Mg–Al LAYERED DOUBLE HYDROXIDES
1019
layered double hydroxides as heterogeneous catalysts for
condensation of cyclohexanone with acetonitrile to give
N-cyclohexylideneacetonitrile were studied.
and can be represented in the most general form by the
scheme:
(
2) It was shown that the sample with the Mg/Al
atomic ratio of 3 demonstrates the highest catalytic
efficiency, which is presumably due to the optimal amount
of acid-base centers on its surface.
REFERENCES
1
. Cavani, F., Trifiro, F., and Vaccari, A., Catal. Today, 1991,
vol. 11, pp. 173–301.
When a synthesis is performed, there occurs competi-
tion of at least two reactions: (a) Knoevenagel condensation
of I with II to the target nitrile III and (b) aldol condensa-
tion of I to dimer IV. Under the action of the basic centers
of Mg–Al LDHs, the methylene-active component can be
formed by abstraction of a proton from both I and II. This
is indirectly indicated by data on the CH-acidity determined
2
3
. Vaccari, A., Catal. Today, 1998, vol. 41, pp. 53–71.
. Monzon, A., Romeo, E., Royo, C., et al., Appl. Catal. A:
General, 1999, vol. 185, pp. 53–63.
4
5
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.Auer, S.M., Gredig, S.V., Koppel, R., and Baiker,A., J. Mol.
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. Faust, G.T. and Millot, G., The Am. Min., 1959, vol. 44,
no. 2, pp. 342–370.
in water [29]: the pK values for cyclohexanone (taken as
a
. Velu, S. and Swamy, C.S., Catal. Lett., 1996, vol. 40,
for acetone) and acetonitrile are 20.0 an 25.0, respectively.
The formation of diacetonitrile by self-condensation of II
pp. 265–272.
. DiBiase, S.A., Lipisko, B.A., Haag, A., et al., J. Org.
Chem., 1979, vol. 44, no. 25, pp. 4640–4649.
(Thorp reaction) was not confirmed by a chromatographic
analysis (identification with a reference sample).
. Prihod’ko, R., Sychev, M., Erdmann, N., et al., Appl. Clay
Sci., 2001, vol. 18, pp. 103–110.
Table 3 lists the results that were obtained under
identical training conditions and enable comparison of
the catalytic properties of the Mg–Al LDH under study
in the vapor-phase synthesis of the unsaturated nitrile
III. It should be recognized that, among the hydrotalcite-
like materials we studied, the best in conversion of
cyclohexanone and selectivity for the target nitrile is the
sample with Mg/Al = 3.Brucite is markedly inferior in
catalytic activity to Mg–Al LDH.
9. Di Cosimo, J.I., Diez, V.K., Xu, M., et al., J. Catal., 1998,
vol. 178, pp. 499–510.
1
0. Kratky, O., Pilz, I., and Schmitz, P.I., J. Colloid Interface
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1
1. Yun, S.K., Constantino, V.R.L., and Pinnavaia, T.J.,
Microp. Mater., 1995, vol. 4, pp. 21–29.
1
1
1
1
2. Bassett, D.W. and Habgood, H.W., J. Phys. Chem., 1960,
Analysis of the data in Tables 2 and 3 suggests that
Mg–Al LDHs with the optimal number of acid-base centers
is necessary for successfully carrying out the reaction of
cyclohexanone condensation with acetonitrile. Presumably,
it is also necessary to take into account the possibility of
a structural transformation of LDHs in the course of syn-
thesis accompanied by release of the reaction water. The
reconstruction of calcined LDHs by their hydration is a
complex process yielding materials with structural features
markedly different from those of the starting LDHs. The
maximum number of centers of this kind is contained in
LDH samples with the Mg/Al ratio of 3.
vol. 64, pp. 769–773.
3. DiBiase, S.A., Beadle, J.R., and Gokel, G.W., Org. Synth.,
1
984, vol. 62, p. 179.
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J. Appl. Chem., 2003, vol. 76, no. 12, pp. 2004–2007.
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Chem., 1995, vol. 5, pp. 323–329.
16. Narayanan, S. and Krishna, K., Appl. Catal. A, 1998,
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1
1
7. Aramendı ́a , M.A., Avilis, Y., Benı ́t ez, J.A., et al., Micro.
Meso. Mater., 1999, vol. 29, no. 3, pp. 319–328.
8. DelArco, M., Rivers, V., and Trujilano, R., Stud. Surf. Sci.
Catal., 1994, vol. 87, pp. 507–515.
CONCLUSIONS
(
1) Specific structural features, nature of active
19. Kooli, F., Depege, C., Ennaqadi, A., et al., Clays Clay
Miner., 1997, vol. 45, no. 1, pp. 92–98.
centers, and possibility of using synthesized Mg–Al
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