Design, characterization, and use of N,N-diethyl-N-sulfoethanaminium hydrogen sulfate {[Et3N-SO3H]HSO4} as a novel and highly efficient catalyst for preparation of α,α′-bis(arylidene)cycloalkanones

Article abstract of DOI:10.1007/s11164-016-2458-2

Abstract: The aim of this work is to introduce a novel and attractive protic acidic ionic liquid as catalyst for organic synthesis. To achieve this aim, N,N-diethyl-N-sulfoethanaminium hydrogen sulfate {[Et₃N-SO₃H]HSO₄} was prepared by reaction of NEt₃ with ClSO₃H and then with H₂SO₄. The novel acidic ionic liquid was identified by Fourier-transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and mass spectroscopies. Its catalytic activity was then examined in the cross-aldol condensation reaction of arylaldehydes with cycloalkanones under solvent-free conditions, obtaining α,α′-bis(arylidene)cycloalkanones in high yield after short reaction time. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-016-2458-2

Res Chem Intermed
DOI 10.1007/s11164-016-2458-2
Design, characterization, and use of N,N-diethyl-N-
sulfoethanaminium hydrogen sulfate {[Et N-SO H]
3
3
HSO } as a novel and highly efficient catalyst for
4
0
preparation of a,a -bis(arylidene)cycloalkanones
1
1
•
Salimeh Ahmadi
Mina Aali-Hosaini
•
Abdolkarim Zare
•
1
1
•
Maryam Maghsoudi
1
•
1
Shadi Izadpanah
Maria Merajoddin
•
Abolfath Parhami
1
Received: 5 November 2015 / Accepted: 20 January 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract The aim of this work is to introduce a novel and attractive protic acidic ionic
liquid as catalyst for organic synthesis. To achieve this aim, N,N-diethyl-N-sul-
foethanaminium hydrogen sulfate {[Et N-SO H]HSO } was prepared by reaction of
3
3
4
NEt with ClSO H and then with H SO . The novel acidic ionic liquid was identified by
3
3
2
4
1
13
Fourier-transform infrared (FT-IR), H nuclear magnetic resonance (NMR), C NMR,
and mass spectroscopies. Its catalytic activity was then examined in the cross-aldol
condensation reaction of arylaldehydes with cycloalkanones under solvent-free condi-
0
tions, obtaining a,a -bis(arylidene)cycloalkanones in high yield after short reaction time.
Graphical Abstract
Keywords Protic acidic ionic liquid
Á
N,N-Diethyl-N-sulfoethanaminium
0
hydrogen sulfate {[Et N-SO H]HSO } Á a,a -Bis(arylidene)cycloalkanone Á Cross-
3
3
4
aldol condensation Á Solvent-free
&
Abdolkarim Zare
abdolkarimzare@pnu.ac.ir; abdolkarimzare@yahoo.com
1
Department of Chemistry, Payame Noor University, PO BOX 19395-3697, Tehran, Iran
123

S. Ahmadi et al.
Introduction
Ionic liquids have been applied as useful alternatives to conventional solvents,
catalysts or reagents in organic synthesis, due to their particular properties
including: (1) chemical and thermal stability, (2) low vapor pressure, (3) controlled
miscibility and polarity, (4) high boiling point, (5) nonflammability, (6) excellent
solvent power for organic and inorganic compounds, and (7) ability to catalyze a
wide range of organic reactions. Among them, protic acidic ionic liquids (AILs)
have been extensively utilized as catalysts and reagents in organic synthesis [1–15].
This class of ionic liquids combine the advantages of both liquid and solid acids.
Consequently, introduction of novel AILs to progress organic reactions is attractive
and highly important.
It is now generally recognized that chemistry is one of the key sciences able to
impact the environment in both a positive and negative fashion. Thus, there is
growing awareness that design of synthetic or chemical processes should follow the
basic principles of green chemistry to reduce risks to humans and the environment.
Among several aspects of green chemistry, removal of volatile organic solvents
from the reaction medium (i.e., use of solvent-free conditions) is of utmost
importance. Furthermore, in many cases, solvent-free technique offers considerable
synthetic advantages in terms of yield, selectivity, and simplicity of reaction
procedure [16–21].
0
a,a -Bis(arylidene)cycloalkanone derivatives have attracted much attention
because of their use as precursors for synthesis of pyrimidine derivatives [22],
interesting biological activities such as cholesterol-lowering [23], quinine
reductase inducer [24], and antiparasitic [25] properties, and application as new
organic materials in nonlinear optical systems [26], units of liquid-crystalline
polymers [27], and cytotoxic analogues [28]. Cross-aldol condensation reaction
between cycloalkanones and arylaldehydes has been used as the best synthetic
0
route toward a,a -bis(arylidene)cycloalkanones [29–37]. Several catalysts have
been used to promote this transformation so far [29–37]. However, most of these
methods are associated with one or more of the following disadvantages: (1)
unwanted side-reactions, (2) need for application of sealed ampoules or tubes, (3)
moderate yield, (4) long reaction time, (5) use of expensive, unavailable, and
toxic catalysts, (6) application of additional energy (microwaves), (7) use of
volatile organic solvents, (8) harsh conditions, and (9) poor agreement with green
chemistry principles. Thus, the search for highly efficient catalysts for preparation
of the mentioned compounds without the above-mentioned drawbacks remains
important.
In this work, we synthesized a novel protic acidic ionic liquid, namely N,N-
diethyl-N-sulfoethanaminium hydrogen sulfate {[Et N-SO H]HSO }, and charac-
3
3
4
1
13
terized it by studying its FT-IR, H NMR, C NMR, and mass spectra. We then
applied the ionic liquid as a highly efficient, green, and homogeneous catalyst for
cross-aldol condensation reaction between cycloalkanones and arylaldehydes in
0
absence of solvent to afford a,a -bis(arylidene)cycloalkanones.
1
23

