Synthesis and crystal structures of new 1,4-disubstituted 1,2,4-triazoline-5-thiones

Article abstract of DOI:10.5560/ZNB.2014-4145

Introduction of sulfur into the 5-position of 1,4-disubstituted quaternary 1,2,4-triazolium salts (1-9; Cl, Br, I, BF₄, PF₆, CH₃OSO₃ were used as anions) by two methods was investigated. The syntheses of nine 1,

Full text of DOI:10.5560/ZNB.2014-4145

Synthesis and Crystal Structures of New 1,4-Disubstituted
1,2,4-Triazoline-5-thiones
Gerhard Lausa, Volker Kahlenbergb, Klaus Wursta, and Herwig Schottenbergera
a
Faculty of Chemistry and Pharmacy, University of Innsbruck, 6020 Innsbruck, Austria
Institute of Mineralogy and Petrography, University of Innsbruck, 6020 Innsbruck, Austria
b
Reprint requests to Dr. Gerhard Laus. Fax: +43 512 507 57099. E-mail: gerhard.laus@uibk.ac.at
Z. Naturforsch. 2014, 69b, 950 – 964 / DOI: 10.5560/ZNB.2014-4145
Received July 8, 2014
Introduction of sulfur into the 5-position of 1,4-disubstituted quaternary 1,2,4-triazolium salts (1–9;
Cl, Br, I, BF4, PF6, CH3OSO3 were used as anions) by two methods was investigated. The syntheses
of nine 1,4-disubstituted 1,2,4-triazoline-5-thiones 10–18 are reported (1, 10: R1 = CH3, R2 = CH3;
2, 11: R1 = NH2, R2 = CH3; 3, 12: R1 = NH2, R2 = CH(CH3)2; 4, 13: R1 = N(CH3)2, R2 = CH3;
5, 14: R1 = N(CH3)2, R2 = CH(CH3)2; 6, 15: R1 = CH3, R2 = NH2; 7, 16: R1 = OCH2Ph,
R2 = CH3; 8, 17: R1 = OCH2Ph, R2 = CH2CH3; 9, 18: R1 = CH3, R2 = CH2Ph). Com-
pounds 11–17 represent 1-amino, 4-amino, 4-dimethylamino, and 4-benzyloxy-1,2,4-triazoline-5-
thiones, whereas 10 served as a reference compound. Thione 18 was identified as an unexpected
by-product in the synthesis of 16 and was also prepared independently. Thermolysis of 10 in air gave
1,4-dimethyl-1,2,4-triazolium hydrogensulfate. Crystal structures of eight 1,4-disubstituted 1,2,4-
triazoline-5-thiones were determined by single-crystal X-ray diffraction. Intermolecular hydrogen
bonds (C–H···S, C–H···N, N–H···N, N–H···S) were observed in the solid state. The solvent-dependent
1H NMR chemical shifts of signals of 10 and 13 were satisfactorily correlated with the Kamlet-
Abboud-Taft π* and β parameters in ten solvents. From the lack of correlation with the α pa-
rameter and from the C=S bond length (average 1.67 Å) a significant contribution of a mesoionic
imidazolium-2-thiolate resonance structure seems unlikely.
Key words: Crystal Structure, Desulfurization, Hydrogen Bond, Ionic Liquid, Thermolysis, Thione,
Triazole
Introduction
nent literature. More recently, cycloaddition of 1-aza-
2-azoniaallenes and isothiocyanates has been reported
Early examples of the title compounds have to give substituted 1,2,4-triazoline-5-thiones [4].
been prepared by cyclization of acyclic precur- In a more general approach, the thione group has
sor molecules. Other substitution patterns have been introduced by reaction of 1,4-disubstituted qua-
been obtained by rearrangement of other heterocy- ternary triazolium salts with elemental sulfur in pyri-
cles or by cycloaddition. Thus, 1,4-dimethyl-1,2,4- dine [5, 6]. This method has been improved by ad-
triazoline-5-thione (10) [1] and 4-amino-1-methyl- dition of triethylamine and successfully employed
1,2,4-triazoline-5-thione (11) [2] have been syn- for the synthesis of 4-amino-1-alkyl-1,2,4-triazoline-
thesized from 2,4-dimethylthiosemicarbazide and 2- 5-thiones [7] and 1-amino-4-benzyl-1,2,4-triazoline-5-
methylthiocarbohydrazide, respectively, by condensa- thiones [8]. Another method, employing sulfur and
tion with formic acid. Although this synthetic route K2CO3 in MeOH and frequently used for imidazoline-
is facile and straightforward, it is of course lim- 2-thiones [9 – 12], to our knowledge has not been ap-
ited by the availability of the respective hydrazines. plied in the triazole series so far. These thionation reac-
In special cases, 2-hydrazino-1,3,4-thiadiazoles were tions have now been studied in more detail and are the
found to rearrange in acid to 4-amino-1,2,4-triazoline- topic of the present work. A third method, using sulfur
5-thiones [3], though the scope and limitations of this and NaOAc in acetonitrile, is reportedly very slow [13]
reaction are not clear because there is not much perti- and was not attempted.
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
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Typical reactions of these triazolinethiones include sive but pure precursors, the synthesis of quaternary
S-alkylation [14], oxidative desulfurization [5, 15, 16], salts was designed to avoid the generation of isomers.
and formation of metal complexes [17 – 20]. Charge- Introduction of two identical substituents at two ni-
transfer complexes with halogens, which are common trogen atoms of 1,2,4-triazole is of course straight-
for imidazoline-2-thiones, are rare in the analogous tri- forward. Thus, 1,4-dimethyl-1,2,4-triazolium methyl-
azole series [21]. Crystal structures of several 1,3,4- sulfate (1a) was obtained in excellent yield by dou-
trisubstituted 1,2,4-triazoline-5-thiones, some of them ble methylation of 1,2,4-triazole. The iodide 1b was
with a 4-amino group [22 – 28], are known. However, preferably prepared from pure 4-methyl-1,2,4-triazole
the number of crystal structures of 1,4-disubstituted although it can also be reasonably synthesized from
examples seems to be more limited [13, 29].
a crude N-methyl isomer mixture. Quaternary salts 2–5
Continuing our interest in N-heterocyclic molecules were obtained by alkylation of 4-amino-1,2,4-triazole,
with heteroatom substituents at the N atoms, prefer- whereas the new 1-amino-4-methyl-1,2,4-triazolium
ably with small ones, we report the synthesis of six cation 6 (2,4-dinitrophenolate 6a and, by ion metathe-
new, alternative syntheses of three known, as well as sis, chloride 6b) was synthesized by electrophilic am-
crystal structures of five new and three known 1,4- ination of 4-methyl-1,2,4-triazole. Salts 7 and 8 were
disubstituted 1,2,4-triazoline-5-thiones.
prepared by alkylation of 4-benzyloxy-1,2,4-triazole,
and salt 9 by benzylation of 4-methyl-1,2,4-triazole.
