Influence of the ammonium salts used in the Br?nsted acid catalyzed hydrothermal decomposition of d-glucose towards 5-HMF

Article abstract of DOI:10.1039/d0nj00155d

In this work, we compare the effect of two ammonium salts (ammonium sulfate and ammonium acetate) used as promoters in the hydrothermal decomposition of d-glucose with the results obtained in the presence of sulfuric acid. For the first time, we demonstrate that ammonium acetate is not a good promoter due to the low conversion of d-glucose. Conversely, ammonium sulfate appears as a much more promising promoter. Indeed, even if a large amount of humins is observed, 5-HMF is obtained in good yield with a fast conversion of d-glucose. After isolation and characterization of the liquid and solid phases, the role of ammonium sulfate was thoroughly investigated. Structural characterization of the humins obtained from d-glucose and ammonium salts is also proposed. In addition, we demonstrated that with an ammonium-containing promoter, part of the nitrogen atoms is inserted in the humin structure as pyrrole derivatives.

Full text of DOI:10.1039/d0nj00155d

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DOI: 10.1039/D0NJ00155D
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Influence of the ammonium salts used in the Brønsted acid
catalyzed hydrothermal decomposition of D-glucose towards 5-
HMF†
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Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
Victor Maruani, Eric Framery * and Bruno Andrioletti
DOI: 10.1039/x0xx00000x
In this work, we compare the effect of two ammonium salts (ammonium sulfate and ammonium acetate) used as promotors
in the hydrothermal decomposition of D-glucose with the results obtained in the presence of sulfuric acid. For the first time,
we demonstrate that the ammonium acetate is not a good promotor due to the low conversion of D-glucose. Conversely,
the ammonium sulfate appears as a much more promising promotor. Indeed, even if a large amount of humins is observed,
5
-HMF is obtained in good yield with a fast conversion of D-glucose. After isolation and characterization of the liquid and
solid phases, the role of the ammonium sulfate was thoroughly investigated. A structural characterization of the humins
obtained from D-glucose and ammonium salts is also proposed. In addition, we demonstrated that with an ammonium-
containing promotor, part of the nitrogen atoms is inserted in the humins structure as pyrrole derivatives.
obtained by rehydration of HMF. However, to the best of our
knowledge, DHH has never been isolated, but Infra-Red study
Introduction
2
1-22
23
carried out by Lund et al.
and by Vlachos et al. has
It is well established that one of the most promising solution to
replace fossil resources involves the use of biomass.1-2 Being
abundant and renewable, the lignocellulosic biomass offers a
revealed that DHH can react with the carbonyl group of 5-HMF
by aldol condensation. C MAS NMR analyses proposed by
Weckhuysen et al. and Seshan et al.25 confirmed this
structure. A revised molecular structure of the humins obtained
from D-glucose has shown that no keto group is directly
connected to a furanic ring, and water soluble oligomers
WSO), which are D-glucose oligomers with a maximum of 9
units, are also inserted in the structure of the humins by
13
24
3
great potential for providing green chemicals. Indeed, the
biomass raw material can be converted by hydrolysis into
oligomers and mono-carbohydrates. Next, by dehydration and
hydration processes, the latter can afford bio-based building
blocks such as 5-hydroxymethylfurfural (5-HMF) which then
2
6
(
4
-8
leads to levulinic acid (LA) and formic acid (FA). Among the
top list of bio-based building blocks listed by the US Department
2
7
reaction with the aldol condensation intermediates. Recently,
28
Vlachos et al. have screened different classes of organic
solvents (polar protic or aprotic and nonpolar) to solubilize part
of the humins obtained after acid catalyzed dehydration of
fructose. The amount of the extracted humins is dependent of
the electron-donor-acceptor type interactions with the solvents
used, suggesting that part of the humins are agglomerated
oligomeric species linked together by weak interactions. The
identified species are in agreement with the mechanism of
condensation of furanic ring as proposed in the literature.
Scheme 1 resumes the hydrothermal decomposition of D-
glucose into LA and FA and the humins.
