Halogen-free room-temperature bronsted acidic ionic liquid [Hmim]+ HSO4- as a recyclable green "dual reagent" catalysis for the synthesis of triarylmethanes (TRAM s) ;

Article abstract of DOI:10.1080/00397911.2011.560742

The halogen-free Brnsted acidic ionic liquid methylimidazolium hydrogen sulfate ([Hmim]⁺ HSO₄^-) acts as a very efficient catalyst for the one-pot, two-component Baeyer condensation of a variety of aromatic aldehydes with dimethyl or diethyl aniline at room temperature. This green reagent behaves as both catalyst and solvent; that is, it exhibits dual-reagent catalysis. The room-temperature acidic ionic liquid could be recycled several times with almost no loss in the yield of the reaction. This is the first report of the Baeyer synthesis with a halogen-free ionic liquid.

Full text of DOI:10.1080/00397911.2011.560742

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Halogen-Free Room-Temperature
Brønsted Acidic Ionic Liquid [Hmim]+
-
HSO4 as a Recyclable Green “Dual
Reagent” Catalysis for the Synthesis of
Triarylmethanes (TRAMs)
Chhanda Mukhopadhyay a , Arup Datta a & Pradip Kumar Tapaswi a
a Department of Chemistry, University of Calcutta, Kolkata, India
Accepted author version posted online: 27 Dec 2011.Published
online: 14 May 2012.
To cite this article: Chhanda Mukhopadhyay , Arup Datta & Pradip Kumar Tapaswi (2012): Halogen-
Free Room-Temperature Brønsted Acidic Ionic Liquid [Hmim]+ HSO4 - as a Recyclable Green “Dual
Reagent” Catalysis for the Synthesis of Triarylmethanes (TRAMs), Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 42:16, 2453-2463
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Synthetic Communications1, 42: 2453–2463, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.560742
HALOGEN-FREE ROOM-TEMPERATURE BRØNSTED
ACIDIC IONIC LIQUID [HMIM]þ HSO4ꢀ AS A
RECYCLABLE GREEN ‘‘DUAL REAGENT’’ CATALYSIS
FOR THE SYNTHESIS OF TRIARYLMETHANES (TRAMS)
Chhanda Mukhopadhyay, Arup Datta, and
Pradip Kumar Tapaswi
Department of Chemistry, University of Calcutta, Kolkata, India
GRAPHICAL ABSTRACT
Abstract The halogen-free Brønsted acidic ionic liquid methylimidazolium hydrogen sulfate
([Hmim]þ HSO4ꢀ) acts as a very efficient catalyst for the one-pot, two-component Baeyer
condensation of a variety of aromatic aldehydes with dimethyl or diethyl aniline at room
temperature. This ‘‘green’’ reagent behaves as both catalyst and solvent; that is, it exhibits
‘‘dual-reagent catalysis.’’ The room-temperature acidic ionic liquid could be recycled
several times with almost no loss in the yield of the reaction. This is the first report of
the Baeyer synthesis with a halogen-free ionic liquid.
Keywords Acidic ionic liquid ([Hmim]þ HSO4ꢀ); Baeyer condensation; dual reagent;
halogen-free; recyclable; room temperature
INTRODUCTION
The acid-catalyzed Baeyer condensation of aromatic aldehydes with N,N-
dialkyl aniline produces triarylmethanes (TRAMs), which are important
leucobases,[1] redox indicators for the Schoenemann reaction,[2] and intermediates
in the preparation of the triarylmethane dyestuffs.[1] In earlier procedures, this con-
densation was carried out by strong protic acids as hydrochloric acid (HCl),[3] sulfuric
Received November 1, 2010.
