New biobased tetrabutylphosphonium ionic liquids: Synthesis, characterization and use as a solvent or co-solvent for mild and greener Pd-catalyzed hydrogenation processes

Article abstract of DOI:10.1039/c6ra23056c

Phosphonium-based Ionic Liquids (PhosILs) with natural organic derived anions (l-lactate, l-tartrate, malonate, succinate, l-malate, pyruvate, d-glucuronate, d-galacturonate, ferulate, p-coumarate) were easily prepared by acid-base method from tetrabutylphosphonium hydroxide and an excess of the corresponding acid with good yields. Their characterization was realized through classical NMR, IR and elemental analysis techniques; their viscosity and ATG parameters were also determined. These ionic liquids showed good performance and recyclability in the selective Pd-catalyzed hydrogenation of alkenes, polyenes like linoleic acid and enantioselective hydrogenation of unsaturated ketones such as isophorone at room temperature under atmospheric H₂ pressure. Furthermore, NMR studies leading to computational calculations were performed to establish easily the composition of the resulting mixture obtained through the hydrogenation of linoleic acid.

Full text of DOI:10.1039/c6ra23056c

View Article Online
View Journal
RSC Advances
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Hayouni, A.
Robert, N. Ferlin, H. Amri and S. Bouquillon, RSC Adv., 2016, DOI: 10.1039/C6RA23056C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/rsc-advances

Page 1 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
New biobased Tetrabutylphosphonium ionic liquids: synthesis, characterization and use
as solvent or co-solvent for mild and greener Pd-catalyzed hydrogenation processes
Safa Hayouni,a Anthony Robert,a Nadège Ferlin,a Hassen Amri,b Sandrine Bouquillon*a
a Institut de Chimie Moléculaire de Reims UMR CNRS 7312 ꢀ Université de Reims
ChampagneꢀArdenne, Boîte n° 44, B.P. 1039, Fꢀ51687 Reims, France
b Université de Tunis El manar, Faculté des Sciences de Tunis, Département de Chimie,
Laboratoire de Synthèse Organique Sélective & Activité Biologique, Campus Universitaire
2092 Tunis, Tunisie
* Corresponding authors: sandrine.bouquillon@univꢀreims.fr ꢀ Phone: +33 (0) 3ꢀ26ꢀ91ꢀ89ꢀ73
Fax: +33 (0) 3ꢀ26ꢀ91ꢀ31ꢀ66
ABSTRACT: Phosphoniumꢀbased Ionic Liquids (PhosILs) with natural organic derived
anions (Lꢀlactate, Lꢀtartrate, malonate, succinate, Lꢀmalate, pyruvate, Dꢀglucuronate, Dꢀ
galacturonate, ferulate, pꢀcoumarate) were easily prepared by acidꢀbase method from
tetrabutylphosphonium hydroxide and an excess of the corresponding acid with good yields.
Their characterization was realized through classical NMR, IR and elemental analysis
techniques; their viscosity and ATG parameters were also determined. These ionic liquids
showed good performance and recyclability in the selective Pdꢀcatalyzed hydrogenation of
alkenes, polyenes like linoleic acid and enantioselective hydrogenation of unsaturated ketones
such as isophorone at room temperature under atmospheric H2 pressure. Furthermore, NMR
studies leading to computational calculations were performed to establish easily the
composition of the resulting mixture obtained through the hydrogenation of linoleic acid.
Keywords: Ionic liquids, tetrabutylphosphonium, (di)acids, aminoacid, hydrogenation,
palladium, linoleic acid, unsaturated ketones, enantioselectivity, recyclability.
Introduction
Ionic liquids (ILs) present a class of salts, usually characterized by low melting points below
100 °C.1 With their numerous properties, ILs qualify as a good candidate to replace classical
organic solvents in many fields:1b electrochemistry, organic synthesis, catalysis,

RSC Advances
Page 2 of 28
View Article Online
DOI: 10.1039/C6RA23056C
complexation, extraction, etc …Compared to their ammonium analogues, ILs containing
phosphonium cations are much rarer and studies involving quaternary phosphonium systems
are scarce.2 Indeed, ILs based on quaternary nitrogen cations such as imidazolium and
pyridinium have been extensively investigated by comparison to phosphonium ILs which
received scant attention; however, there is no predilection for either family as both have their
own advantages and disadvantages.2
Typical phosphonium cations have the general formula [R’PR3]+, in which three of the alkyl
groups are identical while the fourth is different. As well, asymmetric tertiary phosphines
(RR’2P or R2R’P) could lead to [RR’2R’’P]+ and [R2R’R’’P]+ cations through free radical
addition.3 These phosphonium salts associated to halides are commercially available. Through
anion exchange reactions, a large variety of phosphoniumꢀbased ILs have been synthetized.4
Halogen free systems can be also produced by direct reaction of tertiary phosphines with
alkylating agents such as benzenesulfonate, alkyltosylates, trialkylphosphates, and
dialkylsulfates.5 Chiral,6 protic7 and cyclic8 phosphonium based ILs have also been prepared
through classical methods used with ammonium analogues. Respective properties (stability,
conductivity, selfꢀdiffusion) of both ILs families were also compared and revealed important
influence of the nature of the cation.
However, classical ammonium or phosphonium based ILs present toxicity on diverse
microbial strains and are low biodegradable,9 limiting their character of "green compounds or
green solvents". Consequently, greener ILs have been then extensively investigated since
2010 essentially concerning ammonium, imidazolium, thiazolium, choline or betaine cations
associated to aminoacids or esters as counter ions.10 Concerning phosphonium cations,
alkyltrihexylphosphonium acesulfamates were obtained in high yields by a metathesis route,
starting with alkyltrihexylphosphonium chlorides or bromides and the commercially available
acesulfamate potassium salt considered as a nontoxic organoanion.11 This IL was essentially
used in electrochemistry. Ohno and coll. also described the synthesis of ILs with 20 natural
aminoacids with ammonium12 and phosphonium13 cations. However, in general, the
phosphonium analogues showed relatively low levels of biodegradability, in contrast to
dialkylimidazolium and alkylpridinium ILs with incorporated ester moieties and octylsulfate
anions, as demonstrated by Scammells et al..14
For our part, we prepared a few years ago, ILs with a bioderivated anion, such as acids
obtained from biomass (lactic, tartaric, malic… acids), osidic acids or amino acids like proline
or derivatives (Figure 1).15a,b These ILs derived from TBA (tetrabutylammonium) showed
good performance and recyclability in catalytic selective hydrogenation of 1,5ꢀcyclooctadiene
1

