DE3833033A1 - Process for the preparation of the isomeric monoesters of 2,2,4-trimethylpentane-1,3-diol with isobutyric acid - Google Patents

Abstract

It was the object of the invention to develop a simple, selective process for the preparation of the isomeric monoesters of 2,2,4-trimethylpentane-1,3-diol with isobutyric acid. The process which has now been found consists in employing an isobutyraldehyde with an acid value of not more than 2 and carrying out the reaction in the presence of such an amount of 5 to 20% strength aqueous alkali metal hydroxide solution that the molar ratio between isobutyraldehyde and alkali metal hydroxide employed has a value of between 200 and 2000. The ester mixture prepared according to the invention is mainly used as a plasticiser for PVC.

Description

The mixture of the isomeric monoesters of 2,2,4-trimethylpentanediol-1,3 with isobutyric acid, hereinafter 2,2,4-trimethylpentanediol-1,3-mono Isobutyrate (TMPD-IB) is a popular plasticizer for poly vinyl chloride (PVC). It is not only used as such, son is also the starting material for the production of chemically analog PVC Plasticizers. In particular the TMPD-IB benzoate, which is produced by the reaction of TMPD-IB available with methyl benzoate is important because it gives PVC floor coverings a special resistance to stains. TMPD-IB is also used as a film-forming aid in emulsion paints and for applications in the production of lubricants, solvents and herbicides used.

The prior art for the production of TMPD-IB is in DE-OS 34 47 029 listed. After that it was known to use isobutyraldehyde with Kon centered aqueous (earth) alkali hydroxide solutions in a homogeneous phase Implement TMP-IB.

The use of alkaline earth metal hydroxides has the disadvantage that the reak tion mixture must be neutralized with carbon dioxide and in particular difficult to separate special calcium salts from the reaction mixture sen (cf. DE-OS 28 20 518).

In the method that is described in DE-OS 30 24 496 a commercially available isobutyraldehyde and a 30 to 60% alkali metal hydroxide solution used. When the reaction is complete, water becomes set, the unreacted isobutyraldehyde as an azeotrope and the product after acidification of the residue and phase separation distilled off from the organic phase. This procedure indicates the Disadvantage that an aqueous phase is obtained in the dissolved organi connections and not without an elaborate aftermath action can be disposed of.

The subject of DE-OS 34 47 029 is a method for the representation of pure TMPD-IB by reacting isobutyraldehyde in the presence  20% sodium hydroxide solution as a catalyst in a tubular reactor. The Selek Activity with regard to the monoester can only be described as moderate the. Thus, 18% tri are formed under favorable reaction conditions methylpentanediol (TMPD) based on TMPD-IB. This diol has to go through Rectification separated from the desired monoisobutyric acid ester will. The unwanted TMPD can basically respond to three because of arise. When disproportioning 2 equivalents TMPD-IB becomes 2,2,4-trimethylpentanediol-1,3-diisobutyrate (TMPD-DIB) released one equivalent of trimethylpentanediol. The diol can also form by hydrolysis of the monoester, with an additional equi valent isobutyric acid is formed. Finally, the diol can Cannizzaro reaction of isobutyraldehyde with isobutyraldol (3-hydroxy 2,2-dimethyl-4-methyl-pentanal) arise, also an equiva lent isobutyric acid based on the diol. Because in the examples 1 to 4 in DE-OS 34 47 029 hardly TMPD-DIB arises, is assumed receive that trimethylpentanediol either by hydrolysis of TMPD-IB or by Cannizzaro reaction of isobutyraldehyde with isobutyraldol is formed, that is, on a path that is in any case an equiva lent isobutyric acid based on the diol is released. In the DE-OS 34 47 029 is the loss of selectivity due to isobutyric acid bil not included in the accounting because the isobutter dissolves acid in the 20% sodium hydroxide solution and in the form of its sodium salt is removed. The formation of isobutyric acid does not affect only the economics of the process due to the loss of Selek activity, but also creates problems in wastewater treatment.

The US-PS 37 18 689 describes a homogeneously catalyzed process for the preparation of TMPD-IB in a tubular reactor. But even with this procedure, at least 2.4% TMPD based on the monoester is still formed. Under the preferred reaction conditions mentioned in the patent, 5-6% of the TMPD based on TMPD-IB are formed. A disadvantage of this process is not only the high diol content, but also the fact that unreacted isobutyraldehyde hyd after the reaction almost quantitatively as isobutyraldoxane (2,6-diisopropyl-5,5-dimethyl-1,3-dioxane-4 -ol) is present. In order to be able to split this aldoxane into isobutyraldehyde, a stripping column operated with water vapor is required, which works under a pressure of 0.2 MPa at 125 ° C. Of course, this high cost affects the economy of the process. From US-PS 37 18 689 it is also apparent that a 10% sodium hydroxide solution does not allow the isobutyraldehyde to react and is therefore unsuitable as a catalyst.

