Synthesis, quantum chemical calculations and properties of nonionic and nonionic-anionic surfactants based on fatty alkyl succinate

Article abstract of DOI:10.1007/s11743-014-1568-3

Two surfactants based on maleic anhydride were synthesized by esterification with fatty alcohols C₁₀, C₁₂ and C ₁₄ to produce half esters [I-III]. Nonionic surfactant monoesters [I-III]a-c synthesized by ethoxylation of [I-III] with different moles of ethylene oxide [6, 8 and 10] in the presence of K10 clay as an untraditionally catalyst. The later products were sulfonated to produce nonionic-anionic surfactants [IV-VI]a-c. The structures of synthesized surfactant were elucidated by FTIR and¹H-NMR data. Their surface activity and biodegradability were determined. All the synthesized surfactants showed good surface activity and biodegradability, but anionic-nonionic type has better effect than nonionic one. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the highest occupied molecular orbital-lowest unoccupied molecular orbital, ionization potential energy and ESP mapping of these compounds. Also, the absorption, distribution, metabolism, elimination and toxic properties were studied to gain a clear view of the oral bioavailability of these compounds.

Full text of DOI:10.1007/s11743-014-1568-3

J Surfact Deterg (2014) 17:615–627
DOI 10.1007/s11743-014-1568-3
ORIGINAL ARTICLE
Synthesis, Quantum Chemical Calculations and Properties
of Nonionic and Nonionic–Anionic Surfactants Based
on Fatty Alkyl Succinate
•
Ahmed M. Hussein Manal M. Khowdiary
Received: 23 April 2013 / Accepted: 7 January 2014 / Published online: 22 January 2014
Ó AOCS 2014
Abstract Two surfactants based on maleic anhydride
were synthesized by esterification with fatty alcohols C10,
C12 and C14 to produce half esters [I–III]. Nonionic sur-
factant monoesters [I–III]a–c synthesized by ethoxylation
of [I–III] with different moles of ethylene oxide [6, 8 and
10] in the presence of K10 clay as an untraditionally cat-
alyst. The later products were sulfonated to produce non-
ionic–anionic surfactants [IV–VI]a–c. The structures of
Keywords Maleic anhydride ꢀ Nonionic ꢀ Nonionic–
anionic surfactants ꢀ K10 ꢀ Clay catalyst and surface
activity ꢀ Global and local reactivity descriptors
Introduction
1
Maleic anhydride is used as a starting material in the
production of many types of surfactants [1], due to its
processes at many reaction centers. Dialkyl maleates
nonionics, cationics, and zwitterionics with different
chain lengths of the hydrophobic alkyl group were pre-
pared and investigated, the relationship between the
structure of the surfactants and their surface perfor-
mances were studied [2]. Also, two head surfactants of
disodium-4-alkyl-3-sulfosuccinate were synthesized and
their micellar properties were studied [3, 4]. Monoester
sulfosuccinate have non irritating to the eyes and skin
and used as shampoos [5, 6]. Alkyl polyethoxylate sur-
factants having an anionic head at the end of the mol-
ecule are called nonionic–anionic surfactants or
compound surfactants were reported [7–11], but the type
with an anionic group in middle of the molecule was not
reported. Also, a large and growing number of nonionic
surfactants are being used in various applications, so
knowledge of the parameters accounting for their prop-
erties is needed. As most of the available nonionic sur-
factants are the polyethoxylated ones with a distribution
of ethylene oxide chain lengths, their use in polyphasic
systems such as oil–water mixtures leads to a partition of
their molecular species between oil and water [12–16].
The ester group has a pronounced effect on some surface
properties of the behavior of the surfactants molecule
[17].
synthesized surfactant were elucidated by FTIR and H-
NMR data. Their surface activity and biodegradability
were determined. All the synthesized surfactants showed
good surface activity and biodegradability, but anionic-
nonionic type has better effect than nonionic one. Quantum
chemical calculations were utilized to explore the elec-
tronic structure and stability of these compounds. Com-
putational studies have been carried out at the PM3
semiempirical molecular orbitals level, to establish the
highest occupied molecular orbital–lowest unoccupied
molecular orbital, ionization potential energy and ESP
mapping of these compounds. Also, the absorption, distri-
bution, metabolism, elimination and toxic properties were
studied to gain a clear view of the oral bioavailability of
these compounds.
Present Address:
A. M. Hussein
Department of Chemistry, Faculty of Science, Jazan University,
Jazan, Saudi Arabia
A. M. Hussein
Department of Chemistry, Faculty of Science, Benha University,
Benha, Egypt
M. M. Khowdiary (&)
Applied Surfactant Laboratory, Egyptian Petroleum Research
Institute, Nasr City Cairo, Egypt
e-mail: manalforbank@yahoo.com
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toluene (50 ml). A white viscous oily monodecyl maleate
(23.5 g, 91.8 %) was obtained. Dodecyl C12 maleate half
ester (25 g, 88 %) and tetradecyl C14 (27 g, 86.5 %) esters
were prepared in a similar way.
