DE2854195A1 - Di:propyl:acetic acid prodn. for pharmaceuticals etc. - by thermal decarboxylation of di:propyl-malonic acid in suspension in toluene - Google Patents

Abstract

In the prodn. of dipropylacetic acid (I), solid dipropylmalonic acid (II) is suspended in toluene and the suspension is freed by distillation under a reflux condenser from the toluene and from any water still adhering to (II), the temp. being slowly raised after the beginning of the evelution of CO2 and heating being continued until the evolution of gas is completed. (I) is valuable prod. for the pharmaceutical industry. Prepn. of (I) by decarboxylation of molten (II) is known, but this method is unsuitable for large scale use because of e.g. stirring problems. The new process avoids such problems, and gives (I) in almost quantitative yield and in a purity of >99%.

Description

Process for the production of dipropyl acetic acid

Dipropylacetic acid is a valuable product for the pharmaceutical Industry.

Dipropylmalonic acid, which melts at 156 to 1580 C, can be used for their preparation Heat above this melting point. Here, a carboxyl group becomes carbon dioxide split off and the desired DipropylessigsÄure formed. An execution in however, there are various difficulties on the technical scale. An appropriate one Stirring would require special agitators to move the viscous melt special measures had to be taken to ensure the even passage of heat and its dissipation of heat, as well as for the dissipation of the carbon dioxide that forms in the process care for. Now you could add a high-boiling solvent to the melt and in this way seek to avoid the difficulties mentioned. One such However, the solvent must be very polar, because otherwise the carbon dioxide is split off starts slowly or not at all. Separation of the solvent would also be necessary not simple and in any case required a special operation. It is very questionable whether such a solvent, which for technical and economic reasons had to be easily accessible, could be found at all.

The invention is that solid dipropylmalonic acid in toluene slurried and gradually reflux the slurry by distillation toluene and any water still adhering to it is freed from, for example, dipropylmalonic acid, whereupon after the start of the splitting off of carbon dioxide that begins here, the Temperature slowly increased and heating until the evolution of gas has ceased continues. The formed dipropyl acetic acid is distilled off for pure recovery. They are obtained in almost quantitative yield and in a purity of over 99%.

Example: 500 parts by weight of solid crystallized di-n-propyl-malonic acid are suspended in 500 parts by volume of toluene. While stirring evenly, the Mixture heated until toluene begins to distill off. When an internal temperature is reached of 1400 ° C., at which the reaction mixture forms an easily stirrable paste, begins the formation of carbon dioxide. The temperature is gradually increased from 0 to 160.degree and maintained until no more solvent distilled over and the Gas evolution has ended. It is then cooled to 1200.degree. In the now liquid A further 500 parts by weight of di-n-propylmalonic acid are added to the reaction mixture. The heating process to 1600 C is repeated as described above, then is cooled again and the remaining amount of 1049 parts by weight of crystallized di-n-propylmalonic acid admitted.

After heating to 1600 C until the evolution of carbon dioxide ceases the now liquid mixture is cooled to about 1000 c and from this immediately the reaction product formed is distilled off under reduced pressure.

0 1487 parts by weight of a temperature between 117 - 124 C (at 12 - 15 Torr} boiling, colorless, water-clear fraction, which consists of over 99% di-n-propyl acetic acid consists. This corresponds to a yield of 97.4%, based on 100% used Di-n-propylmalonic acid.

Claims (1)

Claim: Process for the production of dipropylacetic acid, characterized in that solid dipropylmalonic acid is slurried in toluene and reflux the slurry gradually by distillation of toluene and about the dipropylmalonic acid still adhering water is freed, whereupon one after the beginning the splitting off of carbon dioxide that occurs in this process slowly increases the temperature and the heating continues until the evolution of gas has ceased.