Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-11-15
2001-10-23
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S346000, C568S356000, C568S383000, C568S388000, C568S391000, C568S398000
Reexamination Certificate
active
06307106
ABSTRACT:
The present invention relates to an improved process for preparing lower unsaturated ketones by reacting the corresponding &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in a Carroll reaction. The essential features of this reaction are already known, apart from the improvements according to the invention.
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 same author reported one year later on the range of application and the mechanism of this reaction in J. Chem. Soc. (London), 1941, pages 507 to 511.
DE 1 068 696 discloses that it is possible to prepare 2-methyl-2-hepten-6-one by metering 2-methyl-3-buten-2-ol into a reaction mixture which has been preheated to 160 to 180° C. and consists of an alkyl acetoacetate, a mixture of an alkyl acetoacetate and an inert solvent or a mixture of 2-methyl-3-buten-2-ol, an alkyl acetoacetate and a solvent. The yields of 66%, based on the alkyl acetoacetate, achieved according to this patent are entirely inadequate for an industrial process.
Reaction of diketene, in place of the alkyl acetoacetate, with 2-methyl-3-buten-2-ol in the presence of aluminum triisopropoxide results in yields of 83% (cf. Advances in Organic Chemistry, Volume II, 1960, page 246). The disadvantage of this process is that the instability of diketene makes very complex apparatus necessary, for safety reasons, and therefore the capital and operating costs for an industrial system are high.
A number of other patents describing diverse variants of the Carroll reaction is known. Thus, in U.S. Pat. No. 2,795,617 (of 1957) or DE-B 1 053 498 (of 1959) or CH 342 947 (of 1959) it is stated that “although as a rule it is neither necessary nor desired, a solvent can be used 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 in these cases. One disadvantage of this process is that the acetoacetate used as the starting compound must be prepared in a separate 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.
It is also stated in DE 1 068 696 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.
The disadvantages of these processes are that the yields stated in these patents are unsatisfactory for an industrial application 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 yield and therefore leads only to a reduction in the space-time yield.
A process for preparing 2-methyl-2-hepten-6-one is described in DE-B 2 652 863 (of 1978). In this case, the alkyl acetoacetate, 2-methyl-2-buten-3-ol and the catalyst are introduced into a reaction vessel with a fitted fractionation column, and then a mixture of the alkyl acetoacetate and 2-methyl-2-buten-3-ol is metered into this. During the reaction, the content of alkyl acetoacetate in the reaction mixture should not exceed 15% by weight, in order to avoid side reactions.
Czech Patent 216 360 (of 1979) recommends carrying out Carroll reactions in a mixture of the unsaturated ketone to be expected as reaction product, and the methyl or ethyl acetoacetate with addition of the unsaturated alcohol in an amount just sufficient to maintain the reaction. In this case, the carbon dioxide and a mixture of unreacted unsaturated alcohol and methanol or ethanol are distilled out of the reaction mixture, said mixture being continuously fractionated in an attached distillation column. The &agr;,&bgr;-unsaturated alcohol, whose boiling point must be below 180° C., is then returned to the reaction. In this process, yields of about 80% of theory are achieved with reaction times of 8 hours. One disadvantage of the process is that additional capital and energy costs arise due to the additional distillation column. Moreover, the yields and reaction times in this process are unsatisfactory for a modern industrial process.
In addition, DE 2 928 944 (of 1979) 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 used and that of the alcohol to be eliminated therefrom. This solvent is referred to therein as “intermediate boiler”. Possible inert intermediate boilers which are mentioned are alcohols, esters, ethers, halogenated hydrocarbons and aromatic hydrocarbons, preferably aliphatic ketones with 4 to 7 C atoms, having appropriate boiling points. The use of 2-methyl-3-buten-2-ol as reactive intermediate boiler is mentioned as a particularly advantageous embodiment, in which case an additional desired side reaction takes place between the latter and the alkyl acetoacetate to give 2-methyl-2-hepten-6-one as further required product. The advantages mentioned for the use of such an intermediate boiler are increased product yields (about 95% of theory based on the alcohol, and about 85% of theory based on the acetoacetate) 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 not only has advantages but also has the following disadvantages. Thus, for example, use of an inert intermediate boiler reduces the reactor volume available for the precursors, i.e. the space-time yields which can be achieved become inevitably smaller. In addition, for example, the presence of a reactive intermediate boiler such as 2-methyl-3-buten-2-ol results in enforced coupling of the production of different unsaturated ketones, which may be unwanted for a variety of reasons.
It is an object of the present invention to improve the reaction of relatively low-boiling &agr;,&bgr;-unsaturated alcohols with alkyl acetoacetates in a Carroll reaction to give the corresponding unsaturated ketones in such a way that it can be carried out in the absence of a high-boiling solvent and without coupling to the preparation of other unsaturated ketones. It was moreover intended to achieve a product yield, based on the unsaturated alcohol and based on the alkyl acetoacetate, which is at least as good as, but if possible higher than, that in the syntheses described in the literature for separate preparation of the unsaturated ketones, with shorter reaction times. It was particularly intended to be able to prepare the ketone 2-methyl-2-hepten-6-one, which is in demand as fragrance and for preparing other fragrances, starting from 2-methyl-3-buten-2-ol without the prior art disadvantages and with higher selectivity and higher space-time yields.
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 can be an additional C—C bond, R
1
is an alkyl group with 1 or 2 C atoms, and R
2
is an alkyl group with 1 to 4 C atoms, by reacting &agr;,&bgr;-unsaturated alcohols of the general formula II
with alkyl acetoacetates of the general formula III
in which R
3
is an alkyl group with 1 to 4 C 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 distillation of the alcohol which is eliminated from the alkyl acetoacetate during the reaction and has the general formula IV
R
3
—OH (IV)
in a reactor system with a fitted fra
Etzrodt Heinz
Jaedicke Hagen
Kaibel Gerd
Oost Carsten
Stroezel Manfred
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Padmanabhan Sreeni
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