DD270063A1 - PROCESS FOR THE PREPARATION OF THIOGLYIC ACID ESTERS - Google Patents

Abstract

The invention relates to a process for the preparation of thioglycolic acid esters. Thioglycolic acid esters are intermediates for the preparation of organotin thioglycolates which serve to stabilize polyvinyl chloride in the chemical industry. The novel process for the preparation of thioglycolic acid esters is characterized by reacting monochloroacetic acid esters with sodium thiosulfate in a dimethylformamide-water mixture, then cleaving the resulting Bunte salt acetic acid ester in an inert, water-immiscible organic solvent, separating the organic phase and working up.

Description

Field of application of the invention

The invention relates to a process for the preparation of thioglycolic acid esters. Thioglycolic esters are raw materials for the production of organotin thioglycolates. These are widely used as stabilizers for polyvinyl chloride (PVC) in the chemical industry.

Characteristic of the known state of the art The processes in use are usually based on the production of thioglycolic acid Monochloroacetic acid and the subsequent esterification. For the synthesis of thioglycolic acid monochloroacetic acid is usually used with sodium thiosulfate, thiourea, Sulfides or polysulfides (Enzyclopedia of Chem. Techn., New York 1955, Vol. 14, pp. 78-83, Japanese Patent 8175 (1957), Japanese Patent Specification No. 17,564

i; 365); Bunte, Ber.7 (1874) 646; Nokoto, M., J. Soc. Org. Synth. Chem. Japan 13 (1955) No. 1, pp. 41-44; Weigand, Hilgetag, Exp.

Methods in the org. Chem. (1969) 583; et al). All these methods have considerable disadvantages and are sometimes very expensive. So on the one hand, the use of toxic Substances required, e.g. Hydrogen sulfide, on the other hand it comes to the emission of toxic Abga> e, so Hydrogen sulfide and sulfur dioxide, or to the formation of toxic gases. Another disadvantage i.i the need for the use of diethyl ether as an extraction agent and in the formation

a number of by-products. Thus, in the case of the technically frequently used process of reaction with sodium thiosulfate, formation of dithiodiglycolic acid, thiodiglycolic acid and polyglycolates, which require a complicated after-treatment, for example reduction with iron / hydrochloric acid. Another disadvantage is the relatively low storage stability of

Thioglycolic acid secondary to secondary reactions, including oxidation and polymerization. An interesting alternative method was first the preparation of monochloroacetic acid, then the preparation of the Alkali S-alkyl thiosulfates of acetic acid esters (Bunte salt acetic acid ester) by reaction with sodium thiosulfate and the

subsequent acidolytic cleavage to the desired ester proposed (DD-PS 214126). However, under the reaction conditions proposed here, the desired reaction does not occur. Thus sodium thiosglfate reacts in the aqueous

Milieu not with the water-insoluble ester, not even with the addition of phase transfer catalysts. In addition, the leads AcidolysedesBuntesalzessigsäureesters in water exclusively to cleave the ester group and thus to form the

Alcohol.

Object of the invention

The aim of the invention is to provide a simple, reproducible. Process for the preparation of thioglycolic acid esters, based on the reaction sequence monochloroacetic acid ester, Bunte salt acetic acid ester and thioglycolic acid ester to develop.

Explanation of the essence of the invention

The object of the invention therefore consists in a suitable process for the preparation of thioglycolic acid esters, preferably of higher alcohols, on the reaction sequence monochloroacetic acid ester and Bunte salt acetic acid ester.

The reaction of the Monochloressigsäureesters with sodium thiosulfate is realized according to the invention in a dimethylformamide-water mixture in excellent yield. In this case, the dimethylformamide content in the solvent can vary widely, between 10 and 90% by weight in%, without appreciable losses in yield occurring.

For the further conversion to the thioglycolic acid ester, the use of 30 to 150% by weight, preferably 60 to 80% by weight, of dimethylformamide is required in comparison to the monochloroacetic acid ester used, with about 1 to 2 times the absolute amount of solvent mixture. The desired acidolysis of the Bunte salt acetic acid ester to the thioglycolic acid ester is then achieved by adding an inert, water-immiscible orgnnischen solvent of aromatic or aliphatic character, preferably toluene or benzene. But also with gasoline, above so with xylene, very useful results are achieved.

By means of sulfuric acid, the pH is adjusted to 1 and the mixture is heated to 80 to 100 ° C for 2 to 4 hours. A longer reaction time is not recommended, it would only lead to further partial ester cleavage. Subsequently, the organic phase is separated and worked up.

In this simple way you get z. B. the Ttvoglykolsäureisooktylester in 90 to 95% yield of theory, based on chloroacetic ester used, in 95% purity.

