Synthesis of N-[2-hydroxy-4(5)-methyl- and -5-(methylcyclohexyl)benzyl] morpholines as antioxidants for transformer oils

Article abstract of DOI:10.1134/S107042721012013X

Aminomethylation of m- and p-cresols and of p-(1-methylcyclohexyl)phenol with formaldehyde and morpholine was studied. The products obtained were tested as antioxidant additives to T-1500 transformer oil.

Full text of DOI:10.1134/S107042721012013X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 12, pp. 2140–2143. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © Ch.K. Rasulov, A.G. Azizov, F.A. Nabiev, S.T. Rustamov, A.S. Askerova, 2010, published in Zhurnal Prikladnoi Khimii, 2010,
Vol. 83, No. 12, pp. 2013–2016.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Synthesis of N-[2-Hydroxy-4(5)-methyl-
and -5-(methylcyclohexyl)benzyl]morpholines as Antioxidants
for Transformer Oils
Ch. K. Rasulov, A. G. Azizov, F. A. Nabiev, S. T. Rustamov, and A. S. Askerova
Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
Received November 26, 2009
Abstract—Aminomethylation of m- and p-cresols and of p-(1-methylcyclohexyl)phenol with formaldehyde
and morpholine was studied. The products obtained were tested as antioxidant additives to T-1500 transformer
oil.
DOI: 10.1134/S107042721012013X
Alkylphenols and their derivatives steadily attract
researchers’ attention owing to practical value of these
compounds, primarily to very wide spectrum of their
antioxidant activity. In particular, numerous patents
and articles on this subject have been published in the
past decade [1–7].
EXPERIMENTAL
As starting substances we used reagent-grade m- and
p-cresols, formaldehyde (30% formalin), and morpholine.
p-(1-Methylcyclohexyl)phenol was prepared by the
reaction of phenol with 1-methylcyclohexene in the
presence of acid catalysts [8]. Its characteristics are as
follows: bp 160–164°С (1333 Pa), mp 95°С, М 190
(exp.).
In this study we performed aminomethylation of m-
and p-cresols and of p-(1-methylcyclohexyl)phenol
with formaldehyde and morpholine and tested the
resulting products as antioxidants for transformer oil.
N-[2-Hydroxy-4(5)-methyl- and 2-hydroxy-5-(methyl-
cyclohexyl)benzyl]morpholines were prepared by the
reactions of m-, p-cresol and p-(1-methylcyclohexyl)
phenol with formaldehyde and morpholine in 1 : 2 : 2
ratio. A three-necked flask was charged with the
calculated amounts of the substituted phenol, mor-
pholine, and benzene, and 30% formaldehyde was
added dropwise with stirring at 25–30°С, after which
the reaction mixture was allowed to stand for 1 h. Then
the temperature was gradually raised to 75°С, and the
mixture was stirred for another 2 h, after which it was
washed with water to remove the unchanged
formaldehyde. The amino compounds were separated
from alkylphenols by conversion into hydrochlorides.
Aminomethylation of m- and p-cresols and of p-(1-
methylcyclohexyl)phenol with formaldehyde and
morpholine can be described as follows:
OH
HN
O
+ CH2O +
OH
R1
R2
CH2
N
O
R1
Then the aqueous solution of the amine hydro-
chloride was treated with concentrated NH4OH, and
the free amino compound was isolated. The amine was
separated from water by extraction with benzene. After
distilling the benzene off, the residue was subjected to
R2
; R1 = CH3, R2 = H.
R1 = H; R2 = CH3,
H2C
2140

