Diethyldisulfoammonium chlorometallates as heterogeneous Br?nsted–Lewis acidic catalysts for one-pot synthesis of 14-aryl-7-(N-phenyl)-14H-dibenzo[a,j]acridines

Article abstract of DOI:10.1002/aoc.3900

A new series of Br?nsted–Lewis acidic diethyldisulfoammonium chlorometallates, [DEDSA][FeCl₄] and [DEDSA]₂[Zn₂Cl₆], were synthesized as solid materials from the reaction of [(Et)₂N(SO₃H)

Full text of DOI:10.1002/aoc.3900

Received: 16 January 2017
DOI: 10.1002/aoc.3900
Revised: 27 April 2017
Accepted: 28 April 2017
F U L L PA P E R
Diethyldisulfoammonium chlorometallates as heterogeneous
Brønsted–Lewis acidic catalysts for one‐pot synthesis of
14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines
Arup Kumar Dutta | Pinky Gogoi | Ruli Borah
Department of Chemical Sciences, Tezpur
University, Tezpur, Assam 784028, India
A new series of Brønsted–Lewis acidic diethyldisulfoammonium chlorometallates,
[DEDSA][FeCl4] and [DEDSA]2[Zn2Cl6], were synthesized as solid materials from
Correspondence
Ruli Borah, Department of Chemical
the reaction of [(Et)2N(SO3H)2][Cl] ionic liquid with transition metal chlorides
(FeCl3 and ZnCl2) at 80 °C in neat condition for 2 h. The chlorometallates were
fully characterized using various spectroscopic and analytical techniques such as
Fourier transform infrared, UV–visible and Raman spectroscopies, powder X‐ray
diffraction, scanning electron microscopy, energy‐dispersive X‐ray and thermogra-
vimetric analyses, Hammett acidity and elemental analyses. Their catalytic activity
was studied as reusable heterogeneous catalysts for the three‐component synthesis
of novel 14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines under solvent‐free condi-
tions at 100 °C.
Sciences, Tezpur University, Tezpur, Assam
784028, India.
Email: ruli@tezu.ernet.in
Funding information
CSIR‐New Delhi, India, Grant/Award Num-
ber: 02(0067)/12/EMR‐II
KEYWORDS
14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines, diethyldisulfoammonium chlorometallates, heterogeneous
catalysis, multicomponent, recyclable catalyst
1 | INTRODUCTION
individual properties. Gogoi et al. developed ‐SO3H‐function-
alized 1‐methylimidazolium‐based chlorometallates of Fe(III)
Ionic liquids (ILs) incorporated with metal chlorides are
commonly known as chlorometallate ILs.
and Zn(II) as Brønsted–Lewis acidic heterogeneous catalysts
for the preparation of bis(indolyl)methane derivatives under
mild conditions.[9] Saikia et al. also prepared 1,3‐
disulfoimidazolium‐based chlorometallates of Fe(III) and Zn
(II) as bifunctionalized acidic materials for the Mannich‐type
reaction at ambient temperature in solution.[8] These
chlorometallates bearing ‐SO3H group provide higher thermal
and water stabilities as compared to their parent ILs. In the
work reported herein, we aimed to synthesize bifunctionalized
diethyldisulfoammonium chlorometallates, namely [(Et)2N
Chloroaluminates(III) were the first example of such type
of Lewis acidic ILs that received growing attention in
the field of catalysis.[1,2] However, their applications were
limited due to their hygroscopic nature. The anionic com-
position determines the properties of chlorometallates which
again depend on the types of metal chloride and the ratios of
metal chloride to parent organic chloride.[3–5] The various
developments of such ionic salts over the last two decades
have recognized these chlorometallates/halometallates as
functional materials with unique and useful properties includ-
ing photophysical, magnetic, catalytic and semiconducting
properties[6–8] among others. Some of them can be developed
as air‐ and water‐stable ionic salts by varying the type of cat-
ionic and anionic compositions and also the concentration of
metal halides that directly relates to characteristic and
(SO3H)2]n[X], where n = 1 and 2 for X = FeCl4− (IL‐2) and
2−
Zn2Cl6
(IL‐3),
from
the
reaction
of
diethyldisulfoammonium chloride [(Et)2N(SO3H)2][Cl] (IL‐
1) with the respective transition metal chlorides (FeCl3 and
ZnCl2) at 80 °C under solvent‐free conditions (Scheme 1).
