46
C. Delhomme et al. / Journal of Molecular Catalysis B: Enzymatic 80 (2012) 39–47
Table 3
Conversions (X) and purity of the recovered esters for the 200-ml scale esterification of succinic acid in distilled water and in fermentation broth using DBSA. Reaction
conditions: 5.24 g DBSA, 100 ml aqueous phase, 100 ml 1-octanol, 90 ◦C, 8 h.
Diester
X (8 h)
Color
Purity (NMR)
Purity (calculated)
88%
% DBSA (NMR)
% SA (calculated)
1%
Pure solution (before filtration)
(after filtration)
Fermentation broth (before filtration)
(after filtration)
91%
Pale yellow
Pale yellow
Brown
90%
95%
63%
83%
6%
5%
4%
4%
85%
65%
1%
Yellow
from the pure solution of succinic acid was high (90%) whereas it
remained limited for the esters from the fermentation broth (63%).
Besides, it should be noted that the purities determined by 1H NMR
were extremely similar to the ones calculated from the mass of
esters obtained and the conversions. Moreover, the extracted suc-
cinic acid into the 1-octanol phase should not contaminate much
the esters (∼1%, based on calculations), while DBSA was found in
limited amount in the esters (up to 6%). In order to reduce the DBSA
and the side products contamination, the esters were filtered on
silica gel. After filtration, the purity was considerably improved for
the fermentation broth (83%) as well as for the pure solution of
succinic acid (95%). The lower purity of the esters from the fermen-
tation broth before filtration is probably due to the extraction of
different less polar side products or medium components from the
fermentation broth into the 1-octanol phase. Furthermore, other
carboxylic acids from the fermentation broth might also have been
esterified by DBSA and extracted in the 1-octanol phase. Finally, 1-
octanol can be recovered with a purity of ∼98% (determination by
1H NMR) after the purification of the ester. It can hence be reused for
further esterifications of succinic acid as it is introduced in excess.
In conclusion, DBSA allowed the esterification of succinic acid
in two-phase systems with conversions up to 93%. For the reac-
tion with fermentation broth, the esters could be recovered with a
purity of 83%.
remained the cheapest and most active option with conversions
of 78–93% after only 8 h of reaction in the broth. The esters could
be isolated with a purity of 83% from fermentation broth solutions.
Furthermore, DBSA can catalyze the esterification of succinic acid
with many alcohols at conversions ≥87%, creating a broad spectrum
of interesting esters. The esters could then be used as final product,
hydrolyzed back to pure succinic acid or hydrogenated to succinic
acid reduced products (e.g. gamma-butyrolactone, 1,4-butanediol
and tetrahydrofuran).
Acknowledgements
This work was generously supported by the International Grad-
uate School of Science and Engineering (IGSSE) at the Technische
Universität München, particularly by an IGSSE Ph.D. grant for Dr.
Clara Delhomme. Dr. Serena L.M. Goh is grateful to the Bavar-
ian Research Foundation for a Ph.D. grant. The assistance of Elona
Hasanbelli was greatly appreciated.
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