Solvent-free synthesis of benzothiazole-based quaternary ammonium salts: Precursors to ionic liquids

Article abstract of DOI:10.3998/ark.5550190.0011.703

A series of 13 benzothiazolium iodide salts have been prepared in solvent-free conditions by optimizing the reaction. An additional 26 benzothiazolium salts with bistrifluoromethanesulfonimide and trifluoromethylsulfonate were prepared via simple metathesis reactions from the iodide precursors. Out of a total of 39 prepared salts, 26 were identified as ionic liquids, with melting points as low as 42 °C observed for dodecylbenzothiazolium bistrifluoromethanesulfonimide. All prepared compounds have been characterized using FTIR, ¹H, ¹³C NMR, and HRMS analyses. The thermal stabilities as well as melting points of these salts were also analyzed.

Full text of DOI:10.3998/ark.5550190.0011.703

Issue in Honor of Prof. Richard Bartsch
ARKIVOC 2010 (vii) 19-37
Solvent-free synthesis of benzothiazole-based quaternary
ammonium salts: precursors to ionic liquids
Sohail Nadeem,a Munawar A. Munawar,*a Saeed Ahmad,b Marcin Smiglak,d
David M. Drab,d Khizar I. Malik,a Rana Amjad,a Chaudhry M. Ashraf,c
and Robin D. Rogers*d
a Institute of Chemistry, University of the Punjab, Lahore, Pakistan
b Department of Chemistry University of Science and Technology Bannu, Pakistan
c Forman Christian College a Chartered University, Lahore, Pakistan
d Department of Chemistry and Center for Green Manufacturing, The University of Alabama,
Tuscaloosa, AL 35487, USA
E-mail: munawaralimunawar@yahoo.com, rdrogers@as.ua.edu
This paper is dedicated to Professor Richard A. Bartsch on the occasion of his 70th
birthday and retirement
Abstract
A series of 13 benzothiazolium iodide salts have been prepared in solvent-free conditions by
optimizing
the
reaction.
An
additional
26
benzothiazolium
salts
with
bistrifluoromethanesulfonimide and trifluoromethylsulfonate were prepared via simple
metathesis reactions from the iodide precursors. Out of a total of 39 prepared salts, 26 were
identified as ionic liquids, with melting points as low as 42 oC observed for
dodecylbenzothiazolium bistrifluoromethanesulfonimide. All prepared compounds have been
characterized using FTIR, 1H, 13C NMR, and HRMS analyses. The thermal stabilities as well as
melting points of these salts were also analyzed.
Keywords: Benzothiazolium iodides, ionic liquids, solvent free synthesis, quaternary
ammonium salts
Introduction
It is now generally recognized that chemistry is one of the key sciences able to impact the
environment in both a positive and negative fashion. As a result there is a growing awareness
that the design of synthetic, or chemical processes, should follow the basic principles of green
chemistry to reduce risks to humans and the environment.1,2 Among several aspects of green
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chemistry, the reduction/replacement of volatile organic solvents from the reaction medium is of
utmost importance3 and one strategy that is now emerging is the use of low melting organic salts,
o
called ionic liquids (ILs, currently defined as salts which melt below 100 C), as alternative
solvents.4
Over the last two decades a lot has been learned about ILs, allowing a more balanced
discussion about their possible ‘greenness’. Many ILs have interesting properties that often can
be tuned for particular applications just by simple variation of the constituent ions. In several
cases ILs can have properties such as high thermal stability, low viscosity, high polarity, and low
melting points that can be advantageous when considering ILs as volatile organic compounds
replacement. In this light the growing interest in the use of ILs in organic synthesis as solvents,
catalysts or reagents is expanding rapidly and this research field has been recently extensively
reviewed by Martins et al.,5 As these authors point out, since the initial reports of the use of ILs
in organic synthesis, ILs are finding more and more applications in various organic reactions
including homogenous and heterogeneous catalysis, transition-metal mediated catalysis, or even
as solvents in bioorganic reactions. Nonetheless, it is equally clear that not all ILs have these
properties and indeed some can be quite toxic or not suitable for particular processes. We have
therefore been searching for new classes of compounds which might exhibit IL behavior in hopes
of developing more benign solvents.
One class of potential cations of interest is based on benzothiazolium. Current literature
reports of the use of this cation are limited,6-9 but it has been suggested that benzothiazolium
salts posses catalytic activity10 in certain organic reactions11 such as benzoin condensations.12,13
Benzothiazoles have also found many applications in the field of dyes14 (e.g., direct yellow 715)
and in medicine where benzothiazolium salts play an important role in pharmaceuticals (e.g.,
Riluzole16 is a benzothiazole-based drug that is used to treat amyotrophic lateral sclerosis).
Our objective for the work presented here, was to prepare a family of benzothiazolium-based
salts utilizing solvent-free synthesis and at the same time expand the pool of available
benzothiazolium salts by incorporation of different organic anions. In addition, from an IL point
of view, the use benzothiazolium-based salts over the now commonly used imidazolium-based
ILs, could offer cost savings (cheaper starting materials and facile syntheses) making them
attractive to explore.17
Here we report the use of solvent-free methods for the quaternization of benzothiazole with a
series of alkyl halides where no excess of reactant is being used while at the same time allowing
for almost quantitative yield of the obtained products. Thirty nine N-alkylated benzothiazolium
salts were prepared with various alkyl chain lengths (C1-C12) and paired with anions such as I-,
[Tf2N]-, and [CF3SO3]-, out of which 26 were identified as ionic liquids, with melting points as
o
low as 42 C observed for dodecylbenzothiazolium bistrifluoromethanesulfonimide. The
preparation, characterization, and analysis of these compounds are discussed below.
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Results and Discussion
Synthesis of N-alkyl benzothiazolium iodide salts
A systematic strategy to prepare benzothiazolium chlorides, bromides, and iodides is limited by
the reactivity of the alkyl halides used as alkylating agent which usually increases in the order
RCl < RBr < RI. We first attempted several N-alkylation reactions of benzothiazole with alkyl
chlorides in a pressure vial at temperatures of 50 - 180 oC, but none of the N-
alkylbenzothiazolium chlorides attempted could be isolated in satisfactory yields. By contrast N-
alkylation of benzothiazole was successful using several different alkyl iodides under the
optimized and relatively convenient conditions reported here. While we did not employ alkyl
bromides in these reactions, we do believe based on our preliminary results that the use of alkyl
iodides was dictated by their much higher reactivity than their bromide or chloride analogs.
Although many literature methods are available for the synthesis of N-alkyl benzothiazolium
iodides they require long reaction times,18,19 use of excess alkyl halide20 and the use of a solvent
in order to obtain close to 100% yields.21 Our initial attempts to synthesize N-methylbenzo-
thiazolium iodide using solvent-free conditions in the reaction of benzothiazole with
iodomethane at different temperatures were successful, but the yield of the product was not
comparable with the previously reported method.22 We then performed the reaction under
ultrasonic irradiation at room temperature with equal mole ratios of reactants and without solvent
resulting in 99.8% yield after 1 h (Table 1). Unfortunately, using these conditions with longer
chain alkyl iodides gave unsatisfactory product yields (average c.a. 20%). For these syntheses,
conventional heating and stirring method was used and optimization of the reaction conditions
led to good yields without use of solvents and with equal mole ratios of the reactants.
Thirteen N-alkylbenzothiazolium iodide salts were obtained using temperatures from 30 to
o
200 C, depending on the alkyl halide chain length, for 2 h to 9 h; (Scheme 1; Table 1). The
reaction protocol was similar to that reported by Hor et al.,22 for the solvent-free synthesis of five
examples of N-alkylbenzothiazolium halides (including 2a, 3a, and 5a reported here), with the
difference that the reaction times reported by Hor et al. were from overnight to 24 h with
temperatures between room temperature and 80 oC.
1
In general, the yields varied between 75 and 99%. Each salt was analyzed by H and 13C
NMR, FTIR, HRMS, and thermal analyses (DSC and TGA). Three of the iodide salts (12a, 13a,
14a) were successfully crystallized and single crystal X-ray diffraction analysis was carried out.
