EP1558558A1

EP1558558A1 - Method for the production of an ester

Info

Publication number: EP1558558A1
Application number: EP03810415A
Authority: EP
Inventors: Thomas Albers; Michael Neuss; Heiko Kraus
Original assignee: Cognis IP Management GmbH
Current assignee: Cognis IP Management GmbH
Priority date: 2002-11-08
Filing date: 2003-10-30
Publication date: 2005-08-03
Also published as: WO2004041769A1; US20060041158A1; DE10251984A1; JP2006505598A

Abstract

The invention relates to a method of the production of an ester from an organic carbonyl compound and an alcohol, by carrying out an esterification reaction in the presence of a catalyst, comprising an inorganic phosphorous (I) compound and a titanate. The method is carried out by firstly mixing the organic carbonyl compound and the inorganic phosphorous (I) compound together, the mixture obtained is then filtered and the alcohol and the titanate added to the filtered mixture and the esterification carried out. The method is particularly suitable for the esterification of (poly)fatty acids or (poly)hydroxyfatty acids to esters with a high degree of esterification and low colouration.

Description

Process for the preparation of an ester

Field of the Invention

The invention relates to a process for the preparation of esters and in particular esters which are obtained by esterification of fatty acids or hydroxyfatty acids with alcohols or polyols and which are used, for example, as additives in cosmetic compositions or pharmaceutical preparations.

State of the art

The problem with numerous esterification reactions and especially in the production of fatty acid or hydroxy fatty acid esters is that the degree of esterification is often not high enough and the product obtained is yellowish to brownish in color. Degree of esterification and discoloration depend, among other things, on the catalysts used in the esterification. Thus, acidic catalysts usually achieve a light-colored product, but an unacceptable degree of esterification, while a good degree of esterification is achieved with basic catalysts, but the esters obtained are darkly colored for this.

EP 0 000 424 B1 describes, for example, the esterification of polymeric monocarboxylic acids such as poly (12-hydroxystearic acid) with alcohols such as polyethylene glycol. Tetrabutyl titanate is mentioned as an esterification catalyst. However, the resulting hydroxy fatty acid esters are unsatisfactory in terms of their color.

To reduce the discoloration of polymeric esters, catalysts have also been proposed which consist of a combination of several compounds. The US patents 6080834, US 6166170 and US6255441 relate to catalyst compositions which can be used for the production of polyesters and here in particular of polyalkylene terephthalates. The catalyst composition is obtained by using a titanium compound in the presence of a Complexing agent is reacted with a phosphorus compound. Suitable titanium compounds are tetraalkyl orthotitanates, the phosphorus compound can be a phosphoric acid such as hypophosphorous acid. However, if the catalyst compositions described are applied to the esterification of fatty acids and in particular hydroxy fatty acids with alcohols such as polyols, esters are obtained which are neither satisfactory in terms of their degree of esterification nor in terms of their color.

The invention was therefore based on the object of providing a process for the preparation of an ester which has a high degree of esterification and at the same time the least possible coloration. The process should be particularly suitable for the production of esterification products of fatty acids or hydroxy fatty acids and alcohols with the properties mentioned above.

Description of the invention

It has now surprisingly been found that esters can be prepared from an organic carbonyl compound and an alcohol with a high degree of esterification and extremely little discoloration using a catalyst which comprises an inorganic phosphorus (I) compound and a titanate if a certain sequence of Procedural steps are followed.

The invention accordingly relates to a process for the preparation of an ester from an organic carbonyl compound and an alcohol by carrying out an esterification reaction in the presence of a catalyst which comprises an inorganic phosphorus (I) compound and a titanate, in which first the organic carbonyl compound and the inorganic phosphorus (l) - compound are mixed with each other, the mixture obtained is filtered and then the alcohol and titanate are added to the filtered mixture and the esterification reaction is carried out.

