Anticorrosive properties of N-acetylmethylpyridinium bromides

Article abstract of DOI:10.1134/S1070427206070111

The inhibiting action of N-acetylmethylpyridinium bromides on the corrosion of low-carbon steel in a 3 M sulfuric acid solution at 20, 40, 60, and 80°C was studied. The mechanism of their protective action was examined using electrochemical methods. Compo

Full text of DOI:10.1134/S1070427206070111

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 7, pp. 1100 1104. Pleiades Publishing, Inc., 2006.
Original Russian Text
R.I. Yurchenko, I.S. Pogrebova, T.N. Pilipenko, T.E. Shubina, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79,
No. 7, pp. 1110 1114.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Anticorrosive Properties of N-Acetylmethylpyridinium Bromides
R. I. Yurchenko, I. S. Pogrebova, T. N. Pilipenko, and T. E. Shubina
Kiev Polytechnic Institute, National Technical University of Ukraine, Kiev, Ukraine
Received October 25, 2005; in final form, February 2006
Abstract The inhibiting action of N-acetylmethylpyridinium bromides on the corrosion of low-carbon steel
in a 3 M sulfuric acid solution at 20, 40, 60, and 80 C was studied. The mechanism of their protective action
was examined using electrochemical methods. Compounds exhibiting high anticorrosive properties at elevated
temperatures were found.
DOI: 10.1134/S1070427206070111
It has been shown previously [1] that N-phenacyl-
methylpyridinium bromides (A) are effective in-
hibitors of the acid corrosion of steel and their protec-
tive properties depend on the nature of the substit-
The pyridinium bromides necessary for the study
were synthesized by the standard procedure involving
the reaction of 2-methyl- or 2-aminopyridine with
the corresponding bromomethyl ketones.
1
uents R and R :
EXPERIMENTAL
R1
+
N
.
The anticorrosive properties of the compounds
studied were evaluated at inhibitor concentrations of
1 10 M by the corrosion hindrance factors and
R
2
Br
degrees Z of corrosion protection of 08KP steel in
a 3 M sulfuric acid solution at 20, 40, 60, and 80 C.
The corrosion tests were carried out using the conven-
tional gravimetric method [1]. Voltammetric measure-
ments were performed in the potentiodynamic mode,
O
A
1
It was found, by varying R and R , that the coef-
ficients of steel corrosion hindrance for these com-
pounds at 20 and 40 C correlate with the
stants characterizing the combined action of the
mesomeric and -induction effects of the substituents
R and with the induction
As temperature increases, their anticorrosive action is
significantly enhanced, but, in this case, the correla-
tion between the corrosion hindrance factors and the
electronic characteristics of the substituents is broken.
0
con-
c
after a free corrosion potential E of steel is attained,
c
1
at a potential sweep rate of 2 mV s .
1
constants of R groups.
I
The results obtained in the corrosion tests demon-
strated that compounds Ia Id and IIa IId exhibit a
stronger inhibiting effect than their phenacyl analogs
Ie and IIe (Table 1). For compounds Ie and IIe at
20 C, the steel corrosion hindrance factors are 15.50
and 23.70, respectively [1]; and for compounds Ia Id
and IIa IId, 19.60 39.60. As temperature increases,
the anticorrosive effect of the compounds studied is
enhanced, and at 60 C the hindrance factors are ap-
proximately 200 560 and 200 860 for compounds
Ia Id and IIa IId; for their phenacyl analogs, the
hindrance factors do not exceed 200 units.
This study is concerned with the anticorrosive
properties of pyridinium bromides containing a CH
or NH group in position 2 and methylacyl groups
with CH , t-Bu, 1-Ad, and 2-thienyl substituents
3
2
3
at the nitrogen atom (compounds Ia Id, IIa IId):
+
N
R
It is known that, owing to the methylene group
separating the pyridinium and phenacyl moieties,
the compounds under study exhibit a conformational
lability, which allows them to occupy, depending on
conditions, a position on the steel surface that is the
,
Br
CH2C(O)R1
1
where R = CH (I), NH (II); R = CH (a), t-Bu (b),
3
2
3
1-Ad (c), 2-thienyl (d).
1100

