N-phenacylpyridinium bromides as acid corrosion inhibitors

Article abstract of DOI:10.1023/B:RJAC.0000044159.65275.47

The inhibiting effect of N-phenacylpyridinium bromides with the amide group in the pyridine ring on corrosion of carbon steel in 3 M sulfuric acid is studied. A relationship between the nature of substituents at the amide group and the corrosion-protectiv

Full text of DOI:10.1023/B:RJAC.0000044159.65275.47

Russian Journal of Applied Chemistry, Vol. 77, No. 7, 2004, pp. 1117 1120. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 7,
2004, pp. 1132 1135.
Original Russian Text Copyright
2004 by Yurchenko, Pogrebova, Pilipenko, Shubina.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
N-Phenacylpyridinium Bromides as Acid Corrosion Inhibitors
R. I. Yurchenko, I. S. Pogrebova, T. N. Pilipenko, and T. E. Shubina
Kiev Polytechnic Institute, National Technical University of Ukraine, Kiev, Ukraine
Received March 11, 2004
Abstract The inhibiting effect of N-phenacylpyridinium bromides with the amide group in the pyridine ring
on corrosion of carbon steel in 3 M sulfuric acid is studied. A relationship between the nature of substituents
at the amide group and the corrosion-protective properties of the compounds studied is revealed. Compounds
demonstrating high protection efficiency in acid solutions at elevated temperatures are found.
In the previous work [1] we demonstrated that the
corrosion-protective efficiency of N-phenacylpyridini-
um bromides (I)
(VI), 2-(thienylcarbonyl)amino-1-(2-oxo-2phenyl-
ethyl)pyridinium bromide (VII), 2-(3-(2-furyl)-
acryloyl]amino-1-(2-oxo-2-phenylethyl)pyridinium
bromide (VIII), 2-(1-adamantoyl)amino-1-(2-oxo-
2-phenylethyl)pyridinium bromide (IX), and 2-octa-
decanoylamino-1-(2-oxo-2-phenylethyl)pyridinium
bromide (X).
+
R
N
Br
O
These compounds bearing three and, in some cases,
even four reactive centers capable of interacting with
the metal surface are of particular interest for further
investigation of the effect of intramolecular synergism
in corrosion-protective action of organic compounds.
They were synthesized by the reaction of 2-aminopyri-
dine with the corresponding acid chlorides, followed
by alkylation of the resulting amides with -bromo-
acetophenone:
at 20 and 40 C can be characterized as the correlation
0
between the inhibiting factor and
constants of
c
the substituent R. At higher temperatures (60 and
80 C), they demonstrate considerably higher inhibit-
ing efficiency, depending on the nature of the sub-
stituent. As the temperature increased from 20 to
60 C, the inhibiting factor of the compound with the
NH group increased by a factor of 8 (from 23.7 to
2
200.3), while that of the compound with the acetyl
group, by a factor of 35 (from 7.6 to 262.8). Such
a difference in the increase of the inhibiting efficiency
between these compounds is due to the fact that, at the
elevated temperature, the metal surface more actively
O
RCOCl
Et N
R
N
H
N
H2 N
BrCH COPh
3
N
O
R
2
interacts with the COCH group as compared to the
+
N
3
,
N
H
amino group under the same conditions. Therefore, for
further study of the relationship between the structure
of N-phenacylpyridinium bromides and their corro-
sion-protective properties, we selected compounds
bearing carbonyl substituents at the position 2 of the
pyridine ring. These are the amides 2-benzoylamino-
1-(2-oxo-2-phenylethyl)pyridinium bromide (II),
2-(3-phenylacryloyl)amino-1-(2-oxo-2-phenylethyl)-
pyridinium bromide (III), 2-(4-methoxybenzoyl)ami-
no-1-(2-oxo-2-phenylethyl)pyridinium bromide (IV),
2-(2-furylcarbonyl)amino-1-(2-oxo-2-phenylethyl)pyri-
dinium bromide (V), 2-(2-tetrahydrofurylcarbonyl)-
amino-1-(2-oxo-2-phenylethyl)pyridinium bromide
Br
O
where R = C6H5 (II), C6H5CH=CH (III), 4-CH3C6H4 (IV),
,
(VI)
(VII),
(V),
S
O
O
O
(
)
(X).
CH2
CH3
(IX),
(VIII),
16
CH
CH
The structures of the products were confirmed
1
by IR and H NMR spectra.
1070-4272/04/7707-1117 2004 MAIK Nauka/Interperiodica

