Triazaheterocyclic compound as an efficient catalyst for dehydration of fructose into 5-hydroxymethylfurfural

Article abstract of DOI:10.1039/c4ra00534a

Hexachlorocyclotriphosphazene and cyanuric chloride are found to be high efficient homogeneous catalysts for dehydration of fructose into 5-hydroxymethylfurfural under mild conditions. The P-Cl or C-Cl bonds play important roles in the reaction, and the strong interaction between the fructose and the electron-withdrawing substituent will help to promote the dehydration. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra00534a

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Triazaheterocyclic compound as an efficient
catalyst for dehydration of fructose into
Cite this: RSC Adv., 2014, 4, 13434
5-hydroxymethylfurfural†
a
b
c
a
b
Received 18th January 2014
Accepted 27th February 2014
*
Zhen Huang,‡ Yuanjia Pan,‡ Yimin Chao, Wei Shen, Changchun Wang
a
*
and Hualong Xu
DOI: 10.1039/c4ra00534a
www.rsc.org/advances
Hexachlorocyclotriphosphazene and cyanuric chloride are found to expended in improving this situation. Kuster et al.6 introduced
be high efficient homogeneous catalysts for dehydration of fructose polyethylene glycol (PEG) as the solvent, and demonstrated that
into 5-hydroxymethylfurfural under mild conditions. The P–Cl or C–Cl the improved HMF yield should be attributed to the formation
bonds play important roles in the reaction, and the strong interaction of HMF–PEG esters, which exhibited better stability in the
between the fructose and the electron-withdrawing substituent will reaction system. Dumesic and co-workers7 described a method
help to promote the dehydration.
using phase modier with various concentrations, and a high
yield (approx. 76%) of HMF was obtained by using hydrochloric
acid as catalyst in an aqueous solution containing dimethyl
sulfoxide (DMSO) and poly(1-vinyl-2-pyrrolidone) with 2-meth-
ylisobutylketone as the phase modier. Nevertheless, the high
energy consumption demanded by the required isolation
procedures, becomes the disadvantage of these processes.
On the other hand, the industrial catalytic dehydration of
saccharides has also been impeded due to the introduction of
corrosive reaction medium. Therefore, the application of ionic
liquids (ILs), which have greatly avoided the use of acids in the
reaction systems, have improved the yield of HMF as well as the
selectivity, and have drawn much attention in the biomass
processing and production of HMF from sugars.8 For instance,
Zhao et al. reported production of HMF from dehydration of
glucose catalyzed by chromium(II) chloride in 1-alkyl-3-methyl-
imidazolium chloride.9 Although it has been improved by many
less or none toxic promoters such as SnCl4,10 GeCl4,11 FeCl2,12
To overcome the growing shortage of fossil resources, many
strategies for efficient conversion of biomass into fuels and
chemicals have been developed, in which the production of
5-hydroxymethylfurfural (HMF) has been considered as a
promising intermediate in the bio-energy transformation in the
past two decades.1,2 Furthermore, HMF as an important plat-
form chemical derived from biomass can be an alternative
compound to those from fossil resources. For example, it can be
selectively oxidized into furan-2,5-dicarboxylic acid, which can
serve as
a
substituent for terephthalic acid in the
manufacturing of plastic, and converted into other valuable
building blocks such as 2,5-di(hydroxymethyl)furan and levu-
linic acid.3 HMF can be derived from hexoses by losing three
molecules of water in an acidic medium. Consequently, acids
including mineral acids and organic acids (e.g., hydrochloric
acid (HCl) and p-toluenesulfonic acid) were rst to be used as
catalysts in this process.3–5 However, the formation of soluble
polymers and insoluble humins and the rehydration of HMF
under acidic conditions have restricted the HMF production,
especially in aqueous systems. Therefore much effort has been
13
CoSO4 and B(OH)3,14 it will signicantly increase the cost of
the process by employing ILs and the difficult separation and
purication operations. The application of heterogeneous
catalysts, as reported in the literature, still have been challenged
by relatively low efficiency, high reaction temperature, and the
product isolation process.15–19 From an eco-friendly and
economic point of view, a noncorrosive, high efficiency and
metal-free catalyst system is intensively needed for the HMF
production from biomass in the future.
According to the references, triazaheterocyclic compounds,
such as hexachlorocyclotriphosphazene (HCCP) and cyanuric
chloride (CNC), have been reported as very effective catalysts
instead of strong acids (e.g., HCl) for the Beckmann rear-
rangement reactions.20 Besides, these compounds, which
possess variable and active substituents as well as stability, have
aDepartment of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and
Innovative Materials and Laboratory of Advanced Materials, Fudan University,
Shanghai 200433, P. R. China. E-mail: shuhl@fudan.edu.cn; Fax: +86-21-65641740
bDepartment of Macromolecular Science, State Key Laboratory of Molecular
Engineering of Polymers and Laboratory of Advanced Materials, Fudan University,
Shanghai 200433, P. R. China. E-mail: ccwang@fudan.edu.cn; Fax: +86-21-65640293
cEnergy Materials Lab, School of Chemistry, University of East Anglia, Norwich, NR4
7TJ, UK
† Electronic supplementary information (ESI) available: Experimental details and
supporting tables and gures. See DOI: 10.1039/c4ra00534a
‡ Contributed equally to this work.
