Synthesis of novel gemini dicationic acidic ionic liquids and their catalytic performances in the Beckmann rearrangement

Article abstract of DOI:10.1002/hlca.200800382

A series of novel gemini dicationic acidic ionic liquids (GDAILs), compounds 1-3 carrying two SO₃H groups at the cation moieties and having anions of the type CF₃SO₃^-, were synthesized in good yields (Scheme 1). Some physicochemical properties of 1-3 were determined; due to their unique structures, these novel GDAILs showed noticeable hydrophilic properties and strong acidities (Table 1). Beckmann rearrangements of oximes catalyzed by 1, 2, or 3/zinc chloride (GDAIL/ZnCl ₂) were investigated (Scheme 2); the corresponding amides were formed in up to 99% yield in the presence of 5 mol-% of GDAIL/ZnCl₂ catalyst under optimized conditions (Tables 2 and 3). The peculiar solubilities of 1-3 made the separation of the catalysts from the products very facile, and the catalytic system could be recycled and reused for three times.

Full text of DOI:10.1002/hlca.200800382

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Helvetica Chimica Acta – Vol. 92 (2009)
Synthesis of Novel Gemini Dicationic Acidic Ionic Liquids and Their Catalytic
Performances in the Beckmann Rearrangement
by Xiaofei Liua)b), Linfei Xiaoa)b), Hugjiltu Wua)b), Jing Chen*a), and Chungu Xia*a)
a) State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
(phone: þ 86-931-4968163; fax: þ 86-931-4968129; e-mail: chenj@lzb.ac.cn, cgxia@lzb.ac.cn)
b) Graduate University of Chinese Academy of Sciences, Beijing 100039, P. R. China
A series of novel gemini dicationic acidic ionic liquids (GDAILs), compounds 1 – 3 carrying two
SO3H groups at the cation moieties and having anions of the type CF3SOꢀ3 , were synthesized in good
yields (Scheme 1). Some physicochemical properties of 1 – 3 were determined; due to their unique
structures, these novel GDAILs showed noticeable hydrophilic properties and strong acidities (Table 1).
Beckmann rearrangements of oximes catalyzed by 1, 2, or 3/zinc chloride (GDAIL/ZnCl2) were
investigated (Scheme 2); the corresponding amides were formed in up to 99% yield in the presence of
5 mol-% of GDAIL/ZnCl2 catalyst under optimized conditions (Tables 2 and 3). The peculiar solubilities
of 1 – 3 made the separation of the catalysts from the products very facile, and the catalytic system could
be recycled and reused for three times.
Introduction. – Ionic liquids (ILs) have been one of the most rapidly growing areas
of chemistry research in recent years. The wide range of possible cation and anion
combinations allows for a large variety of tunable interactions and applications [1][2].
ILs have got broadly attention in synthesis, catalysis, separation, electrochemistry, and
biochemistry [3]. Of a variety of common ILs available, most of the cations are
monoquaternary species with only one quaternization center. In recent years, gemini
dicationic ionic liquids (GDILs), i.e., surfactant molecules possessing two hydrophobic
tails on two ionic groups that are linked by a spacer, attracted increasing attention of
researchers [2][4]. The GDILs usually have different chemical and physical properties
from monocationic ILs such as high densities and viscosities, greater thermal stabilities,
and longer liquid ranges, which make them well suited for specific applications. As
recently reported, GDILs have been successfully used as electrolytes [5], as additives in
chromatography [6], as agents for selectively complexing and extracting mercury(II)
[7], as solvents for high-temperature organic reactions [8], and as high-temperature
lubricants [9]. However, up to now, there has been no report on attempts to use a GDIL
as catalyst.
We now report the synthesis of a series of novel gemini dicationic functionalized
acidic ILs, i.e., of 1,1’-(alkane-a,w-diyl)bis[3-(4-sulfobutyl)-1H-imidazolium] trifluoro-
methanesulfonates (1:2) 1 – 3, consisting of imidazolium-based dications and triflic
acid anions. Due to their unique structures, these GDAILs of a new type are strongly
acidic and very poorly soluble in common organic solvents, except for EtOH and
MeOH. To study the reactivity enhancement in the presence of the GDAILs 1 – 3
ꢀ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 92 (2009)
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during acidic catalytic reactions, we used the GDAILs together with ZnCl2 as catalysts
in Beckmann rearrangements. For comparison, the performances of other acidic ILs
with only one (sulfobutyl)imidazolium unit and different tails and counterions were
also tested.
