Synthesis of new cellulose ethers using Suzuki-Miyaura reactions

Article abstract of DOI:10.1016/j.carbpol.2014.03.089

Cellulose ethers are functionalized biopolymers that are industrially produced through drastic conditions employing gaseous reactants with a high risk of industrial accident. The cellulose ethers that are commercially available generally bear short carbon-chains. In this work, an alternative method using non-gaseous chemicals is proposed. It relies on the use of the Suzuki-Miyaura reaction employing mild, moisture- and air-stable conditions. Relatively innocuous reagents are used for this step, which allows the formation of a wide range of cellulose ethers bearing various functional groups with different chain-length.

Full text of DOI:10.1016/j.carbpol.2014.03.089

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Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Synthesis of new cellulose ethers using Suzuki–Miyaura reactions
Cédric Goncalvesa,b, Camille Favrea, Pierre Feuardanta, Sarah Kleina,
Carlos Vaca-Garciaa,b,c, Christine Cecuttia,b, Sophie Thiébaud-Rouxa,b
Emeline Vedrennea,b,∗
,
a INP-ENSIACET, Laboratoire de Chimie Agro-industrielle (LCA), Université de Toulouse, 31030 Toulouse, France
b INRA, UMR 1010 CAI, 31030 Toulouse, France
c King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Cellulose ethers are functionalized biopolymers that are industrially produced through drastic conditions
employing gaseous reactants with a high risk of industrial accident. The cellulose ethers that are commer-
cially available generally bear short carbon-chains. In this work, an alternative method using non-gaseous
chemicals is proposed. It relies on the use of the Suzuki–Miyaura reaction employing mild, moisture- and
air-stable conditions. Relatively innocuous reagents are used for this step, which allows the formation of
a wide range of cellulose ethers bearing various functional groups with different chain-length.
© 2014 Elsevier Ltd. All rights reserved.
Received 29 December 2013
Received in revised form 20 March 2014
Accepted 27 March 2014
Available online xxx
Keywords:
Cellulose ethers
Biopolymer
Functionalization of polymers
Suzuki–Miyaura reaction
1. Introduction
tallinity of cellulose. It is followed by a functionalization that often
requires the use of gaseous substances such as methyl chloride,
Cellulose ethers are polymers derived from cellulose that dis-
play very interesting properties. Indeed, they can be used as
thickeners, binders, films formers, water-retention agents, emul-
sifiers (Fukasawa et al., 2011; Thielking & Schmidt, 2000; Porter,
1989; Wang & Zhang, 2009), etc. Most of these derivatives are
water-soluble and low concentrations are required to greatly mod-
ify the formulation rheology. The most commercially important
cellulose ethers are carboxymethylcellulose (CMC; Thielking &
Schmidt, 2000) and alkyl cellulose such as methyl cellulose (MC;
Majewicz & Podlas, 2000) and ethyl cellulose (EC; Koch, 1937) but
some derivatives bearing hydroxyl (hydroxyethylcellulose, HEC;
Bert & Wagenknecht, 2008), carboxyl (Liebert & Heinze, 1998) or
amino (Zhang et al., 2012) moieties have also been developed. These
compounds are generally synthesized in two steps. The first step
is a mercerization process, which results in a reduction in crys-
ethyl chloride, and ethylene oxide (Thielking & Schmidt, 2000).
This step is generally realized in continuously stirred tank reactors,
under pressure (around 3 MPa) at 50–120 ◦C or in the presence of
solvents that solubilize gases. Faced to the small number of avail-
able cellulose ethers, their great potential and the drastic conditions
used for their preparation, it is thus necessary to develop new pro-
cesses that could easily provide a wide range of new ethers. These
processes should use mild conditions and respect to the maxi-
mum the Twelve Principles of Green Chemistry (Anastas & Warner,
2000).
In this context, the Suzuki–Miyaura (SM) reaction was chosen
as it matches most of these criteria and displays a great func-
tional group tolerance (Bej, Srimania, & Sarkar, 2012; Bolliger &
Frech, 2010). This pallado-catalyzed reaction involves the coupling
of a boron reagent (boronic acid, esters or organotrifluorobo-
rates) with a halide or a triflate. Most of these compounds do
not require high-pressure equipment. In order to engage cellu-
lose in a Suzuki–Miyaura reaction, a first step of functionalization
was required to introduce a halide moiety on its scaffold. The
SM reaction was then carried out on the halogenated cellulose to
yield a series of new cellulose ethers. Noteworthy, to the best of
our knowledge, this reaction has never been applied to cellulose
derivatives.