Ethoxylation of (I–III)
Ethoxylation was carried out in a semi-micro apparatus
[18], using 0.01 mol of the half ester (I–III) and 0.1 wt%
K10 clay catalyst at 40–50 °C to give (I–III)a–c [19].
Table 1 indicates the reaction conditions of the ethoxyla-
tion process. The amount of ethylene oxide uptake was
determined from increase of the mass in the reaction
mixture (with mole ratio 6, 8 and 10 respectively), and was
controlled by spectroscopic tools [20].
Synthesis of Anionic-Nonionic Surfactants
Scheme 1 Synthesis of nonionic and anionic–non ionic surfactants,
where (I–III)a–c are nonionic surfactants monoesters; I–III (R = C10
C12 and C14); and n = a, b and c = 6, 8 and 10 mol of ethylene oxide
(EO) respectively. (IV–VI)a–c nonionic–anionic surfactants = C10
,
Sulfonation of the Products
,
C12 and C14; and n = a, b and c = 6, 8 and 10 mol of ethylene oxide
(EO) respectively
Compounds (I–III)a–c, (0.01 mol) in ethanol and 150 ml
saturated solution of sodium bisulphate with 5 g of sodium
sulfonate were refluxed for 10–12 h, followed by neutral-
ization with sodium hydroxide solution to give the corre-
sponding nonionic–anionic surfactants (IV–VI)a–c.
Characterizations of the product nonionic–anionic surfac-
tants are in Table 2. The chemical structures of the yield
products were confirmed with spectroscopic tools.
Experimental
Materials
Maleic acid anhydride (Aldrich, purity 99 %), ethylene
oxide (Aldrich, purity, 99.5 %), fatty alcohols (decyl
alcohol; C10, Aldrich, purity C98 %; dodecyl alcohol, C12,
Aldrich, purity C98 %; and myristyl alcohol, C14, Aldrich,
purity 97 %), K10 clay catalyst [18], p-toluene sulfonic
acid from Sigma-Aldrich, with purity C98 %; sodium
sulfite and sodium sulfate obtained from Sigma-Aldrich
with a purity of 99.0 %. Solvents ethanol and toluene were
distilled before using and toluene was dried.
Surface Properties of the Prepared Surfactants
Surface Tension Measurements
Surface tension measurements were performed using a
Kru
¨ss K6 tensiometer using the platinum ring detachment
method ( 0.5 mN/m). Freshly prepared aqueous solutions
of the synthesized surfactants were used with a concen-
tration range of 0.01–0.00001 M/l at 25 °C. The solutions
were poured into a clean Teflon cup with a mean diameter
of 28 mm (a Teflon cup was used to prevent the adhesion
of the surfactant to the glass cup walls). The solutions were
left for 2 h to allow stabilization and complete adsorption
at the solution surface, then the apparent surface tension
values were measured a minimum of three times and the
recorded values were the average of these values. The
platinum ring was then removed, washed with a diluted
HCl solution followed by distilled water [21].
Synthesis of Nonionic Surfactants
Synthesis of Half Esters
Half esters were synthesized as shown in Scheme 1.
Typical Example
Decyl alcohol C10 (15.8 g, 0.1 mol), maleic anhydride
(9.8 g, 0.1 mol) and 0.1 wt% of p-toluene sulfonic acid (p-
TSO3H) were stirred in a melted state at 80 °C for 1 h dry
toluene (50 ml) was added to the homogeneous reaction
mixture which was then stirred for 15 min at 80 °C. The
solution was left at room temperature for 3 h and then at
15 °C for 2 h more with stirring from time to time. The
product formed was collected and recrystallized from
Cloud Point
Cloud point was determined by gradually heating of the
prepared surfactant solution (1.0 wt% concentration) in a
controlled temperature bath and recording the time at
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617
Table 1 Reaction conditions of ethoxylation process using K10 clay
Half esters (g, mol)
(mol. formula)
Temperature °C
Catalyst
wt%
Moles of ethylene oxide
uptake (n)
Products
Mol. wt of
products
(I) (2.56, 0.01) (C14H24O4)
(II) (2.84, 0.01) (C16H28O4)
(III) (3.12, 0.01) (C18H32O4)
40–50
0.1
6, 8 and 10 corresponding to
a, b and c respectively
Ia, Ib and Ic
520, 608 and 696
548, 636 and 724
576, 664 and 752
IIa, IIb and IIc
IIIa, IIIb and IIIc
Table 2 Characterization of nonionic–anionic surfactants (IV–VI)a–c
Prepared compounds
Starting compounds
No. of E.O. mol
g/mol
Reaction t (h)
Yield %
State
C10
Ia
IVa–c
6
8
(5.20, 0.01)
(6.08, 0.01)
(6.96, 0.01)
10
10
10
95
95
93
Viscous yellow oily
Viscous yellow oily
Viscous yellow oily
Ib
Ic
10
C12
IIa
Va–c
6
8
(5.48, 0.01)
(6.36, 0.01)
(7.24, 0.01)
96
95
96
IIb
IIc
10
C14
IIIa
IIIb
IIIc
VIa–c
6
8
(5.76, 0.01)
(6.64, 0.01)
(7.52, 0.01)
94
90
92
10
which the clear, or nearly clear solutions become definitely
turbid the reproducibility of this temperature was checked
by cooling the solutions until they become clear again [22].
