EP1348043A2 - Method for producing alcoxylated carbonyl compounds by an anodic oxidation method using a cathodic coupled reaction for organic synthesis - Google Patents

Abstract

A method for producing alcoxylated carbonyl compounds of general formula (I) (compounds I): R1aR2C(OR3)b wherein R1, R2 represent hydrogen or C¿1?- C6-alkyl, R?3¿ independently means C¿1?- C6-alkyl, a is 0 or 1, b 2 or 3 with the proviso that the sum of a and b is 3, by means of anodic oxidation of germinal dialcoxy compounds of general formula (II) (compounds II) wherein R?4, R5, R6, R7¿ represent hydrogen or C¿1?- C6-alkyl, R?5, R6¿ represent C¿1?- C6-alkyl or C1- C6-alcoxy, in the presence of a C1-C6-alkyl alcohol (compounds III).A usual compound (compound IV) is used as a cathodic depolarizer suitable for electrochemical oxidation. The anodic oxidation and cathodic reduction is carried out in an undivided electrolyte cell in the presence of C1-C6-alkyl alcohols.

Description

Process for the preparation of alkoxylated carbonyl compounds by an anodic oxidation process using the cathodic coupling reaction for organic synthesis

description

The present invention relates to a process for the preparation of alkoxylated carbonyl compounds (compounds I) of the general formula I

R ^l _a R ² C (OR ³ ) _b

in the

R ^ R ^{2 is} hydrogen or Ci to Cökkyl

R ³ independently of one another Cι ~ C to _ß alkyl a is 0 or 1 b is 2 or 3

with the proviso that the sum of a and b is 3, by anodic oxidation of geminal alkoxy compounds of the general formula II (compounds II)

OR ⁹ OR ⁸ _R 4 _{cc R7 χτ}

R ⁵ R ⁶

in the

R ⁴ , R ⁵ , R ⁶ , R ^{7 are} hydrogen or C ₁ -C ₆ -alkyl

R ^5, R ⁶ Ci to Cg alkyl or Ci to C alkoxy _ß mean in the presence of a Cι ~ to C ~ ₆ alkyl alcohol (compounds III)

wherein a conventional organic compound (compounds IV) is used as the cathodic depolarizer, which is suitable for the electrochemical reduction, and the anodic oxidation and the cathodic reduction are carried out in an undivided electrolysis cell in the presence of Ci-C _δ -alkyl alcohols.

The production of organic compounds by simultaneous use of the cathode and the anode reaction is already the subject of intensive research because of the particularly high energy efficiency. work (see MM Baizer, Organic Electroche istry, 3rd Ed. (Eds. H. Lund and MM Baizer), Marcel Dekker, Chapter 35, New York 1991)

In the scientific literature (cf. Nonaka and Li, Electrochemistry, 67, 1999, Jan., 4-10) it is pointed out that there is in principle an abundance of coupling options, but there is only a specific technical teaching for a few and mostly special examples.

Apart from a few mixtures (cf. DE-A-19618854), it has been shown that the so-called coupled electrosynthesis is associated with technical disadvantages which make large-scale industrial use practically impossible. These include, in particular, the difficult separation of the resulting reaction mixtures and chemical reactions of starting materials and products at the respective counterelectrodes, by means of which the yield of the desired valuable products is greatly reduced if the reaction is carried out in undivided electrolysis cells. When using divided electrolysis cells, these disadvantages would be avoided, however, these cell structures can only be realized with great technical effort. In organic electrolytes in particular, commercially available ion exchange membranes have only very limited stability, which makes continuous technical use impossible.

From J. Amer. Chem. Soc. , (1975) 2546 and J. Org. Chem., 61 (1996) 3256 and Electrochim. Acta 42, (1997) 1933, electrochemical processes are known with which C-C single bond between C atoms, each of which has an alkoxy function, can be cleaved oxidatively.

The preparation of orthoesters from alkoxylated diketones is described in the unpublished DE-A-10043789.

However, in the last two publications there is no reference to the use of these manufacturing processes in the context of coupled electrosynthesis.

It was therefore an object of the present invention to provide a coupled electrosynthesis process which allows the production of alkoxylated carbonyl compounds by anodic oxidation coupled with the production of high-quality organic compounds in a cathodic reduction and which does not have the aforementioned disadvantages of conventional coupled syntheses and especially provides the desired products of value in high yields.

Accordingly, the above-described method has been found.

