Ionic liquid [BMIM]PF6 as a medium for the selective hydrogenation of 1,4-diacetoxybut-2-yne on the Pd-containing catalysts

Article abstract of DOI:10.1007/s11172-011-0027-9

A possibility of using a ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆), as a reaction medium in the liquid-phase hydrogenation of 1,4-diacetoxybut-2-yne was examined. Two types of catalysts were studied: Pd(10%)/C and the palladium-containing catalytic system based on the biopolymer chitosan supported on silica gel (Pd(1%)/chitosan/SiO2). The data obtained indicate high selectivity of hydrogenation of 1,4-diacetoxybut-2-yne to cis-1,4-diacetoxybut-2-ene under selected conditions.

Full text of DOI:10.1007/s11172-011-0027-9

Russian Chemical Bulletin, International Edition, Vol. 60, No. 1, pp. 179—181, January, 2011
179
Ionic liquid [BMIM]PF as a medium for the selective hydrogenation
6
of 1,4ꢀdiacetoxybutꢀ2ꢀyne on the Pdꢀcontaining catalysts
E. A. Tarasenko, V. I. Isaeva,b I. P. Beletskaya, and L. M. Kustovb
a
a
aA. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
Building 4, 31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 952 5308. Eꢀmail: beletska@org.chem.msu.ru
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
b
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: sharf@ioc.ac.ru
A possibility of using a ionic liquid, 1ꢀnꢀbutylꢀ3ꢀmethylimidazolium hexafluorophosphate
(
[BMIM]PF ), as a reaction medium in the liquidꢀphase hydrogenation of 1,4ꢀdiacetoxybutꢀ2ꢀ
6
yne was examined. Two types of catalysts were studied: Pd(10%)/C and the palladiumꢀcontainꢀ
ing catalytic system based on the biopolymer chitosan supported on silica gel (Pd(1%)/chitoꢀ
san/SiO ). The data obtained indicate high selectivity of hydrogenation of 1,4ꢀdiacetoxybutꢀ2ꢀ
2
yne to cisꢀ1,4ꢀdiacetoxybutꢀ2ꢀene under selected conditions.
Key words: ionic liquids, 1,4ꢀdiacetoxybutꢀ2ꢀyne, cisꢀ1,4ꢀdiacetoxybutꢀ2ꢀene, Pdꢀcontainꢀ
ing catalysts, hydrogenation.
cisꢀ1,4ꢀDiacetoxybutꢀ2ꢀene is widely used as a synꢀ
thone in organic synthesis.1 One of the main methods
for its preparation is the selective hydrogenation of 1,4ꢀdiꢀ
acetoxybutꢀ2ꢀyne or butꢀ2ꢀyneꢀ1,4ꢀdiol followed by acyꢀ
lation. The problem of selective catalytic hydrogenation
of alkynes to alkenes with a certain configuration of the
double bond and, particular, to butꢀ2ꢀyneꢀ1,4ꢀdiol and its
diacetate attracted attention of researchers attention for
many years and still remains urgent.3—5
The purpose of this work was to reveal a possibility of
selective catalytic hydrogenation of 1,4ꢀdiacetoxybutꢀ2ꢀ
yne by molecular hydrogen using ionic liquids as a reacꢀ
tion medium under the heterogeneous catalytic condiꢀ
tions. 1ꢀnꢀButylꢀ3ꢀmethylimidazolium hexafluorophosꢀ
,2
phate ([BMIM]PF ) was chosen for the present study. It
6
is known that this ionic liquid is resistant to the action of
air and moisture and is characterized by an insignificant
vapor pressure, low viscosity, and high thermal and chemꢀ
7
In recent years, ionic liquids have found wide use in
many areas of chemistry. Numerous data on the use of
ionic liquids in organic synthesis, catalysis, electrochemꢀ
istry, and gas and liquid chromatography are presently
ical stability. The classical catalyst Pd(10%)/C and the
Pdꢀcontaining system based on chitosan supported on
silica gel (Pd(1%)/chitosan/SiO ) were used as hydrogeꢀ
2
1
9
nation catalysts. We have previously shown that the hyꢀ
drogenation of butꢀ2ꢀyneꢀ1,4ꢀdiol in EtOH with the use
of the Pt/chitosan catalysts proceeds with high selectivity
and predominant formation of the cisꢀisomer of butꢀ2ꢀ
eneꢀ1,4ꢀdiol. Therefore, it was of interest to study the
influence of the ionic liquid on the selectivity of formation
of cisꢀ1,4ꢀdiacetoxybutꢀ2ꢀene in the presence of the sysꢀ
6
—12
published.
For instance, the ionic liquids as solvents
corresponding to the requirements of "green" chemistry
have emerged in organic chemistry as an alternative to
lowꢀboiling solvents.1 As for the application of ionic liqꢀ
uid in catalysis, the available data predominantly concern
0
1
3—15
the homogeneous catalytic reactions.
Nevertheless,
they indicate specific merits of using ionic liquids in hetꢀ
tem Pd(1%)/chitosan/SiO in the ionic liquid medium.
2
erogeneous catalysis, in particular, in hydrogenation of
various polyfunctional compounds.1
6,17
For example, the
Experimental
selective hydrogenation of α,βꢀunsaturated aldehydes
cinnamaldehyde and citral) was carried out on Pd/C in
(
1
8
The ionic liquid [BMIM]PF6 (Merck kGAa) was used as
a medium for the hydrogenation of 1,4ꢀdiacetoxybutꢀ2ꢀyne.
Hydrogenation was carried out on Pd(10%)/C (AlfaAesar) and
diverse hydrophilic and hydrophobic ionic liquids. In
this case, the selectivity of reduction of the С=С double
bond was increased compared to the use of standard orꢀ
ganic solvents. At the same time, the reaction rate deꢀ
creased when the hydrogenation was carried out in the
ionic liquids.1
on the catalyst Pd(1%)/chitosan/SiO , which was prepared acꢀ
2
20
cording to the known procedure.
Catalytic experiments were carried out under the following
conditions: a catalyst (1 mol.% Pd) and [BMIM]PF (1—2 mL)
7,18
6
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 171—173, January, 2011.
066ꢀ5285/11/6001ꢀ179 © 2011 Springer Science+Business Media, Inc.
1