Four triazolium salts (1a, 1c, 7 and 8) are liquids at
room temperature. We have recently reported NHC–
Results and Discussion
Some remarks on the synthesis of the quaternary metal complexes of 4 [34], and more carbenes may be
salts and their precursors seem to be appropriate, since expected from the new quaternary precursors, such as
this chemistry is of high relevance for the contempo- the sterically shielded 4-(dimethylamino)-1-isopropyl-
rary field of ionic liquids (ILs). Contrary to the situ- 1,2,4-triazolium salt 5.
ation in related imidazoles, the 1- and 4-positions in
The behavior of quaternary salts and thiones also
1,2,4-triazoles are not equivalent, giving rise to iso- deserves some comment. In principle, both thionation
mers, the concurrent presence of which can be re- methods (Scheme 1) worked for all substrates and
sponsible for spectacular melting point depressions of gave comparable results for the thiones 13, 15 and 18.
triazole-based ILs [30]. On the other hand, the en- However, the “pyridine/Et3N method” gave superior
hanced nucleophilicity of position 1 in 1,2,4-triazoles yields for thiones 12, 14, 16, and 17, and was advanta-
allows direct quaternization of 4-amino-1,2,4-triazole geous for thionation of the hexafluorophosphates 4 and
which is not feasible with 1-aminoimidazole. The 4- 5 and tetrafluoroborates 7 and 8 due to avoiding their
amino group can actually be used as a protective insoluble alkali salts. The “MeOH/K2CO3 method”
group for the preparation of isomer-free 1-alkyl-1,2,4- gave better results for thiones 10 and 11. In all cases,
triazoles [31] and ILs derived thereof [32]. Neutral NMR spectra indicated complete consumption of
4-(dialkylamino)-1,2,4-triazoles are accessible by cy- starting material after the reported reaction time (typ-
clization [33] and, more recently, a quaternary 4- ically two hours at 70 ◦C, with few exceptions), but
(dimethylamino)-1,2,4-triazolium salt was obtained by the work-up procedure had to be adjusted due to the
exhaustive methylation of 4-amino-1,2,4-triazole un- different solubilities of the thiones and accompanying
der forceful conditions [34]. 4-Alkyl-1,2,4-triazoles salts. Thus, the product could be either precipitated
in general are prepared by alkylation of 1-acetyl- by addition of water or, after removal of the solvent,
1,2,4-triazole followed by removal of the acyl group. isolated by extraction of the crude residue with EtOAc
N-Benzyloxy-1,2,4-triazoline-5-thiones have not yet or by partitioning the residue between an organic
been described although the synthesis of N-benzyloxy- solvent and water. Subsequent purification could be
1,2,4-triazoles is known. In contrast to 1-benzyloxy- achieved by either sublimation from the crude residue
1,2,4-triazole, which can be prepared by oxidation or recrystallization of the residue or extract. Although
of 1,2,4-triazole in low yield and subsequent ben- complete conversion was achieved in all cases, the
zylation [35], 4-benzyloxy-1,2,4-triazole can readily isolation and purification steps limited the yields.
be obtained in satisfactory yield by a one-step cy- Interestingly, the N-amino-1,2,4-triazolium salts 2, 3
clization reaction [36]. Starting from these inexpen- and 6b are not as prone to deamination in MeOH as
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952
G. Laus et al. · 1,2,4-Triazoline-5-thiones
the related N-aminoimidazolium salts [12]. Although
a by-product was observed when the thionation of
4-amino-1-isopropyl-1,2,4-triazolium bromide (3)
was attempted in MeOH at 70 ◦C, it was not identical
with an authentic sample of the expected deamination
product 1-isopropyl-1,2,4-triazole, and the reaction
in pyridine yielded pure 4-amino-1-isopropyl-1,2,4-
triazoline-5-thione (12). No deamination occurred
when the thionation of 6b to 15 was conducted
in MeOH at ambient temperature. Thionation of
the 4-benzyloxy-1-methyl-1,2,4-triazolium salt
7
to 16 in methanol gave an unexpected by-product,
1-benzyl-4-methyl-1,2,4-triazoline-5-thione (18), as
suspected from 13C NMR experiments and confirmed
by X-ray crystal structure determination. This incident
was not fully reproducible, the by-product showed
up only twice (up to 15 mol percent by NMR) in
five experiments. Again, the reaction in pyridine
reproducibly gave pure 16. Conversion of the anal-
ogous ethyl derivative 8 to thione 17 was therefore
performed only using the ‘pyridine/Et3N method’.
For the known thiones 10 and 11 an alternative
synthesis is provided which avoids the preparation of
the necessary semicarbazide or carbohydrazide. The
new
4-amino-1-isopropyl-1,2,4-triazoline-5-thione
(12), the 4-(dimethylamino) derivatives 13 and 14, and
1-amino-4-methyl-1,2,4-triazoline-5-thione (15), an
isomer of 4-amino-1-methyl-1,2,4-triazoline-5-thione
(11), are small molecules which are valuable building
blocks for further research. It is also noteworthy that
the 4-benzyloxy-1,2,4-triazoline-5-thiones 16 and 17
are the first of their kind.
Thermal rearrangements (140 ◦C, 60 min) involv-
ing N→S alkyl shifts in related imidazoline-2-thiones
have been reported previously [37]. Nothing of this
kind was observed when compounds 13, 14 and 18
were heated at 160 ◦C for one hour. Interestingly,
thione 10 showed some initial reaction under these
conditions. Consequently, when 10 was heated in an
open test tube at 160 ◦C for 24 h, the 1,3-dimethyl-
1,2,4-triazolium cation was fully regenerated, accord-
1
1
Scheme 1. a) / S8, Et3N/pyridine; b) / S8, K2CO3/
8
8
MeOH; c) O2/H2O, 160 ◦C.
ing to 1H and 13C NMR spectra. No reaction occurred pared by ion metathesis. In contrast to the analogous
when 10 was heated in an argon atmosphere. Obvi- imidazoline-2-thione [12], the N-benzyloxy compound
ously, the sulfur atom was oxidized [38] by air and 17 did not eliminate benzaldehyde at 130 ◦C, but at
subsequently hydrolyzed to the hydrogensulfate an- 160 ◦C complete conversion to a new product was ob-
ion, as indicated by IR spectroscopy and classic ion served, as indicated by the disappearance of the CH2O
1
identification (Scheme 1). This product was spectro- signal in both H and 13C NMR spectra. This work
scopically identical to authentic 1,3-dimethyl-1,2,4- is in progress, and the results are to be published
triazolium hydrogensulfate (1c) independently pre- separately.