Abbreviations: DS, degree of substitution; DG, degree of grafting; DMA,
N,N-dimethylacetamide; GY, grafting yield; THF, tetrahydrofuran.
∗
Corresponding author at: INP-ENSIACET, Laboratoire de Chimie
Agro-industrielle (LCA), Université de Toulouse, 31030 Toulouse, France.
Tel.: +33 5 34 32 33 63; fax: +33 5 34 32 35 97.
E-mail address: emeline.vedrenne@ensiacet.fr (E. Vedrenne).
http://dx.doi.org/10.1016/j.carbpol.2014.03.089
0144-8617/© 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.089

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Fig. 1. Definition of the weight gain, DS, DG, GY, M(3) and mth
.
2. Experimental
ICH is the peak area of the CH2 moiety of the ethyl group.
2
DG
DS
2.1. Materials and equipment
Grafting yield (GY, %) =
× 100
(4)
4-Bromobenzyl bromide, anhydrous dimethylacetamide,
lithium chloride, sodium hydroxide, sodium sulphate, potas-
sium carbonate, tetrahydrofuran, isopropanol, toluene were
purchased from Aldrich and used without further purification.
Palladium-based catalysts were purchased from STREAM and used
without further purification. All boron derivatives were purchased
from Frontier Scientific and used without further purification.
␣-Cellulose (Aldrich) has been dried at 105 ◦C for 3 h prior to use.
NMR spectra were acquired with FOURIER300 (300 MHz) and
AVANCE (500 MHz with cryoprobe) spectrometers from Bruker
Corporation (Karlsruhe, Germany). The temperature probes were
set at 300 K. Samples were dissolved in d6-DMSO or CDCl3. In
that case, chemical shifts were referenced to tetramethylsilane at
0 ppm. Standard pulse sequences were used for 1H-, 13C-, DEPT135
and two-dimensional (COSY, HSQC, HMBC) NMR spectra. The DS
and the DG were determined from the peak area obtained by inte-
gration of the 1H NMR spectra.
M(3)(g mol−1) = MAGU + DS × MCH PhBr + DG × (MPhC
− MBr
)
H
5
2
2
(5)
mth(g) = nstarting material × M(3)
(6)
M(x), mx and nx are respectively the molar mass, the experimental
weight and the number of moles of compound or group x.
2.3. Synthesis of 4-bromobenzyl cellulose 2c
␣-Cellulose (1.0 g, 6.170 mmol) were stirred in 30 mL of DMA
at 160 ◦C for 2 h then cooled down to 100 ◦C. Lithium chloride
(3.4 g, 0.080 mol) was added and the mixture was allowed to cool
to room temperature overnight. Mixture was heated to 65 ◦C and
powdered NaOH (9.4 g, 0.235 mol) was added followed by a solu-
tion of 4-bromobenzyl bromide (25.4 g, 0.102 mol) in DMA (30 mL)
dropwise. The resulting mixture was stirred for 24 h at 65 ◦C and
then cooled to room temperature. 100 mL of distillated water and
100 mL of chloroform were then added. The aqueous layer was
extracted with chloroform. The combined organic layers were col-
lected and washed with distillated water and concentrated. Ethanol
was added and the resulting mixture was stirred for 24 h and then
filtered. The obtained solid was washed with distillated water,
ethanol and cyclohexane and then dried under vacuum to give
2.60 g of the desired compound as a white powder (DS = 2.78, 60%).
1H NMR (500 MHz, CDCl3): ı = 3.13 (H-5), 3.23 (H-2), 3.29 (H-
3), 3.38 (H-7ꢀ), 3.60 (H-6), 3.84 (H-4), 4.34 (H-1), 4.14 (H-7), 4.60
(H-7ꢀꢀa), 4.99 (H-7ꢀꢀb), 6.78–7.68 (H Ar).
2.2. Measurement
Two cellulose ethers 2 and 3 obtained through each step were
characterized (Fig. 1).
The first compound (2) is the result of an etherification reaction
introducing a bromide functionality on the hydroxyl groups of cel-
lulose (1). The weight gain, the isolated product yield and the degree
of substitution of the hydroxyl moieties of 2 (DS) were determined.
