DE102014209412A1 - Phase transfer reagent for the epoxidation of fatty acid alkyl esters - Google Patents

Abstract

The present invention relates to a process for the epoxidation of unsaturated fatty acid alkyl esters by reacting unsaturated fatty acid alkyl esters with hydrogen peroxide in a liquid two-phase system which comprises an organic phase comprising the fatty acid alkyl esters and an aqueous phase comprising hydrogen peroxide in the presence of a catalyst system comprising at least one catalytically active Transition metal compound and a special phase transfer reagent comprises. The invention also relates to the corresponding use of a phase transfer reagent for the epoxidation of fatty acid alkyl esters.

Description

The present invention relates to a process for the catalytic epoxidation of fatty acid alkyl esters using a special phase transfer reagent.

The production of epoxides is carried out by reaction of unsaturated compounds with an oxidizing agent. The simplest example of this is the production of ethylene oxide by reaction of ethene with oxygen under high pressure on a silver catalyst. The direct oxidation with oxygen, however, only works in the case of ethene, and already leads to longer-chain alkenes, such as. Propylene, no longer satisfactory results.

Long-chain epoxides are usually obtained by reaction with peroxide-containing reagents. In this case, for example, hydrogen peroxide, percarboxylic acids or alkyl hydroperoxides are used. An example of this is the in WO 2005/000827 A1 disclosed oxidation of propylene with hydrogen peroxide in the presence of a titanium silicalite catalyst.

Of particular interest here is the epoxidation of unsaturated fatty acid esters, which are used, for example, as plasticizers or can be further processed into polyurethanes.

The oxidation of fatty acid esters with hydrogen peroxide, however, proves to be significantly more difficult than the oxidation of alkenes with hydrogen peroxide due to the low water solubility of fatty acids. While hydrogen peroxide and an optionally used metallic catalyst are present in the aqueous phase, fatty acids form an organic phase, whereby the reaction of fatty acids with hydrogen peroxide is made more difficult.

Out DE 30 27 349 A1 discloses a process for epoxidizing unsaturated compounds with hydrogen peroxide in a biphasic reaction mixture in the presence of a tungsten, molybdenum or vanadium catalyst in combination with a quaternary ammonium compound. The described method succeeds in achieving a high yield of epoxides despite the disadvantages of a two-phase system. However, the epoxidation of fatty acid alkyl esters is not described in detail.

Poli et al. describe the epoxidation of fatty acid alkyl esters with H ₂ O ₂ in the presence of a tungsten catalyst:
Evelyne Poli, Jean-Marc Clacens, Joe Barrault, Yannick Pouilloux: Solvent-free selective epoxidation of fatty esters over a tungsten-based catalyst. Catalysis Today 140 (2009) 19-22. doi: 10.1016 / j.cattod.2008.07.004

The starting materials used were methyl linoleate, rapeseed oil and sunflower oil. The last two compounds are fatty acid esters of glycerol.

It is an object of the present invention to provide an improved process for the epoxidation of unsaturated fatty acid alkyl esters with hydrogen peroxide, with which the yields achieved in the prior art can be increased.

deren Substituenten R unabhängig voneinander gleiche oder verschiedene Alkyl- oder Alkoholgruppen mit 1 bis 4 Kohlenstoffatomen darstellen und mindestens einer der Substituenten R eine Alkoholgruppe mit 1 bis 4 Kohlenstoffatomen darstellt, die mit einer gesättigten oder ungesättigten Fettsäure mit 1 bis 30 Kohlenstoffatomen verestert ist, und wobei X^– für ein Gegenanion steht.The present invention therefore relates primarily to a process for the epoxidation of unsaturated fatty acid alkyl esters by reacting the unsaturated fatty acid alkyl esters with hydrogen peroxide in a liquid two-phase system comprising an organic phase comprising the unsaturated fatty acid alkyl esters and an aqueous phase comprising hydrogen peroxide in the presence of a catalyst system, which comprises at least one catalytically active transition metal compound and a phase transfer reagent, wherein the phase transfer reagent is an esterquat of the formula (I)

their substituents R are independently identical or different alkyl or alcohol groups having 1 to 4 carbon atoms and at least one of the substituents R is an alcohol group with 1 to Represents 4 carbon atoms esterified with a saturated or unsaturated fatty acid of 1 to 30 carbon atoms, and wherein X ^{- represents} a counter anion.

