Hydrothermal conversion of glucose to levulinic acid using multifunctional ionic liquids: Effects of metal ion co-catalysts on the product yield

Article abstract of DOI:10.1039/c7nj03146g

Efficient conversion of glucose to levulinic acid (LA) was achieved with -SO₃H functionalized ionic liquids in combination with a catalytic amount of metal salts under environmentally benign mild reaction conditions. Ionic liquids having different Bronsted acidic functional groups were prepared in the laboratory. The acidity of these ionic liquids was determined on the basis of the Hammett acidity function using UV-Visible spectroscopy. These catalysts were then screened in the conversion of glucose to LA using a batch autoclave under autogenous pressure at a temperature range of 140 to 175 °C. The structure-activity relationship of these multifunctional ionic liquids was correlated based on the Hammett function (H_o) and the catalytic activity results obtained in terms of glucose conversion and LA yield. The catalytic activity of the functionalized ionic liquids decreased in the order: IL-SO₃H > IL-COOH > IL-OH, which is in good agreement with their Bronsted acidity trends. Furthermore, a metal salt based Lewis acidic co-catalyst, with metal ions (Fe, Co, Ni, Cu and Zn), was used in combination with the laboratory prepared Bronsted acidic functionalized ionic liquids in the efficient conversion of glucose to LA. Among all the investigated catalyst and co-catalyst systems, the -SO₃H functionalized ionic liquid with nickel sulfate (NiSO₄·6H₂O) showed the highest LA yield (56.33%) and selectivity (56.37%). The synergistic effect of the metal ions helps in improving the LA yield by 10% as observed in our investigations. The co-catalytic effect of the transition metal chlorides and metal nitrates was not obvious as compared to transition metal sulfates. The catalyst could be recovered easily and reused three times without significant loss of activity.

Full text of DOI:10.1039/c7nj03146g

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. Kumar, F.
Parveen, T. Patra and S. Upadhyayula, New J. Chem., 2017, DOI: 10.1039/C7NJ03146G.
This is an Accepted Manuscript, which has been through the
Volume 40 Number
1 January 2016 Pages 1–846
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Page 1 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
1
2
3
Hydrothermal Conversion of Glucose to Levulinic acid
using Multifunctional Ionic Liquids: Effect of metal ion
co-catalysts on Product Yield
4
5
6
7
8
9
Komal Kumar, Firdaus Parveen, Tanmoy Patra, Sreedevi Upadhyayula*
Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, Hauz Khas, New
Delhi 110016, India.
*Corresponding author. Tel. No: +91 11 26591083, Fax: +91 11 26591120, Eꢀmail id:
sreedevi@chemical.iitd.ac.in
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
ABSTRACT
Efficient conversion of glucose to levulinic acid (LA) was achieved with –SO3H functionalized
ionic liquids in combination with catalytic amount of metal salts under environmentally benign
mild reaction conditions. Ionic liquids having different Bronsted acidic functional groups were
prepared in the laboratory. The acidity of these ionic liquids was determined on the basis of
Hammett acidity function using UVꢀVisible spectroscopy. These catalysts were then screened in
the glucose conversion to LA using batch autoclave under autogenous pressure at 140 to 175 °C
temperature range. Structureꢀactivity relationship of these multifunctional ionic liquids was
correlated based on Hammett function (Ho) and catalytic activity results obtained in terms of
glucose conversion and LA yield. The catalytic activity of functionalized ionic liquids decreased
in the order: ILꢀSO3H>ILꢀCOOH>ILꢀOH, which is in good agreement with their Bronsted
acidity trends. Furthermore, a metal salt based Lewis acidic coꢀcatalyst, with metal ions (Fe, Co,
Ni, Cu and Zn), was used in combination with the laboratory prepared Bronsted acidic
functionalized ionic liquids in the efficient conversion of glucose to LA. Among all the
investigated catalyst and coꢀcatalyst systems, the ꢀSO3H functionalized ionic liquid with Nickel

New Journal of Chemistry
Page 2 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
25
26
27
28
29
sulfate (NiSO4.6H2O) showed highest LA yield (56.33%) and selectivity (56.37%). The
synergistic effect of the metal ions helps in improving the LA yield by 10% as observed in our
investigations. The coꢀcatalytic effect of the transition metal chlorides and metal nitrates was not
obvious as compared to transition metal sulfates. The catalyst could be recovered easily and
reused three times without significant loss of activity.
30
Keywords: Metal ions; Glucose; Ionic liquids; Catalytic conversion; Levulinic acid.
31 1. Introduction
32
33
34
35
36
37
38
39
40
41
42
Production of industrially important fine and bulk chemicals from readily available
lignocellulosic biomass has become the new trend in catalysis.1 Lignocellulosic biomass is
composed of lignin, cellulose and hemicellulose, found to be the natural renewable carbon
resource.2 Cellulose is readily and is sustainable biomassꢀderived raw material, made up of Dꢀ
glucose units linked together by βꢀ1, 4 glycosidic bonds.3 Cellulose can be hydrolyzed to glucose
and further isomerization of glucose leads to the production of industrial important chemicals
such as LA, 5ꢀhydroxymethyl furfural (HMF) and lactic acid as shown in Scheme 1.4 LA is the
rehydrated product that can be produced from the rehydration of HMF, an intermediate that can
be obtained by the catalytic conversion of lignocellulosic biomass.5 LA with two active, carbonyl
and carboxyl functional groups can be converted to γꢀvalerolactone and other liquid
transportation fuel through hydrogenation reactions.6

