Corrosion-protective properties of N-phenacylmethylpyridinium bromides

Article abstract of DOI:10.1023/B:RJAC.0000018679.25429.c2

The inhibiting action of N-phenacylmethylpyridinium bromides on corrosion of carbon steel in a 3 M sulfuric acid solution was studied. A relationship between the structure of the compounds under study and their corrosion-protective properties was revealed

Full text of DOI:10.1023/B:RJAC.0000018679.25429.c2

Russian Journal of Applied Chemistry, Vol. 76, No. 11, 2003, pp. 1764 1768. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 11,
2003, pp. 1814 1818.
Original Russian Text Copyright
2003 by Yurchenko, Pogrebova, Pilipenko, Kras’ko.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Corrosion-Protective Properties
of N-Phenacylmethylpyridinium Bromides
R. I. Yurchenko, I. S. Pogrebova, T. N. Pilipenko, and E. M. Kras’ko
Kiev Polytechnic Institute, National Technical University of Ukraine, Kiev, Ukraine
Received July 1, 2003
Abstract The inhibiting action of N-phenacylmethylpyridinium bromides on corrosion of carbon steel in
a 3 M sulfuric acid solution was studied. A relationship between the structure of the compounds under study
and their corrosion-protective properties was revealed. Compounds ensuring high degree of corrosion protec-
tion of steel in acid media were found.
Despite that the relationship between the structure
of organic compounds and their corrosion-protective
properties have been studied for a relatively long time
[1 3], this problem still remains topical. Particularly
promising is a search for effective corrosion inhibitors
among substances exhibiting the so-called intra-
molecular synergism [4 6]. This effect consists in
that the presence of functional groups of varied nature
in the inhibitor molecule enables multidimensional
action on the corrosion process and ensures effective
protection by the inhibitor.
bridge separating the pyridinium and benzoyl moieties
makes it possible to act upon each of them separately
by varying the substituents R and R and to reveal
1
factors positively affecting the inhibiting action of
the molecule as a whole.
EXPERIMENTAL
Compounds I IV were synthesized by published
procedures; compounds V XI were uknown previous-
1
ly, and their structure was confirmed by IR and H
As objects of study were chosen phenacylmethyl-
pyridinium bromides I XI, which are of interest in
that they are simultaneously quaternary pyridinium
salts and aromatic carbonyl compounds, i.e., belong to
such types of organic compounds whose inhibiting
action is well known [1, 2, 7].
NMR spectroscopy.
2-Amino-1-phenacylmethylpyridinium bromide
V, 2-amino-1-(4-methylphenacyl)methylpyridinium
bromide VII, 2-amino-1-(4-methoxyphenacyl)meth-
ylpyridinium bromide VIII, 2-amino-1-(4-bromo-
phenacyl)methylpyridinium bromide IX, 2-amino-
1-(4-chlorophenacyl)methylpyridinium bromide X,
and 2-amino-1-(4-nitrophenacyl)methylpyridinium
bromide XI. Solutions of equimolar amounts (0.02 M)
of 2-aminopyridine and appropriate -bromoaceto-
phenone in ethyl acetate were mixed. The reaction
mixture was refluxed for 3 h for V and VII and for
5 h for IX XI. The next day, the reaction mixture was
treated with ether, and the precipitate formed was
separated and recrystallized from ethanol ether. For
pyridium bromides V and VII XI, the yields (%) and
melting points ( C) are as follows: V, 82, 218 220;
VII, 75, 191 193; VIII, 80, 232 234; IX, 77, 215
217; X, 82, 220 222; and XI, 60, 252 254.
Compounds I XI were synthesized by alkylation
of 2-substituted pyridines with the corresponding
-bromoacetophenones:
R1
R
N
Br
+
O
R1
R
Br
N
+
O
I XI
2-Acetyl-1-phenacylmethylpyridinium bromide
VI. A mixture of equimolar amounts (0.02 M) of
2-acetylpyridine and -bromoacetophenone was heated
to 125 130 C for 20 min and treated with a minor
where R = H, CH , NH , COCH ; R = H, CH ,
3
2
3
1
3
OCH , Br, Cl, NO .
