Further investigation of the biodegradability of imidazolium ionic liquids

Article abstract of DOI:10.1039/b900787c

In continuation of our earlier investigations, this report presents a rationale behind the design of a series of imidazolium based ionic liquids and their biodegradation using the CO₂ headspace test (ISO 14593 method, OECD 310). The effect on biodegradability of these salts through variation of the N-substituted side chains of imidazolium ions was examined further through incorporation of various functional groups and increased alkyl chain lengths. A series of anions containing moieties known to be biodegradable were also incorporated into a number of imidazolium based salts and examined in a similar fashion.

Full text of DOI:10.1039/b900787c

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Further investigation of the biodegradability of imidazolium ionic liquids
Jitendra R. Harjani,a Jeff Farrell,b M. Teresa Garcia,c Robert D. Singer*b and Peter J. Scammells*a
Received 14th January 2009, Accepted 2nd March 2009
First published as an Advance Article on the web 18th March 2009
DOI: 10.1039/b900787c
In continuation of our earlier investigations, this report presents a rationale behind the design of a
series of imidazolium based ionic liquids and their biodegradation using the CO2 headspace test
(ISO 14593 method, OECD 310). The effect on biodegradability of these salts through variation
of the N-substituted side chains of imidazolium ions was examined further through incorporation
of various functional groups and increased alkyl chain lengths. A series of anions containing
moieties known to be biodegradable were also incorporated into a number of imidazolium based
salts and examined in a similar fashion.
ever, it is important to note that toxicity and biodegradability
Introduction
need not always be mutually exclusive.11b A toxic substance with
Ionic liquids (ILs) initially attracted the attention of chemists
good biodegradability is not necessarily as much of a concern as
because of the advantages they offer in electrochemistry, sepa-
a non-toxic, recalcitrant substance. This is because the latter
ration processes and heterogeneous catalysis.1 The properties of
may persist and bio-accumulate exerting long term chronic
ILs, such as good chemical and thermal stability, lack of vapor
effects. Biodegradation is a natural process involving a collective
pressure and good solubility for a range of organic, inorganic,
effort of different microorganisms breaking down the complex
organometallic compounds and even gases, have presented
organic molecules into biomass and/or inorganic compounds,
several avenues of interest for chemists to explore.2 Their
such as carbon dioxide and water. Hence, a biodegradable,
architectural flexibility has broadened the scope of their ap-
but toxic, substance may exert an acute effect upon exposure
plications to include their use in materials design,3 immobilized
to it but will be rendered non-toxic upon its biodegradation
phases,4 catalyst anchoring,5 functionalized phases,6 supported
into biomass and/or inorganic compounds as mentioned above.
synthesis,7 to name only a few. ILs are now among chemists’
Once released in water or soil, both the environmental and
first picks as unconventional reaction media, not only because
structural factors influence the mineralization of a substance.
of their blend of unique, tunable properties, but also because of
The biodegradation data obtained for any compound greatly
their commercial availability and ease of synthesis and handling.
depends on both the physiological and catabolic nature of the
Although the aforementioned solvent attributes have helped
microbial population present in the medium.
chemists to develop many green, operationally safer processes,
The CO2 headspace test (ISO 14593, OECD 310) was used to
their impact on the environment has been a topic of discussion.8
assess the biodegradability of ILs prepared in this investigation.
In spite of the recent debates on their volatility,9 it is thought that
The methods used for evaluating ready biodegradability are
ILs would not pose any threat to air quality under operational
based on measuring non-specific parameters like dissolved or-
conditions of typical chemical processes. Their impact on water
ganic carbon, biochemical oxygen demand and CO2 production.
and soil quality is certainly a concern to environmental chemists,
The ready biodegradability tests are performed under stringent
mainly because these effects have not been evaluated to any great
conditions of low microbial density and high concentrations
extent and nor are they predictable.10 Several reviews and reports
of the test substance (as the only source of carbon for the
expressing the importance of conscientious design of chemicals
microorganisms). A substance attaining the pass level in these
have appeared over the last few years.11 For new chemicals, such
tests at a certain rate after termination of the lag phase may
as ILs, it is important to evaluate their ecological impact while
be classified as “readily biodegradable”. The pass level depends
assessing them for other properties applicable for their end use.12
on the analytical parameter measured. A substance passes the
Many research groups, including ours, have considered the
CO2 headspace test (OECD 310) when at least 60% of the
environmental effects of ILs by measuring their toxicity.13 How-
theoretical carbon dioxide is liberated within the first 28 days.
A positive result in a test for ready biodegradability can be
considered as indicative of rapid and ultimate degradation in
aMedicinal Chemistry and Drug Action, Monash Institute of
most environments including waste water treatment plants.
Pharmaceutical Sciences, Monash University, Parkville, 3052, Victoria,
Our earlier work on biodegradable ILs was focused on
Australia. E-mail: peter.scammells@vcp.monash.edu.au; Fax: +61 3
investigating the environmental impact of imidazolium based
99039582; Tel: +61 3 9903 9542
ILs.14 Although the conventional and most commonly used
imidazolium based ILs are recalcitrant, higher biodegradability
can be attained by suitably modifying the structure of the
cation and anion. Integrating the ester side chain derived from
C5 alcohol and C2 acid on the imidazolium cation helped to
bDepartment of Chemistry, Saint Mary’s University, Halifax, Nova
Scotia, Canada B3H 3C3. E-mail: robert.singer@smu.ca; Fax: +1 902
496 8104; Tel: +1 902 496 8189
cDepartment of Surfactant Technology, IQAC-CSIC, Jordi Girona
18–26, 08034, Spain. E-mail: mtgbet@iiqab.csic.es; Fax: +34 93 204
5904; Tel: +34 93 400 6100
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Fig. 1 Effect of cation modifications on percentage biodegradation, 1a (ꢀ), 1b ( ), 3a (ꢀ), 3b (+), 5b (ꢀ), 6b (♦),7b (᭺). Compounds 2, 4, 5a, 6a
and 7a underwent <5% biodegradation (data not plotted).
achieve higher biodegradation values.14a,c The ester group was
chosen because esterases are not only the most common enzymes
but are also known to offer broad substrate specificity. The
studies carried out on the pyridinium based ILs have indicated
that perhaps the presence of an ester group is necessary to
obtain acceptable levels of biodegradability; however, unlike the
imidazolium ring,15 the pyridinium core is not refractory.15,16
In the case of the imidazolium based salts/ILs, the C8 based
alkyl sulfate anion has been a preferred choice, since it has the
optimal alkyl chain length to achieve high biodegradability while
retaining good solvent properties.14a,c
starting materials, were of particular interest. In selecting the tar-
gets, we abided by the “rules of thumb” for biodegradability as
described in a review article by Boethling et al.11b Some materials
and anions derived from compounds with known toxicological
profiles were also subjected to the biodegradation test. 3-Methyl-
1-(pentoxycarbonylmethyl)imidazolium octylsulfate (1b), which
was previously shown to meet the requirement for classification
as ‘readily biodegradable’ as determined by the CO2 headspace
test,14c was included for comparative purposes in this study.
