DE1195289B - Process for the preparation of terephthalic acid monoglycol ester - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY Inta .: C07c

GERMAN 4MTWs PATENT OFFICE

German class: 12 ο-14

EDITORIAL * ■ - ^ *

File number: B 69029IV b / 12 ο

1 195 289 filing date: September 29, 1962

Opening day: June 24, 1965

1 method of manufacture

".... ... ,. . ... ". , of terephthalic acid monoglycol ester

Terephthalic acid esters serve as important intermediate

products in the manufacture of polyesters, ins- Applicant

special for the technically significant linear _,. , .... "", _,.,

Polyethylene terephthalate, the film- and fiber-forming Badische Anihn- & Soda-Fabrik
Has properties. Here you go either from 5 Aktiengesellschaft, Ludwigshafen / Rhem

Terephthalic acid dimethyl ester from, esters this in .. " _f . ,,

Presence of ethylene glycol to the monomeric bis- * ~ ^s "■ ^{:, e} 5 ° enaim 5 ^:

(^ -hydroxyäthyl) -terephthalat um and polycondensation- Dr.WalterSchenk, BadDurkheim;

then converted to polyethylene terephthalate a ?? ^S ^ ^e ™ r ^U ii? ' · Mi · '

suitable molecular weight., The direct esterification of 10 Dr. Albrecht Wallis, Ludwigshafen / Rhem

Terephthalic acid with ethylene glycol to form the monomeric ~

Bis (/ 3-hydroxyethyl) terephthalate has so far been tech- 2

nisch not yet carried out, as the degree of purity of monoalkali terephthalates with ethylene glycol or

the tereethylene oxide produced by the usual methods under normal or elevated pressure

phthalic acid for a direct esterification and the poly 15 and at elevated temperature, in a solution or

merization to a suitable Polyäthylentere- suspending agent, obtained in a simple manner, if

phthalate of sufficient purity was not sufficient. The one the implementation at temperatures between 60

Terephthalic acid previously had to be above its and 250 ⁰ C, preferably between 70 and 150 ⁰ C,

Dimethyl ester are purified. carries out the reaction mixture, if necessary

For the technical production of the polyester, 20 is added after separation of unreacted starting material

first of all the terephthalic acid dimethyl ester with ethyl, with an acid that is more acidic than terephthalic acid

lenglycol in the presence of catalysts to the bis-monoglycol ester is added and the terephthalic

(j5-oxyethyl) terephthalate transesterified. acid monoglycol ester separates.

In the subsequent polycondensation when it is obtained by the process according to the invention

elevated temperature under reduced pressure and 25 one the terephthalic acid monoglycol ester in good

in the presence of catalysts is next to the yield and with such a high degree of purity that

the esterification of the water formed per mole of monomer without further purification to a high quality

merem bisglycol ester per 1 mol of glycol ab- polycondensate can be processed. This is

cleaved and separated from the reaction mixture. surprising, since from the German patent specification

This often results in undesirable secondary 3 ° 956 040 it is known that it is the monoglycol ester in particular

reactions such as the formation of mixed glycolic or terephthalic acid due to its acidic character

diglycol and triglycol ester groups. Compounds especially tends to become stubborn contaminants

of this type set to hold on even at the lowest concentration.

the quality of the polycondensates decreases, since they can be used as the The process can be especially then with pre-softener works. 35 part if in a manufacturing process

It is also known that terephthalic acid mono- for terephthalic acid is the di- or monoalkali salt of

alkyl ester is obtained by partial saponification of the corresponding acid. This is e.g. B. in the known

the dialkyl ester with caustic soda or caustic soda process for the production of terephthalic acid by

to deliver. Here, after acidification, the thermal disproportionation of alkali salts is obtained

Reaction mixture a mixture of not around 4 ° benzene carboxylic acid the case, as in the German

set diester, monoester and free terephthalic patent 1081877. One goes with it

acid. The direct esterification of ^ terephthalic acid so that you can in a first reaction step

with a primary alcohol or ethylene oxide for a solution of a dialcalite terephthalate, which in

Terephthalic acid monoester is also already known to be due to thermal disproportion

wrote. However, an ester obtained in this way is not pure. 45 renation of alkali salts of other benzene carboxylic acids

The isolation of the monoester from the reaction has been obtained after separation of the catalyst

mixture with the required degree of purity was prepared, an equivalent amount of an acidic alkali salt

great difficulties. The production of the mono- a benzene dicarboxylic acid other than terephthalic acid or

glycol ester of terephthalic acid in technical grade benzoic acid, whereby the practically water-

Scale is uneconomical according to this process. 50 insoluble alkali hydrogen terephthalate precipitates and

It has now been found that very pure ones are separated off. This acidic salt comes in one

Terephthalic acid monoglycol ester slurried in water by reacting the second reaction step

and with ethylene glycol and / or ethylene oxide, optionally with the addition of known esterification catalysts to the alkali salt of terephthalic acid monoglycol ester at temperatures between 60 and 250 ° C, preferably between 70 and 150 ° C, esterified. The esterification can be carried out under increased pressure, e.g. B. at 0.5 to 10 at, when in use

COOH

of ethylene oxide expediently under nitrogen or carbon dioxide atmosphere, or under normal pressure be made.

