Catalytic hydrogenation of levulinic acid in aqueous phase

Article abstract of DOI:10.1016/j.jorganchem.2012.10.030

The hydrogenation of levulinic acid (LA) yielding γ-valerolactone (GVL) has been examined in aqueous solution using various water soluble phosphine ligands in combination with the metal precursors [Ru(acac) ₃] and [RuCl₃]. Using catalyst loadings of only 0.2 mol%, GVL could be obtained in yields up to 99% conversion and 97% selectivity along with a maximum turnover frequency of 200mol_GVLmol_Ru- 1h^-1 within 5 h, using 3,3′,3′′- phosphinidynetris(benzenesulfonic acid) trisodium salt (TPPTS) and Ru(acac) ₃ as catalytic system. In addition, a ruthenium-phosphine complex immobilized on the amphiphilic copolymer PS-PEG was examined under the same conditions and gave 90% conversion of LA in 24 h.

Full text of DOI:10.1016/j.jorganchem.2012.10.030

Journal of Organometallic Chemistry 724 (2013) 297e299
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Catalytic hydrogenation of levulinic acid in aqueous phase
a
b
c
b
Clara Delhomme , Lars-Arne Schaper , Mei Zhang-Preße , Gabriele Raudaschl-Sieber ,
a
b,c,
*
Dirk Weuster-Botz , Fritz E. Kühn
Institute of Biochemical Engineering, Technische Universität München, Boltzmannstr. 15, 85748 Garching, Germany
Chair of Inorganic Chemistry, Catalysis Research Center, Technische Universität München, Ernst-Otto-Fischer-Str. 1, 85747 Garching, Germany
Molecular Catalysis, Catalysis Research Center, Technische Universität München, Ernst-Otto -Fischer Str. 1, 85747 Garching, Germany
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 September 2012
Received in revised form
The hydrogenation of levulinic acid (LA) yielding g-valerolactone (GVL) has been examined in aqueous
solution using various water soluble phosphine ligands in combination with the metal precursors
[
Ru(acac)
3
] and [RuCl
3
]. Using catalyst loadings of only 0.2 mol%, GVL could be obtained in yields up to 99%
16 October 2012
ꢀ1 ꢀ1
conversion and 97% selectivity along with a maximum turnover frequency of 200 molGVL molRu
within 5 h, using 3,3 ,3 -phosphinidynetris(benzenesulfonic acid) trisodium salt (TPPTS) and Ru(acac) as
3
h
Accepted 17 October 2012
0
00
catalytic system. In addition, a rutheniumephosphine complex immobilized on the amphiphilic copol-
ymer PS-PEG was examined under the same conditions and gave 90% conversion of LA in 24 h.
Ó 2012 Published by Elsevier B.V.
Keywords:
Aqueous hydrogenation
Levulinic acid
Water-soluble phosphines
Polymer immobilized complex
Chemical feedstock and fuels produced from petroleum seem to
have a limited future. The awareness of our planets limited crude oil
resources and new ecological sensibility triggered the search for
alternative energy and carbon sources based on renewables and
of more environmentally benign reactions in aqueous media are
comparatively rare (Scheme 1). Already in 1977, Joó et al. described
the hydrogenation of LA using a ruthenium catalyst under very mild
ꢁ
conditions (60 C, 0.1 MPa), though without mentioning any
CO
these requirements and, in addition, are often nontoxic and
biodegradable [2]. highly promising carbohydrate based
sustainable solvent and fuel additive is -valerolactone (GVL) due
2
neutral raw materials [1]. Biomass-derived alternatives fulfill
selectivity [27]. Later, Mehdi et al. reported the reaction using
[Ru(acac) ] and tri-n-butyl phosphine (PBu ) as catalyst together
3 3
A
with ammonium hexafluorophosphate (NH
4
PF
6
) as additive at
ꢁ
0
00
g
10 MPa and 135 C, or with [Ru(acac)
3
] and 3,3 ,3 -phosphinidy-
to its favorable properties such as inertness towards oxygen and
water, high boiling and flash point, low melting point, low vapor
pressure and decent smell [3]. GVL, accessible from agricultural
waste, can be converted to (liquid) alkenes, fine chemicals and also
used for food additives or energy generation [4e7]. The bulk scale
industrial precursor of GVL is 4-oxopentanoic acid or levulinic acid
netris(benzenesulfonic acid) trisodium salt (TPPTS) at 6.9 MPa and
140 C in water [5]. Chalid et al. used the same ligand successfully in
ꢁ
a biphasic water/DCM system and Serrano-Ruiz et al. reported
successful application of a metal based supported catalyst (5% Ru/C)
ꢁ
for the hydrogenation of aqueous levulinic acid (50 wt%), at 150 C
and 3.5 MPa under continuous flow conditions [28,29]. Just recently,
(
LA), which is among the twelve most promising biomass-derived
Tukacs et al. presented catalytic examination of a series of
building-block chemicals, due to its inexpensive synthesis from
wood, starch or glucose [1,8,9].
3
sulfonated phosphane ligands in combination with [Ru(acac) ] [18].
In this work, we report a kinetic catalyst screening of Ru complexes
with different water-soluble phosphine ligands (Fig. 1), substituted
with carboxylic acids, amines or sulfones as homogeneous, immo-
bilized or heterogeneous catalyst systems, in order to identify
a simple and straightforward catalyst/ligand combination for the
The hydrogenation of LA or its esters has been reported
employing a broad variety of different metal based catalysts and
methodologies [10e21], albeit some of the best results leading to
GVL were obtained with Ruthenium-based catalysts [6,10,11,18].
While most of these catalytic transformations are carried out in
organic solvents such as DCM, acetone or methanol [22e26], reports
pivotal transformation of levulinic acid to g-valerolactone.
*
Corresponding author. Technische Universität München, Department Chemie,
Lichtenbergstr. 4, 85747 Garching, München, Germany. Tel.: þ49 0 89 289 13096;
fax: þ49 0 89 289 13473.
E-mail address: fritz.kuehn@ch.tum.de (F.E. Kühn).
Scheme 1. Aqueous hydrogenation of levulinic acid (LA) into g-valerolactone (GVL).
0
022-328X/$ e see front matter Ó 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.jorganchem.2012.10.030