Address correspondence to Chhanda Mukhopadhyay, Department of Chemistry, University of
Calcutta, 92 APC Road, Kolkata 700009, India. E-mail: cmukhop@yahoo.co.in
2453

2454
C. MUKHOPADHYAY, A. DATTA, AND P. K. TAPASWI
Scheme 1. Synthesis of 4-N,N-dialkylated TRAMs catalyzed by AIL (I).
acid (H2SO4),[4] p-toluene sulfonic acid,[5a,b] or some Lewis acids[6,7a,b] such as FeCl3,
TiCl4, or ZrOCl2. The main drawbacks of these catalysts were that in addition to
being nonrecoverable, nonrecyclable, and corrosive and requiring tedious workup
for the isolation of the products, they had to be used in very high concentrations,
which entailed removal of large amounts of salt waste during neutralization of the
acid. In addition, montmorillonite clay[1,8] has been utilized for this purpose, though
at high temperature. Recently,[9a-c] use of some heterogeneous catalytic systems to
overcome this disadvantage for the preparation of TRAMs proceed with good to
excellent yields, but the majority of these suffer from at least one of the various
disadvantages such as high pressure, limited applicability,[10] corrosive catalyst, high
cost, instability at high temperature, and moisture-sensitive, nonrecoverable, and
nonrecyclable catalysts.[6,7a,b]
Another approach to an environmentally friendly reaction is to minimize the
use of volatile organic solvents (VOCs) in reactions and their subsequent workup.
Recently, room-temperature ionic liquids (RTILs) have been successfully employed
as ‘‘dual reagents’’[11] for a variety of chemical transformations, offering new and
environmentally benign approaches toward modern synthetic chemistry. RTILs have
interesting advantages such as (a) extremely low vapor pressure (being nonvolatile),
(b) excellent thermal stability, (c) recoverability, (d) recyclability and (e) dissolving
many organic and inorganic substrates.[12] Thus, organic synthesis will be provided
Table 1. Scanning of AILs and optimization of reaction conditions on the
reaction of 4-chlorobenzaldehyde (0.35 g, 2.5 mmol) with N,N-dimethylaniline
(0.65 g, 5.2 mmol) at room temperature
Amount of
AIL, g (mol%)
Acidic ionic
liquid (AIL)
Reaction
time (h)
Isolated
yield (%)
Entry
1
2
0.004 (2)
0.004 (2)
0.008 (4)
0.016 (8)
1.00
I
I
5
9
9
9
9
9
9
9
9
9
9
70
70
95
95
95
75
75
75
80
80
80
3
I
4
I
5
I
6
0.006 (4)
0.008 (5)
1.00
II
II
II
III
III
III
7
8
9
0.008 (4)
0.010 (5)
1.00
10
11

TRAM SYNTHESIS WITH IONIC LIQUID
2455
with better reaction rates and greater yields. One reported procedure[13] is available
in the literature using of acidic ionic liquid for the synthesis of TRAMs, but this
procedure also carries some major drawbacks: (a) use of halogenated ionic liquid
(human carcinogenic), (b) reaction carried out at high temperature, and (c) no vari-
ation of N,N-dialkylanilines. Therefore, the search for a new catalyst for the syn-
thesis of TRAMs is still actively pursued when considering the developing
environmental demands.
Many nonhalogenated, environmentally friendly, room-temperature ionic
liquids (RTILs), 1-butyl-3-methyl-imidazolium methyl sulfate [bmim][MeSO4],[14a]
and N-methyl-2-pyrrolidonium methyl sulfate ([NMP]þCH3SO3ꢀ),[14b] have used
for the synthesis of different reactions. Herein, we have used dual-reagent catalysis
of a halogen-free, room-temperature Brønsted acidic ionic liquid with inorganic
ꢀ
and different organic anions of the types HSO4ꢀ, CH3COO2ꢀ, and CF3COO2 for
conversion of various aromatic aldehydes to the corresponding TRAMs (Scheme 1).
We have also done a comparison study of the acidic ionic liquids (Table 1).
RESULTS AND DISCUSSION
Room-temperature acidic ionic liquids (RTAILs) are a new class of solvents
entirely composed of ions. They are environmentally friendly alternatives to
conventional solvents and have gained much attention. We were specifically inter-
ested in the design and catalytic properties of the ionic liquids because they give us
the ability to manipulate the structure with respect to organic and inorganic anions.
To extend the scope of ionic liquids, three acidic ionic liquids were synthesized by
simple protonation of N-methylimidazole with different protic acids such as concen-
trated H2SO4 (I),[15] CH3COOH (II),[15] and CF3COOH (III)[16] (all shown in Fig. 1
and Scheme 2).
