Arylthiocya-
melurates are able to release thiyl radicals during thermal de-
composition.[1] Thiyl radicals are known to be a species with
flame retardant effects.[2–5] Our model arylthio-substituted s-
[13]
and n-pentyl-[13]substituents. Further examples are given in
the literature.[12,17] Beside the substitution of the s-triazine core
with three thio groups, substitution with mixed groups (thio-, oxy-,
amino-) is also known.[18] One example is Irganox® 565 (BASF),
an antioxidant with two octylthiol groups and one amino-2,6-di-
heptazine molecule, triphenylthiocyamelurate (C
6
H
5
S)
3
C
6
N
7
,
tert-butylphenol group as an antioxidant group[19]
.
[
1]
decomposes thermally at around 393 °C. This decomposition
temperature could be too high for thermoplastics like polyeth-
ylene, polystyrene or polypropylene to achieve outstanding
flame retardancy. Thiyl radical generation in the temperature
range just above the polymer processing temperature between
Hitherto, aryl- and alkyl disulfides of s-triazine are not further
discussed in the literature. In Japanese patents the synthesis of
2,4,6-tris(isopropyldithio)-1,3,5-triazine by sulfenylation of thio-
cyanuric acid with N-cyclohexyl-N-isopropylthio-2-
[
20]
benzothiazolesulfonamide is mentioned , as is the reaction of
200 °C and 300 °C should be more effective for these thermo-
thiocyanuric acid with chlorinated 2-propanethiol[ and its use
21]
plastics. Besides, it is known that almost all s-heptazine deriva-
[22]
as scorch inhibitors
in polymers. A synthesis route for 2,4,6-
[
6]
tives such as melem C
6
N
7
(NH
or cymeluric acid C
pounds such as the azide C (N
2
)
3
and its derivatives like
[23]
tris(n-dodecyldithio)-1,3,5-triazine and an application of 2,4,6-
tris(n-octyldithio)-1,3,5-triazine[24] has been described in the
literature.
[6,7]
[6]
C
6
N
7
2
(NR )
3
6
N
7
(OH)
3
and related com-
N
7
3
) [
3
6,8]
are significantly more
6
stable than the corresponding s-triazine derivatives melamine
Disulfide bonds connecting two s-triazine rings have also been
reported.[2,3,25,26] However, this bond type is not the subject of
our present study.
2 3
)
[9], cyanuric acid
C
C
3
N
N
3
(NH
(OH)
2
)
3
[6], its derivatives
C
3
N
3
(NR
[9]
[8,10]
3
3
3
and C
3
N
3
(N
3
)
3
.
According to these hypotheses,
To the best of our knowledge, a comprehensive discussion
of the synthesis and characterization of s-triazines with a tri-fold
substitution by aryl and alkyl disulfides and a corresponding
comparison with s-triazine and s-heptazine monosulfides is
missing in the literature. All these classes of compounds are
considered as potentially promising halogen-free flame retard-
ants.
[
[
a]
C.-C. Höhne, C. Posern, Priv.-Doz. Dr. U. Böhme, Prof. Dr. E. Kroke
Institut für Anorganische Chemie, TU Bergakademie Freiberg
Leipziger Straße 29, 09599 Freiberg (Germany)
E-mail: kroke@tu-freiberg.de
b]
C.-C. Höhne
Fraunhofer-Institut für Chemische Technologie ICT
Joesph-von-Fraunhofer Str. 7, 76327 Pfinztal (Germany)
E-mail: carl-christoph.hoehne@ict.fraunhofer.de
Results and Discussion
Supporting information for this article is provided via a link at the end
of the document.
Syntheses of s-thiotriazines
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For our study, we used the historical synthesis path[13]. Cyanuric
chloride was reacted with the sodium salts of thiophenol, 4-
methylthiophenol, ethanethiol and 2-methylpropane-2-thiol in the
ratio of one-to-three to obtain 2,4,6-tris(phenylthio)-1,3,5-
triazine (1),
2,4,6-tris(p-tolylthio)-1,3,5-triazine (3),
2,4,6-
tris(ethylthio)-1,3,5-triazine (5) and 2,4,6-tris(tert-butylthio)-1,3,5-
triazine (7), see Figure 1. All four compounds were character-
ized using H and 13C NMR spectroscopy, ATR-FTIR spectros-
copy, Raman spectroscopy, elementary analysis and melting
point. From compounds 1 and 5 single crystals were obtained
and analyzed using a single-crystal X-ray diffraction technique.
The thermal behaviour was studied by thermogravimetric analy-
sis. The sodium salts of the four thiols were produced using
elementary sodium.
1
Syntheses of s-dithiotriazines
In our study, we used the reaction of a chlorinated thiol with a
second thiol to form a disulfide bond between these two thiols.
Both, the sulfenyl chloride of thiocyanuric acid[26,27] and the syn-
thesis of sulfenyl chlorides of aryl- and alkyl thiols[28] are known.
Following the synthesis method described in the literature for
2
,4,6-tris(isopropyldithio)-1,3,5-triazine[21]
,
we used sulfenyl
chloride of the aryl and alkyl thiols but used the sodium salt of
thiocyanuric acid instead of thiocyanuric acid. Sodium thiocyanu-
rate was reacted with sulfenyl chlorides of thiophenol, 4-
methylthiophenol, ethanethiol and 2-methylpropane-2-thiol in the
ratio of one-to-three to obtain 2,4,6-tris(phenyldithio)-1,3,5-
triazine (2),
tris(ethyldithio)-1,3,5-triazine (6) and 2,4,6-tris(tert-butyldithio)-
,3,5-triazine (8) - see Figure 1. Compounds 2, 4, and 6 were
2,4,6-tris(p-tolyldithio)-1,3,5-triazine (4),
2,4,6-
1
Figure
1
Aromatic (1-4) and aliphatic (5-8) s-thiotriazines and
1
13
s-dithiotrianzines synthesised for this study.
characterized using H and C NMR spectroscopy, ATR-FTIR
spectroscopy, Raman spectroscopy, elementary analysis and
melting point. From compound 2 single crystals were obtained
and analysed using the single-crystal X-ray diffraction technique.