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S
S
N
no solvent
Alk
N
I
30-200 oC
2-9 h
I-
R
(2-14)a
1
S
Acetone/H2O
r.t., 4 h
S
N
LiTf2N
N
R
Tf2N-
I
R
(2-14)a
(2-14)b
S
N
Acetone/H2O
r.t., 4 h
S
CF3SO3Na
N
R
-
I
CF3SO3
R
(2-14)a
(2-14)c
Scheme 1. Synthesis of N-alkylbenzothiazolium iodide salts and further anion exchange
reactions, where R = CH3 (2); C2H5 (3); C3H7 (4); isoC3H7 (5); C4H9 (6); C5H11 (7); C6H13 (8);
C7H14 (9); C8H17 (10); C9H19 (11); C10H21 (12); C11H23 (13); C12H25 (14). (Syntheses of iodide
salts 2a-9a, and 14a, and trifluoromethanesulfonate salts 2c and 9c have been previously
reported, but the data available is limited to spectroscopic results without physical
characterization.23-25
Table 1. Specific temperatures, reaction times, and yields for compounds (2-14)a (Scheme 1 top)
Yield
%
Temperature
ºC
Time
h
No.
R
2a
3a
CH3
C2H5
82, 99.8*
20-25
9.0
75
68
62
80
79
77
75
80
73
70
75
72
50 – 60
80 – 90
4.0
6.0
7.0
5.5
1.0
3.0
4.0
4.0
2.0
4.5
3.0
5.0
4a
C3H7
5a
isoC3H7
C4H9
70 – 80
6a
110 – 120
125 – 135
160 – 170
180 – 190
210 – 220
150 – 160
110 – 120
95 – 105
140 – 150
7a
C5H11
C6H13
C7H15
C8H17
C9H19
C10H21
C11H23
C12H25
8a
9a
10a
11a
12a
13a
14a
*Reaction performed under ultrasonic irradiation at room temperature with equal mole ratios of
reactants for 5 h.
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Single crystals of 12a, 13a, and 14a could be isolated by slow evaporation from ethyl acetate
and were characterized by single crystal X-ray diffraction. The crystal structures of all three
compounds are quite similar and virtually isostructural. Each crystallizes in the triclinic space
group P-1 with modest differences in the cell parameters. There is evidence of +/- gauche
disorder in the terminal -CH2CH3 group in each alkyl chain (Figure 1). This disorder could not
be resolved for 13a, the C11 derivative, although the ellipsoids shapes for these carbon atoms
suggest it is present. For the C10 (12a) and C12 (14a) derivatives, the disorder could be resolved
and was modeled with 60/40% occupancy for the two distinct orientations for 12a and 75/25%
occupancy for the disorder in 14a.
12a
13a
14a
Figure 1. Plots with thermal ellipsoids (50 % probability) shown for crystal structures of 12a
(top), 13a (middle) and 14a (bottom).
The ions pack in a bilayer-type structure with the alkyl chains interdigitated and the cation
head groups and iodide ions forming a polar region. This type of packing has been observed
previously in long alkyl chain imidazolium ionic liquids,26 as well as other similar molecules
with polar head groups and long non-polar alkyl chains.27 There is no pi-stacking between
cationic head groups.
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13a
Figure 2. A packing diagram for 13a, where I•••S contacts are shown (dashed lines). Hydrogen
atoms have been omitted for clarity.
The iodide environments are characterized by short contacts to four cation head groups via
two S atoms (I•••S ca. 3.562 to 3.715 Å) and the hydrogen atom on the C2 carbon of two
additional cations (H•••I ca. 2.994 to 3.080 Å). Other contacts within the van der Waals
separation include hydrogen atoms of the alkyl chain, particularly the alpha carbon (C9) and
terminal methyl carbon.
Synthesis of N-alkyl benzothiazolium [NTf2]- (b) and [CF3SO3]- (c) salts
After successful preparation and purification of the iodide salts, solvent (acetone) assisted ion
exchange metathesis reactions28-30 were carried out to prepare the [NTf2]- and [CF3SO3]-
derivatives resulting in preparation of 26 compounds out of which 24 are reported here for the
first time. Literature reports vary from using absolutely anhydrous conditions31 to reactions in
water32 for anion exchange reactions between I- and [NTf2]- or [CF3SO3]- anions. Here, for 1 g of
iodide salt, 10 mL of acetone and a molar equivalent of the anion salt (i.e., Li[NTf2] or
Na[CF3SO3]) was added followed by stirring at room temperature for 4 h. Purification and
isolation of the new salts was performed by drying and further extraction of products with
anhydrous ethyl acetate (absolute ethanol where necessary). Successful metathesis was checked
by silver nitrate halide test. The anion exchange reactions gave yields above 80% and all of the
obtained salts were analyzed by 1H and 13C NMR, FTIR, MS, DSC, and TGA.
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Spectroscopic analyses
All 39 reported benzothiazolium salts (2-14(a-c)) were analyzed using FTIR, NMR, and HRMS
in order to confirm their purity and structure. The FTIR spectroscopic data (presented in the
experimental section) are in agreement with the few examples of previously reported N-
alkylbenzothiazolium iodides.33 The most intense and characteristic bands in FTIR spectra of the
benzothiazolium core appear around 3000 cm-1 (C-H from Ar-H stretch), 2852-2924 cm-1 (C-H
from CH2 stretch), 1635-1578 (C=C), 1509-1524 cm-1 (C=N), 1428-1467 cm-1 CH3 asymmetric
deformation and CH2 deformation) and 757-781 cm-1 (skeletal “out of plane” vibration). It was
observed that the intensity of the aliphatic C-H absorption bands increased with the length of the
N-alkyl chain and appeared in the 2826-2994 cm-1 region.
The mass spectra were recorded in CH3OH solutions using a high resolution AutoSpect-Ultima
NT Mass Spectrometer. It is obvious from the spectra that the molecular ion peaks are present
corresponding to the cation structure of all the quaternary ammonium salts. The results are
included in the experimental section.
Thermal analyses (TGA, DSC)
The thermal stabilities of the obtained salts were assessed using thermogravimetric analysis
(TGA). In general all analyzed compounds exhibited onset decomposition temperatures (T5%dec
)
o
above 140 C. The thermal stabilities varied slightly with changes in the length of the alkyl
chain, but greater variation was noted when changing the anion with the [NTf2]- salts being the
o
most stable.34 All of the [NTf2]- salts decompose at temperatures above 240 C, with the
maximum thermal stability of T5%dec = 326 oC observed for 2b (R = CH3).
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Table 2. Melting points and thermal stabilities§
I-
(a)
[NTf2]-
(b)
[CF3SO3]-
(c)
Cation
mp
(oC)
T5% dec (Tdec)
(oC)
mp
(oC)
T5% dec (Tdec)
mp
(oC)
T5% dec (Tdec)
(oC)
(oC)
221-222c
(lit 216)23
136-137c
(lit 140) 23
158-159c
(lit 158) 23
131.1a,b
(lit 131) 23
116.3
2
3
4
5
6
7
194 (214)
177 (205)
179 (205)
181 (205)
175 (201)
172 (199)
79.0
66.2a
69.3a
88.3
326 (366)
191-192c
126.5a,b
124.1a
145 (184)
162(202)
172 (195)
178 (200)
170 (196)
165 (192)
312 (342)
314 (341)
244 (274)
309 (339)
306 (338)
118.3a,b
106.1a
60.6
(lit 114) 23
117.8a
49.3a
80.5a,b
(lit 119) 23
8
126.7
173 (199)
164 (193)
166 (188)
162 (186)
171 (194)
161 (188)
162 (187)
48.9a
39.6a
46.9a
46.3a
49.5a
44.2a
49.9a
280 (326)
303 (327)
302 (327)
295 (326)
304 (334)
300 (359)
299 (326)
74.0a,b
58.9a,b
70.2a,b
64.4a,b
83.1a,b
75.3a,b
80.2a,b
163 (189)
167 (190)
160 (188)
161 (188)
164 (187)
163 (188)
164 (186)
9
65.1a,b
10
11
12
13
14
74.5a,b
82.1a,b
82.4a,b
80.4a,b
90.5a,b
[§] Melting (mp) or glass transition (Tg) points (°C) were measured from the transition onset
temperature and determined by DSC from the second heating cycle at 10 °C min-1, after initially
melting and then cooling samples to -100 °C. Decomposition temperatures shown were
determined by TGA, heating at 10 °C min-1 under dried air atmosphere and are reported as (i)
onset to 5 wt% mass loss (T5%dec) and (ii) onset to total mass loss (Tdec) (in parentheses). Salts
meeting the definition of ionic liquids (mp < 100 °C) are in bold; [a] Sample exhibits additional
glass transition temperatures (°C) of supercooled liquids (i) with consecutive crystallization and
melting on heating; 3b, -42.7; 4b, -48.1; 4c, -17.3; 5c, -5.2; 6c, -4.4;7a, 2.3; 7b, -51.2; 8b, -47.6;
9b, -42.8; 10b, -43.5; 11b, -49.1; 12b, -58.2; 13b, -45.2; 14b, -48.1; (oC); (ii) with no
crystallization and melting under experimental conditions: 3c, -5.2; 5a, 2.4; 7c, -3.2; 8c, -6.5; 9a,
-5.6; 9c, -10.1; 10a, -2.3; 10c, -7.2; 11a, 5.5; 11c, -9.1;12a, -5.6; 12c, -11.2; 13a, -5.8; 13c, -
11.1;14a, -6.0; 14c, -10.3 (oC); [b] Irreversible transition, from first heating; [c] melting point
measured visually due to close proximity to the decomposition temperature and possibility of
contamination of the DSC cell.
