Aluminosilicates with different pores structure in the synthesis of 2,2,4-trimethyl-1,2-dihydroquinoline and N-phenyl-2-propanimine

Article abstract of DOI:10.1007/s11172-017-1989-z

Physicochemical characteristics of microporous zeolites of various structural type (FAU, BEA, MTW), micro-meso-macroporous zeolite (H-Ymmm), and mesoporous aluminosilicate (ASM) were studied. Their catalytic activity in the reaction of aniline with aceton

Full text of DOI:10.1007/s11172-017-1989-z

Russian Chemical Bulletin, International Edition, Vol. 66, No.11, pp. 2115—2121, November, 2017
2115
Aluminosilicates with different pores structure in the synthesis
of 2,2,4ꢀtrimethylꢀ1,2ꢀdihydroquinoline and Nꢀphenylꢀ2ꢀpropanimine
N. G. Grigor´eva,a N. A. Filippova,a A. R. Gataulin,a S. V. Bubennov,a M. R. Agliullin,a
B. I. Kutepov,a and Nama Narenderb
aInstitute of Petrochemistry and Catalysis, Russian Academy of Sciences,
141 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347) 284 2750. Eꢀmail: nggꢀink@mail.ru
bCSIRꢀIndian Institute of Chemical Technology Uppal Road,
Tarnaka, Hyderabad, 500 007, Telangana State, India
Physicochemical characteristics of microporous zeolites of various structural type (FAU,
BEA, MTW), microꢀmesoꢀmacroporous zeolite (HꢀYmmm), and mesoporous aluminosiliꢀ
cate (ASM) were studied. Their catalytic activity in the reaction of aniline with acetone was
examined. It was found that 2,2,4ꢀtrimethylꢀ1,2ꢀdihydroquinoline was the main reaction
product on the catalysts HꢀYmmm and ASM (selectivity up to 68% at 100% conversion of
aniline), while the reaction on zeolites with microporous structure mainly gave Nꢀphenylꢀ2ꢀ
propanimine (selectivity up to 91%).
Key words: dihydroquinolines, imines, zeolites, hierarchical zeolites, mesoporous
aluminosilicates.
A dihydroquinoline ring is present in the structure of
many natural and synthetic compounds possessing bioꢀ
logical activity.1,2 For example, compounds based on
2,2,4ꢀsubstituted 1,2ꢀdihydroquinolines exhibit antibacꢀ
terial, antidiabetic and antiꢀinflammatory properties.3—5
Apart from that, dihydroquinoline derivatives are inhibitors
of lipid peroxidation and HMGꢀCoAꢀreductase, inhibiꢀ
tors of bile acid transporter, agonists and antagonists of
progesterone.6 Oligomers of 1,2ꢀdihydroquinolines (diꢀ, triꢀ,
and tetramers) are also known as antioxidants of rubbers.6
1,2ꢀDihydroquinolines are commonly synthesized by
the acidꢀcatalyzed reaction of aromatic amines with
ketones. This reaction is a modification af the classical
Skraup method, according to which quinoline is obtained by
heating aniline with glicerol in the presence of sulfuric acid.
Much work has been done on the synthesis of 2,2,4ꢀ
trimethylꢀ1,2ꢀdihydroquinoline (1) by the reaction of
aniline with acetone in the presence of HCl, benzeneꢀ or
pꢀtoluenesulfonic acid, iron and copper chlorides.6—9
Besides a multistep pathway, the main disadvantage of
these methods is the formation of of alkylanilines and
oligomers of dihydroquinoline 1 in large amounts.