Results and Discussion. – Synthesis and Physicochemical Properties of the Gemini
Dicationic Acidic Ionic Liquids 1 – 3. For the synthesis of 1 – 3, 1,1’-alkanediylbis[1H-
imidazoles] A were treated with butane-1,4-sultone, and then the corresponding salts B
were reacted with triflic acid (¼1,1,1-trifluoromethanesulfonic acid) (Scheme 1). The
synthetic procedure and workup were quite simple and practical, and afforded the
products 1 – 3 are in excellent overall yield (91 – 97%). The GDAILs 1 – 3 are viscous
liquids at room temperature, being soluble in highly polar solvents such as H2O, EtOH,
and MeOH but insoluble in common organic solvents such as Et2O, acetone, toluene,
CHCl3, and MeCN. These properties, together with the simple synthesis, meet the
requirements for practical applications in acidic catalytic reactions.
Scheme 1. Synthesis of the Novel Acidic Ionic Liquids 1 – 3
Some physicochemical properties of the novel GDAILs 1 – 3 and of the traditional
monocationic IL I (see Fig.) are presented in Table 1. At room temperature (ca. 258),
1 – 3 are liquid and have no distinct freezing points and melting points but possess lower
glass-transition temperatures Tg (ꢀ 30.08, ꢀ 29.28, and ꢀ 28.58, resp.). The thermal
decomposition temperatures Td (with mass loss of 10%) of 1 – 3 (3148, 3408, and 3438,
resp.) are lower than that of I (3508). This is inconsistent with general cases of common
gemini dicationic ILs reported previously [2][10] which have higher thermal stabilities
than monocationic ILs. The Brønsted acidities H0 of ILs 1 – 3 and I were determined by
the Hammett method as reported in [11] with UV/VIS spectroscopy. Ultimately, we
obtained the acidity order of the four ILs with the following H0 values: 3 (ꢀ0.149) < 2
(ꢀ0.115) < 1 (ꢀ0.016) < I (0.424), suggesting that Brønsted acidities of 1 – 3 are
relatively stronger than that of the monocationic I. The ionic conductivities of 1 – 3 are
smaller than that of I (1.21 · 10ꢀ1 Smꢀ1) at 258. Relatively broad electrochemical
windows, 3.5 – 3.7 V, were observed for 1 – 3, which are smaller than that of I (4.2 V).
Beckmann Rearrangement Catalyzed by the IL/ZnCl2 System. Beckmann rearrange-
ment, the conversion of an oxime into an amide (see Scheme 2), has long been an

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Helvetica Chimica Acta – Vol. 92 (2009)
Figure. Acidic Ils I – VI with only one (sulfobutyl)imidazolium unit
and different tails and counterions, synthesized according to [12][13]
(1-methyl-3-(4-sulfobutyl)-1H-imidazolium 1,1,1-trifluoromethane-
sulfonate (1:1) (I), 1-hexyl-3-(4-sulfobutyl)-1H-imidazolium 1,1,1-
trifluoromethanesulfonate (1:1) (II), 1-decyl-3-(4-sulfobutyl)-1H-
imidazolium 1,1,1-trifluoromethanesulfonate (1:1) (III), 1-methyl-3-
(4-sulfobutyl)-1H-imidazolium 2,2,2-trifluoroacetate (1:1) (IV), 1-
methyl-3-(4-sulfobutyl)-1H-imidazolium dihydrogen phosphate (1:1)
(V), and 1-methyl-3-(4-sulfobutyl)-1H-imidazolium 4-methylbenze-
nesulfonate (1:1) (VI))
Table 1. Some Physicochemical Properties of Gemini Dicationic Acidic Ionic Liquids
a
ILs
Tg [8]
Td [8]
H0
)
Ionic conductivity [S mꢀ1]b)
Electrochemical window [V]b)
1
2
3
I
ꢀ 30.1
ꢀ 29.2
ꢀ 28.5
–
313.7
339.7
343.1
350.0
ꢀ 0.016
ꢀ 0.115
ꢀ 0.149
0.424
7.23 · 10ꢀ2
6.41 · 10ꢀ2
4.85 · 10ꢀ2
1.21 · 10ꢀ1
3.5
3.4
3.7
4.2
a) The indicator used was 2-nitroaniline. A 0.5 mm CH2Cl2 solution of IL was used to determine the
acidity scales because of the poor solubility of the GDAILs in CH2Cl2. b) Measured at 258.
