Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-04-15
2004-04-20
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S434000
Reexamination Certificate
active
06723883
ABSTRACT:
The present invention relates to a continuous process for the preparation of cinnamaldehyde or cinnamaldehyde derivatives by continuous reaction of benzaldehyde derivatives with alkanals in the presence of bases and optionally subsequent continuous hydrogenation in a circulation reactor in the presence of a suspension catalyst and hydrogen to give dihydrocinnamaldehyde derivatives.
Cinnamaldehyde derivatives, such as, for example, 2-pentyl-3-phenyl-2-propenal or 2-hexyl-3-phenyl-2-propenal, cinnamaldehyde itself, or the corresponding dihydro compounds, for example cyclamenaldehyde (2-methyl-3-(p-isopropylphenyl)-propanal) or lysmeral (2-methyl-3-(p-tert-butylphenyl)propanal) are used as intermediates for fragrances, or as fragrances themselves and, moreover, are used as starting materials for the synthesis of active ingredients in the pharmaceuticals and crop protection sector (cf. GB 1 086 447).
It is known that cinnamaldehyde derivatives can be prepared by reacting benzaldehyde derivatives with alkanals in the presence of basic catalysts, i.e. by aldol condensation (cf. Houben-Weyl, “Methoden der organischen Chemie” [Methods in Organic Chemistry] volume 7/1, p. 76 et seq. (1954), and U.S. Pat. No. 2,976,321). According to the known prior art, the reactants are reacted in batchwise or semicontinuous processes.
For example, U.S. Pat. No. 2,529,186 from 1947 describes a semicontinuous process for the preparation of cinnamaldehyde by reacting benzaldehyde with ethanal, in which the benzaldehyde, in the presence of, for example, aqueous alkali metal hydroxide, is initially introduced, and the ethanal is slowly added thereto in a slight excess. Here, the alkali metal hydroxide should be used in an amount of from 2.5 to 6.5 parts by weight per part by weight of aldehyde. As is shown by examples, only yields of from 75 to 85% are obtained for this process. Disadvantages of this process are the yields, which are unsatisfactory for use on an industrial scale, and also the requisite large amount of alkali metal hydroxide which, apart from the necessary costs therefor, signifies severe contamination of waste water, and the relatively long reaction time which means that the reaction vessels must be correspondingly large.
D.P. B 9977 from 1950 describes a semicontinuous process for the preparation of cinnamaldehyde by the condensation of benzaldehyde and acetaldehyde by means of alkali in an aqueous medium. In the process, the benzaldehyde should be used in excess and the acetaldehyde should only be added gradually. In addition, per part by weight of benzaldehyde, about 2 to 3 parts by weight of water should be used. Particularly because of the large amount of water which is used, and which has to be purified and disposed of, the process is not economical.
EP 392 579 describes a process for the preparation of &agr;-substituted cinnamaldehydes by reacting benzaldehyde with alkanals. The catalyst used is alkali metal hydroxide, and the solvent used is glycol. Other ancillaries which are used are nonpolar hydrocarbons, such as hexane. It is stated therein (cf. page 2, lines 10-16 and 38-39) that, due to the formation of secondary components which are difficult to remove, the use of reactors through which there is continuous flow is unfavorable. This prejudice has been refuted by our work. In fact, we have surprisingly found that by connecting a plurality of reactors one behind the other and feeding the alkanal into more than one of the reactors, it is possible to prepare, in a relatively simple manner, a cinnamaldehyde derivative whose content of by-products is low, in very good yields.
As well as a semicontinuous procedure, EP 392 579 describes how the process is carried out in a stirred tank reactor through which there is continuous flow and which has a residence time of 9.5 hours. A multistage reactor cascade is not mentioned. Disadvantages of the process described are the long residence time required and the large and expensive reaction vessels which are required as a result. In addition, since the reaction takes place in a system of two liquid, immiscible phases, scale-up from laboratory experiments to an industrial plant is very difficult. Furthermore, regulation of the stirred tank reactor through which there is continuous flow and the exact observance of the correct phase ratio is extremely difficult (computerized control is necessary).
A further disadvantage is the complicated work-up of the reaction mixture, in which the reaction mixture comprising glycol must be extracted repeatedly with hexane. Because of the disadvantages described, the process cannot be carried out economically.
In order to overcome the disadvantages of the process according to EP 392 579, European patent specification EP 771 780 proposes a process for the preparation of &agr;-alkylcinnamaldehyde by reacting benzaldehyde with alkanal with pyrrolidine as basic catalyst. As additional cocatalysts, it recommends acids, such as sulfuric acid or hydrochloric acid. For work-up, the crude reaction product should first be washed with an aqueous sodium hydroxide solution and then neutralized with acid.
A disadvantage of this process is the use of an expensive catalyst, which is added in large amounts and which cannot be recycled. This signifies increased costs for feed materials and disposal. A further disadvantage is the expensive, complicated work-up, in which the reaction product has to be washed with large amounts of hydroxide solution. This operation in turn leads to high feed material costs and disposal costs. Since acids are used as cocatalyts, the apparatuses have to be made from corrosion-resistant materials. The abovementioned disadvantages render the process uneconomical.
The known processes for the preparation of cinnamaldehyde derivatives of the formula II are batchwise or semicontinuous processes which have the disadvantages which stem from this procedure: long reaction times, large reaction apparatuses and batchwise operation which, in the case of use on an industrial scale, results in increased expenditure in terms of personnel and maintenance staff. For processes where the possibility of a continuous operation is mentioned, there is no information on carrying out the reaction, or only individual stirred tank reactors through which there is continuous flow are mentioned, which are unsuitable for the economic preparation of cinnamaldehyde derivatives on an industrial scale for the reasons given above.
The hydrogenation of cinnamaldehyde and derivatives thereof has likewise already been extensively documented in the literature. A review of this is given in the Houben-weyl work, Methoden der organischen Chemie [Methods of Organic Chemistry], 4th edition, 1979, volume 4/1c, page 161 f. and the same work volume 7/1, page 388 ff.
It is known from U.S. Pat. No. 3,280,192 that cinnamaldehyde derivatives, such as dehydrolysmeral (2-methy-3-(p-tert-butylphenyl)propenal) can be transformed to give the dihydro compounds by reaction over palladium-containing catalysts in the presence of hydrogen. The authors give the addition of an aqueous phase which is immiscible with the feed material and has a pH between 8 and 13 as being particularly advantageous for the selectivity of the hydrogenation. Good yields and selectivities are achieved in this batch process.
An improvement in the space-time yield is achieved in DE 26 136 45 if the hydrogenation is carried out at higher temperatures of from 100 to 160° C. compared with the above US application, with repeated exchange of the hydrogen atmosphere.
JP 72 50096 likewise recommends the addition of basic compounds such as K
2
CO
3
in a batch process for the hydrogenation of cinnamaldehyde derivatives over palladium catalysts. In this process, the starting material is used without solvent in a high purity of >97%.
EP 058 326 also describes a batch process for the reaction of a cinnamaldehyde derivative prepared beforehand in situ over palladium catalysts in the presence of amines.
A continuous reaction procedure for the hydrogenation is described in U.
Benfer Regina
Göbbel Hans-Georg
Haake Mathias
Kramer Andreas
Schossig Jürgen
BASF - Aktiengesellschaft
Keil & Weinkauf
Kumar Shailendra
Witherspoon Sikarl A.
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