DE102016122527A1 - Process for the synthesis of citric monoesters - Google Patents

Abstract

The present invention discloses a synthetic method for linking fatty alcohols with citric acids in the presence of an additive.

Description

The present invention relates to the synthesis of citric acid monoesters, in particular with fatty alcohols.

Citric acid esters are of industrial interest, as they may i.a. be used as emulsifiers or surfactants. Of particular importance are the monoesters of fatty alcohols, polyethoxylated fatty alcohols and mono- and diglycerides. Such esters are already used in the food industry, cosmetics and detergents. The advantages are the good compatibility (non-toxic, non-irritating to the skin), the biological degradation work as well as their production starting from renewable raw materials.

The targeted and pure preparation of such compounds is inter alia in the DE 10 2011 054 602 which uses boron compounds as a catalyst. It is, however, the object to provide improved processes for the synthesis of such carboxylic acid esters, which manage in particular without boric acid as a catalyst.

1. a) Vorlegen eines Überschusses an Citronensäure in einem niedermolekularen Additiv, enthaltend eine Verbindung ausgewählt aus der Gruppe Carbonate, β-Hydroxyverbindungen, sekundäre Alkohole sowie Mischungen daraus bei einer Temperatur von ≥ 100°C
2. b) Zugabe eines Fettalkohols und/oder Fettalkoholderivats

This object is solved by claim 1 of the present invention. Accordingly, a method for the synthesis of citric acid monoesters is proposed, comprising the steps:

1. a) presenting an excess of citric acid in a low molecular weight additive containing a compound selected from the group of carbonates, β-hydroxy compounds, secondary alcohols and mixtures thereof at a temperature of ≥ 100 ° C.
2. b) Addition of a fatty alcohol and / or fatty alcohol derivative

Surprisingly, it has been found that by means of this process, such compounds can be prepared in a targeted manner in high yields. In particular, in most applications of the present invention, the diesters are only sparingly, e.g. formed undetectable amounts.

It should be noted that the vast majority of the citric acid esters obtainable by the process according to the invention are chiral compounds, the term "citric acid" and "citric acid monoesters" thus being understood to mean all enantiomers and mixtures thereof.

The term "excess" refers to the citric acid over the fatty alcohol and / or the fatty alcohol derivative from step b). The excess (in mol: mol) is preferably ≥ 1.2: 1 to ≦ 3: 1, more preferably ≥ 1.5: 1 to ≦ 2.5: 1

The term "low molecular weight" means and / or in particular comprises a molecular weight of ≦ 500 Da, more preferably ≦ 300 Da.

According to the present invention, an additive is used. This additive is preferably used based on the citric acid in the ratio (g / g) of ≥ 0.5: 1 to ≦ 3: 1. This has proven itself in practice. Particularly preferred is a ratio of ≥0.1: 1 to ≤1: 1, more preferably ≥0.3: 1 to ≤0.8: 1.

The additive contains a compound selected from the group containing carbonates, β-hydroxy compounds, secondary alcohols or mixtures thereof. Preferably, it consists predominantly of these compounds.

The term "predominantly" for the purposes of the present invention means ≥90% by weight, preferably ≥95%, more preferably ≥98% by weight, and most preferably ≥99% by weight.

Preferred carbonates are 1,2-propylene carbonate, ethylene carbonate, 2,3-butylene carbonate.

Preferred β-hydroxy compounds are on the one hand β-hydroxycarboxylic acids, particularly preferably glycolic acid, lactic acid, lactide. It should be noted that in particular lactic acid or lactide can also be used as an aqueous solution. In this case, ≥60% by weight solutions are particularly preferred.

Other preferred additives are secondary alcohols, although higher alcohols can be used as long as no primary alcohol functions are present. Preference is given here 2,3-butanediol.

