Study of the inhibiting activity of 4-(4′-hydroxyphenyl)-and 4-(2′-hydroxy-5′-methylphenyl)methyl cyclohexane carboxylic acid ethyl esters in photooxidation of petroleum phosphors

Article abstract of DOI:10.1134/S1070427211020157

4-(4′-hydroxyphenyl)-and 4-(2′-Hydroxy-5′-methylphenyl) methyl cyclohexane carboxylic acid ethyl esters were synthesized from phenol and para-cresol. The structure of the esters synthesized was studied, and their inhibiting activity in photooxidation of a

Full text of DOI:10.1134/S1070427211020157

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 2, pp. 256−260. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © Ch.K. Rasulov, L.B. Zeinalova, R.K. Azimova, Ch.K. Salmanova, S.F. Akhmedbekova, A.P. Mamedov, 2011, published in Zhurnal
Prikladnoi Khimii, 2011, Vol. 84, No. 2, pp. 260−264.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Study of the Inhibiting Activity of 4-(4'-Hydroxyphenyl)-
and 4-(2'-Hydroxy-5'-methylphenyl)methyl Cyclohexane
Carboxylic Acid Ethyl Esters in Photooxidation
of Petroleum Phosphors
Ch. K. Rasulov, L. B. Zeinalova, R. K. Azimova, Ch. K. Salmanova,
S. F. Akhmedbekova, and A. P. Mamedov
Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
Received April 7, 2010
Abstract—4-(4'-hydroxyphenyl)- and 4-(2'-Hydroxy-5'-methylphenyl)methyl cyclohexane carboxylic acid ethyl
esters were synthesized from phenol and para-cresol. The structure of the esters synthesized was studied, and
their inhibiting activity in photooxidation of a petroleum phosphor produced from the heavy pyrolysis tar fraction
was examined.
DOI: 10.1134/S1070427211020157
An interesting and promising research area is
photochemical oxidation of petroleum and petroleum
products. In contrast to thermal treatment, light exposure
enables selective delivery of energy to a component
of the reaction mixture, which is important for such
multicomponent systems as oil.
cycloalkylation of phenol and para-cresol with 1-meth-
ylcyclohexenecarboxylic acid ethyl ester (MCHAEE) in
the presence of a KU-23 catalyst in the H-form and in
analysis of synthesized 4-(4'-hydroxyphenyl)- (ester 1)
and 4-(2'-hydroxy-5'-methylphenyl)methyl cyclohex-
ane carboxylic acids ethyl esters (ester 2) as PP photo-
oxidation inhibitors.
Petroleumphosphors(PPs)arelabileoilproductsand,
when exposed to solar light and atmospheric oxygen,
they are subject to photooxidative processes making
shorter their service life. Therefore, it is necessary to
find inhibitors that stabilize PPs without interfering with
the components responsible for luminescence.
EXPERIMENTAL
As starting products served phenol [GOST (State
Standard) 6417–74], para-cresol [TU (Technical
Specification) 6-09-244–77] and MCHAEE produced
by reacting isoprene with acrylic acid ethyl ester in
a 1-l autoclave. The reaction was performed in the
atmosphere of argon at a temperature of 200°C in the
course of 2 h at a 1 : 1 isoprene : ester molar ratio. After
the experiment was complete, the reaction products
were subjected to rectification; MCHAEE: bp 211°C,
nD20 1.4610, ρ420 0.9701, M 168.
It is known [1, 2] that compounds containing OH,
NH, and SH functional groups, capable of homolytic
dissociation under the action of free radicals, and
aromatic rings are oxidation inhibitors.
There are numerous alkyl phenol compounds [3–
7] serving as additives to oils, fuels, and polymeric
materials, emulsifiers, inhibitors, and thermal and light
stabilizers [1, 8–10].
We used KU-23 cation exchanger (GOST 20298–
74) as a catalyst. The KU-23 catalyst was prepared by
In this communication, we present results obtained in
256

