Inhibitory activity of fluorine-containing quaternary ammonium salts comprising an N-methylpiperazinyl moiety

Article abstract of DOI:10.1134/S1070427213070082

New fluorine-containing quaternary ammonium salts comprising an N-methylpiperazinyl moiety, which exhibited a high inhibiting capacity against hydrochloric acid corrosion of low-carbon steel, were synthesized. The polarization-resistance method was applied to determine the uniform corrosion rate of steel-3 in relation to the structure and concentration of the fluorine-containing substituents in the salts. It was found that the structure of the fluorine-containing moiety of the quaternary ammonium salts does not significantly influence the corrosion processes.

Full text of DOI:10.1134/S1070427213070082

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 7, pp. 992−996. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © T.I. Gorbunova, D.N. Bazhin, A.Ya. Zapevalov, V.I. Saloutin, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 7,
pp. 1059−1063.
ORGANIC AND PETROCHEMICAL
PROCESSES
Inhibitory Activity of Fluorine-containing Quaternary
Ammonium Salts Comprising an N-Methylpiperazinyl Moiety
T. I. Gorbunova, D. N. Bazhin, A. Ya. Zapevalov, and V. I. Saloutin
Postovskii Institute of Organic Synthesis, Ural Division, Russian Academy of Sciences, Yekaterinburg, Russia
e-mail: gorbunova@ios.uran.ru
Received May 18, 2013
Abstract—New fluorine-containing quaternary ammonium salts comprising an N-methylpiperazinyl moiety, which
exhibited a high inhibiting capacity against hydrochloric acid corrosion of low-carbon steel, were synthesized.
The polarization-resistance method was applied to determine the uniform corrosion rate of steel-3 in relation to
the structure and concentration of the fluorine-containing substituents in the salts. It was found that the structure
of the fluorine-containing moiety of the quaternary ammonium salts does not significantly influence the corrosion
processes.
DOI: 10.1134/S1070427213070082
N-Methylpiperazine is one of the intermediates
in production of drugs, including commonly known
fluoroquinolone antibiotics, anthelmintics, neuroleptics,
etc. [1]. Also, N-methylpiperazine was used for
synthesizing compounds having antiarrhythmic [2] and
anticancer activity [3]. However, its application is not
limitedtothesynthesisofbiologicallyactivecompounds.
The presence in the molecule of N-methylpiperazine
of two heteroatoms suggests its suitability as an
independent agent for inhibition of corrosion processes
and for synthesis of nitrogen-containing corrosion
inhibitors.
piperazinyl derivatives is followed by deprotonation.
It was shown [5] that medicines, in particular
fluoroquinolone antibiotics, hold promise as corrosion
inhibitors. Nonconventional use of pharmaceutical
products has become the focus of attention of researchers
who are looking for corrosion-resistant materials unable
of inflicting major environmental damage. Most drugs
typically undergo biodegradation under environmental
conditions [6–12].
Here, we synthesized fluorine-containing quaternary
ammonium salts comprising an N-methylpiperazinyl
moiety and examined their inhibition effect against low-
carbon steel corrosion in hydrochloric acid.
Semiempirical quantum chemical calculations [4]
showed that, when N-methylpiperazine acts as inhibitor
of steel corrosion in acid medium, both its nitrogen atoms
initially undergo double protonation. During subsequent
physical adsorption on the negatively charged metal
surface, the piperazinyl moieties can assume two types of
orientation with respect to the substrate, with adsorption
occurring via both nitrogen sites or via one of them.
In the former case, the piperazinyl framework should
adopt a “chair” conformation (flat-lying adsorption). In
the latter case, it is attached vertically via the N4 atom
(vertical adsorption), because specifically this nitrogen
atom has the largest positive charge, as shown by
PM3 calculations. In both cases, the orientation of the
The choice of fluorinated quaternary ammonium salts
(F-QASs) as the subjects of our study was dictated by the
following reasons: enhanced, in many cases, solubility
of organic and more hydrophobic organofluorine
compounds in aqueous media due to the presence of a
quaternary nitrogen atom [13, 14], better performance
characteristics compared to nonfluorinated analogs [15–
17], and the possibility to achieve the desired effect with
low-concentration solutions [13].