In contrast to the known processes, in which a catalyst component is produced in a precursor from inorganic phosphorus (I) compound, titanate and complexing agent, which is then added to the reaction mixture of acid and alcohol, the catalyst components are separated from one another in the process according to the invention Stages added. First, the organic carbonyl compound with the inorganic Pretreated phosphorus (1) compound, and the mixture obtained is then filtered. Without wishing to be bound by any particular theory, the advantage of this procedure is presumably that the pretreatment with the phosphorus (I) compound and the subsequent filtration lead to a purification of the organic carbonyl compound. This significantly reduces the proportion of impurities which, in the subsequent reaction of the filtrate with the alcohol in the presence of the titanate, could lead to discoloration of the ester obtained. The presence of the titanate as an additional catalyst component in the actual esterification reaction ultimately leads to the desired high degrees of esterification. Overall, therefore, slightly colored products with a high degree of esterification are obtained in the process according to the invention.

Organic carbonyl compound

The process according to the invention is not restricted to the production of certain esters. Rather, basically all esterifiable organic carbonyl compounds can be used, such as carboxylic acids or carboxylic acid derivatives, in particular carboxylic acid anhydrides, carboxylic acid halides, carboxylic acid salts, carboxylic acid amides or carboxylic acid esters. If the following generally refers to carboxylic acids as starting compounds for the esterification reaction, this always means the derivatives of the corresponding acid mentioned above.

The process according to the invention is particularly suitable for the production of fatty acid esters having a fatty acid residue which has 8 to 22 and preferably 12 to 18 carbon atoms. The carbonyl component can also be substituted. The process according to the invention can be used particularly advantageously, for example, in the esterification of hydroxy fatty acids such as those having 8 to 22 and preferably 12 to 18 carbon atoms in the fatty acid residue. 12-hydroxystearic acid is particularly suitable as the starting compound of the esterification process according to the invention.

Instead of the monomeric fatty acids or hydroxyfatty acids described above, the corresponding polyfatty acids or polyhydroxyfatty acids can also be used. Those with a degree of self-condensation of 2 to 20 and in particular 2 to 10 are preferred. A preferred example of this group of organic carbonyl compounds is poly-12-hydroxystearic acid.

The esters of poly-12-hydroxystearic acid are used, for example, as emulsifiers in cosmetic preparations. They are available, for example, in compositions which are sold under the brands "Dehymuls® PGPH", "Eumulgin® VL 75" (mixture with Coco Glucosides in Weight ratio 1: 1) or "Dehymuls ® SBL" are sold by Cognis Deutschland GmbH & Co. KG. Polyol polyhydro stearates are also described in EP 0 766 661 B1. These compounds can also be prepared using the process according to the invention.

alcohol

However, the process according to the invention is not limited to the alcohols described in EP 0 766 661 B1 as one of the starting components of the esterification reaction. Rather, basically all mono- and polyfunctional alcohols can be used. The esterification reaction is preferably carried out using a polyol. Those polyols which have 2 to 12 and in particular 2 to 8 hydroxyl groups are preferred here. Particularly preferred among the polyols are polyalkylene glycols and here in particular polyethylene glycols, and also glycerol and polyglycerols.

The amount of the organic carbonyl compound and alcohol used in the process according to the invention is likewise not particularly limited. It can move within the framework which is generally customary for the esterification reactions of these starting components. In addition to a complete esterification of the available hydroxyl groups, they can also be partially esterified. For example, a molar ratio of organic carbonyl compound to alcohol of 1: 1 to 30: 1, in particular 1: 1 to 20: 1, is particularly suitable, and 1: I to 15: 1 is particularly preferred.

titanate

Basically, all titanates already known as esterification catalysts can be used. According to the invention, preference is given to those titanates which are capable of forming esters with the alcohol used. Tetraalkyl orthotitanates are preferred, and in particular tetraisopropyl titanate and tetrabutyl titanate. Suitable amounts of the titanate are, for example, 0.01 to 0.1% by weight, based on the total amount of organic carbonyl compound, alcohol and catalyst in the reaction mixture. An excessive amount of titanate can lead to an undesirable discoloration of the ester obtained, an insufficient amount can slow down the esterification.

Phosphorus (I) compound

In principle, all those compounds which have already been used in the prior art as esterification catalysts can also be used as phosphorus (I) compounds. Phosphorus (I) compounds preferred according to the invention are phosphorus (I) acid (ie phosphinic acid, hypophosphorous acid) or salts of phosphoric acid (phosphinates, hypophosphites). Suitable amounts of the phosphorus (1) compound are 0.1 to 1% by weight, based on the total amount of organic carbonyl compound, alcohol and catalyst in the reaction mixture.