Although the biodegradability of the dialkylimidazolium
ILs with ester containing side chains have been investigated,
in all cases this side chain was derived from an a-halo es-
ter which afforded the corresponding alkyloxycarbonylmethyl
imidazolium salt.14 The biodegradability of imidazolium ILs
that bear either an alcohol functionality on the alkyl side
chain or on the esters derived from them (i.e. with the ester
functionality reversed) has yet to be examined. The presence of
oxygen in the structure increases the tendency of a substance to
metabolize. The quaternary salt 2 contains a primary alcohol
group on the alkyl side chain. Both the quaternary iodide 3a
and the quaternary bromide 2 were conveniently derived from
commercially available starting materials. Whereas 2 did not
show significant biodegradation, 3a showed reasonably good
Results and discussion
We noted that although imidazolium based ILs have been
modified in various ways to enhance their biodegradability,
many structural features that could potentially enhance the
biodegradability of this class of ILs have yet to be explored,
particularly with regards to modification of the anion. Hence,
we aimed to synthesize and test a heretofore uninvestigated series
of the imidazolium based ILs/salts for biodegradability. Some
simple targets that are already known in the literature, or those
that can be easily synthesized starting with commercially known
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tendencies to biodegrade under the test conditions. Compound
3a showed biodegradation at 25% after the standard 28 day
incubation period (Fig. 1). Notably, the cation in both 3a and 3b
can be regarded as a derivative of C4 alcohol with a C2 acid, and
hence, possesses skeletal similarity to the cation of imidazolium
based biodegradable ILs investigated earlier by our group.14a
The replacement of the iodide in 3a with the octyl sulfate anion,
as in 3b, increased the biodegradation to 54%. This is relatively
close to the acceptable 60% level for a substance to be classified
as readily biodegradable by this test.
ion has been previously incorporated as the anion in ILs that
are considered to be greener, since they are produced from a
material that is biocompatible and biorenewable.19 Lactate was
also of interest because polylactate is a commercial bioplastic
that is also used for making biomaterials used for medical
implants. Hence, [bmim][lactate] (9) was obtained from the
reaction involving [bmim][Cl] with a silver salt of lactic acid
and showed only 17% biodegradability after 28 days (Fig. 2).
Therefore, 9 cannot be considered to be readily biodegra-
dable.
The zwitterionic imidazolium compound 4, which was readily
obtained by the N-alkylation of 1-methylimidazole with 1,4-
butane sultone, did not show appreciable biodegradation.
Compound 4 is a precursor for the synthesis of sulfonic acid
containing imidazolium based task specific ILs. Whereas we
have previously shown that the presence of alkyl sulfate anions
paired with N,N-disubstituted imidazolium ions enhanced
biodegradability,14 it is evident that incorporation of the anionic
sulfonate group on the alkyl side chain of the imidazolium cation
does not help improve the biodegradation.
It is known that the incorporation of the phenyl ring in some
molecules helps to improve their biodegradability,11b mainly
because the phenyl ring is prone to attack by the oxygenases
that oxidize the ring facilitating other metabolic processes
that lead to mineralization. However, the quaternization of
1-methylimidazole with benzyl bromide yielded the quaternary
bromide 5a which showed <5% biodegradability after 28 days.
The corresponding octyl sulfate salt 5b showed biodegradation
at 38%, which can be attributed to the anion alone. The poor
biodegradability values obtained for 5a does not necessarily
mean that the phenyl group on the imidazolium salts cannot
act as an oxygen handle, as the position of the phenyl group
influences the ability of a compound to mineralize.11b
Other attempts to improve biodegradation involved the use
of unsaturated groups that might increase the chances of
metabolism of the imidazolium cation by redox enzymes. Un-
saturated synthetic base fluids are known to undergo microbial
biodegradation much faster than their corresponding saturated
counterparts under anaerobic conditions.11b,17 Thus, the allyl
and vinyl group were incorporated onto the imidazolium cation
(6 and 7, respectively). It was rationalized that side chains
that are susceptible to oxidation at the carbon attached to
the imidazolium nitrogen would afford intermediates which are
unstable and not refractory in their nature. Both 6a and 7a,
however, failed to show good biodegradability, whereas their
octyl sulfate counterparts 6b and 7b showed biodegradation at
43% (Fig. 1).
We also endeavored to investigate the inclusion of po-
tentially biodegradable anions such as alkylsulfites, lactates,
dialkylphosphates, and the anion formed from saccharin, into
imidazolium based ILs. ILs containing methylsulfite anions were
prepared using a method reported in the literature.18 Whereas
8a containing the common dialkylimidazolium cation, 1-butyl-
3-methylimidazolium [bmim], showed only 8% biodegradability,
the replacement of this cation with one containing an ester side
chain, 8b, increased the percentage biodegradation to 35%.
Lactic acid, a fairly inexpensive, commercially available
compound that is produced naturally in catabolic processes was
an appealing synthon for an anion in these salts. The lactate
Fig. 2 Effect of anion modifications on percentage biodegradation 8a
(ꢀ), 8b (¥), 9 (ꢀ), 10 (ꢀ), 11a (ꢁ) and 11b (♦).
Several natural products such as DNA, ADP, ATP, phos-
pholipids, etc. and, perhaps more relevantly, some of the
biodegradable detergents, are based on the phosphate group.
The most commonly used phosphate containing IL, 10, was
synthesized according to a known protocol,20 and tested.
However, compound 10 also showed poor biodegradability at
5%.
ILs based on saccharin, a well known synthetic non-nutritive
sweetener, have been reported in the literature.21 Saccharin is a
common ingredient in food products and therefore has a well
established toxicological profile. Its structural features, such as
the presence of a phenyl ring with the mixed N-acyl-N-sulfonyl
imide group, makes it an interesting target for evaluation of
biodegradability when incorporated into ILs. The [bmim] IL
containing the anion produced from saccharin, 11a, showed
biodegradability at 41% (Fig. 2). It is notable that 11a reached
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acid according to a reported procedure.22 As expected, an
increase in the alkyl chain length in the alkyl sulfate ion
resulted in an increase in biodegradability. Thus, going from
hexyl sulfate 12a to dodecyl sulfate 12f the biodegradability
increased from 34% to 58%, (Table 1, entries 1 and 6). These
findings indicate that the biodegradability of the alkyl sulfate
based ILs can be significantly enhanced by increasing the chain
length of the alkyl sulfate anion. The recalcitrant nature of the
simple 1,3-dialkylimidazolium cation, however, seems to limit
the biodegradability values for this series of salts.
