Synthesis and Properties of Three N-Alkyl Bis-Quaternary Ammonium Salt Surfactants

Article abstract of DOI:10.1002/jsde.12443

Three N-alkyl bis-quaternary ammonium salt surfactants were synthesized by using epichlorohydrin, trimethylamine hydrochloride, and N,N-dimethylalkyl amine as raw materials in a two-step manner. The products were characterized by ¹H NMR and MS, confirming the successful synthesis of 2-Hydroxy-N¹,N¹,N³,N³-tetramethyl-N³-dodecylpropane-1,3-diammonium chloride (HPDDC), 2-Hydroxy-N¹,N¹,N³,N³-tetramethyl-N³-tetradecylpropane-1,3-diammonium chloride (HPTDC), and 2-Hydroxy-N¹, N¹, N³, N³-tetramethyl-N³-hexadecylpropane-1,3-diammonium chloride (HPHDC). Moreover, the influence of carbon chain length on surface-active properties, foaming properties, and paraffin liquid emulsion stability was investigated. Results indicated that critical micelle concentrations (cmc) decreased with increasing carbon chain length from 12 to 16, and the cmc and γ_cmc were lower than those of Dodecyl trimethyl ammonium chloride (DTAC). The products exhibited better foam properties and worse emulsifying performance than those of DTAC. The Krafft points of all products were determined to be below 0 °C. Moreover, the products also demonstrated outstanding antibacterial properties.

Full text of DOI:10.1002/jsde.12443

J Surfact Deterg (2020)
DOI 10.1002/jsde.12443
ORIGINAL ARTICLE
Synthesis and Properties of Three N-Alkyl Bis-Quaternary
Ammonium Salt Surfactants
Jiajia Liu1 · Jun Shen2 · Chen Wang1 · Hujun Xu1
Received: 15 December 2019 / Revised: 23 April 2020 / Accepted: 28 May 2020
© 2020 AOCS
Abstract Three N-alkyl bis-quaternary ammonium salt
surfactants were synthesized by using epichlorohydrin,
trimethylamine hydrochloride, and N,N-dimethylalkyl amine
as raw materials in a two-step manner. The products were
Introduction
Owing to the fascinating properties such as low critical
micelle concentration (cmc), unusual micelle structures and
specific aggregation behaviors, Gemini surfactants with
two hydrophilic groups and two hydrophobic groups have
attracted the attention of academic researchers as well as
industrial experts (Ahire and Bhagwat, 2017; Menger and
Keipe, 2000; Monger and Littau, 1991; Sharma
et al., 2017). However, there are limited studies on asym-
metric surfactants containing a hydrophobic group and two
hydrophilic groups, which also have excellent water solu-
bility, surface-active and bactericidal etc. because of their
two ion head groups (Jan and Stauffer, 1994; Zhao
et al., 2017). Xu studied the synthesis and properties of
alkyl diphenyl ether disulfonate and found that it possessed
excellent water solubility, surface-active properties, and
application properties (Xu et al., 2005). The Gemini quater-
nary ammonium salt molecule has two positive ion head
groups and is a typical representative of new fungicides.
Currently, there are many studies on symmetric double
quaternary ammonium salts, but there are few studies on
different hydrophobic groups at both ends. Wang (2001)
pointed out that the asymmetry of molecular structure is
more conducive to the bactericidal performance of double
quaternary ammonium salts.
1
characterized by H NMR and MS, confirming the success-
ful synthesis of 2-Hydroxy-N1,N1,N3,N3-tetramethyl-N3-
dodecylpropane-1,3-diammonium chloride (HPDDC),
2-Hydroxy-N1,N1,N3,N3-tetramethyl-N3-tetradecylpropane-
1,3-diammonium chloride (HPTDC), and 2-Hydroxy-N1, N1,
N3, N3-tetramethyl-N3-hexadecylpropane-1,3-diammonium
chloride (HPHDC). Moreover, the influence of carbon chain
length on surface-active properties, foaming properties, and
paraffin liquid emulsion stability was investigated. Results
indicated that critical micelle concentrations (cmc) decreased
with increasing carbon chain length from 12 to 16, and the
cmc and γcmc were lower than those of Dodecyl trimethyl
ammonium chloride (DTAC). The products exhibited better
foam properties and worse emulsifying performance than
those of DTAC. The Krafft points of all products were deter-
ꢀ
mined to be below 0 C. Moreover, the products also dem-
onstrated outstanding antibacterial properties.