The catalytic performances of these chlorometallates
were examined for the three‐component synthesis of novel
Appl Organometal Chem. 2017;e3900.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3900

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DUTTA ET AL.
SCHEME 1 Preparation of
diethyldisulfoammonium chlorometallates
14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridine derivatives
(1) from the reaction of an equimolar mixture of 2‐naphthol,
N‐phenyl‐2‐naphthylamine and aromatic aldehyde under sol-
vent‐free conditions at 100 °C. The benzoacridine derivatives
have a wide range of pharmacological activities such as anti‐
tumour, antiviral, antimicrobial, antimalarial, analgesic and
anti‐inflammatory activities. They are also used in material
sciences as fluorescent dyes.[10–14] However, limited
approaches have been made to date for the synthesis of
dibenzoacridine derivatives. Dutta et al. in 2003 prepared a
few N‐alkyl derivatives of acridine, benzo[c]acridine and
dibenzo[c,h]acridine in dry tetrahydrofuran at 0 °C through
treatment of these basic units with phenyllithium–
tetramethylethylenediamine and then quenching the reaction
mixture in D2O or alkyl halide.[15] Later on, Benniston and
Rewinska isolated 14‐phenyl‐7‐N‐phenyldibenzo[a,j]acridine
as an unoptimized reaction intermediate in 22% yield by
refluxing an equimolar mixture of 2‐naphthol, N‐phenyl‐2‐
naphthylamine and benzaldehyde in glacial acetic acid.[11]
Tu and co‐workers reported the synthesis of 14‐aryl‐7,14‐
dihydrodibenzo[a,j]acridine derivatives via one‐pot reaction
of 2‐naphthylamine and various aromatic aldehydes under
microwave irradiation in the presence of thiosalicylic acid
catalyst within a short reaction time.[10] Osyanin et al. also
studied the same preparation from the reaction of Betti base
with 2‐naphthylamine in acetic acid for 6 h in argon atmo-
sphere to get 20–50% yield of 14‐aryl‐7,14‐dihydrodibenzo
[a,j]acridines.[16]
spectrophotometer as Hammett plot against 4‐nitroaniline as
indicator. The thermal stability of the three ILs was investi-
gated with a Shimadzu TGA 50. A PerkinElmer 20 analyser
was utilized for elemental analysis of all compounds. Scan-
ning electron microscopy (SEM) images were obtained using
a JEOL JSM‐6390LV SEM, equipped with an energy‐
dispersive X‐ray (EDX) analyser. Powder X‐ray diffraction
(XRD) patterns were obtained with a Rigaku Multiflex
instrument using a nickel‐filtered Cu Kα (0.15418 nm) radi-
ation source and scintillation counter detector. A Horiba
Lab RAMHR spectrometer containing a He–Ne laser was
used to obtain the laser micro‐Raman spectra of the bifunc-
tional catalysts with an excitation wavelength of 514.5 nm.
Inductively coupled plasma optical emission spectrometry
(ICP‐OES) analysis of the chlorometallates was done using
a PerkinElmer Optima 2100DV instrument. Melting points
were recorded with a Buchi‐560 apparatus. The spectral data
of novel dibenzoacridine derivatives are included in the
supporting information.
2.2 | Preparation of Diethyldisulfoammonium
Chlorometallates IL‐2 and IL‐3
The preparation of IL‐2 and IL‐3 involved two‐step reactions.
The initial IL diethyldisulfoammonium chloride, [DEDSA]
[Cl] (IL‐1), was prepared by dropwise addition of ClSO3H
(30 mmol) at 0 °C to a solution of Et2NH (15 mmol) in dry
CH2Cl2 in a two‐necked 100 ml round‐bottomed flask fitted
with a vacuum system through water and alkali trap for
removal of HCl gas. The mixture was stirred continuously
at room temperature for another hour to produce IL‐1 as a
reddish liquid immiscible with CH2Cl2. Then the crude IL
was washed three times with dry CH2Cl2 (3 × 5 ml) and dried
under vacuum to get analytically pure (98%) IL‐1. In the next
step, the transition metal chlorides were added to IL‐1 in their
respective mole fractions (0.5 for both FeCl3 and ZnCl2) and
heated at 80 °C for 2 h under nitrogen atmosphere to afford
the corresponding chlorometallates IL‐2 and IL‐3 in the solid
state in 96–97% yield after washing (3 × 10 ml) with dry
dichloromethane (DCM).