We anticipated that an increase in the alkyl chain length
on the cation of the 1,3-dialkylimidazolium sulfates would
enhance their biodegradability due to increased lipophilicity,
which would, in turn, lead to faster absorption of compounds
through the cell membranes of the microorganisms present
in the test. Thus, the alkyl sulfates based on the 1-hexyl-3-
methylimidazolium, [hmim], cation and hexyl 13a, heptyl 13b,
octyl 13c, nonyl 13d, decyl 13e and dodecyl 13f sulfates were syn-
thesized and tested for biodegradability. When compared with
the corresponding [bmim] based counterparts, the [hmim] based
alkyl sulfates showed slightly lower values of biodegradability.
With an increase in the alkyl chain length from C6 to C12 on the
alkyl sulfate anion, the biodegradability increased from 30% to
49% (Table 1, entries 7–12).
Table 1 Percentage biodegradation of alkyl sulfates based on [bmim]
and [hmim] cations after 28 days as determined by the CO2 headspace
test (ISO 14593)
Entry
No.
Compounda
Biodegradation (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
12a
12b
12c
12d
12e
12f
13a
13b
13c
13d
13e
13f
14
[bmim] [C6H13OSO3]
[bmim] [C7H15OSO3]
[bmim] [C8H17OSO3]
[bmim] [C9H19OSO3]
[bmim] [C10H21OSO3]
[bmim] [C12H25OSO3]
[hmim] [C6H13OSO3]
[hmim] [C7H15OSO3]
[hmim] [C8H17OSO3]
[hmim] [C9H19OSO3]
[hmim] [C10H21OSO3]
[hmim] [C12H25OSO3]
[‘ester’-mim] [C12H25OSO3]
34
36
40
47
54
58
30
33
38
36
44
49
72
a IL concentration = 40 mg L-1.
We initially thought that the slightly lower biodegradability
observed for the [hmim] series (relative to [bmim]) may have been
a result of the longer alkyl chain imparting a biocidal effect.
Previous studies have found that the antimicrobial activity of
dialkylimidazolium ILs is associated with the cation, and that
potency increases with alkyl chain length.23 In order to assess
the potential toxicity of the 1,3-dialkylimidazolium cations to
the aerobic microorganisms responsible for biodegradation, so-
lutions containing a mixture of the test substance and a reference
compound (sodium n-dodecyl sulfate, SDS) were tested (Table 2,
entries 1–3). Biodegradation percentages for the mixtures of
dialkylimidazolium octylsulfates and SDS were calculated based
on the theoretical inorganic carbon (IC) yield from the anion
and SDS only, as the imidazolium cation was found to undergo
negligible mineralisation in this test.14c In both cases, similar
rates were observed for the mixtures (IL + SDS) and the refer-
ence substance SDS alone. This suggests that neither the
[bmim] or [hmim] cations are inhibitory to the inoculum at the
concentration used in the biodegradation tests. Furthermore,
its highest level of biodegradability within 14 days of incubation,
which has been associated with very high rates of biodegradation
of the saccharin anion. The overall biodegradability of the
saccharin based IL can be enhanced by incorporating the ester
group on the alkyl side chain of the imidazolium ion as in 11b,
which showed biodegradability at 61%. Thus, 11b containing
both an ester linkage in the cation and the saccharin derived
anion can be classified as ‘readily biodegradable’. The cation
modifications thus appear to be necessary to increase the overall
biodegradability of saccharin containing ILs to the level where
they can be deemed readily biodegradable.
Our previous attempts to search for a biodegradable IL dis-
closed that the alkyl sulfates are very good anion candidates.14c,16
However, since the overall biodegradability of ILs appears to
be a cumulative contribution from both the cation and the
anion, higher biodegradability values are reached in the case of
imidazolium based ILs by incorporating the ester group on the
side chain in addition to the presence of an alkylsulfate ion.14a,c
Unfortunately, the ester group on the cation introduces chemical
instability, which greatly limits the range of applications for the
imidazolium based biodegradable ILs. Therefore, we thought it
would be worthwhile to do a thorough investigation on alkyl
sulfates based on simple 1,3-dialkylimidazoliums, since they
contain typically chemically inert cations, and also offer scope
of varying alkyl chain lengths on both the cation as well as the
anion.
Table 2 Percentage biodegradation of 12c and 13c at different concen-
trations and in combination with the reference substance SDS
Concentration/ Biodegradation
Entry Compounda
mgC L-1
(%)a
1
2
3
4
5
6
7
8
9
SDS
20
82
85
81
40
45
42
38
40
40
[bmim][C8H17OSO3] + SDS 20 + 20
[hmim][C8H17OSO3] + SDS 20 + 20
To investigate how the length of alkyl chain on the alkyl
sulfate anion influences the biodegradability of the IL, we first
synthesized a series of ILs based on the common imidazolium
cation [bmim]. The ILs based on [bmim] with hexyl 12a, heptyl
12b, octyl 12c, nonyl 12d, decyl 12e and dodecyl 12f sulfate
were synthesized and tested for biodegradability (Table 1).
These ILs were synthesized from [bmim][Cl] and alkyl sulfate
ammonium salts obtained by reacting alcohols with sulfamic
[bmim][C8H17OSO3]
[bmim][C8H17OSO3]
[bmim][C8H17OSO3]
[hmim][C8H17OSO3]
[hmim][C8H17OSO3]
[hmim][C8H17OSO3]
6
11
20
6
11
20
a Percent biodegradation after 28 days as determined by the CO2
headspace test (ISO 14593).
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the dialkylimidazolium octylsulfates 12c and 13c were each
tested at different concentrations (6, 11 and 20 mgC L-1) and
were found to undergo similar levels of biodegradation in each
case (Table 2, entries 4–6 and 7–9). This result also supports
the conclusion that these dialkylimidazolium cations are not
inhibiting the inoculum. Alternatively, the slightly higher values
of biodegradation for the [bmim] based alkyl sulfates, when
compared to the corresponding [hmim] alkyl sulfates, may be
attributed to the larger ratio of mineralized organic carbon
(alkylsulfate anion) to total organic carbon content (alkylsulfate
anion + 1,3-dialkylimidazolium cation).
4H). 13C NMR (DMSO-d6): d 14.0, 22.2, 25.6, 28.8, 28.9, 29.2,
31.4, 66.0. MS (ESI, 20 eV): m/z 209.3 [C8H17OSO3]-.
General method for the synthesis of the dialkylimidazolium
halides 1a, 5a and 6a
Alkyl halide (40.0 mmol) was added to the solu◦tion of
1-alkylimidazole (33.3 mmol) in toluene (20 mL) at 0 C. The
reaction mixture was maintained under a nitrogen atmosphere.
The stirring was continued at room temperature for 1 h under
◦
nitrogen and then heated at 70 C for 24 h. The work-up and
isolation procedures were the same as with method 1 above.
These quaternary salts/ILs, being hygroscopic, were handled
under nitrogen at each stage of synthesis and purification.
Conclusion
In conclusion, functionalization of the N-substituent of imi-
dazolium based ILs appears to impart a degree of biodegrad-
ability. When paired with alkylsulfate ions, biodegradability of
these salts increases appreciably. This is consistent with earlier
studies performed by our group.14 Amongst the anions tested,
lactate and that derived from saccharin seem to possess good
mineralization abilities. The saccharin based ILs offer good
biodegradability values with very high initial biodegradation.
