Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-06-01
2003-05-20
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S693000, C568S667000, C568S669000, C568S681000, C568S682000, C568S686000
Reexamination Certificate
active
06566559
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to an improved process for the production of unsaturated ethers, in particular isopropenyl methyl ether, by pyrolysis of a ketal-containing or acetal-containing mixture, in particular dimethoxypropane, in the presence of an organic carboxylic acid.
Various unsaturated ethers are important starting compounds for the production of pharmaceutical products, fragrances and perfumes. Isopropenyl methyl ether (IPM) is such an ether and may be used in particular for synthesizing vitamins, including inter alia the synthesis of vitamin E and vitamin A, and for producing various carotenoids such as astaxanthin and related compounds. IPM may furthermore be used for the synthesis of fragrances and perfumes. In this connection processes are known for the C-3 extension of allyl alcohols or propargyl alcohols, in which at least two equivalents of unsaturated ether are used per mole of substrate. In this reaction, which is also termed the Saucy-Marbet reaction after its discoverers, one equivalent of the ether is used for the C-3 extension of the substrate and one equivalent is used to trap the alcohol produced in situ, with formation of the ketal.
The production of acetals or ketals from the corresponding alcohols and carbonyl compounds, and the production of the unsaturated ethers from the resultant acetals and ketals, is described in the literature. The prior art is discussed here separately for ketalization and ketal pyrolysis for the production of the unsaturated ethers. It is generally known that dimethoxypropane (DMP) can be prepared from acetone and methanol by reaction in the presence of an acid catalyst.
Lorette et al., J. Org. Chem., 1959, p. 1731, describes the dependence of the educt stoichiometries and the temperatures on the kinetics of this reaction, in particular the fact that the equilibrium of this reaction is displaced predominantly towards the educts and accordingly it is not possible under moderate conditions to achieve a complete educt conversion. It is found that in order to achieve good educt conversions, low temperatures, i.e. down to −30° C., have to be established, with an acetone/methanol ratio of 1:2 to 1:4. The ketalization of Lorette et al. is performed in the presence of acidic ion exchangers, the reaction being carried out as a fixed bed catalysis reaction. The working up of the product solution that is produced, the water content of which is between 3 and 4 wt. %, is complicated due to the formation of azeotropes between DMP and methanol on the one hand and acetone and methanol on the other hand, and the yields of isolated DMP are correspondingly low due to the losses.
U.S. Pat. No. 2,827,495 of Bond et al. is concerned with the working up of the aqueous, methanolic product mixture by extraction with aqueous alkali, in particular sodium hydroxide in a concentration between 13 and 16 wt. %. By this process, which is carried out industrially as a countercurrent extraction process, a methanol-free, almost pure DMP (97%) can be obtained as organic product of the extraction in an outstanding extraction yield (>99%, see Example IV of the cited patent). Nevertheless, the DMP extracted in this way still contains about 1.5 wt. % of water, which in molar terms corresponds to a ratio of 8:92. This mixture cannot however be used to produce IPM in large yields since the water that is present reacts quantitatively with DMP during the pyrolysis, in the presence of an acid catalyst, to form acetone and methanol. The further product purification and the use of the resultant DMP for the production of IPM is not described.
In U.S. Pat. No. 1,850,836 of Guinot et al. two basic possibilities for the production and isolation of acetals are already described, namely the reaction of an aldehyde with an alcohol in the presence of a catalytic amount of a mineral acid, in particular gaseous HCl. After the reaction equilibrium has been established the reaction mixture is neutralized with an amount of base at least equivalent to the acid (in order to suppress the reverse reaction during the working up) and is then worked up by adding an aliphatic auxiliary solvent that is water-insoluble and forms a minimum temperature azeotrope with the alcohol that is used. In this way the nonpolar acetal can be freed by means of the non-water-soluble aliphatic solvent from water and largely from the alcohol, and the alcohol can then be extracted as an azeotrope with the aliphatic compound. It is obvious that considerable amounts of aliphatic compounds are required for the complete removal of the alcohol, following which an aqueous extraction is necessary to separate the methanol from the aliphatic solvent. Overall the process is complicated and is not particularly suitable for industrial application.
In U.S. Pat. No. 2,837,575 of Waters et al. a ketalization with gaseous HCl is described. In order to increase the acetone conversion, up to 8 wt. % of HCl is used, which then has to be neutralized with sodium hydroxide, and a not inconsiderable amount of salt is formed. The subsequent working up is performed by two complicated extractions with sodium hydroxide of different concentrations followed by an additional extraction with a readily volatile aliphatic hydrocarbon. It is clear from the large number of necessary separation operations that the process is not suitable for an economic industrial application.
After the implementation of the ketalization per se had been technically solved by the publication by Lorette et al., J. Org. Chem., 1959, p. 1731, using a stable, acidic ion exchanger, the subsequent relevant patent publications were accordingly only concerned with the recovery of the complex product mixture, which due to the presence of water tends to undergo a reverse reaction and thus complicates the recovery still further.
According to the process described in DE-OS 26 36 278, Zinke-Allmang et al., BASF, the reaction of alcohol and carbonyl compound is carried out in the presence of gaseous HCl and at least equivalent amounts of calcium sulfate as water-binding agent. The same authors concede however in a later publication, DE 29 29 827, Zinke-Allmang, BASF, that this does not represent an optimal solution to the problem, since considerable amounts of the water-binding agent are used and have to be recovered. DE-OS 29 29 827 describes the reaction in an excess of acetone with an acetone/methanol ratio of 3.6 to 4.4, and recovery in a distillation column with 40-60 trays. The azeotrope of acetone and methanol is recycled at the head of the column and a mixture of DMP and water is extracted in a side stream, following which DMP can be obtained after phase separation. In this procedure however an only approximately 4 wt. % DMP mixture with a water content of ca. 0.5 wt. % is produced due to the establishment of the equilibrium. It is clear that almost 95 wt. % of the unreacted product solution has to be distilled off in order to isolate the product, which makes the process extremely energy-intensive, and the spatial requirements of the necessary distillation column can be extremely large, having regard to the recycling required for a clean separation.
U.S. Pat. No. 4,775,447 describes a process for the production of DMP, in which an acidic heterogeneous ion exchanger is likewise used as catalyst and the ratio of acetone to methanol is adjusted to between 1:1 and 1:3. The recovery according to this procedure is however extremely complicated and involves a first distillative removal of an acetone-rich azeotrope of acetone and methanol. A corresponding amount of acetone must be added to the remaining mixture of methanol and DMP so that, in a second distillation, an azeotrope of acetone and methanol of the composition (ca. 86 vol. % acetone and 14 vol. % methanol) is removed. The patent does not discuss the acetone-methanol separation. Also, the separation from the DMP of the water formed in the reaction is not described.
The distillative separation as well as the complex azeotropes in the water-DMP-acetone-methanol system are describ
Häfner Volker
Kretz Stephan
Krill Steffen
Markowz Georg
Degussa - AG
Keys Rosalynd
Smith , Gambrell & Russell, LLP
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