A step towards hydroformylation under sustainable conditions: Platinum-catalysed enantioselective hydroformylation of styrene in gamma-valerolactone

Article abstract of DOI:10.1039/c5gc01778e

Platinum-catalysed enantioselective hydroformylation of styrene was performed in γ-valerolactone (GVL) as a proposed environmentally benign reaction medium. Optically active bidentate ligands, possessing various types of chirality elements e.g. central (B

Full text of DOI:10.1039/c5gc01778e

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A step towards hydroformylation under sustainable conditions:
platinum-catalysed enantioselective hydroformylation of
styrene in gamma-valerolactone
Received 00th January 20xx,
Accepted 00th January 20xx
Péter Pongrácz,c László Kollárb,c and László T. Mikaa,*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Platinum-catalysed enantioselective hydroformylation of styrene was performed in γ-valerolactone (GVL) as a proposed
environmentally benign reaction media. Optically active bidentate ligands, possessing various types of chirality elements
e.g central (BDPP), axial (BINAP, SEGPHOS, DM-SEGPHOS, DTBM-SEGPHOS) and planar/central (JOSIPHOS) elements, were
applied in in situ generated Pt-diphosphine-tin(II)chloride catalyst systems. In general, slightly higher activities and
regioselectivities towards branched aldehyde (2-phenylpropanal) were obtained in toluene as a reference conventional
solvent. However, higher chemoselectivities towards aldehydes (up to 98%) in GVL were obtained at lower temperatures.
The application of GVL proved to be also advantageous regarding enantioselectivity: although moderate
enantioselectivities were obtained in both solvents, in most cases higher ee values were detected in GVL. From
mechanistic point of view, the formation of different catalytic intermediates and/or different kinetics can be envisaged
from the different temperature dependence of ee in GVL and toluene. The 31P-NMR characterization of catalyst species in
GVL was also provided.
limited including toluene, hexane etc. just to name a few.
Introduction
However, if a solvent is crucial to perform the target
transformation, an alternative that has no or limited impact on
the environment and health has to be selected. Several
Solvents are intrinsic part of many chemical reactions and the
“solvent friendly chemical thinking” has evolved due to many
advantages in both industrial and laboratory operations.1 Thus,
the industrial activities involving solvents are resulting in the
release of 10–15 million tons of solvents into the atmosphere
annually, some of which are leading to serious environmental
concerns and economic issues. Consequently, the replacement
of conventional organic solvents with green alternatives having
low vapour pressure even at high temperature, low or no
toxicity, low flammability and limited negative impacts on the
environment is a crucial part in the development of greener
and cleaner chemical technologies.2 Although, “solvent free”
transformation could offer environmental friendly solutions,
many thousands if not millions of reactions can only be
operated in the presence of solvents. According to FDA
guidelines3 the use of several common organic solvents has to
be avoided such as benzene and chlorinated hydrocarbons or
5
alternative solvents such as water,4 ‘fluorous’ solvents and
ionic liquids,6 supercritical carbon-dioxide7 have been
proposed for better solutions and some of them have
industrial importance, e.g. Ruhrchemie/Rhone-Poulenc
aqueous biphasic hydroformylation process.8 Moreover, the
application on a non-toxic reaction media is fundamentally
important in pharmaceutical industry, where the residual
solvent traces could result in serious health issues.
The intensive research activity on biomass conversion, as
the most preferred alternative, has led to the identification of
several platform molecules such as γ-valerolactone (GVL)9
which could replace the currently used fossil-based chemicals
including solvents. Due to the environmentally friendly
chemical and physical properties, GVL has been considered as
a sustainable liquid.9,10 It is renewable and can efficiently be
produced by hydrogenation of levulinic acid (LA).11 GVL has
already been used for the production of alkanes,11e
transportation fuels,12 ionic liquids,13 1,4-pentanediol,11d,e
,
a.Department of Chemical and Environmental Process Engineering, Budapest
University of Technology and Economics, Budapest, Hungary Fax: +36 1 463 3197;
L. T. Mika: Tel.: +36 1 463 1263, e-mail: laszlo.t.mika@mail.bme.hu.
b.Department of Inorganic Chemistry, University of Pécs and Szentágothai Research
Center, Ifjúság u. 6., Pécs, H-7624, Hungary.
adipic acid,14 polymers,15 illuminating liquid and lighter fluid16
etc. Since it was firstly suggested by Horváth, only a few
studies have been published concerning for utilization of GVL
as a solvent. It was shown that GVL could be used as reaction
media for acid catalysed dehydration of various carbohydrates
and wastes.17 We demonstrated that the selective
c. MTA-PTE Research Group for Selective Chemical Syntheses, Ifjúság u. 6., Pécs, H-
7624, Hungary
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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hydrogenation of LA could be performed in GVL and/or GVL- and environmentally benign solvent. It has to be also
water Very recently, heterogeneous emphasized that to the best of our knowledge, some of the
mixture.11a-c
Sonogashira,18 Heck19 and Hiyama20 cross-coupling reactions diphosphines (the SEGPHOS family) were not tested in
were performed in GVL as well.
hydroformylation at all.