important subject for catalyst researchers. It accomplishes both the cleavage of a CꢀC
bond and the formation of a CꢀN bond, and represents a powerful method in organic
synthesis and chemical manufacturing, particularly for the industrial preparation of e-
caprolactam (¼ hexahydro-2H-azepin-2-one) from cyclohexanone oxime. This reac-
tion, however, generally requires high temperature, strong Brønsted acid, and
dehydrating media, which will produce a large number of by-products and bring
serious corrosion problems [14]. Great efforts have been made to overcome these
problems, among which is the catalytic Beckmann rearrangement in the vapor-phase
process or liquid-phase process [15]. But the low selectivity for e-caprolactam and the
rapid decay of the catalyst activity in the vapor-phase process and the risk of
environmental problems caused by the use of organic solvents in the latter liquid-phase
process still remain unsatisfactory. Therefore, it is of utmost importance to accelerate
reaction rates as well as to improve selectivities via more ꢂgreenꢃ or environmentally
friendly chemical processes. Recently, Beckmann rearrangement in supercritical H2O
has been reported [16], in which a short reaction time and excellent selectivity for e-
caprolactam was obtained, and the corrosion problem was controlled to a certain
extent; but a very low conversion and rigorous reaction conditions make this approach
utilizable only for research topics. In recent years, ILs as media or catalysts in
Beckmann rearrangement have been reported [17], affording a new approach for
catalytic Beckmann rearrangement.
Scheme 2. Beckmann Rearrangement of Oximes to Amides Catalyzed by Acidic IL/ZnCl2

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Initially, (E)-acetophenone oxime (¼(1E)-1-phenylethanone oxime; R1 ¼ Ph, R2 ¼
Me) was used as a probe molecule to investigate the feasibility of the oxime Beckmann
rearrangement to acetanilide (¼ N-phenylacetamide) in the presence of 3/ZnCl2 as
catalyst (at 5 mol-%) (Table 2). The rearrangement failed when either 3 or ZnCl2 were
used as a sole catalyst (Table 2, Entries 1 and 2), while a 99% yield of acetanilide was
obtained when the reaction was conducted in the presence of 3/ZnCl2 (Table 2,
Entry 3). The only identified by-product was acetophenone, which was formed by
deoximation of the starting (E)-acetophenone oxime; this implies that such a by-
product can be recovered and reused, and is less detrimental to the purity of the
acetanilide product.
a
Table 2. Beckmann Rearrangement of (E)-Acetophenone Oxime Catalyzed by Acidic IL/ZnCl2
)
Entry
Ionic liquid
Amount of IL [mol-%]
Reaction time [h]
Solvent
Yielde)f) [%]
1b)
2c)
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22d)
3
–
3
1
2
I
II
III
IV
V
VI
3
3
3
3
3
5
0
5
5
5
10
10
10
10
10
10
2
3
4
5
5
5
5
5
5
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
2.0
3.0
4.0
5.0
5.0
5.0
5.0
5.0
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
EtOH
–
–
99
99
99
93
92
93
35
5
47
18
59
86
25
73
95
1
3
3
3
3
3
3
MeNO2
toluene
solvent-free
MeCN
10
–
28
94
5
5
a) Reaction conditions: (E)-acetophenone oxime (1 mmol), IL/ZnCl2 1 : 1 (mol ratio), solvent (5 ml),
T 808. b) ZnCl2 ¼ 0 mmol. c) ZnCl2 ¼ 0.05 mmol. d) The second cycle. e) GC Yield. f) The only by-
product is acetophenone.