STUDY OF THE INHIBITING ACTIVITY OF 4-(4'-HYDROXYPHENYL)-
257
removing water at temperatures not exceeding 110°C
(KU-23 of the 10/60 modification contains 55–70 wt %
water and is thermally stable at 150–170°C). In the
course of operation, KU-23 was gradually deactivated
because of the thermally induced abstraction of sulfo
groups and pore clogging by tarry substances. Owing
to the microporous structure and improved kinetic
properties of the KU-23 cation exchanger, its efficiency
exceeds that of KU-2. KU-23 was regenerated with
2–4% hydrochloric acid (4.0–4.5 volumes of water per
volume of the catalyst).
ester 1 or ester 2 to PPs. As a reference inhibitor was
taken 2,6-di-tert-butyl-4-methylphenol (ionol).
We prepared films with a thickness of about 30 μm
from a benzene solution of the formulations and
irradiated the films with a PRK-2 quartz mercury lamp
for 6 h. The distance between the lamp and a sample
was 20 cm. A BS-4 light filter was used to imitate
1
the solar light. H NMR spectra were measured with
a Varian T-60 instrument. IR spectra of the samples
before and after irradiation were recorded with a UR-20
spectrophotometer in the spectral range 700–4000 cm–1.
Phenols were cycloalkylated with MCHAEE in
a batch-type laboratory installation. Reaction products
were separated from the catalyst by filtration in the
hot state (40–45°C) and then subjected to rectification.
The unreacted starting ester was evaporated under
atmospheric pressure, and then unreacted phenol (or
para-cresol) and the target reaction product were in
a vacuum (at a residual pressure of 1.3 kPa).
The stabilizing efficiency of the inhibitors on the
process of PP photooxidation was studied by analyzing
the n/ninh ratio, where n and ninh are coefficients
characterizing the amount of oxidation products formed
without the inhibitors being tested and in their presence.
The coefficients were calculated from the D1ν/D0ν ratio,
where D0ν and D1ν are the optical densities of the C=O
group at 1730 cm–1 before and after the irradiation,
respectively.
As object of study served heavy pyrolysis tar (HPT)
fraction of straight-run gasoline produced from oil at
Ethylene–Polyethylene oil refinery in Sumgait.
The degree of PP photooxidation in the absence and
in the presence of the inhibitors was determined by IR
spectroscopy from the change in the optical density
of the absorption band at 1730 cm–1 in relation to the
irradiation duration.
In turn, a fraction boiling-out at above 400°C was
isolated by vacuum distillation of HPT. Oil phosphors
were produced by deasphalting and detarring of this
fraction by the method described in [11] and stored at
room temperature without exposure to light.
The electronic absorption spectra of PPs and
esters 1 and 2 were recorded with a Specord UV-VIS
spectrophotometer in the range 200–700 nm.
The inhibiting activity of the synthesized esters 1
and 2 was examined in aerobic photooxidation of PPs.
Formulations were prepared with addition of 2 wt %
The reaction of phenol and para-cresol
cycloalkylation by cyclic esters proceeds by the scheme.
OH
CH3
HO
+
COOC2H5
CH3
COOC2H5
1
OH
HO
CH3
+
COOC2H5
CH3
COOC2H5
CH3
CH3
2
The interaction of phenol with MCHAEE mostly
and disubstituted phenols (2,4- and 2,6-isomers). The
gives para-alkylphenol with a minor amount of ortho-
reaction of para-cresol with MCHAEE mostly gives
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 2 2011

