A new approach to the preparation of lanthanide catalysts for the synthesis of 2-propyl-3-ethylquinoline based on the reactions of LnCl3· 6H2O crystalline hydrates with triisobutylaluminum

Article abstract of DOI:10.1134/S0023158406040136

A new approach to the preparation of lanthanide catalysts for the synthesis of nitrogen heterocycles (exemplified by 2-propyl-3-ethylquinoline) was developed based on the reactions of LnCl₃·6H₂O crystalline hydrates with alkylaluminums. It was found that the interaction of LnCl₃·6H₂O (Ln = Ce, Pr, Tb, and Eu) with iso-Bu₃Al in aromatic solvents (20°C) resulted in the formation of soluble (isobutane and the alumoxane (iso-Bu₂Al)₂O) and insoluble products (with the empirical formula LnCl₃·xH ₂O·y(iso-Bu₂Al)₂O (x = 0.4-0.7; y = 0.04-0.07)). The physiochemical properties of LnCl₃·xH ₂O·y(iso-Bu₂Al)₂O were studied, and these compounds were found to be highly efficient catalysts for the reaction of aniline condensation with butyraldehyde to form 2-propyl-3-ethylquinoline. MAIK Nauka/Interperiodica , 2006.

Full text of DOI:10.1134/S0023158406040136

ISSN 0023-1584, Kinetics and Catalysis, 2006, Vol. 47, No. 4, pp. 572–579. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Original Russian Text © R.G. Bulgakov, S.P. Kuleshov, A.R. Makhmutov, R.R. Vafin, D.S. Karamzina, M.T. Golikova, Ya.V. Shestopal, S.M. Usmanov, U.M. Dzhemilev, 2006,
published in Kinetika i Kataliz, 2006, Vol. 47, No. 4, pp. 589–596.
A New Approach to the Preparation of Lanthanide Catalysts
for the Synthesis of 2-Propyl-3-Ethylquinoline
Based on the Reactions of LnCl · 6H O Crystalline Hydrates
3
2
with Triisobutylaluminum
a
a
a
a
a
R. G. Bulgakov , S. P. Kuleshov , A. R. Makhmutov , R. R. Vafin , D. S. Karamzina ,
a
a
b
a
M. T. Golikova , Ya. V. Shestopal , S. M. Usmanov , and U. M. Dzhemilev
a
Institute of Petrochemistry and Catalysis, Academy of Sciences of Bashkortostan, Ufa Scientific Center,
Russian Academy of Sciences, Ufa, 450075 Bashkortostan, Russia
b
Birsk State Pedagogical Institute, Birsk, 452320 Bashkortostan, Russia
Received March 11, 2005
Abstract—A new approach to the preparation of lanthanide catalysts for the synthesis of nitrogen heterocycles
exemplified by 2-propyl-3-ethylquinoline) was developed based on the reactions of LnCl · 6H O crystalline
(
3
2
hydrates with alkylaluminums. It was found that the interaction of LnCl · 6H O (Ln = Ce, Pr, Tb, and Eu) with
3
2
iso-Bu Al in aromatic solvents (20°C) resulted in the formation of soluble (isobutane and the alumoxane (iso-
3
Bu Al) O) and insoluble products (with the empirical formula LnCl · xH O · y(iso-Bu Al) O (x = 0.4–0.7; y =
2
2
3
2
2
2
0
.04–0.07)). The physicochemical properties of LnCl · xH O · y(iso-Bu Al) O were studied, and these com-
3 2 2 2
pounds were found to be highly efficient catalysts for the reaction of aniline condensation with butyraldehyde
to form 2-propyl-3-ethylquinoline.
DOI: 10.1134/S0023158406040136
INTRODUCTION
aniline condensation with butyraldehyde. In order to
study the above interaction and to characterize the
physicochemical properties of the resulting catalysts,
we used the following techniques: volumetry; UV and
IR spectroscopy; X-ray phase analysis and X-ray dif-
fraction analysis (XRD); gas–liquid chromatography
Lanthanide trichlorides LnCl are efficient catalysts
3
in the syntheses of nitrogen heterocycles [1] and, in
combination with organoaluminum compounds, poly-
dienes [2]. However, the well-known methods for the
preparation of LnCl imply the interaction of the crys-
3
(
(
GLC); gravimetric and differential thermal analysis
TG DTA); photoluminescence; chemiluminescence;
talline hydrates LnCl · 6H O with corrosion-active
3
2
reagents (HCl and SOCl ) at high temperatures (90–
2
and τ-metry (the measurement of the lifetime of the
5
00°C) for long times (48–110 h) [3]. Based on the
3+
Tb * ion). The efficiency of luminescence techniques
for studying synthesis reactions and the action of Zie-
gler–Natta catalysts was demonstrated previously [5–7].
