Comparative hydroamination of aniline and substituted anilines with styrene on different zeolites, triflate based catalysts and their physical mixtures

Article abstract of DOI:10.1016/j.apcata.2013.05.032

Catalytic performances of different zeolites (Beta and mordenites), scandium triflate based catalysts, mesoporous UVM-7 encapsulated scandium triflate and physical mixtures prepared under ultrasound irradiation were evaluated in the hydroamination of aniline and substituted anilines with styrene. The performances of these catalysts were controlled by the type of acidity and strength. Thus, the conversion was mainly controlled by the strength of the acid sites and their accessibility, while the selectivity appeared to be controlled by the Lewis/Br?nsted type of acidity. Lewis acid catalysts directed the reactions mainly to the formation of the Markovnikov adducts while Br?nsted acid catalysts to anti-Markovnikov. Zeolites and scandium triflate led to results very close to those reported in the literature. Among different physical mixtures those of scandium triflate with the mesoporous scandium triflate embedded in a UVM-7 structure provided better conversions with a good selectivity in the Markovnikov adduct. These results were attributed to a better dispersion of scandium triflate during the preparation of physical mixtures.

Full text of DOI:10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
Applied Catalysis A: General xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Comparative hydroamination of aniline and substituted anilines with
styrene on different zeolites, triflate based catalysts and their physical
mixtures
M. Ciobanua, A. Tirsoagaa, P. Amorosb, D. Beltranb, S.M. Comana, V.I. Parvulescua,∗
a University of Bucharest, Faculty of Chemistry, Department of Organic Chemistry, Biochemistry and Catalysis, Bd. Regina Elisabeta 4-12, Bucharest 030016,
Romania
b Institut de Ciencia dels Materials, Universitat de València, PO Box 2085, 46071 Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Catalytic performances of different zeolites (Beta and mordenites), scandium triflate based catalysts,
mesoporous UVM-7 encapsulated scandium triflate and physical mixtures prepared under ultrasound
irradiation were evaluated in the hydroamination of aniline and substituted anilines with styrene. The
performances of these catalysts were controlled by the type of acidity and strength. Thus, the conver-
sion was mainly controlled by the strength of the acid sites and their accessibility, while the selectivity
appeared to be controlled by the Lewis/Brønsted type of acidity. Lewis acid catalysts directed the reactions
mainly to the formation of the Markovnikov adducts while Brønsted acid catalysts to anti-Markovnikov.
Zeolites and scandium triflate led to results very close to those reported in the literature. Among different
physical mixtures those of scandium triflate with the mesoporous scandium triflate embedded in a UVM-
7 structure provided better conversions with a good selectivity in the Markovnikov adduct. These results
were attributed to a better dispersion of scandium triflate during the preparation of physical mixtures.
© 2013 Elsevier B.V. All rights reserved.
Received 1 February 2013
Received in revised form 2 May 2013
Accepted 10 May 2013
Available online xxx
Keywords:
Hydroamination
Aniline
Substituted anilines
Styrene
Lewis/Brønsted catalysts
Physical mixtures
1. Introduction
using metal salts or cationic metal complex catalysts [13–15]. The
interaction of the olefin/alkyne with the metal center reduces the
Amines are very important precursors in the synthesis of fine
chemicals such as natural products or pharmaceuticals, but also in
the production of bulk chemicals [1–5]. In this respect, hydroami-
nation of double or triple carbon bonds represents an elegant and
cheap route since it utilizes cheap and readily available feedstock
of olefins and amines and proceeds theoretically with 100% atom
efficiency.
Literature reported several catalytic routes for hydroamination
reaction [6,7]. Among these, in homogeneous catalysis this reaction
may occur via: (i) hydroamination of olefins via oxidative addi-
tion of the amine to a transition metal (a late transition metal (Pd,
Ru, Rh, Ir) complexed by a phosphine ligand, or early transition
metal complexes, such as rare-earth elements) [8–10]; (ii) ami-
nation of olefins via an alkaline metal or lanthanide compound (Li,
Na, Ln) [11,12]; (iii) a radical mechanism for the alkaline metals-
catalyzed hydroamination of ␣-methylstyrene with aziridine [6];
(iv) hydroamination of alkynes via metal (U, Zr, Ti) imide species,
(v) Lewis acid catalyzed hydroamination of olefins and alkynes
electron density in the ␲-system and allows the nucleophilic attack
of the amine nitrogen atom.
The coordination of substrates with Brønsted or Lewis acids
may catalyze reactions involving unsaturated systems through the
formation of more-electrophilic complexes or charged interme-
diates. Recent studies in hydroamination of dienes and allenes
demonstrated that to achieve this goal under metal-free catalytic
conditions the presence of an acid with certain acidity is necessary
[16]. The use of Ga, Yb, Pr, In, Bi, Cu, Fe, Sc, Ag, or Zn triflate overcome
these problems. Moreover, catalysts based on the late transition
metals and salts like triflates have a high tolerance to water and
oxygen impurities and are, thus, of high interest for practical appli-
cations [17]. Accordingly, the literature reported many examples
of intermolecular hydroamination of a high variety of substrates
with aliphatic or aromatic amines in the presence of such catalytic
species [18–31].
