A chitosan derivative containing both carboxylic acid and quaternary ammonium moieties for the synthesis of cyclic carbonates

Article abstract of DOI:10.1002/cssc.201600499

Chitosan, a renewable feedstock, is modified and used as a catalytic support in the presence of potassium iodide. The system is highly efficient towards the incorporation of carbon dioxide (CO₂) into epoxides. It demonstrates very good thermal stability and is recyclable more than five times without loss of activity. The optimal reaction conditions were determined using allylglycidyl ether as a model and extended to a wide range of other epoxides. Cyclic carbonates were obtained with very high yield in a few hours under mild conditions (2-7 bar ≈0.2-0.7 MPa, 80 °and no solvent.

Full text of DOI:10.1002/cssc.201600499

DOI: 10.1002/cssc.201600499
Full Papers
A Chitosan Derivative Containing Both Carboxylic Acid
and Quaternary Ammonium Moieties for the Synthesis of
Cyclic Carbonates
Vincent Besse,[a, b] Nicolas Illy,[a, c] Ghislain David,[a] Sylvain Caillol,*[a] and Bernard Boutevin[a]
Chitosan, a renewable feedstock, is modified and used as a cat-
alytic support in the presence of potassium iodide. The system
is highly efficient towards the incorporation of carbon dioxide
(CO2) into epoxides. It demonstrates very good thermal stabili-
ty and is recyclable more than five times without loss of activi-
ty. The optimal reaction conditions were determined using al-
lylglycidyl ether as a model and extended to a wide range of
other epoxides. Cyclic carbonates were obtained with very
high yield in a few hours under mild conditions (2–7 barꢀ0.2–
0.7 MPa, 808C) and no solvent.
Introduction
Cyclic carbonates were first described in the early 1930s by
Carothers et al.[1a,b,c] They are gaining a great deal of attention
in both scientific and industrial communities because they are
very versatile; for example, they can be used as synthons in or-
ganic synthesis, as high boiling polar solvents, or as electro-
lytes. In the field of materials chemistry, they have long been
used for the preparation of polycarbonates but they are also
especially promising for the synthesis of non-isocyanate poly-
urethanes (NIPUs).[2a–g]
Scheme 1 shows the conventional routes used to synthesize
five-membered cyclic carbonates. 1,2-diols can react with phos-
gene to form cyclic carbonates with high yields. But the toxici-
ty of phosgene is the main drawback. Greener alternatives
have been developed recently, whereby diols are reacted with
ethylene carbonate, urea, or carbon dioxide.[3] Carbon dioxide
is of particular interest as this reagent is cheap, environmental-
ly friendly and a green source of chemical carbon to substitute
the phosgene. A wide range of CO2 incorporation reactions
has been developed for the synthesis of cyclic carbonates from
dioxolane derivatives, olefins, or epoxides. Currently, cyclocar-
bonates are industrially produced from the 100% atom eco-
Scheme 1. Conventional routes for the synthesis of five membered cyclic
carbonates.
nomic reaction between carbon dioxide and epoxides.[4] How-
ever, CO2 has a low reactivity and this reaction needs a high
activation energy.[5] To reduce the energy input required to
transform CO2 and to overcome the high reaction barrier, the
development of high-performance catalysts is a key technolo-
gy.