As starting compounds (compounds II) -1,2-di- (Ci- to C _ß- alkoxy) -ethane or -propane or 1,1,2,2-tetra (Cχ- to C _δ- alkoxy ) -ethane or -propane used. The corresponding formaldehyde di (Ci to C6 alkyl) acetals or ortho-formic acid tri (Ci to Cβ alkyl) esters are formed as compounds I and, in the case of the propane derivatives, as starting products also acetaldehyde di- (Ci- to C ₆ -alkyl) - acetal or ortho-acetic acid tri- (Ci- to C _δ- alkyl) esters. The aforementioned acetaldehyde or acetic acid derivatives can also be prepared from 2,3-di- (-C ~ to C ₆ -alkoxy) butane.

In particular, formaldehyde dimethyl acetal, trimethyl ortho-formate, acetaldehyde dimethyl acetal or trimethyl orthoacetate can be prepared from the corresponding compounds II and methanol in a particularly simple manner.

Apart from the di- or tetraalkoxyethane or propane derivatives mentioned above, preferred compounds I and II are those in which R ^{4 has} the same meaning as R ⁷ or R ^{5 has} the same meaning as R ⁶ by the number of to keep the compounds contained in the reaction mixture to be worked up as small as possible.

In general, such alcohols are employed whose alkyl radicals have the same meaning as the radicals R ^8, R ^9, or the alkyl radicals in R ^5, R ^6, provided that R ^5, R ⁶ C ~ to C _ß alkoxy.

Suitable cathodic depolisators are conventional organic compounds which are suitable for anodic reduction, such as aromatic hydrocarbon compounds, activated olefins, carbonyl compounds, aromatic carboxylic acids and their derivatives, and also naphthalene or nucleus-substituted naphthalene derivatives.

The process according to the invention is particularly suitable for producing the following compounds or classes of compounds:

a) Maleic acid or derivatives of maleic acid in which the acid function is in the form of alkyl esters to form a butanetetracarboxylic acid tetraalkyl ester with hydrodimerization b) benzene mono-, di- or tricarboxylic acids different from phthalic acid or phthalic acid derivatives, or derivatives of these compounds in which the acid function is in the form of alkyl esters or derivatives substituted on the aromatic nucleus, to give the corresponding mono-, di - and triformylbenzene compounds in which the formyl groups are in the form of an acetal

c) acrylic acid, alkyl acid alkyl ester, acrylamide or acrylonitrile or homologs of these compounds to the corresponding hydrodimerization products. Preferred homologs are those of the general formula V.

R10_CH = CH-X V

where X is an alkoxycarbonyl, nitrile or carbamide group and R ^{10 is} Ci to C ₆ alkyl.

d) phthalic acid, phthalic acid alkyl esters or derivatives substituted on the aromatic nucleus of these compounds to give phthalide or nucleus-substituted phthalide derivatives, cyclohexane or cyclohexane-1, 2-dicarboxylic acid or cyclohexane or cyclohexene-1, 2-dicarboxylic acid dialkyl esters or according to the substitution pattern the phthalic acid derivatives substituted on the aromatic nucleus on the cyclohexane or cyclohexene ring substituted derivatives.

e) naphthalene or nucleus-substituted naphthalene derivatives to 1,2,3,4-tetrahydronaphthalene or the corresponding 1,2,3,4-tetrahydronaphthalene derivatives

f) pyridine or nucleus-substituted pyridine derivatives

1, 4, -Dihydropyridine or the corresponding 1, 4-dihydropyridine derivatives.

Insofar as compounds with alkyl ester groups as starting compounds or products are mentioned above, ci to co-alkyl ester groups are particularly suitable.

Suitable substituents with which the aromatic nuclei in the abovementioned starting compounds can be substituted are inert, difficult-to-reduce groups such as C 1 -C 1 -alkyl, C ₁ -C ₆ -alkoxy or halogen.

What the phthalide derivatives mentioned under point d) or

Phthalide itself concerns, it is particularly those compounds as described in DE-A-19618854. The particularly suitable output connections are also detailed there.

The molar ratio of the starting compounds for the cathode and anode reactions and the products formed in these reactions in electrolytes to one another is not critical.

In general, the molar ratio of the sum of the compounds I and II to the alcohols (compounds IV) is chosen from 0.1: 1 to 5: 1, preferably 0.2: 1 to 2: 1 and particularly preferably 0.3: 1 to 1: 1.

The conductive salts contained in the electrolysis solution are generally alkali, tetra- (C ₁ -C ₆ -alkyl) -ammonium or tri- (Cχ-C _δ- alkyl) -benzylammonium salts. Sulfate, hydrogen sulfate, alkyl sulfates, alkyl sulfonates, halides, phosphates, carbonates, alkyl phosphates, alkyl carbonates, nitrate, alcoholates, tetrafluoroborate or perchlorate are suitable as counterions.

