Enantioselective hydrogenation of 1-phenyl-1,2-propanodione on Pt/ ZrO 2 catalysts

Article abstract of DOI:10.4067/S0717-97072010000100007

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298K and pressure of 40 bar of H₂ over zirconia supported Pt catalysts has been studied. Three different zirconia were prepared: i) ZrO₂- P obtained by a precipitation procedure from ZrOCl₂ ii) MSZrO ₂ obtained by a sol-gel procedure using cetryltrimethylammonium bromide (CTMABR) as surfactant to get a mesostructured solid iii) CNTsZrO ₂ obtained after impregnation of carbon nanotubes with ZrO(NO) ₃ followed by pyrolisis and calcination. Pt (1wt%) was introduced on the support by impregnation of an aqueous solution of H₂PtCl ₆. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, hydrogen chemisorption, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The presence of CD in the reaction medium is necessary to induce an enantiomeric excess (ee) of the desired product R-1phenyl-1 hydroxi-2-propanone. In all the studied systems, the relation between the enantioselectivity and the CD concentration added in situ exhibits a bell type curve; indicative of the importance of competitive adsorption between the modifier and the substrate on the catalyst surface. On the other hand, confinement effect led to an important enhancement in the activity in those catalysts supported on mesostructured supports, mainly in the Pt/CNTsZrO₂ catalyst.

Full text of DOI:10.4067/S0717-97072010000100007

J. Chil. Chem. Soc., 55, Nº 1 (2010)
ENANTIOSELECTIVE HYDROGENATION OF 1-PHENYL-1,2-PROPANODIONE
ON Pt/ ZrO2 CATALYSTS
CLAUDIA URBINA, GINA PECCHI, CRISTIAN CAMPOS, PATRICIO REYES*
Universidad de Concepción, Facultad de Ciencias Químicas. Edmundo Larenas 129, 160-C, Concepción, Chile
(Received: November 30, 2009 - Accepted: January 28, 2010)
ABSTRACT
The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298K and pressure of 40 bar of H over zirconia supported Pt catalysts has been
studied. Three different zirconia were prepared : i) ZrO2- P obtained by a precipitation procedure from ZrOCl2 i2i) MSZrO2 obtained by a sol-gel procedure using
cetryltrimethylammonium bromide (CTMABR) as surfactant to get a mesostructured solid iii) CNTsZrO obtained after impregnation of carbon nanotubes with
ZrO(NO)3 followed by pyrolisis and calcination. Pt (1wt%) was introduced on the support by impregnatio2n of an aqueous solution of H2PtCl6. The catalysts were
characterized by nitrogen adsorption-desorption isotherms at 77 K, hydrogen chemisorption, XRD and TEM techniques. The reactions were carried out in a
stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The presence of CD in the reaction medium is necessary to induce
an enantiomeric excess (ee) of the desired product R-1phenyl-1 hydroxi-2-propanone. In all the studied systems, the relation between the enantioselectivity and
the CD concentration added in situ exhibits a bell type curve; indicative of the importance of competitive adsorption between the modifier and the substrate on the
catalyst surface. On the other hand, confinement effect led to an important enhancement in the activity in those catalysts supported on mesostructured supports,
mainly in the Pt/CNTsZrO2 catalyst.
Keywords: Platinum, mesostructured supports, enantioselective hydrogenation.
form have potential applications in catalysis for their use as enantioselective
catalysts for asymmetric catalysis. One of the main advantages of these
structured solids compared to the traditional supports is that it can produce
a confinement effect which can favourable affect both the activity and the
selectivity in different reactions.
Thus, the use of Pt on mesoporous MCM-41 in the enantioselective
hydrogenation of 1-phenyl-1,2-propanedione was successfully demonstrated.
Toukoniitty et al. [29] have studied three different metal contents (5, 10 and
15 wt.%) of Pt on MCM-41 modified with (-)-cinchonidine (CD), obtaining a
maximum enantiomeric excess of (R)-1-phenyl-1-hydroxy-2-propanone close
to 44% using the 15 wt.% Pt/MCM-41 catalyst. This behaviour was attributed
to the larger metal Pt particles displayed by this catalyst. Similar results in
terms of activity and enantioselectivity were obtained by Reyes et al. [30] in
the same reaction using a 1 wt. % Pt/MCM-41. The observed behaviour has
been attributed to confinement effects produced into the hexagonal channel of
the MCM-41.
