EP1362022B1 - Method for producing orthocarbonic acid trialkyl esters - Google Patents

Description

The invention relates to a process for the preparation of Orthocarbonsäuretrialkylestern (orthoester O) by electrochemical oxidation of alpha-beta-diketones or alpha-beta-hydroxy ketones, wherein the keto function in the form of a derived from C ₁ - to C ₄ alkyl alcohols ketal function and the hydroxyl function, if necessary in the form of one derived from C ₁ to C ₄ alkyl alcohols. Etherfunktion is present (Ketals K), in the presence of C _{1 to} C ₄ alcohols (alcohols A), wherein in the electrolyte, the molar ratio of the sum of the orthoester O and the ketals K to the alcohols A 0.2: 1 to 5: 1 amounts to.

Non-electrochemical processes for the preparation of orthocarboxylic acid trialkyl esters such as trimethyl orthoformate (TMOF) are, for example DE-A-3606472 known, wherein chloroform is reacted together with sodium methylate.

Furthermore, the production of TMOF from hydrocyanic acid and methanol in J. Org. Chem. 20 (1955) 1573 known.

Out J. Amer. Chem. Soc., (1975) 2546 and J. Org. Chem., 61 (1996) 3256 such as Electrochim. Acta 42, (1997) 1933 are known electrochemical processes with which CC single bonds between carbon atoms, each carrying an alkoxy function, can be oxidatively cleaved. A targeted formation of Orthoesterfunktibnen-is not described.

Out Soot. Chem. Bull. 48 (1999) 2093 It is known to decompose vicinal diketones present in the form of their acetals by anodic oxidation using high amounts of charge and in the presence of a high methanol excess (see S 2097, 1st column, 5th paragraph) into the corresponding Dicarbonsäurediemethylester.

In Canadian Journal of Chemistry, 50 (1972) 3424 describes the anodic oxidation of benzil-tetramethyldiketal to trimethyl orthobenzoate in a more than 100-fold methanol excess. However, according to the authors, the product yield is only 62% and the current yield is 5%.

In Journ. At the. Chem. Soc., (1963), 2525 describes the electrochemical oxidation of the orthoquinonotetramethylketal in a basic methanol solution to the corresponding orthoester. The Reaction was carried out in a basic methanol solution with the substrate concentration being 10%. The product yield was 77% with a current efficiency of 6% (16 F / mol). Purely aliphatic orthoesters could not be prepared in an electrochemical manner so far.

Furthermore, it is off EP 179 289 the production of benzoic acid esters by electrooxidation of benzaldehyde acetal known.

EP 212,509 teaches the electrochemical oxidation of benzaldehyde acetals to benzoic acid esters.

In EP 393,668 describes a process in which ethers of Benzylalkohls or derivatives thereof are electrochemically oxidized in the presence of alcohol to the corresponding acetals of benzaldehyde or derivatives thereof.

The object underlying the invention was therefore to provide an electrochemical process in order to make available orthocarboxylic acid trialkyl ester economically and in particular in high current and product yields and with high selectivity.

Accordingly, the method described above was found.

wobei die Reste die folgende Bedeutung haben

R¹:

wasserstoff, C₁- bis C₂₀-Alkyl, C₂- bis C₂₀-Alkenyl, C₂- bis C₂₀-Alkinyl, C₃- bis C₁₂-Cycloalkyl, C₄- bis C₂₀-Cycloalkyl-alkyl, C₄- bis C₁₀-Aryl oder ggf. 1 bis 3-fach substituiert durch C₁- bis C₈ Alkoxy oder C₁- bis C₈-Alkoxycarbonyl

R², R³:

C₁- bis C₂₀-Alkyl, C₃- bis C₁₂-Cycloalkyl, und C₄- bis C₂₀-Cycloalkyl-alkyl oder R² und R³ gemeinsam eine C₂- bis C₁₀-Alkylen bilden

R⁴:

C₁- bis C₄-Alkyl.