A reaction of aromatic amines with ketones catalyzed
by silicotungstic acid (H4[SiW12O40]) in the presence of
solvents was earlier described.12 The yields of 1,2ꢀdihydꢀ
roquinolines varied within 77—94%. In recent works, the
synthesis of dihydroquinolines 1 was carried out under
the influence of microwave irradiation in the presence of
triflates as efficient homogeneous catalysts (for example,
Sc(OTf)3, In(OTf)3, and Yb(OTf)3;5 Zn(OTf)3 or
13
Bi(OTf)14). Compounds 1 were also obtained in the presꢀ
ence of cerium ammonium nitrate.15
Despite the high yields of dihydroquinolines 1, the use
of homogeneous catalysts has several disadvantages: a multiꢀ
step pathway, difficulties in the removal of catalysts from
the reaction mixture, the use of solvents in large amounts.
It should be noted that the use of heterogeneous cataꢀ
lysts in the synthesis of dihydroquinoline 1 has not been
studied at length. For example, the gasꢀphase synthesis of
1,2ꢀdihydroquinoline 1 affected by niobium halides
([(Nb6Cl12)Cl2(H2O)4]•4H2O) proceeded with 71.1%
selectivity at a 34% conversion of aniline.16 A report17 on
the synthesis of dihydroquinoline 1 on polyhedral oligoꢀ
meric silsesquioxanes was published. 1,2ꢀDihydroquinoꢀ
line 1 was obtained in 96% yield by the reaction of aniline
with acetone in the presence of natural aluminosilicate
E4a.18 The latter method is attractive due to the use of an
environmentally friendly heterogeneous catalyst. Howꢀ
ever, its use in large amounts (250% calculated on aniline)
significantly reduces the efficiency of the process. Apart
from that, natural aluminosilicates are characterized by
There is a report10 on the synthesis of 2,2ꢀdisubstitutꢀ
ed 1,2ꢀdihydroꢀ4ꢀphenylquinolines by the reaction of
2ꢀ(1ꢀphenylvinyl)aniline and 4ꢀchloroꢀ2ꢀ(1ꢀphenylvinyl)ꢀ
aniline with acetophenone derivatives in the presence of
pꢀtoluenesulfonic acid. The reaction of 2ꢀisopropenylꢀ
aniline with ketones in the presence of BF3•OEt afforded
2,2,4ꢀtrisubstituted 1,2ꢀdihydroquinolines.11
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2115—2121, November, 2017.
1066ꢀ5285/17/6611ꢀ2115 © 2017 Springer Science+Business Media, Inc.

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Grigor´eva et al.
Methods of study of catalysts. Methods for study of physicꢀ
ochemical properties of zeolite catalysts and mesoporous aluꢀ
minosilicate are described in the literature.23—25
inconstancy of mineralogical and chemical composiꢀ
tion, pore structure, strength and heat resistance indices,
and other important characteristics. Natural zeolite
materials contain such impurities as sand, clay miꢀ
nerals, and quartz. The composition and amount of
metal cations present in natural zeolites can vary signifꢀ
icantly.
Synthetic zeolites have not previously been used for
the preparation of dihydroquinolines, therefore, it is of
interest to study their catalytic properties in the reaction
of aniline with acetone. As it is known, zeolites efficiently
catalyze a variety of chemical processes. However, diffuꢀ
sion of reagent and reaction products through micropores
is often retarded, resulting in a low activity of the catalyst
and is rapid deactivation. Apart from that, the zeolite
structure limits the possibility of synthesis of bulky
molecules with a diameter more than 1 nm. Using mesoꢀ
porous materials, it is possible to overcome the diffusion
limitations characteristic of microporous systems and
develop favorable conditions for the synthesis of bulky
molecules.
Acidic properties of aluminosilicates were studied by IR
spectroscopy in the G. K. Boreskov Institute of Catalysis of the
Siberian Branch of the Russian Academy of Sciences using a
lowꢀtemperature adsorption of the CO probe molecule.26—30
IR spectra were recorded on a Shimadzu FTIRꢀ8400 Fourierꢀ
transform spectrometer in the range of 700—6000 cm–1 with a
resolution of 4 cm–1 and a number of scans equal to 250. Before
experiments, the samples of catalysts were compressed into
pellets with parameters p/S ≈ 0.009—0.013 g cm–2 (where p is
the pellet weight in g; S is the pellet geometric area in cm2).
