Synthesis, characterization and surface activity of hexadecyl o-xylene sulfonate isomers

Article abstract of DOI:10.1007/s11743-009-1165-z

This paper deals with the synthesis of a series of hexadecyl o-xylene sulfonate isomers (with the o-xylene ring located at different positions along the n-hexadecyl chain) by a Friedel-Crafts reaction, and the Grignard reaction followed by a hydrogenation. The structure was confirmed by ¹H NMR. All analytical methods indicated high levels of purities of the isomers with the orthoxylene ring located at the first, third, fifth and seventh carbon atom on the n-hexadecane chain. The critical micelle concentration (CMC), surface tension and maximum surface excess concentration at CMC and area per molecule at the interface were determined. As the o-xylene sulfonate group is shifted toward the center of the hexadecyl chain, the branching degree is enhanced and the surfactant molecule tends to produce a much looser packing at the gas-liquid interface. Accordingly, at CMC, the adsorption density decreases, the CMC increases and the tension reduction is weakened. AOCS 2009.

Full text of DOI:10.1007/s11743-009-1165-z

J Surfact Deterg (2010) 13:149–153
DOI 10.1007/s11743-009-1165-z
ORIGINAL ARTICLE
Synthesis, Characterization and Surface Activity
of Hexadecyl o-Xylene Sulfonate Isomers
•
•
•
Guang-miao Qu Wei Ding Tao Yu
Jie-cheng Cheng
Received: 8 May 2009 / Accepted: 24 October 2009 / Published online: 17 November 2009
Ó AOCS 2009
Abstract This paper deals with the synthesis of a series
of hexadecyl o-xylene sulfonate isomers (with the o-xylene
ring located at different positions along the n-hexadecyl
chain) by a Friedel–Crafts reaction, and the Grignard
reaction followed by a hydrogenation. The structure was
Introduction
Chemical flooding is an important method for Enhanced
Oil Recovery (EOR) [1, 2]. Surfactants play an important
role in chemical flooding. The main function of the sur-
factant is to reduce the interfacial tension between the oil
and water to an ultra-low value (\10-3 mN m-1). Most
surfactants used in EOR are mixtures of different com-
pounds, such as the petroleum sulfonates and the heavy
alkyl benzene sulfonates which are mainly composed of
alkyl benzene sulfonates with different molecular weights
and alkyl chain lengths. Because of the complex compo-
nents and unidentified structures, it is difficult to elucidate
the relationship between the structures and properties in
theory. This enables the researchers to synthesize the alkyl
aryl sulfonates with definite structures. A considerable
number of investigations have been reported on the syn-
thesis and surface properties of alkylbenzene sulfonate
with the definite structures. Baumgartner [3, 4] synthesized
the isomers of dodecyl benzene sulfonate with the benzene
ring attached at different positions on the dodecyl chain for
the first time. The detergence and wetting properties were
reported and related with different structures and much
work was focused on the foaming, wetting, surface tension.
Doe [5, 6] and Wade [7] studied the interfacial tension
between n-alkane and an aqueous solution of hexadecyl
benzene sulfonate isomers, and characterized the surfac-
tants by the concept of the preferred alkane carbon number
(nmin) to attain minimum tension. They found that when the
benzene ring point of attachment is shifted to the center of
the n-hexadecane chain, the surfactant becomes more
hydrophobic, although it is also more water soluble, an
apparently paradoxical association of properties. In recent
years, Yang [8, 9] and Zhao [10] synthesized a series of the
hexadecyl benzene sulfonates. Zhang [11] synthesized
1
confirmed by H NMR. All analytical methods indicated
high levels of purities of the isomers with the orthoxylene
ring located at the first, third, fifth and seventh carbon atom
on the n-hexadecane chain. The critical micelle concen-
tration (CMC), surface tension and maximum surface
excess concentration at CMC and area per molecule at the
interface were determined. As the o-xylene sulfonate group
is shifted toward the center of the hexadecyl chain, the
branching degree is enhanced and the surfactant molecule
tends to produce a much looser packing at the gas–liquid
interface. Accordingly, at CMC, the adsorption density
decreases, the CMC increases and the tension reduction is
weakened.
Keywords Alkyl o-xylene sulfonate ꢀ Isomerization ꢀ
Surface activity
G. Qu ꢀ W. Ding ꢀ T. Yu
Department of Chemistry and Chemical Engineering,
Daqing Petroleum Institute, 163318 Daqing, China
G. Qu
College of Petroleum Engineering,
China University of Petroleum, Beijing, China
J. Cheng (&)
Daqing Oilfield Limited Company of CNPC,
163453 Daqing, China
e-mail: qugm110@126.com
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J Surfact Deterg (2010) 13:149–153
multi-n-alkyl benzene sulfonates and reported characteris-
tic parameters such as the critical micellar concentration
(CMC), and the surface and interfacial tension at CMC.