3
2
The presence in these compounds of a methylene
1070-4272/03/7611-1764$25.00 2003 MAIK Nauka/Interperiodica

CORROSION-PROTECTIVE PROPERTIES OF N-PHENACYLMETHYLPYRIDINIUM BROMIDES 1765
Table 1. Hindrance factors and degree Z of corrosion protection of 08KP steel in 3 M H2SO4 solution in the presence of
phenacylmethylpyridinium bromides I XI
20 C
40 C
60 C
80 C
Com-
pound
R
R1
Z, %
Z, %
Z, %
99.5
99.5
Z, %
I
II
H
H
H
11.3
1.7
15.5
2.3
23.7
7.6
26.5
32.0
3.4
91.1
41.2
93.5
56.5
95.8
86.8
96.2
96.4
70.6
44.4
89.7
12.7
2.2
18.7
2.9
29.0
10.4
34.1
35.4
3.6
92.1
54.5
94.7
65.5
96.5
90.4
97.1
97.1
72.2
54.5
91.9
221.2
209.1
88.3
15.7
150.4
21.7
144.6
198.3
207.1
626.7
63.0
98.7
93.6
99.3
95.4
99.3
99.5
99.5
99.8
98.4
98.3
96.8
NO2
H
NO2
H
III
IV
V
VI
VII
VIII
IX
X
CH3
CH3
NH2
COCH3
NH2
NH2
NH2
NH2
NH2
200.3
262.8
413.6
643.2
25.4
99.5
99.6
99.8
99.8
96.1
95.8
97.8
H
CH3
OCH3
Br
Cl
1.8
9.7
2.2
12.3
23.8
44.9
60.0
31.3
XI
NO2
amount of ethanol; the precipitate formed was sepa-
rated. Yield 35%, mp 198 200 C (from ethanol
ether).
series of electron-donor substituents, the hindrance
factor of steel corrosion grows somewhat. It increases
at 20 C from 11.3 to 15.5 for compounds I and III
and from 1.7 to 2.3 for II and IV. In the case of such
To evaluate the corrosion-protective properties of
the compounds under study, the hindrance factors
and the degree Z of corrosion protection of steel were
a relatively strong electron-donor substituent as NH
2
group, the protective effect is enhanced substantially,
with the corrosion hindrance factor for V and XI
being 23.7 and 9.7, respectively.
2
determined in the presence of 1 10 M of inhibitors
in 3 M H SO solutions at 20, 40, 60, and 80 C. The
2
4
corrosion was monitored gravimetrically using 08KP
This can be accounted for by the electronic influ-
ence of the amino group on the system of the pyri-
dine ring, which favors its -electronic interaction
with the steel surface. Also possible is the direct in-
volvement of the amino group in free or protonated
state in adsorption processes. On introducing a
4
2
steel samples with the working area of 14 10 m .
The test duration was 24 h at 20 C, 2 h at 40 and
60 C, and 1 h at 80 C. Polarization curves were meas-
ured in the potentiodynamic mode at the potential
1
sweep rate of 2 mV s on a steel electrode in the ini-
CH CO group into position 2 of the pyridine ring
tial and inhibited sulfuric acid solutions.
3
(compound VI), the corrosion hindrance factor de-
The test performed demonstrated that most of the
compounds under study show noticeable inhibiting
properties which are largely determined by the nature
of substituents in their molecules (Table 1).
creases to 7.6.
It was established that the observed changes in the
inhibiting action of I, III, V, and VI are strictly deter-
mined by the electronic nature of substituents R.
