Synthesis of symmetric triarylmethane derivatives catalyzed by AIL ionic liquid

Article abstract of DOI:10.1007/s00706-017-2053-2

Abstract: An efficient, eco-friendly ionic liquid was described for the synthesis of symmetric triarylmethane derivatives via Baeyer condensation of N,N-dimethylaniline with different active aromatic aldehyde compounds using amide ionic liquid as a catalyst. The syntheses were achieved for the first time using amide ionic liquid as a catalyst eliminating the need for a volatile organic solvent. The advantages of this ionic liquid are low cost and operational simplicity.

Full text of DOI:10.1007/s00706-017-2053-2

Monatsh Chem
DOI 10.1007/s00706-017-2053-2
ORIGINAL PAPER
Synthesis of symmetric triarylmethane derivatives catalyzed
by AIL ionic liquid
Li Q. Kang1 Han Gao1 Yue Q. Cai2
•
•
Received: 9 December 2016 / Accepted: 4 September 2017
Ó Springer-Verlag GmbH Austria 2017
Abstract An efficient, eco-friendly ionic liquid was
described for the synthesis of symmetric triarylmethane
derivatives via Baeyer condensation of N,N-dimethylani-
line with different active aromatic aldehyde compounds
using amide ionic liquid as a catalyst. The syntheses were
achieved for the first time using amide ionic liquid as a
catalyst eliminating the need for a volatile organic solvent.
The advantages of this ionic liquid are low cost and
operational simplicity.
Introduction
Triphenylmethane (TRAMs) is a very important class of
organic compound with a wide range of applications. Tri-
arylmethanes and their analogues, which are important
leucobases [1], are an important class of synthetic dyes
used to color silk, wool, jute, leather, cotton, and paper.
Several catalysts have been reported for the synthesis of
triarylmethane derivatives, which include such strong
protic acids as p-toluenesulfonic acid [2, 3], sulfuric acid
[4], or some Lewis acids such as FeCl3 [5], TiCl4 [6], or
ZrOCl2 [7], NbCl5 [8], SbCl3 [9], or polymer-supported
sulfonic acid [10], perfluorinated sulfonic acid resin [11], I2
[12], cerium(IV) ammonium nitrate [13], or montmoril-
lonite [14]. These catalysts have their own advantages and
drawbacks. The main drawbacks of these catalysts were
that in addition to being nonrecoverable, corrosive and
requiring tedious workup for the isolation of the products.
Recently, Yb(OTf)3 [15] and transition metal-catalyzed
[16–18] routes have emerged as an alternative method to
provide structurally diverse triarylmethanes. One kind of
amine ionic liquid N-methyl-2-pyrrolidonium methyl sul-
fonate had already been used for esterification [19].
Motivated by these literature voids, we broadened the
scope of amine ionic liquid and used them for condensa-
tion. During our work, we were surprised to find that the
amide ionic liquid derived from N,N-dimethylformamide
can be used as an excellent catalyst for the condensation of
N,N-dimethylaniline with various aromatic aldehydes. It
will be shown that shorter reaction time and high yield are
possible using N,N-dimethylformamide hydrogen sulfate
ionic liquid (AIL) as an alternative, environmentally
benign catalyst (Scheme 1).
Graphical abstract
Keywords Triarylmethanes Á Condensation Á
Amide ionic liquid
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-017-2053-2) contains supplementary
material, which is available to authorized users.
& Li Q. Kang
klq@sit.edu.cn
1
School of Chemical and Environmental Engineering,
Shanghai Institute of Technology, 100 Haiquan Road,
Shanghai 201418, People’s Republic of China
2
School of Chemistry and Molecular Engineering, East China
University of Science and Technology, Shanghai 200237,
China
123

