A divergent approach for the synthesis of (hydroxymethyl)furfural (HMF) from spent aromatic biomass-derived (chloromethyl)furfural (CMF) as a renewable feedstock

Article abstract of DOI:10.1039/d0ra09310f

Extraction of commercial essential oil from several aromatic species belonging to the genus Cymbopogon results in the accumulation of huge spent aromatic waste which does not have high value application; instead, the majority is burned or disposed of to vacate fields. Open burning of spent aromatic biomass causes deterioration of the surrounding air quality. Therefore, a new protocol has been developed for chemical processing of spent biomass to obtain 5-(chloromethyl)furfural (CMF) with high selectivity (～80%) and yields (～26 wt% or ～76 mol% with respect to pre-treated biomass) via refluxing in aqueous HCl in the presence of NaCl as a cheap catalyst. No black tar formation and gasification were observed in the processing of the spent aromatic biomass. Spent aromatic waste-derived CMF was further converted to 5-(hydroxymethyl)furfural (HMF) in good yields by a novel one pot method using iodosylbenzene (PhIO) as a reagent under mild reaction conditions.

Full text of DOI:10.1039/d0ra09310f

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A divergent approach for the synthesis of
(
hydroxymethyl)furfural (HMF) from spent aromatic
biomass-derived (chloromethyl)furfural (CMF) as
a renewable feedstock†
Cite this: RSC Adv., 2020, 10, 45081
Mangat Singh, Nishant Pandey and Bhuwan B. Mishra *a
ab
ab
Extraction of commercial essential oil from several aromatic species belonging to the genus Cymbopogon
results in the accumulation of huge spent aromatic waste which does not have high value application;
instead, the majority is burned or disposed of to vacate fields. Open burning of spent aromatic biomass
causes deterioration of the surrounding air quality. Therefore, a new protocol has been developed for
chemical processing of spent biomass to obtain 5-(chloromethyl)furfural (CMF) with high selectivity
ꢀ80%) and yields (ꢀ26 wt% or ꢀ76 mol% with respect to pre-treated biomass) via refluxing in aqueous
HCl in the presence of NaCl as a cheap catalyst. No black tar formation and gasification were observed
in the processing of the spent aromatic biomass. Spent aromatic waste-derived CMF was further
converted to 5-(hydroxymethyl)furfural (HMF) in good yields by a novel one pot method using
iodosylbenzene (PhIO) as a reagent under mild reaction conditions.
(
Received 2nd November 2020
Accepted 4th December 2020
DOI: 10.1039/d0ra09310f
rsc.li/rsc-advances
etc.), volatile organic compounds (e.g., monoterpenes, sesqui-
terpenes, phenols, oxides, esters, aldehydes etc.), precursors of
Introduction
There are about 400 plant species being cultivated worldwide on
a large commercial scale for the production of essential oils. carbon (BC).
3
O and aerosols, especially organic carbon (OC) and black
2
Among these, lemongrass (Cymbopogon exuosus), citronella
Spent aromatic biomass contains varying composition of
grass (C. winterianus) and palmarosa (C. martini) are economi- hemicellulose, cellulose, and lignin depending on the source,
cally most popular in the tropical and subtropical regions of species, and region of the cultivation. Besides having a high
Asia, Africa and America. Extraction of essential oil from these caloric value, the high cellulose (35–40%) and hemicellulose
aromatic crops results in the accumulation of huge spent (25–30%) content makes it a suitable biomass for bioenergy
aromatic waste as a by-product. Global industrial processing of production. Terpenoids obtained from the aromatic crops have
lemongrass alone accounts for approximately 30 000 000 tons been found economic and fungible with the existing liquid fuels
1
3
per annum of aromatic waste. India, being a worldwide leader due to low temperature operable properties. Ethanol produc-
of citronella and mentha essential oil, generates approximately tion from spent aromatic biomass has also been prospected,
ꢀ
6.0 million tons per annum of spent aromatic waste. This however, residual volatiles e.g. citral, geraniol, limonoids, etc.,
most abundant and underutilized biomass does not have high in the spent waste may inhibit the growth of Saccharomyces
4
value application, hence the majority is burned or disposed of cerevisiae during microbial fermentation in bioreneries. The
to vacate elds. Open burning of spent aromatic biomass causes biomass has been also investigated for supply of nutrients to
5
deterioration of the surrounding air quality due to release the other crops, nutrient recycling for fertilizer economy, and
a substantial amount of pollutants into the atmosphere such as for the production of high value chemicals, e.g., xylose, levulinic
6
trace gases (e.g., carbon dioxide, carbon monoxide, methane acid, lignin, etc., by the chemical processing.