The attractiveness of a catalyst could be evaluated in accord-
ance with the following criteria: its catalytic activity, the re-
quired reaction conditions (temperature, pressure, and time),
the achieved yields and selectivities, its price and availability,
its reusability and recycling abilities, and its environmental sus-
tainability.[6] A large variety of catalytic systems has been devel-
oped to perform the carbonation reaction. Different metal-
based systems have proven to be very efficient and allow the
cycloaddition under mild conditions (atmospheric pressure and
room temperature).[4] Nevertheless, organocatalysts are a prom-
ising alternative because they provide potential economic, en-
vironmental, and scientific benefits. They are often less sensi-
tive to air and moisture allowing an easier experimental proce-
dure, less expensive, and less toxic than metal-based systems.[7]
Recent reviews have summarized the large variety of organo-
catalysts that have been developed for this purpose.[6,8] To the
[a] Dr. V. Besse, Dr. N. Illy, Dr. G. David, Dr. S. Caillol, Prof. B. Boutevin
Institut Charles Gerhardt Montpellier UMR 5253
CNRS, Universitꢀ de Montpellier
l’Ecole Nationale Supꢀrieure de Chimie de Montpellier (ENSCM)
8 rue de l’Ecole Normale, 34296 Montpellier Cedex 5 (France)
E-mail: sylvain.caillol@enscm.fr
[b] Dr. V. Besse
COLAS S.A.
7 place Renꢀ Clair, 92653 Boulogne-Billancourt (France)
[c] Dr. N. Illy
Sorbonne Universitꢀs
UPMC Univ Paris 06, CNRS
Institut Parisien de Chimie Molꢀculaire
Equipe Chimie des Polymꢁres
4 place Jussieu, 75005, Paris (France)
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cssc.201600499.
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best of our knowledge, no organocatalyst currently fulfills all
the above criteria.
conditions. Finally, its efficiency to achieve the synthesis of
structurally different cyclic carbonates will be assessed.
Supported organocatalysts are the easiest way to perform
solvent-free heterogeneous phase reactions and to facilitate
the reusability of the catalyst. Inorganic supports (e.g., sili-
ca[9a–f]) as well as organic supports such as synthetic polymer-
s[9b,f,10a–i] have been reported. However, immobilized catalysts
require harsh conditions (T>1008C, P>12 barꢀ1.2 MPa, and/
or long reaction times) to reach high conversions and high
yields. These restrictive conditions are an obstacle for their de-
velopment of industrial use. Milder conditions with these cata-
lysts inevitably result in a loss of activity. Bio-based platforms
are even more interesting to increase the sustainability of the
process.[6,11]
Chitosan catalyst synthesis
According to the work of Song et al. on lecithin,[26] the chitosan
was modified in a way that the resulting structure is likely to
dissociate KI. Thus, ammonium and carboxylic acid functions
were introduced in two steps as shown in Scheme 2. Numer-
ous papers have reported the modification of the primary
amine of chitosan with epoxides in a water medium.[16d,f] Thus,
in a first step, allyl and trimethylammonium moieties were in-
troduced along the chitosan backbone through epoxide–
amine reactions with allyl glycidyl ether (AGE) and glycidyl tri-
methylammonium (GTA) chloride. The reaction was performed
in water at 858C. Notably, the hydroxyl groups of chitosan are
not sufficiently nucleophilic to induce ring opening of glycidyl
trimethylammonium chloride or AGE, whereas the amine
group of chitosan is nucleophilic enough to do so.[16e,27] The
epoxidized chitosan is water-soluble. The 1H NMR spectrum
shows signals corresponding to the introduction of the allyl
and quaternary ammonium substituents (Figure S1, Supporting
Information). Two multiplets at 5.92 ppm (CH2 =CHCH2O) and
5.20–5.40 (CH2 =CHCH2O) and a doublet at 4.04 ppm (CH2 =
CHCH2O) are typical of the allyl protons. The methyl groups of
the quaternary ammonium group are observed as a very
strong peak at 3.22 ppm. The degrees of substitution were cal-
culated from the comparisons between the signal intensities of
Chitosan is the deacetylation product obtained from chitin,
which is the second most abundant natural polysaccharide
(1013 kg/year) and can be extracted from shells of crustaceans
and the cells walls of fungi and insects.[12] Although only 24 kil-
otons were produced in 2015, the potential production capaci-
ty of chitosan could raise to 250 kilotons. This polymer is
known to be biodegradable,[13] biocompatible,[14] and nontox-
ic.[15] In addition, chitosan offers numerous possibilities for
modification such as alkylation, acylation, quaternization, hy-
droxyalkylation, thiolation, sulfation, and phosphorylation.[16a–h]
The resulting chitosan derivatives are promising high-value
materials; for example, chitosan has been widely used for
tissue engineering,[17] cosmetics,[18] food,[19] or wastewater treat-
ment technologies.[20] Several chitosan-based systems are effi-
cient organocatalysts for the synthesis of cyclic carbonates.[21a–c]
Quaternary ammonium salt-functionalized chitosan derivatives
are active catalyst under conventional heating[22a–b] or micro-
wave irradiation.[23] Sun et al.[24] developed a chitosan-support-
ed ionic liquid catalyst. However, harsh conditions are required
to reach quantitative conversion even under microwave irradi-
ation (P>12 bar; T>1208C).[22a,23] In the case of quaternary
ammonium bearing chitosan, several authors underlined the
role of chitosan hydroxyl groups.[22b] Carboxylic acid groups are
also known to enhance the catalytic activity[11,25] but this effect
has never been combined with quaternary ammonium groups
supported on chitosan derivatives.
