DD289274A5 - PROCESS FOR THE PREPARATION OF DIALKYL CINNTHIOGLYCOLATE - Google Patents

Abstract

The invention relates to a process for the preparation of Dialkylzinnthioglykolaten in chemically pure form, which are obtained by reacting Dialkylzinnoxiden and Mercaptocarbonsaeuren in Molverhaeltnis 1: 1 in the presence of absolute ethanol and anschlieszender azeotropic distillation. These products may be components of compounds which are used either as initiator systems for the synthesis of polyurethanes or silicone elastomers or as stabilizers for halogen-containing vinyl polymers against thermal degradation processes initiated by heat. {Dialkyltin thioglycolates; Synthesis; azeotropic distillation; Dioctylzinnthioglykolat; dibutyltin thioglycolate}

Description

- Task

The object of the invention is the development of a technically low-cost process for the preparation of Dialkylzinnthioglykolaten with good yield and in high purity, d. h., the products obtained must be free from other by-products which impair the use.

Features of the invention

The process according to the invention consists of dialkyltin oxides having the general formula I

R ₂ SnO (I)

wherein R represents the same alkyl groups having 4 to 10 carbon atoms and mercaptocarboxylic acids having the general formula II,

(II)

OH

in which η is between 1 and 2 and preferably has the value 1, dialkyltin thioglycolates prepared by adding solutions of 1 mol of a mercaptocarboxylic acid, preferably thioglycolic acid in 16-24 mol, preferably 19-21 mol absolute ethanol (water content <0.05%) with 1 Mol dialkyltin oxide in the temperature range of 293-333 K within 0.2 to 0.5 hours and then 0.8 to 1 hour at 345-348 K are reacted. Dioctyltin thioglycolate or dibutyltin thioglycolate are preferably prepared by using corresponding dialkyltin oxides.

The addition of dialkyltin oxides to a solution of a mercaptocarboxylic acid in absolute ethanol surprisingly leads to a very homogeneous distribution of said tin compound in the reaction mixture. It was not to be expected that the oxides would not form clumps, since the concentration of thioglycolic acid on the one hand is very low and on the other hand has no dispersing or emulsifying action. Furthermore, the reaction at temperatures of only 293-348 K and in only 0ö-1.5 hours. At the same time not yet achieved yield of> 97%, an indication of another, previously unknown reaction sequence.

Subsequently, the ethanol is distilled off azeotropically together with the water formed in the reaction, optionally under reduced pressure in the range from 0.1 to 2 kPa, over the course of 0.6 to 2 hours in the temperature limits of 343-351K.

The products obtained are distinguished by the fact that they have a very high chemical purity, do not decompose on storage, split off no volatiles under thermal stress, do not discolor and are odorless.

The azeotropic distillation to remove water of reaction in the formation of anhydrides or esters with various organic compounds such as benzene, toluene, ethanol is known as a principle. However, it is surprising that the azeotropic distillation with ethanol in this case leads to particularly pure products, in contrast to the use of z. B. toluene (see comparative and application example). The compounds are obtained in a very pure form.

For a more detailed explanation of the invention serve the following embodiments:

The potentiometric determination of the content of dialkyltin thioglycolate indicated in Examples 1 to 4 was carried out with the method of potentiometric titration with ethanolic potassium hydroxide which is customary in analytical chemistry.

The values given for the content of tin were determined using the method of complexometric Sn determination also used in analytical chemistry, the values for the sulfur content by iodometric sulfur determination and the values for the carbon and hydrogen content by combustion elemental analysis.

For comparison, characteristics of a corresponding compound prepared by the prior art method are listed.

Embodiment 1

Production of dioctyltin thioglycolate by the process according to the invention.

40 g of dioctyltin oxide are added to a solution of 10.2 g of freshly distilled, anhydrous thioglycolic acid in 120 g of absolute ethanol (water content <0.05%) in a 500 ml round bottom flask. This mixture is suspended in a vacuum rotary evaporator at 80 revolutions of the flask per minute at room temperature without additional aids. In this apparatus, the reaction mixture is heated under normal pressure within 30 min from 293 to 333 K and then held for a further 1 hour at 348K to complete the reaction. In the following, the mixture is treated at 1.3 kPa for 1.5 hours at the same temperature and then at 0.13 kPa for 4 hours to completely remove the alcohol.