L. Q. Kang et al.
Scheme 1
R = C6H5, 2-Cl-C6H4, 3-Br-C6H4, 4-CH3-C6H4, 4-CH3O-C6H4, 4-(CH3)2N-C6H4,
4-Cl-C6H4, 2,4-Cl2-C6H3, α-naphthyl
amount of catalyst decreased the yield. Neither higher
Results and discussion
temperature (140 °C) nor lower temperature (50 °C)
improved the yield of reaction (Table 1, entries 7 and 10).
From Table 1 it is evident that AIL was the most efficient
catalyst. The optimized condition for this reaction was
chosen as use of 10 mol% catalyst (AIL) at 120 °C for 4 h
(Table 1, entry 4) which provided 85% yield. In order to
state high reaction rates with the catalyst AIL and judge
which part of the ionic liquid is responsible for the activity,
twelve parallel reactions were chosen by using benzalde-
hyde (2 mmol), N,N-dimethylaniline (5.0 mmol) in the
presence of 10 mol% DMF, H2SO4, and N,N-dimethyl-
formamide hydrogen sulfate ionic liquid at 120 °C in
different reaction time, the results are shown in Fig. 1. The
reaction was slow catalyzed by DMF or H2SO4. After 4 h
the isolated yield of triphenylmethane was only 10 and
50%, respectively. The reaction was efficiently catalyzed
by N,N-dimethylformamide hydrogen sulfate ionic liquid.
To find out a suitable catalyst, a model reaction was chosen
by using benzaldehyde (2 mmol), N,N-dimethylaniline
(5.0 mmol) in the presence of different ILs and the results
are summarized in Table 1.
It is clear from Table 1 that the use of higher quantity of
catalyst did not improve the yield, but the use of lower
Table 1 Effect of catalysts on model reaction
Entry
1
Catalyst
Mol% Temp /°C Yield /%
10
10
10
10
15
5
120
120
120
120
120
120
140
100
80
65
73
75
85
85
76
75
78
67
60
2
3
4
100
5
AIL
80
6
60
7
10
10
10
10
H2SO
4
40
20
8
9
DMF
10
50
0
0
1
2
3
4
aReaction conditions: benzaldehyde (2 mmol), N,N-dimethylaniline
(5.0 mmol), and in neat conditions for 4 h
Reaction time / h
bIsolated yield
Fig. 1 Yield as a function of reaction time
123

