EP0339523A1 - Process for manufacturing hydroxycarboxylic-acid esters - Google Patents

Process for manufacturing hydroxycarboxylic-acid esters Download PDF

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Publication number
EP0339523A1
EP0339523A1 EP89107289A EP89107289A EP0339523A1 EP 0339523 A1 EP0339523 A1 EP 0339523A1 EP 89107289 A EP89107289 A EP 89107289A EP 89107289 A EP89107289 A EP 89107289A EP 0339523 A1 EP0339523 A1 EP 0339523A1
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electrochemical oxidation
acid esters
hydrocarbon radicals
formula
general formula
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EP0339523B1 (en
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Michael Dr. Steiniger
Heinz Hannebaum
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BASF SE
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/23—Oxidation

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  • This invention relates to a new process for the preparation of hydroxy carboxylic acid esters by electrochemical oxidation of hydroxy aldehydes.
  • J. Org. Chem. 53, 218-219 (1988) describes a process in which 3-hydroxy-2,2-dimethylpropanal is oxidized electrochemically to 3-hydroxipivalic acid methyl ester in methanol in the presence of potassium iodide and a strong base such as sodium methoxide .
  • a disadvantage of this process is that the electrolysis is carried out in a divided electrolysis cell on platinum anodes. Compared to undivided electrolysis cells, this means not only a higher investment, but also a higher energy consumption, since the low conductivity of the organic electrolyte at the separator (diaphragm) results in a high voltage drop.
  • Another disadvantage is that this method, which presupposes the presence of sodium methoxide, allows only those aliphatic aldehydes to be oxidized which cannot undergo aldol condensation.
  • R1 and R2 are hydrogen atoms, hydroxyl groups, alkoxy groups or aliphatic or olefinic, straight-chain, branched or ring-shaped hydrocarbon radicals, where R1 and R2 can also together represent an alkylene radical, and the hydrocarbon radicals can also be substituted by halogen atoms, hydroxyl, epoxy or nitrile groups, and R3 represents a low molecular weight alkyl radical, particularly advantageously by electrochemical oxidation of hydroxy aldehydes of the general formula in the presence of alcohols of the formula R3OH, where n, R1, R2 and R3 have the meaning given above, if the electrochemical oxidation is carried out in the presence of ionogenic bromides or chlorides in an undivided electrolysis cell.
  • the hydroxy carboxylic acid esters are obtained with high selectivity and high current yields.
  • This advantageous result is surprising since in J. Electrochem. Soc. 125 , 1401-1403 (1978) describes that the electrochemical oxidation of primary alcohols in undivided electrolysis cells on graphite electrodes in the presence of chloride and bromide ions leads to aldehydes. Accordingly, ⁇ , ⁇ -dialkoxy carboxylic acid esters or dicarboxylic acid esters would have been expected as reaction products of the process according to the invention.
  • n is a number from 0 to 10, preferably 0 to 5.
  • the aliphatic or olefinic straight-chain or branched hydrocarbon radicals mentioned as radicals R 1 and R 2 are, for example, alkyl or alkylene groups having 1 to 10, in particular 1 to 6, preferably 1 to 4 carbon atoms, such as methyl, ethyl, n- or isopropyl, n-, iso- or tert-butyl groups.
  • Substituted hydrocarbon radicals of the type mentioned are, for example, hydroximethyl, chloromethyl or hydroxyethyl groups.
