Choline-based biodegradable ionic liquid catalyst for Mannich-type reaction

Article abstract of DOI:10.1007/s12039-016-1199-5

A three-component Mannich-type reaction of aromatic aldehydes, ketones, and amines was catalyzed by a novel choline-based acidic ionic liquid. The proposed catalyst was a Lewis-Br?nsted dual acid catalyst as well as water-tolerant. The β-amino carbonyl compounds were obtained at room temperature in reasonable to good yields ranging from 63 to 98%. After the reaction, the catalyst could be recycled and reused for 5 times without obvious decrease of the yield. Further, the catalyst was environment-friendly with a significant biodegradation rate. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-016-1199-5

c
J. Chem. Sci. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-016-1199-5
Choline-based biodegradable ionic liquid catalyst for Mannich-type
reaction
PENG HUANa, HU YULINb, XING RONGa,b and FANG DONGa,b,∗
aCollege of Chemical Engineering, Nanjing Tech University, Nanjing 210009, People’s Republic of China
bSchool of Chemistry & Environmental Engineering, Yancheng Teachers University, Yancheng 224002,
People’s Republic of China
e-mail: fangdong106@sina.com
MS received 2 February 2016; revised 20 October 2016; accepted 21 October 2016
Abstract. A three-component Mannich-type reaction of aromatic aldehydes, ketones, and amines was cat-
alyzed by a novel choline-based acidic ionic liquid. The proposed catalyst was a Lewis-Brønsted dual acid
catalyst as well as water-tolerant. The β-amino carbonyl compounds were obtained at room temperature in rea-
sonable to good yields ranging from 63 to 98%. After the reaction, the catalyst could be recycled and reused for
5 times without obvious decrease of the yield. Further, the catalyst was environment-friendly with a significant
biodegradation rate.
Keywords. Mannich-type reaction; choline; Lewis-Brønsted acid; catalysis; biodegradation.
1. Introduction
Satasia et al., designed a new sulfate-functionalized
cholinium cation and catalyzed formamide synthesis
by grindstone chemistry.14 Apart from Brønsted acid15
or Lewis-Brønsted acid, choline-based ionic liquids16
were also designed and synthesized. It has been proved
that all of them have significant catalytic activity and
are friendlier for the environment than conventional
ionic liquids which have catalyzed many reactions like
Biginelli reaction,15 Mannich reaction,16 Kabachnik–
Fields reaction,17 etc.
The Mannich-type reaction is a basic C-C bond forming
multi-component reaction (MCR) which involves an
amino alkylation of an acidic proton beside a carbonyl
functional group by formaldehyde and a primary or
secondary amine or ammonia.1 The products of Man-
nich reaction, β-amino carbonyl compound, are syn-
thetic intermediates of huge value. It is widely
employed in the organic synthesis of natural com-
pounds, medicine and biologically active compounds.2
Today, it has shown broad applicability in other areas
such as pesticides, explosives, dyes and paints. Most
Mannich reactions are catalyzed by Lewis acid or
Brønsted acid.3 In recent years, the researchers con-
tinued to study new synthetic methods and new cata-
lysts including TMG,4 Sm(OTf)3,5 Fe(HSO4)3/SiO2,6
triphenylphosphine,7 nano-Mn(HSO4)2,8 Zeolite9 were
reported.
In continuation of our work on MCRs,18 and con-
sidering the importance of combined catalytic systems,
the choline-based functional Lewis-Brønsted dual acid
ionic liquid catalyst (Figure 1) was discovered and
used as the catalyst in the Mannich-type reaction under
mild reaction conditions. Its use as a novel catalyst
for the synthesis of β-amino carbonyl compound via
Mannich-type reaction has also been explored.
Choline-based ionic liquids are widely applied in
many areas such as the sustainable chemistry,10 syn-
thetic chemistry11 and catalysis,12 due to the excellent
physical, chemical properties, environmental friendli-
ness and low prices. Abbott et al., proposed a novel
deep eutectic ionic liquid based on choline chloride,
and it showed a significant function in catalysis.13 On
the basis of the research of choline-based ionic liquids,
2. Experimental
2.1 Materials and methods
All the reagents and chemicals (AR grade) were pro-
cured from Sinopharm Chemical Reagent Co. Ltd. and
used as received. The sludge used in the biodegradation
rate test was supplied by Nanjing Sewage Treatment
Plant, China.
