Oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen in the absence of base catalysts

Article abstract of DOI:10.1023/A:1023309800752

Use of dimethylformamide as solvent and preliminary addition of 3,5,3′,5′-tetra-tert-butyl-4,4′-diphenoquinone allow oxidation of 3,5,3′,5′-tetra-tert-butyl-4,4′ -dihydroxybiphenyl with atmospheric oxygen to be efficiently performed in the absence of base catalysts.

Full text of DOI:10.1023/A:1023309800752

Russian Journal of General Chemistry, Vol. 72, No. 11, 2002, pp. 1805 1807. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 11, 2002,
pp. 1910 1912.
Original Russian Text Copyright
2002 by Bukharov, Fazlieva, Mukmeneva, Akhmadullin, Morozov.
Oxidation of 3,5,3 ,5 -Tetra-tert-butyl-4,4 -dihydroxybiphenyl
with Atmospheric Oxygen in the Absence of Base Catalysts
S. V. Bukharov, L. K. Fazlieva, N. A. Mukmeneva,
R. M. Akhmadullin, and V. I. Morozov
Kazan State Technological University, Kazan, Tatarstan, Russia
Received February 22, 2001
Abstract Use of dimethylformamide as solvent and preliminary addition of 3,5,3 ,5 -tetra-tert-butyl-4,4 -
diphenoquinone allow oxidation of 3,5,3 ,5 -tetra-tert-butyl-4,4 -dihydroxybiphenyl with atmospheric oxygen
to be efficiently performed in the absence of base catalysts.
The use of oxidants capable of regeneration by
oxidation of their reduced forms with atmospheric
oxygen shows promise in industrial oxidations. Such
oxidants can be used repeatedly without accumulation
of their reduced forms, which often form the main
body of production waste.
One of such oxidants is a mild dehydrogenating
agent, 3,5,3 ,5 -tetra-tert-butyl-4,4 -diphenoquinone I
[1]. Its reduced form, 3,5,3 ,5 -tetra-tert-butyl-4,4 -di-
hydroxybiphenyl II, can be readily oxidized with
atmospheric oxygen in the presence of base catalysts
[2] [scheme (1)].
Bu-t
OH + Ar Ar
Bu-t
t-Bu
HO
Bu-t
t-Bu
O
(2)
O
2ArH +
t-Bu
t-Bu
Bu-t
I
II
O2
The use of alkalis as ionizing agents catalyzing
oxidation of phenols has a significant drawback: The
spent alkalis should be neutralized, with the formation
of waste. At the same time, dipolar aprotic solvents
[3] forming hydrogen bonds with sterically hindered
phenols [4] facilitate to some extent their ionization.
cals were reported in [8 11]. Such a transformation in
the system phenol II quinone I was discussed in [12],
and formation of phenoxyl radical III [scheme (2)]
was presumed.
Oxidation of phenol II with atmospheric oxygen in various
solvents (6 h, 90 100 C, cII 0.25 M)
We found that, with dimethylformamide or its mix-
ture with water as solvent, oxidation of II with atmos-
pheric oxygen can be performed at relatively low tem-
peratures in the absence of base catalysts. Since it is
known that quinones can both catalyze [5, 6] and in-
hibit [7] autooxidation of sterically hindered phenols,
we also examined the effect of quinone I on oxidation
of II. We found that addition of I in amounts compar-
able with those of II appreciably accelerates oxidation
of II (see table).
Solvent
cI, Ma Yield of quinone I, %b
DMF
DMF
DMF
Toluene
DMF H2O, 20: 1
DMF H2O, 10: 1
0
18
20
60
15
70
80
0.025
0.25
0.25
0.25
0.25
a
b
Redox reactions between sterically hindered phen-
ols and quinones with the formation of phenoxyl radi-
In the initial mixture. After subtraction of the amount of I
initially added to the solution.
1070-3632/02/7211-1805$27.00 2002 MAIK Nauka/Interperiodica

1806
BUKHAROV et al.
3 Oe
ESR spectrum of phenoxyl radical III (323 K, c = c = 5 10 M).
H
3
I
II
Thus, regeneration of quinone I from its reduced
form II can be efficiently performed with atmospheric
oxygen in DMF in the absence of base catalysts. Pre-
liminary addition of quinone I results in noticeable
acceleration of the reaction owing to the occurrence of
a self-conjugated process.
Bu-t
O
t-Bu
HO
I + II
(2)
Bu-t
t-Bu
III
EXPERIMENTAL
This equilibrium can account for the effect of I on
oxidation of II. Namely, in the first stage, radicals III
are generated by relatively fast dehydrogenation of the
substrate, whereas in the absence of I radicals III are
generated by slow [13] oxidation of un-ionized phenol
II with atmospheric oxygen [scheme (3)]. This is fol-
lower by reactions (4) and (5).
The ESR spectra of III were recorded on a Radio-
pan SE/X-2544 spectrometer. The solution was de-
aerated by threefold freezing pumping thawing.
Oxidation of 3,5,3 ,5 -tetra-tert-butyl-4,4 -dihy-
droxybiphenyl II. A solution of 1 g of phenol II and
1 g of quinone I in 10 ml of dimethylformamide was
placed in a reactor equipped with an efficient reflux
condenser and an adapter for air bubbling. Through
the reaction mixture heated to 90 100 C, air was
II + O2
III + HO2,
I + HOOH
(3)
(4)
III + HO2
1
bubbled for 6 h at a rate of 39 l h . Then the mixture
was cooled to room temperature, and the precipitate of
I was filtered off.
H2O + 1/2O2,
III + O2
I + HO2.
(5)
Oxidation of II in other solvents and without addi-
tion of I was performed similarly.
The fact that, for significant acceleration of the
oxidation of II, the amount of I should be comparable
with that of II, and not catalytic, counts in favor of
such a mechanism. Furthermore, we detected radicals
III in toluene solutions containing equimolar amounts
of II and I by ESR spectroscopy (see figure). The
multiplicity of the signal (1 : 4 : 6 : 4 : 1) and its
parameters (hyperfine coupling constant 1.67 Oe,
g-factor 2.004) coincide with the published data [14].
The low intensity of the signal, decreasing with tem-
perature, shows that the concentration of radicals III
is low and is determined by the equilibrium constant
of reaction (2).
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 11 2002

OXIDATION OF 3,5,3 ,5 -TETRA-tert-BUTYL-4,4 -DIHYDROXYBIPHENYL
1807
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