  • Annular hydrocarbons are, for example, cycloalkyl radicals having 3 to 8, in particular 5 and 6, carbon atoms. Both radicals R 1 and R 2 also come together to represent an alkylene radical, which can consist, for example, of 2 to 5 methyl groups.
  • R3 represents a low molecular weight alkyl radical, in particular an alkyl radical having 1 to 5 carbon atoms, preferably a methyl or ethyl radical.
  • alkyl radical having 1 to 5 carbon atoms, preferably a methyl or ethyl radical.
  • n- or iso-propanol, n-butanol, n-pentanol and preferably methanol or ethanol can be used.
  • Salts of hydrobromic and hydrochloric acid are suitable as ionogenic halides. Salts of hydrobromic acid, such as alkali, alkaline earth bromides and quaternary ammonium, especially tetraalkylammonium bromides are preferred.
  • the cation does not play an essential role in the invention, therefore other ionic metal halides can also be used, but cheap halides will advantageously be chosen.
  • examples include sodium, potassium, calcium and ammonium bromide, and di-, tri- and tetramethyl- or tetraethylammonium bromide.
  • the process according to the invention can be carried out in the industrially customary electrolysis cells. It can advantageously be carried out in an undivided flow cell, which makes it possible to keep the electrode spacing very small in order to minimize the cell voltage.
  • the preferred electrode spacing is 1 mm or less, in particular 0.25 to 0.5 mm.
  • the preferred anode material is graphite. However, other anode materials which are stable under the reaction conditions can also be used.
  • the cathode material is e.g. from metals such as lead, iron, steel, nickel or precious metals such as platinum.
  • the preferred method material is also graphite.
  • the composition of the electrolyte can be chosen within wide limits.
  • the electrolyte consists of 1 to 80% by weight of hydroxy aldehyde of the formula II 10 to 95 wt% R3OH 0.1 to 10 wt% halide
  • a solvent can be added to the electrolyte, for example to improve the solubility of the hydroxy aldehyde or the halide.
  • Suitable solvents are, for example, nitriles such as acetonitrile and ethers such as tetrahydrofuran.
  • the solvents are added, for example, in amounts of up to 30% by weight, based on the electrolyte.
  • the current density is not a limiting factor for the method according to the invention, it is, for example, 1 to 25 A / dm 2.
  • Electrolysis is preferably carried out at 3 to 12 A / dm 2. When the electrolysis is operated without pressure, the temperature is expediently chosen so that it is at least 5 to 10 ° C.
  • the electrolysis discharges can be worked up by methods known per se.
  • the electrolysis discharge is expediently worked up by distillation. Excess alkanol and any cosolvent used are first distilled off.
  • the halides are made in a known manner, e.g. separated by filtration or extraction, and the hydroxy carboxylic acid esters are distilled or recrystallized. Alkanol, possibly unreacted hydroxy aldehyde and cosolvents as well as halides can advantageously be recycled to the electrolysis.
  • the process according to the invention can be carried out batchwise or continuously.
  • hydroxy carboxylic acid esters produced by the process according to the invention are versatile intermediates for the synthesis of crop protection agents or polymers.
  • the electrooxidation was carried out in an undivided electrolysis cell with anodes and cathodes made of graphite at temperatures of 20 to 25 ° C.
  • the composition of the electrolyte used and the electrolysis conditions are summarized in the table.
  • the electrolyte was pumped through the cell at 200 l / h via a heat exchanger.

