Novel amide-based cationic surfactants as efficient corrosion inhibitors for carbon steel in HCl and H2SO4 media

Article abstract of DOI:10.1007/s11743-012-1356-x

A variety of surface active compounds were synthesized by the quaternization of some straight chain amide derivatives with triethylamine or pyridine. Their structure FT-IR and ¹H-NMR spectra were recorded. In addition their physical properties and corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic media by the gravimetric method. As acidic media 1.5 M HCl and 1.5 M H₂SO ₄ were used and the corrosion inhibition tests fulfilled at room temperature for 24 h. Almost all prepared cationic surfactants showed efficient inhibition around their critical micelle concentrations. The effects of HCl concentration on corrosion inhibition of some synthesized compounds were also investigated. The corrosion tests were supported by contact angle measurements.

Full text of DOI:10.1007/s11743-012-1356-x

J Surfact Deterg
DOI 10.1007/s11743-012-1356-x
ORIGINAL ARTICLE
Novel Amide-Based Cationic Surfactants as Efficient Corrosion
Inhibitors for Carbon Steel in HCl and H2SO4 media
¨
•
•
A. Yıldırım S. Oztu¨rk M. C¸ etin
Received: 5 November 2011 / Accepted: 18 April 2012
Ó AOCS 2012
Abstract A variety of surface active compounds were
synthesized by the quaternization of some straight chain
amide derivatives with triethylamine or pyridine. Their
the most used acids among the acidic cleaning methods [1].
At the time of this process metallic corrosion can also
occur. Metallic corrosion is the degradation of metals and
alloys via an electrochemical reaction that occurs with
different effects. For instance this metallic degradation
causes serious economical disadvantages in several indus-
trial fields of all countries [2]. In acidic cleaning methods,
organic corrosion inhibitors are added to the medium to
prevent the corrosion and to reduce the acid utilization.
Most of the organic inhibitors that are used in acidic media
are compounds that include N, S, O heteroatoms in their
structure. Electrostatic interactions between the inhibitor
molecules and the metal surfaces occur via these hetero-
atoms. Furthermore, these heteroatoms involve unpaired
electrons that offer possible adsorption centers for the
chemical adsorption. In spite of the existence of many
organic compounds as inhibitors, development of new
compounds must be done [3].
1
structure FT-IR and H-NMR spectra were recorded. In
addition their physical properties and corrosion prevention
efficiencies were investigated. All compounds were tested
with steel coupons in acidic media by the gravimetric
method. As acidic media 1.5 M HCl and 1.5 M H2SO4
were used and the corrosion inhibition tests fulfilled at
room temperature for 24 h. Almost all prepared cationic
surfactants showed efficient inhibition around their critical
micelle concentrations. The effects of HCl concentration
on corrosion inhibition of some synthesized compounds
were also investigated. The corrosion tests were supported
by contact angle measurements.
Keywords Synthesis ꢀ Surface active compounds ꢀ
Acidic media ꢀ Contact angle
Amide-based organic compounds have an extensive
utilization field in industry. The use as corrosion inhibitor
is one of the most important usage area of these com-
pounds. In literature, there are many researches into the
corrosion prevention of metals and alloys in acidic media
of the amide-based organic compounds that include long
chains of carbon [4–9]. In recent years, cationic-based
surfactant-oriented corrosion inhibitor research has become
fairly important and new compounds that have corrosion
inhibitor character can be found to the literature [10–13].
Among these researches, there are cationic surfactants that
contained an amide functional group [14].
Introduction
In many industrial processes, acid solutions are used to
remove the undesirable substances and corrosion products
in metallic materials. Hydrochloric and sulfuric acids are
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-012-1356-x) contains supplementary
material, which is available to authorized users.
Synthetic fatty acids and their derivatives are widely
used products, mainly as industrial raw materials. Exam-
ples of potential uses of these materials include oil field
chemicals. Long chain compounds are widely used in the
oil industry as corrosion inhibitors. Industrial corrosion is a
¨
A. Yıldırım (&) ꢀ S. Oztu¨rk ꢀ M. C¸ etin
Department of Chemistry, Faculty of Science and Arts,
˘
Uludag University, 16059 Bursa, Turkey
e-mail: yildirim@uludag.edu.tr
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J Surfact Deterg
General Procedure for the Synthesis of N-Alkyl-2-(4-
formyl-2-methoxyphenoxy)acetamides 1a–1c
serious problem that causes severe economic losses
because of the destruction of metal- and alloy-based pro-
cessing equipment and devaluation of industrial products.