Synthesis of 5-(hydroxymethyl)furfural (HMF) and its deriv-
atives have recently been advanced as a highly promising plat-
a
Center of Innovative and Applied Bioprocessing (CIAB), Sector 81 (Knowledge City),
form compounds for easy access to a range of renewable
S.A.S. Nagar, Mohali-140306, Punjab, India. E-mail: bhuwan@ciab.res.in; Tel:
7
chemicals and materials. However, the HMF has only been
+
91-172-5221541
produced from fructose at pilot scales, and to date no scalable
approach for its production from raw biomass has been re-
b
Department of Chemistry, Faculty of Science, Panjab University, Chandigarh-160014,
India
8
ported. Frequent water solubility, high boiling point, and
†
Electronic supplementary information (ESI) available: FT-IR, EDS and XRD
spectra of isolated lignin, HPLC chromatograms of biomass hydrolysate, GC-MS sensitivity to the acidic conditions impose difficulties in large
chromatograms of CMF and HMF, and NMR spectrum of CMF. See DOI:
scale production of HMF from carbohydrates. Therefore,
1
0.1039/d0ra09310f
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a potentially disruptive innovation in the arena of renewable (HMF) in good yields is not realized so far under mild one pot
chemicals has recently been introduced in the form of the HMF reaction condition using hypervalent iodine reagents. There-
analog, 5-(chloromethyl)furfural (CMF) which unlike HMF, can fore, we envisioned exploring the feasibility of utilizing the
be obtained in high yield and purity from glucose or even oxidation potential of iodosylbenzene (PhIO) in oxidation of
directly from the cellulosic biomass (Table 1). CMF being biomass derived CMF to afford HMF in good yields.
hydrophobic in nature, can readily be isolated from reaction
This manuscript describes an efficacious protocol for
media, and converted further into different compounds, e.g., production of CMF directly from spent aromatic biomass via
2
,5-dimethylfuran (DMF), 5-ethoxymethylfurfural (EMF), HMF, chemical processing in a biphasic reaction media consisting of
9–12
etc., due to the interesting reactive chemistry.
Convention- concentrated HCl and chloroform in the presence of NaCl using
ally, CMF is prepared by the treatment of HMF or cellulose with a sealed pressure glass reactor. No such attempt has been made
dry hydrogen halide, wherein, the hydroxyl group in HMF earlier for waste to wealth recovery of value added products
1
3–15
undergoes substitution by a halogen atom.
Other methods from spent aromatic biomass, and the methodology appears to
11,16
involve, treatment of carbohydrate with HCl–LiCl,
deep be economically attractive due to high selectivity in product
PO in formation with minimal by products, short reaction time, and
under biphasic condition, and metal use of NaCl as a cheap catalyst under mild reaction condition.
chlorides (such as CrCl , AlCl and ZnCl ) or mixed metal The manuscript also describes a novel one pot synthesis of HMF
Notwithstanding the numerous from biomass derived CMF by the application of PhIO as
17,18
eutectic solvents (such as choline chloride),
presence of CHCl
HCl–H
3
4
19
3
3
3
2
20
3 2
chlorides (CrCl –ZnCl ).
efforts depicted above, each of them suffers from at least one of a reagent under mild oxidative reaction conditions.
the following limitations: low product selectivity, formation of
by-products, low conversion efficacy and product yield, harsh
reaction conditions, requirement of costly reagents, prolonged Experimental
reaction times and tedious operations with complex setups
Materials and method
(facility for continuous extraction). These drawbacks seriously
All the reactions were executed in one-hour oven dried glass-
hamper their potential applications in industries and warrant
searching for more general and efficacious route for CMF
synthesis from lignocelluloses.
ꢁ
ware at 100 C. All reagents and solvents including sodium
chloride (NaCl), dichloroethane (DCE), dichloromethane
(DCM), chloroform, 5-hydroxymethylfurfural (HMF), and ethyl-
In recent years, hypervalent iodine(III) compounds, such as
a-D-glucoside, ethyl-b-D-glucoside, levulinic acid (LA), ethyl lev-
ulinate (EL), formic acid (FA), D-xylose, D-glucose, and hydro-
chloric acid (HCl) were purchased from Sigma Aldrich (Merck
KGaA) as analytical grade and used as received without any
modications. Biomass was powdered by using a universal
grinding machine (Kinematica PX-MFC 90 D).
Thin layer chromatography (TLC) was performed on 60 F254
silica gel pre-coated aluminium plates and revealed with either
a UV lamp (lmax ¼ 254 nm) or a specic colour reagent (Dra-
gendorff reagent or iodine vapours) or by spraying with meth-
[
(
(
bis(triuoroacetoxy)iodo]benzene (PIFA) and iodosylbenzene
PhIO), and iodine(V) compounds, such as iodylbenzene
PhIO ), have been extensively used in organic synthesis owing
2
21
to their low toxicity, ready availability and easy handling. In
organic chemistry, they are frequently used for the development
of green methodologies for various oxidative trans-
22–27
formations.
