CS241810B1 - Purification method of 2-hydroxyethylester of metacrylic acid - Google Patents

Description

SUMMARY OF THE INVENTION The present invention relates to a process for the purification of idethacrylic acid 2-hydroxyethyl ethyl ester. AND

2-Hydroxyethyl ester of imethacirylic acid of the formula I .....

CHs

CH ₂ = C-1COOCHCH ₂ OH (I) is the basic monomer which is converted into hydrophilic polymers, used in the field of medical prosthesis, for example for the production of contact lenses, replacement of body tissues, but also for technical purposes, such as fillers ehromatografických columns.

The known and industrially used process for the preparation of the compound of the formula (I) is based on imethacirylic acid and its addition with oxiranes under the catalytic action of metal oxides, for example zinc or copper. However, the 2-hydroxyethyl methacrylic acid 2-hydroxy ester thus produced must be very carefully and intricately purified for therapeutic orthotics because it contains undesirable ethylene dimethacrylate, unreacted starting acid and reaction by-products in relatively high amounts.

A further preferred method for preparing the compound of formula I consists in the simple re-esterification of the methacrylic acid imeithyleister with ethylene glycol from the catalytic action of alkali metal alcoholates, in particular sodium metholate, sodium ethylenene glycolate or quaternary ammonium bases.

Operationally, this method of manufacture is most suitable because the reaction mixture never contains free imetbaicrylic acid but practically contains only the ethylenedl methacrylate of formula II as the main impurity

CH ₃ oh ₃

CH 2 = 'C-COOCH 2 CH 2 OOC-C = CH 2' (II), which is produced in an amount of up to 5 wt. and whose directness in pure monomer intended for medical purposes is completely undesirable. Of the monomer containing diesteir of formula (II) in an amount of above 5 wt. Usable contact lenses cannot be produced at all because they do not meet the mechanical requirements. It has been demonstrated by a series of experiments that the diester of Formula II cannot be removed by fractional distillation or by adjusting the reaction conditions of said re-esterification.

Up until now. The methacirylic acid 2-hydroxyethyl ester obtained by any known method should be purified in the final phase by fractional distillation, preferably under the most gentle conditions, at a temperature as low as possible, in a high vacuum, in order to avoid collapse of the products. This very unpleasant operation prevented the possibility of a simple and economical expansion of production in terms of a substantial increase in the workpieces to be processed, since it was possible to process the feedstocks of the raw product up to a maximum of 2 kg, which is unacceptably low for non-medical purposes.

Even the additional inclusion of further extraction with petirol ether in the treatment of the reaction mixture after dilution with water did not lead to the desired goal, i.e. the removal of vacuum distillation.

SUMMARY OF THE INVENTION The present invention provides a simple, highly efficient process for the purification of 2-hydroxyethyl ester of methacrylic acid prepared by re-esterification of methyl or ethyl methacrylic acid with ethylene glycol under the catalytic action of alkali metal alcoholates, particularly sodium methylate or ethylene glycol additions of a polymerization inhibitor such as phenothiazine, after diluting the reaction mixture with water, separating the unreacted starting methacrylic ester, first extraction with petroleum ether and then saturated with sodium chloride, further extraction with ether and evaporation of the extract.

The process according to the invention is characterized in that, after the addition of activated carbon in an amount of 5 to 10% by weight, based on the weight of the evaporator, the residue is heated to 30 to 60 ° C, preferably 40 to 50 ° C. for 1 to 3 hours, preferably 1.5 to 2.5 hours, after which the active charcoal is removed.

Compared with vacuum distillation, the process according to the invention is technically and economically substantially simpler and more advantageous - and above all - more economical, the possibility of decomposition products being excluded. For most technical purposes, one carbon charcoal cleaning is sufficient; If the handle is extremely dirty, the cleaning operation can be repeated, with the amount of activated carbon being less and the heating time shorter.

The cleaning process according to the invention can also be carried out by stirring at room temperature, but the time (when the usable effect can be prolonged many times and the end effect is not reliable.) After stirring, the activated carbon can be filtered by either the original temperature. or even cooling to room temperature.

The main advantage of the process according to the invention is that it makes it possible to obtain a product (of excellent quality, comparable to that of a distilled product) and that it also allows processing of sticks weighing 100 kilograms or more, depending on the device (available). .

The details of the process are illustrated by the following non-limiting example.

S fl? 1 and id

A mixture of methacrylic acid methyl ester (26.3 g / g), ethylene glycol (26.3 kg), tetramethyl ammonium hydroxide (2.0 kg of a 5% methanolic solution), and phenothiazine (10 g) was heated to 610 ° C with stirring for 4 h. C (internal temperature, Potoim, 30 liters of water is added to the reaction mixture, stirred vigorously for 10 minutes and then left to stand for 20 minutes. The upper layer containing unreacted methacrylic acid ethyl ester and part of the diester of formula II is separated and The aqueous phase having a volume of about -60 liters is divided into 20 liters of id-o 3 glass boilers of 80 liters each and an additional 30 liters of water are added to each kettle. After this treatment, the aqueous solution of the crude monomer (carefully extracted 3 x 15 liters of petroleum ether. The combined petroleum ether extracts are recovered by distillation, the residue is discarded. The aqueous phases are saturated with 10 kg of brine. The extracts were combined and extracted with 0.1 times (10 liters) of ether each time. The copper (II) chloride stabilizer is evaporated. 6-7 wt. of activated carbon and heated to 40-50 ° C with stirring for 2 h, then the activated carbon is filtered off. 14.0 kg of pure 2-hydroxyethyl ethyl methafrylic acid 2-hydroxyethyl ester having a diesiter content of formula II of not more than 0.1 to 0.3% by weight are obtained for purposes other than the production of contact lenses, in particular for the production of chromatographic column packings. , quality fully satisfactory.

Claims (1)

Subject Process for purifying 2-hydnoxyethylesteru acid metihakrylové prepared reesterifi (kaeí imethyl- or ethyl meíthalkrylové ethylene glycol under the catalytic action of alkali metal alkoxides, in particular sodium methylate, or ethylene glycol, which Niehe quaternary ammonium bases, e.g. tetramethylamoniumihydroxifdu for ^one polymerization inhibitor additives ,, e.g. fenothiaziniu After diluting the reaction mixture with water, separating the unreacted invention of the imethacrylic acid ester, first by extraction with petroleum ether and then after saturation with sodium chloride, further extraction of the ether and evaporation of the extract, characterized in that the residue after addition of active carbon is added 10% by weight, based on the weight of the evaporator, is heated to 30 to 60 ° C, preferably 40 to 150 ° C, with stirring for 1 to 3 hours, preferably 1.5 to 12.5 ih, after which removes the activated carbon.