9
of Energy, 5-HMF and LA are of prime interest. For example, LA
10-12
is easily transformed into γ-valerolactone
or in the
presence of FA and amine into N-substituted-5-
1
3-15
methylpyrrolidinnones.
With three functional groups, 5-
16
HMF is the key intermediate towards high value derivatives
by oxidation, hydrogenation or hydrogenolysis, amination,
esterification, etherification, or carboligation reactions.
Compared to the synthesis of LA, access to 5-HMF from
bioresources remains a challenge because of its high
17-18
reactivity.
Indeed, as 5-HMF is not stable in water under
acidic conditions, during the dehydration and hydration
processes of the biomass raw material, LA and FA are generally
obtained along with a black solid considered as a byproduct and
called the humins. The char obtained during the acidic
treatment has received more attention to determine its intrinsic
structure and envision a valorization. The generally accepted
structure consists of a network of furan rings linked with ether
O
HO
LA
O
O
OH
O
OH
OH
HO
HO
O
O
OH
FA
1
9
or acetal aliphatic linkers. In addition to 5-HMF, 2,5-dioxo-6-
hydroxyhexanal (DHH) has been proposed as a key intermediate
in the formation of the humins. This compound has been
5-HMF
OH
OH
D-Glucose
O
20
identified for the first time by Horvat et al. in 1985, and is
humins
O
O
a.Université de Lyon, Université Claude Bernard Lyon 1, ICBMS UMR 5246, 43 Bd du
11 Novembre 1918, F-69622 Villeurbanne cedex, France.
E-mail : eric.framery@univ-lyon1.fr
DHH
†
Electronic
Supplementary
Information
(ESI)
available.
See
DOI: 10.1039/x0xx00000x
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The program of temperature was 40°C during 2 minutes, then
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Scheme 1 Hydrothermal decomposition of D-glucose.
Up to now, one of the most accomplished process to obtain
View Article Online
DOI: 10.1039/D0NJ00155D
6
0°C per minute up to 250°C.
5
-HMF is the biphasic system catalyzed with a mineral acid, as
A mixture of D-glucose (4.00 g, 22.2 mmoles), ammonium
sulfate, ammonium acetate or sulfuric acid (5.2 mmoles) and
water (affording a solid content of 50%) was heated at 150°C for
the indicated time. After cooling to room temperature using an
ice bath, the reaction mixture was treated as described in the
ESI (Figure S1†) to isolate the water soluble compounds on the
one hand and the humins on the other hand.
2
9-30
reported by Dumesic et al.
Generally, the reactions are
carried out in the presence of polar organic solvents with high
boiling points such as dimethylsulfoxide. From the report of
Moreau et al. on the use of 1H-3-methyl imidazolium chloride
as solvent and catalyst for the conversion of fructose to
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-HMF, various ionic liquids such as tetraalkylammonium salts
3
2-33
can be used to replace these solvents.
chloride with glucose or fructose, deep eutectic solvent (DES)
can be prepared and be used in the aqueous Lewis acid-
By mixing choline
34
catalyzed formation of 5-HMF as proposed by Jérôme et al. It
was also shown that the addition of carbon dioxide to the DES Results and discussion
system, decreased the pH with the formation of carboxylic acid,
After treatment of the reaction mixture obtained by heating at 150°C
and 5-HMF was obtained in similar yield (70%) from fructose
with lower temperature (120°C instead of 165°C).
for 80 minutes a mixture of D-glucose (22.2 mmoles), ammonium
sulfate, ammonium acetate or sulfuric acid (5.2 mmoles) as promotor
and water in quantity to afford a solid content of 50%, the liquid
phase gave the water soluble compounds after lyophilisation, and
the solid gave the humins after drying for 24 hours at 40°C. The
Figure 1 discloses the proportion of the humins and the organic
species contained in the water phase (D-glucose, 5-HMF, LA and
WSO) determined during the hydrothermal decomposition of D-
glucose in the presence of one of the three Brønsted acids. FA was
3
5
To the best of our knowledge, there is no recent study using
ammonium salts as acidic promotors in the hydrothermal
decomposition of oses. In 1982, Brown et al. have disclosed the
dehydration reaction of fructose in non-aqueous media, and in
the presence of ammonium chloride or bisulfate as catalyst. In
order to optimize the synthesis of 5-HMF and to have a better
understanding of its formation in the presence of ammonium
salts used as mild promotors (5-HMF being highly sensitive), we
decided to elucidate the formation of the by-products detected not considered because during the lyophilisation step, the majority
during the hydrothermal decomposition of D-glucose. To this of FA was evaporated, and only traces were detected. However, it is
end, we have investigated the acid catalyzed hydrothermal well-established that during the hydrothermal decomposition of
dehydration of D-glucose using ammonium sulfate or acetate as 5-HMF,10, 37 equimolar amounts of LA and FA are produced.
