An efficient, facile, and fast synthesis of 4-alkoxy-4′-hydroxybiphenyls

Article abstract of DOI:10.1081/SCC-120014771

A simple, fast and efficient method of synthesis of 4-alkoxy-4′-hydroxybiphenyls has been described. The reactions of 4,4′-dihydroxybiphenyl with appropriate alkyl halides were carried out over 3 h in DMSO in presence of solid powdered KOH.

Full text of DOI:10.1081/SCC-120014771

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AN EFFICIENT, FACILE, AND FAST SYNTHESIS OF 4-
ALKOXY-4′-HYDROXYBIPHENYLS
Barbara Orzeszko a , Dorota Melon-Ksyta b & Andrzej Orzeszko c
a Department of Chemistry , Technical University , ul. Koszykowa 75, Warsaw, 00-662,
Poland
b Institute of Chemistry , Agricultural University , ul. Rakowiecka 26/30, Warsaw, 02-528,
Poland
c Department of Chemistry , Technical University , ul. Koszykowa 75, Warsaw, 00-662, Poland
Published online: 22 May 2009.
To cite this article: Barbara Orzeszko , Dorota Melon-Ksyta & Andrzej Orzeszko (2002) AN EFFICIENT, FACILE, AND
FAST SYNTHESIS OF 4-ALKOXY-4′-HYDROXYBIPHENYLS, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:22, 3425-3429, DOI: 10.1081/SCC-120014771
To link to this article: http://dx.doi.org/10.1081/SCC-120014771
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 22, pp. 3425–3429, 2002
AN EFFICIENT, FACILE, AND
FAST SYNTHESIS OF
4-ALKOXY-40-HYDROXYBIPHENYLS
Barbara Orzeszko,1 Dorota Melon-Ksyta,2
and Andrzej Orzeszko1,
*
1Department of Chemistry, Technical University,
ul. Koszykowa 75, 00-662 Warsaw, Poland
2Agricultural University, Institute of Chemistry,
ul. Rakowiecka 26/30, 02-528 Warsaw, Poland
ABSTRACT
A simple, fast and efficient method of synthesis of 4-alkoxy-
40-hydroxybiphenyls has been described. The reactions of
4,40-dihydroxybiphenyl with appropriate alkyl halides were
carried out over 3 h in DMSO in presence of solid powdered
KOH.
In the field of liquid crystal (LC) chemistry biphenyl derivatives play a
very important role as mesogenic units for the synthesis of thermotropic
compounds.[1–7] Especially, monoalkoxybiphenols with long methylene
chain are useful for their obtaining. There are many known liquid crystalline
polyethers, polyesters and poly(ester imide)s containing such structure.[4,5]
*Corresponding author. E-mail: orzeszkoa@delta.sggw.waw.pl
3425
DOI: 10.1081/SCC-120014771
Copyright & 2002 by Marcel Dekker, Inc.
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3426
ORZESZKO, MELON-KSYTA, AND ORZESZKO
During the last few years we have been synthesising the new class of
LC—low molecular ester imides carrying biphenyl moieties.[2,3]
The general formula of these compounds is given below:
Usually, 4-alkoxy-40-hydroxybiphenyls are obtained from 4,40-dihy-
droxybiphenyl and proper aliphatic halides or tosyls.[1,2,7] The reactions
occur in boiling methanol in the presence of dissolved KOH for over
16–20h. Under these conditions the practical yields for typical mesogens
(n ¼ 8–11) do not exceed 30–40%. Due to large amounts of by-products,
4,40-biphenyldiethers, produced in such case, separation and purification of
monoalkylated derivatives are difficult and need multiple crystallisation of
crude products. The 4-alkoxy-40-hydroxybiphenyls (for n ¼ 1–18) may be
also prepared according to the five-step complex process described in the
patent literature.[8]
Phase transfer catalysed reactions under basic conditions show higher
selectivity of mono- vs. dialkylation due to the low effective concentration of
the anions in the organic phase.[9,10] This findings prompt us to test the
similar method for synthesis of monoethers from 4,40-dihydroxybiphenyl-
mesogens for liquid crystals preparation. The alkylation reactions were
performed according to the Scheme given below. Powdered KOH makes
the solid phase and DMSO solution of biphenol and proper alkyl halide
composes the liquid phase in the reaction system (Sch. 1).
In this case the catalyst is not necessary, since efficient solvatation of
Kþ cations with DMSO provides lipophilic cations, thus promoting transfer
of the monophenolate anions into solution.[9,12] The similar mechanism is
postulated when poly(ethylene glycol) is used as a solvent for alkylation of
biphenols.[13]
As can be seen, efficiency of majority of the synthesis is higher than in
the conventional method; for the compounds with the longest methylene
Scheme 1.