Hypervalent iodine reagents have been pro-
spected for selective oxidation of benzylic halides to
corresponding carbonyl compounds in good yields. However,
oxidative transformation of CMF to corresponding alcohol
2 4
anolic-H SO solution and subsequent charring by heating at
a
Table 1 Carbohydrate conversion to CMF reported in literature
ꢁ
Entry
Substrate
Catalyst
Temperature ( C)
Time (h)
Solvents
CMF yield (mol%)
Ref.
1
2
3
4
5
6
7
8
9
Corn stover
Cellulose
Chitin
Fructose
Inulin
Sucrose
Eucalyptus kra pulp
Norway spruce so wood TMP
Eucalyptus hard wood
Bamboo pulp
Eucalyptus pulp
Bagasse pulp
Palmarosa
HCl
HCl + LiCl
HCl
ChCl + AlCl
ChCl + AlCl
ChCl + AlCl
HCl + H
HCl + H
HCl + H
HCl + ZnCl
HCl + ZnCl
HCl + ZnCl
HCl + NaCl
HCl + NaCl
HCl + NaCl
100
65
3
>18
1
5
5
DCE
DCE
DCE
MIBK
MIBK
MIBK
CHCl
CHCl
CHCl
CHCl
CHCl
CHCl
CHCl
CHCl
CHCl
70.0
71.0
44.5
50.3
22.6
17.8
21.3
33.7
47.4
32.7
36.2
50.1
76.5
72.4
65.8
10
11
12
18
18
18
19
19
19
20
20
20
150
120
120
120
45
45
45
40
40
3
3
3
5
3
3
3
PO
PO
PO
4
4
4
20
20
20
10
10
5
1
1
1
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
0
1
2
3
4
5
2
+ CrCl
+ CrCl
+ CrCl
3
3
3
2
2
40
100
100
100
This work
This work
This work
Lemon grass
Citronella grass
a
DCE, dichloroethane; MIBK, methyl isobutyl ketone.
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ꢁ
13
1
00 C. Infrared spectra recorded as Nujol mulls in KBr pallets. 6.60 (d, J ¼ 3.6, 1H), 4.62 (s, 2H). C NMR (125 MHz, CDCl
3
):
Monosaccharides, carboxylic acids, HMF, CMF, and ethyl lev- d 177.76, 156.07, 152.86, 121.80, 111.96, 36.52.
ulinate were detected and quantied by HPLC (Agilent, Model
1260) using Hi-Plex H (Agilent) analytical column (300 mm
One pot synthesis of HMF from CMF
length, 8 mm porosity). Gas chromatographic analysis was
performed on Thermo Scientic GC-MS (Model-Trace 1300 gas
chromatograph) with auto sampler and ISQ LT mass spec-
trometer with columns: HP-5MS (0.25 ꢂ 30 m), lm thickness
A RB ask containing CMF (100 mg) along with DMSO and
water in ratio of 4 : 1 (v/v) was taken. The reaction mixture was
29
added with freshly prepared PhIO (455 mg, 3.0 equiv.) and
ꢁ
heated at 55–60 C for 3 h. Aer time elapsed, the reaction was
1
13
1
.0 mm. H and C NMR were recorded at 500 and 125 MHz,
allowed to cool at room temperature followed by removal of
solvent under reduced pressure. Reaction mixture was extracted
with ethyl acetate followed by washing with water and brine.
Organic layer was separated and dried over anhydrous sodium
sulphate. Concentration of the organic phase under reduced
pressure furnished HMF as a light yellow liquid (91 mg, ꢀ90%
yield).
respectively. Chemical shis given in ppm downeld from
internal TMS; J values in Hz.
Feedstock preparation and determination of fractional
composition
Spent aromatic biomass was collected aer the on-farm hydro-
distillation of aromatic crops at Center of Innovative and
Applied Bioprocessing, Mohali (CIAB), Punjab state, India.
Shade dried biomass (moisture content of <7% wt) was sub-
jected to reduction of particle size to 0.5 mm (30 mesh) using
a grinding machine. Primary composition of spent aromatic
biomass (such as carbohydrate sugars, lignin, and ash) was
determined following the Standard National Renewable Energy
Laboratory (NREL) protocol.
