Physicochemical characterization of new sulfonate and sulfate ammonium ionic liquids

Article abstract of DOI:10.1021/je200208h

In this work we describe the synthesis and thermal properties of nine new salts derived from ammonium that incorporate alkanesulfonate and alkanesulfate anions. Their structures were confirmed by ¹H and ¹³C NMR and HRMS-ESI. Their thermal properties were determined by differential scanning calorimetry (DSC). Three of the synthesized salts have been shown to be room temperature ionic liquids: N-ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium butanesulfonate, N-ethyl-N,N-dimethylbutylammonium ethylsulfate, and N-ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium ethylsulfate. Experimental densities, speeds of sound, dynamic viscosities, and refractive indices of these three ionic liquids were measured at T = 298.15 K.

Full text of DOI:10.1021/je200208h

Article
pubs.acs.org/jced
Physicochemical Characterization of New Sulfonate and Sulfate
Ammonium Ionic Liquids
†
†
‡
‡
§
,†
́
Maria Mahrova, Miguel Vilas, Angeles Domínguez, Elena Gomez, Noelia Calvar, and Emilia Tojo*
́
‡
†Department of Organic Chemistry, and Department of Chemical Engineering, University of Vigo, 36310 Vigo, Spain
§Department of Chemical Engineering, University of Porto, 4200-465 Porto, Portugal
ABSTRACT: In this work we describe the synthesis and thermal
properties of nine new salts derived from ammonium that
incorporate alkanesulfonate and alkanesulfate anions. Their
1
structures were confirmed by H and 13C NMR and HRMS-ESI.
Their thermal properties were determined by differential scanning
calorimetry (DSC). Three of the synthesized salts have been shown to be room temperature ionic liquids: N-ethyl-N-
(2-hydroxyethyl)-N,N-dimethylammonium butanesulfonate, N-ethyl-N,N-dimethylbutylammonium ethylsulfate, and N-ethyl-N-
(2-hydroxyethyl)-N,N-dimethylammonium ethylsulfate. Experimental densities, speeds of sound, dynamic viscosities, and
refractive indices of these three ionic liquids were measured at T = 298.15 K.
were received from Quimivita. N,N,N-Trimethylbutylammo-
nium methanesulfonate (I1) and N-(2-hydroxyethyl)-N,N,N-
trimethylammonium methanesulfonate (I2) were purchased
from IoLiTec and dried under high vacuum for 24 h. The rest
of the salts studied in this work (6−14) were synthesized for
the first time as shown below and dried under high vacuum for
24 h. All ILs were obtained with more than 99 % of purity.
Solvents were dried with suitable drying agents and distiled
under argon.
Reactions progress were monitored by thin layer chromatog-
raphy using precoated plates with stationary phase 0.2 mm
SilicaGel. 1H and 13C NMR spectrum were measured on a Bruker
ARX 400 and Electrospray MS were recorded on a Bruker FTMS
APEX/Qe mass spectrometer.
INTRODUCTION
■
Ionic liquids (IL) have received increasing interest during the
last decades as novel nonvolatile organic compounds.1 A broad
range of possible cations and anions allows us to create diverse
ILs, tailored to various needs.2 Their general properties such as
nonvolatily, nonflammability, chemical and thermo stability,
and environmentally friendly nature make them ideal
candidates for new lubricants.3−12 The potential use of ILs as
lubricants was first proposed in 2001.6 A significant number of
articles and patents on this topic have been published, implying
widespread interest from fundamental and industrial points of
veiw.10 However, there is little knowledge about the appropiate
formulation of a lubricant based on ILs.
In this work, a family of salts based on alkanesulfonate and
alkanesulfate anions and ammonium cations, where lengths of
the linear alkyl side chains were varied independently, were
prepared (Figure 1). Their structures were selected according
to the physical properties, toxicity, and tribological behavior of
previously described ILs.13 Nine of them were synthesized for
the first time. Their phase transition temperatures were
determined by differential scanning calorimetry (DSC).
Experimental densities, speeds of sound, refractive indices and
dynamic viscosities of those that have been shown to be room
temperature ILs were measured at T = 298.15 K. These ILs are
new and could be further applied in tribology tests.
Preparation of Alkanesulfonate Esters. Alkane sulfonate
esters were prepared according to the literature.14 The structures
of methyl butanesulfonate (1) and methyl octanesulfonate (2)
1
were confirmed by comparison of their H and 13C NMR data
with those previously reported,15 whereas ethyl methanesulfonate
(3), ethyl butanesulfonate (4), and ethyl octanesulfonate (5) are
described for the first time.
1
Ethyl Methanesulfonate (3). Colorless liquid. H NMR
(400 MHz, CDCl3, ppm, δ): 1.42 [t, 3H, J = 7.1 Hz, OCH2CH3],
3.0 [s, 3H, SCH3], 4.30 [q, 2H, J = 7.1 Hz, OCH2CH3]. 13C
NMR (100.6 MHz, CDCl3, ppm, δ): 15.0, 37.4, 66.4.
1
Ethyl Butanesulfonate (4). Colorless liquid. H NMR
(400 MHz, CDCl3, ppm, δ): 0.98 [t, 3H, J = 7.4 Hz, S(CH2)3-
CH3], 1.42 [t, 3H, J = 7.1 Hz, OCH2CH3], 1.50 [sex, 2H, J = 7.4
Hz, S(CH2)2CH2], 1.86 [quin, 2H, J = 7.7 Hz, SCH2CH2], 3.11
[t, 2H, J = 7.7 Hz, SCH2], 4.31 [q, 2H, J = 7.1 Hz, OCH2].