There exists a linear relationship (r = 0.994) between
As is known [7], adsorption of quaternary pyridini-
um salts may occur both through electrostatic attrac-
tion of the pyridinium cation to the negatively charged
the corrosion hindrance factors for these compounds
0
and the constants
characterizing the combination of
c
metal surface and via specific
interaction of the
the mesomeric and -induction effects of the substit-
uents R [8]. The fact that this dependence is observed
suggests that adsorption of the compounds studied
onto steel at room temperature is due to -electronic
interaction of the pyridinium ring with the metal sur-
face, favored by the presence of electron-donor sub-
stituents in the pyridinium ring. This also indicates
that the amino group in V is not involved directly in
the adsorption, and the decisive role is played by its
pyridine with the metal. Attempts were made, by in-
troducing substituents of varied electronic nature into
the position 2 of the pyridine ring of I and thereby
changing the charge on the nitrogen atom and the
-electron density of the pyridine ring, to reveal the
role played by the pyridinium moiety of the molecule
and evaluate the effect of the substituents introduced
on the inhibiting effect of the forming compounds. It
was found that, in going from I and II to the corre-
sponding compounds with a CH group heading the
influence on the
system of the pyridine ring.
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 11 2003

1766
YURCHENKO et al.
factor for IX and X being as low as 3.4 and 1.8,
respectively.
A comparison of the protective effects of com-
pounds I, III, and V and the corresponding nitro
derivatives II, IV, and XI demonstrated that introduc-
tion of an NO group into the para position of the
2
benzene ring makes their inhibiting action weaker.
Since the nitro group is a much stronger electron
acceptor than a bromine or chlorine atom, it would be
expected that the protective properties should be com-
pletely eliminated on replacing these atoms with a
nitro group. However, it was found that such a re-
placement not only fails to make the hindrance factor
lower, but even raises it substantially. For example,
the corrosion hindrance factor for XI is 9.7.
T, C
Fig. 1. Hindrance factor vs. temperature T in corrosion of
08KP steel in a 3 M solution of H SO in the presence of
2
4
2
1
10
M phenacylmethylpyridinium bromides. Com-
pound: (1) VIII, (2) VII, (3) VI, (4) III, (5) V, (6) I, and
(7) XI.
Variation of the substituents R revealed for com-
pounds V, VII, IX, and X at 20 and 40 C a correla-
1
tion between their
correlation coefficients equal to, respectively, 0.998
and 0.990. The exception are compounds VIII and
XI. Possibly, the substituents R in these compounds
are involved, in addition to exerting influence on the
carbonyl group and the system of the benzene ring,
in some other processes. For VIII, this may be, e.g.,
independent involvement of the MeO group in the free
or protonated form in adsorption, whereas in XI, as
also in II and IV, the observed corrosion hindrance,
probably, results from the combined influence exerted
on corrosion both by these compounds themselves and
by the corresponding amino compounds, which could
be formed under the experimental conditions.
constants and values, with the
0
1
It should be noted that the linear dependence
,
c
observed for compounds I, III, V, and VI, is also
preserved at 40 C, but the correlation coefficient falls
in this case to 0.985. At 60 C, the inhibiting action
1
of the compounds studied increases dramatically
0
(Table 1), but the
relationship is strongly dis-
c
turbed, being completely eliminated at 80 C. Possi-
bly, raising the temperature leads to manifestation in
the corrosion process of a number of other factors.
This may be, e.g., reorientation of molecules bound to
the metal surface via the system of the pyridinium
moiety, enhancement of the role played by electrostat-
ic interaction of pyridinium cations with the metal
surface, and increasing share of the specific adsorption
of compounds via the carbonyl group.
The results of the corrosion tests demonstrated that,
with the temperature increasing to 60 C, the inhibiting
action of most of the compounds studied increases
substantially (Table 1) and remains rather high at
80 C. The observed temperature dependence of the
inhibiting effect of the compounds studied (Fig. 1) is
probably associated with a change in the mechanism
of their adsorption onto the metal and a transition
from physical (or first-order specific) adsorption to
chemisorption as a result of the enhanced donor
acceptor interaction between the carbonyl oxygen and
d levels of iron. A certain decrease in the inhibiting
action of some compounds at 80 C is possibly due to
desorption of inhibitors from the metal surface, result-
ing from the high rate of metal dissolution at this
temperature.
