EP1348043B1 - 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): R<1>aR<2>C(OR<3>)b wherein R<1>, R<2 >represent hydrogen or C1-C6-alkyl, R<3 >independently means C1-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>, R<5>, R<6>, R<7 >represent hydrogen or C1-C6-alkyl, R<5>, R<6 >represent C1-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

The present invention relates to a process for the preparation of formaldehyde di (C ₁ to C ₆ alkyl) acetals, ortho-formic acid tri- (C ₁ to C ₆ alkyl) esters, acetaldehyde di ( C ₁ - to C ₆ -alkyl) - acetals or ortho-acetic tri- (C ₁ - to C ₆ -alkyl) esters (compounds 1) by anodic oxidation of 1,2-di- (C ₁ - to C ₆ - alkoxy) ethane or propane, 1,1,2,2-tetra (C ₁ to C ₆ alkoxy) ethane or propane, or 2,3-di- (C ₁ to C ₆ alkoxy) -butane (compounds II) in the presence of a C ₁ - to C ₆ -alkyl alcohol (compounds III)
in which the cathodic depolarizer used is a customary organic compound (compounds IV) which is suitable for electrochemical reduction and in which the anodic oxidation and the cathodic reduction are carried out in an undivided electrolysis cell in the presence of C ₁ -C ₆ -alkyl alcohols.

The production of organic compounds through simultaneous use the cathode as well as the anode reaction is special because of the high energy efficiency is already the subject of intensive research M. M. Baizer, Organic Electrochemistry, 3rd Ed. (Eds. H. Lund and M. M. Baizer), Marcel Dekker, Chapter 35, New York 1991)

In the scientific literature (see Nonaka and Li, Electrochemistry, 67, 1999, Jan., 4-10), it is pointed out that in principle there is a wealth of coupling possibilities, a concrete technical teaching is found there but only for few and mostly special examples.

Apart from a few mixtures (see DE-A-19618854) it has showed that the so-called coupled electrosynthesis with technical Disadvantages associated with being a large-scale industrial Make use virtually impossible. These include in particular the difficult separation of the resulting reaction mixtures as well chemical reactions of reactants and products to the respective Counterelectrodes, by which the yield of the desired Value products is greatly reduced, provided the implementation in undivided Electrolysis cells is performed. When using split Although electrolysis cells would avoid these disadvantages, However, these cell designs are only of high technical To realize effort. Especially in organic electrolytes have commercial ion exchange membranes only very limited stability, which makes a continuous technical use impossible do.

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

In the non-prepublished DE-A-10043789 is the production of orthoesters of alkoxylated diketones.

However, there is no such thing as the last two Reference to the use of this manufacturing process in the context a coupled electrosynthesis.

Object of the present invention, it was thus a coupled To provide an electrosynthesis process which involves the production of alkoxylated carbonyl compounds coupled by anodic oxidation with the production of high quality organic compounds allowed in a cathodic reduction and that the aforementioned Not having disadvantages of conventional coupled syntheses and in particular provides the desired value products in high yields.

Accordingly, the above-described method has been found.

As starting compounds (compounds II) are 1,2-di (C ₁ - to C ₆ alkoxy) ethane or propane or 1,1,2,2-tetra (C ₁ - to C ₆ alkoxy) ethane or -propane used. As compounds I, the corresponding formaldehyde di (C ₁ - to C ₆ alkyl) acetals or ortho-antric acid tri (C ₁ - to C ₆ alkyl) esters are formed and, in the case of the propane derivatives as starting materials also acetaldehyde di- (C ₁ - to C ₆ alkyl) - acetals or Orthoessigsäuretri- (C ₁ - to C ₆ alkyl) ester. The abovementioned acetaldehyde or acetic acid derivatives can likewise be prepared from 2,3-di- (C ₁ -C ₆ -alkoxy) -butane.

Above all, it is particularly easy to use formaldehyde dimethyl acetal in this way. Ortho-formic acid trimethyl ester, acetaldehyde dimethyl acetal or ortho-acetic acid trimethyl ester from the corresponding Produce compounds II and methanol.

