658
alkaline metals and amine surface modification on HMF conversion and selectivity
of HAc and coke resistance of a nanosheet zeolite were demonstrated. Among the
various alkaline metal exchange zeolites, NaX-NS showed the best performance in
terms of HMF conversion and selectivity to HAc (Table 8). Pupovac and Palkovits
reported copper supported on mesoporous magnesium aluminate as noble metalfree base bifunctional catalysts for sequential aldol condensation of 5-HMF and
acetone and hydrogenation of aldol product [160]. The magnesium aluminate
showed higher activity for aldol condensation reaction (100% HMF conversion)
compared to zinc- and cobalt-based aluminates. The higher activity was correlated
with the higher concentration of surface basic sites on magnesium aluminate. The
Cu/MgAl 2 O 4 catalyst selectively hydrogenates only the C-O, and furan ring remains
unaffected during hydrogenation.
2.4.4 Claisen-Schmidt Condensation of Furfural and 5-HMF
The chalcones with structure of 1,3-diphenyl-2-propen-1-one belong to the flavonoid family and are widespread in plants. Naturally occurring and synthetic chalcones are associated with several biological activities such as antioxidant,
anti-inflammatory, antibacterial, antihyperglycemic, antifungal, antimalarial, anticancer, etc. [161, 162]. The furan-based chalcones or furanochalcones are produced
by the Claisen-Schmidt condensation between FUR derivatives and acetophenones
using various base catalysts.
Arias et al. described the synthesis of furanochalcones by Claisen-Schmidt condensation reaction of 5-HMF and various substituted acetophenones using different
solid acid catalysts (MgO, Al/Mg mixed oxide (HTc) and hydrated A/Mg mixed
oxide (HTr)) [161]. The calcined HTc possesses Lewis acid sites, whereas hydrated
HTr is associated with Brønsted acidity. These three catalysts showed high activity
for the condensation reaction in the absence of solvent. However, this catalyst deactivates very fast in the absence of solvent due to the adsorption of HMF and furanochalcones on the catalyst surface. The polarity of solvent plays a significant role in
catalyst stability, activity, and product selectivity. The condensation reaction performed in the presence of high-polarity solvent mixture such as ethanol-water
exhibited high 5-HMF conversion and selectivity of furanochalcones using HTc and
HTr mixed oxide catalysts. However, MgO deactivates fast in water-based solvent
mixture due to the formation of inactive Mg(OH) 2 . Yadav et al. demonstrated the
Claisen-Schmidt condensation reaction of FUR and acetophenone using various
solid base catalysts [162]. The following solid base catalysts were studied for the
condensation reaction: CaO, 15w% Al 2 O 3 supported on CaO, MgO, and SrO,
hydrated hydrotalcite (HHT), and calcined hydrotalcite (CHT) with different ratios
of Mg/Al. Among these solid base catalysts, 15w% Al 2 O 3 /CaO showed superior
activity giving maximum FUR conversion of 98.5% within 2 h of reaction (Table 9).
Other catalysts showed poor activity for condensation reaction. The 15w% Al 2 O 3 /
CaO showed marginal deactivation after recycling for three times.
M. Baithy et al.
alkaline metals and amine surface modification on HMF conversion and selectivity
of HAc and coke resistance of a nanosheet zeolite were demonstrated. Among the
various alkaline metal exchange zeolites, NaX-NS showed the best performance in
terms of HMF conversion and selectivity to HAc (Table 8). Pupovac and Palkovits
reported copper supported on mesoporous magnesium aluminate as noble metalfree base bifunctional catalysts for sequential aldol condensation of 5-HMF and
acetone and hydrogenation of aldol product [160]. The magnesium aluminate
showed higher activity for aldol condensation reaction (100% HMF conversion)
compared to zinc- and cobalt-based aluminates. The higher activity was correlated
with the higher concentration of surface basic sites on magnesium aluminate. The
Cu/MgAl 2 O 4 catalyst selectively hydrogenates only the C-O, and furan ring remains
unaffected during hydrogenation.
2.4.4 Claisen-Schmidt Condensation of Furfural and 5-HMF
The chalcones with structure of 1,3-diphenyl-2-propen-1-one belong to the flavonoid family and are widespread in plants. Naturally occurring and synthetic chalcones are associated with several biological activities such as antioxidant,
anti-inflammatory, antibacterial, antihyperglycemic, antifungal, antimalarial, anticancer, etc. [161, 162]. The furan-based chalcones or furanochalcones are produced
by the Claisen-Schmidt condensation between FUR derivatives and acetophenones
using various base catalysts.
Arias et al. described the synthesis of furanochalcones by Claisen-Schmidt condensation reaction of 5-HMF and various substituted acetophenones using different
solid acid catalysts (MgO, Al/Mg mixed oxide (HTc) and hydrated A/Mg mixed
oxide (HTr)) [161]. The calcined HTc possesses Lewis acid sites, whereas hydrated
HTr is associated with Brønsted acidity. These three catalysts showed high activity
for the condensation reaction in the absence of solvent. However, this catalyst deactivates very fast in the absence of solvent due to the adsorption of HMF and furanochalcones on the catalyst surface. The polarity of solvent plays a significant role in
catalyst stability, activity, and product selectivity. The condensation reaction performed in the presence of high-polarity solvent mixture such as ethanol-water
exhibited high 5-HMF conversion and selectivity of furanochalcones using HTc and
HTr mixed oxide catalysts. However, MgO deactivates fast in water-based solvent
mixture due to the formation of inactive Mg(OH) 2 . Yadav et al. demonstrated the
Claisen-Schmidt condensation reaction of FUR and acetophenone using various
solid base catalysts [162]. The following solid base catalysts were studied for the
condensation reaction: CaO, 15w% Al 2 O 3 supported on CaO, MgO, and SrO,
hydrated hydrotalcite (HHT), and calcined hydrotalcite (CHT) with different ratios
of Mg/Al. Among these solid base catalysts, 15w% Al 2 O 3 /CaO showed superior
activity giving maximum FUR conversion of 98.5% within 2 h of reaction (Table 9).
Other catalysts showed poor activity for condensation reaction. The 15w% Al 2 O 3 /
CaO showed marginal deactivation after recycling for three times.
M. Baithy et al.