Their biodegradability values are as high as their octyl sulfate
based counterparts, making them a good anion alternative.
The biodegradability of the 1,3-disubstituted imidazolium alkyl
sulfates increases with an increase in the alkyl chain length on the
alkyl sulfate, but decreases slightly with an increase in the alkyl
chain length on the imidazolium cation. Accordingly, the percent
biodegradation found after 21 days reflects the proportions
of the refractory imidazolium cation and the biodegradable
alkylsulfate anion in the IL, when expressed as a percentage
of the theoretical amount of inorganic carbon (ThIC).
1-Methyl-3-(pentoxycarbonylmethyl)imidazolium
bromide
(1a)14c
.
Yield 97%. 1H NMR (DMSO-d6): d 0.86–0.90 (t, J =
6.9 Hz, 3H), 1.26–1.34 (m, 4H), 1.57–1.66 (m, 2H), 3.92 (s, 3H),
4.13–4.18 (t, J = 6.6 Hz, 2H), 5.26 (s, 2H), 7.73–7.74 (m, 2H),
9.11 (s, 1H). 13C NMR (DMSO-d6): d 13.7, 21.6, 27.3, 27.5,
35.9, 49.4, 65.6, 123.3, 123.6, 137.6, 166.8. MS (ESI, 20 eV):
m/z 211.1 [M–Br-]+; MS (ESI, 20 eV): m/z 78.9 and 80.9 [Br]-.
1
3-Benzyl-1-methylimidazolium bromide (5a). Yield 97%. H
NMR (DMSO-d6): d 3.89 (s, 3H), 5.58 (s, 2H), 7.30–7.34 (m,
3H), 7.51–7.54 (m, 2H), 7.86–7.87 (m, 1H), 7.98–7.99 (m, 1H),
9.66 (s, 1H). 13C NMR (DMSO-d6): d 35.9, 51.4, 122.0, 123.7,
128.3, 128.5, 128.7, 134.8, 136.4. MS (ESI, 20 eV): m/z 173.1
[M–Br-]+; MS (ESI, 20 eV): m/z 78.9 and 80.8 [Br]-.
3-Allyl-1-methylimidazolium bromide (6a). Yield 95%. 1H
NMR (DMSO-d6): d 3.90 (s, 3H), 4.93–4.95 (d, J = 6.0 Hz,
2H), 5.26–5.27 (m, 1H), 5.30–5.32 (m, 1H), 5.95–6.08 (m, 1H),
7.87 (s, 2H) 9.45–9.46 (s, 1H). 13C NMR (DMSO-d6): d 35.8,
50.4, 120.1, 122.1, 123.5, 131.6, 136.4. MS (ESI, 20 eV): m/z
123.1 [M–Br-]+; MS (ESI, 20 eV): m/z 78.9 and 80.8 [Br]-.
Experimental
1H and 13C NMR spectra of the purified products were recorded
in CDCl3 (Cambridge Isotope Laboratories Inc., 99.8% D) or
DMSO-d6 (Cambridge Isotope Laboratories Inc., 99.9% D) on
a Bruker Avance DPX 300 spectrometer at 300 and 75.4 MHz,
respectively. Low resolution mass spectra using electrospray
ionisation (MS-ESI) were obtained using a Micromass Platform
II instrument.
General method for the synthesis of the dialkylimidazolium
halides 2, 3a and 7a
A mixture of 1-alkylimidazole (33.3 mmol) and alkyl halide
(40.0 mmol) in toluene (20 mL) was heated at 110 ◦C for
24 h under a nitrogen atmosphere. The completion of reaction
was marked by the separation of either dense IL or salt.
The product was isolated by decanting toluene to remove any
unreacted starting materials and solvent. Subsequently, the IL
was washed with diethyl ether (4 ¥ 20 mL) and the ether layer
was separated from the IL/salt by decantation. In some cases,
the ether washings resulted in the formation of a solid. The
solid was purified by dissolving in acetonitrile (10–20 mL) and
precipitation with diethyl ether (60–70 mL). In each case, the IL
or salt was finally dried under reduced pressure to get rid of the
volatile organic compounds.
Synthesis of ammonium octylsulfate22
1-Octanol (3.00 g, 15.7 mL, 100 mmol) and sulfamic acid (9.70 g,
100 mmol) were heated at 110 ◦C for 24 h in a moisture guarded
assembly. The reaction mixture was allowed to cool down to
room temperature, when it solidified. The fused waxy mass was
treated with hexane (500 mL) and stirred vigorously for 1 h after
mechanically crushing the lumpy solid. The filtration of hexanes
yielded the crude product which was washed with hexane (3 ¥
50 mL) and dried under reduced pressure. The crude product
was stirred with dichloromethane (200 mL) for 1 h, followed by
precipitation with hexane (800 mL) to yield the pure product.
The product was filtered, washed with hexane (3 ¥ 50 mL) and
dried under reduced pressure. Yield 69%. 1H NMR (DMSO-d6):
d 0.83–0.87 (t, J = 6.6 Hz, 3H), 1.24 (br s, 10H), 1.44–1.51 (m,
2H), 3.67–3.71 (t, J = 6.6 Hz, 2H), 6.93–7.26 (t, J = 49.2 Hz,
3-(2-Hydroxyethyl)-1-methylimidazolium bromide (2). Yield
98%. 1H NMR (DMSO-d6): d 3.68–3.73 (m, 2H), 3.88 (s, 3H),
4.23–4.26 (t, J = 5.1 Hz, 2H), 5.11–5.14 (t, J = 5.25 Hz, 1H),
7.76–7.79 (m, 2H), 9.24 (s, 1H). 13C NMR (DMSO-d6): d 35.8,
51.4, 59.1, 122.5, 123.1, 136.6. MS (ESI, 20 eV): m/z 127.0 [M–
Br-]+; MS (ESI, 100 eV): m/z 78.8 and 80.8 [Br]-.
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3-(4-Acetoxybutyl)-1-methylimidazolium iodide (3a). Yield
96%. H NMR (DMSO-d6): d 1.48–1.58 (m, 2H), 1.78–1.88
(m, 2H), 1.97 (s, 3H), 3.86 (s, 3H), 3.95–3.99 (t, J = 6.5 Hz,
2H), 4.20–4.25 (t, J = 7.2 Hz, 2H), 7.75 (s, 1H), 7.83–7.84 (m,
1H), 9.22 (s, 1H). 13C NMR (DMSO-d6): d 20.8, 24.7, 26.1, 36.0,
48.3, 63.0, 122.1, 123.4, 136.4, 170.3. MS (ESI, 20 eV): m/z 197.1
[M-I-]+; MS (ESI, 70 eV): m/z 127.0 [I]-.