The second compound (3), obtained through the
Suzuki–Miyaura cross-coupling reaction between 2 and a boron
derivative, is characterized by its degree of grafting (DG). It
represents the number of hydroxyl groups substituted by O-CH2-
Ph-Ph-R per anhydroglucose unit (AGU), after the SM reaction
carried out on 2. The grafting yield (GY) represents the yield of the
SM reaction (ratio between the DG and the DS).
13C NMR (125 MHz, CDCl3): ı = 68.1 (C-6), 72.2 (C-7), 74.3 (C-7ꢀꢀ),
74.7 (C-7ꢀ), 75.0 (C-5), 77.0 (C-4), 81.8 (C-2), 83.5 (C-3), 102.7 (C-1),
121.1, 121.5, 121.7 (C-11/11ꢀ/11ꢀꢀ), 129.1, 129.2, 129.4 (C-9/9ꢀ/9ꢀꢀ),
131.3, 131.5, 131.6 (C-10/10ꢀ/10ꢀꢀ), 137.0, 137.1, 138.3 (C-8/8ꢀ/8ꢀꢀ).
FT-IR (KBr, cm−1): 3452 vOH (weak), 2960, 2865 vC H, 1595,
The weight gain, DS, DG, GY, M(3) and mth were calculated by
Eqs. (1)–(6).
1487 vC C, 1404, 1358, vC H, 1152–1037 vC
2c soluble in THF, DMSO and chloroform.
O C, 802 vC Br.
mexp − mstarting material
Weight gain(WG, %) =
(1)
(2)
mstarting material
2.4. General procedure for Suzuki reactions: synthesis of
compounds 3
7
Degree of substitution(DS)
4 × (IAGU/Iphenyl − 1/2)
4-Bromobenzylcellulose 2c (300 mg, DS = 2.78), the correspond-
ing boronic acid (1.471 mmol), sodium sulfate (15 mg, 0.106 mmol),
palladium chloride (7 mg, 0.049 mmol) and potassium carbonate
(550 mg, 4.4 mmol) were added to a mixture of 9 mL of THF and
1 mL of water. The resulting mixture was stirred at 45 ◦C for 8 h. Sol-
vents were evaporated and the resulting grey powder was washed
with 3× 100 mL of cold water, 3× 100 mL of ethanol and then dried
under vacuum.
IAGU is the peak area of the protons on the AGU scaffold and CH2
of the benzyl moiety from 5.25 ppm to 2.88 ppm. Iphenyl is the peak
area corresponding to the phenyl group of the benzyl moiety from
6.60 ppm to 7.88 ppm.
ICH
7 + 2 × DS
2
Degree of grafting (DG) =
×
(3)
2
IAGU
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Table 1
Results for the preparation of halogenated cellulose derivatives.
.
Entry
Reagent
Number of eq.,
addition mode
Sample
DS
Weight
gain
Yield (isolated
product)
Comments
1
2
3
4
1,3-Dibromopropane
12 eq., one portion
12 eq., one portion
12 eq., one portion
12 eq., three
2a
2b
2c
2c
–
–
–
2.76
–
–
–
–
10%
35%
Elimination reaction
Elimination reaction
Insoluble
1-Bromo-4-(2-bromoethyl)benzene
1-Bromo-4-(bromomethyl)benzene
1-Bromo-4-(bromomethyl)benzene
−63%
38%
Soluble in THF/CDCl3
portions
12 eq., dropwise
5
1-Bromo-4-(bromomethyl)benzenea
2c
2.78
130%
60%
Soluble in THF/CDCl3
a
Reaction time: 24 h.
Compound 3a was obtained as
a
grey powder (330 mg,
3. Results and discussion
3.1. Preparation of the halogenated cellulose derivatives
DG = 2.18), using (4-ethylphenyl)boronic acid.
1H NMR (500 MHz, CDCl3): ı = 1.25
( CH2 CH3), 2.68
(
CH2 CH3), 3.15 (H-5), 3.24 (H-2), 3.36 (H-3), 3.63 (H-6),
3.90 (H-4), 4.13, 4.36 (H-7/7ꢀ/7ꢀꢀ), 4.38 (H-1), 4.59, 5.00 (H-7/7ꢀ/7ꢀꢀ),
6.88–7.69 (H Ar).
