Selective Syntheses and Properties of Anionic Surfactants Derived from Isosorbide

Article abstract of DOI:10.1002/jsde.12182

Two series of anionic surfactants (endo-5-O-alkyl isosorbide-2-O-propyl sulfonic acid sodium salt and exo-2-O-alkyl isosorbide-5-O-propyl sulfonic acid sodium salt) with straight alkyl chains (hexyl, octyl, decyl, and dodecyl) were synthesized from isosorbide derived from biomass, through steps of allylation, alkylation, and sulfonation. The selectivity and efficiency of the reactions were optimized by adjusting the solvent, catalyst, reactant molar ratio, and temperature. The product 2-O-allyl isosorbide was obtained with a yield of 81% and selectivity of 23:1 (endo:exo), and 2-O-alkyl isosorbide was obtained with a yield of 72% and selectivity of 24:1 (exo:endo). The synthesized anionic surfactants were characterized using the critical micelle concentration (CMC), surface activity, emulsion stability, foaming height, and the Turbiscan Stability Index. The CMC decreased with increasing alkyl chain length. The properties of endo form and exo form were compared.

Full text of DOI:10.1002/jsde.12182

J Surfact Deterg (2018)
DOI 10.1002/jsde.12182
ORIGINAL ARTICLE
Selective Syntheses and Properties of Anionic Surfactants Derived
from Isosorbide
1
,2
1,2
1,3
4
2
Jung-Eun Cho · Dae-Seon Sim · Young-Wun Kim · Jongchoo Lim · Noh-Hee Jeong ·
1,3
Ho-Cheol Kang
Received: 4 January 2018 / Revised: 26 May 2018 / Accepted: 30 May 2018
2018 AOCS
©
Abstract Two series of anionic surfactants (endo-5-O-
alkyl isosorbide-2-O-propyl sulfonic acid sodium salt and
exo-2-O-alkyl isosorbide-5-O-propyl sulfonic acid sodium
salt) with straight alkyl chains (hexyl, octyl, decyl, and
dodecyl) were synthesized from isosorbide derived from
biomass, through steps of allylation, alkylation, and sulfona-
tion. The selectivity and efficiency of the reactions were
optimized by adjusting the solvent, catalyst, reactant molar
ratio, and temperature. The product 2-O-allyl isosorbide was
obtained with a yield of 81% and selectivity of 23:1 (endo:
exo), and 2-O-alkyl isosorbide was obtained with a yield of
Introduction
A major focus of bioenergy is using plant-derived biomass
from crops such as corn, rapeseed, cassava, and sweet pota-
toes (Seo et al., 2009; Studer et al., 2009). Carbohydrates
obtained from the biomass can be used to create surface-
active compounds (i.e., surfactants) by linking an alkyl
chain (hydrophobic tail group) to a hydrophilic head group
(Stubenrauch, 2001). Generally, surfactants can be divided
into three types: cationic, nonionic, and anionic. Cationic
surfactants are adaptable for many applications, including
antibacterials, antielectrostatics, bentonite inhibitors in oil
fields, corrosion inhibitors for metals, and as structural and
mesoporous templates. Nonionic surfactants such as alco-
hol ethoxylate (AE) and nonylphenol ethoxylate have use-
ful properties such as low foam, high temperature
sensitivity, high tolerance to water hardness, and good oily
soil detergency. Meanwhile, anionic surfactants such as lin-
ear alkylbenzene sulfonate and alkyl ethoxylate sulfates
(AES) have high foam, low temperature sensitivity, low
tolerance to water hardness, and good particulate soil deter-
gency (Raney, 1991). Anionic surfactants account for more
than 60% of the total surfactant production globally.
72% and selectivity of 24:1 (exo:endo). The synthesized
anionic surfactants were characterized using the critical
micelle concentration (CMC), surface activity, emulsion sta-
bility, foaming height, and the Turbiscan Stability Index.
The CMC decreased with increasing alkyl chain length. The
properties of endo form and exo form were compared.
Keywords Isosorbide ꢀ Surfactants ꢀ Surface tension ꢀ
Critical micelle concentration ꢀ Foam stability
J Surfact Deterg (2018).
Despite the effectiveness of traditional surfactants
derived from petrochemicals, their possible toxicity is an
environmental concern (Geng et al., 2017; Laudet-Hesbert,
*
Ho-Cheol Kang
hckang@krict.re.kr
1
Environment and Sustainable Resources Research Center, Korea
Research Institute of Chemical Technology, Gajeongro
2
005). Alkylbenzene sulfonates, AES, and alkyl sulfates
are anionic surfactants that are commonly used in deter-
gents (Miller and Neogi, 2007), home and industrial clean-
ing agents, and in cosmetics and medicines. However, they
also negatively impact the environment and have toxicity
issues (Cserháti et al., 2002). In contrast, sugar-based sur-
factants, such as alkyl polyglucoside (APG, developed by
Henkel Corp., Düsseldorf, Germany), sucrose esters, and
sorbitan esters are eco-friendly, renewable, nontoxic, and
1
41, Yuseong-gu, Daejeon 34114, South Korea
2
3
Department of Engineering Chemistry, Chungbuk National
University, Chungdaero 1, Cheongju 28644, South Korea
Department of Advanced Materials and Chemical Engineering,
University of Science and Technology, Gajeongro 141,
Yuseong-gu, Daejeon 34114, South Korea
4
Department of Chemical and Biochemical Engineering, Dongguk
University, Phildongro 1, Jung-gu, Seoul 04620, South Korea
J Surfact Deterg (2018)

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biodegradable. As a result, the demand for them is growing
despite their currently small scale of industrial production
foaming power, emulsifying capacity, and dispersion stability
were measured and compared with two commercial surfac-
tants: linear AE (LAE-9) and sodium lauryl ether sulfate
(SLES-3).