The very low toxicity of GVL9 makes it a particularly
attractive reaction media in the synthesis of pharmaceuticals.
Since chiral aldehydes are potential precursors of non-
steroidal anti-inflammatory drugs (NSAI), such as ibuprofen,
naproxen or suprofen,21,22 the enantioselective hydrofor-
mylation of vinyl aromatics to 2-arylpropanals in the presence
of rhodium and platinum catalysts is of the utmost
importance. Soon after the recognition of the hydrofor-
mylation activity of in situ generated platinum-
monophosphine-tin(II)halide systems,23 the corresponding
‘preformed’ PtCl(SnCl3)(chiral diphosphine) catalysts and
PtCl2(chiral diphosphine) + tin(II) halide systems were tested in
enantioselective oxo-synthesis.24,25a In addition, to the most
widely used vinyl aromatics, 1,1-disubstituted olefins were also
used as model substrates in highly enantioselective
hydroformylation.25 During the past three decades, various
types of chiral mono- and bidentate phosphorus ligands were
tested in platinum-based hydroformylation with the aim of
increasing activity, chemo-, regio- and enantioselectivity.26
Since the industrial hydroformylation was carried out in
alternative solvents to facilitate catalyst recycling,27 even the
enantioselective hydroformylation was performed in water,28
in ionic liquids,29 as well as fluorous/scCO2 media.30
Results and discussion
Initially, the formation of the corresponding platinum
complexes of the applied ligands in gamma-valerolactone was
investigated. The 31P-NMR measurement clearly established
the in situ formation of PtCl2(diphosphine) complexes from
PtCl2(PhCN)2 (0.005 mmol) and 0.005 mmol ligands (S,S)-BDPP,
(R)-SEGPHOS, (R),(S)-JOSIPHOS and (R)-BINAP (Fig 1.)
representing square-planar geometry in GVL (0.6 mL). The
1J(31P,195Pt) coupling constants of diagnostic value show that
phosphorus donor atoms are coordinated trans to the chloro
ligands (Table 1). Similarly, the excellent solubility of the
PtCl2(diphosphine) complexes and SnCl2 in GVL allows us to
study the structure of the PtCl(SnCl3)(diphosphine) complexes
formed in the ‘carbene-like’ insertion of tin(II)-chloride into the
Pt-Cl bond. The formation of the trichlorostannato ligand was
undoubtedly proved by increasing the chemical shift and
decreasing the 1J(31P,195Pt) coupling constants of the
phosphorus trans to SnCl3. The 2:1 mixture of two isomers (
I
and II) were formed when JOSIPHOS possessing two chemically
different phosphorus was used. It is worth mentioning that the
NMR characteristics were found to be almost identical to those
obtained in CDCl3.26c It should be emphasized, that the
characterization of bidentate phosphine modified Pt- and even
Pt/SnCl3-complexes in GVL has not yet been described.
Accordingly, it can be proposed that GVL could also be a good
solvent for characterization of transition metal complexes, as
well.