SYNTHESIS OF N-[2-HYDROXY-4(5)-METHYL-...
Table 1. Physicochemical parameters of N-benzylmorpholines
2141
Found/
Calculated
М
Tb
Tm
Found, %/Calculated, %
Compound
OH
Formula
°С
C
H
N
158–160
(666.5 Pa)
60
207/
207
70.20/
69.54
8.70/
8.27
7.30/
6.76
C12H17O2N
N
CH2
O
H3C
OH
152–154
(666.5 Pa)
56
86
207/
207
70.10/
69.54
8.45/
8.27
6.60/
6.76
C12H17O2N
N
CH2
O
CH3
OH
196–198
(266.6 Pa)
289/
289
75.20/
74.70
9.60/
9.40
4.60/
4.84
C18H27O2N
N
CH2
O
CH3
fractional distillation in a vacuum, and the physico-
chemical characteristics and purity of the products
were determined. The composition and structure of the
products were determined by chromatographic and
spectral analysis.
N-(2-Hydroxy-4-methylbenzyl)morpholine (I). A
three-necked flask was charged with 26.0 g of m-cresol,
22.0 g of morpholine, and 100 ml of benzene, after
which 25.0 g of a 30% formaldehyde solution was
added dropwise. Then the mixture was heated with
stirring and worked up as described above. After
distillation, the target product was in 70.0% yield.
Chromatographic analysis of methyl- and methyl-
cyclohexylphenols and N-benzylmorpholines was
performed with an LKhM-72 chromatograph equipped
with a thermal conductivity detector. The column length
was 2 m. The solid support was Chromaton N-AW-
DMC washed with acid and silanized with dimethyl-
dichlorosilane, fraction 0.2–0.25 mm. The stationary
phase was 5% methylsiloxane elastomer SE-30. The
initial column temperature was 50, and the final tem-
perature, 280°С; the heating rate was 10 deg min–1.
The carrier gas was He (flow rate 50 ml min–1). The
detector temperature was 300°С. The paper feed rate
was 60 mm h–1. The calculations were performed by
the method of internal normalization, i.e., the peak
areas were calculated relative to their sum taken as
100%.
The physicochemical parameters and elemental com-
position of I are given in Table 1.
In the 1Н NMR spectrum, the protons of the aromatic
ring give signals in the region of 6.3 ppm, and the СН3
protons, at 0.9 and 1.0 ppm. The integral intensity of
the signals at 3.55 and 4.75 ppm is consistent with the
CH2
CH2
number of protons in the substituents СН2 and –N<
.
In the IR spectra of the compounds synthesized, the
stretching vibrations of С–Н groups are manifested at
3000–2800 cm–1, and the phenol OH groups absorbs at
3610 and 1200 cm–1. The bands at 1590 and 1605 cm–1
belong to vibrations of the aromatic ring.
N-(2-Hydroxy-5-methylbenzyl)morpholine (II).
A three-necked flask was charged with 26.0 g of p-
cresol, 22.0 g of morpholine, and 100 ml of benzene,
and 25.0 g of a 30% formaldehyde solution was added
from a dropping funnel with stirring at 30°C. The
The IR spectra were recorded with a UR-20 spec-
1
trometer, and the H NMR spectra, with a Varian FT-
84 device (USA) with HMDS as internal reference.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 12 2010