13C NMR (100.6 MHz, CDCl3, ppm, δ): 13.5, 15.2, 21.5, 25.4,
50.2, 65.9.
EXPERIMENTAL SECTION
■
Materials and Methods. N,N-Dimethylbutylamine
(≥ 99.0 %), N,N-dimethylethanolamine (≥ 99.5 %), 1-octanesul-
fonyl chloride (≥ 97.0 %), and triethylamine (≥ 99.0 %) were
purchased from Aldrich and used as received. 1-Butanesulfonyl
chloride (98.0 % mass fraction) was purchased from Acros
Organics. Diethyl sulfate (≥ 99.0 %) is commercially available
(Fluka). Toluene (≥ 99.9%), dichloromethane (≥ 99.9 %),
ethyl acetate (≥ 99.5 %), hexane (≥ 99.9 %), and diethyl ether
(≥ 99.9 %) were purchased from Merck. Methanol and ethanol
Received: March 1, 2011
Accepted: January 8, 2012
Published: January 27, 2012
© 2012 American Chemical Society
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Figure 1. Ammonium salts studied in this work: 6, [BM3N][BSO3]; 7, [BM3N][OSO3]; 8, [M3N(CH2)2OH][BSO3]; 9, [M3N(CH2)2OH][OSO3];
10, [EM2N(CH2)2OH][MSO3]; 11, [EM2N(CH2)2OH][BSO3]; 12, [EM2N(CH2)2OH][OSO3]; 13, [BEM2N][ESO4]; 14, [EM2N(CH2)2OH]-
[ESO4]; I1, [BM3N][MSO3]; I2, [M3N(CH2)2OH][MSO3]. Compounds 6−14 were synthesized for the first time; compounds I1 and I2 were
supplied by IoLiTec.
1
Ethyl Octanesulfonate (5). Colorless liquid. H NMR
(400 MHz, CDCl3, ppm, δ): 0.88 [t, 3H, J = 6.4 Hz, S(CH2)7-
CH3], 1.28 [m, 10H, S(CH2)2(CH2)5], 1.40 [t, 3H, J = 7.1 Hz,
OCH2CH3], 1.85 [quin, 2H, J = 7.7 Hz, SCH2CH2], 3.07
N-(2-Hydroxyethyl)-N,N,N-trimethylammonium Buta-
nesulfonate [M3N(CH2)2OH][BSO3] (8). Reagents: N,N-
dimethylethanolamine (0.07 mL, 0.66 mmol) and methyl
butanesulfonate (1) (101.0 mg, 0.66 mmol). Reaction time:
1
[t, 2H, J = 7.7 Hz, SCH2], 4.29 [q, 2H, J = 7.1 Hz, OCH2]. 13
C
24 h. The yield was 71% (114.2 mg of a white powder). H
NMR (400 MHz, CDCl3, ppm, δ): 0.92 [t, 3H, J = 7.3 Hz,
S(CH2)3CH3], 1.41 [sex, 2H, J = 7.4 Hz, S(CH2)2CH2], 1.74
[quin, 2H, J = 7.8 Hz, SCH2CH2], 2.78 [t, 2H, J = 6.7 Hz,
SCH2], 3.34 [s, 9H, N(CH3)3], 3.71 [t, 2H, J = 6.7 Hz, NCH2],
4.08 [m, 2H, NCH2CH2], 5.52 [bs, 1H, NCH2CH2OH]. 13C
NMR (100.6 MHz, CDCl3, ppm, δ): 13.8, 22.0, 27.3, 51.8, 54.4
[t, J(C,N) = 3.3 Hz], 56.4, 67.8. HRMS-ESI m/z (%):
345.24159 {[M3N(CH2)2OH]2[BSO3]}+ (C14H37N2O5S re-
quires 345.24177, 100), 346 {[M3N(CH2)2OH]2[BSO3] + 1}+
(18), 586.37685 {[M3N(CH2)2OH]3[BSO3]2}+ (C23H60N3O9S2
requires 586.37655, 32), 587 {[M3N(CH2)2OH]3[BSO3]2 + 1}+
(12), 588 {[M3N(CH2)2OH]3[BSO3]2 + 2}+ (5).
NMR (100.6 MHz, CDCl3, ppm, δ): 14.0, 15.1, 22.6, 23.4, 28.2,
28.9, 31.7, 50.5, 65.8.
General Procedure for the Synthesis of Ammonium
Alkanesulfonate Ionic Liquids. The desired tertiary amine
was added dropwise to a solution of equal molar amounts of
previously prepared alkanesulfonate ester (CmH2m+1SO3-
CnH2n+1) in ethyl acetate (3 mL). The reaction mixture was
stirred at room temperature (in case of compounds 6−9) or
under reflux (in case of compounds 10−12) until reaction
completion. Ethyl acetate was removed under low pressure. The
product was washed with diethyl ether and solvent was removed
by decantation. After washings, remaining diethyl ether was
eliminated under reduced pressure and the product was dried
under high vacuum for 24 h.