As is known [1, 2], the corrosion hindrance under
the action of carbonyl compounds is mainly due to
involvement of the oxygen from the carbonyl group in
adsorption processes because of the presence of a sub-
stantial electron density on this atom. Electron-donor
substituents make higher the nucleophilicity of
the oxygen atom of the carbonyl group, thereby
enhancing the donor acceptor interaction of carbonyl
compounds with the metal surface, whereas electron-
acceptor substituents passivating the carbonyl group
make this interaction weaker. Introduction into the
para position of the benzene ring of V of CH or
CH O groups, which exhibit electron-donor effect,
3
3
enhances the protective action of the inhibitor, with
the result that the corrosion hindrance factor increases
to 26.5 and 32.0 for VII and VIII, respectively, at
20 C. If these substituents are replaced with a brom-
ine or chlorine atom, the corrosion-protective effect
decreases dramatically, with the corrosion hindrance
Voltammetric measurements on steel in the pres-
ence of compounds V, VIII, and XI demonstrated that
these compounds are inhibitors of mixed type, which
inhibit both the cathodic and anodic reactions of the
corrosion (Fig. 2). Under stationary conditions, they
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 11 2003

CORROSION-PROTECTIVE PROPERTIES OF N-PHENACYLMETHYLPYRIDINIUM BROMIDES 1767
affect the process to a greater extent by shifting the
2
log i [A cm ]
free corrosion potential E of steel in the positive
f
direction. The hindrance factors calculated from the
intersection of the Tafel portions of polarization
curves for V, VIII, and XI are, respectively, 22.5,
29.2, and 4.0, and those for V and VIII are close
to those obtained from gravimetric measurements
(Table 1).
The nature of substituents in these compounds
strongly affects the run of the cathodic polarization
curves, and to a lesser extent, that of the anodic
curves. The influence of compound XI containing a
nitro group on the cathodic reaction is low, which
may be due to its partial reduction on the steel sur-
E, V
face. The extent to which compound XI affects the
cathodic reaction of steel corrosion decreases marked-
Fig. 2. Polarization curves measured on 08KP steel in a
3 M solution of H SO at 20 C in the presence of 1
10 M phenacylmethylpyridinium bromides. (i) Current
density and (E) potential (vs. standard hydrogen electrode).
(1) Supporting electrolyte solution; compound: (2) XI,
(3) VIII, and (4) V.
2
4
ly when the electrode potential is shifted in the nega-
tive direction, which may also be due to the reduction
of XI. Inhibitors V and VIII enhance substantially the
electrode polarization of the cathodic reaction of the
corrosion process, thereby markedly changing the run
of the cathodic curves at high polarizations. When
the electrode potential is shifted in the negative direc-
tion, inhibition of the cathodic reaction of the corro-
sion process is enhanced in their presence. This can be
accounted for by an increase in adsorption of V and
VIII onto steel and their reorientation on the metal
surface, which ensures formation of a more closely
packed protective layer of an inhibitor [7].
2
on E by a number of additional factors: conjugated
f
reduction of oxygen, occurring in an acid medium in
the presence of effective inhibitors; selective adsorp-
tion of surfactants on active centers of the metal; etc.
CONCLUSIONS
(1) Phenacylmethylpyridinium bromides are effec-
tive inhibitors of acid corrosion of steel, whose pro-
tective action depends on the nature of substituents
present in these compounds.