2 | MATERIALS AND METHODS
2.1 | General Remarks
All chemicals were of analytical grade and used without fur-
ther purification. TLC was conducted on glass plates using
Merck silica gel. NMR spectra were obtained with a JEOL
400 MHz spectrometer (δ in ppm) in DMSO‐d6 and CDCl3
solvents. Fourier transform infrared (FT‐IR) spectra were
recorded with a Nicolet Impact‐410 spectrometer. The acidity
of ionic salts was measured using
a
UV 2550

DUTTA ET AL.
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1044–1052 cm−1, respectively. The strong stretching vibra-
tion band at 869–879 cm−1 can be attributed to N‐S bond
which confirms the attachments of ‐SO3H groups with the
ammonium nitrogen. Two small peaks at around 1362–
1385 and 1408–1427 cm−1 can be assigned to C‐H bending
and rocking vibrations of methyl groups. The ‐OH broad
2.3 | General Method for Preparation of 14‐
Aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridine
Derivatives (1)
In a 50 ml round‐bottomed flask, a mixture of 2‐naphthol
(1 mmol), aldehyde (1 mmol) and N‐phenyl‐2‐naphthylamine
(1 mmol) was heated at 100 °C in the presence of 10 mol% of
[DEDSA][FeCl4] or [DEDSA]2[Zn2Cl6] as catalyst under
solvent‐free conditions. The course of the reaction was mon-
itored by TLC using ethyl acetate–hexane (1:3) as solvent
system. To the reaction flask, 3 ml of dry DCM was added
to dissolve the crude organic product after completion of
the reaction. The solution of DCM was filtered for separation
of solid residue of catalyst on the filter paper. Then the cata-
lyst was washed with dry DCM (2 × 3 ml) and dried in a vac-
uum oven at 80 °C for the next cycle of the reaction. The
DCM solution was dried over anhydrous Na2SO4 and then
evaporated in a rotary evaporator to isolate the crude
dibenzoacridine as a solid mixture. The crude product was
again precipitated from absolute ethanol which provided ana-
lytically pure product.
band is observed at 3380–3420 cm−1
.
3.1.2 | NMR analysis
The 1H NMR spectrum of IL‐1 shows one two‐proton singlet
at 11.3 ppm for two ‐SO3H groups. The same spectrum also
indicates the presence of two ethyl groups with a triplet at
1.41 ppm for six ‐Me protons and a multiplet at around
2.82–2.92 ppm for four ‐CH2‐ protons. Similarly, the 13C
NMR spectrum of this IL shows signals of ‐CH3 carbon at
16.7 ppm and ‐CH2‐ carbon at 54 ppm. The low solubility
of the two chlorometallates in DMSO‐d6 restricted their
NMR studies. Both spectra are included in the supporting
information.
3.1.3 | Spectral data of chlorometallates
3 | RESULTS AND DISCUSSION
3.1 | Characterization of IL Materials
[DEDSA][Cl] (IL‐1)
Light reddish liquid. FT‐IR (KBr, cm−1): 3410, 1411, 1370,
1
1147, 1044, 871. H NMR (400 MHz, DMSO‐d6, δ, ppm):
The three ammonium‐based acidic IL systems were charac-
terized using various spectroscopic and analytical techniques
and then subjected to UV–visible acidity study and thermo-
gravimetric analysis (TGA).
1.41 (t, 6H, J = 7.32 Hz), 2.82–2.92 (m, 4H), 11.30 (s,
2H). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 16.7, 54.0.
CHN analysis: calculated for C4H12ClNO6S2 (%): C, 17.81;
H, 4.48; N, 5.19; found (%): C. 17.96; H, 4.62; N, 5.33.
3.1.1 | FT‐IR analysis
[DEDSA][FeCl4] (IL‐2)
Light yellow solid; 97% yield; m.p. 117 °C. FT‐IR (KBr,
cm−1): 3397, 1427, 1385, 1161, 1049, 869. CHN analysis:
calculated for C4H12Cl4FeNO6S2 (%): C, 5.95; H, 2.00; N,
3.47; found (%): C, 5.91; H, 2.06; N, 3.52.
