DE1207377B - Process for the preparation of acrylic acid alkyl esters by decarboxylating maleic acid anhydride and / or a maleic acid or fumaric acid half ester of a low molecular weight alkanol - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. σ .:

C07c

German class: 12 ο-21

Number: 1207 377

File number: R 32622IV b / 12 ο

Filing date: May 4, 1962

Opening day: December 23, 1965

The main patent application R 31 960 IVb / 12 o (German Auslegeschrift 1195 297) is a process for the production of acrylic acid alkyl esters by decarboxylating maleic and fumaric acid compounds, after which maleic anhydride and / or a maleic acid or fumaric acid half ester of a low molecular weight alkanol with a low molecular weight alkanol Alkanol to temperatures of 300 to 750 ⁰ C, preferably 500 to 600 ⁰ C, heated briefly. Metals with a high coefficient of thermal conductivity, eg. B. Copper; Metal oxides such as copper, cadmium or silver oxide can also promote decarboxylation.

It has long been known that dicarboxylic acids or their anhydrides can be partially decarboxylated in the presence of steam at elevated temperatures. In this way, z. B. convert maleic acid into acrylic acid. This process is described by LH F1 e 11 and WH Gardner, Maleic Anhydride Derivatives, 1952, pp. 244 to 249, and in German patent specification 445 565. Suitable catalysts which promote the decarboxylation of dicarboxylic acids and their anhydrides to form monocarboxylic acids are reported in American patents 1,964,516 and 1,953,232. According to Austrian Patent Specification 201 579 acrylic acid can be prepared in such a way by the catalytic decarboxylation of maleic acid, that a mixture of water vapor and Maleinsäuredampf in the presence of oxygen over a catalyst to z at temperatures between 200 and 300 ⁰ C,. B. via copper oxide, conducts. The yields achieved when carrying out the process are around 70 to 75%.

The transfer of this known process, i.e. the decarboxylation of dicarboxylic acids to unsaturated monocarboxylic acids, to the decarboxylation of monoesters of maleic or fumaric acid had to be carried out in view of the fact that the esters mentioned were thermally converted into the acid anhydride and the anhydride at temperatures above 200 ° C If alcohol is split, it can be seen as hopeless. On the decomposition of the maleic acid monomethyl ester in maleic anhydride and methanol at temperatures of 140 to 150 ⁰ C z. B. in the German patent 1179 929, column 1, pointed out. In fact, the decarboxylation of dicarboxylic acid monoesters has not been evaluated or previously described. The high temperatures to be used in accordance with the process of the invention allowed processes for the preparation of
Acrylic acid alkyl esters by decarboxylation
of maleic anhydride and / or one
Maleic or fumaric acid half-esters
of a low molecular weight alkanol

Addition to registration: R 31960IV b / 12 ο -
Interpretation document 1195 297

Applicant:

Rohm & Haas G. m. B. H.,

Darmstadt, Mainzer Str. 42

Named as inventor:

Dr. Theodor Völker, Friborg (Switzerland);

Heinz Graefe, Darmstadt;

Alfred Neumann, Raunheim (Hess.)

rather expect a decomposition of the anhydride than the formation of the unsaturated monocarboxylic acid ester.

The German patent 1179929 mentioned above describes the production of acrylic acid esters and acrylic acid amides by decarboxylating maleic acid and fumaric acid half-esters or maleic acid or Fumaric acid half-amides proposed in the presence of certain phosphorus, arsenic or antimony compounds.

It has now been developed in a further development of the process for the preparation of acrylic acid alkyl esters by decarboxylating maleic anhydride and / or a maleic or fumaric acid half ester of a low molecular weight alkanol with brief heating with a low molecular weight alkanol to a temperature of 300 to 750 ° C, preferably 500 to 600 ⁰ C, advantageously on the surface of a metal with a high thermal conductivity, such as copper, or optionally in the presence of the oxides of copper, cadmium or silver, according to the main patent application R 31 960 IVb / 12 ο found that the decarboxylation of maleic acid or fumaric acid half-ester can carry out to the corresponding acrylic acid ester if maleic or fumaric acid half-esters or a mixture of maleic anhydride or maleic acid and the excess low molecular weight alkanol in the vapor form or in

509 759/574

a fine distribution produced by mechanical means, such as in the form of a mist, advantageously in countercurrent, into an alcohol vapor heated to the decarboxylation temperature, especially of one temperature of about 800 ° C, conducts or sprays.