However, the synthesis and surface properties of alkyl
o-xylene sulfonates were not reported. In this paper we
present the synthesis of a series of isomers of hexadecyl
o-xylene sulfonates and we report on some of their
properties.
China). o-Xylene, ethyl ether, magnesium strips, anhydrous
calcium chloride and sodium hydroxide were obtained from
Kemiou (Tian Jin China). All reagents were distilled prior to
use. Pd/C catalyst (5%) was provided by the Dalian Institute
of Chemical Physics (Dalian China). Hydrogen and nitrogen
were of high grade purity from XueLong ([99.99% purity,
Daqing China). After some optimization trials, the hexa-
decyl o-xylene sulfonate (C16OXS) different isomers was
carried out through the following steps.
The correct name of the sulfonate final product in which
the sulfonated o-xylene group is attached to the 3rd carbon
atom of the n-hexadecane chain could be n-hexadecane
3-o-xylene sulfonate or 3-hexadecyl o-xylene sulfonate and
it is abbreviated in what follows as C16-3OXS. The same
kind of abbreviation is used for the other isomers, with the
number before OXS indicating the point of attachment of
the aryl group on the n-hexadecane chain. The routes to
attain the synthesized compounds are illustrated in
Schemes 1 and 2. The details are discussed later in the
experimental section. Because of the steric hindrance, the
acylation cannot take place in the ortho position of one of
the methyl groups of the xylene ring, as a consequence,
there is only one possible final isomer of the alkyl
orthoxylene sulfonate. It means that the only isomeric
variation is due to the attachment position of the o-xylene
ring on the n-hexadecane chain.
Synthesis of Hexadecyl o-Xylene Ketones
Acyl chloride (0.10 mol) was added dropwise to a stirred
solution of anhydrous AlCl3 (17.33 g, 0.13 mol) and
o-xylene (42.47 g, 0.40 mol), the mixture was cooled in an
ice-water bath for 30 min and then heated at a reflux for
3 h. The mixture was then cooled and decomposed with
ice-cooled dilute hydrochloric acid (100 mL). After the
phase separation, the upper layer was washed with a
NaHCO3 solution and deionized water until it became
neutral, and finally dried over anhydrous calcium chloride.
The excess of o-xylene was removed by distillation and the
solvent was evaporated under reduced pressure. The above-
mentioned procedure lead to ketones labeled K1, K3, K5
and K7 in 79.20, 84.82, 80.27, and 79.63% yields,
respectively. K1 was used to synthesize the hexadecane
o-xylene alkane directly by hydrogen addition reduction
without the two following steps.
Experimental Procedures
Materials
Synthesis of Hexadecyl o-Xylene Tertiary Alcohols
The purity of all the chemicals used was high grade. Hexa-
decanoyl chloride, tetradecanoyl chloride, dodecanoyl
chloride, decanoyl chloride were from Shalong (Huzhou
Zhejiang Province China). n-Bromoethane, n-bromobutane,
n-bromohexane were from Yancheng (Jiangsu Province
The reaction was conducted under nitrogen. Traces amount
of iodine were used to initiate the Grignard reaction. Alkyl
bromide (0.1 mol) was added dropwise to the mixture of
the magnesium strips (50.4 g, 2.1 mol) and Et2O (50 mL),
then the reaction was placed in reflux until the magnesium
C
15H31C=O
Scheme 1 Synthesis route of
C16-10XS
C15H31CH2
C
15H31CH
C15H31CH2
2
reduction
sulfonation
ClSO3H
neutralization
NaOH
acylation
C15H31COCl
CH3
CH3
H
2
CH3
CH3
CH3
CH3
CH3
CH3
HO3S
NaO3S
CH3
CH3
C16-1OXS
K1
Scheme 2 Synthesis route of
C16-30XS, C16-50XS,
C16-70XS
OH
R2
R1CH
R1CH
R2
sulfonation
R1C
R2
R1C=O
R1CH
R
Grignard reaction
acylation
R1COCl
neutralization
NaO3S
reduction
CH3
CH3
CH3
CH3
NaOH
CH3
CH3
ClSO3H
CH3
CH3
R2Br
CH3
CH3
HO3S
CH3
CH3
K3
R2=C2H5
R1=C H
C16-3OXS
C16-5OXS
C16-7OXS
13
27
R1=C H
K5
K7
R2=C4H9
R2=C6H13
11
23
R1=C H
9
19
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J Surfact Deterg (2010) 13:149–153
151
where R is the tip’s radius, Dq the difference of the two
phases, g the local gravity acceleration, V the volume of
one drop, F(R/V)1/3 is a correction factor which accounts
for the nonsphericity of the drop. Each surface tension
value was determined from the average at least five
measurements.