Detection and quantication of HMF and CMF by GC-MS
analysis
The compounds CMF and HMF were validated using gas
chromatography (GC) method stated as: a column HP-5MS (0.25
ꢂ 30 m), lm thickness, 1.0 mm; helium at ow rate of 1.0
ꢃ1
mL min was used as a carrier gas. Oven temperature gradient
ꢁ
ꢁ
ꢁ
ꢁ
ꢃ1
was performed from 60 C to 210 C at 3 C min ramp rate and
ꢁ
ꢁ
ꢁ
ꢃ1
1
min hold time at 210 C; then 210 C to 280 C at 20 C min
ramp rate with 5 min hold time at 280 C. Samples were injected
Pre-treatment of spent aromatic waste
ꢁ
Powdered biomass was pre-treated with p-cymene sulphonic
acid (p-CSA), a Brønsted acid synthesised from D-limonene as
a renewable feed stock from solid citrus waste, under autoclave
with 1 mL with split ratio of 1 : 20 and inlet temperature at
ꢁ
2
50 C. Mass spectra were scanned from 50 to 400 amu mass
range with electron impact ionization energy at 70 eV, source
28
condition following the protocol reported in literature. The
ꢁ
temperature of 280 C and mass transfer line temperature of
pre-treated biomass was separated from hydrolysate simply by
ꢁ
2
80 C.
ꢁ

ltration followed by drying in a hot air oven at 45–50 C.
Quantitative HPLC analysis of spent aromatic biomass
hydrolysate
Synthesis of 5-(chloromethyl)furfural (CMF) from pre-treated
biomass
Xylose, glucose, arabinose, acetic acid, HMF, formic acid and
levulinic acid in the hydrolysate of spent aromatic biomass were
quantied by high-performance liquid chromatography
Pre-treated spent aromatic biomass (1.0 g), concentrate HCl (5
mL), chloroform (15 mL) and NaCl (50 mg) were loaded on
a thick-walled high-pressure glass reactor (Ace Glass, USA) of
(Thermo Scientic UltiMate 3000 HPLC) using the analytical
1
20 mL capacity sealed (back) with silicone rubber. The reaction
standards of D-xylose, D-glucose, D-arabinose, acetic acid, HMF,
formic acid and levulinic acid under chromatographic condi-
tions stated as: Agilent Hi-Plex H column (300 mm length; 8 mm
ꢁ
mixture was heated at 100 C in an oil bath for 1 h. Aer time
elapsed, the sealed glass tube was removed from oil bath and
subsequently cooled to room temperature by the application of
cold water. The reaction mixture was centrifuged at 8000 rpm
for 20 min. Pallet was collected and stored for further use.
Organic phase was separated from reaction liquid while the
aqueous phase was repeatedly washed with chloroform. Aer
pooling, the organic phase was subjected to GC-MS analysis for
detection and quantication of CMF. Aqueous phase was
separately analysed by HPLC for detection and quantication of
carbohydrates (e.g., glucose, fructose, arabinose etc.) and their
degradation products (HMF, levulinic acid, formic acid, acetic
acid etc.).
ꢁ
porosity), RI detector operated at 60 C, mobile phase of 5 mM
H
2
SO
4
, ow rate of 0.7 mL per min, refractive index (RI) as
ꢁ
detector at 60 C and run time of 40 min. Quantitative estima-
tions of xylose, glucose, arabinose, acetic acid, HMF, formic
acid, ethyl-a-D-glucoside, ethyl-b-D-glucoside, and levulinic acid
in hydrolysate was made using a calibration curve drawn by
plotting concentration of known standards versus peak area
values from the RI chromatograms.
Recovery of lignin from hydro-char
Concentration of organic phase under reduced pressure The lignin from the hydro-char was obtained by boiling it in 2%
ꢁ
resulted in a dense yellow liquid which was further puried by aq. NaOH solution for 2 h at 100 C. Centrifugation of the
column chromatography to afford a light yellow oil in good yield reaction liquid at 8000 rpm for 20 min followed by separation
(
ꢀ26% with respect to pre-treated biomass) and purity (ꢀ98%). and neutralization of the black liquid with 0.5 N H
2
SO
4
solution
1
H NMR (500 MHz, CDCl
3
): d 9.64 (s, 1H), 7.22 (d, J ¼ 3.6, 1H), resulted in the precipitation of the lignin at pH 3.0. The
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precipitate was ltered out, washed with water and dried in solution of p-CSA in an autoclave for 90 min. Aer time elapsed,
a hot air oven to afford lignin in crystalline state. Yield of lignin reaction mixture was cooled followed by ltration to separate
was calculated using the following formulae.
the hydrolysate from unreacted biomass. HPLC analysis of the
hydrolysate demonstrated a high concentration of xylose
residual spent aromatic biomass ðgÞ
Lignin yield ðwt%Þ ¼
ꢂ 100 (162 mg, >90% yield with respect to hemicellulose; ꢀ16% yield
initial spent aromatic biomass ðgÞ
with respect to initial spent aromatic biomass) while other side
3
products e.g. glucose, arabinose, CH COOH were observed only
in traces. The hydrolysate was in vaccuo concentrated, where-
from, xylose was recovered by precipitation with alcohol.