was withdrawn and each aliquot portion was transferred to
a Petri dish. The solution was evaporated on a water bath
and the residue dried at 105–108 °C to constant weight.
Calculation: 105–108 °C to constant weight [24]
Foaming Height
C ¼ WꢁD=6;000
where C is the percentage of the solid dispersed, W the
weight in mg of the residue, D the weight in mg of the
surface active agent present in 5 ml of the solution of
surface active agent when dried at 105–108 °C to constant
weight.
Foaming height was determined by shaking 25 ml of the
surfactant solution (0.1 wt%) vigorously for 10 s in a
100-ml glass-stoppered graduated cylinder at 25 °C. The
solution was allowed to stand for 30 s then the foam height
was measured [23].
Dispersing Power
Biodegradability
Dispersing power of the prepared surfactants was deter-
mined by putting 6 g of fine carbon black in a 250-ml
graduated cylinder then adding 5 ml of paraffin oil with
40 ml of 2.5 % solution of the prepared surfactants
increasing the volume to 200 ml by adding water. Holding
the closed cylinder upright it was then rolled in a clock-
wise direction to invert it with stopper down and restoring
it back to vertical in the same way. The procedure was
repeated 10 times then the cylinder was kept stationary
without disturbing the contents. After periods of 1.5, 3, 6
and 9 h, 5 ml of solution from the center of the cylinder
Biodegradability of the products tested in river water was
determined using the surface tension method (Du-Nou¨y
tensiometer, Kru¨ss type K6) using a platinum ring [25] at
1 % surfactant concentration. Each surfactant was dis-
solved in river water at a concentration of 100 ppm and
incubated at 38 °C. A sample was withdrawn daily (for
30 days), filtered and the surface tension value was mea-
sured. The biodegradation percentage (D %) was calcu-
lated as follows
D ¼ ðct ꢁ c0= cbt ꢁ c0Þ ꢂ 100
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(where ct is the surface tension at time t; c0 is the surface
tension at time zero (initial surface tension) and cbt is
surface tension of the control sample at time t.
where R = 8.314 J mol-1 K-1, T is absolute temperature,
(dc/d log C) is the slope of the. c versus Log c plot at
25 °C. A substance which lowers the surface tension is thus
present in excess at or near the surface, i.e. when the sur-
face tension decreases with increasing the activity of the
surfactant, C is positive.
Surface Parameter Calculation
Critical Micelle Concentration (CMC)
Minimum Surface Area (Amin
)
The critical micelle concentration is the concentration of a
surfactant solution at which micelles start to form. The
CMC of the prepared surfactant was determined by the
surface tension method. In this method, values of the sur-
face tension obtained for various concentrations of aqueous
solutions of the prepared surfactants were plotted against
the corresponding concentrations.
Amin is the minimum area per molecule of the prepared
compounds at the interface and was calculated from the
following equation
1016
Amin
¼
Cmax:N
where N is Avogadro’s number and Cmax is the maximum
surface excess concentration.
Efficiency (PC20)
The standard free energies of micellization (DGmo ic
and adsorption (DGaods
)
The efficiency (PC20) was determined as the concentration
(mol/l) capable of suppressing the surface tension by
20 dyn/cm. The efficiency have been determined by
extrapolating from c = 52 to the linear portion before
CMC of the c versus-Log C plot at 25 °C.
)
Understanding the process of micellization and adsorption
are important for explaining the effects of structural and
environmental factors on the value of the CMC and for
predicting the effects on environmental variations. The
standard free energy of micellization DGomic, and adsorption
DGoads, play an important role in such understanding.
The standard free energy of micellization and adsorption
are given by
Effectiveness (PCMC
)
The surface tension ‘‘cCMC’’ values at the CMC were used
to calculate values of surface pressure (effectiveness) from
the following expression:
Y
DDGomic ¼ RT ln CMC
¼ co ꢁ cCMC
Y
CMC
DGaods ¼ DGomicꢁ 6:023 ꢂ 10ꢁ1
Amin
CMC
where co is the surface tension measured for the pure water
at the appropriate temperature and cCMC is the surface
tension at the CMC. The effectiveness of adsorption is an
important factor to determine such properties of surfactant
as foaming, wetting and emulsification, since tightly
packed coherent interfacial films have very different
interfacial properties than loosely packed, no coherent
films.