Page 3 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
43
44
Scheme 1. Mechanistic representation of formation of LA and formic acid from Glucose.
45
46
47
48
49
50
51
52
Till date, several studies have been reported on conversion of lignocellulosic biomass to LA
using mineral acids,7 metal sulfates8 and heteropoly acid as catalyst. Despite the good yield, the
above processes possess the disadvantage of product separation, recycling of catalyst, reactor
corrosion, selectivity to the desired products and economically expensive heteropoly acids.
Recently, ionic liquids have been reported as solvents as well as catalysts for catalytic
transformation of cellulose to LA.9 Ionic liquids are also known as the designer solvents due to
their unique properties of low vapor and task specificity that can be achieved by the modification
of cation and anion.10–13 Tao et al. recently reported functionalized carboxylic acid based ionic

New Journal of Chemistry
Page 4 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
53
54
55
56
57
58
59
60
61
62
63
64
liquids for alcoholysis reaction.14 Yu et al. reported high glucose conversion using Bornsted
acidic ionic liquid as a catalyst and metal chlorides as a coꢀcatalyst to HMF.15 Amin et al.
reported the conversion of glucose to LA using dual Bronsted and Lewis acidic ionic liquid with
tetrachloroferrate as an anion.16 However, available literature on glucose conversion to LA still
lacks a detailed study of the effect of transition metal ions (chlorides, sulfates, and nitrates) as
coꢀcatalyst along with the ionic liquid as catalyst.
In this study, ionic liquids with varied functional groups (ILꢀSO3H, ILꢀCOOH, ILꢀOH) were
employed in catalytic conversion of glucose to LA. Moreover, the effect of metal salts (MSO4,
MCl, MNO3) in combination with the ionic liquids has been investigated. The effect of various
reaction conditions like time and temperature was also investigated on the glucose conversion to
LA. The recyclability of the ionic liquids was also investigated for the costꢀoptimization of the
process.
65 2. Materials and Methods
66
67
68
69
70
71
72
73
74
Glucose, fructose (99%), LA (99%), 5ꢀhydroxymethylfurfural (98%) (HMF), Formic acid (99%)
(FA) were purchased from Fischer Scientific, India. 1, 6ꢀAnhydroꢀßꢀDꢀglucose (99%), 5ꢀ
chlorovaleric acid (96%) was purchased from TCI chemicals, USA. 4ꢀchloro 1ꢀbutanol (85%), 1ꢀ
methylimidazole (99%), 1,4ꢀbutane sultone (99%) were purchased from Alfa Aesar, China.
Diethyl ether, FeCl3 (97%), CoCl2 (97%), NiCl2 (98%), CuCl2 (98%) and ZnCl2 (97%) were
purchased from Merck, India. FeSO4.7H2O (98%), CoSO4.7H2O (97%), NiSO4.6H2O (97%),
CuSO4.5H2O (99%) and ZnSO4.7H2O (95%) were purchased from, Sigma Aldrich and BDH
chemicals. Metal nitrates Fe(NO3)2.7H2O (99%), Co(NO3)2.7H2O (97%), Ni(NO3)2.6H2O (98%),
Cu(NO3)2.5H2O (99%) and Zn(NO3)2.7H2O (96%) were purchased from CDH chemicals. 1ꢀ

Page 5 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
75
76
77
78
79
80
Butylꢀ2, 3ꢀdimethylꢀimidazolium hexafluorophosphate (98%), 1ꢀButylꢀ3ꢀmethylꢀimidazolium
tetrafluoroborate (98%) were purchased from Merck, Germany.
2.1 Synthesis of functionalized ionic liquids
A series of Bronsted acid functionalized ionic liquids were synthesized as shown in Scheme 2
for the catalytic conversion of glucose to LA and their catalytic activity was compared with
literature reported ionic liquids.
81
82
Scheme 2. Chemical structures of the functionalized ionic liquids used in this study.
83
84
85
86
87
2.1.1 1-(4-sulfonic acid) butyl-3-methylimidazolium chloride
Sulfonic acid functionalized ionic liquid was synthesized according to the reported literature.17–22
1ꢀMethyl imidazole and 1, 4 butane sultone in 1: 1.2 equimolar amounts were mixed in a flask
with toluene as a solvent and stirred at 80 °C for 6 h to obtain the solid zwitterion. Zwitterionic
solid was washed three times (8 mL×3) with diethyl ether and dried under vacuum at room

New Journal of Chemistry
Page 6 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
88
89
90
91
92
93
temperature for 8 h. The resultant zwitterion was neutralized by adding equimolar amount of
hydrochloric acid with stirring at room temperature for 8ꢀ9 h. The yield of the synthesized ionic
1
liquid, ILꢀSO3H, was obtained to be 89%. H NMR: (400 MHz, D2O): δ (ppm) 1.67ꢀ1.74 (m,
2H), 1.95ꢀ2.02 (m, 2H), 2.88ꢀ2.92 (t, 2H), 3.86 (s, 3H), 4.19ꢀ4.23 (t, 2H), 7.41ꢀ7.47 (d, 2H), 8.71
(s, 1H). 13C NMR: (100 MHz; D2O): δ (ppm) 20.84, 28.02, 35.58, 48.80, 49.98, 122.06, 123.55,
135.88.
94
95
2.1.2 1-(5-Carboxypentyl)-3-methylimidazolium Chloride
Carboxylic acid functionalized ionic liquid was synthesized by stirring the mixture of equimolar
amount of 1ꢀmethylimidazole and 5ꢀchlorovaleric acid at 70 °C for 12 h. The resultant pale
yellow mixture was washed with ether (50 mL × 3). The yellow sticky product was dried under
vacuum at 40°C overnight. The yield of the synthesized ionic liquid, ILꢀCOOH, was found to be
96
97
98
1
99
92%. H NMR: (400 MHz; D2O): δ (ppm) 1.52ꢀ1.58 (m, 2H), 1.85ꢀ1.89 (m, 2H), 2.35ꢀ2.39 (t,
13
100
101
2H), 3.87 (s, 3H), 4.18ꢀ4.22 (t, 2H), 7.43ꢀ7.49 (d, 2H), 8.68(s, 1H). C NMR: (100 MHz, D2O):
δ (ppm) 20.98, 28.65, 35.60, 35.81, 49.09, 122.17, 123.60, 135.88, and 178.01.
102
103
104
105
106
107
108
109
2.1.3 Synthesis of 1-(4-Hydroxybutyl)-3-methylimidazolium Chloride
Ionic liquid containing OH as functional group was synthesized according to the reported
procedure by.23 1ꢀMethylimidazole and 4ꢀchloroꢀ1ꢀbutanol were mixed in 1:1.2 molar ratios and
stirred at 80 °C for 5 h. The desired ionic liquid was obtained in a viscous liquid form and the
unreacted materials were washed off by diethyl ether (8 mL × 3). The reminiscent diethyl ether
was removed under reduced pressure at room temperature. The yield of the obtained colorless
viscous ionic liquid, ILꢀOH, was found to be 89%. 1H NMR (400 MHz, D2O) δ (ppm) 1.59ꢀ1.62
(2H, m, CH2), 1.95ꢀ1.98 (m, 2H, CH2), 3.94 (s, 3H, N–CH3), 3.63ꢀ3.66 (t, 2H, N–CH2), 4.28 (dt,