+
the ÀCH=CH2 protons and the ÀC(CH3)3 protons with the
signal of acetyl groups and were found to be approximately
0.70 and 0.30, respectively. The functionalization with glycidyl
trimethylammonium chloride seems to be more difficult proba-
bly owing to the charge repulsion between quaternary ammo-
nium moieties. The allyl-group-containing compound 1 (see
Scheme 3 for structure of compounds 1 and 2) was then func-
tionalized with 3-mercaptopropionic acid using a thiol-ene ad-
dition reaction to afford compound 2 according to a procedure
reported by Illy et al.[16f] 1H NMR analysis of compound 2 dem-
onstrated that the addition of the thiol to the allyl groups oc-
curred in 100% yield, with data consistent with that expected
for the modified side chain groups (Figure S2).
In this paper, we report on the synthesis of a chitosan-based
catalytic system that shows high activity even at a temperature
of 808C and under a CO2 pressure of 7 bar. To the best of our
knowledge, such mild pressure and temperature conditions
have never been reported for supported organocatalysts. Chi-
tosan was functionalized by both quaternary ammonium and
a carboxylic group and used as a catalyst in combination with
potassium iodide in solvent-free conditions. The optimal condi-
tions in terms of concentration, temperature, and pressure
were determined with allyl glycidyl ether prior to the carbona-
tion of various epoxides.
The resulting polymer contains both quaternary ammonium
and carboxylic acid groups with a ratio of 30/70 and is, there-
fore, zwitterionic. Chitosan was also functionalized with glycid-
yl trimethylammonium chloride only (compound 3, see Fig-
ure S3 and Supporting Information for its synthesis). Its degree
of substitution was approximately equal to 0.75.
Thermal characterization of the catalyst
Thermogravimetric analysis (TGa) of compound 2 (see Fig-
ure S4 and S5) shows that its thermal degradation starts at ap-
proximately 2208C. This value is similar to the degradation
temperature of unmodified chitosan. The stability of com-
pound 2 at 808C was assessed by a 64 h isothermal TGA ex-
periment. We observed a relatively rapid weight decrease of
8.9% after which a plateau was reached. This mass loss is only
Results and Discussion
First, the modification of chitosan and its characterization will
be described. Then, the obtained chitosan derivative will be
evaluated as a carbonation catalyst under different reaction
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the most efficient in terms of energy consumption
for this type of catalyst. Compound 2 was designed
to induce the greatest possible dissociation of KI,
thus the quantity of compound 2 is related to the
functionalization of chitosan. As shown in Table 1
(Entry 14), compound 2 associated with KI displayed
a remarkable activity to catalyze the propylene oxide
carbonation. A quantitative yield was achieved with
half the amount of catalyst and under milder condi-
tions compared to the previously published ammoni-
um-supported catalytic systems. In particular, the re-
quired pressure is below the pressures previously
used in the literature. This outcome is very promising
and additional studies were performed using allyl
glycidyl ether (AGE) as a model substrate.