N-(2-Hydroxyethyl)-N,N,N-trimethylammonium Octa-
nesulfonate [M3N(CH2)2OH][OSO3] (9). Reagents: N,N-
dimethylethanolamine (0.24 mL, 2.40 mmol) and methyl
octanesulfonate (2) (500.0 mg, 2.40 mmol). Reaction time:
N,N,N-Trimethylbutylammonium Butanesulfonate
[BM3N][BSO3] (6). Reagents: N,N-dimethylbutylamine (0.1 mL,
0.72 mmol) and methyl butanesulfonate (1) (109.6 mg,
0.72 mmol). Reaction time: 12 h. The yield was 73% (133.7 mg
1
16 h. The yield was 82% (590.0 mg of a white powder). H
NMR (400 MHz, CDCl3, ppm, δ): 0.87 [t, 3H, J = 7.2 Hz,
S(CH2)7CH3], 1.26 [m, 8H, S(CH2)2(CH2)4], 1.36 [m, 2H,
S(CH2)6CH2], 1.76 [quin, 2H, J = 7.8 Hz, SCH2CH2], 2.77
[t, 2H, J = 6.8 Hz, SCH2], 3.34 [s, 9H, N(CH3)3], 3.70 [m, 2H,
NCH2], 4.08 [m, 2H, NCH2CH2], 5.52 [bs, 1H, NCH2CH2OH].
13C NMR (100.6 MHz, CDCl3, ppm, δ): 14.0, 22.6, 25.2, 28.8, 29.1,
29.3, 31.7, 52.1, 54.3, 56.4, 67.8. HRMS-ESI m/z (%): 401
{[M3N(CH2)2OH]2[OSO3]}+ (60), 698 {[M3N(CH2)2-
OH]3[OSO3]2}+ (100), 995 {[M3N(CH2)2OH]4[OSO3]3}+ (17).
N-Ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
Methanesulfonate [EM2N(CH2)2OH] [MSO3] (10). Reagents:
N,N-dimethylethanolamine (0.15 mL, 1.45 mmol) and ethyl
methanesulfonate (3) (180.0 mg; 1.45 mmol). Reaction time: 20 h.
1
of a white powder). H NMR (400 MHz, CDCl3, ppm, δ): 0.91
[t, 3H, J = 7.3 Hz, S(CH2)3CH3], 1.00 [t, 3H, J = 7.3 Hz,
N(CH2)3CH3], 1.43 [m, 4H, S(CH2)2CH2 and N(CH2)2CH2],
1.70 [m, 2H, SCH2CH2], 1.78 [m, 2H, NCH2CH2], 2.80 [t, 2H,
J = 7.6 Hz, SCH2], 3.35 [s, 9H, N(CH3)3], 3.49 [m, 2H, NCH2].
13C NMR (100.6 MHz, CDCl3, ppm, δ): 13.7, 13.9, 19.6, 22.2,
25.0, 27.5, 51.9, 53.0, 66.4. HRMS-ESI m/z (%): 369.31475
[(BM3N)2(BSO3)]+ (C18H45N2O3S requires 369.31454, 100), 370
[(BM3N)2(BSO3) + 1]+ (21), 371 [(BM3N)2(BSO3) + 2]+ (6),
622.48622 [(BM3N)3(BSO3)2]+ (C29H72N3O6S2 requires
622.48570, 53), 623 [(BM3N)3(BSO3)2 + 1]+ (19).
N,N,N-Trimethylbutylammonium Octanesulfonate
[BM3N][OSO3] (7). Reagents: N,N-dimethylbutylamine (0.17
mL, 1.21 mmol) and methyl octanesulfonate (2) (251.6 mg,
1.21 mmol). Reaction time: 20 h. The yield was 63% (235.9 mg
of a white powder). 1H NMR (400 MHz, CDCl3, ppm, δ): 0.86
[t, 3H, J = 6.8 Hz, S(CH2)7CH3], 0.99 [t, 3H, J = 7.3 Hz,
N(CH2)3CH3], 1.26 [m, 8H, S(CH2)3(CH2)4], 1.34 [m, 2H,
S(CH2)2CH2], 1.42 [sex, 2H, J = 7.4 Hz, N(CH2)2CH2], 1.70
[m, 2H, SCH2CH2], 1.75 [m, 2H, NCH2CH2], 2.78 [t, 2H, J =
6.7 Hz, SCH2], 3.34 [s, 9H, N(CH3)3], 3.49 [m, 2H, NCH2].
13C NMR (100.6 MHz, CDCl3, ppm, δ): 13.7, 14.1, 19.6, 22.6,
24.9, 25.5, 28.9, 29.1, 29.4, 31.8, 52.2, 52.9, 66.4. HRMS-ESI m/z
(%): 425 [(BM3N)2(OSO3)]+ (100), 734 [(BM3N)3(OSO3)2]+
(50), 1043 [(BM3N)4(OSO3)3]+ (5).
1
The yield was 73% (225.6 mg of a white powder). H NMR
(400 MHz, CDCl3, ppm, δ): 1.40 [t, 3H, J = 7.3 Hz, NCH2CH3],
2.70 [s, 3H, SCH3], 3.24 [s, 6H, N(CH3)2], 3.60 [q, 2H, J = 7.3 Hz,
NCH2CH3], 3.65 [m, 2H, NCH2CH2OH], 4.07 [m, 2H,
NCH2CH2OH], 5.51 [bs, 1H, NCH2CH2OH]. 13C NMR (100.6
MHz, CDCl3, ppm, δ): 8.4, 39.6, 51.1 [t, J(C,N) = 3.3 Hz], 56.1, 61.1,
65.1. HRMS-ESI m/z (%): 331.22751 [(EM2N(CH2)2OH)2-
(MSO3)]+ (C13H35N2O5S requires 331.22612, 100), 544.32741
[(EM2N(CH2)2OH)3(MSO3)2]+ (C20H54N3O9S2 requires
544.32960, 33).