Sol-gel technique has been used in some studies in the synthesis of Si and
Ti nanotubes. This kind of systems have attracted the attention due to their
important applications, because of their excellent properties and technological
characteristics such as thermal and chemical stabilities, low electrical
conductivities and high degree of biocompatibility [31-32]. Thus, ZrO2 has
showed important properties from the catalytic point of few and also ZrO films
on a metal surface have been extensively used as a protection agent a2gainst
corrosion [33-34]. ZrO mesoestructured has been prepared from a surfactant,
such cetiltrimethylamo2nium bromide (CTMABr), which acts as template of
nanotubes with a given diameter of channel [35]. Gels of oxides in the presence
of a surfactant or appropriates templates produce nanotubes. They also may be
obtained by covering of carbon nanotubes with gels of the oxides followed by
calcination [36]. These solids display high surface areas being materials with
potential catalytic applications [33].
INTRODUCTION
Heterogeneous enantioselective hydrogenation of diketones on cinchona
alkaloid modified platinum represents a promising route for the synthesis
of chiral molecules with high optical purity [1-3]. As catalysts Pt, Pd and
Ir supported on SiO2 , Al O among others are used [4-8]. Since Orito et al.
reported the enantioselec2tiv3e hydrogenation of ethyl pyruvate to (R)-ethyl
lactate over cinchonidine-modified Pt catalysts with ee’s up to 95%, many
other research teams have evaluated their catalytic systems in the mentioned
reaction [9-11]. Indeed, this reaction is nowadays a sort of test reaction in the
field of asymmetric catalysis. However, when the substrate has more than one
centre to be hydrogenated the reaction becomes more difficult, as occurs during
the hydrogenation of diones as 1-phenyl-1,2-propanedione both in terms of
enantio- and regioselectivity (rs)[12-19]. In the latter, the product of interest
is (R)-1-phenyl-1-hydroxy-2-propanone, which has interesting application in
the synthesis of compounds used as precursors for hypertension and asthma
treatments, among others[20-21] .
Supported platinum catalysts have been widely studied for this type of
applications [22]. It has been found that metal particle size plays an important
role in asymmetric synthesis when performed in the presence of cinchonidine
as a chiral inducer. Metal crystals around 3.0 nm obtained with catalysts
having metal loading close to 5 wt. % have led to the most promising catalytic
behaviour. The catalysts containing lower metal loadings usually display
smaller particle sizes, they are not appropriate for this purpose.
The selection of the support has been relevant in the preparation of
heterogeneous catalysts for the hydrogenation enantioselective of a-ketoesters,
a-funcionalized ketones and a, b-diketones[23]. Several groups have tried
to improve the hydrogenation of ethyl pyruvate by preparing cinchonidine-
modified Pt catalysts on various supports. Thus, Hall et al.[24] described the
used of a Pt/MCM-41 catalyst which exhibits low reaction rate due to mass
transfer limitation and enantiomeric excess up to 64%. Zeolites of different
structures and acidities can also display high enantioselective hydrogenation
on supported on Pt catalysts. In fact, Böhmer et al.[25] have reported the re-
use of Pt/HNaY zeolite in the hydrogenation of ethyl pyruvate in acetic acid
and cyclohexane reaching an important e.e. (88%). Additionally, e.e. up to
75% were reported for Pt/clay catalysts (28% e.e. for Rh/K-10)[26], while e.e.
below 35% were described for Pt/C catalysts despite improvement by oxidative
treatment [27]. Nevertheless, two commercially available 5% Pt/Al2O3 catalysts
have emerged as “standard” catalysts: E4759f from Engelhard and JMC 94
from Johnson Matthey [28]. In the last few years, researches have been focused
in improving the structural and morphological properties of the support to
enhance the catalytic behavior. Creating successful mesoporous silicates
enantioselective catalysts remains as an important goal for the chemicals
and pharmaceuticals industries, with considerable attention being focused on
chirally modified metals as promising candidates. These materials in silicate
The aim of the present work is to obtain and evaluate new series of Pt
catalysts supported in mesostructured ZrO solids of MCM-41 type as an
alternative to the classic catalyst for the e2nantioselective hydrogenation of
1-phenyl-1,2-propanedione using cinchonidine (CD) as modifier (Fig. 1). The
effect of the method used to obtain the support, which strongly affects the
morphologic characteristics as well as the concentration of the chiral modifier
on the catalytic behaviour of the solids is studied.
e-mail: preyes@udec.cl
25

J. Chil. Chem. Soc., 55, Nº 1 (2010)
apparatus. TEM micrographs were obtained in a Jeol Model JEM-1200 EXII
System, X-ray diffraction studies were performed in a Rigaku diffractometer.
