Development of a one-stage synthesis of 2,6-di-tert-4-ethylbutylphenol from 2,6-di-tert-butylphenol

Article abstract of DOI:10.1134/S1070363208090144

Investigation of the catalyzed reaction of 2,6-di-tert-butylphenol with ethanol, ethylene glycol, oligomeric glycols, and paraldehyde in a strongly basic medium permitted to develop a technologically suitable procedure for manufacture of 2,6-di-tert-4-ethyl-butylphenol, used in the synthesis of Antioxidant-425.

Full text of DOI:10.1134/S1070363208090144

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 9, pp. 1728–1733. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © A.P. Krysin, L.M. Pokrovskii, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 9, pp. 1496–1501.
Development of a One-Stage Synthesis
of 2,6-Di-tert-4-ethylbutylphenol from 2,6-Di-tert-butylphenol
A. P. Krysin and L. M. Pokrovskii
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Akad. Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: benzol@nioch.ncs.ru
Received July 12, 2007
Abstract―Investigation of the catalyzed reaction of 2,6-di-tert-butylphenol with ethanol, ethylene glycol,
oligomeric glycols, and paraldehyde in a strongly basic medium permitted to develop a technologically suitable
procedure for manufacture of 2,6-di-tert-4-ethyl-butylphenol, used in the synthesis of Antioxidant-425.
DOI: 10.1134/S1070363208090144
2,6-Di-tert-butyl-4-ethylphenol (I) is a structural
homolog of a well-known antioxidant 2,6-di-tert-
butyl4-methylphenol II. They are used in the
manufacture of a great number of stabilized polymeric
compositions and generally patented under a common
name 4-alkyl-2,6-di-tert-butylphenols [1]. Compounds
I and II have recently been found in the foam of seas
and limnetic rivers in Europe and America. Compound
I was found among pollutants the ground waters in
Sweden [2], China, and Israel. This finding means that
compound I is present in industrial wastes and is
widely used in agriculture and as polymer additive.
The large-scale industrial production of compounds I
and II necessitated development of ecologically safe
methods of their use. Note such negative properies of
compounds I and II as the tendecy for water migration,
high solubility in fats, and slow biological degradation
under natural conditions.
as well as for prolonging the useful life of medicinals,
creams, food stuff, and perfumes.
Among the previously developed methods of
manufacturing compound I we can mention its
synthesis by tert-butylation of 4-ethylphenol with
isobutylene in the presence of acidic catalysts at 70–
80°C [8, 9]. The reaction of these compounds taken in
an equimolar ratio gives a mixture containing 6% of
compound III, 10% of compound I, and 80% of 2-tert-
butyl-4-ethylphenol (IV) used for manufacturing
Antioxidant-425 (V) [9]. The main problem is to
obtain starting compound III free of isomers. By now
three approaches have been suggested. The furst
involves the acylation of phenol, leading to 4-
acetylphenol (60% yield), and its subsequent reduction
[10]. The second is sulfonation of ethylbenzene
followed by alkaline melting of the resulting mixture
of sulfonic acids [11]. The third approach involves
oxidation of 1,4-diethylbenzene to form hydroperoxide
and decomposition of the latter [12]. The purest com-
pound III could be obtained by the first procedure [10].
No reviews on the manufacture and properties of
compound I have been published. It is noted that this
compound is a promising antioxidant additive to
monomeric olefins, which provides polymerization of
the latter under heating [4]. It is nontoxic and due to
that principally differs from 2,6-di-tert-butyl-4-
methylphenol [5]. When advertizing compound I,
Ethyl Co. states that it possesses a unique ability to
preserve a natural color of polymeric articles during
their use and is safe in contact with food [6]. This latter
property of compound I is widely used for protecting
fruits from oxidation and putrefaction on storage [7],
With 2,6-di-tert-butylphenol (VI), a number of
highly selective two-stage syntheses of compound I
become available. The acylation of compound VI with
acetic anhydride in the presence of magnesium
perchlorate in an acidic medium yields 4-acetyl-2,6-
di-tert-butylphenol (VII). The latter is reduced with
hydrogen in the presence of Pd/BaSO4 to obtain
compound I in a nearly quantitative yield. The
acylation of compound VI with acetyl chloride and the
1728

DEVELOPMENT OF A ONE-STAGE SYNTHESIS OF 2,6-Di-tert-4-ETHYLBUTYLPHENOL
1729
subsequent reduction of product VII with LiAlH4 was
reported by Volod’kin et al. [14].
benzyl alcohol derivatives formed in the first stage
[16].