N-Ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
Butanesulfonate [EM2N(CH2)2OH] [BSO3] (11). Reagents:
N,N-dimethylethanolamine (0.14 mL, 1.34 mmol) and ethyl
butanesulfonate (4) (222.8 mg, 1.34 mmol). Reaction time: 72 h.
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1
The yield was 83% (280.0 mg of a slightly yellow liquid). H
NMR (400 MHz, CDCl3, ppm, δ): 0.93 [t, 3H, J = 7.3 Hz,
S(CH2)3CH3], 1.43 [m, 5H, S(CH2)2CH2 and NCH2CH3],
1.78 [m, 2H, SCH2CH2], 2.82 [t, 2H, J = 6.9 Hz, SCH2], 3.28
[s, 6H, N(CH3)2], 3.63 [q, 2H, J = 7.3 Hz, NCH2CH3], 3.69
[m, 2H, NCH2CH2OH], 4.13 [m, 2H, NCH2CH2OH], 5.62
[bs, 1H, NCH2CH2OH]. 13C NMR (100.6 MHz, CDCl3, ppm,
δ): 8.4, 13.8, 22.0, 27.3, 51.0, 51.8, 56.1, 61.0, 65.1. HRMS-ESI
m/z (%): 373.27198 [(EM2N(CH2)2OH)2(BSO3)]+ (C16H41N2O5S
requires 373.27362, 100), 628.42456 [(EM2N(CH2)2OH)3(BSO3)2]+
(C26H66N3O9S2 requires 628.42405, 54), 884 [(EM2N-
(CH2)2OH)4(BSO3)3]+ (38), 1139 [(EM2N(CH2)2OH)5(BSO3)4]+
(11), 1394 [(EM2N(CH2)2OH)6(BSO3)5]+ (9). The mass fraction of
water was found to be 5 × 10−5 (determined by 756 Karl Fischer
coulometer).
361.23723, 100), 604.34935 {[EM2N(CH2)2OH]3[ESO4]2}+
(C22H58N3O11S2 requires 604.35128, 32), 847 {[EM2N(CH2)2-
OH]4[ESO4]3}+ (45), 1091 {[EM2N(CH2)2OH]5[ESO4]4}+
(23), 1334 {[EM2N(CH2)2OH]5[ESO4]4}+ (21). The mass
fraction of water was found to be 6 × 10−5 (determined by 756
Karl Fischer coulometer).
Apparatus and Procedures. DSC. The thermal analysis of
the pure salts synthesized in this work was performed using a
Mettler-Toledo differential scanning calorimeter (DSC), model
DSC822e, with Mettler-Toledo STARe software version 8.01.
Zinc and indium reference sample (provided by Mettler-Toledo)
were used for the calibration of the temperature and heat flow.
The sample pan and empty pan reference were placed within the
furnace and they were exposed to a flowing N2 atmosphere. The
method used for the thermal analysis consisted in cooling the
samples from (393 to 233) K, at a rate of 10 °C·min−1, followed
by heating from (233 to 423) K at a rate of 10 °C·min−1. Because
the presence of volatiles affects the glass transition and melting
temperature,16,17 the samples were heated at T = 393.15 K for
30 min inside the furnace of the DSC. The uncertainty of the
temperature measurement was 1 K, and the uncertainty of the
transition enthalpies was 4 J·g−1, which were determined by
using a common procedure consisting in three consecutive scans
of the same sample and three scans removing and replacing the
sample carried out by different operators.
N-Ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
Octanesulfonate [EM2N(CH2)2OH] [OSO3] (12). Reagents:
N,N-dimethylethanolamine (0.23 mL, 2.25 mmol) and ethyl
octanesulfonate (5) (500.3 mg, 2.25 mmol). Reaction time:
1
48 h. The yield was 79% (554.0 mg of a white powder). H
NMR (400 MHz, CDCl3, ppm, δ): 0.86 [t, 3H, J = 6.0 Hz,
S(CH2)7CH3], 1.25 [m, 8H, SCH2CH2(CH2)4], 1.39 [m, 5H,
NCH2CH3, and S(CH2)6CH2], 1.76 [m, 2H, SCH2CH2], 2.77
[t, 2H, J = 8.0 Hz, SCH2], 3.25 [s, 6H, N(CH3)2], 3.60 [q, 2H,
J = 7.3 Hz, NCH2CH3], 3.64 [m, 2H, NCH2CH2OH], 4.07 [m,
2H, NCH2CH2OH], 5.58 [bs, 1H, NCH2CH2OH]. 13C NMR
(100.6 MHz, CDCl3, ppm, δ): 8.4, 14.1, 22.6, 25.3, 28.9, 29.2,
29.4, 31.8, 51.1, 52.1, 56.1, 61.0, 65.1. HRMS-ESI m/z (%): 429
[(EM2N(CH2)2OH)2(OSO3)]+ (100), 740 [(EM2N-
(CH2)2OH)3(OSO3)2]+ (77), 1052 [(EM2N(CH2)2OH)4-
(OSO3)3]+ (6).