Molecular Modeling Calculation
Conformational Analysis
In trying to achieve a better insight into the molecular
structure of the most preferential structure for its com-
pounds (I–III)a–c and (IV–VI)a–c, the conformational
analysis of the target compounds was performed using the
MMFF94 force-field [26] (calculations in vacuo, bond
dipole option for electrostatics, PolakeRibiere algorithm,
RMS gradient of 0.01 kcal/mol) implemented in MOE)
[27]. The most stable conformer for 3 were fully geomet-
rical optimized with molecular orbital function AM1 semi-
empirical Hamiltonian molecular orbital calculation
MOPAC 7 package [28]. The computed molecular
parameters, total energy, electronic energy, heat of for-
mation, the highest occupied molecular orbital (HOMO)
energies, the lowest unoccupied molecular orbital (LUMO)
Maximum Surface Excess Concentration Cmax
The surface excess concentration is defined as the surface
concentration at surface saturation; the maximum surface
excess concentration Cmax is a useful measure of the
effectiveness of adsorption of the surfactant at the water–
air interface, since it is the maximum value to which
adsorption can attain.
ꢀ
ꢁ
1
dc
CMax
¼
T
2:303 RT d log C
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619
energies and the dipole moment for studied compounds
were calculated.
40 and 130. In addition, the total polar surface area
(TPSA) is another key property linked to drug bio-
availability, the passively absorbed molecules with
(TPSA [ 140) have low oral bioavailability [37].
Global and Local Reactivity Descriptors
Several global and local chemical reactivity descriptors for
molecules have been defined, such as S: softness (measures
stability of molecules and chemical reactivity with direct
proportional [29], g: hardness (reciprocal of softness), l:
chemical potential, v: electronegativity (strength of the
atom for attracting electrons to itself), x: electrophilicity
index (measuring lowering energy due to maximal flowing
electron between donor and acceptor), the Fukui function
and the philicity [30–35]
Results and Discussion
Chemistry of Preparation
In the present work, two types of surfactants were syn-
thesized from maleic anhydride, since maleic anhydride
possess many function groups in its molecule that can be
used in this purposed. The esterification process may be
completed with or without catalyst [5, 38] depending on
the reactivity of the reactants but reduction of the periodic
time of reaction is industrial important aim, so p-toluene
sulfonic acid [39] was used as a catalyst to reduce the
reaction time. The nucleophilic addition of bisulfate takes
place at the activated double bond of maleic ester eth-
oxylated to give nonionic–anionic surfactants with good
yield. These products were characterized by good solubility
and polarity [40]. The structures of the yield products were
confirmed with IR and H1NMR spectroscopy.
ꢀ
ꢁ
1
2
ꢂ
o2E
g ¼
l ¼
ð1Þ
ð2Þ
o2N2
VðrꢀÞ
ꢃ
oE
oN
VðrꢀÞ
ꢂ
ꢃ
oE
oN
v ¼ ꢁl ¼ ꢁ
ð3Þ
ð4Þ
ð5Þ
VðrꢀÞ
1
S ¼
g
1
Monodecyl maleate ester (I): H NMR (300 MHz): d
l2
x ¼
2g
(ppm) relative to TMS = 0.6–0.85 (t, 3H, of terminal CH3);
1.2–1.5 ppm (m, 16H of CH3–(CH2)8CH2–), of methylene
groups in alkyl chain; 3.2–3.4 ppm (t, 2H of CH2–OOC
adjacent to carboxylate) and 5.6–5.8 ppm d, d, 2H of ole-
finic protons.
´
where E is the electronic energy, and V(r) is the external
potential of an N-electron system.
IR in the film of compound I: 3,200 cm-1 (OH of car-
boxylic acid), 2,900–2,820 cm-1 (C–H aliphatic),
1,735 cm-1 (C=O of ester), 1,705 cm-1 (C=O of acid),
1,630 cm-1 (C=C) are the most important characteristic
bands.
ADMET Factors Profiling
Oral bioavailability was considered as playing an
important role for the development of bioactive mole-
cules as therapeutic agents. Many potential therapeutic
agents fail to reach the clinic, because of their absorp-
tion, distribution, metabolism, elimination and toxic
(ADMET) Factors. Therefore, a computational study for
the prediction of ADMET properties of the molecules
was performed for compounds (I–III)a–c and (IV–VI)a–
c, by the determination of the topological polar surface
area (TPSA), a calculated percent absorption (%ABS)
which was estimated by the equation of Zhao et al. [30–
35], and the ‘‘rule of five’’ formulated by Lipinski [36],
which established that a chemical compound could be
an orally active drug in humans, if there was no more
than one violation of the following rules: (1) log P
(partition coefficient between water and octanol) \5, (2)
number of hydrogen bond donors sites B5, (3) number
of hydrogen bond acceptors sites B10, (4), molecular
weight \500 and molar refractivity should be between
Monotetradecyl maleate ester III: d(ppm) = 0.8–0.93 (t,
3H, of terminal CH3); 1.20–1.45 ppm (m, 24 H of CH3–
(CH2)12CH2-, of methylene groups in the alkyl chain;
3.1–3.3 (t, 2H of CH2–OOC adjacent to the carboxylate
and 5.8–6.0 ppm (d, d, 2H) of olefinic protons.