298
C. Delhomme et al. / Journal of Organometallic Chemistry 724 (2013) 297e299
Fig. 1. Ligands used for the aqueous hydrogenation of levulinic acid to
g-valerolactone: 1: Tris(2-carboxyethyl) phosphine; 2: 1,3,5-Triaza-7-phosphaadamantane (PTA); 3: Tris(2,4-
dimethyl-5-sulfophenyl) phosphine trisodium salt (TXTPS); 4: [2-(dicyclohexylphosphino)ethyl] trimethylammonium chloride; 5: 3-(diphenylphosphino)benzenesulfonic acid
0
00
sodium salt (TPPMS); 6: 3,3 ,3 -Phosphinidynetris(benzenesulfonic acid) trisodium salt (TPPTS).
In a general synthetic procedure, the substrate (26.4 mmol), the
metal precursor, [Ru(acac) (0.044 mmol), and the ligand
0.44 mmol) (Fig. 1) were introduced in a flask filled with 40 mL of
observable. The decomposition product, most likely Ru clusters,
3
]
catalyze the hydrogenation of levulinic acid into GVL heteroge-
neously, with high conversion and selectivity. This observation
suggests the conclusion that heterogeneous catalysts are superior
to homogeneous systems under the applied reaction conditions.
(
degassed water and stirred until total dissolution. This solution was
transferred under argon into the autoclave PTFE insert that was
subsequently introduced in the autoclave, which was sealed and
flushed with nitrogen for several minutes. The reaction was
2 3
In order to provide further evidence, an alumina (Al O ) sup-
ported 5% Ru catalyst, similar to the one reported by Serrano-Ruiz
et al., was examined (entry 8, Table 1) [17]. With a TOF of
ꢁ
ꢁ
warmed up to 140 C at an agitation rate of 1400 rpm. At 140 C,
MPa of hydrogen were introduced into the autoclave. Pressure
ꢀ1
ꢀ1
5
575 molGVL molRu
higher than for [Ru(acac)
the active species in the case of [Ru(acac)
h
, the results obtained are even somewhat
], further supporting the hypothesis that
] are Ru clusters. It should
was maintained through free supply of hydrogen to the reaction
vessel. Samples were obtained through the liquid sampling valve
each hour for the first 6 h and subsequently after 21 h or 24 h,
respectively. The samples were then filtered through filter paper
and deep-frozen for later analysis by HPLC. At the end of the
3
3
be noted though, that for the reaction with the alumina supported
catalyst selectivity to GVL slowly decreases after 3 h (from 99% after
3 h to 86% after 21 h), possibly due to further hydrogenation of GVL
into subsequent reduction products.
ꢁ
reaction, the autoclave was cooled down to 50 C in a water bath
and pressure was released (see Supporting information).
Although LA was reduced to GVL by all examined catalyst
systems, significant differences could be detected. Ligands 1
Given the more convenient product isolation associated with
heterogeneous catalyst systems, higher relevance for industrial
application and the satisfying results for the hydrogenation of LA to
GVL catalyzed by Ru on alumina, supported types of catalysts were
studied in more detail, because the question remained, whether
better defined heterogeneous catalysts e i.e. immobilized Ruthe-
nium complexes e would yield even more promising results. For
and
2 with less bulky substituents gave poor activities
ꢀ
1
ꢀ1
ðTOFs < 20 mol
molRu
h
Þ and even after a reaction time of
1 h no complete conversion could be observed (Table 1). However,
the more sterically demanding ligands 3e6 gave satisfactory TOFs
GVL
2
ꢀ
1
ꢀ1
from 117 to 202 molGVL molRu
h
. The two phosphine ligands
this purpose, a catalyst on an amphiphilic polystyrenee
giving the best catalytic results were TPPMS 5 and TPPTS 6,
polyethylene glycol (PSePEG) copolymer was chosen, as this kind
of support promises good contact to the aqueous reaction solution
