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Figure 2. Iodine test performed with (A) cellulose, (B) cellulose treated with
microwaves at 150 °C for 60 min, (C) starch, (D) starch treated with microwaves at
150 °C for 60 min.
Figure 1. Mass spectra of cellulose reaction mixture after treatment with micro-
wave irradiations at 150 °C for (A) 20 min, (B) 60 min. (C) LC–MS (MeOH–H2O, 2:3)
of product obtained after microwave irradiation of cellulose at 150 °C for 60 min
and its comparison with commercial sample of D-glucose.
reaction time,10–12 experimental methods for the hydrolysis of
cellulose, making use of microwaves at high temperatures and un-
der significant acidic conditions are also reported.13,14 Further,
making the methodology more environmental friendly, here, we
demonstrate microwave assisted conversion of cellulose to
monosaccharide under very mild conditions, at relatively low
temperatures in the presence of catalytic amount of FÀ/ClÀ. Mass
spectrometry (MS), HPLC, LC–MS, and scanning electron micros-
copy (SEM) were some of the analytical techniques used for the
analysis of the product.
Figure 3. SEM micrographs of (A) cellulose; (B) cellulose treated for 1 h at 150 °C
under microwave irradiations.
Therefore, in consistent with the literature reports, it seems that
microwaves disturb the H-bond network of the cellulose and pro-
mote its breaking to its monomeric units. For comparison, starch
solution was also treated with microwaves at 150 °C for 60 min.
The mass spectrum of the reaction mixture also showed a major
peak at m/z 222.1262 [M+CH3CN]+ supporting the formation of glu-
cose (calcd m/z 222.1172) (Fig. S1). The classical iodine test of cel-
lulose and its reaction mixture also supported the observations of
breakdown of cellulose to its monomeric units under the effect of
microwaves (Fig. 2). Furthermore, silver mirror test was also per-
formed to check the presence of glucose and the obvious results
were obtained (Fig. S2).
As it is evident from the SEM images, the cellulose particles
(Fig. 3A) on treatment with microwaves were disintegrated
(Fig. 3B) into smaller particles. Similar results were obtained on
recording the SEM images of hydrolysate of starch treated under
same conditions (Fig. S3).
The warmed water suspension of cellulose at pH 6 was irradi-
ated under microwaves at 100 °C.15 Cellulose remains suspended
in water even on irradiation for 60 min. The temperature was
increased stepwise and the progress of cellulose hydrolysis was
monitored by recording the mass spectrum of the reaction mixture
(Table S1). The reaction mixture becomes homogeneous at 150 °C.
Mass spectrum of the reaction mixture after 20 min of irradiation
at 150 °C showed the presence of various oligosaccharides
(Fig. 1A; C2–C8, Chart 2). However, after 60 min of irradiation,
the mass spectrum of the reaction mixture exhibited a major peak
at m/z 203.0501 corresponding to mass of glucose (calcd m/z
203.0526 [M+Na]+) (Fig. 1B). After removing the solvent, a thick
oil was obtained (55%, [
product with a commercial sample of
a
]
16 = +60°). Comparison of LC–MS of this
-glucose (Fig. 1C) confirmed
D
the formation of glucose when cellulose was irradiated under
microwaves.