The organic carbonyl compound and the inorganic phosphorus (I) compound are in a first step of the process according to the invention in a temperature range from 20 to 220 ° C, preferably from 60 to 180 ° C and particularly preferably from 80 to 120 ° C over a period of mixed for at least 20 minutes. The mixing times depend on the temperature and are usually from 15 to 180 minutes, times from 30 to 60 minutes in the temperature range from 80 to 120 ° C. are preferred,

Inorganic base

Particularly good results with regard to the coloration of the esterification product obtained are obtained if an inorganic base is added to the mixture of organic carbonyl compound and inorganic phosphorus (I) compound before the filtration step. It is particularly preferably a basic salt and in particular a carbonate such as sodium or potassium carbonate. The inorganic base is expediently added in an amount which is sufficient to substantially completely neutralize the phosphorus (I) compound. The inorganic base is therefore expediently added in an equivalent amount to the phosphorus (1) compound used, but may also be present in excess of the latter.

The advantage of adding an inorganic base is presumably on the one hand that the preneutralization means that the reaction mixture in the subsequent esterification step is not too acidic and a higher degree of esterification can be achieved as a result. On the other hand, if an inorganic salt is added, the salt presumably acts as a filtration aid and thus improves the cleaning effect in the filtration step.

filtration aids

As an alternative to or in addition to the addition of an inorganic salt, a filtration aid can be added to the mixture of organic carbonyl compound and inorganic phosphorus (I) compound before filtering. All slightly alkaline to slightly acidic filtration aids, such as bleaching earth in particular, are suitable in principle. Suitable filtration aids are, for example, under the brands "Hyflow® Supercel" (Manville Corp.) or "Tonsil® Standard" (Südchemie) commercially available. These filtration aids increase the cleaning effect in the filtration step and thus help to reduce the color in the end product.

The process according to the invention can be carried out either in the melt or in solution. From a cost and environmental point of view, the process is preferably carried out in the melt. However, reaction in a non-polar, inert organic solvent is also possible. Those solvents are particularly preferred here which form an azeotrope with a lowering of the boiling point with the water formed in the course of the esterification, such as toluene or xylene. Which procedure is chosen in the esterification process according to the invention depends primarily on the starting materials selected. The selection of suitable process parameters such as the selection of suitable solvents and the selection of the reaction temperatures are basically known to the person skilled in the art.

In order to keep the discoloration of the end product as low as possible, the esterification temperature in the course of the process according to the invention is chosen to be as low as possible. When reacting in the melt, the esterification reaction preferably takes place at a temperature below 240 ° C. and in particular in a range between 180 and 220 ° C. A rapid decolorization of the reaction mixture is usually observed from a temperature of about 170 ° C. in the esterification step of the process according to the invention if phosphorus (I) acid or a salt thereof is used as the phosphorus (I) compound. This is presumably due to the decomposition of phosphoric acid, which forms phosphorus and phosphoric acid via intermediates, which ultimately leads to bleaching of the reaction mixture.

Particularly good results are achieved if the reaction mixture is slowly heated to the maximum reaction temperature in the course of the esterification step, so that water is separated off continuously. This is especially true when using hydroxy fatty acids as the organic carbonyl compound. Too rapid an increase in temperature can lead to the elimination of water from the hydroxy fatty acid and thus to the undesirable formation of unsaturated fatty acids in the reaction mixture.

Carrying out the reaction, either only the actual esterification or the reaction as a whole, under protective gas such as nitrogen or argon can bring about an improvement in the quality of the end product.

The invention will be further explained below with the aid of examples. Examples

example 1

Synthesis of a polyethylene glycol polyhydroxystearate

726.8 g (2.37 mol) of 12-hydroxystearic acid are mixed with 5 g of phosphoric (I) acid (50% strength) and stirred at 90 ° C. for 1 hour. After adding 8 g sodium carbonate and 5 g Hyflow® Supercel, the hot mixture is filtered. 273.2 g (0.18 mol) of polyethylene glycol 1500 and 0.4 g of Tyzor® TPT are added to the filtrate. The reaction mixture is slowly heated to 190 ° C. under protective gas (nitrogen) within 2 hours and esterified for 18 hours while continuously separating water in vacuo and gradually increasing the temperature to 210 ° C. After cooling to about 100 ° C and filtration, the product is obtained as a filtrate.