To study the inhibitory effect, reactions of
esters of perfluorocarboxylic acids Ia–Id, or of
2,3,4,5-tetrafluorobenzoic acid chloride Ie, with
992

INHIBITORY ACTIVITY OF FLUORINE-CONTAINING QUATERNARY AMMONIUM SALTS
993
N-methylpiperazine were carried to produce amides
IIa–IIe. The latter were quaternized with methyl iodide
to yield highly water-soluble F-QASs IIIa–IIIe, which
were obtained in quantitative yield:
Iа–Ie
IIа–IIe
IIIа–IIIe, 92–97%
X=OEt; RF = (a) CF3, (b) C3F7, (c) C4F9, and (d) C6F13; i: toluene, bp, 2 h; ii: CH3I, toluene, room temperature; X=Cl; (e)
F4
RF =
; i: CH2Cl2, room temperature, 2 h; ii: CH3I, CH2Cl2, room temperature.
The uniform corrosion rate Kn of low-carbon steel-3
and the inhibitory activity of compounds IIIa–IIIe
used in 1 × 10–4 M concentration were studied in a 1 m
HClconc solution at room temperature by the polarization-
resistance technique. Four parallel measurements were
performed for each Kn value presented in Fig. 1, with
the root-mean-square deviation not exceeding 3%. For
comparison we used the Kn values obtained in blank
runs for steel-3.
(Kn1 and Kn2 are uniform corrosion rates without and
with inhibitor, respectively), were 67, 59, 58, 69, and
60 %.
Surprisingly, compound IIIe having an additional
coordination site with the d-metal surface, π electrons of
the aromatic ring, exhibited a lower inhibitory activity.
This may be due to the presence in the aromatic moiety
of four fluorine atoms whose cumulative inductive effect
causes substantial depletion of the π density and does not
promote its strong coordination to the electrode surface.
Another possible reason is inflexible carbonyl spacer
interconnecting the fluoroaromatic and piperazinyl
substituents, responsible for weak coordination of π
electrons to the d metal.
The inhibitory activity of quaternary ammonium
salts is underlain primarily by the electrostatic
interaction between the positively charged nitrogen
atom of the ammonium group and the negatively
charged electrode [18]. For compounds having complex
structures and possessing multiple metal-coordination
sites, inhibition follows a more complex mechanism.
Possible mechanisms include interaction of unpaired
electrons of heteroatoms with vacant d orbitals of the
metal, formation on the electrode surface of stable
chelates which create major corrosion-resistant barriers,
and interaction of π electrons (if any) with the metal, as
well as all these types of interaction combined [19–21].
The general trend revealed for salts IIIa–IIIe when
used in 1 × 10–4 M concentration is that they cause
As seen from Fig. 1, the highest inhibitory effect is
exhibited by F-QAS IIIa comprising a trifluoromethyl
substituent. Although the available data suggest
an increase in hydrophobicity of compounds with
increasing length of the fluoroalkyl moiety, it is only
in the end portion of the curve for salt IIId that there
are a number of unstable Kn values, lower compared
to F-QAS IIIa. The respective values of the degree of
protection Z, calculated for F-QASs IIIa, IIIb, IIIc,
IIId, and IIIe by the equation
Fig. 1. Uniform corrosion rate Kn, μm year–1, of steel-3 vs.
time τ, min, in a 1 M HCl solution at 1 × 10–4 m concentration
of salts IIIa–IIIe. (1) Blank (without salt) run and (2–6) runs
with (2) IIIa, (3) IIIb, (4) IIIc, (5) IIId, and (6) IIIe salts; the
same for Fig. 2.
Kn1 – Kn2
Z = ————– × 100%,
Kn1
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994
GORBUNOVA et al.
reduction in the hydrochloric acid corrosion rate for
low-carbon steel by a factor of 2–4.
EXPERIMENTAL
The IR spectra were recorded on a Perkin Elmer
Spectrum One B spectrophotometer, and NMR spectra,
on Bruker DRX-400 spectrometers (1H: 400 MHz,
internal reference Me4Si; 19F: 376 MHz, internal
reference C6F6). Chemical shifts were measured
accurately to within 0.01 ppm, and spin-spin coupling
constants, to 0.1 Hz. Elemental analysis was performed
on a Perkin Elmer PE 2400 Series II CHNS/O EA1108.4
elemental analyzer. Melting points were measured
in open capillaries on a Stuart SMP3 melting point
apparatus.