Page 3 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
(1,5ꢀCOD) into cyclooctene at room temperature under atmospheric H2 pressure and were less
toxic to E. coli than commercial TBABr. Our system was already largely competitive
compared to other selective hydrogenation processes of 1,5ꢀCOD conducted under harsh
conditions
(5ꢀ50
bar,
50ꢀ100°C
and
4ꢀ6
h)
with
different
systems
16b
BMIM.PF6/Na2[Ru6C(CO)16],16a Ni catalyst coated with BMIM.C8H17SO4
BMIM.BF4/Pd(acac)2.16c
and
Figure 1 ꢀ Biobased TBA ionic liquids
In fact, catalytic hydrogenations in ILs have become the subject of extensive studies since
1995 triggered by the simultaneous work of Chauvin17a and Dupont.17b Ever since, catalytic
reactions involving metal complexes in ILs have been actively investigated. Around 300 ILs
have been screened and have led to the production of useful products and intermediates.18 The
majority of these ILs contained heterocyclic cations, such as pyridinium, imidazolium,
polyalkylammonium and recently synthesized guanidinium, piperidinium, pyrrolium,
pyrrolidinium, morpholinium, cholinium, piperazinium, thiazolium. Hydrogenation processes
in ILs have been recently reviewed by Gathergood et al.19 in a quite complete book chapter.
Many organometallic catalytic systems were already described for the hydrogenation of
isophorone, essentially based on palladium derivatives associated to chiral ligands. These
systems consist on black palladium or palladium supported over Al2O3, MgO, BaCO3, SrCO3,
CaCO3 or modified silica, associated to proline,20 prolineꢀbased chiral modifiers,20h,21 or (−)ꢀ
dihydroapovincaminic acid ethyl ester in high pressure conditions.22 Other organometallic
systems are used like Ruꢀ23 or Raney Niꢀbased24 catalytic systems which preferentially lead to
trimethylcyclohexanol (TMCH), wahile CrꢀNiꢀ,25 Zn26ꢀ or Rh27ꢀ based ones yield only the
saturated ketone. In general, these catalytic systems are performed in harsh reaction
conditions (very high pressure, toxic solvents).20ꢀ22 scCO2 as a reaction medium as a
replacement for organic solvents for heterogeneously catalyzed hydrogenation of carvone was
also highlighted by enhancing conversion.28
2

RSC Advances
Page 4 of 28
View Article Online
DOI: 10.1039/C6RA23056C
Apart from our work with ILs or CILs (Chiral Ionic Liquids)15a,b, to our knowledge only one
work concerning hydrogenation process in biobased ILs has been reported.15c,29 It concerned
γꢀvalerolactoneꢀbased ILs used for transfer hydrogenation, so without the use of metallic
species. These ILs were successfully applied as alternative solvents for homogenous catalytic
transfer hydrogenation of acetophenone and its substituted forms, as well as other
functionalized ketones and alkenes.
Chiral ionic liquids (CILs) tetrabutylammoniumꢀ(S)ꢀprolinate, tetrabutylammoniumꢀ(R)ꢀ
prolinate and tetrabutylammonium transꢀ4ꢀhydroxyꢀ(S)ꢀprolinate were also easily prepared by
our team in one step from the aminoacid and tetrabutylammonium hydroxide (TBAOH) and
revealed interesting properties in ecotoxicity and in asymmetric catalysis of α,βꢀunsaturated
ketones such as isophorone.15b
Furthermore, as hydrogenation of vegetable oils represents a real challenge, we were
interested to develop these hydrogenation processes in ILs. In 2012, Pagliaro and coꢀworkers
prepared some Pt(0) nanoparticles stabilized on silica which could lead in mild conditions
(RT, 1 atm. H2) to the complete hydrogenation of vegetal oils for many runs.30
Electrochemical pathways were also performed using Pd/Al2O3 and PdꢀCo/Al2O3 as catalysts
in various pH conditions: oleic acid was obtained with 80% yield at pH equal to 13.31a The
partial hydrogenation of this polyunsaturated acid was also performed by Pd/Al2O3 doped
with various thiolate selfꢀassembled monolayers under high H2 pressure and at high
temperature.31b
So, this paper covers a detailed description of tetrabutylphosphonium based ionic liquids
(PhosILs) and their major influence on hydrogenation catalysis especially their contribution to
selective mild hydrogenation procedures of fatty acids or to asymmetric catalysis of α,βꢀ
unsaturated ketones.
Results and Discussion
Synthesis of phosphonium-based ionic liquids (PhosILs) with tetrabutylphosphonium
(TBP) as cation:
3

Page 5 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
As previously described for ammonium based ILs,15a PhosILs were prepared from
tetrabutylphosphonium hydroxide (TBPOH) and an acid following an acidꢀbase method
developed by Ohno and coꢀworkers.12 The acids issued from the biomass were
tartaric, malonic, succinic, ꢀmalic, pyruvic, ꢀglucuronic, ꢀgalacturonic acids and S
L
ꢀlactic,
Lꢀ
L
D
D
ꢀproline
(Scheme 1). Three different pathways were improved considering the different physical
properties (solubility, melting points, etc..) of the employed acids. All pathways were simple
and efficient, as corresponding ILs were obtained with high yields and most of them were
liquid at room temperature.
Scheme 1 ꢀ Synthesis of PhosILs
R-COOH
PhosILs
Pathway / Yield (%)/ aspect (at RT)
A / 87/ oil
L-Lactic acid
A / 81/ wax
L-tartaric acid
A / 92/ Solid
L-malonic acid
L-succinic acid
A / 91/ viscous oil
A / 92/ oil
B / 87/ oil
L-malic acid
Pyruvic acid
4

RSC Advances
Page 6 of 28
View Article Online
DOI: 10.1039/C6RA23056C
C / 80/ viscous oil
D-glucuronic acid
C / 77/ wax
D-galacturonic acid
A / 87/ oil
A / 94/ oil
A / 90/ oil
S-Proline
R-Proline
4-hydroxy-S-Proline
Table 1 ꢀ Phosphoniumꢀbased ionic liquids with biomass based carboxylates
These PhosILs have been characterized by usual analytical methods involving NMR, IR and
elemental analysis. Thermogravimetric and DSC analyses were also performed and allowed
respectively the determination of the decomposition and glass transition temperatures.
Decomposition temperatures were relatively high, up to 315°C and furthermore higher than
ammonium analogs15a except for osidic acid derivatives (7, 8). These sugar derivatives
generally present low thermal stability limited by the strength of heteroatom/heteroatom
associations and carbon/hydrogen bonds.32a The higher thermal stability of the synthesized
PhosILs was expected, as phosphoniums ILs are generally described in the literature as
having better thermal stability than imidazolium or ammonium ILs.32b Therefore, PhosILs 1-6
could play an important role as solvent for different chemical reactions.
The glass transition temperature (Tg) values were all under 0°C. A negative Tg is classical for
ionic liquids. But the fact that negative Tgs were observed with osidic carboxylates
5

Page 7 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
derivatives 7 and 8 was different from what was previously found with ammonium analogs,
which presented Tgs above 0°C.15a
Finally, the viscosity was following the relationship between the number of carbon and/or
hydrogen bonds as described in the literature32c and it was also influenced by the nature of the
anions. Values at 80°C were in general quite low, except for compounds 2 and 8, which
values were 268 cP and 617 cP respectively and lower than their TBA analogues (Figure 2).
ILs with low viscosity are expected, to avoid difficulties of mixing homogeneously or
dispersing reactants during reaction
PhosILs
1
Viscosity (cP) at 80°C
Tg (°C)
Tdec (°C)
21
ꢀ
314
268
ꢀ
ꢀ20
ꢀ9.8
ꢀ49.3
ꢀ40.2
ꢀ59.3
ꢀ8.7
ꢀ22.5
ꢀ56.8
ꢀ
167
288
277
203
315
130
142
301
241
278
2
3
125
105
16
ꢀ
4
5
6
7
617
47
ꢀ
8
9
10
11
ꢀ
ꢀ
6

