DD232048A1 - METHOD FOR THE PRODUCTION OF CYCLIC OLETOMERS OF THE ACETALDEHYDE - Google Patents

Abstract

The invention relates to a process for the preparation of cyclic oligomers of acetaldehyde, which can be easily separated from each other. The bulk of the resulting oligomeric products consists of paraldehyde and metaldehyde. Good separability of the reaction mixture by filtration due to a favorable crystal structure of the metaldehyde is achieved by the following procedure: The reaction is carried out at 16 to 12C in a Vorreaktionskessel at a conversion up to 40 to 50%, then 50 to 60% of the reaction mass in a main reactor pumped and brought here to a temperature between 10 to 6C. After the conversion in both boilers is at least 60%, the remaining amount of the reaction mass from the prereactor is also transferred to the main reactor and the reaction at 10 to 6C is brought to conversions greater than 80%.

Description

Field of application of the invention

The invention relates to a process for the preparation of cyclic Oügomerer of the acetaldehyde, which can be easily separated from each other. The bulk of the inventively formed oligomeric products are paraldehyde and metaldehyde. Paraldehyde serves as a selective solvent for acetylene and metaldehyde as a solid fuel or molluscicide.

Characteristic of the known technical solutions

The oligomerization of acetaldehyde to metaldehyde and paraldehyde is known and described in various publications.

For example, (H. Beyer, Lehrbuch der organischen Chemie, Hirzel Verlag Leipzig, 1966, p. 160 ff.) Describes the cyclization of acetaldehyde as an anionoid ion chain mechanism, which leads to paraldehyde as a trimer and to metaldehyde as a tetra- to hexamer.

The formation of the meta-aldehyde takes place only at low temperatures and only to a very small percentage, which varies between 0.5 and 5%, depending on the production conditions.

The low proportion of metaldehyde is explained by the fact that due to the methyl group, a sterically influenced reaction occurs.

Since the polyreaction proceeds via the C = O moiety, it is readily apparent that this sterically-directed reaction must result in cyclization. Of course, the formation of the six-membered structures is preferred.

Only extreme reaction conditions, such as lower temperatures, which are known to increase the degree of polymerization, therefore lead to the formation of metaldehyde, ie higher cyclized products.

Thus, the preparation of a mixture of paraldehyde and metaldehyde at low temperatures between -4 and -10 ⁰ C is described in the English patent 1055210. The reaction is triggered by acid. This can be sulfuric, hydrochloric, nitric or phosphoric acid.

But also the catalyzing effect of salts of weak bases, such as ammonium bromide, pyridinium bromide, titanium chloride, aluminum chloride, iron chloride, halides of sulfur and the catalyst used has been described. Antimony also has a catalyzing effect. The amount of catalyst used is between 0.05 and 0.70%, generally lower catalyst concentrations yielding an increased level of metaldehyde.

The reaction is highly exothermic and runs very fast in its initial phase / so that it is difficult to control.

The resulting reaction mixture, consisting of liquid paraldehyde with its boiling point of 124 ° C and the crystalline metaldehyde, which is subtimed at 112 ° C is technically separated by filtration. However, as a result of the rapid reaction, the resulting metaldehyde crystals are very fine, this can only be achieved with considerable effort.

Most of the separated metaldehyde still contains a considerable amount of paraldehyde or paraldehyde or a proportion of very fine crystalline metaldehyde. In principle, it is possible with modern filtration methods to achieve a quantitative separation. However, this means a very high amount of time and technology.

Working up by distillation is even more complicated since the resulting paraldehyde is slightly depolymerized.

Object of the invention

The aim of the invention is to achieve an easy workability of the resulting in the oligomerization of acetaldehyde cyclic oligomers by filtration.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of cyclic oligomers of acetaldehyde, wherein the above requirements are met.

The object is achieved in that the reaction is carried out at low temperatures under acid initiation, wherein in a Vorreaktionskessel at -16 to -12 ° C to a conversion of 40 to 50% oligomerized, 50 to 60% of the reaction mass in a main reactor pumped and then a temperature between -10 to -6 ° C is brought. After the conversion in both boilers is over 60%, the remaining amount of the reaction mass from the pre-reactor is also transferred to the main reactor and the reaction at -10 to -6 ° C to turn over 80%.

Surprisingly, in the procedure according to the invention, a reaction mixture with very readily filterable metaldehyde crystals is obtained.