Collection, washing and crystallization of precipitate afforded
xylose in good purity.
Results and discussion
This study has been carried out to explore a divergent approach
for the production of HMF in high yield and purity from spent
aromatic waste (such as lemongrass, citronella grass, and pal-
marosa bres) derived CMF as a renewable feed stock. The
approach recruited includes: (a) pre-treatment of spent
aromatic waste; (b) production of CMF from pre-treated
biomass; (c) recovery of lignin from hydro-char; (d) synthesis
of HMF from CMF using iodosyl benzene (PhIO).
Production of CMF from pre-treated biomass
Mascal group reported the rst pathway for CMF production
from carbohydrates (e.g., glucose, sucrose, or cellulose, etc.) in
8
good yields. However, application of this method in the pro-
cessing of biomass resulted in the formation of furfural as a co-
product due to an analogous conversion of the hemicellulosic
C5 sugars. Therefore, additional steps were required for isola-
tion of products from reaction mixture which may increase the
Pre-treatment of spent aromatic waste
The complex recalcitrant structure of the spent aromatic waste cost of downstream processing. The pre-treatment of biomass
prevents it from being efficiently hydrolysed, hence, a pre- before thermochemical processing for CMF production appears
treatment stage is usually essential to overcome the biomass promising in minimizing the formation of co-products in
recalcitrance for having effective biomass utilization. Several reaction liquid. The pre-treated biomass obtained aer hydro-
biomass pre-treatment approaches so far have been explored, lysis of spent aromatic waste with p-CSA exhibits improved
such as physical (milling, energy irradiation), physicochemical characteristics such as low ash and high content of cellulose
(liquid hot water, steam explosion), chemical (acid, alkali, and lignin. Therefore, in a typical run, 1.0 g pre-treated biomass
organosolv), and biological pretreatments (bacteria media- and concentrate HCl in a ratio of 1 : 1 (w/v), NaCl (2.5 wt%), and
30
tion). In literature reports, the bio-based p-cymenesulfonic CHCl3 (total solid–liquid ration 1 : 20 w/v) were loaded to
acid (p-CSA) containing a sulfonic (–SO H) group has been cited a thick-walled high pressure glass reactor. Aer 1 h reuxing at
3
ꢁ
as an efficient alternative to petrochemical derived toluene 100 C in an oil bath, the reactor was cooled to room temper-
sulfonic acid (p-TSA) for the hydrolysis of cellulosic material in ature. The reaction mixture was subjected to centrifugation, the
aqueous medium. p-CSA can be produced directly from D- pallet was collected and dried separately in a hot air oven. The
2
8
limonene as a renewable feed stock form citrus waste.
selective and near complete (>90%) hydrolysis of xylan poly- over anhydrous Na
saccharide in spent aromatic biomass by p-CSA under autoclave established the formation of CMF as a major product (60 mg,
A
organic phase was separated form reaction liquid and dried
2
SO . GC-MS analysis of organic phase
4
31,32
condition has been prospected.
The method shows efficacy ꢀ6% yield with respect to pre-treated biomass) while glucose,
for xylose production with minimum side products. Accord- ethyl-a,b-glucosides, levulinic acid, 5-HMF, and ethyl levulinate
ingly, the spent aromatic waste was treated with aqueous were observed only in traces.
Table 2 Detection and quantification of compounds in aqueous and organic phase
c
Cellulose degradation products (wt%)
Organic phase
Aqueous phase
a,b
Entry
NaCl (wt%)
Furfural
EL
HMF
CMF
Glucose
EADG
EBDG
LA
FA
HMF
1
2
3
4
5
6
BLK
2.5
5.0
10
20
40
0.01
0.06
0.06
0.07
0.09
0.04
0.35
0.68
1.40
1.41
0.66
0.92
0.19
0.22
0.14
0.13
0.13
0.06
14.52
18.18
25.87
25.37
24.23
21.08
6.77
5.21
2.15
2.68
3.07
2.17
0.44
0.17
0.23
0.21
0.31
0.19
0.81
0.12
0.05
0.06
0.05
0.08
0.23
0.57
1.34
1.00
1.81
1.43
0.10
0.18
0.64
0.48
0.76
0.47
0.34
0.16
0.22
0.23
0.19
0.20
a
ꢁ
b
Reaction condition: biomass, 1.0 g; concentrate (35%) HCl, 5 mL; chloroform, 15 mL; temperature, 100 C; reaction time, 1 h. Solid–liquid ratio,
c
1
: 20 in all sets of reaction. BLK, blank; EL, ethyl levulinate; EADG, ethyl-a-D-glucopyranoside; EBDG, ethyl-b-D-glucopyranoside; LA, levulinic acid;
FA, formic acid.