To more accurately examine how the structure of the
fluoroalkyl (fluoroaromatic) moiety of salts IIIa–IIIe
affects Kn of low-carbon steel we studied the corrosion
processes with the use of IIIa–IIIe in 1 × 10–3
M
concentration under identical conditions. The results
are shown in Fig. 2. The increase in the concentration
of F-QASs IIIa–IIIe causes their inhibitory activity to
increase in all the cases: The parameter Z was estimated
at 88, 85, and 90% for IIIa, IIIb, and IIIc, respectively,
and at 91% for both IIId and IIIe. The use of salts IIIa–
IIIe in 1 × 10–3 M concentration causes reduction of the
corrosion rate by a factor of 7–11.
The uniform corrosion rate of low-carbon steel was
examined in a 1 m HClconc solution using an Expert-004
universal automatic corrosion meter and a two-electrode
sensing device, available from Ekoniks Ekspert Limited
Liability Company, Moscow. The electrode material was
steel-3 [composition, %: Si 0.05–0.15, Mn 0.40–0.65,
P no greater than 0.04, Cr no greater than 0.30, S no
greater than 0.05]; each electrode area was 0.00078 m2.
The fact that all the profiles demonstrating the
time dependence of Kn (Fig. 2, curves 2–6) get close
together suggest that, with F-QASs IIIa–IIIe as
inhibitors, the corrosion processes do not significantly
depend on the structure of the fluorine-containing
substituent. It becomes evident that the factor deciding
the inhibitory properties of compounds IIIa–IIIe is
physical adsorption of these derivatives on the electrode
surface via the positively charged nitrogen atom of the
piperazinyl moiety. Considering the data from [4], it
can be concluded that F-QASs IIIa–IIIe synthesized
are prone to vertical adsorption. The effect of the
electrode surface protection against corrosive media by
hydrophobic fluorine-containing moieties does exist but
is not of decisive importance for inhibition of corrosion
of steel-3 in hydrochloric acid by compounds IIIa–IIIe.
General Procedure for Synthesis
of Compounds IIIa–IIId
Step 1. To 0.02 mol of compounds Ia–Id in 5 ml of
toluene, 0.025 mol of N-methylpiperazine was added
with stirring. The resulting mixture was heated to boiling
and kept for 2 h. Low-boiling compounds and excess
N-methylpiperazine were distilled off to 140°C. The
residues were light yellow viscous liquids, compounds
IIa–IId, which were used without further purification.
Step 2. Compounds IIa–IId were dissolved in 5 ml of
toluene, and 0.03 mol of methyl iodide was added with
stirring at room temperature. The resulting solids were
filtered off and dried for 1 day at room temperature. The
products IIIa–IIId were obtained in a 92–97% yield.
1, 1-Dimethyl-4-(2, 2, 2-trifluoroacetyl)
piperazinium iodide IIIa. White powder, yield 97%,
mp 236–237°C (dec.). IR spectrum, ν, cm–1: 1700
1
(C=O). H NMR spectrum [(CD3)2SO, δ, ppm]: 3.22 s
(6H, 2Me), 3.55 t (4H, 2CH2, J = 5.3 Hz), 3.96 m (4H,
2CH2). 19F NMR spectrum [(CD3)2SO, δ, ppm]: 94.34 s
(3F, CF3). Found, %: C 28.34, H 4.18, F 16.49, N 8.34.
C8H14F3IN2O. Calculated, %: C 28.42, H 4.17, F 16.86,
N 8.29.
Fig. 2. Uniform corrosion rate Kn, μm year–1, of steel-3 vs.
time τ, min, in a 1 m HCl solution at 1 × 10–3 M concentration
of salts IIIa–IIIe.
1,1-Dimethyl-4-(2,2,3,3,4,4,4-heptafluorobutyryl)
piperazinium iodide IIIb. Yellowish powder, yield
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 86 No. 7 2013

INHIBITORY ACTIVITY OF FLUORINE-CONTAINING QUATERNARY AMMONIUM SALTS
995
94%, mp. 247–249°C (dec). IR spectrum, ν, cm–1: 1697
(C=O). H NMR spectrum [(CD3)2SO, δ, ppm]: 3.22 s
(6H, 2Me), 3.55 t (4H, 2CH2, J = 5.0 Hz), 4.00 m (4H,
2CH2). 19F NMR spectrum [(CD3)2SO, δ, ppm]: 37.26 m
(2F, CF2), 51.04 m (2F, CF2), 83.57 m (3F, CF3). Found,
%: C 27.36, H 3.18, F 30.12, N 6.34. C10H14F7IN2O.
Calculated, %: C 27.41, H 3.22, F 30.35, N 6.39.
filtered off and dried for 1 day at room temperature.