The inventive method is particularly suitable for the preparation of ortho esters 0 of the general formula I,

where the radicals have the following meaning

R ¹ :

hydrogen, C ₁ - to C ₂₀ -alkyl, C ₂ - to C ₂₀ -alkenyl, C ₂ - to C ₂₀ -alkynyl, C ₃ - to C ₁₂ -cycloalkyl, C ₄ - to C ₂₀ -cycloalkyl-alkyl, C ₄ - to C ₁₀ -aryl or optionally 1 to 3-times substituted by C ₁ - to C ₈ alkoxy or C ₁ - to C ₈ alkoxycarbonyl

R ² , R ³ :

C ₁ - to C ₂₀ -alkyl, C ₃ - to C ₁₂ -cycloalkyl, and C ₄ - to C ₂₀ -cycloalkyl-alkyl or R ² and R ³ together form a C ₂ - to C ₁₀ -alkylene

R ⁴ :

C ₁ - to C ₄ -alkyl.

wobei die Reste die folgende Bedeutung haben

R⁵, R¹⁰:

die gleiche Bedeutung wie R¹

R⁶, R⁷:

die gleiche Bedeutung wie R²

R⁸:

Wasserstoff unter der Bedingung, dass R⁹ die gleiche Bedeutung wie R¹ hat, oder die gleiche Bedeutung wie R²

R⁹:

die gleiche Bedeutung wie R¹ oder -O- R².

For this purpose, starting from ketals II of the general formula II

where the radicals have the following meaning

R ^5, R ^10:

the same meaning as R ¹

R ⁶ , R ⁷ :

the same meaning as R ²

R ⁸ :

Hydrogen under the condition that R ^{9 has} the same meaning as R ¹ , or the same meaning as R ²

R ⁹ :

the same meaning as R ¹ or -O- R ² .

wobei die Reste die folgende Bedeutung haben:

R¹¹:

die gleiche Bedeutung wie R⁴

R¹²:

die gleiche Bedeutung wie R²

R¹³, R¹⁴:

die gleiche Bedeutung wie R¹

It is also possible to obtain the orthoester I in the form of a mixture with ketals IV of the general formula IV,

where the radicals have the following meaning:

R ¹¹ :

the same meaning as R ⁴

R ¹² :

the same meaning as R ²

R ¹³ , R ¹⁴ :

the same meaning as R ¹

This is based on ketals II, which are those in which R ^{9 has} the same meaning as R ¹ exclusively.

bei denen die Reste die folgende Bedeutung haben:

R¹⁵, R¹⁶:

die gleiche Bedeutung wie R²

R¹⁸:

die gleiche Bedeutung wie R²

R¹⁷, R²⁰:

die gleiche Bedeutung wie R⁴,

R¹⁹:

die gleiche Bedeutung wie R² und

X

C₂- bis C₁₂-Alkylen bedeutet (Orthoester Ia),

The process according to the invention can be used particularly advantageously for the preparation of orthoesters of the general formula Ia (orthoester Ia)

in which the radicals have the following meaning:

R ¹⁵ , R ¹⁶ :

the same meaning as R ²

R ¹⁸ :

the same meaning as R ²

R ^17, R ^20:

the same meaning as R ⁴ ,

R ^19:

the same meaning as R ² and

X

C ₂ - to C ₁₂ -alkylene means (ortho ester Ia),

bei denen die Reste die folgende Bedeutung haben:

R²¹, R²² :

die gleiche Bedeutung wie R²

R²³:

die gleiche Bedeutung wie R⁸

R²⁴:

die gleiche Bedeutung wie R⁹ und

Y

die gleiche Bedeutung wie X hat (Ketale IIa)

For this one starts from ketals of the general formula IIa,

in which the radicals have the following meaning:

R ²¹ , R ²² :

the same meaning as R ²

R ²³ :

the same meaning as R ⁸

R ²⁴ :

the same meaning as R ⁹ and

Y

has the same meaning as X (Ketale IIa)

The ketals used according to the invention are accessible by generally known preparation processes. In the case of functional groups, these are most easily prepared by starting from a precursor which has a C-C double bond in place of the desired functional group and then functionalized by standard methods (s. Synthesis, (1981) 501-522 ).