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
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Fig. 1. Interatomic distances (Å) and angles (deg) in 1,4-disubstituted 1,2,4-triazoline-5-thiones.
Crystallography
ring angles and the type of substituents in the triazole
series. Although the corresponding bond lengths and
The crystallographic data and refinement details are angles in the triazole rings of the title compounds are
summarized in Table 1. In contrast to the related imida- reasonably similar (Fig. 1), crystal packings and inter-
zole compounds [12], there is no correlation between molecular interactions are quite different.
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955
Fig. 2 (color online). Network of C–H···S contacts in the
crystal structure of 10.
A network of C–H···S contacts is found in thione
10 (Fig. 2). Columns of two independent molecules
are formed in the direction of the b axis by N–H···S
contacts in 11. These columns are crosslinked by N–
H···N hydrogen bonds (Fig. 3), similar to analogous
imidazole compounds [12]. In thione 12 short N–H···N
hydrogen bonds form chains in the direction of the b
axis (Fig. 4). Weak C–H···S and C–H···N contacts are
found in 13 (Fig. 5). Bifurcated C–H···S and C–H···N
Fig. 3 (color online). Columns of two independent molecules
formed by N–H···S interactions along b in the crystal struc-
ture of 11.
contacts are observed in thiones 14 (Fig. 6) and 15 In crystals of 18, typical C–H···π interactions [39, 40]
(Fig. 7); in 15 there are also N–H···S hydrogen bonds between the triazole and benzene rings are observed,
present. Several attempts to solve the structure of 16 linking the molecules in the direction of the crystallo-
were made, but severe disorder in the crystals prohib- graphic c axis (Fig. 9). The six Htriazole···Car distances
ited refinement, and only high R values were obtained. range from 2.79 to 2.90 Å, and the distance between
It was hoped that compound 17, with an ethyl instead the triazole H atom and the plane of the aromatic ring
of a methyl group, would give better crystals. As it hap- was found to be 2.485 Å. The distance between the
pens, in the asymmetric unit of 17 there are two inde- H atom and the ring centroid is 2.488 Å, and the C–
pendent ‘half’ molecules, which are disordered over H···centroid angle is 172◦. Weak C–H···S contacts link
a crystallographic mirror plane perpendicular to the a the molecules into chains parallel to the a axis. The
axis. Only the phenyl groups are ordered with C6, C9, details of the C–H···S, C–H···N, N–H···S, N–H···N hy-
C16, and C19 on the mirror plane and C7, C8, C17, drogen bonds are summarized in Table 2.
and C18 above the plane. SA, SB and C2 are placed
The C=S bond lengths in seven of the thiones range
exactly on mirror planes with normal occupancies of from 1.66 to 1.68 Å in agreement with the accepted
1.0. All other atoms of the disordered part are out of value of 1.68 Å in thioureas [41]. The C=S bond
the plane with occupancies of 0.5. The disorder can lengths in the two independent molecules of the N-
be described by regular chains of molecules along the benzyloxy derivative 17 are 1.540 and 1.686 Å, re-
a axis with weak hydrogen bonds between C2–H···SA spectively, but this structure is severely disordered,
and C12–H···SB. Each of these chains can reverse its and the measurements possibly do not represent typ-
direction at other locations in the crystal. The disorder ical values. In any case, there is no elongated C–S
of the two independent molecules is shown in Fig. 8. bond. The average value for compounds containing
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
Fig. 5 (color online). Interactions in the crystal structure of
13.
Fig. 4 (color online). Crystal structure of 12 showing a chain
of N–H···N hydrogen bonds along b.
donor) acidity α [48], (hydrogen bond acceptor) ba-
sicity β [49], and dipolarity/polarizability π∗ [50, 51].
a propanethione fragment is 1.67 Å [12]. Thus, there Thus, spectra of 1,4-dimethyl-1,2,4-triazoline-5-thione
is no evidence for a significant triazolium-5-thiolate (10) and 4-(dimethylamino)-1-methyl-1,2,4-triazoline-
resonance contribution (Scheme 2) in the solid state. 5-thione (13) were recorded in ten common NMR sol-
Mesoionic structures of this type have also been postu- vents covering a wide range of these parameters. The
lated for imidazoline-2-thiones [42 – 45], but have re- parameters for non-deuterated solvents from a recent
cently been dismissed due to lack of evidence [12]. compilation [52] were applied to unravel the individual
In 2,3-diphenyltetrazoline-5-thione, however, the in- contributions of the terms in the linear solvation energy
creased C–S bond length of 1.70 Å [46] supports relationship (LSER) [47] by multiple regression anal-
a mesoionic contribution.
ysis:
1H NMR spectroscopy
δ(1H) = δ0 +sπ∗ +aα +bβ
1
The H NMR signals of the thiones are shifted up-
From the data the following equations were derived
(standard errors of δ0, s, and b, correlation coefficient
r, relative standard deviation σ of the correlation, and
number N of data points given).
field from those of the quaternary precursor salts by
0.4 – 0.9 ppm, which may be attributed to the loss of
cationic character. It is noteworthy that 1H NMR chem-
ical shifts of the triazolinethiones depend quite signifi-
cantly on the solvent (even more than in the imidazole
series [12]). It seemed to be of interest to analyze this
behavior in terms of the Kamlet–Abboud–Taft parame-
ters [47] of solvent properties, i. e. (hydrogen bond
For 10: δ(1H) = (7.420±0.116)+(0.390±0.180)π∗
+(0.892±0.158)β
(r = 0.95, rel. σ = 1.24%, N = 10).
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
957
Fig. 7 (color online). Crystal structure of 15 showing
N–H···S hydrogen bonds as well as bifurcated C–H···S and
C–H···N contacts.
here the C–H···solvent interactions dominate. In con-
trast, the α term constituted the major contribution to
the observed solvatochromism of unquestionable 2,3-
diaryltetrazolium-5-thiolates [53]. Thus, there is no ev-
idence of involvement of a mesoionic triazolium-5-
thiolate resonance structure here (Scheme 2).
Conclusion
Fundamental groundwork has been laid for a gen-
eral synthetic approach, with few limitations, pro-
viding an extension of the methodic repertory for
the preparation of 1,2,4-triazoline-5-thiones. There is,
however, no general procedure for isolation and pu-
rification. It must be noted that some of the exper-
iments were conducted on a small scale, and yields
were not fully optimized. A compilation of 1,2,4-
Fig. 6 (color online). Bifurcated C–H···S and C–H···N
contacts in the crystal structure of 14.