The effects of the various Brønsted-acidic ILs on the Beckmann rearrangement of
(E)-acetophenone oxime were also investigated (Table 2). Since there were two SO3H
groups in ILs 1, 2, or 3 compared to one SO3H group in the ILs I – VI (Fig.), 5 mol-% of
IL/ZnCl2 with respect to the oxime were used in the case of 1 – 3 and 10 mol-% in the
case of I – VI to allow for the comparison of their catalytic activities. The yield of
acetanilide increased slightly when the ILs with a single SO3H group were replaced by
the ILs with two SO3H groups (see e.g., Entry 8 (93%), vs. Entry 3 (99%)). While the
differences in the alkanediyl chain length between the two imidazolium moieties did

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Helvetica Chimica Acta – Vol. 92 (2009)
not influence the catalytic activities (Entries 3 – 5, yields 99%), significantly different
catalytic activities were observed on variation of the counterions (Entries 6 and 9 – 11).
Among the ILs I and IV– VI, the highest yield of acetanilide was obtained with the I/
ZnCl2 catalyst (Entry 6), probably as a result of the highest Brønsted acidity in the case
of the triflic acid anion.
To optimize the reaction conditions of the Beckmann rearrangement of (E)-
acetophenone oxime (Scheme 2), the effect of catalyst dosage, reaction time, and
solvent were also investigated (Table 2). The catalyst dosage had a great effect on the
yield of acetanilide. When the amount of IL 3 was increased from 2 mol-% to 4 mol-%
(Entries 12 and 14), the yield of acetanilide increased from 18% to 86% at 808, and a
further increase to 5 mol-% resulted in a 99% yield (Entry 3). Increasing of the
reaction time had also a propitious influence on the yield of acetanilide (Entries 15 – 17
and 3), the highest yield being obtained after 5 h. Several solvents such as MeCN,
MeNO2, toluene, and EtOH were tested to study the solvent effect, and the reaction
was also investigated under solvent-free conditions for comparison. The results show
that MeCN was the most suitable solvent for this catalyst system (Entry 3). The yield of
acetanilide was 28% under solvent-free condition (Entry 21), only 10% when the
reaction was processed in MeNO2 (Entry 19). When toluene or EtOH was used as
solvent, no Beckmann rearrangement product was detected (Entries 18 and 20).
Therefore, the solvent plays an important role in this reaction.
Then, the reusability of the 3/ZnCl2 catalyst was tested in the Beckmann
rearrangement of (E)-acetophenone oxime. The two SO3H groups of 1 – 3 cause these
ILs to be more hydrophilic than the ILs I – VI bearing a single SO3H group. The latter
are soluble in some organic solvents such as MeCN, toluene, CH2Cl2, and alcohol to
some extent, while the ILs 1 – 3 are hardly soluble in common organic solvents, except
for MeOH and EtOH at room temperature. The immiscibility of 3 with MeCN and the
good solubility of acetanilide in MeCN make the separation of the catalyst from the
product quite facile, and a 94% yield of acetanilide was achieved when the catalyst was
directly reused for the second time just after the organic phase was decanted and
without need of supplementary ZnCl2 (Table 2, Entry 21).
Finally, the generality and scope of the Beckmann rearrangement of various ketone
oximes in the presence of 3/ZnCl2 in MeCN was investigated (Table 3), the by-
products being only the corresponding ketones (by GC/MS). Excellent yields were
obtained with aromatic ketoximes, and (E)-acetophenone oxime showed the best
reactivity among all the oximes (Entries 1 – 5) under the given conditions. Cyclo-
dodecanone oxime was also very reactive and was converted to the corresponding
amide in 94% yield (Entry 6), this amide being useful as a staring material for the
production of nylon. While cyclohexanone oxime was converted into e-caprolactam in
moderate yield (Entry 7), acetone oxime was extremely unreactive, and no amide was
isolated (Entry 8).
Conclusions. – We prepared a series of novel gemini dicationic acidic ionic liquids
(GDAILs) with noticeable hydrophilic properties and strong acidities and established
the potential application of these GDAILs as catalysts in acidic catalytic reactions. The
GDAILs-mediated ZnCl2 catalyst (IL/ZnCl2) demonstrated successful catalytic
performances in the Beckmann rearrangement: satisfactory yields of amides were

Helvetica Chimica Acta – Vol. 92 (2009)
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Table 3. Beckmann Rearrangement of Various Oximes Catalyzed by [3/ZnCl2
Entrya)
Substrate
Product
Yieldb)c) [%]
96
1
2
3
4
76
92
94
5
6
93
94
7
8
37
–
a) Reaction conditions: oxime (1 mmol), 3 (5 mol-%), 3/ZnCl2 1 : 1 (mol/mol), MeCN (5 ml),
temperature 808, time 5 h. b) Yields of isolated product. c) Purity of amide tested by GC; content of
amide in the product > 99% (GC).