The invention provides for the epoxidation to be carried out in the presence of a phase transfer reagent with the aid of which the catalytically active transition metal compound, which in itself is water-soluble, can be converted into the organic phase. From the prior art alkyl-substituted quaternary ammonium compounds are known for this purpose. It has now surprisingly been found that the use of esterquats according to formula (I) can increase the conversion of epoxidized fatty acid esters in comparison with the phase transfer reagents known from the prior art. In the context of this invention, the term esterquat denotes quaternary ammonium compounds which have at least one carboxylic acid ester group.

Preferred counteranions X ^- are, for example, chloride, Cl ^- , and methyl sulfate, CH ₃ SO ₄ ^- .

The substituents R according to formula (I) independently represent identical or different alkyl or alcohol groups having 1 to 4 carbon atoms, wherein at least one substituent R represents an esterified alcohol group. The alcohol groups are preferably monohydric alcohols. Suitable alkyl groups are, in particular, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl. Suitable alcohols are in particular all monohydroxylated derivatives of these alkyl groups, in particular hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxypropyl, 2-hydroxypropyl, 3-hydroxypropyl, 1-hydroxy-1-methyl-ethyl, 2-hydroxy-1-methyl -ethyl, 1-hydroxybutyl, 2-hydroxybutyl, 3-hydroxybutyl, 4-hydroxybutyl, 1-hydroxy-1-methyl-propyl, 2-hydroxy-1-methyl-propyl, 3-hydroxy-1-methyl-propyl, 1 -Hydroxymethyl-propyl and 1-hydroxymethyl-1-methyl-ethyl.

The esterified alcohol group is esterified according to the invention with a saturated or unsaturated fatty acid having 1 to 30 carbon atoms. The suitable unsaturated fatty acids may be mono- or polyunsaturated. Particularly preferred are saturated or unsaturated fatty acids having 8 to 20 carbon atoms, most preferably 16 to 18.

mit Z gleich einer oder mehreren, gesättigten oder ungesättigten Fettsäuren mit 1 bis 30 Kohlenstoffatomen erwiesen, wobei X^– für ein Gegenanion steht. Besonders bevorzugt sind dabei gesättigte oder ungesättigte Fettsäuren mit 8 bis 20 Kohlenstoffatomen, am meisten bevorzugt 16 bis 18.Particularly suitable esterquats are esters of a quaternary alkanolamine compound of the formulas (II) or (III)

where Z is equal to one or more saturated or unsaturated fatty acids containing from 1 to 30 carbon atoms, where X ^{- is} a counteranion. Particularly preferred are saturated or unsaturated fatty acids having 8 to 20 carbon atoms, most preferably 16 to 18.

The described ester quats can be prepared by reacting the corresponding tertiary alkanolamines, e.g. N-methyldiisoproanolamine or triethanolamine, esterified with a suitable fatty acid and then treated with a suitable alkylating agent, e.g. Dimethyl sulfate or diethyl sulfate or methyl chloride, are reacted to the quaternary alkanolamine compounds.

The esterquats of the formulas (I) to (III) are generally present as mixtures of different esters, wherein both the fatty acid group and the number of esterified fatty acid groups per Alkanolamine compound can vary. Ester quats are therefore characterized by their degree of esterification. This is the average number of esterified fatty acids per alkanolamine compound.

Preferably, the degree of esterification is in the range of 1 to 2.0, more preferably from 1.2 to 2.0, most preferably from 1.5 to 1.95. For the synthesis of an esterquat having a desired degree of esterification, the alkanolamine compound is reacted with a fatty acid amount corresponding to the degree of esterification. The reaction of the esterification is checked by the acid number. If the acid number is less than 5 mg KOH per g of substance, the reaction is sufficiently complete.

The amount of phase transfer reagent to be used depends greatly on the selected phase transfer reagent and on the fatty acid ester used. However, studies by the inventors show that the molar ratio of the phase transfer reagent to the transition metal should be in the range of 0.1 to 6.0, more preferably 0.25 to 3.0, most preferably 0.5 to 1.5.

The catalyst system according to the invention comprises, in addition to the described phase transfer reagent, a catalytically active transition metal compound, such as, for example WO 00/44704 (A1) or DE 30 27 349 A1 is described. Preferably, the catalytically active transition metal compound comprises at least one metal selected from the group consisting of tungsten, molybdenum and vanadium or a derivative thereof. The catalytically active transition metal compound particularly preferably comprises tungsten or a tungsten derivative.

