Clay supported titanium catalyst for the solvent free synthesis of tetrasubstituted imidazoles and benzimidazoles

Article abstract of DOI:10.1016/j.molcata.2013.04.004

A series of clay supported metal containing catalysts were prepared and their catalytic performance was evaluated in the synthesis of tetrasubstitued imidazoles under solvent free condition. It was found that K10 supported titanium catalyst showed higher activity compared to other catalysts. The catalysts were characterized by FTIR, XRD, TG/DTA, BET surface area and SEM. The general applicability of the method was demonstrated for the synthesis of tetra- substituted imidazoles from aldehydes and amines containing various electron donating and electron withdrawing substituents. The diversity of the catalyst was studied by synthesis of benzimidazoles and quinoxalines. The mechanism of formation of the products is explained in detail. The catalyst was found to be active for three cycles.

Full text of DOI:10.1016/j.molcata.2013.04.004

Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Clay supported titanium catalyst for the solvent free synthesis of tetrasubstituted
imidazoles and benzimidazoles
V. Kannana, K. Sreekumarb,∗
a Department of Chemistry, Government College Kattappana, Idukki District, Kerala 685 508, India
b Department of Applied Chemistry, Cochin University of Science and Technology, Cochin 22, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of clay supported metal containing catalysts were prepared and their catalytic performance was
evaluated in the synthesis of tetrasubstitued imidazoles under solvent free condition. It was found that
K10 supported titanium catalyst showed higher activity compared to other catalysts. The catalysts were
characterized by FTIR, XRD, TG/DTA, BET surface area and SEM. The general applicability of the method
was demonstrated for the synthesis of tetra- substituted imidazoles from aldehydes and amines contain-
ing various electron donating and electron withdrawing substituents. The diversity of the catalyst was
studied by synthesis of benzimidazoles and quinoxalines. The mechanism of formation of the products
is explained in detail. The catalyst was found to be active for three cycles.
Received 2 February 2013
Received in revised form 4 April 2013
Accepted 5 April 2013
Available online xxx
Keywords:
Clay
Solvent free synthesis
Imidazoles
© 2013 Elsevier B.V. All rights reserved.
Benzimidazoles
1. Introduction
free conditions using various heteropoly acid catalysts [17]. In
recent years, considerable interest has been devoted to find a new
Imidazoles are important class of compounds in pharmaceutical
industries [1]. The imidazole pharmacophore is of therapeutic
interest due to its hydrogen bond donor–acceptor capability [2].
Triaryl imidazoles are used as photosensitive material in photogra-
phy [3]. In addition, they are of interest because of their herbicidal
[4], analgesic [5], fungicidal [6], anti-inflammatory [7], anti-allergic
activities [8]. They act as ligands in metallo enzymes and non nat-
ural metal complexes [9]. They are components of a number of
highly significant biomolecules [10]. The imidazole moiety as a
part of the side chain in histidine plays a major role in the biological
functions of proteins and peptides. Imidazoles can be synthesized
using InCl3·3H2O as catalyst [11], hetero-Cope rearrangement with
aldehyde, ammonium acetate and benzil [12], four component con-
densations of aryl glyoxals, primary amines, carboxylic acids and
isocyanides on Wang resin [13] etc. Synthesis of highly substituted
imidazole rings cannot be carried out under neutral conditions
[14]. Use of conventional acids imposes many disadvantages such
as handling, corrosion etc. In the classical approach, for the synthe-
sis of tetrasubstituted imidazoles, cyclo condensations proceeded
with low yields after many hours in refluxing AcOH [15]. Keggin
type heteropoly acids as solid acid catalysts were recently reported
for the synthesis of tetrasubstituted imidazoles [16]. Rafiee et al.
reported the synthesis of tetrasubstituted imidazoles under solvent
methodology for the synthesis of highly substituted imidazoles
under solvent-free conditions [18,19]. The toxicity and volatile
nature of many organic solvents, particularly, chlorinated hydro-
carbons that are widely used in large amounts for organic reactions
have posed a serious threat to the environment [20,21]. Design of
solvent free condition and use of water as solvent are the active
area of research in green chemistry [22,23]. Substituted imidazoles
are also synthesized by using ionic liquids [24,25]. N-heterocyclic
carbenes are generated from substituted imidazoles [26–30].