above and taking into account that catalytic composi-
tions based on lanthanide compounds frequently
include organoaluminum compounds [2, 4], we devel-
oped a new approach to the preparation of lanthanide The properties of catalysts based on other metal oxides
catalysts, which is characterized by the use of orga- (TiO , Al O , ZrO , and MgO) and containing no orga-
2
2
3
2
noaluminum compounds for the dehydration of the noaluminum compounds were described elsewhere [8].
crystalline hydrates. Thus, it was found that an effi-
The lanthanides Tb, Eu, and Ce were chosen
cient homogeneous catalyst for butadiene polymeriza-
tion can be easily prepared by the interaction of the because of their relatively bright f–f and f–d lumines-
3
+
crystalline hydrates with organoaluminum compounds cence [9]. In addition, using Eu , which can be reduced
2
+
in toluene in the presence of (BuO) PO at room tem-
3
to Eu [10], as an example, we studied the effect of the
lanthanide oxidation number on the composition of
products in the reaction of the crystalline hydrate with
perature in a few minutes [5].
In this work, we studied the preparation of lan-
thanide catalysts for the synthesis of nitrogen heterocy- TIBA and on the catalytic activity of the products of
cles by the interaction of the crystalline hydrates with this reaction. Praseodymium was chosen because of its
iso-Bu Al (TIBA). As an example, we used the synthe- high catalytic activity in the preparation of substituted
3
sis of 2-propyl-3-ethylquinoline by the reaction of quinolines [1].
5
72

A NEW APPROACH TO THE PREPARATION OF LANTHANIDE CATALYSTS
573
EXPERIMENTAL
tane was identified by GLC. The IR, UV, visible
absorption, and photoluminescence spectra of solutions
and solid Cat-Ln were measured in airtight cells or
ampules in an atmosphere of Ar. Chemiluminescence
was generated by oxygen puffing onto the surface of
Cat-Ln, which was uniformly scattered at the optically
transparent bottom of a quartz cell. In the measurement
of XRD patterns, the samples of Cat-Ln were pelleted
in an atmosphere of argon and then impregnated with a
toluene solution of rubber adhesive (4508) in order to
exclude contact with air. The TG DTA of Cat-Ln sam-
ples was performed in an atmosphere of air in accor-
dance with standard procedures.
The crystalline hydrates of chemically pure grade
were used in this study; all of the other reagents and sol-
vents were of reagent grade. A commercial gasoline
solution of TIBA (90%) was subjected to vacuum dis-
tillation according to Korneev [11]; the concentration
of the alkoxy derivatives of aluminum in TIBA was no
1
higher than 1% (according to H NMR data). Aniline
was distilled in a vacuum (10 Torr; 70°C), and butyral-
dehyde was distilled from hydroquinone [12]; Ph P was
3
used without purification. Solvents were purified in
accordance with published procedures [12]: benzene,
toluene, ethylbenzene, and cumene were purified with
the subsequent distillation from sodium metal, whereas
dimethylformamide (DMF) was distilled from BaO.
Argon was passed through a gas absorbing apparatus.
Isobutane and the products of aniline condensation
with butyraldehyde were analyzed on Karlo Erba GC
6
000 (3-m column 4 mm in diameter; stationary liquid
phase, 15% PEG 6000 on Chromaton) and Chrom 5
The reactions of the crystalline hydrates with TIBA at (3-m column 4 mm in diameter; stationary liquid phase,
0°C in an argon atmosphere were performed in a ther- 30.5% SE-30 on Chromaton N-AW HMDS) chromato-
2
mostated glass reactor, which was equipped with a mag- graphs. The elemental analysis of Cat-Ln was per-
netic stirrer and connected to a gas burette for measuring formed on a Karlo Erba 106 analyzer. The absorption
the volume of released gases. A crystalline hydrate (0.54 spectra in the IR and UV–visible regions were mea-
mmol) was loaded in the reactor, and a solvent and TIBA sured on Specord 75IR and Specord M40 spectropho-
were added (crystal water/TIBA ratios of 1/2 and 1/20; tometers, respectively. The photoluminescence spectra
total volume of 10 ml). The reaction mixture was stirred were measured on an Aminco Bowman spectrofluorim-
to the completion of gas liberation and centrifuged; the eter. The analysis of samples for aluminum was per-
solution was separated from a solid phase. The solid formed on a Shimadzu GFA-4B atomic absorption
phase was washed with the solvent, which was then spectrophotometer (graphite cell atomizer). The XRD
removed by evacuation (10 Torr; 20 min) to obtain a patterns were measured on a Philips PW-1800 diffrac-
loose powder (henceforth denoted by Cat-Ln).