Brønsted HOTf displayed a high activity in the intramolecular
hydroamination of N-(2-cyclohex-2ꢀ-enyl-2,2-diphenylethyl)-p-
toluene-sulfonamide [32]. In spite of the fact that pure triflic acid
showed rather poor efficiency in intermolecular hydroamination
[33] mechanistic investigations demonstrated that the coordina-
tion of the amine to the copper cationic complex generated a
Brønsted acid which was the prominent catalytic species, thus
∗
Corresponding author. Tel.: +40 21 410 02 41; fax: +40 21 410 02 41.
E-mail addresses: vasile.parvulescu@g.unibuc.ro,
v parvulescu@yahoo.com (V.I. Parvulescu).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.05.032
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
2
M. Ciobanu et al. / Applied Catalysis A: General xxx (2013) xxx–xxx
questioning whether a true metal-catalyzed process is involved or
if the role of the metal is to generate Brønsted acidity [34]. Triflate
salts of cationic metal complexes ([(BINAP)Pd(solvent)2]2+) cat-
alyze hydroamination of primary (and secondary) aromatic amines
with ␣,␤-unsaturated oxazolidinones [35]. In addition to triflate,
bis(trimethylsilyl)amide represents another anion strong enough
to activate rare-earth elements for hydroamination reactions using
non-activated alkenes [36].
Biphasic catalysis methodology may economically improve the
hydroamination reactions especially due to the simple and com-
plete separation of the product from the catalyst. A system formed
from a polar phase (e.g., 1-ethyl-3-methylimidazolium trifluo-
romethanesulfonate ionic liquid) with dissolved Rh(I), Pd(II), Cu
or Zn(II) catalytic complexes and a non-polar phase (e.g., heptane)
with dissolved substrate exemplified this concept [37–39].
Bi-functional catalysts combining soft Lewis acidic function
(activation of the alkene) and strong Brønsted acidic function
(acceleration of the rate determining step (r.d.s.)) were reported
to provide high catalytic activities in this reaction [40]. Electron
rich anilines react more readily and the presence of a Brønsted
acid accelerates the reaction. The role of the acidic promoter was
explained through protonolysis of the pre-catalyst to give cationic
complexes, which seem to be the active species involved in the
mechanism [40].
The hydroamination of aromatic amines with activated olefins
(methyl acrylate, i.e. an aza-Michael addition) was also examined
over Y, MOR or LTA zeolites in both Na- and H-forms showing
that amines with an electron-withdrawing functional group gave
products in moderate conversions because of their low basicity
[61,62]. Methyl acrylate is an ␣,␤-unsaturated carbonyl compound
and the addition of a nucleophile occurs via a conjugate addition,
where an anti-Markovnikov selectivity is thus expected. The same
adduct (e.g., anti-Markovnikov) was in majority formed on a mont-
morillonite clay [63] in a conjugate addition of ␣,␤-unsaturated
carbonyl compounds, while using non-activated substrates on the
exchanged Brønsted acid sites was accompanied by a change in the
selectivity in the favor of Markovnikov regioisomers [64,65].
As a short conclusion, the literature indicates a continuous inter-
est for this reaction. All the investigated catalysts exhibit either
Brønsted or Lewis acid sites, or both. However, in spite of the
sustained effort it is still unclear which kind of acidity is deter-
minant for this reaction and how is it correlated to the selectivity
to the Markovnikov or anti-Markovnikov products. Based on this
state of the art the scope of the present study was to re-visit the
hydroamination reaction from the perspective of the influence of
the nature of the acid sites to conversion and selectivity. To this pur-
pose zeolites, triflates, and mesoporous silica embedded triflates
were comparatively investigated.
Heterogeneous catalysis provides a more versatile route to carry
out the hydroamination reaction and several classes of materials
have been reported in literature. Among these are hybrid organic
modified TiO2 nanoparticles [41], heteropolyacid catalysts [42],
simple Al-SBA-15 catalysts [43] or heteropolyacid encapsulated
SBA-15/TiO2 nanocomposites [44], copper(II) exchanged Al-SBA-
15 [45], zeolites [46], immobilized triflic acid on silica [47] and SILP
(supported ionic liquid phase) systems with organometallic com-
plexes like Pd-1,1ꢀ-bis(diphenylphosphino)-ferrocene combined
with TfOH dissolved in it [48,49]. Catalytic amounts of Brønsted
or Lewis acid in ionic liquids were found to provide higher selec-
tivity and yields than those performed in classical organic solvents
[50]. The ionic liquid increases the acidity of the media and stabi-
lizes ionic intermediates through the formation of supramolecular
aggregates. The simple addition of TfOH to the supported ionic
liquid phase was also indicated to promote the intermolecular
hydroamination [48]. In contrast to these studies, it was shown
that the presence of n-Bu4PBr has no beneficial effect for the
platinum-catalyzed hydroamination of terminal alkynes. Pristine
PtBr2 catalyze the hydroamination of terminal alkynes with aniline,
and according to its Lewis nature the reaction is fully regioselective
affording the branched imine (Markovnikov) [51].