It was therefore the task to develop a method that the ge does not have any shortcomings in the state of the art. The production of 2,2,4-trimethylpentanediol-1,3-monoisobutyrate should be without distilla tive separation of the trimethylpentanediol occurring as a by-product to be possible. In addition, the Iso used as the starting product butyraldehyde can be easily recycled.

The invention relates to a process for the preparation of TMPD-IB from isobutyraldehyde by homogeneous alkaline catalysis. A homogeneous reaction mixture is understood here to mean a solution which, when left to stand at the reaction temperature, shows no deposition of a second phase and also no cloudiness. Surprisingly, TMPD-IB can be prepared in homogeneous solution with 10% sodium hydroxide solution as catalyst. The formation of TMPD is reduced in such a way that there is no need to remove the diol by distillation. It is very important for the implementation of the process that an isobutyraldehyde with an acid number of at most 2, preferably at most 1, is used as the starting product. The usual, commercially available isobutyraldehyde has acid numbers which are usually well above these limit values and is then unusable. Iso-butyric acid forms under practical conditions, ie in storage tanks and in transport containers in which the access of oxygen can usually not be prevented, by oxidation of the aldehyde. If such a product containing isobutyric acid is used, the yield of TMPD-IB drops significantly (see comparative experiment A). The prior art contained no indication that the acid content of the isobutyraldehyde used is of critical importance for the process. On the contrary: The process described in DE-OS 28 20 518 even provides for 1.5 to 5 percent by weight carboxylic acid to be used in addition to an alkaline earth metal hydroxide. Although in US Pat. No. 3,718,689 (column 3 , line 10), an acid content of at most 0.5% is given, which corresponds to an acid number of 3.2, but shortly thereafter who also describes the higher acid contents as tolerable.

A largely acid-free isobutyraldehyde falls during hydroformy propene. This product is carefully checked against access by Protect atmospheric oxygen. A largely free of isobutyric acid tes product can be by adding alkaline compounds and after make the following distillation.

The process for producing TMB-IB by reacting isobuty Raldehyde with aqueous alkali is, as already stated above known. The present process is carried out in a homogeneous phase guided. To achieve this, the reaction temperature should not significantly compared to the optimal range given below be increased or decreased. It is also advantageous for an in to ensure aggressive mixing.

The preferred procedure according to the invention for the production of TMPD-IB is shown in Figure 1 and should be used as follows write:.

A centrifugal pump ( A ) working as a mixing unit is fed with isobutyraldehyde and sodium hydroxide solution. The dwell time in the dwell time container ( B ) and the sodium hydroxide concentration in the isobutyralde hyd can be set via the delivery rate of the aldehyde or lye pump ( C and D ). The centrifugal pump ( A ), which causes an intensive mixing of isobutyraldehyde with sodium hydroxide solution and recycled product mixture from the residence time container, conveys the reaction mixture back into the residence time container ( B ) via a reaction tube ( E ) acting as an air cooler. Excess product mixture is removed with the help of an overflow ( F ), while the remaining product is circulated by the mixing pump ( A ).

The isobutyraldehyde used had the following composition:

Isobutyraldehyde <99.35%, water content <0.5%, acid number <1 and n-butyraldehyde <0.15%. It should be noted that with isobutter acidic isobutyraldehyde under homogeneous reaction conditions with 10% sodium hydroxide solution as catalyst only a small amount of TMPD-IB forms (see comparative example A)! The water content of isobutyral Dehyds, on the other hand, is not critical.  

An aqueous solution of alkali metal hydroxide with a Concentration of 5 to 20 wt .-% particularly suitable. The preferred Alkali hydroxide concentration is 10% by weight. Preferred alkali hydroxide is sodium hydroxide.

The molar ratio of aldehyde to alkali hydroxide in the reaction mixture is 1000: 5 to 1000: 0.5; a ratio is particularly preferred nis of about 1000: 2.5.