More attractive are one-stage syntheses of I, starting
from 2,6-di-tert-butylphenol (V). Hence, the reaction
of compound VI with ethanol in the presence of KOH
gives a mixture containing 74% of I [3]. This process
is catalyzed by zinc oxide [15]. As known, ZnO forms
zincates in an alkaline medium. They catalyze redox
methylation of compound VI with methanol [15].
Introduction of Pd/C accelerates reduction of the
We showed that using a mixture of the Pd/C and
ZnO catalytic additives during the ethylation of
compound VI with ethanol increases the fraction of
target compound I in the reaction mixture from 70 to
85%. But the high reaction temperature (220–225°C)
and pressure developed in the course of the process (4–
10 MPa), as well as long reaction time (7 h) hinder
commercialization of this procedure.
OH
OH
C2H5OH
NaOH
ZnO, Pd/C
200oC
VI
I
paraldehyde, this reaction proceeded under at 2–
4 MPa and 230°C; under these conditions, the reaction
time was 20 times shorter compared with the initial
variant.
As known, compound I is formed in an alkaline
medium when compound
I
is reacted with
acetaldehyde and ethanol [17]. However, this process
could not be optimized. In the presence of
OH
OH
C2H5OH
NaOH
(CH3CHO)3
VI
I
+
+
220oC
OH
OH
VIII
IX
The by-product 3-(3,5-di-tert-butyl-4-hydroxy-
phenyl)butan-1-ol (VIII) and 1,3-bis(3,5-di-tert-butyl-
4-hydroxyphenyl)butane (I) are probably formed by
condensation of compound VI with crotonaldehyde
formed in its turn by dehydrocondensation of
acetaldehyde. The primary condensation products un-
dergo reduction in the course of the process. Really,
short heating of an alkaline ethanol solution of
compound VI and crotonaldehyde at 230°C in an
autoclave gave a mixture of phenols. According to
GC–MS data, the mixture contained 37% of 2-di-tert-
butyl-4-ethylphenol, 16.4% of compound VIII, 13% of
compound IX, and a series of other compounds. The
composition of the reaction products is close to that
formed under analogous conditions in the ethylation of
compound VI in the presence of paraldehyde.
Since compound VIII can be used as the starting
material for the synthesis of polymer thermostabilizers,
while tert-butyl derivatives of bis(hydroxypenyl)
propane, compound IX among them, are recommended
for manufacture from polyesters of cast articles
exhibiting enhanced whiteness, transparency, and
thermostability [18], we resorted to a simplex approach
to optimize the process and increase the fraction of
compounds VIII and IX in the reaction mixture. As a
result, the ethylation of compound VI gave a mixture
containing 60–65% of compound I, 20–25% of alcohol
VIII, and 10% of compound IX, easily separable by
vacuum distillation.
It was found that the reaction of paraldehyde with
compound VI in presence of ethylene glycol instead of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

1730
KRYSIN, POKROVSKII
ethanol at a high temperature results in preferential
formation of compound I. This process was ac-
companied by a significantly slower alkylation of
compound VI with ethylene glycol, resulting in forma-
tion of 2,6-di-tert-butyl-4-(2-hydroxyethyl)phenol (X).
In the absence of paraldehyde, the reaction of
compound VI with ethylene glycol under similar
conditions gives little compound I. The only product
isolated was compound X (yield 10%).
OH
OH
(CH3CHO)3
HOC2H4OH
NaOH
VI
I +
+
220oC
CH2CH2
OH
OH
X
XI
Further improvement of the synthesis of compound
I, starting from VI, resulted in the development of an
atmospheric-pressure process. It was found that
compound I is formed as the main product upon
refluxing of an alkaline solution of compound VI with
excess di- or triethylene glycol.
