An Improved Strategy for the Synthesis of Ethylene Glycol by Oxamate-Mediated Catalytic Hydrogenation

Article abstract of DOI:10.1002/cssc.201700157

The present study reports an improved approach for the preparation of ethylene glycol (EG) by using carbon monoxide as C1 chemical by a two-step oxidative carbonylation and hydrogenation sequence. In the first step, oxamates are synthesized through oxidative cross double carbonylation of piperidine and ethanol by using Pd/C catalyst under phosphine ligand-free conditions and subsequently hydrogenated by Milstein's catalyst (carbonylhydrido[6-(di-t-butylphosphinomethylene)-2-(N,N-diethylaminomethyl)-1,6-dihydropyridine]ruthenium(II)). The presented stepwise oxamate-mediated coupling provides the basis for a new strategy for the synthesis of EG by selective upgrading of C1 chemicals.

Full text of DOI:10.1002/cssc.201700157

Accepted Article
Title: An improved strategy for the synthesis of ethylene glycol via
oxamate-mediated catalytic hydrogenation
Authors: Anilkumar Satapathy, Sandip T. Gadge, and Bhalchandra
Mahadeo Bhanage
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To be cited as: ChemSusChem 10.1002/cssc.201700157
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10.1002/cssc.201700157
ChemSusChem
COMMUNICATION
An improved strategy for the synthesis of ethylene glycol via
oxamate-mediated catalytic hydrogenation
Anilkumar Satapathy,[a,b] Sandip T. Gadge[a] and Bhalchandra M. Bhanage*[a]
Abstract: Present study reports an improved approach for the
preparation of ethylene glycol (EG) by using carbon monoxide as C1
chemical via oxidative carbonylation and hydrogenation sequence.
In the first step oxamates have been synthesized by oxidative cross
double carbonylation of piperidine and ethanol using Pd/C catalyst
under phosphine ligand-free conditions and subsequently
hydrogenated by Milstein catalyst. The presented stepwise oxamate-
mediated coupling provides the basis for a new strategy for
synthesis of EG by selective upgrading of C1 chemicals.
valuable products such as acetaldehyde, alcohols, and
carboxylic acid derivatives. Among the different type of
carbonylation reactions, palladium catalysed oxidative
carbonylation apply different organic nucleophiles or
electrophiles in the presence of CO and oxidation reagents to
prepare various carbonyl containing compounds.[12] Recently
Beller and group have developed a new and innovative
approach for the synthesis of EG by catalytic hydrogenation of
oxamide using Ru and Fe-based catalyst (Scheme 1).[13] These
oxamides are prepared by oxidative coupling piperidine by using
homogeneous Pd-based catalyst, tri(o-tolyl)phosphine ligand
and CO/air pressure (25 bar:25 bar). In our previous work we
have successfully synthesized oxamates by oxidative cross
double carbonylation of amines and alcohols using Pd/C as
heterogeneous and recyclable catalyst under ligand-free
condition.[14] To extend our continued interest in this
carbonylation and hydrogenation reactions, we used oxamates
as key intermediates for an improved EG process.
Ethylene glycol (EG) is an important bulk chemical finds
numerous application in different fields, such as precursor for
the manufacture of polyester fibre, PET (Polyethylene
Terephthalate) resin, used as solvent, anti-freeze agent and so
on.[1,2] Rapid increase of population results in the growing
demand of PET resin and polyester fibres, which leads to a
constant growth of fibre grade EG. Conventional methods for
large scale of EG production still relies on vapour phase
oxidation of ethylene to ethylene oxide.[3,4] The major drawback
for the conventional process is the use of harsh reaction
condition and generation of large byproducts. Direct synthesis of
EG starting from syngas under reductive condition, though an
ideal method, it has significant difficulties to overcome low
reactivity and selectivity. Alternative methods like EG
preparation from methanol, formaldehyde and methylformate are
some ideal methods, but low selectivity limits their applications
too.[5,6,7,8] Because of commercial importance in EG academic
and industrial attention has been increased in recent years to
find alternative methods for their preparation. Rapid
industrialization in recent years which contributes large amount
of CO and CO2 to the atmosphere is a major concern worldwide.
Use of easily available feedstock in new transformations is a
source for innovation in material science and chemistry.
Synthesis of bulk chemicals by upgrading C1 chemicals (for
example, CO, CO/H2, CO2) via C–C bond formation is essential,
economical and sustainable way.[9] Growing demand of bulk
chemicals and materials, various innovative and novel methods
are the main interests of researcher to use alternative resources.
[10] Compared to ethylene, CO is easily available from renewable
feed stock like biogas. Moreover it is economically
advantageous. Carbonylation chemistry constitutes an industrial
key technology which produces many products in our daily
life.[11] More precisely carbonylative cross coupling reactions
based on the refinement of arenes, olefins which comprise the
basic raw materials for the chemical industry, provide access to
Herein we have developed two steps approach for synthesis of
EG by oxidative cross double carbonylation of piperidine and
ethanol and subsequent catalytic hydrogenation of oxamates
using Milstein catalyst (Scheme 2).