(Nickel et al., 2007). APG is derived using plant-based
food resources (such as maize and coconuts) and com-
pounded using fatty alcohols and glucose. It is also known
to have a synergistic effect when used with anionic surfac-
tants. However, because APG is currently priced higher
than alkylphenolethoxylates, it is only used for specialized
purposes such as cosmetics, medicines, and food (Roussel
et al., 2005; Rybinski and Hill, 1998). Another example of
sustainable, eco-friendly surfactant is fatty-acid methyl ester
sulfonate, which can be easily synthesized using biological
oils as raw material, and is widely used in the chemical
industry on account of its great surface activity and self-
assembly behavior (Jin et al., 2016).
Biomass is used to synthesize sorbitan esters such as the
nonionic surfactants Tween and Span (through the single
dehydration of sorbitol) and to produce isosorbide. Thus,
research has been conducted on synthesizing related ionic
surfactants. Isosorbide, or dianhydrohexitol, is a primary
product of the starch industry: thousands of tons of it are
produced by Roquette Frères (Zhu et al., 2008). Scheme 1
shows the different reactivity based on the geometry of the
two hydroxy groups. The hydroxy group of C2 appears to
be in the exo orientation, whereas that of C5 appears to be
in the endo orientation, because of the fused tetrahydrofu-
ran (THF) cycles (Abenhaïm et al., 1994; Claffey et al.,
Experimental Procedures
Materials
All the following chemicals were used as received: isosorbide
(
1
1
TCI, [Tokyo, Japan] 98%), 1-bromohexane (TCI, 98%),
-bromooctane (TCI, 98%), 1-bromodecane (TCI, 98%),
-bromododecane (TCI, 98%), potassium hydroxide (KOH;
Samchun, [Pyeongtaek, Korea] 95%), sodium chloride
Samchun, 98%), toluene (Samchun, 99.5%), hexane
Samchun, 99.5%), ethyl alcohol (Samchun, 99.5%), methanol
Samchun, 99%), ethyl acetate (Samchun, 98%), sodium sulfite
anhydrous (Samchun, 95%), tetrabutylammonium bromide
TBAB; Samchun, 99%), allyl bromide (Junsei, [Tokyo, Japan]
8%), and sodium bisulfite (Duksan, [Ansan, Korea] 95%).
(
(
(
(
9
Instruments
The purity of the synthesized compounds was ascertained
1
by gas chromatography (GC) and H nuclear magnetic res-
13
onance (NMR) and C NMR spectroscopy. GC analyses
were performed on an Agilent apparatus equipped with a
DB-1HT column (J & W Scientific, Folsom, CA) (length:
2004; Kumar and Ramachandran, 2005; Zhu et al., 2009).
The reaction shown in Scheme 1 is used to prepare many
compounds such as isosorbide nitrates (used to treat cardiac
or vascular disease) and alkyl derivatives (used as solvents
in pharmaceutical and cosmetic compositions) (Durand
et al., 2009; Fenouillot et al., 2010; Lavergne et al., 2011).
In this study, a new method is proposed for the synthesis of
isosorbide-based sulfonate anionic surfactants with hexyl,
octyl, decyl, and dodecyl side chains. Compared with the tra-
ditional synthesis routes, the new reactions are more efficient,
simpler, highly selective, and provide higher yield and compa-
rable purity. The two series of synthesis products are endo-
3
(
0 m, ID: 0.32 mm), with nitrogen as gas vector and a FID
Flame Ionization Detector) detector. The GC conditions
were: column pressure of 55 kPa, carrier gas flow rate of
−
1
2
.2 mL min , split ratio of 20:1, initial oven temperature
ꢁ
ꢁ
−1
of 60 C, initial time of 3 min, ramp of 12 C min , final
temperature of 360 C, and final time of 30 min. The NMR
ꢁ
spectra were recorded on Brucker AC spectrometers at
1
13
3
00.13 MHz for H and 75.47 MHz for C.
The surface tension was measured using a DuNuoy plati-
num ring tensiometer (K100; Kruss, Hamburg, Germany) at
room temperature (El-Shahawi et al., 2016; Kang et al.,
5-O-alkyl isosorbide-2-O-propyl sulfonic acid sodium salt
2
2
1
000; Zhou et al., 2013). The foaming power was tested at
5 C with 25 mL of 0.1% aqueous surfactant solution in a
00-mL measuring cylinder. After shaking 20 times, the ini-
(ENISS-n) and exo-2-O-alkyl isosorbide-5-O-propyl sulfonic
ꢁ
acid sodium salt (EXISS-n) with n = 6, 8, 10, and 12. Their
critical micelle concentration (CMC) value, surface tension,
tial height of the foam was measured for foam height. After
min, it was used to assess the foaming power (Mohamed
et al., 2005). For emulsion stability measurement, 20 mL of
5
0
.1% aqueous solution of the surfactant and 10 mL of tolu-
ꢁ
ene were used. The emulsifying property at 25 C was deter-
mined by the time it took for 80% of the aqueous volume to
separate from the emulsion layer, starting immediately after
the mixture was shaken 20 times (El Dib et al., 1988).