It has been reported that cationic type surfactants are good
inhibitors in certain acidic media [15]. Molecules of these
compounds form a monomolecular hydrophobic protective
layer at the metal surface that effectively prevents further
attack by the corrosive media. In some corrosive systems
especially in water–oil liquid system certain compounds
require hydrophilic group or groups present on their
structures for the effectiveness as corrosion inhibitors.
These groups effects solubility behaviors of corrosion
inhibitors compounds and make them more soluble or
dispersible in such media.
In a 100-mL round-bottom flask, 1 equivalent of vanillin,
2 equivalent of K2CO3 and 25 mL of DMF as the solvent
were placed and the solution was mixed for a few min-
utes. One equivalent of the corresponding 2-chloro-N-
alkylacetamide was added to this mixture and the flask
was fitted to a reflux condenser. The reaction mixture was
stirred over night under reflux at 65–70 °C in a water
bath. After the completion of the reaction, cold water was
added to the flask and the reaction mixture was extracted
with chloroform. The organic phase was dried over
sodium sulfate and the solvent was removed with a rotary
evaporator. The residue was crystallized from THF/
petroleum ether.
In the present study, some organic cationic surfactants
contain amide functional group was synthesized. Corrosion
inhibitory properties of these compounds were investigated
in aqueous acidic media. 1.5 M HCl and H2SO4 solutions
were used as acidic media. Sample metals were treated
with an acidic medium for a period of 24 h at room tem-
perature, and inhibition efficiencies were determined by the
gravimetric method. The effect of the HCl concentration on
corrosion inhibition of some synthesized compounds was
also investigated. In addition the possible corrosion inhi-
bition mechanisms of inhibitors were also investigated by
contact angle measurements.
General Procedure for the Synthesis of N-Alkyl-2-[4-
(hydroxymethyl)-2-methoxyphenoxy]acetamides 2a–2c
One equivalent of (1a–1c) was dissolved in 15 mL of
ethanol in a 100-mL round-bottom flask and cooled to
0–5 °C. To the observed mixture, 2 equivalent amounts of
NaBH4 were added in portions and the reaction was
allowed to return to room temperature, with stirring con-
tinued for 3 h. The ethanol was removed under reduced
pressure and to the residue was added cold water and the
white solid obtained was filtered under vacuum. After
drying at room temperature, the crude product was crys-
tallized from methanol/water. Unlike (2b) and (2c), the
compound (2a) was obtained as an oily product which was
dissolved in ethyl acetate, washed with water and dried
over sodium sulfate. Solvent was removed under reduced
pressure to give yellowish oily product.
Experimental Procedures
Materials and Instrumentation
All the reagents and solvents were purchased from either
Merck or Fluka Chemie and used without further purifi-
cation. Melting points were recorded with a Bu¨chi melting
point B-540 apparatus. IR spectra were measured by
Thermo Nicolet 6700 FT-IR spectrometer. 1H-NMR
spectra were measured using a Varian Mercury Plus
spectrometer (400 MHz) in CDCl3 using TMS as the
internal standard. The static water contact angle measure-
ments were carried out at room temperature with a contact
angle measurement system (KSV Instrument Attension
Optical Tensiometers Theta Lite).
General Procedure for the Synthesis of N-Alkyl-2-[4-
(chloromethyl)-2-methoxyphenoxy]acetamides 3a–3c
In a 100-mL two-necked flask fitted with a reflux con-
denser (protected by a calcium chloride guard-tube), 1
equivalent of (2a–2c) was dissolved in 20 mL of dichlo-
romethane. The flask was cooled to 0 °C in an ice bath and
2 equivalent of SOCl2 was added dropwise over a 30-min
period. The reaction mixture was stirred for 4 h at room
temperature and then refluxed for 30-min in a water bath at
60–70 °C. After this time, the flask was cooled to room
temperature and the mixture was washed with water and
5 % NaHCO3 solution. The organic phase was dried over
sodium sulfate and the solvent was removed with a rotary
evaporator. The residue was crystallized with petroleum
ether.