The FT‐IR spectra of the three IL systems displayed charac-
teristic bands of ‐SO3H group as shown in Figure 1. For
example, the strong symmetric and antisymmetric stretching
vibrations of S‐O bond are observed at 1147–1166 and
[DEDSA]2[Zn2Cl6] (IL‐3)
Off‐white solid; 96% yield; m.p. 122 °C. FT‐IR (KBr, cm−1):
3380, 1408, 1362, 1166, 1052, 879. CHN analysis: calcu-
lated for C8H24Cl6Zn2N2O12S4 (%): C, 6.36; H, 2.13; N,
3.71; found (%): C. 6.44; H, 2.22; N, 3.78.
3.1.4 | Surface morphology
SEM images identify unique types of surface morphology for
the two chlorometallates as shown in Figure 2. The image of
the Fe salt has a distribution of some rod‐like structures with
non‐uniform aggregation of small or medium size particles.
The surface of the Zn salt appears as a highly viscous mate-
rial distributed as plain surfaces with various size holes with-
out any aggregations.
FIGURE 1 FT‐IR spectra of disulfonic ammonium IL systems

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DUTTA ET AL.
FIGURE 3 EDX analysis of (a) [DEDSA][FeCl4] and (b) [DEDSA]2
[Zn2Cl6]
FIGURE 2 SEM images of (a) [DEDSA][FeCl4] and (b) [DEDSA]2
[Zn2Cl6]
the chlorometallate.[17,18] Similarly the spectrum of the Zn
2−
3.1.5 | EDX analysis
salt exhibits characteristic peaks of dimeric Zn2Cl6 anion
at 257 and 315 cm−1 in agreement with literature
values.[19,20]
EDX analysis confirms the presence of corresponding con-
stituent elements of the chlorometallates on their surfaces,
as shown in Figure 3.
3.1.6 | Powder XRD analysis
Powder XRD patterns exhibit several peaks with sharp inten-
sity for the chlorometallate ILs [DEDSA][FeCl4] and
[DEDSA]2[Zn2Cl6] as shown in Figure 4. The peaks at 2θ
= 15.1°, 33.0°, 33.5° and 42.5° for the Fe salt match well
the planes (0,0,12), (1,1,‐12), (0,0,26) and (0,0,‐24) of
JCPDS‐770999. Likewise, for the Zn salt, the observed 2θ
values at 16.2°, 25.3°, 29.2° and 48.1° can be assigned to
the planes (0,0,2), (1,0,1), (1,0,2) and (1,1,4) from literature
data (JCPDS‐704517). All these data confirm the existence
of metal chlorides in the ionic solid chlorometallates.
3.1.7 | Raman analysis
In the Raman spectrum of [DEDSA][FeCl4] (Figure 5), a
FIGURE
[DEDSA]2[Zn2Cl6]
4
Powder XRD patterns of [DEDSA][FeCl4] and
sharp peak at 332 cm−1 confirms the presence of FeCl4 in
−

DUTTA ET AL.
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TABLE 1 Values of Hammett function for the three ILs
Entry
IL
Amax [I] (%) [IH] (%)
H°
1
2
3
4
Blank
2.63
1.00
0.86
0.74
100.0
38.02
32.70
28.14
0
—
[DEDSA]Cl
[DEDSA]2[Zn2Cl6]
[DEDSA][FeCl4]
61.98
67.30
71.86
0.78
0.68
0.58
H° ¼ pKðIÞaq þ log½Iꢀ=½IHꢀþ
(1)
where pK(I)aq is the pKa value of the basic indicator in aque-
ous solution. From this experiment the Brønsted acidity of
the ILs decrease in the order [DEDSA][FeCl4] > [DEDSA]2
FIGURE 5 Raman spectra of [DEDSA][FeCl4] and [DEDSA]2
[Zn2Cl6]
3.1.8 | Hammett plot for acidity study
The Brønsted acidity of the two chlorometallates and parent
IL was determined from the Hammett plots (Figure 6)
obtained using a UV–visible spectrophotometer with 4‐
nitroaniline as indicator.[21] A typical procedure involved
the equimolar mixing of 4‐nitroaniline (pKa = 0.99) and IL
in ethanol. The relative acidity of the ILs can be obtained
by determining the values of H° (Table 1).using equation 1.