The stability of the emulsions was monitored by mea-
suring the transmittance and backscattering of a pulsed
Scheme 1 The conversion of biomass to isosorbide
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near infrared light (λ = 880 nm) using a Turbiscan Lab
Expert system (Formulaction, Toulouse, France). The
transmittance detector received the light passing through
monoallyl isosorbide (R = 0.04 in 50/50 mixture). The
purity of the compounds was checked by H NMR spectra
and GC. The synthesis and purification procedures were
identical for 2-O-monoallyl isosorbide and 5-O-monoallyl
isosorbide.
f
1
ꢁ
the dispersion in a Turbiscan tube at an angle of 180
with respect to the source, while the backscattering
detector received that scattered backward by the disper-
The purified 2-O-monoallyl isosorbide (9.31 g, 0.05 mol)
ꢁ
ꢁ
sion at an angle of 45 . The stability of emulsions can
was dissolved in hexane (30 mL) and heated to 65 C under
be evaluated by the Turbiscan Stability Index (TSI) using
Turbiscan EasySoft: the higher the TSI value, the less
stable the emulsion (Chanamai et al., 2000; Kang et al.,
stirring. KOH (5.6 g, 0.1 mol), alkyl bromide (9.9 g,
0.06 mol), and TBAB (0.81 g, 0.05 mol) were then added,
and the mixture was refluxed for 3 h. Afterward, the crude
residue was extracted with hexane and 5% NaCl solution
twice. The product was purified by distillation and obtained
in the pure form after column chromatography on silica with
elution by hexane/methanol (100:0 and 0;100 v/v). The
2011; Mengual et al., 1999; Pu et al., 2016).
Synthesis and Purification of the Compounds
1
Synthesis of Endo-5-O-Hexyl Isosorbide-2-O-Propyl
Sulfonic Acid Sodium Salt
purity of the compounds was identified using the H NMR
spectra and GC. The synthesis and purification procedures
were identical for the other compound endo-5-O-alkyl-2-O-
allyl isosorbide.
Sodium salts of endo-5-O-alkyl isosorbide-2-O-propyl sul-
fonate and exo-2-O-alkyl isosorbide-5-O-propyl sulfonate
are denoted as ENISS-n and EXISS-n, respectively. Here,
n = 6, 8, 10, and 12 correspond to the hexyl, octyl, decyl,
and dodecyl alkyl groups, respectively (Scheme 2). As all
the ENISS-n and EXISS-n were prepared similarly, here
we only give the procedure for one compound (endo-5-O-
hexyl isosorbide-2-O-propyl sulfonic acid sodium salt
The sulfonation reaction of endo-5-O-alkyl-2-O-allyl iso-
sorbide was as follows. Na SO (2.16 g, 0.02 mol) and
2
3
NaHSO3 (2.03 g, 0.02 mol) were dissolved in distilled
water (100 mL), and then ethyl alcohol (100 mL) was
added under stirring. Endo-5-O-alkyl-2-O-allyl isosorbide
(9 g, 0.04 mol) was added to the mixture and heated at
ꢁ
70 C for 24 h. After evaporating the water and ethyl alco-
[
ENISS-6]) as a representative.
Isosorbide (7.3 g, 0.05 mol), KOH (2.8 g, 0.05 mol),
hol, the product was extracted with hexane and deionized
water. The extracted product was dried in an oven over-
night, and then washed with EtOH and filtered. The purity
and allyl bromide (6.05 g, 0.05 mol) were dissolved in tol-
uene (20 mL). The solution was stirred at 65 C. After 3 h,
ꢁ
1
of the compounds was ascertained by H NMR spectros-
the residue was extracted with toluene and 5% NaCl solu-
tion. 5-O-Monoallyl isosorbide and 2-O-monoallyl isosor-
bide were observed in the extract by GC. This crude
mixture was separated chromatographically on silica under
pressure with ethyl acetate/hexane (10/90–90/10 v/v) as the
copy. The NMR spectra of ENISS-n and EXISS-n are
given below.
The synthesized compounds ENISS-6 and exo-2-O-
hexyl isosorbide-5-O-propyl sulfonic acid sodium salt
(EXISS-6) were examined by the nuclear Overhauser effect
for signal assignment. Irradiation of ENISS-6 at δ 3.49
(CH ) enhanced the intensity of the signal at δ 3.91 (H )
eluent. The diallyl derivative was eluted first (R = 0.21 in
f
10/90 mixture), followed by isolating 2-O-monoallyl iso-
2a
6
sorbide (R = 0.1 in 10/90 mixture), and then 5-O-
by 4.45% and that at δ 3.64 (H ) by 2.05%, while
1a
f
Scheme 2 The synthesis of anionic surfactants from isosorbide
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irradiation of EXISS-6 at δ 3.54 (CH ) enhanced the inten-
sodium salt (EXISS-10) was conducted using the same
2
a
sity of the signal at δ 3.90 (H ) by only 3.86%.
ENISS-6 (yield: 99%) H NMR (300 MHz, D O): δ
method, with high product purity and a yield of 97%.