Synthesis of 2,2,4ꢀtrimethylꢀ1,2ꢀdihydroquinoline (1) and
Nꢀphenylꢀ2ꢀpropanimine (2). Aniline (0.1 g, 1 mmol), acetone
(0.3 g, 5 mmol), and a catalyst (0.04 g, 10% calculated on the
aniline—acetone mixture) were placed into a tube. The sealed
tube was transferred into an autoclave, which was heated to
230 °C in a thermostatically controlled oven during 24 h with
continuous rotation. After the reaction reached completion,
the autoclave was cooled to ~20 °C, the tube was unsealed. The
reaction mixture was filtered from the catalyst.
The reaction products were analyzed by GLC on a HRGS
5300 chromatograph (Carlo Erba) (a flameꢀionizing detector,
a 50 m×0.2 mm glass capillary column, an SEꢀ30 phase, proꢀ
grammed heating 50—280 °C, carrier gas helium). Mass spectra
were obtained on a SHIMADZU GCMSꢀQP2010Plus chroꢀ
mateꢀmass spectrometer (a SPBꢀ5 phase, a 30 m×0.25 mm
capillary column, carrier gas helium, programmed temperaꢀ
ture 40—300 °C, the source of ions temperature 200 °C, ionizaꢀ
tion energy 70 eV). 1H and 13C NMR spectra of compounds in
solution of CDCl3 were recorded on a Bruker AVANCEꢀ400
spectrometer (400.13 MHz (for 1H) and 100.62 MHz (for 13C))
in standard NMR tubes 5 mm in diameter.
In order to search for and develop efficient heteroꢀ
geneous catalysts for the synthesis of dihydroquinolines
by the reaction of aniline with acetone, in the present
work we studied physicochemical and catalytic properꢀ
ties of microporous zeolites (HꢀY, HꢀBeta, HꢀZSMꢀ12),
the zeolite HꢀYmmm with a combined microꢀmesoꢀ
macroporous structure, and an amorphous mesoporous
aluminosilicate ASM.
Experimental
2,2,4ꢀTrimethylꢀ1,2ꢀdihydroquinoline (1). The yield was
81.2%, a dark brown liquid, b.p. 75 °C (5 Torr), nD 1.521.
20
1H NMR (CDCl3), δ: 1.35 (s, 3 H, C(9,10), Me); 2.07 (d, 3 H,
C(11), Me); 5.39 (d, 1 H, H(3)); 6.50 (d, 1 H, H(8), J = 8 Hz);
6.72 (m, 1 H, H(7), J = 4 Hz); 7.07 (m, 1 H, H(6), J = 8 Hz);
7.15 (dd, 1 H, H(5), J = 8 Hz). 13C NMR (CDCl3), δ: 18.66
(C(11)); 31.07 (C(9,10)); 51.85 (C(2)); 113.03 (C(8)); 117.21
(C(6)); 121.59 (C(4a)); 123.68 (C(7)); 128.44 (C(4), C(5));
128.58 (C(3)); 143.33 (C(8a)). The data obtained correspond to
the literature data.18 MS (EI, 70 eV), m/z (Irel (%)): 173 [M]+
(13), 158 (100), 143 (12), 130 (6), 115 (17), 103 (2), 91 (5),
79 (9), 65 (6), 51 (4), 42 (1). Found (%): C, 83.21; H, 8.70;
N, 8.07. C12H15N. Calculated (%): C, 83.01; H, 8.55; N, 8.00.
Nꢀphenylꢀ2ꢀpropanimine (2). The yield was 97%, a dark
Reagents and catalysts. Aniline and acetone distilled and
purified according to the standard procedures19 were used in
the work.