The Elemental analyses were done using a Perkin-
Elmer CHN analyzer. The IR spectra (KBr pellet) were
∗For correspondence

Peng Huan et al.
2.3 General procedure for the Mannich-type reaction
catalyzed by [Ch-OSO3H]Cl·2ZnCl2
In a typical experiment (Scheme 1), to a round-
bottomed flask charged with aromatic aldehyde
(10 mmol), aromatic amine (10 mmol) and aromatic
ketones (10 mmol) in 2–3 mL 85% aqueous ethanol was
added [Ch-OSO3H]Cl·2ZnCl2 (0.49 g; 1 mmol) under
stirring. The mixture was then stirred for a length of
time at room temperature. After completion of the con-
densation (monitored by TLC), the solid crude prod-
uct was filtered and recrystallized from 95% ethanol
to afford pure β-amino carbonyl derivatives. The prod-
Figure 1. Structure of Lewis-Brønsted choline–based
ionic liquid.
recorded on a Bruker WERTEX80 spectrometer and
1
expressed in cm−1. H NMR spectra were recorded
on a Bruker DRX300 (300 MHz) and Bruker Ultra-
shield (400 MHz) spectrometer. 13C NMR spectra were
recorded on a Bruker DRX300 (75 MHz) and Bruker
Ultrashield (101 MHz) spectrometer. Mass spectra were
obtained with an automated Fininigan TSQ Quantum
1
ucts obtained were identified by H NMR, and phys-
ical data (M.p.) with those reported in the literature.
[Ch-OSO3H]Cl·2ZnCl2, could be recovered from the
filtrate and reused directly for the next run without
Ultra AM (Thermal) LC/MS spectrometer. Thermal any treatment. The characterization data for the new
stability measurements were conducted using a NET- compounds are given below.
ZSCH STA 449F5 system.
2.3a 1-Phenyl-3-(p-hydroxylphenyl)-3-(m-trifluoro-
methylphenylamino)-1-propanone (Table 3, entry 13):
2.2 Synthesis of Lewis-Brønsted choline-based Ionic
liquid ([Ch-OSO3H]Cl·2ZnCl2)
White solid, M.p. 157–158◦C; Analysis: Calculated
(%) for C22H18F3NO2 (385.379): C, 68.57; H,4.71;
N, 3.63. Found (%): C, 68.33; H,4.72; N, 3.58. MS
The intermediate [Ch-OSO3H]Cl (1) was synthesized
1
(m/z): 386.1308 ([M + H]+). H NMR (400 MHz,
according to the reported methods,14 dried under vac-
CDCl3) δ 7.94–7.86 (m, 2H), 7.58 (t, 1H), 7.46
uum to afford the white powder. The characterization
(t, 2H), 7.16 (t, 1H), 6.88 (d, 1H), 6.79 (dd, 3H), 6.67
data for the intermediate are as follows: [Ch-OSO3H]Cl
(dd, 1H), 4.99–4.92 (m, 1H), 4.80 (s, 2H), 3.60–3.22
(1):IR /cm−1:3417, 3043, 2987, 1483, 1405, 1231, 1038,
(m, 4H). 13C NMR (101 MHz, CDCl3) δ 197.26,
985, 761, 628, 571 cm−1. 1H NMR (300 MHz, D2O): δ
153.84, 146.07, 135.55, 133.23, 132.57, 128.72,
3.06 (s, 9H), 3.60–3.63 (t, 2H), 433–437 (m, 2H).
128.46, 127.74, 127.18, 126.57, 118.97, 115.41,
A mixture of the above intermediate [Ch-OSO3H]Cl
114.67, 113.01, 109.32, 53.08, 45.11.