The waxy reaction product is washed extensively with pure water at room temperature for purification and then dissolved in 200 ml of gasoline (bp 338-353 K) with heating, this solution is filtered through a pleated filter and concentrated to 50% of the original volume. Thereafter, the product precipitates again on cooling. To remove the last gasoline residue, it is stored for 3 hours at 333K in a vacuum drying oven (1.3kPa).

Yield: 46.9 g (97.1% d.fh)

The product produced on the path shown has the following characteristics:

- Potentiographical determination of dioctyltin thioglycolate content: 99.8%

IR spectroscopy: band at 1550 cm ^-1

- Mass loss under thermal stress (1 h, 433 K): 0.05%

- Color: colorless

- Odor: very low

Sb.,.: 7.36%; S _g . . _(7.38% Sn "" .: 27.31%; Sn ₈ ,,: 27.19% C _ber: 49.69%; C ,,,.:. 49.60% Hb,... : 8.28%; H "f .: 8.31%

Implementation Bills 2 Production of Oibutyltinthloglykolat by the method according to the invention.

28 g of dibutyltin oxide are added to a solution of 10.2 g of freshly distilled, anhydrous thioglycolic acid in 102 g of absolute ethanol (water content < 0.05%) in a 500 ml round bottom flask. This mixture is suspended in a vacuum rotary evaporator at 80 revolutions of the flask per minute at room temperature without additional aids. In this

Apparatus, the reaction mixture is heated under normal pressure within 30 minutes from 293 to 348 K and

then held at 348K for 1 hour to complete the reaction. In the following, the reaction mixture is treated at the same temperature at 1.3 kPa for 1.5 hours and then at 0.13 kPa for 4 hours to allow this to occur

Walk the Alkonc. completely remove. The waxy reaction product is washed extensively with pure water at room temperature for purification, and

then dissolved in 300 ml of petrol (bp: 338-353K) with warming, the solution filtered through a pleated filter and concentrated to 33% of the original volume. Thereafter, the product precipitates again on cooling. To remove the last

Gasoline residue is stored for 3 hours at 333K in a vacuum oven (1.3kPa). Yield: 35 g (97.6% of theory) The product produced on the path shown has the following characteristics:

- Potentiographic determination of the content of dibutyltin thioglycolate: 99.8%

IR spectroscopy: band at 1550 cm ^-1

- Mass loss under thermal stress (1 h, 433 K): 0.06%

- Color: colorless

- Odor: very low

Sb.,.: 9.90%; S ₈ ,,.: 10.0% Sn _b ".: 36.75%; Sn,.,.: 36.64% Cb ,,.: 37.15%; C ₈ .,: 37.06% Hb. ": 6.19%; H _e ".: 6.21%.

Embodiment 3 (Comparative Example) A process according to the invention, but instead of ethanol azeotropic distillation using a toluene Azeotropic distillation produced Dioctylzinnthioglykoiat has the following characteristics:

- Potentiographic determination of the content of dioctyltin thioglycolate: 76%

IR spectroscopy: band at 1550 cm ^-1

- Mass loss under thermal stress (1h, 433K): 7.3%

- Color yellow

- smell: intense

Sb ,,.: 7.36%; S ₈ ,,.: 6.98% Sn _b . ": 27.31%; Sn ₈ ,,.: 26.21% C _b ".: 49.69%; C ₈ ,,.: 48.21% Hb ,,.: 8.28%; H ₈ ,,.: 7.62%

Embodiment 4 (Comparative Example) A dioctyl tin thioglycolate made by heating diisopropyltin diisooctyl thioglycolate in the prior art

has the following characteristics:

- Potentiographic determination of the content of dioctyltin thioglycolate: 74%

IR spectroscopy: band at 1550 cm ^-1

- Mass loss under thermal stress (1 h, 433 K): 6.2%

- Color yellow

- smell: intense

Sb ,,.: 7.36%; S ₀ ,,.: 7.01% Sn _b ".: 27.31%; Sn ₈ ,,.: 26.1% C _be .,: 49.69%; . C ,, _8: 48.25% Hb ,,: 8.28%;. H ₈ ,,.: 7.65%