Hydrogenation reaction
The hydrogenation of 1-phenyl-1,2-propanedione, was studied at 298
K and 40 bar of H2 with 0.01 mol L-1 of substrate, 100 mg of catalysts and
cyclohexane as solvent in a stainless steel batch reactor. In reactions that
include addition of the CD in situ the concentration 0.1 to 1.0 mol L-1 was
added at the beginning of the reaction. The analysis of reactants and products
was followed by a GC-MS device (Shimadzu GCMS-QP5050), using a chiral
β-dex 225, 30 m column (SUPELCO) and helium as carrier gas.
RESULTS AND DISCUSSION
Figure 2 display the X-ray diffraction pattern of the prepared supports.
ZrO prepared by precipitation of ZrOCl2 shows the characteristic reflexions
due 2to monoclinic and tetragonal phases whereas no low angle XRD reflexions
were observed for the nanostructured ZrO neither to that prepared by
impregnation of carbon nanotubes. Similar fac2t was found by Larsen et al [40]
and Blin et. Al [38] describing the synthesis of sulfated mesoporous zirconia
mediated by lauryl sulfate in alkaline solution and CTMABr respectively.
The authors suggest that in contrary to the synthesis of silica mesoporous
structured materials, the pore formation mechanism does not imply bi or three
dimensional X-ray detectable ordering. Indeed, even if low angle signal is not
observed in the XRD-pattern, samples exhibit a uniform pore size distribution
in the range of mesoporous. In the present study, in agreement with Blin [38]
the absence of small angle reflexion line can be attributed to a relative large
pore size distribution. The textural characteristic of zirconia will be discussed
below.
Figure 1 Reaction scheme of the hydrogenation of (A) 1-phenyl-1,2-
propanedione. (B) (R)-1-hydroxi-1-phenyl-2- propanone; (C) (S)-1-hydroxy-1.
phenyl-2- propanone; (D) (S)-2-hydroxi-1-phenyl-1- propanone; (E) (R)-2-
hydroxi-1-phenyl-1- propanone; (F) (1R,2S)-1-phenyl-1,2-propanediol; (G)
(1S,2S)-1-phenyl-1,2-propanediol; (H) (1S,2R)-1-phenyl-1,2-propanediol; (I)
(1R,2R)-1-phenyl-1,2-propanediol.
EXPERIMENTAL
Supports preparation.
Precipitated ZrO2. (ZrO -P).
ZrO was obtained by pr2ecipitation of ZrOCl2 with ammonia solution using
a proced2ure already described [37]. The solid was dried with bidistilled H O
to constant conductivity. The solid was dried at 120ºC during 8 h and calcin2ed
at 550ºC for 2 h.
Mesostructured ZrO2 (MSZrO2).
Cetyltrimethylammonium bromide (CTMABr) was dissolved in water
under continuous stirring at 40ºC to obtain a clear micellar solution [38]. Then
zirconyl chloride was added to the solution and the pH value of the gel was
adjusted with sodium solution (1.4 mol L-1) to 11.5 in order to induce around
the formed micellles the hydrolisis and the polycondensation of the inorganic
precursor. After stirring for several minutes with the molar composition of
1:0.10:102 = CTMABr: ZrOCl ·8H2O:H O was sealed in a teflon autoclave.
The hydrothermal treatment wa2s at 60ºC 2for 24 h. The template was removed
by solvent extraction (using ethanol), during 30 h. Later on, the solid was
calcined in nitrogen flow 3 h at 540ºC and then in air flow at 540ºC for 8 h to
removed the remaining organic matter.
Figure 2. XRD patterns of ZrO2 supports.
Table 1. Surface area and pore volume of the prepared ZrO2 supports
Impregnation of carbon nanotubes (CNTsZrO ).
Carbon nanotubes were prepared following a2procedure already reported
[39].