Furthermore, the acids derived from the above-mentioned anions can be considered as conductive salts.

Methyltributylammonium methyl sulfate (MTBS), methyltriethylammonium methyl sulfate or methyl tripropylmethylammonium methyl sulfate are preferred.

If necessary, customary cosolvents are added to the electrolysis solution. These are the inert solvents with a high oxidation potential that are common in organic chemistry. Examples include dimethyl carbonate or propylene carbonate.

The process according to the invention can be carried out in all customary undivided types of electrolysis cells. One preferably works continuously with undivided flow cells. Plate stack cells with series-shaped stack electrodes, as described for example in DE-A-19533773, are particularly suitable.

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, normal pressure is used. Higher pressures are preferably used if at higher temperatures structures should be worked to avoid boiling of the starting compounds or cosolvents.

For example, noble metals such as platinum or metal oxides such as ruthenium or chromium oxide or mixed oxides of the Ruo _x Tio _x type are suitable as anode materials. Graphite or carbon electrodes are preferred.

Examples of suitable cathode materials are iron, steel, stainless steel, nickel or precious metals such as platinum and graphite or carbon materials. The system is preferably graphite as anode and cathode and graphite as anode and nickel, stainless steel or steel as cathode.

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

It is unexpected that the anodic oxidation of the compounds I to II in good results in the presence of a cathodic production of a large number of organic compounds in an undivided cell is unexpected, since the compounds I, acetals and orthoesters are themselves reactive compounds.

example 1

In an undivided cell, 11 annular disk electrodes, each with an area of 140 cm ² and an outer diameter of 14 cm, are arranged so that they form a stack. The disks are set to a distance of 1 mm using spacers, thus creating 10 gaps between the ring disks. The electrode material is graphite. The inner 0.5 cm thick disks are switched bipolar under electrolysis conditions. The top electrode is anodically contacted by means of a graphite stamp and a cover disk, the bottom electrode is contacted cathodically, the cathodic contact runs over the base plate of the cell. The electrolyte flows through the central hole in the base plate into the cell, spreads over the gaps and leaves the cell above the top electrode. The cell is part of a circulation apparatus in which the electrolyte is pumped around, heated or cooled. 975 g of tetramethoxyethane, 936 g of dimethyl maleate, 170 g of a 60% methanolic solution of methyltributylammonium methyl sulfate and 419 g of methanol were electrolyzed at a current of 3 A, the current strength decreased to 2.5 A during the electrolysis, the voltage per gap rose from 5 V to 6 V, electrolysis was continued until 95% of the dimethyl maleate had been converted. Temperature: 38 ° C, pump volume. 183 1 / h.

The electrolysis discharge contained 24.4% methyl butanetetracarboxylic acid, 14.2% trimethyl orthoformate, 25.6% tetramethoxyethane and 1.7% dimethyl maleate. The selectivity of the ortho ester formation was 82%. The composition of the electrolysis discharge was determined using a gas chromatograph and is shown in% by area (GC area%).

The current yield based on the dimethyl maleate was 80%. By-products were dimethyl succinate and dimethyl 2-methoxy-succinate (total: 11%).

Example 2

A cell according to Example 1 was used, the number of columns was 7.

1062 g of tetramethoxymethane, 303 g of methyl benzoate, 225 g of 60% methyltributylammonium methyl sulfate solution in 910 g of methanol were electrolyzed at 3A. The voltage per gap was kept below 5 V, the temperature was 30 ° C. and the pumped-around quantity was 190 l / h. At the end of the electrolysis, 10.0 GC-Fl. % Trimethoxymethane and 13.2 GC area. % Benzaldehyde dimethyl acetal formed, tetramethoxyethane had increased from 42.5% to 25.6 GC area. % degraded, benzoic acid methyl ester was over 95% to 0.4 GC area. % implemented, as low-boiling by-products Methyl formate with 2.2 GC fl. % formed in the electrolyte

Example 3

A cell according to Example 2 was used.

1200 g of tetramethoxymethane, 776 g of dimethyl o-phthalate, 166 g of 60% methyltributylammonium methylsulfate solution in 385 g of methanol were electrolyzed at 2.6 A. The voltage per gap was kept at 5.1-5.3 V, the temperature was at 30 ° C, the pumping rate was 170 l / h. Sales were tracked via GC. After 2.4 F, corresponding to 120% of the theoretical amount of electricity, tetrahedral 66% methoxymethane converted In the solution 28.4% trimethyoxymethane had formed, 88% dimethyl o-phthalate had been used up and had converted to pthalide with a selectivity of 90%.