1118
YURCHENKO et al.
Table 1. Inhibiting factors of phenacylpyridinium bromides II X and protection rates Z of 0.8KP steel in 3 M H2SO4
Compound
20 C
40 C
60 C
80 C
R
Z, %
Z, %
Z, %
Z, %
II
C6H5
2.60
32.10
33.30
24.30
30.00
28.10
36.00
26.60
24.30
61.54
96.88
96.99
95.88
96.66
96.44
97.22
96.24
95.88
4.78
43.45
47.80
33.70
43.45
43.45
45.52
28.80
43.45
79.08
97.70
97.91
97.03
97.70
97.70
97.80
96.53
97.70
17.20
365.90
731.85
317.15
365.90
456.16
475.70
432.45
365.90
94.19
99.73
99.86
99.68
99.73
99.78
99.79
99.77
99.73
12.00
91.66
99.72
99.83
99.55
99.70
99.78
99.72
99.69
99.69
III
IV
V
VI
VII
VIII
IX
X
C6H5CH=CH
4-CH3OC6H4
2-Furyl
2-Tetrahydrofuryl
2-Thienyl
2-Furyl CH=CH
1-Adamantyl
1-Octadecyl
360.10
595.00
220.20
333.80
453.00
360.10
318.26
325.80
EXPERIMENTAL
(R = NH ) to amide II, the inhibiting factor consider-
2
ably decreases not only at 20 or 40 C, but also at
higher temperatures. Evidently, in this case, the proc-
esses blocking the negative electron induction of the
benzamide group and promoting protective action
do not occur.
A mixture of 0.02 mol of appropriate acid chloride,
prepared from the acid and thionyl chloride, 0.02 mol
of 2-aminopyridine, 0.22 mol of triethylamine, and
20 ml of anhydrous benzene was refluxed for 3 h.
Then benzene was removed in a vacuum (water-jet
pump), and the residue was treated with water. Solid
amides were separated, and oily amides were extracted
with benzene. The resulting benzene solutions were
dried over anhydrous sodium sulfate, and benzene was
removed in a vacuum (water-jet pump). Equimolar
amounts (0.0015 mol) of the amides thus obtained and
-bromoacetophenone were refluxed with 15 ml of
ethyl acetate for 3 h. The reaction mixture was treated
with diethyl ether, and a solid (II, V, VIII, or IX) was
separated. In the case of oily products, the solvent was
removed by decantation, and the residue was washed
with ether and dried in a vacuum (water-jet pump).
The yields (%) and melting points ( C) of compounds
II, V, VIII, and IX are as follows: II 80, 176 179;
V 75, 210 212; VIII 72, 180 181; and IX 82, 237
240.
Different behavior was observed for the other
amides, whose acyl residue contains (in addition to
the phenyl group or in its place) such substituents as
an ethylene bridge (compound III), p-methoxy group
(IV), heterocyclic systems: furan, tetrahydrofuran, and
thiophene rings (compounds V VII), or a vinyl group
and a furan ring (VIII). The inhibiting factor of these
compounds at all the temperatures studied was con-
siderably higher as compared not only to amide II,
but also to the compound with an NH group. In-
2
crease in the protective rate was observed also with
substitution of the phenyl group in II by a bulky
adamantyl group (compound IX) or stearic acid resi-
due (X). Following [1 4], enhancement of the inhibit-
ing action in compounds II VIII is caused to a con-
siderable extent by immediate participation of the
substituents R in adsorption, and, in amides IX and X,
by either the shielding effect of the adamantyl and
octadecyl groups or small electron-donating effects
characteristic of these groups [2 5].
The corrosion-protective properties of compounds
II X were studied at their concentration of 1 10
by determining the inhibiting factor and protection
2
M
rate Z of 08KP steel in 3 M H SO at 20, 40, 60, and
80 C using the gravimetric method. The results are
summarized in Table 1.
2
4
For compounds I, II, and V VII we have made
quantum-chemical calculations of the charge distribu-
tion in the molecules (Table 2). The geometry was
optimized by the B3LYP method [6] with the standard
basis 6-31G using the GAUSSIAN program pack [7].
All the stationary points were fixed on the basis of
full analysis of normal modes of harmonic vibrations,
where NIMAG = 0 corresponds to the minima on the
potential energy surfaces for all the optimized struc-
tures. The results showed that, on passing from I (R =
Since substitution of the hydrogen atom of the
amino group by an acyl residue is accompanied by
a decrease in the electron-donating power of this
group, it could be expected that the compounds in
hand would demonstrate lower protective efficiency at
room temperature as compared to their unsubstituted
analogs. Indeed, we found that, on passing from I
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 7 2004