AGE carbonation using compound 2
Table 2 summarizes the results obtained for the car-
bonation reaction of AGE. Runs 1–3 were performed
without KI as a control. A preliminary experiment was
conducted without any catalyst (Entry 1). As expect-
ed, no reaction took place. The second entry was per-
formed with only native chitosan (Entry 2) and no
conversion was observed. Tharun et al.[22b] have dem-
onstrated the efficiency of a chitosan quaternized
with methyl iodide (CH3I) for the carbonation reac-
tion of propylene oxide. The conditions described
remain harsh as the best carbonation conditions
were obtained at 11.7 bar at 1208C and the conver-
sion was not quantitative (87%). As a consequence,
we decided to proceed to an experiment with com-
pound 3, which contains quaternary ammonium moi-
eties thanks to glycidyl trimethylammonium (see syn-
thesis in Supporting Information). In that case, we
clearly see that the use of compound 3 without KI re-
sults in low yield (15%). This could be explained by
the presence of chlorine anions, which are known to
show a lower activity compared to iodide for the syn-
thesis of cyclic carbonates. Nevertheless, Zhao
et al.[22a] have shown that a similar chitosan derivative
with IÀ as a counterion required a temperature of
1408C and a CO2 pressure of 40bar to perform the
carbonation (Table 1, Entry 6). The subsequent tests
were then conducted using Compound 2 and KI as
the catalytic system (Entries 4–11). The conversion
Scheme 2. Modification of chitosan with AGE and GTA followed by thiol-ene addition
with 3-mercaptopropionic acid.
owing to the moisture content of compound 2, which shows
a very high stability at this temperature.
was completed after 4 h at 808C and under 7 bar (Entry 4),
thus confirming the preliminary result obtained with propylene
oxide. The concentration of the catalytic system was then re-
duced to 0.125 mol% (Entry 5) and 0.06 mol% (Entry 6) and
the reactions were stopped after 4 h; the yields were still
quantitative according to AGE conversion. This clearly demon-
strates a synergistic effect between the synthesized compound
2 and KI.
Catalytic properties of compound 2
Table 1 shows the poor catalytic effects of chitosan as well as
KI when they are used separately for the carbonation of pro-
pylene oxide (PO). Different polymer-supported ammonium-
based catalytic systems have been developed and reported for
the carbonation of PO. Very recently, polystyrene-supported
triethanolammonium iodide displayed a high activity and was
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room temperature and remains slow at 508C (6%)
compared to the quantitative conversion reached at
808C after only 2 h.
In addition, the sample of compound 2 that was
subjected to a 64 h TGA experiment at 808C was
used to evaluate its stability over time. No loss of ac-
tivity was noticed as AGE was converted into the cor-
responding cyclic carbonate quantitatively after 3 h
(P=7 bars,
T=808C,
[compound
2]=[KI]=
0.125 mmol).
The effect of the reaction time on the conversion
of AGE was also investigated. Tests were performed
in the presence of 0.125 mmol of chitosan and
0.125 mmol KI under a CO2 pressure of 7 bars and
a temperature of 808C. The reaction proceeds very
fast as 50% of the initial AGE was converted into its
carbonation product after 30 min. The reaction is
almost finished after only 2 h with a conversion of
98%. As a consequence, under these conditions, a re-
action time of 2 h is sufficient for this system. Nota-
bly, under milder conditions and a lower concentra-
tion of the catalytic system, this system is twice as ef-
ficient as any other catalytic systems described in the
literature. Carbonation experiments were also per-
formed under different pressure conditions (En-
tries 9–11). After 4 h, the conversion increased with
a carbon dioxide pressure rising to 7 bars and then
reached up to 98% over 7 bar. However, an increase
of the pressure led to a decrease of the conversion;
the yield was only 86% after 4 h under 12 bar. A
widely accepted interpretation is that the pressure of
carbon dioxide affects the mass transfer during the
reaction. Two phases exist under the reaction condi-
tion: a gas phase (carbon dioxide-rich) and a liquid
phase (AGE-rich). The concentrations of both CO2
and AGE in the two phases changes with CO2 pres-
sure. At a lower CO2 pressure range the concentra-
tion of carbon dioxide in the liquid phase increases
with CO2 pressure, which is favorable for the reaction
because the catalyst is located in the liquid phase
and CO2 is a reactant. However, the solubility of AGE
in CO2 increases with increasing CO2 pressure and
thus leads to a dilution effect in the liquid phase at
a higher CO2 pressure range, which might hinder the
adsorption of AGE on the surface of the catalyst.