Synthesis of symmetric triarylmethane derivatives catalyzed by AIL ionic liquid
It shows the high reaction rate catalyzed by AIL is the
interaction of anionic and cationic of ionic liquid.
Scheme 2
Various aromatic aldehydes (containing both electron-
withdrawing and electron-donating groups) were converted
to their corresponding TRAMs 3 in good to excellent yields
with AIL. The aromatic aldehyde with electron-with-
drawing groups showed higher reactivity than the electron-
donating group. The aromatic substrate with electron-
withdrawing groups such as chloro (Table 2, entry 2),
bromo (Table 2, entry 3) and 2,4-dichloro (Table 2, entry
8) reacted quickly, whereas those with electron-donating
groups such as methyl (Table 2, entry 4), methoxy
(Table 2, entry 5), and N,N-dimethylamino (Table 2, entry
6) reacted slowly because of the decrease in electrophilicity
of the aldehydic carbonyl carbon. To further demonstrate
the scope of the reaction catalyzed by AIL, indole was
reacted with aldehydes (Scheme 2). Three kinds of tri-
arylmethanes were synthesized under the optimal
conditions (Table 2, entries 10–12). Continuing these
efforts, we designed a simple plan to get asymmetrically
substituted triarylmethanes employing N,N-dimethylani-
line, indole, and benzaldehyde under the optimized
condition (Scheme 3). It was observed that as expected a
mixture of triarylmethanes containing asymmetrically
R = C6H5, 4-HO-C6H4, α-furyl
extension of the reaction time to 1 day led to a very
complex mixture with only traces of the asymmetrically
substituted triarylmethane.
We propose the following mechanism for the formation
of TRAMs (Scheme 4). The role of the AIL is to protonate
the aldehydic carbonyl carbon and thereby increase the
electrophilicity of this functional group followed by
nucleophilic attack by N,N-dialkylaniline.
We investigated the thermostability of AIL via ther-
mogravimetric
analysis
(TGA)
measurement.
Thermodynamic stability of AIL is in N2 performed at a
scan rate of 100 cm3/min. TGA curve measured for the
catalyst of AIL revealed a two-step weight loss process
with a thermal decomposition temperature (T) in 0–400 °C
range (Fig. 2). As shown in Fig. 2, a sharp mass loss below
100 °C suggests loss of sorbed water. A mass loss begins at
250 °C which is attributed to the dehydration of AIL.
Therefore, AIL retained a high thermostability before
250 °C. This provides the basis for our later catalytic
experiments.
substituted
triarylmethane
(9%),
4,40-(phenyl-
methylene)bis(N,N-dimethylaniline) (26%), and 3,30-
(phenylmethylene)bis(1H-indole) (45%) was formed. Ele-
vated temperature or lower temperature inclined toward the
formation of mixture and hence the sole asymmetrically
substituted triarylmethane could not be obtained. Further
Table 2 Formation of TRAMs using AIL ionic liquid as catalyst
Entry
Producta
R
t/h
Yieldb/%
M.p./°C
Found
Reported
1
3a
3b
3c
3d
3e
3f
C6H5
4
85
83
87
79
79
78
81
76
75
82
79
78
95.1–95.4
93–94 [8]
2
2-Cl-C6H4
3-Br-C6H4
4-CH3-C6H4
4-CH3O-C6H4
4-(CH3)2N-C6H4
4-Cl-C6H4
2,4-Cl2-C6H3
a-Naphthyl
C6H5
3.5
3.5
3.0
4.5
4.5
4.5
3.5
5
143.7–144.6
111.1–111.5
102.1–102.8
100.2–100.7
147.3–147.6
97.8–98.2
143–144 [8]
111–112 [20]
102–103 [21]
100–102 [7]
167–168 [20]
98–100 [8]
104–105 [22]
170.3 [23]
3
4
5
6
7
3g
3h
3i
8
103.8–104.2
170.1–170.5
148.8–148.9
124.4–125.1
220.3–220.4
9
10
11
12
a
6j
3.5
4.0
4.0
149–150 [24]
125–126 [25]
–
6k
6l
4-HO-C6H4
a-Furyl
Reaction conditions: aldehyde (2.0 mmol), N,N-dimethylaniline (5.0 mmol) or indole (5.0 mmol), AIL (0.2 mmol), 120 °C
Isolated yield
b
123