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4-ALKOXY-40-HYDROXYBIPHENYLS
3427
chain, suitable for liquid crystals preparation, the yields are almost doubled.
Monoalkoxybiphenols with long methylene tail are slightly soluble in
DMSO. It results that products of interest are removed from reaction
medium and, in this way, diethers cannot form which simplifies the purifica-
tion and separation processes and make the reaction yields higher. Also, the
differences in solubility of products and by-products have a bearing on
efficiency of crystallisation.
Great advantage of presented manner is shortening of reaction time, it
is 3 h for alkyl bromides as starting substrates and even up to 2 h for iodides.
All compounds obtained are known, but not all their melting points
are published, so on Fig. 1 we present temperature of the melt measured for
compounds studied. The typical odd–even effect is observed on this plot.
In summary, this methodology consumes much less time and needs
much less investment taking into account that due to high selectivity of the
process, yields of the final products, particularly for the compounds useful
for liquid crystals preparation (n > 7), are much higher than when
traditional method is used.
Figure 1. Odd–even effect of melting points (ꢀC) of 4-alkoxy-40-hydroxybiphenyls.

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3428
ORZESZKO, MELON-KSYTA, AND ORZESZKO
EXPERIMENTAL
General
All chemicals used were commercial products of analytical grade
(Aldrich) and used without further purification. Melting points were taken
in open capillary tubes on a Gallenkamp 5 apparatus and were uncorrected.
The purity of 4-alkoxy-40-hydroxybiphenyls was checked by TLC (Merck
silica gel 60plates) method using chloroform–methanol (v : v ¼ 20: 1) as an
eluent. Though compounds are known their structures were confirmed by
1H NMR spectroscopy (in CDCl3) and by elemental analysis. (Analysis
indicated by symbols was within ꢁ 0.4% of theoretical values).
4-Alkoxy-40-hydroxybiphenyls: A round-bottomed flask equipped with
a magnetic stirrer was charged with 9.3 g (0.05 m) of 4,40-dihydroxybiphenyl
and 50mL of freshly distilled DMSO. Then 8.5 g (0.15 m) of powdered
KOH was added. Next 0.05 m of proper alkyl bromide (for n ¼ 1, 2
and 12 alkyl iodides were used, respectively) was added dropwise at such
rate that the room temperature was kept. The mixture was vigorously stirred
over 3 h and the course of reaction was followed by TLC. The 200 mL of
Table 1. Synthesis of 4-Alkoxy-40-hydroxybiphenyls
Lit. M.P.
(ꢀC)
M.P.
(ꢀC)
n
Rf
Yields (%)
Purification
1
2
3
4
5
6
7
8
9
174[14]
186
174
178
172
167
158
158
153
155
151
153
.165200
151
0.56
0.58
0.58
0.58
0.59
0.59
0.59
0.60
0.60
0.61
0.62
55
54
40
43
45
40
40
45
64
66
68
Flash column chromatography
Flash column chromatography
Double crystallisation
Double crystallisation
Double crystallisation
Double crystallisation
Double crystallisation
Single crystallisation
147[15]
154[8]
Single crystallisation
Single crystallisation
Single crystallisation
[2,8]
10151
11
12
63
0.63
Single crystallisation
80
13
Single crystallisation

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4-ALKOXY-40-HYDROXYBIPHENYLS
3429
cold water and concentrate HCl (up to pH < 7) were added. The precipitate
was filtered off and with care washed with water. For 4-methylenoxy and
4-ethylenoxybiphenols the crude product was purified by flash column chro-
matography (SiO2) using CHCl3 as an eluent. For n ¼ 3–7 the crude product
was crystallised from methanol two times. The other precipitates were
crystallised from methanol only once. The appropriate yields are given in
Table 1.
As an example, for 4-decyloxy-40-hydroxybipenyl the H NMR data
1
are given below: 0.89 (m, 3H), 1.28 (m, 12H), 1.80 (m, 4H), 3.99 (t, 2H,
J ¼ 6.6 Hz), 6.99–7.55 (m, 8H), 8.34 (s, 1H).
The Rf values for all compounds listed in Table 1 were in the range
0.56–0.63.
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Received in the Netherlands November 16, 2001

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