The samples of zeolites NH4ꢀBeta (SiO2 : Al2O3 = 18) and
HꢀZSMꢀ12 (SiO2 : Al2O3 = 34) were synthesized at the Angarꢀ
sk Plant of Catalysts and Organic Synthesis Inc. Zeolite Beta
obtained in the NH4 form was converted to the H form by
calcination during 4 h at 540 °C. Zeolite NaꢀY (SiO2 : Al2O3 = 6)
was synthesized according to the known procedure20 and conꢀ
verted to the H form by triple ion exchange in a solution of
NH4NO3 at 70 °C to a decationization degree of α = 0.96.
Na
The preparation method for microꢀmesoꢀmacroporous zeolite
Ymmm in the H form (SiO2 : Al2O3 = 7.2) is based on selective
crystallization in solutions of sodium silicate at 96—98 °C of
granules consisting of highly dispersed zeolite NaY and amorꢀ
phous binder material (metakaolin).21,22 With this method of
preparation, the content of the crystalline phase in the sample
is greater than that of the amorphous phase. The degree of
exchange of Na+ with H+ (αNa) in the sample of HꢀYmmm was
0.95. Amorphous mesoporous aluminosilicate ASM (Si : Al = 40)
was obtained by sol—gel synthesis according to the procedure
described earlier.23,24
20
brown liquid, b.p. 35 °C (16 Torr), nD 1.490. 1H NMR,
δ: 1.84 (s, 6 H, C(9, 10), Me); 6.71—6.73 (dd, 2 H, C(2,6)H);
7.20 (t, 1 H, C(4)H); 7.73 (t, 2 H, C(3,5)H). 13C NMR,
δ: 20.62 (C(9,10)); 115.11 (C(2,6)); 123.13 (C(4)); 129.31
(C(3,5)); 146.47 (C(1)); 169.18 (C(8)). MS (EI, 70 eV), m/z
(Irel (%)): 133 [M]+ (60), 118 (100), 103 (2), 93 (1), 77 (80),
59 (7), 51 (25), 41 (3). Found (%): C, 81.18; H, 8.30; N, 10.48.
C9H11N. Calculated (%): C, 81.01; H, 8.21; N, 10.40.
Results and Discussion
Prior to catalytic tests, the catalysts were subjected to
a highꢀtemperature treatment (at 540 °C) in the atmosphere of
dried air during 3–4 h.
Characteristics of catalysts. Physicochemical properꢀ
ties of zeolites HꢀY, HꢀBeta, HꢀZSMꢀ12, HꢀYmmm and

Synthesis on aluminosilicates
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 11, November, 2017 2117
Table 1. Physicochemical characteristics of zeolites
Cataꢀ
lyst
SBET
/m2 g–1
Aa
Acidic properties
/ cm3 g–1
Lewis acid sites
Mediumc
Brönsted acid sites
Strongb
Weakd
QCO
ν
NH
e
Δν
OH
OH
/μmol g–1
f
g
H2O C6H6 NCO
QCO
NCO
QCO
NCO
cm–1
НꢀY
870
470
0.30
0.30
33
52
—
—
37
38
3675
3675
38
3610—3650
220
300
60
73
324
315
330
308
320
163
3613
3745
3621
HꢀBeta
0.28
0.14
0.28
—
0.32
0.13
0.28
—
55
4
52
53
54
22
1
45
46
293
1
128
51
75
31
70
50
5
HꢀZSMꢀ12 320
34
3738
НꢀYmmm
ASМ
741
650
8
25
43—44.5
45—44
64
50
32.5—39
40—34
3600—3660 300—320
h
3735
3615—3725
3740
—
58 54.5—50.5 11
300
270—320
23
a A is the equilibrium adsorption capacity at 20 °C, P/Ps = 0.8.