R¹:

Wasserstoff, C₁-C₂₀-Alkyl, C₃-C₁₂-Cycloalkyl oder C₄-C₂₀-Cycloalkyl-alkyl

R², R³:

C₁- bis C₂₀-Alkyl, C₃- bis C₁₂-Cycloalkyl, und C₄- bis C₂₀-Cycloalkyl-alkyl oder R² und R³ gemeinsam C₂- bis C₁₀-Alkylen bilden

R⁴:

C₁- bis C₄-Alkyl (Orthoester Ib)

ausgehend von Ketalen II, bei denen die Reste die folgende Bedeutung haben:

R⁵, R¹⁰:

die gleiche Bedeutung wie R¹ in Orthoester Ib

R⁶ bis R⁹:

die gleiche Bedeutung wie R² oder R³ in Orthoester Ib (Ketalen IIb)

The process according to the invention can also be used particularly advantageously for the preparation of orthoesters Ib, which are compounds of the formula I in which

R ¹ :

Hydrogen, C ₁ -C ₂₀ -alkyl, C ₃ -C ₁₂ -cycloalkyl or C ₄ -C ₂₀ -cycloalkyl-alkyl

R ² , R ³ :

C ₁ - to C ₂₀ -alkyl, C ₃ - to C ₁₂ -cycloalkyl, and C ₄ - to C ₂₀ -cycloalkyl-alkyl or R ² and R ³ together form C ₂ - to C ₁₀ -alkylene

R ⁴ :

C ₁ - to C ₄ -alkyl (orthoester Ib)

starting from ketals II, in which the radicals have the following meaning:

R ^5, R ^10:

the same meaning as R ¹ in orthoester Ib

R ⁶ to R ⁹ :

the same meaning as R ² or R ³ in orthoester Ib (ketals IIb)

R¹:

Wasserstoff, C₁- bis C₆-Alkyl,

R², R³, R⁴:

Methyl oder Ethyl bedeutet (Orthoester Ic)

ausgehend von Ketalen II, bei denen die Reste die folgende Bedeutung haben:

R⁵, R¹⁰:

die gleiche Bedeutung wie R¹ in Orthoester Ic

R⁶ bis R⁹:

die gleiche Bedeutung wie R² oder R³ in Orthoester Ic (Ketale IIc).

In the group of orthoesters Ib, the inventive method can be used in particular for the preparation of orthoesters Ic, which are orthoester Ib, in which

R ¹ :

Hydrogen, C ₁ - to C ₆ -alkyl,

R ² , R ³ , R ⁴ :

Methyl or ethyl means (orthoester Ic)

starting from ketals II, in which the radicals have the following meaning:

R ^5, R ^10:

the same meaning as R ¹ in orthoester Ic

R ⁶ to R ⁹ :

the same meaning as R ² or R ³ in orthoester Ic (ketals IIc).

In the ketals IIb and IIc, the radicals R ⁵ and R ¹⁰ preferably have the same meaning.

The process according to the invention for the production of methyl orthoformate (TMOF) or ethyl ester or methyl orthoacetate or ethyl ester can be carried out particularly favorably (Orthoester Id) (these are compounds of formula I, wherein R ^{1 is} hydrogen or methyl and R ² , R ³ and R ^{4 are} methyl or R ² , R ³ and R ^{4 is} ethyl), wherein as starting compounds 1,1,2,2-tetramethoxyethane (TME) or 1,1,2,2-tetraethoxyethane (Ketale IId) serve.

In the electrolyte, the molar ratio of the sum of the orthoester O and the ketals K to the alcohols A is 0.2: 1 to 5: 1, preferably 0.2: 1 - 2: 1 and particularly preferably 0.3: 1 to 1: 1.

Conducting salts which are contained in the electrolysis solution are generally alkali metal, tetra (C ₁ - to C ₆ -alkyl) ammonium or tri (C ₁ - to C ₆ -alkyl) benzylammonium salts. Suitable counterions are sulfate, bisulfate, alkyl sulfates, aryl sulfates, halides, phosphates, carbonates, alkyl phosphates, alkyl carbonates, nitrate, alcoholates, tetrafluoroborate or perchlorate.

Furthermore, the acids derived from the abovementioned anions are suitable as conductive salts.

Preference is given to methyltributylammonium methylsulfates (MTBS), methyltriethylammonium methylsulfate or methyltri-propylmethylammonium methylsulfates.