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been widely applied in organic synthesis and polymeric mate- water molecules.21 In view of this, some phosphonium salts such
rials.21 Based on these and our previous works, we try to adopt as benzyltriphenylphosphonium chloride (BTPPCl) and meth-
HCCP and CNC as the catalysts for the dehydration of D-fructose yltriphenylphosphonium bromide (MTPPBr), in which a type of
into HMF by using these compounds in DMSO as a solvent ionic bond exist between halogen atoms and phosphorus, had
under mild conditions.
been employed as the catalyst. But the results showed (entry 8
Firstly, we compared the catalytic performance of HCCP, and 9) poor activity of BTPPCl and MTPPBr, only giving a HMF
CNC, HCl and some reference compounds in a 5 wt% fructose/ yield of 6.9% and 12.3%, respectively. Thus, based on these
ꢀ
DMSO solution under 90 C for 2 h. As listed in Table 1 (entry results, it can be presumed that the bonded chlorine on the
1 and 2), HCCP showed the best activity which gave a HMF yield triazine derivatives (P–Cl or C–Cl) should play a key role in the
of 91.0%, and a good catalytic performance with an 86.9% yield catalytic activity.
of HMF was conducted by CNC. In contrast, a lower HMF yield of
In addition, the catalytic performance of a serials of
76.4% (entry 3) was received when HCl was used as the catalyst s-triazine derivatives with different substituent groups
under the same conditions. By considering the special structure including 2,4,6-tris-(triuoromethyl)-1,3,5-triazine (TFTZ), tri-
of HCCP and CNC molecules, we supposed that the active thiocyanuric acid (TCA), melamine and CNA had been
substituent chloride atoms should be associated with the cata- compared, and the results are illustrated in Fig. 1. A moderate
lyst activity, which had been approved to have strong interaction HMF yield of 28.7% with 51.5% fructose conversion was
with fructose.22 Thus we repeated the reactions with different received under the given reaction conditions in the presence of
dosages of HCl (3 mol% and 6 mol% to fructose). As a result TCA. But when the functional groups of triazine were replaced
(entry 4 and 5), HCCP still had a better performance in activity by amino groups (melamine), there was no conversion of fruc-
than HCl, while CNC was slightly inferior. Moreover, the catalytic tose detected aer the reaction. By comparing with that of
performance tests of high concentrate of substrate (entry 11–14) HCCP and CNC, it was found that the different electro-with-
also reveal the superiority of HCCP and CNC over HCl on the drawing ability of the substituent on each triazine derivative
dehydration of fructose. In order to demonstrate the active site of should be responsible for the catalytic activity. Furthermore, a
the catalysts, we designed and carried out a series of experi- uoride-rich analogue, TFTZ, which possessed a stable struc-
ments. Firstly, HCCP was capped with phenol by replacing the ture with carbon–carbon bonded triuoromethyl groups was
substituent chlorine atoms with phenoxy groups, which formed adopted to catalyse the dehydration of fructose, and a small
hexaphenoxycyclo-triphosphazene (PCP). However, PCP showed amount of HMF with 10.3% in yield was obtained. However,
nearly no catalytic activity on the reaction (entry 6), which only when this compound was reperformed together with HCl
gave a 2.1% of HMF yield in 2 h, by comparison with the control (0.1 mol% to fructose), an obvious increase of fructose conver-
experiment which was carried out with no catalyst (entry 10) sion and HMF yield was achieved aer a reaction time of 0.5 h,
under the same conditions. Similarly, when cyanuric acid (CNA) which was 30.3% and 10.4% respectively, compared to the iso-
was used instead of CNC, only 10.3% yield of HMF (entry 7) was lated performance of TFTZ (3.9% conversion, 1.1% yield) and
received aer the reaction. As referred above, the strong inter- HCl (12.0% conversion, 1.9% yield) (Table S1, ESI†). These
action between Clꢁ anion and fructose through hydrogen bonds results revealed that there might be a synergetic effect on the
bridging structure OH/Cl/HO could help fructose to lose the reaction due to the substituent groups with electron-with-
drawing ability, which acted in the form of hydrogen bonds
between the groups and the fructose. Moreover, further
evidence from mass spectrometric analysis had proved that an
Table 1 Catalytic performance of HCCP, CNC and relative catalysts
on dehydration of fructose into HMFa
Fructose
content
(wt%)
Catalyst
dosage
(mol%)
Fructose
conversion
(%)
HMF yield
(%)
Entry
Catalyst
1
2
3
4
5
6
7
8
HCCP
CNC
HCl
HCl
HCl
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1.0
1.0
1.0
3.0
6.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
3.0
98.9
96.3
90.0
96.7
98.2
12.2
28.5
14.6
34.6
9.8
91.0
86.9
76.4
87.8
88.5
2.1
10.3
6.9
12.3
1.9
PCP
CNA
BTPPCl
MTPPBr
None
HCCP
CNC
HCl
9
10
11
12
13
14
5.0
30.0
30.0
30.0
30.0
98.6
97.2
91.9
97.3
75.7
69.6
56.9
69.3
HCl
Fig. 1 Catalytic activities of different triazine derivatives with varied
substituent. (Reaction conditions: 12.5 g of 5 wt% fructose/DMSO
solution, 1 mol% catalyst, 90 ꢀC, 2 h).