The subsequent optimization experiments for the reaction of 4-chlorobenzalde-
hyde and N,N-dimethyl aniline (Table 1) revealed that 8 mg (4 mmol) of AIL (I) for
9 h (entry 3) was the necessary and ultimate condition to get maximum yield (95%) of
the product. Then we gradually increased the amount of AILs up to 1 g (entries 5, 8,
and 11) at the same time scale (9 h); there was no change in the product yield, and so
AILs were used as a catalyst and solvent (‘‘dual reagent’’) in this reaction. For prep-
aration of AILs in all cases we used strong acid (greater reactivity but toxic in nature
reported in the earlier procedure[4]) to get good yields. After purification, the toxic
nature was removed by the washing it with ether. From Table 1, we can conclude that
Figure 1. Structures of the synthesized (AILs).

2456
C. MUKHOPADHYAY, A. DATTA, AND P. K. TAPASWI
Scheme 2. Preparation of RTAILs.
AIL (I) (Figure 1) derived from a strong acid, sulfuric acid, has much better activity
than the weaker ones derived from acetic acid or trifluoroacetic acid (Scheme 2). The
strength of AIL (III) is greater than AIL (II) because the negative charge density on
the oxygen atom is less, due to delocalization (-I effect of the CF3, and group), and
therefore it cannot properly stabilize the 1-methyl imidazolium cation. Easy accept-
ance of, a proton makes AIL (III) have much greater reactivity than AIL (II), so
the strengths of AILs were AIL (I) > AIL (III) > AIL (II) with respect to the isolated
yield. It is clear from mechanism (Fig. 2) that the anion part from acid has a major
contribution to the maximum yield of the product.
Two-component Baeyer condensation of various aromatic aldehydes (1), N,N-
dimethyl aniline or N,N-diethyl aniline (2), were carried out, and the results are
Figure 2. Plausible mechanism of the formation of TRAMs with AIL (I).

TRAM SYNTHESIS WITH IONIC LIQUID
2457
depicted in Table 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 (I) (Scheme 1). The aromatic substrate with
electron-withdrawing groups such as nitro (Table 2, entries 1, 2, 3, and 20), chloro
(Table 2, entries 4, 5, and 14), and bromo (Table 2, entry 18) reacted quickly, whereas
those with electron-donating groups such as methoxy (Table 2, entries 8, 12, 16, and 17),
hydroxy (Table 2, entry 4), and N,N-dimethyl amino (Table 2, entry 9) reacted slowly
because of the decrease in electrophilicity of the aldehydic carbonyl carbon, and conse-
quently the yield of the products decreased. Benzophenone and ethylformate did not
react with N,N-dialkyl aniline even after carrying out the reaction for 48 hs. This reac-
tion was highly chemoselective because N,N-dialkyl aniline only reacts with the aromatic
aldehyde group, leaving other functional groups on the aromatic ring and aliphatic
chain (keto, ester) intact.
This chemoselectivity is obvious because of the greater electrophilicity of the
aldehyde carbonyl compared to ketone or ester. Here N,N-dialkyl aniline was used
in low acidic medium to maintain the free amine concentration in the reaction
medium, in contrast to strong acid medium,[3–5] thereby increasing the reaction rate
during electrophilic addition. A detailed reaction mechanism[14a] of the formation of
TRAMs is depicted in Fig. 2. The AIL (I) exhibited a dual activation role during the
reaction. The role of the AIL (I) is to protonate the aldehydic carbonyl carbon and
thereby increase the electrophilicity of this functional group followed by nucleophilic
attack by N,N-dialkyl aniline. The negative part of the AIL (I) (HSO4ꢀ) acts as a
strong base to accept proton for rearomatization of N,N-dialkyl aniline. After the
reaction was complete, AILs remains unchanged and could be used again.