Support
SBET ,m2 g-1
Pore volume, cc g-1
MSZrO2
CNTsZrO2
ZrO2-P
95
87
018
0.18
0.13
0.3000 g of carbon nanotubes were mixed with 20 mL of a 0.5 mol L-1 of
a ZrO(NO) solution. This suspension was kept under ultrasonic vibrations for
10 min and3then under boiling conditions for 3 h to evaporate the solvent. The
final solid was calcined in Ar at 600ºC for 2 h. A grey powder was obtained
which was then calcined in air at 600ºC for 2 h to remove the CNTs leading
to a white powder.
101
Figure 3 shows the nitrogen adsorption isotherms of the studied supports.
The isotherms correspond to type IV in the classification of BDDT [39].
The adsorption branch of the isotherm can be decomposed in three parts:
the monolayer-multiple adsorption of nitrogen, the capillary condensation
of nitrogen within the mesopores and then the saturation. The differences in
the hysteresis loops reveal the presence of open capillaries characteristic of
MCM-41 kind of materials for MSZrO and CNTsZrO2 however, in the former
the pore size distribution is narrower.2The ZrO2-P displays a hysteresis loop
indicative of transitional ink bottle pores. Table 1 compiles surface area and
pore volumes of the prepared supports. All ZrO2 samples display a surface area
close to 100 m2g-1 and pore size in the range of mesopores. The ZrO2 exhibits
a wider pore size distribution in the range of 2.5 to 20 nm, whereas in the
MSZrO2 and CNTsZrO2 supports, the pores distribution is narrower and exhibit
an important fraction close to 2.0 to 4.0 nm.
Catalysts preparation
ZrO MSZrO2, CNTsZrO2 supports above described and an aqueous
solution 2o, f chloroplatinic acid containing the amount of Pt precursor necessary
to get catalysts containing 1 wt% of Pt were placed in a rotaevaporator under
stirring at 35oC for 1h. Then the solvent was removed by evacuation at the
same temperature. The obtained solids were calcined in air at 300ºC for 2 h and
reduced in hydrogen flow of 100 mL/min at 500ºC for 2h. The obtained catalysts
were labeled as lwt%Pt/ZrO2, lwt%Pt/MSZrO2 and lwt%Pt/CNTsZrO2.
Characterization
Nitrogen adsorption at 77K was carried out in a Micromeritics ASAP 2010
26

J. Chil. Chem. Soc., 55, Nº 1 (2010)
Figure 4.Transmission electron micrographs of Pt/ZrO2 catalysts
a) Pt/NTZrO2 b)Pt/CNTZrO2 c) Pt/ZrO2-P
Figure 3. Nitrogen adsorption-desorption isotherms at 77 K on ZrO2
supports.
Catalytic activity in 1-phenyl-1,2-propanedione hydrogenation
Figure 1 shows a scheme of the enantioselective hydrogenation of
1-phenyl-1,2-propanedione. The reaction was studied at 25 ºC and 40 bar of H2
zirconia supported Pt catalysts. It was found that using these systems is possible
to induce a preferential formation of (R)-1-phenyl-1-hydroxy-2-propanone.
A comparison of the conversion with time for the studied catalyst under
the same experimental conditions, temperature of 25°C, hydrogen pressure of
40 bar, catalyst weight 100 mg and modifier concentration 1.0 mM is given
in Figure 5. Even though the trends displayed by the catalyst is the same,
significant differences in activity can be detected. Thus, to get the same
conversion level, i. e. 50% requires, 15 min for Pt/CNTsZrO2, 40 min for Pt/
MSZrO2 and 100 min for Pt/ZrO2-P.
Table 2 summarizes the average particle sizes obtained from TEM
results and the estimated metal dispersion. As can be seen, the results show
that platinum display good dispersion levels and the obtained particle size
values are in the range 2.4 to 4.0 nm. The smallest average metal crystals was
displayed by Pt catalysts supported on CNTZrO2 in which is likely that the
metallic species can be located into the channel of the support and the grow
of the Pt crystals as consequence of calcinations and reduction treatments is
highly restricted. Conversely, the highest average metal particle was exhibited
by the Pt/ZrO2-P catalyst, in which the support possesses a broader pore size
distribution and the metallic crystals are deposited on open mesopores.