RSC Advances
Page 8 of 28
View Article Online
DOI: 10.1039/C6RA23056C
Table 2 ꢀ Glass transition temperature, decomposition temperature and viscosity values of
phosphoniumꢀbased ionic liquids
400
350
300
250
200
TBA
TBP
150
100
50
0
Figure 2 ꢀ Viscosity (cP) of TBA and TBP ionic liquids at 80°C
Other biobased acids were also employed, as pꢀcoumaric or ferulic acids. pꢀCoumaric can be
found in a wide variety of edible plants such as peanuts or vegetables (navy beans, tomatoes
and carrots), wine and also barley grain.23 Ferulic acid (FA), an ubiquitous natural phenolic
phytochemical is present in seeds, leaves, both in its free form and covalently conjugated to
the plant cell wall polysaccharides, glycoproteins, polyamines, lignin and hydroxy fatty
acids.34
The experimental pathway had to be modified taking in account the physical properties of the
phenolic acids (scheme 2) and the synthesis was extended to tetrabutylammonium (TBA) salts
to complete the preliminary study.15a
Scheme 2 ꢀ Synthesis of ILs with pꢀcoumarate and ferulate anions
7

Page 9 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
The respective salts were obtained with good yields and were all solid at room temperature.
But it is more adequate to consider them as molten salts due to their high melting point which
is higher than 100°C. Their decomposition temperatures were also relatively low fluctuating
between 132 to 181°C. As a result, they won’t be considered for the hydrogenation studies.
Aspect
ILs
Yield %
Tdec (°C)
Melting point
White solid
115°C
86
132
12
13
White solid
119°C
89
157
H
O
O
TBP
White solid
145°C
H
14
89
93
HO
156
181
14
H
O
O
TBN
White solid
150°C
H
HO
15
15
Table 3 ꢀ Physical properties of ILs with pꢀcoumarate and ferulate anions
Catalytic hydrogenation
Hydrogenation of 1,5-cyclooctadiene (1,5-COD)
8

RSC Advances
Page 10 of 28
View Article Online
DOI: 10.1039/C6RA23056C
For the study, the selective hydrogenation of the 1,5ꢀcyclooctadiene (1,5ꢀCOD) was chosen as
a model reaction to improve the ability of our ionic liquids to be ‘selective’ coꢀsolvents and
appropriate for the recycling process.
Scheme 3 ꢀ Hydrogenation of 1,5ꢀCOD in PhosIL/water
In the absence of an IL, complete conversion of 1,5ꢀCOD into COA was obtained in water in
the first run. Recycling the Pd catalyst led to the formation of COE until 90% with conversion
attained at the eight run (Figure 3a).
(a)
100
80
60
COE
COA
40
1-4COD
20
Conversion
0
1
2
3
4
5
6
7
8
Run
(b)
100
80
60
40
20
0
COE
COA
1,4-COD
1,3-COD
Conversion
1
2
3
4
5
Run
Figure 3 ꢀ Pdꢀcatalyzed Hydrogenation of COD in water (a) and in TBABr/H2O (b)
9

Page 11 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
Similar results were obtained in commercial TBPOH, while hydrogenation reactions in
TBPBr (Figure 3b) led also to COE but with lower conversions each run after the other and
generation of isomerization compounds. This phenomenon was already observed in presence
of other copper or zincꢀbased catalysts (CuOꢀAl2O3, CuOꢀSiO2 or ZnOꢀAl2O3) via water gas
shift reaction.35 These results confirmed the importance of the nature of the counter anion on
the hydrogenation mechanism.
Next, in the presence of PhosILs 2-7, the results were close to those obtained with water as
solvent. But improvements were observed as no isomerization compounds traces were
present, as shown in Figures 4a with compound 3/water system.
(a)
100
80
60
COE
40
COA
20
Conversion
0
1
2
3
4
5
Run
(b)
100
80
60
40
20
0
COE
COA
conversion
1
2
3
4
5
Run
Figure 4 ꢀ Pdꢀcatalyzed Hydrogenation of COD in TBP malonate 3/H2O (a) and
in TBP lactate 1/H2O (b)
10

RSC Advances
Page 12 of 28
View Article Online
DOI: 10.1039/C6RA23056C
On the contrary, with PhosIL 1/H2O, COA was mainly obtained for all cycles (Figures 4b).
This result was probably due to the low viscosity of TBP Lꢀlactate 1 with regard to the other
ILs tested. Indeed, even if few data in the literature are available on the solubility of H2 in ILs,
the diffusion of gases depends generally on the viscosity of the environment.36
Hydrogenation of linoleic acid
Linoleic acid is being a growing subject of interest in chemistry and biology. This
polyunsaturated fatty acid can be found in large amounts in vegetable oils. Its hydrogenation
could lead to saturated stearic acid (C18:0) and monoꢀunsaturated acids cisꢀ12ꢀoctadecenoic
acid (C18:1ꢀ12) and oleic acid (C18:1ꢀ9), and their isomerization products (Scheme 4). Our
goal was to produce mainly a monoꢀunsaturated compound (C18:1) without formation of
isomers and furthermore without changing the cis configuration.
The focus of our laboratory was to develop a simple and mild process using the synthesized
biosourced PhosILs with water as coꢀsolvent to induce partial hydrogenation and recycling
(Scheme 4).
Scheme 4 ꢀ Hydrogenation of linoleic acid in H2O / PhosIL
The identification of the composition of the resulting mixture, was assured using gas
chromatography (GC), completed by NMR techniques. By GC, after postꢀhydrogenation
esterification of the acids,37 various columns (Column TRꢀ1 : 100% Dimethyl Polysiloxane,
Column TRꢀ5: 5% phenyl methyl polysiloxane, INNOWAX (PEG)) and conditions38 were
11

Page 13 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
tested without success to separate and quantify specifically mono and polyꢀunsaturated
isomers presented in the resulting mixture. To solve this problem, a NMR method was
developed in our laboratory inspired from reported works concerning the determination of the
1
composition of plant oils.39 Mixtures obtained after hydrogenation were then analyzed by H
NMR without preliminary separation of constituents.
Assignment of proton signals:
The products of linoleic acid hydrogenation in ILs were saturated acid (X), monoꢀunsaturated
acid (Y) and polyꢀunsaturated acid (Z).
The 1H NMR spectrum of linoleic acid hydrogenation product in ILs is shown in figure 5. The
spectrum signals are annotated from a to g.39b These groups are assigned as follows: a,
olefenic protons; b, divinyl methylene protons; c, α-methylene protons adjacent to carbonyl
carbon; d, allyl methylene protons; e, β-methylene protons adjacent to carbonyl carbon; f,
methylene protons on saturated carbon atoms; g, terminal methyl protons of saturated,
monounsaturated and polyunsaturated acids; g’, terminal methyl protons of residual PhosIL
traces.
12

