CZ281432B6 - Process for preparing 2-propenyl ester of (e,e)-2,4-hexadienic acid - Google Patents

Abstract

Acid-catalysed azeotropic esterification of allyl alcohol with sorbic acid.

Description

A process for the preparation of (E, E) -2,4-hexadienoic acid 2-propenyl ester

Technical field

The invention relates to a process for the preparation of (E, E) -2,4-hexadienoic acid (allysorbate) 2-propenyl ester of the formula I

O

BACKGROUND OF THE INVENTION

The (E, E) -2,4-hexadienoic acid 2-propylene ester has so far been prepared by esterifying (E, E) -2,4-hexadienoic acid with 2-propenyl alcohol in the presence of benzene and sulfuric acid in a yield of 67.8% (Met. Reaction prep 23.7 (1991), CA 78: 29186m), by reacting (E, E) -2,4-hexadienoic acid chloride with 2-propenyl alcohol (Synth, Commun, 12 (3), 3 (1982), or by re-esterification of (E, E) -2,4-hexadienoic acid alkyl ester with 2-propenylacetate in the presence of metal met, ΙΙ, ΙΙ metal methoxides (US 3,784,578 (1974), CA 80: 82110Z).

A disadvantage of the prior art processes is the preparation of more reactive intermediates, (E, E) -2,4-hexadienoic acid ester or chloride and the consequent higher demands on labor and raw material consumption. Other disadvantages are long reaction times, work with benzene as a potential carcinogen, lower yield. Another disadvantage is the treatment of the acid-catalysed mixture by esterification with aqueous alkali solutions, where, due to specific masses, the ester (approx.

0.950 t / m ³ ) and aqueous layers, which are similar values, are difficult to separate. Technically managing this problem requires increased investment requirements for the extraction equipment and the laboriousness of the process. An alternative procedure of neutralizing with aqueous alkali solutions prior to distilling off the 2-propenyl alcohol is limited by its considerable solubility in the aqueous layer.

SUMMARY OF THE INVENTION

The disadvantages of the prior art methods are substantially reduced by the production method of the invention. It is based on the fact that (E, E) -2,4-hexadienoic acid reacts with 2-propenyl alcohol in the presence of sulfuric acid in molar ratios of 1: 1,5-2,5: 0,028 - 0,037 at temperatures of 80 - 120 ' C of the reaction mixture with simultaneous azeotropic separation of water in the presence of toluene.

Advantageously, after distilling off the volatile components, the reaction mixture is mixed with solid carbonate or sodium bicarbonate, which acts not only as a neutralizing agent but also as an adsorbent trapping organic impurities and polymers. After filtration of the solid salts, the filtrate is subjected to vacuum distillation at 0.133 to 1.33 KPa.

-1GB 281432 B6

DETAILED DESCRIPTION OF THE INVENTION

Example 1 g (0.642 mol) of (E, E) -2,4-hexadienoic acid is stirred in 74 g (1.274 mol) of 2-propenyl alcohol and 40 ml of toluene and 2.75 g (0.043 mol) of acid are carefully added dropwise with stirring. sulfur conc. and the reaction mixture was refluxed with azeotrope for 6 hours. Thereafter, a mixture of toluene-2-propylene alcohol and water residues (ca. 2% by K.F.) is distilled off under vacuum (66 kPa). This can be deployed in the next reaction. The distillation residue was charged with 10 g of sodium bicarbonate and after stirring for one hour at 40-50 ° C, the salts were filtered off and washed with 10 ml of toluene. The filtrate is vacuum distilled at 0.150 KPa.

Yield: 83 g (84.9% of theory, calculated on (E, E) -2,4-hexadienoic acid).

The content of active substance (GC) is min. 97%.

Example 2 g (0.642 mol) of (E, E) -2,4-hexadienoic acid are stirred in 77 ml of the mixture distilled off in the previous example and containing 2.46 g of 2-propenyl alcohol per 10 ml and 2.32 g of toluene per 10 ml. ml. 55.4 g of fresh 2-propenyl alcohol (total amount of 2-propenyl alcohol is 74 g, i.e. 1.274 mol) and 16.5 g of toluene are added and 3.3 g (0.037 mol) of sulfuric acid conc. and the reaction mixture was refluxed with azeotrope for 6 hours. Thereafter, a mixture of toluene-2-propenyl alcohol and the remainder of water (ca. 2% by K.F.) is distilled off under vacuum (66 kPa).

This can be deployed in the next reaction. 11 g of sodium carbonate are introduced into the distillation residue and after stirring at 40-50 ° C for 1 hour, the salts are filtered off and washed with 10 ml of toluene. The filtrate is vacuum distilled at 1.25 KPa.

Yield: 84 g (85.9% of theory, calculated on (E, E) -2,4-hexadienoic acid).

The content of active substance (GC) is min. 97%.

Industrial applicability

(E, E) -2,4-hexadienoic acid 2-propenyl ester is used as a monomer in copolymerization reactions, as an admixture in cosmetic products or as a compound for diene synthesis.

Claims (1)

PATENT CLAIMS A process for the preparation of (E, E) -2,4-hexadienoic acid characterized in that the esterification of (E, E) -2,4-hexadienoic acid with 2-propenyl alcohol is carried out in molar ratios of 1.0 mol of acid (E, E) -2,4-hexadiene: 1.5-2.5 moles of 2-propenyl alcohol in the presence of 0.028-0.037 moles of sulfuric acid at temperatures of the reaction mixture of 80-120 ° C in the presence of toluene, neutralizing the reaction mixture with solid sodium bicarbonate or sodium carbonate and the product of formula I is purified by distillation under reduced pressure in the range of 0.133 - 1.33 KPa.