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used as reaction solvent. Similarly, DCE displayed moderate
efficacy in CMF extraction from aqueous phase. The solvent
CHCl performed well due the high ability of CMF extraction
3
from aqueous phase, hence, established as the solvent of choice
for the reaction.
The effect of temperature on the yield of CMF was also
studied at constant loading of NaCl and HCl. Lowering of the
ꢁ
temperature below 100 C caused a rapid decrease in the CMF
yield. Maximum yield of CMF from the biomass could be ob-
ꢁ
tained at 100 C. An increase in reaction temperature beyond
ꢁ
1
00 C lowered the CMF yield due to the formation of uniden-
tied soluble products (Fig. 1). Similarly, the reaction time was
also found to have a profound impact on cellulose degradation
and transformation of resulting monosaccharide to CMF.
Lowering of the reaction time from 1 h at constant temperature
ꢁ
(
100 C) resulted in a lot of glucose remained unreacted in
reaction liquid. Processing of biomass under prolonged reac-
ꢁ
Fig. 1 Effect of temperature on CMF yields via solvo-thermal pro- tion time beyond 1 h at 100 C resulted into an increased
cessing of biomass.
concentration of LA and polymeric materials in the hydrolysate
Fig. 2). Since, the designed methodology shows high selectivity
towards CMF (Table 3), the reaction predominantly produces
(
In order to access the yield further, we optimize the reaction CMF which being insoluble in aqueous phase, simply diffuses
condition with respect to temperature, reaction time, effect of to organic phase and recovered therefrom in good yields via
solvents, amount of conc. HCl, and loadings of NaCl. Without concentration under the reduced pressure. Pure CMF (ꢀ98%)
NaCl, the liquid products of pre-treated biomass under thermal was produced by column chromatography followed by valida-
processing in presence of HCl alone were many, with low yield tion through GC analysis (see ESI Fig. S3†) and characterization
and selectivity. GC-MS analysis of the organic phase displayed by spectroscopic techniques such as NMR (see ESI Fig. S4 and
the presence of CMF and ethyl levulinate in low yields, mean- S5†) and MS (see ESI Fig. S6†).
while the HPLC analysis of aqueous phase (see ESI Fig. S1†)
The cellulose degradation products, e.g., glucose, LA, FA, and
displayed the formation of monosaccharides and cellulose ethyl glucosides etc. were all together detected in a very small
degradation products e.g. glucose, levulinic acid, 5-HMF, formic quantity (ꢀ2–3%) in aqueous phase. Further, dissolving the
acid, ethyl-a,b-glucosides etc. A rise in HCl loading did not residue (solid le aer the reaction) in methanol established no
cause a substantial change in the selectivity and yield of prod- black tar formation. Hence, neither black tar formation nor
ucts. Upon addition of NaCl, a signicant enhancement in the gasication could be observed in processing of biomass with
concentration of CMF was observed in the organic phase aer NaCl and HCl under the optimized reaction conditions. As
1
h reaction time (Table 2). This indicated that the NaCl evident from Table 2, the highest concentration of CMF from
promotes both the yield of, and selectivity to CMF under heat-
ing condition. In HPLC analysis of aqueous phase, a decreasing
glucose concentration at increasing NaCl loadings was attrib-
uted to its efficient conversion to CMF which being insoluble to
aqueous phase readily diffuses to organic phase and detected
therefrom by GC analysis (see ESI Fig. S2†). Thus, the yield of
CMF increased with increasing the amount of NaCl at xed HCl
loading in the reactions. Highest CMF concentration in organic
phase was detected at 0.05 equivalent of NaCl (5 wt% with
respect to pre-treated biomass). A further increase in the
amount of NaCl did not cause an enhancement of CMF yield
due to near complete degradation of cellulose occurring in the
pre-treated biomass.
10–12
Mascal group
has earlier established the crucial role of
chlorinated solvents in the synthesis of CMF from carbohy-
drates under thermal condition. Therefore, the effect of organic
solvents on the yield of CMF from biomass was investigated by
3
carrying out reactions in presence of CHCl , DCM, and DCE as
the solvent system. The results suggested that the ability of
organic solvents to extract out CMF from aqueous phase is
Fig. 2 Effect of reaction time on CMF yields via solvo-thermal pro-
highly desired. CMF was detected in low yields when DCM was cessing of biomass.
