Synthesis of 3,3′,5,5′-Tetra-tert-butyl-4,4′-stilbenequinone and Its Catalytic Activity in the Liquid-Phase Oxidation of Inorganic Sulfides

Article abstract of DOI:10.1134/S1070428018070060

The oxidation of 2,6-di-tert-butyl-4-methylphenol with hydrogen peroxide in the presence of potassium iodide gave 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone which catalyzed liquid-phase oxidation of sodium sulfide with oxygen more efficiently than di

Full text of DOI:10.1134/S1070428018070060

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2018, Vol. 54, No. 7, pp. 1008–1013. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © H.Y. Hoang, R.M. Akhmadullin, F.Yu. Akhmadullina, R.K. Zakirov, A.G. Akhmadullina, A.S. Gazizov, 2018, published in Zhurnal
Organicheskoi Khimii, 2018, Vol. 54, No. 7, pp. 1006–1010.
Synthesis of 3,3′,5,5′-Tetra-tert-butyl-4,4′-stilbenequinone
and Its Catalytic Activity in the Liquid-Phase Oxidation
of Inorganic Sulfides
a
b
a
a
H. Y. Hoang ,* R. M. Akhmadullin , F. Yu. Akhmadullina , R. K. Zakirov ,
b
c
A. G. Akhmadullina , and A. S. Gazizov
a
Kazan National Research Technological University, ul. Karla Marksa 68, Kazan, 420015 Tatarstan, Russia
e-mail: nhochieny@gmail.com
*
b
“AhmadullinS Science and Technologies” Research and Development Center,
Sibirskii trakt 34, bld. 10, Kazan, 420029 Tatarstan, Russia
c
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
Received August 30, 2017
Abstract—The oxidation of 2,6-di-tert-butyl-4-methylphenol with hydrogen peroxide in the presence of potas-
sium iodide gave 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone which catalyzed liquid-phase oxidation of
sodium sulfide with oxygen more efficiently than did 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone.
DOI: 10.1134/S1070428018070060
An important environmental problem in oil proces-
sing and petrochemical industries is efficient neutral-
ization of sulfide-containing alkaline wastes before
their discharge into biological treatment facilities. For
this purpose, various methods of catalytic liquid-phase
oxidation with atmospheric oxygen are widely used in
industry [1–4]. The main disadvantages of the existing
catalysts include low catalytic activity, low selectivity,
and low stability in alkaline medium. In this work we
have synthesized 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbene-
quinone [1, IUPAC name 4,4′-(ethane-1,2-diylidene)-
bis(2,6-di-tert-butylcyclohexa-2,5-dien-1-one)], con-
firmed its structure, and studied its catalytic activity in
Stilbenequinone 1 was synthesized by oxidation of
2,6-di-tert-butyl-4-methylphenol (2) with hydrogen
peroxide in the presence of potassium iodide. The
formation of stilbenequinone 1 is the result of C–C
dimerization of phenoxy radicals generated by oxida-
tion of sterically hindered phenol 2, which was ac-
companied by dehydrogenation [5]. The formation of
phenoxy radicals in the oxidation of 2 was confirmed
by ESR and was thoroughly reviewed in [6–9]. The
primary act of the oxidation is elimination of hydrogen
from the hydroxy group [7, 10, 11] by the action of
iodine atom arising from homolytic dissociation of
molecular iodine (Scheme 1). Phenoxy radical 3 pos-
sesses an alkyl group in the para position and is un-
the liquid-phase oxidation of Na S with oxygen.
2
Scheme 1.
2
KI
+
2H O
I2 + O2
+
2KOH
+
H O
2
2
2
·
2I
I2
·
OH
O
O
t-Bu
Bu-t
t-Bu
Bu-t
t-Bu
Bu-t
·
I
2
+
–
HI
Me
Me
CH2
2
3
4
1
008

SYNTHESIS OF 3,3′,5,5′-TETRA-tert-BUTYL-4,4′-STILBENEQUINONE
1009
Scheme 2.
·
O
Bu-t
t-Bu
t-Bu
Bu-t
4
O
O
Bu-t
t-Bu
Me
5
6
Bu-t
Bu-t
t-Bu
t-Bu
HO
OH
+
O
O
Bu-t
Bu-t
t-Bu
t-Bu
7
1
Scheme 3.
OH
t-Bu
Bu-t
2
H O
2 2
3
7
1
·
CH2
8
stable. It undergoes disproportionation to initial phenol
and methylenequinone 4 [12, 13]. The reaction
mixture acquires lemon yellow tint due to formation of
. Spontaneous dimerization of unstable methylene-
quinone 4 gives bisphenoxy radical 6 which is con-
verted to a mixture of stilbenequinone 1 and dihy-
droxydiphenylethane 7 (Scheme 2) [12–15].
formation of compound 7 which is oxidized with hy-
drogen peroxide to final stilbenequinone 1 (Scheme 3).
2
In the preceding study [22] we presumed that
stilbenequinone acts as redox catalyst in the oxidation
of sulfide sulfur. This process is likely to include two
4
2–
stages: (1) oxidation of S with stilbenequinone 1 and
reduction of the latter to dihydroxydiphenylethene 9
and (2) regeneration of the catalyst by oxidation of 9 in
alkaline medium (Scheme 4). In order to confirm the
proposed mechanism, in this work we studied the
oxidation of sodium sulfide with stilbenequinone 1 at
Apart from disproportionation, initially formed
radical 3 is capable of isomerizing to hydroxybenzyl
radical 8 via hydrogen transfer from the methyl group
to oxygen [16–21]. Dimerization of 8 leads to the
Scheme 4.
H O
2
O2
Second stage
Bu-t
Bu-t
t-Bu
t-Bu
O
O
HO
OH
Bu-t
Bu-t
t-Bu
t-Bu
1
9
First stage
S2
Products
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