The reaction is carried out at a temperature of 50 to 80 ° C, in particular at 60 to 70 ° C performed. Printing is not a critical para meter. The residence time is 10-60 minutes, preferably 15-30 Minutes.

example 1

The reaction of isobutyraldehyde to TMPD-IB under the catalytic action of sodium hydroxide solution, which is homogeneously dissolved in the reaction mixture, is carried out in an apparatus as shown in Figure 1. It consists essentially of the 700 ml holding tank B with overflow and descending cooler. The reaction mixture in B is circulated by a gear pump A with a delivery rate of 100 l / h. The pipeline from the pressure side of the pump to the entry into the retention tank has a diameter of 6 mm and a length of 2 m.

Isobutyraldehyde (IBA) at 1810 ml / h and 10% sodium hydroxide solution at 18 ml / h (corresponds to 0.247 mol% based on IBA) are fed in directly in front of the gear pump, while 1828 ml / h of reaction mixture are removed from the overflow. A reaction temperature of 65 ° C. is set in the reaction tube E and in the residence time container B ; this results in a dwell time of 23 minutes. After 2 hours, an equilibrium has been established in the reactor so that a partial stream can be collected at the overflow for workup by distillation. Unreacted isobutyraldehyde is distilled off from the reaction mixture thus obtained under normal pressure at a bottom temperature of up to 135.degree. Based on 1000 g of product mixture, 758 g of isobutyraldehyde and water and 242 g of residue are obtained. The isolated isobutyraldehyde contains no isobutyric acid and can be recycled immediately. According to gas chromatographic analysis, the residue is composed as follows:

10.5% isobutyraldehyde
0.6% isobutyraldol
0.3% 2,2,4-trimethylpentane-1,3-diol
84.2% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
0.1% 2,2,4-trimethylpentane-1,3-diol diisobutyrate
4.3% other components

By further distillation of the residue in vacuo at 0.1 hPa 199 g TMPD-IB in a purity of 99.5%, based on 1000 g pro duct mix, won.

Example 2

In the apparatus described in Example 1, 2000 ml / h of isobutyr aldehyde and 35 ml / h 5% sodium hydroxide solution (corresponds to 0.207 mol% based to IBA) at a reaction temperature of 66 ° C, while 2035 ml / h of product mixture are taken from the overflow. This results in there is a dwell time of 21 minutes. After 2 hours the reak Tor set an equilibrium, so that a partial flow at the overflow can be collected for a distillative workup. From that reaction mixture obtained is unreacted isobutyraldehyde un distilled normal pressure at a bottom temperature up to 135 ° C. Based on 1000 g of product mixture, 814 g of a mixture are formed Isobutyraldehyde and water and 186 g of residue obtained according to gas chromatographic analysis as follows:

12.6% isobutyraldehyde
0.4% isobutyraldol
0.6% 2,2,4-trimethylpentane-1,3-diol
82.7% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
0.1% 2,2,4-trimethylpentane-1,3-diol diisobutyrate
3.6% other components

Example 3

In the apparatus described in Example 1, 2000 ml / h of Isobu tyraldehyde and 7.8 ml / h 20% sodium hydroxide solution (corresponds to 0.22 mol% be  moved to IBA) at a reaction temperature of 62 ° C, while 2007.8 ml / h of product mixture are removed from the overflow. There this results in a dwell time of 21 minutes. After 2 hours an equilibrium is established in the reactor, so that a partial flow on Overflow can be caught for a distillative workup. The reaction mixture thus obtained becomes unreacted isobu tyraldehyde under normal pressure at a bottom temperature up to 135 ° C distilled off. Based on 1000 g of product mixture, 745 g of one Get mixture of isobutyraldehyde and water and 255 g of residue according to gas chromatographic analysis as follows puts:

12.8% isobutyraldehyde
0.4% isobutyraldol
0.7% 2,2,4-trimethylpentane-1,3-diol
82.4% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
3.6% other components

Example 4

In the apparatus described in Example 1, 2900 ml / h of isobutyr aldehyde and 15.9 ml / h 10% sodium hydroxide solution (corresponds to 0.136 mol% bezo gen on IBA) at a reaction temperature of 69 ° C, wäh rend 2915.9 ml / h product mixture can be collected at the overflow. There this results in a dwell time of 15 minutes. After 2 hours an equilibrium is established in the reactor, so that part current at the overflow for a distillative workup can. The reaction mixture thus obtained is not converted Isobutyraldehyde under normal pressure at a bottom temperature up to Distilled 135 ° C. Based on 1000 g of product mixture, 840 g a mixture of isobutyraldehyde and water and 160 g of residue obtained, which according to gas chromatographic analysis as follows consists of:

11.2% isobutyraldehyde
0.3% isobutyraldol
0.1% 2,2,4-trimethylpentane-1,3-diol
85.7% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
2.7% other components