Page 7 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
13
110
111
2H, CH2ꢀOH), 7.50, 7.56 [two singlets, 2H, C(4,5)–H], 8.74 [s, 1H, C(2)–H]. C NMR: (100
MHz, D2O): δ (ppm) 26.24, 28.00, 35.59, 49.29, 60.88, 122.21, 123.04 and 135.93.
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
2.1.4 Synthesis of [BMIM]Cl
Ionic liquid [BMIM]Cl was synthesized following the reported literature.24 1ꢀmethyl imidazole
and 1ꢀchlorobutane was stirred at 60 °C for overnight. The unreacted material was washed by
diethyl ether and acetonitrile. The diethyl ether was removed by reduced pressure followed by
heating at room temperature. The resultant ionic liquid was characterized using 1H NMR and 13C
1
NMR prior to use. H NMR (400 MHz, D2O) δ (ppm) 0.797 (3H, t, CH3), 1.18 (m, 2H, CH2),
1.707 (m, 2H, CH2), 3.75 (s, 3H, N–CH3), 4.03ꢀ4.08 (t, 2H, N–CH2), 4.60 (s, 2H, CH2ꢀOH),
7.29ꢀ7.34 [two singlets, 2H, C(4,5)–H], 8.584 [s, 1H, C(2)–H]. 13C NMR: (100 MHz, D2O): δ
(ppm) 12.81, 18.84, 31.32, 35.75, 49.28, 122.22, 123.49 and 135.57.
2.2 Catalytic activity tests in Glucose conversion to LA
Catalytic conversion of glucose to LA was carried out in a 25 mL autoclave by heating aqueous
reaction mixture in the temperature of 140ꢀ175 °C. In a typical reaction, 0.56 mmol glucose, 1.8
wt% metal salts and 1 g of aqueous solution of the ionic liquid were charged into the autoclave.
After the reaction, heating was terminated and reaction was quenched by cooling the autoclave in
an ice bath. During the separation of the product, viscosity of the reaction mixture was reduced
by adding some amount of the distilled water. Recycling of the ionic liquids was done as
described in the reported literature.4,25,26
2.3 Product analysis from HPLC
Quantitative analysis of the liquid sample was performed using high pressure liquid
chromatography (HPLC). The liquid samples were collected from the reactions aliquot and the
samples were filtered by using cellulose acetate membrane filters (0.2 µm) and analyzed by

New Journal of Chemistry
Page 8 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
133
134
135
136
137
138
139
140
141
142
143
144
Agilent HPLC using HPXꢀ87H column equipped with RID using 5mM sulfuric acid as the
mobile phase.
Conversion of the glucose was estimated according to the Eq. (1):
Conversion of glucose (%) = {(Initial no of moles of glucose − remaining moles of the glucose
after reaction) / Initial moles of the glucose added} * 100%
(1)
Yield of LA was estimated according to Eq. (2):
Yield of LA (%) = (Moles of LA obtained/ Initial moles of Glucose) * 100%
2.4 Determination of acidity of ionic liquids using UV–vis spectroscopy
(2)
The Bronsted acid strength of the synthesized ionic liquids was determined using Hammett
function. Solution of 4ꢀnitroaniline was used as indictor to trap the dissociated acidic proton of
ionic liquids in water using literature reported procedure.24,27–32 The acidity function (Ho) value
was estimated according to Eq. (3):
ꢇ ꢉ
ꢈ
145
ꢀꢁ = ꢂꢃ (ꢄ)ꢅꢆ + log(ꢇꢈꢊꢉ
)
(3)
ꢋ
146
147
148
149
Where pK(I)aq is the pKa value of the indicator, and [I] and [IH+] are the molar concentrations of
unprotonated and protonated forms of the indicator in the solvent, respectively. The absorbance
of the probe (4ꢀnitroaniline solution) and probe in presence of different concentrations of ionic
liquids was recorded at 380 nm using HALO DBꢀ20 UVꢀvisible double beam spectrophotometer.
150 3. Results and discussion
151
152
153
154
155
3.1 Screening of ionic liquids for glucose conversion to LA
The effect of different functional group on the conversion of glucose and selectivity of LA was
studied at 155 °C for 5 h as shown in the Figure 2. From the Figure 2, it is evident that Bronsted
acid functionalized ionic liquid (ILꢀSO3H, ILꢀCOOH, ILꢀOH) showed higher catalytic
conversion of glucose to LA as compared to the nonꢀfunctionalized ionic liquids. Among

Page 9 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
156
157
158
Bronsted acidic ionic liquids, ILꢀSO3H showed maximum conversion which can be attributed to
its highest acidity as shown in Table 1 and Figure 1, and possess maximum Bronsted acidity
with minimum value of Hammett function (H0).
1.0
25 mM
50 mM
60 mM
0.8
100 mM
200 mM
300 mM
400 mM
0.6
0.4
0.2
0.0
250
300
350
400
450
500
550
Wavelength (nm)
159
160
Figure 1. Absorption spectra of 4ꢀnitroaniline in presence of various concentration of ILꢀSO3H
161
in H2O.
162
163
164
165
166
Further, the highly acidic proton of ILꢀSO3H and chloro anion create polar environment through
hydrogen bonding that is required for glucose conversion to LA.33 Among nonꢀfunctionalized
ionic liquids [BMIM]Cl gave higher conversion of glucose but low selectivity of the LA due to
the absence of the Bronsted acidity. The presence of nonꢀinteracting hydrophobic cation in
−
−
[BMIM]Cl results in free chloro groups to be more reactive than the BF4 and PF6 anion.