Brønsted acid promotors. Firstly, we have compared the results
3
6
obtained from ammonium acetate and ammonium sulfate with
those obtained from sulfuric acid. Secondly, we studied the
kinetics of the hydrothermal decomposition of D-glucose using
ammonium sulfate as promotor.
Experimental
The reactions were performed in an Ace Pressure Tube®
purchased from Sigma-Aldrich®. All compounds were
purchased from Sigma-Aldrich® and were used without further
purification. Tap water was used. H NMR spectra were
recorded on a Bruker ALS 300 MHz spectrometer with a QNP
1
1
3
probe in D
2
O containing acetonitrile as internal standard.
C
15
and N CP MAS NMR spectra were recorded on a Bruker Avance
III 500 WB using a 4 mm MAS Bruker probe and zirconia rotors
with Kel-F drive caps using a recycling delay of 5 s, a contact time
of 2 and 3 ms, and a spinning rate of 13 and 10 KHz, respectively.
The chemical shifts are given relative to adamantine (δ 38 ppm)
13
in the case of C CP MAS NMR and glycine (δ 34 ppm) in the
case of 15N CP MAS NMR. Elemental analyses were carried out
by Welience – Pôle Chimie Moléculaire Dijon, and oxygen
percentages were calculated by difference with the other
atoms. Infra-Red spectra were recorded on a NicoletTM iS 10 Fig. 1 Evolution of the humins, D-glucose, WSO, 5-HMF and LA in the
FT-IR spectrometer of Thermo Fisher Scientific. The gas phase
was analysed by a gas phase chromatography 6890 Agilent with
TM
hydrothermal decomposition of D-glucose heated at 150°C during 80
min. in the presence of 5.2 mmoles of (NH
4
)
2
SO
4
, NH
4
OAc or H
2
SO . The
4
conversion of D-glucose and the yields of 5-HMF and LA were based on
the starting amount in mole of D-glucose. The yields of WSO and the
humins were based on the starting amount in mass of D-glucose.
a CP-Molsieve 5Å column Varian. 200 μL of gas were injected.
2
| J. Name., 2012, 00, 1-3
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yield increased slightly (from 3.5 to 8.3 mole % basedVoienwsAtraticrlteinOgnliDne-
The activity of the three promotors was proven totally different. In glucose) with the reaction time. For shoDrOtI:r1e0a.1c0t3io9n/D0tiNmJ0e0s15(52D0
the case of sulfuric acid, 93% of conversion of D-glucose was minutes), D-glucose was mainly converted into WSO. Then, for
measured. Conversely, with ammonium sulfate or ammonium longer reaction time (80 minutes), the D-glucose conversion was in
acetate, the conversions were lower, reaching 79 or 58%, favor of the formation of the humins (16.3 weight % based on
respectively. In addition, these different acids did not afford the starting D-glucose), and not of the formation of 5-HMF. Meanwhile,
formation of the same species. Indeed, in the case of sulfuric acid, a the amount of WSO decreased over time (from 35.5 to 23.0 weight
large quantity of LA was obtained (41.1 mole % based on starting D- % based on starting D-glucose). Hence, the use of ammonium acetate
glucose), whereas in the case of the ammonium salts, no LA was as promotor is probably not a good candidate for the production of
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formed in the case of NH
4
OAc or only in small amount in the case of 5-HMF, even if no LA was obtained during the hydrothermal
(
NH SO (4.0 mole % based on the starting D-glucose). No 5-HMF decomposition of D-glucose.