258
RASULOV et al.
ortho-alkylphenol with a minor amount of disubstituted
compounds.
the spectrum. Also, bands of deformation and stretching
vibrations characteristic of the methyl group are
observed at, respectively, 1380 and 2860 cm–1, and
bands characteristic of the methylene group, at 1470,
2920, and 2940 cm–1. In addition to the absorption
bands mentioned above, the spectrum contains a band at
1200 cm–1, which corresponds to stretching vibrations
of the O–H group of phenol. Also, a band of stretching
vibrations, responsible for the C=O group of the ester, is
observed at 1750 cm–1. The absorption band at 950 cm–1
is responsible for CH2 groups in the ring.
We studied the effect of temperature in the range
80–140°C, phenol (para-cresol) : MCHAEE ratios
of 0.5 : 1 to 3 : 1 mol : mol, catalyst amount of 5 to
25 wt % relative to the raw material, and experiment
duration in the range from 3 to 6 h on the yield and
composition of the reaction products. Experimental data
demonstrated that the yield of the target product grows
with increasing temperature, but the selectivity with
respect to the alkyl-substituted phenol falls under the
same conditions because of the reaction of dealkylation
and realkylation. As the amount of the catalyst is raised
from 5 to 25 wt %, the overall yield of esters 1 and 2
becomes higher, but the selectivity with respect to
monocyclo alkyl phenol decreases. The yield of esters 1
and 2 is strongly affected by the phenol (para-cresol) :
MCHAEE molar ratio. A 1 : 1 molar ratio of the starting
components provides a high yield of the esters and high
selectivity with respect to monocyclo alkyl phenol. We
found that reactions catalyzed by cation exchangers
are slow; their optimal duration is 5–5.5 h, whereas
deviation from this time leads to a decrease in the yield
of esters 1 and 2.
The IR spectra of esters 1 and 2 are nearly the same.
However, the spectrum of ester 1 contains absorption
bands of a para-substituted benzene ring (840 cm–1),
and the spectrum of ester 2, those of ortho- (760 cm–1)
and para-substituted (840 cm–1) benzene rings.
1H NMR spectrum of ester 1 (CCl4, δ, ppm): 1.12
and 2.8 (CH3); 1.2–1.8 (multiplet of protons of the
cyclohexane ring); 5.4 (OH); 6.4–7.2 (multiplet of
1
protons of the benzene ring). The H NMR spectra of
esters 1 and 2 are nearly the same.
A broad band at 250–280 nm is observed in the
electronic absorption spectrum of esters 1 and 2. This
band indicates that the ester contains a phenolic group
and an ester group (COOR) not bonded directly to the
benzene ring, which indirectly confirms the structure of
esters 1 and 2.
An analysis of the data obtained enabled us to find
the optimal experimental conditions: temperature 120–
125°C, 1 : 1 molar ratio of the starting components,
catalyst amount 10–12 wt % relative to the raw
material at a reaction duration of 5–5.5 h. Under these
conditions, the yields of esters (1) and (2) reach a value
of 63.5–68.6%, and the selectivity, 89.7–93.2%. The
physicochemical characteristics of esters 1 and 2 are
listed in the table.
The electronic absorption spectrum of PPs covers
a spectral range from 200 to 500 nm. The esters we
synthesized absorb in the short-wavelength UV range
(200–280 nm); the molar extinction coefficient of PPs is
εmax = 8 105, and that of the esters, εmax = 4 105. Because
the absorbing capacity of PPs substantially exceeds that
of esters 1 and 2 and the concentration of the esters does
not exceed 2 wt %, they cannot serve as UV absorbers
for PPs. In addition, the triplet state energy of PPs
(~1.12 eV) is lower than that of the esters synthesized
(3.53 eV). It is known [12, 13] that the triplet state
energy of the quenching acceptor must be lower than
that of a donor. Therefore, it can be suggested that the
esters cannot be used as quenching agents for excited
states of PPs.
The IR spectrum of ester 1 shows absorption
bands at 700, 780, 820, and 880 cm–1, associated with
nonplanar deformation vibrations of a substituted
benzene ring. The absorption bands peaked at 1510 and
1580 cm–1 are related to deformation vibrations of the
benzene ring, and that at 1610 cm–1, to the C=C bond
of the aromatic ring. A pendulum vibration peaked at
725 cm–1, characteristic of the CH2 group, appears in
The photooxidation of PPs yields active species, such
as singlet oxygen and alkyl and peroxide radicals (1O2,
R , RO2) [14]. Phenols having comparatively weak O–H
bonds, compared with the C–H bond of a hydrocarbon,
interact with these active species, as shown in [12].
The differences between the reactivities of these bonds
Physicochemical characteristics of esters 1 and 2
Ester bp, °C/P, Pa
mp, °С
nD20
1.5030 1.0426 260
276
ρ420
М
·
·
1
2
183–187/666.5
–
215–217/666.5 81–82
–
–
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 2 2011

STUDY OF THE INHIBITING ACTIVITY OF 4-(4'-HYDROXYPHENYL)-
259
are due to the difference in activation energies. The
activation barrier of the reaction of a peroxide radical
with the O–H bond of phenol is 28 kJ mol–1 lower than
the activation energy of the reaction of a peroxide radical
with the C–H bond of hydrocarbons, This difference in
the reactivities of O–H and C–H bonds can be attributed
... ...
to the fact that the transition state O H OOR has
a bipolar structure in which a hydrogen atom is between
two negatively charged oxygen atoms. Such a bipolar
structure is characterized by an energy gain associated
with the interaction of two dipoles with a positively
charged hydrogen atom. It is this Coulomb attraction
that is responsible for the decrease in the activation
τ, h
·
energy of the reaction of RO2 with phenol. At the same
Optical density D of carbonyl groups vs. the irradiation
duration τ. (1) PPHPT; PPHPT + additive: (2) ionol, (3) ester
1, and (4) ester 2.
time, the rate of this reaction is affected by the formation
of a hydrogen bond. Being a polar species, the peroxide
radical tends to form a hydrogen bond with the O–H
group. The stronger the O–H bond in phenol, the slower
containing compounds. It follows from the figure that
introduction of 2 wt % ester 1 or 2 into PPs diminishes
the accumulation of oxidation products. The stabiliza-
tion efficiencies for esters 1 and 2 are 5.3 and 5.7. These
values are comparable, which is presumably due to the
position of the substituent in the structure of the esters.
Substituents in ortho- and para- positions to the pheno-
lic group affect the strength of the O–H bond and its in-
hibiting capacity. In the presence of alkyl electron-donor
substituents in the structure of the esters, the –O–H bond
is weakened and detachment of a hydrogen atom is facili-
tated, which facilitates formation of low-activity radicals.
·
its reaction with RO2.
Taking into account the aforesaid, we tested esters
1 and 2 as PP oxidation inhibitors. To study photoxi-
dative processes occurring in PPs in the presence and
absence of inhibitors, the variation of the optical density
of carbonyl-containing groups, D1730(C=O), with the ir-
radiation duration was examined (see the figure). The
intensity of this band is an objective criterion character-
izing the depth of PP oxidation. The nature of the ab-
sorption bands of carbonyl groups in the IR spectrum
of PPs is complex; their peak intensity at 1730 cm–1 is
a qualitative characteristic for all the overlapping bands
and, consequently, reflects the total content of carbonyl-
The inhibiting action of esters in the course of PP
photooxidation involving RO2 occurs by the scheme
·
O
.
·
RO2
+
C
O.
COOC2H5
COOC2H5
HO
ROOH
OC2H5
CH3
CH3
CH3
.
·
RO2
O
COOC2H5
O
.
·
CH3
OOR
·
1
In the case of 1O2, we have
RO2 and O2 interact with the phenolic group of
esters 1 and 2 to give low-activity radicals involved
in chain termination reactions. In the photooxidation
of PPs, not only the OH group, but also the carbonyl
group of an ester exhibits the inhibiting activity. Having
absorbed a photon, this group forms a biradical, which,
CH3
O
COOC2H5
OOH
·
·
interacting with R , leads to chain termination:
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 2 2011