For 13: δ(1H) = (7.114±0.171)+(0.887±0.267)π∗ triazoline-5-thione ring geometries and hydrogen bond
interactions in the crystalline state is presented. The
thiones are valuable building blocks for substituted
triazolium compounds via S-methyl derivatives. The
+(0.977±0.234)β
(r = 0.95, rel. σ = 1.81%, N = 10).
Both the standard deviations and correlation coeffi- bifunctional amino-thiones offer access to new an-
cients are very satisfactory. It was to be expected that nelated heterocyclic systems. The thiones are also in-
a thiolate would be affected by the hydrogen bond do- teresting ligands on their own. Many metal complexes
nating strength of the solvents. However, the influence of 1,3-disubstituted imidazoline-2-thiones are known,
of the α term was found to be negligible. Interestingly, but comparatively few examples with 1,4-disubstituted
the β term is predominant (more than in the imida- triazoline-5-thiones. Thus, the new thiones open new
zole series [12]), and the resulting correlation of cal- fields, and the results of our ongoing research will
culated vs. observed values is shown in Fig. 10. The be published in due course. Certainly, this work has
dimethylamino compound 13 displayed higher sen- erased some blank areas from the map of heterocycle
sitivity than the dimethyl compound 10. Obviously, territory.
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958
G. Laus et al. · 1,2,4-Triazoline-5-thiones
Fig. 9 (color online). Typical C–H···π interactions in the
crystal structure of 18.
tion of O-benzylhydroxylamine and dimethylformamide
azine [36]. O-(2,4-Dinitrophenyl)hydroxylamine (DNPH)
was prepared according to the published procedure [59].
Synthesis of 1,4-dimethyl-1,2,4-triazolium methylsulfate
(1a) from 1-methyl-1,2,4-triazole has been reported [60], and
there are known procedures for the synthesis of 1,4-dimethyl-
1,2,4-triazolium iodide (1b) from either 1,2,4-triazole or 1-
methyl-1,2,4-triazole [61 – 65]. We prepared 1a from 1,2,4-
triazole and 1b from 4-methyl-1,2,4-triazole in one step
and much shorter reaction times. The quaternary precursor
salts 4-amino-1-methyl-1,2,4-triazolium iodide (2) [66], 4-
amino-1-isopropyl-1,2,4-triazolium bromide (3) [66] and 4-
(dimethylamino)-1-methyl-1,2,4-triazolium hexafluorophos-
phate (4) [34] were prepared as previously described. We
scored a quantitative yield of 3 by refluxing the starting ma-
terials for 5 weeks.
Fig. 8 (color online). Disordered structure of the two inde-
pendent molecules A and B of 17.
1,4-Dimethyl-1,2,4-triazolium methylsulfate (1a)
Experimental Section
1,2,4-Triazole (5.0 g, 72 mmol) was dissolved in 25%
NMR spectra were recorded with a Bruker Avance DPX methanolic NaOMe (16.5 mL). The solvent was evaporated,
300 spectrometer. IR spectra were obtained with a Nico- and the colorless residue was powdered and vacuum-dried
let 5700 FT instrument. High resolution mass spectra were to constant weight. Caution: the following reaction is very
measured with a Finnigan MAT 95 mass spectrometer. exothermic! The sodium triazolide was suspended in CH3CN
1,2,4-Triazole, 4-amino-1,2,4-triazole, and 4-methyl-1,2,4- (25 mL), and dimethyl sulfate (13.7 mL, 145 mmol) was
triazole-3-thiol were purchased from Sigma-Aldrich and added dropwise during 40 min with stirring at such a rate
used as received. 4-Methyl-1,2,4-triazole was prepared by as to keep the temperature below 70 ◦C. Higher temperature
two methods, desulfurization of 4-methyl-1,2,4-triazole-3- gave a brown product. The mixture was stirred for an addi-
thiol [54, 55] or via 1-acetyl-1,2,4-triazole [56 – 58]. In one tional hour at 70 ◦C, cooled and filtered. The volatiles were
step, desulfurization yielded the purest product in highest removed from the filtrate under reduced pressure at 50 ◦C to
yield. 4-Benzyloxy-1,2,4-triazole was obtained by cycliza- yield 14.8 g (98%) of a colorless, viscous oil; n2D0 = 1.469.
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
959
Table 2. Hydrogen bonding
geometries (Å, deg).
Compound Interaction
H···A
D···A
D–H···A
145.6(1)
166.0(1)
136.4(1)
147(3)
146(3)
149.8(2)
133(3)
Symmetry codes (A)
−x, −1/2+y, 3/2−z
1/2−x, 2−y, 1/2+z
−1/2+x, y, 3/2−z
−1+x, y, z
10
C2–H···S
C3–H···S
C3–H···S
2.8123(4)
2.8113(4)
2.9002(4)
3.636(2)
3.769(2)
3.672(2)
3.122(4)
3.491(3)
3.539(4)
3.444(4)
3.526(4)
3.539(4)
3.094(3)
3.380(3)
3.781(3)
3.797(3)
3.784(2)
3.267(3)
3.651(2)
3.223(2)
3.592(2)
3.499(2)
3.695(2)
3.457(3)
3.754(2)
3.56(2)
11
N3A–H···N2B 2.39(3)
N3A–H···SB
2.79(3)
x, 1+y, z
C2A–H···N3A 2.686(2)
1−x, 1−y, 1−z
N3B–H···SA
N3B–H···SA
2.84(4)
2.79(2)
x, y, z
149(3)
154.2(2)
168(2)
x, −1+y, z
C2B–H···N3B 2.660(3)
2−x, 1−y, 2−z
1−x, 1/2+y, 1/2−z
3/2−x, 1−y, −1/2+z
3/2−x, −y, −1/2+z
3/2−x, 1−y, −1/2+z
x, 1/2−y, 1/2+z
x, 1/2−y, 1/2+z
−1+x, 1/2−y, −1/2+z
−1+x, 1/2−y, −1/2+z
1+x, y, z
12
13
N3–H···N3
C2–H···N3
C3–H···S
2.17(2)
2.628(2)
2.8314(6)
2.8911(6)
2.8612(5)
136.4(1)
158.2(2)
154.0(2)
163.9(1)
125.0(1)
164.6(1)
122.3(1)
162(2)
C4–H···S
14
15
C2A–H···SB
C2A–H···N3B 2.628(2)
C2B–H···SA
2.7274(4)
C2B–H···N3A 2.615(2)
N3–H···S
N3–H···S
C2–H···S
C2–H···N3
C2–H···SA
C12–H···SB
C4–H···S
2.80(3)
2.65(3)
158(2)
1−x, 1−y, 1−z
1−x, −1/2+y, 1/2−z
1−x, −1/2+y, 1/2−z
1+x, y, z
1+x, y, z
1+x, y, z
2.9395(5)
2.705(2)
2.92(3)
2.800(1)
2.8300(5)
137.5(1)
136.6(1)
150(3)
138.1(7)
170.2(1)
17
18
3.809(2)
– 1H NMR (300 MHz, [D6]DMSO): δ = 3.37 (s, 3H), 3.88 145.3 ppm. – IR (neat): ν = 1590 m, 1159 s, 1022 s, 835 s,
(s, 3H), 4.04 (s, 3H), 9.06 (s, 1H), 9.92 (s, 1H) ppm. – 13C 734 m, 658 m, 622 m, 569 s cm−1
.