Design, characterization, and use of…
Experimental
General
All chemicals were purchased from Merck or Fluka chemical companies. All known
compounds were identified by comparison of their melting points and spectral data
with those reported in literature. Reaction progress was monitored by thin-layer
1
chromatography (TLC) using silica gel SIL G/UV 254 plates. H NMR (250 or
5
1
00 MHz) and C NMR (62.5 or 125 MHz) spectra were run on a Bruker Avance
3
DPX FT-NMR spectrometer. Mass spectra were obtained with a Shimadzu GC–MS-
QP 1100 EX model. Melting points were recorded on a B u¨ chi B-545 apparatus in
open capillary tubes.
Procedure for preparation of ionic liquid [Et N-SO H]HSO
4
3
3
A solution of triethylamine (0.50 g, 5 mmol) in CH Cl2 (40 mL) was added
2
dropwise to a stirring solution of chlorosulfonic acid (0.58 g, 5 mmol) in dry
CH Cl (40 mL) over a period of 10 min at 10 °C. Afterward, the reaction mixture
2
2
was allowed to heat to room temperature (accompanied with stirring), and stirred for
another 4 h. The solvent was evaporated, and the liquid residue was triturated with
t-butyl methyl ether (3 9 10 mL) and dried under powerful vacuum at 90 °C to
give [Et N-SO H]Cl as a viscous pale-yellow oil in 93 % yield [7]. Then, sulfuric
3
3
acid (99.99 %, 0.49 g, 5 mmol) was added dropwise to [Et N-SO H]Cl (1.089 g,
3
3
5
mmol) over a period of 5 min at room temperature under pressure of nitrogen gas
to remove HCl produced during the reaction). The resulting mixture was stirred for
(
1
viscous pale-yellow liquid in 99 % yield.
0 h at 60 °C under continuous flow of nitrogen gas to give [Et N-SO H]HSO as a
3
3
4
Spectral data of [Et N-SO H]HSO
4
3
3
-
1
1
IR (Nujol): 583, 880, 1059, 1167, 1207, 2950, 2500–3500 cm
(
.
H NMR
250 MHz, DMSO-d ): d (ppm) 1.42 (t, J = 7.5 Hz, 9H), 3.30 (q, J = 7.5 Hz, 6H),
6
1
3
8
MS: m/z 280 (M ?1), 279 (M ), 262 (M –OH), 182 (M –HSO ), 101 (M –
.43 (br, 1H), 11.59 (br, 1H). C NMR (62.5 MHz, DMSO-d ): d (ppm) 8.3, 45.7.
6
? ? ? ? - ?
4
-
[
SO H,HSO ]).
3 4
0
General procedure for production of a,a -bis(arylidene)cycloalkanones
A mixture of cycloalkanone (1 mmol), aldehyde (2.1 mmol), and [Et N-SO3-
3
H]HSO (0.042 g, 0.15 mmol) in a test tube connected to a reflux condenser was
4
stirred at 90 °C for the appropriate time (Table 2). After completion of the reaction,
as monitored by TLC, the reaction mixture was cooled to room temperature, and
recrystallized from EtOH (95 %) or by column chromatography on silica gel eluted
with n-hexane/EtOAc (1/5) to give the pure product.
123