Keywords Synthesis ꢁ Surface-active ꢁ Foaming
properties ꢁ Emulsion stability ꢁ Antibacterial properties
J Surfact Deterg (2020).
In the present study, three N-alkyl bis-quaternary ammo-
nium salt surfactants 2-Hydroxy-N1,N1,N3,N3-tetramethyl-
N3-dodecylpropane-1,3-diammonium chloride (HPDDC),
2-hydroxy-N1,N1,N3,N3-tetramethyl-N3-tetradecylpropane-
1,3-diammonium chloride (HPTDC), and 2-hydroxy-N1,N1,
N3,N3-tetramethyl-N3-hexadecylpropane-1,3-diammonium
chloride (HPHDC) were synthesized from N,N-dim-
ethylalkylamine, trimethylamine hydrochloride, and
* Hujun Xu
xu6209@163.com
1
School of Chemical and Material Engineering, Jiangnan
University, Wuxi, 214122, P. R. China
2
Unilever (China) Investing Co., Ltd, Taicang, Jiangsu 215400,
P. R. China
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epichlorohydrin. Systematic experiments were carried out to
investigate their surface chemical properties, foaming prop-
erties, emulsifying properties, and antibacterial properties,
with the motivation to provide some guidance as well as fun-
damental research data for the synthesis and application of
such surfactants (Scheme 1).
Synthesis of N-Alkyl Bis-Quaternary Ammonium Salt
Surfactants
Herein, the preparation of HPDDC was selected as an
example to elaborate the synthetic procedure. The reactants
were prepared by dissolving 0.10 mol of N,N-
dimethyldodecylamine into 40 mL of ethanol and 0.10 mol
of M into 10 mL of distilled water. Afterward, the as-
prepared reactants were mixed and added into a three-
necked flask, followed by being refluxed uniformly at
80 ꢀC for 5 h. After removing solvent, the obtained product
was recrystallized using a mixture of ethanol and ethyl ace-
tate (Vethanol:Vethyl acetate = 1:20) and being dried under vac-
uum. In this way, white-solid HPDDC powders can be
produced, with a yield of 83.7%.
Materials and Methods
Materials
Epichlorohydrin (AR), Dodecyl trimethyl ammonium
chloride (AR), and liquid paraffin (CP, colorless, and
odorless mixture obtained from the fractional distillation
of crude oil, relative density (d20/20) = 0.83–0.88, dis-
tillation temperature ≥ 300 ꢀC) were purchased from Sin-
opharm Group Chemical Reagent Co., Ltd., Shanghai,
China. N,N-dimethyldodecylamine (> 97%) was from
Cool Biological Engineering Co, Ltd, Anhui, China. N,
N-Dimethyltetradecylamine and N, N-Dimethylhexadecylamine
(> 98%) were provided by Lianshui Xinyuan Biotechnology
Co., Ltd., Jiangsu, China.
Same procedure was applied to the synthesis of HPTDC and
HPHDC by replacing N,N-dimethyldodecylamine with N,N-
dimethyltetradecylamine, and N,N-dimethylhexadecylamine,
respectively. The corresponding yields were 82.5% and 85.6%.
Structural Characterization
Chemical structures of the surfactants were examined by
MS (MALDI SYNAPT MS, Waters company in Shanghai,
1
China) and H NMR (AVANCE III HD 400 MHz, Bruker
company in Beijing, China).