However search for new reusable catalysts, which are environ-
mentally friendly, is still continuing. Clays are suitable candidates
for this purpose. Due to the presence of layered structure, clays
are capable of accommodating ligands [31], the metal ions present
in the clays can be exchanged with transition metal ions [32].
Clays can be modified with transition metal ions which show Lewis
acidity in the range of H2SO4 and HNO3 and satisfies the above
mentioned conditions. Here, we report K10 supported titanium as
a potential catalyst for the synthesis of tetrasubstituted imidazoles
under solvent free conditions.
2. Experimental
2.1. Materials and catalysts
The commercially available clay montmorillonite K10 was
obtained from Sigma–Aldrich, Bangalore, India. Benzil, amines,
ammonium acetate and solvents were purchased from Merk. Ltd.,
∗
Corresponding author. Tel.: +91 484 2862430/2575804; fax: +91 484 2577595.
E-mail address: ksk@cusat.ac.in (K. Sreekumar).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.04.004

V. Kannan, K. Sreekumar / Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
35
Table 1
India. Surface area and porosity of clay catalysts were measured by
Textural properties of catalysts.
nitrogen adsorption on a Micromeritics Tristar 3100 instrument.
TGA and DTA were carried out using simultaneous TG-DTA thermal
analyzer of Perkin Elmer Diamond model pyris 6 under a flow of dry
Nitrogen. The temperature was raised from room temperature to
1000 ◦C using a linear program at a heating rate of 10 ◦C/min. UV–vis
DRS spectra were obtained with Varian, Cary 5000 spectrometer.
FT-IR spectra were recorded with KBr pellets using a Jasco 4100
spectrophotometer. 1H NMR spectra were recorded on a Bruker
Avance 400 and 300 MHz NMR spectrometer with CDCl3 as the sol-
vent and TMS as the internal standard. Powder X-ray diffraction
(XRD) measurements were performed using a Bruker AXS Com-
pany, D8 ADVANCE diffractometer. Scans were taken with a 2ꢀ
with an increment of 0.05◦ ranging from 10◦ to 80◦ using Cu K˛
radiation source generated at 40 kV and 30 mA. The morphology of
supported catalyst was studied by scanning electron microscopy
(SEM) on a JEOL Model JSM – 6390LV instrument. These analysis
were performed at SAIF, STIC, CUSAT.
Samples
SBET (m2/g)
Pore volume (cm3/g)
K10Ti
KSF Ti
K10Cu
K10Na
K10
185.26
26.79
233.23
182.21
200
0.30
0.059
0.41
–
0.36
0.11
0.0084
KSF
KSFCo
15
72.24
filtered and dried with anhydrous sodium sulphate. The crude
products were recrystallised with ethyl acetate.
3. Results and discussion
Different metal supported catalysts were prepared and char-
actersied. The textural properties of the different catalysts are
presented in Table 1.
The prepared catalysts were screened for the synthesis of
tetrasubstituted imidazole by selecting, benzil (2 mmol), alde-
hyde (2 mmol), amine (2 mmol), ammonium acetate (2 mmol) and
500 mg of the catalyst. The reaction mixture was stirred at 100 ◦C
for 2 h; the crude products were separated by extraction using ethyl
acetate followed by filtration. The K10Ti was selected as the catalyst
of choice because, it gave best results. The results are summarized
in Table 2.
2.2. Preparation of the catalysts
The clay sample was activated overnight at 100 ◦C. 3 g of acti-
vated clay suspended in 50 ml chloroform was stirred at room
temperature under N2 atm for about 30 min. 2 ml of triethyl amine
was added to activate the surface silanol groups and the slurry was
stirred for 30 min. Different weight percentage from 1% to 5% (w/w)
Titanocene dichloride dissolved in CHCl3 was added under stirring.
The slurry was stirred until the color of the suspension was changed
from red to yellow over a period of 3 h. This was washed with CHCl3
(30 ml × 3 times). After washing, the solids recovered were calcined
under dry oxygen at 500 ◦C for 8 h. The catalyst is abbreviated as
K10Ti.