OH
OH
NaOH
I +
VI + H(OCH2CH2)nOH
n 2, 3
+
220oC
OR
R = H, CH2CH2OH
Alk
Alk = CH3, C3H7, C4H9
+
OH
(CH2)n
HO
n 1, 2, 3, 4
The process with triethylene glycol was realized at
atmospheric pressure in a glass reactor. The fraction of
compound I, the main reaction product, in the reaction
mixture was 50–65%. According to GC–MS data, the
mixture contained three groups of compounds. The
first one was a mixture of 4-alkyl-2,6-di-tert-
butylphenols with a C1–C4 alkyl radical, the second
contained compound X and its ethers, and the third,
bis-phenols with the aromatic fragments intervened by
a C1–C4 alkyl chain and two unidentified products (frac-
tion ca/10%) with the molecular masses 294 and 338.
We found no data in the literature, concerning C-
alkylation of aromatic compounds with oligomeric
glycols in an alkaline medium. The occurrence of this
reaction is probably explained by an unusual way of
generation of the alkylating agents from oligomeric
glycols in an alkaline medium. The latter are known to
form complexes with Li+ and Na+. Under ionizing
irradiation, these complexes can generate radical
species detected by tandem mass spectrometry [19]. It
was established that the cleavage of oligomeric alkali
metal glycolates proceeds via 1,4- and 1,5-hydride
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

DEVELOPMENT OF A ONE-STAGE SYNTHESIS OF 2,6-Di-tert-4-ETHYLBUTYLPHENOL
1731
shifts to form ethyl or hydroxyethyl radical. As judged
from the composition of the reaction products, these
species are also generated in our case and react with
2,6-di-tert-butylphenol to form its various C-alkylation
products.
Siberian Branch, Russian Academy of Sciences
(supervisor A.G. Khmel’nitskii), and a batch of
product I was used for the synthesis of 2,2-
methylenebis(6-tert-butyl-4-ethylphenol (V) via mono-
de-tert-butylation of compound I [20, 21] followed by
reaction of product IV with methylal in presence of an
acidic catalyst. Compound V is used as a stabilizer for
medical rubbers and transparent polymers [7].
Compound I was manufactured at the Pilot Plant
of the Novosibirsk Institute of Organic Chemistry,
OH
OH
OH
_
(CH3O)2CH2
H+
I
Et
Et
Et
IV
V
The above-presented scheme was employed at the
Sterlitamak Petrochemical Plant to manufacture from a
batch of product I the first Russian butch of compound
V, which was successfully tested at the Bobruisk Plant
of General Rubber Goods.
autoclave was cooled and depressurized. The reaction
mixture was extracted with 0.5 l of petroleum ether.
The extract was washed with 5% HCl and water
until neutral and evaporated to obtain 230 g of a solid
material. According to GLC data, it contained 85% of
2,6-di-tert-butyl-4-ethylphenol and 0.5% of starting
compound VI. The reaction product was purified by
vacuum distillation. The fraction with bp 110–120°C
(1–2 mm Hg) was collected. It contained 176 g (76%)
of product I of 97% purity, mp 42–44°C (published
data [11]: mp 44°C).
EXPERIMENTAL
Gas chromatography–mass spectrometry analysis
of phenols was performed on a Hewlett–Packard
instrument comprising an HP 5890 gas chromatograph
(11 series), an HP 5971 mass-selective detector.
Separation was performed on an HP5MS 30 m × 0.25 ×
0.25 μm capillary column, carrier gas helium. The
composition of the reaction mixtures was determined
on a Tsvet gas chromatograph.