Synthesis of Compounds
Synthesis of 2-Chloro-N-alkylacetamides
The synthesis of 2-chloro-N-octyl, -dodecyl and -hexa-
decylacetamides was performed under similar reaction
conditions to those previously described in the literature
[16, 17].
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J Surfact Deterg
General Procedure for the Synthesis of N, N-Diethyl-N-(3-
methoxy-4-(2-(alkylamino)-2-oxoethoxy)benzyl)
ethanaminium chlorides 4a–4c
was added to the mixture. The solid obtained was filtered
under vacuum and then crystallized from a mixture of
hexane/ethyl acetate.
One equivalent of (3a–3c), 4 equivalents of triethylamine
and 15 mL of acetonitrile as the solvent were placed in a
100-mL round-bottom flask fitted with a reflux condenser.
The reaction mixture in the flask was stirred overnight under
reflux. After the reaction had ended (monitored by TLC) the
solvent was evaporated under reduced pressure and diethyl
ether was added to the oily residue. The crude product
obtained was crystallized from diethyl ether/acetone.
General Procedure for the Synthesis of N,N,N-Triethyl-2-
{4-[2-(alkylamino)-2-oxoethoxy]phenyl}-2-
oxoethanaminium bromides 8a–8c
In a 100-mL round-bottom flask fitted with a reflux con-
denser, 1 equivalent of (7a–7c) and 15 mL of acetonitrile
as solvent were placed. To this mixture, 4 equivalents of
triethylamine were added and the reaction mixture was
refluxed overnight. After the reaction was complete, the
solvent was removed under vacuum. To the oily residue
diethyl ether and acetone were added respectively and the
flask was cooled in an ice-bath. The solid obtained was
filtered under vacuum.
General Procedure for the Synthesis of 1-{4-[2-
(Alkylamino)-2-oxoethoxy]-3-methoxybenzyl}pyridinium
chlorides 5a–5c
One equivalent of (3a–3c), 1.5 equivalents of pyridine and
15 mL of acetonitrile as solvent were placed in a 100-mL
round-bottom flask fitted with a reflux condenser. The
reaction mixture in the flask was refluxed for 24 h. As the
reaction completed (monitored by TLC) the solvent was
evaporated under vacuum and the residue was washed with
a mixture of diethyl ether/hexane (1:1). The solid obtained
was filtered under vacuum.
General Procedure for the Synthesis of 1-(2-{4-[2-
(Alkylamino)-2-oxoethoxy]phenyl}-2-oxoethyl)pyridinium
bromides, 9a–9c
One equivalent of (7a–7c), 2 equivalents of pyridine and
15 mL of acetonitrile as solvent were placed in a 100-mL
round-bottom flask fitted with a reflux condenser. The flask
was refluxed overnight and then the reaction mixture was
cooled to room temperature. Diethyl ether was added to the
mixture and the solid obtained was filtered under vacuum.
The crude product obtained was crystallized from acetone/
diethyl ether.
General Procedure for the Synthesis of 2-(4-
Acetylphenoxy)-N-alkylacetamides 6a–6c
To a 100-mL round-bottom flask, 1 equivalent of
4-hydroxyacetophenone, 2 equivalents of K2CO3 and 20 mL
of DMF as solvent were placed and the solution was mixed
for a few minutes. One equivalent of the corresponding
2-chloro-N-alkylacetamide was added to this mixture and the
flask was fitted to a reflux condenser. The reaction mixture
was stirred over night under reflux at 65–70 °C in a water
bath. After completion of the reaction, cold water was added
to the flask and reaction mixture was extracted with dichlo-
romethane. The organic phase was dried over sodium sulfate
and the solvent was removed with a rotary evaporator. The
residue was crystallized from methanol/water.
