Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-09-07
2001-12-11
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S383000, C568S388000, C568S391000
Reexamination Certificate
active
06329554
ABSTRACT:
The present invention relates to an improved process for the continuous preparation of unsaturated ketones by reacting &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in a Carroll reaction.
The preparation of unsaturated ketones by reacting &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in the presence of organic aluminum compounds with elimination of the alcohol originating from the acetoacetic ester is, disregarding the improvements according to the invention, already known in its essential features. The non-catalyzed reaction between an unsaturated alcohol and an alkyl acetoacetate was described for the first time by M. F. Carroll [J. Chem. Soc. (London) 1940, pages 704 to 706]. The field of application and mechanism of this reaction were reported one year later by the same author [J. Chem. Soc. (London) 1941, pages 507 to 511].
A process method for the preparation of 6,10,14-trimethyl-5-pentadecen-2-one by transesterification of ethyl acetoacetate with 3,7,11-trimethyl-1-dodecen-3-ol in the presence of aluminum trialkoxides is given in French Patent 1 219 166. According to this process, the reactants and the catalyst are charged together into the reaction still and the reaction is carried out batchwise with the alcohol being released separated off by distillation. In this process, the desired ketone is obtained in 77% yield in a reaction time of about 10 hours.
Both the relatively long reaction times and the inadequate yields are unsatisfactory with this process for an industrial synthesis. The inadequate yields are particularly serious in the preparation of higher ketones, i.e. when use is made of higher alcohols of the formula II, since their preparation becomes increasingly expensive with increasing chain length. If attempts are made to improve the yields by using the cheaper component, here the alkyl acetoacetate, in excess, dehydroacetic acid is readily formed as by-product, which firstly deactivates the catalyst and secondly can only be separated off again with difficulty from the desired product. In addition, the dehydroacetic acid can crystallize out and thus block the outlet lines of the towers used.
A number of other patents are known which describe differing variants of what is termed this Carroll reaction. Thus, U.S. Pat. No. 2,795,617 and DE-AS 1 053 498 and CH-PS 342947 state that “although it is generally neither necessary nor desirable, a solvent can be used to moderate the exothermic reaction course”. According to these patents, the aluminum trialkoxide is added to the acetoacetate of the &agr;,&bgr;-unsaturated alcohol and the mixture is refluxed with vigorous stirring, yields up to 80% being achieved. The corresponding acetoacetate must be prepared in a preceding step. U.S. Pat. No. 2,839,579 and DE-PS 1078112 report that the thermal rearrangement of acetoacetates can be carried out in a solvent. The corresponding acetoacetates are prepared by condensing diketenes with a corresponding unsaturated alcohol in a separate step. DE-PS 1 068 696 also states that the accompanying use of a solvent could be advantageous. In all cases, high-boiling solvents are mentioned which have boiling points far above the reaction temperature.
The yields specified in these patents are unsatisfactory for an industrial application. The accompanying use of a high-boiling solvent is not generally accompanied by significant increases in yields and therefore leads to a decrease in the space-time yields. It is considerably disadvantageous that, to prepare the acetoacetates of the &agr;,&bgr;-unsaturated alcohol, a further process step is necessary, since further costs are associated therewith.
A process for the preparation of 2-methyl-2-hepten-6-one is described in DE-AS 2 652 863. Here, alkyl acetoacetate, 3-methyl-1-buten-3-ol (methylbutenol) and the catalyst are charged into a reaction vessel having a mounted fractionation tower and then a mixture of alkyl acetoacetate and methylbutenol is added. During the reaction, the content of alkyl acetoacetate in the reaction mixture is to be no greater than 15% by weight, in order to avoid side reactions. However, a disadvantage of this process is that simple metering of alkyl acetoacetate into excess methylbutenol is not possible, since the boiling point of methylbutenol is far below the reaction temperature. The use of a high-boiling solvent decreases the space-time yield, however. The yield of 90% is unsatisfactory.
Czech Patent 216 360 describes that the Carroll reaction is carried out in a mixture of unsaturated ketone and methyl acetoacetate or ethyl acetoacetate with addition of an amount of the unsaturated alcohol which is just sufficient for the reaction. In this case, from the reaction mixture there is distilled off the carbon dioxide and a mixture of the unreacted unsaturated alcohol and methanol or ethanol, which mixture is continuously fractionated in a coupled distillation tower. The &agr;,&bgr;-unsaturated alcohol, whose boiling point must be below 180° C., is then recirculated to the reaction. In the case of reaction times of 8 hours, yields of approximately 80% are achieved. This procedure is, according to details in this patent, advantageous, because entrainment of the two lower-boiling components from the reaction mixture by the resultant carbon dioxide cannot be avoided. The coupling described in this patent of a distillation tower to the actual reactor system is not absolutely necessary, since entrainment of the &agr;,&bgr;-unsaturated alcohol by carbon dioxide can be avoided by correct design of the reactor system. For example, according to the process of DE 2 928 944, it is possible to separate off only methanol and carbon dioxide and to keep the &agr;,&bgr;-unsaturated alcohol in the reaction still. Thus, mainly, additional capital and energy costs result from the coupled distillation tower. In addition, the yields and reaction times in this process are unsatisfactory. A further disadvantage of the process is the restriction of the boiling temperature of the &agr;,&bgr;-unsaturated alcohol to below 180° C., because most of the alcohols relevant to vitamin E synthesis boil above 200° C.
In contrast to the abovementioned patents, DE 2 928 944 describes the use of a solvent whose boiling point is between that of the acetoacetic ester used and that of the alcohol being cleaved therefrom. This solvent is termed “an intermediate boiler”. Possible inert intermediate boilers mentioned are appropriately boiling alcohols, esters, ethers, halogenated hydrocarbons and aromatic hydrocarbons, but preferably aliphatic ketones having from 4 to 7 carbons. As a particularly advantageous embodiment, the use of 3-methyl-1-buten-3-ol as reactive intermediate boiler is mentioned, with its reaction with the alkyl acetoacetate to form 2-methyl-2-hepten-6-one as a further product of value occurring as an additional wanted side reaction. Advantages of the use of such an intermediate boiler mentioned are increased product yields (approximately 95% based on the alcohol and approximately 85% based on the acetoacetic ester) and shorter reaction times (approximately from 4 to 5 h) and therefore high space-time yields. For a batchwise reaction procedure, a distillation still having an attached fractionation tower is proposed as a reactor system and for a continuous reaction procedure, a heated vessel cascade is proposed.
However, the use of an intermediate boiler is accompanied not only by advantages but also by the disadvantages below. When an inert intermediate boiler is used, the reactor volume available for the starting materials decreases, i.e. the achievable space-time yield must also be decreased. The use of the reactive intermediate boiler 3-methyl-1-buten-3-ol, in contrast, leads to forced coupled production of 2-methyl-2-hepten-6-one, which can be undesirable. Furthermore, the process is limited to systems in which the &agr;,&bgr;-unsaturated alcohol boils above the alkyl acetoacetate used. The continuous process proposed in the patent requires a reactor cascade and thus high capital costs. A fu
Bockstiegel Bernhard
Etzrodt Heinz
Jaedicke Hagen
Kaibel Gerd
Oost Carsten
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Padmanabhan Sreeni
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