Synthesis of 2,6-di-tert-butyl-4-ethylphenol (I)
with paraldehyde. Technical grade 95% 2,6-di-tert-
butylphenol, 103 g, 230 ml of the 95% hydrolytic
ethanol, 28 ml of paraldehyde, and 28 g of potassium
hydroxide were loaded in a 0.5-l steel autoclave, and
the autoclave was heated with rotation to 230°C and
kept at this temperature for 20 min. By the end of this
time (the highest pressure inside the autoclave was
4 MPa), the autoclave was cooled and unloaded.
Excess ethanol was distilled off, and the residue was
neutralized with 10% HCl and extracted with petro-
leum ether. The solvent was evaporated to leave 120 g
of an oil. According to GLC data, it contained 59–63%
of 2,6-di-tert-butyl-4-ethyl-phenol, 18–21% of 3-(3,5-
di-tert-butyl-4-hydroxyphenyl)butan-1-ol (VIII), 11–
13% of 1,3-bis-(3,5-di-tert-butyl-4-hydroxyphenyl)butane
(IX), 1% of the starting 2,6-di-tert-butylphenol, 2% of 2,4-
di-tert-butylphenol, and 1–2% of other components.
The melting points were measured on a Kofler hot
stage. The UV spectra were measured on a Specord
UV-Vis spectrophotometer in ethanol (c 10–4 M). The
1H NMR spectra were taken on a Bruker AV-300
(300.13 MHz) spectrometer for 10% CDCl3 solutions
at 25°C; the chemical shifts were measured against
internal CHCl3 (δ 7.24 ppm). The elemental analyses
were obtained on a Carlo Erba CHN-analyzer (model
1106).
High-pressure synthesis of 2,6-di-tert-butyl-4-
ethylphenol (I). Absolute methanol, 500 ml, 200 g of
98% 2,6-di-tert-butylphenol, 80 g of 85% KOH, 1.0 g
of 4% Pd/C, and 10 g of zinc oxide were loaded in
succession into a 2-l steel autoclave. The autoclave
was heated at 200°C for 15 h. By the end of this time,
the pressure inside the autoclave reached 10 MPa. The
Vacuum distillation gave three fractions.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

1732
KRYSIN, POKROVSKII
First fraction. Yield 75 g, bp 110–120°C (2–
215°C for 7 h in a glass reactor equipped with a stirrer
under an inert gas flow. The liberating water was
distilled off over the course of the reaction. After
neutralization of the reaction mixture 18 g of an oil
was obtained. According to GLC data, it contained
78% of starting phenol VI, 10% of 2,6-di-tert-butyl-4-
(2-hydroxyethyl)phenol (X), and 10% of a high-
boiling bisphenol.
3 mm Hg). According to GLC data, the material
contained 96% of 4-ethyl-2,6-di-tert-butylphenol, mp
43–44°C (from n-heptane). Yield 65%.
Second fraction. Yield 20 g, bp 160–175°C (2–
3 mm Hg). The material was dissolved in 25 ml of
petroleum ether and cooled to 0°C. A precipitate
formed and was filtered off and washed with
petroleum ether to obtain 15 g (11.3%) of 3-(3,5-di-
tert-butyl-4-hydroxyphenyl)butan-1-ol (VIII), mp 74–
76°C (from n-pentane). UV spectrum, λmax, nm (log ε):
Reaction of compound VI with paraldehyde in
the presence of ethylene glycol. Compound VI, 100
g, 200 g of ethylene glycol, 20 g of NaOH, and 15 g of
paraldehyde were loaded into a 0.5 l steel rotating
autoclave and heated at 240°C for 15 h. The autoclave
was cooled, and the reaction mixture was neutralized
and extracted with ether. The extract was evaporated to
give 95 g of an oil containing 65% of compound I,
12% of 2-tert-butyl-4-ethylphenol (IV), 10% of
compound X, and some other products (GLC data).
1
277 (3.20). H NMR spectrum, δ, ppm (J, Hz): 6.82 s
(2H, Harom), 4.52 s (1H, ArOH), 3.48 t (2H, -CH2CH2OH,
J 7), 2.72 m [1H, ArCH(CH3)-], 2.02 s (1H, -CH2OH),
1.72 m (2H, –CH2CH2OH), 1.40 s (18H, 3- and 5-tert-
butyl groups), 1.14 d (3H, CHCH3, J 7). Found, %: C
77.70, H 10.62. MM 278 (isothermic distillation).
C18H30O2. Calculated, C 77.73, H 10.86. MM 278.
Third fraction. Yield 12 g, bp 210–230°C (2–
3 mm Hg). The material was dissolved in 25 ml of
ethanol. After a day a precipitate formed and was
filtered off to obtain 8 g (8%) of 1,3-bis(3,5-di-tert-
butyl-4-hydroxyphenyl)butane (IX), mp 132.0–132.5°C.