(2.197 g; 10 mmol) and ZnCl2 (2.726 g; 20 mmol)
was rapidly grinded for 5 min; then, the uniform
mixture was heated for 2 h at 100◦C to afford the
2.3b 1-Phenyl-3-(p-methylphenyl)-3-(m-trifluoromethyl-
target ionic liquid [Ch-OSO3H] Cl·2ZnCl2 (2). The
phenylamino)-1-propanone (Table 3, entry 14): White
solid, M.p. 111–112◦C; Analysis: Calculated (%) for
C23H20F3NO (383.406): C, 72.05; H, 5.26; N, 3.65.
Found (%): C, 71.85; H, 5.28; N, 3.60. MS (m/z):
characterization data for the compound are as fol-
lows: [Ch-OSO3H]Cl·2ZnCl2 (2): Analysis: Calculated
(%) for C5H14Cl5NO4SZn2 (486.767): C, 12.34; H,
2.90; N, 2.88. Found (%): C,12.05; H, 2.89; N, 2.83.
IR / cm−1: 3357, 2975, 2889, 1650, 1384, 1089, 881,
1
384.1520 ([M + H]+). H NMR (400 MHz, CDCl3) δ
7.91 (dd, 2H), 7.60–7.50 (m, 2H), 7.45 (t, 2H), 7.31
(d, 2H), 7.16–7.12 (m, 3H), 6.89 (d, 1H), 6.80 (s, 1H),
6.68 (dd, 1H), 4.98 (dd, 1H), 3.53–3.40 (m, 2H), 2.31
(s, 3H).13C NMR (101 MHz, CDCl3) δ 197.12, 146.28,
1
662 cm−1. H NMR (300 MHz, D2O): δ 3.13 (s, 9H),
3.65–3.67 (t, 2H), 440 (s, 2H) 13C NMR (101 MHz,
D2O): δ 51.05, 59.12, 61.91.
Scheme 1. Process of Mannich-type reaction.

Choline-based Biodegradable Ionic Liquid
137.99, 136.24, 135.54, 132.53, 130.43, 128.60, at 254.3◦C and 341.6◦C. The peak at 254.3◦C was due
128.49, 127.72, 127.18, 125.12, 120.08, 115.34, to the phase transition. [Ch-OSO3H]Cl had changed
113.10, 109.35, 53.36, 45.14, 20.04.
from solid into molten state. The melting enthalpy was
58.93 J/g. Another peak was due to the decomposition,
the decomposing enthalpy was 509.5 J/g. The decom-
posing enthalpy of [Ch-OSO3H]Cl·2ZnCl2 was 509.5
J/g. The endothermic peak was at 344.6◦C.
One-pot Mannich-type model reaction with ben-
zaldehyde, aniline and acetophenone was established in
the presence of [Ch-OSO3H]Cl·2ZnCl2 and the reaction
time was monitored by TLC (Table 1).
3. Results and Discussion
3.1 Synthesis and characterization
The intermediate [Ch-OSO3H]Cl was synthesized
according to the reported methods; then a mixture of
[Ch-OSO3H]Cl and ZnCl2 was rapidly grinded for
5 min, and heated for 2 h at 100◦C to afford the target
ionic liquid [Ch-OSO3H]Cl·2ZnCl2. In the FTIR spec-
trum for [Ch-OSO3H]Cl·2ZnCl2, (Figure S2 in Sup-
plementary Information), the peaks of O-H bond
(3300–3500 cm−1), C-H bond (2880–2990 cm−1),
C-O bond (1000–1100 cm−1) were well-retained. How-
ever, the Zn-Cl vibration peak in ZnCl2 is at 503
cm−1, whereas the Zn-Cl vibration peak in [Ch-OSO3H]
Cl·2ZnCl2 appears at 663 cm−1. The peak was enhanced
and position shifted from 503 cm−1 to 663 cm−1, which
indicated that the significant catalytic effect of [Ch-
OSO3H] Cl· 2ZnCl2 is due to the complexation between
[Ch-OSO3H]Cl and ZnCl2.