The strongest influence on the rate of acid corro-
sion of metals is commonly exerted by the energetic
(
1) and blocking ( ) inhibition effects, whose
(2) The inhibiting properties of the compounds
under study are enhanced by electron-donor sub-
contribution to the overall corrosion hindrance factor
can be calculated using a system of equations reported
in [7]. The corrosion hindrance associated with the
Table 2. Experimental ( ) and calculated ( ) corrosion
e
hindrance factors for 08KP steel in a 3 M csolution of
appearance of an additional step of potential,
,
1
H2SO4 in the presence of V, VIII, IX, and XI
can be calculated using simple kinetic relations taking
into account the Tafel slopes of the polarization
curves, b and b , and the shift of the free corrosion
Com-
pound
c, M
Ef, mV
*
c
a
e
c
potential, E , caused by the inhibitor (Table 2).
f
2
3
4
4
2
2
2
3
A comparison of the experimental ( ) and cal-
V
1
4
10
10
60
56
45
17
71
21
50
31
23.7
23.2
17.0
2.6
32.0
3.4
26.8
21.4
11.8
2.5
48.9
3.2
e
culated ( ) hindrance factors demonstrated that the
c
1.6 10
6.4 10
1
1
1
4
compounds studied hinder acid corrosion of steel
mainly by the energetic mechanism, and the effect of
blocking of the metal surface is only of secondary im-
portance in their presence. As also for other cation-
like compounds, this is probably due to the presence
in the phenacylmethylpyridinium bromides of pyri-
dinium cations ensuring the appearance at the metal
solution interface of a positive adsorption step of
potential. The excess of over , observed for some
VIII
IX
XI
10
10
10
10
9.7
7.8
10.2
5.4
K
1
* It was taken in calculations that
= 10
, K = b /b (b +
c
c 0 a
b ),
= E /[1 b b /b (b + b )], where b and b are
c
1
c c a 0 a c c a
the Tafel slopes of the cathodic and anodic polarization curves
c
e
compounds, is possibly due to the influence exerted
in a 3 M solution of H SO , b = 2.3RT/F [7].
2
4
0
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 11 2003

1768
YURCHENKO et al.
stituents introduced both in the pyridinium and in
benzoyl moieties of their molecules and weakened by
electron-acceptor substituents. The key role in the cor-
rosion-protective action of the compounds under study
at room temperature is the pyridinium moiety, with
the corrosion hindrance by the energetic inhibition
mechanism, and the benzoyl moiety of the molecule
ensures their chemisorption and high performance at
elevated temperatures. Such a polyfunctionality of
phenacylmethylpyridinium bromides allows them to
preserve their strong inhibiting action in a 3 M solu-
tion of sulfuric acid in a wide range of solution tem-
peratures (20 80 C).
cal Structure and Protective Action of Corrosion In-
hibitors), Rostov-on-Don: Rostov. Univ., 1978.
2. Reshetnikov, S.M., Ingibitory kislotnoi korrozii metal-
lov (Inhibitors of Acid Corrosion of Metals), Lenin-
grad: Khimiya, 1986.
3. Ivanov, E.S., Ingibitory korrozii metallov v kislykh
sredakh: Spravochnik (Inhibitors of Metal Corrosion in
Acid Media: Reference Book), Moscow: Metallurgiya,
1986.
4. Antropov, L.I., Zashch. Met., 1977, vol. 13, no. 4,
pp. 387 399.
5. Pogrebova, I.S., Effekty sinergizma pri ingibirovanii
korrozii metallov (Synergism in Inhibition of Metal
Corrosion), Kiev: Znanie, 1980.
(3) The most effective of the compounds studied
are 2-amino-1-phenacylmethylpyridinium bromide V,
2-amino-1-(4-methylphenacyl)methylpyridinium brom-
ide VII, and 2-amino-1-(4-methoxyphenacyl) methyl-
pyridinium bromide VIII.
6. Antropov, L.I., Makushin, E.M., and Panasenko, V.F.,
Ingibitory korrozii metallov (Inhibitors of Metal Corro-
sion), Kiev: Tekhnika, 1981.
7. Antropov, L.I. and Pogrebova, I.S., Itogi Nauki, Ser.:
Korroz. Zashch. Korroz., 1973, vol. 2, pp. 27 112.
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 11 2003