As cathodic Depolisatoren come usual organic Compounds suitable for anodic reduction, such as aromatic hydrocarbon compounds, activated olefins, Carbonyl compounds, aromatic carboxylic acids and their derivatives and naphthalene or nucleus-substituted naphthalene derivatives.

a) Maleinsäure bzw. Derivate der Maleinsäure, bei denen die Säurefunktion in Form von Alkylestern vorliegt zu einem Butantetracarbonsäuretetraalkylester unter Hydrodimerisierung

b) von Phthalsäure- oder Phthalsäurederivaten verschiedene Benzolmono-, di-, oder tricarbonsäuren, bzw. Derivate dieser Verbindungen, bei denen die Säurefunktion in Form von Alkylestern vorliegt oder am aromatischen Kern substiuierte Derivate, zu den entsprechenden Mono-, Di- und Triformylbenzolverbindungen, bei denen die Formylgruppen in Form eines Acetals vorliegt

c) Acrylsäure, Alkylsäurealkylester, Acrylamid oder Acrylnitril oder Homologe dieser Verbindungen zu den entsprechenden Hydrodimerisierungsprodukten. Bevorzugte Homologe sind solche der allgemeinen Formel V R¹⁰-CH=CH-X wobei X für eine Alkoxycarbonyl-, Nitril- oder Carbamidgruppe und R¹⁰ für C₁- bis C₆-Alkyl steht.

d) Phthalsäure, Phthalsäurealkylester oder am aromatischen Kern substituierte Derivate dieser Verbindungen zu Phthalid bzw. kernsubstituierten Phthalidderivaten, Cyclohexan- oder Cyclohexan-1,2-dicarbonsäure oder Cyclohexan- oder Cyclohexen-1,2-dicarbonsäuredialkylestern bzw. entsprechend dem Substitutionsmuster der am aromatischen Kern substituierten Phthalsäurederivate am Cyclohexan- bzw. Cyclohexenring substituierte Derivate.

e) Naphthalin oder kernsubstituierte Naphthalinderivate zu 1,2,3,4-Tetrahydronaphthalin bzw. den entsprechenden 1,2,3,4-Tetrahydronaphthalinderivaten

f) Pyridin oder kernsubstituierte Pyridinderivate zu 1,4,-Dihydropyridin bzw. den entsprechenden 1,4-Dihydropyridinderivaten.

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

a) maleic acid or derivatives of maleic acid in which the acid function is present in the form of alkyl esters to give a butanetetracarboxylic acid tetraalkyl ester with hydrodimerization

b) benzene mono-, di- or tricarboxylic acids other than phthalic acid or phthalic acid derivatives, or derivatives of these compounds in which the acid function is present in the form of alkyl esters or derivatives substituted on the aromatic nucleus, to the corresponding mono-, di- and triformylbenzene compounds, where the formyl groups are in the form of an acetal

c) acrylic acid, Alkylsäurealkylester, acrylamide or acrylonitrile or homologues of these compounds to the corresponding Hydrodimerisierungsprodukten. Preferred homologs are those of the general formula V R ¹⁰ -CH = CH-X where X is an alkoxycarbonyl, nitrile or carbamide group and R ^{10 is} C ₁ - to C ₆ -alkyl.

d) phthalic acid, alkyl phthalate or substituted on the aromatic nucleus derivatives of these compounds to 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 of the aromatic nucleus substituted phthalic acid derivatives on cyclohexane or cyclohexene substituted derivatives.

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

f) pyridine or nucleus-substituted pyridine derivatives to 1,4-dihydropyridine or the corresponding 1,4-dihydropyridine derivatives.

If it is mentioned above of compounds with alkyl ester groups as starting compounds or products, so come here in particular C ₁ - to C ₆ -alkyl ester groups into consideration.

Suitable substituents with which the aromatic nuclei can be substituted in the abovementioned starting compounds are inert, hardly reducible groups, such as C ₁ -C ₁₂ -alkyl, C ₁ -C ₆ -alkoxy or halogen.

What the mentioned under point d) phthalide derivatives or the Phthalide itself, these are in particular those Compounds as described in DE-A-19618854.

There are also the most suitable starting compounds detailed.

The molar ratio of the starting compounds for cathode and Anode reaction and the products formed in these reactions in electrolytes to each other is not critical.

In general, one chooses the molar ratio of the sum of Compounds I and II to the alcohols (compounds IV) 0.1: 1 to 5: 1, preferably 0.2: 1 to 2: 1 and more preferably 0.3: 1 to 1: 1.

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

Furthermore, derived from the abovementioned anions come Acids as conductive salts into consideration.

Preference is given to methyltributylammonium methylsulfate (MTBS), methyltriethylammonium methylsulfate or methyl tripropylmethylammonium methyl sulfates.

If appropriate, the electrolysis solution is subjected to customary cosolvents to. These are those in organic chemistry Commonly used inert solvents with a high oxidation potential. Examples include dimethyl carbonate or Propylene carbonate.

The process of the invention can be in all the usual undivided Electrolysis cell types are performed. Preferably works one continuously with undivided flow cells. Especially plate stack cells with serially designed stacking electrodes are suitable, as described for example in DE-A-19533773 are.