We report here the investigation of asymmetric
hydroformylation of styrene (Scheme 1) in the presence of
platinum–chiral diphosphine–tin(II)chloride in situ generated
catalyst systems comparing their activity and selectivities in
toluene as a conventional and in γ-valerolactone as a non-toxic
CHO
Since the in situ formation of precursors of catalytically
active species from PtCl2(PhCN)2, optically active bidentate
phosphine, and tin(II)chloride in GVL was established, they
were applied for the hydroformylation of styrene. Various
types of chiral ligands possessing stereogenic centres (BDPP,
CHO
∗
+ CO + H2
+
+
2-phenylpropanal
3-phenylpropanal
(B)
ethylbenzene
(A)
(C)
Scheme 1 Hydroformylation of styrene
Table 1 31P-NMR data of the platinum complexes formed in situ in GVLa
PA
PA
PB
PA
Cl
Cl
,
Pt
Pt
SnCl3
SnCl3
P
P
P
Fe
P
P
P
δ(PA)
(ppm)
6.8
1J(Pt,PA)
(Hz)
δ(PB)
(ppm)
1J(Pt,PB)
(Hz)
-
Complex
PtCl2(BDPP)
(S,S)-BDPP
(R),(S)-JOSIPHOS
(R)-BINAP
3394
3662
3570
3665
3302
3512
3450
3048
3515
-
PtCl2(SEGPHOS)
PtCl2(JOSIPHOS)c
PtCl2(BINAP)
7.5
-
-
OMe
tBu
tBu
-0,7
9.7
44.4
-
3537
-
tBu
OMe
O
O
O
P
P
PtCl(SnCl3)(BDPP)
7.8
13.1
17.2
59.5
58.9
18.8
2780
3110
3072
3496
3070
O
O
tBu
tBu
P
P
P
P
O
O
O
O
PtCl(SnCl3)(SEGPHOS)
6.8
PtCl(SnCl3)(JOSIPHOS) (I)
PtCl(SnCl3)(JOSIPHOS) (II)b
1.3
OMe
O
O
O
tBu
11.7
8.4
tBu
tBu
PtCl(SnCl3)(BINAP)
OMe
(R)-SEGPHOS
(S)-(DM)-SEGPHOS
(S)-(DTBM)-SEGPHOS
aPtCl2(PhCN)2/SnCl2 = 1/2, PA: trans to Cl; PB: trans to SnCl3; bPA trans to SnCl3,
c
PB trans to Cl. chemically different phosphorus atoms; Solvent: GVL; for
spectra see (ESI Fig. S1-9).
Fig. 1 Ligands used in Pt-catalysed hydroformylation
2 | J. Name., 2012, 00, 1-3
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Table 2 Hydroformylation of styrene in the presence of Pt-L-SnCl2 catalysts in toluene and GVL a
b
c
Entry
Ligand (L)
Solvent
T
(°C)
Time
(h)
Conv.
(%)
Rc
Rbr
e.e.d
(%)
(%)
81
86
85
93
78
88
82
92
94
91
59
86
84
84
72
94
90
95
82
80
77
83
90
55
86
92
73
74
82
93
98
82
88
80
97
94
(%)
1
2
(S,S)-BDPP
(S,S)-BDPP
toluene
toluene
GVL
100
80
3
20
20
96
20
20
20
70
144
120
20
20
20
20
20
72
240
336
24
20
5
99
99
91
99
99
99
96
99
99
16
99
83
58
94
98
99
70
46
99
14
83
99
99
30
45
10
2
33
36
23
26
48
44
48
45
36
31
20
19
22
21
21
21
26
23
48
23
36
39
46
25
24
32
23
42
16
24
12
28
34
22
30
28
7 (R)
14 (R)
2 (S)
3
(S,S)-BDPP
100
80
4
5e
(S,S)-BDPP
GVL
18 (S)
16 (S)
28 (S)
30 (S)
2 (S)
(R)-BINAP
toluene
toluene
toluene
toluene
toluene
toluene
GVL
120
100
100
80
6
7f
(R)-BINAP
(R)-BINAP
8
(R)-BINAP
9
(R)-BINAP
60
19 (R)
32 (R)
5 (S)
10
11g
12
13 f
14 h
15 i
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30 i
31
32
33
34
35
36 i
(R)-BINAP
40
(R)-BINAP
130
100
100
100
100
80
(R)-BINAP
GVL
26 (S)
16 (S)
15 (S)
25 (S)
10 (S)
28 (S)
49 (S)
21 (S)
45 (S)
1 (S)
(R)-BINAP
GVL
(R)-BINAP
GVL
(R)-BINAP
GVL
(R)-BINAP
GVL
(R)-BINAP
GVL
60
(R)-BINAP
GVL
40
(R)-SEGPHOS
(R)-SEGPHOS
(S)-DM-SEGPHOS
(S)-DM-SEGPHOS
(S)-DM-SEGPHOS
(S)-DM-SEGPHOS
(S)-DM-SEGPHOS
(S)-DM-SEGPHOS
(S)-DTBM-SEGPHOS
(S)-DTBM-SEGPHOS
(S)-DTBM-SEGPHOS
(S)-DTBM-SEGPHOS
(S)-DTBM-SEGPHOS
(R)-(S)-JOSIPHOS
(R)-(S)-JOSIPHOS
(R)-(S)-JOSIPHOS
(R)-(S)-JOSIPHOS
(R)-(S)-JOSIPHOS
toluene
GVL
100
100
120
100
80
toluene
toluene
toluene
GVL
20
72
20
20
71
24
48
24
24
48
24
48
24
72
240
10 (S)
21 (S)
24 (S)
14 (S)
36 (S)
n.d.