New Journal of Chemistry
Page 10 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
167
Table 1. The Hammett acidity function (Ho) values of all Bronsted acidic ionic liquids in water.
ILs
Amax
1
[I](%)
100
[IH+]%
0
[Ho]
ꢀ
None
0.83
0.84
0.86
93.29
94.93
97.13
6.71
5.07
2.87
1.97
2.12
2.39
IL-SO3H
IL-COOH
IL-OH
168
169
170
171
172
From the Figure 2, the order of activity is observed to be ILꢀSO3H>ILꢀCOOH>ILꢀ
OH>[BMIM]Cl>1ꢀ[Bꢀ2,3ꢀdiIM]PF6>[BMIM]BF4>Blank. This trend can be explained by the
Hammett function of the acidic ionic liquid and reactivity of the anion of nonꢀfunctionalized
ionic liquid. Thus, it can be concluded that ILꢀSO3H having higher Bronsted acidity results in
almost 100% conversion of glucose with the yield of LA as high as 46.60%.

Page 11 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
% Glucose Conversion
100
80
60
40
20
0
% LA Yield
% LA Selectivity
173
174
Figure 2. Effect of different ionic liquids on catalytic conversion of glucose. Reaction
175
conditions: 100 mg glucose, 400 mg ionic liquid, 0.6 mL water, T=155 °C, t= 5 h.
176
177
178
179
180
181
182
3.2 Effect of temperature on LA yield
The effects of reaction parameters were studied using ILꢀSO3H as the catalyst to determine the
optimum reaction conditions for the glucose conversion to LA. The reactions were carried out in
a temperature range of 140ꢀ175 °C. From Figure 3, it is evident that 155 °C reaction temperature
and reaction time of 5 h are optimum reaction conditions for glucose conversion to LA. The
maximum glucose conversion and LA yield achieved are 99.90% and 46.60% respectively at 155
°C and 5 h. Figure 3 illustrates the significant effect of temperature and time on the yield of LA.

New Journal of Chemistry
Page 12 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
183
184
185
186
187
188
189
At lower reaction temperature of 140 °C, the maximum glucose conversion and yield of LA were
obtained to be 99% and 43%, respectively. This can be attributed to the formation of HMF at
lower temperature rather than rehydrated product LA that requires higher reaction temperature.
Whereas, at higher temperatures of 165 °C and 175 °C the yield of LA further decreased due the
formation of humins and other side products.34,30 Hence, it can be concluded that 155 °C is the
optimum temperature for glucose conversion to LA since at lower temperatures HMF resist to
rehydrate to LA and at higher temperature side reactions occur.
50
140oC
155oC
165oC
45
175oC
40
35
30
25
20
1
2
3
4
5
6
Time (h)
190
191
Figure 3. Effect of reaction temperature and reaction time on conversion of glucose to LA using
ILꢀSO3H as the catalyst. Reaction conditions: 100 mg glucose, 400 mg ionic liquid, 0.6 mL
water.
192
193

Page 13 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
3.3 Effect of transition metal chlorides as co-catalysts on LA yield
A series of reactions were performed in order to gain a better perspective of the effect of the
metal chlorides as a coꢀcatalyst with the ionic liquid, ILꢀSO3H. Around 1.8 wt% metal chloride
salts were added in the reaction mixture as coꢀcatalyst and the reaction was conducted for 5 h at
155 °C reaction temperature. Table 2 summarizes the performance of the ILꢀSO3H with different
transition metal chlorides as coꢀcatalyst in the conversion of glucose into LA. From Table 2, it is
clear that in absence of the metal chlorides, 100% glucose conversion and 46.60% yield of the
LA was obtained at 155 °C reaction temperature within 5 h reaction time. Moreover, in presence
of only water, around 68.52% glucose conversion was obtained with only 2.76% yield of
levulinic acid (LA). However, in presence of catalytic amounts of metal chlorides like FeCl3,
CoCl2, NiCl2, CuCl2 and ZnCl2, higher catalytic activity was obtained as compared to ILꢀSO3H.
In case of NiCl2, the maximum LA yield of 49.65% was obtained with LA selectivity as high as
49.68%. However, not all metal chlorides were effective coꢀcatalyst. The conversion of glucose
and yield of LA using these metal chlorides was found in the order: Water<FeCl3<ILꢀ
SO3H<CuCl2<CoCl2<ZnCl2<NiCl2 under the same reaction conditions. While the selectivity to
LA followed the order: Water<FeCl2<ILꢀSO3H<CuCl2<CoCl2<ZnCl2<NiCl2. Based on the
results shown in Table 2, it is evident that ILꢀSO3H zwitterionic form is highly stable and it
shows acidity via in situ HCl. This is evident from the experimentally obtained incremented
yield of LA (46.60%) at 155 °C within 5 h reaction time. However, addition of similar types of
the metal chloride salts cannot affect significant changes to the LA yield except in the case of
NiCl2. These results further imply that nickel acts as an active metal as a coꢀcatalyst and hence,
plays important role in glucose conversion and LA yield as compared to other transition metals
used in this study. Moreover, in addition to the in situ formation of HCl, metal chlorides in