S. Ahmadi et al.
Selected spectral data of products
,6-Bis(3-chlorobenzylidene)cyclohexanone (4) H NMR (500 MHz, CDCl ): d
1
2
3
(
ppm) 1.69 (quintet, J = 5.7 Hz, 2H), 2.78 (t, J = 5.7 Hz, 4H), 7.30–7.37 (m, 6H),
1
3
7
2
.41 (s, 2H), 7.62 (t, J = 1.2 Hz, 2H). C NMR (125 MHz, CDCl ): d (ppm) 23.7,
3
7.9, 126.3, 127.9, 129.3, 130.4, 130.9, 133.2, 135.8, 137.8, 188.9.
1
2
,6-Bis(2-chlorobenzylidene)cyclohexanone (6) H NMR (500 MHz, CDCl ): d
3
(
(
(
ppm) 1.75 (quintet, J = 5.8 Hz, 2H), 2.78 (t, J = 5.8 Hz, 4H), 7.28 (m, 4H), 7.34
1
3
d, J = 3.4, 2H), 7.45 (d, J = 3.3 Hz, 2H), 7.89 (t, J = 1.2 Hz, 2H). C NMR
125 MHz, CDCl ): d (ppm) 23.2, 28.7, 126.8, 130.8, 130.9, 131.0, 134.5, 135.0,
3
1
35.5, 138.3, 189.2.
1
2
,5-Bis(3-chlorobenzylidene)cyclopentanone (12) H NMR (500 MHz, CDCl ): d
3
(
ppm) 3.01 (s, 4H), 7.29–7.33 (m, 4H), 7.39–7.42 (m, 2H), 7.43 (s, 2H), 7.51 (t,
1
3
J = 1.2 Hz, 2H). C NMR (125 MHz, CDCl ): d (ppm) 27.0, 128.6, 129.6, 130.5,
3
1
30.7, 132.5, 135.3, 137.1, 138.6, 196.0.
Results and discussion
Catalyst characterization
As mentioned in the ‘‘Introduction,’’ the introduction of novel protic acidic ionic
liquids (AILs) to promote organic reactions is important. Thus, we decided to
prepare a novel AIL, namely N,N-diethyl-N-sulfoethanaminium hydrogen sulfate
{
[Et N-SO H]HSO }. To achieve this aim, NEt (1 eq.) was reacted with ClSO H
3 3 4 3 3
(
H SO (1 eq.) to provide [Et N-SO H] HSO as a viscous pale-yellow liquid
1 eq.) to afford [Et N-SO H]Cl [7]. Then, [Et N-SO H]Cl (1 eq.) was reacted with
3 3 3 3
2
4
3
3
4
(
Scheme 1).
After production of the novel ionic liquid, it was characterized by FT-IR, H
1
1
NMR, C NMR, and mass spectra.
3
In the FT-IR spectrum of N,N-diethyl-N-sulfoethanaminium hydrogen sulfate, a
-
broad peak observed at 2500–3500 cm is related to OH of SO H groups. The
1
3
-
band at 1059 cm was assigned to S–OH bending. The strong absorptions at 1207,
1
-
1
1
bending S–O vibrations of SO H and HSO . Symmetric N–S stretching vibration
167, and 583 cm
are related to asymmetric and symmetric stretching and
-
3
4
Scheme 1 Production of [Et
3
N-SO H]HSO
3 4
1
23

Design, characterization, and use of…
1
Fig. 1 H NMR spectrum of [Et
3
N-SO
3
H]HSO
4
1
Fig. 2 C NMR spectrum of the AIL
3
123

S. Ahmadi et al.
-
1
-1
was also observed at 880 cm . The peak at about 2950 cm is assigned to
stretching of hydrogens bonded to carbons.
1
In the H NMR spectrum of [Et N-SO H]HSO (Fig. 1), a triplet peak
3
3
4
appearing at 1.42 ppm is related to nine hydrogens of three methyl groups. The
quartet peak at 3.30 ppm corresponds to six hydrogens of three methylene groups.
-
The two acidic hydrogens (HSO4 and SO H) of the AIL were observed at 8.43
3
and 11.59 ppm.
1
3
In the C NMR spectrum (Fig. 2), two peaks appearing at 8.3 and 45.7 ppm are
related to carbons of methyl and methylene groups.
?
?
In the mass spectrum of the AIL (Fig. 3), its molecular mass (M ) and M ?1
were observed at m/z = 279 and 280. The other peaks which assist in identification
?
?
-
4
?
of [Et N-SO H]HSO are seen at 262 (M –OH), 182 (M -HSO ), and 101 (M -
3
3
-
4
SO H, HSO ).
3
4
In another study, to prove that [Et N-SO H]Cl was completely converted to
3
3
[
Et N-SO H]HSO , a solution of AgNO in distilled water was added to a solution
3 3 4 3
of the AIL in distilled water. The absence of AgCl precipitate indicated complete
conversion of [Et N-SO H]Cl to [Et N-SO H]HSO .
3
3
3
3
4
3 3 4
Fig. 3 Mass spectrum of [Et N-SO H]HSO
1
23