Corrosion Tests Performed in Acidic Media
Preparations of Coupons and Acidic Solutions
Gravimetric measurements were done using coupons made
from cold-rolled low-carbon steel and possessed DIN EN
10130-99 with the composition of 0.07 % C, 0.35 % Mn,
0.015 % P, 0.015 % S. Coupons were cut into a rectangular
shape of 0.1 9 2.2 9 5.0 cm in thickness, width and
length, respectively. The following cleaning procedure was
carried out before the immersion test: firstly coupons were
kept in 15 % HCl, polished lightly with paper tissue and
washed twice with deionized water. Secondly, they were
kept in acetone and finally dried. Solutions of 1.5 M HCl
and 1.5 M H2SO4 were prepared from concentrated HCl
(37 %) and concentrated H2SO4 (95–97 %) (Merck) grade
respectively.
General Procedure for the Synthesis of 2-[4-
(Bromoacetyl)phenoxy]-N-alkylacetamides 7a–7c
One equivalent of (6a–6c), and 15 mL of 1,4-dioxane as
solvent were placed in a 100-mL two-necked flask fitted
with a reflux condenser. Three drops of HBr (47 %) were
added to the mixture and the flask was cooled to 0 °C in an
ice bath. One point two equivalents of Br2 was then
dropped slowly into the flask and the reaction mixture was
stirred overnight at room temperature. After the reaction
had completed (monitored by TLC) 100 mL of cold water
Weight Loss Measurements
Inhibition efficiencies of (4a–4c), (5a–5c), (8a–8c) and
(9a–9c) derivatives were tested at 25, 50, and 100 ppm
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J Surfact Deterg
concentrations in 100 mL of 1.5 M HCl and 1.5 M H2SO4
solutions respectively. The corrosion inhibitors (4a–4c)
and (5a–5c) were directly dissolved in acid solutions while
(8a–8c) and (9a–9c) were added to the acid solutions dis-
solved in 10 % acetone. Later the treatment solutions were
poured into 150-mL -sealed glass bottles and the coupons
were suspended in these solutions without stirring and kept
for 24 h at room temperature. Control tests were done in
the same way without the inhibitors. After the corrosion
test, the samples were treated as follows: coupons were
taken out and wiped with paper tissues. The coupons were
gently polished with emery paper to clean the rust as
needed, rinsed with water then acetone and dried in an
oven until the had a constant weight.
were treated with SOCl2 to give (3a–3c). Finally benzyl
chlorides (3a–3c) were heated with triethylamine in ace-
tonitrile under reflux to obtain the desired cationic surfac-
tants (4a–4c) (Scheme 1).
Cationic surfactants (5a–5c) were synthesized with
better yields and in a similar manner to that described for
compounds (4a–4c) except that pyridine was used instead
of triethylamine (Scheme 1). Starting from 2-chloro-N-al-
kylacetamides and 4-hydroxyacetophenone, compounds
(6a–6c) were obtained in fairly good yields. 2-[4-
(Bromoacetyl)phenoxy]-N-alkylacetamides, (7a–7c) were
prepared via the a-bromination under mild conditions of
the corresponding acetophenones (6a–6c). Finally a-bro-
minated acetophenones were refluxed with triethylamine in
acetonitrile to give the corresponding cationic surfactants
(8a–8c) (Scheme 2). Cationic surfactants (9a–9c) were
synthesized in a similar manner to that described for
compounds (8a–8c) except that pyridine was used instead
of triethylamine (Scheme 2).
Contact Angle Measurements
The static water contact angle measurements were carried
out at room temperature with the commercially available
contact angle measurement system. The oxide layer of four
metal plates was removed as described previously in the
experimental part of this article. One of the metal plates
was immersed in inhibitor-free and 1.5 M 100 mL of HCl
solution, while the remaining three plates were immersed
in 1.5 M 100 mL of HCl solution containing one of the
inhibitors, (4a–4b) or (9c) at 100 ppm concentration. All
the samples were stored for 24 h at room temperature.
Thereafter, the metal plates were removed from the acidic
solutions and kept until dry in a vacuum desiccator. The
contact angle was measured at both ends of the water drop
placed on a thoroughly dried metal surface.