1
80
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
Tarasenko et al.
were placed in the Schlenk vessel under argon atmosphere,
and the vessel was evacuated and purged with argon with stirꢀ
ring. This procedure was repeated three times. Then the system
was again evacuated and filled with hydrogen (3 times). The
catalyst was preꢀtreated with hydrogen for 10 min in the temperꢀ
ature range from 20 to 60 °С. Then 1,4ꢀdiacetoxybutꢀ2ꢀyne
previous case). The selectivity of the process also increases
for both the total amount of the partial hydrogenation
products (S ) and the ratio to the cisꢀisomer of unsaturatꢀ
2
ed diacetate (S ).
1
2
1
It is known that the introduction of the nitrogenꢀ
containing modifying additives into the heterogeneous catꢀ
alytic system enhances the selectivity of partial hydroꢀ
genation of the triple bond of a series of compounds with
respect to the products with the double bond. Indeed,
when using the chitosanꢀbased threeꢀcomponent system,
(
0.4—0.8 mmol, 68.0—136.0 mg) was added. Hydrogenation
was carried out with magnetic stirring (1400 rpm, 1 atm H2,
0—60 °С).
The reaction course was preꢀmonitored by TLC on plates of
2
silica gel 60 F254 (Merck) using CHCl as an eluent; two succesꢀ
3
sive runs of the eluent were used for better separation. The comꢀ
position of the catalytic mixture was analyzed by GLC and NMR.
Pd(1%)/chitosan/SiO (60 °С), selectivity higher than
2
9
7.6% with respect to partial hydrogenation products is
Each control sample was extracted with Et O (5×1 mL), and the
2
achieved, and the selectivity for the cisꢀisomer of unsaturꢀ
ated diacetate increases simultaneously (entry 3). This is
probably associated with the influence of the amino groups
of chitosan. In the absence of a ionic liquid, when ethanol
is used as the solvent (entry 4), the hydrogenation reaction
occurs somewhat more slowly. A conversion of ∼ 50% is
achieved in 3 h; however, selectivity of the process with
respect to cisꢀ1,4ꢀdiacetoxybutꢀ2ꢀene remains still high,
the same as that in [BMIM]PF6.
extracts were evaporated and dissolved in CDCl for recording
3
1
Н NMR spectra. The GLC analysis was performed on a
Biokhromꢀ1 chromatograph equipped with a flameꢀionization
detector on capillary columns SEꢀ30 and FFAP.
Results and Discussion
The results obtained are presented in Table 1. The maꢀ
jor product of 1,4ꢀdiacetoxybutꢀ2ꢀyne hydrogenation is
the cisꢀisomer of 1,4ꢀdiacetoxybutꢀ2ꢀene. The following
reactions run in parallel: hydrogenation of cisꢀ1,4ꢀdiacetꢀ
oxybutꢀ2ꢀene and isomerization (cis—transꢀtransformaꢀ
tion). The selectivity of the process on the studied palladiꢀ
umꢀcontaining systems was determined as the ratio of the
contents of hydrogenation products in the reaction mixture:
S = cis/cis + trans + ane, S = cis + trans/cis + trans + ane,