strips had disappeared. A suspension of alkyl o-xylene
ketone (0.05 mol) in Et2O (50 mL) was added dropwise
over 30 min to the Grignard reagent and heated at reflux
for 2 h. The resulting mixture was decomposed by ice-cold
dilute hydrochloric acid (100 mL). After the phase sepa-
ration, the aqueous solution was extracted three times with
ether. All extracts were combined, washed with deionized
water until neutral and dried over anhydrous calcium
chloride. The hexadecyl o-xylene alcohol was distilled
under reduced pressure.
Results and Discussion
Properties and Purity of Intermediates
and Final Products
Synthesis of Hexadecyl o-Xylene Isomers
C16-OXS isomers were prepared following Scheme 1 and
Scheme 2. The boiling points of the intermediates are lis-
ted in Table 1. It can be seen that the o-xylene group
position on the hexyldecyl chain has little effect on the
boiling point. The purity of the C16-OXS isomers was
determined by two-phase titration methods. C16-3OXS and
C16-5OXS form crystals and may be filtered, and their
purity is high, i.e. 98.5 and 97.0% (Table 2). C16-1OXS
and C16-7OXS are brown and tacky semi-solids, may be
because of the isomer structure, or because of their lower
purity, i.e. 96.7 and 93.4%, respectively.
The hexadecyl o-xylene isomers were synthesized by
hydrogenation of the corresponding tertiary alcohols
(20.0 g) in glacial acetic acid (50 mL) and perchloric acid
(1.0 mL) using 1.0 MPa H2 and 1.0 g Pd/C (5%) catalysts.
Pd/C catalyst was filtered off and washed with petroleum
ether. The filtrate was then decomposed with water. The
aqueous solution was extracted twice with petroleum ether.
The solvent was washed with NaHCO3 solution and
distilled water, respectively, until neutral, and dried over
anhydrous calcium chloride. The hexadecyl o-xylene
isomers were obtained after distillation under reduced
pressure.
Synthesis of Hexadecyl o-Xylene Sulfonates
Chlorosulfonic acid was added dropwise to the hexadecyl
o-xylene (molar ratio 1.5:1). The reaction proceeded for
2 h at 20 °C. The sulfonation product was neutralized with
a sodium hydroxide solution. After the phase separation,
the mixture was recrystallized three times with anhydrous
ethanol. The final product was filtered and dried in a vac-
uum oven at 80 °C. The purity of the product was deter-
mined by the two-phase titration methods. The structure
Table 1 Boiling stage of the intermediates
R1
R2
Boiling stage (°C)
Pressure (MPa)
Hexadecyl o-xylene ketone
C9H19
314–317
285–288
227–230
189–194
0.080
0.080
0.082
0.081
C
C
C
11H23
13H27
15H31
1
was confirmed by H NMR.
Hexadecyl o-xylene alcohol
C9H19
C6H13
C4H9
C2H5
304–312
302–305
312–315
0.076
0.080
0.078
Analytical Methods
C
C
11H23
13H27
1H-NMR spectra were obtained with a Bruker FT-200
spectrometer using CDCl3 as solvent. Chemical shifts (d)
were reported in ppm related to internal tetramethylsilane.
The surface tension was measured by the drop-volume
technique in a water bath with thermostat control at
298 0.1 K. The time scale for one drop was 3–50 min
depending on the time required to attain equilibrium. The
surface tension was then measured three times for each
sample with a 3–50 min interval between each reading to
ensure equilibrium data. The surface tension (c) is given by
Hexadecyl o-xylene alkane
C9H19
C6H13
C4H9
C2H5
284–286
290–292
304–306
282–286
0.078
0.080
0.078
0.082
C
C
C
11H23
13H27
15H31
Table 2 Purity of the products
Products C16-1OXS C16-3OXS C16-5OXS C16-7OXS
FVDqg
Purity (wt%) 96.7
98.5
97.0
93.4
c ¼
R
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J Surfact Deterg (2010) 13:149–153
Ar–CH13, 3H), 2.165 (s, Ar–CH23, 3H), 2.348 (m, –CH–,
1H), 6.974(s, Ar–H1, 1H), 7.594(s, Ar–H2, 1H).