Synthesis Procedures
Measurement of Performance
Synthesis of Intermediate
Determination of Krafft point: HPDDC, HPTDC, and
HPHDC were formulated into aqueous solutions (1%, wt),
which were gradually heated to be clear and transparent
under stirring. Then the as-prepared solution was placed in
an ice water bath to be slowly cooled down. When the solu-
tion became cloudy, the real-time temperature was recorded
(Bales et al., 2001).
3-Chloro-2-hydroxypropyltrimethylammonium
chloride
(M) was synthesized according to the method reported by
Zhu et al. (2016). In brief, trimethylamine hydrochloride
and epichlorohydrin were chosen as raw materials. Firstly,
0.20 mol of trimethylamine hydrochloride was mixed with
40 mL of ethanol and added into a single neck flask,
followed by the addition of 0.20 mol epichlorohydrin.
Then, the mixed solution was heated at 45 ꢀC for 5 h. After
removing solvent, the obtained product was recrystallized
using a mixture of ethanol and water (Vethanol: VH2O = 3:20)
and dried under vacuum to get the white-solid M. The yield
was 87.8%.
Surface tension measurement: The surface tension mea-
ꢀ
surement was conducted at 25 C using the pendent drop
method on an optical contact angle measuring instrument
(OCA 40, manufactured by dataphysics company in Fil-
derstadt near Stuttgart, Germany). The accuracy of the mea-
surement was within ꢂ0.1 mN m−1. The surface tension of
pure water was measured as being 71.9 mN m−1 at 25 ꢀC.
The cmc and γcmc of Dodecyl trimethyl ammonium chlo-
ride (DTAC) were measured at the same condition (Fig. 1).
Foaming property measurement: Foam ability of surfac-
tant solutions and the produced foam stability were mea-
sured according to the Ross-Miles method. Briefly, the test
solution was prepared by adding 2.5 g of the sample and
100 mL of hard water (150 PPM) into a 1000 mL volumet-
45 °C
Cl
Cl
N
Cl
+
N(CH3)3 HCl
O
OH
80 °C
H2n+1Cn
N
N
2Cl
CnH2n+1N(CH3)2
OH
ꢀ
ric flask at 40 C. The foam height was measured with a
n=12, 14, 16
Roche foam meter, and the measurement was repeated
three times (Ding and Hao, 2010).
Scheme 1 Synthetic routines of HPDDC, HPTDC, and HPHDC
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(a)
(b)
HPTDC
HPDDC
D2O
D2O
15H
18H
15H
22H
2H
3H
3H
7H
7H
1H
2H
1H
8
6
4
2
0
8
6
4
2
0
δ
δ
(c)
HPHDC
D2O
26H
15H
3H
7H
2H
1H
8
6
4
2
0
δ
Fig 1 (a) 1H NMR spectrum of HPDDC (b) 1H NMR spectrum of HPTDC and (c) 1H NMR spectrum of HPHDC
Determination of emulsion stability: The water separa-
tion time method was adopted to determine emulsifying
properties. Surfactant aqueous solutions (40 mL, con-
taining of 1 wt% HPDDC, HPTDC or HPHDC) and par-
affin liquid (40 mL) were poured into a 100 mL
dropwise to the aqueous phase and the oil phase used to
prepare the emulsion, respectively. If the droplets were
dispersed in the water phase but not in the oil phase, the
emulsion was O/W type; otherwise, it was W/O type.
Antimicrobial assay: The antibacterial activities of
N-Alkyl Bis-quaternary Ammonium Salt Surfactants
were determined by following the Chinese National
Standard GB15979-2002 (People’s Republic of China
National Standards, 1996). The concentration of the sur-
factants aqueous solution was 5 × 10−4 mol L−1. The
microorganisms were Staphylococcus aureus (ATCC
6538), Candida albicans (ATCC 10231), and
Escherichia coli (ATCC 9637).