The thermal behaviour was studied by thermogravimetric analy-
sis. The sulfenyl chlorides of the four thiols were produced using
sulfuryl chloride. Purification is a frequent problem in triazine
derivative synthesis. The raw product is obtained as a liquid with
high viscosity caused by reactant-product and solvent-product
interactions. Often repeated trituration of the liquid product with
NMR spectroscopy
As reported[14] for tris-arylthiotriazines, the NMR spectra of thio-
triazines and dithiotriazines indicate a C3 symmetry at common
solution NMR conditions. 13C NMR spectroscopy was used to
study the electronic effects (indicated by a chemical shift) of the
sulfide bond and the disulfide bond on the aryl group.
The 13C NMR spectra for the aryl derivatives (1-4) are shown in
Figure 2 and the signals of the phenyl group of 1 and 2 are
shown in Figure 3.
a
volatile solvent removes impurities and solidification is
achieved. However, the impurities of compound 8 remain, even
after column chromatography.
Figure 2. 13C NMR spectra of 1-4.
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Figure 3. 13C NMR signals of the phenyl groups of 1 (red) and 2 (blue). The
13
C NMR signal assignment by 2D NMR measurements are given in the
supporting information.
All four aryl derivatives show one peak of the triazine core at
about 180 ppm. In comparison to the aryl thiotriazines, this
Figure 4. ATR-FTIR (top) and Raman (bottom) spectra of 1 and 2.
signal is shifted downfield by 0.7 ppm for the aryl dithiotriazines.
The pattern of the 13C NMR phenyl group shifts of 1 and 2 in
Description of crystal structures (1, 2, 5)
Single crystals of compound 1, 2, and 5 were grown by cooling
crystallization from n-heptane. Single crystal X-ray diffraction
analysis of these crystals allows access to the structural param-
eters.
Compound 1 crystallizes with two crystallographically inde-
pendent molecules in the monoclinic space group I2/c with an
angle β = 100.740(3)°. The alternative setting C2/c has a larger
angle β of 133.022°. The crystal structure of 1 was already re-
ported.[14] Data from our structure determination are included
here for comparison with the other structures (see Figure 5 and
supporting information).
Figure
(
3
show
a
different electronic character for the
mono)sulfide and disulfide bond. In comparison to 1, the 3C
1
NMR signals of the phenyl core carbon atoms of 2 on position b
and d are shifted upfield and the signals a and c are shifted
downfield. This suggests that in the (mono)sulfide, the sulfide
substituent creates an –M effect on the phenyl group. However,
the main effect of the disulfide substituent is an -I effect on the
phenyl group due to the partially positive sulfur atom of the
disulfide bond caused by strong lone pair interactions between
the two sulfur atoms[29]
.
ATR-FTIR and Raman spectroscopy
As expected, the ATR-FTIR and Raman spectra of the thiotria-
zines and dithiotriazines are quite similar. The main differences
-1
can be seen at the Raman spectra around 500 cm , a typical
area for disulfide bonds[30]. Figure 4 shows the ATR-FTIR and
Raman spectra of 1 and 2. Table 1 shows the Raman signals for
-1
the dithiotriazines at about 500 cm .
Figure 5. One crystallographically independent molecule of 1. The thermal
displacement ellipsoids of the non-hydrogen atoms are drawn at the 50 %
probability level.
Table 1. Raman signals for 2, 4 and 6 indicating the disulfide bond.
#
2
4
6
5
37
533 529
494 496
466 465
-
1
Wave number [cm ]
503
64
3 3
The bond lengths and angles in the C N core are in the ex-
pected range[31] for all three structures. The bond lengths from
the triazine carbon to the sulfur atom are 1.75 Å (mean value) in
4
1. The S-C-bonds to the phenyl groups in 1 are somewhat long-
er with a mean value of 1.771 Å. The ipso-carbon atoms of the
phenyl groups of 1 are nearly in plane with the triazine unit. This
is indicated by the torsion angles of -2.4° to 7.9° (see Table S2).
The phenyl groups themselves are orientated perpendicularly to
the triazine plane of 1.
The molecular structure of 2 is shown in Figure 6 and nu-
meric values for bond lengths and angles as well as further
information on the structure analysis are listed in the supporting
information. The bond lengths from the triazine carbon atoms to
the sulfur atoms are somewhat longer in 2 than in 1, with a
mean value of 1.769 Å. The S-C-bonds to the phenyl groups in 2
have a mean value of 1.782 Å.
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Figure 6. Molecular structure of 2. The thermal displacement ellipsoids of the
non-hydrogen atoms are drawn at the 50 % probability level.
Differences between structures 1 and 2 arise mainly from the
different orientation of the substituents at the triazine unit. The
sulfur-sulfur bond in 2 adds additional flexibility for possible
orientations of the phenyl groups. All six sulfur atoms lie nearly
in plane with the triazine core with a maximal deviation of 8.6°
for the torsion angle N2-C1-S1-S2. The phenyl groups are rotat-
ed out of this plane with torsion angles C-S-S-C around ± 90°.
Figure 8. Intermolecular interaction of 2 (carbon: grey, nitrogen: light blue,
sulfur: yellow, hydrogen: not drawn, center of triazine ring: purple, center of
phenyl ring: red; distance: [Å]).
Intermolecular interactions of compound 5 are given in Fig-
ure 9 and Table 2. Two molecules of 5 are connected by inter-
...
molecular S(lp) π interaction with a distance (DS(lp)...π) of
The molecular structure of 5 is shown in Figure 7 and nu-
meric values are listed in the supporting information. The bond
lengths from the triazine carbon atoms to the sulfur atoms are
similar to those in 1 with a mean value of 1.748 Å. The S-C-
bonds to the ethyl groups in 5 have a mean value of 1.815 Å.
