DE956506C - Process for the separation of isomeric Menthandicarbonsäuren - Google Patents

Description

Process for separating isomeric menthedicarboxylic acids It is known that carbon oxide and hydrogen can be added catalytically under elevated pressure to both double bonds of diolefinic terpenes of the formula CH H, 6, for example limonene or dipentene. In yields of more than 50%, often of more than 70%, dialdehydes are formed which can be converted into the corresponding dimethylols by reduction and into menthane dicarboxylic acids by oxidation or alkali melt.

If the dimethylol-containing reaction product in a known manner is oxidized with chromic acid in the presence of 100% acetic acid, then obtained man after separation from the alkali-precipitated chromium precipitate and acidification the filtered off chromium-free acetic acid or acetic acid salt solution a mixture of two isomeric menthane dicarboxylic acids.

You can get the dimethylol fraction at Zoo up to 26o ° .with iio% of the for the conversion of both OH groups calculated amount of caustic potash melt. The one here Hydrogen which is split off is continuously removed from the melting vessel under pressure. After the elimination of hydrogen has ended, water is poured into the melt with constant stirring depressed. The resulting Paste is made from the melting vessel removed and completely dissolved in water. This creates a saline solution that after neutralizing the excess alkali with mineral acid or carbonic acid can be decolorized with hydrogen in the presence of a nickel catalyst. By step-by-step extraction with paraffinic hydrocarbons of different chain lengths, for example with octadecane, dodecane or heptane, they are considered non-carboxylic acid Any accompanying substances present in salts are removed. After that, the saline solution is added by adding acidified by mineral acids up to pH 2 to 3.

The menthane dicarboxylic acid mixture obtained in one way or another forms a syrupy mass and is made by adding approximately the same amount of benzene brought into solution. The benzene solution floating on top is replaced by the salt solution separated and washed several times with water free of mineral acids. From this solution The two isomeric Menthandicarbonsäuren could not be technically pure so far Shape to be separated.

It has now been found that the reaction mixture obtained by catalytic addition of water gas to diunsaturated menthadienes of the formula Cl, H "", carried out simultaneously or subsequently, can easily be broken down into two isomeric menthedicarboxylic acids by extraction with a mixture of heptane and pentanone . It is most advantageous if the solvent mixture used for the extraction contains 5 parts by weight of heptane per part by weight of pentanone. After the benzene has been distilled off from the benzene solution of the isomer mixture, the remaining distillation residue is dissolved in approximately the same volume of a mixture of, for example, 1 part pentanone and 5 parts heptane by heating in a reflux condenser. When the solution obtained cools down, a crystallized product is obtained which, based on its analytical characteristics, is a uniform menthane dicarboxylic acid.

In heptane alone there is neither of the two isomeric men: thanedicarboxylic acids soluble, while in pentanone both isomeric acids are very easily soluble and at something higher temperature can even be mixed in any ratio. Under these circumstances It was therefore very surprising that a mixture of heptane and pentanone, in particular a mixture which contains 5 parts of heptane per 1 part of pentanone, only one of the two dissolves isomeric Menthandicarbonsäüren and for the selective extraction of the isomeric dicarboxylic acid mixture suitable is.

From the mother liquor remaining after crystallization this becomes Solvent distilled off and the resulting distillation residue several times stripped with heptane. After the extraction agent has been completely removed the extraction residue gives a viscous, water-white substance which According to its key figures, it also proves to be a menthane dicarboxylic acid, The the two isomeric dicarboxylic acids obtained differ in their nature and by their residual acid number.

Of the two carboxyl groups of the menthedicarboxylic acids prepared according to the invention, one is on the cyclohexane ring and one on the isopropyl side chain. If the carbon atoms of the basic hydrocarbon are numbered in the following way, then the isomerism of the two menthedicarboxylic acids produced according to the invention consists in the fact that the carboxyl group which is located on a carbon atom of the cyclohexane ring can either be on carbon atom i or on carbon atoms 2 or 6 and the other carboxyl group is attached to carbon atom io in both cases will.

The menthedicarboxylic acids separated according to the invention in two isomeric forms are suitable, for example, as esterification components in the production of polyesters and plasticizers. Example i A dipentene was used as the starting material that had the following key figures Density. .... ......... Deodorant -. 0.846 Molecular weight .... = 136, o Refractive index ..... u '= 1., 4735 Iodine number. . . . . . . . . . . . . JZ = 362, o (after Kaufmann 2 minutes) Iodine number. . . . . . . . . . . . . JZ = 3722.0 (according to Kaufmann 15 minutes) Ozone iodine number. .. .. .. .. OJZ = 369, o Neutralization number .. NZ = o Ester number ........... EZ = 1.5 Hydroxyl number, l ....... OHZ = 6, o Carbonyl number ........ COZ = o This dipentene was treated with water gas at about 150 ° and 192 atmospheres using a catalytic cobalt sulfate-magnesium sulfate solution containing 16 g cobalt and 30 g magnesium oxy.d per liter. The resulting reaction mixture was freed from the acetals present at 230 ° under a pressure of 173 atm in the presence of a cobalt-magnesia-Ki.eselgur catalyst (100 parts by weight of Co, 10 parts by weight of MgO, aoo parts by weight of kieselguhr) by the action of hydrogen and water and organometallic compounds.