The absorbance of the basic indicator [I] was determined in
IL solution which decreases with increasing acidity of IL.
The protonated form [HI]+ of the indicator never appeared
because of low molar absorptivity. The Hammett function
H° for each IL was calculated using equation 1 by measuring
the absorption differences [I]/[IH]+:
FIGURE 7 TGA curves of three diethyldisulfoammonium‐based
ionic salts
FIGURE 6 Hammett plots of three diethyldisulfoammonium‐based
FIGURE 8 Electronic spectra of chlorometallates
ionic salts

6 of 9
DUTTA ET AL.
TABLE 2 ICP analyses for metal content of the disulfoammonium chlorometallates
Amount of metal (mg l−1
)
Mol. weight
Atomic weight of
Entry
Sample
(g mol−1
403.88
)
metal (g mol−1
55.85
)
Exp.
1.38
1.73
Calcd
1.43
Spent catalyst (after sixth cycle)
1
2
[DEDSA][FeCl4]
[DEDSA]2[Zn2Cl6]
1.01
1.17
755.94
130.76
1.76
TABLE 3 Optimization of reaction conditions
Entry
Catalyst
Catalyst amount (mol%)
Temp. (°C)
110
Time (min)
Yield of 1a (%)a
1
2
[DEDSA][FeCl4]
[DEDSA][FeCl4]
[DEDSA][FeCl4]
[DEDSA][FeCl4]
[DEDSA][FeCl4]
[DEDSA]2[Zn2Cl6]
[DEDSA]2[Zn2Cl6]
[DEDSA]2[Zn2Cl6]
[DEDSA]2[Zn2Cl6]
[DEDSA]2[Zn2Cl6]
15
15
15
10
8
45
45
50
45
55
50
50
60
50
65
84
84
81
84
77
81
81
75
81
70
100
3
90
4
100
5
100
6
15
15
15
10
8
110
7
100
8
90
9
100
10
100
aIsolated yield.
TABLE 4 Synthesis of acridine derivatives 1 using IL‐2 and IL‐3 as catalystsa
[DEDSA][FeCl4]
[DEDSA]2[Zn2Cl6]
Entry
R
Time (min)
Yield (%)b
84 (1a)
83 (1b)
81 (1c)
81 (1d)
80 (1e)
81 (1f)
Time (min)
Yield (%)b
81 (1a)
81 (1b)
77 (1c)
78 (1d)
78 (1e)
80 (1f)
1
2
3
4
5
6
7
8
C6H5
45
45
50
50
55
50
60
50
50
50
55
60
60
55
60
50
p‐NO2C6H4
p‐ClC6H4
p‐CH3C6H4
p‐OMeC6H4
2‐Naphthyl
n‐Butanal
44 (2a)
38 (2b)
41 (2a)
35 (2b)
Paraformaldehyde
aReactions were performed at 100 °C under neat condition using IL‐2 and IL‐3.
bIsolated yield.

DUTTA ET AL.
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[Zn2Cl6] > [DEDSA][Cl], which is also supported by H°
values calculated for these ILs (Table 1).
3.1.11 | Elemental analysis
The quantity of C, H and N present in [DEDSA][Cl] and the
two chlorometallate salts was determined using a CHN ele-
mental analyser after heating the samples in a vacuum oven
at 80 °C for 1 h, the data for which are included in Section
3.1.3. The metal contents in the two diethyldisulfoammonium
transition metal chlorides were measured using ICP elemen-
tal analysis with 10 ppm solution of each solid ionic salt in
aqua regia. The results as presented in Table 2 are very close
to the calculated values which confirms the actual combina-
tion of metal chlorides with [DEDSA][Cl] for the formation
of ionic salts IL‐2 and IL‐3.
3.1.9 | Thermogravimetric analysis
TGA was used to determine the thermal stability of the
chlorometallates as well as the parent IL as shown in Figure 7.