In order to understand the phase transition and
decomposition behavior of [Ch-OSO3H]Cl and [Ch-
OSO3H]Cl·2ZnCl2, DSC and TGA study were car-
ried out. The results are shown in Figure 2. It can be
seen that [Ch-OSO3H]Cl and [Ch-OSO3H]Cl· 2ZnCl2
have high thermal stability. The addition of zinc chlo-
ride did not change significantly the thermal stabil-
ity. The high thermal stability suggests that both of
them can be used in a wide temperature range. In
DSC for [Ch-OSO3H]Cl, endothermic peaks appeared
It showed that the three-component Mannich-type
reaction could be accomplished smoothly in aqueous
ethanol at room temperature. Satisfactory results were
obtained in 80–85% ethanol medium (entries 5, 6).
But, when pure water or ethanol were used as medium
(entries 1, 7), the reaction was suppressed. The yield
rose with the addition of ethanol in water, and the
yield reached maximum when the content of ethanol
is 85%. It is noteworthy that the proposed catalyst
[Ch-OSO3H]Cl·2ZnCl2 could retain its activity in the
aqueous media. In aqueous media, most of the tradi-
tional Lewis acid catalysts may react with water first.
It greatly affects the activity of catalyst, leading to
lower yields of the target product. This work indi-
cated that [Ch-OSO3H]Cl· 2ZnCl2 overcame the fear of
water when compared with many traditional Lewis acid
catalysts.19 21
In order to evaluate the catalytic activity of [Ch-
OSO3H]Cl·2ZnCl2, different catalysts were explored
in the model reaction (Table 2) in aqueous ethanol
medium at the room temperature. It is inferred from
Table 2 that [Ch-OSO3H]Cl catalyzed more effectively
than choline chloride and results in substantial increase
of yield (entries 1, 2), which confirmed that the replace-
ment of hydroxyl to sulfonic acid group could increase
the catalytic activity. Besides, it could be inferred that
ZnCl2 showed some catalytic activity and introducing
1
100
80
60
Table 1. The effects of different solvent systems to the
[Ch-OSO3H]Cl
40
20
4
Mannich reaction.a
.
[Ch-OSO3H]Cl2ZnCl2
Entry
Solvent
Time (min)
Yield (%)b
2
1
2
3
4
5
6
7
H2O
10
8
8
8
8
<10
59
76
86
93
3
50% ethanol
65% ethanol
75% ethanol
80% ethanol
85% ethanol
C2H5OH
2
1
0
8
8
98
<10
50
100
150
200
250
300
350
400
exo
Temperature ( C)
aReaction conditions: benzaldehyde (10 mmol), aniline
(10 mmol) and acetophenone (10 mmol), catalyst (1 mmol),
solvent (2 mL), r.t. bIsolated yield.
Figure 2. TGA (1)—DSC (2) scans of [Ch-OSO3H]Cl and
[Ch-OSO3H]Cl·2ZnCl2.

Peng Huan et al.
and heated under 100◦C for 2 h, the Lewis-Brønsted
dual acid ionic liquid ([Ch-OSO3H]Cl·2ZnCl2) was
generated which showed significant catalytic effect on
Mannich reaction (entry 7). Choline chloride and zinc
chloride were treated in the same way, and used as the
catalyst for Mannich reaction in 85% aqueous ethanol
(entry 4), and in pure water (entry 5). It was found that
the catalytic activity of ChCl·2ZnCl2 for Mannich reac-
tion was far less than [Ch-OSO3H]Cl·2ZnCl2. Thus, it
proved that a combination of Lewis and Brønsted acid
under heated condition and sulfonic acid group played
a significant role in promoting the catalytic activity of
the catalyst.
Table 2. The activity of different catalysts for Mannich
reaction.a
Entry
Catalyst
Yield (%)
1
2
3
4
5b
6
7
Choline Chloride
[Ch-OSO3H]Cl
51
71
55
68
71
61
98
ZnCl2
ChCl·2ZnCl2
ChCl·2ZnCl2
[Ch-OSO3H]Cl and ZnCl2
[Ch-OSO3H]Cl·2ZnCl2
aReaction conditions: benzaldehyde (10 mmol), aniline
(10 mmol) and acetophenone (10 mmol), catalyst (1mmol),
85% ethanol (2 mL), 8 h, r.t. bIn H2O.