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The decomposition temperatures of the I- salts varied between 161 oC (13a) and 194 oC (2a),
o
o
and for the [CF3SO3]- salts between 145 C (2c) and 178 C (5c). Interestingly, the thermal
stabilities of the N-iso-propylbenzothiazolium I- and [CF3SO3]- salts (5a and 5c) were found to
be the among the highest of their respective homologs (181 C and 178 C, respectively), but in
the case of the [NTf2]- salts, 5b had the lowest thermal stability (244 oC).
o
o
Melting points were obtained using differential scanning calorimetry (DSC). All melting
points were collected twice on different samples. Some of the crystalline salts exhibited a sharp
melting transition on heating, and a crystallization event on cooling, however, the majority of the
salts exhibited supercooled behavior, not allowing any direct observation of a crystallization
event on cooling from the melt. For many of these samples, the melting transitions were poorly
defined in the DSC, commonly having a characteristic broad transition with a strong “leading
edge”. (Such behavior has been previously observed for other examples of IL-forming salts.35) A
few of the samples exhibited even more interesting behavior giving irreversible thermal
transitions observable only during the first DSC heating cycle. The melting points and glass
transitions for 2-14(a-c) are shown in (Table 2).
Among all analyzed salts, those of the [NTf2]- anion exhibited the lowest melting points as it
is often observed for salts with this anion.36 In this series of compounds, the melting points of the
o
[NTf2]- salts meet the definition of ILs (melting points less than 100 C) with melting points
o
o
between 39.6 C (9b) and 83.3 C (5b). The melting points of the remaining salts ranged from
o
o
o
o
65.1 C (9a) to 221 C (2a) for I- based salts, and from 58.9 C (9c) to 191.0 C (2c) for
[CF3SO3]- salts. In general across all the salts, the melting points decreased as the alkyl chain
length increased, reaching a minimum melting point for all three families of salts with an alkyl
o
o
o
chain length of 7 carbon atoms: 65.1 C for 9a, 39.6 C for 9b, and 58.9 C for 9c. At C8 and
above, the melting points increased. Six of the I- salts (9-14a), all of the [NTf2]- salts (2-14b),
and 8 of the [CF3SO3]- salts (7-14c) had melting points below 100 oC.
Conclusions
Thirteen N-alkylated benzothiazolium iodides salts were prepared (4 compounds, 10a, 11a, 12a,
and 13a, for the first time) using various alkyl iodides and solvent free conditions. Optimization
of each reaction, primarily the reaction temperature, afforded good yields of these salts
comparable or better to those previously reported.24,25,37 The yields were found to increase with
increasing chain length of the alkylating agent. The iodide salts 2-14a were further used in ion
exchange reactions to prepare the related [NTf2]- (2-14b) and [CF3SO3]- (2-14c) salts with almost
quantitative yields. All prepared compounds were analyzed using spectroscopic and thermal
techniques in order to evaluate their composition and thermophysical properties such as melting
point and decomposition temperature. Among all of the 39 analyzed compounds, 26 can be
o
classified as ionic liquids with melting points below 100 C. The lowest melting point was
recorded for dodecylbenzothiazolium bistrifluoromethanesulfonimide (14b; 42 oC).
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Three crystal structures of long chain alkylbenzothiazolium iodides were analyzed (12-14a).
All three are virtually isostructural and pack in a bilayer-type arrangement with the alkyl chains
interdigitated and the cation head groups and iodide ions forming a polar region. Such packing
characteristics have been observed previously in long alkyl chain imidazolium ILs, as well as
other similar molecules with polar head groups and long non-polar alkyl chains.
Experimental Section
General. All reagents and chemicals were obtained from Sigma-Aldrich (St. Louis, MO).
Solvents were of analytical grade. Reactions were monitored by thin layer chromatography using
0.20 mm aluminum-backed Silica Gel plates (Merck GF254). The plates were eluted with ethyl
acetate/n-hexane in 1:2 ratio and the spots examined under UV light (254-365 nm). FTIR spectra
were recorded on a Perkin Elmer FTIR Spectrum RX I. Characteristic absorptions are given in
1
13
cm-1. H NMR and C NMR spectra were recorded in CD3OD on Bruker instruments of 500
MHz and 125 MHz, respectively. Chemical shifts are reported as δ values in ppm using TMS as
the internal standard. Coupling constants (J) are given in Hz. High resolution mass spectra
(HRMS) were recorded on Autospec-Ultima NT.
Synthesis of quaternary ammonium salts
The general method used for the synthesis of quaternary ammonium salts of benzothiazole was
as follows: a solution of benzothiazole and the corresponding alkyl iodide, in equimolar
quantities, was stirred and heated in a dry 10 mL round bottom flask fitted with a reflux
condenser carrying a CaCl2 drying tube at the other opening end. The heating temperature range
and the time required for each salt is mentioned in Table 1. After the desired time, the reaction
mixture was slowly cooled which in most cases solidified or became a thick semi-solid mass.
The crude products were triturated with ethyl acetate and filtered. The starting materials were
freely soluble in ethyl acetate in contrast to the products which were sparingly soluble in this
solvent, allowing for efficient purification. In most of the cases, a precipitate of the product was
readily obtained just after the dissolution, while in a few cases the mixture was put in a freezer
for precipitation. The filtered crude products were washed with ethyl acetate several times to
remove the unreacted material and any colored impurities. The purified products were dried
under vacuum and recrystallized by dissolving in either hot ethyl acetate or acetone, however,
only a few of the salts could be crystallized in this way. The crystals/precipitates obtained were
dried under vacuum at room temperature. TGA analysis confirmed that only salts 2a, 9a, and 11a
contained any water (~2% w/w) and this was removed from the salts by isothermal heating at 75
oC for 30 min.
o
N-Methylbenzothiazolium iodide (2a). 82% yield; yellow solid; mp (visual) 221-222 C; IR
(neat) 2923, 2853, 1578, 1460, 1376, 759 cm-1; 1H NMR (500 MHz, CD3OD) 10.45 (s, 1H), 8.41
(d, J 10.0 Hz, 1H), 8.30 (d, J 10 Hz, 1H), 7.98 (t, J 7.5 Hz, 1H), 7.88 (t, J 7.5 Hz, 1H), 4.50 (s,
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3H); 13C NMR (75 MHz, CD3OD) 165.2, 141.0, 133.8, 132.0, 130.1, 125.9, 118.0, 40.4, HRMS
calcd for cation [M-I]+ C8H8NS: 150.0377, found: 150.0372.