RSC Advances
Page 14 of 28
View Article Online
DOI: 10.1039/C6RA23056C
f
c
f
f
d
b
d
Z =
Y =
g
linoleic acid
oleic acid
HO
HO
e
a
f
f
f
f
a
a
a
O
f
f
f
g
d
f
c
f
f
f
f
f
d
a
e
f
f
a
O
f
Y =
cis-12-
d
O
g
f
f
f
d
octadecenoic acid
e
e
f
a
HO
HO
f
f
f
f
f
a
f
c
c
f
O
f
f
f
f
f
f
f
X =
stearic acid
g
f
f
f
f
Figure 5 ꢀ 1H NMR spectrum in CDCl3 of the mixture obtained after hydrogenation of linoleic
acid in TBP lactate 1/H2O
In the divinyl methylene protons chemical shift, there were three signals (Figure 6). The
triplet at 2.77 ppm corresponded to linoleic acid divinyl methylene protons and was
confirmed by NMR spectrum of linoleic acid. The other signals were attributed to isomer
product of linoleic acid divinyl methylene protons.
Figure 6 ꢀ Divinyl methylene 1H NMR spectrum in CDCl3 of hydrogenation product in
PhosILs/H2O.
(triplet at 2.77ppm corresponded to linoleic acid divinyl methylene protons)
13

Page 15 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
After calculations (see ESI), composition of hydrogenated products could be determined. The
analytical results for the hydrogenation of linoleic acid in TBP malonate 3/H2O can be
summarized on the following graph (Figure 7). Selective hydrogenation towards monoꢀ
unsaturated compounds Y was observed with almost complete conversion of the linoleic acid.
The selective hydrogenation was also realized without formation of compounds presenting a
trans configuration as observed with NMR coupling constants. Moreover, catalytic system
was could be easily recycled and reused without changes in reactivity for 6 cycles. Results
were strongly similar regardless of the nature of the used PhosILs. Contrary to what was
previously observed with 1,5ꢀCOD, it seemed there was no effect of neither the anion nor the
viscosity of the used PhosILs for hydrogenation of linoleic acid.
Figure 7 ꢀ Hydrogenation of linoleic acid in TBP malonate 3 / H2O
The results obtained during our study in soft conditions (RT, atmospheric pressure, water)
were quite near to those obtained by Suarez and coll. in 2011 for the selective hydrogenation
of biodiesel, however a drastic system (Pd(OAc)2/[BMIM] [BF4], H2 (5ꢀ75 bar) and 80°C)
was used.40
As a fair assessment, it is safe to say that our system of hydrogenation was very competitive
towards all systems of hydrogenation described until today in the literature for such
compounds. It was realized under 1 atm. of H2 at room temperature and did not require
preliminary preparation of catalysts. The selective hydrogenation of the linoleic acid towards
14

RSC Advances
Page 16 of 28
View Article Online
DOI: 10.1039/C6RA23056C
monoꢀunsaturated compounds was also realized without formation of compounds presenting a
trans configuration as observed with NMR coupling constants.
Hydrogenation of α,β-unsaturated ketones
Previous work concerning tetrabutylammonium based CILs (TBA (R) – or (S)ꢀ prolinate and
TBA 4ꢀhydroxyꢀ ꢀprolinate) showed that these ILs were good chiral modifiers for the
S
hydrogenation of carbonꢀcarbon double bond of α,βꢀunsaturated ketones in isopropanol (iꢀ
PrOH) under mild conditions.15b Consequently, we tested our CPhosILs 9-11 (chiral
phosphonium ionic liquids) in such enantioselective hydrogenation process.
Isophorone was chosen as model substrate to define the best conditions. The conversion and
the selectivity were determined by GC; the determination of the enantiomeric excess (ee)
requiring the use of a ßꢀcyclodextrine chiral column.
First of all, the influence of the CPhosILs ratio CPhosIL/substrate was studied. Results are
summarized in Table 4 and best conditions were met with 0.5 eq. of CPhosIL 9. Indeed, good
conversion of isophore was observed with high selectivity for trimethylcyclohexanone
(TMCH) and with an important ee of 40% in favour of the isomer S. It also proved that
CPhosIls were suitable solvents to induce good conversion, high selectivity and good ee for
such mild process compared to other harder processes.41
O
O
(CPhosIL 9)
H2 ( 1 atm. ), 18h, RT
TBP S-prolinate 9
PdCl2
+
*
TMCH
0,01 eq
isophorone
( 2 mmol)
Scheme 5 ꢀ Hydrogenation of isophorone in CPhosIL 9
Equivalent of 9
Conv. (%)
Select. (%)
e.e. (%)
32 (S)
1
7
93
95
0.5
60
40 (S)
Table 4 ꢀ Influence of the ratio of CPhosIL 9 for the hydrogenation of isophorone
Recycling of the catalytic system led unfortunately to byꢀproducts as for example
trimethylcyclohexanol by reduction of the C=O bond.
15

Page 17 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
Next, to envisage the recycling of the catalytic species, we tested several polar coꢀsolvents
which could facilitate the adsorption of the substrate on the catalyst and also participate to the
solubilization of the hydrogen (H2) in the medium.42
Scheme 6 ꢀ Hydrogenation of isophorone in CPhosIL 9/solvent
Solvent
H2O
Conv. (%)
Select. (%)
e.e. (%)
96
100
70
95
90
98
95
96
67
93
5
37 (S)
6
iꢀPrOH
MeOH
H2O / MeOH (1/1)
Acetonitrile
iꢀPrOH/ H2O (2/1)
iꢀPrOH/ H2O (3 /1)
52
13
54
34 (S)
11
17
43
2
Table 5 ꢀ Influence of coꢀsolvent for the hydrogenation of isophorone with CPhosIL 9
The best ee (37%) was obtained using 9 /iꢀPrOH as solvents. It also gave total conversion of
isophorone with high selectivity for TMCH. Other coꢀsolvents were tested as MeOH or
mixtures H2O/MeOH or H2O/iꢀPrOH but led to lower conversions, selectivity and ee.
Acetonitrile, a nonꢀpolar solvent gave similar ee than iꢀPrOH but with lower conversion,
probably due to the weak solubility of H2. However, the recycling remained difficult as iꢀ
PrOH was miscible to diethylether. To conclude, no improvement of ee was observed using
coꢀsolvent.
The enantioselective hydrogenation was then performed on other α,βꢀunsaturated ketones
using respectively TBP Sꢀprolinate 9 or TBP transꢀhydroxyꢀSꢀ prolinate 11 as solvents.
16