tometer with CuKα radiation using the following
parameters: step, 0.05° 2θ; time step, 2''; sample revo-
lution, 1 rps. The TG DTA curves were obtained on a
Mettler Toledo Star TGA-851E derivatograph. The life-
The condensation of aniline with butyraldehyde was
3
performed in a steel autoclave (V = 17 cm ) in an atmo-
sphere of argon. The autoclave was successively loaded
with aniline (20 mmol), butyraldehyde (44 mmol), and
DMF (6 ml). Next, a solution of Cat-Ln (0.54 mmol) in
DMF (1 ml) in the absence or in the presence of Ph3P
3
+
3+
time of the Tb * ion (τ Tb *) was measured on a
τ-metric system including an LGI-23 pulsed nitrogen laser
(λexcitation = 337 nm; measurement error of 10%). The
determination limit was 10 µs; therefore, the measurement
(
1.2 mmol) was added. The autoclave was heated with
3+
of the much shorter value of τ for Ce * was impossible.
The system and the procedure used for chemilumines-
cence measurements were described previously [15].
continuous stirring for 4–6 h at 80–100°C and then
cooled. The reaction mass was three times extracted with
diethyl ether (50 ml), and the combined extracts were
dried with anhydrous MgSO . The solvent was distilled
4
off, and the residue was fractionated in a vacuum.
RESULTS AND DISCUSSION
The solution after the reaction of a crystalline
hydrate with TIBA and Cat-Ln was analyzed to deter-
Interaction of Crystalline Hydrates with TIBA
3
+
3+
Liquid and gaseous products. The crystalline
hydrates are insoluble in aromatic solvents. Upon the
addition of TIBA to a crystalline hydrate suspension in
a solvent, intense gas release occurred. According to
the results of the GLC analysis of liquid and gas phases,
this gas was isobutane.Alumoxane was identified as the
second soluble product based on IR spectra [14]:
mine the concentrations of Ln and Al by trilonome-
try and atomic absorption spectrometry, respectively, in
accordance with published procedures [13]. The water
contents of the crystalline hydrates and reaction prod-
ucts were determined by the Karl Fischer method [13].
The presence and number (N) of metal–carbon bonds in
Cat-Ln were determined from the volume of isobutane
–
1
absorption at 680, 620, and 1460 cm (stretching and
released in hydrolysis with 10% aqueous HNO . The
3
deformation vibrations of CH groups at the Al atom)
following equation was used for calculations: N =
2
–
1
V/22400 (where V is the volume of isobutane with con- and in the region 780–810 cm (asymmetrical defor-
sideration for its water solubility (ml), and 22400 ml is mation vibrations of the Al–O bond). Chelatometric
3
+
the volume of a mole of isobutane at 20°C). Alumoxane and fluorescence analysis demonstrated that Ln ions
(
(iso-Bu Al) O) was identified using IR spectra accord- were absent from the solution after the reaction of a
2 2
ing to Boleslawski and Serwatowski [14], and isobu- crystalline hydrate with TIBA; that is, the lanthanide
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

5
74
BULGAKOV et al.
Visobutane, % (on theoretical basis)
00
hydrates exhibited the same crystal structure: mono-
4
1
4
3
clinic system; space group P –C [16]. Changes in
2/c
2h
the rates of reactions of the crystalline hydrates with
TIBA at the beginning of the process (to 2 min) are
characterized by the following order: Ce > Pr > Eu >
Tb. Therefore, we related the effect of the nature of the
lanthanide on the rate of dehydration of the crystalline
hydrate in this time interval to different bond strengths
8
6
4
2
0
0
0
0
1
2
3
'
3
+
of crystal water with Ln ions. According to Ukraint-
seva et al. [17], the bond strengths of crystalline
hydrates increased with the atomic number of the ele-
ment. After the second minute, the rate of isobutane
release decreased in the order Eu > Ce > Pr > Tb. We
related the maximum rate of dehydration of EuCl ·
3
3
+
2+
0
10
20 t, min
6H O in this order to the reduction of Eu to Eu as a
2
result of an attack of TIBA, which leads to a decrease
in the coordination number of europium. Note that, pre-
viously [5], the effect of the nature of the lanthanide on
the rate of isobutane release was not found in the dehy-
dration of crystalline hydrates at temperatures of
Fig. 1. Effect of the nature of the lanthanide on the kinetics
of isobutane release (20°C) in the interaction of LnCl ·
3
6
H O (0.54 mmol) with iso-Bu Al in toluene. Ln = (1) Ce,
2 3
(
2) Pr, (3) Tb, and (4) Eu. Ln/iso-Bu Al = (1–4) 1/12 or
3
(3') 1/20.