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Table 3 Selectivity of products in biomass hydrolysate by HPLC analysis
Products selectivity
a
b
c
SN
Biomass
Furfural
EL
HMF
CMF
LA
FA
Others
Glucose (wt%)
Conversion (wt%)
1
2
3
Palmarosa
Lemon grass
Citronella grass
0.18
0.22
0.19
4.36
4.84
3.88
1.10
1.62
1.78
80.56
80.27
79.55
4.20
5.23
6.11
1.98
2.62
3.21
7.60
5.21
5.28
2.15
1.30
1.16
71.08
69.43
66.38
a
b
c
Both in aqueous and organic phases. Others such as ethyl-a,b-glucopyranosides and unreacted glucose. Based on glucan content in spent
biomass.
into glucose by the activity of mineral acid in presence of NaCl.
A subsequent isomerization of glucose generates fructose which
on dehydration results into the formation of 5-hydrox-
ymethylfurfural (HMF) as intermediate that undergoes chlori-
10
nation to form CMF in good yields.
Recovery of lignin from hydro-char
The hydro-char recovered as pallet aer the synthesis of CMF
from palmarosa biomass was boiled in a dilute NaOH solution.
The aqueous phase (black liquid) was removed and neutralized
2 4
separately by dilute H SO solution, wherein, the lignin present
in the black liquid was precipitated at pH 3.0. Separation,
washing, and drying of precipitate furnished lignin (ꢀ14%
yield) which was further characterization by FT-IR, XRD and
EDS analysis.
The FT-IR spectrum of the isolated lignin exhibited absorp-
Fig. 3 Comparative yield of cellulose degradation products from tion bands indicative to the presence of phenolic and alcoholic
spent aromatic waste under the optimized reaction condition.
ꢃ1
groups (3500 cm ), –CH
2
–H and pC–H stretching (2800–
ꢃ1
ꢃ1
2
900 cm ), carbonyl function (1600–1780 cm ) and aromatic
ꢃ1
ring (ꢀ1400 cm ). Absorption bands corresponding to syringyl
ꢃ1
pre-treated aromatic biomass (1.0 g) was obtained with
and guaiacyl residues were observed between 1300–1100 cm
ꢁ
a condition of 100 C temperature, 1 h reaction time, 0.05
(
see ESI Fig. S7†). X-ray diffraction pattern of lignin showed
many sharp diffraction peaks in which the peaks centred at
equivalent NaCl, 1 : 5 w/v loading of conc. HCl and 1 : 15 w/v
loading of CHCl3.
ꢁ
ꢁ
19.19 and 32.31 were typical to pure lignin (see ESI Fig. S8†).
Other sharp peaks indicated a certain level of crystallinity due to
the impurities and/or small crystalline fragments. Elemental
composition of the isolated lignin was determined by energy-
dispersive X-ray spectroscopy (EDS) analysis which established
the elemental composition: C, 71.33%; O, 21.94% as presented
in (see ESI Fig. S9†). Other elements such as Na (3.19%), Cl
Once the production of CMF from pre-treated palmarosa
biomass was established using NaCl and HCl under solvo-
thermal condition, the methodology was successfully
extended over the other pre-treated biomass such as lemongrass
and citronella grass, wherein, the results demonstrated a near
complete conversion of cellulose to CMF (Fig. 3). A plausible
mechanism involves the acid hydrolysis of polymeric cellulose
(
1.79%), and S (1.03%) were also detected as impurities due to
Table 4 Mass balance of products produced from pre-treated biomass
Liqueed products
(
wt%)
b
c
Type of
biomass
Qty. of
biomass (g)
Organic
phase
Aqueous
phase
Residue
(wt%)
Biomass conversion
(wt%)
Carbon balance
(wt%)
a
SN
Lignin (wt%)
1
2
3
Palmarosa
Lemon grass
Citronella
1.0
1.0
1.0
27.47
25.12
22.29
4.42
4.04
4.03
29.0
27.5
27.0
14.21
13.47
13.23
58.35
59.64
57.61
91.08
83.14
79.31
a
ꢁ
b
Biomass loading at conc. HCl (5 mL), chloroform (15 mL), 100 C temperature, reaction time 1 h. Unreacted biomass recovered in reaction.
Carbon balance aer degradation of cellulose.
c
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Table 5 Weight based analysis for the formation of gases during the biomass processing
b
Reaction mixture weight (g)
Gaseous products
a
ꢁ
Entry
Reaction temperature ( C)
Before reaction
Aer reaction
Weight lose (wt%)
2 4
(CO, CO , CH )
1
2
3
80
100
120
269.0
270.7
266.9
268.87
270.65
266.53
0.05
0.02
0.14
ND
ND
ND
a
b
Reaction condition: biomass, 1.0 g; concentrate (35%) HCl, 5 mL; chloroform, 15 mL; reaction time, 1 h. Weight of reaction mixture including
the sealed glass reactor.
