DE960187C - Process for the decomposition of mixtures of isomeric aldehydes - Google Patents

Description

ISSUED MARCH 21, 1957

Jfr. 96Q

B 19298IV l I'12

Mixtures of carbonyl compounds with one another, e.g. B. Mixtures of isomeric aldehydes can often not easily be separated by distillation in effective fractionating colonies. Is distilled, for example, a mixture of about 45 ° / o iso-butyraldehyde (bp. 65 °) and 55% n-butyraldehyde (bp. 75 ⁰⁾ under normal conditions, so even the siedegerechten fractions consist of the distillate from mixtures of both isomeric aldehydes.

It has now been found that mixtures of isomeric aldehydes can be converted very effectively into the individual can decompose pure aldehydes if one makes use of the property that the various Bisulfite addition compounds differ in stability with increasing temperatures demonstrate. Namely, if the mixtures of aldehydes are converted into their bismuth compounds and left if you act on these rising temperatures, the individual aldehydes are surprisingly set free in the order of their boiling points. When heated, the The bisulfite compound of the lower-boiling aldehyde is split and this can now be achieved by distillation be separated from the solution without the higher-boiling aldehydes, which are still used as bisulfite compounds are available, significant quantities are carried along. After removing the aldehyde released first, the higher boiling points isolated by further heating the solution in the same way.

For transferring to the bismuth compounds the mixture of aldehydes is treated with an aqueous solution of a neutral sulfite

simultaneous exposure to the approximately equivalent amount of a weakly acidic compound, e.g. B. a weak acid or an acidic salt of such. On the isolation of the bisulfite compounds can be done without. The solution or suspension of the addition compounds is then heated, the aldehydes in the order of their boiling points in pure form distill off. The remaining sulfite solution is

ίο without further ado, or - in the case of application volatile weak acids - after renewed saturation with the acid, reusable.

Are suitable for the method according to the invention

especially sodium, potassium and ammonium sulphite, but also sulphites of non-volatile organic compounds Bases, e.g. B. the alkanolamines. Examples of weakly acidic compounds are: carbonic acid, Boric acid, molybdic acid, tungstic acid, glycocoll, alanine, secondary sodium citrate, disodium phosphate and the like. Mixtures of these weak acids or acidic salts with one another can also be used. The weak acids or acid salts can be added before, during or after the addition of the aldehyde mixture to the sulfite solution

As these are added or, if they are gaseous - as in the case of the use of carbonic acid - ■ are introduced into this. Using volatile acids, which are driven off when the aldehyde-containing solutions are heated the escaping acids can be collected and reused. A suitable solution of a neutral sulphite can also be obtained in that one starts from a bisulfite and to the solution of this salt a salt of one of the mentioned adds weak acids.

The aqueous solution of molar amounts of alkali metal sulfite and a weak acid, or the salt of such, has in the cold, a _pH value between about 6 and 7 and has the property in the cold or at moderate heat aldehydes under slight increase in its to loosen or bind the p _{H value.} On heating such a solution, the aldehydes are cleaved again to regenerate the initial p _H -value, unless a volatile acid was used. This process can be repeated as often as desired, since the solution does not suffer any irreversible changes. If you work with volatile acids, it is sufficient to reintroduce them into the remaining solution in order to get back a usable separating solution.

Neutral sulfite and weak acid are used in approximately equivalent amounts. In the event of

the boric acid can also be less, z. B. ² Z ₃ mol, suffice if the acidity of this acid is increased by adding a polyhydric alcohol such as mannitol, diglycol, glycerol or 1,3-butylene glycol. The addition of glycerine or another polyhydric alcohol is also advisable because it increases the resistance of the solution to oxidation by atmospheric oxygen and increases the solubility of the aldehyde bisulfite compound. The water content of the alkali metal sulfite solution is expediently chosen so high that the aldehyde bisulfite compound remains completely dissolved at the working temperature.

It has already been proposed (see US Pat. No. 2,544,562), aliphatic aldehydes and To obtain ketones from mixtures containing such, by treating the mixtures with a Solution of water-soluble bisulfites, which was adjusted to dfen Pa value 5 to 8, shaken out and the aqueous solution containing the bismuth compounds is then brought to temperatures without the addition of alkali above the decomposition point of the bismuth compounds heated. It is possible to break down aldehyde mixtures into the pure components, nowhere mentioned and apparently not recognized either.

It is also known (see. The USA. Patent 2555553), from mixtures, the aliphatic Methyl ketones and aldehydes contain, the aldehydes to be separated by the fact that the mixtures at about 40 to 100 ° treated with aqueous bisulfite solutions, essentially only the bisulfite compounds form the aldehydes, then the methyl ketones, e.g. B. by extracting with a To remove solvents and finally to break down the bisulfite compounds of the aldehydes again. Here, too, there is the possibility of converting mixtures of isomeric aldehydes into their pure components separate, neither mentioned nor suggested.

example

800 ecm a mixture consisting of equal parts of n- and iso-butyraldehyde with a solution of 1.26 kg of anhydrous sodium sulfite and 0.62 kg of boric acid mixed in 3.5 1 of water and 0.5 1 of glycerine, until complete solution has occurred. The mixture is then heated with stirring and that continuously distilling over aldehyde-water mixture condenses.

The template is changed at 65 ° head temperature. The fractions that have passed above and below this temperature are separated from the water, dried and distilled again. 90% of the first fraction (isobutyraldehyde) pass between 63 and 66 °, and 80% of the second fraction (n-butyraldehyde) between 72 and 75 °. By cutting out an intermediate fraction of about 64 to 70 ^° when distilling off the aldehydes, these can be obtained in an even greater purity. The remaining sulfite solution can be used again after adding the distilled water.

Claims (2)

Patent claims: I. Process for the decomposition of mixtures of isomeric aldehydes via bisulfite addition compounds and decomposition of the accumulation bonds, characterized in that the mixture of aldehydes by treating with the aqueous solution of a neutral sulfite and eifter approximately equivalent amount of one weakly acidic compound converted into a mixture of bisulfite compounds, the obtained The mixture is then heated to increasing temperatures, in this case in the order of their Boiling points one after the other released aldehydes are removed separately and the remaining aldehydes Solution cools and is used again for the production of the bismuth compounds. 2. Embodiment of the method according to claim i, characterized in that one Sulphite solutions are used which, in addition to the weakly acidic compound, also contain polyhydric alcohols contain. Considered publications:
U.S. Patent Nos. 2555553, 2544562. © 609 620/455 9.56 (609 843 3.57)