Table 2. Synthesis of 4-N,N-disubstituted triarylmethanes with AIL (I) (1g) at room temperature
Entry
Product
R
R1
Time (h)
Isolated yield (%)
References
1
2
3a
3b
3c
3d
3e
3f
2-NO2
3-NO2
4-NO2
CH3
CH3
6
5
96
91
92
90
95
86
83
78
72
97
85
75
90
89
80
90
91
92
90
89
1
1
3
CH3
CH3
5
1
4
2-Cl
4-Cl
7
1
5
CH3
CH3
9
1
6
H
4-CH3
4-OMe
8
1
7
3g
3h
3i
CH3
CH3
14
16
20
15
8
1
8
1
9
4-N, N-(CH3)2
2,5-(OCH3)2
H
CH3
CH3
1
10
11
12
13
14
15
16
17
18
19
20
3j
—
17
18
3
3k
3l
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
CH2-CH3
4-OCH3
4-NO2
4-Cl
16
5.5
9
3m
3n
3o
3p
3q
3r
3s
3t
19
19
—
—
—
—
—
4-OH
12
14
15
10
14
5
2,5-(OCH3)2
3,4-(OCH3)2
4-Br
2-OH-3-OCH3
2,4-(NO2)2

2458
C. MUKHOPADHYAY, A. DATTA, AND P. K. TAPASWI
Table 3. Reaction of 4-chlorobenzaldehyde (2.5 mmol) with
N,N-dimethyl aniline (5.2 mmol) with AIL (I) (1g)
Cycles
Isolated yield (%)
1
2
3
4
5
6
95
95
93
92
92
92
RECYCLING EXPERIMENT
To investigate the possibility of recycling of the Brønsted AIL (I), a recycling
experiment was conducted (Table 3). For each recycling reaction, 4-chlorobenzalde-
hyde (0.35 g, 2.5 mmol) and N,N-dimethyl aniline (0.65 g, 5.2 mmol) [or N,N-diethyl
aniline (0.77 g, 5.2 mmol)] were vigorously stirred at room temperature in the presence
of AIL (I) (1 g) for 9 h. After completion of the reaction, the workup was conducted as
before. On being treated under vacuum at 100 jC for 1 h, the AIL (I) was assessed by
1H NMR spectroscopy, and no traces of H2O and ethyl acetate were detected. This
ionic liquid was charged for another reaction. This procedure was repeated for six
cycles in an exactly similar fashion.
Table 3 shows that the catalytic activity of AIL (I) slightly decreased (92%)
after being used six times. The slight decrease in the yield of the reaction might be
ascribed to the slight deactivation of AIL (I).
CONCLUSION
The present protocol of the utility of dual-reagent catalysis concept for the
bis-arylation of aromatic aldehydes by 4-N,N-dialkylanilines to TRAMs (a) is very
mild, (b) avoids use of any hazardous solvent, (c) is extremely rapid, (d) is highly
efficient and, (e) produces no by-products. Therefore, the use of the acidic ionic
ꢀ
liquid ([Hmim])þHSO4 as both catalyst and solvent is definitely a green approach
to the synthesis of N,N-dialkylated TRAMs.
EXPERIMENTAL
All solvents were distilled before use. All the chemicals were purchased from
Aldrich Chemical Company and Spectrochem, Pvt. Ltd. (Mumbai, India). Silica gel
G with binder from Spectrochem, Pvt. Ltd., Mumbai, India was used for thin-layer
chromatography (TLC). 1H and 13C NMR spectra were obtained on a Bruker
300-MHz instrument at 300 and 75 MHz respectively. CDCl3 was purchased from
Aldrich Chemical Company. Melting points were determined on an electrical melting-
point apparatus with an open capillary and are uncorrected. Infrared (IR) spectra were
recorded on a Perkin-Elmer Spectrophotometer RX=Feourier transfrom (FT) IR sys-
tem. The CHN analyses were carried out on a 2400 series II CHNS analyzer, Perkin-
Elmer (USA). Mass spectra of the ionic liquids were recorded on a Waters liquid chro-
matogrephy–tandem mass spectrometry (LC-MS-MS: quattro micro mass) instrument.

TRAM SYNTHESIS WITH IONIC LIQUID
2459
Preparation of the Acidic Ionic Liquids
(i) AIL (I) ([Hmim]þ HSO4ꢀ) (methylimidazolium hydrogen sulfate): This ionic
liquid was prepared according to the literature15 procedure. The formation of the
1
acidic ionic liquid AIL (I) was confirmed from H NMR, 13C NMR, and mass
spectra.