1
b
1
1
ENISS-10 (yield: 98%) H NMR (300 MHz, D O): δ
2
2
0
.87 (3H, m, CH ), 1.29–1.34 (6H, m, CH ), 1.54–1.61
0.84 (3H, m, CH ), 1.18–1.25 (14H, m, CH ), 1.54 (2H, m,
3
2
3
2
(
2H, m, CH ), 1.96–2.03 (2H, m, CH ), 2.94–2.98 (2H,
CH ), 1.93–2.00 (2H, m, CH ), 2.89–2.93 (2H, m,
2b 2B
2b
2B
m, CH ), 3.49–3.59 (2H, m, CH ), 3.64–3.72 (3H, m,
CH ), 3.36–3.42 (1H, m, CH2a1), 3.48–3.52 (1H, m,
2C
2a
2C
H , CH ), 3.86–3.92 (1H, m, H ), 3.98–4.04 (2H, m,
CH2a2), 3.60–3.66 (3H, m, H , CH ), 3.83–3.89 (2H, m,
1
a
2A
1b
1a
2A
H ), 4.11 (1H, m, H ), 4.19–4.24 (1H, m, H ), 4.64 (1H,
H ), 3.92–3.95 (1H, m, H ), 3.99–4.04 (2H, m, H , H ),
6 1b 2 5
6
2
5
m, H ), and 4.73 (1H, m, H ).
EXISS-6 (yield: 98%) H NMR (300 MHz, D O): δ
4.55–4.59 (1H, m, H ), and 4.64–4.70 (1H, m, H ).
3 4
EXISS-10 (yield: 97%) H NMR (300 MHz, D O): δ
3
4
1
1
2
2
0
.87 (3H, m, CH ), 1.29–1.31 (6H, m, CH ), 1.55–1.58
0.82–0.84 (3H, m, CH ), 1.25–1.30 (14H, m, CH ), 1.53 (2H,
3
2
3
2
(
2H, m, CH ), 1.99–2.06 (2H, m, CH ), 2.96–2.99 (2H,
m, CH ), 1.95–2.03 (2H, m, CH ), 2.90–2.94 (2H, m,
2b 2B
2b
2B
t, CH ), 3.54–3.66 (3H, m, CH H ), 3.66–3.71 (1H, m,
CH ), 3.45–3.53 (3H, m, CH H ), 3.55–3.67 (1H, m,
2C 2a, 1a
2C
2a, 1a
CH2A1), 3.75–3.79 (1H, m, CH2A2), 3.90–3.93 (1H, m,
H ), 4.00–4.03 (2H, m, H ), 4.06–4.10 (1H, m, H ),
CH2A1), 3.70–3.76 (1H, m, CH2A2), 3.91 (1H, m, H1b),
3.94–3.96 (2H, m, H ), 3.97–3.98 (1H, m, H ), 4.10–4.17 (1H,
1
b
6
2
6
2
4
.21–4.26 (1H, m, H ), 4.62–4.63 (1H, m, H ), and 4.75
m, H ), 4.47–4.48 (1H, m, H ), and 4.63–4.65 (1H, m, H ).
5 3 4
5
3
(1H, m, H4).
Synthesis of endo-5-O-dodecyl Isosorbide-2-O-Propyl
Sulfonic Acid Sodium Salt
Synthesis of Endo-5-O-Octyl Isosorbide-2-O-Propyl
Sulfonic Acid Sodium Salt
Endo-5-O-dodecyl isosorbide-2-O-propyl sulfonic acid
sodium salt (ENISS-12) was prepared using the same
Endo-5-O-octyl isosorbide-2-O-propyl sulfonic acid
sodium salt (ENISS-8) was synthesized using a method
similar to that of ENISS-6, except that reaction step 2 used
octyl bromide as a reagent and the reaction time of step
2
-step reaction as for ENISS-8, using dodecyl bromide as a
reagent. The final product was confirmed by NMR. The
synthesis of exo-2-O-dodecyl isosorbide-5-O-propyl sul-
fonic acid sodium salt (EXISS-12) was also conducted
using this method with high product purity, and the yield
3
was 24 h under stirring. The final product was confirmed
by NMR. Exo-2-O-octyl isosorbide-5-O-propyl sulfonic
acid sodium salt (EXISS-8) also was synthesized in the
was 97%.
same way with high purity and a yield of 98%.
1
ENISS-12 (yield: 97%) H NMR (300 MHz, D O): δ
1
2
ENISS-8 (yield: 98%) H NMR (300 MHz, D O): δ
2
0
.81 (3H, m, CH ), 1.24–1.28 (18H, m, CH ), 1.54 (2H, m,
3 2
0
.83 (3H, m, CH ), 1.26–1.28 (10H, m, CH ), 1.54–1.55
3 2
CH ), 1.95–1.98 (2H, m, CH ), 2.89–2.92 (2H, m,
2b
2B
(
2H, m, CH ), 1.94–2.01 (2H, m, CH ), 2.91–2.95 (2H,
2b 2B
CH ), 3.37–3.41 (1H, m, CH2a1), 3.48–3.51 (1H, m,
2C
m, CH ), 3.40–3.45 (2H, m, CH ), 3.49–3.53 (3H, m,
2C
2a
CH2a2), 3.62–3.63 (3H, m, H , CH ), 3.86–3.88 (2H, m,
1a
2A
H , CH ), 3.62–3.68 (1H, m, H ), 3.84–3.97 (3H, m,
1
a
2A
1b
H ), 3.92–3.94 (1H, m, H ), 3.98–4.01 (2H, m, H , H ),
6
1b
2
5
H6, H ), 4.03–4.06 (1H, m, H ), 4.57–4.58 (1H, m, H ),
2
5
3
4
.54–4.55 (1H, m, H ), and 4.64 (1H, m, H ).
3 4
EXISS-12 (yield: 96%) H NMR (300 MHz, D O): δ
and 4.66 (1H, m, H4).