≥
40°C. It is likely that at higher temperatures this effect
was compensated by an increase in the rate of reaction
with temperature. The effect of the nature of the solvent
(Fig. 2) is characterized by the following order: ben-
zene > toluene > ethylbenzene > cumene, which corre-
lates with the well-known order [11] of decreasing
reactivity of alkylaluminums due to their solvation with
solvent molecules. The rate of isobutane release
increased with the TIBA/crystalline hydrate ratio
(Fig. 1). The total amount of released isobutane was
found to be smaller than the stoichiometric amount
determined by the reaction
Visobutane, % (on theoretical basis)
1
2
3
3
4
2
1
0
LnCl · 6H O + 12(iso-Bu Al)
3
2
3
6
(iso-Bu Al) é + 12(iso-BuH).
2 2
This fact suggests that 2.7–4.5% of unreacted crystal
water remained in Cat-Ln.
Thus, the interaction of crystalline hydrates with
TIBA resulted in the formation of the same soluble prod-
ucts as in the well-known reaction of free water with
TIBA [11]
0
.75
1.50
t, min
Fig. 2. Effect of the nature of the solvent on the kinetics of
isobutane release (20°C) in the interaction of TbCl · 6H O
3
2
(
0.54 mmol) with iso-Bu Al (6.48 mmol): (1) benzene,
3
(2) toluene, (3) ethylbenzene, and (4) cumene.
H O + 2(iso-Bu Al)
2
3
(
iso-Bu Al) é + 2(iso-BuH).
2 2
remained completely in a solid phase. Thus, the vigor-
ous reaction of the crystal water of a crystalline hydrate
with TIBA occurred not only in toluene at elevated tem-
peratures, as reported previously [5], but also in various
aromatic solvents at room temperature.
The rate of isobutane release depends on the nature
of the lanthanide, its ability to change the oxidation
number, the solvent, and the TIBA/crystalline hydrate
ratio. Figure 1 demonstrates the effect of the nature of
the lanthanide. This effect can be due to the following
two main factors: the strength of the bond of a lan-
thanide ion with crystal water and the type of the crystal
On this basis, we believe that the mechanism of for-
mation of these products is the same in the reactions of
TIBA with free and crystal water; that is, the presence of
a lanthanide ion does not affect the mechanism of reac-
tion between the above reactants, as is often the case with
other reactions. According to published data [11], the
interaction of TIBA with water is a two-step process. At
the first step, isobutane and iso-Bu AlOH are formed. At
the second step, iso-Bu AlOH reacts with another TIBA
molecule to form alumoxane and isobutane.
2
2
Solid products. According to the Karl Fischer anal-
lattice of the crystalline hydrate. The test crystalline ysis, the samples of Cat-Ln contained 0.4–0.7 water
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

A NEW APPROACH TO THE PREPARATION OF LANTHANIDE CATALYSTS
575
molecules, which corresponds to the amount of formed
D
1.0
isobutane. The amount of unreacted crystal water after
the termination of isobutane release was independent of
the nature of the solvent and the lanthanide and its abil-
ity to undergo reduction. The residual crystal water
cannot be removed even with a 20-fold excess of TIBA
with respect to crystal water and with thoroughly
ground samples of the crystalline hydrates. We believe
that the incomplete dehydration of the crystalline
hydrates was due to heterogeneous interactions, which
resulted in the passivation of the solid phase.
1
2
0.8
0.6
0
0
.4
.2
Along with water, Cat-Ln contained Ln and Cl
(
Ln/Cl = 1/3), as well as Al (Ln/Al = 1/0.04–0.07). In
the hydrolysis of Cat-Ln with a 10% HNO solution,
3
isobutane was released; this fact was indicative of the
presence of an organometallic compound in Cat-Ln. In
this case, the concentration of iso-Bu–metal fragments
in Cat-Ln determined from the amount of released isob-
utane was lower than the concentration of the lan-
thanide by more than two orders of magnitude and
greater than the concentration of aluminum by a factor
of more than 2. It is well known that a tenfold (or
higher) excess of TIBA [2] and an alumoxane amount
greater by two orders of magnitude [18] are required for
the alkylation of lanthanide chlorides. In the interac-
tions of the crystalline hydrates with TIBA, more than
200
250
300
350
λ, nm
Fig. 3. Absorption spectra of the solutions of (1) Cat-Eu and
–
3
(2) EuCl · 6H O in 0.65 M HCl; [Cat-Eu] = 10 mol/l;
3 2
–
1
[EuCl · 6H O] = 2 × 10 mol/l.