NMR (75 MHz, [D6]DMSO): δ = 34.0, 38.6, 53.1, 143.6,
4-(Dimethylamino)-1-isopropyl-1,2,4-triazolium
hexafluorophosphate (5)
145.4 ppm. – IR (neat): ν = 3090 w, 1590 m, 1211 s, 1059
m, 998 s, 732 s, 577 s cm−1. – HRMS (FAB): m/z = 98.0836
(calcd. 98.0713 for C4H8N3, [M]+).
A mixture of 4-amino-1-isopropyl-1,2,4-triazolium bro-
mide (3) (2.0 g, 9.7 mmol) and dimethyl sulfate (1.83 mL,
2 equiv.) was stirred at 100 ◦C for 12 h. The solution was al-
1,4-Dimethyl-1,2,4-triazolium iodide (1b)
A solution of 4-methyl-1,2,4-triazole (0.55 g, 6.6 mmol) lowed to cool to 20 ◦C, and H2O (6 mL) was added. A so-
and CH3I (2.1 g, 15 mmol) in MeOH (1.5 mL) was heated lution of NH4PF6 (1.57 g, 9.7 mmol) in H2O (4 mL) was
in a pressure vessel (bath temperature 100 ◦C) for 1 h. Af- added, and the colorless precipitate was stirred for 10 min,
ter cooling the solvent was evaporated. The residue was sus- filtered off, washed with H2O (4 mL), and dried. Yield: 2.2 g
pended in Et2O, filtered and dried to yield a gray powder (76%). M. p. 151 ◦C. – 1H NMR (300 MHz, [D6]DMSO):
(1.27 g, 85%). The spectroscopic data were as previously re- δ = 1.51 (d, J = 6.6 Hz, 6H), 2.95 (s, 6H), 6.70 (sept,
ported [49].
J = 6.6 Hz, 1H), 9.62 (s, 1H), 10.48 (s, 1H) ppm. – 13C
NMR (75 MHz, [D6]DMSO): δ = 21.0 (2C), 47.7 (2C),
55.8, 140.6, 142.4 ppm. – IR (neat): ν = 3154 w, 1561 w,
1469 w, 1129 w, 1072 w, 985 w, 885 w, 817 s, 655 m, 555
s cm−1. – C7H15F6N4P (300.18): calcd. C 28.01, H 5.04, N
18.66; found C 27.90, H 4.85, N 18.42.
1,4-Dimethyl-1,2,4-triazolium hydrogensulfate (1c)
A solution of 1,4-dimethyl-1,2,4-triazolium iodide (1b)
(0.50 g, 2.2 mmol) in H2O (3 mL) was added dropwise to
a stirred solution of Ag2SO4 (0.35 g, 1.1 mmol) and H2SO4
(2.22 mL 0.5 M, 1.1 mmol) in H2O (15 mL) at 50 ◦C. The
mixture was stirred for 30 min and filtered (0.45 µm). The
volatiles were removed from the filtrate under reduced pres-
1-Amino-4-methyl-1,2,4-triazolium 2,4-dinitrophenolate
(6a)
sure at 50 ◦C to yield a colorless oil (0.43 g, 99%); n2D0
=
A solution of 4-methyl-1,2,4-triazole (1.08 g, 13 mmol)
1.487. – 1H NMR (300 MHz, [D6]DMSO): δ = 3.90 (s, 3H), and DNPH (2.60 g, 13 mmol) in CH2Cl2 (20 mL) was stirred
4.06 (s, 3H), 5.0 (br, 1H), 9.13 (s, 1H), 10.20 (s, 1H) ppm. at 20 ◦C for 4 d. The product precipitated and was collected
–
13C NMR (75 MHz, [D6]DMSO): δ = 33.9, 38.5, 143.8, by filtration, washed with CH2Cl2 (5 mL) and Et2O (5 mL),
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
[D6]DMSO): δ = 3.86 (s, 3H), 9.10 (s, 1H), 10.17 (s, 1H)
ppm. – 13C NMR (75 MHz, [D6]DMSO): δ = 34.2, 140.4,
143.4 ppm. – IR (neat): ν = 3214 m, 3107 m, 3002 m, 1528
w, 1179 m, 1061 m, 987 m, 901 m, 651 m, 619 s, 461 m
cm−1
.
4-Benzyloxy-1-methyl-1,2,4-triazolium tetrafluoroborate (7)
solution of 4-benzyloxy-1,2,4-triazole (0.80 g,
A
4.6 mmol) and Me3O+ BF4−(0.71 g, 1.05 equiv.) in CH2Cl2
(4 mL) was stirred at room temperature for 20 h. MeOH
(0.1 mL) was added, and the volatiles were removed under
reduced pressure. The residue was washed with Et2O
(2 × 5 mL) to yield 1.03 g (81%) of crude 7 as a syrup. –
1H NMR (300 MHz, [D6]DMSO): δ = 4.04 (s, 3H), 5.52 (s,
2H), 7.4 – 7.5 (m, 5H), 9.53 (s, 1H), 10.60 (s, 1H) ppm.
4-Benzyloxy-1-ethyl-1,2,4-triazolium tetrafluoroborate (8)
A
solution of 4-benzyloxy-1,2,4-triazole (1.0 g,
5.7 mmol) and Et3O+ BF−4 (1.14 g, 1.05 equiv.) in
CH2Cl2 (5 mL) was stirred at room temperature for 17 h.
MeOH (0.3 mL) was added, and the volatiles were removed
under reduced pressure. The residue was washed with Et2O
(2 × 5 mL) to yield 1.54 g of crude 8 as a syrup which
was used in the next step without purification. – 1H NMR
(300 MHz, [D6]DMSO): δ = 1.46 (t, J = 7.3 Hz, 3H), 4.36
(q, J = 7.3 Hz, 2H), 5.55 (s, 2H), 7.50 (m, 5H), 9.55 (s, 1H),
10.65 (s, 1H) ppm.