1H NMR (300 MHz, DMSO-d6) d: 8.85 (s, 1H, C2-H), 7.54 (s, 1H, C4-H), 7.48
(d, J ¼ 1.2 Hz, 1H, C5-H), 5.03 (brs, 1H, NH), 3.79 (s, 3H, N-CH3). 13C NMR
(75 MHz, DMSO-d6) d: 136.2 (C2), 123.9 (C4=C5), 120.3 (C5=C4), 36.1 (N-CH3);
MS: m=z (%): 164.9 (100%) (M-CH3), 263.0 (64), 264.0 (7), 443.0 (13).
(ii) AIL (II) ([Hmim]þ CH3COOꢀ) (methylimidazolium acetate): This ionic
liquid was prepared according to the literature15 procedure. The formation of the
acidic ionic liquid AIL (II) was confirmed from 1H NMR, 13C NMR, and mass spec-
tra.1H NMR (300 MHz, DMSO-d6) d: 9.35 (s, 1H, NH), 7.62 (s, 1H, C2-H), 7.07 (s,
1H, C4-H=C5-H), 6.89 (s, 1H, C5-H=C4-H), 3.61 (s, 3H, N-CH3), 1.87 (s, 3H, CH3).
13
=
C NMR (75 MHz, DMSO-d6) d: 172.5 (C O), 138.0 (C2), 127.9 (C4=C5), 120.9
(C5=C4), 33.1 (N-CH3). MS: m=z (%): 126.8 (100%) (M-CH3), 153.7 (15), 219.8
(22), 227.9 (36), 256 (86), 258.7 (41), 260.7 (11), 374 (25).
(iii) AIL (III) ([Hmim]þ CF3COOꢀ) (methylimidazolium trifluoroacetate): This
ionic liquid was prepared according to the literature[16] procedure. The formation of
the acidic ionic liquid AIL (III) was confirmed from 1H NMR, 13C NMR, and mass
spectra.1H NMR (300 MHz, DMSO-d6) d: 9.00 (s, 1H, C2-H), 7.61 (s, 1H, C4-H=C5-
H), 7.57 (s, 1H, C5-H=C4-H), 5.36 (s, 1H, NH), 3.82 (s, 3H, N-CH3). 13C NMR
=
(75 MHz, DMSO-d6) d: 159.3 (C O), 136.0 (C2), 120.0 (C4=C5), 118.6 (C5=C4),
35.5 (N-CH3). MS: m=z (%): 112.7 (100%) (M-CF3COOꢀ).
1
1H NMR and 13C NMR data of N-methylimidazole: H NMR (300 MHz,
CDCl3) d: 7.54 (s, 1H, C2-H), 7.06 (s, 1H, C4-H=C5-H), 6.88 (s, 1H, C5-H, C4-H),
3.62 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3) d: 138.1 (C2), 128.6 (C4=C5), 120.6
(C5=C4), 32.8 (N-CH3).
It must be noted that for N-methylimidazole, the C2-H proton comes at d 7.54,
whereas when ionic liquids are formed, the C2-H proton comes at d 8.85 [AIL (I)], 7.62
[AIL (II)], and 9.00 [AIL (III)]. In addition, the N-CH3 proton comes at d 3.62 (for
N-methylimidazole), wherea, in ionic liquids it comes at d 3.79 [AIL (I)], 3.61 [AIL
(II)], and 3.82 [AIL (III)]. This indicates that the AILs are actually formed under this
condition.
Typical Experimental Procedure for the Preparation of TRAMs
A mixture of aromatic aldehyde (0.35 g, 2.5 mmol) and N,N-dialkyl aniline
[0.65 g (0.77 g), 5.2 mmol] was taken in a 25-mL, round-bottomed flask and vigor-
ously stirred for room temperature in the presence of [Hmim]þ HSO4ꢀ(1 g) at the
specified time period (Table 2). After the completion of the reaction, monitored by
thin-layer chromatography (TLC), the mixture was diluted with water (1 mL) and
ethylacetate (5 mL). The organic layer was separated, dried over sodium sulfate,
and concentrated under reduced pressure to afford the corresponding TRAMs in
good isolated yields. The aqueous layer containing the AIL (I), was subjected to
j
rotary evaporation at 100 C under reduced pressure for 1 h to afford the recovered

2460
C. MUKHOPADHYAY, A. DATTA, AND P. K. TAPASWI
AIL (I) which was reused several times. The IR, 1H NMR, 13C NMR, and analytical
data of all unknown compounds are given.