3
2
Photoluminescence intensity, arb. units
0
6
9
0% of TIBA was consumed in the reaction with crystal
water. Taking into account these circumstances, we can
3
+
exclude the alkylation of Ln with TIBA molecules
and conclude that the organometallic compound is
40
20
0
(
iso-Bu Al) O. Small amounts of (iso-Bu Al) O con-
2 2 2 2
tained in Cat-Ln did not allow us to detect it by IR spec-
tra. Based on elemental analysis data, the results of
hydrolysis, and analysis for water, we found the empir-
ical formula of Cat-Ln: LnCl · (0.4–0.7)H O · (0.04–
3
2
2
2
0
.07)(iso-Bu Al) O. For example, for Cat-Tb we found
1
1
2
2
'
the following (%): Tb, 54.83; Al, 0.92; Cl, 36.84;
'
C, 3.41; H, 0.98; O, 3.02; Al–C/Al = 2. For TbCl ·
3
x(H O) · y(iso-Bu Al) O (where x = 0.5; y = 0.05; aver-
2
2
2
350
400
450
500
550
600
λ, nm
age values obtained in six experiments are given).
Calcd. (%) Tb, 54.93; Al, 0.93; Cl, 36.81; C, 3.32;
H, 0.97; O, 3.04; Al–C/Al = 2.
Fig. 4. Photoluminescence spectra (20°C) of (1) TbCl ·
3
6
H O, (1') Cat-Tb, (2) CeCl · 6H O, and (2') Cat-Ce.
2 3 2
λexcitation = (1, 1') 365 or (2, 2') 300 nm.
Physicochemical Properties of Cat-Ln
Absorption spectra of Cat-Ln solutions. The
absorption spectra (visible region) of the solutions of not described previously. At the same time, the reduc-
Cat-Ln (Ln = Ce, Pr, or Tb) in HCl (0.65 M) contained
3+
tion of Eu as a constituent of organic lanthanide com-
3
+
maximums characteristic [9] of Ln ions (not given). plexes with alkylaluminums is well known [10].
By contrast, the absorption spectrum of an analogous
solution of Cat-Eu (Fig. 3) exhibits new diffuse and
Luminescence properties of Cat-Ln. The photolu-
minescence spectra of Cat-Tb (Fig. 4) contain maxi-
more intense maximums at 250 and 325 nm, which are
mums at 493, 546, 586, and 593 nm and a shoulder at
2
+
characteristic of Eu compounds [19], in place of nar-
5
50 nm, and the spectra of Cat-Ce contain a diffuse
3
+
row maximums of Eu . Thus, of all of the lanthanides maximum at 356 nm and a shoulder at 368 nm, the
3
+
2+
tested, only Eu was reduced to Eu because of the positions of which are slightly different from those in
interaction of the crystalline hydrate with TIBA. The the spectra of parent TbCl · 6H O (488, 493, 545, 586,
3
2
3
+
reduction of Eu as a constituent of EuCl · 6H O and 591 nm) and CeCl · 6H O (351 nm and a shoulder
3
2
3
2
under the action of organoaluminum compounds was at 365 nm). Despite the above difference between the
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

5
76
BULGAKOV et al.
3
+
8
6
4
2
τ for Tb * before and after the oxidation of Cat-Tb
with oxygen remained unchanged. This additionally
evidenced that Cat-Ln does not contain Ln–alkyl bonds
1
3
+
because otherwise the value of τ for Tb * would
increase as a result of the appearance of Tb–O–alkyl
bonds, which are characterized [6, 7] by longer values
2
3
3+
of τ for Tb *. The intensity and shape of spectra and
the nature of chemiluminescence emission centers
depend on the nature of the lanthanide. Thus, the fol-
lowing maximum chemiluminescence intensities were
8
6
4
2
0
1
50
300
450
600 t, s
–1
–1
7
7
obtained (photon s ml ): 6.4 × 10 (Cat-Tb), 1.5 × 10
1
'
7
(
Cat-Pr), and 1.6 × 10 (Cat-Ce); that is, chemilumines-
cence intensities were almost equal in the cases of Cat-
Pr and Cat-Ce, whereas the chemiluminescence inten-
sity of Cat-Tb was much higher. In the case of Cat-Tb,
2
'
3
'
3+
the Tb * ion is the emitter of chemiluminescence
4
00
450
500
550
600
λ, nm
(
λmax = 490 and 545 nm), whereas the excited triplet
3
state of isobutyraldehyde ( BA*) was identified as a
chemiluminescence emitter (λmax = 420 nm) in the oxi-
dation of Cat-Ce and Cat-Pr. Based on the spectro-
scopic and brightness parameters of chemilumines-
cence and published data on chemiluminescence acti-
vation in the autooxidation of (iso-Bu Al) O with terbium
Fig. 5. (1–3) Kinetic curves and (1'–3') chemiluminescence
spectra measured on oxygen puffing onto the surface of Cat-
Ln (20°C). Ln = (1, 1') Tb, (2, 2') Ce, and (3, 3') Pr. (A set
of boundary light filters was used).