You can, as detailed in the following example, proceed in such a way that a mixture of maleic anhydride and excess methanol is poured onto a loosely poured and poured onto z. B. 600 ⁰ C heated heat exchanger, through which or over the methanol vapor with a temperature of 800 ⁰ C flows, is sprayed on. When the maleic acid half-ester or the mixture of maleic anhydride or maleic acid and alcohol hits the heat exchanger, immediate evaporation takes place, with partial decarboxylation already occurring.

The method of the invention can also be carried out in such a way that a mixture of maleic anhydride and alcohol or the maleic acid half-ester in the form of a mist is poured into a mixture of e.g. B. 800 ⁰ C heated alcohol vapor is sprayed in countercurrent. The presence of the maleic acid half-ester is essential for the formation of the acrylic acid alkyl ester, since only this, but not the mixture of maleic anhydride and alcohol, can convert into the acrylic acid ester with decarboxylation.

However, the temperature required for the evaporation or decarboxylation does not favor the Formation of the half ester from maleic anhydride and alcohol, but shifts the balance between Anhydride and alcohol on the one hand and half esters on the other hand in favor of the anhydride. If you leave the For the purposes of the invention, the acrylic acid alkyl ester formation proceed in the presence of a large excess of alcohol, so the said equilibrium is shifted to the ester side, so that the maleic anhydride does not occur in the reaction product or occurs only in small amounts. The highly heated stream of alcohol therefore has a double effect, namely the formation or maintenance of the maleic acid half-ester at the decarboxylation temperature and on the other hand as a heat exchanger to effect the decarboxylation.

The reaction mixture leaving the reaction space is liquefied in the usual way. The thereby formed alcoholic solution of the resulting acrylic acid alkyl ester and the non-decarboxylated maleic acid half ester is worked up in a manner known per se. During the distillation of the acrylic acid methyl and ethyl esters, these are separated off as an azeotropic mixture with methanol or ethanol. The extraction the acrylic acid alkyl ester from the azeotropic mixture can be carried out, for example, in such a way that it is in water is added to such an extent that a layer is formed between the acrylic acid alkyl ester and aqueous methanol is done.

example

980 g of methanol were evaporated from a round bottom flask. The vapors were passed from below through a vertical quartz tube, which was heated from the outside by a refrigerator set at 800 ⁰ C oven. The temperature measured by a thermocouple was about 750 ^° C. A solution consisting originally of 98 g of maleic anhydride and 32 g of methanol was continuously added dropwise to the top of the quartz tube. The entry point of this solution was filled by loosely piled up quartz shards. The reaction products were passed from the quartz tube into a vertical spherical cooler. A total of 1037 g of liquid reaction product were obtained. In a water jet vacuum, 949 g of a 4.27% solution of methyl acrylate in methanol were distilled therefrom in a cold trap. The concentration of the methyl acrylate was determined by gas chromatographic determination and by determining the saponification number. 88 g of a highly viscous product with an acid number of 290 and an ester number of 345 remain as residue. These values are used to calculate 0.223 mol of monomethyl maleate and 0.048 mol of dimethyl maleate. Accordingly, the experiment proceeded with a conversion of 50.6% of theory and a selectivity of around 80% for methyl acrylate. The yield of methyl acrylate was accordingly 47.1% with a single throughput. After the methanol had been separated off, the unreacted ester could be returned to the decarboxylation stage in the manner described above.

Claims (1)

Claim: Process for the preparation of acrylic acid alkyl esters by decarboxylating maleic anhydride and / or a maleic or fumaric acid half ester of a low molecular weight alkanol with brief heating with a low molecular weight alkanol to a temperature of 300 to 750 ° C, preferably 500 to 600 ° C, advantageously on the surface of a Metal with high thermal conductivity, such as copper, or optionally in the presence of the oxides of copper, cadmium or silver, according to the main patent application R 31960 IVb / 12o (German Auslegeschrift 1195 297), characterized in that maleic or fumaric acid half esters or a mixture of Maleic anhydride or maleic acid and the excess low molecular weight alkanol in the vapor form or in a fine distribution produced by mechanical means, such as in mist form, advantageously in countercurrent, into an alcohol vapor heated to the decarboxylation temperature, especially at a temperature of about 800 ^° C. or spray. Considered publications:
German Patent No. 445 565;
Austrian Patent No. 201 579;
U.S. Patent Nos. 1,964,516, 1,953,232. Legacy Patents Considered:
German Patent No. 1179 229. 509 759/574 12.65 © Bundesdruckerei Berlin