L. Q. Kang et al.
Scheme 3
Scheme 4
123

Synthesis of symmetric triarylmethane derivatives catalyzed by AIL ionic liquid
Fig. 2 Weight at a function of T for TGA of AIL
Fig. 3 Yield as a function of run no.
Conclusion
layer containing the AIL was subjected to rotary evapora-
tion at 60 °C under reduced pressure to afford the
recovered AIL. Also, the catalyst could be reused easily six
times without apparent loss of activity in terms of yield
(85–83%; Fig. 3).
Over just a few years, there has been remarkable progress
for the synthesis of triarylmethanes. Here we have
demonstrated a facile AIL-catalyzed synthesis of sym-
metric triarylmethane derivatives from readily available
N,N-dimethylaniline or indole with different active aro-
matic aldehyde compounds. Hopefully the work described
here will stimulate further work for the synthesis of
unsymmetrical triarylmethanes.
All compounds were known and their physical data were
compared with those of authentic samples and found to be
identical.
Acknowledgements We are grateful to the Science and Technology
Foundation of Shanghai Institute of Technology for financial support.
Experimental
References
Melting points were measured on a WRS-IB digital melt-
1
ing point instrument. H NMR was recorded on AVANG
1. Li TS, Zhang ZH, Yang F, Fu CG (1997) Synth Commun
27:3823
2. Khosropour AR, Esmaeilpoor K, Moradie A (2006) J Iran Chem
Soc 3:81
3. Kraus GA, Jeon I, Nilsen-Hamilton M, Awad AM, Banerjee J,
Parvin B (2008) Molecules 13:986
500 MHz spectrometer with TMS as an internal standard.
The ionic liquid AIL is synthesized and purified according
to reference [26].
4. Ritchie CD, Sager WF, Lewis ES (1962) J Am Chem Soc
84:2349
5. Wang Z, Sun X, Wu J (2008) Tetrahedron 64:5013
6. Periasamy M, Jayakumar KN, Bharathi P (2000) J Org Chem
65:3548
General procedure for the synthesis
of 3a–3i and 6j–6l
To a mixture of aromatic aldehyde (2.0 mmol) and N,N-
dimethylaniline or indole (5.0 mmol), ionic liquid AIL
(0.2 mmol) was added, and the mixture was heated on an
oil bath at 120 °C with good stirring. After the completion
of the reaction, monitored by thin-layer chromatography
(TLC), the mixture was diluted with 5 cm3 ethyl acetate
and 1 cm3 water. The organic layer was separated, dried
over magnesium sulfate, and concentrated under reduced
pressure. The residue was recrystallized with ethanol and
afforded the corresponding TRAMs 3a–3h and 6j–6l in
good isolated yields. Or the residue was purified by silica
gel column chromatography (200–400 mesh silica gel, 1:8
petroleum ether/ethyl acetate) to afford 3i. The aqueous
7. Sanjeeva RC, Nagaraj A, Srinivas A, Purnachandra RG (2009)
Indian J Chem Sect B 48B:248
8. Hou JT, Gao JW, Zhang ZH (2011) Monatsh Chem 142:495
9. Bardajee GR (2011) Beilstein J Org Chem 7:135
10. An LT, Ding FQ, Zou JP (2008) Dyes Pigment 77:478
11. Prakash SGK, Fogassy G, Olah GA (1983) Nippon Kagaku
Kaishi 4:556
12. Bachhav HM, Takale BS, Telvekar VN (2013) Synth Commun
43:1909
13. Bardajee GR (2009) Int J ChemTech Res 1:452
14. Shanmuga P, Varma L (2001) Indian J Chem Sect B 40B:1258
15. Gomes RFA, Coelho JAS, Frade RFM, Trindade AF, Afonso
CAM (2015) J Org Chem 80:10404
16. Kothandapani J, Ganesan A, Vairaprakash P, Ganesan SS (2015)
Tetrahedron Lett 56:2238
17. Nambo M, Crudden CM (2015) ACS Catal 5:4734
123

L. Q. Kang et al.
18. Rao HSP, Rao AVB (2016) Beilstein J Org Chem 12:496
19. Zhang H, Xu F, Zhou X, Zhang G, Wang C (2007) Green Chem
9:1208
20. An LT, Ding FQ, Zou HP (2008) Dyes Pigment 77:478
21. Khosropour AR (2006) J Iran Chem Soc 3:81
22. Coghlan MJ, Luly JR, Schkeryantz JM, Wang AX (2000)
Preparation of bis(aminophenyl) phenylmethanes and analogs as
glucocorticoid receptor modulators. Patent WO 20000061374,
Feb 10, 2000. Chem Abstr 132:137172
23. Masahiko Y, Kohshin Y, Isao S, Tatsuo S (1989) Nippon Kagaku
Kaishi 7:1099
24. Tayebee R, Nehzat F, Rezaei-Seresht E, Mohammadi FZ, Rafiee
E (2011) J Mol Catal A Chem 351:154
25. Sonar SS, Sadaphal SA, Kategaonkar AH, Pokalwar RU (2009)
Bull Korean Chem Soc 30:825
26. Huang JF, Baker GA, Luo HM, Hong KL, Li QF (2006) Green
Chem 8:599
123