Other ionic catalysts reported in this reaction are double metal
cyanides [52] and cation exchanged resins (Amberlyst-15, Nafion)
[53]. A cooperative behavior between Lewis and Brønsted acid sites
in mesostructured materials was also reported for bifunctional Au
nanoparticle-acid catalysts obtained via reduction of Au3+ with HS-
functionalized periodic mesoporous organosilicas [54].
In the case of zeolites, the initial studies using H-BEA or ZSM-5
zeolites indicated that they are able to protonate the iso-butene to
the corresponding tert-butyl carbenium ion [55,56] that can further
react with ammonia or an amine. Ionic-exchange of zeolites (H-
BEA) with Rh(I), Cu(I) or Zn(II) led to catalysts with a higher catalytic
activity than the corresponding homogeneous Zn(CF3SO3)2 cata-
lyst, but smaller than that of the parent BEA-zeolite [17,40,57,58].
However, this rule is not general. For the cyclization of 6-amino-1-
hexyne the activity of ion-exchanged zeolites is higher [57].
The activity of ion exchanged heterogeneous catalysts was
assigned to residual protons in the material [59]. In fact the reac-
tion was supposed to be initiated by the Lewis acidic metal centers,
while the presence of the protons can only enhance the reaction
rate [60].
2. Experimental
Zeolites with different structures and different chemical compo-
sitions were purchased from different companies. H-beta zeolites
(PQ25, PQ 30 and PQ 75) were received from PQ-Valfor Company,
Mordenite CBV 20A and 30A were purchased from Zeolyst Interna-
tional. Sc(OTf)3 was purchased from Aldrich. Mesoporous UVM-7
encapsulated scandium triflate catalyst with the Si/Sc atomic ratio
of 60 (TfSc(60)) was prepared by Atrane route using a methodol-
ogy reported elsewhere [66,67]. Physical mixtures of these catalysts
were prepared following a methodology proposed by Delmon [68].
Accordingly, the concerned samples were dipped in n-pentane and
stirred for 10 min and then were submitted to ultrasounds for
10 min. Ultrasonic irradiation was performed at 70 kHz at 298 K.
Thereafter, n-pentane was evaporated under reduced pressure in
a rotavapor at 298 K. The solid was thereafter dried in air at 353 K
overnight. No additional thermal treatment was carried out. The
ratios of the components in the different mechanical mixtures are
indicated at the appropriate places in the text.
The samples were characterized by a series of techniques such
as nitrogen adsorption–desorption isotherms and Py- and NH3-
FT-IR. The NH3-TPD profiles were done using a Micromeritics
Auto-ChemII apparatus. FT-IR measurements were performed at
room temperature on a Magna-IR 550 FTIR spectrometer from Nico-
let using a MCT-B liquid nitrogen cooled detector, and equipped
with a heatable cell (up to 773 K) with NaCl windows connected
to a vacuum system and a gas manifold. The FTIR spectra were
recorded after desorption of pyridine at RT, 423 K, 523 K, 623 K and
723 K, respectively, at a pressure of 10−5 mbar for 15 min. Particle
size distribution was determined from DLS measurements using a
Mastersize2000 from Malvern Instruments.
The catalytic tests were carried out in a stainless steel autoclave
loaded with 50 mg of catalyst, 1 mmol amine (aniline, 4-nitro-
aniline, 4-chloro-aniline and 3-aminophenol), 2 mmol styrene
under autogenic pressure and temperatures of 363–423 K. A non-
polar aprotic solvent, toluene (4 mL), was used. All the reagents
were of Aldrich purity. Reactants and products were analyzed by
GC–MS using a Trace GC 2000 coupled with DSQ MS from Thermo
Electron Corporation. The structure of the resulted products was
confirmed by 1H and 13C NMR spectroscopy using a Bruker AV 400
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
M. Ciobanu et al. / Applied Catalysis A: General xxx (2013) xxx–xxx
3
Fig. 1. Conversion and selectivity in the reaction of aniline and styrene on zeolites Beta and mordenite: (a) 363 K, (b) 423 K (1 mmol aniline, 2 mmol styrene, 4 mL toluene,
50 mg catalyst, 24 h).
