828
Chemistry Letters 2000
One-Step Synthesis of Terephthalic Acid from Benzene in Water Using Cyclodextrin as Catalyst
Yukihide Shiraishi, Shigetoshi Tashiro, and Naoki Toshima*
Department of Materials Science and Engineering, Science University of Tokyo in Yamaguchi, Onoda, Yamaguchi 756-0884
(Received April 28, 2000; CL-000410)
The one-pot synthesis of terephthalic acid from benzene
has been achieved by treatment with tetrachloromethane, cop-
per powder, and an aqueous sodium hydroxide solution using
cyclodextrin as a catalyst at 30 ˚C under nitrogen in 46 mol%
yield with 100% selectivity.
chloromethane was added and the mixtures were stirred for 7 h
at 30 ˚C under nitrogen. After the reaction, the excess tetra-
chloromethane was removed by evaporation under reduced
pressure. The reaction mixtures were neutralized with
hydrochloric acid. The product analysis on the reaction mix-
tures was made by high performance liquid chromatography
(HPLC).9 The main product was isolated and confirmed to be
terephthalic acid by comparison with the authentic sample
(HPLC, IR, MS, 1H-NMR). The yield and selectivity of tereph-
thalic acid were calculated on the basis of the starting amount
of benzene, and the total amount of carboxylated products,
respectively.
Table 1 exhibits a catalytic effect of CyDs for carboxyla-
tion of benzene. The yield of terephthalic acid is 26 mol% in
the presence of β-CyD, where the yields of both phthalic acid
(ortho-carboxylated product) and isophthalic acid (meta-car-
boxylated product) are 0 mol%. In other words, the selectivity
for the production of terephthalic acid among carboxylated
products is 100%. In the absence of β-CyD, however, the reac-
tion does not proceed at all. The solubility of benzene in water
is poor as described above. Therefore, benzene itself may be
little concerned with the reaction in an aqueous alkaline solu-
tion. In the presence of β-CyD, benzene can be solubilized in
an aqueous alkaline solution by inclusion in the cavity of the β-
CyD and concerned with the reaction.
When α-CyD or γ-CyD was used instead of β-CyD, the
carboxylation did not occur at all. This may be attributed to the
much smaller formation constants of benzene inclusion com-
plexes of α- and γ-CyDs than that of β-CyD.10 In addition the
poor solubility of tetrachloromethane in water might cause the
present difference in the reactivity. The formation constant of
the inclusion complex of tetrachloromethane with α-CyD (42
17 dm3 mol–1) is smaller than that with β-CyD (150 35 dm3
mol–1), determined by the volatilization rate.11 The association
between γ-CyD and tetrachloromethane is not observed at all.11
Thus, the carboxylation of benzene with tetrachloromethane by
using α-CyD or γ-CyD hardly proceeded.
In recent years, there has been a great interest in the syn-
thesis of aromatic dicarboxylic acids as versatile raw materials
for high-performance polymers and liquid crystalline com-
pounds.1 Terephthalic acid is an essential monomer for
poly(ethylene terephthalate), poly(p-phenylene terephthal-
amide), poly[(terephthalic acid)-alt-(p-phenylene diamine; 3,4´-
diaminodiphenylether)], etc., and is produced in industries by
liquid-phase oxidation of p-xylene,2 or by disproportionation of
potassium benzoate.3 The conventional preparation process of
terephthalic acid is composed of many steps: separation of
xylene from petroleum, isomerization of xylene, separation of
p-xylene, and oxidation of p-xylene. In addition purification is
required in each step.
One-pot synthesis, in which a target compound is synthe-
sized by successive addition of reagents to a reaction vessel
without separation or purification of intermediates in each step,
is ideal for organic synthesis. This method requires high selec-
tivity and high yield in each reaction step, since otherwise sepa-
ration of the desired compound from various by-products in the
final reaction mixtures should be difficult. Komiyama and
Hirai reported one-pot preparation of 4-hydroxychalcone from
phenol by the use of cyclodextrin (CyD).4
α-, β- and γ-CyD, cyclic oligosaccharides consisting of
6, 7 and 8 glucose units linked by α (1–4) bonds, have
hydrophobic cavities which can solubilize hydrophobic organic
compounds into water by inclusion.5–7 We have reported selec-
tive synthesis of terephthalic acid from benzoic acid in an aque-
ous sodium hydroxide solution.8 In this reaction benzoic acid
can be easily soluble in an aqueous alkaline solution as benzoate,
which can be concerned with the reaction. On the other hand,
benzene will be little concerned with the reaction in an alkaline
solution because of the low solubility (0.7 g dm–3 at 22 ˚C) with-
out CyD. Here we report for the first time a selective one-step
synthesis of terephthalic acid in water using CyD (Scheme 1).
To the best of our knowledge, there is no report on the introduc-
tion of two carboxyl groups into benzene by one-step reaction.
Benzene (2.8 mmol), copper powder (0.8 mmol), and CyD
(2.0 mmol) were mixed in 30 cm3 of 30 wt% aqueous solution
of sodium hydroxide. To the mixtures 27 mmol of tetra-
Figure 1 shows the dependence of the yield of terephthalic
acid on the initial mole ratio of β-CyD to benzene. The yield
increases with increasing amounts of β-CyD, and has the maxi-
Copyright © 2000 The Chemical Society of Japan
Shiraishi, Yukihide