ꢀ
graduated measuring cylinder at 40 C. The graduated
cylinder was continuously inverted up and down five
times and being kept vertically for 1 min, then re-
inverted again for five more times. Emulsion stability
was evaluated by the time when 10 mL of water was sep-
arated from the emulsion. All measurements were
repeated three times. Using drop test to determine emul-
sion type: 1–2 drops of the emulsion were added
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Results and Discussion
Chemical Structures
3.26–3.10 (m, 5NCH3 15H), 1.76 (s, NCH2CH2, 2H), 1.27
(d, J = 30.7 Hz, CH2(CH2)13CH3, 26H), 0.82 (d, J = 6.9 Hz,
CH2CH3, 3H), 4.70 belongs to D2O.
The results are as follows:
HPDDC: 1H NMR (400 MHz, D2O) δ 4.83 (t, J = 8.9 Hz,
OH 1H), 3.56–3.28 (m, NCH2 and HOCH(CH2)2 7H),
3.23–3.10 (m, 5NCH3, 15H), 1.71 (s, NCH2CH2, 2H),
1.23 (d, J = 30.5 Hz, CH2(CH2)9CH3 18H), 0.78 (d,
J = 6.9 Hz, CH2CH3 3H), 4.70 belongs to D2O.
Krafft Point (Tk)
Preceding studies indicated that the gradual increase in tem-
perature can initially improve the solubility of ionic surfac-
tants in water slowly. However, once the temperature
reaches a certain value (the so-called critical dissolved tem-
perature Tk), the solubility will increase drastically (Rosen
and Kunjappu, 2012). Therefore, lower Krafft point ensures
better solubility, and being favored by practical applications.
In this study, the Tk of HPꢀDDC, HPTDC, and HPHDC were
measured to be below 0 C, suggesting our products have
good water solubility throughout the series (Fig. 2).
HPTDC: 1H NMR (400 MHz, D2O) δ 4.86 (t, J = 8.9 Hz,
OH 1H), 3.60–3.32 (m, NCH2 and HOCH(CH2)2, 7H),
3.27–3.16 (m, 5NCH3, 5H), 1.75 (s, NCH2CH2, 2H), 1.26
(d, J = 30.9 Hz, CH2(CH2)11CH3 22H), 0.81 (d, J = 6.7 Hz,
CH2CH3, 3H), 4.70 belongs to D2O.
HPHDC: 1H NMR (400 MHz, D2O) δ 4.92 (t, J = 8.5 Hz
OH, 1H), 3.64–3.37 (m, NCH2 and HOCH(CH2)2, 7H),
(a)
(b)
HPTDC
179.2
HPDDC
165.2
179.7
165.7
150
160
170
180
160
170
180
m/z
190
200
m/2z
(c)
HPHDC
193.2
193.7
170
180
190
200
210
220
m/2z
Fig 2 (a) The mass spectrum of HPDDC (b) The mass spectrum of HPTDC and (c) The mass spectrum of HPHDC
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Table 1 Surface chemical properties of the surfactants
Surfactant
cmc (mol L−1
)
γcmc (mN m−1
)
pC20
cmc (C20)
1010Γmax (mol cm−2
)
Amin (nm2)
HPDDC
HPTDC
HPHDC
7.4 × 10−3
4.4 × 10−3
3.1 × 10−3
32.9
33.8
35.0
2.79
2.94
3.05
4.57
4.12
3.46
1.53
1.65
1.81
1.08
1.01
0.92
Surface Properties
The maximum surface adsorption amount (Γmax) and the
minimum surface area per molecule (Amin) can be calcu-
lated by the following Eqs 1 and 2 (Xu et al., 2011).
