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dehydrative etherification of fructose to EMF. Different inorganic salts were tested
for fructose conversion to EMF [66]. Among all, SnCl 4 ·5H 2 O and FeCl 3 showed
acceptable activity with moderate EMF yields.
Many researchers reported solid acid catalysts for EMF preparation from fructose. Christopher M. Lew et al. disclosed Sn-beta and Amberlyst-15 combination
catalyst for dehydrative etherification of carbohydrates with less EMF yields at
90 °C [67]. Polymer modified with H 2 SO 4 catalysts were evaluated for conversion
of fructose to EMF by Song Yang and co-workers [68]. About 72% of EMF was
obtained at 110 °C in 10 h of reaction time. Sulphated organic polymer exhibited
89% conversion with 67% EMF yield [69]. A magnetically separable catalyst was
prepared and used for EMF synthesis from various carbohydrates. About 63% EMF
yield was attained from fructose [62]. Sulfonic acid-functionalized silica catalyst
(silica-SO 3 H) was also used as solid acid catalyst by Zhang et al. [70].
HAPs-based catalysts are attractive compared to other catalysts for transformation of carbohydrates to EMF in place of traditional homogeneous catalysts. Yang
et al. used heteropoly tungstate as able catalyst for converting fructose, inulin and
sucrose to EMF [62]. They got 65% of EMF yield from fructose in ethanol solvent
under microwave irradiation. The EMF yield was improved from 65 to 76% when
THF was added as co-solvent. Sucrose and inulin were converted to EMF with 33
and 62% yields, respectively, at their optimum reaction conditions. In this report
they observed that increase in reaction time resulted in the formation of EL. Wang
et al. [71] developed Fe 3 O 4 @SiO 2 -HPW for fructose conversion with 54.8% of
EMF yield. Poly(VMPS)-HPA catalyst exhibited better performance with EMF
yield up to 72.8% under the optimized reaction conditions [72]. Ag-exchanged heteropolytungstate was used for HMF and fructose conversion to EMF by Ren et al.
[73]. They got a good EMF yield of 70% when fructose was used as a feed and 88%
yield from HMF. Heteropoly tungstate supported on K-10 clay was developed by
Zhang et al. for the etherification of HMF and dehydrative etherification of fructose
with noticeable EMF yield of 91 and 61%, respectively [74]. Silicotungstic acid and
phosphotungstic acids are supported on MCM-41 [75, 76] and used for EMF synthesis from fructose and HMF. TPA/MCM-41 catalyst showed a high activity for
HMF etherification with 83% of EMF yield. The yield of EMF (43%) was moderate
in direct conversion of fructose. STA/MCM-41 catalyst was used for HMF etherification and reported a maximum of 91% EMF yield. Mesoporous SBA-15-supported
phosphotungstic acid catalysts were prepared by Rode et al. [77], and their catalytic
activity was carried out for the conversion of fructose to HMF and EMF. HMF was
the major product when the lower loading of HPW on SBA-15 was used as catalyst.
5%HPW/SBA-15 catalyst showed 78% fructose conversion with 70% of HMF
yield. With increasing the loading of HPW to 20%, HMF was converted to EMF,
and a maximum of 67% EMF was achieved.
Our group studied Ta-modified heteropoly tungstate supported on SnO 2 catalysts
for the etherification of both HMF and fructose [78]. Thirty percent TaTPA/SnO 2
resulted in 90% EMF yield from HMF and 67% from fructose. Modification of
heteropoly tungstate with Ta ions introduced Lewis acidity to the heteropoly acid,
and it is driven towards high activity even if fructose is used as starting material. The
B. S. Rao et al.
dehydrative etherification of fructose to EMF. Different inorganic salts were tested
for fructose conversion to EMF [66]. Among all, SnCl 4 ·5H 2 O and FeCl 3 showed
acceptable activity with moderate EMF yields.
Many researchers reported solid acid catalysts for EMF preparation from fructose. Christopher M. Lew et al. disclosed Sn-beta and Amberlyst-15 combination
catalyst for dehydrative etherification of carbohydrates with less EMF yields at
90 °C [67]. Polymer modified with H 2 SO 4 catalysts were evaluated for conversion
of fructose to EMF by Song Yang and co-workers [68]. About 72% of EMF was
obtained at 110 °C in 10 h of reaction time. Sulphated organic polymer exhibited
89% conversion with 67% EMF yield [69]. A magnetically separable catalyst was
prepared and used for EMF synthesis from various carbohydrates. About 63% EMF
yield was attained from fructose [62]. Sulfonic acid-functionalized silica catalyst
(silica-SO 3 H) was also used as solid acid catalyst by Zhang et al. [70].
HAPs-based catalysts are attractive compared to other catalysts for transformation of carbohydrates to EMF in place of traditional homogeneous catalysts. Yang
et al. used heteropoly tungstate as able catalyst for converting fructose, inulin and
sucrose to EMF [62]. They got 65% of EMF yield from fructose in ethanol solvent
under microwave irradiation. The EMF yield was improved from 65 to 76% when
THF was added as co-solvent. Sucrose and inulin were converted to EMF with 33
and 62% yields, respectively, at their optimum reaction conditions. In this report
they observed that increase in reaction time resulted in the formation of EL. Wang
et al. [71] developed Fe 3 O 4 @SiO 2 -HPW for fructose conversion with 54.8% of
EMF yield. Poly(VMPS)-HPA catalyst exhibited better performance with EMF
yield up to 72.8% under the optimized reaction conditions [72]. Ag-exchanged heteropolytungstate was used for HMF and fructose conversion to EMF by Ren et al.
[73]. They got a good EMF yield of 70% when fructose was used as a feed and 88%
yield from HMF. Heteropoly tungstate supported on K-10 clay was developed by
Zhang et al. for the etherification of HMF and dehydrative etherification of fructose
with noticeable EMF yield of 91 and 61%, respectively [74]. Silicotungstic acid and
phosphotungstic acids are supported on MCM-41 [75, 76] and used for EMF synthesis from fructose and HMF. TPA/MCM-41 catalyst showed a high activity for
HMF etherification with 83% of EMF yield. The yield of EMF (43%) was moderate
in direct conversion of fructose. STA/MCM-41 catalyst was used for HMF etherification and reported a maximum of 91% EMF yield. Mesoporous SBA-15-supported
phosphotungstic acid catalysts were prepared by Rode et al. [77], and their catalytic
activity was carried out for the conversion of fructose to HMF and EMF. HMF was
the major product when the lower loading of HPW on SBA-15 was used as catalyst.
5%HPW/SBA-15 catalyst showed 78% fructose conversion with 70% of HMF
yield. With increasing the loading of HPW to 20%, HMF was converted to EMF,
and a maximum of 67% EMF was achieved.
Our group studied Ta-modified heteropoly tungstate supported on SnO 2 catalysts
for the etherification of both HMF and fructose [78]. Thirty percent TaTPA/SnO 2
resulted in 90% EMF yield from HMF and 67% from fructose. Modification of
heteropoly tungstate with Ta ions introduced Lewis acidity to the heteropoly acid,
and it is driven towards high activity even if fructose is used as starting material. The
B. S. Rao et al.