Table 2. Platinum particle size (d) obtained by TEM and metal dispersion
(D) evaluated from chemisorption results of Pt/ZrO2 catalysts
Catalysts
l%Pt/MSZrO2
1%Pt/CNTsZrO2
l%Pt/ZrO2-P
dTEM , nm
3.2
DCHEM
0.51
0.58
0.41
2.4
4.0
TEM micrograph of the calcined ZrO2 materials, show for the Pt/MSZrO2
and Pt/CNTsZrO samples, typical shapes of nanostructured solids with a
regular hexagonal2array of mesoporous channels, in good agreement with those
previously reported by Beck et al. [41] as can be seen in Figure 4. However,
it is convenient to mention that studying TEM micrographs of the former
catalyst, it was also found areas in which amorphous support was detected. The
presence of Pt crystals located inside the channel of structured supports can be
clearly observed, being the metal crystal size rather uniform for these samples,
showing values comparable with the pore size of these supports. With regard
to the Pt/ZrO2-P catalysts, it exhibits a broader metal particle size distribution,
in the range of 1.5 to 8.0 nm being the average of 4.0, higher than those found
by the metal supported on the structured carriers. A summary of the average Pt
particle size in the studied catalysts is given in Table 2.
Figure 5. Evolution of the conversion level with time during 1-phenyl-1,
2-propanodione hydrogenation on Pt/ZrO2 catalysts . T= 25°C, P H2= 40 bar,
catalyst weight 100 mg and CD concentration= 0.25 mmolL-1.
Under the conditions employed the main products were the regioisomers
(R) and (S)-1-hydroxy-1-phenylpropanone. This behaviour may be explained
mainly in terms of electronics factors because of the aromatic ring contributes
to polarize to a higher extent the C=O bond close to the ring, and therefore
the reactions leading to (R)-1-phenyl-1-keto-2-propanol and (S)-1-phenyl-1-
keto-2-propanol; (E) (R)-1-phenyl-1-keto-2-propanol and (S)-1-phenyl-1-keto-
2-propanol are less favoured.
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J. Chil. Chem. Soc., 55, Nº 1 (2010)
Figure 6 shows the evolution of the substrate and products concentration
on time during the 1-phenyl-1,2-propanedione hydrogenation on one
representative catalyst, at 25 ºC, 40 bar of H2 , CD concentration of 2.5 10-4
molxL-1 and 100 mg of 1wt% Pt/CNTsZrO2 catalyst. The results indicate
that under the experimental conditions used here the catalyst is highly active,
conversion level close to 80% at 60 min but having a moderate ee and high
rs. The evolution of the dione concentration and the various reaction products
follow the expected trends, the dione concentration decreases through a first
order law, leading to hydroxiketones, (R)- 1-hydroxi-1-phenylpropanone and
(S)- 1-hydroxi(R)-1-phenylpropanone as intermediate compounds (B and C in
the scheme given in Fig. 1), showing a maximum close to 75 min of reaction
for the most active catalyst (Pt/CNTsZrO ) being larger the time to reach a
maximum hydroxiketone concentration for2the other catalysts 105 and 150 min
for Pt/MSZrO2 and Pt/ZrO respectively (not shown). The studied catalysts were
completely regioselective,2because no products generated by the hydrogenation
of the C=O bond located far from the aromatic ring were obtained, that means
(R)- 2-hydroxi-1-phenylpropanone and (S)- 2-hydroxi-1-phenylpropanone (E
and D respectively in the scheme) were not detected. In all cases, the presence
of the over hydrogenated products, dioles were observed, and the evolution of
the concentration of diols, follow the expected sigmoid curve, characteristic
of final products of consecutive reactions. Thus, the reaction pathway may be
represented by irreversible parallel and consecutive reactions.
Table 3. First order reaction rate constants, in the hydrogenation of
1-phenyl-1, 2-propanodione at 298 K on Pt/ZrO2 catalysts.