Fig. 4 Synthesis of HMF from CMF using PhIO.
the use of dilute NaOH and H SO in the process of lignin from the reaction mixture. We carried out a weight based
2
4
isolation.
analysis to check the formation of gases during the processing
The mass balance and the carbon balance of product of spent aromatic biomass for production of CMF under the
distribution from spent aromatic biomass was calculated based optimized reaction condition. Results of screening test carried
ꢁ
on the experiments performed in this paper, results are out at different temperatures such as 80, 100, and 120 C as
summarized in Table 4. The main products were xylose, CMF, summarized in Table 5, established that no signicant loss in
and lignin. In the designed process, most of lignin present in the weight of reaction mixture before and aer the reaction was
the spent biomass was degraded (ꢀ10–15%). About ꢀ10–20% observed, hence, ruled out the formation of gases e.g. CO
2
, CO,
weight loss was attributed to the presence of solvent extractives CH etc.
4
and residual volatiles. It is noticeable that the mass balance
closures were not close to 100% because some degradation
products from the hemicelluloses and cellulose were not Synthesis of HMF from CMF using iodosyl benzene (PhIO)
detected in HPLC analysis. Additionally, some solids were
In the past several decades, hypervalent iodine chemistry has
adsorbed on to the lter paper and wall of funnel during the
witnessed prosperous development in the eld of organic

ltration process, therefore, could not be collected. Moreover,
synthesis by the use of the hypervalent iodine reagents as mild
the designed methodology produces CMF in high selectivity
which being highly soluble in chloroform, is isolated easily
13
oxidants. Therefore, we investigated the feasibility of utilizing
the oxidising properties of iodosylbenzene (PhIO) for an
Fig. 5 Reaction mechanism for conversion of CMF to HMF under the oxidative reaction condition.
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efficient conversion of CMF to HMF in good yields and selec- nature, may be recovered from aqueous medium in high yields
tivity. Accordingly, the CMF was reacted with PhIO in presence and purity. CMF can be potentially used as a versatile chemical
of DMSO and water as solvent system under the mild heating for production of furfurals, LA, EL, EADG etc. while xylose being
condition. HMF in the reaction mixture was validated by GC-MS a precursor for many valuable chemicals and an abundant
analysis which demonstrated a complete conversion of CMF to building unit of hemicellulose, can be specically produced in
HMF (Fig. 4).
this approach to add an economic advantage.
The reaction was investigated with respect to effect of
To date no scalable method is available for production of
temperature, effect of reaction time, and the ratio of DMSO and HMF from raw biomass. High sensitivity of HMF to the acidic
water as solvent system. The reaction carried out in DMSO as conditions results in the formation of numerous side products
a solvent alone under the anhydrous condition did not cause which impose difficulties in its production from biomass.
the formation of HMF even at the prolonged reaction time (24 h) Therefore, a new method for synthesis of HMF from the
that established the essentiality of water for a successful reac- biomass derived CMF under oxidative condition using hyper-
2
tion. The reaction performed in presence of H O as solvent valent iodine reagent PhIO has also been investigated in this
alone could result in the low yield of HMF probably due to the manuscript. Use of PhIO as an oxidant provides easy access to
substrate insolubility in the water. Hence, the use of two-phase HMF from CMF in high yields and selectivity under the mild
solvent system comprising of water and organic solvent was reaction condition. Thus, this approach would be promising
anticipated, wherein, the mixtures of H O and water immiscible and commercially more acceptable method for the production
2
solvents, i.e., dichloromethane, chloroform, ethyl acetate, etc., of CMF, HMF and their derivatives from spent aromatic
did not work due to the high affinity of CMF to remain in the residues.
organic phase. Similarly, the reaction could not be successful
with water miscible solvents, e.g., methanol, ethanol, acetoni-
trile, etc. Considering the DMSO as a high-polarity water
Conflicts of interest
miscible solvent, we performed the oxidation of CMF with PhIO The authors declare no conict of interest.
in a mixture of DMSO–water under mild heating condition,
wherein, the peak corresponding to HMF was signicantly
Acknowledgements
detected in GC-MS analysis. Increasing the reaction tempera-
ꢁ
ture beyond 60 C resulted into the formation of levulinic acid DBT-Center of Innovative and Applied Bioprocessing, Mohali
as a side product. Moreover, the concentration of water deci- (India) is sincerely acknowledged for infrastructural and
sively inuenced the efficacy of oxidation as no reaction was research facility.
observed with excess of water when used along with DMSO as
2
solvent. Thus, different gradients of DMSO/H O were screened
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