2
2
photoluminescence spectra of Cat-Ln and the crystal- complexes [20], we propose the following mechanism of
line hydrates and with consideration for well-known chemiluminescence excitation: The primary emitter
3
data on the photoluminescence of terbium and cerium
BA* results from the oxygen oxidation of (iso-
compounds [9], we can state that the photolumines- Bu Al) O, which is a constituent of all of the Cat-Ln spe-
cence of Cat-Tb is due to f–f transitions ( D – F , D – cies. In the case of the oxidation of Cat-Ce and Cat-Pr, the
2
2
5
7
5
4
6
4
7
5
7
3
F , and D – F ), whereas the photoluminescence of emitter BA* is deactivated with the emission of short-
5
4
4
2
wavelength chemiluminescence (λmax = 420 nm). In the
Cat-Ce is due to transitions from the lower level D to
2
2
3
the sublevels F and F . The peak positions and oxidation of Cat-Tb, energy is transferred from BA* to
7
/2
5/2
the terbium ion, which is converted into the excited state
intensities in the photoluminescence spectra of Cat-Tb
3+
and Cat-Ce did not depend on the nature of the solvent Tb *; then, it emits brighter long-wavelength chemilu-
in which the dehydration of crystalline hydrates minescence (λmax = 490, 545 nm). This mechanism was
3
occurred. As a result of the dehydration of TbCl · supported by the absence of BA* emission from the
3
3
+
6
H O, the value of τ for Tb * decreased from 425 to chemiluminescence spectra of Cat-Tb samples.
2
1
00 µs for Cat-Tb. The photoluminescence intensities
3+
The absence of Ce * emission from chemilumines-
of Cat-Tb and Cat-Ce were lower than the photolumi-
nescence intensities of the crystalline hydrates. We
related these changes to a decrease in the number of
water molecules in the coordination sphere of lan-
thanide ions and to structural changes in the crystal lat-
tices of the crystalline hydrates.
cence in the oxidation of Cat-Ce was due to a higher
energy of the emitting level of Ce * (350 nm, 4.2 eV),
as compared with that of BA* (420 nm, 3 eV). It is
well known [9] that the photoluminescence spectra of
the solutions of Pr compounds contain maximums at
46, 260, 271, 395, and 480 nm. However, short-wave-
3
+
3
3
+
2
In the case of Cat-Eu, red photoluminescence, length excitation is required for the detection of these
3
+
which is characteristic of Eu * [9], was not detected emission bands (λ
= 213 nm, 5.8 eV). Therefore,
excitation
3+
3
+
2+
3+
because of the reduction of Eu to Eu as a result of the absence of Pr , as well as Ce , emission from the
the interaction of EuCl · 6H O with TIBA. The photo- chemiluminescence spectrum of Cat-Pr is due to an
3
2
luminescence intensities of PrCl · 6H O and Cat-Pr energy deficiency.
3
2
were very weak; because of this, luminescence mea-
surements in praseodymium compounds were not per-
formed in this study.
TG DTA. The TG DTA curves of a Cat-Tb sample
(
Fig. 6) exhibited four segments. In the range 30–
1
45°C, a small weight increase (1.2%) occurred. We
related this increase to the oxidation of (iso-Bu Al) O
In addition to the release of isobutane in the course
2
2
of hydrolysis, chemiluminescence (Fig. 5), which was to an alkoxy derivative, which has a greater molecular
detected upon oxygen puffing onto the surface of pow- weight than that of (iso-Bu Al) O. The increase in the
2 2
dered Cat-Ln (Ln = Tb, Ce, and Pr), evidenced the pres- sample weight was quantitatively consistent with the
ence of (iso-Bu Al) O in Cat-Ln. Note that the value of formation of (iso-Bu OAl) O, and it began even before
2
2
2
2
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

A NEW APPROACH TO THE PREPARATION OF LANTHANIDE CATALYSTS
577
the heating was turned on. The oxidation of (iso-
Bu Al) O, as well as other organoaluminum com-
Weight change, %
∆T, °C
2
2
2
Exo
pounds, is an exothermic process [11], which manifests
itself as a diffuse maximum in the DTA curve. The TG
DTA curves of crystalline hydrate samples did not
exhibit an increase in the weight over the segment 30–
100
1
9
8
0
0
0
1
45°C [21]. The weight loss in a Cat-Tb sample over
the range 145–200°C was due to an endothermic pro-
cess of the removal of residual crystal water (5%),
whereas the weight loss in the range 200–250°C was
due to the complete combustion of organics (5%) as a
result of the exothermic oxidation of the hydrocarbon
fragments of (iso-Bu OAl) O with the formation of
–1
–2
0
100 200 300 400 500 600 700
T, °C
2
2
Fig. 6. TG DTA curves for Cat-Tb.