New Journal of Chemistry
Page 14 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
aqueous solution similarly produce metal hydrate complexes. Hence, regeneration possibility of
the similar acidity during aqueous phase reaction mixture causes the less affectivity of the metal
chlorides in the reaction system. A plausible reaction mechanism is proposed based on the
catalytic activity results as shown in Figure 4 to summarize all the possible observations and
experimental outcomes in order to explain the effect of these metal chlorides (Co, Ni, Cu and Zn)
as coꢀcatalysts in combination with Bronsted acidic ionic liquids.31 The metal salts in the
complex form [MClx(H2O)n](xꢀ2)− bind with the –OH groups of the glucose molecule through the
hydrogen bonding. Similar mechanism is followed in case of FeCl3 as the coꢀcatalyst in the
complex form [MClx(H2O)n)](xꢀ1)ꢀ. The hydrated metal salt complex promotes the rapid
conversion of the αꢀanomers of glucose to the βꢀanomers through hydrogen bonding between Clꢀ
atom of the complex and –OH group of glucose. However, the extent of hydrogen bonding
capability of Clꢀatom is not high enough to alter the process to a greater extent. Hence, metal
halides were also found to be less active in aqueous phase, overall outcomes of the reaction were
also mentioned in earlier literature reports.35
Table 2. Effect of metal chlorides in conversion of Glucose and yield of LA.
Glucose Conversion
Catalysts
LA Yield (%)
2.76
LA Selectivity (%)
(%)
Water
4.02
68.52
ILꢀSO3H
46.60
46.64
37.29
47.35
49.68
47.10
48.28
99.90
99.86
99.92
99.93
99.94
99.99
ILꢀSO3H + FeCl3
ILꢀSO3H + CoCl2
ILꢀSO3H + NiCl2
ILꢀSO3H + CuCl2
ILꢀSO3H + ZnCl2
37.24
47.32
49.65
47.08
48.28
232
Reaction conditions: 100 mg glucose, 400 mg ionic liquid, 0.6 mL water, T=155 °C; t= 5 h; amount of MClx used= 1.8 wt%.

Page 15 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
3.4 Effect of the transition metal sulfates as co-catalysts on LA yield
Furthermore, to investigate the effect of metal sulfates as coꢀcatalyst, along with ILꢀSO3H on the
conversion of glucose and yield of LA, a series of the transition metal sulfate salts were added
into the reaction system to carry out the catalytic reactions at a reaction temperature of 155 °C
for 5 h. Several combinations of cations and anions in the reaction system showed significant
effects on LA production as shown in Table 3. The conversion of glucose followed the order:
Water<CoSO4.7H2O<FeSO4.7H2O<CuSO4.5H2O<ILꢀSO3H<ZnSO4.7H2O<NiSO4.6H2O. While
the selectivity to LA followed the order: Water<CoSO4.7H2O<FeSO4.7H2O<CuSO4.5H2O<ILꢀ
SO3H<ZnSO4.7H2O<NiSO4.6H2O. The catalytic activity trends of the metal sulfates were in the
following order CoSO4.7H2O˂FeSO4.7H2O˂CuSO4.5H2O˂ZnSO4.7H2O˂NiSO4.6H2O. The
yield of LA varied from 40.37% to 56.33% in the presence of these metal sulfates as coꢀcatalysts
as compared to only ILꢀSO3H catalyzed reactions (46.60%). The first three metal salts show
negative synergy effect on the yield of LA. Among the metal sulfates, the ILꢀSO3HꢀNiSO4.6H2O
system showed highest synergistic effect in terms of LA yield.
Table 3. Effect of metal sulfates in conversion of Glucose and yield of LA.
Glucose conversion
Catalysts
LA yield (mol %)
2.76
LA Selectivity (%)
(mol%)
Water
4.02
68.52
ILꢀSO3H
46.60
46.64
41.25
40.38
56.37
41.54
52.35
99.90
99.61
99.97
99.92
99.77
99.90
ILꢀSO3H + FeSO4.7H2O
ILꢀSO3H + CoSO4.7H2O
ILꢀSO3H + NiSO4.6H2O
ILꢀSO3H + CuSO4.5H2O
ILꢀSO3H + ZnSO4.7H2O
41.09
40.37
56.33
41.45
52.30
248
249
Reaction conditions: 100 mg glucose, 400 mg ionic liquid, 0.6 mL water, T=155 °C; t= 5 h, amount of MSO4.nH2O used= 1.8
wt%.

New Journal of Chemistry
Page 16 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
250
251
252
253
254
255
256
257
258
259
Furthermore, as is evident from Table 3, the effect of metal sulfates as coꢀcatalyst more
predominant in this reaction as compared to the metal chlorides (as shown in Table 2). The
higher activity of the sulfates can be attributed to the reduced side product formation in this
reaction. Moreover, these observations indicate that the Bronsted acidity alone is not the sole
factor affecting the glucose conversion to LA. The anions play significant roles in the glucose
dehydration and rehydration process to yield LA as per the plausible mechanism shown in
Figure 4. The sulfate salts in the complex form [M(SO4)x(H2O)n](2xꢀ2)− coꢀordinate with the –OH
groups of the αꢀanomers of glucose by forming stronger hydrogen bonds than the chloride salts.
Consequently, metal sulfates play significant role in the rapid conversion of the αꢀanomers to βꢀ
anomers to facilitate the dehydration process.