Synthesis of 2,6-di-tert-butyl-4-ethylphenol from
2,6-di-tert-butylphenol and triethylene glycol at
atmospheric pressure. 2,6-Di-tert-butylphenol, 6 g,
triethylene glycol, 6 ml, and 2 g of granulated NaOH
were loaded into a three-necked flask equipped with a
stirrer, an air cooler, and a collar trap. The mixture was
heated with stirring under an inert gas flow for 5 h at
220°C, and the liberating water was collected in the
trap. The reaction mixture was poured into water,
acidified with HCl, and extracted with pertoleum ether.
The extract was evaporated to give 6 g of an oil which
was distilled in a vacuum. Two fractions were
collected. The first fraction, 3 g, was an oil, bp 80–
120°C (3–4 mm Hg). According to GC–MS data, it
contained 0.5% of 2-tert-butyl-4-ethylphenol, 1% of
2,6-di-tert-butylphenol, 15.5% of 2,6-di-tert-butyl-4-
methylphenol, 65.5% of 2,6-di-tert-butyl-4-ethyl-
phenol, 12% of 2,6-di-tert-butyl-4-isopropylphenol,
2% of 2,6-di-tert-butyl-4-propylphenol, and 2% of 4-
butyl-2,6-di-tert-butylphenol. The second fraction, 2.5 g,
bp 120–210°C (3-4 mm Hg), contained 0.5% of 4-
methyl-, 6.3% of 4-ethyl-, 2% of 4-propyl-, 4.3% of 4-
n-butyl-, 3.3% of 4-(2-hydroxyethyl)-2,6-di-tert-
butylphenol, 19.5% of 2,6-di-tert-butyl-4-(5-hydroxy-
3-oxapentyl)phenol, 12% of a product with MM 294,
8.3% of a product with MM 338, and 30% of
bisphenols with prevailing 1,2-bis(2,6-di-tert-butyl-4-
hydroxyphenyl)ethane and 1,4-bis(2,6-di-tert-butyl-4-
hydroxyphenyl)butane.
1
UV spectrum, λmax, nm (log ε): 279 (3.53). H NMR
spectrum, δ, ppm (J, Hz): 6.92 s and 6.83 s (2H each,
Harom), 4.84 s and 4.82 s (1H each, OH), 2.54 m [1H,
ArCH(CH3)-], 2.38 t (2H, ArCH2-, J 7), 1.8 m (2H,
-CH2-), 1.40 s and 1.44 s (18H each, two tert-butyl
groups), 1.20 d (3H, -CH2CH3, J 7). Found, %: C
82.54, H 10.41, MM 466. C32H50O2. Calculated, %: C
82.35, H 10.80, MM 466.
Reaction of compound VI with crotonaldehyde.
2,6-Di-tert-butylphenol, 20 g, 7 g of crotonaldehyde,
7 g of 85% KOH, and 40 ml of ethanol were loaded in
a 100 ml steel autoclave and kept at 230°C for 30 min.
After that the reaction mixture was neutralized with
HCl and extracted with tert-butyl methyl ether. The
solvent was evaporated to leave 23.5 g of an oil.
According to GC–MS data, it contained 14% of 2,6-di-
tert-butylphenol, 37% of compound I, 16.5% of
compound VIII, 13% of compound IX, 2.7% of bis
(3,5-di-tert-butyl-4-hydroxyphenyl)methane, 6% of
1,1-bis(3,5-di-tert-butyl-4-hydroxyphenyl)ethane, and
some other components (1% each). Vacuum
distillation gave 10 g of compound I and 3 g of
compound VIII.
Reaction of compound VI with ethylene glycol.
A solution of 20 g of 2.6-di-tert-butylphenol and 5.6 g
of NaOH in 40 ml of ethylene glycol was heated at
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DEVELOPMENT OF A ONE-STAGE SYNTHESIS OF 2,6-Di-tert-4-ETHYLBUTYLPHENOL
1733
12. Yamahara, Takeshi, Takano, Tetsuo, Tamura, Mitsu-
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