b
ν
ν
ν
CO = 2231—2226 cm–1
CO = 2212—2210 cm–1
;
c
d
e
;
CO = 2200—2190 cm–1
;
ΔνOH is the shift of frequency of OH groups during adsorption of CO, cm–1
;
f NCO is the amount of adsorbed CO, μmol g –1
.
g QCO is the heat of adsorption, kJ mol–1
;
h cannot by accurately measured.
amorphous mesoporous aluminosilicate ASM are given
in Table 1.
the macropores of zeolite HꢀYmmm determined by merꢀ
cury porosimetry is equal to 12.1 m2 g–1. The volumes of
microꢀ, mesoꢀ, and macropores are 0.28, 0.15, and
0.15 cm3 g–1, respectively.
According to the powder Xꢀray diffraction data and
the adsorption capacity values for the H2O and C6H6
vapors, the samples of zeolites HꢀY, HꢀBeta, and
HꢀZSMꢀ12 are characterized by the degree of crystalliniꢀ
ty close to 100%, while for zeolite HꢀYmmm it is 95%.
According to the lowꢀtemperature nitrogen adsorption—
desorption data, the "apparent" BET specific surface area
of zeolites is 870 (HꢀY), 470 (HꢀBeta), 320 (HꢀZSMꢀ12),
and 741 m2 g–1 (HꢀYmmm). A hysteresis loop of type
H 1 is observed on the nitrogen adsorption—desorption
isotherm for zeolite HꢀYmmm (Fig. 1), which is typical
of microꢀmesoporous structures.31 A specific surface of
Acidic properties of the samples of zeolites and mesoꢀ
porous aluminosilicate were studied by IR spectroscopy
of the adsorbed CO. The vibrations of the OH groups
present in the IR spectra of the samples of zeolite HꢀY
(SiO2 : Al2O3 = 6) and zeolites HꢀBeta and HꢀZSMꢀ12
were interpreted earlier.29,30 In zeolite HꢀY, four types of
Brönsted acid sites (BAS) are present, which are related
to bridging Si—O(H)—Al groups in large cavities (abꢀ
sorption bands at 3610 and 3638 cm–1), and two types of
weakly acidic OH groups bonded to the outꢀofꢀlattice
aluminum (absorption bands at 3675 cm–1). The surface
of the samples of zeolites HꢀBeta and HꢀZSMꢀ12 conꢀ
tain three types of BAS: the bridging OH groups in
the channels characterized by the absorption bands at
3613 cm–1 (HꢀBeta) and 3621 cm–1 (HꢀZSMꢀ12); the
bridging OH groups on the external surface of crystals,
and weakly acidic terminal SiOH groups (absorption
bands at 3738—3745 cm–1). The values of the BAS conꢀ
A/cm3 g–1
300
250
200
150
centrations and the Δν
values of the shift of the abꢀ
OH
sorption bands of the OH groups upon the formation of
a hydrogen bond with CO are given in Table 1. The
0.2
0.4
0.6
0.8
1.0 P/Ps
strength of the acid centers can be inferred from the Δν
OH
shift value: the larger is the shift value, the stronger is the
Fig. 1. Isotherm of nitrogen adsorption at 77 K for zeolite
HYꢀmmm.
acid site. According to the presented data, the concentraꢀ

2118
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 11, November, 2017
Grigor´eva et al.
tion of BAS of microporous zeolites decreases in the orꢀ
der: HꢀY > HꢀBeta > HꢀZSMꢀ12. The strength of BAS
increases in the reverse order: HꢀY < HꢀBeta < HꢀZSMꢀ12.
Apart from BAS, Lewis acid sites (LAS) of various
strength were found on the surface of the zeolites: strong
(most likely, dimeric Al—O—A1 clusters, stabilized on
Brönsted centers) and weak (apparently, clusters containꢀ
ing six—eight A1 atoms and complexes of CO with nuclei
of aluminum oxide phase), which are characterized by
A signal in the region of 3735 cm–1 is related to the vibꢀ
rations of strongly acidic Si—OH group on the exterꢀ
nal surface of zeolite crystallites, which are located in
the immediate vicinity of the LAS formed by threeꢀcoꢀ
ordinated Al or Si atoms (Si—O(H)…Al3+ or
Si—O(H)…Si3+). The band at 3747 cm–1 belongs to the
terminal Si—OH groups.