Abott et al., pointed out that actual species presented
in ChCl·2ZnCl2 which acted as Lewis acid catalyst,
ZnCl2 would benefit the reaction (entry 3). However, could be [ZnCl3]−, [ZnCl5]− and [ZnCl7]−.10 Liu and
the performance of individual use of the Lewis acid and coworkers reported [HO3S-(CH2)4-min]Cl-xZnCl2 was
Brønsted acid was unsatisfactory (entries 2, 3).
Brønsted-Lewis acidic ionic liquid. Anion in the ionic
Based on the above results, we considered a combi- liquid could be [ZnCl3]−, [Zn2Cl5]−, [Zn4Cl9]−.22 The
nation of the Lewis acid and Brønsted acid. Initially, forms of anion existing in such structures are semi-
[Ch-OSO3H]Cl and ZnCl2 were mixed directly with a empirical. These species may attract a proton from
molar ratio of 1:2, and the mixture was simply used in acetophenone to give anionic enolate species. More-
the reaction without any pre-treatment (entry 6). But the over, [Ch-OSO3H]Cl·2ZnCl2 can form an acceptor-
catalytic effects were still unsatisfactory. However, if donor complex with the aldehyde and the imine in
the pre-treatment process was optimized to grind them the first stage. Therefore, addition of the enolate
Scheme 2. The mechanism of [Ch-OSO3H]Cl·2ZnCl2-catalyzed Mannich-type reaction.

Choline-based Biodegradable Ionic Liquid
form of acetophenone could be facilitated. When The yield in the 5 cycles were 96, 96, 94, 93 and 92%.
[Ch-OSO3H]Cl and ZnCl2 were mixed directly without In the 5th cycle, the yield was slightly lower, which may
any pre-treatment, they did not have such a catalytic be due to the unavoidable loss in the recovery process.
effect.
But on the whole, the recovered catalyst still showed a
On the basis of these assumptions, the experimen- significant catalytic activity on the reaction.
tal results and reported studies, the mechanism can
be inferred. The mechanism of [Ch-OSO3H]Cl·2ZnCl2
3.3 The biodegradation rate of the catalyst
catalysis of Mannich-type reaction involving benzalde-
hyde, aniline and acetophenone as substrate is shown in
[Ch-OSO3H]Cl·2ZnCl2
Lastly, the biodegradation of [Ch-OSO3H]Cl·2ZnCl2
Scheme 2.
was investigated with the sludge of Nanjing sewage
treatment plant. Sodium lauryl sulfate (SDS) was
used as a reference. The standards were according to
OECD301D.23 The results are shown in Figure 3.
With the best reaction conditions in hand, some con-
trolled experiments were explored with various aro-
matic aldehydes, aromatic amines and ketones as the
substrate. The results presented in Table 3 shows that
all the one-pot three-component Mannich-type reac-
tions were accomplished in the optimal conditions, cat-
alyzed by [Ch-OSO3H]Cl·2ZnCl2. It could be easily
seen that no matter whether the electron donating group
or the electron withdrawing group on the aromatic ring,
reasonable to good yield could be obtained.
100
80
60
3.2 Reusability of the catalyst
HIL
40
In order to investigate the recycling of the catalyst,
several repeat experiments were made with the recov-
ered catalyst. The reaction was run with hydroxy-
benzaldehyde, p-toluidine and acetophenone as raw
materials, [Ch-OSO3H]Cl·2ZnCl2 as the catalyst, 85%
aqueous ethanol as the solvent. After the reaction,
the mixture was filtered, washed several times with
85% aqueous ethanol. The filtrate containing the
[Ch-OSO3H]Cl·2ZnCl2 was subsequently used as the
catalyst - solvent system in the next run of the reaction.