Sodium exchanged clay was prepared by weighing 1.5 g acti-
vated clay, stirred with 0.5 M NaNO3 overnight, washed with water
until the filtrate was free from nitrate ions and dried in an air oven
at 200 ◦C. The Co and Cu exchanged clays were prepared by stirring
3 g each of sodium exchanged clay with 25 ml of 0.5 M solution of
cobalt(III)chloride and Cu(II)chloride for 24 h, filtered and washed
with water until the filtrate was free from chloride ions. The cata-
lyst was dried at 200 ◦C for 2 h. The catalysts were abbreviated as
K10Co, K10Cu and KSFCo, KSFCu respectively.
3.1. Catalyst characterization
The UV-DRS spectra of the parent and modified catalyst showed
a band around 220 nm, 260–270 nm. Spectra of Ti/Si catalysts are
characterized by broad absorption band centered around 220 nm,
∼260–270 nm and above 330 nm, as reported by Zhang et al. [36].
Band at ∼220 nm in Ti/Clay catalyst is associated with isolated Ti
(IV) sites, shoulder at 270 nm is probably due to partially polymer-
ized hexacoordinate Ti species.
The SEM image of the catalyst shows that the crystalline nature
of the clays was maintained and the Ti metal is uniformly dis-
tributed (Fig. 1). The SEM result is supported by XRD results. XRD
pattern of the catalyst (Fig. 2) indicates that the basic clay structure
is maintained after modification. The FT-IR spectra of montmo-
rillonite K10 and titanium incorporated montmorillonite K10 are
shown in Fig. 3. The band around 1010 cm−1 was broadened indi-
cating the successful incorporation of titanium in the clay. The band
2.3. Typical procedure for the synthesis of tetrasubstituted
imidazoles
at 950 cm−1 (Si
O
Ti) was merged with band at 1010 cm−1. Ther-
mal stability of the catalyst was studied by TG/DTA analysis under
nitrogen flow. The weight loss in the region 80–150 ◦C may be
attributed to the loss of adsorbed water in the catalyst system. The
weight loss between 200 ◦C and 300 ◦C may be due to the loss of
hydrated water (Fig. 4).
The decrease in the surface area and pore volume obtained
from BET results (from 200 m2/g to 185.2 m2/g and 0.36 cm3/g to
0.3 cm3/g for the K10Ti sample is ascribed to the incorporation
A mixture of benzil (2 mmol), benzaldehyde (2 mmol), aniline
(2 mmol), ammonium acetate (2 mmol) and 0.250 gm of catalyst
was stirred at 120 ◦C for 2 h, the progress of the reaction was mon-
itored using TLC (Thin Layer Chromatography) using hexane and
ethyl acetate (9:1) as elutents. After the completion of the reac-
tion, the crude product was extracted with ethyl acetate followed
by filtration. The crude products were further purified by Column
Chromatorgraphy using (hexane: ethyl acetate in the ratio 9:1). The
products were identified by comparing the results of FT-IR, NMR
with those of the authentic samples [33–35].
Table 2
Synthesis of tetrasubstituted imidazoles using metal supported catalysts.
Samples
Time (h)
Yield (%)a
2.4. General procedure for the synthesis of substituted
benzimidazoles/quinoxalines
K10Ti
KSFTi
K10Cu
K10
KSF
KSFCo
2
2
2
2
2
2
80
46
61
62
30
34
A mixture of aldehyde/diketone (5 mmol), o-phenylene diamine
(5 mmol), and activated K10Ti clay catalyst (0.25 g) was stirred
at 120 ◦C for 2 h. The progress of the reaction was monitored by
TLC. After the completion of the reaction, the reaction mixture
was washed with water, extracted with dichloromethane (20 ml),
Mole ratio. Aniline:benzaldehyde:benzil: ammonium acetate is 1:1:1:1.2.
Yields refer to isolated crude products.
a

36
V. Kannan, K. Sreekumar / Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
Fig. 1. SEM image of K10Ti.
Fig. 4. TG/DTA of K10Ti.
Fig. 2. XRD pattern (a) K10 and (b) K10Ti.
of titanium in the clay framework. This is also supported by the
relatively low initial adsorption isotherm plot (Fig. 5).