These two competing factors resulted in a maximum
reaction activity at approximately 7 bar.
Scheme 3. Proposed carbonation mechanism using the chitosan-based catalytic system.
Table 1. Comparison of the activity of different ammonium-supported catalytic sys-
tems toward carbonation of propylene oxide.
Entry Catalyst
Cat. amt.
[mol%]
t
[h]
P
T
Yield
[bars] [8C] [%]
1
2
3
4
5
6
7
8
9
chitosan
1
1
5
2
0.6
1.7
1.7
1.6
0.75
2
4
2
12
3
6
6
20
20
80
20
12
40
40
11.7
120
120
100
110
120
140
2[24]
3[28]
KI
PS Me3N+ClÀ
97[10a]
92[10g]
98[29]
73[22a]
PS EtN(CH2CH2OH)+BrÀ
PS-hexyl-NMe3+IÀ
chitosan-N+Me3ClÀ
chitosan-N+Me3IÀ
CH3I-quaternized chitosan
bis-ammonium PS
6
6
140 100[22a]
120
130
90
89[23]
99[30]
93[9f]
96[24]
2.5 12
4
4
+
10
11
PS-MeN(CH2CH2OH)3 IÀ
chitosan-functionalized
10
20
1
120
1-ethyl-3-methyl imidazolium Br
chitosan-grafted quaternary
phosphonium ionic liquid
carboxymethyl cellulose/ionic liquid 1.2
2+KI [this work] 0.38
12
–
4
25
120
99[31]
13
14
2
3
18
7
110
80
98[11]
97
Proposed mechanism of the coupling reaction
Effect of the temperature, reaction time, and pressure on
the catalytic system efficiency
The best activity of KI is found if the interaction between K+
and IÀ is low, meaning that the anion is free to react with elec-
trophilic species. As a result, the presence of a well-defined
support in the medium allows for better dissociation. Song
et al. described a mechanism for the lecithin/potassium halide
system.[26] In this mechanism, KI dissociates owing to the car-
An important aspect of such a carbonation reaction is the tem-
perature needed to obtain complete conversion of the epoxide
reactants. To investigate the effect of the temperature we per-
formed three experiments at room temperature (258C), 508C,
and 808C (Entries 7–9). The carbonation does not occur at
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Synthesis of a library of cyclic carbonates from CO2 and ep-
oxides
Table 2. Carbonation reactions performed with 32.2 mmol AGE as sub-
strate.
Run
Catalyst
system
Support
[mol]
KI
[mol]
T
[8C]
t
[h]
P
[bar]
Conv.
[%]
The effectiveness of a good carbonation catalyst is not only
measured by its ability to selectively yield a product in a short
time but even more so, its ability to efficiently catalyze a wide
range of epoxides. Therefore, we investigated the synthesis of
different cyclic carbonates using the corresponding epoxides,
KI, and compound 2 in a stainless steel autoclave (50 mL)
equipped with a mechanical stirrer. Table 3 summarizes the re-
sults obtained, which show that the catalytic system is highly
efficient for the synthesis of all the mono-substituted terminal
epoxides we investigated (Entries 1–6). After 4 h of reaction,
AGE showed the highest yield (100%) whereas epichlorohy-
drin, containing an electron withdrawing group (CH2ÀCl),
1
2
3
4
5
6
7
8
9
–
0
0
0
0
80
80
80
80
80
80
25
50
80
80
80
24
24
24
4
7
7
7
7
7
7
7
7
7
0
0
chitosan
3
0.25
0.25
0.25
0.125
0.06
0.125
0.125
0.125
0.125
0.125
15
100
98
98
0
2/KI
2/KI
2/KI
2/KI
2/KI
2/KI
2/KI
2/KI
0.25
0.125
0.06
0.125
0.125
0.125
0.125
0.125
4
4
4
4
2
2
2
6
97
41
86
10
11
2
12
boxylic acid function and the ammonium moiety,
which leads to better activity of the iodide anion.