Scheme 1. Various approach for synthesis of ethylene glycol.
[a]
[b]
A. Satapathy, S.T. Gadge and B. M. Bhanage
Department of Chemistry
Institute of Chemical Technology
N.P. Marg, Matunga, Mumbai-400019
E-mail: bm.bhanage@ictmubai.edu.in
A. Satapathy
Scheme 2. Oxamate-mediated synthesis of ethylene glycol.
Reliance Industries limited
Patalganga, Rasayani, Raigad, Maharashtra 410 220 India
The synthesis of oxamates have been done as per our previous
protocol (Scheme 3).[14] Initial attempts focused on exploring the
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10.1002/cssc.201700157
ChemSusChem
COMMUNICATION
feasibility of the proposed process. We first tested various Ru-
precursors and ligands in the hydrogenation of oxamate and the
results are summarized in Table 1.
catalyst has no profound effect on yield and conversion (Table 2,
entry 3).
Polar and non-polar solvents were studied for its effectiveness in
reduction of oxamate (Table 3, entries 1-3). The polar solvents
such as THF methanol found ineffective. Best yields were
obtained by employing toluene as solvent, which provided 92%
yield. Hence, toluene was selected as suitable solvent for
reduction of oxamates.
Table 2. Study of catalyst loading.[a]
Scheme 3. Synthesis of oxamate by oxidative cross double carbonylation
reaction.
Entry
Catalyst
Catalyst loading
(mol%)
Conversion
(%)
Glycol (%)[b]
Table 1. Study of catalysts[a]
1
2
3
Milstein Catalyst
Milstein Catalyst
Milstein Catalyst
0.5
1.0
2.0
100
100
100
71
92
92
[a]Reaction Conditions: Oxamate (0.50 mmol), KOtBu (0.05 mmol), toluene
(10.0 ml), H2 (60 bar), 160 oC, 10 hrs. [b]GC yields
Entry
Catalyst
Conversion (%)
Glycol
(%)[b]
Table 3. Study different reaction parameters.[a]
*1
*2
*3
4
Ru(acac)3 Triphos
RuCl2 Triphos
74
69
7
Trace
12
Ru(OAc)2 (Binap)
Ru-MACHO catalyst
Milstein Catalyst
79
90
78
Entry
Solvent
Base
Temperature
(oC)
H2
Pressure
(atm)
Glycol
(%)[b]
5
100
100
92
6
Ru-MACHO-BH
catalyst
88
Study of solvents
1
THF
KOtBu
KOtBu
KOtBu
160
160
160
60
60
60
78
92
10
[a]Reaction Conditions: Oxamate (0.50 mmol), catalyst (0.01 mmol), *ligand
(0.02 mmol), KOtBu (0.05 mmol), toluene (10.0 ml), H2 (60 bar), 160 oC, 10
hrs. [b]GC yields
2
Toluene
MeOH
3
Study of bases
Ru(OAc)2, RuCl2, and Ru(acac)3 were found to be ineffective
catalysts with various ligand (Table 1, entries 1–3). Over the
past decade, progress in the development of highly efficient
catalyst has greatly accelerated.[15] Ruthenium based
organometallic complexes are reported for the reduction of
carboxylic acid derivatives and hydrogenation of β-lactam.[16,17]
Milstein and co-workers have reported highly active ruthenium
PNN pincer catalyst for ester and amide hydrogenation.[18,13] Our
proposed intermediate oxamate contain both ester and amide
functionality. Based on the high activity of ruthenium based
pincer complex for reduction of ester and amide, the Ru-Macho-
BH and Milstein catalysts were found suitable to get EG from
oxamate. The catalytic activity strongly depended on the choice
of ligand, and dramatic changes in yields were observed by
using Milstein catalyst (Table 1, entry 5). Milstein catalyst gave
excellent yield with complete conversion of oxamate to EG and
hence selected as efficient catalyst for present protocol. Further
optimization of the reaction conditions, especially the optimal
amounts of catalyst and base was investigated (Table 2).
4
5
6
Toluene
Toluene
Toluene
KOH
NaOH
K2CO3
160
160
160
60
60
60
68
57
Trace
Study of temperature
7
8
9
Toluene
KOtBu
KOtBu
KOtBu
140
150
170
60
60
60
67
76
91
Toluene
Toluene
Study of pressure
10
11
Toluene
Toluene
KOtBu
KOtBu
160
160
40
50
25
79
[a]Reaction Conditions: Oxamate (0.50 mmol), Milstein catalyst (0.01 mmol),
Base (0.05 mmol), solvent (10.0 ml), H2 (60 bar), 160 oC, 10 hrs. [b]GC yields
In the case of the KOtBu/toluene system, the amount of Milstein
catalyst could be increase to 1 mol% without significant loss of
reactivity (Table 2, entry 2), whereas further decrease of catalyst
caused less conversion (Table 2, entries 1 ). Further increase in
Various bases such as KOH, NaOH, K2CO3 and KOtBu were
studied for reduction of oxamates catalyzed by Milstein catalyst.