Fig. 5. Adsorption isotherm of K10Ti.
3.2. Pyridine adsorption studies of the catalyst
Adsorption of pyridine on the surface of catalysts is one of the
most frequently used methods for the determination of surface
acidity. The use of IR spectroscopy to detect adsorbed pyridine
enables us to distinguish different acid sites. The presence of acid-
ity (Bronsted and Lewis acidity) was determined for K10Ti using
pyridine adsorption with FT-IR Spectroscopy (Fig. 6). The catalyst
showed Bronsted and Lewis acidity at 1492 cm−1 and 1450 cm−1
,
respectively which was assigned to pyridine molecules interacting
Fig. 3. IR Spectra of (a) K10Ti and (b) K10.
Fig. 6. FT-IR spectra of pyridine adsorbed (a) K10 and (b) K10Ti.

V. Kannan, K. Sreekumar / Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
37
Table 3
Solvent free synthesis of tetrasubstituted imidazoles using K10Ti.
Sl. no.
R1
R2
Time (h)
Yield % a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
C6H5
C6H5
C6H5
C6H5
C6H5CH2
CH3
CH3
4-BrC6H4
C6H5
C2H5
C2H5
C2H5
CH3
C6H5
C6H5CH2
C6H5CH2
2.5
2
2
3
4
2.5
3.5
3
4
2.5
3
78
80
81
84
68
76
74
69
72
74
73
72
78
79
71
Scheme 1. Synthesis of tetrasubstituted imidazoles.
4-ClC6H4
3-NO2C6H4
C6H5
C6H5
4-NO2C6H5
C6H5
with Bronsted and Lewis acid sites of the catalyst. It is shown in ear-
lier reports that Bronsted acid sites in the vicinity of Lewis acidic
metal center (active sites) act as co catalyst [37,38]. The mechanism
can be written as Bronsted acid catalyzed or Lewis acid catalyzed
reaction.
Thiophene
C6H5
3-NO2 C6H4
4-Cl C6H5
Thiophene
4-Br C6H4
4-Cl C6H4
Thiophene
3
3.5
4
3.3. Catalytic activity studies
Several methods are used for the synthesis of tetrasubstituted
imidazoles and their derivatives. Tetrasubstituted imidazoles are
generally synthesized in a four component condensation of alde-
hydes, 1,2-diketones, amines and ammonium acetate in acetic acid
or on various supports such as acidic, basic, and neutral alumina,
bentonite, montmorillonite K10, KSF and Silica gel. The reported
methods suffer from low yield and longer reaction time or using
rigorous acid treatment. Among the reported methods, those using
clays deserve mention as a convenient laboratory method for the
synthesis of these compounds. To the best of our knowledge, no
reports have been found in the use of clay supported titanium
catalyst using titanocene dichloride as the titanium source for
the synthesis of tetrasubstituted imidazoles. The catalyst was also
found good for the synthesis of benzimidazoles. This method not
only affords the product in excellent yields, but also avoids the
problems associated with handling, safety and pollution. This cata-
lyst can act as eco-friendly for a variety of organic transformations.
It is non- volatile, recyclable, non-explosive and easy to handle.
Tetrasubstitued imidazoles were synthesized using clay sup-
ported titanium catalyst under solvent free condition invoking
1 mmol aldehyde, 1 mmol benzil, 1 mmol amine, 1.2 mmol NH4OAc
under solvent free condition in a sealed glass apparatus (Scheme 1).
The catalyst loading was varied as 0.05 g, 0.1 g, 0.15 g 0.2 g, 0.25 g
and 0.3 g. With increase in catalyst loading, the yield was found
to increase up to 0.25 g further increase has no effect on the yield.
The optimum catalyst loading was taken as 0.25 g. Similarly, tem-
perature of the reaction was varied from 80 ◦C to 120 ◦C, the yield
was found to increase with increase in temperature up to 120 ◦C,
and further increase resulted in the formation of a charred product.
The optimum temperature for the reaction was selected as 120 ◦C.
Different aldehydes and amines were studied at optimized reac-
tion conditions, all the substrates gave good yield irrespective of
the electron donating or withdrawing groups attached on them.
