Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-11-15
2001-10-09
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S383000, C568S388000, C568S391000
Reexamination Certificate
active
06300524
ABSTRACT:
The present invention relates to an improved process for preparing higher unsaturated ketones by reacting the corresponding &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in a Carroll reaction.
Apart from the improvements according to the invention, this reaction is already known in its essential features. A reaction of this type between an unsaturated alcohol and an alkyl acetoacetate was described for the first time by Carroll in
J. Chem. Soc
. (London), 1940, pages 704 to 706. The range of application and the mechanism of this reaction were reported one year later by the same author in J. Chem. Soc. (London), 1941, pages 507 to 511.
One procedure for preparing 6,10,14-trimethyl-5-pentadecen-2-one by transesterification of ethyl acetoacetate with 3,7,11-tri-methyl-1-dodecen-3-ol in the presence of aluminum trialcoholates is to be found in French Patent 1 219 166 (of 1959). In this process, the reactants and the catalyst are introduced together into the reaction vessel and the reaction is carried out batchwise with removal of the alcohol liberated from the ethyl acetoacetate by distillation. In this case, the required ketone is obtained in 77% yield in a reaction time of about 10 hours.
This process is unsatisfactory for an industrial synthesis both because of the relatively long reaction times and because of the inadequate yields. The inadequate yields are particularly serious in the preparation of higher ketones, i.e. on use of higher alcohols of the formula II because the preparation thereof increases in cost as the chain length grows. Attempting to improve the yields by using the less costly component, in this case the alkyl acetoacetate, in excess easily leads to the formation of dehydroacetic acid as by-product which, on the one hand, deactivates the catalyst and, on the other hand, can be removed from the desired product only with difficulty. In addition, the dehydroacetic acid may crystallize out and thus block the outflow lines of the columns used.
A number of other patents describing some variants of the Carroll reaction are known. Thus, U.S. Pat. No. 2,795,617 (of 1957) and DE AS 1 053 498 (of 1959) and CH 342 947 (of 1959), state that “although it is as a rule neither necessary nor desirable, it is possible to use a solvent in order to moderate the exothermic progress of the reaction”. In the processes in these patents, the aluminum trialcoholate was added to the acetoacetate of the &agr;,&bgr;-unsaturated alcohol, and the mixture was heated to reflux with vigorous stirring. Yields of up to 80% of theory were achieved thereby. The disadvantage of this process is that the preparation of the acetoacetate used as starting compound must take place in a preceding stage.
U.S. Pat. No. 2,839,579 (of 1958) and DE 1 078 112 (of 1960) report that the reaction can be carried out in a solvent. The appropriate acetoacetate is prepared by condensing the appropriate unsaturated alcohol with diketene in a separate stage.
DE 1 068 696 also states that the presence of a solvent might be advantageous. High-boiling solvents with boiling points far above the reaction temperature are mentioned in all cases.
Disadvantages of this process are that the yields stated in these patents are unsatisfactory for industrial use and, in particular, that an additional process stage is necessary to prepare the acetoacetate of the &agr;,&bgr;-unsaturated alcohol, which leads to additional costs. The proposed presence of a high-boiling solvent moreover generally results in negligible increases in the yield and therefore leads only to a reduction in the space-time yield.
The Czech Patent 216 360 (of 1979) recommends carrying out Carroll reactions in a mixture of the unsaturated ketone to be expected as product of the reaction, and of methyl or ethyl acetoacetate, with the addition of an amount of the unsaturated alcohol which is just necessary to maintain the reaction. In this case, the reaction mixture is distilled to remove the carbon dioxide and a mixture of the unreacted unsaturated alcohol and methanol or ethanol, and the mixture is fractionated continuously in a connected distillation column. The &agr;,&bgr;-unsaturated alcohol, which must have a boiling point below 180° C., is subsequently returned to the reaction. The yields achieved in this process with reaction times of 8 hours were about 80% of theory. This process has the disadvantage that the additional distillation column gives rise to additional capital and energy costs. In addition, the yields and reaction times in this process are unsatisfactory for a modern industrial process.
DE 2 928 944 (of 1979) further describes the preparation of &agr;,&bgr;-unsaturated ketones by a Carroll reaction in the presence of small amounts of a solvent whose boiling point is between that of the alkyl acetoacetate employed and that of the alcohol to be eliminated therefrom. This solvent is referred to therein as “intermediate boiler”. Possible inert intermediate boilers mentioned are appropriately boiling alcohols, esters, ethers, halogenated hydrocarbons and aromatic hydrocarbons, preferably aliphatic ketones having 4 to 7 C atoms. A particularly advantageous embodiment mentioned is the use of 2-methyl-3-buten-2-ol as reactive intermediate boiler, in which case an additional desired side reaction takes place by reaction thereof with the alkyl acetoacetate to give 2-methyl-2-hepten-6-one as another required product. The advantages mentioned on use of such an intermediate boiler are increased yields of product (about 95% of theory based on the alcohol, and about 85% of theory based on the acetoactate) and shorter reaction times (about 4-5 h) and thus high space-time yields. The reaction temperatures used in all the examples do not exceed 165° C.
However, the use of an intermediate boiler has not only advantages but also the following disadvantages. Thus, for example, on use of an inert intermediate boiler the reactor volume available for the precursors is reduced, i.e. the space-time yields which can be achieved are inevitably lower. In addition, for example, the presence of a reactive intermediate boiler such as 2-methyl-3-buten-2-ol, results in obligatory coupling of the production of different unsaturated ketones, which may be undesired.
It is an object of the present invention to improve the reaction of high-boiling &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in a Carroll reaction to give unsaturated ketones in such a way that it can also be carried out in the absence of a solvent or the absence of a so-called intermediate boiler, and thus without coupling with the preparation of other unsaturated ketones. It was moreover intended to achieve a higher yield of product, based on the unsaturated alcohol and based on the alkyl acetoacetate, with shorter reaction times, than in the syntheses described in the literature for the separate preparation of the unsaturated ketones. It was particularly intended to be able to prepare the ketones which are in demand as intermediates for preparing the essential vitamin E precursor isophytol, such as 6,10-dimethyl-5,9-undecadien-2-one (geranylacetone), 6,10,14-trimethyl-5,9,13-pentadecatrien-2-one (farnesylacetone), 6,10-dimethyl-5-undecen-2-one (dihydrogeranylacetone) and 6,10,14-trimethyl-5,9-pentadecadien-2-one (dihydrofarnesylacetone) with higher selectivity and higher space-time yield.
We have found that this object is achieved by a process for preparing unsaturated ketones of the general formula I
in which the dotted line may mean an additional C—C bond, R
1
is an alkyl group having 1 to 4 C atoms, and R
2
is a saturated or unsaturated aliphatic, cycloaliphatic or cycloaliphatic-aliphatic radical having 4 to 30 C atoms, by reacting the corresponding &agr;,&bgr;-unsaturated alcohols of the general formula II
with alkyl acetoacetates of the general formula III
in which R
3
is alkyl having 1 to 4 carbon atoms, in the presence of from 0.1 to 5 mol %, based on the alkyl acetoacetate to be reacted, of an organic aluminum compound as catalyst with elimination and continuous removal by d
Etzrodt Heinz
Jaedicke Hagen
Kaibel Gerd
Krug Thomas
Oost Carsten
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Padmanabhan Sreeni
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