3H), 4.83–4.85 (d, J = 6.0 Hz, 2H), 5.27–5.39 (m, 2H), 5.98–6.11
(m, 1H), 7.70–7.72 (m, 2H) 9.09 (s, 1H). 13C NMR (DMSO-d6):
d 13.8, 22.0, 25.5, 28.6, 28.7, 29.0, 31.2, 35.7, 50.7, 65.5, 120.1,
122.3, 123.7, 131.7, 136.6. MS (ESI, 20 eV): m/z 123.0 [M–
1
C8H17OSO3 ]+; MS (ESI, 20 eV): m/z 209.2 [C8H17OSO3]-.
-
1-Butyl-3-vinylimidazolium octylsulfate (7b). Yield 87%. 1H
NMR (DMSO-d6): d 0.83–0.94 (m, 6H), 1.24–1.36 (m, 12H),
1.43–1.50 (m, 2H), 1.76–1.86 (m, 2H), 3.66–3.70 (t, J = 6.9 Hz,
2H), 4.18–4.23 (t, J = 7.2 Hz, 2H), 5.40–5.44 (dd, J = 2.4, 9.0 Hz,
1H), 5.92–5.98 (dd, J = 2.1, 15.6 Hz, 1H), 7.24–7.32 (dd, J =
8.7, 15.6 Hz, 1H), 7.92–7.93 (m, 1H), 8.18–8.19 (m, 1H), 9.48
(s, 1H). 13C NMR (DMSO-d6): d 13.2, 13.8, 18.7, 22.0, 25.5,
28.6, 28.7, 29.0, 31.0, 31.2, 48.9, 65.5, 108.6, 119.1, 123.2, 128.8,
1-Butyl-3-vinylimidazolium iodide (7a). Yield 100%. 1H
NMR (DMSO-d6): d 0.85–0.90 (t, J = 7.4 Hz, 3H), 1.21–1.33
(m, 2H), 1.76–1.86 (m, 2H), 4.20–4.25 (t, J = 7.4 Hz, 2H), 5.40–
5.44 (dd, J = 2.4, 8.7 Hz, 1H), 5.94–6.00 (dd, J = 2.4, 15.6 Hz,
1H), 7.26–7.34 (dd, J = 8.7, 15.6 Hz, 1H), 7.97–7.98 (m, 1H),
8.21–8.23 (m, 1H), 9.60–9.61 (m, 1H). 13C NMR (DMSO-d6): d
13.2, 18.6, 30.9, 48.9, 108.7, 119.1, 123.1, 128.6, 135.0. MS (ESI,
20 eV): m/z 151.2 [M–I-]+; MS (ESI, 70 eV): m/z 127.0 [I]-.
-
135.3. MS (ESI, 20 eV): m/z 151.2 [M–C8H17OSO3 ]+; MS (ESI,
70 eV): m/z 209.1 [C8H17OSO3]-.
1-Methyl-3-(pentoxycarbonylmethyl)imidazolium dodecylsul-
fate (14). Yield 95%. H NMR (DMSO-d6): d 0.83–0.91 (m,
General method for the synthesis of the dialkylimidazolium
octylsulfates 1b, 3b, 5b, 6b, 7b and 14
1
6H), 1.25–1.33 (m, 22H), 1.45–1.49 (m, 2H), 1.60–1.64 (m, 2H),
3.64–3.69 (t, J = 6.8 Hz, 2H), 3.91 (s, 3H), 4.13–4.18 (t, J =
6.6 Hz, 2H), 5.24 (s, 2H), 7.72 (s, 2H), 9.07 (s, 1H). 13C NMR
(DMSO-d6): d 13.7, 13.8, 21.6, 22.0, 25.5, 27.3, 27.6, 28.6, 28.7,
28.9, 29.0, 29.0, 31.2, 35.9, 49.4, 65.4, 65.6, 123.3, 123.7, 137.7,
The quaternary 1,3-dialkylimidazolium halide (2 mmol) was
dissolved in water to obtain a clear solution. The aqueous
solution of quaternary halide was treated with the aqueous
solution of ammonium octyl sulfate (2 mmol in 10 mL of water)
and the resulting mixture was stirred for 10 min. The product
was isolated by solvent extraction using dichloromethane (3 ¥
10 mL). The extracts were dried over anhydrous MgSO4
and evaporated under reduced pressure to yield the required
product.
166.8. MS (ESI, 20 eV): m/z 211.1 [M–C12H25OSO3 ]+; MS (ESI,
-
20 eV): m/z 265.2 [C12H25OSO3]-.
4-(1-Methylimidazolium-3-yl)butane-1-sulfonate (4). Com-
pound 4 was prepared using literature methodology;24 yield
100%. 1H NMR (D2O): 1.80–1.90 (m, 2H), 2.08–2.18 (m, 2H),
3.02–3.07 (t, J = 7.7 Hz, 2H), 4.00 (s, 3H), 4.33–4.38 (t, J =
7.1 Hz, 2H), 7.54–7.55 (m, 1H), 7.60–7.61 (m, 1H), 8.83 (s, 1H).
13C NMR (D2O): d 21.1, 28.2, 35.8, 49.0, 50.2, 122.3, 123.8,
136.1. MS (ESI): m/z 219.1 (100%, [C8H14N2O3S + 1]+).
1-Methyl-3-(pentoxycarbonylmethyl)imidazolium octylsulfate
(1b).14c Yield 98%. 1H NMR (DMSO-d6): d 0.84–0.90 (m, 6H),
1.25–1.34 (m, 14H), 1.45–1.50 (m, 2H), 1.60–1.64 (m, 2H), 3.64–
3.69 (t, J = 7.4 Hz, 2H), 3.91 (s, 3H), 4.13–4.18 (t, J = 6.6 Hz,
2H), 5.24 (s, 2H), 7.72 (s, 2H), 9.07 (s, 1H). 13C NMR (DMSO-
d6): d 13.7, 13.8, 21.6, 22.0, 25.5, 27.3, 27.6, 28.6, 28.7, 29.0,
31.2, 35.9, 49.4, 65.4, 65.7, 123.3, 123.7, 137.7, 166.8. MS (ESI,
General method for the synthesis of the dialkylimidazolium
methanesulfonates 8a–b18
20 eV): m/z 211.2 [M–C8H17OSO3 ]+; MS (ESI, 20 eV): m/z
-
209.1 [C8H17OSO3]-.
The mixture of 1-alkylimidazole (33.3 mmol) and butylmethane-
sulfonate (36.6 equiv.) was refluxed for 24 h in toluene (20 mL)
maintaining an inert atmosphere. The IL separates from the
reaction mixture. The toluene layer was separated from the IL
by decantation. The separated IL was washed with diethyl ether
(3 ¥ 20 mL) followed by drying/removal of volatile components
by evaporation under reduced pressure.
3-(4-Acetoxybutyl)-1-methylimidazolium octylsulfate (3b).