The results are summarized in Table 3. The mechanism of forma-
tion of tetrasubstiuted imidazoles mediated by the clay supported
titanium catalyst is given in Scheme 2
3
Aldehyde (1 mmol): amine (1 mmol), benzil (1 mmol), NH4OAc (1.2 mmol), catalyst:
K10Ti (0.25 g).
a
Yields refer to isolated pure products.
(Entry 4, Table 3), Mp: 167 ◦C; IR ꢁmax (cm−1): 2982 (C H),
1600(C C), 1574 (C N), 1H NMR, (400 MHz, CDCl3); ı (ppm); 5
(2H, s, CH2), 6.9–7.7 (20H, m, Ar H).
(Entry 5, Table 3), Mp: 142 ◦C; IR ꢁmax (cm−1): 2889 (C H), 1602
(C C), 1531 (C N), 1H NMR, (300 MHz, CDCl3); ı (ppm); ı 7.2–7.7
(m, 15H), 3.5 (s, 3H).
(Entry 6, Table 3), Mp: 172 ◦C; IR ꢁmax (cm−1): 2982 (C H), 1592
(C C), 1530 (C N), 1H NMR, (400 MHz, CDCl3);ı (ppm); 7.1–8.5
(14H, m Ar H), 3.3 (3H, s).
(Entry 7, Table 3), Mp: 168 ◦C; IR ꢁmax (cm−1): 2986 (C H), 1592
(C C), 1477 (C N), 1H NMR, (400 MHz, CDCl3); ı (ppm); 5.1 (2H,
s, CH2), 6.9–7.7 (20H, m, Ar H).
(Entry 8, Table 3), Mp: 162 ◦C; IR ꢁmax (cm−1): 2986 (C H), 1600
(C C), 1574 (C N), 1H NMR, (300 MHz, CDCl3); ı (ppm); 6.5–7.6
(18H, m, Ar H).
(Entry 9, Table 3), Mp: 169 ◦C; IR ꢁmax (cm−1): 2985 (C H), 1600
(C C), 1574 (C N), 1H NMR, (400 MHz, CDCl3); ı (ppm); 7–7.8
(15H, m, Ar H), 4.1 (2H, q, J = 6.969 Hz) 1.1 (3H, t, J = 7.18 Hz).
(Entry 10, Table 3), Mp: 166 ◦C; IR ꢁmax (cm−1): 2982 (C H), 1605
(C C), 1510 (C N), 1H NMR, (400 MHz, CDCl3); ı (ppm); 7.1–8.7
(m, 19H, Ar H), 4.1 (q, 2H, J = 7.143 Hz) 1.1 (3H, t, J = 7.026 Hz).
(Entry 1, Table 4), Mp: 294 ◦C 1H NMR (400 MHz, CDCl3) ı (ppm)
8–8.2 (m, 2H), 7.6 (dd, 2H, J = 8, 3.2 Hz), 7.2–7.6 (m, 5H), 4.9 (s, 1H).
The products were characterized by 1H NMR, IR and through
comparison of the physical properties with those reported in the
literature.
3.3.1. Characterization of selected products
(Entry 1, Table 3), Mp: 220 ◦C; IR ꢁmax (cm−1): 2986 (C H),
1600 (C C), 1580 (C N), 1H NMR, (300 MHz, CDCl3); ı (ppm); ı
6.80–7.60 (m, 20H).
(Entry 2, Table 3), Mp: 105 ◦C; IR ꢁmax (cm−1): 2982 (C H), 1589
(C C), 1574 (C N), 1H NMR, (300 MHz, CDCl3); ı (ppm); ı 6.4–8.2
(m, 15H) 7.4–7.6 (dd, 4H J = 7 Hz).
(Entry 3, Table 3), Mp: 255 ◦C; IR ꢁmax (cm−1): 2987 (C H), 1604
(C C), 1510 (C N), 1H NMR, (300 MHz, CDCl3); ı (ppm); ı 7–7.45
(m, 15H, Ph) 7.58 (d, 1H, J = 8.3 Hz) 7.8 (d, 1H, J = 7.8 Hz), 8–8.1 (d,
1H, J = 8.1 Hz) 8.24 (s, 1H).