EXISS-8 (yield: 97%) H NMR (300 MHz, D O): δ
1
1
2
2
0
.82–0.84 (3H, m, CH ), 1.25–1.28 (18H, m, CH ), 1.53
3
2
0
1
2
3
3
4
.86–0.89 (3H, m, CH ), 1.28–1.30 (10H, m, CH ),
3
2
(
2H, m, CH ), 1.97–2.01 (2H, m, CH ), 2.90–2.94 (2H,
2b 2B
.54–1.56 (2H, m, CH ), 1.99–2.06 (2H, m, CH ),
2
b
2B
m, CH ), 3.44–3.52 (3H, m, CH H ), 3.57–3.63 (1H,
2C
2a, 1a
.94–2.98 (2H, m, CH ), 3.48–3.57 (3H, m, CH H ),
2
C
2a, 1a
m, CH2A1), 3.70–3.74 (1H, m, CH2A2), 3.88–3.90 (1H, m,
H ), 3.93–3.96 (2H, m, H ), 3.98 (1H, m, H ), 4.09–4.14
.62–3.68 (1H, m, CH2A1), 3.74–3.79 (1H, m, CH2A2),
.91–3.93 (2H, m, H1b, H ), 3.95–3.97 (2H, m, H ),
1b
6
2
2
6
(
1H, m, H ), 4.46–4.47 (1H, m, H ), and 4.63–4.71 (1H,
5 3
.16–4.21 (1H, m, H ), 4.52–4.53 (1H, m, H ), and 4.67
5
3
m, H4).
(1H, m, H4).
Synthesis of Endo-5-O-Decyl Isosorbide-2-O-Propyl
Sulfonic Acid Sodium Salt
Results and Discussion
The synthesis of endo-5-O-decyl isosorbide-2-O-propyl
sulfonic acid sodium salt (ENISS-10) was similar to that of
ENISS-8, except that in step 2 decyl bromide was used as a
reagent. The final product was confirmed by NMR. Synthe-
sis of Exo-2-O-decyl isosorbide-5-O-propyl sulfonic acid
Synthesis of Endo-5-O-Alkyl Isosorbide-2-O-Propyl
Sulfonic Acid Sodium Salt
ꢁ
Allylation of isosorbide was carried out at 65 C by mixing
isosorbide, allyl bromide, and a base in a 1/1/1 M ratio in a
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suitable solvent, resulting in a product mixture of monomer
Table 1 Effects of solvent and base on the allylation of isosorbide
Solvent Base A (%) B (%) C (%) Isosorbide (%)
2-O-allyl isosorbide (A), monomer 5-O-allyl isosorbide
(B), and dimer 2,5-O-diallyl isosorbide (C) (Scheme 3).
Dimethyl sulfoxide KOH
15
3
16
16
7
8
1
61
70
91
10.5
36
68
22
42
91
20
58
83
27
30
34
51
58
80
The reaction solvent was dimethylsulfoxide (DMSO), tolu-
ene, cyclohexane, THF, or distilled water; and the base was
sodium hydroxide, KOH, or lithium hydroxide (Table 1).
The goal was to find the reaction conditions that selectively
formed A and avoided the formation of C. The reaction
employing KOH and DMSO was carried out at a reaction
LiOH
NaOH
2
0
Toluene
KOH
LiOH
NaOH
KOH
LiOH
NaOH
KOH
LiOH
NaOH
KOH
LiOH
NaOH
KOH
LiOH
NaOH
81
33
22
47
31
7
3.5
5
29
10
15
19
2
2
0
ꢁ
Cyclohexane
THF
16
8
temperature of 25 C and completed after 5 h, yielding
2
6
1
0.8% A, 14.6% B, and 4.8% C. The same reaction at
ꢁ
0
5 C did not progress after 3 h, yielding 33.7% A,
ꢁ
29
20
10
32
38
43
27
24
10
17
10
7
34
12
0
3% B, and 8% C; and that at 90 C did not proceed fur-
ther after 5 h, resulting in 2.6% A, 2.5% B, and 6.7%
C. The products were analyzed using NMR and GC. A fast
reaction rate was observed in the initial neat reaction. How-
ever, the reaction did not proceed further due to solid prod-
uct formation. A low yield of A (2–33%) was obtained
when using lithium hydroxide or sodium hydroxide as the
base in various solvents, while it was 15–81% when using
KOH. The highest selectivity and efficiency were observed
when using KOH in toluene (81% A, 3.5% B, and 5% C).
The salt affected the reactivity and selectivity after 3 h of
Neat
15
27
14
10
17
8
23
5
9
Distilled water
12
1
2
ꢁ
Isosorbide/AllylBr/base = 1:1:1, 3 h, 65 C, 10 mL of solvent.
ꢁ
reaction at 65 C. These data were compared with the
results obtained by Abenhaïm’s group. They performed the
reaction in DMSO at 90 C for 18 h, resulting in 3% A,
of alkyl chains), and a yield of 99% was obtained in all
cases.
ꢁ
69% B, and 6% C. In comparison, our new method is fas-
ter, uses milder conditions, and has higher selectivity for
the desired product. The regioselectivity of the base was in
the order of K > Li > Na regardless of the solvent. As a
result, the regioselective reaction of monoallyl isosorbide
could yield a maximum ratio of A:B = ~23:1 when using
allyl bromide and KOH in toluene.