1
010
HOANG et al.
–
1
Rate constant,
min
Conversion
of Na S, %
appeared (960 cm ). The melting point of the product
coincided with that reported in the literature for com-
pound 9 (240°C [21]).
–
1
2
0
0
0
.045
.030
.015
100
The catalytic activity of stilbenequinone 1 is deter-
mined by a number of factors, including temperature,
pH, sulfide nature, etc. The rate of oxidation of sulfide
sulfur (Fig. 1) and regeneration of stilbenequinone 1
Fig. 3) increased as the temperature rose; correspond-
ingly, the efficiency of catalytic oxidation increased.
8
6
0
0
(
The catalytic activity of stilbenequinone is also
sensitive to pH of the medium. The data in Table 1
illustrate variation of the conversion of sodium sulfide
pH 13.5) and sodium hydrogen sulfide (pH 9) in the
presence of stilbenequinone 1. It is seen that the rate of
oxidation of Na S is higher than the rate of oxidation
of NaHS. According to published data [8, 23],
hydroxide ions catalyze oxidation of hydroquinone to
40
6
0
75
Temperature, °C
Fig. 1. Temperature dependences of the (1) rate constant of
catalytic oxidation of Na S in the presence of stilbene-
quinone 1 and (2) conversion of Na
90
105
(
2
2
2
S.
–
benzoquinone; therefore, higher concentration of OH
ions favors regeneration of the catalyst in the oxidation
of sulfide sulfur.
1
00
1
2
Addition of an inhibitor could reduce the catalytic
activity or completely deactivate the catalyst. This was
observed in the oxidation of ammonium sulfide in the
presence of stilbenequinone 1. The rate of catalytic
oxidation of (NH ) S was the same as the rate of non-
8
6
4
2
0
0
0
0
0
4
2
catalytic process. Furthermore, addition of aqueous
ammonia to a solution of Na S appreciably reduced the
2
rate of catalytic oxidation of the latter: y = –0.0098x +
0
.0111, where y is the rate of catalytic oxidation of
Na S, and x is the concentration of ammonia.
2
The observed pattern can be rationalized as follows.
Quinones are conjugated α,β-unsaturated dicarbonyl
compounds characterized by large dipole moments,
and excess electron density therein is localized on the
oxygen atom. Therefore, quinones are very sensitive to
electrophiles [24]. Ammonium ions generated by dis-
sociation of ammonium sulfide are strong electrophilic
species capable of blocking active sites of the catalyst
with subsequent complete deactivation.
0
30
60
90
120
τ, min
Fig. 2. Kinetic curves for the oxidation of Na
2
S in the pres-
ence of (1) stilbenequinone 1 and (2) diphenoquinone 10;
Na S] = 0.7 M, [quinone] = 0.05 M, oxygen flow rate
00 L/h, temperature 90°C.
[
3
2
0
0
7
0–110°C in an inert medium (Figs. 1, 2); after
completion of the reaction, the light yellow powder
separated from the reaction mixture was analyzed to
identify compound 9.
Table 1. Oxidation efficiency (%) of inorganic sulfides in
a
the presence of stilbenequinone 1
The rate of oxidation of sodium sulfide with stil-
benequinone 1 in an inert medium increased with rise
in temperature. The IR spectrum of 9 lacked absorp-
tion bands due to conjugated diene fragment (=C–C=,
Oxidation time, min
Sulfide
0
30
60
90
120
–
1
Na
2
S
0.00
0.00
70.89
65.00
96.56
88.00
99.99
96.02
100.00
098.36
1
1
640–1605 cm ) and carbonyl group (C=O,
605 cm ) typical of stilbenequinone 1. Instead, ab-
–
1
NaHS
a
sorption bands belonging to OH groups (3627–3607,
Temperature 90°C, initial sulfide concentration 0.7 M, amount of
stilbenequinone 0.45 g, oxygen flow rate 300 L/h.
–
1
1
420, 1231–1133 cm ), and C=C double bond
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