spectrometer. Thus, the analytic data for Markovikov adduct were
GC-MS (z/m): 197 (M+, 50), 198 (M+, +1, 5), 182 (100), 183 (10),
180 (7), 120 (6), 105 (36), 93 (21), 77 (16); NMR 1H NMR (CDCl3;
400 MHz): (1.5 ppm; J = 6.5 Hz; 3H; d); (3.9 ppm; J = 6.5 Hz; 1H, m);
(5.3 ppm; J = 0 Hz, 1H, s); (7.19 ppm; J = 7.05 Hz; 1H; t); (7.3 ppm;
J = 7.6 Hz/7.05 Hz; 2H, m); (7.27 ppm; J = 7.6 Hz; 2H; d); (6.8 ppm;
J = 7.4 Hz; 2H, d); (7.27 ppm; J = 7.38 Hz/8.2 Hz; 2H; m); (6.8 ppm;
J = 8.2 Hz; 2H; d); 13C NMR (CDCl3; 400 MHz) ı (ppm) = 27.7; 52.8;
114; 129.8; 116.8; 147.7; 125.9; 128.6; 126.9; 143.8; while for
the anti-Markovnikov adduct were GC–MS (z/m): 197 (M+, 76),
198 (M+, +1, 8), 183 (10), 182 (100), 180 (24), 120 (6), 165(27),
105 (4), 91 (5), 77 (4); NMR 1H NMR (CDCl3; 400 MHz): (2.2 ppm;
J = 6.9 Hz; 2H; t); (3.2 ppm; J = 6.9 Hz; 2H; t); (4.4 ppm; J = 0 Hz; 1H;
s); (6.84 ppm; J = 7.05 Hz; 1H; t); (6.9 ppm; J = 7 Hz/7.05 Hz; 2H, m);
(6.6 ppm; J = 7 Hz; 2H; d); (6.82 ppm; J = 7.4 Hz; 1H, t); (6.9 ppm;
J = 7.38 Hz/8.2 Hz; 2H; m); (6.8 ppm; J = 8.2 Hz; 2H; d) 13C NMR
(CDCl3; 400 MHz ı (ppm) = 36.7; 41.5; 112.8; 127.4; 118.2; 147;
127.6; 128.5; 126.6; 140.
addition [61,62,69]. At 363 K, the change of the Si/Al ratio in the
range 25–75 did not generate a major change in the conversion
(Fig. 1a). However, the selectivity in the anti-Markovnikov iso-
mer reached a maximum (70%) for a Si/Al ratio of 30, while the
increase of the Si/Al ratio to 75 led to an almost equal selectiv-
ity in Markovnikov and anti-Markovnikov adducts that is again in
agreement with previous findings showing that less acidic zeolites
generate higher yields in the anti-Markovnikov isomer.
The increase of the temperature to 423 K led to an increase of
the conversion (almost double compared to that at 363 K). How-
ever, a decrease in the selectivity to the anti-Markovnikov isomer
was determined for the zeolite with a Si/Al ratio of 30, especially
because at this temperature a certain percent of polystyrene (less
than 10%) was detected on all zeolites. Actually, the performances
of the BEA zeolites were very close in terms of the conversion.
Mordenites showed no activity, irrespective of the Si/Al ratio. In
a previous work of Müller and Lercher [40] it was reported that
the products face strong constraints to diffuse out of the pores and
that the larger, but one-dimensional, pores of Mordenite led to low
activity. Zeolite BEA presents two interconnecting channel systems
forming a smaller space than the faujasite supercage. Consequently,
the reactants and the desired products can diffuse into and out of
the pores, and the reaction rate is higher, but also the selectivity.
In addition, although both kinds of materials possess Lewis and
Brønsted acid sites, BEA zeolites are characterized by a stronger
acidity (with preponderantly Brønsted acid sites) while morden-
ites possess softer acidity (with preponderantly Lewis acid sites)
(see FTIR and TPD results and Table 1). For BEA zeolites these char-
acteristics correlate to the selectivity in the hydroamination. In a
way they also well correlate to the differences in the particle size
(34.3 ␮m (BEA-25), 31.2 ␮m (BEA-30), 28.7 ␮m (BEA-75). Müller
3. Results and discussions
Fig. 1 shows results in the hydroamination of styrene with
aniline on the investigated catalysts (Scheme 1). Zeolites with
different structure (Beta and mordenite) and Si/Al ratios (25–75)
showed different behavior. Mordenites, characterized by a bi-
dimensional channel system with straight 12-membered ring
channels with crossed 8-membered ring channels showed no activ-
ity in this reaction, while on BEA zeolite the anti-Markovnikov
isomer was the main reaction product. These results however agree
with data reported previously on zeolites and clays where the
anti-Markovnikov adducts were the main product as a conjugate
R
NH
NH2
R
catalyst
NH
+
+
toluene
0
R
423 K,
150 C, 24h
R = H, p-NO2, p-Cl, m-OH
anti-Markovnikov
Markovnikov
Scheme 1. Hydroamination of styrene with substituted anilines.
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
4
M. Ciobanu et al. / Applied Catalysis A: General xxx (2013) xxx–xxx
Table 1
Textural and chemical characteristics of beta zeolites and mordenites.
Catalyst
Surface areaa (m2/g)
Pore volumea (mL/g)
Pore sizea (nm)
Density of acidic sitesb (mmol/g)
B acid sitesc
L acid sitesc
BEA-75
BEA-30
BEA-25
Mordenite-20A
Mordenite-30A
534
480
465
362
438
0.18
0.18
0.19
0.16
0.18
<1.0
<1.0
<1.0
<1.0
<1.0
0.02
0.16
0.18
0.29
0.48
0.2
0.8
0.9
0.4
0.6
0.05
0.5
0.7
1.6
2.6
a
Textural properties measured with N2 at 77 K.