2,5-Dimethoxy-4’,4’’-bis(dimethylamino)-triphenylmethane
(3j). (Table 2, entry 10) Dirty white solid; mp 71 ꢁC (ethyl acetate þ petroleum ether);
1
0
0
00
00
H NMR (300 MHz, CDCl3) d: 6.96 (d, J ¼ 8.4 Hz, 4H, C3 -H, C5 -H, C3 -H, C5 -H),
0
0
00
00
6.77 (d, J ¼ 8.7 Hz, 1H, C3-H = C4-H), 6.69–6.62 (m, 5H, C2 -H, C6 -H, C2 -H, C6 -H,
C4-H=C3-H), 6.53 (d, J ¼ 3.3 Hz, 1H, C6-H), 5.72 (s, 1H, C-H), 3.65, 3.64 (two singlets
merged together, 6H, -2OMe), 2.88 (s, 12H, 2 ꢂ -NMe2); 13C NMR (75 MHz, CDCl3)
0
00
0
00
0
d: 153.4 (C2=C5), 151.6 (C5=C2), 148.8 (C1 , C1 ), 135.6 (C1), 132.6 (C4 , C4 ) 129.8 (C3 ,
0
00
00
0
0
00
00
C5 , C3 , C5 ) 117.3 (C3=C6), 112.5 (C2 , C6 , C2 , C6 ), 111.9 (C6=C3), 110.6 (C4), 56.5
(C2-OMe=C5-OMe), 55.5 (C5-OMe=C2-OMe), 47.7 (C-H), 40.7 (4 ꢂ -CH3); IR (KBr,
cmꢀ1): 2885, 1613, 1519, 1491, 1345, 1227, 1051, and 799. Anal. calcd. for
C25H30N2O2; C, 76.89; H, 7.74; N, 7.17. Found: C, 76.77; H, 7.88; N, 7.32%. MS:
m=z (%): 392.1 (31), 391.1 (M þ 1) (100%), 216.5 (6), 196.0 (88), 188.5 (36).
2,5-Dimethoxy-4’,4’’-bis(diethylamino)-triphenylmethane (3p). (Table 2,
1
Entry 16) Dirty white solid; mp 78 ꢁC (ethyl acetate þpetroleum ether); H NMR
0
0
00
00
(300 MHz, CDCl3) d: 6.93 (d, J ¼ 8.7 Hz, 4H, C3 -H, C5 -H, C3 -H, C5 -H), 6.78
(d, J ¼ 8.7 Hz, 1H, C3-H), 6.67 (dd, J ¼ 9.0 Hz and 3.0 Hz, 1H, C4-H), 6.59–6.56
0
0
00
00
(m, 5H, C2 -H, C6 -H, C2 -H, C6 -H, C6-H), 5.69 (s, 1H, C-H), 3.67, 3.66 (two singlet
merged together, 6H, 2-OMe), 3.29 (q, J ¼ 9.0 Hz, 8H, 4 ꢂ -N-CH2-CH3), 1.12 (t,
J ¼ 9.0 Hz, 12H, 4 ꢂ -N-CH2-CH3); 13C NMR (75 MHz, CDCl3) d: 153.4 (C2=C5),
0
00
0
00
0
0
00
151.7 (C5=C2), 146.1 (C1 , C1 ), 136.0 (C1), 131.5 (C4 , C4 ), 130.0 (C3 , C5 , C3 ,
00
0
0
00
00
C5 ), 117.4 (C3=C6), 112.0 (C2 , C6 , C2 , C6 ), 111.8 (C6=C3), 110.4 (C4), 56.6 (C2-
OMe=C5-OMe), 55.5 (C5-OMe=C2-OMe), 47.5 (C-H), 44.3 (4 ꢂ -N-CH2-), 12.7
(4 ꢂ -N-CH2-CH3); IR (KBr, cmꢀ1): 2968, 1608, 1512, 1357, 1265, 1199, and 795.
