242
B. Veldurthy et al. / Journal of Catalysis 229 (2005) 237–242
lysts used (after four cycles) revealed no loss of Cs, K, or F,
and thus that the lower activity cannot be due to leaching.
With MgLa mixed oxides, the situation is similar, with little
change of activity after four recycles and a clear loss of ac-
tivity after the fifth recycling only. The longer reaction time
can be attributed to two main factors: some loss of catalyst
remaining in suspension in the reaction mixture and inhibi-
tion by traces of water present in each new feed of reactants.
4. Conclusions
In conclusion, a quantitative relation does exist between
the catalytic activity and the basic properties of the catalysts
employed for the transesterification reaction. MgLa mixed
oxides and CsF/α-Al2O3 were the best catalysts and could
be recycled a few times. The high activity observed with
CsF/α-Al2O3 may be due to the higher nucleophilicity of
the alcoholate formed as an intermediate, leading to a faster
rate.
3
.4. Inhibition effect of water on reaction kinetics
This hypothesis was checked by measurement of the ki-
netics in the presence of water (added initially at the level
−1
of 1 mmolmmol of alcohol). It was observed that water
inhibits but does not completely suppress the reaction: the
rate is very low for the reaction catalysed by CsF/α-Al2O3
Acknowledgments
(
Fig. 3), showing kinetic inhibition, but the yield after 1 h
Thanks are due to the technical services of IRC, espe-
cially for chemical and GC-MS analysis.
reached 57% with high selectivity. Up to this time, the ki-
netics was still first order and corresponded to a much lower
rate constant. After this time, the ether corresponding to the
alcohol, not detected in the absence of water, appeared as a
by-product in large quantities (about 30%). With the MgLa
mixed oxides, the same phenomenon was observed, with a
yield reaching 52% after 2 h, followed by a slow rate with
the appearance of ether as a by-product (20%). The forma-
tion of ether by reaction of diethylcarbonate with a diol,
References
[1] L. Krumenacker, S. Ratton, Actualite Chimique (1986) 29.
[2] W.F. Holderich, Stud. Surf. Sci. Catal. 75 (1993) 127.
[3] J.M. Thomas, R. Raja, G. Sankar, B.F. Johnson, D.W. Lewis, Chem.
Eur. J. 7 (2001) 2973.
[4] K. Tanabe, W.F. Holderich, Appl. Catal. A 181 (1999) 399.
[5] J.P. Parrish, R.N. Salvatore, K.W. Jung, Tetrahedron 56 (2000) 8207.
[6] S. Gryglewicz, F.A. Oko, G. Gryglewicz, Ind. Eng. Chem. Res. 42
(2003) 5007.
1
,4:3,6-dianhydrosorbitol, has been reported to be catalysed
at 523 K by sodium methoxide or organic bases such as
diazobicyclo[2,2,2]octane (DABCO) [26]. It was also ob-
served earlier that in the absence of water in the reaction
medium, esters were readily hydrolysed on hydrated hydro-
talcites at about 323 K [27], a phenomenon not observed on
dehydrated solids and therefore attributed to the presence of
hydroxyls at the surface. Indeed, CsF/α-Al2O3 is dehydrated
in vacuum at about 400 K (Fig. 2) and readily rehydrated in
air, and faster in water. A simple mechanism for the forma-
tion of ether by a base-catalysed reaction could be based on
the following scheme, involving the hydrolysis of DEC, fol-
lowed by decarboxylation of the anion to an alkoxide, which
can react on the alcoholic substrate to form an ether:
[7] J.L.R. Williams, K.R. Dunham, US 2843567, 1958.
[
[
8] F. Mizia, F. Rivetti, US 20020056468, 2002.
9] Y. Ono, Appl. Catal. A: General 155 (1997) 133.
[10] D. Delledonne, F. Rivetti, U. Romano, Appl. Catal. A: General 221
(2001) 241.
[
[
11] P. Tundo, M. Selva, Acc. Chem. Res. 35 (2002) 706.
12] Y. Proux, M. Pellegrina, Fr 2608812, 1988.
[13] B. Veldurthy, F. Figueras, Chem. Commun. 10 (2004) 734.
[14] J.-M. Clacens, D. Genuit, B. Veldurthy, G. Bergeret, L. Delmotte,
A. Garcia-Ruiz, F. Figueras, Applied Catalysis, B: Environmental 53
(2004) 95.
[15] B.M. Choudary, M. Lakshmi Kantam, V. Neeraja, K. Koteswara Rao,
F. Figueras, L. Delmotte, Green Chem. 3 (2001) 257.
[
16] F. Figueras, B. M. Choudary, M. Lakshmi Kantam, V. Neeraja, K. Ko-
teswara Rao, WO 0166246, 2001.
−
−
EtO–CO–OEt + OH → EtOH + EtOCOO ,
−
−
EtOCOO → CO2 + EtO ,
EtO + ROH → EtOR + OH .
[17] J. Palomeque, J.-M. Clacens, F. Figueras, J. Catal. 211 (2002) 103.
[
[
[
18] F. Figueras, H. Kochkar, L.K. Mannepalli, Fr 2834228, 2003.
19] J. Palomeque, J. Lopez, F. Figueras, J. Catal. 211 (2002) 150.
20] J.-M. Clacens, D. Genuit, L. Delmotte, A. Garcia-Ruiz, G. Bergeret,
R. Montiel, J. Lopez, F. Figueras, J. Catal. 221 (2004) 483.
21] P.C. Gravelle, Adv. Catal. 22 (1972) 191.
−
−
Scheme 2. Possible mechanism for ether formation.
[
[
[
[
22] A. Auroux, A. Gervasini, J. Phys. Chem. 94 (1990) 6371.
23] F. Chu, E.E. Dueno, K.W. Jung, Tetrahedron Lett. 40 (1999) 1847.
24] S.K. Kang, J.H. Jeon, K.S. Nam, C.H. Park, H.W. Lee, Synth. Com-
mun. 24 (1994) 305.
The continuous decrease in activity for transesterification
upon recycling can then be accounted for by, on one hand,
the kinetic effect of the water contained in the reactants, and,
on the other hand, by the development of the side reaction of
hydrolysis of DEC and etherification of the alcoholic sub-
strate.
[25] R.M. Burk, M.B. Roof, Tetrahedron Lett. 34 (1993) 395.
[26] J.N. Greenshields, Application: US 4770871, 1988.
[27] J. Lopez, F. Figueras, unpublished results.