Russian Journal of Organic Chemistry, Vol. 40, No. 9, 2004, pp. 1288–1290. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 9, 2004,
pp. 1337–1339.
Original Russian Text Copyright © 2004 by Kuznetsova, Postnova, S. Koshel’, Lebedeva, Yun’kova, G. Koshel’.
Synthesis of Hydroxybiphenyls
E. A. Kuznetsova, M. V. Postnova, S. G. Koshel’, N. V. Lebedeva,
T. A. Yun’kova, and G. N. Koshel’
Yaroslavl State Technical University, Moskovskii pr. 88, Yaroslavl, 150023 Russia
e-mail: koshel@ygtu.yar.ru
Received December 10, 2003
Abstract—Cyclohexylphenols were converted into hydroxybiphenyls via dehydration over large-scale
palladium catalysts. The process involves slow reaction of the substrate with active centers of the catalyst with
subsequent fast product formation and hydrogen desorption.
We previously developed an effective procedure
for the preparation of functionalized biphenyl and
terphenyl derivatives via aromatization of cyclohexyl-
substituted methylbenzenes [1, 2]. These compounds
are used as monomers and intermediate products in the
synthesis of liquid crystalline heat-resistant polymers,
biologically active substances, photographic materials,
etc. [3]. However, there are almost no published data
on analogous transformations of cyclohexyl-substi-
tuted phenols. Therefore, we examined liquid-phase
catalytic dehydrogenation of o-cyclohexylphenol (I),
p-cyclohexylphenol (II), 4-methyl-2-cyclohexylphenol
(III), and 1,4-dihydroxy-2-cyclohexylbenzene (IV)
with a view to obtain the corresponding hydroxybi-
phenyls V–VIII (Scheme 1, Table 1).
with respect to the target product. The nature of the
support is important: In the presence of aluminum
oxide-supported palladium, the conversion of II is only
48%, while charcoal-supported catalysts give rise to
twice as large conversion (90–99%); no reaction occurs
over MA-15. The best results in the dehydrogenation
of compound III were obtained with KPG. In all cases,
decrease in the weight fraction of the catalyst below
5%, as well as increase over 20%, impairs quantitative
parameters of the process (i.e., the conversion and
selectivity).
Thus large-scale palladium catalysts (5% Pd/C,
KPG) in an amount of 20–40 wt % (with respect to the
substrate) can successfully be used in the hydrogena-
tion of cyclohexylphenols without appreciable loss in
activity over 6–8 turnovers. The procedures developed
for regeneration of the catalysts ensured 90–92%
conversion of cyclohexylphenols I–IV and high yields
(60–95%) of target compounds V–VIII.
We studied the effect of catalyst, temperature, and
reaction time on the substrate conversion and reaction
selectivity in the dehydrogenation of p-cyclohexyl-
phenol (II). As catalysts we used a number of indus-
trial palladium compounds, namely Pd/C (5 and 2%),
KPG, MA-15, and IK-71, taking into account their
accessibility and large-scale application in petrochem-
ical syntheses. We have found that palladium-rich
catalysts (such as Pd/C, 5%) ensure 98–99% conver-
sion of the substrate and more than 70% selectivity
The effect of the temperature was examined in
the range from 250 to 300°C (the mixture boiled) over
5% Pd/C. Raising the temperature within the above
interval resulted in increased conversion, but the yield
almost did not change (Fig. 1). The hydrogenation of
compound IV at 250–300°C was characterized by low
Scheme 1.
R3
R3
6
1
5
R2
R2
2
–3H2
4
3
R1
R1
I–IV
V–VIII
I, V, R1 = R2 = H, R3 = OH; II, VI, R1 = R3 = H, R2 = OH; III, VII, R1 = CH3, R2 = H, R3 = OH; IV, VIII, R1 = R3 = OH, R2 = H.
1070-4280/04/4009-1288 © 2004 MAIK “Nauka/Interperiodica”