ANTICORROSIVE PROPERTIES OF N-ACETYLMETHYLPYRIDINIUM BROMIDES
1101
Table 1. Hindrance factors and degree Z of corrosion protection of 08KP steel in a 3 M H2SO4 solution in the presence
of N-acetylmethylpyridinium bromides
+
N
R
Br
CH2C(O)R1
20 C
40 C
60 C
80 C
Com-
pound
R
R1
Z, %
Z, %
Z, %
Z, %
Ia
Ib
Ic
Id
CH3
CH3
CH3
CH3
CH3
C(CH3)3
1-Ad
19.60
22.50
23.70
19.10
94.90
95.56
95.58
94.76
22.00
95.45
216.23
99.54
99.66
99.68
99.82
59.8
98.33
297.31
317.13
559.60
36.40
31.90
97.25
96.86
157.00
369.86
99.36
99.73
S
Ie
CH3
NH2
NH2
NH2
NH2
C6H5
CH3
C(CH3)3
1-Ad
15.50
32.00
34.62
39.60
24.30
93.54
96.88
97.11
97.47
95.88
18.70
40.50
39.10
43.00
35.40
94.65
97.53
97.44
97.67
97.18
209.10
218.70
339.79
413.70
864.90
99.52
99.54
99.71
99.76
99.88
150.40
68.00
99.34
98.53
IIa
IIb
IIc
IId
273.70
651.66
99.63
99.85
S
IIe
NH2
C6H5
23.70
95.78
29.00
96.55
200.30
99.50
144.60
99.31
most favorable for adsorption. As also in pyridinium
bromides Ie, IIe [1], the most probable reaction center
responsible for adsorption of the compounds under
study at room temperature is the pyridinium moiety of
the molecule, which gives rise to a positive adsorp-
tion-related step of the potential and hinders corrosion
by the energy mechanism of inhibition. At the same
time, the carbonyl group contained in these com-
pounds is responsible for chemisorption of the com-
pounds, which becomes more pronounced as the solu-
tion temperature increases [2].
zability of the compounds and, consequently, on their
adsorbability on the steel surface. It should also be
noted that compounds Id and IId are not described by
the dependences obtained and their inhibiting effect is
considerably stronger than that expected with account
of only the strength and type of the induction effect
of the 2-thienyl radical. Such a behavior of inhibitors
Id and IId can be attributed on the assumption that
not only the main adsorption centers, but also the
thiophene ring directly interact with the steel surface,
as previously observed in [3]. As temperature in-
1
creases, the linear relations log
*R cease to be
It was found that compounds Ia Ic, Ie, IIa IIc,
and IIe at 20 C show linear relationships between
log and the induction * constants of the substit-
valid, which may occur for various reasons: transition
from physical sorption to chemisorption; change of
the mechanism of the protective action of the in-
hibitors; high rate of steel dissolution, which hinders
their adsorption on the metal; and some other factors.
In this case, the correlation coefficients decrease to
0.939, 0.936 at 40 C and 0.877, 0.886 at 60 C.
1
uents R :
log = 1.30
log = 3.45
0.174 *R1, r = 0.999,
0.455 *R1, r = 0.991.
(1)
(2)
Quantum-chemical calculations of the charge dis-
tribution within the molecule were carried out for
compounds Ia Ie and IIa IIe (Table 2). The molecu-
lar configurations were optimized by the B3LYP
method [4] with the standard 6-31G basis set, using
the GAUSSIAN software package [5]. All the station-
ary points were characterized via a complete analysis
The coefficients (0.174 and 0.455) in Eqs. (1) and
(2) point to different sensitivities of the adsorption
centers in compounds Ia Ic, Ie and IIa IIc, IId to
the induction effect of the substituents R . This may
be due to difference in the induction and mesomeric
effects of the methyl and amino groups on the polari-
1
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 7 2006

