Kinetic features of the synthesis of an acid corrosion inhibitor, 5-methyl-1,2,3,3a,4,8b-hexahydrocyclopent[b]indole

Article abstract of DOI:10.1023/A:1014809214971

Kinetic features of thermal cyclization of 2-methyl-6-(cyclopent-2-enyl)aniline hydrochloride at 200-220°C were studied. The cyclization product shows a high performance as acid corrosion inhibitor.

Full text of DOI:10.1023/A:1014809214971

Russian Journal of Applied Chemistry, Vol. 74, No. 11, 2001, pp. 1910 1912. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 11,
2001, pp. 1850 1852.
Original Russian Text Copyright
2001 by Gataullin, Khaziev, Khusnutdinov, Borisov, Abdrakhmanov.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Kinetic Features of the Synthesis of an Acid Corrosion Inhibitor,
5-Methyl-1,2,3,3a,4,8b-hexahydrocyclopent[b]indole
R. R. Gataullin, E. V. Khaziev, R. N. Khusnutdinov,
I. M. Borisov, and I. B. Abdrakhmanov
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
Bashkir State University, Ufa, Bashkortostan, Russia
Bashkir State Agricultural University, Ufa, Bashkortostan, Russia
Received April 16, 2001
Abstract Kinetic features of thermal cyclization of 2-methyl-6-(cyclopent-2-enyl)aniline hydrochloride at
200 220 C were studied. The cyclization product shows a high performance as acid corrosion inhibitor.
Indoline compounds inhibit oxidation processes
and acid corrosion [1, 2]; the highest performance is
shown by 2-alkyl- and 2,2-dialkyl-substituted indo-
lines [3]. With the aim of searching for new effective
acid corrosion inhibitors, we studied in [4] formation
of perhydrocyclopent[b]indolines by heterocyclization
of hydrochlorides of o-(cyclopent-2-enyl)anilines [5]
and their N-precursors which can be readily prepared
from commercially available dicyclopentadiene. Het-
erocycles of this series, which are potential inhibitors
of acid corrosion, are well known, but the kinetic
features of their synthesis and the effect of reaction
conditions on the product yield are studied insuffi-
ciently. In this work we studied some kinetic features
of cyclization of 2-methyl-6-(cyclopent-2-enyl)aniline
hydrochloride I (MCPA) and the inhibiting activity
of the reaction product, 5-methyl-1,2,3,3a,4,8b-hexa-
hydrocyclopent[b]indole II.
where m is the weight loss (g), S is the sample sur-
2
face area (m ), is the test time (h),
sion rate without inhibitor (g m h ), and
corrosion rate in the presence of inhibitor (g m h ).
is the corro-
1
2
1
is the
2
2
1
The kinetic features of intramolecular cyclization
of aniline I to indoline II were studied by the one
experiment one point procedure. The mixture was
heated in sealed ampules in a thermostat at a definite
temperature for a definite time. The concentrations of
reaction products were determined by gas chromatog-
raphy.
Data on the inhibiting activity of II are listed in
Table 1. Thus, compound II can be regarded as a new
inhibitor of acid corrosion of carbon steels.
When developing a synthesis process, it is neces-
sary to elucidate how the reaction conditions (temper-
ature, component ratio, reaction time, etc.) affect the
yield of the target product. It was shown previously
EXPERIMENTAL
Table 1. Performance of indoline II as inhibitor of acid
corrosion of steel
Tests for protection of structural steels with inhib-
itor II were performed under laboratory conditions in
15% HCl and 20% H SO . Samples of St.3 steel
[GOST (State Standard) 380 87], pretreated for corro-
sion tests, were placed in a corrosive medium for a
2
4
Inhibitor
Acid
,
z, %
g m 2 h
1
wt %
HCl, 15
prescribed time
at 20 C. After that, the samples
were worked up by an appropriate procedure and
weighed with an accuracy of 0.0002 g. The corrosion
rate and degree z (%) of metal corrosion protection
with the given inhibitor were determined by the for-
mulas
5.0
0.4
0.2
0.1
HCl, 15
HCl, 15
HCl, 15
H2SO4, 20
H2SO4, 20
H2SO4, 20
0.225
0.585
1.685
21.0
3.318
6.279
95.5
88.3
66.3
0.4
0.2
84.2
70.1
= ( m)/ S ,
z = (
2)/
100,
1
1
1070-4272/01/7411-1910$25.00 2001 MAIK Nauka/Interperiodica