The first step of this study was the preparation of a halogenated
cellulose derivative. Cellulose was thus solubilized in N,N-dimethyl
acetamide (DMA)/LiCl in the presence of sodium hydroxide and 1,3-
dibromopropane was added (Table 1, entry 1) (Sachinvala et al.,
2000). Even after 20 h at 70 ◦C, we could not observe the for-
mation of the desired halogenated cellulose 2a, but the presence
of allyl-cellulose, issued from an elimination reaction of a HBr
molecule in this basic medium, was detected. The same behaviour
was observed on 1-bromo-4-(2-bromoethyl)benzene, leading to
the formation of 1-allyl-4-bromobenzene (Table 1, entry 2). 1-
Bromo-4-(bromomethyl)benzene was then chosen (Table 1, entry
3) as no elimination can occur on this reagent. Indeed, the desired
halogenated cellulose 2c was obtained but with a DS too low to be
soluble in common solvents, such as CDCl3 (which prevented the
DS to be determined by NMR). It seems highly likely that cellulose
ethers that have even lower DS are soluble in the aqueous phase
and are thus lost during the extraction process, accounting for the
negative weight gain.
The brominated reagent was then added in three portions
instead of one at the beginning of the reaction, which led to the for-
mation of 2c in 10% yield. Noteworthy, 2c is soluble in THF, DMSO
and CDCl3. It was thus dissolved in DMSO-d6 in order to be ana-
lyzed by NMR spectroscopy (Fig. 2). A DS of 2.76 was determined
thanks to the addition of a few drops of d1-TFA in the NMR tube
in order to displace downfield the NMR signals of exchangeable
protons and water (Ross & Lowe, 2000). An excellent yield of 60%
was then obtained when 1-bromo-4-(bromomethyl)benzene was
added dropwise over the course of 24 h (Table 1, entry 5), which
seems to show the poor stability of this reactant in our reaction
conditions. Full structure characterization of 2c was carried out at
500 MHz using one-, two-dimensional homo- and 1H–13C hetero-
correlated techniques. Experiments were run in CDCl3 as d6-DMSO
caused spectral line broadening and required long accumulation
time because of the poor solubility of 2c in this solvent. Thanks to
the 1H/1H COSY and 1H/13C HSQC NMR analyses (Fig. 4), the 1H
and 13C signals of the modified AGU can be respectively assigned
as follows (Fig. 3): 3.13 ppm (H-5), 3.23 ppm (H-2), 3.29 ppm (H-
3), 3.60 ppm (H-6), 3.84 ppm (H-4), 4.34 ppm (H-1) and 68.1 ppm
(C-6), 75.0 ppm (C-5), 77.0 ppm (C-4), 81.8 ppm (C-2), 83.5 ppm (C-
3), 102.7 ppm (C-1). The signals for H-7 and H-7ꢀ were respectively
found at 4.14 and 3.38 ppm, while the protons in position 7ꢀꢀ are
13C NMR (125 MHz, CDCl3): ı = 15.6
(
CH2 CH3), 28.5
(
CH2 CH3), 68.0 (C-6), 72.1, 72.8, 74.5 (C-7/7ꢀ/7ꢀꢀ), 75.0 (C-
5), 77.1 (C-4), 81.6 (C-2), 83.5 (C-3), 102.7 (C-1), 121.5 (Cq-Ar),
126.8, 126.9, 128.2, 129.0, 129.3, 131.1, 131.4 (C Ar), 136.4, 137.7,
138.4, 140.1, 140.6, 143.1, 143.6 (Cq-Ar).
FT-IR (KBr, cm−1): 3434 vOH (weak), 3024, 2961, 2926, 2868
vC H, 1498 vC C, 1458, 1400 vC H, 1152–1037 vC
vC Br.
O C, 810
3a is soluble in THF and chloroform.
Compound 3b was obtained as
a grey powder (326 mg,
DG = 1.76), using (4-butylphenyl)boronic acid.
1H NMR (500 MHz, CDCl3): ı = 0.89 ( CH2 CH2 CH2 CH3),
1.41 ( CH2 CH2 CH2 CH3), 1.61 ( CH2 CH2 CH2 CH3), 2.64
(
CH2 CH2 CH2 CH3), 3.11 (H-5), 3.21 (H-2), 3.30 (H-3), 3.60 (H-
6), 3.88 (H-4), 4.12 (H-7), 4.33 (H-1), 4.55 (H-7ꢀꢀa), 4.63 (H-7ꢀ), 4.99
(H-7ꢀꢀb), 6.77–7.70 (H Ar).