N-PHENACYLPYRIDINIUM BROMIDES AS ACID CORROSION INHIBITORS
1119
Table 2. Effective charges q on the heteroatoms of the compounds
O4
3
+
N2
R
N
H
Br
O1
q
R*
O1
N2
N3
O4
O(S)5
C6H5
O5
0.54580
0.54576
0.29956
0.32251
0.66758
0.65968
0.58872
0.55209
0.50162
0.64280
0.46288
0.53863
0.56683
0.32422
0.34702
0.65884
0.65833
2
0.55516
0.56042
3
5
O
S5
1
* Effective charges q in I (R = NH ): 0.57072 (O ), 0.35093 (N ), and 0.80152 (N ).
2
NH ) to compounds II and V VIII, the negative
charge on the nitrogen atom N at the pyridine ring
The electrocapillary curves obtained on mercury in
3 M H SO at 20 C in the presence of some of the
2
3
2
4
compounds studied showed that these compounds are
readily adsorbed on both negatively and positively
charged electrode surfaces (maximum in the electro-
capillary curve slightly shifted toward positive values).
This suggests the possibility that oppositely charged
reactive centers of the compounds participate in the
adsorption and that their presence induces a positive
adsorption jump of the potential.
decreases to about the same level (somewhat higher
value was obtained for II). This fact and also practic-
ally equal charges on the oxygen atoms of the acyl
groups in these compounds suggest that the value of
the negative charges on the amide nitrogen and oxy-
gen atoms is not the factor determining the inhibiting
factor of the compounds studied, and the observed dif-
ferences in their protective characteristics are caused,
without question, by the nature of substituents R.
The voltammetric measurements made in the pres-
ence of compounds V and IX revealed that they are
corrosion inhibitors of a mixed type. Being adsorbed
on a negatively charged surface of corroded steel,
these compounds inhibit both the anodic and cathodic
corrosion processes. Comparison of the experimental
and theoretical (calculated from the kinetic equations
[8]) inhibiting factors showed that, in the presence of
some of the compounds, inhibition of acid corrosion
of steel at 40 and 60 C proceeds by the coupled
energy-blocking mechanism. However, making such
calculations at 20 C is complicated by the occurrence
of a mixed hydrogen oxygen depolarization in their
presence.
The calculation data showed that, in amides V VII,
the oxygen atoms of the furan and tetrahydrofuran
rings bear negative charges, and the sulfur atom of
the thiophene ring, a positive charge, which is re-
sponsible for different mechanisms of interaction of
the heterocyclic fragments in the indicated compounds
with the metal surface. Adsorption of the oxygen-con-
taining heterocyclic structures on the metal proceeds
via the nucleophilic oxygen atoms. Therefore, the
larger negative charge localized on the oxygen atom
of the tetrahydrofuran ring is responsible for some-
what higher protective performance of VI as com-
pared to amide V. In compound VII containing a
thiophene ring, specific adsorption on the steel surface
can occur by virtue of formation of back coordination
bond with electron transfer from the metal to the
sulfur atom, thanks to its ability to accept electrons
on d orbitals.
As the temperature increased from 20 to 60 C, the
inhibiting factor of amide II increased by a factor
of 6, and that of compounds II X, by a factor of
11 22, which is higher by a factor of 1.5 3.6 than the
inhibiting factor of the unsubstituted compound at the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 7 2004