Scheme 2. Plausible mechanism of formation of tetrasubstituted imidazoles on clay
supported Ti catalyst.

38
V. Kannan, K. Sreekumar / Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
Scheme 3. Synthesis of benzimidazoles using K10Ti as catalyst.
Scheme 4. Proposed mechanism of titanium catalyst assisted benzimidazole synthesis.
(Entry 2, Table 4), Mp: 294 ◦C 1H NMR (400 MHz, CDCl3) ı (ppm)
and (SiO)3TiCl, titanium sites. The mechanism is explained by con-
sidering the participation of Ti species of the clay matrics.
The general applicability of the catalyst was verified by the
synthesis of benzimidazoles and quinoxalines. The synthesis of
benzimidazoles was carried out by the reaction of aldehyde and
orthophenylene diamine under solvent free condition. The syn-
thesis of substituted benzimidazoles using conventional heating
was carried out for a series of aldehydes using the clay sup-
ported titanium catalyst (Scheme 3). The results are summarized
in Table 4.
The reaction between an aldehyde and a diamine leads to
the formation of Schiff base (I) which is stabilized by clay sup-
ported titanium catalyst. Intramolecular attack by the second
amino group on C N double bond facilities the formation of
hydrobenzimidazole (II) which undergoes subsequent air oxi-
dation to give the desired benzimidazole as the final product
(Scheme 4).
8.0 (d, 2H, J = 8.2 Hz), 7.6 (m, 2H, J = 8.2 Hz), 7.2 (d, 2H, J = 7.6 Hz),
70.7.2 (m, 2H) 4.8 (s, 1H), 2.4 (s, 3H).
(Entry 3, Table 4), Mp: 224 ◦C; 1H NMR (400 MHz, CDCl3) ı (ppm)
7.4 (d, 2H, J = 7.4 Hz), 7–7.2 (m, 4H), 6.6 (d, 2H, J = 7.8) 4.6 (s, 1H),
3.7 (s, 3H).
(Entry 4, Table 4), Mp: 289 ◦C; 1H NMR (400 MHz, CDCl3) ı (ppm)
8.2 (d, 2H, J = 8.4 Hz), 7.4 (d, 2H, J = 8.4 Hz) 7–7.2 (m, 2H), 6.6 (d, 2H,
J = 7.8) 4.6 (s, 1H).
(Entry 5, Table 4), Mp: 314 ◦C; 1H NMR (400 MHz, CDCl3) ı (ppm)
8.0–8.2 (m, 2H), 7.1–7.2 (m, 2H), 6.7–6.9 (m, 4H), 4.4 (s, 1H).
The mechanism involves the participation of titanium Lewis acid
sites. The catalyst may contain a mixture of (SiO)2TiCl2, SiOTiCl3
Table 4
Clay supported titanium catalyst facilitates the formation of
quinoxaline derivatives as outlined in the mechanism (Scheme 5).
1,2-Diketone was stabilized in the interlayer of clay via interaction
with Ti4+ by partial polarization of carbonyl group which reacts
readily with o-phenylenediamine. The resultant amino-1,2-diol
undergoes dehydration to give quinoxaline as the end product.
Synthesis of benzimidazoles and quinoxaline derivatives.
Entry
R
Product
Yield% a
1
2
3
4
5
6
7
H
CH3
2a
2b
2c
2d
2e
2f
79
74
62
82
71
68
91
OCH3
4-Cl
4-NO2
Thio
Benzilb
3.4. Recyclability
2g
Mole ratio. Aldehyde, o-phenylene diamine, 1:1, K10Ti catalyst (0.25 g), Tempara-
ture 120 ◦C, reaction time, 2 h.
Finally, the catalyst recyclability was considered, and the cata-
lyst was found to be stable over three cycles without appreciable
loss in activity.
a
Yields refer to isolated pure products.
b
Quinoxaline.

V. Kannan, K. Sreekumar / Journal of Molecular Catalysis A: Chemical 376 (2013) 34–39
39
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Acknowledgments
One of the authors KV is grateful to UGC for teacher fellowship.
Help received from SAIF CUSAT, NMR Research Centre IISc, Banga-
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analysis.
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