These bonds are longer than all other C-S-bonds discussed in
this paper. The reason is the lower electronegativity of the ethyl
group in comparison to the phenyl groups. The ethyl groups are
in plane with the triazine unit with torsion angles N-C-S-C close
to 0°. Only one methyl function (C7) of the ethyl group –C6-C7 is
out of the triazine plane.
3.524 Å. These dimers are connected to an adjacent dimer by
hydrogen...πtriazine ring interaction with
a distance (DH...π) of
2.726 Å. The out of plane methyl function (C7) is located be-
tween the S(lp)...π connected molecule dimers.
Figure 9. Intermolecular interaction of 5 (carbon: grey, nitrogen: light blue,
sulfur: yellow, hydrogen (calculated): white, center of triazine ring: purple;
distance: [Å]).
Figure 7. Molecular structure of 5. The thermal displacement ellipsoids of the
non-hydrogen atoms are drawn at the 50 % probability level.
Table 2 Distances of intermolecular interactions of 2 and 5.
Intermolecular interactions of compound 2 are shown in Fig-
ure 8. The molecules of crystalized 2 form double layers con-
#
2
Centroid
3.443
Plane
3.386
3.436
2.720
3.499
S-Ph
.
..
nected by S(lp)
πTriazine ring interaction with a distance (DS(lp)...π) of
S-Triazine core
H-Triazine core
S-Triazine core
3.528
2.726
3.524
3.528 Å. One of the three phenyl groups is located in the double
5
.
..
layer by S(lp)
πPhenyl ring interaction with a distance (DS(lp)...π) of
3.443 Å. Both other phenyl groups are located in the area be-
tween two double layers.
Thermal behaviour
For application, for example as flame retardants, the melting
point (mp) of a new compound is important. In polymer pro-
cessing materials are often easier to process if they are liquid at
processing temperatures, e.g. because blending or infiltration of
fibre reinforcements are more feasible.
The four aryl triazines are solids at room temperature. Their
mps are given in Table 3. Both dithiotriazines 2 and 4 melt at
lower temperatures than their thiotriazine analogs 1 and 3. The
alkyl triazines 5 and 7 are liquid at room temperature but 5 do
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not recrystallize at room temperature after melting. Like 6 and 8,
compound 5 is a liquid with high viscosity at room temperature.
Table 3. Melting point (mp) of compounds 1-7.
#
1
2
3
4
5
23-
6
7
mp [°C]
97-
93-
94
116-
117
95-
96
<23
147
9
8
25
Literature 97[13]
114[13]
27[13]
The thermal behaviour of the derivatives, especially the de-
rivatives of the disulfides, is of great interest for future applica-
tions. It is known, that organic disulfides act as thiyl radical gen-
erators. However, in one of our previous studies we were able to
show the thermally initiated thiyl radical generation of the
s-heptazine analog (triphenyl thiocyamelurate) of 1.[1] On the
basis of this knowledge, we started thermal studies with alkyl
and aryl thiocyanurates and dithiocyanurates. Table 4 shows the
results of TGA measurements.
Figure 10. TGA of the compounds 1, 3, 5 and 7.
However, for the dithiocyanurates 2, 4, and 6 a stepwise
thermal decomposition is observed (see Table 4). The main
decomposition products detected by TGA-MS measurements
are shown in Figure 11, Figure 12 and Figure 13. All three Fig-
ures show important MS signals observed during the thermal
decomposition which indicate the release of expected molecule
fragments. Due to large differences in the MS signal intensity,
four separate MS plots are shown for each component.
Table 4. TGA results of compounds 1-7.
#
Onset tem-
perature [°C]
291
Mass loss [%]
1
2
total
41.4
223
2
5
97
67
39.1
10.0
at 995
349
240
4.8 (residual mass)
total
74.1
3
4
504
9.4
at 995
231
228
11.3 (residual mass)
total
78.8
5
6
565
19.2
at 995
219
2.0 (residual mass)
total
7
Table 5. Temperature at which compounds 1-7 reach a 2.0 % mass loss.
#
1
2
3
4
5
6
7
T [°C]
223
210
283
217
158
184
157
[
1]
In contrast to thiocyamelurates , the thiocyanurates 1, 3, 5
and 7 (see Figure 10) show just one thermal effect – the com-
plete transition into the gaseous phase. All four aryl and alkyl
thiocyanurates decompose above 210 °C. Incorporation into
polymeric materials with low processing temperatures like poly-
ethylene and polypropylene seems to be possible.
Figure 11. TGA-MS results of 2 (* smoothed signals).
The thermal decomposition of 2 shows three decomposition
steps. During the first and second decomposition step at 223 °C
and 297 °C, a mass loss of around 40 % for each step is ob-
served. An explanation for this mass loss is the formation of a
sulfide bridged triazine network (C
3 3
N S1,5, mass loss: 75 %) with
the release of phenyl sulfide and phenyl disulfide. The third
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decomposition step at 567 °C, with a mass loss of 10 %, is
assumed to be the incomplete decomposition of this CNS net-
work. The TGA-MS analysis of the decomposition steps shows
no MS signal for the first decomposition step. We assume that
phenyl sulfide is released during the first decomposition step. In
the gaseous phase, diphenyl disulfide is formed and precipitates
at the walls of the TGA unit. Due to the mass loss of about 41 %,
the release of two phenyl sulfide groups per molecule seems to
be plausible. At the temperature of the second decomposition
step, the released components and the residue of 2 decompose.