The KOtBu was found to be best base in comparison with
potassium KOH, NaOH, K2CO3 (Table 3, entries 2, 4-6). KOtBu
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10.1002/cssc.201700157
ChemSusChem
COMMUNICATION
mg Milstein catalyst (0.01 mmol) and 5.45 mg KOtBu (0.05 mmol) under
argon atmosphere. 10.0 mL toluene was added to the reaction mixture.
At room temperature the autoclave was flushed with H2 three times, and
then pressurized with H2 to 60 bar. The reaction was performed at 160 oC
for 10 h. Full conversion of oxamate was detected by GC analysis. The
desired product gets separated from solvent (toluene) and co-product
(piperidine) due to formation of biphasic system. The product was
isolated by simple phase separation with purity >94%.
has better solubility both in organic and aqueous media and it
has higher basicity. Other inorganic bases have poor solubility in
organic solvent. Moreover compared to other mentioned bases,
this reaction proceeded well in the presence of very strong base.
Other bases failed to give complete reduction of oxamate to EG.
The reaction was carried out at different temperature ranging
from 140 oC to 170 oC (Table 3, entries 2, 7-9). It was observed
that at temperature 140 oC and 150 oC yields were lower (table 3,
entry 8 and 9). Increasing the temperature to 160 oC, higher
yield of product was obtained (Table 3, entry 2). However,
Acknowledgements
o
further increasing temperature to 170 C showed no profound
effect on yield (Table 3, entry 9). At 160 C, complete reduction
o
The author AKS is thankful to Reliance Industries Limited for
providing the research grant. The authors STG is thankful to
CSIR (Council of Scientific and Industrial Research) New Delhi,
India for providing senior research fellowship.
of oxamate was observed and optimum yield of EG achieved.
Optimization of the reaction times showed that the reaction was
completed within 10 hrs at 160 °C under 60 atmospheric
pressure of hydrogen (Table 3, entry 2). At lower pressure yield
was found to be low (Table 3, entry 10).
Keywords: ethylene glycol • carbonylation • oxamates • Ru-
In summery we have developed oxamate-mediated production
of EG from CO via two steps approach. In the first step the
oxamate is synthesized by easily available and economical Pd/C
catalyst. The recovered catalyst showed excellent recyclability.
EG can be synthesized (92%) by subsequent selective
hydrogenation of oxamate. Simple and new starting materials,
shorter reaction time, low pressure of CO/O2 and avoidance of
the use of phosphine ligand in step-I adds an additional credit to
the present study along with Pd/C catalyst recovery and
recyclability. Though this proposed method offers a possible
alternative to conventional method of preparing EG, still
commercial development of this process is a challenge. The
protocol would be practical for use as an economical synthetic
method and offer an alternative synthetic strategy for the
preparation of EG.
catalyst • hydrogenation
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Materials and Methods: All the chemicals were purchased from Sigma
Aldrich, S.D. Fine chemical, Lancaster (Alfa-Aesar) and commercial
suppliers. The progress of the reaction was monitored by gas
chromatography Perkin Elmer Clarus 400 GC equipped with flame
ionization detector (FID) and capillary column (30 m × 0.25 mm × 0.25
μm), thin layer chromatography using Merck silica gel 60 F254 plates.
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spectroscopic techniques. Mass spectra are obtained on GCMS-QP
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Oxamate-mediated production of EG from CO via two steps:
Step 1: Piperidine (10 mmol), ethanol (100 mL), 10% Pd/C (8 mol %),
and TBAI (0.2 mmol) were added to a 300-mL stainless steel autoclave,
and the autoclave was closed and pressurized with oxygen (1 atm) and
CO (6 atm) without flushing. The reaction mixture was stirred with a
mechanical stirrer at 60 °C for 2 h. After cooling to room temperature, the
pressure was carefully released. The catalyst was filtered and washed
with 25.0 mL ethanol, dried under vaccuo and used for next cycle. 97%
yield of the corresponding oxamate was observed by GC analysis.
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Step 2: Ethanol was removed and recovered by vaccum distillation from
reaction mixture of step 1 followed by addition of 80 mL toluene. After
stirring at room temperature for 20 min, the resulted mixture was filtrated
through thin silica gel (2-3 cm). 20 mL toluene was used to wash the
residue. The concentration of oxamate in 1 mL of toluene was found 18
mg (0.10 mmol) by GC analysis. Then 10 mL toluene solution of oxamate
(1 mmol) was added into a 100 mL autoclave which charged with 4.82
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10.1002/cssc.201700157
ChemSusChem
COMMUNICATION
Entry for the Table of Contents
Layout 1:
COMMUNICATION
A
two steps approach has been
A. Satapathy, S. T. Gadge, B. M.
developed for the synthesis of
ethylene glycol by using carbon
monoxide as C1 chemical. The Pd/C
catalyzed oxidative carbonylation of
piperdine and ethanol under ligand-
free condition provides oxamate as
Bhanage*
Page No. – Page No.
An improved strategy for the
synthesis of ethylene glycol via
oxamate-mediated catalytic
hydrogenation
intermediate
which
subsequently
hydrogenated by Milstein catalyst,
provide ethylene glycol in excellent
yield.
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