There are published data on the reduction in [BMIM]PF6
of a series of substituted alkenes and alkynes under the
conditions of hydrogen transfer and microwave frequency
2
2
activation of the reaction mixture (catalyst Pd(10%)/C).
In the case of alkynes, the reaction occurs with low seꢀ
lectivity with respect to the partial reduction products
(cis : trans : ane = 6 : 1 : 1, conversion 50%) or the exhausꢀ
tive hydrogenation of the triple bond occurs to form the
С—С bond. Thus, the reaction studied is the first example
of selective hydrogenation of alkynes to alkenes with moꢀ
lecular hydrogen in ionic liquids.
1
2
where ane is the content of the completely hydrogenated
product (1,4ꢀdiacetoxybutane) at ∼ 50% conversion. It is
seen that, when Pd(10%)/C is used as the catalyst in
[
BMIM]PF at 20 °С (entry 1), hydrogenation proceeds
It follows from the data obtained that the use of the
6
with moderate selectivity for the cisꢀisomer of 1,4ꢀdiacetꢀ
ionic liquid [BMIM]PF as a solvent in heterogeneous
6
oxybutꢀ2ꢀene (S ) and for the total amount of the cisꢀ and
catalysis is a promising approach to the search for the
optimal conditions of selective hydrogenation of alkynes
to alkenes. The Pdꢀcontaining chitosanꢀbased catalyst
immobilized on the mineral support (Pd(1%)/chitosan/
1
transꢀisomers of 1,4ꢀdiacetoxybutꢀ2ꢀene (S ). As the temꢀ
2
perature of the reaction rises to 60 °С (entry 2), 50% conꢀ
version is achieved already in 1.5 h (not in 2.5 h as in the
Table 1. Hydrogenation of 1,4ꢀdiacetoxybutꢀ2ꢀyne in the presence of the supported palladium catalysts in a ionic liquid
a
medium
Entry
Catalytic system
tb/h
Composition of reaction mixture (%)
S1/S2c
Substrate cisꢀ1,4ꢀene transꢀ1,4ꢀene 1,4ꢀane
1d
2
Pd(10%)/C
Pd(10%)/C
Pd(1%)/chitosane/SiO2
Pd(1%)/chitosane/SiO2
2.5
1.5
2.0
3.0
49.0
50.6
48.6
51.0
42.0
43.9
47.3
46.3
2.5
2.5
1.9
1.3
6.5
2.9
2.2
1.4
82.4/87.3
89.0/94.1
93.8/97.6
94.5/97.1
3
e
4
a
Conditions: 68.0—136.0 mg of 1,4ꢀdiacetoxybutꢀ2ꢀyne (0.4—0.8 mmol), 1 mol.% Pd, 1—2 mL of [BMIM]PF6,
1
atm H , 60 °С.
Reaction time.
2
b
c
d
e
S = cis/cis + trans + ane, %; S = cis + trans/cis + trans + ane, %.
1
2
Reaction temperature 20 °С.
Solvent EtOH.

Ionic liquid [BMIM]PF for alkyne hydrogenation
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
181
6
SiO ) is the most efficient catalyst for hydrogenation of
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2
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1
,4ꢀdiacetoxybutꢀ2ꢀyne in the [BMIM]PF medium.
6
1
1
1
3. R. Sheldon, Chem. Commun., 2001, 2399.
4. T. Welton, Coord. Chem. Rev., 2004, 248, 2459.
5. H. OlivierꢀBourbigou, L. Magna, D. Morvan, Appl. Catal. A,
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Received July 12, 2010;
in revised form November 24, 2010