For the second decomposition step MS fragments of the phenyl
Compound 4 decomposes thermally in two steps. For the
first decomposition step at 240 °C a mass loss of 74.1 % is
measured up to a temperature of 400 °C. This mass loss is
slightly more than expected for the release of three tolyl sulfide
groups (mass loss: 68.0 %) but less than expected for the re-
lease of three tolyl disulfide groups (mass loss: 85.6 %). The
formation of sulfur bridged s-triazine cores by releasing tolyl
groups and 75 % of the sulfur (mass loss: 76.8 %) achieves the
best match. For the second decomposition step at 504 °C a
mass loss of 9.4 % is observed. The residue mass at 995 °C is
11.3 %. At the first decomposition step, the TGA-MS analysis of
4 (see Figure 12) shows the typical MS signals of the tolyl group
group (m/z: 76 (C
6
H
4
+), 77 (C
6
H
5
+) and 78 (C
6
+
H
6
+)), MS frag-
+), 45
+), 78 (C
H
+
) and 91 (C
H
+
)), fragments of the
ments of the phenyl sulfide group (m/z: 33 (SH ), 34 (SH
2
(m/z: 77 (C
tolyl sulfide group (m/z: 33 (SH ), 34 (SH
6
H
5
6
6
7
7
+
+
+
+
+
+
(
CHS ), 109 (C
6
H
5
S ) and 110 (C
6
H
6
S )) and MS indicators for
2
) and 45 (CHS )) and
+
+
the formation of disulfides (diphenyl disulfide) (m/z: 64 (S
2
), 65
fragments of the tolyl disulfide group (m/z: 64 (S
2
) and 66
+
+)) are observed. Between 300 °C and
+
(
S
2
H ) and 66 (S
2
H
2
(S
2
H
2
)). For the second decomposition step, MS fragment sig-
+
+
800 °C, a constant release of phenyl sulfide (m/z: 109, 110) and
nals of the triazine core are observed: m/z: 26 (CN ), 27 (HCN ),
+), 43 (CN +) and 52 (C +).
30 (N H H ), 44 (CS , CN H N
2 2 2 3 2 4 2 2
+
+
disulfide (m/z: 65, 66) is measured. This observation supports
the assumption that diphenyl disulfide is formed and precipitates
on the TGA chamber walls during the first decomposition step.
For the third decomposition step, indicators for the decomposi-
The MS results show the release of all tolyl groups and most
of the sulfur during the first decomposition step. The remaining
carbon-nitrogen-sulfur material decomposes incompletely in the
second decomposition step.
+
+
tion of a CNS network are observed; m/z: 26 (CN ), 27 (HCN ),
and 44 (CS , CN H ).
2 4
+
+
The MS analysis shows the release of all phenyl groups dur-
ing the first and second decomposition step. The remaining
carbon-nitrogen-sulfur material decomposes incompletely in the
third decomposition step.
Figure 13. TGA-MS results of the alkyl disulfide 2,4,6-tris(ethyldithio)-1,3,5-
triazine 6 (* smoothed signals).
The TGA of compound 6 shows two thermal decomposition
steps. For the first decomposition step at 228 °C, a mass loss of
7
8.8 % is observed up to a temperature of 465 °C. According to
Figure 12. TGA-MS results of the aryl disulfide 2,4,6-tris(p-tolyldithio)-1,3,5-
triazine (4).
the molecular structure of 6, this mass loss corresponds to the
calculated loss of three ethyl disulfide groups (mass loss:
78.2 %). The second decomposition step is observed at 565 °C.
From 465 °C to 995 °C, a mass loss of 19.2 % is measured. The
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Chemistry - A European Journal
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MS analysis of the first decomposition step shows typical MS
tion with a low additive amount, effects C and D are suppressed.
Effects D and G are more pronounced in foams or foils and are
suppressed by using bulky samples. Flame resistance observed
in bulky PP samples containing 1.0 wt.% flame retardant is
therefore attributed to effect H - radical scavenging.
To confirm the thermal thiyl radical formation, we used the
LOI test with PP bulky samples which contain 1.0 wt.% of 1 or 2.
Table 7 shows the LOI test results. The LOI value is slightly
+
+
signals for the ethyl group (m/z: 27 (C
ethyl sulfide group (m/z: 33 (SH ), 34 (SH
2
H
3
) and 29 (C
2
H
5
)), the
+
+
+
2
), 45 (CHS ), 47
+
+
(
CH
3
S ) and 61 (C
2
H
5
S )) and MS indicator signals for the ethyl
+), 66 (S +) and 94 (C +)). MS
disulfide group (m/z: 64 (S
2
2
H
2
2 5 2
H S
+
indicator signals for the triazine core (m/z: 26 (CN ) and 27
+
(
HCN )) are overlapped by the ethyl group MS signals. In the
increased by 1 (ΔLOI = 0.6 O
(ΔLOI = 3.5 O %). The observed flame retardancy could be
caused by 1) char formation, however the additive amount of
.0 wt.% is too low for sufficient char formation, 2) fuel dilution
by an inert filler, however 1 and 2 are incorporated with the
same amount but the observed LOI value is not the same and 3)
flame retarding effects of the triazine core, however the LOI
value of 1 (higher triazine core proportion) is significantly lower
than the LOI value of 2. The substantially higher LOI value of 2
is therefore caused by radical scavenging. Since 2 differs only
by one sulfur atom and the disulfide bond from 1, the thermal
decomposition of the disulfide bond and the release of thiyl
radicals seem to be the appropriate explanation.
2
%) and significantly increased by 2
second decomposition step, two MS signals are observed: 30
+
+
+). Due to the weakness of both of
2
(
N
2
H
2
) and 44 (CS , CN H
2 4
these signals, we assume that relatively stable fragments with a
m/z > 120 are released. According to the MS results, in the first
thermal decomposition step all ethyl groups and most of the
sulfur is released from 6. The MS results suggest the release of
1
•
•
•
EtS , S and EtS radicals from 6. These radicals recombine in
2
the gaseous phase leading to the observed MS species. The
remaining carbon-nitrogen-sulfur material decomposes in the
second decomposition step at 565 °C.
All three dithiocyanurates (2, 4, and 6) release all of their ar-
yl/alkyl groups in the form of sulfides and disulfides between
2
20 °C and 350 °C. As thermally induced thiyl radical generators,
Table 7. LOI test result of PP containing 1 wt.% 1 or 2.
#
Additive content [wt.%]
2
LOI [O %]
the dithiocyanurates seem to be highly efficient.