• • primäre lineare Alkohole mit mehr als 6 Kohlenstoffatomen, besonders dabei bevorzugt sind Decanol, Dodecanol, Hexadenaol, Oleylalkohol, Octadecanol
• • technische Fettalkoholgemische
• • Ricinolsäure oder Ricinolsäureester, Ricinus-öl, 12-Hydroxystearinsäure oder 12-Hydroxystearinsäureester

The term "fatty alcohol and / or fatty alcohol derivative" includes or includes in particular:

• Primary linear alcohols having more than 6 carbon atoms, especially preferred are decanol, dodecanol, hexadecanol, oleyl alcohol, octadecanol
• • technical fatty alcohol mixtures
• Ricinoleic acid or ricinoleic acid ester, Ricinus oil, 12-hydroxystearic acid or 12-hydroxystearic acid ester

Preferably, step a) takes place at a temperature of ≥130 ° C and ≤180 ° C. This has been proven in most applications of the present invention.

Preferably, step b) also takes place at a temperature of ≥100 ° C., preferably of ≥130 ° C. and ≦ 180 ° C. In particular, it is preferred that step b) take place at about the same temperature as step a), i. the temperature difference in steps a) and b) is ≤10 ° C.

The time interval between step a) and step b) is preferably ≥ 5 to ≦ 30 minutes. This has proven itself in practice, since in most applications a clear reaction solution is created.

• c) Reagierenlassen der Mischung aus Schritt b) über einen Zeitraum von ≥30 min und ≤3h

According to a preferred embodiment of the invention, the method according to the invention comprises a step c)

• c) allowing the mixture of step b) to react for a period of ≥30 min and ≤3h

This reaction time has been proven in many applications of the present invention. Particularly preferred in step c) is a period of ≥1h and ≤2h

According to another embodiment of the present invention, it is preferred that step c) take place at about the same temperature as step b), i. the temperature difference in step c) and b) is ≤10 ° C.

Usually, the products thus obtained are used directly without further purification steps. However, e.g. by aqueous extraction of the product mixture, the excess of citric acid and in most cases the additive are removed as far as possible, so that the proportion of citric acid monoester in the product can rise to 94-99%.

Highly pure monoesters can finally be obtained by the recrystallization of solid crude products.

Further details, features and advantages of the subject matter of the invention will become apparent from the subclaims and from the following description of the accompanying examples, in which - by way of example - several embodiments of the method according to the invention are shown. The examples are purely illustrative and not restrictive.

Examples

Preparation of (technical) citric acid mono-octyl ester mixtures

40.0 g of citric acid (0.21 mol) were each stirred with the amounts of additive / solubilizer specified in Examples 1-5 for about 10 minutes at 160 ° C. oil bath temperature with a mechanical stirrer in an open 250 ml beaker. This results in clear reaction solutions. example Additive / solubilizer Quantity (g) Addition time Octanol (min) Proportion of citric acid monoester in the product mixture (% by weight) 1 propylene carbonate 15 <1 48-58 2 ethylene 15 <1 48-58 3 Glycolic acid solution (70%) 15 2 42-56 4 Lactic acid solution (about 85%) 10 <1 42-50 5 2,3-butanediol 9 <1 49-60

Subsequently, 13.0 g octanol (0.10 mol) was added to this reaction melt in the specified time and then the temperature of the oil bath changed to 145 ° C. At this temperature, stirring was continued for ¹ h ( ¹ H-NMR analyzes showed complete conversion of the fatty alcohol). The reaction mixture thus obtained can be used directly after cooling. The proportion of citric acid in the product mixture (% by weight) can be taken from Examples 1-5 in the table above.