obtained in the presence of 5 mol-% of Brønsted-acidic ILs/ZnCl2 as catalysts in MeCN
under mild reaction conditions, especially from aromatic oximes, and the novel
GDAILs could easily be separated from the products due to their immiscibility with
organic solvents. Ionic liquids with triflate anions showed better catalytic activities than

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Helvetica Chimica Acta – Vol. 92 (2009)
acidic ILs with other anions. The performance of these novel catalyst was still excellent
in a second-time reuse. Further work is in progress in our laboratories to study the
mechanism of the catalytic system in the Beckmann rearrangement of oximes.
This study was financially supported by the National Science Fund for Distinguished Young Scholars
of China (20625308).
Experiment Part
General. Toluene was distilled over Na. MeCN was distilled over CaH2. All other solvents and
chemicals were commercially available and used without further purification. The oximes were prepared
according to standard methods, and their purities were established by their melting points before
1
utilization. The ILs I – VI were synthesized according to [12][13]. H- and 13C-NMR Spectra: Varian
INOVA-400-M spectrometer; d in ppm rel. to Me4Si as internal standard, J in Hz. ESI-MS: Waters ZQ
4000; in m/z (rel. %). Elemental analyses: Elementar Analysensysteme GmbH VarioEL, with the
software version V3.00. Ion conductivity: Mettler FE30 digital conductivity meter at 258. Cyclic
Voltammetry: CHI-660C electrochemical work station; at r.t. with a glassy carbon working electrode, a
Pt wire counter electrode, and a Ag/AgCl reference electrode. Brønsted Acidity: measurement of the H0
values with an Agilent 8453 UV/VIS spectrophotometer and a basic indicator. Thermal Analysis and
Temp.-Dependent Phase Behavior: Mettler-Toledo DSC822e differential-scanning calorimeter, scan rate
108/min, under N2 in the circular range of ꢀ 100 to 1108, with samples tightly sealed in Al pans; the glass
transition temp. (Tg) and was recorded as the midpoint of the glass transition; the decomposition temp.
(Td) was recorded by thermogravimetry with 10% of mass loss by means of a Pyris Diamond Perkin-
Elmer TG/DTA, scan rate 208/min, under N2, with samples tightly sealed in Al2O3 pans.
1,1’-Methylenebis[3-(4-sulfobutyl)-1H-imidazolium] 1,1,1-Trifluoromethanesulfonate (1:2) (1). As
described in [18], 1,1’-methylenebis[1H-imidazol] (A, n ¼ 1) was prepared from 1H-imidazole (1 equiv.),
CH2Cl2, and KOH (2 equiv.) in the presence of 3% Bu4N · Br soln. at r.t. Extraction with EtOH followed
by column chromatography yielded A (n ¼ 1). According to a similar approach reported previously [13],
a mixture of A (n ¼ 1; 1 equiv.) and butane-1,4-sultone (¼1,2-oxathiane 2,2-dioxide; 2 equiv.) at 808 in
anh. MeCN was stirred for 24 h. The resulting white powder was pulverized, washed with EtOH, and
dried in vacuo. The white powder and CF3SO3H were mixed in a molar ratio of 1:2 in anh. toluene and
heated at 808 for 24 h, followed by washing with MeCN and Et2O and drying in vacuo: 1 (91%). Yellow
viscous liquid. 1H-NMR (400 MHz, D2O): 9.15 (s, 2 H); 7.64 (s, 2 H); 7.62 (s, 2 H); 6.57 (s, 2 H); 4.16 (t,
J ¼ 7.2, 4 H); 2.78 (t, J ¼ 7.2, 4 H); 1.89 (t, J ¼ 7.6, 4 H); 1.58 (t, J ¼ 7.2, 4 H). 13C-NMR (100 MHz, D2O):
136.31; 122.40; 122.29; 119.71 (q, J(C,F) ¼ 315.2, CF3); 59.01; 50.03; 49.76; 27.85; 20.97. ESI-MS: 421.7.