PP-Std.
PP + 1
PP + 2
0.0
1.0
1.0
18.4 ± 0.15
19.0 ± 0.15
21.9 ± 0.30
Since for the thiocyanurates (1, 3, 5 and 7) no thermal de-
composition is observed with the release of fragments (especial-
ly thiyl radicals) from the condensed phase, we expect thiocy-
anurates to have a lower ability to act as thermally induced thiyl
radical generators, in particular with regard to flame retardancy.
Flame retardant effects of disulfides attributed to thermally
induced thiyl radical release are known in the literature[2–5]. LOI
test results with bulky PP samples of several organic disulfides
are reported[2,3]. The highest LOI value is observed for 2,2’-
Thermal thiyl radical generation
The potential formation of thiyl radicals takes place at tempera-
tures between 200 °C and 300 °C. Due to the difficulty of meas-
uring radicals at these temperatures, we chose the limiting oxy-
gen index (LOI) flammability test as an indirect method to con-
firm the presence of thiyl radicals.
2
dithiobis(benzothiazole) (DTBB) with 20.6 O % (1.0 wt.% of
[3]
2
DTBB; ΔLOI = 3.6 O %) . In comparison to these results, dithio-
cyanurates, represented by compound 2, seem to be a promis-
ing flame retardant for PP, but further investigations are required
and are currently being performed.
The interaction of thermally released radicals of a flame re-
tardant with the thermally released radicals of the decomposing
polymer influences the flammability[32,33]. Higher LOI values
Quantum chemical calculations
Bond dissociation energies were calculated for the compounds 1,
correlate with lower amounts of radicals in the gas phase[32]
.
Thermally released radical species are able to act as radical
2
and triphenylthiocyamelurate (9) in order to learn more about
.
.
.
scavengers for free HOO , HO and H , species which promote
polymer degradation[32]
the bond breaking processes in the compounds under investiga-
tion. Three main bond breaking pathways are expected in these
compounds (see Scheme 1):
.
To prove the existence of radical species, flammability tests
can be used. As mentioned before, compounds which are able
to release radicals by thermal degradation affect the flammability
of polymers. Besides, flame retardant effects are attributed
mainly to the physical and chemical effects shown in Table 6.
a
b
c
Formation of a phenyl-S-radical
Dissociation of the phenyl-carbon sulfur bond
Formation of a phenyl-S-S-radical from 2
The enthalpies and Gibbs free energies of these compounds
are listed in Table 8. Full details are given in the supporting
information. The comparison of the Gibbs free energies shows
the following: the breaking of a triazin- or heptazin-carbon-sulfur
bond under formation of a phenyl-sulfur-radical needs about
230 kJ/mol to 240 kJ/mol. This energy is lowered by about
Table 6. Main physical and chemical flame retardant effects.
Physical effects
Chemical effects
A Dilution of the fuel source (poly-
mer) with inert fillers
E Endothermic decomposition
B Dilution of the gas phase by inert
F Char formation
gases
C Inhibition of heat and gas transfer
by inert layer (char)
G Increased polymer degradation
(drop-off effects)
1
00 kJ/mol in case of the 2,4,6-tris(phenyldithio)-1,3,5-
triazine (2). Cleavage of the sulfur-sulfur bond needs only
33.8 kJ/mol (section a in Table 8). This value is comparable to
D Enhanced melt dripping (drop-off
H Radical scavenging
effects)
1
To observe thermally induced radical formation, flame retardant
effects which are not caused by radical species have to be sup-
pressed. Thermally induced radicals are mainly involved in the
flame retardant effects G and H. To observe the flame retardant
effects A, B and E, high amounts of flame retardant are required.
By adding just a low amount (e.g. 1.0 wt.%) of a flame retardant,
effects A, B and E are suppressed. Moreover, if a polyolefin with
no char formation tendency, such as PP[33], is used in combina-
the value of 140.8 kJ/mol for breaking a sulfur-sulfur-bond in
bis(benzothiazolyl) disulfide.[5] Formation of a phenyl radical
from 1 or 9 needs 277 kJ/mol. The Gibbs free energy for the
analogous process in 2 needs only 227.3 kJ/mol (section b in
Table 8). The formation of a phenyl-S-S radical from 2 needs
199 kJ/mol (section c of Table 8). All in all the dithio-derivative 2
has the lowest bond dissociation energies of all three com-
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Chemistry - A European Journal
10.1002/chem.201802427
FULL PAPER
pounds. Compounds 1 and 9 have very similar bond dissociation
energies. This can be explained by the identical bonding situa-
tion of the peripheral substituents.
ed to the release of thiyl radical species during thermal decom-
position of the dithio s-triazines, an effect which is known from
organic disulfides[ . Quantum chemical calculations show that
the formation of thiyl radicals by disulfide bond cleavage lowers
enthalpies and Gibbs free energies by about 100 kJ/mol in com-
parison to sulfides.
3,5]
The TG-MS and LOI results show the ability of organic s-
triazines to act as thermal thiyl radical generators with a flame
retardant effect in PP.
For flame retardant applications, the ability of dithio s-
triazines to release thiyl radicals in the gas and condensed
phases seems to be promising. A detailed analysis of these
phenomena will form part of further investigations.
Experimental Section
Materials
All chemicals were used as received from Sigma Aldrich. Solvents
were dried over a molecular sieve. PP Daploy® WB 140 HMS
(MFR = 2.1 g/10 min (230 °C/2.16 kg) from BOREALIS was used
for the LOI test.
Scheme 1. Bonds of compounds 1, 2, and 9 for dissociation energy calcula-
tion.
Methods
Table 8. Computed reaction thermodynamics at 298 K and 1 atm (values in
NMR: Standard 1H and 13C NMR spectra were recorded on an
kJ/mol).