a
Reaction conditions: all reactions were performed with 12.5 g fructose/
DMSO solution and the catalyst (mol% to fructose) under 90 ꢀC for 2 h.
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intermediate consisting of a TFTZ molecule and a fructose deprotonationofintermediateC, anditwouldnallyconvertinto
molecule existed during the reaction (Fig. S2, ESI†). Another the product HMF by loss of another two water molecules through
aspect should be mentioned that the unique triazine ring a similar pathway. Then, reformation of HCCP by losing the
structure (–C]N–) could be another important factor to the water molecule would end the catalytic step of this process.
catalytic activity. Herein, the catalytic dehydration of fructose Although there was HCl coming out in this mechanism, we
using a phenyl containing analogue, 1,3,5-trichlorobenzene believed that it should be involved as an instantaneous state
(TCB), had also been conducted, and only a 12.3% yield of HMF during the reaction. Thus, we used triethylamine (TEA) as an
with a 38.1% conversion of fructose was received. By comparing additive to the reaction, which could capture the proton so as to
the difference of CNC and TCB, the introduction of nitrogen inhibit the reaction. As a result (Table S2†), the addition of TEA
to the body ring might result in the highly active structure, had barely effect on the activity of HCCP (90.1%, 2 h) and CNC
where the substituent groups were highly active and the carbon (81.1%, 2 h), while a clear decrease of HMF yield (76.1%, 2 h) was
atoms could be easily attacked through the nucleophilic inter- observed for HCl as the catalyst.
action. As for HCCP, the higher levels of activity observed when
In summary, the triazaheterocyclic compounds with covalent
compared against CNC could be contributed to the greater bonded chlorine, HCCP and CNC, are proved as efficient cata-
number of chlorine atoms, which could lead to a stronger lysts for the dehydration on fructose into HMF, and a series of
interaction with fructose and a more electropositive phos- triazine analogues have also shown their catalytic activities in
phorus atom as well, and to the easier accessible active sites due this reaction. The reason should be attributed to the active
to the bigger sized phosphorus atoms.
substituents withelectron-withdrawing ability, whichcould have
As it was revealed, HCCP and CNC, as two chlorine- strong interactions with fructose through hydrogen bonds, and
substituted s-triazine derivatives, were both efficient homoge- to the electropositive center (phosphorus or carbon atom) on the
neous catalysts for dehydration of fructose into HMF under mild body ring structure. Moreover, O-triphosphazene compounds
conditions. In Scheme 1, a possible mechanism for the reaction were considered as the important intermediates in this reaction
catalysed by HCCP had been presented. The high resolution system, based on which a possible mechanism of dehydration of
mass spectrometric analysis of a reaction mixture, which was fructose into HMF was proposed. And these triazine compounds
heated under 90 ꢀC for only 5 min, had showed a very important provide a new pathway for synthesis of HMF from biomass with
intermediate (A, Scheme 1) (both mono- and dual-fructose- high efficiency and without pollutions. Finally, it is worthwhile
substituent intermediates were discovered, see Fig. S3, ESI†) to note that HCCP can be reused once it is immobilized
formed during the reaction. And the formation of the O-triazine (for example, poly-nanoparticles made by HCCP and
compound should initialize the dehydration process, which was 4,40-sulfonyldiphenol have shown excellent catalytic activity on
followedby theprotonationsteptoformintermediateB. Aer the this reaction), and the relative work on this aspect is underway.
loss of the hydroxylgroup (redin color)from fructose(in the form
of fructofuranose), the intermediate product 2-hydroxymethyl-
Acknowledgements
5-hydroxylmethylene-tetrahydrofuran-3,4-diol was formed by
This work was supported by Department of Chemistry and
Shanghai Key Laboratory of Molecular Catalysis and Innovative
Materials, Fudan University. This work was also supported by
the Shanghai Science and Technology Committee
(12DZ2275100) and the CSC program (no. 201301310147) and
the Fudan Tyndall Centre research programme.
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