water and CO . In the region 250–750°C, the TG DTA
2
curves of the Cat-Tb sample reflect the successive for-
mation of the mixed oxychloride TbOCl · 2TbCl and
the oxychloride TbOCl; it is well-known that these pro-
cesses occur in the crystalline hydrate [21].
3
0
0
.8
(a)
XRD analysis. Figure 7 shows the XRD patterns of
Cat-Tb and TbCl · 6H O (well-crystallized substance).
.4
3
2
The intensity ratio between reflections and the posi-
tions of their centers in the diffraction patterns of Cat-
Tb do not coincide with the corresponding parameters
of TbCl · 6H O and TbCl as a possible product of the
3
2
3
reaction of TbCl · 6H O with TIBA. Moreover, the dif-
3
2
(
b)
0
0
.10
.05
fraction pattern of Cat-Tb allowed us to conclude that
the ordered substance occurred in two forms: crystal-
line and amorphous. XRD analysis suggests that the
crystalline phase of Cat-Tb has the structural type of the
TbCl · 6H O lattice (monoclinic system; space
3
2
4
group P –C ) but another lattice spacing. The esti-
1.0
0.5
2/c
2h
(
c)
mated average block diameters of the crystalline phase
of Cat-Tb and TbCl · 6H O are 600 and 700 Å, respec-
3
2
tively (mean-square microdeformations of 0.35 and
0
.2%, respectively). Based on quantitative XRD analy-
sis, the phase composition of Cat-Tb was calculated
assuming a two-phase system. The volume fractions of
crystalline and amorphous phases were equal to ~40
and ~60%, respectively. The amorphous component,
the smoothed X-ray spectrum of which is shown in Fig.
(d)
0.04
.02
7
(smoothing parameters: rectangular window; window
halfwidth, 50), exhibited a certain ordering. The amor-
phous phase hypothetically crystallized in an orthor-
hombic system, space group Cmmn.
0
The empirical formula of Cat-Ln and the XRD data
for the Cat-Tb sample allowed us to propose the follow-
ing most probable structures (A and B) of compounds
that form the basis of the amorphous and crystalline
0
20
40
60
θ, deg
80
100
2
Fig. 7. Diffraction patterns of (a) TbCl · 6H O, (b) Cat-Tb,
and (c) TbCl ; (d) smoothed spectrum of an amorphous
3
2
3
+
Cat-Ln phases (where Ln = Ln ):
3
component of Cat-Tb.
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Ln
Ln
Ln
O
Ln
O
Bridging units, in which lanthanide ions are bound
Cl
Cl
Cl n
Cl
Cl m
to each other through chlorine atoms, are the main
common elements of these structures. Amorphous
structure A fully consists of these units. Despite the
complete dehydration of the lanthanide ion with the
H
H
H
B
H
A
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

5
78
BULGAKOV et al.