o
N-Ethylbenzothiazolium iodide (3a). 75% yield; yellow solid; mp (visual) 136-137 C; IR
(neat) 2921, 2853, 1576, 1459, 1376, 767 cm-1; 1H NMR (500 MHz, CD3OD) 10.52 (s, 1H), 8.41
(d, J 8.2 Hz, 1H), 8.37 (d, J 8.6 Hz, 1H), 7.97 (t, J 7.8 Hz, 1H), 7.88 (t, J 7.7 Hz, 1H), 4.90 (q, J
7.3 Hz, 2H), 1.70 (t, 3H); 13C NMR (75 MHz, CD3OD) 164.5, 142.0, 134.0, 133.0, 131.3, 126.2,
118.2, 50.0, 14.5; HRMS calcd for cation [M-I]+ C9H10NS: 164.0534, found: 164.0538.
o
N-Propylbenzothiazolium iodide (4a). 68% yield; yellow solid; mp (visual) 158-159 C; IR
(neat) 2925, 2853, 1580, 1460, 1377, 747 cm-1; 1H NMR (500 MHz, CD3OD) 10.60 (s, 1H), 8.43
(d, J 8.30 Hz, 1H), 8.37 (d, J 8.5Hz, 1H), 7.91 (s, J 7.9 Hz, 1H), 7.88 (t, J 7.7Hz, 1H), 4.90 (t, J
13
7.3 Hz, 2H), 2.10 (hex, J 7.4 Hz, 2H), 1.00 (t, J 7.4 3H); C NMR (75 MHz, CD3OD) 164.0,
142.0, 133.6, 132.9, 130.2, 126.2, 118.2, 55.8, 23.5, 11.0; HRMS calcd for cation [M-I]+
C10H12NS: 178.0690, found: 178.0687.
o
N-Iso-propylbenzothiazolium iodide (5a). 62% yield; yellow solid; mp (DSC) 131.1 C; IR
(neat) 2922, 2854, 1580, 1460, 1377, 757 cm-1; 1H NMR (500 MHz, CD3OD) 10.6 (s, 1H), 8.43
(d, J 8.23 Hz, 1H), 8.37 (d, J 8.54 Hz, 1H), 7.89 (t, J 7.9Hz, 1H), 7.88 (t, J 8.0Hz, 1H), 5.50 (sep,
13
J 6.6 Hz, 2H), 1.80 (d, J 6.7 Hz, 6H); C NMR (75 MHz, CD3OD) 131.3, 130.3, 126.2, 118.4,
58.0, 22.2; HRMS calcd for cation [M-I]+ C10H12NS: 178.0690, found: 178.0690.
N-Butylbenzothiazolium iodide (6a). 80% yield; yellow solid; mp (DSC) 116.3 C; IR (neat)
o
2919, 2851, 1575, 1459, 1376, 762 cm-1; 1H NMR (500 MHz, CD3OD) 10.55 (s, 1H), 8.41 (d, J
8.26 Hz,1H), 8.36 (d, J 8.56 Hz, 1H), 7.98 (t, J 7.9 Hz, 1H), 7.88 (t, J 7.8Hz, 1H), 4.93 (t, J 7.6
Hz, 2H), 2.02 (pen, J 2.4 Hz, 2H), 1.53 (hex, J 7.7 Hz, 2H), 1.04 (t, J 7.4 Hz, 3H); 13C NMR (75
MHz, CD3OD) 131.4, 130.2, 126.1, 118.2, 13.8, 20.7, 32.0, 54.5; HRMS calcd for cation [M-I]+
C11H14NS: 192.0848, found: 192.0847.
o
N-Pentylbenzothiazolium iodide (7a). 79% yield; yellow solid; mp (DSC) 117.8 C; IR (neat)
2922, 2854, 1578, 1459, 1376, 767 cm-1; 1H NMR (500 MHz, CD3OD) 10.56 (s, 1H), 8.43 (d, J
8.27 Hz, 1H), 8.37 (d, J 8.56 Hz, 1H), 7.98 (t, J 7.8 Hz, 1H), 7.88 (t, J 7.8 Hz, 1H), 4.91 (t, J 7.7
Hz, 2H), 3.32 (t, J 1.2 Hz,,2H), 1.41 (hex, J 3.5 Hz, 2H), 2.14 (pen, J 7.5 Hz, 2H), 0.93 (t, J 7.0
Hz, 3H); 13C NMR (75 MHz, CD3OD) 164.2, 141.6, 132.2, 131.4, 130.2, 126.2, 118.2, 54.5,
29.8, 29.6, 23.2, 14.2; HRMS calcd for cation [M-I]+ C12H16NS: 206.1011, found: 206.1003.
o
N-Hexylbenzothiazolium iodide (8a). 77% yield; yellow solid; mp (DSC) 126.7 C; IR (neat)
1
2918, 2853, 1574, 1459, 1376, 763 cm-1; H NMR (500 MHz, CD3OD) 10.57(s, 1H), 8.43 (d, J
8.25 Hz, 1H), 8.38 (d, J 8.58 Hz, 1H), 7.97 (t, J 7.7 Hz, 1H), 7.88 (t, J 7.5 Hz, 1H), 4.95 (t, J 7.5
Hz, 2H), 2.11 (m, 2H), 1.38 (m, 8H), 0.89 (t, J 6.9 Hz, 3H); 13C NMR (75 MHz, CD3OD) 164.2,
141.6, 132.2, 131.4, 130.2, 126.2, 118.3, 54.6, 32.3, 30.0, 27.2, 23.5, 14.3; HRMS calcd for
cation [M-I]+ C13H18NS: 220.1154, found: 220.1160.
o
N-Heptylbenzothiazolium iodide (9a). 75% yield; yellow solid; mp (DSC) 65.1 C; IR (neat)
2927, 2855, 1579, 1460, 1428, 762 cm-1; 1H NMR (500 MHz, CD3OD) 10.54 (s, 1H), 8.42 (d, J
8.23 Hz, 1H), 8.37 (d, J 8.59 Hz, 1H), 7.97 (t, J 7.8 Hz, 1H), 7.88 (t, J 7.6 Hz, 1H), 4.91 (t, J 7.5
13
Hz, 2H), 2.11 (pen, J 7.4 Hz, 2H), 1.39 (m, 10H), 0.90 (t, J 6.7 Hz, 3H); C NMR (75 MHz,
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CD3OD) 164.2, 141.8, 134.0, 130.2, 133.0, 126.2, 118.2; HRMS calcd for cation [M-I]+
C14H20NS: 234.1313, found: 234.1316.
o
N-Octylbenzothiazolium iodide (10a). 80% yield; yellow solid; mp (DSC) 74.5 C; IR (neat)
2925, 2854, 1579, 1460, 1428, 762 cm-1; 1H NMR (500 MHz, CD3OD) 10.54 (s, 1H), 8.42 (d, J
8.26 Hz, 1H), 8.36 (d, J 8.55 Hz, 1H), 7.97 (t, J 7.9 Hz, 1H), 7.88 (t, J 7.6 Hz, 1H), 4.90 (t, J 7.6
13
Hz, 1H), 2.10 (pen, J 7.7 Hz,,2H), 1.39 (m, 12H), 0.89 (t, J 7.0 Hz, 3H); C NMR (75 MHz,
CD3OD) 164.2, 142.2, 134.1, 132.9, 131.2, 126.2, 118.3; HRMS calcd for cation [M-I]+
C15H22NS: 248.1477, found: 248.1473.
o
N-Nonylbenzothiazolium iodide (11a). 73% yield; yellow solid; mp (DSC) 82.1 C; IR (neat)
2915, 2849, 1574, 1458, 1428, 762 cm-1; 1H NMR (500 MHz, CD3OD) 10.55 (s, 1H), 8.43 (d, J
8.27 Hz, 1H), 8.37 (d, J 8.56 Hz, 1H), 7.98 (t, J 7.8 Hz, 1H), 7.88 (t, J 7.7 Hz, 1H), 4.38 (t, J 7.5
13
Hz, 2H), 2.01 (pen, J 7.4 Hz, 2H), 1.35 (m, 14H), 0.95 (t, J 6.8 Hz, 3H); C NMR (75 MHz,
CD3OD) 164.0, 142.6, 134.5, 130.3, 131.3, 126.1, 118.2; HRMS calcd for cation [M-I]+
C16H24NS: 262.1629; found: 262.1629.
