Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-01-30
2001-11-06
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
Reexamination Certificate
active
06313347
ABSTRACT:
This application is a 371 of PCT/EP99/05292 filed Jul. 23, 1999. The invention relates to a process for the preparation of vinyloxime ethers by reacting ketoximes with alkynes.
It is known to react dimethyl acetylenedicarboxylate in the presence of a basic catalyst with ketoximes to give O-vinyloxime ethers (T. Sheradsky, Tetrahedron Letters 1970, No. 1, P. 25-26).
It is further known to react acetone oxime with acetylene in dimethyl sulfoxide to give O-vinylacetone oxime (Trofimov, Izv. Akad. Nauk SSSR, Ser. Khim, 1979, No. 3, p. 695). The yields are up to 10%.
In Russ. J. Org. Chem. Vol. 30 (1994), No. 6, pages 810 to 815, Tarasova et al. describe the reaction of ketoximes with acetylene in dimethyl sulfoxide in the presence of potassium hydroxide to give O-vinyloxime ethers. Yields of from 10 to 72% are achieved. For higher yields, reaction times up to 6 hours are required. In this connection, it is necessary to interrupt the reaction several times in order to remove the desired product from the mixture since the desired vinyloxime ether, when left in the reaction mixture for a prolonged time, reacts further with ring closure to give the corresponding pyrrole.
It is an object of the present invention to carry out the known reaction of ketoximes with alkynes, in particular acetylene, such that the O-vinyloxime ethers are obtained in a higher overall yield at higher space-time yields with the formation of fewer by-products, in a form which is accordingly more pure or is easier to purify.
The invention proceeds from a process for the preparation of vinyloxime ethers of the formula I
by reacting a ketoxime of the formula II
with an alkyne of the formula III
R
3
−C=C−R
4
(III)
where
R
1
and R
2
are identical or different and are alkyl or aryl radicals,
R
3
is hydrogen, an alkyl or aryl radical, and
R
4
is a radical having the meaning of R
3
, which can be different than R
3
, or is an hydroxyalkyl radical,
in a superbasic polar organic solvent in the presence of a strong base.
The novel process comprises carrying out the reaction under conditions such that the vinyloxime ether formed stays in contact with the other constituents of the reaction mixture for only a short time so that it is unable to decompose or react to give secondary products to a significant extent.
A simple way of limiting the contact time involves interrupting the reaction after just a short time, for example by cooling. This may result in the ketoxime used being converted only incompletely. In this case, the reaction product must be separated off from the other constituents of the mixture, and such constituents must be returned to the reaction zone. This relatively laborious procedure is generally more than compensated for by the fact that the significantly fewer by-products form compared with the amount of product.
The abovementioned reaction time is dependent on a number of parameters, such as temperature, pressure, nature of the superbasic solvent, of the base and of the reactants used etc. As explained below, in each individual case simple experiments can be used to ascertain the dependency of the reaction on the reaction time, meaning that in each specific case it is possible to find the optimum reaction time in relation to the yield. Although it is not possible here to give values which are generally applicable for the reaction times, the optimum values at the preferred temperatures and pressures are in most cases between 10 seconds and 1 hour, preferably between 1 and 30 minutes.
The reaction of ketoxime with alkyne can be carried out at room temperature or at elevated temperature. The reaction temperature is also dependent in individual cases on the nature of the reactants. While some combinations of reactants react quickly enough only at relatively high temperatures, above 50° C., say in the range from 60 to 125° C., in other cases the reaction products are no longer stable at temperatures in this range and tend to decompose. In most cases the most favorable reaction temperatures are in the range from 50 to 100° C., preferably from 65 to 85° C.
The reaction can be carried out under atmospheric pressure or under increased pressure. In general, higher pressures are advantageous. They can be in the range from more than 1 to 50 bar, preferably from 10 to 40 bar.
According to an advantageous embodiment of the process, the vinyloxime ether formed is removed from the reaction mixture during the reaction. This can be done in various ways. In a very simple manner, the reaction product can be separated off from the mixture with the other constituents by carrying out the reaction in an inert nonpolar organic solvent which is immiscible with the superbasic polar solvent and which is a good solvent for the resulting O-Vinyloxime ether. In this case, the reaction product is distributed between the polar and the nonpolar solvent phase, the majority going into the nonpolar phase, depending on the type of solvent. Here, it is not in direct contact with the other constituents, particularly with the strong base, and, under these conditions, has a significantly lower tendency to decompose or to react further to give undesired secondary products such as polymers or pyrrole derivatives.
Another method of separation involves driving out the vinyloxime ether formed from the reaction mixture by evaporation. The resulting mixture of vaporous vinyloxime ether and alkyne, for example acetylene, is then expediently separated into its constituents, and the alkyne is returned to the reaction zone. This procedure is naturally particularly suitable for continuous operation.
The nonpolar organic solvents used are preferably hydrocarbons, particularly preferably saturated aliphatic hydrocarbons. The nonpolar solvent should expediently have a boiling point under atmospheric pressure in the range from about 25 to 200° C., preferably from 30 to 100° C. It is essential that the nonpolar organic solvent is immiscible with the superbasic organic solvent, but is a good solubilizer for the vinyloxime ether formed. It is also possible to use mixtures of nonpolar organic solvents. A particularly preferred example is n-pentane.
According to general language usage, the superbasic organic solvent is a solvent of high polarity which is suitable for forming carbanions by deprotonating other compounds. Examples are dimethyl sulfoxide, sulfolane (tetramethylene sulfone) an hexamethylphosphor amide. The concentration of the oxime used in the reaction solution likewise has a significant effect on the yield. In general, the yield decreases with increasing starting concentration of oxime. Conversely, the amount of solvent volumes to be handled increases with dilution, thus increasing the cost of the process. Also, too dilute a solution may result in the reaction time being longer. In general, starting concentrations are chosen in the range from about 4 to 20% by weight, preferably from 6 to 15% by weight it can also be expedient to use only some of the oxime at the start of the reaction and to add the remainder during the course of the reaction. In this procedure it is possible to manage with smaller amounts of solvent.
For the purpose of the novel process, strong bases are, in particular, inorganic bases, preferably hydroxide. The hydroxides of the alkali metals and alkaline earth metals, particularly of the alkali metals, are generally preferred.
The strong base can be used in stoichiometric or substoichiometric amounts relative to the ketoxime. It is also possible to use amounts which are greater than the stoichiometric amounts. An unreacted excess of base generally remains in the reaction mixture, i.e. undissolved in the polar superbasic solvent, where it is unable to adversely affect the constituents of the reaction mixture, particularly the reaction product. Since an excess of base has no effect on the reaction, the deliberate use of an excess is usually avoided. A deficit of base, e.g. an amount of only from 80 to 90% of the stoichiometric amount is in many cases sufficient for complete conversion. It is als
Henkelmann Jochem
Mikhaleva Albina
Preiss Thomas
Trofimov Boris
Vasiltsov Alexander M.
Barts Samuel
BASF Aktiengesekkschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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