DE4318456A1 - Process for the preparation of glycolide and lactide - Google Patents

Abstract

Glycolide (Ia) or lactides (Ib) <IMAGE> are prepared by thermocatalytic cleavage of condensation products of glycolic acid or, respectively, an alpha -hydroxypropionic acid while removing Ia or Ib, respectively, from the reaction mixture by distillation, converting the distillate into the solid phase by cooling, and purifying the resulting crude product by washing it with an ether having 4 to 12 carbon atoms.

Description

The present invention relates to a new method for manufacturing position of glycolide (Ia; 1,4-dioxane-2,5-dione) or of lacti den (Ib; 3,6-dimethyl-1,4-dioxan-2,5-dione)

through thermal-catalytic cleavage of condensation products glycolic acid (IIa) or an α-hydroxypropionic acid (IIb) with distillation removal

of Ia or Ib from the reaction mixture, transfer of the distil lates by cooling to the solid phase and cleaning the sun obtained crude product.

Glycolide and lactide are the raw materials for high molecular weight Polyglycolide or polylactide. These polymers find u. a. Ver use as resorbable surgical sutures.

The known technical production of glycolide or Lactides for further processing into polymers are generally possible mean the monomeric α-hydroxycarboxylic acids glycolic acid and Lactic acid, this in the D or L form and as a race mixed mixture may be present. These acids are caused by heating zen condensed to oligomeric esters, which then thermally in Cleaved presence of catalysts into the dimers Ia and Ib and be distilled off.

The cleaning of the crude product thus obtained from impurities (predominantly oligomers of the starting acids used and these Acids themselves), was previously carried out by recrystallization from ver different solvents, e.g. B. iso-propanol (EP-A 261 572), tert-amyl alcohol (DE-A 18 08 939), carbon tetrachloride (DE-A 12 34 704) or ethyl acetate (US-A 4727163).  

However, these cleaning methods are unsatisfactory because of the Do not always crystallize products, but sometimes as oil occur, and because the recrystallization usually several times must be carried out to produce products of such high purity obtained, which is essential for the production of high molecular weight polymers is casual.

In addition, solvents such as alcohols with cleavage of Ia or Ib to esters of glycolic acid IIa or α-hydroxypropionic acid IIb lead.

WO 92/00974 relates to the purification of crude lactide in one Two-phase system consisting of water and a ketone, ether or ester. In this way of working it can react with the water Lactide will result in losses in the valuable product.

The task was therefore to provide a method make it possible to get the raw products after the above described methods are produced in a simple manner to clean.

Accordingly, the above-mentioned method has been found which thereby is characterized in that the crude product with an ether Washes 4 to 12 carbon atoms.

The ethers to be used according to the invention are Ethers with a total of 4 to 12 carbon atoms. It comes ali phatic ethers such as diethyl ether, di-iso-propyl ether, di-n-butyl ether and methyl tert-butyl ether into consideration, cyclo aliphatic ethers such as tetrahydrofuran, araliphatic ethers such as Anisole, aliphatic polyethers such as glycol dimethyl ether and Glycol di-n-butyl ether and cyclic polyethers such as dioxane. Before are aliphatic ethers with 4 to 7 carbon atoms, ins special diethyl ether, di-iso-propyl ether and methyl tert.- butyl ether.

The glycolide and lactides can be prepared by heating of aqueous solutions of IIa or IIb. Thereby in a preferred embodiment, distilled off water. The sow oligomerize ren IIa or IIb and are then converted into the dimers the acids, namely Ia and Ib split. For this split reaction catalysts are used, e.g. B. tin, tin halo genide or tin salts of carboxylic acids such as Sn (II) -2-ethylhexanoate (EP-A 261 572), titanium alkylates (DE-A 12 34 703) and antimony oxide or Antimony halides (Prep. Meth. Of Polymer Chem., 2nd edition, 1968, p. 363). Glycolide or the lactides are then distilled off liert, if necessary with simultaneous passage of an inert  ten gas such as nitrogen (e.g. US-A 4,835,293), and solid Cooled raw product.

The crude glycolide or Lactide can be washed directly on a filter with an ether be or previously slurried in the ether and then be filtered.

In general, 1 kg of raw is used for cleaning product 0.1 to 100, preferably 0.3 to 3 kg of ether.

It can preferably be in the range from -78 to 50 ° C., particularly preferably be worked at 0 to 30 ° C. But it is easiest that Carry out cleaning at room temperature.

The ether dissolves the impurities and it remains Separation of the ether phase a colorless product. The ether phase can be evaporated to dryness, and the resulting festival Substance can again be used to produce the glycolide or lactide be set.

The method according to the invention allows technically simpler Way to produce glycolide and lactide in high purity.

The method is of particular importance for optically active [L, L] lactide and [D, D] lactide, which consists of optically active D or L-lactic acid is produced. The method according to the invention enables the ratio of the particularly sought-after optically active lactides compared to the meso form by cleaning increase step.

Examples

88 wt .-% aqueous L-lactic acid was at 130 ° C over a Distillation bridge drained until no more water was able to condense sated. Then the bottom temperature was raised to 200 ° C. in 8 hours, to remove the water of reaction. The oligo milk thus obtained acid was split with 1.5% by weight of Sn (II) ethylhexanoate at 250 ° C The product (crude lactide) was obtained as a crystal slurry.

General manufacturing instructions

90 g of crude lactide were stirred in 30 g of ether and cooled to 0 ° C. The colorless solid was filtered off and several times with total washed together with 30 g of the corresponding ether. The experimental results can be found in the table.

The experiments show that the product by the invention Cleaning step is obtained in the highest purity. The amount of the optically active lactide in the solid is compared to that in the Mother liquor increased.

Claims (1)

Process for the preparation of glycolide (Ia) or lactides (Ib) by thermal-catalytic cleavage of condensation products of glycolic acid or an α-hydroxypropionic acid with distillative removal of Ia or Ib from the reaction mixture, conversion of the distillate by cooling into the solid phase and purification of the crude product thus obtained, characterized in that the crude product washes with an ether with 4 to 12 carbon atoms.