o
N-Decylbenzothiazolium iodide (12a). 70% yield; yellow solid; mp (DSC) 82.4 C; IR (neat)
2916, 2852, 1576, 1460, 1376, 758 cm-1; 1H NMR (500 MHz, CD3OD) 10.56 (s, 1H), 8.43 (d, J
8.28 Hz, 1H), 8.35 (d, J 8.56 Hz, 1H), 7.97 (t, J 7.8 Hz, 1H), 7.88 (t, J 7.88 Hz, 1H), 4.39 (t, J 7.5
13
Hz, 2H), 2.11 (pen, J 7.0 Hz, 2H), 1.75 (m, 16H), 0.9 (t, J 6.3 Hz, 3H); C NMR (75 MHz,
CD3OD) 164.2, 142.0, 133.8, 126.2, 130.2, 131.3, 118.2, 14.4, 23.7, 27.4, 30.0, 30.1, 30.4, 30.5,
30.6, 33.0, 54.4; HRMS calcd for cation [M-I]+ C17H26NS: 276.1786, found: 276.1782.
N-Undecylbenzothiazolium iodide (13a). 75% yield; yellow solid; mp (DSC) 80.4 oC; IR (neat)
2922, 2853, 1580, 1460, 1376, 758 cm-1; 1H NMR (500 MHz, CD3OD) 10.55 (s, 1H), 8.43 (d, J
8.26 Hz, 1H), 8.37 (d, J 8.56 Hz, 1H), 7.97 (t, J 7.9 Hz, 1H), 7.88 (t, J 7.8 Hz, 1H), 4.89 (t, J 7.4
13
Hz, 2H), 2.11 (pen, J 7.4 Hz, 2H), 1.40 (m, 18H), 0.90 (t, J 6.7 Hz, 3H); C NMR (75 MHz,
CD3OD) 164.0, 142.6, 132.8, 130.2, 131.3, 126.2, 118.2; HRMS calcd for cation [M-I]+
C18H28NS: 290.1942, found: 290.1943.
N-Dodecylbenzothiazolium iodide (14a). 72% yield; yellow solid; mp (DSC) 90.5 oC; IR (neat)
1
2924, 2852, 1578, 1461, 1376, 759 cm-1; H NMR (500 MHz, CD3OD) 10.53 (s, 1H), 8.42 (t, J
8.23 Hz, 1H), 7.98 (t, J 7.8 Hz, 1H), 7.89 (t, J 7.6 Hz, 1H), 4.39 (t, J 7.4 Hz, 2H), 2.11 (pen, J 7.4
Hz, 2H), 1.40 (m, 20H), 0.88 (t, J 6.7 Hz, 3H); 13C NMR (75 MHz, CD3OD) 164.2, 141.8, 132.9,
131.4, 130.2, 126.2, 118.3, 54.6, 33.0, 30.6, 30.4, 30.2, 30.1, 30.0, 27.5, 23.7, 14.4; HRMS calcd
for cation [M-I]+ C19H30NS: 304.2099, found: 304.2097.
Metathesis reactions
The anion exchange of the prepared quaternary benzothiazolium iodide salts was carried using
the following protocol: 1 g of compound, 10 mL of acetone and an equivalent amount of the
anion salt (Li[NTf2] or Na[CF3SO3]) were added followed by stirring at room temperature for 4
to 6 h. After successful anion exchange and purification of the compound by drying, the
compounds were extracted with anhydrous ethyl acetate (absolute ethanol where necessary) and
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the new salts isolated. Completion of the purification step was monitored by silver nitrate halide
tests. The anion exchange reactions gave the desired products in yields above 80%.
N-Methylbenzothiazolium bistrifluoromethanesulfonimide (2b). Brown Solid; mp (DSC)
1
79.0 oC; IR (neat), 3124, 3093, 2329, 1466, 1342, 1175, 1130, 1051, 768 cm-1; H NMR (500
MHz, CD3OD) 10.40 (s, 1H), 8.40 (d, J 8.5 Hz, 1H), 8.29 (d, J 8.5 Hz, 1H), 7.98 (t, J 8.5 Hz,
13
1H), 7.89 (t, J 8.25 Hz, 1H), 4.46 (s, 3H); C NMR (125 MHz, CD3OD) 165.2, 131.6, 130.4,
126.1, 122.8, 120.2, 118.2, 40.4; HRMS (EI) calcd for cation [M-NTf2]+ C8H8NS: 150.0534,
found: 150.0377.
N-Ethylbenzothiazolium bistrifluoromethanesulfonimide (3b). Yellow Solid; mp (DSC) 66.2
oC; IR (neat) 3109, 1580, 1512, 1433, 1342, 1180, 1130, 1049, 892, 783, 758, 735 cm-1; 1H NMR
(500 MHz, CD3OD) 10.46 (s, 1H), 8.41 (d, J 8.0 Hz 1H), 8.35 (d, J 9.0 Hz 1H), 7.98 (t, J 8.5Hz,
1H), 7.89 (s, J 8.25 Hz, 1H), 4.90 (t, J 7.25 Hz, 3H), 1.74 (t, J 7.5 Hz, 3H); 13C NMR (125 MHz,
CD3OD) 165.3, 131.9, 130.8, 126.5, 123.0, 120.5, 118.6, 109.7, 50.4, 14.9; HRMS (EI) calcd for
cation [M-NTf2]+ C9H10NS: 164.0534, found: 164.0529.
N-Propylbenzothiazolium bistrifluoromethanesulfonimide (4b). Yellow Solid; mp (DSC)
o
69.3 C; IR (neat) 3098, 2982, 1580, 1509, 1456, 1433, 1342, 1180, 1132, 1046, 786, 761, 735.
cm-1; 1H NMR (500 MHz, CD3OD) 10.47 (s, 1H), 8.41 (d, J 10.0 Hz, 1H), 8.36 (d, J 8.5 Hz, 1H),
7.98 (t, J 8.50 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.84 (t, J 7.5 Hz 2H), 1.08 (t, J 7.5 Hz, 3H); 13C
NMR (125 MHz, CD3OD) 157.9, 133.7, 132.1, 130.9, 126.7, 120.6, 118.8; HRMS (EI) calcd for
cation [M-NTf2]+ C10H12NS: 178.2750, found: 178.2750.
N-Iso-propylbenzothiazolium bistrifluoromethanesulfonimide (5b). Yellow Solid; mp (DSC)
o
88.3 C; IR (neat) 3118, 2997, 1578, 1507, 1461, 1342, 1178, 1127, 1044, 905, 786, 738, 758
1
cm-1; H NMR (500 MHz, CD3OD) 10.50 (s, 1H), 8.42 (t, J 7.5 Hz, 2H), 8.40 (t, J 8.5 Hz, 1H),
13
7.89 (t, J 8.25 Hz, 1H), 5.46 (m, 1H), 1.81 (d, J 6.5 Hz, 6H); C NMR (125 MHz, CD3OD)
163.8, 132.0, 131.0, 126.8, 123.2, 120.7, 119.0, 58.7, 22.7; HRMS (EI) calcd for cation [M-
NTf2]+ C10H12NS: 178.2750, found: 178.2750.
N-Butylbenzothiazolium bistrifluoromethanesulfonimide (6b). Yellow Solid; mp (DSC) 60.6
oC; IR (neat) 3068, 2962, 2870, 1580, 1507, 1431, 1461, 1325, 1345, 1228, 1175, 1122, 1054,
1
875, 783, 763, 731, cm-1; H NMR (500 MHz, CD3OD) 10.47 (s, 1H), 8.41 (d, J 8.0 Hz, 1H),
8.36 (d, J 9.0Hz, 1H), 7.99 (t, J 8.5 Hz, 1H), 7.89 (t, J 8.0 Hz, 1H), 4.86 (t, J 7.5 Hz, 2H), 2.07
(m, 2H), 1.50 (m, 2H), 1.04 (t, J 7.5 Hz, 3H); 13C NMR (125 MHz, CD3OD) 165.2, 131.6, 129.9,
128.8, 124.7, 122.3, 116.7, 52.9, 30.6, 19.3, 12.3; HRMS (EI) calcd for cation [M-NTf2]+
C11H14NS: 192.3020, found: 192.3020.