120
100
80
GVL
GVL
toluene
toluene
GVL
100
100
100
100
80
11
17
20
20
99
99
52
6
40 (S)
46 (S)
56 (S)
57 (S)
13 (S)
6 (S)
GVL
GVL
toluene
toluene
GVL
100
60
100
60
31 (S)
70 (S)
36 (S)
GVL
GVL
60
13
A: 2-phenylpropanal, B: 3-phenylpropanal, C: ethylbenzene.
a Reaction conditions: Pt/styrene = 1/100, Pt/SnCl2 = 1/2; p(CO) = p(H2) = 40 bar, 1 mmol of styrene, solvent: 5 mL of toluene (or GVL).
b Chemoselectivity towards aldehydes (A, B). [(moles of A + moles of B)/(moles of A + moles of B + moles of C) × 100].
c Regioselectivity towards branched aldehyde (A). [moles of A/(moles of A + moles of B) × 100].
d Enantioselectivities were determined by chiral GC.
e ca. 8% alcohols as side-products
i
f p(CO)= p(H2)=20 bar; g ca. 5% alcohols as side-products; h p(CO)=20 bar, p(H2)=60 bar; p(CO)= 40 bar, p(H2)=80 bar
entries 1-4), perpendicular dissymmetric planes due to investigated in all cases. It has to be added that the SEGPHOS
restricted rotation (BINAP, entries 5-18; SEGPHOS, entries 19- family were not tested in hydroformylation, even using GVL as
20; DM-SEGPHOS, entries 21-26; DTBM-SEGPHOS, entries 27- a solvent.
31) and both stereogenic center and planar element of
All catalysts show remarkable catalytic activity in GVL
chirality (JOSIPHOS, entries 32-36) were used (Figure 1, Table under standard ‘oxo-conditions’ (p(CO) = p(H2) = 40 bar, 60-
1). As a major aim of this paper, the applicability of GVL in 100 °C). As generally observed in the hydroformylation of
hydroformylation was tested and the most important issues styrene (Scheme 1), in addition to the branched and linear
such as activity, chemo-, regio- and enantioselectivity were formyl regioisomers (2-phenylpropanal
investigated. As a comparison, toluene as generally used phenylpropanal ), respectively) the hydrogenation by-
) was also formed.
(
A
)
and 3-
(
B
solvent in platinum-catalysed hydroformylation was also product ethylbenzene (
C
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The catalytic activity of the above systems in GVL was configuration in the temperature range of 40-100oC was
comparable to those observed in toluene. However, in general observed with Pt-BINAP system. 26f
lower activities were obtained in GVL when experiments were
The GVL-based system differs substantially from the
carried out under identical conditions (compare for instance toluene-based one in case of both ligands: neither the
entries 1 and 3 (BDPP), entries 6 and 12 (BINAP, entries 19 and application of the Pt-BDPP system nor that of the Pt-BINAP
20 (SEGPHOS), entries 22 and 25 (DM-SEGPHOS), entries 32 system resulted in the reversal of the enantioselectivity as a
and 34 (JOSIPHOS). The only exception is DTBM-SEGPHOS function of temperature. The formation of the (S)-2-
which formed more active catalysts in GVL (entries 27 and 29). phenylpropanal as predominating enantiomer was observed
It has to be added that the activities obtained with Pt-DTBM- both with (S,S)-BDPP (entries 3, 4) and (R)-BINAP (entries 11-
SEGPHOS catalyst in both solvents fall far behind those ones 18) in the temperature range investigated.
generally observed in platinum-catalysed hydroformylation of
To investigate the effect of the hydrogen partial
styrene.24-26 It should be noted, that the hydroformylations pressure, a rather complicated picture was obtained. While
carried out above 120oC resulted in the formation of some the increase of the hydrogen pressure from 20 to 60 bar
alcohols as side-products, i.e., the hydrogenation products of (entries 13, 14), as well as from 40 to 80 bar (entries 12, 15)
the aldehydes (
A
and
B
) (entries 5 and 11).