Example 5

In the apparatus described in Example 1 2200 ml / h Iso butyraldehyde and 33 ml / h 10% sodium hydroxide solution (corresponds to 0.373 mol% based on IBA) fed at a reaction temperature of 65 ° C, while 2233 ml / h of product mixture are removed from the overflow. Thereby there is a dwell time of 19 minutes. After 2 hours an equilibrium is set in the reactor, so that a partial flow on Overflow can be caught for a distillative workup. The reaction mixture thus obtained becomes unreacted isobu tyraldehyde under normal pressure at a bottom temperature up to 135 ° C distilled off. Based on 1000 g of product mixture, 694 g of one Get mixture of isobutyraldehyde and water and 306 g of residue according to gas chromatographic analysis as follows puts:

10.0% isobutyraldehyde
0.1% isobutyraldol
1.7% 2,2,4-trimethylpentane-1,3-diol
86.3% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
0.1% 2,2,4-trimethylpentane-1,3-diol diisobutyrate
1.8% other components

Comparative Example A

In the apparatus described in Example 1, 1650 ml / h of Isobu tyraldehyde containing 0.5% isobutyric acid (this corresponds to one Acid number of 3.2), and 18 ml / h 10% sodium hydroxide solution (corresponds 0.271 mol% based on IBA) at a reaction temperature of 63 ° C fed in, while 1668 ml / h of product mixture taken from the overflow will. This results in a dwell time of 23 minutes. After 2 Hours has reached an equilibrium in the reactor, so that a Partial stream collected at the overflow for a distillative workup can be. The reaction mixture thus obtained is not reversed set isobutyraldehyde under normal pressure at a bottom temperature distilled off up to 135 ° C. Based on 1000 g of product mixture 963 g of a mixture of isobutyraldehyde and water and 37 g of re obtained, which, according to gas chromatographic analysis, is as follows composed:  

34.8% isobutyraldehyde
12.5% isobutyraldol
1.6% 2,2,4-trimethylpentane-1,3-diol
45.5% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
5.6% other components

Comparative Example B

In the apparatus described in Example 1, 1650 ml / h of Isobu tyraldehyde and 433 ml / h 10% sodium hydroxide solution in one reaction temperature fed from 65 ° C, while 2083 ml / h two-phase product mixture at the overflow. After switching off the mixing pump and the agitator in the retention tank separate two phases. The dwell time is 20 minutes. After 2 hours it was in the reactor an equilibrium is set so that a partial flow at the overflow for a work-up by distillation can be collected. After phases separation, based on 1000 g of product mixture, 657 g of organic and 342 g of aqueous phase. The unreacted isobutyraldehyde the organic phase becomes a sump temp under normal pressure distilled up to 135 ° C. Based on 1000 g of organic Phase become 787 g of a mixture of isobutyraldehyde and water how to obtain 213 g of residue, which according to gas chromatography The analysis is composed as follows:

13.6% isobutyraldehyde
0.3% isobutyraldol
2.9% 2,2,4-trimethylpentane-1,3-diol
77.2% 2,2,4-trimethylpentane-1,3-diol monoisobutyrate
0.3% 2,2,4-trimethylpentane-1,3-diol diisobutyrate
5.7% other components

Claims (7)

1. Process for the preparation of isomeric mixtures of monoesters of 2,2,4-trimethylpentanediol-1,3 with isobutyric acid by aldol condensation of isobutyraldehyde and subsequent Tischchencheneaction of the isobutyraldol obtained with isobutyraldehyde with the addition of aqueous alkali hydroxide solution in a homogeneous phase at elevated temperature, thereby characterized in that an isobutyraldehyde with an acid number of at most 2 is used and the reaction is carried out in the presence of 5 to 20% strength aqueous alkali metal hydroxide solution such that the molar ratio x between the isobutyraldehyde and alkali metal hydroxide used has a value between 200 and 2000. 2. The method according to claim 1, characterized, that an isobutyraldehyde with an acid number of at most 1 starts. 3. The method according to claims 1 and 2, characterized, that one uses sodium hydroxide as alkali hydroxide. 4. The method according to claim 3, characterized, that an 8 to 15% aqueous sodium hydroxide solution is used. 5. The method according to claims 1 to 4, characterized in that the molar ratio x has a value between 300 and 700. 6. The method according to claims 1 to 5, characterized, that the reaction at a temperature of 50 to 80 ° C, before preferably 60 to 70 ° C, is carried out.   7. The method according to claims 1 to 6, characterized, that the residence time of the reaction is 10 to 60 minutes, especially 15 up to 30 minutes.