The heat capacities of the compounds were determined
by using the sapphire sample. Aluminum pans of 100 μL
with 80 mg of the sample were used. The rate for the heat
capacities measurements was 20 °C/min and the uncertainty
in experimental measurements of heat capacity was
1
J·K−1·mol−1.
Physical Properties. The apparatus used for the
determination of density, speed of sound, refractive index and
dynamic viscosity of the pure salts were described elsewhere.13
Briefly, an Anton Paar DSA-5000 M digital vibrating-tube
densimeter was employed for the density and speed of sound
determination. It is important to remark that the influence of
viscosity on the density measurement is automatically corrected.
The uncertainties in the density and speed of sound experi-
mental measurements were 2 × 10−6 g·cm−3 and 0.3 m·s−1,
respectively.
The refractive indices were measured with an automatic
refractometer Abemat-HP Dr. Kernchen; the uncertainty in its
measurement was 4 × 10−5.
The dynamic viscosities were determined by using an
automatic viscosimeter Lauda PVS1 with two Ubbelhode
capillary microviscosimeters of (3 × 10−3 and 4.7 × 10−3) m
diameter (the uncertainty in experimental measurement was
1 and 3 mPa·s respectively).
General Procedure for the Synthesis of Ammonium
Alkanesulfates Ionic Liquids. Ammonium alkanesulfates were
prepared according to a procedure previously described.13
N-Ethyl-N,N-dimethylbutylammonium Ethylsulfate
[BEM2N][ESO4] (13). Reagents: N,N-dimethylbutylamine
(3.0 mL, 19.6 mmol) and diethyl sulfate (2.6 mL, 19.6 mmol).
Reaction time: 5 h. The yield was 98% (4.9 g of a colorless
1
liquid). H NMR (400 MHz, CDCl3, ppm, δ): 0.86 [t, 3H, J =
7.4 Hz, N(CH2)3CH3], 1.14 [t, 3H, J = 7.1 Hz, OCH2CH3], 1.25
[t, 3H, J = 7.3 Hz, NCH2CH3], 1.29 [sex, 2H, J = 7.4 Hz,
N(CH2)2CH2], 1.58 [m, 2H, NCH2CH2], 3.03 [s, 6H,
N(CH3)2], 3.22 [m, 2H, NCH2], 3.38 [q, 2H, J = 7.3 Hz,
NCH2CH3], 3.90 [q, 2H, J = 7.1 Hz, OCH2CH3]. 13C NMR
(100.6 MHz, CDCl3, ppm, δ): 8.3, 13.6, 15.2, 19.5, 24.4, 50.1 [t,
J(C,N) = 3.5 Hz], 59.2, 62.9, 63.2. HRMS-ESI m/z (%): 385.30843
[(BEM2N)2(ESO4)]+ (C18H45N2O4S+ requires 385.30891, 100), 640
[(BEM2N)3(ESO4)2]+ (25), 895 [(BEM2N)4(ESO4)3]+ (12), 1151
[(BEM2N)5(ESO4)4]+ (3), 1406 [(BEM2N)6(ESO4)5]+ (3). The
mass fraction of water was found to be 4 × 10−5 (determined by 756
Karl Fischer coulometer).
RESULTS AND DISCUSSION
■
N-Ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
Ethylsulfate [EM2N(CH2)2OH][ESO4] (14). Reagents: N,N-
dimethylethanolamine (6.2 mL, 61.6 mmol) and diethyl sulfate
(8.1 mL, 61.6 mmol). Reaction time: 5 h. The yield was 88%
Synthesis of ILs. Ammonium alkanesulfonate salts were
synthesized by alkylation of the corresponding tertiary amines
with alkyl sulfonates (CmH2m+1SO3CnH2n+1), which were
prepared by simple treatment of alcohols (CnH2n+1OH, n = 1, 2)
with alkanesulfonyl chlorides (CmH2m+1SO2Cl, m = 1, 4, 8) in the
presence of a base (Scheme 1). Ammonium alkanesulfates salts
were synthesized by alkylation of the corresponding tertiary amines
with alkyl sulfates.13
1
(13.2 g of a colorless liquid). H NMR (400 MHz, CDCl3,
ppm, δ): 1.29 [t, 3H, J = 7.1 Hz, OCH2CH3], 1.40 [t, 3H, J =
7.3 Hz, NCH2CH3], 3.23 [s, 6H, N(CH3)2], 3.59 [m, 4H,
NCH2CH2OH and NCH2CH3], 3.95 [m, 2H, NCH2CH2OH],
4.07 [q, 2H, J = 7.1 Hz, OCH2CH3], 4.96 [bs, 1H, NCH2-
CH2OH]. 13C NMR (100.6 MHz, CDCl3, ppm, δ): 8.4, 15.2,
51.1, 56.3, 61.2, 63.7, 65.2. HRMS-ESI m/z (%): 361.23548
{[EM2N(CH2)2OH]2[ESO4]}+ (C14H37N2O6S requires
Thermal Properties. Thermal data derived from DSC
traces are summarized in Table 1. In this table, the melting tem-
perature (Tm), the cold crystallization temperature (Tcc), and
the solid−solid transition temperature (Ts‑s) are taken to be the
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Scheme 1. Synthesis of Ammonium Alkanesulfonates
a
Table 1. Thermal Properties for Pure Salts
Tm (K) and ΔH
(J·g−1)
Tf (K) and ΔH
Tg (K) and ΔH
Ts‑s (K) −an1 d ΔH
(J·g )
Tcc (K) and ΔH
(J·g−1)
Tx (K) and ΔH
−1
−1
compound
(J·g−1)
(J·g )
(J·g )
[BM3N][MSO3] (I1)
