CHEMSUSCHEM
COMMUNICATIONS
DOI: 10.1002/cssc.201402131
Poly-benzylic Ammonium Chloride Resins as Solid
Catalysts for Fructose Dehydration
Siew Ping Teong, Guangshun Yi, Xueqin Cao, and Yugen Zhang*[a]
5-hydroxymethylfurfural (HMF) is one of the most promising
platform molecules, and can be converted into a variety of in-
teresting chemicals. The production of HMF is essentially tar-
geted at bulk chemicals downstream, such as chemicals for
the fuels and plastics industries. One critical challenge in HMF
production processes is the link to further value-adding reac-
tions in a simple and efficient way (e.g., fewer isolation and
purification steps). Herein, a novel poly-benzyl ammonium
chloride (PBnNH3Cl) resin is developed as a highly efficient and
stable catalyst for dehydration of carbohydrates into HMF. In
the isopropanol system, PBnNH3Cl produces high purity HMF
that is suitable as feedstock for oxidation to 2,5-furandicarbox-
ylic acid (FDCA). The excellent catalytic properties together
with its easy synthesis, low cost, and nontoxic nature make
this poly-ammonium resin a promising catalyst for the devel-
opment of new and efficient processes for biomass-based
chemicals.
heteropolyacids (HPAs),[12] and porous TiO2/TiPO4.[13,14] Among
these heterogeneous catalysts, ion-exchange resins (such as
Amberlyst-15) are most widely used and have been tested in
almost all types of carbohydrate dehydration systems.[14,15]
Indeed, Amberlyst resins as acidic catalysts are cost-efficient
and accessible. They can dehydrate fructose into HMF in high
yields (>90%), in high-boiling-point polar aprotic solvent sys-
tems, such as DMSO or ionic liquids. Generally, solid catalysts
often suffer from low stability. They may partially lose their
acidic sites or change from their original structure during the
reaction, which may lead to catalyst deactivation.
Recently, the use of low-boiling-point, readily available, and
cost-efficient solvents in HMF production has attracted more
attention owing to the ease of HMF isolation.[16] Single-phase,
low-boiling-point (environmentally benign) solvent systems
may provide new opportunities for large-scale economically
viable processes.[17] Our group has developed an isopropanol-
mediated reaction system for the production of HMF from
fructose. High HMF yields (>80%) were achieved by using this
system with HCl as catalyst.[18] To avoid the use of corrosive
HCl as catalyst and allow for more efficient solvent/catalyst re-
cycling, Amberlyst-15 was tested as acidic heterogeneous cata-
lyst in isopropanol for fructose dehydration. However, this led
to low HMF selectivity and poor recyclability. We thus screened
other Brønsted-acid catalysts in isopropanol, and found that
the weak acid ammonium chloride can produce high yields of
HMF in this solvent.[19] This stimulated us to screen other am-
monium salts as well, as shown in Scheme 1. We found that
The depletion of fossil fuels and their negative impact on the
environment promote the search for renewable carbon resour-
ces, such as biomass, to use in the production of chemicals
and fuels.[1,2] Recently, great efforts have been devoted towards
converting biomass into 5-hydroxymethylfurfural (HMF), a ver-
satile and key intermediate in biofuel chemistry and the petro-
chemical industry.[3,4] However, the high production costs of
HMF are a major drawback preventing the application of this
biomass-based compound. The development of sustainable,
large-scale chemical biomass processing methods is critical for
their efficient utilization.[5] Biomass-derived HMF is most com-
monly obtained by the dehydration of carbohydrates with
acidic catalysts.[6,7] Mineral acids formed the first generation of
catalysts for carbohydrate dehydration reactions, and are cur-
rently still widely used.[7] Owing to their corrosive and nonre-
cyclable nature, however, large-scale production processes
using mineral acid catalysts would put a heavy burden on the
environment. In pursuit of economical, simple, efficient, and
environmentally friendly HMF production process, various het-
erogeneous catalysts have been tested under different condi-
tions, such as acidic carbons,[8] zeolites,[9] functionalized
silica,[10] functionalized metal–organic frameworks (MOFs),[11]
Scheme 1. Ammonium salts screened for dehydration of fructose into HMF
in isopropanol. General conditions: fructose (0.18 g), catalyst (10 mol%), iso-
propanol (2 mL), 1208C, 2 h.
benzyl ammonium chloride gave a very good yield of HMF (up
to 80% in 5 h). Ionic-liquid ammonium salts have been used as
medium for HMF production with other catalysts.[20] The disso-
ciation of HCl from benzyl ammonium chloride is believed to
be a key factor for the catalytic activity of these salts. The equi-
librium between ammonium salt and HCl/amine in this system
also makes it a potentially recyclable catalyst. These prelimina-
[a] S. P. Teong, Dr. G. Yi, Dr. X. Cao, Dr. Y. Zhang
Institute of Bioengineering and Nanotechnology
31 Biopolis Way, The Nanos #04-01
Singapore 138669 (Singapore)
Fax: (+65)6478-9080
Supporting Information for this article is available on the WWW under
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ChemSusChem 2014, 7, 2120 – 2126 2120