has no effect on the ee-s in case of BINAP, some increase was
As for the chemoselectivity towards hydroformylation, in observed with DTBM-SEGPHOS (entries 29, 30) and substantial
general the GVL-based systems provided higher aldehyde decrease with JOSIPHOS (entries 35, 36).
selectivities. When chemoselectivities at higher reaction
The reproducibility of the catalytic results was confirmed
temperatures (100 oC) are compared, the values fall in the by repeating the experiments performed in the presence of
range of 80–88%, with similar chemoselectivities in GVL and BDPP in GVL (Table 2, entry 4) at 80oC. The parallel
toluene. For instance, 81 and 85% (BDPP), 88 and 86% (BINAP), experiments resulted practically in the same chemo-, regio-
83 and 86% (DM-SEGPHOS), 82 and 80% (JOSIPHOS) were and enantioselectivity. That is, the selectivity values differ by
obtained in toluene and GVL, respectively. However, in some less than 1.5%.
cases more pronounced differences in chemoselectivities
obtained in GVL and toluene at lower temperature (80oC) were catalyst. Using PtCl2(PhCN)2 together with (S,S)-BDPP or (R)-
observed. For instance, 86 and 93% for BDPP was obtained. BINAP ligands, we were able to separate the products as GVL
Additionally, efforts were made to separate and re-use the
When the partial pressure of hydrogen was increased from solution from the catalyst by vacuum (10 mmHg) distillation at
40 to 80 bar (while carbon monoxide pressure was kept at 40 80–82 °C. The glue-like residue containing the catalyst,
bar) decrease in aldehyde selectivity was detected, expectedly remained in the bottom of the distillation unit, was re-
(entries 12 and 15). A similar effect was observed when dissolved in GVL and reused in the next catalytic run. The
hydrogen partial pressure was increased from 20 to 60 bar activity and also the regioselectivity of the reaction decreased
(while carbon monoxide partial pressure was kept at 20 bar) in those reactions carried out at 100 °C, reflecting to the
(entries 13 and 14). As in case of activity, the DTBM-SEGPHOS- partial degradation of the catalyst. When recirculation
containing systems behave in a different way (entries 29 and experiments with the Pt-BINAP-tin(II)chloride system were
30). As for the regioselectivity, the linear aldehyde (
B)
carried out at lower temperature (85 °C) the decrease in the
predominated over the branched one (A) in all cases as catalytic activity was accompanied by the slight decrease in
observed generally when platinum-diphosphine catalysts were regioselectivity. Surprisingly, some increase in chemo- and
used in the hydroformylation of styrene.26 It can be stated that enantioselectivities was observed (Table 3).
the application of GVL instead of toluene resulted in a drop of
The reused catalysts were investigated by 31P-NMR after
ca. 10%. While regioselectivities in GVL are in general below 30 removal of volatile compounds from the reaction mixture by.
%, the corresponding values in toluene fall in the range of 36- Surprisingly, the characteristic 1/4/1 pattern of the
48% (BINAP), 36–46% (DM-SEGPHOS). No pronounced effect PtCl2(diphosphine) complex could be seen but no presence of
of the change of the partial pressures on regioselectivities was the corresponding trichlorostannato complex (Table 1) was
observed.
detected. In addition, neither the signals of the uncoordinated
Although moderate enantioselectivities were obtained diphosphine and its oxide nor that of the hemioxide were
using the above systems, some important phenomena
regarding enantioselectivity were observed. The application of
Table 3 Re-use of the Pt-BINAP-tin(II)chloride catalyst in the hydroformylation of
GVL instead of toluene resulted in two important features.
First, the ee-s obtained in GVL were higher in case of all six
ligands. Second, the strong dependence of the
enantioselectivity on the reaction temperature was not
observed neither in case of BDPP nor that of BINAP. As
published before, the formation of (S)-2-phenylpropanal was
found to be favoured at low temperatures while that of the
(R)-enantiomer at higher temperatures when (S,S)-BDPP was
used in toluene. 26c,d The results were rationalized on the basis
of a kinetic phenomenon.31 A similar change of the absolute
styrene at 85oC a
Cycle
Conv.(%)
Rc(%)
Rbr (%)
ee (%)
1.
2.
3.
4.
76
57
33
25
94
96
97
97
16
14
12
12
22 (S)
20 (S)
26 (S)
25 (S)
a
Reaction conditions: Pt/styrene = 1/100, Pt/SnCl2 = 1/2; p(CO) = p(H2) = 40
bar, 1 mmol of styrene, solvent: 5 mL of GVL, reaction time 24 h. For Rc, Rbr
and e.e. see footnotes to Table 2.