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Abstract

Process for manufacturing hydroxycarboxylic acid esters of the general formula: <IMAGE> in which n is an integer from 0 to 10, R<1> and R<2> are hydrogen atoms, hydroxyl or alkoxy groups, aliphatic or olefinic, straight-chain, branched or ring-type hydrocarbon radicals, where R<1> and R<2> may also stand jointly for an alkylene radical and the hydrocarbon radicals may also be substituted by halogen atoms, or hydroxyl, epoxy or nitrile groups, and R<3> is a low-molecular-weight alkyl radical, by electrochemical oxidation of hydroxyaldehydes of the general formula: <IMAGE> in the presence of alcohols of the formula R<3>OH and of ionogenic bromides or chlorides in an unpartitioned electrolysis cell.

Description

Diese Erfindung betrifft ein neues Verfahren für die Herstellung von Hydroxicarbonsäureestern durch elektrochemische Oxidation von Hydroxialdehyden.This invention relates to a new process for the preparation of hydroxy carboxylic acid esters by electrochemical oxidation of hydroxy aldehydes.

Es sind schon verschiedene Verfahren für die einstufige Überführung von Aldehyden in Carbonsäureestern bekannt geworden, von denen jedoch nur wenige dafür geeignet sind, aliphatische Hydroxialdehyde unter Erhalt der primären oder sekundären Hydroxylfunktion in Gegenwart von niederen Alkoholen zu Hydroxicarbonsäureestern zu oxidieren. So ist z.B. aus Acta Chem. Scand. 27, 3009 (1973) bekannt, daß sich Glykolaldehyd mit Silbercarbonat auf Kieselgur in Methanol zu Glykolsäuremethylester oxidieren läßt. Die Verwendung des teuren Silbers als Oxidationsmittel und die zur Vermeidung von Silberverlusten aufwendige Regenerierung machen dieses Verfahren für eine industrielle Anwendung wirtschaftlich uninteressant.Various processes have already become known for the one-step conversion of aldehydes into carboxylic acid esters, of which only a few are suitable for oxidizing aliphatic hydroxy aldehydes to hydroxy carboxylic acid esters while maintaining the primary or secondary hydroxyl function in the presence of lower alcohols. For example, from Acta Chem. Scand. 27, 3009 (1973) discloses that glycol aldehyde can be oxidized with methyl carbonate on kieselguhr in methanol to methyl glycolate. The use of expensive silver as an oxidizing agent and the costly regeneration to avoid silver losses make this process economically uninteresting for industrial use.

In J. Org. Chem. 53, 218-219 (1988) wird ein Verfahren beschrieben, bei dem man 3-Hydroxi-2,2-dimethylpropanal in Methanol in Gegenwart von Kaliumjodid und einer starken Base wie Natriummethanolat elektrochemisch zu 3-Hydroxipivalinsäuremethylester oxidiert. Nachteilig bei diesem Verfahren ist, daß die Elektrolyse in einer geteilten Elektrolysezelle an Platinanoden durchgeführt wird. Das bedeutet im Vergleich zu ungeteilten Elektrolysezellen nicht nur einen höheren Investitionsaufwand, sondern auch einen höheren Energieverbrauch, da durch die geringe Leitfähigkeit des organischen Elektrolyten an dem Separator (Diaphragma) ein hoher Spannungsabfall auftritt. Weiterhin ist von Nachteil, daß sich nach dieser Methode, die die Anwesenheit von Natriummethanolat voraussetzt, nur solche aliphatische Aldehyde oxidieren lassen, die keine Aldol-Kondensation eingehen können.J. Org. Chem. 53, 218-219 (1988) describes a process in which 3-hydroxy-2,2-dimethylpropanal is oxidized electrochemically to 3-hydroxipivalic acid methyl ester in methanol in the presence of potassium iodide and a strong base such as sodium methoxide . A disadvantage of this process is that the electrolysis is carried out in a divided electrolysis cell on platinum anodes. Compared to undivided electrolysis cells, this means not only a higher investment, but also a higher energy consumption, since the low conductivity of the organic electrolyte at the separator (diaphragm) results in a high voltage drop. Another disadvantage is that this method, which presupposes the presence of sodium methoxide, allows only those aliphatic aldehydes to be oxidized which cannot undergo aldol condensation.

Es wurde nun gefunden, daß man Hydroxicarbonsäureester der allgemeinen Formel

Figure imgb0001
in der n eine ganze Zahl von 0 bis 10 bedeutet, R¹ und R² Wasserstoff­atome, Hydroxigruppen, Alkoxigruppen oder aliphatische oder olefinische, geradkettige, verzweigte oder ringförmige Kohlenwasserstoffreste bedeuten, wobei R¹ und R² auch gemeinsam für einen Alkylenrest stehen können, und die Kohlenwasserstoffreste noch durch Halogenatome, Hydroxi-, Epoxi- oder Nitrilgruppen substituiert sein können, und R³ für einen niedermolekularen Alkylrest steht, besonders vorteilhaft durch elektrochemische Oxidation von Hydroxialdehyde der allgemeinen Formel
Figure imgb0002
 in Gegenwart von Alkoholen der Formel R³OH, wobei n, R¹, R² und R³ die oben angegebene Bedeutung haben, herstellen kann, wenn man die elektrochemische Oxidation in Gegenwart von ionogenen Bromiden oder Chloriden in einer ungeteilten Elektrolysezelle durchführt.It has now been found that hydroxy carboxylic acid esters of the general formula
Figure imgb0001
 in which n is an integer from 0 to 10, R¹ and R² are hydrogen atoms, hydroxyl groups, alkoxy groups or aliphatic or olefinic, straight-chain, branched or ring-shaped hydrocarbon radicals, where R¹ and R² can also together represent an alkylene radical, and the hydrocarbon radicals can also be substituted by halogen atoms, hydroxyl, epoxy or nitrile groups, and R³ represents a low molecular weight alkyl radical, particularly advantageously by electrochemical oxidation of hydroxy aldehydes of the general formula
Figure imgb0002
 in the presence of alcohols of the formula R³OH, where n, R¹, R² and R³ have the meaning given above, if the electrochemical oxidation is carried out in the presence of ionogenic bromides or chlorides in an undivided electrolysis cell.