[BM3N][BSO3] (6)
[BM3N][OSO3] (7)
442
349 (−18.42)
328 (−12.27)
404
335 (11.86)
b
484
347 (10.62)
413 (1.60)
350 (29.48)
365 (13.65)
246 (−24.18)
409 (−1.22)
340 (−13.49)
360 (−18.64)
323 (−33.50)
[M3N(CH2)2OH][MSO3] (I2)
393 (24.83)
378 (−25.13)
[M3N(CH2)2OH][BSO3] (8)
[M3N(CH2)2OH][OSO3] (9)
324 (103.59)
390 (15.46)
305 (−103.40)
387 (−14.99)
307 (22.16)
337 (17.65)
346 (17.65)
342 (−21.65)
323 (−41.47)
279 (−21.65)
307 (−15.89)
c
d
[EM2N(CH2)2OH][MSO3] (10)
[EM2N(CH2)2OH][BSO3] (11)
[EM2N(CH2)2OH][OSO3] (12)
[BEM2N][ESO4] (13)
317 (94.03)
318 (−63.10)
293 (93.08)
320 (95.89)
326 (−101.80)
e
307 (45.71)
[EM2N(CH2)2OH][ESO4] (14)
a
Tm, melting temperature (K); Tf, freezing temperature (K); Tg, glass-transition temperature (K); Ts‑s, solid−solid transition temperature (K); Tcc,
b
cold crystallization temperature (K); Tx, phase-transition temperature on cooling (K); ΔH, enthalpy (J·g−1). Exhibits cold crystallization
c
d
(crystallization on heating) at 259.09 K (24.07 J·g−1). Exhibits endothermic transition on heating at 337.64 K (7.34 J·g−1). Exhibits two exotherms
e
on cooling at 317.2 K (−9.02 J·g−1) and 309.28 K (−1.41 J·g−1). Exhibits endothermic transition on heating at 334.58 K (5.31 J·g−1).
peak of an endothermic curve on heating; the freezing tem-
perature (Tf) and the phase-transition temperature on cooling
(Tx) are taken to be the peak of an exothermic curve on
cooling; and the glass-transition temperature (Tg) is the
midpoint of a small heat capacity change on heating from the
amorphous glass state to a liquid state. The cold crystallization
temperature is defined as the midpoint of an exothermic peak
on heating from a subcooled liquid state to a crystalline solid
state.21 It should also be noted that the DSC scans were always
started at 233 K and finished at 423 K for all salts studied in
this work. Because [BM3N][MSO3] (I1) and [BM3N][OSO3]
(7) melting points were not observed, DSC scans from 298 to
523 K were performed.
Illustrative DSC thermograms obtained on cooling and
heating are shown in Figures 2−14. Figure 2 showed a glass-
transition at 404 K and freezing point at 349 K for [BM3N]-
[MSO3] (I1), whereas a melting transition was not observed.
However, Figure 3 showed a melting point at 442 K. [BM3N]-
[BSO3] (6) (Figure 4) and [M3N(CH2)2OH][BSO3] (8)
(Figure 8) present distinct freezing points [(328 and 305) K,
respectively] on cooling and distinct melting points [(335 and
324) K, respectively] on heating.
Multiple solid−solid transitions are shown before melting
points for compounds [BM3N][OSO3] (7) (Figures 5 and 6),
[M3N(CH2)2OH][MSO3] (I2) (Figure 7), and [M3N(CH2)2-
OH][OSO3] (9) (Figure 9). The melting point of [BM3N]-
[OSO3] (7) can be seen in Figure 6 at 484 K. Thus, the DSC
thermogram of this compound showed a cold crystallization
temperature at 246 K; two solid−solid transition temperatures
at (347 and 413) K before the melting point and two phase-
transition temperatures on cooling [(409 and 340) K]. The
broadnes of the final melting peak observed for [M3N(CH2)2-
OH][MSO3] (I2) at 393 K could indicate the onset of one or
more solid−solid transitions coincident with the melting point.18
This compound also showed two solid−solid phase-transitions at
(350 and 365) K, following with a melting point at 393 K and
phase-transition temperatures at (359 and 323) K on cooling.
Thermogram of [M3N(CH2)2OH][OSO3] (9) showed three
solid−solid transitions at (307, 336, and 346) K before melting
point (390 K); a freezing point at 387 K, and three phase-
transition temperatures on cooling at (342, 323, and 279) K.
The [EM2N(CH2)2OH][MSO3] (10) thermogram (Figure 10)
showed a broad melting peak on heating at 317 K, where
coincidence of solid−solid transition with melting point is
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Figure 2. DSC scan for [BM3N][MSO3] (I1); upper curve is cooling
Figure 5. DSC scan for [BM3N][OSO3] (7); upper curve is cooling
and lower curve is heating.
and lower curve is heating.
Figure 6. DSC scan from (293 to 523) K for [BM3N][OSO3] (7).