1102
YURCHENKO et al.
Table 2. Charges q in compounds Ia Id and IIa IId
q
Compound*
N1
C2
C3
C4
C5
C6
C8
O9
N10
S10
S11
I:
R = CH3 (a)
R = t-Bu (b)
R = 1-Ad (c)
0.295 0.078
0.296 0.075
0.295 0.074
0.244
0.243
0.244
0.126
0.126
0.127
0.233
0.233
0.233
0.296
0.295
0.294
0.597
0.607
0.610
0.516
0.526
0.530
0.296 0.077
0.244
0.125
0.234
0.300
0.518
0.545
0.477
R =
(d)
S
11
R = Ph (e)
II:
0.295 0.078
0.244
0.126
0.233
0.296
0.552
0.541
R = CH3 (a)
R = t-Bu (b)
R = 1-Ad (c
0.348 0.060
0.347 0.060
0.346 0.061
0.269
0.272
0.273
0.129
0.131
0.132
0.278
0.278
0.279
0.466
0.465
0.465
0.599
0.619
0.629
0.541
0.551
0.556
0.806
0.803
0.804
0.351 0.059
0.275
0.134
0.280
0.466
0.524
0.572
0.800
0.488
R =
(d)
S
11
R = Ph (e)
0.351 0.059
0.274
0.133
0.279
0.465
0.563
0.573
0.802
4
4
*
5
5
,
3
3
.
+
6
10
NH2
+
6
2
2
1N
CH3
1N
Br
Br 7
7
8
8
R
R
9O
I
9O
of the normal modes of harmonic vibrations, in which
NIMAG = 0 corresponds to minima on the potential
energy surface for all of the optimized structures.
The calculations demonstrated that, as the substituents
The plots of the dependences logK 1/T (K is
m m
the gravimetric corrosion index, and T, absolute tem-
perature) in Fig. 1 indicate that N-acylmethylpyridini-
um bromides affect the effective activation energy of
corrosion. In the temperature range 20 40 C, the ef-
1
R in the compounds studied are varied, the effective
fective activation energies W increase in the presence
charges on the respective atoms within each series
remain virtually the same and change only slightly on
passing from Ia Id to IIa IId. The only exception
are charges on -carbon atoms of the pyridine ring
c
1
of compounds Ia Ie and IIa IIe from 81.69 kJ mol
1
(no inhibitor) to 86.16 102.44 kJ mol , which points
to the activation mechanism of the inhibiting effect.
At higher temperatures, a deviation from the linear
6
(C ), which strongly differ between the series I and
dependences logK 1/T is observed and inflections
II. This is due to the different electronegativities of
m
appear, which are probably due to transition from the
physical (specific) adsorption of the compounds to
the carbon and nitrogen atoms in the CH and NH
groups.
3
2
chemisorption. The effective activation energy of cor-
1
The results obtained (Table 1) suggest that an im-
portant role in the inhibiting action of acylmethyl-
pyridinium bromides is played by steric factors. In
rosion decreases to 58.88 26.33 kJ mol
in the
presence of compounds Ia Ic, Ie and to 19.15 and
1
9.57 kJ mol for compounds Id and IId, respec-
the series of compounds Ia Ic and IIa IIc with CH ,
tively. This indicates that the inhibition mechanism
changes as the temperature increases and the diffusion
limitations appearing when reacting particles penetrate
across the adsorbed film of an inhibitor play an im-
portant role. For these compounds, a noticeable after-
effect is observed, which consists in that their protec-
3
t-Bu, and 1-Ad groups, for which the steric constants
c
E are, respectively, 0.00, 2.40 [6], and 2.68 [7],
s
a correlation between the corrosion hindrance factors
and the steric effect exerted by these substituents is
observed.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 7 2006

ANTICORROSIVE PROPERTIES OF N-ACETYLMETHYLPYRIDINIUM BROMIDES
1103
1
2
logKm [g cm 2 h ]
logi [A cm ]
E, V
Fig. 2. Anodic and cathodic polarization curves measured
on 08KP steel in a 3 M H SO solution at 20 C in the pres-
2
4
2
ence of 1 10 M of the compounds under study. (i) Curr-
ent density and (E) potential (vs. SHE); the same for Fig. 3.
Inhibitor: (1) none, (2) Ic, (3) IIc, (4) Id, and (5) IIb.
1
103/T, K
2
Fig. 1. Temperature dependence of the corrosion rate of
logi [A cm ]
08KP steel in a 3 M H SO solution in the presence of 1
2
4
2
10 M N-acylmethylpyridinium bromides. (K ) Gravimet-
m
ric corrosion index and (T) absolute temperature. Inhibitor:
(1) none, (2) Ie, (3) Id, and (4) IId.
tive action is preserved after metal samples are re-
moved from the inhibiting medium. For example, the
corrosion of steel in a 3 M H SO solution at 60 C in
2
4
2
the presence of 1 10 M Ic and Id is hindered by
factors of 317 and 560, respectively, and that after
their being kept in the same solutions for 1 h, washed
with distilled water, and submerged in the acid solu-
tion without inhibitor at the same temperature, by
factors of 30 and 38, respectively.
E, V
Fig. 3. Anodic and cathodic (forward and back runs) polari-
zation curves measured on 08KP steel in a 3 M H SO
2
4
2
Voltammetric measurements demonstrated that
both the cathodic reaction of hydrogen evolution and
the anodic reaction of iron ionization are hindered in
the presence of compounds Ic, Id, IIb, and IId
(Fig. 2). The presence of these compounds in 3 M
H SO solutions affects only slightly the slopes of the
solution in the presence of 1 10 M of compounds Id,
IIc. Inhibitor: (1) none, (2) Id, and (3) IIc.
formed in partial chemical transformations of the
inhibitor on the electrode. However, the hindrance
factors calculated from the polarization curves satis-
factorily coincide for all the compounds with the
hindrance factors found in more prolonged gravimet-
ric tests. This indicates that no noticeable chemical
transformations of the inhibitors occur at the steel
surface at 20 C.
2
4
cathodic and anodic polarization curves, i.e., has vir-
tually no effect on the mechanism of partial reactions
involved in corrosion. Only at weak cathodic polariza-
tions of steel the curves show poorly pronounced
regions of limiting current, which are possibly due to
the occurrence of concurrent reactions of oxygen ioni-
zation or partial reduction of the compounds under
study. A stronger change in the slope of the cathodic
curve is observed in the presence of compound Id,
which possibly indicates that the sulfur atom of the
thiophene ring is involved in adsorption. The appear-
ance, in its presence, of a narrow hysteresis loop
(Fig. 3) is probably due to hindered desorption from
the steel surface of inhibitor molecules or of products
The results of the calculations in Table 3 demon-
strated that the corrosion of steel at 20 C in the pres-
ence of compounds Ia, Ic, Id and IIa, IIc, IId is
hindered by the energy-related and blocking inhibition
mechanisms with the predominant contribution of the
energy effect. However, the effect of blocking of the
metal surface dominates at 60 C, which is indicated
by the fact that
markedly exceeds
calculated
exp
1
assuming an energy-related inhibition mechanism.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 7 2006