AVANCE DPX 400 NMR spectrometer at 293 K ( H: 400 MHz, 13C:
1
Reaction
ΔH
ΔG
1
01 MHz). The chemical shifts are reported relative to tetrame-
a
- Formation of a phenyl-S-radical
thylsilane. ATR-FTIR: For the attenuated total reflection (ATR)
fourier transform infrared (FTIR) spectroscopy a FTIR spectrometer
Nicolet 6700 from Thermo Scientific and a DuraScope diamond
ATR unit was used. Raman: The Raman spectroscopy was per-
formed with a Bruker RFS 100 Raman spectrometer (Nd:YAG,
(
(
(
1): Triazine(SPh)
2): Triazine(S-SPh)
9): Heptazine(SPh)
3
 Triazine(SPh)
 (Ph-S-S) Triazine-S radical + PhS-radical
 Heptazine(SPh) radical + PhS-radical
2
radical + PhS-radical
283.2
185.5
290.6
231.7
133.8
239.5
3
2
3
2
b
- Dissociation of the phenyl-carbon sulfur bond
1
064 nm). EA: Elemental analyses were performed with a CHNS-O
(
(
(
1): Triazine(SPh)
2): Triazine(S-SPh)
9): Heptazine(SPh)
3
 (PhS)
 (Ph-S-S)
 (PhS) Heptazine-S radical + Ph-radical
2
Triazine-S radical + Ph-radical
329.8
282.2
329.0
277.5
227.3
277.1
analyzer Flash EA 1112 from Thermo Fisher. TGA: The measure-
ments were performed with a TG 209 F1 Iris ASC from Netzsch in
nitrogen with a heating rate of 10 K/min. TGA-MS: The measure-
ments were performed with a TG 209 F1 Iris ASC coupled with a
QMS 403 C Aeolos from Netzsch in nitrogen with a heating rate of
3
2
Triazine-S-S radical + Ph-radical
3
2
c
-
Formation of a phenyl-S-S-radical
254.8
(
2): Triazine(S-SPh)
3
 (Ph-S-S)
2
Triazine radical + Ph-S-S-radical
199.0
1
0 K/min. MS signals in the range of m/z 10 to 120 were observed.
mp: For the determination of the melting points a melting point
apparatus Melting Point B-540 from Büchi was used. LOI test:
Conclusions
Grounded PP was premixed with the compound 1 or 2 and extrud-
ed with a MiniLab form ThermoHaake and granulated. The LOI
samples were prepared with a MiniLab extruder from ThermoHaake
at 210 °C and a MiniJet II injection molding system from Thermo
In this paper, the synthesis and characterization of aliphatic and
aromatic thio and dithio s-triazines, and their ability to release
thiyl radicals by thermal induction, are reported.
3
Scientific, Haake. The sample size is type IV (70 x 6.5 x 3 mm ).
The LOI value was measured by using an oxygen index module
from FIRE according to DIN EN ISO 4589-2 standardized proce-
dure. Molecular structure determination: Single-crystal X-ray
diffraction data were collected on a STOE IPDS-2T image plate
diffractometer equipped with a low-temperature device using graph-
ite monochromated Mo Kα radiation (λ = 0.71073 Å). Software for
data collection: X-AREA, cell refinement: X-AREA and data reduc-
tion: X-RED[34]. Preliminary structure models were derived by direct
It was found that neither aliphatic nor aromatic thio s-
triazines are capable of releasing thiyl radicals from the con-
densed phase. Thio s-triazines are released into the gaseous
phase without previous thermal decomposition. However, thio s-
heptazines are thermally decomposed with the release of thiyl
radicals. Since quantum chemical calculations of bond dissocia-
tion energies show that the thiyl radical formation from thio s-
triazines and thio s-heptazines is similar, lower evaporability of
thio s-heptazines, resulting from the molar mass, is responsible
for this.
However, both aliphatic and aromatic dithio s-triazines are
able to release decomposition products due to thermal induction
at about 220 °C. The decomposition products, characterised by
TG-MS, consist of sulfur species which show flame retardant
effects in the LOI test. These flame retardant effects are attribut-
[
35]
methods
and the structures were refined by full-matrix least-
squares calculations based on F2 for all reflections using
[36]
SHELXL . Hydrogen atoms were included in the models in calcu-
lated positions and were refined as constrained to the bonding
atoms. Further details regarding crystallographic results are report-
ed in the Supporting Information. CCDC 1832062-1832064 contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallograph-
ic Data Centre via www.ccdc.cam.ac. uk/data _request/cif. Quan-
tum chemical calculations: The geometries of the compounds 1,
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Chemistry - A European Journal
10.1002/chem.201802427
FULL PAPER
2
, and
9
were optimized with the density functional method
and the basis set 6-31G*[38], using the Gaussian 09[39]
resulting red solution was vacuum distilled (around 4.0 g, 25 mmol
p-tolylsulfenyl chloride) and immediately added dropwise to a sus-
pension of sodium thiocyanurate (1.84 g, 7.6 mmol) in 50 mL tolu-
ene and stirred for 22 h at r.t.. After that, the suspension was ex-
tracted with water (3 x 25 mL), dried over magnesium sulfate and
the solvent was evaporated. The crude product was finally purified
by flash chromatography (cyclohexane with dichloromethane gradi-
[
37]
B3LYP
package. The calculation of Hessian-matrices verified the presence
of local minima on the potential energy surface with zero imaginary
frequencies. Thermodynamic values have been calculated for
isolated molecules in the gas phase at 298 K and 1 atm.
ent). 1.8 g (η = 44 %) of compound
4 were obtained as a white and
Synthetic procedures
1
odourless powder. Mp: 95-96 °C. H NMR (400 MHz, CDCl
3
): δ
Synthesis of 2,4,6-tris(phenylthio)-1,3,5-triazine (1). The
.55 (d, J = 8.0, 2H), 7.05 (d, J = 7.9, 2H), 2.31 (s, 3H); 13C NMR
3
3
7
synthesis of compound
NGAMUTHU et al.[14]. However, we used another method. Thiophe-
nol (0.91 g, 8.3 mmol) was added to a solution of sodium (0.21 g,
.0 mmol) in 16 mL diethyl ether at r.t. and stirred for 9.5 h under
1 has been reported in the literature by
(
100 MHz, CDCl ): δ 181.2, 139.2, 131.9, 131.8, 129.9, 21.2. Anal.
3
A
calcd (%) for (C24 ): C 53.00, H 3.89, N 7.73, S 35.38, found:
21 3 6
H N S
C 52.8, H 3.6, N 7.6, S 35.0.