Exemplary Embodiment 5 (Verglelchsbelsplel)

A dioctyltin thioglycolate prepared from thioglycolic acid and dioctyltin oxide in the prior art has the following characteristics:

- Potentiographic determination of the content of dioctyltin thioglycolate: 78%

IR spectroscopy: band at 1550 cm ^-1

- Mass loss under thermal stress (1 h, 433K): 5.8%

- Color: colorless

- smell: intense

_Sb ": 7.36%; S, 7.03% Sn _b ": 27.31%;... Sn _{g, (:} 26.70% C _b. ": 49.69% C, _g.": 48.32% Hi ,,,: 8.28%; H _{fl, (.:.} 7.92%.

Claims (4)

1. A process for the preparation of dialkyltin thioglycolates in chemically pure form, by reaction of dialkyltin oxides of the general formula (I), R ₂ SnO (I) wherein R is linear, in each case identical alkyl groups having 4 to 10 carbon atoms and mercaptocarboxylic acids of the general formula (II), HS- (CH _a ) r, -C ^ ₍ OH in which η preferably has the value 1, in the presence of ethanol, characterized in that the dialkyltin oxides are introduced into a solution containing alcoholic mercaptocarboxylic acids, the ratio of the dialkyltin oxides to the mercaptocarboxylic acids in moles being 1: 1 and that of the ethanol being from 16 to 24 mol, based on 1 mol of dialkyltin oxide, the reaction temperature is 293 to 348K and the reaction time is 0.5 to 1.5 hours, followed by an ethanol-water azeotropic distillation at temperatures of 343 to 353 K, in a time of 0.5 to 2 hours and a pressure of 0.1 to 2, OkPa connects. 2. The method according to claim 1, characterized in that the dialkyltin oxides are dioctyl or dibutyltin oxide. 3. The method according to claim 1, characterized in that is used as mercaptocarboxylic thioglycolic acid. Field of application of the invention The invention relates to a process for the preparation of pure Dialkylzinnthioglykolaten, which may be components of compounds which are used either as initiator systems for the synthesis of polyurethanes as well as silicone elastomers or as stabilizers for halogen-containing vinyl polymers against degradation processes initiated by heat. Characteristic of the known state of the art Dialkyltin thioglycollates can be formed from dialkyltin diisooctyl thioglycolates over prolonged storage and / or by thermal action on said compounds (see Beilenger, V. Verdu, J. Carette, LB, Vymazalova, Z. and Vymazal, Z. Polym. Degr. And staff. 4 [1982], 577; Cooray, B.B. and Scott, G .; Polym. Degr. and staff. 2 [1980], 35). In this way, the dioctyltin thioglycolate and the dibutyltin thioglycolate are accessible. Further, dioctyltin thioglycolate can be prepared according to British Patent 1,430,933 from dioctyltin oxide and thioglycolic acid in the presence of denatured alcohol. The disadvantage here is a high technical complexity for the dispersion of dialkyltin oxides in the alcohol, which results from the fact that the powdery oxides tend to form clumps when introduced into the alcoholic phase. For a subsequent complete reaction, the optimally reactive preparation of the oxide by shearing stirring is therefore necessary first. Disadvantages of the dialkyltin thioglycolates prepared or obtained according to the known prior art are their insufficient purity, which has a negative effect on the use of thioglycolates and an odor adhering to its substances, based on the presence of volatile products, leading to nuisance in handling, and a more or less less strong discoloration. It has not yet been possible, the Dialkylzinnthioglykolate which by the known methods in yields ranging from 5 to 92% (boiled to the starting materials), quantitatively from the still present after the separation of a large amount of dialkyl tin diisooctyithioglykolat and / or a number of other by-products. Therefore, with the use of the products produced according to the previously known principles, the mentioned significant disadvantages associated. Object of the invention The aim of the invention is to develop a process for the preparation of chemically pure dialkyl thioglycolates. In this case, products are to be obtained which can be produced with less technical effort and which do not lead to odor nuisance.