CS252800B1 - Method of metacrylic acid's 2-hydroxyethoxyethyl ester's continuous refining - Google Patents

Abstract

A method for continuously refining methacrylic acid 2-hydroxyethoxyethyl ester from a reaction mixture prepared by re-esterifying a methyl or ethyl methacrylate with diethylene glycol under the catalytic action of alkali metal alcoholates, in particular sodium methylate or glycollate or quaternary ammonium bases. countercurrent continuous organic solvent extraction with alkanes having a boiling point of 40 DEG to 120 DEG C. or mixtures thereof, preferably hexane or heptane under vibration motion, dispersing the diluted reaction mixture in drops into said alkane solvent and then counter-continually extracting with ethereal solvent , preferably diethyl ether under the action of vibration movement, wherein it is possible to disperse in the droplets either the reaction mixture or the solvent.

Description

The present invention relates to a process for the continuous refining of 2-hydroxyethoxyethyl methacrylic acid of formula I ch ₂ sC-cooch ₂ ch ₂ and ₂ ch ₂ oh

CH, (I>

· Compound 1 is a basic monomer that is converted by polymerisation into hydrophilic polymers used in the field of medical prosthetics, eg as a substitute for body organs, in the production of contact lenses, etc., and also for some industrial purposes, eg for the preparation of pharmaceutical forms. , as filling of chromatographic columns and the like.

On an industrial scale, a compound of formula I is produced primarily in two ways:

(a) From methacrylic acid which is condensed with ethylene oxide under the catalytic action of metal oxides such as copper, chromium or zinc. The 2-hydroxyethoxyethyl ester thus produced contains unreacted methyl methacrylic acid starting material, undesirable diethylene glycol methacrylate and other reaction by-products in relatively high amounts and needs to be carefully refined, especially when used for medical prosthetics and pharmaceuticals.

b) Reesterification of the methyl or ethyl ester of methacrylic acid with diethylene glycol under the catalytic action of alkali metal alcoholates, preferably sodium methylate, sodium glycolate or quaternary ammonium bases. The product obtained in this way always contains a substance resulting from double re-esterification of diethylene glycol with methyl methacrylate (hereinafter referred to as diester) of the formula II

2S2 800

_SC-CH2 C00CH ₂ «» -0CH ₂ CH ₂ CH ₂ C _00C-b CH ₂ (II) which is formed in an amount up to 7 wt. %, further contains unreacted methyl methacrylate and diethylene glycol and finally also methanol. Certain types of contact lenses cannot be produced from a monomer of formula I which contains, in particular, a diester of formula II in an amount of more than 1 wt. An advantage of this process is that the reaction mixture never contains unreacted methyl methacrylic acid. Numerous experiments have shown that the diester of formula II cannot be removed by traction distillation or by adjusting the reaction conditions of said re-esterification.

The only known refining process is based on the liquid extraction described in U.S. Pat. auterakém © testimony. The extraction is carried out by repeatedly dispersing the reaction mixture, which is diluted with water in a ratio of 2: 1 into an organic phase, such as, for example, petroleum ether or alkanes. The scattering is carried out by scattering by rotary movement and subsequent settling of the liquid phases.

It has now been found that 1 to 4 aqueous raffinate to organic solvent is best dosed each time. In this way unreacted methyl methacrylic acid methyl ester and diester of formula II are extracted, while the 2-hydroxyethoxyethyl ester of formula I remains in the aqueous phase to which sodium chloride is added in a 1: 1 weight ratio based on the ester. Extraction of the methacrylic acid ester is then carried out again 3 times by repeatedly dispersing the aqueous phase into ether in a weight ratio of 4: 1. In spite of repeated scattering and settling, a pure solvent is always used in both cases.

The described method has several drawbacks. Firstly, it is a batch, which in turn brings a rapid increase in the volume of equipment with an increase in production capacity and a significant proportion of manual skilled labor.

Furthermore, only one-time contact with the solvent is envisaged, which leads to a large consumption of solvent and high energy consumption during its regeneration. Another major disadvantage of the described process is the release of the ester of formula I from the aqueous phase by salting out, which causes corrosion of the equipment and contamination of the aqueous solution of unreacted diglycol

252 800 sodium chloride, which prevents its subsequent use and finally leads to large, up to 50% product losses ·