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 are, 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 Anode and cathode as well as graphite as anode and nickel, stainless steel or steel as a cathode.

After completion of the reaction, the electrolyte solution is after worked up general separation methods. For this purpose, the electrolysis solution generally distilled first and the individual Compounds separated in the form of different fractions won. Further purification can be carried out, for example, by crystallization, Distillation or by chromatography.

That the anodic oxidation of the compounds I to II in the presence a cathodic production of a variety of organic Compounds in an undivided cell succeed in good yields, is unexpected, the compounds are I, acetals and Orthoester but even reactive compounds.

example 1

In an undivided cell, 11 ring disk electrodes each having a surface area of 140 cm ² and an outer diameter of 14 cm are arranged so as to form a stack. By spacers, the discs are set to a distance of 1 mm, resulting in 10 gaps between the annular discs. The electrode material is graphite. Under electrolysis conditions, the inner 0.5 cm thick disks are bipolar. The top electrode is anodically contacted by means of a graphite punch and a cover plate, the bottom electrode is cathodically contacted, the cathodic contact extends over the bottom plate of the cell. The electrolyte flows through the central bore of the bottom plate into the cell, spreads over the column and leaves the cell above the top electrode. The cell is part of a circulating apparatus in which the electrolyte is circulated, heated or cooled.

975 g of tetramethoxyethane, 936 g of dimethyl maleate, 170 g 60% methanolic solution of methyltributylammonium methylsulfate and 419 g of methanol were at a current of 3 A. electrolysed, during the course of electrosysis took the current strength to 2.5 A, the voltage per gap increased from 5 V to 6 V, Total was electrolyzed until the dimethyl maleate was implemented to 95%. Temperature: 38 ° C, pumping rate. 183 l / h.

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

The current yield based on the dimethyl maleate was 80%. By-products were succinic acid dimethyl ester and 2-Methoxy-succinic acid dimethyl ester (total: 11%).

Claims (5)

1. A process for preparing formaldehyde di(C₁- to C₆-alkyl) acetals, tri(C₁- to C₆-alkyl) orthoformates, acetaldehyde di(C₁- to C₆-alkyl) acetals or tri(C₁- to C₆-alkyl) orthoacetates (compounds 1)
   by anodically oxidizing
   1,2-di(C₁- to C₆-alkoxy)ethane or -propane, 1,1,2,2-tetra(C₁- to C₆-alkoxy)ethane or -propane, or 2,3-di-(C₁- to C₆-alkoxy)butane (compounds II)
   in the presence of a C₁- to C₆-alkyl alcohol (compounds III) using a customary organic compound (compound IV) which is suitable for electrochemical reduction as a cathodic depolarizer, and performing the anodic oxidation and the cathodic reduction in an undivided electrolysis cell in the presence of C₁-C₆-alkyl alcohols.
2. A process as claimed in claim 1, wherein the compounds I are trimethyl orthoformate or formaldehyde dimethyl acetal and these compounds may also be formed in the form of a mixture.
3. A process as claimed in claim 1 or 2, wherein compound IV is an aromatic hydrocarbon compound, activated olefin, aromatic carboxylic acid or derivative thereof, carbonyl compound, imine, heterocycle, naphthalene or ring-substituted naphthalene derivative.
4. A process as claimed in claim 3, wherein the cathodic depolarization is one of the following conversions:

   a) maleic acid or maleic acid derivatives in which the acid function is in the form of alkyl esters to a tetraalkyl butanetetracarboxylate by hydrodimerization

   b) benzenemono-, -di- or -tricarboxylic acids other than 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 ring to the corresponding mono-, di- and triformylbenzene compounds in which the formyl groups are in the form of an acetal

   c) acrylic acid, alkyl acrylates, acrylamide or acrylonitrile or homologs of these compounds to the corresponding-hydrodimerization products

   d) phthalic acid, alkyl phthalates or derivatives of these compounds substituted on the aromatic ring to phthalide or ring-substituted phthalide derivatives, cyclohexane- or cyclohexene-1,2-dicarboxylic acid, dialkyl cyclohexane- or cyclohexene-1,2-dicarboxylates, or derivatives substituted on the cyclohexane or cyclohexene ring corresponding to the substitution pattern of the phthalic acid derivatives substituted on the aromatic core

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

   f) pyridine or ring-substituted pyridine derivatives to 1,4-dihydropyridine or the corresponding 1,4-dihydropyridine derivatives.
5. A process as claimed in any of claims 1 to 4, which is carried out in a stacked plate cell using stacked electrodes connected in series.