4
)
2
4
was detected in the case of sulfuric acid, whereas in the case A second and more detailed study was carried out using ammonium
ammonium promotors, low similar yields based on starting D-glucose sulfate as the promotor for several durations. The main compounds
were determined with 9.0 mole % in the case of (NH
mole % in the case of NH OAc. The maximum amount of WSO was LA, WSO, ammonium salts (NH ) SO and NH HSO . As previously
obtained when NH OAc was used (23.0 weight % based on starting discussed, FA was not considered because during the lyophilisation
D-glucose). In the case of sulfuric acid, the yield was divided by 2 step, the majority of FA was eliminated, and only traces were
10.5 weight % based on starting D-glucose), and divided by 4 in the detected. The Table 2 gathers the yields of each species depending
4 2 4
) SO and 8.3 detected in the water soluble compounds were D-glucose, 5-HMF,
4
4
2
4
4
4
4
(
case of ammonium sulfate (6.5 weight % based on starting D- on the reaction time. As reported in the ESI, the amounts of D-
glucose). Regarding the formation of the humins, a maximum glucose, 5-HMF and LA were determined by 1H NMR using
amount (36.8 weight % based on starting D-glucose) was observed acetonitrile as standard, and the amount of WSO was calculated from
when ammonium sulfate was used. For the two other Brønsted acids, the elemental analyses. WSO were isolated and characterized as
the humins yields were lower, with 16.3 weight % (based on starting already reported in the case of sulfuric acid as promotor.27 The WSO
D-glucose) in the case of NH
starting D-glucose) when H SO
These preliminary results confirmed the low stability of 5-HMF and ammonium bisulfate, we compared the pKa values of the 2
4
OAc and 25.5 weight % (based on presented a similar structure of D-glucose oligomers with a
2
4
was used.
maximum of 9 units. To determine the ratio of ammonium sulfate
-
2-
-
during the hydrothermal treatment of oses in the presence of sulfuric acidities HSO /SO (1.9) and H SO / HSO (-3.0) with the pH of the
acid. Instead, in the presence of ammonium salts, 5-HMF was not aqueous phase before treatment. The pH range (1.4 – 1.8) evidenced
decomposed into LA. The difference in quantities of organic species that the amount of H SO was negligible compared to that of HSO .
4
4
2
4
4
-
2
4
4
and the humins depending on the Brønsted acid promotor used, can Thanks to the amount of the water soluble compounds and the
possibly be explained by the pH of the water phase. It is known that corresponding elemental analyses, we were able to determine the
the formation of 5-HMF is pH dependent, with an optimal pH area amount of (NH ) SO and NH HSO (see ESI). While all the total
4
2
4
4
4
between 1.5 and 2.38 In the case of NH
OAc, the pH of the water amount of sulfur was found (within the experimental errors), the
4
phase from 6.1 to 4.3 was out of the ideal zone of the 5-HMF quantity of nitrogen was in default, suggesting an incorporation of
formation, the key intermediate in the synthesis of LA and the nitrogen in the structure of the humins. The loss in nitrogen atoms
humins. The drop in pH value was explained by the formation of gradually increased with the reaction time, and explained the release
-
-
3 2 3 2
4
acetic acid (pKa CH CO H / CH CO 4.4). In the case of sulfuric acid, of HSO ions responsible for the decrease of the pH. The amounts of
the initial pH was too acid (from 1.0 to 1.5), and the 5-HMF was the water soluble compounds obtained after lyophilization were
transformed into LA in large amount. Hence, in the case of compared to the total amounts of the different organic (residual D-
ammonium sulfate, the water phase offered the most appropriate glucose, 5-HMF, LA and WSO) and inorganic (ammonium sulfate and
acidity (from 4.5 to 1.4) to transform D-glucose into 5-HMF. Using ammonium bisulfate). The values appeared very similar (Table S6†),
the latter promotor, 5-HMF was converted mainly into the humins, suggesting a total identification of the compounds.
and only some traces of LA were observed, while the pH of the
Table 1 Hydrothermal decomposition of D-glucose in the presence of
aqueous solution (1.4) was close to the one measured from sulfuric
acid (1.5). This observation suggests that the cationic ammonium
ammonium acetate as promotor.
ions prevent the formation of LA from 5-HMF. In the presence of
Conv. b
5-HMF c
LA c
WSO d
Humins d
Time
pH a
+
+
water, the NH
4
cations are in equilibrium with NH
3
and H
3
O . In the
[
min.]