RSC Advances
Page 18 of 28
View Article Online
DOI: 10.1039/C6RA23056C
Conv.
(%)a
Select.
Substrate
CPhosIL
9
Runs
de (%) b
Products
(%)
1
2
1
2
1
2
1
2
100
52
98
69 (3R, 6S)
10 (3R, 6S)
36 (3R, 6S)
28 (3R, 6S)
40 (2S, 5R)
44 (2S, 5R)
40 (2S, 5R)
38 (2S, 5R)
Rꢀcarvone
84
29
33
11
9
27
27
100
57
100
79
Rꢀpulegone
menthone
39
77
11
16
64
βꢀionone
1
2
70
36
88
86
ꢀ
ꢀ
9
9
transꢀChalcone
1*
100
100
ꢀ
*In the presence of 1 mL of iꢀPrOH to facilitate the solubilization of the chalcone.
a: Determined by GC ; b: Determined by GC using a chiral colum
Scheme 7 ꢀ Hydrogenation of α,βꢀunsaturated ketones with TBP
hydroxyꢀ ꢀprolinate 11 as solvents
Sꢀprolinate 9 or TBP transꢀ
S
We observed complete conversions and good diastereoisomeric excess (de) for the
hydrogenation of ꢀcarvone and ꢀpulegone in presence of 9. These results were excellent in
R
R
comparison to literature data obtained with high pressure of H2 (5ꢀ10 bar) and/or high
temperatures (40ꢀ100°C).43 After a first run, the catalytic system had unfortunately lost some
17

Page 19 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
crucial activity and the use of 9 led generally to lower conversion for all ketones. The anion
had an important effect on the reactivity. With PhosILs 11, both conversion and selectivity
were significantly lowered; de was maintained with Rꢀpulegone, but a drastic decreased was
observed with Rꢀcarvone. The presence of the alcohol function on the chiral anion might
cause steric hindrance or/and change H2 solubility of the CPhosILs. As a consequence, other
substrate hydrogenations were pursued with only CPhosIL 9. Good conversion of βꢀionone
was measured with a good selectivity, the double carbon bond of the chain being
preferentially hydrogenated compared to the cyclic one. Total conversion of transꢀChalcone
was observed with only formation of 3ꢀphenylpropiophenone, as system was too soft to attack
the aromatic double carbon bonds.
Experimental
All reagents were commercially available and used as received (TBPOH.30H2O, acids or
diacids from SigmaꢀAldrich). NMR spectra were recorded at 298 K at 500 MHz for 1H and at
63 MHz for 13C and 202 MHz for 31P on an Avance III Bruker spectrometer in CDCl3 as
solvent with TMS or phosphoric acid as references.
Concerning the quantification of the hydrogenation of linoleic acid, NMR spectroscopy was
performed at 500MHz with Bruker Avance III spectrometer equipped with a BBFO+ probe
and at 600MHz with Bruker Avance III spectrometer equipped with a CPTCI cryoprobe. The
sample was dissolved in CDCl3 or in MeODꢀd4 and the resulting solution was placed in a 5
1
mm diameter NMR tube. H NMR spectra were taken with 30 degree pulse angle, 10s
relaxation delay and 16 scans.
IR spectra were recorded on a NICOLET IMPACT 400 spectrometer (KBr pellets or films).
Elemental analysis (C, H, N, S) were realized on a Flash EAꢀ1112 Series.
GC analyses were recorded on a Hewlett–Packard HPꢀ6890 gas chromatograph, fitted with
DBꢀ1 capillary column (25 m, 0.32 mm), a flame ionization detector and HPꢀ3395 integrator
under the following conditions: helium as vector gas (5.104 Pa), temperature of injector: 250
°C, temperature of the oven: isotherm 150 °C, 5 min, then 150ꢀ300 °C (10 °C/min) and
isotherm 300 °C, 5 min.
18

RSC Advances
Page 20 of 28
View Article Online
DOI: 10.1039/C6RA23056C
GC/MS analyses were recorded on a THERMOQUEST Draw GC on 2000 Series by using
the techniques of chemical ionization under the following conditions: capillary column DB1
(length: 25 m, diameter: 0.32 mm), vector gas: helium (0.5 bar), temperature injector: 250°C.
ee were determined with a βꢀcyclodextrinesꢀbased chiral gas chromatography column and byꢀ
produtcs by GC/MS.
Thermogravimetric analyses coupled with a mass spectrometer were performed between 30
°C and 500 °C under a constant flow of dry argon (50 mL/min) using a Simultaneous Thermal
Analyzer STA 449C Jupiter from Netzsch, and a heating rate of 10 K/min. The isothermal
drift and sensitivity values are 0.6 µg/h and 0.1 µg, respectively. Alumina crucibles were
loaded with 10ꢀ20 mg of sample powder.
The mass spectrometer was a quadrupole QMS 403 Aëolos® with a stainless steel capillary
and a SEV detector (Channeltron). The counting time for mass spectrometer is of 20 ms per
m/z values (scanning width: m/z = 10ꢀ150 amu) with a resting time of 1 s.
The DSC experiments were carried out on a Netzsch DSC 204F1 heat flux differential
calorimeter at a heating/cooling rate of 10 K/min under a constant argon flow with 200
mL/min. The crucibles were loaded with 10ꢀ20 mg of sample powder/liquid. Samples were
weighed in aluminium sample pans covered with a pierced lid. An empty aluminium sample
pan with a pierced lid was used as a reference.
The viscosities measurements in cP (or mPa.s) were performed with a Brookfield LVꢀDVII+
PRO viscometer using a CP51 cone spindle. The instrument was connected to a HUBERꢀ
ministat circulationꢀtype thermoꢀregulated water bath, and measures were realized between
298.15 and 353.15 K. The repeatability of the viscometer was of 0.20 % with an uncertainty
in the viscosity measurements of 1.00 % of the full scale range, declared by the manufacturer.
General procedure for the synthesis of PhosILs 1-3
Pathway A
In a 250 mL roundꢀbottom flask, a 40% wt aqueous solution of TBPOH (7 mL, 10 mmol) was
diluted in distilled water (100 mL). The acid (6 mmol, 1.2 eq.) was then added and the
19

Page 21 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
mixture was stirred and refluxed during 24h. After evaporation of the solvent under reduced
pressure, the excess of acid was precipitated by addition of Et20 (3 x 50 mL) and removed by
filtration. The resulting product was dried in vacuo at 50°C during 24h.
Pathway B
In a 250 mL roundꢀbottom flask, a 40% wt aqueous solution of TBPOH (7 mL, 10 mmol) was
diluted in EtOH (100 mL). Pyruvic acid (6 mmol, 1.2 eq.) was then added and mixture was
stirred and refluxed during 24h. After evaporation of the solvent under reduced pressure, the
excess of acid was precipitated by addition of Et2O (3 x 50 mL) and removed by filtration.
The resulting product was dried in vacuo at 50°C during 24h.
Pathway C
In a 250 mL roundꢀbottom flask, a 40% wt aqueous solution of TBPOH (7 mL, 10 mmol) was
diluted in distilled water (100 mL). The osidic acid (12 mmol, 1.2 eq.) was then added and the
mixture was stirred during 24h at room temperature. After evaporation of the solvent under
reduced pressure, excess of acid was precipitated by addition of EtOH or MeOH (3 x 50 mL)
and removed by filtration. The resulting product was dried in vacuo at 50°C during 24h.
Pathway D
In a 250 mL roundꢀbottom flask, phenolic acid was dissolved (1.2 eq.) in 100 mL EtOH 99%.
A 40% wt aqueous solution of TBPOH (7 mL, 10 mmol) was then added and the mixture was
stirred during 24h at room temperature. After evaporation of the solvent under reduced
pressure, the excess of acid was removed by washing with Et2O or by filtration after
precipitation following the addition of distilled water (3 x 50 mL). The resulting product was
dried in vacuo at 50°C during 24h.
Pathway D’
In a 250 mL roundꢀbottom flask, TBAOH (8 g, 10 mmol) was dissolved in EtOH 99% (100
mL). The phenolic acid (12 mmol, 1.2 eq.) was then added and the mixture stirred during 24h
at room temperature. After evaporation of the solvent under reduced pressure, the excess of
acid was removed by washing with Et2O or by filtration after precipitation following the
addition of distilled water (3 x 50 mL). The resulting product was dried in vacuo at 50°C
during 24h.
20