1
Yield 94%. H NMR (DMSO-d6): d 0.84–0.88 (t, J = 6.6 Hz,
3H), 1.25 (br s, 10H), 1.45–1.61 (m, 4H), 1.79–1.89 (m, 2H), 2.00
(s, 3H), 3.64–3.69 (t, J = 6.8 Hz, 2H), 3.85 (s, 3H), 4.00–4.04
(t, J = 6.6 Hz, 2H), 4.17–4.21 (t, J = 7.2 Hz, 2H), 7.70 (s, 1H),
7.76 (s, 1H), 9.09 (s, 1H). 13C NMR (DMSO-d6): d 13.8, 20.6,
22.0, 24.7, 25.5, 26.1, 28.6, 28.7, 29.0, 31.2, 35.7, 48.3, 63.0,
65.4, 122.2, 123.6, 136.6, 170.3. MS (ESI, 20 eV): m/z 197.1
3-Butyl-1-methylimidazolium methanesulfonate (8a). Yield
1
97%. H NMR (DMSO-d6): d 0.87–0.92 (t, J = 7.4 Hz, 3H),
[M-C8H17OSO3 ]+; MS (ESI, 20 eV): m/z 209.0 [C8H17OSO3]-.
-
1.22–1.30 (m, 2H), 1.71–1.81 (m, 2H), 2.31–2.32 (m, 3H), 3.85
(s, 3H), 4.14–4.19 (t, J = 7.1 Hz, 2H), 7.69–7.70 (m, 1H), 7.76–
7.77 (m, 1H), 9.14 (s, 1H). 13C NMR (DMSO-d6): d 13.2, 18.7,
31.3, 35.6, 39.7, 48.4, 122.3, 123.6, 136.7. MS (ESI, 20 eV): m/z
3-Benzyl-1-methylimidazolium octylsulfate (5b). Yield 88%.
1H NMR (DMSO-d6): d 0.84–0.88 (t, J = 6.2 Hz, 3H), 1.25
(br s, 10H), 1.45–1.50 (m, 2H), 3.65–3.69 (t, J = 6.6 Hz, 2H),
3.86 (s, 3H), 5.42 (s, 2H), 7.39–7.43 (m, 5H), 7.70–7.71 (m, 1H),
7.77–7.78 (m, 1H) 9.20 (s, 1H). 13C NMR (DMSO-d6): d 13.9,
22.0, 25.5, 28.6, 28.7, 29.0, 31.2, 35.8, 51.8, 65.4, 122.3, 124.0,
128.3, 128.7, 128.9, 134.8, 136.7. MS (ESI, 20 eV): m/z 173.2
139.2 [M–CH3SO3 ]+; MS (ESI, 20 eV): m/z 95.0 [CH3SO3]-.
-
1-Methyl-3-(2-oxo-2-(pentyloxy)ethyl)imidazolium methane-
sulfonate (8b). Yield 88%. 1H NMR (DMSO-d6): d 0.85–0.93
(m, 6H), 1.22–1.31 (m, 6H), 1.58–1.63 (m, 2H), 1.75–1.80 (m,
2H), 2.30–2.31 (m, 3H), 4.13–4.17 (t, J = 6.6 Hz, 2H), 4.22–4.26
(t, J = 7.1 Hz, 2H), 5.24 (s, 2H), 7.74–7.75 (m, 1H), 7.82–7.83
(s, 1H), 9.16–9.17 (s, 1H). 13C NMR (DMSO-d6): d 13.2, 13.7,
18.7, 21.6, 27.3, 27.6, 31.3, 39.7, 48.7, 49.5, 65.7, 122.1, 123.9,
-
[M–C8H17OSO3 ]+; MS (ESI, 20 eV): m/z 209.1 [C8H17OSO3]-.
3-Allyl-1-methylimidazolium octylsulfate (6b). Yield 91%.
1H NMR (DMSO-d6): d 0.84–0.88 (t, J = 6.3 Hz, 3H), 1.25 (br s,
10H), 1.45–1.50 (m, 2H), 3.64–3.69 (t, J = 6.6 Hz, 2H), 3.86 (s,
826 | Green Chem., 2009, 11, 821–829
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137.3, 166.8. MS (ESI, 20 eV): m/z 253.4 [M–CH3SO3 ]+; MS
J = 8.6 Hz, 3H), 1.26–1.33 (m, 4H), 1.58–1.67 (m, 2H), 4.05
-
(ESI, 20 eV): m/z 95.0 [CH3SO3]-.
(s, 3H), 4.14–4.18 (t, J = 6.9 Hz, 2H), 5.34 (s, 2H), 7.33–7.34
(m, 1H), 7.43–7.45 (m, 1H), 7.55–7.59 (m, 2H), 7.71–7.79 (m,
2H), 9.94 (s, 1H). 13C NMR (DMSO-d6): d 14.0, 22.3, 27.9,
28.1, 36.7, 50.2, 67.0, 119.9, 123.2, 123.4, 123.8, 131.7, 132.2,
134.7, 139.2 144.6, 166.6, 170.2. MS (ESI, 20 eV): m/z 211.4
[M–C7H4NO3S-]+; MS (ESI, 20 eV): m/z 182.3 [C7H4NO3S]-.
3-Butyl-1-methylimidazolium lactate (9). To the solution of
[bmim][Cl] (2.44 mmol) in water (10 mL) was added the solution
of silver lactate (2.93 mmol) in water (10 mL). The reaction
mixture was stirred for 10 min at room temperature in the dark.
The reaction mixture was freeze dried to yield the IL containing
silver chloride. The IL was extracted in chloroform. The extract
was filtered to remove the insoluble silver chloride, dried over
anhydrous magnesium sulfate and finally evaporated at reduced
pressure to yield 9: yield 91%. 1H NMR (DMSO-d6): d 0.87–0.91
(t, J = 7.4 Hz, 3H), 1.04–1.08 (d, J = 5.6 Hz, 3H), 1.22–1.29
(m, 2H), 1.71–1.81 (m, 2H), 3.45–3.52 (q, J = 7.1 Hz, 1H), 3.86
(s, 3H), 4.15–4.20 (t, J = 7.2 Hz, 2H), 7.73–7.74 (m, 1H), 7.80–
7.81 (m, 1H), 9.42 (s, 1H). 13C NMR (DMSO-d6): d 13.2, 18.7,
21.5, 31.3, 35.6, 48.4, 67.00, 122.2, 123.6, 136.9, 176.9. MS (ESI,
General method for the synthesis of dialkylimidazolium
alkylsufates (12a–f and 13a–f)25
The primary alcohol (26.4 mmol) and sulfamic acid (26.4 mmol)
◦
were heated at 85 C for 24 h in a moisture guarded assembly.
The reaction mixture was allowed to cool down to room
temperature, during which it might solidify. The reaction mass
was extracted into water (100 mL) and [bmim][Cl] or [hmim][Cl]
(20.24 mmol) was added to the solution and the mixture stirred
for 10 min. The resultant aqueous solution was washed with
diethyl ether (3 ¥ 50 mL), and the product was finally extracted
into dichloromethane (3 ¥ 50 mL). The dichloromethane
extracts were dried over anhydrous MgSO4, and concentrated by
evaporation of the solvent under reduced pressure. The resulting
oil was stirred at reduced pressure at 60 ◦C for 4 h.