Table 1 lists the surface-active parameters (Γmax, Amin and
pC20) of HPDDC, HPTDC, and HPHDC at 25 ꢀC. The
cmc and γcmc values of DTAC were 1.20 × 10−2 mol L−1
and 39.0 mN m−1. Meanwhile, the relationship between
surface tension and the concentration was established in the
γ-lgc curve (Fig. 3), from which we can derive the value of
cmc and γcmc. It is shown that the surface tension gradually
decreases with the surfactant concentration in the range of
4 × 10−4 to 0.02 mol L−1. After that, it maintains a con-
stant level, indicating the formation of micelles from mono-
mers. Another observation is that cmc value decreases from
7.35 × 10−3 to 3.08 × 10−3 mol L−1 as the hydrophobic
chain length increases from 12 to 16. This is attributed to
the increased hydrophobicity of surfactant with the growth
of the hydrophobic chain, which increases the ability to
form micelles for surfactant molecules. Among them, the
γcmc increased as the hydrophobic chain length increases
from 12 to 16. The reason may be that the carbon chain is
too long, causing the hydrophobic tail to bend inward at the
air-water interface. Thus a part of methylene are certainly
exposed to the air-side which is unfavorable to reduce the
surface tension. Therefore, it is not that the longer the
hydrophobic chain, the lower the surface tension. More-
over, compared to the γcmc and cmc of the monomeric sur-
factant DTAC, all products show better surface activity,
since they contain two hydrophilic ion head groups.
−1
dγ
Γmax
=
ð1Þ
ð2Þ
2:303nRT dlgc
1014
Amin
=
NAΓmax
where R is the ideal gas constant (8.314 J mol−1 K−1), γ is
the surface tension, NA is the Avogadro constant
(6.022 × 1023), n is the number of dissociating ionic spe-
cies that are affected by the type of surfactant and the coun-
terion in the solution (in our case is 3), T is the
thermodynamic temperature, c is the molar concentration
of the surfactant, and (dγ/dlgc) is the slope of the γ-lg
c curve.
When the hydrophobic chain changes from C12 to C16,
the density of the surfactant molecules at the interface
increases, resulting in increased Γmax values as well as
decreased Amin values. In general, pC20 is used to indicate
the adsorption efficiency of the surfactant at the air-water
interface, where higher absorbance ability corresponds to
improved efficiency in lowering the surface tension. This is
confirmed by our results. As shown in Table 1, the increase
of the alkyl chain length from 12 to 16 leads to the
improvement of the pC20, inferring the enhanced absor-
bance ability at the air-water interface.
Emulsifying Properties
HPHDC
HPTDC
HPDDC
Emulsion is a liquid/liquid dispersion system. A representa-
tive example is the mixture of aqueous and oil phases
(Nesterenko et al., 2014; Sharma et al., 2014). In the pre-
sent study, the emulsifying properties of the surfactants
were determined by the water separation time method,
where longer water separation time corresponds to higher
emulsifying ability. The key factor determining the emul-
sion stability is whether droplet interface film (adsorption
layer) is stable and strong. The oligomeric surfactant has
two or more hydrophobic and hydrophilic groups at the
interface. Such arrangement is more compact and stable.
According to the drop test, the emulsion is O/W type. As
reflected by Fig. 4, the growth of the alkyl chain causes a
gradual increase of the emulsifying ability. A reasonable
explanation is when the hydrophobic chain grows, the
70
60
50
40
30
–3.6
–3.2
–2.8
–2.4
–2.0
–1.6
lg[c/(mol·L–1)]
Fig 3 The γ-lgc curves of the surfactants
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400
350
300
250
200
150
100
0 min
5 min
150
120
90
60
30
0
HPDDC
HPTDC
HPHDC
Surfactants
DTAC
HPDDC
HPTDC
HPHDC
DTAC
Surfactants
Fig 5 Foaming properties of the products (the foam height was
within ꢂ5 mm)
Fig 4 Water separation time of products (the time was within ꢂ5 s)
amount of saturated adsorption on the interface increases.