13C NMR (125 MHz, CDCl3): ı = 14.3 ( CH2 CH2 CH2 CH3),
22.8 ( CH2 CH2 CH2 CH3), 32.0 ( CH2 CH2 CH2 CH3), 37.3
(
CH2 CH2 CH2 CH3), 68.2 (C-6), 72.3 (C-7), 74.3 (C-7ꢀ), 74.7 (C-
7ꢀꢀ), 75.1 (C-5), 76.9 (C-4), 81.8 (C-2), 83.6 (C-3), 102.7 (C-1), 121.2,
121.5 (Cq-Ar), 129.1, 129.2, 129.3, 129.4, 129.7, 131.3, 131.4, 131.5,
131.6, 131.7, 131.8 (C Ar), 136.8, 137.0, 137.1, 138.3 (Cq-Ar).
FT-IR (KBr, cm−1): 3424 vOH (weak), 2924, 2867 vC H, 1488
vC C, 1458, 1358 vC H, 1174–970 vC
O
C, 802 vC Br.
3b is soluble in THF and chloroform.
Compound 3c was obtained as
a
grey powder (330 mg,
DG = 1.20), using (4-(ethoxycarbonyl)phenyl)boronic acid.
1H NMR (500 MHz, CDCl3): ı = 1.34 ( CH2 CH3), 3.06 (H-5), 3.17
(H-2), 3.49 (H-3), 3.51 (H-6), 3.77 (H-4), 4.05 (H-7/7ꢀ/7ꢀꢀ), 4.27 (H-
1), 4.33 ( CH2 CH3), 4.43 (H-7/7ꢀ/7ꢀꢀ), 4.64 (H-7/7ꢀ/7ꢀꢀ), 6.71–8.15
(H Ar).
13C NMR (125 MHz, CDCl3): ı = 14.4
( CH2 CH3), 61.1
(
CH CH3), 69.9 (C-6), 72.2, 74.3, 74.6 (C-7/7ꢀ/7ꢀꢀ), 75.2 (C-5),
76.9 (C-4), 81.8 (C-2), 83.6 (C-3), 102.7 (C-1), 121.8 (Cq-Ar), 126.9,
127.2, 128.3, 129.0, 129.1, 129.3, 130.0, 130.2, 131.2, 131.4, 131.5
(C Ar), 143.9, 144.3, 144.9, 166.6 (Cq-Ar).
FT-IR (KBr, cm−1): 3435 vOH (weak), 2867 vC H, 1710 vC O,
1487 vC C, 1397, 1365 vC H, 1183–950 vC
3c is soluble in THF and chloroform.
O C, 803 vC Br.
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
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Fig. 2. 1H NMR spectrum of cellulose ether 2c in DMSO-d6 (with addition of a few drops of d1-TFA).
split and give peaks at 4.60 and 4.99 ppm. The corresponding car-
bons appear at 72.2 ppm (C-7), 74.3 ppm (C-7ꢀꢀ), 74.7 ppm (C-7ꢀ).
Further confirmation of the structure of 2c was then obtained from
the HMBC correlation peaks between H-2 and C-7ꢀꢀ, H-3 and C-7ꢀ
and H-7 and C-6 (Fig. 4).
compared to the cost of boronic acids, this yield improvement was
not significant enough and the subsequent assays were carried out
with only one equivalent of boron species.
In order to study the influence of the temperature on the grafting
yield, the SM reaction was then carried out at room temperature
and 78 ◦C (Table 2, entries 6 and 7). A drop of the grafting yields
was observed, indicating that it is better to run this cross-coupling
reaction at 45 ◦C.
3.2. Preparation of new cellulose ethers using Suzuki–Miyaura
reactions
We then focused our study on the screening of different
palladium-based catalysts. Classical Suzuki–Miyaura catalysts,
such as palladium(II) acetate or [1,1ꢀ-bis(diphenylphosphino)
ferrocene]dichloropalladium(II) were used (Table 2, entries 8 and
9) and palladium chloride appeared to give the best results. The
amount of this catalyst was then optimized (Table 2, entries
10–12) with loading varying from 1 to 10 mol%. Similar yields were
obtained with 4 and 10 mol% (Table 2, entries 4 and 12). For eco-
nomical reasons, a catalyst loading of 4 mol% was chosen for the
rest of the study.
