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J. Chem. Sci. (2018) 130:36
carboxylic acids, forms Bronsted acidic ionic liquids.13 (CCBU ionic liquid). In the above step involving addition of
sulphuric acid to CCBU zwitter ion, a separate round-bottom
flask containing water was connected to the main RB flask
containing reaction mixture. Throughout the course of reac-
tion, the HCl formed was dissolved in water. The evolved
HCl dissolved in water was confirmed by formation of white
precipitate with AgNO3 solution. The complete evolution of
HCl was confirmed by changing water at regular intervals of
time. After 4 h, the water was inert to AgNO3 test. The HCl
collected in water was evaluated stoichiometrically by means
of standard NaOH titration.
When combined with metal salts, Lewis acidic ionic
liquids of choline chloride can be obtained.14 These
Bronsted and Lewis acidic systems of choline chlo-
ride have been effectively applied for many organic
transformations such as Fischer-indole synthesis, metal
coatings, Knoevenagel reactions, etc.15–18
Ionic liquid systems are yet to be explored for the
synthesis of phenol from CHP. Hence, the formulation
of choline chloride-based Bronsted acid ionic liquid for
the decomposition of CHP was adopted as a premise
of this study. 1,4-butane sultone, which is a cyclic
sulfonate ester with –S-O linkage, was chosen to be
combined with choline chloride. The objective was to
effect ring opening of electrophilic 1,4-butane sultone
with the nucleophilic choline chloride to form a zwitter
ion, which can be further converted to sulphonic acid-
functionalized ionic liquid.
2.3a Spectral data of (I) CCBU zwitter ion: C9H22O4
ClNS Anal. Found: C, 37.3; H, 9.11; N, 5.18; S, 10.57%;
Calc.: C, 39.19; H, 8.04; N, 5.08; S, 11.63%. AT-IR data
(cm−1): 3307, 2950, 1473, 1163, 1023, 952, 777, 707, NMR
data: 1H NMR (400 MHz, CDCl3, TMS) δ 4.25 (s, 1H); 4.09
(t, 2H); 3.70 (t, 2H); 3.58 (t, 2H); 3.34 (s, 9H); 2.83 (t, 2H);
1.93 (m, 4H). 13C NMR (400 MHz, CDCl3, TMS) δ 22.81;
31.51; 44.89; 50.95; 54.47; 56.39; 67.92. M cation, 104.1; M
anion, 171.
2. Experimental
2.3b Spectral data of (II) CCBU ionic liquid:
C9H23O8NS2 Anal. Found: C, 28.48; H, 7.41; N, 3.88; S,
17.68% Calc.: C, 32.04; H, 6.87; N, 4.15; S, 19.01%. ATIR
data (cm−1): 3405, 2955, 1479, 1149, 1037, 952, 862, 741.
NMR data: 1H NMR (400 MHz, CDCl3, TMS) δ 4.57 (t, 2H);
4.17 (s, 1H); 3.70 (t, 2H); 3.59 (t, 2H); 3.26 (s, 9H); 2.26 (t,
2H); 1.97 (m, 4H). 13C NMR (400 MHz, CDCl3, TMS) δ:
21.41; 30.77; 44.17; 48.28; 50.95; 54.22; 74.04. M cation,
104.1, M anion, 233.4.
2.1 Materials
Choline chloride, cumene, cumene hydroperoxide (80%) and
1,4-butane sultone were purchased from Alfa aeser. The
chemicals were used as received without further purification.
2.2 Instruments
Elemental analysis data were recorded on Perkin Elmer CHN-
2400 series analyser. The analysis of sulphur was performed
by Perkin Elmer Optima 5300 DV ICP-OES analyser. AT-
IR of the synthesized ionic liquid was recorded on Perkin
Elmer Spectrophotometer. The samples were scanned directly
in the range of 4000–400 cm−1. NMR studies for the ionic
liquid were performed on Bruker Avance 400 MHz NMR
Spectrometer using deuterated chloroform (CDCl3) as sol-
vent and Tetramethylsilane (TMS) as an internal standard.
Electrospray Ionisation mass spectra of the ionic liquid were
recorded on High resolution Q-Tof Mass Spectrometer. Gas
chromatography of the samples was performed on Agilent
6890N using HP5 column (30 m x 0.32 mm x 0.25 µm) and
FID detector.
2.4 Decomposition of cumene hydroperoxide
A 20% solution of CHP in cumene (2 mL of CHP in 10
mL cumene) was taken along with 0.2 g of ionic liquid in a
100 mL round-bottom flask. The mixture was placed on a
thermostatic oil bath and stirred using a magnetic stirrer for
30 min. The temperature was maintained at 50 ◦C. The
progress of the reaction was monitored by withdrawing
aliquots of the reaction mixture at regular intervals and sub-
jecting them to gas chromatographic analysis.
3. Results and Discussion
When an equimolar amount of 1,4-butane sultone was
added gradually in smaller portions to choline chlo-
ride, the chloride anion of choline chloride took active
part as a nucleophile in the ring opening and effected a
complete conversion under mild reaction conditions in
24 h. The choline chloride-butane sultone CCBU zwit-
ter ion (with chloroalkylsulphonate anion) was free from
chloride impurities, as confirmed through AgNO3 titra-
tion.19 The presence of the two ionic moieties in the
zwitter ion was evident from the AT-IR spectral studies
(see Supplementary Information for AT-IR spectra). The
2.3 Preparation of the ionic liquid
Choline chloride (0.01 M) and 1,4-butane sultone (0.01 M)
were mixed in a 100mL RB flask, fitted with a condenser.
The RB flask was immersed in a thermostatic oil bath placed
on a magnetic stirrer. The temperature was maintained at 80
to 90 ◦C and the contents were stirred for 24 h. After 24 h,
a white solid zwitter ion was obtained (CCBU zwitter ion).
Stoichiometric amount of concentrated sulphuric acid was
added to the resultant zwitter ion and the reaction mixture was
subjected to heating at 60 ◦C for 4 h. A colourless and homo-
geneous viscous liquid was obtained in a quantitative yield addition of concentrated sulphuric acid to the zwitter ion