[mol%]
[mol%]
[mol%]
[wt%]
[wt%]
-
case of ammonium acetate, the CH
affording acetic acid that buffers the medium around pH 4.3. As for
3
CO anions are protonated
2
20
40
80
4.4
4.3
4.3
33.5
42.5
57.8
3.5
5.9
8.3
0.0
0.0
0.0
35.5
36.5
0.2
3.2
2-
ammonium sulfate, the SO
4
anions are mono-protonated to give
-
23.0
16.3
the HSO
4
anions hence, explaining the low pH to 1.4.
a
b
A kinetic study was considered for the two ammonium salts. In the
case of the ammonium acetate promotor (Table 1), the conversion
of D-glucose increased with the time from 33 to 58%. The 5-HMF
pH of aqueous phase before treatment (initial pH 6.1). Conversion of D-
glucose. Based on the starting amount in mole of D-glucose. Based on
c
d
the starting amount in mass of D-glucose.
This journal is © The Royal Society of Chemistry 20xx
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View Article Online
DOI: 10.1039/D0NJ00155D
Table 2 Composition of the water soluble compounds obtained during the hydrothermal decomposition of D-glucose in the presence
of ammonium sulfate as promotor.
Time
min.]
Conv. b
[mol%]
5-HMF c
[mol%]
LA c
WSO d
[wt%]
(NH
4
)
2
SO e
4
NH
4
HSO e
4
Loss of N f
[mmol]
pH a
[
[mol%]
[mmol]
[mmol]
2
4
6
8
0
0
0
0
1.8
1.5
1.4
1.4
51.7
74.1
76.5
79.1
18.3
16.9
11.2
9.1
0.0
1.3
2.2
4.0
17.7
16.7
14.3
4.7
3.1
2.6
2.3
0.5
2.4
2.9
2.3
0.5
1.8
2.3
0
1
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9
0
6.6
c
3.5
d
a
pH of aqueous phase before treatment (initial pH 4.5). b Conversion of D-glucose. Based on the starting amount in mole of D-glucose. Based
e
f
on the starting amount in mass of D-glucose. Amount determined from the elemental analyses of the water soluble compounds (see ESI). Loss
determined by comparison between the number of mole of nitrogen introduced and the quantity found by the elemental analyses of the water
soluble compounds.
While the amount of 5-HMF was low in the hydrothermal The ratio O/C and H/C of the humins obtained after 80 minutes of
decomposition of D-glucose in the presence of ammonium acetate, reaction, were compared to those of D-glucose, WSO, HMF and LA in
in the presence of ammonium sulfate in the same experimental a van Krevelen diagram (Figures S3†). The plots corresponding to the
conditions, the amounts of 5-HMF was six times larger after 20 humins match nicely with the dehydration line of D-glucose, even if
minutes (Table 2, entry 1), and close after 80 minutes (Table 2, entry the plots are slightly below the line. This observation can be easily
4
). The consumption of 5-HMF was not related to the formation of explained by the incorporation of the nitrogen atoms at the expense
LA. Indeed, the amount of LA did not exceed 4.0 mole % based on of oxygen atoms in the structure of the humins. The more
starting D-glucose. dehydrated solids obtained in the case of sulfuric acid was confirmed
Regarding the formation of the WSO, their quantity decreased by the IR spectra of the humins (Figure S2†).