Example 4

The cell and the cell circuit are constructed analogously to example 1, 11 electrodes with a diameter of 65 mm and an area of 31.6 cm 2 form 10 gaps.

229 g of tetramethoxymethane, 229 g of pentenenitrile, 28.8 g of 60% methyltributylammonium methylsulfate solution in 114 g of methanol were re-timed at an initial current of 1 A at 23 ° C. and a pumped-over rate of 25 l / h. The cell voltage was kept below 50 V, the final current was 0.55 A.

After 10 h, the mixture was stopped and 64% of tetramethoxyethane and 76% of pentenenitrile had reacted. Anodically, trimethyl orthoformate, methyl formate and formaldehyde dimethyl acetal had formed in a ratio of 1: 0.17: 0.1: the main products being 3.4-diethyladipodinitrile, pentanitrile and 3-methoxypentanenitrile in a ratio of 1: 0.3: 0.8 emerged. In the working up by distillation, the hydrimersation product of pentenenitrile, 3,4-diethyladipodinitrile, was obtained with a purity of 97%.

Claims

claims 1. Process for the preparation of alkoxylated carbonyl compounds of the general formula I (compounds I) R ^l _a R ² C (OR3) _b in the R ^ R ^{2 is} hydrogen or Ci to C _δ alkyl R ³ independently of one another is C 1 -C 4 -alkyl a 0 or 1 b 2 or 3 with the proviso that the sum of a and b is 3 by anodic oxidation of geminal dialkoxy compounds of the general formula II (compounds II) OR ⁹ OR ⁸ R4 _{cc R7 τI} R ^~ R ⁶ in the R ⁴ , R ^{7 are} hydrogen or C _x - to C _δ -alkyl R ⁵ , R ^{6 are} hydrogen, Ci to C ₆ alkyl or Ci to Cε alkoxy in the presence of a Ci to C _ß -alkyl alcohol (Compounds III), wherein a conventional organic compound (Compound IV) is used as the cathodic depolarizer, which is suitable for the electrochemical reduction and in which the anodic oxidation and the cathodic reduction in an undivided electrolysis cell in the presence of C ₆ -C ₆ alkyl alcohols. 2. The method according to claim 1, wherein the compounds I are ortho-formate tri ethyl ester or formaldehyde dimethyl acetal, which compounds can also be formed in the form of a mixture. 3. The method according to claim 1 or 2, wherein in the compounds II R ^{4 has} the same meaning as R ⁷ and R ^{5 has} the same meaning as R ⁵ . 4. The method according to claims 1 to 3, wherein the compounds I of l, 2-di (Cι- to Cβ-alkoxy) ethane or 1,1, 2, 2-tetra (Cι ~ to C _δ alkoxy) ethane derived. 5. The method according to claims 1 to 4, wherein the compound IV is aromatic hydrocarbon compounds, activated olefins, aromatic carboxylic acids and their derivatives, carbonyl compounds, imines, heterocycles, naphthalene or nucleus-substituted naphthalene derivatives. 6. The method according to claim 5, wherein the cathodic depolarization is one of the following reactions: a) Maleic acid or derivatives of maleic acid in which the acid function is in the form of alkyl esters to form a butanetetracarboxylic acid tetraalkyl ester with hydrodimerization b) benzene mono-, di- or tricarboxylic acids other than phthalic or phthalic acid derivatives, or derivatives of these compounds in which the acid function is in the form of alkyl esters or derivatives substituted on the aromatic nucleus, to give the corresponding mono-, di- and Triformylbenzene compounds in which the formyl groups are in the form of an acetal c) acrylic acid, acrylic acid alkyl ester, acrylamide or acrylonitrile or homologs of these compounds to the corresponding hydrodimerization products d) phthalic acid, phthalic acid alkyl esters or derivatives substituted on the aromatic nucleus of these compounds to give phthalide or nucleus-substituted phthalide derivatives, cyclohexane or cyclohexene-1, 2-dicarboxylic acid, cyclohexane or cyclohexene-1, 2-dicarboxylic acid dialkyl esters or according to the aromatic substitution pattern of am substituted phthalic acid derivatives on the cyclohexane or cyclohexene ring substituted derivatives. e) naphthalene or nucleus-substituted naphthalene derivatives to 1,2,3,4-tetrahydronaphthalene or the corresponding 1,2,3,4-tetrahydronaphthalene derivatives f) pyridine or nucleus-substituted pyridine derivatives 1, 4, -Dihydropyridine or the corresponding 1,4-dihydropyridine derivatives. 7. The method according to claims 1 to 6, wherein the method is carried out in a plate stack cell with series-connected stack electrodes.