Activity of Cat-Ln in the reaction of aniline condensation
with butyraldehyde
As the predominant product, 2-propyl-3-ethylquino-
line (1) was formed in a high yield. The structure of com-
1
3
1
pound 1 was found based on the C and H NMR spec-
Yield Aniline con- Yield of resin-
Catalytic system
tra, a comparison with an authentic sample [1], and the
results of elemental analysis. C NMR (CDCl ) δ (ppm):
161.33 (s, C ), 134.7 (s, C ), 133.2 (d, C ), 127.0 (d, C ),
26.48 (d, C ), 128.1 (d, C ), 125.15 (d, C ), 146.07 (s, C ),
25.05 (s, C ), 37.22 (t, C ), 23.4 (t, C ), 13.91 (q, C ),
4.7 (t, C ), 14.0 (q, C ). H NMR (CDCl ) δ (ppm):
.03 (t, J = 7.3 Hz, CH (C )), 1.23 (t, J = 7.4 Hz, CH
(C )), 1.8 (m, J = 7.5 Hz, CH (C )), 2.7 (q, J =
7.4 Hz, CH (C )), 2.9 (t, J = 7 Hz, CH (C )), 7.3 (t,
J = 7.3 Hz, H (C )), 7.5 (t, J = 7.6 Hz, H (C )), 7.66 (d,
J = 8 Hz, H (C )), 7.8 (s, H (C )), 8.04 (d, J = 8.4 Hz,
H (C )). For C H N anal. calcd. (%): C, 84.5; H, 8.5;
of I, % version, % ous products, %
13
3
2
3
4
5
PrCl –Ph P*
61
80
7
10
20
21
14
4
3
3
6
7
8
9
1
1
2
1
Cat-Pr–Ph3P
78.6
68.0
57.2
58.7
81.6
69.3
59
98
10
11
12
13
Cat-Ce–Ph3P
80.1
98
14
15
1
3
Cat-Tb–Ph3P
3
15
3
3
3
2
+
Cat-Eu –Ph P
98
13
3
12
3
3
2
1
4
3
11
Cat-Pr
98.5
80.4
98
2
2
3
6
3
7
Cat-Ce
Cat-Tb
Cat-Eu2+
13
15
7
3
5
4
3
8
14
17
71.3
98
N, 7.0. Found (%): C, 84.2; H, 8.4; N, 7.4.
Note: Condensation conditions: T = 80°C; 4 h; autoclave; solvent,
As by-products, N-butylaniline (2) and oligomeriza-
tion products (3) and (4) of the parent aldehyde were
identified. Unidentified resinous products were also
formed in the reaction.
DMF.
*
Well-known PrCl –Ph P catalyst [1]. Condensation condi-
3 3
tions: T = 100°C; 6 h; autoclave; solvent, DMF.
The table summarizes the results of testing the effi-
ciency of Cat-Ln, as compared with the well-known
formation of structure A, the formation of the crystal-
most active and selective PrCl –Ph P catalyst [1]. It
line form of LnCl did not occur. Previously, the forma-
3
3
3
was found that Cat-Pr was superior to the PrCl –Ph P
tion of an amorphous phase of LnCl as a result of the
3
3
3
catalyst in all parameters (2-propyl-3-ethylquinoline
yield, aniline conversion, and by-product amount).
Moreover, the reaction effectively occurred on Cat-Ln
at lower temperatures and in a shorter time. The nature
of the lanthanide insignificantly affected the conversion
of aniline and the yield of 2-propyl-3-ethylquinoline.
The most active catalyst was Cat-Pr. Note that Cat-Ln
interaction of LnCl · 3TBP with TIBA was found [2].
3
Unlike A, crystal structure B contained residual water
molecules (unreacted with TIBA) coordinated to the
lanthanide ion. Based on the low alumoxane content of
Cat-Ln (5.0–5.5%), its presence can be due to the trap-
ping of alumoxane molecules in the dehydration of
crystalline hydrates and the transformation of the crys-
tal lattices of crystalline hydrates into the new crystal
lattice of structure B. It is likely that these small alu-
moxane amounts had no effect on the formation of
structures A and B.
efficiently operated in the absence of Ph P, which is an
3
activator frequently used in catalysis. Moreover, the
addition of Ph P decreased the yield of the target prod-
3
uct and increased the amount of resinous products. The
consideration of the operation mechanism of Cat-Ln is
beyond the scope of this paper because this is the sub-
ject matter of our further studies.
Catalytic Properties of Cat-Ln
Thus, we developed a simple procedure for the prep-
aration of a highly efficient lanthanide catalyst for the
reaction of aniline condensation with butyraldehyde to
form 2-propyl-3-ethylquinoline. A new approach to the
preparation of lanthanide catalysts for the synthesis of
nitrogen heterocycles was proposed based on the reac-
tions of LnCl · 6H O crystalline hydrates with orga-
The samples of Cat-Ln (Ln = Ce, Pr, Tb, and Eu)
were tested for catalytic activity in the reaction of
aniline condensation with butyraldehyde. The follow-
ing reaction scheme represents the composition of
identified products:
3
2
NH2
noaluminum compounds.
Et
Pr
Cat-Ln
+
O
ACKNOWLEDGMENTS
N
1
This work was supported by the Russian Foundation
for Basic Research (project no. 05-03-97906).
NHBu
O
+
+
+
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KINETICS AND CATALYSIS Vol. 47 No. 4 2006

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KINETICS AND CATALYSIS Vol. 47 No. 4 2006