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present even after the catalyst was re-circulated three times of their physicochemical properties and their utilization for
(ESI Fig. S10-11). It can be assumed that the complete separation and sensor chemistry” project (SROP-4.2.2.A-
dissociation of the tin(II)chloride in the presence of the rest of 11/1/KONV-2012-0065). L.T. Mika is grateful to the support of
the reaction products led to the decreased activity of the János Bolyai Research Scholarship of the Hungarian Academy
catalyst. Presumably, the partial degradation of the catalyst of Sciences. The present scientific contribution is dedicated to
cannot be related to the (partial) oxidation of the diphosphine the 650th anniversary of the foundation of the University of
ligand.
Pécs, Hungary.
Notes and references
Conclusions
We have demonstrated that γ-valerolactone can be excellent
1
2
C. Reichardt, Org. Proc. Res. Dev., 2007, 11, 105.
(a) F. M. Kerton, Alternative Solvents for Green Chemistry,
RSC, Cambridge, 2009.; (b) P. T. Anastas and J. C. Warner,
Green Chemistry: Theory and Practice, Oxford University
Press, Oxford, UK, 1998. (c)
solvent in the enantioselective hydroformylation of styrene in
the presence of platinum-diphosphine-tin(II)chloride ‘in situ’
generated catalysts. Various chiral diphosphines with central,
axial and planar elements of chirality were tested. Although
more active catalysts were formed in the widely used toluene,
the higher chemo- and enantioselectivities, as well as the
green properties of GVL would deserve further investigations.
3….http://www.fda.gov/downloads/AboutFDA/CentersOffices/C
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Experimental
Platinum(II)chloride-dibenzonitrile complex was prepared as
described before.32 The chiral ligands were purchased from
Sigma-Aldrich and were used without further purification.
Gamma-valerolactone was purchased from Sigma-Aldrich Kft.,
Budapest, Hungary and was purified by vacuum distillation (2
Torr, 80-82 °C). The purified GVL was stored under nitrogen.
In a typical hydroformylation experiment, a solution of
PtCl2(PhCN)2 (2.4 mg, 0.005 mmol), chiral diphosphine (0.005
mmol), and tin(II) chloride (1.9 mg, 0.01 mmol) in 5 mL of GVL
containing 0.115 mL (1.0 mmol) of styrene was transferred
under argon into a 100 mL stainless steel autoclave. The
reaction vessel was pressurized to 80 bar total pressure (CO/H2
= 1/1) and placed in an oil bath of appropriate temperature
and the mixture was stirred with a magnetic stirrer. Samples
were taken from the mixture and the pressure was monitored
throughout the reaction. After cooling and venting of the
autoclave, the pale yellow solution was removed and
immediately analysed by GC and chiral GC (on a capillary
Cyclodex-column, (S)-2-phenylpropanal was eluted before the
(R) enantiomer). For appropriate determination of
enantiomeric excess, 10 mL of hexane was added to a sample
of the reaction mixture (2 mL) and washed with water (twice
10 mL). The hexane phase was dried over Na2SO4, filtered and
concentrated to a colorless oil. The CH2Cl2 solution of this GVL
free sample was applied for chiral GC.
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This work was supported by the Hungarian Scientific Research
Fund (Grant No. OTKA K113177 and PD 116559),
“Environmental industry related innovative trans- and
interdisciplinary research team development in the University
of Pécs knowledge base” (SROP-4.2.2.D-15/1/KONV-2015-
0015) and “Synthesis of supramolecular systems, examination
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DOI: 10.1039/C5GC01778E
A step towards hydroformylation under sustainable conditions: platinum-catalysed
enantioselective hydroformylation of styrene in gamma-valerolactone
Péter Pongrácz,c László Kollárb,c and László T. Mikaa,*
aDepartment of Chemical and Environmental Process Engineering, Budapest University of Technology and
Economics, Budapest, Hungary Fax: +36 1 463 3197; L. T. Mika: Tel.: +36 1 463 1263, e-mail:
laszlo.t.mika@mail.bme.hu.
bDepartment of Inorganic Chemistry, University of Pécs and Szentágothai Research Center, Ifjúság u. 6., Pécs, H-
7624, Hungary
cMTA-PTE Research Group for Selective Chemical Syntheses, Ifjúság u. 6., Pécs, H-7624, Hungary
Table of Contents Entry
Platinum-catalysed enantioselective hydroformylation of styrene was investigated in γ-valerolactone as
solvent.
1