Design, characterization, and use of…
0
Examination of catalytic activity of [Et N-SO H]HSO for synthesis of a,a -
3
3
4
bis(arylidene)cycloalkanones
After the AIL had been fully characterized, its catalytic activity to promote a
0
significant organic transformation, i.e., synthesis of a,a -bis(arylidene)cycloalka-
nones by condensation of arylaldehydes with cycloalkanones, was checked. First,
the reaction of 3-nitrobenzaldehyde with cyclohexanone was carried out using
different molar ratios of [Et N-SO H]HSO in the range of 80–100 °C; the
3
3
4
corresponding results are summarized in Scheme 2 and Table 1, indicating that the
best results were obtained when the reaction was carried out in the presence of
1
5 mol % AIL at 90 °C.
After the reaction had been optimized, the generality and effectiveness of the
catalyst were explored by studying reactions of different arylaldehydes and
cycloalkanones; the respective results are displayed in Table 2. As can be seen from
this table, all the arylaldehydes (bearing halogens, and electron-withdrawing and
0
electron-releasing substituents on their aromatic rings) afforded the desired a,a -
bis(arylidene)cycloalkanones in high to excellent yield and short reaction time.
0
Thus, the ionic liquid is highly efficient and general for preparation of a,a -
bis(arylidene)cycloalkanone derivatives.
In another study, the regenerability and reusability of the catalyst were studied.
For this purpose, the reaction of 3-nitrobenzaldehyde with cyclohexanone using
[
combined. Afterward, H O was added to the combined reaction mixtures, followed
Et N-SO H]HSO was carried out several times, and the reaction mixtures were
3 3 4
2
by stirring for 3 min and filtering (the catalyst is soluble in H O, whereas the
2
Scheme 2 Reaction of 3-nitrobenzaldehyde with cyclohexanone used for optimization of reaction
conditions
Table 1 Effect of catalyst
amount and temperature on
reaction of 3-nitrobenzaldehyde
with cyclohexanone
a
Entry Mol % of
3 4
Et N-SO H]HSO
Temp. (°C) Time (min) Yield (%)
[
3
1
2
3
4
5
10
15
18
15
15
90
90
40
25
25
35
25
89
92
92
87
92
90
80
100
a
Isolated yield
123

S. Ahmadi et al.
0
Table 2 Preparation of a,a -bis(arylidene)cycloalkanones via cross-aldol condensation of cycloalka-
nones with aromatic aldehydes using [Et N-SO H]HSO
3
3
4
a
Time (min)/yield (%)
Product
X
R
C
M.p. (°C)
Found
Reported
1
2
3
4
5
6
7
8
9
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
2
2
2
2
2
2
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
2
2
2
2
6
H
5
34/93
25/94
30/96
32/93
23/92
40/83
16/93
15/92
25/92
20/93
30/92
35/94
114–116
154–156
120–122
106–108
143–145
104–106
169–171
163–165
184–186
160–162
186–188
175–177
116–117 [35]
156–157 [33]
119–120 [33]
105–107 [31]
143–145 [31]
103–105 [37]
170 [35]
4-FC
6
H
4
3-BrC
6
H
4
4
4
4
3-ClC
4-ClC
2-ClC
6
H
H
H
6
6
4-MeC
6
H
4
4-MeOC
6
H
4
162–164 [36]
184–186 [31]
162–163 [36]
188.5 [35]
3-NO
4-NO
2
C
C
6 4
H
1
1
1
a
0
1
2
2
6 4
H
6 5
C H
3-ClC
6
H
4
174–176 [31]
Isolated yield
reaction mixture is not). The filtrate (containing the catalyst) was basified by NaOH;
under these conditions, [Et N-SO H]HSO was completely converted to Et N and
Na SO . Then, the solution was extracted by CH Cl , washed by H O, and dried
3
3
4
3
2
4
2
2
2
over Na SO . The recovered NEt in CH Cl was reacted with chlorosulfonic acid,
2
4
3
2
2
and then with H SO according to the mentioned procedure to give [Et N-
2
4
3
SO H]HSO . The catalytic activity of the reproduced catalyst was the same as the
4
3
first one.
Conclusions
We introduce a novel protic acidic ionic liquid as a highly efficient catalyst in
organic synthesis by preparing [Et N-SO H]HSO and applying it as catalyst for
3
3
4
0
synthesis of a,a -bis(arylidene)cycloalkanones. The benefits of our new catalyst in
this reaction include: (1) low cost of starting materials for catalyst preparation, (2)
easy preparation of catalyst, (3) generality, effectiveness, novelty, and nontoxicity
of catalyst, and (4) performing the reaction in high yield and short time under
solvent-free conditions.
Acknowledgments The authors thank the Research Council of Payame Noor University for financial
support of this work.
1
23

Design, characterization, and use of…
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