The catalytically active transition metal compound is typically formed in situ under the conditions of the epoxidation reaction. The process according to the invention therefore provides for the use of a transition metal compound as starting material, which is converted in situ into a catalytically active form. The catalytically active transition metal compound is particularly preferably formed in situ from metallic tungsten, molybdenum and / or vanadium or a derivative thereof.

The starting material is added to the two-phase system preferably at a mass fraction of 0.1 to 50 g / kg based on the weight of disodium tungsten dihydrate on the total mass of the two-phase system, particularly preferably 0.2 to 15 g / kg, in particular 2 to 10 g / kg.

Derivatives of tungsten, molybdenum and / or vanadium are particularly suitable as starting material for the formation of the catalytically active transition metal compound. Suitable derivatives are in particular an oxide, a mixed oxide, an oxygen-containing acid, a salt of an oxygen-containing acid, a carbonyl derivative, a sulfide, a chloride, an oxychloride or a stearate of the elements tungsten, molybdenum and / or vanadium.

Examples of suitable derivatives are the metal carbonyls W (CO) ₆ or Mo (CO) ₆ , the oxides MoO ₂ , MoO ₅ , Mo ₂ O ₃ , MoO ₃ , WO ₂ , W ₂ O ₅ , WO ₃ , VO ₂ , V ₂ O ₃ , or V ₂ O ₅ , the sulfides WS ₂ or WS ₃ . Further examples are the oxygen acids H ₂ WO ₄ and H ₂ MoO ₄ or their alkali metal or alkaline earth metal salts. Especially suitable are tungstic acid salts, in particular sodium, potassium and ammonium tungstate. As a particularly suitable compound for the formation of the catalytically active transition metal compound in situ, sodium tungstate, Na ₂ WO ₄ , has been found.

The formation of the catalytically active transition metal compound in situ is preferably carried out by reaction with a derivative of phosphorus and / or arsenic. Particularly suitable for this purpose is an oxide, an oxygen acid, a salt of an oxygen acid, a sulfide, a chloride, an oxychloride or a fluoride of phosphorus and / or arsenic.

However, the formation of the catalytically active transition metal compound can also be carried out in a separate reaction, wherein initially a transition metal compound described above with a derivative of phosphorus and / or arsenic and hydrogen peroxide is reacted and the resulting catalytically active transition metal compound is added to the two-phase system of the epoxidation reaction.

The derivative of phosphorus and / or arsenic is added to the two-phase system. This produces a catalytically active transition metal compound which comprises both the transition metal and phosphorus or arsenic.

Particularly effective derivatives of phosphorus and / or arsenic are phosphoric acid, phosphorous acid, polyphosphoric acid, pyrophosphoric acid, arsenic acid and arsenous acid or their alkali metal salts.

In a particularly preferred embodiment, the catalytically active transition metal compound is formed in situ by reacting a tungstic acid salt, in particular sodium, potassium or ammonium tungstate, with phosphoric acid and with hydrogen peroxide.

Preferably, the molar ratio of the phosphoric acid to the transition metal ranges from 0.1 to 10.0, more preferably from 0.25 to 5.0, most preferably from 1 to 2.

The reaction according to the invention of the fatty acid alkyl esters with hydrogen peroxide takes place with vigorous stirring in an aqueous-organic two-phase system in the presence of the catalyst system described above. The organic phase comprises the ester and optionally an organic solvent.

The mass fraction of the fatty acid alkyl esters in the organic phase is preferably in the range from 5 to 100% by weight, particularly preferably in the range from 5 to 98% by weight.

The compounds to be epoxidized according to the invention are unsaturated fatty acid alkyl esters. It has been shown that the use of the phase transfer reagent according to the invention leads to high conversion rates in the epoxidation of unsaturated fatty acid alkyl esters.

The unsaturated fatty acid alkyl esters are preferably esters of unsaturated fatty acids having 2 to 30 carbon atoms and alcohols having 1 to 13 carbon atoms. The fatty acids can be monounsaturated or polyunsaturated. The fatty acids preferably comprise 8 to 20 carbon atoms, more preferably 12 to 18, most preferably 16 to 18. Mixtures of fatty acid methyl esters of this type are obtained, for example, from vegetable or animal fats, for example from rapeseed oil, and are particularly suitable as starting material for the epoxidation.

The alcohols are preferably monohydric alcohols. The alcohol group preferably comprises 1 to 10 carbon atoms, more preferably the alcohol group is methanol, ethanol, isononanol, 2-penthylheptanol and 1-pentanol. Preferably, the alcohols have no unsaturated carbon-carbon bond.