In order to broaden the scope of the synthesized products, we
next proposed to modify the nature of the boronic acid using our
optimized conditions. Boronic acids were chosen so that a part of
the grafted moiety NMR signals do not superimpose itself on the
AGU peaks in order to obtain accurate integrations and so accurate
degrees of grafting. Cellulose ether 3b, bearing a longer alkyl chain,
was obtained in good yield (Table 2, entry 13) with the use of 4-
butylphenylboronic acid. Furthermore, electron-poor boronic acids
appeared to be compatible with these reaction conditions as 3c was
obtained in 43% yield, when 4-(ethoxycarbonyl)phenylboronic acid
was engaged in the reaction (Table 2, entry 14). This lower yield can
be explained by the low nucleophilicity of electron-deficient aryl
boronic acids that decreases the transmetalation rate. These boron
The brominated cellulose 2c was then engaged in the key step
of this synthesis: the Suzuki–Miyaura reaction. Based on the reac-
tion conditions described by Bora’s team (Mondal and Bora, 2012),
a solution of 2c and 4-ethylphenylboronic acid (1 equiv.) in i-PrOH
was stirred in the presence of PdCl2 (4 mol%), Na2SO3 (8 mol%) and
K2CO3 (3 equiv.) at 45 ◦C for 8 h. These mild, moisture- and air-
compatible conditions led to the formation of the cellulose ether
3a (Table 2, entry 1).
A degree of grafting of 1.09 was determined thanks to the 1H
NMR spectra analyses. A typical 1H NMR of 3a is shown in Fig. 5.
Noteworthy, the chemical shift of the ethyl group is not in the
region of cellulose scaffold, which allows to obtain reliable integra-
tions of the different signals. The DG determination thus indicated
that only a part of the brominated ether moieties have been chem-
ically modified by the SM reaction.
For subsequent assays (Table 2, entries 2–4), i-PrOH was
replaced by toluene, water or a mixture of THF/water (9/1). The
latest conditions gave the best results with a grafting yield of 79%
(Table 2, entry 4). THF/water was thus used for the rest of this work.
The influence of the amount of boronic acid was then inves-
tigated. The number of equivalents of 4-ethylphenylboronic acid
was doubled (Table 2, entry 5), yielding 3a in 84% yield. However,
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
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Fig. 3. 1H- and 13C NMR spectra of cellulose ether 2c in CDCl3.
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.089

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Fig. 4. 1H/1H-COSY NMR, 1H/13C-HSQC and 1H/13C-HMBC NMR spectra of cellulose ether 2c in CDCl3.
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.089

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Fig. 4. (Continued ).
Fig. 5. 1H NMR spectrum of cellulose ether 3a in CDCl3.
Please cite this article in press as: Goncalves, C., et al. Synthesis of new cellulose ethers using Suzuki–Miyaura reactions. Carbohydrate
Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.03.089

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Table 2
Results for the preparation of various cellulose ethers.
.
a
Entry
Reagent
Solvent
Temperature (◦C)
Catalyst
Catalyst
amount
(mol%)
Sample
Weight
gain (%)
DG
GY (%)
mexp/mth
(100×, %)
1
2
3
4
5
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic
acidb
i-PrOH
Toluene
H2O
THF/H2O (9/1)
THF/H2O (9/1)
45
45
45
45
45
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
4
4
4
4
4
3a
3a
3a
3a
3a
5.0
7.2
3.2
10.0
9.0
1.09
1.71
ND
2.18
2.34
39
61
ND
78
84
100.5
100.1
ND
101.0
88.0
6
7
8
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Ethylphenylboronic acid
4-Butylphenylboronic acid
4-(Ethoxycarbonyl)phenyl
boronic acid
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
THF/H2O (9/1)
RT
78
45
45
45
45
45
45
45
PdCl2
PdCl2
Pd(OAc)2
Pd(dppf)Cl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
4
4
4
4
1
2
10
4
4
3a
3a
3a
3a
3a
3a
3a
3b
3c
5.7
5.8
7.2
5.5
1.0
1.57
1.04
1.71
1.40
ND
1.40
2.24
1.76
1.20
56
37
61
50
ND
50
80
63
43
99.3
101.5
100.1
99.7
9
10
11
12
13
14
ND
8.6
102.7
100.7
99.3
10.0
14.1
10.1
99.6
a
mth was calculated using the DG that was determined with the NMR analysis.
Two equivalents of 4-ethylphenylboronic acid were used.
b
species are also prone to react in homo-coupling side reactions
(Wong & Zhang, 2001) and more susceptible to metal-catalyzed
protodeboronation (Kuivila, Reuwer, & Mangravite, 1964).
Noteworthy, in all cases, the experimental and theoretical
masses were very close to each other, indicating that the mass bal-
ance is in agreement with the NMR analysis and that no degradation
occurred during the SM reaction.
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