The structures of all the compounds were confirmed by
IR and 1H-NMR spectroscopic methods. For instance the IR
spectra of (4a) showed absorption bands at 3,228 cm-1 due
to the amide –NH group, at 3,033 cm-1 due to the aromatic
=C–H stretching, and at 1,677 cm-1 due to the amide C=O
group. The IR spectra of (5a) showed absorption bands at
3,411 cm-1 due to the amide –NH group, at 3,123 cm-1
due to the pyridine =C–H stretching, and at 1,652 cm-1 due
to the amide C=O group. On the other hand the IR spectra of
(8b) showed absorption bands at 3,329 cm-1 due to the
amide –NH group, at 1,701 cm-1 due to the ketone C=O
stretching, and at 1,680 cm-1 due to the amide C=O group.
Additionally the IR spectra of (9b) showed absorption
bands at 3,423 cm-1 due to the amide –NH group, at
3,138 cm-1 due to the pyridine =C–H stretching, and at
Results and Discussion
1
1,671 cm-1 due to the amide C=O group. The H-NMR
Several cationic surfactants as potential corrosion inhibi-
tors for mild steel in acidic media were synthesized.
Starting compounds required for the synthesis of these
surfactants were easily prepared. To our knowledge, all the
synthesized surfactants in this study are novel. Our
approaches for the synthesis of the amide-based cationic
surfactants investigated in this research are shown in
(Schemes 1, 2). Their physical properties and spectral data
(except of the ones that had been previously described in
the literature) including detailed synthetic procedures for
each compound are given under the experimental section of
this study. To accomplish synthesis of the compounds (4a–
4c), a series of long chain amines obtained were treated
with chloroacetyl chloride as described previously in the
literature [16, 17]. Thereafter the 2-chloro-N-alkylaceta-
mides were reacted with vanillin to give compounds (1a–
1c). Subsequently (1a–1c) were reduced with NaBH4 in a
suitable solvent and then the compounds obtained (2a–2c)
spectrum of (4a) showed a singlet at d = 4.89 ppm for the
ArCH2–N? protons, a quadruplet at d = 3.46 ppm for
the –N?(CH2CH3)3 protons and a triplet at d = 1.47 ppm
for the methyl protons of the –N?(CH2CH3)3 group. The 1H-
NMR spectrum of (5a) showed a singlet at d = 6.27 ppm for
the ArCH2–Py? protons, a singlet at d = 4.50 ppm for the
–CH2O–protons a quintet at d = 1.53 ppm for the methylene
protons of the –CH2CH2CH2NH group. The 1H-NMR spec-
trum of (8b) showed a singlet at d = 5.53 ppm for
the O=CCH2–N? protons, a singlet at d = 4.55 ppm for
the –CH2OAr protons, a quintet at d = 3.87 ppm for the
–N?(CH2CH3)3 group and a triplet at d = 1.45 ppm for the
1
nine methyl protons of the –N?(CH2CH3)3 group. The H-
NMR spectrum of (9b) showed a singlet at d = 7.12 ppm
for the methylene protons of the O=CCH2–Py? group, a
triplet at d = 6.87 ppm for the amide –HNC=O proton, and
a singlet at d = 4.54 ppm for the methylene protons of the
–CH2O–group.
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Scheme 1 Synthesis reactions and structures of 4a–4c and 5a–5c
Corrosion Tests in Acidic Media and Contact Angle
Measurements
where (IE %) is the percentage inhibition efficiency, Wo is
the weight loss of the coupon in the absence of inhibitor
and W is the weight loss of the coupon in the same envi-
ronment with the presence of an inhibitor. Acetone (10 %)
was added to facilitate solubility of the inhibitors (8a–8c)
and (9a–9c) in acidic solutions and to the reference solu-
tions to eliminate the solvent factor.
Corrosion inhibition capabilities of synthesized compounds
tested in 1.5 M HCl and 1.5 M H2SO4 acidic media are given
as percentage inhibition efficiencies (IE %). Observed
results for the triethylaminium and pyridinium surfactants
are given in Tables 1 and 2. Molecular formulas of the tested
compounds are given in Scheme 3. Percentage inhibition
efficiencies were calculated using the following equation:
Compounds prepared in this study containing straight
chain alkyl and quaternary ammonium groups that form
hydrophobic and hydrophilic parts of the molecules respec-
tively. The results obtained of the corrosion inhibition effi-
ciency of the synthesized cationic type surface active
compounds are listed in Tables 1 and 2.