RSC Advances
Page 22 of 28
View Article Online
DOI: 10.1039/C6RA23056C
General procedure for hydrogenation
Hydrogenation of alkenes:
A Schlenk tube was charged with the ionic liquid (c.a. 400 mg) and the catalyst (3.5 mg, 0.02
mmol, 0.01 equiv/substrate) and left for 10 min under vacuum. Next, the substrate (2 mmol, 1
equiv) and solvent (2 mL) were added under argon. The argon atmosphere was then replaced
by hydrogen through a gas bag and the mixture was vigorously stirred for 18 h at room
temperature. The aqueous phase was next extracted with Et2O (3x5 mL); the combined
organic layers were dried over MgSO4 and then filtered through cotton (1 ꢀL was injected
into GC to evaluate the conversion). The aqueous phase was kept in the Schlenk tube to be
reused.
Recycling experiments: After a short vacuum/argon sequence (three times), the
substrate (2 mmol, 1 equiv) was added, and the mixture was stirred vigorously for 18 h at
room temperature under a hydrogen atmosphere (gas bag). Product isolation and
characterization is the same as described above.
Hydrogenation of unsaturated ketone:
In a schlenk tube, ionic liquid (400 mg) and PdCl2 (3.5 mg, 0.02 mmol, 0.01 eq.) were
introduced. After 10 minutes under vacuum, isophorone (300 ꢀL, 2 mmol, 1 eq.) in 2 g of
solvent was added under argon. A hydrogen atmosphere was filled into the reactor with the
help of a gas bag and the mixture was stirred at room temperature during the required time.
Then, distillated water (2 mL) was introduced and the aqueous layer was extracted three times
with 5 mL of diethyl ether. The organic layers were gathered, dried over MgSO4 and filtered
through cotton. 1 µL of the organic phase was injected in a gas chromatography to determine
the conversion. Enantiomeric excesses (ee) were determined with a βꢀcyclodextrineꢀbased
chiral gas chromatography column and byꢀproducts by GC/MS.
Conclusions
Phosphonium ionic liquids (PhosILs) with natural organic acid derived anions (
Lꢀlactate,
Lꢀ
tartrate, malonate, succinate,
Lꢀmalate, pyruvate,
Dꢀglucuronate, Dꢀgalacturonate, Sꢀprolinate,
21

Page 23 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
pꢀcoumarate and ferulate) were easily prepared from tetrabutylphosphonium hydroxide and an
excess of the corresponding acid with good yields. Their characterization was realized
through routine NMR, IR, elemental analysis, viscosity, and ATG techniques. These PhosILs
as coꢀsolvents showed good performance, recyclability and better efficiency than commercial
ILs in catalytic selective hydrogenation of 1,5ꢀcyclooctadiene (1,5ꢀCOD) into cyclooctene at
room temperature under atmospheric H2 pressure. Interesting extension of this hydrogenation
process has been performed on unsaturated fatty acids, like linoleic acid. Fine NMR
investigations proved the performance essentially concerning the selectivity of the catalytic
system towards monoꢀinsaturated acids in the presence of PhosILs under mild conditions.
Furthermore, enantioselective hydrogenation of α,βꢀunsaturated ketones in mild conditions
was performed in pure chiral PhosILs. Very good conversion of substrates, combined with
high selectivity and good enantiomeric or diastereoisomeric excesses revealed the high
potentialities of our PhosILs for such processes compared to literature data.
Onꢀgoing investigations will deal with the evaluation of the biodegradability and/or
(eco)toxicity of these new PhosILs in order to used them in other catalytic processes or
extraction procedures.
Acknowledgements
This work was supported by the Fondation du Site Paris Reims (post doctoral fellowship for
Nadège Ferlin) and the FEDER for material funds. We also deliver our many thanks and
gratitude to the Tunisian Ministry of Education and Research for financial support for the
cotutoring PhD of Safa Hayouni.
References
1
(a) J. D. Holbrey and K. R. Seddon, Clean Prod. Process., 1999, 1, 223ꢀ236.
(b) P. Wassercheid and T. Welton, Ionic liquids in synthesis 2nd edition, Wiley – VCH
Weinheim, 2008.
2
(a) C. M. Gordon, Appl. Cat. A, 2001, 222, 101ꢀ117.
(b) J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer, G. A. Broker and
R. D. Rogers, Green Chem., 2001, 3, 156ꢀ164.
(c) K. R. Seddon, J. Chem. Tech. Biotech., 1997, 68, 351ꢀ356.
(d) K. R. Seddon, A. Stark and M. J. Torres, Pure Appl. Chem., 2000, 72, 2275ꢀ2287.
22