IR spectra of compound I showed absorption bands at:
3,150 cm-1 (OH of carboxylic acid), 2,940–2,810 cm-1
(C–H aliphatic), 1,735 cm-1 (C=O of ester), 1,710 cm-1
(C=O of acid), and 1,630 cm-1 (C=C) are the most
important characteristic bands.
1H NMR of IVc: d(ppm) = 0.8–0.9 (t, 3H, term.CH3);
1.2–1.6 ppm (m, 16H) of CH3–(CH2)8–), 1.6–1.8 ppm (t,
2H) of CH3–(CH2)8–CH2–); 2.9–3.1 ppm (d, 2H) of COO–
CH2–CH(SO3Na)–COO–; 3.4–3.9 ppm (m, 40 H) of eth-
ylene glycols protons –(CH2CH2O)10H; 3.1.3–3.2 ppm (t,
2H, –COO–CH2–CH2–); and 4.3–4.4 ppm (t, H) of COO–
CH2–CH(SO3Na)–COO).
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Fig. 1 1H NMR of dodecyl
ethoxylated maleate
(C12E10) II c
Fig. 2 1H NMR of sulfo
tetradecyl ethoxylated succinate
(VIc C14, E10
)
IR of IVc: 3,241 cm-1 (O–H of glycol); 2,915,
2,820 cm-1 (C–H aliphatic protons); 1,735 cm-1
(C = O of ester); 1,450, 1,260, 1,120 cm-1 (C–O) and
(SO3 Sulfonate group) at 1,260, 1,040 cm-1
respectively.
1H NMR of Va : 0.7–0.9 ppm (t, 3H, term.CH3);
1.1–1.3 ppm (m, 20 H) of CH3–(CH2)12–), 2.3–2.5 ppm (t,
2H) of CH3–(CH2)10–CH2–) 2.8–3.0 (s, 2H) of COO–CH2–
C(SO3Na)–COO–; 3.4–3.8 ppm (m, 24H) of ethylene
glycol protons (CH2CH2O)6 H; 3.2–3.3 ppm (t, 2H,
–COO–CH2–CH2–); and 4.2–4.4 ppm (t, H) of COO–CH2–
CH(SO3Na)–COO) (Figs. 1, 2).
IR V a 3,226 cm-1 (O–H of glycol); 2,900, 2,820 cm-1
(mC–H aliphatic protons); 1,735 cm-1 (C = O of ester);
1,450, 1,260, 1,105 cm-1 (C–O) and (SO3 Sulfonate group)
at 1,270, 1,080 cm-1 respectively.
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621
Fig. 5 Surface tension versus—log conc. of (IIIa–c)
Fig. 3 Surface tension versus—log conc. of (Ia–c)
IVa-c
55
50
45
40
35
30
25
20
IVa
IVb
IVc
6
5
4
3
2
1
0
- Log c
Fig. 6 Surface tension versus—log conc. of (IVa–c)
Va-c
Fig. 4 Surface tension versus—log conc. of (IIa–c)
70
60
50
40
Surface Active Properties
Va
30
Vb
20
Vc
10
0
Surface Tension
6
5
4
3
2
1
0
It is well known that the prepared surfactant using the
untraditional catalyst gave a narrow range distribution [41],
containing low unreacted materials and required moles of
ethylene oxide. So, the ethoxylation using K10-clay cata-
lyst gave a narrow range distribution [19]. The surface
activities of the prepared surfactants (I–III)a–c and (IV–
VI)a–c were investigated. The surface tensions of the
prepared surfactants solutions were measured at 25 °C.
From the data, the surface tension values gradually
decreased as their hydrophobic chain lengths increased.
This is due to the adsorption of their molecules at the air/
water interfaces [10], and to investigate their surface
activity (CMC and their surface parameters), the relation-
ships between the surface tensions (c) versus concentra-
tions (-log c) were plotted and are depicted in Figs. 3, 4, 5
of (I–III)a–c for the prepared ethoxylated monoester and in
Figs. 6, 7, 8 of (IV–VI)a–c for the anionic–nonionic
monoester surfactants. Obviously, the values of the CMC
depend mainly on the chemical structure of the hydro-
phobic chain lengths of the hydrophobic molecules [9]. The
CMC values as shown in Table 3 ranged between
3.12 9 10-3 and 1.15 9 10-3. Generally, the synthesized
surfactant molecules showed consistent behavior according
to their hydrophobic chain lengths. The CMC of anionic-
- Log c
Fig. 7 Surface tension versus—log conc. of (Va–c)
VIa-c
60
50
40
30
VIa
20
VIb
10
VIc
0
6
5
4
3
2
1
0
- Log c
Fig. 8 Surface tension versus—log conc. of ((VIa–c))
nonionic (IV–VI)a–c have lower values than nonionic (I–
III)a–c due to bifunctional properties (i.e., very low critical
micelle concentration and high solubilizing capacity) [42].