As a result, the molecular arrangement becomes more com-
pact, which in turn, helps to increase the interaction
between molecules and the strength within the interface
film. However, compared to that of DTAC, the products
exhibited worse emulsifying properties.
the surfactant molecule contains two positive charges,
which increases the surface charge density. When the liquid
film is thin to a certain extent, the mutual charge repelling
effect begins to be remarkable, preventing the liquid film
from being further drained, and also contributing to the sta-
bility of the foam. In addition, it can be seen from Fig. 5
that the foaming capacity order of the synthesized surfac-
tants is HPHDC > HPTDC > HPDDC. This can be ascribed
that the growth of alkyl chain can enhance the cohesive
force between the molecules, which further increases the
elasticity and strength of the liquid film. In addition, it can
be seen from Fig. 5 that the foam height of DTAC is much
lower than that of the HPTDC and HPHDC, indicating that
the products have better foam ability and stabilization than
those of DTAC.
Foaming Properties
The foam is actually a thermodynamically unstable system
where gas dispersed in the liquid. The surfactant can consti-
tute a double-layered foam structure to prevent the dis-
charge of liquid between the bubbles. This structure
possesses rigidity and a certain mechanical strength at the
gas–liquid interface (Jian et al., 2015; Vikingstad
et al., 2006). In addition, the surfactant can reduce the sur-
face tension of the gas–liquid interface. There are mainly
two factors leading to unstable foam: the expansion of gas
through the liquid membrane as well as the gravity drain-
age. According to the Gibbs principle, the system always
tends to be in a low energy state, so low surface tension
can reduce the energy of the foam system. The capillary
pressure is proportional to the surface tension of the solu-
tion. When the surface tension is low, the capillary pressure
is small, and the foam discharge speed is slow, which is
beneficial to the stability of the foam. In this case, the pres-
sure inside small bubble is larger than that in large bubble,
causing the gas to diffuse from the small bubble through
the liquid film into the large bubble, eventually leading to
liquid film rupture.
Antibacterial Properties
The positively charged ion heads in the cationic surfactant
molecules can strongly adsorb on the cell wall of the nega-
tively charged bacteria, penetrate, and diffuse into the cell,
destroy the protein ribozyme and other substances, inhibit
or kill the biological activity of the bacteria (Obłąk
et al., 2014; Zhang et al., 2015). Compared with other types
of surfactants, cationic surfactants have a broad spectrum
of antibacterial properties during a broad pH. Thus, they
are widely used in the fields of sterilization, disinfection,
and mildew proof.
The antibacterial properties were tested by applying the
prepared quaternary ammonium salt against Escherichia
coli (EC), Staphylococcus aureus (SA), and Candida
albicans (CA). As shown in Table 2, it was found that the
asymmetric quaternary ammonium salt surfactants show
good antibacterial and antifungal activities against the three
microorganisms including Escherichia coli (EC),
The two ion head groups of products are connected by a
covalent bond thus the repulsion between them is greatly
reduced. The surfactant is arranged more closely at the
gas/liquid interface, and the intermolecular interaction force
is stronger, further increasing the strength of the surface
film and contributing to foam stability. On the other hand,
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Table 2 Antibacterial properties of products
lower γcmc and cmc compared to that of DTAC, suggesting
they have better surface-active properties. Moreover, it is
shown that HPHDC has the best foaming and emulsifying
properties among the products, inferring the growth of
hydrophobic chain can lead to a better foaming and emulsi-
fying behavior. Finally, the series of as-synthesized surfac-
tants exhibit excellent anti-bactericidal activities against
EC, SA, and CA. It is expected that they can be used as
promising bactericides in a wide range of fields.
Products
Time (min)
Antibacterial rate (%)
EC
SA
CA
HPDDC
2
5
98.96
99.99
99.99
99.99
98.96
99.99
99.99
99.99
54.55
81.25
98.96
99.79
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
62.50
90.91
99.99
99.99
99.56
99.68
99.99
99.99
99.55
99.68
99.99
99.99
99.28
99.28
99.82
99.82
10
20
2
HPTDC
HPHDC
5
Conflict of Interest The authors declare that they have no conflict
of interest.
10
20
2
5
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ꢀ
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