The fatty acid alkyl esters of unsaturated fatty acids used as starting material can be used in a mixture with fatty acid alkyl esters of saturated fatty acids. However, the proportion of unsaturated fatty acid alkyl esters in the organic phase is preferably at least 10% by weight, based on the total weight of the organic phase, more preferably 50% by weight, in particular 80% by weight.

The pH of the aqueous phase is preferably in the range of 1.5 to 3, very particularly preferably 2. Usually, this range is already obtained by the presence of the reactants and of the described catalyst system. If necessary, however, the pH can be adjusted by adding a mineral acid such as HCl or H2SO4. Although a markedly acidic pH increases the stability of hydrogen peroxide, it impairs the stability of the epoxide and can thus reduce the yield.

The reaction temperature of the epoxidation reaction is preferably in the range of 20 to 100 ° C.

The duration of the epoxidation reaction is usually a few minutes to several hours and depends on the type and amount of the catalyst system, the solvent and the ester to be epoxidized.

Hydrogen peroxide is added to the two-phase system in the usual amount, such that the molar ratio of double bonds to be hydrogen peroxide to be epoxidized is 10 to 50, preferably 10 to 20.

The process according to the invention can be carried out, for example, as follows. First, hydrogen peroxide or a hydrogen peroxide solution and the ester or a solution of the ester in an organic solvent are introduced into a suitable reactor. Subsequently, the components of the catalyst system, in particular the phase transfer reagent and the compounds required for the formation of the catalytically active transition metal compound, are optionally added in a suitable amount of solvent. With vigorous stirring, the mixture is brought to the reaction temperature for the desired duration. Upon completion of the reaction, cooling and phase separation, the reactants can be purified in a conventional manner, e.g. be separated by distillation.

The present invention also relates to the use of a described esterquat as a phase transfer reagent for the epoxidation of unsaturated fatty acid alkyl esters. The described ester quats are suitable in particular as phase transfer reagent in combination with the above-described catalytically active transition metal compounds.

Examples

In a reactor, 244 g of a mixture of saturated and unsaturated fatty acid methyl esters were submitted. By means of 1H-NMR, a molar ratio of the double bonds to the fatty acid methyl ester group of 1.55 mol mol ^{-1 was} analyzed. 0.80 g of disodium tungstate dihydrate, 0.28 g of 85% phosphoric acid were dissolved in 34 mL H ₂ O and fed to the reactor. The aqueous phase was adjusted to a pH of 2.0 with 50% sulfuric acid.

Different amounts of the following phase transfer reagents were added to the reaction mixture. The phase transfer reagents of Examples 1 to 8 were prepared by esterifying N-methyldiisopropanolamine (MDIPA) or triethanolamine (TEA) with varying amounts of fatty acids and then reacting with dimethyl sulfate to form the quaternary ammonium compounds. As the fatty acid, either hydrogenated tallow fatty acid or vegetable mixed oil fatty acid was used. The resulting phase transfer reagents thus differ in their basic structure (MDIPA or TEA), the fatty acid and the degree of esterification. The composition of the individual phase transfer reagents is shown in Table 1. example basic structure fatty acid esterification 1 MDIPA hydrogenated tallow fatty acid 1 2 MDIPA hydrogenated tallow fatty acid 1.93 3 MDIPA Vegetable blend oil 1.95 4 TEA hydrogenated tallow fatty acid 1 5 TEA hydrogenated tallow fatty acid 1.65 6 TEA hydrogenated tallow fatty acid 2 7 TEA Vegetable blend oil 1.65 Table 1: Composition of the phase transfer reagent

As a comparative example (Example 8), trioctylmethylammonium chloride (Aliquat 336) was used.

The reaction mixture was heated with stirring to a reaction temperature of 90 ° C. Subsequently, 138 g of a 35% hydrogen peroxide solution were added within 3 min. The reaction mixture was stirred under reflux at 90 ° C for a further 60 min.