Page 17 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
260
261
Figure 4. Plausible reaction mechanism of glucose conversion to LA and formic acid in presence
of metal salts.
262
263
264
265
266
267
268
3.5 Effect of transition metal nitrates as co-catalysts on LA yield
To investigate the role of metal nitrate salts as coꢀcatalyst with ILꢀSO3H, a series of reactions
were performed at a reaction temperature of 155 °C for 5 h. The addition of the transition metal
nitrates of Fe, Co, Ni, Cu and Zn with ILꢀSO3H, resulted in negative synergistic effect on the
yield of LA as shown in Table 4. The negative synergistic effect for the metal nitrates can be
attributed to the formation of more side products via multiple side reactions. The coꢀcatalytic

New Journal of Chemistry
Page 18 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
effect of the Cu, Fe, Co and Zn metal nitrates effectively decreased the yield of the LA due to the
formation of the other side products during the reaction which is unfavorable for the formation of
the LA. The decreased yield during the LA synthesis from the glucose can be attributed to the
formation of soluble polymers and insoluble humins, darkꢀcolored tarry solids. The maximum
yield of the LA drop from 47.16% in case of Ni to 37.29% in case of Fe. The conversion of
glucose followed the order: Water <CuNO3.5H2O <FeNO3.7H2O <CoNO3.7H2O <ZnNO3.7H2O
<ILꢀSO3H <NiNO3.6H2O. While the selectivity of LA followed the order: Water <CuNO3.5H2O
<FeNO3.7H2O <CoNO3.7H2O <ZnNO3.7H2O <ILꢀSO3H <NiNO3.6H2O. The transition metal
nitrate salts in the form [M(NO3)x(H2O)n](xꢀ2)− bind less weakly with the –OH groups of the αꢀ
anomers of glucose. Hence, the rate of their conversion to the βꢀanomers decreases and
consequently, the conversion of glucose to LA also decreases. Moreover, nitrates are inherently
weaker ligands to form stable coordination bond with the αꢀanomer. In general, nitrates possess
strong oxidizing property and can oxidize glucose to other insoluble products, which is
effectively unfavorable for the conversion of glucose into LA.26 The obtained glucose conversion
in case of nitrates were found to be comparable with the metal chlorides and sulfates with a
distinct change in yield of LA. This indicates that the converted glucose formed more side
products other than LA. This is also evident from the decreasing glucose conversion and LA
yield as shown in Table 4.
Table 4. Effect of metal nitrates in conversion of Glucose and yield of LA.
Glucose Conversion
Catalysts
LA Yield (Mol%)
LA Selectivity (%)
(Mol%)
Water
2.76
46.60
37.29
4.02
46.64
40.15
68.52
ILꢀSO3H
99.90
92.87
ILꢀSO3H + FeNO3.7H2O

Page 19 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
ILꢀSO3H + CoNO3.7H2O
ILꢀSO3H + NiNO3.6H2O
ILꢀSO3H + CuNO3.5H2O
ILꢀSO3H + ZnNO3.7H2O
41.10
41.17
47.21
38.56
44.31
99.82
99.89
98.49
98.18
47.16
37.98
43.51
288
289
Reaction conditions: amount of MClx used= 1.8 wt%; T=155 °C; t= 5 h; amount of MNO3.nH2O used= 1.8 wt%.
3.6 Reusability of catalyst
290
291
292
293
294
295
296
297
298
299
300
301
302
Reusability of the ionic liquid catalyst was investigated in the glucose conversion to LA with ILꢀ
SO3H as well as with ILꢀSO3H with Ni metal salt. Ionic liquids were regenerated following the
earlier reported literature.4,10,26 After completion of the reaction, the reaction mixture was diluted
with 2 mL deionized water to reduce the viscosity. The products were extracted using ethyl
acetate and the rest of the solution contained ionic liquidꢀwater or ionic liquidꢀNi metal salt
mixture. Water was removed from the ionic liquid or ionic liquidꢀNi metal salt mixture by drying
overnight under reduced pressure (0.01 Torr) at 120 °C. The recovered ionic liquids or ionic
liquidꢀNi metal salt mixtures were subjected to further catalytic runs and the results are
summarized in Table 5. Glucose conversion and yield of LA were almost retained till the first
three recycle reactions. The decrease in recyclability in the further recycle experiments can be
attributed to the increasing water content as well as side products accumulating in each step of
the reaction, which required harsh recycling conditions.
Table 5. Recyclability of ILꢀSO3H and ILꢀSO3H with Ni metal salt.
No. of
Runs
LA Yield a
(Mol%)
LA
Glucose
LA Yield b
(Mol%)
LA
Glucose
Selectivity a Conversion a
Selectivity b Conversion b
(%)
(Mol%)
(%)
(Mol%)
Fresh run
Recycle 1
46.60
42.40
46.64
99.90
56.33
51.46
56.37
99.92
44.25
95.80
55.17
93.27

New Journal of Chemistry
Page 20 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
Recycle 2
Recycle 3
39.60
37.30
46.37
46.33
85.40
80.50
47.86
43.92
57.70
55.82
82.94
78.67
303
304
305
Reaction conditions: Reaction temperature=155 °C; reaction time= 5 h.
a
b
LA yield and selectivity and conversion of glucose in presence of only ILꢀSO3H; LA yield and selectivity and conversion of
glucose in presence of only ILꢀSO3H with Ni metal salt.
306 4. Conclusions
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
In this study, glucose conversion to LA was investigated using multifunctional ionic liquids
containing ꢀOH, ꢀCOOH and ꢀSO3H groups. The ionic liquids were synthesized in the laboratory
and characterized using spectroscopic techniques like 1H NMR and 13C NMR. From the detailed
catalytic activity study, ꢀSO3H functionalized ionic liquid was found to be the most efficient
catalyst in terms of LA selectivity and high conversion of glucose. The parameters like reaction
temperature and reaction time were optimized and maximum LA yield of 46.60% was obtained
using ILꢀSO3H at 155 °C temperature within 5 h. From the recyclability experiments, ILꢀSO3H
and combination of ILꢀSO3H with Ni metal salt were found to retain their catalytic activity upto
3 recycles. Furthermore, to investigate the effect of transition metal salts as coꢀcatalysts along
with the ILꢀSO3H, a series of transition metal chlorides, sulfates and nitrates were added and the
reactions were carried out at optimum reaction conditions. Metal sulfates showed predominant
synergistic effect on the catalytic activity in terms of the LA yield as compared to the chloride
and nitrate salts. Among these catalyst and coꢀcatalyst combinations, ILꢀSO3HꢀNiSO4 showed
highest catalytic efficiency with highest LA yield of 56.33% at 155 °C within 5 h reaction time
with 56.37% LA selectivity. This study is highly beneficial for the development of an efficient
catalytic system for glucose conversion into high value platform chemical.