RSC Advances
Page 24 of 28
View Article Online
DOI: 10.1039/C6RA23056C
(e) R. Sheldon, Chem. Commun., 2001, 2399ꢀ2407.
(f) T. Welton, Chem. Rev., 1999, 99, 2071ꢀ2084.
(g) P. Wasserscheid and W. Keim, Angew. Chem.Int. Ed. Engl., 2000, 39, 3772ꢀ3789.
(h) D. Zhao, M. Wu, Y. Kou and E. Min, Cat. Today, 2002, 74, 157ꢀ189.
(i) J. Dupont, C. S. Consorti and J. Spencer, J. Braz. Chem. Soc., 2000, 11, 337ꢀ344.
(j) C. J. Bradaric, A. Downard, C. Kennedy, A. J. Robertson and Y. Zhou, The Strem
Chemiker Vol. XX, 2003, 1, 1ꢀ333.
3
M. M. Rahut, H. A. Currier, A. M. Semsel and V. P. Wystrach, J. Org. Chem., 1961,
26, 5138ꢀ5145.
4
5
A. J. Robertson, WO0187900 2001 (Cytec Industries).
N. Karodia, S. Guise, C. Newlands and J. Andersen, Chem. Commun., 1998, 2341ꢀ
2342.
6
a) S. Bose, A. B. Wijeratne, A. Thite, G. A. Kraus, D. W. Armstrong and J. W.
Petrich, J. Phys. Chem. B, 2009, 113, 10825ꢀ10829.
b) X. Chen, X. Li, A. Hua and F. Wang, Tetrahedron: Asymmetry 2008, 19, 1ꢀ14.
U. A. Rana, R. Vijayaraghavan, M. Walther, J. Sun, A. A. J. Torriero, M. Forsyth and
D. R. Mac Farlane, Chem. Commun., 2011, 47, 11612ꢀ11614.
S. I. LallꢀRamnarine, J. A. Mukhlall, J. F. Wishart, R. R. Engel, A. R. Romeo1, M.
Gohdo, S. Ramati, M. Berman and S. N. Suarez, Beilstein J. Org. Chem. 2014, 10,
271ꢀ275.
7
8
9
D. Coleman and N. Gathergood, Chem. Soc. Rev., 2010, 39, 600ꢀ637.
a) P. Wasserscheid, A. Bösmann and C. Bolm, Chem. Commun., 2002, 3, 200ꢀ201.
b) H. Clavier, L. Boulanger, N. Audic, L. Toupet, M. Mauduit and J. C. Guillemin,
Chem. Commun., 2004, 1224ꢀ1225.
10
c) L. González, B. Altava, M. Bolte, M. I. Burguete, E. GarcíaꢀVerdugo and S. V.
Luis, Eur. J. Org Chem., 2012, 26, 4996–5009.
d) W. Bao, Z. Wang and Y. Li, J. Org. Chem., 2003, 68(2), 591ꢀ593.
e) J. C. Plaquevent, J. Levillain, F. Guillen, C. Malhiac, A. C. Gaumont, Chem. Rev.
2008, 108(12), 5035ꢀ60.
f) S. Luo, X. Mi, L. Zhang, S. Liu, H. Xu and J. P. Cheng, Angew. Chem. Int. Ed.
2006, 45, 3093ꢀ3097.
g) D. Coleman, M. Špulák, M. T. Garcia and N. Gathergood, Green Chem., 2012, 14,
1350ꢀ1356.
23

Page 25 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
h) A. Haiß, A. Jordan, J. Westphal, E. E. Logunova, N. Gathergood and K. Kümmerer,
Green Chem., 2016, 18, 4361ꢀ4373.
i) A. Jordan, A. Haiß, M. Špulák, Y. Karpichev, K. Kümmerer and N. Gathergood,
Green Chem. 2016, 18, 4374ꢀ4392.
j) Y. De Gaetano, J. Hubert, A. Mohamadou, S. Boudesocque, R. PlantierꢀRoyon, J. H.
Renault and L. Dupont, Chem. Eng. J., 2016, 285, 596ꢀ604.
k) J. Pernak, M. Niemczak, L. Chrzanowski, L. Ławniczak, P. Fochtman, K.
Marcinkowska and T. Praczyk, Chem. Eur. J., 2016, 22, 12012ꢀ12021.
J. Pernak, F. Stefaniak and J.Weglewski, Eur. J. Org. Chem., 2005, 4, 650ꢀ652.
K. Fukumoto, M. Yoshizawa and H. Ohno, J. Am. Chem. Soc., 2005, 127, 2398ꢀ2399.
J. Kagimoto, K. Fukumoto and H. Ohno, Chem. Commun., 2006, 2254ꢀ2256.
F. Atefi, M. T. Garcia, R. D. Singer and P. J. Scammells, Green Chem., 2009, 11,
1595ꢀ1604.
11
12
13
14
15
16
17
a) N. Ferlin, M. Courty, S. Gatard, M. Spulak, B. Quilty, I. Beadham, M. Ghavre, N.
Gathergood and S. Bouquillon, Tetrahedron, 2013, 69, 6510ꢀ6518 .
b) N. Ferlin, M. Courty, S. Gatard, M. Pour, B. Quilty, I. Beadham, M. Ghavre, N.
Gathergood and S. Bouquillon, RSC Adv., 2013, 3, 26241ꢀ26251.
c) S. Hayouni, N. Ferlin and S. Bouquillon, Hydrogenation Catalysis in biobased Ionic
Liquids, InTech ꢀ open science | open minds, just accepted.
a) D. Zhao, P. J. Dyson, G. Laurenczy and J. S. McIndoe, J. Mol. Catal. A: Chem.
2004, 214, 19ꢀ25.
b) U. Kernchen, B. Etzold, W. Korth and A. Jess, Chem. Eng. Technol. 2007, 30, 985ꢀ
994.
c) J. Dupont, P. A. Z. Suarez, A. P. Umpierre and R. F. de Souza, J. Braz. Chem. Soc.
2000, 11, 293ꢀ297.
a) Y. Chauvin, L. Mussmann and H. Olivier, Angew. Chem. Int. Ed. 1995, 34, 2698ꢀ
2700.
b) A. Z. P. Suarez, E. L. J. Dullius, S. Einloft, F. R. De Souza and J. Dupont,
Polyhedron, 1996, 15, 217ꢀ1219.
18
19
R. A. Sheldon, I. Arends and U. Hanefeld editors. Green chemistry and catalysis. John
Wiley & Sons, 2007. 448 p.
M. Ghavre, S. Morrissey and N. Gathergood, “Hydrogenation in Ionic Liquids, Ionic
Liquids: Applications and Perspectives”, Kokorin A editor. InTech, 2011, 331ꢀ392.
24