-
20 eV): m/z 139.1 [M–C3H5O3 ]+; MS (ESI, 20 eV): m/z 89.1
[C3H5O3]-.
3-Butyl-1-methylimidazolium dibutylphosphate (10)20
The mixture of 1-methylimidazole (33.3 mmol) and tributyl
phosphate (33.3 mmol) were heated in a moisture guarded
assembly at 150 ◦C for 24 h. The resulting brown viscous liquid
was washed with diethyl ether (3 ¥ 20 mL). The resultant IL was
first heated at reduced pressure by rotary evaporation followed
by removal of all volatile residues under reduced pressure over
24 h under vacuum; yield 92%. 1H NMR (CDCl3): d 0.84–0.96
(m, 9H), 1.29–1.43 (m, 6H), 1.54–1.63 (m, 4H), 1.79–1.89 (m,
2H), 3.82–3.89 (m, 4H), 4.04 (s, 3H), 4.25–4.30 (t, J = 7.4 Hz,
2H), 7.20–7.21 (m, 1H), 7.31–7.32 (m, 1H), 10.48 (s, 1H). 13C
NMR (CDCl3): d 13.4, 13.8, 19.1, 19.5, 32.2, 33.0, 33.1, 36.4,
49.6, 64.9, 65.0, 121.7, 123.6, 139.2. MS (ESI, 20 eV): m/z 139.2
[M–C8H18O4P-]+; MS (ESI, 20 eV): m/z 209.2 [C8H18O4P]-.
3-Butyl-1-methylimidazolium hexylsulfate (12a). Yield 37%.
1H NMR (CDCl3): d 0.64–0.77 (m, 6H), 1.07–1.30 (m, 8H),
1.39–1.50 (m, 2H), 1.62–1.74 (m, 2H), 3.68–3.83 (m, 5H), 4.04–
4.10 (t, J = 7.2 Hz, 2H), 7.36–7.38 (m, 1H), 7.44–7.46 (m, 1H),
9.27 (s, 1H). 13C NMR (CDCl3): 13.0, 13.6, 19.0, 22.1, 25.1,
29.1, 31.1, 31.7, 35.9, 49.2, 67.2, 122.1, 123.6, 136.9. MS (ESI,
20 eV): m/z 139.6 [M–C6H13OSO3 ]+; MS (ESI, 20 eV): m/z
-
181.1 [C6H13OSO3]-.
3-Butyl-1-methylimidazolium heptylsulfate (12b). Yield 36%.
1H NMR (CDCl3): d 0.61–0.73 (m, 6H), 0.95–1.23 (m, 10H),
1.32–1.50 (m, 2H), 1.60–1.73 (m, 2H), 3.73–3.81 (m, 5H), 4.00–
4.06 (t, J = 7.2 Hz, 2H), 7.34–7.36 (m, 1H), 7.41–7.42 (m, 1H),
9.21 (s, 1H). 13C NMR (CDCl3): 12.9, 13.5, 18.9, 22.0, 25.3, 28.5,
29.1, 31.3, 31.6, 35.7, 49.1, 67.0, 122.0, 123.5, 136.7. MS (ESI,
General method for the synthesis of the dialkylimidazolium
saccharinates 11a–b
20 eV): m/z 139.2 [M–C7H15OSO3 ]+; MS (ESI, 20 eV): m/z
-
The syntheses of 11a and 11b was achieved by slightly modifying
the procedure reported earlier, in that a two fold excess of
sodium saccharin was used which bypassed the purification
step that involves column chromatography.21 Acetone (100 mL)
was added to the mixture of 1,3-dialkylimidazolium chloride
(33.3 mmol) and finely crushed saccharin sodium salt (66.6
equiv.). The resultant biphasic mixture was stirred vigorously at
room temperature for 24 h. After completion of the metathesis,
the reaction mixture was filtered and the filtrate was evaporated
under reduced pressure to yield the saccharin based ILs.
195.4 [C7H15OSO3]-.
3-Butyl-1-methylimidazolium octylsulfate (12c). Yield 83%.
1H NMR (DMSO-d6): d 0.84–0.93 (m, 6H), 1.23–1.30 (m, 12H),
1.45–1.50 (m, 2H), 1.74–1.79 (m, 2H), 3.65–3.70 (t, J = 6.6 Hz,
2H), 3.85 (s, 3H), 4.14–4.19 (t, J = 7.2 Hz, 2H), 7.69–7.70 (m,
1H), 7.76–7.77 (m, 1H), 9.10 (s, 1H). 13C NMR (DMSO-d6):
d 13.2, 13.8, 18.7, 22.0, 25.5, 28.6, 28.7, 29.0, 31.2, 31.3, 35.7,
48.4, 65.4, 122.2, 123.6, 136.5. MS (ESI, 20 eV): m/z 139.1 [M–
C8H17OSO3 ]+; MS (ESI, 20 eV): m/z 209.3 [C8H17OSO3]-.
-
3-Butyl-1-methylimidazolium saccharinate (11a). Yield 88%.
1H NMR (CDCl3): d 0.88–0.93 (t, J = 7.4 Hz, 3H), 1.25–1.40
(m, 2H), 1.79–1.89 (m, 2H), 4.07 (s, 3H), 4.26–4.31 (t, J =
7.4 Hz, 2H), 7.25–7.27 (m, 1H), 7.32–7.33 (m, 1H), 7.55–7.59
(m, 2H), 7.74–7.81 (m, 2H), 10.00 (s, 1H). 13C NMR (CDCl3):
d 13.3, 19.3, 32.0, 36.4, 49.6, 119.5, 122.1, 123.1, 123.6, 131.3,
132.0, 134.8, 137.2, 144.7, 170.1. MS (ESI, 20 eV): m/z 139.1
[M–C7H4NO3S-]+; MS (ESI, 20 eV): m/z 182.1 [C7H4NO3S]-.
3-Butyl-1-methylimidazolium nonylsulfate (12d). Yield 83%.
1H NMR (CDCl3): d 0.82–0.96 (m, 6H), 1.27–1.41 (m, 14H),
1.58–1.69 (m, 2H), 1.78–1.90 (m, 2H), 3.97–4.03 (m, 5H), 4.18–
4.24 (t, J = 7.2 Hz, 2H), 7.37–7.39 (m, 1H), 7.47–7.49 (m, 1H),
9.42 (s, 1H). 13C NMR (CDCl3): 13.4, 14.1, 19.5, 22.7, 26.0,
29.3, 29.4, 29.6, 29.7, 31.9, 32.1, 36.4, 49.8, 67.9, 122.2, 123.9,
-
137.5. MS (ESI, 20 eV): m/z 139.2 [M–C9H19OSO3 ]+; MS (ESI,
20 eV): m/z 223.4 [C9H19OSO3]-.