Fig. 10. Correlation of calculated and observed 1H NMR
shifts of 1,4-dimethyl-1,2,4-triazoline-5-thione 10 (•) and
4-(dimethylamino)-1-methyl-1,2,4-triazoline-5-thione 13 (◦)
in different solvents: (1) CCl4, (2) CDCl3, (3) CD2Cl2, (4)
CD3CN, (5) [D6]acetone, (6) [D8]THF, (7) CD3OD, (8)
D2O, (9) [D7]DMF, (10) [D6]DMSO.
1-Benzyl-4-methyl-1,2,4-triazolium bromide (9)
A solution of 4-methyl-1,2,4-triazole (0.32 g, 3.9 mmol)
and benzyl bromide (0.50 mL, 1.1 equiv.) in CH3CN (5 mL)
was refluxed for 21 h. On cooling, the product crystallized
and was collected by filtration and dried. Yield: 0.72 g
(74%). M. p. 158 ◦C. – 1H NMR (300 MHz, [D6]DMSO):
δ = 3.91 (s, 3H), 5.66 (s, 2H), 7.38 – 7.43 (m, 5H), 9.21 (s,
1H), 10.32 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO):
δ = 34.2, 54.5, 128.8 (5C), 133.4, 143.2, 145.8 ppm. – IR
(neat): ν = 2988 w, 2940 w, 1582 m, 1457 w, 1357 w, 1152
Scheme 2.
and dried to yield 2.45 g (67%) of a yellow powder. – 1H
NMR (300 MHz, [D6]DMSO): δ = 3.84 (s, 3H), 6.32 (d, J =
9.7 Hz, 1H), 7.41 (s, 2H), 7.77 (dd, J = 9.7 Hz, J = 3.1 Hz,
1H), 8.59 (d, J = 3.1 Hz, 1H), 8.98 (s, 1H), 9.98 ppm. – 13
C
NMR (75 MHz, [D6]DMSO): δ = 34.1, 125.0, 126.5, 127.4,
136.0, 140.7, 143.4, 170.3 ppm. – IR (neat): ν = 3294 w,
3236 w, 3081 m, 2988 m, 1595 s, 1550 m, 1525 s, 1475 m,
1431 m, 1371 m, 1307 s, 1258 s, 1175 m, 1128 s, 983 m, 834
s, 710 m, 654 m, 618 s cm−1. – C9H10N6O5 (282.21): calcd.
C 38.30, H 3.57, N 29.78; found C 38.28, H 3.42, N 29.40.
m, 999 w, 912 w, 721 s, 695 s, 640 m, 621 m, 614 m cm−1
.
1,4-Dimethyl-1,2,4-triazoline-5-thione (10)
A mixture of 1,4-dimethyl-1,2,4-triazolium methylsul-
fate (1a) (1.0 g, 4.8 mmol), sulfur (153 mg, 1.0 equiv.) and
K2CO3 (0.79 g, 1.2 equiv.) in MeOH (7 mL) was stirred at
70 ◦C (bath temperature) for 2 h. Insoluble material was re-
1-Amino-4-methyl-1,2,4-triazolium chloride (6b)
A
suspension of the dinitrophenolate 6a (2.40 g, moved by filtration and washed with MeOH. The solvent
8.5 mmol) in 1 M HCl (70 mL) was stirred at 80 ◦C for was evaporated, and the residue was dissolved in hot H2O
1 h. The solids were filtered off, well washed with hot 1 M (2 mL). On cooling to 5 ◦C, fine needles precipitated and
HCl (2 × 20 mL) and hot H2O (20 mL), and the filtrate was were collected by filtration. The mother liquor was concen-
taken to dryness under reduced pressure. The product was trated and cooled to give a second crop of the product which
recrystallized from MeOH and washed with Et2O. Yield: was dried over P2O5. Yield: 0.45 g (73%). Single crystals
1.03 g (90%). M. p. 194 – 196 ◦C. – 1H NMR (300 MHz, were obtained by slow evaporation of a tetrachloromethane
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961
solution. M. p. 92 ◦C (lit. 93 ◦C [1]). – 1H NMR (300 MHz, ganic phase was repeatedly washed with 1 M HCl (3 × 2 mL)
[D6]DMSO): δ = 3.44 (s, 3H), 3.64 (s, 3H), 8.46 (s, 1H) and taken to dryness under reduced pressure to yield 13
ppm. – 13C NMR (75 MHz, [D6]DMSO): δ = 32.4, 36.1, (0.42 g, 72%).
141.4, 165.5 ppm. – IR (neat): ν = 3109 w, 3040 w, 1533 w,
1389 m, 1357 s, 1227 m, 1171 m, 1049 m, 977 m, 846 m, triazolium hexafluorophosphate (4) (1.0 g, 3.7 mmol), sul-
768 m, 628 s cm−1
b) A mixture of 4-(dimethylamino)-1-methyl-1,2,4-
.
fur (118 mg, 1.0 equiv.) and K2CO3 (0.61 g, 1.2 equiv.) in
MeOH (5 mL) was refluxed for 2 h. The solvent was removed
under reduced pressure, and the residue was dissolved in
H2O (10 mL). The aqueous phase was extracted with EtOAc
(3 × 3 mL). The combined organic extracts were washed
with H2O (2 × 3 mL), brine (3 mL) and taken to dryness
under reduced pressure to yield 13 (0.47 g, 81%) as an oil
which soon solidified. Recrystallization from hot H2O re-
sulted in unacceptable losses. Sublimation at 55 ◦C/0.1 mbar
gave 0.45 g (77%) colorless crystals. Single crystals were
obtained from pyridine-Et2O (1 : 1) at −20 ◦C. M. p. 72 ◦C. –
1H NMR (300 MHz, [D6]DMSO): δ = 2.93 (s, 6H), 3.61 (s,
3H), 8.69 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO):
δ = 35.8, 44.4 (2C), 139.4, 163.2 ppm. – IR (neat): ν = 3079
w, 3016 w, 2967 w, 2876 w, 2833 w, 2797 w, 1460 m, 1444
m, 1368 s, 1350 m, 1235 w, 1187 m, 1156 m, 1144 m, 1098
w, 1022 m, 970 m, 918 m, 889 m, 747 m, 677 m, 631 s
cm−1. – HRMS (EI): m/z = 158.0526 (calcd. 158.0621 for
C5H10N4S, [M]+).
