3.4. Conversion of D-glucose to GVL by TFA in combination
with a homogeneous water soluble ruthenium hydrogenation
catalyst
hydrogen is slow (order of hours), although apparently very
selective.
The dehydration/hydrogenation of D-glucose to GVL with
molecular hydrogen was also explored using TFA in combina-
tion with a water soluble homogeneous Ru catalyst prepared in
situ from RuCl3 and TPPTS. The yields of GVL (23 mol%) were
lower than for the reactions with Ru/C and substantial amounts
of LA were present in the mixture (19 mol%). This suggests that
at the reaction conditions and intakes applied in this study, the
hydrogenation activity of the homogeneous catalyst is lower than
for Ru/C.
The study also identified TFA as an attractive alternative for
mineral acids for the conversion of C6-sugars to LA. With this
finding, aqueous/fluoro-biphasic system for the conversion of
C6-sugars to LA may be envisaged with a fluoro-phase (e.g.
perfluorohexane)42 soluble TFA derivative like heptadecafluo-
rononanoic acid (pKa: 0.36). This would facilitate acid catalyst
recycle considerably, which is one of the main drawbacks of the
current mineral acid based concepts for LA synthesis.
The dehydration/hydrogenation of D-glucose to GVL with
molecular hydrogen was also performed using a homogeneous
Ru catalyst in combination with TFA. For this purpose, a water-
soluble Ru-catalysts prepared in situ from RuCl3 and TPPTS
was applied. NaI was added to increase the reaction rate.41 The
reaction was performed at a reaction temperature of 180 ◦C
using 0.5 mol/l TFA and 94 bar of hydrogen. A catalyst to
D-glucose ratio of 1 to 270 mol/mol was applied, the initial
concentration of D-glucose was 0.5 mol/l.
After 8 h reaction time, the reaction was terminated and
the composition of the liquid phase was determined using
HPLC. Complete D-glucose conversion was observed. The
major products in the liquid phase were LA (19 mol%) and
GVL (23 mol%), furthermore substantial amounts of insoluble
humins were formed. The presence of significant amounts of LA
indicates that the hydrogenation reaction of LA to GVL is far
from quantitative at these conditions. The sum of the GVL and
LA yields is 42 mol%. This value is close to the maximum LA
yield for the acid catalysed conversion of D-glucose under these
conditions (46 mol%). The observed GVL yield is lower than
reported by Horva´th20,21 for a similar catalyst using sulfuric acid
in combination with sucrose (40 mol%). Sucrose is a dimer of
D-fructose and D-glucose and higher yields of the intermediate
LA are expected compared to D-glucose only. Further studies,
e.g. by applying longer reaction times and/or higher catalyst
intakes and D-fructose instead of D-glucose will be required to
attain complete LA conversion to GVL. When assuming that
the hydrogenation of LA to GVL is highly selective at these
conditions, a maximum yield of 42 mol% is to be expected under
the experimental conditions/intakes applied.
Acknowledgements
B. Girisuta thanks the University of Groningen for financial
support to perform his PhD study by an Ubbo Emmius Schol-
arship. R. Handana thanks the Indonesian Higher Education
Council for financial support through the TPSDP Programme.
C. Dai thanks the Dutch Organization for International Coop-
eration in Higher Education and the China Scholarship Council
for financial support through a Huygens China Scholarship.
C.B. Rasrendra thanks the University of Groningen for a
Bernoulli Fellowship to perform his PhD research.
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The yield and the rate of GVL formation is a delicate balance
between the two individual reactions (acid catalysed dehydration
of the C6-sugar to LA followed by a catalytic hydrogenation) in
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1254 | Green Chem., 2009, 11, 1247–1255
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