Synthesis of Exo-2-O-Alkyl Isosorbide-5-O-Propyl
Sulfonic Acid Sodium Salt
+
+
+
An experiment was carried out to synthesize monoalkyl
isosorbide selectively. The reaction was performed at
ꢁ
90 C using isosorbide, 1-bromoalkane, a base, and TBAB
Next, 5-O-hexyl-2-O-allyl isosorbide was synthesized
with various alkyl groups using the previously synthesized
in a molar ratio of 1:2:4:0.05. A product mixture of mono-
mers D and E and dimer F was obtained (Scheme 4).
DMSO, toluene, or hexane was used as the solvent, while
sodium hydroxide, KOH, and lithium hydroxide were used
as the base (Table 2). The reaction using lithium hydroxide
in hexane at reflux temperature occurred slowly, yielding
16% D, 30% E, and 0% F. The reaction did not proceed
further after 3 h. Reaction in toluene showed no apparent
selectivity (20% D, 26% E, and 10% F). However, selec-
tive synthesis could be carried out in DMSO for 3 h at
2-O-allyl isosorbide. The reaction was performed in
DMSO, toluene, or hexane, with respective yields of 34%,
68%, and 98%.
Endo-5-O-alkyl-2-O-allyl isosorbide from the previous
step was converted into the sodium salt of endo-5-O-
alkyl isosorbide-2-O-propyl sulfonate, by adjusting the
ꢁ
pH to 7 at 50 C using Na SO and NaHSO . The reac-
2
3
3
tion was carried out for 5–24 h (depending on the length
Scheme 3 Allylation of isosorbide
J Surfact Deterg (2018)

J Surfact Deterg
Scheme 4 Alkylation of isosorbide
reflux temperature, resulting in 72% D, 3% E, and 6%
F. The products were analyzed using GC and NMR.
Although a fast reaction rate was observed initially in the
neat reaction, the reaction did not proceed further due to
solid product formation. Thus, a solvent was used. The
reaction using sodium hydroxide proceeded more slowly
than those using KOH or lithium hydroxide. In terms of
selectivity and reaction rate, the effect of lithium hydroxide
respectively. For both the ENISS-n and EXISS-n series, the
CMC decreased as the chain length of the alkyl group
increased. There is a known linear relationship between the
CMC and the carbon number, n, of the alkyl group within a
series of the surfactants:
Log CMC = A−Bn
ð1Þ
where A is an empirical constant dependent on the tempera-
ture and hydrophilicity, B is a constant with saturated alkyl
chains and a single ionic head group, and n is the number
of carbon atoms of the alkyl chain. The values of A and
B for ENISS-n were determined to be −1.52 and 0.36, and
those for EXISS-n were − 2.07 and 0.20, respec-
tively (Fig. 3).
The maximum surface excess (Гmax) and the minimum
area per molecule (Amin) of the surfactant at the interface
are calculated using Eq. (2) (El-Shahawi et al., 2016; Kang
et al., 2000; Zhou et al., 2013):
+
+
+
was more significant than KOH (Li > K > Na ). The
reaction between alkyl bromide and lithium hydroxide in
ꢁ
DMSO at 90 C produced 72% D, 3% E, and 6% F (D:E
ratio of 24:1) after 3 h, showing the highest selectivity. Zhu
et al. performed an alkylation of isosorbide using lithium
hydroxide in DMSO, and obtained 5% D and 32% E after
separation and purification (Jin et al., 2016). Abenhaïm’s
group performed this reaction with lithium hydride in
Dimethylformamide (DMF) with ultrasound, and the reac-
tion yielded 5% D, 60% E, and 15% F. Owing to the
effects from the solvent, the bases showed a selectivity
dγ=dμ = ∂γ=∂lnC = −2ГRT
ð2aÞ
+
+
+
order of Li > Na > K (Abenhaïm et al., 1994). Accord-
ingly, we concluded that lithium hydroxide had the highest
selectivity.
−
1
Гmax = ð1=2RTÞð−dγ=dlnCÞ = ð4:606RTÞ ð−∂γ=∂logCÞ
T
T
ð2bÞ
ð2cÞ
14
In the second step, the previously synthesized 2-O-alkyl
isosorbide was reacted with allyl bromide and KOH through
Amin = 10 =ðNГmaxÞ
−1
−1
where R is the ideal gas constant (8.314 J mol K ), T
ꢁ
a neat reaction at 65 C to synthesize 2-O-alkyl-5-O-allyl
is the temperature in Kelvin, (−∂γ/∂ log C) is the gradi-
T
isosorbide. A high-purity product was obtained after filtra-
tion. The final product was obtained by sulfonation.
ent of the surface tension versus log C, and N is Avoga-
23
dro’s number (6.023 × 10 ). According to Table 3, the
2
Amin values were 1.21, 1.10, 1.02, and 0.81 nm for
2
Surface Activity
ENISS-n and 1.23, 1.16, 1.06, and 0.92 nm for EXISS-n
with n = 6, 8, 10, and 12, respectively. It was observed
that Гmax gradually decreased and Amin was noticeably
reduced, as the hydrophobic alkyl chain became longer.
The difference in Amin between the endo and the exo
forms may be attributed to their different molecular struc-
tures (planar and bent).