SDS
20
0
0
10
20
30
T d
Figure 3. The
biodegradation
[Ch-OSO3H]Cl·2ZnCl2. Plot of D (% vs time in days).
of
the
catalyst
Table 3. [Ch-OSO3H]Cl·2ZnCl2-catalyzed three-component Mannich-type reaction.a
Entry
R1
R2
R3
Yield/%b
M.p. (◦C)
1
H
H
ph
98
153−154
2
H
4-Me
4-Me
4-OCH3
4-OCH3
4-F
4-Me
4-Me
4-Cl
H
ph
86
65
76
93
84
95
87
91
92
80
96
63
73
86
163−164
148−149
150−151
106−107
157−158
126−127
117−118
152−153
126−127
180−181
171−172
157−158
111−112
138−139
3
ph
4
ph
5
ph
6
4-Me
4-Cl
H
4-Me
4-Cl
H
4-Me
3-CF3
3-CF3
H
ph
7
ph
8
4-Cl
ph
9
4-Cl
ph
10
11
12
13
14
15
4-Cl
ph
4-OH
4-OH
4-OH
4-CH3
H
ph
ph
ph
ph
4-MeC6H4
aReaction conditions: benzaldehyde (10 mmol), aniline (10 mmol) and acetophenone
b
(10 mmol), catalyst (1 mmol), 85% ethanol (2−3 mL), 6−12 h, r.t. Isolated yield;
products were confirmed by 1H NMR, MS.

Peng Huan et al.
Kinet. Catal. 52 559; (d) Ghatole A M, Lanjewar K R,
It was worth to note that the biodegradation rate
of the catalyst can reach 70% after 3 weeks and
remained stable subsequently. It was confirmed that
[Ch-OSO3H]Cl·2ZnCl2 should be an easily biodegrad-
able catalyst if compared with SDS, and this highlight
was superior to our previous works.
Gaidhane M K and Hatzade K M 2015 Spectrochim.
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In summary, a new biodegradable Lewis-Brønsted dual
acid ionic liquid was discovered and used as the cat-
alyst for the Mannich reaction of aromatic aldehydes,
ketones and amines. The easily biodegradable catalyst
could be recycled and reused. The procedure offers sev-
eral advantages including high efficiency, good yield,
and operational simplicity.
10. (a) Abbott A P, Boothby D, Capper G, Davies D L
and Rasheed R K 2004 J. Am. Chem. Soc. 126 9142;
(b) Abbott A P, Nandhra S, Postlethwaite S, Simth E L
and Ryder K S 2005 Phys. Chem. Chem. Phys. 9 3735;
(c) Sunitha S, Kanjialal S, Reddy P S and Prasad R B N
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M A 2014 J. Cleaner Prod. 65 246
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Chem. Sus. Chem. 5 1223; (b) Chen X, Souvanhthong
B, Wang H, Zheng H, Wang X and Huo M 2013 Appl.
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13. Abbott A P, Capper G, Davies D L, Raymond K R and
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Supplementary Information (SI)
All additional information pertaining to characteriza-
tion of the catalyst using elemental analysis (Table S1),
1
IR spectra (Figures S1 and S3), H NMR, 13C MNR
spectra (Figures S2, S4 and S5), and characterization of
the new compounds using elemental analysis (Tables S2
1
and S3), MS (Figure S6 and S9), H NMR, 13C MNR
spectra (Figures S7, S8, S10 and S11) are given in
the supporting information, available at www.ias.ac.in/
chemsci.
14. (a) Satasia P S, Kalaria P N, Avalani J R and Raval D K
2014 Tetrahedron 70 5763; (b) Satasia S P, Kalaria P N
and Raval D K 2014 J. Mol. Catal. A: Chem. 391 41
15. Zhu A L, Li Q Q, Li L J and Wang J J 2013 Catal. Lett.
143 463
16. Fariba K and Hossein T 2015 Catal. Lett. 145 1062
17. Disale S T, Kale S R, Kahandal S S, Srinivasan T G and
Jayaram R V 2012 Tetrahedron Lett. 53 2277
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Lett. 116 76; (b) Fang D, Fei Z and Liu Z 2009 Catal.
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Acknowledgements
We express our sincere thanks to the National Natu-
ral Science Foundation of China (21506115) and Nat-
ural Science Foundation of Jiangsu Province (CN)
(BK20141257) for financial assistance.
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