Page 21 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
323 Acknowledgements
324
325
326
327
328
329
Komal Kumar and Firdaus Parveen thanks University Grants Commission (UGC), India, for a
research fellowship. Tanmoy Patra thanks the Council of Scientific and Industrial Research
(CSIR) for research fellowship. Dr. Sreedevi Upadhyayula thanks Indian Institute of Technology
Delhi for the research grants. The authors are also thankful to NRF (Nanoscale Research
Facility) for providing High pressure liquid chromatography (HPLC) for the detection of LA
yield and conversion of glucose.
330 References
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
(1)
(2)
Kumar, V. B.; Pulidindi, I. N.; Gedanken, A. Synergistic catalytic effect of the ZnBr2 –
HCl system for levulinic acid production using microwave irradiation. RSC Adv. 2015, 5
(15), 11043ꢀ11048.
Yang, F.; Fu, J.; Mo, J.; Lu, X. Synergy of Lewis and Brønsted acids on catalytic
hydrothermal decomposition of hexose to levulinic acid. Energy and Fuels 2013, 27 (11),
6973ꢀ6978.
(3)
(4)
(5)
(6)
Jäger, G.; Büchs, J. Biocatalytic conversion of lignocellulose to platform chemicals.
Biotechnology Journal. 2012, 7 (9), 1122ꢀ1136.
Fu, J.; Xu, X.; Lu, X.; Lu, X. Hydrothermal decomposition of carbohydrates to Levulinic
acid with catalysis by ionic liquids. Ind. Eng. Chem. Res. 2016, 55 (42), 11044ꢀ11051.
Zhang, Z. Synthesis ofꢁγꢀValerolactone from carbohydrates and its applications.
ChemSusChem 2016, 9 (2), 156ꢀ171.
Mukherjee, A.; Dumont, M.ꢀJ.; Raghavan, V. Review: Sustainable production of
Hydroxymethylfurfural and levulinic acidꢁ: Challenges and Opportunities. Biomass and
Bioenergy, 2015, 72, 143.

New Journal of Chemistry
Page 22 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
(7)
(8)
Chun, C.; Xiaojian MA.; Peilin, C.; Kinetics of Levulinic acid formation from glucose
decomposition at high temperature. Chinese J. Chem. Eng. 2006, 14 (5), 708.
Cao, X.; Peng, X.; Sun, S.; Zhong, L.; Chen, W.; Wang, S.; Sun, R.ꢀC. Hydrothermal
conversion of xylose, glucose, and cellulose under the catalysis of transition metal
sulfates. Carbohydr. Polym. 2015, 118, 44.
(9)
Li, H.; Zhang, Q.; Liu, X.; Chang, F.; Zhang, Y.; Xue, W.; Yang, S. Immobilizing Cr3+
with SO3Hꢀfunctionalized solid polymeric ionic liquids as efficient and reusable catalysts
for selective transformation of carbohydrates into 5ꢀHydroxymethylfurfural. Bioresour.
Technol. 2013, 144, 21.
(10) Shen, Y.; Sun, J.ꢀK.; Yi, Y.ꢀX.; Wang, B.; Xu, F.; Sun, R.ꢀC.; Oneꢀpot Synthesis of
Levulinic acid from cellulose in ionic liquids. Bioresour. Technol. 2015, 192, 812.
(11) Chen, F. F.; Huang, K.; Zhou, Y.; Tian, Z.ꢀQ.; Zhu, X.; Tao, D.ꢀJ.; Jiang, D.; Dai, S.
MultiꢀMolar Absorption of CO2 by the Activation of Carboxylate Groups in Amino Acid
Ionic Liquids. Angew. Chemie Int. Ed. 2016, 55 (25), 7166.
(12) Tao, D. J.; Chen, F. F.; Tian, Z. Q.; Huang, K.; Mahurin, S. M.; Jiang, D. E.; Dai, S.
Highly Efficient Carbon Monoxide Capture by CarbanionꢀFunctionalized Ionic Liquids
through CꢀSite Interactions. Angew. Chemie Int. Ed. 2017, 56 (24), 6843.
(13) Ouyang, F.; Wang, Z. Z.; Zhou, Y.; Cheng, Z.; Lu, Z. H.; Yang, Z.; Tao, D. J. Highly
Efficient and Selective Synthesis of Dibutyl Carbonate via the Synergistic Dual Activation
Catalysis of Tetraethylammonium Prolinate Ionic Liquids. Appl. Catal. A Gen. 2015, 492,
177.
(14) Tao, D. J.; Ouyang, F.; Li, Z. M.; Hu, N.; Yang, Z.; Chen, X. S. Synthesis of
Tetrabutylphosphonium Carboxylate Ionic Liquids and Its Catalytic Activities for the