The formation of the cyclic carbonate is typical
and can be described as follow. The first step is the
dissociation of KI. Secondly, the IÀ anion attacks the
less hindered carbon of the epoxy ring, prior to
a ring opening reaction step. The next step is the in-
troduction of CO2 to form an alkyl carbonate anion.
The last step is an intramolecular cyclic step to form
the desired cyclic carbonate and at the same time re-
generate the catalytic system.
Table 3. Various carbonates obtained by epoxide carbonation catalyzed by KI in the
presence of compound 2 (P=7 bar, 32.2 mmol epoxide, 0.125 mmol KI, 0.125 mmol
compound 2, 808C).
Entry
1
Epoxide
Products
t [h]
Yield [%] TOF [hÀ1
]
TON
4
89
57.3
63.9
57.3
62.6
229.2
2
3
4
4 (2) 100 (98)
255.6
229.2
250.2
4
4
89
Nevertheless, it should be underlined that chloride
anions are also present in our catalytic system as the
initial counter-ions of the ammonium groups. ClÀ
and IÀ act as competitors. When it comes to nucleo-
philic attack in such reaction media, iodide ions are
way more reactive toward ring opening compared to
chloride ions.[32] The iodide based catalysts are about
8–10 times more reactive than those based on chlo-
ride anion. Therefore, by interacting with the ammo-
nium group, ClÀ might decrease the dissociation of
KI and reduce the catalytic activity of our system.
Thus, our system might not be fully optimized and
the elimination of the ClÀ anions might result in an
improvement of our system.
100
5
6
7
4
4
4
91
81
0
58.6
52.2
0
234.4
208.8
0
showed the lowest yield (81%). The turnover frequency (TOF)
and turnover number (TON) correlated with the reaction yields.
As an example, the best TOF of 63.9 hÀ1 (TON=255.6) was ob-
tained for the quantitative conversion of AGE (Table 3, Entry 2),
whereas the lowest TOF of 52.2 hÀ1 (TON=208.8) was obtained
with epichlorohydrin, which had a conversion of 81% (Table 3,
Entry 6). This can be explained by a reduced electron density
of the epoxide oxygen atom in the latter.[26] We tried to obtain
a 6-membered cyclic carbonate (6-CC) from 3-methyl-3-oxeta-
nemethanol but the reaction did not succeed. The synthesis of
six-membered heterocycles based on the direct coupling be-
tween oxetanes and CO2 is generally more difficult than the
carbonation of epoxides. Carbon dioxide insertion into a heter-
ocyclic ring requires a high-energy substrate to favor the reac-
tion. Epoxides have higher ring-strain and are therefore easier
to ring-open. Recently, several papers have been able to
design transition metal based bi-component catalysts that
Reusability of compound 2
The reusability of compound 2 was investigated following
a procedure similar to that described by Tharun et al.[22b] Chito-
san (0.125 mmol) and KI (0.125 mmol) were used for the carbo-
nation of AGE at 7 bar and 808C. The reactor was opened after
4 h. Compound 2 was regenerated by washing with acetone,
which allows for the complete removal of KI. It was then fil-
tered and dried at 408C for 18 h. The regenerated compound
2 was then used for the carbonation of AGE under similar con-
ditions. The catalytic system was perfectly stable even after 5
cycles as no loss of activity was observed.
This result can be explained by the excellent thermal stabili-
ty of the modified chitosan at 808C according to the isother-
mal TGA experiments (see Figure S5).