1120
YURCHENKO et al.
same temperature. Such an enhancement of the protec-
tive properties of the indicated compounds is due to
increase in the contribution of the specific adsorption
via the carbonyl group of the phenyl residue, and also
to more effective participation of the acylamide
groups in adsorption. With further increase in the
temperature, the protective activity of the most of
these compounds slightly decreases, which, as known,
is a result of a high renewal rate of the surface of
corroded steel, retarding adsorption of the inhibitor.
acid corrosion inhibitors. The inhibiting factor of
these compounds depends on the nature of substit-
uents in the acyl group, insofar as they can directly
participate in the interaction with the metal surface.
(2) High inhibiting value of N-phenacylpyridinium
bromides is a result of a combined action of all the
reactive centers of the molecules, which is particularly
pronounced at elevated temperatures. The inhibiting
factor of the compounds is as high as 300 700, and
the protective rate of steel, 99.7 99.9%.
It should be pointed out that the inhibiting factors
of the compounds in hand at 20 and 40 C only slight-
ly differ from each other, suggesting that the effect of
substituents in the acyl groups is leveled off under
these conditions. As the temperature rises to 60 80 C,
interaction of these compounds with the metal surface
considerably increases, and the differences in their in-
hibiting activity become more pronounced. For exam-
ple, at 20 C, the inhibiting factors of compounds III
and IV differ by about unity (or by a factor of 1.04),
while at 60 C, this difference becomes equal to 366
(or by a factor of 2). The difference between IV and V
is 6 (1.37) at 20 C and 414 (2.31) at 60 C. The reason
is that, at low temperatures, the same reactive centers
are responsible for adsorption of all the amides
studied, and the substituents R have only insignificant
effect. At higher temperatures, more favorable condi-
tions for effective participation of the substituents are
realized, whose different structure provides their dif-
ferent contributions to the corrosion-inhibiting activity
of the molecule as a whole.
REFERENCES
1. Yurchenko, R.I., Pogrebova, I.S., Pilipenko, T.N., and
Kras’ko, E.M., Zh. Prikl. Khim., 2003, vol. 76, no. 11,
pp. 1814 1818.
2. Zhdanov, Yu.A. and Minkin, V.I., Korrelyatsionnyi
analiz v organicheskoi khimii (Correlation Analysis in
Organic Chemistry), Rostov-on-Don: Rostov. Univ.,
1966.
3. Grigor’ev, V.P. and Ekilik, V.V., Khimicheskaya struk-
tura i zashchitnoe deistvie ingibitorov korrozii (Chemi-
cal Structure and Protective Action of Corrosion In-
hibitors), Rostov-on-Don: Rostov. Univ., 1978.
4. Reshetnikov, S.M., Ingibitory kislotnoi korrozii metal-
lov (Acid Corrosion Inhibitors), Leningrad: Khimiya,
1986.
5. Yurchenko, R.I., Klepa, T.I., Voitsekhovskaya, O.M.,
et al., Zh. Obshch. Khim., 1990, vol. 60, no. 10,
pp. 2280 2282.
6. Becke, A.D., J. Chem. Phys., 1993, vol. 98, p. 5648.
7. Frisch, M.J., Trucks, G.W., Schlegel, H.B., et al.,
CONCLUSIONS
GAUSSIAN 98, Pittsburgh, PA: Gaussian, 1999.
(1) N-Phenacylpyridinium bromides bearing an
amide group in the pyridine ring are highly efficient
8. Antropov, L.I. and Pogrebova, I.S., Itogi Nauki Tekh.,
Ser.: Korroz. Zashch. Korroz., 1973, vol. 2, pp. 27 112.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 7 2004