The product has an acid number of 8 and an iodine number of 2. The Hazen color number is 100. The process according to the invention provides particularly light-colored and low-odor products.

Example 2

Synthesis of a polyethylene glycol polyhydroxystearate

The procedure is as in Example 1, but 0.4 g of Tyzor® TBT are used instead of the 0.4 g of Tyzor® TPT.

The product has an acid number of 8 and an iodine number of 2. The Hazen color number is included

100th

Comparative Example 1

Synthesis of a polyethylene glycol polyhydroxystearate

672 g (2.19 mol) of 12-hydroxystearic acid, 328.3 g (0.219 mol) of polyethylene glycol 1500 and 0.2 g of Ti (OBu) are heated to 240 ° C. under nitrogen. After the water separation has ended, a vacuum is applied and condensation is continued until no further reduction in the acid number is observed. After cooling to 100 ° C and adding 0.5% filter aid (Hyflow® Supercel), the product is filtered.

The product (filtrate) has an acid number of 9.5. The color is dark brown. The color number according to Hazen or Gardner cannot be determined. Comparative Example 2

Synthesis of a polyethylene glycol polyhydroxystearate

754.3 g (2.46 mol) of 12-hydroxystearic acid and 245.8 g (0.164 mol) of polyethylene glycol 1500 are heated to 240 ° C. under nitrogen. After the water separation has ended, a vacuum is applied and condensation is continued until no further reduction in the acid number is observed. After cooling to 120 ° C and filtration with the addition of 0.5% filter aid (Hyflow® Supercel), the product is obtained as a filtrate.

The product has an acid number of 23. The color is dark brown. The color number according to Hazen or Gardner cannot be determined.

Comparative Example 3

Synthesis of a polyethylene glycol polyhydroxystearate

506 g (1.65 mol) of 12-hydroxystearic acid, 494 g (0.165 mol) of polyethylene glycol 3000 and 5 g (0.038 mol) of H3PO2 (50%) are heated to 240 ° C. under nitrogen. After the water separation has ended, a vacuum is applied and condensation is continued until no further reduction in the acid number is observed. Finally, the catalyst is neutralized with sodium carbonate. To this end, the product is mixed with the theoretically double amount of Na2CO3 (anhydrous) at 80 ° C (calculated from the acid number). The salts are filtered off with the addition of 0.5% filter aid (Hyflow® Supercel). The product is obtained as a filtrate.

The product has an acid number of 26. The color is light brown. The color number according to Hazen or Gardner cannot be determined.

Comparative Example 4

Synthesis of a polyethylene glycol polyhydroxystearate

711 g (2.316 mol) of 12-hydroxystearic acid are heated to 80 ° C. and mixed with 0.5 g of H3PO2. After 30 minutes at 160 ° C., 289 g (0.193 mol) of polyethylene glycol 1500 and a further 30 minutes later 0.4 g of Ti (OBu) are added under nitrogen and heated to 210 ° C. After the water separation has ended, a vacuum is applied and condensation is continued at 240 ° C. until no further reduction in the acid number is observed. After cooling to 120 ° C and filtration with the addition of 0.5% filter aid (Hyflow® Supercel), the product is obtained as a filtrate. The product has an acid number of 11.1. The color is dark brown. The color number according to Hazen or Gardner cannot be determined. Example 3

Synthesis of a polyglycerol poly ydroxystearate

893.6 g (2.91 mol) of 12-hydroxystearic acid are mixed with 5 g of hypophosphorous acid and 1

Stirred at 90 ° C for one hour. After adding 2 g sodium carbonate and 5 g filter aid (Hyflow ^®

Supercel) the hot mixture is filtered.