One important feature of surfactant solutions is the forma-
tion of micelles above a specific concentration. The CMC
of ENISS-n and EXISS-n was determined by measuring
the surface tension at 25 C. Plots of surface tension
against the logarithm of concentration are shown in Figs. 1
ꢁ
and 2 for ENISS-n and EXISS-n, respectively. For ENISS-
It is well known that the Krafft temperature depends on
the alkyl chain length, the type of polar head, the nature of
counterions, and the head group interaction including
hydrogen bonding. The determined Krafft temperatures
(1% aqueous surfactant solution) for n = 6 and 8 are below
freezing temperature; whereas those of ENISS-12 and
−
2
n with n = 6, 8, 10, and 12, the CMC was 1.62 × 10 ,
−
3
−4
−4
−1
4
.46 × 10 , 7.76 × 10 , and 1.12 × 10 mol L , and
the surface tension was 29.78, 25.81, 27.24, and 29.95 mN
−
1
m , respectively. For EXISS-6, EXISS-8, EXISS-10, and
−
3
−3
EXISS-12, the CMC was 7.24 × 10 , 1.99 × 10 ,
7
−4
−4
−1
ꢁ
.94 × 10 , and 4.17 × 10 mol L , and the surface ten-
sion was 27.99, 26.91, 28.53, and 31.61 mN m ,
EXISS-12 are 10 and 35 C, respectively. These observa-
tions show that the Krafft temperature depends on the alkyl
−1
J Surfact Deterg (2018)

J Surfact Deterg
Table 2 Effects of solvent and base on the alkylation of isosorbide
Solvent and base effect
Solvent
Base
D (%) E (%) F (%) Isosorbide (%)
Dimethyl sulfoxide KOH
18
72
0
19
3
30
6
33
19
LiOH
NaOH
0
0
100
95
Toluene
Hexane
KOH
LiOH
NaOH
KOH
LiOH
NaOH
0
0
5
20
3
26
4
10
0
43
93
0
0
9
91
16
1
30
0
0
54
9
90
ꢁ
1:2:4:0.05, 3 h, 90 C,
Isosorbide/1-bromoalkane/base/TBAB
0 mL of solvent.
=
1
Fig. 2 Surface tension versus concentration for the four isosorbide
derivatives EXISS-6 ▪, EXISS-8 □, EXISS-10 ●, and EXISS-12 ○
chain length due to the isomeric effects on the molecular
properties and on the isosorbide synthon in aqueous solu-
tions. In this case, the structural effect imposed by the V-
shaped isosorbide moiety should be considered. EXISS-n
has more efficient packing in the solid state, leading to a
strong tendency for crystallization. It is not compensated
by an increase in hydrophilicity, and thus leads to a higher
Krafft temperature.
2–4 mL lower than in the corresponding ENISS-n. Except
ENISS-6 and EXISS-6, all other synthesized surfactants
had a foam height above 40 mL. For reference, the foam
height of the general surfactant LAE-9 was reduced from
3
2
9 to 36 mL after 5 min, while that of SLES-3 remained at
1 mL. From the comparison with LAE-9 and SLES-3, the
foam heights of the newly synthesized surfactants (except
ENISS-6 and EXISS-6) after 5 min were significantly
higher (by 21–27 mL).
Foaming Test
A simple test was performed to assess the foaming power.
Five minutes after shaking the 0.1% surfactant solution, the
height of the foam was measured (Mohamed et al., 2005)
to be 13, 46, 48, and 49 mL for ENISS-6, ENISS-8,
ENISS-10, and ENISS-12 and 9, 42, 45, and 47 mL for
EXISS-6, EXISS-8, EXISS-10, and EXISS-12, respectively
Emulsion Stability
The emulsion stability was assessed by the time it takes for a
mixture containing 0.1% surfactant, toluene, and water to
recover 80% of the aqueous layer at 25 C (El Dib et al.,
ꢁ
(Table 4). Overall, the foam height in EXISS-n was
1988). The measured time for ENISS-n increased with the
carbon length, with the respective times of ENISS-6, ENISS-
8
, ENISS-10, and ENISS-12 being 140, 244, 380, and 478 s.
As the alkyl chain length increased from 6 to 12, the emul-
sion stability increased from 140 to 478 s. The emulsion sta-
bility time for EXISS-6, EXISS-8, EXISS-10, and EXISS-12
was 75, 208, 282, and 383 s, respectively. Notably, EXISS-6
showed much lower emulsion stability compared with other
surfactants. As the carbon chain length increased, the time
taken to recover 80% of the aqueous layer increased from
7
5 to 383 s. Therefore, the emulsion stability is twice as high
for ENISS-6 (140 s versus 75 s) than that for EXISS-6. The
stereostructural differences between the endo and exo forms
of the molecule have an effect: excluding ENISS-6 and
EXISS-6, the emulsion stability of ENISS-n is 40–100 s bet-
ter than EXISS-n. The common surfactant LAE-9 took 125 s
and SLES-3 took 181 s for the emulsion to stabilize. In com-
parison, the surfactants prepared in this study with eight or
more carbon atoms showed >100 s difference compared with
Fig. 1 Surface tension versus concentration for the four isosorbide
derivatives ENISS-6 ▪, ENISS-8 □, ENISS-10 ●, and ENISS-12 ○
J Surfact Deterg (2018)

J Surfact Deterg
Table 4 Foaming and emulsion tests for the isosorbide derivatives
ꢁ
ENISS-n, EXISS-n, LAE-9, and SLES-3 at 25 C
Surfactant
Foaming power
vol, mL)
Emulsion life time
(80% destroyed) (s)
(
Initial
After
5
min
ENISS-n ENISS-6
ENISS-8
18
49
52
53
12
45
49
51
39
21
13
46
48
49
9
140
244
380
478
75
ENISS-10
ENISS-12
EXISS-n EXISS-6
EXISS-8
42
45
47
36
21
208
282
383
125
181
EXISS-10
EXISS-12
LAE-9
Fig. 3 Cologarithm of the CMC versus carbon chain for the surfac-
tants ENISS-n ▪ and EXISS-n ● (n = 6,8,10, and 12)
SLES-3
LAE-9 and SLES-3, indicating better emulsion stability
layer, backscattering decreased because when the concen-
tration surpasses the saturation point, light does not distin-
guish between individual particles and “sees” the sample as
one large particle, and the resultant packed creaming
decreases the backscattering. In some parts of the top layer,
the backscattering first decreased and then increased. This
is known as the wall effect, in which light is reflected by
the walls of the tube and re-enters as backscattered light
even when there is a clear separation of the sample (Fig. 4).
