Calcium oxide and strontium oxide as environmentally benign and
highly efficient heterogeneous catalysts for the Tishchenko reaction of
furfural
Tsunetake Seki, Kazumasa Akutsu and Hideshi Hattori*
Center for Advanced Research of Energy Technology, Hokkaido University, Kita-13, Nishi-8, Kita-ku,
Sapporo 060-8628, Japan. E-mail: hattori@carbon.caret.hokudai.ac.jp
Received (in Cambridge, UK) 13th March 2001, Accepted 24th April 2001
First published as an Advance Article on the web 15th May 2001
CaO and SrO exhibit high activities for the challenging
Tishchenko reaction of furfural.
The reaction was carried out in an H-shaped glass batch
reactor. The two branches of the reactor were separated by a
breakable seal. A sample of the catalyst precursor was placed in
one branch, outgassed at an elevated temperature for 2 h, and
sealed. The reactant was stored in the other branch until it was
introduced through the breakable seal by distillation into the
branch containing the catalyst thermostated at liquid nitrogen
temperature. Reaction was initiated by melting the reactant at a
reaction temperature followed by stirring. The product was
The Tishchenko reaction is dimerization of aldehydes to yield
the corresponding esters by the action of aluminium alk-
oxides.1–5 For about a century, a number of catalysts for the
Tishchenko reaction of various types of aldehydes have been
developed to obtain the product esters in high yields. While
many aldehydes have been converted to the Tishchenko dimers
in good yields, few studies have been successfully carried out on
the Tishchenko reaction of furfural. This reaction has been
reported to be difficult when carried out using traditional
aluminium alkoxides, boric acid or tetracarbonylferrate(2II) as
catalysts.2,6,7 Recently, some homogeneous catalysts such as
(C5Me5)2LaCH(SiMe3)2 and La[N(SiMe3)2]3 have been re-
ported to be effective for the Tishchenko reaction of furfural,
though these catalysts require a long reaction time to give the
product ester in a synthetically satisfactory level of yield.8,9 In
addition, removal of those homogeneous catalysts from the
resulting solution causes loss of catalyst and reduction of the
product yields. Moreover, in view of environmental concerns,
avoidance of use of toxic transition metal catalysts in industrial
processes is encouraged. Herein, we report environmentally
benign, highly effective heterogeneous catalysts for the Ti-
shchenko reaction of furfural. The general reaction equation is
shown in Scheme 1.
Alkaline earth oxides, MgO, CaO, SrO and BaO, were
prepared from Mg(OH)2, Ca(OH)2, SrCO3 and BaCO3, re-
spectively, by thermal decomposition at elevated temperatures
in vacuo. Lanthanum oxide was prepared from La(OH)3 by the
same procedure as the alkaline earth oxides, the La(OH)3 being
obtained from an aqueous solution of La(NO3)3 upon hydrolysis
with aqueous ammonia, followed by washing with distilled
water and drying at 373 K. ZrO2 and ZnO were prepared from
Zr(OH)4 and Zn(OH)2, respectively, by thermal decomposition
at elevated temperatures in vacuo. g-Alumina used as a catalyst
and as a KOH/alumina-supported catalyst was supplied from
the Catalysis Society of Japan (JRC-ALO4). Hydrotalcite (Mg/
Al = 2) was synthesized as reported.10 Alumina-supported KF
(KF/alumina) was purchased from Fluka, and its KF content
was determined as 8.2 mmol g21 by XRF. Alumina-supported
KOH catalyst (KOH/alumina) was prepared by impregnation of
g-alumina (JRC-ALO4) with an aqueous solution of KOH,
followed by drying at 373 K in air; the KOH content was 1.2
mmol g21. The pretreatment temperatures and surface areas of
the catalysts examined are listed in Table 1.
1
identified by H NMR and GC–MS analysis. GC analyses to
determine yields of the product ester were carried out using a
column of DB-1 (total length: 60 m; diameter: 0.25 mm).
Table 1 shows the activities of solid base catalysts for the
Tishchenko reaction of furfural when the reaction was carried
out with 100 mg of catalyst using 10 mmol of furfural as
reactant. Among the solid base catalysts examined, only CaO
and SrO gave the product ester in high yields. When the reaction
was carried out at 353 K for 6 h in the presence of 100 mg of
SrO, the product ester was obtained in almost quantitative yield.
To our knowledge, there have been no reports of catalysts
giving the Tishchenko dimer in > 77% yield.8 Even at a lower
reaction temperature of 323 K, the product ester was obtained in
a yield of 70% over SrO. In addition to the high activities, the
catalytic selectivities of CaO and SrO to 2-furylmethyl
2-furancarboxylate were almost 100%. This clearly emphasizes
that CaO and SrO are highly efficient for the Tishchenko
reaction of furfural. Although MgO and BaO were reported to
Table 1 Activities of solid base catalysts for the Tishchenko reaction of
furfurala
Pretreatment
temperature/K m2 g21
Surface area/ Yieldb
Catalyst
(%)
MgO
CaO
CaO
SrO
SrO
SrO
BaO
La2O3
873
873
873
1273
1273
1273
1273
873
267
48
48
12
12
12
2
33
42
2
< 1
61
78c
83
95c
70d
0
0
0
0
ZrO2
ZnO
873
873
g-Alumina
773
673
673
873
173
118
40
160
0
0
0
0
Furfural was purchased from Aldrich, and was purified by
distillation under a reduced pressure.
Hydrotalcite (Mg/Al = 2)
Fluka-KF/alumina
1.2 mmol g21-KOH/alumina
a Catalyst weight, 100 mg; furfural, 10 mmol; reaction temp., 353 K;
reaction time, 4 h. b Yield was determined by the GC analysis of the
resulting solution and was calculated by the equation: yield (%) = {[2 3
(mol% of 2-furylmethyl 2-furancarboxylate)]/[(mol% of furfural) + 2 3
(mol% of 2-furylmethyl 2-furancarboxylate)]} 3 100. c Reaction time, 6 h.
d Reaction temp., 323 K; reaction time, 12 h.
Scheme 1 Tishchenko reaction of furfural.
1000
Chem. Commun., 2001, 1000–1001
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b102389f
Seki