Calculated from TPD measurements.
The relative population of Lewis (L) acid sites and Brønsted (B) acid sites calculated from the ratio of the integrated area of IR adsorption peak to the sample weight.
b
c
and Lercher [40] also claimed that the rates of reaction decreased
with the particle size. Differences between our results and those
reported by Müller and Lercher can be related to the fact we used
BEA with different particle sizes and acidity than reported in that
study.
sites are initiating the reaction while the presence of the pro-
tons enhances the reaction rate [60]. Extending these results it
was expected that the intimate physical mixture of the two cat-
alysts will increase both the conversion and the selectivity in one
of adducts. Actually such an effect was not determined and they
demonstrated that if this approach is correct it could become effec-
tive only in the case the two active sites (Lewis and Brønsted) are in
an intimate atomic proximity. We should also note that our results
were verified using five successive 50:50 mixtures.
Beside this, the decrease in conversion comparing the two indi-
vidual catalysts may suggest two parallel reactions on individual
catalysts that are modified by each other. A similar behavior was
determined for the physical mixture of Beta zeolite with TfSc(60).
Interestingly, a synergistic effect was determined for a 50:50
physical mixture of mesoporous TfSc(60) embedded scandium tri-
flate and scandium triflate. On this system, the conversion was
almost 70% and the selectivity in the Markovnikov adduct was over
70%. The reaction occurred with no polymerization of styrene.
Based on this result, different TfSc(60)–Sc(OTf)3 physical mix-
tures were investigated. Data presented in Fig. 4 demonstrate that,
indeed, a 50:50 ratio provided the best results. While the con-
version showed the maximum for this mixture, the selectivity
suffered a slight depletion for TfSc(60)–Sc(OTf)3 ratio higher than
50:50. This slight decrease may account to the fact that the OH
of silica UVM-7 is not completely inert in this reaction. The weak
Brønsted acidity of these species may be responsible for the very
slight increase of the selectivity in the anti-Markovnikov adduct.
However, the pure siliceous UVM-7 was completely inert in this
reaction.
Fig. 2 shows results in the hydroamination of styrene with ani-
line on Sc(OTf)3 and mesoporous UVM-7 silica embedded scandium
triflate (TfSc(60)), and on physical mixtures of Sc(OTf)3 with Beta
zeolites or TfSc(60), and of TfSc(60) with Beta 30 zeolite. On pure
Sc(OTf)3 the conversion was moderate that is in a good agree-
ment with the previous reports [28]. TfSc(60) showed a very close
behavior to Sc(OTf)3. In both cases, the dominant product was the
Markovnikov adduct, accordingly to the Lewis acid character of
these catalysts. Indeed, in the case of TfSc(60) NH3-DRIFT spec-
tra indicated the presence of Lewis acid sites as inferred from the
band located at 1627 cm−1 (Fig. 3). A band with a smaller intensity
located at 1490 cm−1 was also detected and assigned to Brønsted
acid sites. Nevertheless, the relative intensity of Lewis/Brønsted
band ratios indicated a very high excess of the Lewis acid sites
(higher than 10). Increasing the NH3-desorption temperature from
room temperature to 423 K, the band located at 1490 cm−1 com-
pletely disappear that means that on the surface remained almost
only Lewis acid sites.
Interestingly, although Sc(OTf)3 is supposed to be a purely Lewis
acid and TfSc(60) was demonstrated as a predominantly Lewis acid
type catalyst, the anti-Markovnikov adduct was formed as well on
both catalysts. No polystyrene formation was evidenced.
The 50:50 mixture of the Sc(OTf)3 with zeolites led to both
a decrease of the conversion and a change in the isomer distri-
bution. Using these mixtures the selectivity was quite different
comparing to the individual catalysts. While on the mixture BEA-
25–Sc(OTf)3 the two adducts were equally resulted, for the mixture
BEA-30–Sc(OTf)3 the dominant product was the anti-Markovnikov
adduct. Previous results reported that the Lewis acidic metal
Fig. 2. Conversion and selectivity in the reaction of aniline and styrene on Sc(OTf)3,
TfSc(60), and 50:50 physical mixtures of these and with zeolites (1 mmol aniline,
2 mmol styrene, 4 mL toluene, 50 mg catalyst, 423 K, 24 h).
Fig. 3. NH3-FT-IR for (a) TfSc(60), (b) BEA-30, (c) physical mixture of TfSc(60) and
BEA-30 (NH3-desorption at 423 K).
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
M. Ciobanu et al. / Applied Catalysis A: General xxx (2013) xxx–xxx
5
Fig. 4. Conversion and selectivity in the reaction of aniline and styrene on Sc(OTf)3, TfSc(60), and different physical mixtures of these (1 mmol aniline, 2 mmol styrene, 4 mL
toluene, 50 mg catalyst, 423 K, 24 h).
Table 2
Conversion and selectivity in the hydroamination of 4-nitro-aniline, 4-chloro-aniline and 3-aminophenol with styrene on the investigated physical mixtures.