The IR spectrum of the HꢀYmmm sample in the reꢀ
gion of vibrations of the OH groups after adsorption of
CO is shown in Fig. 2, b. The shifts of the absorption
bands of the OH groups upon formation of hydrogen
bonds, the band frequency of the adsorbed CO, and the
concentrations of acid sites are given in Table 1. It should
be noted that the surface of the sample contains strong
absorption bands at 2225—2230 and 2195—2187 cm–1
,
respectively.26—28 The maximum amount of LAS (both
in type and concentration) was found for the sample of
zeolite HꢀBeta, namely, 370.3 μmol g–1
.
The IR spectrum of the sample of microꢀmesoporous
zeolite HꢀYmmm in the region of stretching vibrations of
the OH groups is shown in Fig. 2, a.
type I BAS (Δν
= 300 cm–1) related to the bridging
OH
Si—O(H)—Al groups and strong type II BAS related to
The IR spectrum of the HꢀYmmm sample exhibits
absorption bands for nine types of hydroxy groups. A broad
absorption band in the region of 3600 cm–1 is attributed
to the vibrations of the OH groups in small zeolite caviꢀ
ties, these OH groups are not available for the adsorption
of CO molecules. The absorption bands at 3610, 3630,
and 3660 cm–1 can be assigned to strong bridging hydrꢀ
oxy groups Si—O(H)—Al in the zeolite cavities. The bands
at 3680, 3690, and 3785 cm–1 belong to the OH groups
bonded to the nonꢀframework aluminum atoms (Al—OH).
the acid sites presumably on the external surface of the
zeolite crystals with ν
= 3735 cm–1
.
O—H
By estimating the amount of adsorbed CO on the surꢀ
face of the HꢀYmmm sample, the existence of three types
of LAS can be assumed (see Table 1).
Comparing the acidic properties of the finely dispersed
zeolite HꢀY with the microporous structure and the granꢀ
ular zeolite HꢀYmmm with the microꢀmesoꢀmacroporous
structure, it can be pointed out that zeolite HꢀYmmm is
characterized by a wider diversity of the OH groups. The
concentration of strong BAS (ΔνOH = 300—320 cm–1) in
zeolite HꢀYmmm is considerably lower (120 μmol g–1
)
A
a
than in zeolite HꢀY (320 μmol g–1), however, almost half
of them are located on the external surface of the crystals.
The amount of LAS in zeolite HꢀYmmm is higher than in
zeolite HꢀY, though, the majority of them are sites of
medium and weak strength.
60
30
0
3680
3747
3610
3660
The characteristics of mesoporous aluminosilicate
ASM are presented in Table 1. More details on the texꢀ
ture and acidic properties of aluminosilicate ASM are
given in an earlier published work.24 The ASM sample is
characterized by a narrow distribution of mesopores from
2 to 5 nm with a volume of 0.70 cm3 g–1. Two types of
strong BAS are present on its surface: the bridging
Si—O(H)—Al groups (absorption at 3615 cmꢀ1) and
Si—O(H)…Al3+ groups (absorption at 3730 cm–1) or
Al—O(H)—Al groups (absorption at 3650 cm–1). Apart
from that, the weakly acidic silanol groups are also present
(absorption at 3740 cm–1). The total concentration of
strong BAS is 28 μmol g–1, the total concentration of
3785
3200
3400
3600
3800 ν/cm–1
A
b
60
30
0
pCO
LAS is 119 μmol g–1
.