Wo ꢁ W
ðIE %Þ ¼
ꢂ 100
ð1Þ
Wo
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Scheme 2 Synthesis reactions and structures of 8a–8c and 9a–9c
Otherwise the effect of HCl concentration on corrosion
inhibition was investigated for selected compounds (4b–
4c) and (5b) at 50 ppm fixed inhibitor concentration in
100 mL of 2, 4 and 6 M HCl solutions respectively. The
results obtained are given in Table 3. Contact angles were
measured at room temperature with the compounds (4a),
(4b) and (9c) and theresults obtained are given in Table 4.
These results prompted us to propose that a reliable
mechanism of corrosion inhibition of these surfactants
depends on the variety of factors related both to physical
Table 1 Corrosion inhibition
Cationic surfactants
Inhibition efficiencies (IE %) of cationic surfactants
efficiencies (IE %) for varying
concentrations of tested
25 ppm
50 ppm
100 ppm
inhibitors in 1.5 M HCl for 24 h
at room temperature
N,N,N-triethylaminium surfactants
4a
86.15 0.45
98.23 0.16
98.76 0.11
76.20 0.33
89.48 0.45
89.01 0.15
92.35 0.33
98.44 0.20
98.74 0.13
77.07 0.38
90.30 0.27
87.78 0.15
96.92 0.38
97.85 0.22
98.69 0.11
80.57 0.45
93.80 0.33
91.64 0.26
4b
4c
8aa
8ba
8ca
Pyridinium surfactants
5a
91.05 0.22
99.23 0.12
82.59 0.23
80.10 0.39
93.69 0.27
32.94 0.13
93.12 0.16
99.21 0.12
80.52 0.32
83.58 0.20
93.45 0.31
35.98 0.23
95.64 0.41
99.16 0.19
89.17 0.34
88.56 0.61
94.62 0.19
51.28 0.14
5b
5c
9aa
9ba
9ca
a
10 % acetone was added to
reach the solubility of the
inhibitors in the acidic medium
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Table 2 Corrosion inhibition
efficiencies (IE %) for varying
concentrations of tested
Cationic surfactants
Inhibition efficiencies (IE %) of cationic surfactants
25 ppm
50 ppm
100 ppm
inhibitors in 1.5 M H2SO4 for
24 h at room temperature
N,N,N-triethylaminium surfactants
4a
25.62 0.22
97.13 0.12
94.80 0.26
58.57 0.45
94.89 0.12
89.41 0.10
46.08 0.19
97.78 0.15
95.58 0.11
69.69 0.16
95.71 0.44
93.43 0.33
81.38 0.37
97.98 0.11
95.59 0.21
73.75 0.32
95.71 0.21
85.24 0.28
4b
4c
8aa
8ba
8ca
Pyridinium surfactants
5a
13.02 0.22
91.09 0.29
9.76 0.57
63.03 0.61
97.08 0.34
22.74 0.56
24.97 0.12
88.74 0.22
13.62 0.11
67.75 0.51
96.72 0.24
38.60 0.39
34.45 0.24
80.10 0.32
-
5b
5c
9aa
9ba
9ca
77.19 0.44
96.93 0.19
24.20 0.52
a
10 % acetone was added to
reach the solubility of the
inhibitors in the acidic medium
Scheme 3 Molecular formulas
of the tested inhibitors
and chemical properties of inhibitor molecules. For
instance, alkyl chain length of the hydrophobic moieties,
critical micelle concentration (CMC) and solubility prop-
erties of these inhibitors, and additionally a molecular
monolayer or a molecular bilayer or multilayers formed by
these inhibitor molecules play important roles on their
tendency toward corrosion inhibition.
are adsorbed on the dipoles to build a monomolecular layer
below and at the critical micelle concentration. The dipoles
are observed via interaction of bromide ions and the pos-
itively charged metal surface. The hydrophilic quaternary
ammonium head group of the surfactant molecules is
adsorbed onto to the dipole via electrostatic attraction. On
the other hand the hydrophobic tail of the surfactant mol-
ecule is oriented perpendicularly to the metal surface. Thus
bilayer or multimolecular layers designated as protective
layers are formed which behave as barrier between the
metal and the corrosive medium.