Substrate
Physical mixture TfSc(60)–Sc(OTf)3
C (%)
TON
Selectivity (%)
Markovnikov
anti-Markovnicov
4-Nitro-aniline
4-Nitro-aniline
4-Nitro-aniline
4-Nitro-aniline
4-Nitro-aniline
4-Nitro-aniline
4-Chloro-aniline
4-Chloro-aniline
4-Chloro-aniline
4-Chloro-aniline
4-Chloro-aniline
4-Chloro-aniline
3-Aminophenol
3-Aminophenol
3-Aminophenol
3-Aminophenol
3-Aminophenol
3-Aminophenol
0:100
25:75
40:60
50:50
75:25
100:0
0:100
25:75
40:60
50:50
75:25
100:0
0:100
25:75
40:60
50:50
75:25
100:0
88
92
95
100
91
86
92
94
96
100
91
86
92
94
95
99
91
85
9.0
12.0
15.0
18.0
29.0
98.0
9.0
12.0
15.0
18.0
29.0
98.0
9.0
100
100
100
100
100
100
72
72
73
75
70
68
50
51
54
56
50
46
–
–
–
–
–
–
28
28
27
25
30
32
50
49
46
44
50
54
12.0
15.0
18.0
29.0
97.0
Reaction conditions: 1 mmol amine, 2 mmol styrene, 4 mL toluene, 50 mg catalyst, 423 K, 24 h.
Ultrasound has an effect a better dispersion of the added molec-
ular scandium triflate in the reaction mixture. It is also known that
under ultrasounds irradiation using powders the energy is enough
high to cause their fragmentation [70]. On the other hand, in the
case of very fine powders, the particles are accelerated to high
velocity by cavitational collapse and may collide to cause surface
abrasion. In this way the interaction of ScTf3 with TfSc(60) as a
physical mixture is enhanced. As an effect, TfSc(60) allows a better
dispersion of the added Sc(OTf)3 and thus an increase of the con-
version. Some chemical interaction of Sc(OTf)3 with TfSc(60) could
not be neglected. However, such an effect is limited by the ratio
of the two components. We should notice again that the reactions
were carried out in batch conditions, namely, where the catalysts
are dispersed in the liquid phase.
Table 2 compiles the values of the conversion, TON and selectiv-
ity in the hydroamination of 4-nitro-aniline, 4-chloro-aniline and
3-aminophenol with styrene on the same physical mixtures. For all
the substrates the variation of the conversion followed the same
order as for aniline. However, the use of these substituted anilines
led to considerable higher values of the conversion. The selectiv-
ity in the hydroamination of these substrates was found to depend
on the nature of the substituent. Using 4-nitro-aniline as substrate
the selectivity was total in the Markovnikov adduct, while for 4-
chloro-aniline and 3-aminophenol the anti-Markovnikov adduct
resulted as well. The selectivity in the anti-Markovnikov adduct
had the same evolution with the TfSc(60)–Sc(OTf)3 ratio as for ani-
line and, therefore, is supposed to based on the same explanation.
It is also worth to mention that the pKb of substituted anilines par-
allels the selectivity of the reaction (aniline: 9.4, 3-aminophenol:
9.8, 4-chloro-aniline: 10.0 and 4-nitro-aniline: 13.0) [71]. From our
measurements it appears the role of the anion into hydroamination
reaction is that to control the Lewis acidity of Sc. In the presence of
triflate, scandium is more naked due to the strong electrondrawn
effect of the anion [72].
4. Conclusions
Hydroamination of aniline and substituted anilines with styrene
occurred on both zeolites and triflate based catalysts with per-
formances controlled by the type of acidity and strength. The
conversion in these reactions was controlled by the strength of
the acid sites and their accessibility. The selectivity was controlled
by the type of acidity and Brønsted and Lewis acidity have to be
taken into account to allow the formation of the anti-Markovnikov
or Markovnikov adducts. While the use of zeolites and scandium
triflate led to results very close to those reported in the litera-
ture, physical mixtures of scandium triflate with a mesoporous
scandium triflate embedded in a UVM-7 structure provided bet-
ter conversions with a good selectivity in the Markovnikov adduct.
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032

GModel
APCATA-14244; No. of Pages6
ARTICLE IN PRESS
6
M. Ciobanu et al. / Applied Catalysis A: General xxx (2013) xxx–xxx
These results were attributed to a better dispersion of scandium
triflate during the preparation of physical mixtures.
[35] K. Li, K.K. Hii, Chem. Commun. (2003) 1132–1133.
[36] C. Quinet, A. Ates, I.E. Markó, Tetrahedron Lett. 49 (2008) 5032–5035.
[37] V. Neff, T.E. Muller, J.A. Lercher, J. Chem. Soc. Chem. Commun. (2002) 906–907.
[38] J. Bódis, T.E. Müller, J.A. Lercher, Green Chem. 5 (2003) 227–231.
[39] S. Breitenlechner, M. Fleck, T.E. Müller, A. Suppan, J. Mol. Catal. A: Chem. 214
(2004) 175–179.