The TGA curve of [DEDSA][Cl] shows an approximately
20% weight loss for elimination of adsorbed moisture around
100 °C which is reduced to 5–8% for the two
chlorometallates and thus represents the less hygroscopic
nature of the Fe‐ and Zn‐containing ionic salts. For the Zn
salt, a weight loss of around 20% is observed in the tempera-
ture range 140–300 °C which can be attributed to elimination
of ‐SO3H groups. Similarly the second decomposition of the
Fe salt starts at around 300 °C which indicates its higher ther-
mal stability than both [DEDSA][Cl] and [DEDSA]2
[Zn2Cl6].
3.1.12 | Leaching test
The possibility of leaching [DEDSA][FeCl4] and [DEDSA]2
[Zn2Cl6] was studied by stirring 100 mg of chlorometallate
salts in 5 ml of four different solvents, namely EtOH,
CH3CN, DCM and water at room temperature for 3 h. The
pH of the filtrates was found as neutral, except that for water.
The pH of the water filtrate was observed as 5, and thus indi-
cated slight solubility of ionic salts in water within the stir-
ring period. The TGA profiles of these chlorometallates
also show 5–8% of weight loss for physisorbed water below
100 °C (Figure 7). The above studies were also performed
in ethanol and DCM for 1 h without change of the pH value
of 7 for each solvent. However, the catalytic recycling stud-
ies showed lowering of catalytic activities after the third
run by taking 10–15 min additional time to give better
results up to the sixth cycle. This can be attributed to the
breakup of some chlorometallate salts in the presence of
moisture because of repeated washing and reactivation in
atmospheric conditions under thermal treatment up to the
sixth cycle.
3.1.10 | Electronic spectra
Solid‐state UV spectral analysis was employed in support to
determine the composition of anionic species of the two
chlorometallates IL‐2 and IL‐3 as shown in Figure 8. It is
observed that for the Fe salt the transition for ligand‐to‐metal
charge transfer in the range 270–380 nm is merged with a
broad peak around 250–450 nm. There is also another weak
d–d transition at 567 nm for FeCl4 anion.[22,23] Similarly
−
the two absorption peaks at around 226 and 340 nm for the
Zn salt can be assigned as inter‐ligand charge transfer transi-
−
tions of two tetrahedral ZnCl4 which are present in the
Zn2Cl62− anion via two bridging Cl ligands.[24] The determi-
nation of anionic component of the chlorometallate ILs
through solid‐state UV spectral analysis provides good sup-
port to the Raman study.
SCHEME 2 Plausible mechanism of
synthesis of dibenzoacridines

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DUTTA ET AL.
bonding with acidic IL followed by nucleophilic attack of 2‐
naphthol and then subsequent steps according to Scheme 2.
3.2 | Catalytic Activity
3.2.1 | Optimization of reaction conditions
The catalytic activity of [DEDSA][FeCl4] and [DEDSA]2
[Zn2Cl6] chlorometallates was explored for the three‐compo-
nent synthesis of derivatives 1 according to the reaction
scheme included in Tables 3 and 4 starting from a mixture
of 2‐naphthol, aromatic aldehyde and N‐2‐naphthylamine
under solvent‐free conditions.
3.2.3 | Reusability of catalysts
The reusability of the two heterogeneous catalysts was exam-
ined for the model reaction at 5 mmol scale under the opti-
mized conditions in solvent‐free medium up to six cycles.
In order to optimize the reaction conditions, the reaction of
2‐naphthol, benzaldehyde and N‐phenyl‐2‐naphthylaminewas
investigated with 15 mol% of [DEDSA][FeCl4] and [DEDSA]
2[Zn2Cl6] salts at three different temperatures (90, 100 and 110
°C) under solvent‐free conditions for 45–60 min reaction time
(Table 3, entries 1–3 and 6–8). Of these three temperatures, we
obtained the best results at 100 °C as 81–84% of product (1a)
was formed within 45–50 min (Table 3, entries 2 and 7) while
at 90 °C there was a small decrease in reaction rate (Table 3,
entries 3 and 8). The model reaction produced aryldi(2‐
hydroxy‐1‐naphthyl)methane as single product at room tem-
perature in ethanol for 2 h where we collected N‐phenyl‐2‐
naphthylamine as unreacted substrate. The amount of both cat-
alysts was optimized as 10 mol% after investigating the model
reaction with 8 and 10 mol% at 100 °C without any solvent
(Table 3, entries 4, 5, 9 and 10).