SYNTHESIS OF 3,3′,5,5′-TETRA-tert-BUTYL-4,4′-STILBENEQUINONE
1011
The structure of quinones largely determines their
ability to participate in chemical reactions. With the
goal of elucidating the relation between the structure of
quinones and their catalytic activity in the oxidation of
sodium sulfide, we compared the activities of stilbene-
quinone 1 and 3,3′,5,5′-tetra-tert-butyl-4,4′-dipheno-
quinone [1,1′-bi(cyclohexa-2,5-dien-1-ylidene)-4,4′-di-
one] 10. It is seen (Fig. 2) that the catalytic activity of
1
0
0
0
0
0
0
.010
.008
.006
.004
.002
.002
1
is higher than the activity of 10. Presumably, this is
2
related to the mechanism of oxidation of sulfide sulfur
in the presence of quinones, which is determined by
both stages (Scheme 4).
t-Bu
Bu-t
6
0
75
90
O
O
Temperature, °C
t-Bu
Bu-t
Fig. 3. Temperature dependences of the accumulation of (1)
stilbenequinone 1 and (2) diphenoquinone 10 in the oxida-
tion of their reduced forms at different temperatures in the
presence of 10% NaOH; initial concentration of the reduced
form 0.013 M, oxygen flow rate 300 L/h, kerosene volume
50 mL, regeneration time 90 min.
1
0
This assumption was confirmed by the results of
oxidation of Na S with quinones in an inert medium
2
(
first stage in Scheme 4). Stilbenequinone 1 is superior
to diphenoquinone 10 in the oxidizing ability (Fig. 4).
Unlike compound 10, the two cyclohexadiene frag-
ment in molecule 1 are separated bu two CH units. The
higher reactivity of stilbenequinone 1 is determined by
higher accessibility of the CH groups to attack of
nucleophile [25, 26].
1
00
80
1
6
4
2
0
0
0
2
The second stage in the catalytic oxidation of
sulfide sulfur in the presence of quinones (Scheme 4)
is the oxidation of 9 or 3,3′,5,5′-tetra-tert-butyl-1,1′-bi-
phenyl-4,4′-diol (11, reduced form of 10). Here, the
polarity of the hydroxy group is important. Change of
the O–H bond polarity in going from one hydro-
quinone to another determines the difference in the
energies of dissociation of that bond and hence their
different oxidizabilities [6].
7
5
90
105
Temperature, °C
Fig. 4. Temperature dependences of the conversion of Na
in the oxidation with (1) stilbenequinone 1 and (2) dipheno-
quinone 10; [Na S] = 0.09 M, [quinone] = 0.14 M, 90 min.
2
S
Unlike compound 11, the conjugated bond system
in molecule 9 includes the CH=CH double bond in
addition to the aromatic rings. Therefore, the electro-
negativity of the oxygen atom in 9 is higher, and the
Coulomb integral of the oxygen δ-orbitals is more
negative. Such change of the δ-electron structure of the
OH bond increases its polarity and reduces the energy
of dissociation, so that compound 9 should be oxidized
more readily than 11. This was confirmed experi-
mentally (Fig. 4).
2
0
0
EXPERIMENTAL
The IR spectra were recorded on a Perkin Elmer
Spectrum Two spectrometer equipped with an ATR
1
accessory. The H NMR spectra were recorded on
a Bruker Avance-600 spectrometer using DMSO-d as
6
solvent and reference (δ 2.50 ppm). The elemental
analysis of stilbenequinone was obtained with
an AURIGA Cross Beam workstation equipped with
an IncaX-MAX energy dispersive spectrometer (reso-
Thus, we have shown that the rate of regeneration
of stilbenequinone 1 is higher than the rate of regen-
eration of diphenoquinone 10.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 7 2018

1
012
HOANG et al.
lution 127 eV). The melting points were measured on
a Buchi M-560 melting point apparatus.
sium iodide, sodium sulfide, toluene, and aqueous
ammonia of analytical grade, 3,3′,5,5′-tetra-tert-butyl-
4
,4′-diphenoquinone, 3,3′,5,5′-tetra-tert-butyl-1,1′-bi-
The concentration of quinone was determined by
photocolorimetry. A 0.5-cm sample of kerosene frac-
3
phenyl-4,4′-diol, and straight kerosene fraction of pure
grade, and oxygen and argon of ultrapure grade (from
gas cylinders) were used. Solutions of sodium hydro-
gen sulfide and ammonium sulfide were prepared
according to the procedures described in [27, 28].
tion was withdrawn from a three-necked cylindrical
reactor without preliminary cooling. The sample was
3
diluted with toluene to a volume of 50 cm (by a factor
of 100) in a volumetric flask. The kerosene fraction
containing dissolved quinone endows toluene solution
with a bright yellow color which becomes more
intense as the concentration of quinone increases. The
absorbance at λ 500 nm was measured with an Ekros
PE5300V spectrophotometer using a 10-cm path-
length cell, and the concentration of quinone was cal-
culated using a calibration curve.
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1013
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