k1g,
k1R,
k1R,
k2R,
k2S,
Catalyst
103 min-1 103 min-1 103 min-1 103 min-1
103 min-1
Pt/MSZrO2
Pt/CNTsZrO2
Pt/ ZrO2-P
1.55
3.52
0.37
1.01
2.47
0.22
0.54
1.05
0.15
8.72
6.80
5.18
13.2
17.5
9.51
k1g = k1R + k
k2R = k´2R + 1kS´´2R
k2S = k´2S + k´´2S
Considering the previous results obtained in the ethyl pyruvate
hydrogenation and also in the 1-phenyl-1, 2-propanodione hydrogenation [7-
10,13-18] , it would be possible to enhance the yield to the desired products
by adjusting CD coverage. For that reason the effect of the CD concentration
added at the beginning of the reaction has been studied. Fig. 7 shows the
effect of the CD concentration on the evolution of conversion level on time
for one of the studied catalysts (1wt% Pt/CNZrO catalyst). Significant
differences depending of the CD concentration present2in the reaction mixture
at the beginning of the reaction can be observed. The curves follow the trends
already shown and approach the first order reaction rate. When the reaction is
performed in absence of CD, the reaction takes place but at lower reaction rate.
Similar behavior was displayed by the other studied catalysts, but obviously
having differences in conversion and enantioselectivity levels. Therefore,
the CD contributes to the generation of modified catalytic sites which are
enantioselective and more active than the metallic sites.
Figure 6. Evolution of the concentration of the susbstrate and different
reaction products during 1-phenyl-1, 2-propanodione hydrogenation. T= 25°C,
P H2= 40 bar, catalyst Pt/CNTsZrO2 weight 100 mg and CD concentration=
0.25 mmolL-1.
¨1-phenyl-1,2-propanedione ■ (R)-1-hydroxi-1-phenyl-2- propanone; X
(S)-1-hydroxy-1.phenyl-2- propanone; ▲ Diols
The first order reaction rate constants , denoted as kg for the consumption
of the dione can be easily obtained from log CAoC vs t plots and the respective
rate constants k1R and k1S corresponding to the foArmation of (R)- 1-hydroxi-1-
phenylpropanone and (S)- 1-hydroxi(R)-1-phenylpropanone respectively may
be obtained from the global first order constant and the ratio of the concentration
of these compounds (B and C in the scheme), that is CB/CS. Additionally, the
reaction rate constants associated to the consecutive reactions, k and k2S can
be evaluated from the well known equations for intermediates o2fRconsecutive
reactions, in terms of Cmax and tmax being the former the maximum concentration
and the time required to get that level of the corresponding intermediates. The
obtained results are summarized in Table 3. It can be seen that the rate constant
for the first and second hydrogenation steps (k1 and k2) are higher in the Pt
catalysts supported in mesostructured supports. This fact may be attributed to
the confinement effect produces by the support. The presence of CD in the
Figure 7. Evolution of conversion level on time in 1-phenyl-1,
2-propanodione hydrogenation. T= 25°C, P H2= 40 bar, catalyst:1wt% Pt/
CNZrO2
In Figure 8, the enantiomeric excess to the desired product (R)-1-phenyl-
1-hydroxy-2-propanone vs the conversion level obtained on the different
catalysts using a same concentration of the chiral modifier (0.50 mmolL-1)
is given. It can be seen that the three studied catalysts display similar ee in
a wide range of conversion level. These results may be expected taking into
account that the reaction is sensitive to metal particle size and the studied
catalysts display similar Pt crystal size. The effect of the CD concentration
on the enantiomeric excess of the (R)-1-phenyl-1-hydroxy-2-propanone for a
representative catalyst is given in Figure 9. The observed trends is similar to
those previously reported: a bell-type plot with the maximum corresponding to
an ee value of 38% was found showing comparable behavior the three studied
catalysts
reaction medium favored the pathway to produce the R-intermediate (k1R
>
k1S) and also in the second step the hydrogenation of the S- intermediate is
improved (k2S > k2R).
28

J. Chil. Chem. Soc., 55, Nº 1 (2010)
dione is displayed by Pt/CNTZrO2 , followed by Pt/MSZrO2 and then Pt/ZrO2
P.
CONCLUSIONS
The obtained results in the hydrogenation of 1-phenyl-1, 2-propanodione
on Pt/ZrO2 catalysts show that not only the nature of the support may affect the
catalytic behavior in this reaction but also the porosity of the support. It was
demonstrated that mesostructured supports lead to a significant enhancement
in the reaction rates due to a confinement effect. The catalysts were completely
regioselective. Thus, only the hydrogenation of the C=O bond located near to
the aromatic ring took place, and preferentially led to the R-hydroxiketone. The
enantiomeric excess of the desired product was similar to the best reported in
the literature.
ACKNOWLEDGMENTS
The authors thank to FONDECYT 1061001 for financial support.
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