Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1998-06-09
1999-11-02
Truong, Duc
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
528220, 528230, 502 64, 502 60, 502 78, C08G 600, C08G 1004
Patent
active
059772905
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the condensation of aldehydes or ketones (carbonyl component) with C--H-acidic compounds (methylene component) in the presence of at least one molecular sieve in the form of a zeolite or sheet silicate and one alkali carbonate, alkaline earth carbonate or ammonium carbonate as catalyst system.
The Knoevenagel reaction is a special case of the aldol condensation where methylene components of particularly high C--H acidity are used. The reaction belongs to the standard methods of organic chemistry and is described, inter alia, in Principles of Organic Synthesis, R. O. C. Norman, Science Paperbacks 1970, pages 233-234. Basic catalysts are required for this reaction. Suitable catalysts are in particular nitrogen bases, especially organic bases such as piperidine, ammonium acetate, .beta.-alanine in glacial acetic acid, or also alcoholates. This reaction procedure has the disadvantage of requiring the removal of the resulting water of reaction, which can be achieved e.g. by addition of toluene with azeotropic distillation. However, this requires temperatures of above 100.degree. C. which is a big disadvantage in the case of temperature-sensitive compounds. During the processing of the product the base must be removed e.g. by distillation, which cannot always be achieved quantitatively and which can easily result in discoloured products.
The use of NaOH or Na.sub.2 CO.sub.3 has also been known for a long time and is described, inter alia, by Bertini in Gazz. Chim. Ital. 31 I (1901), 266. One of its disadvantages is that it also requires removal of the water and that ester groups which may be present under these conditions can saponify again.
In recent times many attempts have been made to provide heterogeneous basic catalysts which can be easily removed after the reaction. The preparation of a catalyst by basic modification of hydrotalcite is described, inter alia, by A. Corma et al. in J. Catal. 134 (1992), 58-65. This preparation is extremely time-consuming. The resulting gel is dried repeatedly for 12 or 18 hours and calcinated. A Knoevena-gel reaction at 130.degree. C. is described using these catalysts. Another proposal, also by A. Corma et al. in J. Catal. 130 (1991), 130-137, is based on the partial exchange of the Mg.sup.2+ ions in sepiolites, thereby increasing the basicity, and carrying out the reaction at lower temperatures. In this case, too, the catalyst needs to be prepared prior to use by a time-consuming ion exchange process.
B. M. Choudary et al. in Synthetic Comm., 21 (10 &11), 1163-1166 (1991) describe silylpropylethylenediamine-modified montmorillonites as solid basic catalysts for the Knoevenagel reaction. Although this catalyst can be easily removed and reused, its activity cannot fully satisfy. The preparation of this catalyst also requires a time-consuming reaction of 3-tri-ethoxysilylpropylethylenediamine with montmorillonite.
Surprisingly, it has now been found that it is possible to forego an elaborate catalyst preparation if the catalyst system used is a molecular sieve in the form of a zeolite or sheet silicate, additionally using alkali carbonate, alkaline earth carbonate or ammonium carbonate. This constitutes a catalyst system which is extremely easily accessible and which has excellent activity. Depending on the reactivity of the methylene component and on the melting point of both components, the aldol reactions can be carried out e.g. at room temperature. The reaction times are short, and the yield is high and often virtually quantitative.
It is not necessary to remove the water and no solvents need to be added for the azeotropic distillation. The product quality is excellent since no impurities can result from organic bases. The easy removal of the catalyst by filtration simplifies the working up of the product substantially.
The catalyst can be used again immediately after drying without any substantial loss in activity being observed even if this cycle is carried out repeatedly.
The invention relates to a process for the basically catal
REFERENCES:
M. A. Aramendia et al., Chemistry Letters No. 4, 1995, pp. 279-280.
B. Danieli et al., HelveticaChimica Acta, vol. 76, No. 8, 1993, pp. 2981-2991.
A. Corma, et al., Journal of Catalysis 134, 58-62 (1992).
A. Corma, et al., Journal of Catalysis 130, 130-137 (1991).
Y. V. Subba Rao et al., Synthetic Communication, 21 (10 & 11), 1163-1166 (1991).
Dohmann George R.
Kalinchak Stephen G.
Novartis AG
Truong Duc
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