Anal. calcd. for C29H38N2O2; C, 77.99; H, 8.58; N, 6.27. Found: C, 77.88; H,
8.73; N, 6.41%.
3,4-Dimethoxy-4’,4’’-bis(diethylamino)-triphenylmethane (3q). (Table 2,
1
Entry 17) Light brown liquid; H NMR (300 MHz, CDCl3) d: 6.95 (d, J ¼ 8.7 Hz,
0
0
00
00
4H, C3 -H, C5 -H, C3 -H, C5 -H), 6.76 (d, J ¼ 8.4 Hz, 1H, C5-H), 6.73 (d, J ¼ 2.1 Hz,
0
0
00
00
Hz, 1H C2-H,), 6.65-6.58 (m, 5H, C6-H, C2 -H, C6 -H, C2 -H, C6 -H), 5.27 (s, 1H,
C-H), 3.84 (s, 3H, C3-OMe=C4-OMe), 3.77 (s, 3H, C4-OMe=C3-OMe), 3.31 (q,
J ¼ 7.2 Hz, 8H, 4 ꢂ -N-CH2-CH3), 1.13 (t, J ¼ 7.2 Hz, 12H, 4ꢂ-N-CH2-CH3); 13C
0
00
NMR (75 MHz, CDCl3) d: 148.6 (C3=C4), 147.1 (C4=C3), 146.1(C1 , C1 ), 138.4
0
00
0
0
00
00
(C1), 132.0 (C4 , C4 ), 130.0 (C3 , C5 , C3 , C5 ), 121.3 (C6), 112.9 (C2=C5), 111.8
0
0
00
00
(C2 , C6 , C2 , C6 ), 110.8 (C5=2), 55.9 (C3-OMe=C4-OMe), 55.8 (C4-OMe=C3-
OMe), 54.5 (C-H), 44.3 (4ꢂ -N-CH2-CH3), 12.6 (4 ꢂ -N-CH2-CH3); IR (neat, cmꢀ1):
2962, 1591, 1512, 1269, 1138, and 1022. Anal. calcd. for C29H38N2O2; C, 77.99;
H, 8.58; N, 6.27. Found: C, 77.86; H, 8.72; N, 6.41%.
4-Bromo-4’,4’’-bis(diethylamino)-triphenylmethane (3r). (Table 2, Entry
18) Light brown liquid; 1H NMR (300 MHz, CDCl3) d: 7.36 (d, J ¼ 8.4 Hz, 2H, C3-H,
0
0
C5-H), 7.02 (d, J ¼ 8.4 Hz, 2H, C2-H, C6-H), 6.91 (d, J ¼ 8.7 Hz, 4H, C3 -H, C5 -H,
00
00
0
0
00
00
C3 -H, C5 -H), 6.58 (d, J ¼ 8.7 Hz, 4H, C2 -H, C6 -H, C2 -H, C6 -H), 5.27 (s, 1H,
13
C-H), 3.31 (q, J ¼ 7.2 Hz, 8H, 4 ꢂ -N-CH2-CH3), 1.13 (t, J ¼ 7.2 Hz, 12H, 4 ꢂ -NCH2-
0
00
0
00
-CH3); C NMR (75 MHz, CDCl3) d: 146.3 (C1 , C1 ), 144.9 (C4 , C4 ), 132.4 (C1),

TRAM SYNTHESIS WITH IONIC LIQUID
2461
0
0
00
00
0
0
131.1 (C3þC5), 131.0 (C2þC6), 130.0 (C3 , C5 , C3 , C5 ), 119.5 (C4), 111.7 (C2 , C6 ,
00
00
C2 , C6 ), 54.4 (C-H), 44.3 (4 ꢂ -N-CH2-CH3), 12.62 (4 ꢂ -N-CH2-CH3); IR (neat,
cmꢀ1): 2970, 1609, 1516, 1360, 1264, 1196, and 1012. Anal. calcd. for C27H33N2Br;
C, 69.67; H, 7.15; N, 6.02. Found: C, 69.57; H, 7.28; N, 6.14%.