260
RASULOV et al.
.
·
O
O
hν
C
.C
HO
HO
·
OC2H5
OC2H5
CH3
CH3
OR
.
·
2R
C
OC2H5
HO
R
CH3
Protsess. Neftekhim. Neftepererab., 2007, no. 2, pp. 11–
15.
CONCLUSIONS
(1) The optimal conditions of synthesis of
4-(4'-hydroxyphenyl)- and 4-(2'-hydroxy-5'-methyl-
phenyl)methyl cyclohexane carboxylic acid ethyl
esters from phenol and para-cresol were found and
the physicochemical characteristics of the esters were
determined.
7. Korenev, D.K., Zavorotnyi, V.A., and Kelarev, V.I., Khim.
Tekhnnol. Topl. Masel, 2003, no. 1, pp. 61–63.
8. Kuliev, B.V., Azizov, A.G., Ibragimova, M.D., et al.,
Protsess. Neftekhim. Neftepererab., 2006, no. 1, pp. 71–
77.
9. Mamedova, P.Sh., Farzaliev, V.M., and Babaev, E.R.,
Neftekhimiya, 2007, vol. 47, no. 1, pp. 58–62.
(2) It was found that the esters synthesized exhibit a
high inhibiting activity in photooxidation of petroleum
phosphors via scavenging of alkyl and peroxide radicals.
10. Rasulov, Ch.K., Zeinalova, L.B., Azimova, R.K., et al.,
Neftekhimiya, 2007, vol. 47, no. 6, pp. 442–444.
11. Akhmedbekova, S.F., Antioxidative Activity of
Photooxidized Heavy Petroleum Residues, Cand. Sci.
Dissertation, Baku, 2007.
REFERENCES
12. Krichevskii, G.E., Fotokhimicheskie prevrashcheniya
krasitelei i svetostabilizatsiya okrashennykh materialov
(Photochemical Transformations of Dyes and Light-
Stabilization of Pigmented Materials), Moscow: Khimiya,
1986.
1. Rasulov, Ch.K., Azizov, A.G., Salmanova, Ch.K., et al.,
Neftekhimiya, 2006, vol. 46, no. 4, pp. 306–309.
2. Uglev, V.V. and Kam’yanov, V.F., Neftekhimiya, 2000,
vol. 40, no. 2, pp. 140–144.
3. Dyubchenko, O.I., Nikulina, V.V., Terakh, E.I., et al.,
13. Shlyapintokh, V.Ya., Fotokhimicheskie prevrashcheniya i
stabilizatsiya polimerov (Photochemical Transformations
and Stabilization of Polymers), Moscow: Khimiya, 1979.
Neftekhimiya, 2005, vol. 45, no. 1, pp. 1–5.
4. Markov, A.F., Prosenko, A.E., Shvarts, Ya.Sh., et al.,
Khim.-Farm. Zh., 2006, vol. 40, no. 4, pp. 117–121.
14. Nadzhafova, M.A., Mamedov, A.P., Rustamov, M.I., and
Salmanova, Ch.K., Neftekhimiya, 2003, vol. 43, no. 4,
pp. 273–281.
5. RF Patent 2233262.
6. Rasulov, Ch.K., Zeinalova, L.B., Babaeva, R.K., et al.,
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