3735
3747
3690
Reaction of aniline with acetone in the presence of zeoꢀ
lites with microꢀ and microꢀmesoꢀmacroporous structure
and mesoporous aluminosilicates. The results of the invesꢀ
tigation of the reaction of aniline with acetone in the
presence of the HꢀY, HꢀBeta, HꢀZSMꢀ12, HꢀYmmm,
and ASM samples are given in Table 2.
3610
3785
3200
3400
3600
3800 ν/cm–1
Fig. 2. IR spectra of the HꢀYmmm sample in the region of
vibrations of surface hydroxyl groups before adsorption (a) and
difference spectra after adsorption of CO (0.2—4 Torr) at 77 K (b).
2,2,4ꢀTrimethylꢀ1,2ꢀdihydroquinoline (1) and Nꢀpheꢀ
nylꢀ2ꢀpropanimine (2) are the main products of the reacꢀ

Synthesis on aluminosilicates
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 11, November, 2017 2119
Table 2. The results of the reaction of aniline with acetone in
the presence of zeolites with microꢀ and microꢀmesoꢀmacroꢀ
porous structure and mesoporous aluminosilicate*
Thus, zeolite HꢀY possessing the highest concentration
of BAS has the lowest activity in the reaction (the conꢀ
version of aniline 11%), while on zeolite HꢀBeta, in which
the amount of BAS is 2.5 times lower, the conversion of
aniline reaches 78%. It should be noted that Nꢀphenylꢀ2ꢀ
propanimine (2) predominates in the reaction products
obtained on microporous zeolites.
Catalyst
Conversion
Selectivity of formation (%)
of aniline (%)
1
2
Other
HꢀBeta
HꢀZSMꢀ12
HꢀY
HꢀYmmm
ASM
178
112
111
100
185
15
13
17
68
49
71
91
88
30
47
14
16
15
12
14
Scheme 2
* Synthesis conditions: the molar ratio of aniline : acetone =
= 1 : 5; 10% of catalyst, 24 h, 230 °C.
tion of aniline with acetone in the presence of catalysts
under study (Scheme 1).
Scheme 1
The results obtained, namely, the absence of a correꢀ
lation between activity and acidity and a selective formaꢀ
tion of predominantly compound 2, indicate a significant
dependence of the catalytic properties on the textural
characteristics of zeolites. Since in zeolites, as it is known,
most of the active sites (strongly acidic structural OH
groups) are located inside channels or cavities, it is their
availability for the reacting molecules that is the main
factor determining the catalytic properties.
The calculations by the ACD/3D Viewer program
show that the sizes of the molecules of the parent comꢀ
pounds and reaction products 1 and 2 are close to or even
exceed the diameter of the channels and cavities of the
zeolites (Fig. 3).
The activity of the catalysts in the reaction was evaluꢀ
ated from the degree of aniline conversion. Among zeoꢀ
lites with microporous structure, zeolite HꢀBeta exhibitꢀ
ed a high activity in the reaction, while zeolites HꢀY and
HꢀZSMꢀ12 were found to be low active. From the comꢀ
parison of the catalytic activity of zeolites with the data
on their acidity (see Table 1), it follows that there is no
correlation between the conversion of aniline and the conꢀ
centration of acid sites on the catalysts, though, accordꢀ
ing to the assumed reaction mechanism, it should proꢀ
ceed with the involvement of the acid sites (Scheme 2).
Dihydroquinoline 1 has the bulkiest molecule with
a size of 0.64×0.83 nm, the synthesis of which in micropores
of the zeolite lattice is difficult and apparently possible
0.6 nm
0.71 nm
0.5 nm
0.83 nm
0.64 nm
0.5 nm
Aniline
1
2
Fig. 3. Sizes of molecules of aniline and reaction products 1 and 2.