106.4 g (0.64 mol) of polyglycerol and 0.4 g of tetrabutyl titanate are added to the filtrate. The

The reaction mixture is slowly heated to 190 ° C. under protective gas (nitrogen) within 2 hours and, after continuous water separation in a vacuum, heated to up to 210 ° C.

Condensed for 18 hours until no further decrease in acid number is observed.

After cooling to about 100 ° C and the product is obtained as a clear filtrate.

The product has an acid number of 0.8 and an iodine number of 5.3. The color is light beige. The

Gardner color number is 2.1, Hazen 299.

attachment

1) Hyflow® Supercel INCI: diatomaceous earth

Manufacturer: Manville Corporation, USA

2) Tyzor® TBT

INCI: tetrabutyl titanate

Manufacturer: E.l. du Pont de Nemours and Company, Wilmington, Delaware, USA

3) Tyzor® TPT

INCI: tetraisopropyl titanate

Manufacturer: E.l. du Pont de Nemours and Company, Wilmington, Delaware, USA

Claims

claims

1. A process for the preparation of an ester from an organic carbonyl compound and an alcohol by carrying out an esterification reaction in the presence of a catalyst which comprises an inorganic phosphorus (I) compound and a titanate, characterized in that

(1) the organic carbonyl compound and the inorganic phosphorus (I) compound are mixed together,

(2) the mixture obtained is filtered and then

(3) the alcohol and titanate are added to the filtered mixture and the esterification reaction is carried out.

2. The method according to claim 1, characterized in that a carboxylic acid, in particular a fatty acid having 8 to 22 carbon atoms, preferably 12 to 18 carbon atoms, is used as the organic carbonyl compound.

3. The method according to claim 1, characterized in that a hydroxy fatty acid, in particular a hydroxy fatty acid having 8 to 22, preferably 12 to 18 carbon atoms and in particular 12-hydroxystearic acid, is used as the organic carbonyl compound.

4. The method according to claim 2 or 3, characterized in that a polyfatty acid or polyhydroxyfatty acid with a degree of self-condensation of 2 to 20, in particular 2 to 10, is used as the organic carbonyl compound.

5. The method according to any one of claims 1 to 4, characterized in that a polyol and in particular a polyalkylene glycol, preferably polyethylene glycol, glycerol, polyglycerol or any mixture of these substances is used as the alcohol.

n

6. The method according to any one of claims 1 to 5, characterized in that the titanate used is one which is capable of forming esters with the alcohol used, in particular a tetraalkyl orthotitanate and preferably tetraisopropyl titanate or tetrabutyl titanate.

7. The method according to claim 6, characterized in that the titanate in an amount of 0.01 to 0.1 wt .-%, based on the total amount of organic carbonyl compound, alcohol and catalyst, is used.

8. The method according to any one of claims 1 to 7, characterized in that phosphorus (l) acid or a salt thereof is used as the phosphorus (l) compound.

9. The method according to claim 8, characterized in that the phosphorus (l) compound in an amount of 0.1 to 1 wt .-%, based on the total amount of organic carbonyl compound, alcohol and catalyst, is used.

10. The method according to any one of claims 1 to 9, characterized in that the organic carbonyl compound and inorganic phosphorus (I) compound containing mixture before the filtration step (2), an inorganic base, preferably a basic salt and in particular a carbonate, is added.

11. The method according to claim 10, characterized in that the inorganic base is added in an amount sufficient to substantially completely neutralize the phosphorus (I) compound.

12. The method according to any one of claims 1 to 11, characterized in that the organic carbonyl compound and the inorganic phosphorus (l) compound in step (1) of the reaction in the temperature range from 20 to 220 ° C, preferably 60 to 180 ° C and particularly preferably 80 to 120 ° C are mixed over a period of at least 20 minutes.

13. The method according to any one of claims 1 to 12, characterized in that the reaction is carried out in the melt or in a non-polar, inert organic solvent, preferably one which forms an azeotrope with water which lowers the boiling point.

14. The method according to any one of claims 1 to 13, characterized in that the esterification reaction in the melt is carried out at a temperature below 240 ° C, in particular between 180 and 220 ° C.

15. The method according to any one of claims 1 to 14, characterized in that at least the esterification reaction is carried out under a protective gas.