Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-12-06
2001-04-03
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S591000, C568S630000, C568S631000, C568S640000, C568S657000, C568S664000, C502S232000, C502S253000
Reexamination Certificate
active
06211416
ABSTRACT:
The present invention relates to a process for the preparation of enol ethers by comproportionation of ketals or acetals with alkynes or allenes in the gas phase in the presence of a zinc- or cadmium- and silicon- and oxygen-containing heterogeneous catalyst.
It is known that ketals or acetals can be converted into the corresponding enol ethers, either in the liquid phase with acidic catalysts (according to EP 703 211 or EP 490 221) or in the gas phase over heterogeneous catalysts (according to DE 19544450) with elimination of alcohol, according to the following equation:
The enol ethers thus obtained are important starting compounds of the preparation of pharmaceutical products and fragrances.
The stated known processes permit the preparation of the enol ethers in good yields in some cases but have the following disadvantages:
The reaction in the liquid phase according to EP 703 211 requires the use of a dissolved foreign substance, namely an organic acid, the removal of which from the reaction mixture necessitates an additional separation step, and the process according to EP 490 221 is applicable only to acetals. Compared with the processes in the liquid phase using homologously dissolved catalyst, the process according to DE 19544450 has the advantage of the reaction in the gas phase over a heterogeneous catalyst but requires rather high temperatures.
Common to all these processes is the fact that one mole of alcohol is liberated per mole of ketal or acetal and has to be separated off with additional and in some cases considerable purification costs and as a rule discarded. This applies in particular to methanol, which frequently forms azeotropic mixtures. The weight yield, based on ketal or acetal, is thus inevitably reduced.
It is an object of the present invention to provide a process which can be carried out continuously over a heterogeneous catalyst with good yields and is applicable both to ketals and to acetals and in which the alcohol originating from the ketal or acetal is not obtained as an associated product in stoichiometric amounts.
We have found that this object is achieved, according to the invention, by a process for the preparation of enol ethers of the formula I
where R
1
is an aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic radical which may carry further substituents which do not react with acetylenes or allenes, and the radicals R, independently of one another, are hydrogen or aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic radicals, which may be bonded to one another to form a ring, and m is 0 or 1, wherein an acetal or ketal of the formula II
is reacted with an acetylene or allene of the formula III or IV
where R and R
1
have the abovementioned meanings, in the gas phase in the presence of a zinc- or cadmium- and silicon- and oxygen-containing heterogeneous catalyst.
Although the mechanism of the novel reaction is not known in detail, the reaction may be formally considered as if one mole of an alcohol R
1
OH from the dialkoxy compound of the formula II is transferred to the acetylene or allene with formation of the enol ether of the formula I.
The ketals or acetals of the formula II which are to be used as starting materials are disclosed in the literature, for example in U.S. Pat. No. 2,667,517 and EP-A-0197283, the two radicals R
1
generally being identical.
R is preferably alkyl, in particular of 1 to 6 carbon atoms, or hydrogen and R
1
is an alkyl in particular of 1 to 8 carbon atoms.
Particularly suitable acetals are open-chain compounds. Examples of such acetals are dimethyl acetals, diethyl acetals, di-n-propyl acetals, di-n-butyl acetals, diisobutyl acetals, di-n-pentyl acetals, diisopentyl acetals, di-n-hexyl acetals and diisohexyl acetals of aldehydes of the formula
where R has the abovementioned meanings.