gradually until 20 minutes, from 17.7 to 6.6 weight % based on The comparison of the 13C CP MAS NMR spectra (Figure 2) of the
starting D-glucose (Table 2). This is reminiscent with the fact that the humins were similar to those reported in the literature 24-27 with the
WSO are a “D-glucose reservoir” or can also react directly with aldol observation of saturated aliphatic groups (region of δ 0 to 55 ppm),
condensation intermediates resulting in their insertion in the alcohol or ether groups (region from δ 60 to 90 ppm), aromatic
structure of the humins.27
groups such as furan rings (region from δ 100 to 160 ppm), ester or
In order to confirm the insertion of some nitrogen atoms into the carboxylic groups (region from δ 165 to 180 ppm) and ketone or
structure of the humins, the latter were characterized by elemental aldehyde groups (region from δ 195 to 210 ppm). Even if the 13C CP
analyses, 13C and 15N CP MAS NMR and Infra-Red. The elemental MAS NMR sequence is not quantitative, as the spectra were recorded
analyses of the humins (Table 3) shown clearly the insertion of using the same experimental conditions, the main difference was
nitrogen atoms in the structure of the solids when ammonium salts found in the area of alcohol or ether groups (region from δ 60 to 90
were used as promotor. In agreement with a different activity ppm). The spectra recorded for the humins obtained from
between the promotors, the humins obtained after 80 minutes from ammonium salts were similar, suggesting very close structures with
NH
the humins obtained after the same reaction time in the presence of spectrum recorded for the humins obtained from sulfuric acid
NH SO and H SO with a formula of C6.0 2.5 and revealed low intensity for the signal in this area, suggesting also a
2.3, respectively. The yields of the humins obtained in the more dehydrated structure.
4 6.4 0.4
OAc were more hydrated with a formula of C6.0H N O2.8 than a high intensity for the signals in this area. On the contrary, the
(
4
)
2
4
2
4
5.7 0.4
H N O
6.0 5.0
C H O
presence of ammonium sulfate as promotor increased with the A hydrothermal decomposition of D-glucose using 15N enriched
reaction time reaching 36.8 weight % (based on starting D-glucose) ammonium sulfate was carried out to enable a 15N CP MAS NMR
after 80 minutes of reaction.
spectrum of the humins obtained in similar conditions of
temperature and concentration and after a reaction time of 80
minutes. On the 15N CP MAS NMR spectrum (Figure 3), 2 signals are
mainly present, centered at δ 130 and 155 ppm. These chemical
shifts are in good agreement with the formation of pyrrole
Table 3 Elemental analyses of the humins obtained during the
hydrothermal decomposition of D-glucose.
Time
Yield a
[wt%]
Promotor
NH SO
Formula
O/C
H/C
[
min.]
derivatives. To explain the formation of pyrrole derivatives, knowing
(
4
)
2
4
20
8.7
C
C
C
C
C
6.0
6.0
6.0
6.0
6.0
H
H
H
H
H
6.5
5.9
5.8
5.7
6.4
N
0.4
N
0.4
N
0.4
N
0.4
N
0.4
O
2.8
O
2.7
O
2.5
O
2.5
O
2.8
0.47
0.45
0.42
0.41
0.47
0.39
1.08
0.98
0.96
0.95
1.08
0.85
+
that NH
4
3
and NH are in equilibrium and based on the DHH
4
6
8
0
0
0
26.8
32.5
36.8
16.3
25.5
intermediate in the humins formation as proposed by Lund et al.,22
we postulated a Paal-Knorr reaction between NH and DHH (Scheme
), as already described by Amarnath et al.
oxoaldehyde derivatives and primary amines.
3
39
2
between 4-
NH
4
OAc
80
80
H
2
SO
4
C
6.0
H
O
5.0 2.3
a
Based on starting amount in mass of D-glucose.
4
| J. Name., 2012, 00, 1-3
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Pl eNa es we dJ oo u nr no at l ao df jCu hs et mm i as tr rgy ins
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sulfate, a very little amount of LA was observed. TVhieew AprHticleoOf ntlhinee
aqueous phases after 80 minutes of reactionDOatI:1105.01°0C39in/Dt0hNeJc0a0s1e55oDf
NH4
+
H2O
NH3 + H3O
sulfuric acid and ammonium sulfate as promotor, were very close,
suggesting that the ammonium part inhibits the LA formation in favor
of the humins. The analyses the humins showed that a part of
nitrogen atoms was inserted into the solid when ammonium salts
were used as promotor. In our conditions, we never observed the
DHH intermediate due to its high reactivity, but it may play a key role,
O
H
H
O
N
+
HO
HO
H
HO
NH
H
O
O
O
DHH
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-
H2O
reacting with NH
3
to give pyrrole derivatives, which can be
H
O
incorporated in the structure of the humins. In the presence of
ammonium acetate, LA was not formed even after a reaction time of
80 minutes. However, the absence of LA can also be explained by the
low conversion of D-glucose, probably related to the buffered
OH
O
HO
O
HO
N
H
HO
N
2
- H O
H
NH
O
Scheme 2 Synthesis of pyrrole derivative from DHH.