1-Methyl-3-(pentoxycarbonylmethyl)imidazolium
sacchari-
3-Butyl-1-methylimidazolium decylsulfate (12e). Yield 19%.
1H NMR (CDCl3): d 0.81–0.95 (m, 6H), 1.21–1.40 (m, 16H),
nate (11b). Yield 91%. 1H NMR (CDCl3): d 0.85–0.91 (t,
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1.57–1.65 (m, 2H), 1.81–1.89 (m, 2H), 3.96–4.01 (m, 5H), 4.18–
4.24 (t, J = 7.2 Hz, 2H), 7.39–7.40 (m, 1H), 7.49–7.50 (m, 1H),
9.47 (s, 1H). 13C NMR (CDCl3): 13.3, 14.0, 19.4, 22.6, 25.8, 29.2,
29.3, 29.5, 29.5, 29.6, 31.8, 32.0, 36.3, 49.7, 67.6, 122.3, 123.9,
3-Hexyl-1-methylimidazolium dodecylsulfate (13f). Yield
81%. H NMR (CDCl3): d 0.76–0.82 (m, 6H), 1.04–1.35 (m,
1
24H), 1.54–1.60 (m, 2H), 1.76–1.82 (m, 2H), 3.90–3.98 (m, 5H),
4.11–4.18 (t, J = 7.4 Hz, 2H), 7.37–7.40 (m, 1H), 7.51–7.53 (m,
1H), 9.43 (s, 1H). 13C NMR (CDCl3): 13.9, 14.1, 22.3, 22.6, 25.8,
25.9, 29.3, 29.4, 29.51, 29.54, 29.5, 29.6, 29.6, 30.1, 31.0, 31.8,
36.3, 49.9, 67.6, 122.2, 123.9, 137.3. MS (ESI, 20 eV): m/z 167.1
137.4. MS (ESI, 20 eV): m/z 139.2 [M–C9H19OSO3 ]+; MS (ESI,
-
20 eV): m/z 237.4 [C10H21OSO3]-.
3-Butyl-1-methylimidazolium dodecylsulfate (12f). Yield
[M–C12H25OSO3 ]+; MS (ESI, 20 eV): m/z 265.0 [C12H25OSO3]-.
-
1
95%. H NMR (DMSO-d6): d 0.83–0.93 (m, 6H), 1.21–1.30
(m, 20H), 1.45–1.49 (m, 2H), 1.74–1.79 (m, 2H), 3.65–3.69 (t,
J = 6.6 Hz, 2H), 3.85 (s, 3H), 4.14–4.18 (t, J = 7.2 Hz, 2H),
7.69 (s, 1H), 7.76 (s, 1H), 9.10 (s, 1H). 13C NMR (DMSO-d6):
d 13.3, 14.0, 19.3, 22.6, 25.8, 29.3, 29.3, 29.5, 29.5, 29.6, 29.6,
29.6, 31.8, 32.0, 36.2, 49.6, 67.6, 122.2, 123.9, 137.3. MS (ESI,
ISO 14593-carbon dioxide head space test
To evaluate the biodegradability of the test ILs, the ‘‘CO2
headspace’’ test (ISO 14593) was applied. This method allows
the evaluation of the ultimate aerobic biodegradability of an
organic compound in an aqueous medium at a given concen-
tration of microorganisms by analysis of inorganic carbon.
The test IL, as the sole source of carbon and energy, was
added at a concentration of 40 mg L-1 to a mineral salt
medium. These solutions were inoculated with activated sludge
collected from an activated sludge treatment plant, washed
and aerated prior to use and incubated in sealed vessels with
a headspace of air. Biodegradation (mineralization to carbon
dioxide) was determined by measuring the net increase in the
total organic carbon (TOC) levels over time compared with
unamended blanks. Sodium n-dodecyl sulfate (SDS) was used
as a reference substance. The tests ran for 28 days. The extent of
biodegradation was expressed as a percentage of the theoretical
amount of inorganic carbon (ThIC) based on the amount of test
compound.
20 eV): m/z 139.1 [M–C12H25OSO3 ]+; MS (ESI, 20 eV): m/z
-
265.2 [C12H25OSO3]-.
3-Hexyl-1-methylimidazolium hexylsulfate (13a). Yield 46%.
1H NMR (CDCl3): d 0.84–0.90 (m, 6H), 1.27–1.39 (m, 12H),
1.59–1.69 (m, 2H), 1.83–1.92 (m, 2H), 3.98–4.06 (m, 5H), 4.22–
4.28 (t, J = 7.5 Hz, 2H), 7.52–7.55 (m, 1H), 7.65–7.67 (m, 1H),
9.50 (s, 1H). 13C NMR (CDCl3): 13.9, 14.0, 22.4, 22.6, 25.6, 25.9,
29.5, 30.2, 31.1, 31.5, 36.3, 49.9, 67.5, 122.5, 124.1, 137.1. MS
(ESI, 20 eV): m/z 167.1 [M–C6H13OSO3 ]+; MS (ESI, 20 eV):
-
m/z 180.8 [C6H13OSO3]-.
3-Hexyl-1-methylimidazolium heptylsulfate (13b). Yield
1
74%. H NMR (CDCl3): d 0.84–0.90 (m, 6H), 1.26–1.41 (m,
14H), 1.62–1.69 (m, 2H), 1.85–1.91 (m, 2H), 3.98–4.05 (m, 5H),
4.21–4.28 (t, J = 7.3 Hz, 2H), 7.51–7.53 (m, 1H), 7.64–7.66
(m, 1H), 9.46 (s, 1H). 13C NMR (CDCl3): 13.9, 14.0, 22.4, 22.6,
25.9, 29.0, 29.2, 29.6, 30.2, 31.1, 31.7, 36.3, 49.9, 67.6, 122.4,
Acknowledgements
124.1, 137.2. MS (ESI, 20 eV): m/z 167.1 [M–C7H15OSO3 ]+;
-
MS (ESI, 20 eV): m/z 194.8 [C7H15OSO3]-.
The authors thank Pfizer Global R & D, the Spanish Ministerio
de Educacio´n y Ciencia (CTQ2007-60364/PPQ), the Australian
Research Council (LX0561094), and the Natural Sciences and
Engineering Research Council of Canada (NSERC Discovery
to R.D.S.) for financial support.
3-Hexyl-1-methylimidazolium octylsulfate (13c). Yield 93%.
1H NMR (CDCl3): d 0.83–0.90 (m, 6H), 1.21–1.41 (m, 16H),
1.62–1.69 (m, 2H), 1.83–1.90 (m, 2H), 3.99–4.06 (m, 5H), 4.20–
4.26 (t, J = 7.4 Hz, 2H), 7.39–7.41 (m, 1H), 7.53–7.55 (m, 1H),
9.47 (s, 1H). 13C NMR (CDCl3): 13.9, 14.1, 22.4, 22.6, 25.9, 29.3,
29.4, 29.5, 29.6, 30.2, 31.1, 31.8, 36.3, 49.9, 67.6, 122.3, 124.0,
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