The second reaction step can be used for the implementation from Z. B. potassium hydrogen terephthalate with

Reproduce ethylene oxide to the potassium salt of monoglycol terephthalate by the reaction scheme:

COOCH ₂ -CH ₂ OH

+ CH ₂

-CH ₂

COOK

The presence of the acid terephthalate, which has not yet reacted, has an effect here Function of the acid catalysts normally used in esterification, such as sulfuric acid or Sulphonic acid takes over, particularly advantageously, since the esterification here also takes place without the presence additional catalysts can be carried out with good yield and high esterification rate kanfi. However, esterification catalysts such as zinc borate, titanium dioxide, Silica gel catalysts, aluminum oxide or cobalt sintering catalysts can be used.

The ethylene glycol and / or ethylene oxide can be used in excess. The excess can be used within wide limits, e.g. B. from 2 to 5 times the molar excess.

After cooling the reaction mixture to about room temperature, any precipitate formed, which consists of bisglycol terephthalate, is removed by z. B. filtration, separated. The filtrate is diluted with 2.5 to ten-fold amount of water, heated to about 60 to 95 ⁰ C and then acidified to a pH of 2 to 3.5. Inorganic or organic acids such as hydrochloric or sulfuric acid can be used for acidification. The use of organic acids, such as phthalic acid, isophthalic acid, benzoic acid or phthalic anhydride, is particularly advantageous if these acids are to be converted into dialcalite terephthalate by thermal disproportionation of their alkali salts.

The acidified hot solution is filtered and the terephthalic acid remaining on the filter is also filtered washed out with hot water. When the filtrate cools, the terephthalic acid monoglycol ester crystallizes from, the z. B. separated by suction and further purified by recrystallization from water can be.

The parts given in the example are parts by weight.

example

Ethylene oxide is injected into a suspension of 50 parts of potassium hydrogen terephthalate in 300 parts of water in a stirred tank kept at 90 to 95 ° C. with thorough stirring until the reaction mixture has dissolved clearly in the course of about 35 hours. The introduction of ethylene oxide is then continued for another hour under the specified conditions. After cooling to about 2O ⁰ C the forming precipitate is separated by filtration with suction. After drying, it consists of 0.6 parts of terephthalic acid bisglycol-COOK

ester with a melting point of 109 ^° C. The filtrate is then diluted to 1200 parts with water, ^{heated to 90 °} C. and acidified with phthalic anhydride until the solution has a pH of 2.4. It is filtered off with suction while hot, the filter residue is washed out with 100 parts of boiling water and, after drying, 3.75 parts of terephthalic acid with an acid number of 672 are obtained. ^{33 parts of this filtrate crystallize on cooling to 20 °} C. and, after concentration, to half the amount Another 12 parts by volume of terephthalic acid monoglycol ester, which have a melting point of 170 to 178 ^° C. after washing with ice water and drying.

The mother liquor, which contains all of the phthalic acid used for the precipitation as acidic potassium phthalate, is then reacted at the boiling point with enough dipotassium terephthalate until a pH of 5.7 to 6.0 has been established. Here, the terephthalic acid fraction is quantitatively precipitated as potassium hydrogen terephthalate, which, after being separated off at 30 ^° C., serves to produce the terephthalic acid monoglycol ester. All of the phthalic acid remains dissolved in the filtrate as dipotassium phthalate. After adding the appropriate amount of metal catalyst and evaporating to dryness, the dipotassium phthalate produced in this way can finally be converted into dipotassium terephthalate in a known manner by thermal conversion at 450 ^° C. under carbon dioxide pressure.

The acidification of the filtrate solution can also be done with an organic carboxylic acid that is more acidic than the terephthalic acid monoglycol ester is e.g. B. with benzoic acid or phthalic acid. In this way, a quantitative return of the potassium content to the thermal can be practically achieved Accomplish rearrangement reaction.

Claims (1)

Claim: Process for the preparation of terephthalic acid monoglycol ester by reacting monoalkali terephthalates with ethylene glycol or ethylene oxide under normal or elevated pressure and at elevated temperature, in a solvent or suspension medium, characterized in that the reaction is carried out at temperatures between 60 and 250 ⁰ C, the reaction mixture If necessary after removal of unreacted starting material, an acid which is more acidic than the terephthalic acid monoglycol ester is added and the terephthalic acid monoglycol ester is separated off. 509 597/410 6.65 © Bundesdruckerei Berlin