4-Amino-1-methyl-1,2,4-triazoline-5-thione (11)
A mixture of 4-amino-1-methyl-1,2,4-triazolium iodide
(2) (1.0 g, 4.4 mmol), sulfur (142 mg, 1.0 equiv.) and K2CO3
(0.73 g, 1.2 equiv.) in MeOH (7 mL) was stirred at 70 ◦C
(bath temperature) for 2 h. The solvent was removed un-
der reduced pressure, and the residue was recrystallized
from hot H2O (6 mL). Yield: 0.46 g (80%). Single crys-
tals were obtained from pyridine at room temperature.
M. p. 140 – 142 ◦C (lit. 139 ◦C [2], 142 ◦C [7]). – H NMR
1
(300 MHz, [D6]DMSO): δ = 3.64 (s, 3H), 5.74 (br s, 2H),
8.52 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO): δ =
36.6, 140.9, 165.4 ppm. – IR (neat): ν = 3269 m, 3177 w,
3113 w, 3034 w, 2940 w, 1604 m, 1531 w, 1473 m, 1388 m,
1331 m, 1235 m, 1213 m, 1153 m, 1060 w, 1003 m, 962 m,
846 s, 784 m, 666 w, 627 s cm−1
.
4-Amino-1-isopropyl-1,2,4-triazoline-5-thione (12)
4-(Dimethylamino)-1-isopropyl-1,2,4-triazoline-5-thione
(14)
A mixture of 4-amino-1-isopropyl-1,2,4-triazolium bro-
mide (3) (1.0 g, 4.8 mmol), sulfur (155 mg, 1.0 equiv.) and
Et3N (0.67 mL, 1.0 equiv.) in pyridine (5 mL) was stirred at
70 ◦C for 2 h. The volatiles were evaporated under reduced
pressure, and the residue was partitioned between 0.1 M HCl
(10 mL) and EtOAc (4 mL). The aqueous phase was ex-
tracted with EtOAc (2 × 3 mL). The combined organic ex-
tracts were washed with brine (3 mL) and taken to dryness
under reduced pressure to yield 12 (0.69 g, 90%) as an off-
white powder which could be recrystallized from hot H2O.
Single crystals were obtained from pyridine-H2O (2 : 1) at
A
solution of 4-(dimethylamino)-1-isopropyl-1,2,4-
triazolium hexafluorophosphate (5) (0.50 g, 1.7 mmol),
sulfur (53 mg, 1.0 equiv.) and Et3N (0.23 mL, 1.0 equiv.)
in pyridine (2 mL) was stirred at 70 ◦C for 2 h. The solvent
was removed under reduced pressure, and the residue was
dissolved in EtOAc (10 mL). The organic phase was washed
with 1 M HCl (4 × 2 mL) and H2O (2 × 1 mL) and taken to
dryness under reduced pressure to yield 14 (0.30 g, 97%).
Recrystallization from hot H2O involved heavy losses, but
sublimation at 75 ◦C/0.1 mbar gave 0.29 g (93%) colorless
crystals. Single crystals were obtained from H2O. M. p.
95 ◦C. – 1H NMR (300 MHz, [D6]DMSO): δ = 1.27 (d,
J = 6.7 Hz, 6H), 2.93 (s, 6H), 4.95 (sept, J = 6.7 Hz, 1H),
8.69 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO):
δ = 20.4 (2C), 44.5 (2C), 48.9, 139.5, 162.0 ppm. – IR
(neat): ν = 3071 w, 3005 w, 2984 w, 2871 w, 1529 w,
1410 s, 1363 s, 1347 s, 1327 s, 1221 m, 1115 w, 1038 w,
1021 w, 991 m, 916 w, 885 m, 831 w, 686 m, 642 m, 592 s
cm−1. – HRMS (EI): m/z = 186.0970 (calcd. 186.0934 for
C7H14N4S, [M]+).
1
−20 ◦C. M. p. 104 ◦C. – H NMR (300 MHz, [D6]DMSO):
δ = 1.29 (d, J = 6.7 Hz, 6H), 4.87 (sept, J = 6.7 Hz, 1H),
5.75 (br s, 2H), 8.53 (s, 1H) ppm. – 13C NMR (75 MHz,
[D6]DMSO): δ = 20.5 (2C), 50.1, 141.0, 164.1 ppm. – IR
(neat): ν = 3278 w, 3169 w, 3097 w, 3036 w, 2978 w, 2946
w, 1639 m, 1538 w, 1433 s, 1397 m, 1332 s, 1220 m, 1125
m, 975 m, 876 m, 755 m, 637 m, 566 m cm−1. – HRMS (EI):
m/z = 158.0560 (calcd. 158.0621 for C5H10N4S, [M]+).
4-(Dimethylamino)-1-methyl-1,2,4-triazoline-5-thione (13)
a)
A mixture of 4-(dimethylamino)-1-methyl-1,2,4-
triazolium hexafluorophosphate (4) (1.0 g, 3.7 mmol), sulfur
(118 mg, 1.0 equiv.) and Et3N (0.51 mL, 1.0 equiv.) in pyri-
dine (5 mL) was stirred at 70 ◦C for 2 h. The volatiles were
evaporated under reduced pressure, and the residue was par-
1-Amino-4-methyl-1,2,4-triazoline-5-thione (15)
a) A solution of 1-amino-4-methyl-1,2,4-triazolium chlo-
titioned between 1 M HCl (2 mL) and EtOAc (5 mL). The or- ride (6b) (0.30 g, 2.2 mmol), sulfur (72 mg, 1.0 equiv.) and
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G. Laus et al. · 1,2,4-Triazoline-5-thiones
Et3N (0.31 mL, 1.0 equiv.) in pyridine (2 mL) was stirred at NMR (300 MHz, [D6]DMSO): δ = 1.26 (t, J = 7.2 Hz, 3H),
70 ◦C for 2 h. The volatiles were evaporated under reduced 4.10 (q, J = 7.2 Hz, 2H), 5.38 (s, 2H), 7.42 – 7.50 (m, 5H),
pressure, and the residue was partitioned between 1 M HCl 8.67 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO): δ =
(3 mL) and EtOAc (8 mL). The aqueous phase was extracted 12.9, 43.8, 79.0, 128.6 (2C), 129.5, 130.0 (2C), 132.9, 137.8,
with EtOAc (2 mL). The combined organic extracts were 160.5 ppm. – IR (neat): ν = 3112 w, 1444 m, 1420 s, 1348 s,
washed with 1 M HCl (2 × 2 mL) and brine (2 mL) and taken 1301 m, 1189 m, 1145 m, 952 s, 741 s, 699 s, 665 s, 618 s,
to dryness under reduced pressure to yield 15 as an off-white 579 m, 538 s cm−1. – HRMS (FAB): m/z = 236.0829 (calcd.
powder (0.13 g, 45%).