All analytical methods indicated a high level of purity of
all the isomers.
Surface Tension Studies of Different C16-OXS
Figure 1 shows the plot of surface tension versus concen-
tration of C16-OXS isomers (on log scale) showing a break
point which correspond to a well-defined CMC beyond
which it remains essentially constant. As the o-xylene
sulfonate group is shifted toward the center of the hexa-
decyl chain, the CMC increases probably because of a
reduction in the hydrophobic effects, the minimum tension
(at CMC) gradually decreases, thus indicating enhanced
surface activity.
Fig. 1 Surface tension versus aqueous molar concentration (log
scale) of synthesized C16-OXS isomers
Area per Molecule and Efficiency of Adsorption
1H-NMR Characterization of the Products
The surface excess, C at the air–water interface was cal-
culated by applying the Gibbs adsorption isotherm equa-
tion. The area per molecule at the interface was estimated
from the corresponding value of C. Table 3 summarized
the CMC, cCMC, C, A, pC20 values. As the o-xylene sul-
fonate group is shifted toward the center of the hexadecyl
chain, there is an increase in the branching, the surface area
per molecule becomes larger, and C and cCMC decrease,
and the branched hydrophobic chain tends to reduce the
packing density at the gas–liquid interface.
The structures of C16-1OXS, C16-3OXS, C16-5OXS and
1
C16-7OXS were confirmed by H-NMR spectral analyses.
1
C16-1OXS H NMR [300 MHz, (CDCl3)] d = 0.860–
0.903 (t, –CH3, 3H), 1.061–1.328 (b, –CH2–, 24H), 1.411
(t, Me–CH2–, 4H), 1.783 (s, Ar–CH13, 3H), 2.082 (s, Ar–
CH23, 3H), 2.751 (t, Ar–CH2–, 2H), 6.799 (s, Ar–H1, 1H),
7.432 (s, Ar–H2, 1H).
1
C16-3OXS H NMR [300 MHz, (CDCl3)] d = 0.637–
0.685 (t, –CH13, 3H), 0.758 (t, –CH23, 3H), 1.040–1.239 (b,
–CH2–, 22H), 1.492 (m, Me–CH2–, 4H), 1.902 (s, Ar–CH13,
3H), 2.151 (s, Ar–CH23, 3H), 2.227–2.305 (m, –CH–, 1H),
6.948 (s, Ar–H1, 1H), 7.567 (s, Ar–H2, 1H).
A convenient measurement of the efficiency of adsorp-
tion at the gas–liquid interface is the pC20 parameter
introduced by Rosen [12], which is the negative of the
logarithm of the surfactant concentration in the bulk phase
required to produce a 20 mN m-1 reduction in the surface
tension of the solvent. As shown in Table 3, pC20 decreases
as the o-xylene sulfonate group is shifted toward the center
of the hexadecyl chain. The results indicate that energeti-
cally speaking, the increase in branching of the hydro-
phobic chain inhibits the transfer of a surfactant molecule
from the bulk to the interface.
1
C16-5OXS H NMR [300 MHz, (CDCl3)] d = 0.864–
0.907 (t, –CH13, 3H), 1.068 (t, –CH32, 3H), 1.250 (b, –CH2–,
22H), 1.391 (m, Me–CH2–, 4H), 1.750 (s, Ar–CH13, 3H),
2.066 (s, Ar–CH23, 3H), 2.719 (m, –CH–, 1H), 6.770 (s, Ar–
H1, 1H), 7.377 (s, Ar–H2, 1H).
C16-7OXS1H NMR [300 MHz, (CDCl3)] d = 0.701–
0.722 (t, –CH13, 3H), 0.790–0.840 (t, –CH23, 3H), 1.050–
1.211 (b, –CH2–, 22H), 1.492 (m, Me–CH2–, 4H), 1.938(s,
Table 3 cCMC and CMC values of hexadecyl o-xylene sulfonates
Surfactant
CMC (10-4 mol L-1
)
cCMC (mN m-1
)
C (10-10 mol cm-2
)
A (nm2)
pC20
C16-1OXS
C16-3OXS
C16-5OXS
C16-7OXS
0.7975
1.125
2.391
2.555
33.76
33.44
29.68
26.64
6.291
3.506
2.085
1.870
0.2640
0.4738
0.7967
0.8883
4.099
3.949
3.622
3.594
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153
Acknowledgments This research was financially supported by the
National Key Basic Research Development Program (2005CB
221305).
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