Effectiveness (pCMC
)
The most effective surfactant is the one that gives the
greatest lowering of the surface tension for a critical
micelle concentration (CMC). According to the results
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Table 3 Surface activity of the prepared surfactants (I–III)a–c and (IV–VI)a–c
Comp.
n
CMC 9 10-3 mol/dm3
pCMC mN/m
pc20 mol/dm3
Umax 9 10-11 mol/cm2
Amin A0 nm2
Ia
6
8
1.38
1.15
1.39
1.99
2.44
2.53
2.78
3.12
2.15
1.54
1.49
1.37
1.53
1.72
2.22
1.47
3.07
1.37
37.00
36.23
35.85
36.23
35.48
34.61
34.86
34.38
33.43
38.92
38.54
37.68
38.92
37.77
33.91
37.39
36.62
35.08
1.13 9 10-6
3.48 9 10-6
1.21 9 10-5
2.93 9 10-5
5.66 9 10-5
7.60 9 10-5
6.34 9 10-5
8.70 9 10-5
1.29 9 10-4
5.70 9 10-6
2.95 9 10-6
9.72 9 10-6
4.03 9 10-6
1.62 9 10-5
6.00 9 10-5
8.95 9 10-6
2.90 9 10-5
3.33 9 10-5
5.46
5.56
6.03
9.01
10.90
11.00
10.60
10.70
11.80
7.23
7.08
7.16
6.91
8.73
9.69
7.84
9.67
8.73
3.04
2.99
2.75
1.84
1.52
1.51
1.56
1.56
1.41
2.30
2.34
2.32
2.40
1.90
1.71
2.12
1.72
1.90
Ib
Ic
10
6
IIa
IIb
IIc
8
10
6
IIIa
IIIb
IIIc
IVa
IVb
IVc
Va
Vb
Vc
VIa
VIb
VIc
8
10
6
8
10
6
8
10
6
8
10
Error of measurements 0.5 °C and 1.0 mm
n number of ethylene oxide units
listed in Table 3, the effectiveness of the anionic–nonionic
surfactants was found to be higher because they achieved
the maximum of the surface tension at CMC.
Table 4 Cloud point and foam of the prepared nonionic compounds
(I–III)a–c
Compounds
n
Cloud point °C
1.0 wt%
Foam height
(mm) 0.1 wt%
Efficiency (PC20
)
C10
a
b
Ia
6
8
80
82
88
174
175
178
Values of efficiency of the prepared surfactants are shown
in Table 3, the efficiency increase with increasing hydro-
phobic chain length. This is due to the fact that the effi-
ciency of adsorption at interfaces increases linearly with
increases in the number of carbon atoms of the hydro-
phobic group.
Ib
Ic
c
10
C12
a
IIa
IIb
IIc
6
8
85
90
176
180
184
b
c
10
[100
C14
a
Maximum Surface Excess (Umax
)
IIIa
IIIb
IIIc
6
8
85
93
179
183
186
b
It is evident from Table 3 that by increasing the hydro-
phobic chain length the Cmax increases. Thus by increasing
the hydrophobicity of the surfactant contributes to the
molecules’ migration to the water–air interface causing a
consequent increase in Cmax values.
c
10
[100
molecules. The data of minimum surface area of the short
chain surfactant molecules showed higher Amin of these
molecules than those of longer hydrophobic chains.
Minimum Surface Area (Amin
)
Results given in Table 3 indicate that as a consequence of
increasing the Cmax, disorder occurred at the interface
causing a decrease in Amin values. That is due to the
minimum surface area decreasing with increasing hydro-
phobic chain length of the synthesized surfactant
Cloud Point
Results listed in Tables 4 and 5 indicate that nonionic
surfactants show higher cloud points in their aqueous
solutions with a particular hydrophobic group and an
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J Surfact Deterg (2014) 17:615–627
623
Table 5 Cloud point and foam of the prepared nonionic–anionic
compounds (V–VI)a–c
Table 8 Biodegradability of the prepared nonionic surfactants (I–
III)a–c
Compounds
n
Cloud point
°C 1.0 wt%
Foam height
(mm) 0.1 wt%
Compd.