2142
RASULOV et al.
Table 2. Results of tests of N-benzylmorpholines as AOs for T-1500 transformer oil [135°С, 30 h, V(О2) = 50 ml min–1, AO
amount 0.4%]
Resistance to oxidation according to GOST 981–75 and
paragraph 5.4 of GOST 982–80
Weight fraction of
Sample
precipitate, %
amount of volatile low-molecular-
acid number, mg KOH/g
weight acids, mg KOH/g
Oil without AO
0.8
–
0.96
0.01
0.24
0.04
Oil + Ionol (according to GOST
982–80)
Oil + IKhP-21
''
''
''
''
0.09
0.06
0.03
0.04
0.03
0.02
Oil + compound I
Oil + compound II
Oil + compound III
Neutral medium
The same
subsequent procedure was the same as described
above. The target product was obtained in 68.3% yield
by vacuum distillation. Its characteristics are as
follows: bp 152–154°С (666.5 Pa), mp 56°С, М 207.
disubstituted cyclohexane ring exhibits С–Н stretching
vibration bands at 2920 and 2845 cm–1 and the ring
CH2 bending bands at 1108 and 1345 cm–1. The methyl
group is characterized by bending vibration bands at
1370 and 1460 cm–1.
1
The IR and Н NMR spectra of N-(2-hydroxy-5-
methylbenzyl)morpholine are similar to those of I.
The physicochemical characteristics of the com-
pounds synthesized are given in Table 1.
N-[2-Hydroxy-5-(1-methylcyclohexyl)benzyl]mor-
pholine (III) was prepared similarly to II, starting
from 23.7 g of p-(1-methylcyclohexyl)phenol, 11.0 g
of morpholine, 100 ml of benzene, and 12.5 g of a 30%
formaldehyde solution. The target product was isolated
by fractional distillation at reduced pressure (2 mm Hg).
Its physicochemical characteristics are as follows: bp
196–198°С (266.6 Pa), mp 86°С, М 289. Yield 58.7%.
The synthesized N-benzylmorpholines were tested
as antioxidants (AOs) for T-1500 transformer oil. We
examined the oxidation resistance of the oil without
additives and with AOs added, according to GOSTs
(State Standards) 981–75 and 982–80. The tests were
performed at 135°С for 30 h at an oxygen feed rate of
50 ml min–1. As AOs we tested Ionol, IKhP-21 ad-
ditive, and the N-benzylmorpholines we prepared. The
results are given in Table 2.
The IR and 1Н NMR spectra of N-[2-hydroxy-5-(1-
methylcyclohexyl)benzyl]morpholine are similar to
1
those of I, except that the Н NMR signal of the 1.4-
As can be seen, addition of the N-benzylmor-
pholines to the oil enhances its resistance to oxidation.
The best result was obtained with N-benzylmor-
pholines derived from m-cresol and p-(1-methylcyclo-
hexyl)phenol, with which no precipitate was formed,
the acidity was absent, and the amount of volatile low-
molecular-weight acids corresponded to 0.02–
0.03 mg KОН/g.
substituted benzene ring is observed at 6.87 ppm, and
the singlet of the СН3 group, at 1.22 ppm. The integral
intensity of the signals at 3.50 and 4.70 ppm is
consistent with the number of protons in the sub-
CH2
stituents СН2 and –N<
.
CH2
The IR absorption spectrum of III contains bands at
1505, 1592–1610 (benzene ring), 3010, 3030 (СН2
stretching vibrations), and 825 cm–1 (out-of-plane
bending vibrations of the СН2 group); the ОН group
absorbs at 1240 and 3100–3500 cm–1. The gem-
Thus, the compounds we synthesized can be used
as effective antioxidant additives to transformer oils.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 12 2010

SYNTHESIS OF N-[2-HYDROXY-4(5)-METHYL-...
2143
2. Korenev, D.K., Zavorotnyi, V.A., Kelarev, V.I., and
Lagutina, T.A., Khim. Tekhnol. Topl. Masel, 2003,
nos. 1–3, pp. 61–63.
CONCLUSIONS
(1) N-[2-Hydroxy-4(5)-methyl- and -5-(methylcyclo-
hexyl)benzyl]morpholines were prepared in 58.7–
70.0% yield by aminomethylation of m- and p-cresols
and of p-(1-methylcyclohexyl)phenol with formal-
dehyde and morpholine.
3. Rasulov, Ch.K., Azizov, A.G., Zeinalova, L.B., et al.,
Neftekhimiya, 2006, vol. 46, no. 4, pp. 306–309.
4. Prosenko, A.E., Markov, A.F., Khomchenko, A.S., et al.,
Neftekhimiya, 2006, vol. 46, no. 6, pp. 471–476.
5. Rasulov, Ch.K., Azizov, A.G., Zeinalova, L.B., et al.,
Prots. Neftekhim. Neftepererab., 2007, no. 2, pp. 11–15.
6. Mamedova, P.Sh., Farzaliev, V.M., and Babaev, E.R.,
Neftekhimiya, 2007, vol. 47, no. 2, pp. 115–119.
(2) The synthesized products proved to be effective
additives to T-1500 transformer oil.
7. US Patent 6417410.
REFERENCES
8. Rasulov, Ch.K., Azizov, A.G., and Zeinalova, L.B.,
Neftekhimiya, 2007, vol. 47, no. 6, pp. 442–444.
1. RF Patent 2174506.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 12 2010