1104
YURCHENKO et al.
Table 3. Experimentally found ( exp) and calculated (
)
It is also not improbable that the steel corrosion is
hindered by the compounds studied by a more com-
plex mechanism, e.g., with a possible reduction of the
carbonyl group they contain and subsequent formation
of chemisorbed protective films on the metal surface
[9].
1
corrosion hindrance factors of 08KP steel in a 3 M H2SO4
solution for N-acylmethylpyridinium bromides Ia, Ic, Id,
IIa, IIc, and IId
Ec,
mV
Compound, M T, C
exp
1
CONCLUSIONS
Ia:
2
3
3
4
4
1 10
4 10
20
20
20
20
20
46
45
15
6
19.60
18.37
3.17
1.81
1.20
14.96
13.33
2.37
1.41
1.12
1.38
1.37
1.34
1.28
1.07
(1) The N-acylmethylpyridinium bromides studied
are highly effective inhibitors of acid corrosion of
steel, especially at elevated temperatures.
1.6 10
6.4 10
2.56 10
(2) The presence in the acyl moiety of the mole-
cule of groups that can be directly involved in an
interaction with the steel surface or have a consider-
able volume markedly enhances the anticorrosive ef-
fect of the compounds studied. The hindrance factors
at 60 C are as large as 414 865 units in separate
cases, and the degree of corrosion protection of steel
exceeds 99.5% for all of the compounds studied.
2
Ic:
2
3
3
4
4
1 10
4 10
20
20
20
20
20
20
60
49
44
39
13
3
23.70
17.31
13.04
2.34
1.18
19.10
16.78
12.59
9.44
2.11
1.18
1.41
1.37
1.38
1.10
1.00
1.35
1.6 10
6.4 10
2.56 10
2
Id, 1 10
Id, 1 10
46
14.12
7.14 78.37
2
30 559.60
REFERENCES
IIa:
2
3
3
4
4
1 10
20
20
20
20
20
54
48
29
14
8
32.00
21.95
5.40
2.30
1.66
22.38
15.85
5.31
2.24
1.58
1.43
1.38
1.02
1.03
1.05
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4 10
1.6 10
6.4 10
2.56 10
IIc:
2
3
3
4
4
1 10
4 10
20
20
20
20
20
20
60
58
53
45
22
4
39.60
28.13
16.91
4.45
1.28
24.30
28.18
21.13
13.33
3.54
1.26
17.78
1.40
1.33
1.27
1.25
1.02
1.37
1.6 10
6.4 10
2.56 10
IId, 1 10
Ic, 1 10
2
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2
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Note: It was taken in the calculations [8] that
=
,
exp
1
where
and blocking hindrance factors;
b /b (b + b ), 1 = E /[1 b b /b (b + b )]; E ,
and
are, respectively, the energy-related
1
1
K
1
= 10
; K =
1
c
0
a
c
c
c
a
0
a
c
c
shift of the free corrosion potential, caused by the in-
hibitor; b and b , Tafel slopes of the cathodic and anodic
c
a
polarization curves in a 3 M H SO solution; and b =
2
4
0
2.3RT/F.
Electrochemistry), Kiev: Libid’, 1993.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 7 2006