Synthesis of 2,4,6-tris(ethylthio)-1,3,5-triazine (5). Ethan-
ethiol (1.35 g, 21.8 mmol) was added to a suspension of sodium
9
reflux. The resulting suspension was treated with a suspension of
cyanuric chloride (0.46 g, 2.5 mmol) in 10 mL diethyl ether and
stirred for 6.5 h under reflux. After that, the solvent was removed
and the crude product washed with 75 mL water and recrystallized
in n-heptane. 0.49 g (η = 49 %) of compound
white and odourless powder. Mp: 97-98 °C. H NMR (500 MHz,
(
0.50 g, 21.8 mmol) in 20 mL diethyl ether at r.t.. The suspension
was stirred under reflux until all sodium was consumed. The result-
ing suspension was treated with a suspension of cyanuric chloride
1 was obtained as a
1
(
1.20 g, 6.5 mmol) in 30 mL diethyl ether and stirred for 20.5 h
under reflux. Then the mixture was filtrated and the solvent evapo-
rated from the filtrate. The obtained crude product was dissolved in
3
3
3
CDCl
7
1
3
): δ 7.34 (d, J = 8.4, 2H), 7.29 (t, J = 7.4, 1H), 7.19 (t, J =
.4, 2H); 13C NMR (125 MHz, CDCl
): δ 180.2, 134.8, 129.3, 128.9,
27.0. Anal. calcd (%) for (C21 ): C 62.19, H 3.73, N 10.36,
3
1
00 mL dichloromethane, extracted with water (3 x 20 mL), dried
over magnesium sulfate, the solvent removed and dried under high
vacuum. 1.17 g (η = 67 %) of compound were obtained as a
slightly yellow and odourless liquid, which solidified at 23-25°C. H
): δ 3.10 (q, 3J = 7.4, 2H), 1.38 (t, 3J = 7.4,
NMR (400 MHz, CDCl
H); 13C NMR (100 MHz, CDCl
): δ 179.3, 24.6, 14.3. Anal. calcd
%) for (C ): C 41.35, H 5.78, N 16.07, S 36.80, found:
15 3 3
H N S
S 23.72, found: C 62.0, H 3.7, N 10.1, S 23.5.
5
Synthesis of 2,4,6-tris(phenyldithio)-1,3,5-triazine (2). Thio-
phenol (22.4 g, 203 mmol) was added to a solution of sulfuryl chlo-
ride (35.0 g, 259 mmol) in 50 mL dichloromethane at 0 °C and
stirred for 2 h. The reaction mixture was then stirred for 1 h at r.t..
The resulting red solution was vacuum distilled (around 24.75 g,
1
3
3
(
3
9 15 3 3
H N S
C 41.2, H 5.5, N 15.8, S 36.3.
Synthesis of 2,4,6-tris(ethyldithio)-1,3,5-triazine (6). Sulfuryl
chloride (4.5 g, 32 mmol) was added to a solution of ethanethiol
1
71 mmol phenylsulfenyl chloride) and immediately added dropwise
to a suspension of sodium thiocyanurate (12.9 g, 53 mmol) in
00 mL toluene and stirred at r.t.. After 17 h, the suspension was
1
(
2.0 g, 32 mmol) in 24 mL dichloromethane at r.t.. The reaction
diluted with 100 mL dichloromethane and stirred for 3 h. After that,
the resulting suspension was filtrated, the filtrate extracted with
water (3 x 100 mL, pH = basic by potassium carbonate), dried over
magnesium sulfate and the solvent was evaporated. After solidifica-
tion, the crude product was washed with diethyl ether and recrystal-
mixture was then stirred for 19.5 h at r.t.. The solvent was removed
by vacuum from the resulting orange solution. The product was
immediately added dropwise to a suspension of sodium thiocyanu-
rate (2.3 g, 10 mmol) in 10 mL toluene. After 1.5 h, 30 mL dichloro-
methane were added and the dispersion was stirred for a further
lized from n-heptane. 11.0 g (η = 41 %) of
white and odourless powder. Mp: 93-94 °C. H NMR (400 MHz,
CDCl
): δ 7.53 (dd, 3J = 7.7, 2H), 7.22-7.11 (m, 3H); 13C NMR
100 MHz, CDCl ): δ 181.1, 135.3, 131.0, 129.1, 128.6. Anal. calcd
%) for (C21 ): C 50.27, H 3.01, N 8.38, S 38.34, found:
2 were obtained as a
1
.5 h at r.t.. The suspension was then extracted with water
1
(
3 x 40 mL), dried over magnesium sulfate and the solvent was
3
evaporated. The crude product was finally purified by flash chroma-
tography (cyclohexane with dichloromethane gradient). 0.95 g (η =
(
(
3
H
15
N
3
S
6
1
2
8 %) of compound
NMR (400 MHz, CDCl
H); 13C NMR (100 MHz, CDCl
%) for (C ): C 30.23, H 4.23, N 11.75, S 53.80, found:
6
were obtained as a slightly yellow liquid.
H
C 50.6, H 2.7, N 8.6, S 38.3.
3
3
3
): δ 2.88 (q, J = 7.4, 2H), 1.29 (t, J = 7.4,
): δ 181.3, 32.1, 13.9. Anal. calcd
Synthesis of 2,4,6-tris(p-tolylthio)-1,3,5-triazine (3). This
compound has been reported in the literature by ANGAMUTHU et
al.[ and MOHAMMADPOOR-BALTORK and MIRKHANI et al.[16] with
synthesis methods different from our approach. 4-Methylthiophenol
3
(
3
9 15 3 6
H N S
14]
C 29.5, H 4.0, N 11.2, S 53.2.