The invention will be explained below by way of examples. The quantities are parts by weight. Examples 1-3 document the state of the art and are not according to the invention.

Exemplary embodiments Example 1

In a 2501-kettle with stirrer 150Tl. Submitted to acetaldehyde and cooled to -14 ° C. Thereafter, the reaction is started by introducing 0.05Tl. Hydrochloric acid gas. The reaction lasts for 5h and leads to a conversion of 90%. The resulting reaction mixture is separated by filtration with a 0.04 mm mesh Dederon filter; from the filtrate is distilled under depolymerization in a vacuum, the paraldehyde. The analytical determinations are then carried out gravimetrically. The separation results are summarized in Table 1.

Example 2

The procedure is as in Example 1, with the difference that at -8 ⁰ C was worked.

-I-

Example 3

The procedure is as in Example 1, with the difference that the reaction in the first 2 ¹ / 2h at -14 ° C and in the remaining 2V2 at -8 ⁰ C was driven.

Example 4

In a 250I kettle with stirrer 150Tl. Submitted to acetaldehyde and cooled to -20 ⁰ C. Thereafter, the reaction is started by introducing 0.5Tl. Hydrochloric acid gas and oligomerized at -14 ° C. If a turnover of about 40% is reached in this boiler, 125Tl. of the reaction mixture pumped into another 250 l kettle. Here, the reaction is carried out at a temperature of -8 ⁰ C to a conversion of 60%. Sales in the first boiler are then around 55%.

Now both mixtures are combined in the 2nd kettle and the conversion is brought to 80% at -8 ° C. The resulting reaction mixture is filtered and analyzed. The values obtained can be found in Table 1.

Example 5

The procedure is as in Example 4, with the difference that the oligomerization temperature in the 1st boiler is -12 ° C and in the 2nd boiler-6 ⁰ C.

Example 6

The procedure is as in Example 4, with the difference that the oligomerization temperature in I. boiler - 16 ° C and in. 2. boiler -6 ⁰ C amounts.

Example 7

The procedure is as in Example 4, with the difference that the conversion before the transfer of 50-60% of the reaction mixture in the 2nd boiler 45%, the oligomerization ^temperature in the 1st boiler -12 ^C C, the conversion in the 2nd kettle when combining both reaction parts in the 2nd boiler 65% and the oligomerization temperature in the 2nd boiler -8 ⁰ C.

Example 8

The procedure is as in Example 4, with the difference that the conversion before conversion of 50-60% of the reaction mixture in the 2.Kessel 50%, the oligomerization temperature in I.Kessel -12 ⁰ C and in the 2nd vessel -8 ⁰ C and the conversion in combination of both reaction parts in the 2nd boiler is 62%.

Example 9

The procedure is as in Example 4, with the difference that the conversion before conversion of 50-60% of the reaction mixture in the 2.Kessel 50%, the oligomerization temperature in I.Kessel -16 ⁰ C and 2.Kessel -8 ⁰ C and the conversion at the union of both reaction parts in the 2nd boiler is 65%.

Table 1 - Results of cyclooligomerization

Example I. Boiler 2. Boiler Endproduktzus% Metaldehyde im

% Conversion temp.% Conversion temp

° C b. Unite. ° C% paraidehyd% metaldehyde filtration

1 stew -14 60 - 8th 4.5 95.5 0.20 2 stew -12 60 - 6 4.0 96.0 0.15 3 -16 60 -10 4.8 95.2 0.50 4 -12 65 - 8th 4.8 95.2 0.02 5 -12 62 - 8th 5.2 94.8 0.01 6 -16 65 - 8th 5.0 95.0 - + 7 Stew with 2 temperature levels 4.5 95.5 - 8th 40 4.7 95.3 0.01 9 40 4.6 95.4 - 40 45 50 50

+ undetectable

Claims (1)

Invention claim: Process for the preparation of cyclic oligomers of acetaldehyde by acid-initiated oligomerization at low temperatures, characterized in that the reaction at -16 to -12 ° C in a Vorreaktionskessel led to a conversion of 40 to 50%, then 50 to 60% of the reaction mass in transferred the main reactor and brought here to a temperature between -10 and -6 ° C, and after the conversion in both reaction boilers is greater than 60%, the remaining mass transferred from dam Vorreaktionskessel in the main reactor and here the reaction at -10 to -6 ° C is brought to over 80% conversion.