First of all, when a metal surface is positively charged,
anions like chlorides or bromides can adsorb onto the
surface to create dipoles in acidic solutions (Fig. 1).
In this way, cationic corrosion inhibitors can readily
adsorb onto the observed negatively charged metal surface
to give protection against corrosive damage. In this sense,
the possible corrosion inhibition mechanism can be
explained based on the adsorption of the long chain cat-
ionic molecules on the metal. Firstly inhibitor molecules
As shown in Table 1 the highest inhibition values for the
compounds (4b–4c), (5b–5c), (8c) and (9b) were obtained
at the critical micelle concentrations (CMC) of the inhib-
itors. As it can be seen from the evaluated results there is
no increase in inhibition efficiency above the CMC. The
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J Surfact Deterg
packing provided by hydrophobic alkyl chains of mole-
cules contributes to an increase in inhibition. As seen in
Table 2, the compounds (5c) and (9c) including the longest
hydrophobic alkyl chains demonstrated low protection of
metal against acidic attack because of their poor solubility
in the medium. The possible inhibition mechanism for
these inhibitors is shown in Fig. 4.
Table 3 Corrosion inhibition efficiencies (IE %) of some synthesized
surfactants in varying concentrations of HCl for 24 h at room
temperature
Cationic
surfactants in different HCl concentrations
Inhibition efficiencies (IE %) of cationic surfactantsa
2 M
4 M
6 M
4b
4c
5b
a
93.82 0.31
93.94 0.49
93.32 0.52
98.08 0.11
97.81 0.23
99.02 0.37
97.04 0.56
89.11 1.01
96.93 0.61
The above-discussed mechanisms in relation to the
corrosion inhibition of synthesized inhibitors are also
supported by the contact angle measurements. As seen in
the second column in Table 4, the measured contact angle
values of the that water droplet on the inhibitor free metal
surface changed between 14.72 and 19.51. Furthermore,
measured values of the contact angles on the surfaces of
the metals containing inhibitors (4a–4b) or (9c), changed
between, 35.09–35.45, 79.85–81.97 and 53.87–54.56 respec-
tively. The photographs taken of the contact angle measure-
ments are given in Fig. 5.
Concentration of cationic surfactants in acidic medium is fixed to
50 ppm
orientations of the inhibitor molecules (4b–4c), (5b–5c),
(8c) and (9b) at the metal-acidic solution interface and the
possible inhibition mechanism was shown in Fig. 2.
On the other hand, the inhibition efficiencies of the
compounds (4a), (8a–8b), (5a) and (9a) increased with an
increase in inhibitor concentration. Orientation of the
molecules and the possible inhibition mechanism for these
inhibitors is shown in Fig. 3.
As is clear from these results, cationic surface-active
agents increased the metal’s surface hydrophobicity which
gave rise in the value of the measured contact angle for the
water droplet. As well as these observations, for the com-
pound (9c) contact angle was measured in a different place
on the metal surface. In this case quite different result was
obtained according to the first measurement. Depending on
the time the first contact angle measurement showed little
change, while the angle of the second measurement is quite
varied. See the second line from the bottom in (Fig. 6).
These results indicate the presence of partially hydrophobic
and partially hydrophilic regions on the surface of the
The hydrophobic part plays an important role in corro-
sion inhibition of the inhibitor molecules. Non-polar
interactions between the long alkyl chains of the molecules
due to Van der Waals forces provides a better protective
layer against corrosive media. The length of the chain is
very important in this case. Usually longer hydrocarbon
chains provide better corrosion protection but sometimes
solubility of the inhibitors decreases and this leads to a
reduction in the inhibitory activity. Additionally, tight
Table 4 Static water contact
Time (s)
Blank
Measured contact angles (average values)
Inhibitors
angle measurements on the
metal surface that immersed in
1.5 M 100 mL HCl solution
containing one of the inhibitors
4a, 4b or 9ca at 100 ppm
concentration
4a
4b
9ca
9ca
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
19.51
17.63
17.09
16.43
16.21
15.84
15.59
15.16
14.95
14.72
35.45
35.40
35.36
35.30
35.28
35.29
35.27
35.28
35.14
35.09
81.97
80.71
80.55
80.39
80.32
80.14
79.99
80.00
79.85
54.35
53.98
53.87
54.41
54.56
54.46
54.41
54.24
54.23
54.18
23.48
23.83
21.88
23.04
21.81
23.25
24.19
24.25
22.58
20.78
79,69
a
Contact angles were measured
at two different places on the
metal surface
Mean and standard
deviations
16.31 1.45 35.29 0.11
80.36 0.65 54.27 0.22 22.09 1.15
Fig. 1 Dipoles created by
halide ions in an acidic medium
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J Surfact Deterg
Fig. 2 Corrosion inhibition by compounds 4b–4c, 5b–5c, 8c and 9b at CMC
Fig. 3 Corrosion inhibition by compounds 4a, 8a–8b, 5a and 9a
metal due to low solubility of the inhibitors (5c) and (9c).