Synthesis of 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7). 2-
Methylpropane-2-thiol (1.96 g, 21.8 mmol) was added to a suspen-
sion of sodium (0.50 g, 21.8 mmol) in 10 mL diethyl ether at r.t.. The
suspension was stirred under reflux until all sodium was consumed.
The resulting mixture was treated with a suspension of cyanuric
chloride (1.16 g, 6.3 mmol) in 10 mL diethyl ether and stirred for 6 h
under reflux. The suspension was then filtrated and the solvent
evaporated from the filtrate. The obtained crude product was dis-
solved in 100 mL dichloromethane, extracted with water
(
2.70 g, 21.8 mmol) solved in 10 mL diethyl ether was added to a
solution of sodium (0.50 g, 21.8 mmol) in 20 mL diethyl ether at r.t..
The suspension was stirred under reflux until all sodium was con-
sumed. The resulting suspension was treated with a suspension of
cyanuric chloride (1.16 g, 6.3 mmol) in 10 mL diethyl ether and
stirred for 6.5 h under reflux. The suspension was then filtrated and
the solvent evaporated from the filtrate. The crude product obtained
was resolved in 100 mL dichloromethane, extracted with water
(
3 x 20 mL), dried over magnesium sulfate, the solvent removed
and dried under high vacuum. 2.23 g (η = 79 %) of compound
were obtained as a white and odourless powder. Mp: 116-117 °C.
1H NMR (500 MHz, CDCl ): δ 7.17 (d, 3J = 8.0, 2H), 6.96 (d, 3J =
.0, 2H), 2.30 (s, 3H); 13C NMR (125 MHz, CDCl
): δ 180.4, 139.2,
34.8, 129.6, 123.7, 21.4. Anal. calcd (%) for (C24 ):
(
3 x 20 mL), dried over magnesium sulfate, the solvent removed
and dried under high vacuum. 1.4 g (η = 64 %) of compound were
obtained as a white and odourless powder. Mp: 147 °C 1H NMR
): δ 1.51 (s); 13C NMR (100 MHz, CDCl
400 MHz, CDCl ): δ 179.0,
7.7, 29.9. Anal. calcd (%) for (C15 ): C 52.13, H 7.87,
3
7
3
(
4
3
3
8
1
3
27 3 3
H N S
21 3 3
H N S
N 12.16, S 27.84, found: C 52.2, H 7.7, N 12.0, S 27.6.
Synthesis of 2,4,6-tris(tert-butyldithio)-1,3,5-triazine (8). Sulfuryl
chloride (2.4 g, 18 mmol) was added to a solution of tert-butylthiol (1.6 g,
C 64.39, H 4.73, N 9.39, S 21.49, found: C 64.3, H 4.4, N 9.1,
S 21.5.
Synthesis of 2,4,6-tris(p-tolyldithio)-1,3,5-triazine (4). Sulfu-
ryl chloride (5.72 g, 41 mmol) was added to a solution of 4-
methylthiophenol (4.0 g, 32 mmol) in 30 mL dichloromethane at
18 mmol) in 5 mL dichloromethane at r.t.. The reaction mixture was then
stirred for 4.5 h at r.t.. The solvent was removed by vacuum from the
resulting orange solution. The product was immediately added dropwise
to a suspension of sodium thiocyanurate (1.1 g, 9 mmol) in 19 mL tolu-
0
°C. The reaction mixture was then stirred for 67 h at r.t.. The
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201802427
FULL PAPER
ene and stirred for 2 h. 50 mL dichloromethane were then added and the
dispersion stirred for a further 15.5 h at r.t.. After that, the suspension
was extracted with water (3 x 50 mL), dried over magnesium sulfate and
the solvent was evaporated. 1.05 g (η = 53 %) of the crude product was
obtained as a slightly yellow liquid. Purification by flash chromatography
[15] a) S. Ray, F. R. Smith, J. N. Bridson, Q. Hong, V. J. Rich-
ardson, S. K. Mandal, Inorg. Chim. Acta 1994, 227(1), 175–
179; b) S. Mandal, G. Bérubé, E. Asselin, I. Mohammad, V.
J. Richardson, A. Gupta, S. K. Pramanik, A. L. Williams, S.
K. Mandal, Bioorg. Med. Chem. Lett. 2007, 17(17), 4955–
4960;
[16] A. Isfahani, I. Mohammadpoor-Baltork, V. Mirkhani, M.
Moghadam, A. Khosropour, S. Tangestaninejad, M. Nasr-
Esfahani, H. Rudbari, Synlett 2014, 25(05), 645–652.
[17] a) S. Niembro, A. Vallribera, M. Moreno-Mañas, New J.
Chem. 2008, 32(1), 94–98; b) Z. Xiangqiong, S. Heyang, R.
Wenqi, H. Zhongyi, R. Tianhui, Wear 2005, 258(5-6), 800–
(
cyclohexane with dichloromethane gradient) gave a colourless liquid.
1
Impurities were observed by NMR and EA: H NMR (400 MHz, CDCl
1
3
): δ
.42 (s); 13C NMR (100 MHz, CDCl
3
): δ 180.6, 49.5, 29.7. Anal. calcd (%)
for (C15
S 48.3.
H N S ): C 40.8, H 6.2, N 9.5, S 43.5, found: C 35.7, H 5.0, N 6.9,
27 3 6
8
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Chemistry - A European Journal
10.1002/chem.201802427
FULL PAPER
FULL PAPER
Thermal thiyl radical generators:
Sulfides and disulfides of s-triazine
are synthesised and their thermal
degradation is studied. The s-triazine
disulfids show significant potential as
thermal thiyl radical generators.
Carl-Christoph Höhne*, Christian
Posern, Uwe Böhme, Edwin Kroke
Page No. – Page No.
Sulfides and Disulfides of
s-Triazine: Potential Thermal Thiyl
Radical Generators
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