Page 23 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
Alcoholysis Reaction of Propylene Oxide. Ind. Eng. Chem. Res. 2013, 52 (48), 17111.
(15) Yu, I. K. M.; Tsang, D. C. W. Conversion of biomass to hydroxymethylfurfural: A review
of catalytic systems and underlying mechanisms. Bioresour. Technol. 2017, 238, 716.
(16) Ramli, N. A. S.; Amin, N. A. S. A New functionalized ionic liquid for efficient glucose
conversion to 5ꢀHydroxymethyl furfural and Levulinic acid. J. Mol. Catal. A Chem. 2015,
407, 113.
(17) Cole, A. C.; Jensen, J. L.; Ntai, I.; Tran, K. L. T.; Weaver, K. J.; Forbes, D. C.; Davis, J.
H. Novel Bronsted Acidic ionic liquids and their use as dual solventꢀcatalysts. J. Am.
Chem. Soc. 2002, 124 (21), 5962.
(18) Gui, J.; Ban, H.; Cong, X.; Zhang, X.; Hu, Z.; Sun, Z. Selective alkylation of phenol with
tertꢀbutyl alcohol catalyzed by Brönsted acidic imidazolium salts. J. Mol. Catal. A Chem.
2005, 225 (1), 27.
(19) Gui, J.; Cong, X.; Liu, D.; Zhang, X.; Hu, Z.; Sun, Z. Novel Brønsted acidic ionic liquid
as efficient and reusable catalyst system for esterification. Catal. Commun. 2004, 5 (9),
473.
(20) FragaꢀDubreuil, J.; Bourahla, K.; Rahmouni, M.; Bazureau, J. P.; Hamelin, J. Catalysed
esterifications in room temperature ionic liquids with acidic counteranion as recyclable
reaction media. Catal. Commun. 2002, 3 (5), 185.
(21) Kondamudi, K.; Elavarasan, P.; Dyson, P. J.; Upadhyayula, S. Alkylation of pꢀcresol with
tertꢀbutyl alcohol using benign Bronsted acidic ionic liquid catalyst. J. Mol. Catal. A
Chem. 2010, 321 (1–2), 34.
(22) Patra, T.; Ahamad, S.; Upadhyayula, S. Highly efficient alkylation of phenol with tertꢀ
butyl alcohol using environmentally benign Bronsted acidic ionic liquids. Appl. Catal. A

New Journal of Chemistry
Page 24 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
Gen. 2015, 506, 228.
(23) Mirzai, M.; Valizadeh, H. Microwaveꢀpromoted synthesis of 3,4ꢀDihydropyrimidinꢀ
2(1H)ꢀ(Thio)ones using ILꢀONO as recyclable base catalyst under solventꢀfree conditions.
Synth. Commun. 2012, 42 (9), 1268.
(24) Parveen, F.; Patra, T.; Upadhyayula, S. Hydrolysis of microcrystalline cellulose using
functionalized Bronsted acidic ionic liquids – A comparative study. Carbohydr. Polym.
2016, 135, 280.
(25) Shen, Y.; Sun, J.ꢀK.; Yi, Y.ꢀX.; Wang, B.; Xu, F.; Sun, R.ꢀC. Oneꢀpot synthesis of
Levulinic acid from cellulose in ionic liquids. Bioresour. Technol. 2015, 192, 812.
(26) Tao, F.; Song, H.; Chou, L. Efficient Conversion of Cellulose into Furans Catalyzed by
Metal Ions in Ionic Liquids. J. Mol. Catal. A Chem. 2012, 357, 11.
(27) Smith, G. P.; Dworkin, A. S.; Pagni, R. M.; Zingg, S. P. Bronsted superacidity of HC1 in
a liquid chloroaluminate A1C13ꢀ1ꢀEthylꢀ3ꢀMethylꢀ1HꢀImidazolium chloride. J. Am.
Chem. Soc. 1989, 111, 525.
(28) King, D.; Mantz, R.; Osteryoung, R.; Carolina, N.; June, R. V.; Re, V.; Recei, M.; August,
V. Acidity of HCl in neutral buffered chloroaluminate molten salts. J. Am. Chem. Soc.
1996, 118 (47), 11933ꢀ11938.
(29) Thomazeau, C.; OlivierꢀBourbigou, H.; Magna, L.; Luts, S.; Gilbert, B. Determination of
an acidic scale in room temperature ionic liquids. J. Am. Chem. Soc. 2003, 125 (18), 5264ꢀ
5265.
(30) Kondamudi, K.; Elavarasan, P.; Dyson, P. J.; Upadhyayula, S. Alkylation of PꢀCresol with
TertꢀButyl Alcohol Using Benign Bronsted Acidic Ionic Liquid Catalyst. J. Mol. Catal. A
Chem. 2010, 321, 34.

Page 25 of 26
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ03146G
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
(31) Duan, Z.; Gu, Y.; Deng, Y. Green and Moistureꢀstable lewis acidic ionic liquids (Choline
chloride.xZnCl2) catalyzed protection of carbonyls at room temperature under solventꢀfree
conditions. Catal. Commun. 2006, 7 (9), 651.
(32) Kumbar, S. M.; Shanbhag, G. V.; Lefebvre, F.; Halligudi, S. B. Heteropoly acid supported
on titania as solid acid catalyst in alkylation of pꢀCresol with tertꢀbutanol. J. Mol. Catal. A
Chem. 2006, 256 (1–2), 324ꢀ334.
(33) Li, J.; Li, J.; Zhang, D.; Liu, C. Theoretical elucidation of glucose dehydration to 5ꢀ
Hydroxymethylfurfural catalyzed by a SO3Hꢀfunctionalized ionic liquid. J. Phys. Chem. B
2015, 119 (42), 13398ꢀ133406.
(34) Bayu, A.; Guan, G.; Karnjanakom, S.; Hao, X.; Kusakabe, K.; Abudula, A. Catalytic
synthesis of levulinic acid and formic acid from glucose in choline chloride aqueous
solution. ChemistrySelect 2016, 1 (2), 180ꢀ188.
(35) PaganꢀTorres, Y. J.; Wang, T.; Gallo, J. M. R.; Shanks, B. H.; Dumesic, J. A. Production
of 5ꢀHydroxymethylfurfural from glucose using a combination of Lewis and Bronsted
acid catalysts in water in a biphasic reactor with an alkylphenol solvent. ACS Catal. 2012,
2 (6), 930ꢀ934.

New Journal of Chemistry
Page 26 of 26
View Article Online
DOI: 10.1039/C7NJ03146G
Table of Contents
Efficient catalytic system comprised of Bronsted acidic ionic and Lewis acidic metal salts for
hydrothermal glucose conversion to platform chemicals