N-Pentylbenzothiazolium bistrifluoromethanesulfonimide (7b). Yellow Solid; mp (DSC)
o
49.3 C; IR (neat) 3068, 2931, 2855, 1578, 1504, 1461, 1428, 1342, 1325, 1180, 1125, 1054,
867, 783, 763, 735 cm-1; 1H NMR (500 MHz, CD3OD) 10.48 (s, 1H), 8.42 (d, J 8.5 Hz, 1H), 8.36
(d, J 8.5 Hz, 1H), 7.98 (t, J 8.25 Hz, 1H), 7.88 (t, J 8.0 Hz, 1H), 4.86 (t, J 7.5 Hz, 2H), 2.11 (m,
13
2H), 1.44 (m, 4H), 0.95 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 163.5, 131.3, 130.1,
126.0, 120.8, 120.2, 118.1, 54.4, 29.7, 29.4, 23.0, 14.0; HRMS (EI) calcd for cation [M-NTf2]+
C12H16NS: 206.3280, found: 206.3280.
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N-Hexylbenzothiazolium bistrifluoromethanesulfonimide (8b). Yellow Solid; mp (DSC) 48.9
oC; IR (neat) 3114, 2926, 2850, 1580, 1507, 1431, 1340, 1317, 1188, 1125, 1049, 786, 766, 738,
cm-1; 1H NMR (500 MHz, CD3OD) 10.44 (s, 1H), 8.38 (d, J 8.5 Hz, 1H), 8.33 (d, J 8.5 Hz, 1H),
7.95 (t, J 8.25 Hz, 1H), 7.85 (t, J 7.75 Hz, 1H), 4.83 (t, J 7.5 Hz, 2H), 2.05 (m, 2H), 1.47-1.21
(m, 6H), 0.89 (t, J 7.0 Hz, 3H); 13C NMR (125 MHz, CD3OD) 163.9, 132.9, 131.3, 130.1, 125.9,
122.4, 118.0, 54.4, 32.2, 29.9, 27.0, 23.3, 14.1; HRMS (EI) calcd for cation [M-NTf2]+
C13H18NS: 220.3550, found: 220.3550.
N-Heptylbenzothiazolium bistrifluoromethanesulfonimide (9b). Yellow Solid; mp (DSC)
39.6 oC; IR (neat) 3083, 2931, 2860, 1580, 1509, 1464, 1431, 1347, 1183, 1132, 1044, 897, 789,
758, 730 cm-1; 1H NMR (500 MHz, CD3OD) 10.47 (s, 1H), 8.41 (d, J 8.0 Hz, 1H), 8.35 (d, J 8.5
Hz, 1H), 7.99 (t, J 7.75 Hz, 1H), 7.88 (t, J 7.75 Hz, 1H), 4.85 (t, J 7.6 Hz, 2H), 2.09 (m,
2H),1.49-1.29 (m, 8H), 0.89 (t, J 7.0 Hz, 3H); 13C NMR (125 MHz, CD3OD) 163.8, 132.8,
131.2, 130.0, 125.8, 117.9, 108.9, 54.3, 32.5, 29.8, 29.5, 27.2, 23.3, 14.1; HRMS (EI) calcd for
cation [M-NTf2]+ C14H20NS: 234.3810, found: 234.3810.
N-Octylbenzothiazolium bistrifluoromethanesulfonimide (10b). Yellow Solid; mp (DSC)
o
46.9 C; IR (neat) 3073, 2926, 2855, 1582, 1509, 1458, 1431, 1347, 1327, 1178, 1125, 1052,
864, 781, 766, 733 cm-1; 1H NMR (500 MHz, CD3OD) 10.46 (s, 1H), 8.41 (d, J 8.0 Hz, 1H), 8.35
(d, J 8.5 Hz, 1H), 7.98 (t, J 8.5 Hz, 1H), 7.89 (t, J 8.5 Hz, 1H), 4.86 (t, J 7.5 Hz, 2H), 2.09 (m,
13
2H), 1.49-1.28 (m, 10H), 0.89 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 163.9, 132.5,
130.9, 129.7, 125.5, 122.0, 119.4, 117.6, 54.0, 32.3, 29.7, 29.57, 29.5, 26.9, 23.1, 13.9; HRMS
(EI) calcd for cation [M-NTf2]+ C15H22NS: 248.4080, found: 248.4080.
N-Nonylbenzothiazolium bistrifluoromethanesulfonimide (11b). Yellow Solid; mp (DSC)
o
46.3 C; IR (neat) 3108, 2946, 2870, 1580, 1504, 1454, 1436, 1342, 1319, 1180, 1127, 1059,
783, 763, 730 cm-1; 1H NMR (500 MHz, CD3OD) 10.47 (s, 1H), 8.41 (d, J 8.5 Hz, 1H), 8.36 (d, J
8.5 Hz, 1H), 7.88 (t, J 8.25 Hz, 1H), 4.85 (t, J 7.5 Hz, 3H), 2.09 (m, 2H), 1.49-1.28 (m, 12H),
13
0.88 (t, J 6.7 Hz, 3H); C NMR (125 MHz, CD3OD) 164.0, 131.3, 130.1, 126.0, 122.4, 120.2,
118.0, 54.4, 32.8, 30.3, 30.2, 30.0, 29.9, 27.3, 23.6, 14.3; HRMS (EI) calcd for cation [M-NTf2]+
C16H24NS: 262.4350; found: 262.4350.
N-Decylbenzothiazolium bistrifluoromethanesulfonimide (12b). Yellow Solid; mp (DSC)
o
49.5 C; IR (neat) 3068, 2921, 2850, 1580, 1507, 1461, 1431, 1347, 1327, 1178, 1127, 1054,
783, 766, 730 cm-1; 1H NMR (500 MHz, CD3OD) 10.47 (s, 1H), 8.41 (d, J 8.5 Hz, 1H), 8.36 (d, J
8.5 Hz, 1H), 7.99 (t, J 8.5,Hz 1H), 7.89 (t, J 8.25 Hz, 1H), 4.86 (t, J 7.0 Hz, 2H), 2.08 (m, 2H),
13
1.46-1.28 (m, 14H), 0.88 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 162.8, 132.2, 131.1,
126.9, 121.7, 120.3, 119.0, 55.3, 33.9, 31.4, 31.3, 31.2, 30.9, 28.3, 24.6, 15.3; HRMS (EI) calcd
for cation [M-NTf2]+ C17H26NS: 276.4610, found: 276.4610.
N-Undecylbenzothiazolium bistrifluoromethanesulfonimide (13b). Yellow Solid; mp (DSC)
o
44.2 C; IR (neat) 3068, 2926, 2855, 1577, 1507, 1464, 1428, 1342, 1327, 1178, 1127, 1054,
872, 783, 763, 733 cm-1; 1H NMR (500 MHz, CD3OD) 10.46 (s, 1H), 8.40 (d, J 8.5 Hz, 1H), 8.35
(d, J 8.5 Hz, 1H), 7.97 (t, J 8.0 Hz, 1H), 7.88 (t, J 7.75 Hz, 1H), 4.85 (t, J 7.5 Hz, 3H), 2.09 (m,
2H), 1.48-1.27 (t, J 6.25 Hz, 3H); 13C NMR (125 MHz, CD3OD) 163.8, 131.3, 130.1, 125.9,
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122.7, 120.5, 118.1, 54.4, 32.9, 30.5, 30.4, 30.3, 29.9, 27.3, 23.6, 14.3; HRMS (EI) calcd for
cation [M-NTf2]+ C18H28NS: 290.4880, found: 290.4880.