3.2.2 | Substrate scope and plausible
mechanism
From the results discussed above, 10 mol% of
chlorometallate salt at 100 °C were considered as the opti-
mized conditions for generation of complex molecules of
dibenzoacridine derivatives through variation of substituted
aromatic aldehydes and also aliphatic aldehydes. These
results are summarized in Table 4. Aromatic aldehydes bear-
ing electron‐donating or electron‐withdrawing group pro-
duced very good amounts of dibenzoacridine in reasonable
reaction time using the two catalysts without any side prod-
ucts (Table 4, entries 1–6). The overall catalytic activities of
[DEDSA]2[Zn2Cl6] and [DEDSA][FeCl4] salts were
observed to be equivalent for the three‐component one‐pot
synthesis of derivatives 1 under optimized conditions. The
reactions of aliphatic aldehydes, namely n‐butanal and para-
formaldehyde, generated 14‐alkyl‐14H‐dibenzo[a,j]xan-
thenes (2a, 2b) as products of incomplete reactions without
formation of any dibenzoacridine derivatives (Table 4, entries
7 and 8). These types of dibenzoxanthene derivatives can be
expected from favourable parallel reactions of 2‐naphthol and
aliphatic aldehydes in the presence of acidic chlorometallates
under solvent‐free conditions at 100 °C.[25]
FIGURE 9 (a) Reusability of chlorometallate catalysts. (b) Powder
XRD characterization of reused catalysts after sixth cycle. (c) FT‐IR
analysis of reused catalysts after sixth cycle
The plausible mechanism of dibenzoacridine synthesis
can be explained via activation of aldehyde through hydrogen

DUTTA ET AL.
9 of 9
[7] J. Estager, J. D. Holbrey, M. Swadźba‐Kwaśny, Chem. Soc. Rev.
2014, 43, 847.
After each run, the catalyst was recovered from the reaction
mixture as solid residue by simple filtration using DCM.
Then it was dried in a vacuum oven at 80 °C and reused for
the next run. These catalysts lost their activities slowly after
the third cycle as reaction time was increased to produce a
good amount of dibenzoacridine (1a) as shown in Figure 9
(a). These changes were evidenced from powder XRD analy-
sis (Figure 9b) and ICP‐OES determination of metal contents
for the reused catalysts after the sixth run (Table 2). The FT‐
IR spectra of used Zn and Fe catalysts (Figure 9c) also
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revealed one additional peak each at 1621 and 1629 cm−1
,
357.
respectively, ascribed to bending vibration of adsorbed water
with slight change in the position of peaks in the fingerprint
region as compared to the FT‐IR spectra of fresh catalysts
(Figure 1).[26]
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4 | CONCLUSIONS
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In summary, we have developed two ‐SO3H group‐
functionalized diethyldisulfoammonium chlorometallate ILs,
IL‐2 and IL‐3, as solid acidic materials. Their compositions
and properties were characterized using various spectro-
scopic and analytical techniques such as FT‐IR, UV–visible
and Raman spectroscopies, powder XRD, SEM‐EDX, ICP‐
OES, TGA and CHN analysis. The acidity and thermal stabil-
ity of [DEDSA][FeCl4] and [DEDSA]2[Zn2Cl6] salts also
supported their uses as efficient heterogeneous acidic cata-
lysts for the three‐component synthesis of 14‐aryl‐7‐(N‐phe-
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nyl)‐14H‐dibenzo[a,j]acridine
derivatives
for
six
consecutive cycles under optimized reaction conditions.
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ACKNOWLEDGEMENTS
Lingaiah, Catal. Commun. 2008, 9, 1575.
The authors are grateful to the Sophisticated Analytical Instru-
mentation Centre, Tezpur University, for analysis of various
samples for this work, and also to CSIR‐New Delhi, India
for granting research project no. 02(0067)/12/EMR‐II to R.B.
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SUPPORTING INFORMATION
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How to cite this article: Dutta AK, Gogoi P, Borah
R. Diethyldisulfoammonium chlorometallates as
heterogeneous Brønsted–Lewis acidic catalysts for
one‐pot synthesis of 14‐aryl‐7‐(N‐phenyl)‐14H‐
dibenzo[a,j]acridines. Appl Organometal Chem. 2017;
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