RSC Advances
Page 26 of 28
View Article Online
DOI: 10.1039/C6RA23056C
20
(a) S. C. Mhadgut, M. Török, S. Dasgupta and B. Török, Catal. Lett., 2008, 123, 156;
(b) N. Győrffy, A. Tungler and M. Fodor, J. Catal., 2010, 270, 2; (c) S. C. Mhadgut,
M. Török, J. Esquibel, B. Török, J. Catal., 2006, 238, 441; (d) S. C. Mhadgut, I.
Bucsi, M. Török and B. Török, Chem. Commun., 2004, 984; (e) S. Li, C. Chen, E.
Zhan, S.ꢀB. Liu and W. Shen, J. Mol. Cat. A, 2009, 304, 88; (f) S. Li, E. Zhan, Y. Li,
Y. Xu and W. Shen, Catal. Today, 2008, 131, 347; (g) S. C. Mhadgut, I. Bucsi, M.
Török, S. Dasgupta and B. Török, Catal. Lett., 2008, 123, 156; (h) M. Fodor, A.
Tungler and L. Vida, Catal. Today, 2009, 140, 58; (i) S. Li, E. Zhan, Y. Li, Y. Xu and
W. Shen, Catal. Comm., 2007, 8, 1239.
21
(a) M. Fodor, A. Tungler and L. Vida, Catal. Today, 2009, 140, 58; (b) M. Fodor, A.
Tungler and L. Vida, React. Kinet. Catal. Lett., 2007, 90, 413; (c) É. Sípos, A. Tungler
and I. Bitter, React. Kinet. Catal. Lett., 2003, 79, 101; (d) É. Sípos, A. Tungler and I.
Bitter, J. Mol. Cat. A, 2003, 198, 167; (e) A. Tungler, T. Máthé, T. Tarnai, K. Fodor,
G. Tóth, J. Kajtár, I. Kolossváry, B. Herényi and R. A. Sheldon, Tetrahedron: Asymm.,
1995, 6, 2395; (f) N. Győrffy and A. Tungler, J. Mol. Cat. A, 2011, 336, 72; (g) N.
Győrffy and A. Tungler, J. Mol. Cat. A, 2011, 336, 72; (h) G. Fogassy, A. Tungler, A.
Lévai and G. Tóth, J. Mol. Cat. A, 2002, 179, 101; (i) É. Sípos, A. Tungler and I.
Bitter, J. Mol. Catal. A, 2003, 198, 167; (j) É. Sıpos, A. Tungler, I. Bitter and M.
́
Kubinyi, J. Mol. Cat. A, 2002, 186, 187; (k) G. Farkas, K. Fodor, A. Tungler, T.
Máthé, G. Tóth and R. A. Sheldon, J. Mol. Cat. A, 1999, 138, 123.
22
(a) É. Sıpos, G. Farkas, A. Tungler and J. L. Figueiredo, J. Mol. Cat. A, 2002, 179,
́
107; (b) G. Farkas, É. Sıpos, A. Tungler, A. Sárkány and J. L. Figueiredo, J. Mol. Cat.
́
A, 2001, 170, 101; (c) A. Tungler, Y. Nitta, K. Fodor, G. Farkas and T. Máthé, J. Mol.
Cat. A, 1999, 149, 135.
23
24
25
H.ꢀU. Funk, G. Senft, H.ꢀD. Quest, Eur. Patent EP 1318130A1.
H. Yoshiyuki, Jpn. Kokai Tokkyo Koho JP 63057545.
(a) M. Pisarek, M. Lukaszewski, P. Winiarek, P. Kedzierzawski and M. Janikꢀ
Czachor, Catal. Comm., 2008, 10, 213; (b) M. Pisarek, M. Lukaszewski, P. Winiarek,
P. Kedzierzawski and M. JanikꢀCzachor, Mater. Chem. Phys., 2009, 114, 774.
T. Sato, S. Watanabe, H. Kiuchi, S. Oi, and Y. Inoue, Tetrahedron Lett., 2006, 47,
7703.
26
27
28
T. Sato, C. V. Rode, O. Sato, M. Shirai, Appl. Catal. B: Environmental, 2004, 49, 181.
C. I. Melo, R. BogelꢀŁukasik, M. Gomes da Silva and E. BogelꢀŁukasik, Green
Chem., 2011, 13, 2825.
25

Page 27 of 28
RSC Advances
View Article Online
DOI: 10.1039/C6RA23056C
29
a) A. Strádi, M. Molnár, M. Óvári, G. Dibó, F. U. Richter and L. Mika, Green Chem.,
2013, 15(7), 1857ꢀ1862.
b) A. Strádi, M. Molnár, P. Szakál, G. Dibó, D. Gáspár and L. T. Mika, RSC Adv
2015, 5(89), 72529ꢀ72535.
30
31
V. Pandarus, G. Gingras, F. Béland, R. Ciriminna and M. Pagliaro, Org. Process Res.
Dev. 2012, 16, 1307ꢀ1311
a) S. Breton, A. BrisachꢀWittmeyer, J. J. Rios Martin, M. L. Camacho, A. Lasia and H.
Ménard, Int. J. of Electrochem. 2011, 1ꢀ9.
b) K.R. Kahsar, D.K. Schwartz and J.W. Medlin, ACS Catal. 2013, 3, 2041ꢀ2044.
a) F. Endres and S. Zein El Abedin, Phys. Chem. Chem. Phys. 2006, 8, 2101ꢀ2116.
b) J. Tindale, C. Na, M. Jennings and P. Ragogna, Can. J. Chem. 2007, 85 (10), 660ꢀ
667.
32
33
c) F. Endres and S. Zein El Abedin, Phys. Chem. Chem. Phys. 2006, 8, 2101ꢀ2116.
a) M. C. Gálvez, C. G. Barroso and J. A. PérezꢀBustamante, Z. Lebensm.Unters.For
1994, 199, 29ꢀ31.
b) Z. QuindeꢀAxtell, B. K. Zory, J. Agr. Food Chem. 2006, 54 (26), 9978ꢀ84.
N.Kumar and V. Pruthi, Biotechnology Reports 2014, 4, 86ꢀ93.
V. Di Castro, C. Furlani, C. Fragale, M. Gargano, M. Rossi and N. Ravasio, Gazz.
Chim. Ital. 1987, 117, 43ꢀ50.
34
35
36
a) D. Camper, C.Becker, C. Koval and R. Noble, Ind. Eng. Chem. Res. 2006, 45, 445ꢀ
450
b) P.J. Dyson, G. Laurenczy, C.A. Ohlin, J. Vallance and T. Welton, Chem. Commun.
2003, 2418ꢀ2419
37
38
K. Yamamoto, A. Kinshita and A. Shibahara, J. Chromatogr. A 2008, 1182, 132ꢀ135.
J. K. G. Kramer, C. CruzꢀHernandez and J. Zhou, Eur. J. Lipid Sci. Technol. 2001,
103, 594ꢀ632.
39
a) R. Sacchi, F. Addeo and L. Paolillo, Magn. Reson. Chem. 1997, 35, S133ꢀS145.
b) Y. Miyake, K.Yokomizo and N. Matsuzaki, J. Am. Oil Chem. Soc. 1998, 75, 1091ꢀ
1094.
40
41
M. S. Carvalho, R. A. Lacerda, J. P. Leão, J. D. Scholten, B. A. Neto and P. A. Z.
Suarez, Catal. Sci. Technol. 2011, 1, 480ꢀ488.
a) M. Fodor, A. Tungler and L. Vida, Catal. Today 2009, 140, 58ꢀ63.
b) A. Tungler, J. Kajtar, T. Mathé, G. Toth, E. Fogassy and J. Petro, Catal. Today
1989, 5, 159ꢀ171.
26

RSC Advances
Page 28 of 28
View Article Online
DOI: 10.1039/C6RA23056C
c) A. Tungler, T. Máthé, J. Petró and T. Tarnai, J. Mol. Catal. A 1990, 61, 259ꢀ267.
d) E. Sipos, A. Tungler, I. Bitter and M. Kubinyi, J. Mol. Catal. A 2002, 186, 187ꢀ192.
c) E. Sipos, A. Tungler and I. Bitter, J. Mol. Catal. A 2003, 198, 167ꢀ173.
d) E . Sipos, G. Fogassy, A. Tungler, P.V. Samant and J.L. Figueiredo,, J. Mol. Catal.
A 2004, 212, 245ꢀ250.
42
43
a) S. Kishida and S. Teranishi, J. Catal.1968, 12, 90ꢀ96.
b) Y. Sun, R. N. Landau, J. Wang, C. Le Blond and D.G. Blackmond, J. Am. Chem.
Soc. 1996, 118, 1348ꢀ1353.
c) P. Dyson, G. Laurenczy, A. Ohlin, J. Vallance and T. Welton, Chem. Comm. 2003,
2418ꢀ2419.
F.A. Khan, A. Vallat and G. SüssꢀFink, J. Mol. Catal. A: Chem. 2012, 355, 168ꢀ173.
27