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(TGA) were obtained on a TA Instruments Q50 apparatus. The ini-
tial weight of each sample tested was approximately 15 mg. Data
were collected using the following temperature programs:
a 108CminÀ1 ramp between 35 and 6008C or a 64 h isotherm at
808C. All experiments were performed under a stream of air.
allow the conversion of oxetanes into 6-membered cyclocarbo-
nates.[8,33a–c] They required the use of an organometallic cata-
lyst and a nucleophilic compound under carbon dioxide pres-
sure above 10 bar.[34] The metal complex serves as a Lewis acid
to form an adduct with the heterocycle to activate the oxetane
by increasing its electrophilicity. In a second step, the activated
oxetane is ring-opened by the nucleophilic compound. Our
catalytic system does not rely on Lewis acid metals and is,
therefore, unsuitable for oxetanes.
Synthesis of compound 1
Chitosan (2.0 g, 10.9 mmol of primary amine groups, 1 eqiuv.) was
dispersed in 100 mL of deionized water at 858C. Glycidyltrimethy-
lammonium chloride (1.65 g, 9.79 mmol, 0.9 eqiuv.) and AGE
(0.60 g, 5.26 mmol, 0.48 eqiuv.) were added dropwise to the reac-
tion mixture under vigorous stirring. Subsequently, the same
amounts of the reactants were added dropwise after 24 and 48 h
of reaction. The reaction was stopped after 72 h. The polymer was
recovered by precipitation in acetone. The precipitate was washed
several times with acetone and dried under vacuum at 458C for
48 h to obtain compound 1 as a white powder (2.55 g). 1H NMR
(D2O, 400 MHz): d=5.92 (m, 0.70H, CH2CH=CH2), 5.20–5.40 (m,
1.36H, CH2CH=CH2), 4.40–4.80 (m, H-1, HDO), 4.25 (m, 0.5H,
Conclusions
The first part of this work was dedicated to the modification of
chitosan to improve the dissociation of potassium iodide. This
work demonstrates the convenience of the chitosan-based cat-
alytic system, which allows the synthesis of 5-membered cyclic
carbonates under low pressure (7 bar or less), low temperature
(808C), with a low amount of potassium iodide (compound 2/
KI, 1:1, 0.125 mmol) and without solvent. Our study provides
proof of the stability of the chitosan-based system even after 5
cycles. Moreover, compound 2 is stable after 64 h at 808C as it
can be reused without any noticeable deterioration in its per-
formance. Chitosan derivative 2 and potassium iodide have an
excellent synergetic effect. As a consequence, chitosan has the
potential to be an abundant, greener, and active catalyst for
the synthesis of cyclic carbonates from CO2 and epoxides. No-
tably, this system is not active toward 3-methyl-3-oxetaneme-
thanol. Oxetane carbonation requires an increase in the elec-
trophilicity of the heterocycle. However, our catalytic system
does not rely on a heterocycle activation process and is there-
fore not suitable for 6-CC synthesis.
CH2CH(OH)CH2N), 3.32–4.16 (m, 7.8H, CH2CH=CH2, CH2N(CH3)3+
,
CH2CH(OH)CH2O, CH2OCH2CH=CH2, H-3, H-4, H-5, H-6), 3.19 (s,
2.88H, CH2N(CH3)3+), 2.35–3.08 (m, 2.5H, NHCH2, H-2), 2.05 ppm (s,
0.3H, C(O)CH3).
Synthesis of compound 2
Compound 1 (0.5 g, 1 eqiuv. of allyl groups) was dissolved in
20 mL of deionized water at 508C. After complete dissolution and
cooling of the solution to room temperature, 3-mercaptopropionic
acid (2.0 g, ꢀ15 eqiuv.) and 4,4’-azobis(4-cyanovaleric acid) (0.1 g,
ꢀ0.2 eqiuv.) dissolved in 2.0 mL of methanol were added. After
20 min of argon bubbling, the stirred homogeneous reaction mix-
ture was heated at 708C and stirred for 20 h. The pH of the solu-
tion was adjusted to 5.5 by the addition of a NaOH solution. The
polymer was recovered by precipitation in acetone, dissolved
de novo in deionized water, precipitated again in acetone, and fi-
nally dried under vacuum at 458C for 48 h to obtain compound 2.