Preparation of (technical) citric acid mono-decyl ester mixtures

40.0 g of citric acid (0.21 mol) were stirred in each case with the amounts of additive / solvent indicated in Examples 6-10 for about 10 minutes at 160 ° C. oil bath temperature with a mechanical stirrer in an open 250 ml beaker. This results in clear reaction solutions. example Additi v / Solver Quantity (g) Addition time Decanol (min) Proportion of citric acid monoester in the product mixture (% by weight) 6 propylene carbonate 15 <1 52-60 7 ethylene 15 <1 52-63 8th Glycolic acid solution (70%) 15 5 55-65 9 Lactic acid solution (about 85%) 10 <1 55-65 10 2,3-butanediol 9 <1 55-63

Subsequently, to this reaction melt, 15.8 g of decanol (0.10 mol) was added in the specified time and then the temperature of the oil bath changed to 145 ° C. At this temperature, stirring was continued for ¹ h ( ¹ H-NMR analyzes showed complete conversion of the fatty alcohol). The reaction mixture thus obtained can be used directly after cooling. The proportion of citric acid monodecyl ester in the product mixture (% by weight) can be taken from Examples 6-10 in the table above.

Preparation of (technical) citric acid mono-dodecyl ester mixtures

40.0 g of citric acid (0.21 mol) were each stirred with the amounts of additive / solubilizer specified in Examples 11-15 for about 10 minutes at 160 ° C. oil bath temperature with a mechanical stirrer in an open 250 ml beaker. This results in clear reaction solutions. example Additi v / Solver Quantity (g) Addition time dodecanol (min) Proportion of citric acid monoester in the product mixture (% by weight) 11 propylene carbonate 15 10 50-58 12 ethylene 15 20 53-60 13 Glycolic acid solution (70%) 25 40 50-63 14 Lactic acid solution (about 85%) 10 20 50-65 15 2,3-butanediol 9 20 53-65

Subsequently, to this reaction melt, 18.6 g of dodecanol (0.10 mol) was added in the specified time and then the temperature of the oil bath to 145 ° C changed. At this temperature, stirring was continued for ¹ h ( ¹ H-NMR analyzes showed complete conversion of the fatty alcohol). The reaction mixture thus obtained can be used directly after cooling. The proportion of citric acid mono-dodecyl ester in the product mixture (wt .-%) can be found in Examples 11-15 of the table above. example Crude product from Ex. Proportion of citric acid monoester in the product mixture (% by weight) 16 11 90-98 17 12 90-98 18 16/17 > 99

Depending on requirements, the further purification of the products can be carried out as follows: The reaction mixtures (from Examples 11-15) are taken up in adequate amounts of water / ethyl acetate and mixed well. The organic phase is washed two more times with water and once with sat. NaCl solution, dried over Na ₂ SO ₄ and the solvent is completely removed. (Examples 16, 17)

The resulting solid can be recrystallized from hexane / ethyl acetate (6: 2) mixtures. (Example 18)

Preparation of (technical) citric acid mono-hexadecyl esters and monooleyl esters and mono-octadecyl ester mixtures

40.0 g of citric acid (0.21 mol) were stirred in each case with the amounts of additive / solubilizer specified in Examples 19-27 for approximately 10 minutes at 160 ° C. oil bath temperature with a mechanical stirrer in an open 250 ml beaker. This results in clear reaction solutions. example Fatty alcohol / quantity used (g) Additive / solubilizer / amount used (g) Addition time dodecanol (min) Proportion of citric acid monoester in the product mixture (% by weight) 19 Hexadecanol / 24.2 Propylene carbonate / 20 30 56-67 20 Hexadecanol / 24.2 Ethylene carbonate / 20 40 50-67 21 Hexadecanol / 24.2 2,3-butanediol / 9 30 50-65 22 Oleyl alcohol / 26.8 Propylene carbonate / 20 20 46-53 23 Oleyl alcohol / 26.8 Ethylene carbonate / 20 30 45-53 24 Oleyl alcohol / 26.8 2,3-butanediol / 9 20 53-58 25 Oleyl alcohol / 26.8 Lactic Acid Solution / 18g 20 53-58 26 Octadecanol / 26.8 Lactic Acid Solution / 18g 20 53-60 27 Octadecanol / 26.8 Propylene carbonate / 25 20 56-70