N-Dodecylbenzothiazolium bistrifluoromethanesulfonimide (14b). Yellow Solid; mp (DSC)
o
49.9 C; IR (neat) 3053, 2926, 2850, 1580, 1507, 1431, 1458, 1342, 1325, 1175, 1127, 1054,
872, 768, 730. cm-1; 1H NMR (500 MHz, CD3OD) 10.48 (s, 1H), 8.43 (d, J 8.5 Hz, 1H), 8.38 (d,
J 8.5 Hz, 1H), 8.00 (t, J 8.0 Hz, 1H), 7.91 (t, J 7.75 Hz, 1H), 4.87 (t, J 7.5 Hz, 3H), 2.11 (m, 2H),
13
1.51-1.30 (m, 18H), 0.91 (t, J 6.5 Hz, 3H); C NMR (125 MHz, CD3OD) 163.2, 131.9, 130.7,
126.5, 122.2, 120.4, 118.6, 55.0, 33.5, 31.1, 31.0, 30.9, 30.5, 30.5, 27.9, 24.1, 14.8; HRMS (EI)
calcd for cation [M-NTf2]+ C19H30NS: 304.5140, found: 304.5140.
N-Methylbenzothiazolium trifluoromethylsulfonate (2c). Brown Solid; mp (visual) 191-192
1
oC; IR (neat) 2997, 1575, 1517, 1431, 1398, 1251, 1163,1122, 1029, 953, 882, 758 cm-1; H
NMR (500 MHz, CD3OD) 10.45 (s, 1H), 8.42 (d, J 8.19 Hz, 1H), 8.31 (d, J 8.82 Hz, 1H), 7.99 (t,
J 8.19 Hz, 1H), 7.90 (t, J 7.88 Hz, 1H), 4.47 (s, 3H); 13C NMR (125 MHz, CD3OD) 163.4, 141.2,
132.0, 130.8, 126.5, 122.3, 120.1, 118.7, 41.0; HRMS (EI) calcd for cation [M-CF3SO3]+
C8H8NS: 150.0377, found: 150.0377.
N-Ethylbenzothiazolium trifluoromethylsulfonate (3c). Yellow Solid; mp (DSC) 126.5 oC; IR
(neat) 3073, 3043, 2916, 1580,1514, 1458, 1439, 1388, 1307, 1259, 1191, 1153, 1024, 958, 892,
1
839, 753 cm-1; H NMR (500 MHz, CD3OD) 10.55 (s, 1H), 8.44 (d, J 8.35 Hz, 1H), 8.38 (d, J
8.51 Hz, 1H), 7.98 (t, J 7.88 Hz, 1H), 7.88 (t, J 7.82 Hz, 1H), 4.93 (m, 2H), 1.75 (t, J 7.4 Hz,
3H); 13C NMR (125 MHz, CD3OD) 164.5, 142.0, 132.5, 130.9, 129.7, 125.6, 122.4, 120.3,
117.7, 108.7, 49.5, 14.0; HRMS (EI) calcd for cation [M-CF3SO3]+ C9H10NS: 164.0534, found:
164.0529.
o
N-Propylbenzothiazolium trifluoromethylsulfonate (4c). Yellow Solid; mp (DSC) 124.1 C;
IR (neat) 3043, 2997, 2962, 1580, 1512, 1458, 1431, 1385, 1342, 1251, 1218, 1153, 1026, 857,
1
794, 756 cm-1; H NMR (500 MHz, CD3OD) 10.54 (s, 1H), 8.44 (d, J 8.22 Hz, 1H), 8.39 (t, J
8.41 Hz, 1H), 7.99 (t, J 7.90 Hz, 1H), 7.88 (t, J 7.79 Hz, 1H), 4.87 (t, J 7.5 Hz, 3H), 2.17-2.10
(m, 2H), 1.08 (s, J 7.4 Hz, 3H); 13C NMR (125 MHz, CD3OD) 163.7, 141.0, 132.9, 131.3, 130.1,
126.0, 122.0, 118.1, 55.8, 23.5, 10.9; HRMS (EI) calcd for cation [M-CF3SO3]+ C10H12NS:
178.0690, found: 178.0685.
N-Iso-propylbenzothiazolium trifluoromethylsulfonate (5c). Yellow Solid; mp (DSC) 118.3
oC; IR (neat) 3022, 2992, 2967, 1577, 1507, 1436, 1375, 1309, 1264, 1249, 1163, 1117, 1021,
905, 849,756, 730 cm-1; 1H NMR (500 MHz, CD3OD) 10.59 (s, 1H), 8.45 (t, J 7.7 Hz, 2H), 7.99
13
(t, J 8.5 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 5.49 (m, 1H), 1.82 (d, J 6.5 Hz, 6H); C NMR (125
MHz, CD3OD) 162.6, 141.8, 133.4, 131.7, 130.6, 126.5, 122.3, 118.7, 58.4, 22.5; HRMS (EI)
calcd for cation [M-CF3SO3]+ C10H12NS: 178.0686, found: 178.0690.
N-Butylbenzothiazolium trifluoromethylsulfonate (6c). Yellow Solid; mp (DSC) 106.1 oC; IR
1
(neat) 3068, 2977, 2951, 1719, 1580, 1514, 1453, 1319, 1249, 1155, 1024, 902, 761 cm-1; H
NMR (500 MHz, CD3OD) 10.57 (s, 1H), 8.45 (d, J 8.19 Hz, 1H), 8.39 (d, J 8.5 Hz, 1H), 7.98 (t,
J 8.25 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.90 (t, J 7.5 Hz, 2H), 2.09 (m, 2H), 1.51 (m, 2H), 1.03 (t,
13
J 7.25 Hz, 3H); C NMR (125 MHz, CD3OD) 162.3, 141.5, 132.8, 131.3, 130.1, 126.1, 118.2,
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54.2, 31.9, 20.7, 13.7; HRMS (EI) calcd for cation [M-CF3SO3]+ C11H14NS: 192.0847, found:
192.0842.
N-Pentylbenzothiazolium trifluoromethylsulfonate (7c). Yellow Solid; mp (DSC) 80.5 oC; IR
(neat) 3068, 2946, 2855, 1673, 1577, 1507, 1458, 1423, 1241, 1148, 1029, 887, 796, 761, 720
cm-1; 1H NMR (500 MHz, CD3OD) 10.58 (s, 1H), 8.45 (d, J 9.0 Hz, 1H), 8.40 (d, J 8.5 Hz, 1H),
7.98 (t, J 8.5 Hz, 1H), 7.88 (t, J 8.25 Hz, 1H), 4.91 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.45 (m, 4H),
13
0.94 (t, J 7.25 Hz, 3H); C NMR (125 MHz, CD3OD) 163.0, 142.1, 133.2, 131.7, 130.5, 126.5,
118.6, 54.8, 30.1, 29.1, 23.5, 14.5; HRMS (EI) calcd for cation [M-CF3SO3]+ C12H16NS:
206.1003, found: 206.1010.
o
N-Hexylbenzothiazolium trifluoromethylsulfonate (8c). Yellow Solid; mp (DSC) 74.0 C; IR
1
(neat) 3017, 2916, 2845, 1575, 1494, 1458, 1421, 1221, 1257, 1140, 1024, 864, 758 cm-1; H
NMR (500 MHz, CD3OD) 10.57 (s, 1H), 8.45 (d, J 9.0 Hz, 1H), 8.39 (d, J 8.5 Hz, 1H), 7.99 (t, J
8.5 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.89 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.52-1.28 (m, 6H), 0.92
(t, J 7.25 Hz, 3H); 13C NMR (125 MHz, CD3OD) 163.2, 141.7, 132.8, 131.3, 130.1, 126.1, 118.2,
109.0, 54.5, 32.2, 29.9, 27.0, 23.4, 14.2; HRMS (EI) calcd for cation [M-CF3SO3]+ C13H18NS:
220.1160, found: 220.1156.