The process for the continuous refining of methacrylic acid 2-hydroxyethoxyethyl ester according to the present invention is characterized in that the reaction product diluted with water in a 1: 2 ratio by weight is fed continuously in intimate contact with a water-immiscible organic alkane solvent boiling at 40-12 ° C. by dispersing the aqueous phase into drops into an organic solvent by means of a vibrational movement. The droplets of the aqueous phase drop down because they have a specific gravity higher than the organic solvent. The solvent saturated with unreacted methacrylic acid methyl ester and diester of formula II is recovered by distillation, while the aqueous phase containing methacrylic acid 2-hydroxyethoxyethyl ester and the unreacted diethylene glycol is again fed continuously in continuous contact with an organic solvent with a water-immiscible ether, e.g. The aqueous phase is dispersed into drops into an organic solvent, such as diethyl ether, or the solvent is dispersed into drops into the aqueous phase by means of a vibrational movement. The aqueous phase containing diethylene glycol is returned to the reaction after concentration or is useful as an antifreeze. The ether phase is fed to a continuous film evaporator, where the ether is separated from the refined 2-hydroxyethoxyethyl ester of methacrylic acid of formula I. The contacting temperature is maintained between 15 ° C to 10 ° C, preferably 20 ° C.

The process of continuously refining methacrylic acid 2-hydroxyethoxyethyl ester from the reaction mixture after reesterification of the methacrylic acid methyl ester with diethylene glycol according to the present invention makes it possible to largely eliminate the disadvantages of the prior art methods of removing unreacted starting materials. Continuous countercurrent contact of the product-containing aqueous phase droplets with the alkane solvent using the vibration motion and subsequent continuous countercurrent contact of the product-containing phase with the ether solvent using the vibration motion ensures a high degree of refinement of methacrylic acid 2-hydroxyethoxyethyl ester with minimal solvent consumption, human work the volume of the device, the product losses not exceeding 12%. It also removes the disadvantageous salting-out of the ester of formula I from the aqueous phase during extraction with ether. Method according to

232,800 of the invention has been verified both laboratory and pilot and has been found to provide high purity products with a diester content of pattern 11 of less than 0.3 wt%. For the above purposes, this degree of purity is sufficient.

The details of the method according to the invention are described in more detail in the following examples, which are not to be construed as limiting.

Example 1 liters of the reaction mixture after re-esterification containing 48 wt. % of formula I, 7.0 wt. diesters of formula II, 5.8% ha. % methyl methacrylate, 26.3 wt. diethylene glycol was undiluted with 3 liters of water and cooled to 20 ° C. Thereafter, the reaction mixture was subjected to countercurrent extraction with hexane in a flow rate ratio of 11.2. The obtained aqueous raffinate contained less than 0.05 wt. % diester of formula II, 18.7 wt. % ester of formula I and 10.4 wt. The raffinate thus obtained was extracted with diethyl ether at a flow rate ratio of 1.5. The resulting methacrylic acid 2-hydroxyethoxyethyl ester contained 0.25 wt. % diester of formula II and 3.1 wt. diethylene glycol. Both exbrakoes were performed on a countercurrent column with vibrating trays.

Example 2 liters of the reesterification reaction mixture having the same composition as in Example 1 were diluted with 3 liters of water and cooled to 20 ° C. The reaction mixture treated in this way was subjected to extraction with petroleum ether at a flow rate ratio of 1.3. The obtained aqueous raffinate contained 0.07 wt.%. diesters of formula II,

17.3% wt. % ester of formula I and 9.6 wt. diethylene glycol. This raffinate was subjected to extraction with diisopropyl ether in a flow rate ratio of 11.7. The extract obtained was stripped of solvent on a vacuum film evaporator. The resulting 2-hydroxyethoxyethyl ester of methacrylic acid contained 0.23 wt% of diesters of formula 11 and 2.9 wt%. diethylene glycol. The yield of the ester of formula 1 based on the ester content of the reaction mixture is 89%. Both extraceses were carried out on a countercurrent column with vibrating trays. • 5 OBJECT OF THE INVENTION

Claims (3)

SUBJECT OF THE INVENTION 252 800 Process for the continuous refining of 2-hydroxyethoxyethyl methacrylic acid ester and reaction mixture prepared by re-esterification of methyl or ethyl methacrylic acid diethylene glycol under catalytic treatment with alkali metal alcoholates, in particular sodium methylate or glycolate or quaternary ammonium bases, characterized in subjecting it to countercurrent continuous extraction with an alkane type organic solvent having a boiling point of 40 to 120 ° C or mixtures thereof, preferably hexane or heptane, under a vibration motion, dispersing the diluted reaction mixture in drops into said alkane solvent and then countercurrent continuous extraction with ether solvent , preferably with a diethyl ether under the action of a vibration motion, wherein it is possible to disperse into the droplets either a reaction mixture or a solvent. Process according to claim 1, characterized in that the extraction is carried out at a temperature of 5 to 55 ° C, preferably 20 ° C. 5. The method of claim 1, wherein the ratio of the volumetric flow rates of the aqueous solution to said alkane and ether solvent is 1: 1 to 1: 4, preferably 1: 1.5.