Figure 3. DSC scan from (298 to 523) K for [BM3N][MSO3] (I1).
Figure 7. DSC scan for [M3N(CH2)2OH][MSO3] (I2); upper curve
is cooling and lower curve is heating.
its DSC curve exhibited two exotherms at (317 and 309) K, corre-
sponding to the subsequent transitions from the isotropic liquid to
the crystalline state.20 The broadnes of melting peak showed
coincidence of solid−solid transition with the melting point at
320 K. The freezing point was registered at 326 K.
Compounds [EM2N(CH2)2OH][BSO3] (11), [BEM2N]-
[ESO4] (13) and [EM2N(CH2)2OH][ESO4] (14) were
shown to be room temperature ILs. The [EM2N(CH2)2OH]-
[BSO3] (11) (Figure 11) DSC thermogram showed one melting
peak at 293 K and no peaks on cooling. The [BEM2N][ESO4]
(13) (Figure 13) DSC thermogram showed a melting point at
307 K and an endothermic transition at 334 K. The onset melting
Figure 4. DSC scan for [BM3N][BSO3] (6); upper curve is cooling
and lower curve is heating.
observed again.19 The freezing point was registered at 318 K
and one phase-transition at 307 K.
The [EM2N(CH2)2OH][OSO3] (12) DSC (Figure 12) anal-
ysis was quite complicated as several weak endothermic (and/or
exothermic) transitions were observed. We could suppose that the
DSC thermogram shows endothermic transition (337 K) from
the crystalline to the isotropic liquid state. When the compound
was cooled from the isotropic liquid state to the crystalline state,
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Figure 8. DSC scan for [M3N(CH2)2OH][BSO3] (8); upper curve is
Figure 11. DSC scan for [EM2N(CH2)2OH][BSO3] (11); upper
cooling and lower curve is heating.
curve is cooling and lower curve is heating.
Figure 12. DSC scan for [EM2N(CH2)2OH][OSO3] (12); upper
curve is cooling and lower curve is heating.
Figure 9. DSC scan for [M3N(CH2)2OH][OSO3] (9); upper curve is
cooling and lower curve is heating.
Figure 13. DSC scan for [BEM2N][ESO4] (13); upper curve is
cooling and lower curve is heating.
Figure 10. DSC scan for [EM2N(CH2)2OH][MSO3] (10); upper
curve is cooling and lower curve is heating.
cation asymmetry increase (I2 versus 10, 8 versus 11, and 9
versus 12) melting point decreases.
Heat Capacities. Heat capacities of some salts with melting
points below T = 373 K were measured in different tempera-
ture ranges. The next polynomial equation was used to adjust
them, where T is temperature and a, b, and c are adjustable
parameters
temperature of this compound was 293 K. Therefore, this IL is
liquid at room temperature. In the case of [EM2N(CH2)2OH]-
[ESO4] (14) no peaks were observed.
It is well-known that thermal properties of ILs depend on the
structure of cation and anion.2 As it can be observed in Figure 15,
when the anion alkyl chain length increase from n = 1 to n = 4,
the melting point decrease. However, when the anion alkyl
chain length increase from n = 4 to n = 8, the melting point
increase. Figure 15 also shows the melting point variation for
sulfonates when the anion alkyl chain increase. The influence of
cation asymmetry on the melting point is also observed. As the
2
C = aT + bT + c
p
(2)
The characteristic parameters a, b, and c are given in Table 2
together with temperature ranges of measurements and the
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Table 3. Experimental Heat Capacities [Cp (J·K−1·mol−1)] as
a Function of Temperature of Some Ammonium Salts
(6, 8, and 10−14)
−1
Cp (J·K ·mol−1)
T (K)
6
8
10
11
12
13
14
300.15
305.15
310.15
315.15
320.15
325.15
330.15
335.15
340.15
345.15
350.15
355.15
360.15
365.15
370.15
375.15
380.15
385.15
390.15
395.15
400.15
451
456
461
466
470
474
477
481
485
489
491
494
497
500
504
507
Figure 14. DSC scan for [EM2N(CH2)2OH][ESO4] (14); upper
curve is cooling and lower curve is heating.
406
411
415
419
422
425
428
432
435
93
711
715
720
725
730
736
740
744
748
701
706
711
717
723
728
733
736
741
518
519
520
521
523
525
527
528
529
94
451
467
478
485
491
496
500
95
97
98
99
100
101
102
104
Table 4. Density, ρ, Refractive Index, nD, Speed of Sound, u,
and Dynamic Viscosity, η, of [EM2N(CH2)2OH][BSO3],
[BEM2N][ESO4], and [EM2N(CH2)2OH][ESO4] at 298.15 K
ρ
103 η
u−1
Figure 15. Melting point variation with the anion alkyl chain length of
alkanesulfonate salts: N,N,N-trimethylbutylammonium alkanesulfonate
( ), N-(2-hydroxyethyl)-N,N,N-trimethylammonium alkanesulfonate
(red circle), and N-ethyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
alkanesulfonate (blue triangle).