medium at pH 4.3. Conversely, the use of ammonium sulfate as the
+
During the hydrothermal decomposition of D-glucose, the process promotor offers a double benefit: the NH
occurs with the formation of water. In the case of ammonium sulfate formation of LA and the equilibrium between NH
as promotor, by comparing the number of mole of all atoms (C, H, N, the slow release of HSO
4
ions prevent the
+
4
and NH
3
allowed
-
4
ions, decreasing the pH to the optimal 1.5-
O, and S) initially introduced with those determined from elemental 2 range for osidic cleavage of the WSO and for 5-HMF formation,
analyses of the water soluble compounds and the humins, the even if the humins formation could not be avoided.
amount of formed water during the reaction was estimated (Table
S7†).
This study allowed us to determine all the species present during the
hydrothermal decomposition of D-glucose using ammonium sulfate
as promotor (Table S8† and Figure S5†) with a total mass balance
very close to the initial amount introduced in the sealed tube (D-
glucose and ammonium sulfate). The mass difference is less than 2.5
wt %, which is expected within the experimental errors. In addition,
in the case of the reaction ran for 80 minutes, when the sealed tubed
was opened after cooling down to room temperature, a little over
pressure was detected, even if the mass difference was only about
1
.6%. A qualitative head-space GC analysis of the gas phase did not
evidence the formation of SO . CO and CO were main gases detected
in the gas phase in 97.5 and 2.5 molar %, respectively (Figure S4†).
As for NH , it was only detected at the level of traces. The
quasi)absence of NH in the gas phase is easily explained by the fact
x
2
3
(
3
that DHH reacts with it to give pyrrole derivatives in a Paal-Knorr
reaction, as already stated.
Conclusions
The acidic hydrothermal decomposition of D-glucose using
ammonium sulfate or ammonium acetate as promotor was studied.
With ammonium sulfate as the promotor, the first steps of the
decomposition of D-glucose are very similar to those observed with
sulfuric acid. The dehydration of D-glucose to 5-HMF competes with
the oligomerization to WSO. We proposed that in these two
Brønsted acidic conditions, the WSO played the role of a “D-glucose
reservoir”, but we cannot exclude the direct incorporation in the
humins by aldol condensations. The formation of 5-HMF from D-
glucose is limited by 2 hydration routes known to be in competition.
On the one hand, 5-HMF can be transformed into LA and FA, and on
the other hand it can it can incorporate into the humins structure via
aldol condensation with the DHH. These two routes were observed
when sulfuric acid was used. However, in the case of ammonium
Fig. 2 13C CP MAS NMR spectra of the humins obtained after 80
minutes.
1
5
Fig. 3
N CP MAS NMR spectra of the humins obtained after 80
15
minutes in the presence of N enriched (NH
4
)
2
4
SO .
This journal is © The Royal Society of Chemistry 20xx
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7 V. Maruani, S. Narayanin-Richenapin, E. FramVieewrAyrticalenOdnliBne.
Conflicts of interest
There are no conflicts to declare.
Andrioletti, ACS Sustainable Chem. Eng., 2018,
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DOI: 10.1039/D0NJ00155D
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New Journal of Chemistry
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View Article Online
DOI: 10.1039/D0NJ00155D
Influence of the ammonium salts used in the Brønsted acid catalyzed
hydrothermal decomposition of D-glucose towards 5-HMF
Victor Maruani, Eric Framery and Bruno Andrioletti
1
1
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2
2
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2
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2
3
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4
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0
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0
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9
0
Graphical resume of the hydrothermal decomposition of D-glucose at 150°C in the presence of ammonium
sulfate