Equally good results are obtained in the analogous preparation of thioglycolic acid hexyl and other higher esters.

The advantages of the method presented here are:

1. Elimination of Thioglykolsäureherstellung with the aforementioned chemical and technological disadvantages.

2. Considerable savings of manual work.

3. Höhrer yields of thioglycolic acid ester, based on monochloroacetic acid used and general savings of raw materials.

4. Significantly environment-friendly process.

5. Guts stability and shelf life of Buntesalzessigsäureesters optionally in dilute solution as well as in enriched form. After completion of the reaction, dimethylformamide can be recovered from the extraction water after neutralization, preferably with soda, by distillation as water-dimethylformamide mixture and used again.

In addition to the acidolytic cleavage, a reductive with zinc / sulfuric acid or zinc / hydrochloric acid, also in the presence of an inert organic solvent, is possible. But here are the yields of about 65 to 70%, well below the levels of acidolytic cleavage.

embodiments

example 1

Synthesis of thioglycolic acid isooctyl ester

62 g of monochloroacetic acid isooctyl ester (0.3 mol), 74.4 g of sodium thiosulfate-5-hydrate (0.3 mol), 45 ml of dimethylformamide and 45 ml of water are reacted at 70 ° C for one hour. Anschießend is set to 500 ml of toluene and 2 g of 50% sulfuric acid and stirred gently for 3 hours at 9O ⁰ C internal temperature. Then cool, wash first with 200ml of water. This aqueous extraction mother liquor is neutralized with soda and distilled to recover dimethylformamide. The organic phase is repeated twice with 200m! Washed water and then concentrated in vacuo. This leaves 57 g (93.6% of theory) of ester, which has a content of 95%.

Example 2

Synthesis of thioglycolic acid isooctyl ester

Analogously to Example 1, first 62 g of monochloroacetic acid ester, 74.4 g of sodium thiosulfate-5-hydrate, 30 ml of dimethylformamide and 60 ml of water are reacted. The Buntesalzspaltung and ester workup is analogous.

Yield: 53.5 g (88% of theory). Ester content: 92%.

Example 3

Synthesis of thioglycolic acid hexyl ester

53.4 g of monochloroacetic acid hexyl ester (0.3 mol), 74.4 g of sodium thiosulfate-5-hydrate, 45 ml of dimethylformamide and 45 ml of water are first reacted analogously to Example 1 to Bunte salt ester and then split acidolytlsch to Thioglykolsäurehexylester.

The yield is 48g (90% of theory) at a level of 96%.

Example 4

Synthesis of thioglycolic acid decyl ester

70.4 g of monochloroacetic acid decyl ester (0.3 mol), 74.4 g of sodium thiosulfate-5-hydrate, 50 ml of dimethylformamide and 30 ml of water

are reacted for 1 hour at 80 ⁰ C with stirring. Are then added 600ml of toluene and 2g of 50% sulfuric acid and stirred for 3 hours at 100 ⁰ C. Working up is carried out analogously to Example. 1

The yield is 65.3 g (94.5% of theory) at a level of 96%.

Claims (10)

1. A process for preparing thioglycolic esters by reacting Monochloresslgsäureestern with Natriumthiosulfatzu Buntesalzessiysäureestern, characterized in that the Monochloressigsäureester reacted with Natriumtios. Filfat in a dimethylformamide-water mixture, the obtained Buntosalzessigsäuroester then cleaved in the presence of an inert, water-immiscible organic solvent and then the organic phase is separated and worked up in a known manner. 2. The method according to claim 1, characterized in that the dimethylformamide Gohalc is between 10 and 90% by weight in% in the solvent. 3. An ancestor according to claim 1, characterized in that 30 to 150% by weight in%, preferably 50 to 80% by weight of dimethylformamide in comparison to the Monochloressigsäureester used in a 1 to 2faohen absolute amount of dimethylformamide-water mixture are used. 4. The method according to claim 1, characterized in that a solvent of aromatic or aliphatic character is used. 5. Process according to claims 1 and 4, characterized in that toluene, benzene, xylene or gasoline are used. 6. The method according to claims 1,4 and 5, characterized in that the Buntosalzessigsäuroestoracidolytically cleaved. 7. The method according to claims 1,4,5 and 6, characterized in that the acidolytic cleavage with silicic acid is carried out at a pH of 1. 8. Process according to claims 1 and 4 to 7, characterized in that the acidolytic cleavage in the period of 2 to 4 hours at a temperature of 80 to 100 ⁰ C is performed. 9. The method according to claims 1,4 and 5, characterized in that the Buntesalzessigsäureester is cleaved reductively. 10. The method according to claims 1,4,5 and 9, characterized in that the reductive cleavage with zinc / sulfuric acid odor zinc / hydrochloric acid is performed.