KINETIC FEATURES OF THE SYNTHESIS OF AN ACID CORROSION INHIBITOR
1911
[4] that heating of hydrochloride I at 200 220 C in
excess o-toluidine yields indoline II and minor (up to
10%) amounts of 2-methyl-4-(cyclopent-2-enyl)ani-
line III:
CMCPA, Ci, M
H
.
_
o
200 220 C
.
H
NH2 HCl
+ H 2 N
NH
Me
Me
II
I
t, min
.
(1)
Fig. 1. Kinetic curves of (1) MCPA consumption and
(2) indoline accumulation in intramolecular cyclization of
2-methyl-6-(cyclopent-2-enyl)aniline at 200 C. (C
,
MCPA
C ) Concentrations of MCPA and indoline, respectively;
Me
i
III
( ) time; the same for Fig. 2.
To find how the yield of the target product depends
on the initial conditions and heating time, we studied
the kinetic features of MCPA I consumption and
indoline II accumulation. As seen from the kinetic
curves shown in Fig. 1, the rate of MCPA consump-
tion is the highest in the initial stages, and at 90%
MCPA conversion the indoline concentration reaches
lnCMCPA [M]
a certain limit, C . The yield of the target product was
i
determined as the ratio of the limiting concentration
0
of indoline II to the initial concentration C
MCPA
(Table 2).
t, min
Fig. 2. Kinetic curve of MCPA consumption at 200 C,
plotted in semilog coordinates.
The kinetic curves of MCPA consumption are line-
ar in the coordinates of the first-order reaction equa-
tion (Fig. 2):
were performed with an MCPA sample that had been
stored for a month and had taken up moisture. At
relatively high temperatures, traces of moisture could
initiate the following side reactions:
lnCMCPA = lnC0MCPA
kt,
(2)
0
where C
and C are the initial and current
MCPA
MCPA
NH2
NH2
concentrations of MCPA, respectively; k is the appar-
ent rate constant of consumption of I.
CH3
CH3
H O
2
From the semilog kinetic plots, we determined the
rate constants at various temperatures (Table 2) and
obtained the Arrhenius equation
OH
V
I
NH2
lnk = (20.1 5.2)
(98.1 2.2) 103 /RT,
CH3
_
.
H O
2
1
1
where R = 8.31 J mol K .
IV
The activation energy of MCPA transformation,
E = 98.1 2.2 kJ mol , is consistent with published
data. It should be noted that this is an apparent quan-
tity, describing transformation of MCPA not only by
scheme (1), but also into by-products.
1
a
It was found previously [6] that, indeed, MCPA
can transform into 2-methyl-6-(cyclopent-1-enyl)ani-
line IV in both alkaline and acid solutions. At high
temperatures in the presence of HCl, this compound
undergoes extensive tarring. An intermolecular reac-
tion of 2-(2-hydroxycyclopentyl)aniline with MCPA,
decreasing the yield of the target product, cannot be
For example, in the experiment performed at 200 C
(Table 2) the yield of the target product was low.
This may be due to the fact that the runs at 200 C
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 11 2001

1912
GATAULLIN et al.
Table 2. Yield of indoline II and apparent rate constant k
as influenced by reaction temperature T (C0MCPA = 1.53 M)
CONCLUSIONS
(1) 5-Methyl-1,2,3,3a,4,8b-hexahydrocyclopent[b]-
indole inhibits acid corrosion of carbon steels.
1
T, C
Ci, M
Ci /C0MCPA
k
102, min
(2) The kinetic features of intramolecular cycliza-
tion of 2-methyl-6-(cyclopent-2-enyl)aniline were
studied. The yield of the target product, indoline,
decreases with decreasing initial concentration of the
starting compound.
190
200
210
220
230
1.16
0.36
0.85
0.77
0.69
0.75
0.24
0.55
0.50
0.45
0.84
0.90
1.38
2.18
3.95
(3) Increase in temperature in the range 190
230 C is accompanied by a decrease in the yield of
indoline.
Table 3. Apparent rate constant and yield of indoline in
isomerization of aniline I at 200 C, as influenced by the
initial concentration of I
REFERENCES
102,
1. Shapiro, A.B., Medzhidov, A.A., and Rozantsev, E.G.,
Zh. Obshch. Khim., 1966, vol. 36, no. 2, pp. 1873
1877.
k
min
C0MCPA, M
Ci , M
Ci /C0MCPA
1
1.53
1.15
0.76
0.9
0.6
0.8
0.36
0.18
0.05
0.24
0.16
0.07
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ruled out either. Under the experimental conditions
(sealed ampules), moisture is not evaporated; there-
fore, this pathway of MCPA transformation strongly
affects the yield of the target product as a function of
temperature (Table 2) and initial MCPA concentration
(Table 3).
As seen from Table 3, the yield of II drastically
decreases as the initial MCPA concentration is de-
creased.
6. Gataullin, R.R., Kazhanova, T.V., Fatykhov, A.A.,
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