Anal. calc. for C17H26F6N4O12S4 (720.66): C 28.33, H 3.64, N 7.77; found: C 28.26, H 3.75, N 7.71.
1,1’-(Hexane-1,6-diyl)bis[3-(4-sulfobutyl)-1H-imidazolium] 1,1,1-Trifluoromethanesulfonate (1:2)
(2). The starting 1,1’-(hexane-1,6-diyl)bis[1H-imidazol] (A, n ¼ 6) was prepared according to a similar
procedure [19]: A mixture of 1H-imidazole-1-propanenitrile (2.1 mol-equiv.) and 1,6-dibromohexane
(1 mol-equiv.) in EtOH was stirred at 80 – 908 for 24 h. Then, the mixture was cooled, the precipitated
solid filtered and washed with cold acetone to give the bis-imidazolium salt. The salt was then dissolved in
CHCl3, the soln. mixed with 40% (w/w) NaOH soln., and the mixture was stirred at r.t. for 0.5 – 1 h. Then,
the mixture was extracted with CHCl3, the org. phase washed with H2O (6ꢁ), and the combined org.
extract concentrated. To the obtained yellow reddish viscous liquid, Et2O/H2O 2 :1 was added, and the
immediately formed white crystals were filtered, washed with Et2O and H2O, and dried in vacuo: pure A
(n ¼ 6). As described for 1, A (n ¼ 6) was then transformed to 2 (96%).Yellow viscous liquid. 1H-NMR
(400 MHz, D2O): 8.64 (s, 2 H); 7.34 (s, 2 H); 7.32 (s, 2 H); 4.07 (t, J ¼ 6.8, 4 H); 4.01 (t, J ¼ 7.2, 4 H); 2.75
(t, J ¼ 7.6, 4 H); 1.85 (t, J ¼ 7.6, 4 H); 1.68 (t, J ¼ 6.8, 4 H ); 1.49 (t, J ¼ 7.6, 4 H); 1.42 (t, J ¼ 6.0, 4 H).
13C-NMR (100 MHz, D2O): 135.29; 122.56; 122.41; 119.71 (q, J(C,F) ¼ 315.2, CF3); 50.13; 49.05; 49.54;
29.00; 28.14; 24.91; 21.01. ESI-MS: 491.8. Anal. calc. for C22H36F6N4O12S4 (790.80): C 33.41, H 4.59, N
7.09; found: C 33.35, H 4.67, N 7.20.
1,1’-(Decane-1,10-diyl)bis[3-(4-sulfobutyl)-1H-imidazolium] 1,1,1-Trifluoromethanesulfonate (1:2)
(3). As described for 2: 3 (97%). Yellow viscous liquid. 1H-NMR (400 MHz, D2O): 8.60 (s, 2 H); 7.31 (s,

Helvetica Chimica Acta – Vol. 92 (2009)
1021
2 H); 7.29 (s, 2 H); 4.04 (t, J ¼ 6.8, 4 H); 3.98 (t, J ¼ 6.8, 4 H); 2.72 (t, J ¼ 7.6, 4 H); 1.81 (t, J ¼ 7.6, 4 H);
1.64 (t, J ¼ 6.0, 4 H); 1.53 (t, J ¼ 7.2, 4 H); 0.95 – 1.06 (m, 12 H). 13C-NMR (100 MHz, D2O): 135.25;
122.55; 122.37; 119.71 (q, J(C,F) ¼ 315.2, CF3); 50.12; 49.69; 49.02; 29.14; 28.35; 28.21; 28.01; 25.32; 21.02.
ESI-MS: 547.8. Anal. calc. for C26H44F6N4O12S4 (846.90): C 36.87, H 5.23, N 6.62; found: C 36.90, H 5.31,
N 6.56.
Beckmann Rearrangement: General Procedure. A mixture of the oxime (1.00 mmol), IL (0.05 –
0.10 mmol), ZnCl2 (0.05 – 0.10 mmol), and solvent (5 ml) was stirred for 2 – 5 h at 808. Then, the
mixture was cooled and analyzed qualitatively by GC/MS (HP 6890/5793) and quantitatively by GC
(Agilent-6820-GC system, FID detector). The GC yield was obtained from the product of conversion of
starting material and selectivity of amide.
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Received October 10, 2009