Subsequently, the two phases of the reaction mixture were separated. By means of 1 H-NMR, the epoxide groups and unreacted double bonds of the fatty acid methyl ester in the organic phase were analyzed and the yield of the epoxide groups was determined based on the initial number of double bonds of the fatty acid methyl ester used as starting material. The results are shown in Table 2. example 1 2 3 4 5 6 7 8 (Vergeich) amount Yield Epoxide (%) 3.8 g 18 80 45 13 n / A n / A 9 n / A 7.6 g 15 63 51 17 17 41 9 7 11.4 g 15 57 42 18 16 35 9 6 Table 2: Test results

As the results in Table 2 show, the use of esterquats in all cases leads to higher yields of epoxide groups than the use of a prior art alkyl-substituted quaternary ammonium compound.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005/000827 A1 [0003]
• DE 3027349 A1 [0006, 0020]
• WO 00/44704 A1 [0020]

Cited non-patent literature

• Poli et al. [0007]
• Evelyne Poli, Jean-Marc Clacens, Joe Barrault, Yannick Pouilloux: Solvent-free selective epoxidation of fatty esters over a tungsten-based catalyst. Catalysis Today 140 (2009) 19-22. doi: 10.1016 / j.cattod.2008.07.004 [0007]

Claims (15)

A process for the epoxidation of unsaturated fatty acid alkyl esters by reacting the unsaturated fatty acid alkyl esters with hydrogen peroxide in a liquid two-phase system comprising an organic phase comprising the fatty acid alkyl esters and an aqueous phase comprising hydrogen peroxide in the presence of a catalyst system comprising at least one catalytically active transition metal compound and a phase transfer reagent , characterized in that the phase transfer reagent is an esterquat of the formula (I)

wherein the substituents R independently represent the same or different alkyl or alcohol groups having 1 to 4 carbon atoms and at least one of the substituents R represents an alcohol group having 1 to 4 carbon atoms esterified with a saturated or unsaturated fatty acid having 1 to 30 carbon atoms, and where X ^{- stands} for a counteranion. Method according to one of the preceding claims, characterized in that the degree of esterification of the esterquat is between 1 and 2. Method according to one of the preceding claims, characterized in that the esterquat is an ester of a quaternary alkanolamine compound according to the formulas formulas (II) or (III)

where Z is one or more saturated or unsaturated fatty acids of 1 to 30 carbon atoms, where X ^{- is} a counteranion. Method according to one of the preceding claims, characterized in that the transition metal compound comprises at least one metal selected from the group consisting of tungsten, molybdenum and vanadium or a derivative thereof. Method according to one of the preceding claims, characterized in that the catalytically active transition metal compound is formed in situ from metallic tungsten, molybdenum and / or vanadium or a derivative thereof. A method according to claim 5, characterized in that the derivative of tungsten, molybdenum and / or vanadium, an oxide, a mixed oxide, an oxygen-containing acid, a salt of an oxygen-containing acid, a carbonyl derivative, a sulfide, a chloride, an oxychloride or a stearate of the elements is tungsten, molybdenum and / or vanadium. Method according to one of claims 5 and 6, characterized in that the catalytically active transition metal compound is formed in situ by reaction with a derivative of phosphorus and / or arsenic and with hydrogen peroxide. A method according to claim 7, characterized in that the derivative of phosphorus and / or arsenic is an oxide, an oxygen acid, a salt of an oxygen acid, a sulphide, a chloride, an oxychloride or a fluoride of phosphorus and / or arsenic. Method according to one of claims 1 to 8, characterized in that the catalytically active transition metal compound is formed in situ by reacting a tungstic acid salt with phosphoric acid and with hydrogen peroxide. Process according to any one of the preceding claims, characterized in that the unsaturated fatty acid alkyl esters are esters of unsaturated fatty acids of 2 to 30 carbon atoms and alcohols of 1 to 13 carbon atoms. A method according to claim 10, characterized in that the alcohols are selected from the group comprising: methanol, ethanol, isononanol, 2-propylheptanol, 1-pentanol. Process according to claim 10 or 11, characterized in that the unsaturated fatty acid alkyl esters are methyl esters of unsaturated fatty acids containing 8 to 20 carbon atoms. Method according to one of the preceding claims, characterized in that the pH of the aqueous phase is adjusted between 1.5 and 3, in particular that the pH is adjusted to 2. Use of a phase transfer reagent for the epoxidation of unsaturated fatty acid alkyl esters, characterized in that the phase transfer reagent is an esterquat of the formula (I)

wherein the substituents R independently represent the same or different alkyl or alcohol groups having 1 to 4 carbon atoms and at least one of the substituents R represents an alcohol group having 1 to 4 carbon atoms esterified with a saturated or unsaturated fatty acid having 1 to 30 carbon atoms, and where X ^{- stands} for a counteranion. Use according to Claim 14, characterized in that the unsaturated fatty acid alkyl esters are methyl esters of unsaturated fatty acids containing 8 to 20 carbon atoms.