The purified reaction product was converted into a vacuum distillation at a pressure of 10 mm Hg between. 161 and 65 ° boiling Menthandimethylolfraktion separated, the following figures had hydroxyl number ... ... . OHZ = 552.0 neutralization number .. NZ = o ester number ........... EZ = 1.7 refractive index . ... . nD = 1, q.900 100 g of this fraction were added dropwise with stirring to a mixture of zoo g of chromic acid and 80o cm3 of glacial acetic acid, which was located in a 21-capacity flask with reflux condenser and stirrer. The temperature was kept at 50 ° by cooling and adjusting the drop speed. The reaction time was 21/2 hours. The temperature was then increased to 70 ° and the mixture was post-oxidized for a further 4 hours by blowing in air.

The reaction mixture was then treated with aqueous 2oo /% sodium hydroxide solution blunted and brought to a pH of 9. Then filtered from the precipitated chromium (III) hydroxide precipitate. This resulted in a yellowish color Filtrate, from which a dicarboxylic acid mixture when mineral acid is added up to a pH value of 2 could be deposited as an emulsion and partly as a sediment.

The emulsion was extracted with benzene and the benzoli-cal After the acidic solution has been separated off, the solution is washed several times with water until the The odor of free acetic acid had disappeared. Then the benzene and that Dicarboxylic acid mixture in an equal volume of a mixture of 1 part of pentanone and 5 parts of heptane dissolved on the reflux condenser with gentle heating. When cooling down this solution gave a crystallized substance which, on the basis of its neutralization number and saponification number, both of which were 488, as menthane dicarboxylic acid of the formula C12 H20 04 could be identified. This dicarboxylic acid showed a clear melting point from 147 °. The residual acid number was 19o.

That remaining after the above acid has crystallized out Mother solution was distilled. The distillation residue consisted of an isomeric Menthedicarboxylic acid of the formula C12 H20 04, its neutralization number and saponification number both were 482 while the residual acid number was 90. This dicarboxylic acid was highly viscous and stringy.

EXAMPLE e 370 g of the menthane dimethylol fraction obtained according to Example i were heated to 200 ° with 160 g of NaOH in a 2.8 l copper-clad pressure vessel at a nitrogen pressure of 5 atmospheres. At 20 ° the pressure was already 13 atm after 32 minutes. At 26o ° a pressure of 52 atm was reached after a further 6 minutes. The temperature was kept at this level for a further 1/2 hour and the pressure, which was above 50 atmospheres, was continuously equalized. The melting process was then ended by interrupting the supply of heat.

Then zoo cm3 of water were added to the melt with the help of nitrogen pressed in and the mass stirred for 15 minutes. The resulting paste was dissolved in 5 times the amount of water. The solution was made by introducing carbonic acid brought to a pH value of 9.1 and placed in a pressure vessel with 100 cm3? \ TTickel-magnesium oxide-kieselguhr catalyst (100 parts by weight 1`T1, 10 parts by weight M90, 50 parts by weight kieselguhr) for one Hydrogen pressure of 100 atmospheres heated to 210 ° for 1 hour with stirring and then leave to cool. The salt solution filtered off from the added catalyst was colorless and clear as water. 400 cm3 of petroleum ether denatured were added to the saline solution Ethanol added and the unsaponifiable by repeated step-by-step extraction with octadecane, dodecane and heptane removed. Following this, the extraction residue was used mixed with 20% sulfuric acid up to a pH value of about 2 and the resulting precipitate Menthandicarboxylic acid mixture with benzene added. The benzene solution was washed twice more with water, whereupon the benzene was distilled off from the solution.

A heptane-pentanone mixture (6: 1) was used to separate the two isomeric menthedicarboxylic acids of the formula C12 H20 04. In the manner evident from Example i, when the solution was cooled, 140 g of solid dicarboxylic acid were obtained, the saponification number and neutralization number of which were 488 and the melting point of which was 1 ° 7 °. This carboxylic acid was identical to the acid obtained according to Example i.

As a non-crystallizing viscous mass were during the distillation the mother liquor obtained 235 g of a menthane dicarboxylic acid that was tested in all Indicators matched the syrupy dicarboxylic acid prepared according to Example i.

Claims (1)

PATENT CLAIM: Process for the separation of isomeric menthedicarboxylic acids, which are made from diunsaturated menthadienes of the general formula C10 H10 in dilution with other hydrocarbons by catalytic carbon oxide-hydrogen addition (oxo synthesis), simultaneous or subsequent hydrogenation of the reaction mixture and oxidation of the dimethylols formed in the process obtained in a known manner, characterized in that the dicarboxylic acid mixture is treated with a mixture of heptane and pentanone, preferably in a weight ratio of 5: 1.