0.47 g of slightly yellow powder are obtained. 1H NMR (D2O,
400 MHz): d=4.20–5.15 (m, H-1, CH2CH(OH)CH2N, HDO), 3.03–4.32
Experimental Section
Materials and methods
Chitosan 652 (Chitine, France) is an ivory white powder originating
from shrimp shells. Its degree of deacetylation is 90% (supplier
data), its molecular weight is approximately 150000 gmolÀ1 and its
hydration degree is 10 w% (TGA). Sodium iodide (KI, 99.5%),
sodium hydroxide (97%), and 1-methyl-2-pyrrolidinone (99%) were
purchased from Sigma–Aldrich and used without further purifica-
tion. Allyl glycidyl ether (97%, AGE) and other epoxides were also
obtained from Sigma–Aldrich and used as received. Glycidyltrime-
thylammonium chloride (>90%), 4,4’-azobis(4-cyanovaleric acid)
(>75%), 3-mercaptopropionic acid (>99%) were purchased from
Sigma–Aldrich and used as received. CO2 of 99.999% purity was
used without further purification. CH2Cl2 was obtained from SK
Chemicals, Korea, and used as received. Deuterated solvents (D2O,
CDCl3, and [D6]DMSO) were purchased from Eurisotop (Saint-Aubin,
France).
(m, 13.51H, CH2CH(OH)CH2O, CH2N(CH3)3+
, CH2OCH2CH=CH2,
OCH2CH2CH2S, CH2N(CH3)3+, H-3, H-4, H-5, H-6), 2.33–3.03 (m,
6.74H, NHCH2, CH2SCH2CH2COOH, H-2), 2.07 (s, 0.3H, C(O)CH3),
1.89 ppm (m, 1.43H, OCH2CH2CH2S).
Synthesis of cyclic carbonates
Carbonation reactions of the epoxide reactants were typically per-
formed according to the following procedure. The epoxide
(32.2 mmol), modified chitosan (0.125 mmol), and potassium
iodide (KI, 0.125 mmol) were introduced in an autoclave (50 mL).
The carbon dioxide was then added (7 bar) and the reaction pro-
ceeded at 808C during 2 h. The conversion was determined using
1H NMR for all the monomers using the specific chemical shifts of
the oxirane and carbonate protons. The crude material was filtered
off and distilled to remove chitosan and KI.
Characterization
1
All H NMR measurements were recorded on Bruker 250 MHz and
AC-400 MHz spectrometers at room temperature in deuterium
oxide (D2O), deuterated chloroform (CDCl3) or deuterated dimethyl-
sulfoxide ([D6]DMSO). The chemical shifts are reported in parts per
million relative to tetramethylsilane. Thermogravimetric analyses
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Full Papers
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Keywords: chitosan
·
cyclic carbonates
·
epoxides
·
heterogeneous catalysis · supported catalyst
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Revised: June 6, 2016
Published online on && &&, 0000
ChemSusChem 2016, 9, 1 – 8
www.chemsuschem.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

FULL PAPERS
V. Besse, N. Illy, G. David, S. Caillol,*
B. Boutevin
Renewable catalysis: A chitosan-based
catalyst for epoxide carbonation is de-
scribed. The catalyst is efficient for the
synthesis of a wide range of com-
pounds under significantly milder oper-
ating conditions (pressure and tempera-
ture) compared to previously reported
bio-based supported catalysts. It is also
recyclable more than five times without
loss of activity.
&& – &&
A Chitosan Derivative Containing Both
Carboxylic Acid and Quaternary
Ammonium Moieties for the Synthesis
of Cyclic Carbonates
&
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!