n
1st
day
2nd
day
3rd
day
4th
day
5th
day
6th
day
7th
day
C10
Ia
6
8
57
56
64
62
59
63
62
61
60
59
57
73
70
65
72
69
65
65
64
63
80
78
74
80
76
72
70
69
68
88
85
82
87
84
79
76
75
73
93
90
88
91
88
85
80
82
80
–
95
93
97
93
92
88
90
87
a
b
IVa
IVb
IVc
6
8
70
76
84
210
214
221
Ib
Ic
10 54
c
10
IIa
IIb
IIc
IIIa
IIIb
IIIc
6
8
55
55
C12
a
Va
Vb
Vc
6
8
73
82
89
215
219
225
10 54
b
6
8
53
52
c
10
C14
a
10 50
VIa
VIb
VIc
6
8
75
85
93
222
226
232
b
Table 9 Biodegradability of the prepared nonionic–anionic surfac-
tants (V–VI)a–c
c
10
Error of measurements 0.5 °C and 1.0 mm
n number of ethylene oxide units
Compd.
n
1st
day
2nd
day
3rd
day
4th
day
5th
day
6th
day
7th
day
IVa
IVb
IVc
Va
6
8
55
53
60
60
60
60
59
58
59
60
60
73
68
67
71
65
63
68
69
66
82
77
75
81
73
70
75
77
72
93
83
80
90
80
77
83
83
80
98
89
87
96
88
85
90
88
86
–
93
92
–
Table 6 Dispersing power (%) of nonionic surfactants (I–III)a–c
10 52
Time
(h)
Ia
Ib
Ic
IIa
IIb
IIc
IIIa IIIb IIIc
6
8
54
53
Vb
93
91
–
1.5
3
5.6
7.0
9.8
7.9
8.3 11.5
9.0 14.2 19.7
Vc
10 52
8.5 10.3 13.4 11.5 14.3 16.2 17.6 21.6 27.6
13.6 15.8 19.9 17.8 18.5 23.7 26.8 29.9 34.4
VIa
VIb
VIc
6
8
54
52
6
92
90
9
12.2 14
17
14.2 16.7 20.6 21.7 23.3 26.6
10 52
Error of calculations was: Biodegradation rate = 1.0 %
n number of moles of ethylene oxide units
Table 7 Dispersing power (%) of nonionic–anionic surfactants (IV–
VI)a–c
Foaming Height
Time
(h)
Iva IVb IVc Va
Vb
Vc
VIa VIb VIc
In general, nonionic surfactants form low and unstable
foam. It was reported that the foaming height of the pre-
pared surfactants increases with an increase in both the
number of ethylene oxide units and the hydrophobic parts
per molecule of surfactant [43, 44]. From Tables 4, 5 the
prepared compounds (IV–VI)a–c showed the highest foam
and this may be due to a sulfate group effect and their
higher surface activities.
1.5
3
12.2 17.3 20.6 22.4 21.5 23.3 22.7 24.4 26.8
21.7 26.6 29.7 31.5 26.2 28.4 28.5 33.2 34.4
27.9 33.5 38.9 39.4 36.6 38.5 26.7 43.6 45.7
22.2 30.1 31.5 32.8 31.4 33.8 21.2 36.3 38.7
6
9
Calculation error = 0.3 %
Dispersing Power
increasing number of ethoxy groups per molecule. This
may be attributed to the fact that increased hydration of
ethylene oxide oxygen with increased ethylene oxide chain
length requires higher temperatures until phase separation
occurs [42] giving a good performance in hot water. The
prepared nonionic surfactants (I–III)a–c show cloud points
higher than nonionic–anionic (IV–VI)a–c, this is due to the
latter having a sulfonated group cooperating with the E.O.
adduct.
The ability to disperse fine soil is considered one of the
most important criteria for evaluating the detergent effi-
ciency of surfactants [45]. The dispersion ability of the
prepared surfactants (I–III)a–c and (IV–VI)a–c was studied
for four different durations, i.e. 1.5, 3, 6 and 9 h. The
dispersing powers of anionic-nonionic surfactants and
nonionic ones are shown in Tables 6, 7 the maximum
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J Surfact Deterg (2014) 17:615–627
Table 10 The optimized calculations energies at the AM1 molecular orbital for (I–III)a–c and (IV–VI)a–c
Cpd
E
Eele
HF
IP
ASA
ASA?