Optionally, the electrolysis solution is added to customary cosolvents. These are the inert solvents generally used in organic chemistry with a high oxidation potential. Examples include dimethyl carbonate or propylene carbonate.

The process according to the invention can be carried out in all customary types of electrolytic cell. Preferably, one works continuously with undivided flow cells.

When the process is carried out continuously, the feed rate of the starting materials is generally chosen such that the weight ratio of the ketals K used to the orthoesters I formed in the electrolyte is from 10: 1 to 0.05: 1.

The current densities at which the process is carried out are generally 1 to 1000, preferably 10 to 100 mA / cm ² . The temperatures are usually -20 to 60 ° C, preferably 0 to 60 ° C. In general, working at atmospheric pressure. Higher pressures are preferably used when operating at higher temperatures to avoid boiling of the starting compounds or cosolvents.

Suitable anode materials include, for example, noble metals such as platinum or metal oxides such as ruthenium or chromium oxide or mixed oxides of the type RuO _x TiO _x . Preference is given to graphite or carbon electrodes.

As cathode materials are, for example, iron, steel, stainless steel, nickel or precious metals such as platinum and graphite or carbon materials into consideration. Preferably, the system is graphite as the anode and cathode and graphite as the anode and nickel, stainless steel or steel as the cathode.

After completion of the reaction, the electrolysis solution is worked up by general separation methods. For this purpose, the electrolysis solution is generally first distilled and the individual compounds are recovered separately in the form of different fractions. Further purification can be carried out, for example, by crystallization, distillation or by chromatography.

Experimental part Example 1:

An undivided cell with graphite electrodes in bipolar arrangement was used. The total electrode area was 0.145 m ² (anode and cathode). The electrolyte used was a solution consisting of 2 mol of methanol per mole of TME, which contained 2% by weight of MTBS as the conductive salt. The electrolysis was carried out at 300 A / m ² and an amount of charge of 2 F based on TME was passed through the cell. The temperature during the electrolysis was 20 ° C. After completion of the electrolysis of the electrolysis products were determined by gas chromatography quantitatively and by GC-MS coupling qualitatively. It was formed with a TME conversion of 69% TMOF with a selectivity of 77%. The by-products were mainly methyl formate and methylal.

Example 2:

In an electrolytic cell with an electrode area of 316.4 cm ² , otherwise described in Example 1, 240.3 g of 1,1,2-trimethoxyethane, 320 g of methanol and 5.8 g of ammonium tetrafluoroborate were used and subjected to an electrolyte. The electrolysis conditions were as described in Example 1. 9.5 GC area% formaldehyde dimethyl acetal and 5.9 GC area% trimethyl orthoformate were obtained in the electrolysis discharge.

Example 3:

In an electrolytic cell with an electrode area of 298.8 cm ² , otherwise described in Example 1, 89, g were 2,2,3,3-tetramethoxybutene (80%, prepared from diacetyl and trimethyl orthoformate), 64 g of methanol and 1 , 7 g of ammonium tetrafluoroborate reacted. The electrolysis conditions were as described in Example 1. After electrothermal feed of 2. Faraday, 1.7 GC area% trimethyl orthoacetate was obtained in the electrolysis discharge and 18 GC area% after 8 F power input.

Example 4:

In a continuously operated electrolysis was obtained at a current density of 310 A / m ² of graphite electrodes and an inlet of methanol to 1,1,2,2-tetramethoxyethane of 1.5 mol to 1 mol and an MTBS content of 8 wt. -% in Elektrolyseaustrag at a conversion of 41% TME selectivity to TMOF of 95% and a current efficiency for TMOF of 78%.