As a result these data supports our proposed inhibition
mechanism for the compounds (5c) and (9c).
activities of the inhibitors at higher than 1.5 M concentra-
tions of HCl. Despite the relatively high HCl concentration
and also as low as 50 ppm of inhibitor concentration, the
results of inhibition obtained were very good. It was
observed that the tested three compounds gave maximum
protection in 4 M of HCl solution (Table 3).
In addition to the tests performed on the synthesized
cationic surfactants that are specified in the experimental
section of this study, we also investigated inhibitory
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J Surfact Deterg
Fig. 4 Orientation and low inhibition exhibited by compounds 5c and 9c
Fig. 5 View of the water
droplet on the metal surface
As a result we can conclude that almost all the synthe-
sized cationic surface-active compounds exhibited fairly
good corrosion inhibitory efficiencies in both HCl and
H2SO4 media. In addition both weight loss test results and
contact angle measurement data supported the mechanisms
we proposed for the corrosion inhibition. On the other
hand, all of the inhibitors investigated in this study were
synthesized on the basis of biodegradable compounds.
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Fig. 6 Contact angle measurements versus time
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Author Biographies
˘
Ayhan Yıldırım received his Ph.D. in organic chemistry from Uludag
University in 2009. His research field is the synthesis and character-
ization of new organic compounds (oleochemicals, long chain
heterocycles via the 1,3-dipolar cycloaddition reactions) suitable for
9. Zaafarany I, Abdallah M (2010) Ethoxylated fatty amide as
corrosion inhibitors for carbon steel in hydrochloric acid solution.
Int J Electrochem Sci 5:18–28
˘
industrial applications. He works at the Uludag University chemistry
department as a research and teaching assistant in the organic
chemistry laboratory.
10. Asefi D, Arami M, Sarabi AA, Mahmoodi NM (2009) The chain
length influence of cationic surfactant and role of nonionic co-
surfactants on controlling the corrosion rate of steel in acidic
media. Corros Sci 51:1817–1821
11. Achouri M El, Infante MR, Izquierdo F, Kertit S, Gouttaya HM,
Nciri B (2009) Synthesis of some cationic gemini surfactants and
their inhibitive effect on iron corrosion in hydrochloric acid
medium. Corros Sci 43:19–35
¨
˘
Serkan Oztu¨rk is a Ph.D. student at Uludag University. He is
continuing his studies under the supervision of Professor Mehmet
˘
C¸ etin and now works in the Uludag University chemistry department
as a research and teaching assistant in the organic chemistry
laboratory.
12. Hegazy MA, Abdallah M, Ahmed H (2010) Novel cationic
gemini surfactants as corrosion inhibitors for carbon steel pipe-
lines. Corros Sci 52:2897–2904
13. Likhanova NV, Dominguez-Aguilar MA, Olivares-Xometl O,
Nava-Entzana N, Arce E, Dorantes H (2010) The effect of ionic
liquids with imidazolium and pyridinium cations on the corrosion
inhibition of mild steel in acidic environment. Corros Sci
52:2088–2097
˘
Mehmet C¸ etin is a Professor at the Uludag University Department of
Chemistry. His primary research field is physics and chemistry
of fatty acids and their derivatives. He is also interested in the subject
of corrosion and its prevention with organic corrosion inhibitors.
123