N-Heptylbenzothiazolium trifluoromethylsulfonate (9c). Yellow Solid; mp (DSC) 58.9 oC; IR
1
(neat) 3043,, 2916, 2855, 1577, 1501, 1456, 1426, 1213, 1160, 1029, 885, 761, cm-1; H NMR
(500 MHz, CD3OD) 10.55 (s, 1H), 8.44 (d, J 9.0 Hz, 1H), 8.38 (d, J 8.5 Hz, 1H), 7.99 (t, J 8.5
Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.88 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.51-1.31 (m, 8H), 0.90 (t,
13
J 7.25 Hz, 3H); C NMR (125 MHz, CD3OD) 163.6, 141.4, 130.9, 129.7, 125.7, 117.7, 108.6,
54.1, 32.2, 29.6, 29.3, 26.9, 23.0, 13.8; HRMS (EI) calcd for cation [M-CF3SO3]+ C14H20NS:
234.1316, found: 234.1318.
N-Octylbenzothiazolium trifluoromethylsulfonate (10c). Yellow Solid; mp (DSC) 70.2 oC; IR
(neat) 2952, 2911, 2850, 1575, 1494, 1458, 1426, 1347, 1251, 1198, 1148, 1029, 872, 756 cm-1;
1H NMR (500 MHz, CD3OD) 10.58 (s, 1H), 8.45 (d, J 9.0 Hz, 1H), 8.39 (d, J 8.5 Hz, 1H), 7.99
(t, J 8.75 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.89 (t, J 7.75 Hz, 2H), 2.10 (m, 2H), 1.51-1.25 (m,
13
10H), 0.89 (t, J 7.00 Hz, 3H); C NMR (125 MHz, CD3OD) 163.2, 133.2, 131.7, 130.5, 126.5,
118.6, 109.4, 54.9, 33.1, 30.5, 30.4, 27.8, 23.9, 14.7; HRMS (EI) calcd for cation [M-CF3SO3]+
C15H22NS: 248.1473, found: 248.1467.
o
N-Nonylbenzothiazolium trifluoromethylsulfonate (11c). Yellow Solid; mp (DSC) 64.4 C;
IR (neat) 3037, 2921, 2845, 1575, 1453, 1423, 1259, 1191, 1158, 1082, 1031, 887, 852, 758, 720
cm-1; 1H NMR (500 MHz, CD3OD) 10.59 (s, 1H), 8.46 (d, J 8.0 Hz, 1H), 8.40 (d, J 9.0 Hz, 1H),
7.99 (t, J 8.5 Hz, 1H), 7.88 (t, J 8.25 Hz, 1H), 4.90 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.51-1.24 (m,
13
12H), 0.88 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 164.0, 141.7, 132.8, 131.3, 130.1,
126.1, 118.2, 54.5, 32.8, 30.3, 30.1, 30.1, 30.0, 27.4, 23.6, 14.3; HRMS (EI) calcd for cation [M-
CF3SO3]+ C16H24NS: 262.1629; found: 262.1623.
N-Decylbenzothiazolium trifluoromethylsulfonate (12c). Yellow Solid; mp (DSC) 83.1 oC; IR
1
(neat) 2951, 2921, 2840, 1574, 1458, 1426, 1256, 1165, 1142, 1026, 872, 758, 718 cm-1; H
NMR (500 MHz, CD3OD) 10.58 (s, 1H), 8.45 (d, J 8.0 Hz, 1H), 8.40 (d, J 8.5 Hz, 1H), 7.98 (t, J
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8.5 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.91 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.51-1.25 (m, 14H),
13
0.89 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 164.7, 141.7, 132.8, 131.3, 130.1, 126.1,
118.2, 54.5, 32.9, 30.5, 30.4, 30.3, 30.1, 30.0, 27.3, 23.6, 14.4; HRMS (EI) calcd for cation [M-
CF3SO3]+ C17H26NS: 276.1786, found: 275.1787.
N-Undecylbenzothiazolium trifluoromethylsulfonate (13c). Yellow Solid; mp (DSC) 75.3 oC;
1
IR (neat) 2911, 2840, 1577, 1496, 1464, 1426, 1350, 1254, 1142, 1026, 877, 758, 718 cm-1; H
NMR (500 MHz, CD3OD) 10.58 (s, 1H), 8.45 (d, J 8.5 Hz, 1H), 8.40 (d, J 8.5 Hz, 1H), 7.99 (t, J
7.75 Hz, 1H), 7.89 (t, J 7.50 Hz, 1H), 4.89 (t, J 7.75 Hz, 2H), 2.11 (m, 2H), 1.51-1.25 (m, 16H),
13
0.89 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 164.1, 141.7, 132.8, 131.3, 130.1, 126.2,
118.2, 54.5, 32.9, 30.6, 30.5, 30.4, 30.3, 30.0, 27.4, 23.6, 14.3; HRMS (EI) calcd for cation [M-
CF3SO3]+ C18H28NS: 290.1942, found: 290.1937.
N-Dodecylbenzothiazolium trifluoromethylsulfonate (14c). Yellow Solid; mp (DSC) 80.2 oC;
1
IR (neat) 2951, 2911, 2845, 1580, 1458, 1423, 1350, 1259, 1142, 1026, 875, 756, 718 cm-1; H
NMR (500 MHz, CD3OD) 10.55 (s, 1H), 8.43 (d, J 8.0 Hz, 1H), 8.38 (d, J 8.5 Hz, 1H), 7.97 (t, J
8.5 Hz, 1H), 7.89 (t, J 8.25 Hz, 1H), 4.89 (t, J 7.5 Hz, 2H), 2.11 (m, 2H), 1.50-1.19 (m, 18H),
13
0.89 (t, J 7.0 Hz, 3H); C NMR (125 MHz, CD3OD) 164.0, 141.7, 132.9, 131.3, 130.1, 126.0,
118.1, 54.4, 32.9, 30.6, 30.5, 30.4, 30.3, 30.1, 30.0, 27.3, 23.6, 14.3; HRMS (EI) calcd for cation
[M-CF3SO3]+ C19H30NS: 304.2099, found: 304.2102.
Thermal analysis
For most of the salts (excluding 2a, 3a, 4a, and 2c for which the melting points were analyzed
visually with triplicate measurements), melting points were determined by differential scanning
calorimetry (DSC) using a TA Instruments model 2920 Modulated DSC (New Castle, DE)
cooled with a liquid nitrogen cryostat. The calorimeter was calibrated for temperature and cell
constants using indium (mp 156.61 °C, ∆H 28.71 J/g). Data were collected at constant
atmospheric pressure, using samples between 10-20 mg in aluminum sample pans. Experiments
were performed with heating at a rate of 10 °C/min. The DSC instrument was adjusted so that
zero heat flow was between 0 and -0.5 mW, and the baseline drift was less than 0.1 mW over the
temperature range 0–180 °C. An empty sample pan was used as reference.
Thermal decomposition temperatures were measured in the dynamic heating regime using a
TGA 2950 TA TGA. Samples between 5–15 mg were heated from 40–500 °C with isocratic
heating rate at 10 °C/min under an air atmosphere. Decomposition temperatures were determined
from both (i) the onset to 5 wt% mass loss (T5%dec), which provides a more realistic
representation of thermal stability at elevated temperatures, and (ii) from the onset to complete
decomposition (Tonset).
Single crystal X-ray diffraction analyses
Samples were recrystallized from ethyl acetate by slow evaporation. Single crystals suitable for
X-ray analysis were isolated in air, mounted on fibers, and transferred to the goniometer. Single-
crystal X-ray diffraction data were collected on a Bruker CCD area detector-equipped
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diffractometer (Madison, WI) with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å).
The crystals of 12a, 13a, and 14a were cooled to -100 oC under a nitrogen gas stream during data
collection. Absorption corrections were made with SADABS, and SHELXTL software was used
for structure solution and refinement.38
Each structure was refined by using full-matrix least-squares methods on F2. All atoms were
readily located and the positions of all non-hydrogen atoms were refined anisotropically, where
all hydrogens were located in calculated positions riding on the bonded atom. Disorder was
found to be pronounced in the even-numbered chains for alkyl-substituted crystals (12a and 14a,
60/40 % and 75/25 %, respectively) compared with the odd-numbered N-undecyl-substituted
species, 13a. Disordered atoms were refined in alternate least squares cycles.
Crystallographic data (excluding structure factors) for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supplementary information;
CCDC 750157, CCDC 750156 and CCDC 750158. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
SN is grateful to the HEC (Higher Education Commission) Pakistan for financial support of this
work.
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