Claims (10)

1. A process for the preparation of trialkyl orthocarboxylates (orthoesters O) by the electrochemical oxidation of alpha,beta-diketones or alpha,beta-hydroxyketones, the keto group being present in the form of a ketal group derived from C₁- to C₄-alkyl alcohols and the hydroxyl group if appropriate being present in the form of an ether group derived from C₁- to C₄-alkyl alcohols (ketals K), in the presence of C₁- to C₄-alcohols (alcohols A), the molar ratio of the sum of the orthoesters O and the ketals K to the alcohols A in the electrolyte being 0.2:1 to 5:1.
2. The process according to claim 1 wherein the orthoesters O are compounds of general formula I:

   

   in which the radicals are defined as follows:

   R¹ is hydrogen, C₁- to C₂₀-alkyl, C₂- to C₂₀-alkenyl, C₂- to C₂₀-alkynyl; C₃- to C₁₂-cycloalkyl, C₄- to C₂₀-cycloalkylalkyl, C₄- to C₁₀-aryl or optionally monosubstituted to trisubstituted by C₁ to C₈-alkoxy or C₁- to C₈-alkoxycarbonyl;

   R² and R³ are C₁- to C₂₀-alkyl, C₃- to C₁₂-cycloalkyl or C₄- to C₂₀-cycloalkylalkyl, or R² and R³ together form C₂- to C₁₀-alkylene; and

   R⁴ is C₁- to C₄-alkyl,

   starting from ketals II of general formula II:

   

   in which the radicals are defined as follows:

   R⁵ and R¹⁰ are as defined for R¹;

   R⁶ and R⁷ are as defined for R²;

   R⁸ is hydrogen if R⁹ is as defined for R¹, or is as defined for R²; and

   R⁹ is as defined for R¹ or is -O-R².
3. The process according to claim 2 wherein the orthoesters I of general formula I are formed as a mixture with ketals IV of general formula IV:

   

   in which the radicals are defined as follows:

   R¹¹ is as defined for R⁴;

   R¹² is as defined for R²; and

   R¹³ and R¹⁴ are as defined for R¹,

   starting from ketals II in which R⁹ is exclusively as defined for R¹.
4. The process according to claim 1 wherein the orthoesters 0 are compounds of general formula Ia:

   

   in which the radicals are defined as follows:

   R¹⁵ and R¹⁶ are as defined for R²;

   R¹⁸ is as defined for R²;

   R¹⁷ and R²⁰ are as defined for R⁴;

   R¹⁹ is as defined for R²; and

   X is C₂- to C₁₂-alkylene (orthoesters Ia),

   starting from ketals of general formula IIa:

   

   in which the radicals are defined as follows:

   R²¹ and R²² are as defined for R²;

   R²³ is as defined for R⁸;

   R²⁴ is as defined for R⁹; and

   Y is as defined for X (ketals IIa).
5. The process according to claim 2 wherein the orthoesters I are compounds in which:

   R¹ is hydrogen or C₁- to C₆-alkyl; and

   R², R³ and R⁴ are methyl or ethyl (orthoesters Ic),

   starting from ketals II in which the radicals are defined as follows:

   R⁵ and R¹⁰ are as defined for R¹ in orthoesters Ic; and

   R⁶ to R⁹ are as defined for R² or R¹ in orthoesters Ic (ketals IIc).
6. The process according to claim 5 wherein the orthoesters I are methyl or ethyl orthoformate or methyl or ethyl orthoacetate (orthoesters Id), starting from 1,1,2,2-tetramethoxyethane or 1,1,2,2-tetraethoxyethane (ketals IId), or 1,1,2,2-tetramethoxypropane or 1,1,2,2-tetraethoxypropane, or 2,2,3,3-tetramethoxybutane or 2,2,3,3-tetraethoxybutane.
7. The process according to any of claims 1 to 6 which is carried out in an electrolyte containing tetra(C₁- to C₆-alkyl)ammonium or tri(C₁- to C₆-alkyl)benzylammonium salts as conducting salts with sulfate, hydrogensulfate, alkylsulfates, arylsulfates, halides, phosphates, carbonates, alkylphosphates, alkylcarbonates, nitrate, alcoholates, tetrafluoroborate or perchlorate as counterions.
8. The process according to any of claims 1 to 7 wherein the conducting salt used is methyltributylammonium ethylsulfate, methyltripropylammonium methylsulfate, methyltriethylammonium methylsulfate or tetramethylammonium methylsulfate.
9. The process according to any of claims 1 to 8 which is carried out in a non-compartmentalized electrolysis cell.
10. The process according to any of claims 1 to 9 wherein the charge quantity per mol of converted alpha,beta-diketone or alpha,beta-hydroxyketone is 2 to 4 F.