Acknowledgment
[40] O. Jimenez, T.E. Müller, W. Schwieger, J.A. Lercher, J. Catal. 239 (2006) 42–50.
[41] W.J. Bae, A.R. Davis, J. Jung, W.H. Jo, K.R. Carter, E.B. Coughlin, Chem. Commun.
47 (2011) 10710–10712.
[42] L. Yang, L.-W. Xu, C.-G. Xia, Tetrahedron Lett. 49 (2008) 2882–2885.
[43] G.V. Shanbhag, S.M. Kumbar, S.B. Halligudi, J. Mol. Catal. A: Chem. 284 (2008)
16–23.
The authors kindly acknowledge CNCS for the Project PNII
275/2011.
References
[44] D.P. Sawant, J. Justus, V.V. Balasubramanian, K. Ariga, P. Srinivasu, S. Velmathi,
S.B. Halligudi, A. Vinu, Chem. Eur. J. 14 (2008) 3200–3212.
[45] G.V. Shanbhag, T. Joseph, S.B. Halligudi, J. Catal. 250 (2007) 274–282.
[46] R.S. Neale, L. Elek, R.E. Malz, J. Catal. 27 (1972) 432–441.
[47] P.N. Liu, F. Xia, Z. Le Zhao, Q.W. Wang, Y.J. Ren, Tetrahedron Lett. 52 (2011)
6113–6117.
[1] D.M. Roundhill, Chem. Rev. 92 (1992) 1–27.
[2] T.E. Muller, M. Beller, Chem. Rev. 98 (1998) 675–703.
[3] F. Alonso, I.P. Beletskaya, M. Yus, Chem. Rev. 104 (2004) 3079–3159.
[4] J.F. Hartwig, Pure Appl. Chem. 76 (2004) 507–516.
[5] D.W. Robbins, J.F. Hartwig, Science 333 (2011) 1423–1427.
[6] J. Seayad, A. Tillack, C.G. Hartung, M. Beller, Adv. Synth. Catal. 344 (2002)
795–813.
[48] O. Jimenez, T.E. Muller, C. Sievers, A. Spirkl, J.A. Lercher, Chem. Commun. (2006)
2974–2976.
[49] C. Sievers, O. Jimenez, R. Knapp, X. Lin, T.E. Muller, A. Turler, B. Wierczinski, J.A.
Lercher, J. Mol. Catal. A: Chem. 279 (2008) 187–199.
[50] A.A.M. Lapis, B.A. DaSilveira Neto, J.D. Scholten, F.M. Nachtigall, M.N. Eberlin, J.
Dupont, Tetrahedron Lett. 47 (2006) 6775–6779.
[51] J.-J. Brunet, N.C. Chu, O. Diallo, S. Vincendeau, J. Mol. Catal. A: Chem. 240 (2005)
245–248.
[52] A. Peeters, P. Valvekens, F. Vermoortele, R. Ameloot, C. Kirschhock, D. de Vos,
Chem. Commun. 47 (2011) 4114–4116.
[53] M.J. Bhanushali, N.S. Nandurkar, M.D. Bhor, B.M. Bhanage, Catal. Commun. 9
(2008) 425–430.
[54] F.-X. Zhu, W. Wang, H.-X. Li, J. Am. Chem. Soc. 133 (2011) 11632–11640.
[55] N. Mizuno, M. Tabata, T. Uematsu, M. Iwamoto, J. Catal. 146 (1994)
249–256.
[7] J.L. Klinkenberg, J.F. Hartwig, Angew. Chem. Int. Ed. 50 (2011) 86–95.
[8] M. AI-Masum, M. Meguro, Y. Yamamoto, Tetrahedron Lett. 38 (1997)
6071–6074.
[9] T.E. Muller, Tetrahedron Lett. 39 (1998) 5961–5962.
[10] H. Schaffrath, W. Keim, J. Mol. Catal. A: Chem. 168 (2001) 9–14.
[11] P. Horrillo-Martínez, K.C. Hultzsch, A. Gil, V. Branchadell, Eur. J. Org. Chem.
(2007) 3311–3325.
[12] C. Brinkmann, A.G.M. Barrett, M.S. Hill, P.A. Procopiou, J. Am. Chem. Soc. 134
(2012) 2193–2207.
[13] R.S. Robinson, M.C. Dovey, D. Gravestock, Tetrahedron Lett. 45 (2004)
6787–6789.
[14] J. Michaux, V. Terrasson, S. Marque, J. Wehbe, D. Prim, J.-M. Campagne, Eur. J.
Org. Chem. (2007) 2601–2603.
[56] M. Lequitte, F. Figueras, C. Moreau, S. Hub, J. Catal. 163 (1996) 255–261.
[57] J. Penzien, C. Haeßner, A. Jentys, K. Köhler, T.E. Müller, J.A. Lercher, J. Catal. 221
(2004) 302–312.
[58] J. Penzien, T.E. Muller, J.A. Lercher, Chem. Commun. (2000) 1753–1754.