ASA-
ASA_H
ASA_P
E_sol
Ia
-103,903
-114,690
-114,690
-111,097
-111,090
-111,094
-118,273
-118,283
-118,286
-123,644
-130,827
-134,422
-130,828
-130,822
-130,828
-138,017
-138,014
-138,017
-762,456
-268.60
-295.63
-294.84
-288.52
-281.84
-264.40
-291.29
-301.85
-303.44
-457.55
-492.52
-499.66
-493.07
-487.48
-493.65
-509.13
-483.47
-509.11
10.96
10.83
10.77
10.78
11.03
10.95
10.92
10.83
10.857
7.85
678.46
804.08
814.08
751.02
770.23
773.81
792.81
818.47
818.87
811.76
812.37
873.71
828.39
844.64
829.03
918.77
826.64
930.44
99.88
104.32
108.49
105.41
88.45
103.73
99.29
508.95
670.19
660.68
616.33
617.96
626.34
635.23
683.42
686.91
560.58
582.25
593.92
586.05
594.24
554.86
649.73
594.19
676.05
169.51
133.89
153.39
134.69
152.27
147.46
157.57
135.04
131.95
251.17
230.12
279.79
242.34
250.40
274.16
269.04
232.44
254.39
-16.24
-5.35
Ib
-859,719
-867,480
-839,651
-828,423
-840,159
-911,242
-920,683
-937,902
-906,794
-1,046,800
-1,082,666
-1,042,025
-1,023,099
-1,053,872
-1,145,595
-1,177,015
-1,123,847
Ic
104.91
100.11
108.62
105.01
108.55
99.31
-13.36
-8.69
IIa
IIb
IIc
-12.79
-6.291
-12.85
-5.56
101.71
90.01
IIIa
IIIb
IIIc
Iva
IVb
IVc
Va
95.812
106.88
144.98
138.91
152.95
143.46
150.99
167.93
157.44
128.87
162.21
97.21
-6.33
110.18
98.09
-3.29
7.88
-16.28
-26.20
-11.68
-7.08
8.22
129.86
104.01
103.71
111.81
113.56
106.75
97.195
7.98
Vb
Vc
7.83
8.01
-12.28
-7.58
VIa
VIb
VIc
7.99
7.88
-20.38
-9.03
7.96
E Total energy (kcal/mol), E-ele electronic energy (kcal/mol), HF heat of formation (kcal/mol), IP ionization potential energy(kcal/mol), (A)2
water accessible surface area, (A2) positive accessible surface area, (A2)s negative accessible surface area, (A2) Solvation energy hydrophobic
surface area Polar surface area (kcal/mol)
dispersion of solids took place when the duration was 5 h
irrespective of surfactant type. The maximum dispersing
power was found at 6 h and it was 43.6 and 45.7 % for VIb
and VIc, respectively, and the dispersion ability of non-
ionic surfactants at 6 h was 29.9 and 34.4 % for IIIb and
IIIc respectively. Among the prepared two types of sur-
factant, the maximum dispersing power was found For VIb
and VIc at 6 h. Increasing the duration after 6 h had no
positive influence on an increase in the dispersion of solids
in both cases.
A biodegradation die-away test in ordinary river water
showed satisfactory results for the tested compounds in
Tables 8, 9. The biodegradation was expressed by mea-
surement of the surface tension with time (day). The rate of
degradation of these compounds depends on the size of the
molecule; a bulky molecule diffuses slowly through the cell
membrane and their degradation is more difficult, this
means that these compounds with lower moles of ethylene
oxide are more degradable than those which contain higher
moles of ethylene oxide [46]. In general, the products have a
much higher rate of degradation ranging about 92 % deg-
radation after around 6–7 days. It could also be shown that
the biodegradation of the surfactants decreased with an
increasing number of carbon atoms in the alkyl chain and
independent of the catalyst used in the ethoxylation process.
Biodegradability
Biodegradation is the conversion of organic compounds
into less complex structures under the influence of
microorganisms. Under aerobic conditions, this process
results in the formation of water, carbon dioxide, and
biomass. With traditional surfactants, the rate of bio-
degradation varied from 1 to 2 h for fatty acid-derived
surfactants; 1–2 days for linear alkyl benzene sulfonates,
and several months for branched alkyl benzene sulfo-
nates (ABS). Two criteria are important when testing for
biodegradation: first, primary degradation that results in
loss of surface activity; second, ultimate biodegradation,
i.e. conversion into CO2, which can be measured using
closed bottle tests.
Molecular Modeling Results
Conformational Analysis
The calculated molecular parameters in Table 10 showed
that the lowest minimization energy for (I–III)a–c and (IV–
VI)a–c were shown with a common arrangement of two
hydrocarbon chains parallel to each other, the higher
HOMO energy values show that the molecule is a good
electron donor, on the other hand, the lower HOMO energy
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625
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J Surfact Deterg (2014) 17:615–627
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Ahmed M. Hussein was awarded his Ph.D. from the Technical
University of Budapest, Hungary in the field of surfactants. He is an
associate professor at the Faculty of Science, Benha University,
Egypt. His research work is in the synthesis and evaluation of
surfactants. He currently works on the Faculty of Science, Jazan
University, Saudia Arabia.
Manal M. Khowdiary is a researcher from the petrochemicals
department at the Egyptian Petroleum Research Institute, Nasr City
Cairo, Egypt. Her interests are the synthesis and evaluation of
surfactants in several applications including detergency and biocidal
activity.
123