1
The product IIIe was obtained as a yellow powder, mp
above 233°C (charring), yield 96%. IR spectrum, ν,
1
cm–1: 1698 (C=O). H NMR spectrum [(CD3)2SO, δ,
ppm]: 3.19 s (6H, 2Me), 3.40 m (2H, CH2), 3.51 m (2H,
CH2), 3.69 m (2H, CH2), 3.98 m (2H, CH2), 7.52 m (1H,
C6F4H). 19F NMR spectrum [(CD3)2SO, δ, ppm]: 8.22 m
(2F), 21.74 m (1F), 24.35 m (1F). Found, %: C 37.26,
H 3.51, F 18.04, N 6.59. C13H15F4IN2O. Calculated, %:
C 37.34, H 3.62, F 18.17, N 6.70.
1,1-Dimethyl-4-(2,2,3,3,4,4,5,5,5-nonafluoro-
valeryl)piperazinium iodide IIIc. White powder,
yield 95%, mp 249–251°C (dec.). IR spectrum, ν, cm–1:
1
1695 (C=O). H NMR spectrum [(CD3)2SO, δ, ppm]:
CONCLUSIONS
3.22 s (6H, 2Me), 3.56 t (4H, 2CH2, J = 4.8 Hz), 4.00 m
(4H, 2CH2). 19F NMR spectrum: [(CD3)2SO, δ, ppm]:
38.56 m (2F, CF2), 40.95 m (2F, CF2), 51.50 m (2F,
CF2), 82.01 t (3F, CF3, J = 9.8 Hz). Found, %: C 27.02,
H 2.84, F 34.93, N 5.69. C11H14F9IN2O. Calculated, %:
C 27.07, H 2.89, F 35.03, N 5.74.
(1) Reactions of esters of perfluorocabroxylic acids,
or of 2,3,4,5-tetrafluorobenzoic acid chloride, with
N-methylpiperazine were carried out to produce amides
whose quaternization with methyl iodide resulted in
new water-soluble quaternary ammonium salts.
1,1-Dimethyl-4-(2,2,3,3,4,4,5,5,6,6,7,7,7- trideca-
fluoroenanthyl)piperazinium iodide IIId. Yellow
powder, yield 92%, mp 261–262°C (dec.). IR spectrum,
ν, cm–1: 1695 (C=O). 1H NMR spectrum [(CD3)2SO, δ,
ppm]: 3.22 s (6H, 2Me), 3.56 t (4H, 2CH2, J = 5.0 Hz),
4.00 m (4H, 2CH2). 19F NMR spectrum [(CD3)2SO, δ,
ppm]: 37.00 m (2F, CF2), 40.00 m (2F, CF2), 41.76 m (2F,
CF2), 42.38 m (2F, CF2), 51.80 m (2F, CF2), 82.32 m (3F,
CF3, J = 9.8 Hz). Found, %: C 26.62, H 2.38, F 41.84,
N 4.68. C13H14F13IN2O. Calculated, %: C 26.55, H 2.40,
F 41.99, N 4.76.
(2) Examination of the uniform corrosion rate of
steel-3inhydrochloricacidbythepolarization-resistance
method with the use of quaternary ammonium salts in
different concentrations showed that they are effective
corrosion inhibitors. When in 1 × 10–4 and 1 × 10–3 M
concentrations they cause reduction in the uniform
corrosion rate by factors of 2–4 and 7–11, respectively.
(3) It was presumed that the inhibiting action of the
compounds examined is not substantially dependent
on the structure of the fluorine-containing moiety and
is determined by physical adsorption of the positively
charged nitrogen atom on the electrode surface.
1,1-Dimethyl-4-(2,3,4,5-tetrafluorobenzoyl)
piperazine (IIe). To 0.12 mol of compound Ie in 100 ml
of dichloromethane, 0.24 mol of N-methylpiperazine
was added with stirring. The resulting mixture was kept
for 2 h at room temperature, after which the organic
layer was separated, washed with a sodium carbonate
solution, and distilled under vacuum created by an oil
pump, bp 170–175°C (10 Torr). Compound IIe was
obtained as a yellow liquid, yield 75%. IR spectrum,
ACKNOWLEDGMENTS
This study was financially supported by the Ural
Division, Russian Academy of Sciences (project no. 12-
M-123-2045).
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ν, cm–1: 1700 (C=O). H NMR spectrum (CDCl3, δ,
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