[59] J. Penzien, R.Q. Su, T.E. Müller, J. Mol. Catal. A: Chem. 182/183 (2002) 489–498.
[60] R.Q. Su, T.E. Müller, Tetrahedon 57 (2001) 6027–6033.
[61] K. Komura, J. Tsutsui, R. Hongo, Y. Sugi, Stud. Surf. Sci. Catal. 170B (2007)
1111–1119.
[62] K. Komura, R. Hongo, J. Tsutsui, Y. Sugi, Catal. Lett. 128 (2009) 203–209.
[63] T. Joseph, G.V. Shanbhag, D.P. Sawant, S.B. Halligudi, J. Mol. Catal. A: Chem. 250
(2006) 210–217.
[64] G.V. Shanbhag, S.B. Halligudi, J. Mol. Catal. A: Chem. 222 (2004) 223–228.
[65] G.V. Shanbhag, S.M. Kumbar, T. Joseph, S.B. Halligudi, Tetrahedron Lett. 47
(2006) 141–143.
[66] V.I. Parvulescu, S.M. Coman, N. Candu, J. El Haskouri, D. Beltran, P. Amoros, J.
Mater. Sci. 44 (2009) 6693–6700.
[67] N. Candu, M. Ciobanu, P. Filip, J.E. Haskouri, C. Guillem, P. Amoros, D. Beltran,
S.M. Coman, V.I. Parvulescu, J. Catal. 287 (2012) 76–85.
[68] E.M. Gaigneaux, S.R.G. Carrazan, P. Ruiz, B. Delmon, Thermochimica Acta 388
(2002) 27–40.
[15] J.-M. Huang, C.-M. Wong, F.-X. Xu, T.-P. Loh, Tetrahedron Lett. 48 (2007)
3375–3377.
[16] I. Dion, A.M. Beauchemin, Angew. Chem. Int. Ed. 50 (2011) 8233–8235.
[17] T.E. Muller, J.A. Lercher, N.V. Nhu, AIChE J. 49 (2003) 214–224.
[18] H. Li, C. Wang, H. Huang, X. Xu, Y. Li, Tetrahedron Lett. 52 (2011) 1108–1111.
[19] J.G. Taylor, L.A. Adrio, K.K. Hii, Dalton Trans. 39 (2010) 1171–1175.
[20] J.G. Taylor, N. Whittall, K.K. Hii, Org. Lett. 8 (2006) 3561–3564.
[21] A. Tsuhako, D. Oikawa, K. Sakai, S. Okamoto, Tetrahedron Lett. 49 (2008)
6529–6532.
[22] G.K. Surya Prakash, C. Do, T. Mathew, G.A. Olah, Catal. Lett. 137 (2010) 111–117.
[23] F. Epifano, C. Pelucchini, O. Rosati, S. Genovese, M. Curini, Catal. Lett. 141 (2011)
844–849.
[24] P. Yin, T.-P. Loh, Org. Lett. 11 (2009) 3791–3793.
[25] R. Sarma, D. Prajapati, Chem. Commun. 47 (2011) 9525–9527.
[26] L. Wu, M. Shi, Chem. Eur. J. 17 (2011) 13160–13165.
[27] K. Komeyama, Y. Kouya, Y. Ohama, K. Takaki, Chem. Commun. 47 (2011)
5031–5033.
[28] K. Alex, A. Tillack, N. Schwarz, M. Beller, ChemSusChem 1 (2008) 333–338.
[29] G.-Q. Liu, Y.-M. Li, Tetrahedron Lett. 52 (2011) 7168–7170.
[30] A. Pews-Davtyan, M. Beller, Chem. Commun. 47 (2011) 2152–2154.
[31] S. Werkmeister, S. Fleischer, S. Zhou, K. Junge, M. Beller, ChemSusChem 5 (2012)
777–782.
[69] J. Horniakova, K. Komura, H. Osaki, Y. Kubota, Y. Sugi, Catal. Lett. 102 (2005)
191–196.
[70] T.J. Mason, P. Cintas, in: J. Clark, D. Macquarrie (Eds.), Handbook of Green
Chemistry & Technology, Blackwell Science Ltd., United Kingdom, 2002, p. 378
(chapter 16).
[71] K.C. Gross, P.G. Seybold, Z. Peralta-Inga, J.S. Murray, P. Politzer, J. Org. Chem. 66
(2001) 6919–6925.
[32] R.E. McKinney Brooner, R.A. Widenhoefer, Chem. Eur. J. 17 (2011)
6170–6178.
[33] X. Giner, C. Najera, G. Kovacs, A. Lledos, G. Ujaque, Adv. Synth. Catal. 353 (2011)
3451–3466.
[34] C. Michon, F. Medina, F. Capet, P. Roussel, F. Agbossou-Niedercorn, Adv. Synth.
Catal. 352 (2010) 3293–3305.
[72] S. Kobayashi, Eur. J. Org. Chem. (1999) 15–27.
Please cite this article in press as: M. Ciobanu, et al., Appl. Catal. A: Gen. (2013), http://dx.doi.org/10.1016/j.apcata.2013.05.032