IL
(g·cm−3
)
(Pa·s)
nD
(m·s )
[EM2N(CH2)2OH][BSO3] (11) 1.11157
[BEM2N][ESO4] (13) 1.20810
1354
333
1.45985 1694.0
1.46252 1817.9
1.47303 1714.0
■
[EM2N(CH2)2OH][ESO4] (14) 1.12566
1617
CONCLUSIONS
■
Table 2. Fitting Coefficients of eq 2 of Some Ammonium
Salts (6, 8, and 10−14)
In this work we designed and synthesized nine new ammonium
salts: seven ammonium alkanesulfonates and two ammonium
alkanesulfates. The selection of their structures was made
according to the physical properties, toxicity, and trybological
behavior of previously described ILs, in order to obtain new ILs
as potential lubricants. Ammonium alkanesulfonates [BM3N]-
[BSO3], [BM3N][OSO3], [M3N(CH2)2OH][BSO3], [M3N-
(CH2)2OH][OSO3], [EM2N(CH2)2OH][MSO3], [EM2N-
(CH2)2OH][BSO3], and [EM2N(CH2)2OH][OSO3] were
prepared by alkylation of the corresponding tertiary ammine
with an alkyl sulfonate. Ammonium alkanesulfates [BEM2N]-
[ESO4] and [EM2N(CH2)2OH][ESO4] were prepared by
simple quaternization of the corresponding tertiary amine
with diethyl sulfate. Three of the synthesized salts shown to be
room temperature ILs: [EM2N(CH2)2OH][BSO3], [BEM2N]-
[ESO4], and [EM2N(CH2)2OH][ESO4]. Their density, speed of
sound, dynamic viscosity, and refractive index were experimentally
measured at room temperature.
Cp (J·K−1·mol−1)
salt
ΔT (K)
360−400 −0.0043 4.3421 −300.86
360−400 0.0020 −1.1947 691.36
a
b
c
6: [BM3N][BSO3]
8: [M3N(CH2)2OH][BSO3]
10: [EM2N(CH2)2OH][MSO3] 351−397 −0.0041 3.8245 −430.53
11: [EM2N(CH2)2OH][BSO3] 352−400 −0.0011 1.0622 −147.81
12: [EM2N(CH2)2OH][OSO3] 355−398 −0.0027 3.0380
−22.604
13: [BEM2N][ESO4] 360−390 −0.0314 25.111 −4518.9
14: [EM2N(CH2)2OH][ESO4] 300−360 −0.0017 1.5388 −238.00
experimental heat capacities for each temperature are
summarized in Table 3.
Physical Properties. The density, speed of sound, dynamic
viscosity, and refractive index of [EM2N(CH2)2OH][BSO3]
(11), [BEM2N][ESO4] (13), and [EM2N(CH2)2OH][ESO4]
(14) ILs were experimentally measured at T = 298.15 K. The
obtained values are summarized in Table 4.
The thermal properties of the synthesized compounds were
determined by differential scanning calorimetry (DSC).
Illustrative DSC thermograms obtained on cooling and heating
showed several solid−solid transitions in salts with melting
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Journal of Chemical & Engineering Data
Article
(16) Fredlake, P. C.; Crosthwaite, J. M; Hert, D. G; Aki, S. N. V. K;
Brennecke, J. F. Thermophysical properties of immidazolium-based
ionic liquids. J. Chem. Eng. Data 2004, 49, 954−964.
(17) Crosthwaite, J. M.; Muldon, M. J.; Dixon, J. K.; Anderson, J. L.;
Brennecke, J. F. Phase transition and decomposition temperatures,
heat capacities and viscosities of pyridinium ionic liquids. J. Chem.
Thermodyn. 2005, 37, 559−568.
point higher than 373 K such as [BM3N][OSO3], [M3N-
(CH2)2OH][MSO3], and [M3N(CH2)2OH][OSO3].
The anion alkyl chain length influence on the ammonium
salts thermal properties was also determined. When the anion
alkyl chain length increased from n = 1 to n = 4, the melting
point decreased. However, when the anion alkyl chain length
increased from n = 4 to n = 8, the melting point increased. As
expected, an influence of the cation asymmetry on the melting
point was also observed: when the asymmetry of the cation
increased, the melting temperature decreased.
(18) Golding, J; Forsyth, S; MacFarlane, D. R.; Forsyth, M.; Deacon,
G. B. Methanesulfonate and p-toluenesulfonate salts of the N-methyl-
N-alkylpyrrolidinium and quaternary ammonium cations: novel low
cost ionic liquids. Green Chemistry. 2002, 4, 223−229.
(19) Busi, S; Lahtinen, M; Mansikkamaki, H; Valkonen, J; Rissanen,
̈
K. Synthesis, characterization and thermal properties of small
R2R’2N+X− -type quaternary ammonium halides. J. Solid State Chem.
2005, 178, 1722−1737.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: etojo@uvigo.es. Tel.: 34-986812290. Fax: 34-986812382.
(20) Iwan, A; Janeczek, H; Rannou, P; Kwiatkowski, R. Mesomorphic
and optical properties of undoped and doped azomethines. J. Mol. Liq.
2009, 148, 77−87.
Funding
The authors are grateful to the E.C. (MINILUBES Project, FP-
7-PEOPLE-2007-1-1-ITN), Ministerio de Educacion
of Spain (Projects CTQ2010-18147 and CTQ2007-61788),
the Pos-doc scholarships from Fundacao para a Ciencia e a
Tecnologia (FCT, Portugal; ref SFRH/BDP/37775/2007), and
́
y Ciencia
̧
̂
̃
́
the Xunta de Galicia (Angeles Alvarino Programme, INCI-
̃
TE08PXIB314253PR and INCITE08ENA314019ES Projects).
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