As the carbon chain length of ENISS-n increased, backscat-
tering decreased in the bottom layer, and the TSI gradually
decreased with time and n.
Figure 5 shows that the concentration in the bottom layer
decreased with time. Thus, in the case of EXISS-6, this
layer became clear. As the bottom layer became clear, a
small decrease in the middle layer indicated coagulation. In
the top layer, backscattering decreased due to packed
creaming, although such coagulation effect did not occur as
much as in ENISS-6. For EXISS-n, the backscattering
decreased as the carbon chain length increased, and the TSI
values decreased with time. At 6 h, the TSI values of
ENISS-n were 107.5, 42.1, 30.1, and 27.6, and those of
(Table 4).
Finally, detailed Turbiscan device measurements were
carried out to assess the emulsion stability. In Turbiscan
measurements, the particles in a sample at a high concen-
tration produce backscattered light from a light source.
When the sample has a low concentration, the emulsion sta-
bility is analyzed by measuring the transmitted light inten-
sity as a function of time (Chanamai et al., 2000; Kang
et al., 2011; Mengual et al., 1999; Pu et al., 2016). Figures 4
and 5 show the graphs of light backscattering and transmis-
sion measured in 25 s intervals for 30 min. After 15 min of
stirring, a clear bottom layer was observed in the sample
tube, and the transmission became stronger with time. The
sample was divided into three layers: the bottom, middle,
and top. The TSI was calculated every hour for 6 h. The
backscattering data changed according to the height of
ENISS-6, indicating that the backscattering decreased
because of the lower concentration in the bottom layer dur-
ing 0–30 min of the measurement, leading to a clearer
layer. In the middle layer of the sample, coagulation
occurred due to the overall decrease in stability. In the top
ꢁ
Table 3 Surface properties of ENISS-n and EXISS-n measured at 25 C (n = 6, 8, 10, and 12)
ꢁ
−1
−1
−3
2
Surfactant
T Krafft ( C)
γ
cmc (mN m
)
CMC (mol L
)
Г
max (mol cm
)
A
min (nm )
−
−
−
−
−
−
−
−
2
ENISS-n
EXISS-n
ENISS-6
ENISS-8
ENISS-10
ENISS-12
EXISS-6
EXISS-8
EXISS-10
EXISS-12
<0
<0
4
29.78
25.81
27.24
30.63
27.99
26.91
28.53
31.61
1.62 × 10
4.46 × 10
7.76 × 10
1.12 × 10
7.24 × 10
1.99 × 10
7.94 × 10
4.17 × 10
1.37
1.51
1.63
2.06
1.35
1.44
1.57
1.81
1.21
1.10
1.02
0.81
1.23
1.16
1.06
0.92
3
4
4
3
3
4
4
10
<0
<0
5
35
J Surfact Deterg (2018)

J Surfact Deterg
Fig. 4 Changing of delta transmission and backscattering light with time for surfactant formulation ENISS-6
Fig. 5 Changing of delta transmission and backscattering light with time for surfactant formulation EXISS-6
−
2
EXISS-n were 118.6, 82.3, 61.2, and 43.1. The smaller TSI
values of ENISS-n indicate their better emulsion stability
compared with EXISS-n. The TSI values of LAE-9 from
2. The CMC values of ENISS-n were 1.62 × 10 to
−
4
−1
1.12 × 10 mol L , and those of EXISS-n were
−3
−4
−1
7.24 × 10 to 4.17 × 10 mol L . The CMC
decreased with increasing length of the carbon chain,
and the minimum area per molecule also decreased.
The steric difference between ENISS-n and EXISS-n
affected the characteristics of the surfactants.
1
to 6 h were 5.7, 11, 17, 22.5, 26.3, and 28.2; while those
of SLES-3 were 8.8, 16.2, 22.3, 26.8, 29.7, and 31.4,
respectively. At 6 h, the values of LAE-9 and SLES-3
(31.4 and 28.2) were higher than that of ENISS-12 (27.6).
Moreover, the emulsion stability improved (lower TSI
value) as the carbon chain length increased, which was also
shown in terms of the emulsion separation timescale after
shaking. ENISS-n also displayed better stability than
EXISS-n in both the emulsion separation experiment and
the measured TSI data.
3. ENISS-n had better foaming power than EXISS-n. The
foaming power increased as the carbon chain length
increased. This indicated that a longer carbon chain
length led to a lower TSI and thus better stability.
Acknowledgement This study was funded by the R&D Program of
MOTIE/KEIT (10044645).
Conclusion
Conflict of Interest The authors declare that they have no conflict
of interest.
In this study, we synthesized isosorbide-based anionic sur-
factants ENISS-n and EXISS-n with sulfonic acid groups
and different carbon chain lengths (hexyl, octyl, decyl, and
dodecyl).
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