DE1291739B - Process for the preparation of mono- and diesters of fumaric acid with monohydric alcohols - Google Patents

Description

It is known that fumaric acid half-esters can be made from the corresponding maleic acid half-esters . Can produce isomerization in the presence of various catalysts. As such, z. B. Thiourea, hydrochloric acid, organic and inorganic acid chlorides, such as. B. oxalyl chloride or Phosphorus oxychloride. These processes have the disadvantage that the esters produced therewith through the catalysts or are contaminated by reaction products of the catalysts with the esters. The esters isomerized with acid chlorides as catalysts are usually strongly discolored, those with Hydrochloric acid isomerized esters contain chlorosuccinic acid esters while those in the presence of Thiourea isomerized esters contain sulfur-containing addition compounds.

It is also known that thermal isomerization of Maleic acid can reach into fumaric acid; the yields of fumaric acid are about 60%. Furthermore, the separation of the unrearranged maleic acid is difficult and expensive. Diester the In contrast, maleic acid is very difficult to isomerize thermally.

It has now been found, surprisingly, that the half-esters of maleic acid are thermally Isomerization easily and completely to the half-esters of fumaric acid without the use of a catalyst let isomerize.

The invention therefore relates to a process for the preparation of mono- and diesters of fumaric acid with monohydric alcohols, which is characterized in that maleic anhydride is reacted with the alcohol in question in a manner known per se to form the monoester of maleic acid, this then at temperatures from 180 to 280 ° C, preferably of 200 to 240 ⁰ C, for 1 to 6 hours, preferably 2 to 3 hours thermally isomerized to the corresponding fumaric acid monoester and this weiterverestert if appropriate in the manner known per se to the fumaric acid diester.

The process can be carried out in such a way that the maleic acid half-ester is first prepared in a known manner from maleic anhydride and the stoichiometric amount of alcohol required for the formation of the half-ester, optionally also with a small excess of alcohol. This is then optionally in the presence of an excess of up to 100%, preferably up to 20%, over the stoichiometric amount of alcohol required for the formation of the half-ester ^{heated to temperatures of 180 to 250 0} C for 1 to 6 hours, this thermal isomerization, depending on the Boiling point of the half-ester, if necessary in a pressure vessel. Thereafter, the reaction mixture, which, in accordance with the equilibrium under the conditions used, contains not only monoalkyl fumarate but also diesters and free fumaric acid, is esterified with excess alcohol and the customary esterification catalysts in a known manner to give the corresponding diester. Pure dialkyl fumarate is obtained in this way.

If you want to isolate the fumaric acid half-ester, the one present in equilibrium is filtered Fumaric acid and separates the resulting diester from the desired monoester by fractionated Distillation in vacuo.

The reaction takes place in such a way that the maleic acid half-ester to the corresponding one Fumaric acid half ester is isomerized. Furthermore, the establishment of equilibrium proceeds through disproportionation according to the following scheme:

CH-COOH

Ml

CH - COOR

CH - COOR CH-COOH

ROOC-CH HOOC-CH

It is therefore possible in the thermal isomerization of maleic acid half-esters, including the free one Obtain fumaric acid. By adding another component, e.g. B. water vapor, is it possible by saponification of part of the ester, the equilibrium in favor of the free fumaric acid is achieved move.

The method of the invention can also be carried out by one in a known manner produced purified half-ester of maleic acid goes out with the alcohol in question.

The parts mentioned in the examples are parts by weight.

example 1

392 parts of maleic anhydride and 264 parts of isopropyl alcohol were heated to 100 ° C. for 1 hour in a pressure vessel to form half-esters. then the temperature was held at 200 ° C. for a further 4 hours, a pressure of about 7 atmospheres being established. It was then cooled. How the UR spectrum of a sample showed was practical all maleic half-esters converted to fumaric acid. An additional 360 parts were added to the reaction mixture Isopropyl alcohol, 100 parts benzene and 10 parts concentrated sulfuric acid. The further esterification took place in a suitable round bottom flask equipped with a packed column and a water separator was provided. Esterification was carried out in it until the water was completely removed. The esterification product became neutral with 5% sodium hydroxide solution washed, dried and distilled. After the first run of isopropanol and benzene, 760 g went of the pure diisopropyl fumarate at 110 ° C. and 12 Torr above. The yield was 95% of the Theory.

Example 2

392 parts of maleic anhydride and 828 parts of n-dodecyl alcohol were heated ^{, as in Example 1, initially to 100 ° C. for 1 hour and then to 220 °} C. for a further 4 hours. 1116 parts of n-dodecyl alcohol were then added to the reaction mixture and further esterification was carried out as in Example 1 for the rest. After the excess alcohol had been distilled off, the pure dododecyl fumarate was obtained in 95% yield.

The purity of both fumarates was determined by gas chromatography.

Claims (1)

Claim: Process for the preparation of mono- and diesters of fumaric acid with monohydric alcohols, characterized in that maleic anhydride is reacted with the alcohol in question in a manner known per se to form the monoester of maleic acid, this then at temperatures of 180 to 280 ^° C., preferably 200 to 240 ⁰ C, for 1 to 6 hours, preferably 2 to 5 hours, thermally isomerized to the corresponding fumaric acid monoester and this optionally further esterified in a manner known per se to give the fumaric acid diester.