ꢀ
1
ꢀ1
revealing highest TOFs (194 and 202 molGVL molRu
h
, respec-
tively) and conversions (94% and 99%, respectively) after 5 h,
combined with high selectivities (94% and 97%, respectively).
Employing only 0.02 mol% of the same catalyst system, Tukacs et al.
observed 23% yield of GVL within 1.8 h, using a pressure of 10 MPa
and otherwise comparable conditions [18].
as well as easy catalyst removal by filtration, [RuCl
adppp)
] 7 (adppp ¼ 2-aza-1,3-bi(diphenyl-phosphino)propane)
developed by Kayaki et al. was synthesized (see Fig. 2) [30,31].
Since this compound represents an analogue of [RuCl (PPh
both complexes were examined for hydrogenation of levulinic acid
to GVL in water under the same conditions. For further comparison,
a homogeneous catalyst was also examined, formed in-situ from
2
(PSePEG-
2
2
3 3
) ],
3
In order to determine the influence of the ligand, [Ru(acac) ]
was examined without any phosphine ligands present (entry 7,
Table 1). Interestingly, the metal precursor gave a high TOF
RuCl
3
and TPPTS ligand 6. Catalysis results are presented in Table 2.
ꢀ
1
ꢀ1
ð570 mol
molRu
h
Þ. However, fast discoloring of the reac-
The homogeneous catalyst system yielded a similar TOF
GVL
ꢀ
1
ꢀ1
tion solution took place and after 1 h black particles were
ð210 mol
molRu
h
Þ as the one observed with the same ligand
1
GVL
ꢀ
Ru
ꢀ1
and [Ru(acac)
3
]
as metal precursor (202 mol
mol
h
,
GVL
entry 6 in Table 1). The amount of anionic ligand 6 does not seem to
Table 1
have any impact on the initial TOF. The immobilized material
Hydrogenation of levulinic acid (26.4 mmol) with [Ru(acac)
ligands 1-6 (0.44 mmol) at 140 C and 5 MPa H
3
] (0.044 mmol) and
in 40 ml water (general procedure
ꢀ1
ꢀ1
ꢁ
2
shows lower activity (TOF of 78 molGVL molRu
after 24 h, higher conversion was achieved. The non-water-soluble
complex [RuCl (PPh ] is associated with a relatively low TOF
h
), however,
A); for entry 8, 0.044 mmol of supported Ru was used, based on elemental analysis
general procedure B): Turnover frequency (TOF), conversion (X) and selectivity (S)
(
2
3 3
)
were determined after 5 or 21 h.
ꢁ
N
Catalyst
TOF,
molGVL molRu
After 5 h
After 21 h
ꢀ
1
ꢀ1
h ]
[
X, %
S, %
X, %
S, %
1
2
3
4
5
6
7
8
[Ru(acac)
[Ru(acac)
[Ru(acac)
[Ru(acac)
[Ru(acac)
[Ru(acac)
[Ru(acac)
3
3
3
3
3
3
3
] þ 1
] þ 2
] þ 3
] þ 4
] þ 5
] þ 6
]
10
13
1
3
e
62
34
26
84
100
100
N.D
100
39
14
100
91
92
92
100
95
100
94
97
98
98
117
135
194
202
569
575
23
59
94
99
100
100
a
a
N.D
86
Ru 5% on Al
2 3
O
Fig. 2. Ruthenium complex
7 with two polymer supported phosphine ligands
a
N.D.: not determined.
[RuCl (PSePEG-adppp)
2
2
] (with adppp ¼ 2-aza-1,3-bi(diphenylphosphino) propane).

C. Delhomme et al. / Journal of Organometallic Chemistry 724 (2013) 297e299
299
Table 2
C.D. is grateful to IGSSE (project 2.07) for a PhD grant and L.A.S.
is grateful to TUM Graduate School and the Bavarian Elite Network
NanoCat for financial support.
Hydrogenation of levulinic acid (1.58 mmol) with Ru catalyst following general
procedure C (0.0158 mmol Ru, calculated by elemental analysis) at 140 C and
ꢁ
2
5.5 MPa H in 40 ml water; in entry 11, 6 (0.0513 mmol) was added: Turnover
frequency (TOF), conversion (X) and selectivity (S) were determined after 5 or 24 h.
Appendix A. Supplementary material data
ꢁ
N
Catalyst
TOF,
molGVL molRu
X after S after X after S after
ꢀ
1
ꢀ1
h
5 h, %
5 h, %
24 h, % 24 h, %
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.jorganchem.2012.10.030.
9
7
78
210
92
49
74
22
81
91
86
97
90
23
87
86
97
10
[RuCl
[RuCl
3
2
] þ 6
(PPh
11
3 3
) ]
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ꢁ
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