236.0852 for C11H14N3OS, [M+H]+).
b) A mixture of 1-amino-4-methyl-1,2,4-triazolium chlo-
ride (6b) (0.30 g, 2.2 mmol), sulfur (72 mg, 1.0 equiv.) and
K2CO3 (0.37 g, 1.2 equiv.) in MeOH (3 mL) was stirred for
4 h at room temperature. The solids were filtered off, washed
well with MeOH, and the filtrate was taken to dryness under
reduced pressure. The product was recrystallized from hot
H2O (2 mL) and dried. Single crystals were obtained from
1-Benzyl-4-methyl-1,2,4-triazoline-5-thione (18)
a) A mixture of 1-benzyl-4-methyl-1,2,4-triazolium bro-
mide (9) (0.15 g, 0.59 mmol), sulfur (19 mg, 1.0 equiv.) and
K2CO3 (98 mg, 1.2 equiv.) in MeOH (1 mL) was stirred at
70 ◦C for 2 h. Addition of H2O (2 mL) gave a clear solution
which on cooling to 20 ◦C deposited the crystalline product.
Yield: 93 mg (77%).
1
H2O. Yield: 0.17 g (58%). M. p. 134 ◦C (dec.). – H NMR
(300 MHz, [D6]DMSO): δ = 3.44 (s, 3H), 6.12 (s, 2H), 8.33
(s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO): δ = 32.8,
138.0, 162.9 ppm. – IR (neat): ν = 3255 m, 3151 m, 3104
m, 3049 w, 2953 w, 1629 m, 1537 m, 1446 m, 1415 m, 1338
s, 1245 w, 1218 m, 1088 w, 1015 m, 937 m, 875 s, 775 m,
667 m, 628 s, 507 m cm−1. – HRMS (EI): m/z = 130.0326
(calcd. 130.0308 for C3H6N4S, [M]+).
b) A mixture of 1-benzyl-4-methyl-1,2,4-triazolium bro-
mide (9) (0.40 g, 1.6 mmol), sulfur (51 mg, 1.0 equiv.) and
Et3N (0.22 mL, 1.0 equiv.) in pyridine (2 mL) was stirred
at 70 ◦C for 2 h. The product was precipitated by addi-
tion of H2O (4 mL), collected by filtration, washed with
H2O (4 mL), and dried in a vacuum. Yield: 0.25 g (77%).
Single crystals were obtained from aqueous acetone. M. p.
118 – 120 ◦C (lit. 118 – 119 ◦C [67]). – 1H NMR (300 MHz,
[D6]DMSO): δ = 3.48 (s, 3H), 5.31 (s, 2H), 7.31 (m, 5H),
8.50 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO): δ =
32.5, 51.5, 127.8, 127.9 (2C), 128.5 (2C), 135.9, 141.7,
165.9 ppm. – IR (neat): ν = 3144 w, 1546 m, 1447 m, 1414 s,
1351 s, 1216 m, 1099 m, 1017 m, 794 m, 734 s, 703 s, 665 m,
630 m, 579 m, 531 m cm−1. – HRMS (EI): m/z = 205.0603
(calcd. 205.0668 for C10H11N3S, [M]+).
4-Benzyloxy-1-methyl-1,2,4-triazoline-5-thione (16)
A
mixture of crude 4-benzyloxy-1-methyl-1,2,4-
triazolium tetrafluoroborate (7) (0.50 g, 1.8 mmol), sulfur
(58 mg, 1.0 equiv.) and Et3N (0.25 mL, 1.0 equiv.) in
pyridine (2 mL) was stirred at room temperature for 76 h.
The product was precipitated by addition of H2O (10 mL),
collected by filtration, washed with H2O (2 mL), and
dried under vacuum. Yield: 0.15 g (38%). Crystals were
obtained from aqueous acetone. M. p. 102 – 104 ◦C. – 1H
NMR (300 MHz, CDCl3): δ = 3.76 (s, 3H), 5.41 (s, 2H),
7.29 (s, 1H), 7.41 (m, 5H) ppm. – 1H NMR (300 MHz,
[D6]DMSO): δ = 3.64 (s, 3H), 5.36 (s, 2H), 7.42 – 7.49 (m,
5H), 8.68 (s, 1H) ppm. – 13C NMR (75 MHz, [D6]DMSO):
δ = 36.4, 79.0, 128.7 (2C), 129.5, 130.0 (2C), 133.0, 137.7,
161.1 ppm. – IR (neat): ν = 3133 w, 1456 m, 1398 m, 1362
m, 1348 m, 1147 m, 960 m, 915 m, 818 m, 747 s, 703 s,
677 m, 651 m, 616 s, 578 m, 533 m cm−1. – HRMS (EI):
m/z = 221.0634 (calcd. 221.0617 for C10H11N3OS, [M]+).
Oxidative desulfurization of 10 to 1,4-dimethyl-
1,2,4-triazolium hydrogensulfate (1c)
In an open test tube, thione 10 (50 mg) was heated at
160 ◦C for 24 h. On cooling the product (40 mg, 53%) was
obtained as a colorless liquid. The spectroscopic data were
matching those of authentic 1c.
Crystal structure determination
X-Ray diffraction data were collected with an Oxford
Diffraction Gemini-R Ultra diffractometer using MoKα (λ =
4-Benzyloxy-1-ethyl-1,2,4-triazoline-5-thione (17)
A mixture of crude 4-benzyloxy-1-ethyl-1,2,4-triazolium 0.7107 Å) or CuKα radiation (λ = 1.5418 Å), as noted in
tetrafluoroborate (8) (1.5 g, 5.2 mmol), sulfur (165 mg, 1.0 Table 1, at 173 K. Absorption corrections were applied in
equiv.) and Et3N (0.72 mL, 1.0 equiv.) in pyridine (5 mL) all cases (multi-scan). The crystal structures were solved
was stirred at 70 ◦C for 2 h. Addition of H2O (35 mL) pre- by Direct Methods and refined by full-matrix least-squares
cipitated an oil which was stirred overnight at room temper- techniques [68, 69]. All non-hydrogen atoms were assigned
ature until it solidified. The product was filtered off, washed anisotropic displacement parameters in the refinement. The
with H2O and dried in a vacuum. Yield: 0.49 g (40%). Sin- Flack parameter x of the non-centrosymmetric crystal struc-
1
gle crystals were obtained from CH3CN. M. p. 63 ◦C. – H ture of 13 was 0.0(3).
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CCDC 977713–977720 contain the supplementary crys- Acknowledgement
tallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
We are grateful to H. Kopacka for the NMR spectra and
to T. Müller for the HR mass spectra.
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