2-Hydroxy-3-methoxy-4’,4’’-bis(diethylamino)-triphenylmethane (3s).
1
(Table 2, Entry 19).White solid; mp 142 ꢁC (ethyl acetate þpetroleum ether); H
0
0
00
00
NMR (300 MHz, CDCl3) d: 6.97 (d, J ¼ 8.4 Hz, 4H, C3 -H, C5 -H, C3 -H, C5 -H),
6.74–6.70 (m, 2H, C4-H, C6-H=C5-H, C4-H=C5-H, C6-H), 6.60–6.56 (m, C4-H=C6-
0
0
00
00
H, C5-H=C6-H, C4-H=C5-H, C2 -H, C6 -H, C2 -H, C6 -H), 5.67 (s, 2H, -C-H, OH),
3.84 (s, 3H, C3-OMe), 3.29 (q, J ¼ 7.2 Hz, 8H, 4 ꢂ -CH2-CH3), 1.12 (t, J ¼ 7.2 Hz,
12H, 4 ꢂ -N-CH2-CH3); 13C NMR (75 MHz, CDCl3) d: 146.3 (C3), 146.1 (C2),
0
00
0
00
0
0
00
00
143.2 (C1 , C1 ), 131.7 (C4 , C4 ), 131.1 (C1), 130.0 (C3 , C5 , C3 , C5 ), 122.7 (C5),
0
0
00
00
118.8 (C6), 111.8 (C2 , C6 , C2 , C6 ), 108.4 (C4), 56.0 (C3-OMe), 47.7 (C-H), 44.0
(4 ꢂ -N-CH2-CH3), 12.7 (4 ꢂ N-CH2-CH3); IR (KBr,cmꢀ1) : 2967, 1611, 1516,
1469, 1359, 1265, and 1202, Anal. calcd. for C28H36N2O2; C, 77.74; H, 8.39; N,
6.48. Found: C, 77.62; H, 8.52; N, 6.62%.
2,4-Dinitro-4’,4’’-bis(diethylamino)-triphenylmethane (3t). (Table 2,
1
Entry 20) Sticky brown liquid; H NMR (300 MHz, CDCl3) d: 8.64 (d, J ¼ 2.1 Hz,
1H, C3-H), 8.26 (dd, J ¼ 9 Hz and 2.4 Hz, 1H, C5-H), 7.44 (d, J ¼ 8.7 Hz, 1H, C6-
0
0
00
00
H), 6.86 (d, J ¼ 8.7 Hz, 4H, C3 -H, C5 -H, C3 -H, C5 -H), 6.60 (d, J ¼ 8.7 Hz, 4H,
0
0
00
00
C2 -H, C6 -H, C2 -H, C6 -H), 6.07 (s, 1H, C-H), 3.34 (q, J ¼ 7.8 Hz, 8H, 4 ꢂ N-C-
H2-CH3), 1.14 (t, J ¼ 7.2 Hz, 12H, 4 ꢂ N-CH2-CH3); 13C NMR (75 MHz, CDCl3)
0
00
0
00
0
0
00
00
d: 146.7 (C2 þC4), 133.3 (C1 , C1 ), 132.9 (C4 , C4 ), 130.1 (C3 , C5 , C3 , C5 ),
0
0
00
00
127.7 (C1), 125.9 (C6), 119.8 (C5), 111.8 (C2 , C6 , C2 , C6 ), 110.2 (C3), 49.7 (C-H),
44.3 (4 ꢂ N-CH2-CH3), 12.5 (4 ꢂ N-CH2-CH3); IR (KBr, cmꢀ1): 2971, 1609, 1520,
1347, and 1264, Anal. calcd. for C27H32N4O4; C, 68.05; H, 6.77; N, 11.75. Found:
C, 67.94; H, 6.89; N, 11.89%.
ACKNOWLEDGMENTS
We thank the CAS Instrumentation Facility, University of Calcutta, for spec-
tral data. We also acknowledge a grant received from univercity grants commission
Major Project F. No. 37-398=2009 (SR).
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