2120
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Grigor´eva et al.
only on acid sites located on the external surface of the
catalyst. The selectivity of the formation of dihydroquinꢀ
oline 1 on zeolite HꢀBeta, that is higher than that obꢀ
served on other zeolites, is due to the presence of strong
with acetone (see Table 2). It was found that the amorꢀ
phous aluminosilicate ASM exhibited a lower activity
compared to that of zeolite HꢀYmmm: the aniline conꢀ
version was 85% under the conditions used. This is likely
due to a lower concentration of acid sites present on the
surface of aluminosilicate ASM (see Table 1). The selecꢀ
tivity of the formation of imine 2 and dihydroquinoline 1
is approximately the same.
BAS on the external surface of this zeolite (551 μmol g–1
,
Δν
= 315 cm–1, see Table 1). It is obvious that the
OH
same reason explains the high catalytic activity of zeolite
HꢀBeta, especially since the presence of a maximum
amount of LAS (370 μmol g–1), located mainly on the
external surface of the crystals, is typical of zeolite HꢀBeta.
It is believed32 that the role of LAS consists in the inꢀ
crease in proton acidity effected by pulling the electron
density away from the O—H bond. Apart from that, the
reaction medium contains water formed in the course of
the reaction. The dissociation of water molecules coordiꢀ
natively bound to LAS can result in the appearance of
new BAS.33 Taking into account these suggestions, one
can conclude that there is much more BAS on zeolite
HꢀBeta than it was determined by IR spectroscopy, which
explains a high catalytic activity of this zeolite.
A low activity of zeolite HꢀZSMꢀ12 is associated
with considerable difficulties for the diffusion of the
molecules of reagents and imine 2 caused by its crystal
lattice with a diameter of channels of 0.53×0.56 nm and
0.51×0.55 nm.34 The reason for the low activity of zeolite
HꢀY can not only be sought in steric hindrance for the
diffusion and interaction of reagents. The blocking of large
cavities by the formed molecules of dihydroquinoline 1
can be also considered when one bears in mind that the
diameter of the entrance windows to a large cavity is
smaller than the diameter of the cavity itself (0.75 and
1.2 nm, respectively).34
In conclusion, the present study revealed the relationꢀ
ship between the acid properties and characteristics of
the porous structure of various zeolite catalysts and meꢀ
soporous aluminosilicate with their activity and selectivity
in the cyclocondensation reaction of aniline with acetꢀ
one. It was found that the main product of the reaction of
aniline with acetone in the presence of microporous zeoꢀ
lite catalysts is Nꢀphenylꢀ2ꢀpropanimine (2), which is
explained by the molecularꢀsieve effect of the zeolite crysꢀ
tal lattice. 1,2ꢀDihydroquinoline (1) is most selectively
formed on the microꢀmesoporous zeolite HꢀYmmm
(68%), the selectivity of the formation of compound 1
decreases to 49% on the mesoporous aluminosilicate
ASM. The presence of mesopores in the aluminosilicates
described above contributes to the reduction of steric
hindrance for the transport of reagents and development
of conditions for the formation of compound 1. The acꢀ
tivity of the catalysts decreases in the following order:
HꢀYmmm (100% conversion of aniline) > ASM (85%) >
> HꢀBeta (78%) > HꢀZSMꢀ12 (12%) > HꢀY (11%).
This work was financially supported by the Russian
Science Foundation (RussianꢀIndian Project No. 16ꢀ43ꢀ
02010).
One way to improve the diffusion properties of zeoꢀ
lites and increase the availability of their active sites for
reacting molecules is the creation of mesopores in their
microcrystalline lattice. Various methods can be used to
develop the mesoporosity in zeolite, for example, by
means of templates, chemical or steam treatment.35,36 In
the present study, we used a granular zeolite HꢀYmmm,
in the porous structure of which micropores of primary
crystals (d = 0.75 nm) are present along with mesoꢀ
(2—50 nm) and macropores (100—1000 nm) formed as
a result of the formation of intergrowths of crystals in the
process of the synthesis of granules of high degree of crysꢀ
tallinity.
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Received April 6, 2017;
in revised form June 23, 2017