Examples of such acetals are:
Acetaldehyde dimethyl acetal, acetaldehyde diethyl acetal, acetaldehyde dipropyl acetal, propionaldehyde dimethyl acetal, propionaldehyde diethyl acetal, propionaldehyde dipropyl acetal, propionaldehyde dibutyl acetal, butyraldehyde dimethyl acetal, butyraldehyde diethyl acetal, butyraldehyde dipropyl acetal, butyraldehyde dibutyl acetal, butyraldehyde dipentyl acetal, valeraldehyde dimethyl acetal, valeraldehyde diethyl acetal, valeraldehyde dipropyl acetal, valeraldehyde dibutyl acetal, valeraldehyde dipentyl acetal, isovaleraldehyde dimethyl acetal, isovaleraldehyde diethyl acetal, isovaleraldehyde dipropyl acetal, isovaleraldehyde dibutyl acetal, isovaleraldehyde dipentyl acetal, hexanal dimethyl acetal, hexanal diethyl acetal, hexanal dipropyl acetal, hexanal dibutyl acetal, hexanal dipentyl acetal, hexanal dihexyl acetal, 2-ethylhexanal dimethyl acetal, 2-ethylhexanal diethyl acetal, 2-ethylhexanal dipropyl acetal, 2-ethylhexanal dibutyl acetal, 2-ethylhexanal dipentyl acetal, 2-ethylhexanal dihexyl acetal and nonanal dimethyl acetal.
Examples of suitable ketals are:
Dimethyl, diethyl, di-n-propyl, di-n-butyl, diisobutyl ketals of acetone, of 2-butanone, of 2- or 3-pentanone, of 2- or 3-hexanone, of cyclopentanone or of cyclohexanone. A particularly preferred starting material is 2,2-dimethoxypropane (acetone dimethyl ketal).
Although any desired acetylenes or allenes may be chosen as starting materials, technically readily obtainable acetylenes and/or allenes of 2 or 3 to 8, preferably 3 to 8, carbon atoms, in particular methylacetylene or allene or mixtures thereof, for example as can be isolated from a C
3
stream of a steam cracker, are preferably used. In general, the ketals or acetals are preferably reacted with acetylenes or allenes to give a uniform enol ether I. This means, for example, that, in the formula II, a compound in which m is 1 corresponds to an allene having the same radicals R and a compound in which m is 0 corresponds to an acetylene having the same radicals R.
The reaction of the ketals or acetals with the acetylenes or allenes is carried out in the presence of the heterogeneous zinc- or cadmium- and silicon- and oxygen-containing catalyst in the gas phase, either over a fixed bed or in a fluidized bed at from 50 to 400° C., preferably from 100 to 250° C., particularly preferably from 120 to 200° C. and at from 0.1 to 50, in particular from 0.8 to 20, particularly preferably from 0.9 to 10, bar (all pressures are based on the sum of the partial pressures of the starting materials).
If required, for reasons of operational safety and for better heat removal, the reaction mixture can be diluted with inert gas, such as nitrogen, argon, low molecular weight alkanes or olefins.
The molar ratio of ketal or acetal to alkyne or allene may be from 0.01 to 100, preferably from 0.1 to 2, particularly preferably from 0.7 to 1.3.
Suitable zinc- or cadmium- and silicon- and oxygen-containing catalysts are cadmium silicates and preferably zinc silicates, for example silicates selected from the group consisting of
(a) X-ray amorphous zinc silicate or cadmium silicate, prepared by impregnating a silica carrier with a zinc or cadmium salt,
(b) crystalline zinc silicate having essentially the composition and structure of the hemimorphite of the formula Zn
4
Si
2
O
7
(OH)
2
.H
2
O, where the zinc may be present in an amount up to 25% below or above the stoichiometric amount, based on the stoichiometric composition, and/or
(c) essentially X-ray amorphous zinc silicate, prepared by precipitation in aqueous solution of a soluble silicon and zinc compound, of the formula V
Zn
a
Si
c
O
−2c−0.5e
(OH)
e
.f H
2
O V,
where e is from 0 to 2a+4c, the ratio a/c is from 1 to 3.5 and the ratio f/a is from 0 to 200.
(a) X-ray amorphous zinc silicate or cadmium silicate catalysts are obtained, for example, by loading amorphous silica with a zinc salt or cadmium salt and forming the catalyst by a thermal treatment.
The SiO
2
carrier is at least predominantly amorphous, has a BET surface area of from 10 to 1500, particularly preferably from 100 to 500, m
2
/g and a water absorptivity of from 0.1 to 2, particularly preferably from 0.7 to 1
Breuer Klaus
Demuth Dirk
Etzrodt Heinz
Hibst Hartmut
Rheude Udo
BASF - Aktiengesellschaft
Keys Rosalynd
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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