Subsequently, the amounts of fatty alcohol (0.10 mol) indicated in Examples 19-27 were added to this reaction melt in the specified time and then the temperature of the oil bath was changed to 150.degree. At this temperature, stirring was continued for ¹ h ( ¹ H-NMR analyzes showed complete conversion of the fatty alcohol). The reaction mixture thus obtained can be used directly after cooling. The proportion of citric acid monoester in the product mixture (% by weight) can be taken from Examples 19-27 of the above table. example Crude product from Ex. Proportion of citric acid monoester in the product mixture (% by weight) 28 19 90-98 29 27 90-98 30 28 > 99 31 29 > 99

Depending on requirements, the further purification of the products can be carried out as follows: The reaction mixtures (from Examples 11-15) are taken up in adequate amounts of water / ethyl acetate and mixed well. The organic phase is washed two more times with water and once with sat. NaCl solution, dried over Na ₂ SO ₄ and the solvent is completely removed. (Examples 28, 29)

The resulting solid can be recrystallized from hexane / ethyl acetate (95: 5) mixtures. (Examples 30, 31)

Preparation of (technical) citric acid mono-ricinoleic acid ester mixtures

40.0 g of citric acid (0.21 mol) were stirred in each case with the amounts of additive / solubilizer specified in Example 32 for about 10 minutes at 160 ° C. oil bath temperature with a mechanical stirrer in an open 250 ml beaker. This creates a clear reaction solution. example Fat derivative Amount used (g) Additive / solubilizer / amount used (g) Addition time dodecanol (min) Proportion of citric acid monoester in the product mixture (% by weight) 32 Ricinoleic acid / 29.8 Propylene carbonate / 30 30 56-67

Subsequently, the amounts of ricinoleic acid (0.10 mol) indicated in Example 32 were added to this reaction melt at 170 ° C. in the indicated time and stirring was continued for a further hour at this temperature for 2 h and then at 150 ° C. oil bath temperature. ( ¹ H-NMR analyzes showed a complete conversion of the fatty alcohol). The reaction mixture thus obtained can be used directly after cooling.

The individual combinations of the components and the features of the already mentioned embodiments are exemplary; the exchange and substitution of these teachings with other teachings contained in this document with the references cited are also expressly contemplated. Those skilled in the art will recognize that variations, modifications and other implementations described herein may also occur without departing from the spirit and scope of the invention. Accordingly, the above description is illustrative and not restrictive. The word "comprising" used in the claims does not exclude other ingredients or steps. The indefinite article "a" does not exclude the meaning of a plural. The mere fact that certain measures are recited in mutually different claims does not make it clear that a combination of these dimensions can not be used to advantage. The scope of the invention is defined in the following claims and the associated equivalents.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102011054602 [0003]

Claims (8)

Process for the targeted synthesis of citric acid monoester synthesis comprising: a) presenting an excess of citric acid in a low molecular weight additive containing a compound selected from the group of carbonates, β-hydroxy compounds, secondary alcohols and mixtures thereof at a temperature of ≥ 100 ° C. b) Addition of a fatty alcohol and / or fatty alcohol derivative Method according to Claim 1 or 2 wherein step a) takes place at a temperature of ≥130 ° C and ≤180 ° C. Method according to one of Claims 1 to 3 wherein the additive contains a compound selected from the group consisting of 1,2-propylene carbonate, ethylene carbonate, 2,3-butylene carbonate, glycolic acid, lactic acid, lactide and 2,3-butanediol Method according to one of Claims 1 to 3 in which the ratio of citric acid to fatty alcohol (in mol: mol) is ≥1.2: 1 to ≤3: 1. Method according to one of Claims 1 to 4 , wherein the additive based on the citric acid in the ratio (g / g) of ≥0.5: 1 to ≤3: 1 is used. Method according to one of Claims 1 to 5 , wherein the time interval between step a) and step b) is ≥5 to ≤30 minutes. Method according to one of Claims 1 to 6 comprising a step c) c) allowing the mixture from step b) to react over a period of ≥30 min and ≤3h Method according to one of the steps 1 to 7, wherein the temperature difference in step c) and b) ≤10 ° C.