Nach dem neuen Verfahren erhält man die Hydroxicarbonsäureester mit hoher Selektivität und hohen Stromausbeuten. Dieses vorteilhafte Ergebnis ist überraschend, da in J. Electrochem. Soc. 125, 1401-1403 (1978) beschrieben ist, daß die elektrochemische Oxidation primärer Alkohole in ungeteilten Elektrolysezellen an Graphitelektroden in Gegenwart von Chlorid- und Bromidionen zu Aldehyden führt. Demnach wären als Reaktionsprodukte des erfindungsgemäßen Verfahrens ω,ω-Dialkoxicarbonsäureester oder Dicarbonsäureester zu erwarten gewesen.According to the new process, the hydroxy carboxylic acid esters are obtained with high selectivity and high current yields. This advantageous result is surprising since in J. Electrochem. Soc. 125 , 1401-1403 (1978) describes that the electrochemical oxidation of primary alcohols in undivided electrolysis cells on graphite electrodes in the presence of chloride and bromide ions leads to aldehydes. Accordingly, ω, ω-dialkoxy carboxylic acid esters or dicarboxylic acid esters would have been expected as reaction products of the process according to the invention.

Das Ergebnis des erfindungsgemäßen Verfahrens war weiterhin nicht naheliegend, da in J. Org. Chem. 53, 218 (1988) erwähnt ist, daß die elektrochemische Oxidation der Aldehyde nicht in Gegenwart von Kaliumbromid oder Kaliumchlorid gelingt, sondern nur mit Jodiden oder Jod in Gegenwart von Natriummethanolat in geteilten Elektrolysezellen zu zufriedenstellenden Ausbeuten führt.The result of the process according to the invention was further not obvious, since it is mentioned in J. Org. Chem. 53 , 218 (1988) that the electrochemical oxidation of the aldehydes does not succeed in the presence of potassium bromide or potassium chloride, but only with iodides or iodine in the presence leads to satisfactory yields of sodium methoxide in divided electrolysis cells.

In den Hydroxialdehyden der Formel II bedeutet n eine Zahl von 0 bis 10, vorzugsweise 0 bis 5. Die als Reste R¹ und R² genannten aliphatischen oder olefinischen geradkettigen oder verzweigten Kohlenwasserstoffreste sind z.B. Alkyl- oder Alkylengruppen mit 1 bis 10, insbesondere 1 bis 6, vorzugsweise 1 bis 4 C-Atomen, wie Methyl-, Ethyl-, n- oder iso-Propyl, n-, iso- oder tert.Butylgruppen. Substituierte Kohlenwasserstoffreste der genannten Art sind z.B. Hydroximethyl-, Chlormethyl- oder Hydroxiethyl­gruppen. Ringförmige Kohlenwasserstoffe sind z.B. Cycloalkylreste mit 3 bis 8, insbesondere 5 und 6 Kohlenstoffatomen. Beide Reste R¹ und R² kommen auch zusammen für einen Alkylenrest, der z.B. aus 2 bis 5 Methylgruppen bestehen kann, stehen.In the hydroxy aldehydes of the formula II, n is a number from 0 to 10, preferably 0 to 5. The aliphatic or olefinic straight-chain or branched hydrocarbon radicals mentioned as radicals R 1 and R 2 are, for example, alkyl or alkylene groups having 1 to 10, in particular 1 to 6, preferably 1 to 4 carbon atoms, such as methyl, ethyl, n- or isopropyl, n-, iso- or tert-butyl groups. Substituted hydrocarbon radicals of the type mentioned are, for example, hydroximethyl, chloromethyl or hydroxyethyl groups. Annular hydrocarbons are, for example, cycloalkyl radicals having 3 to 8, in particular 5 and 6, carbon atoms. Both radicals R 1 and R 2 also come together to represent an alkylene radical, which can consist, for example, of 2 to 5 methyl groups.

In den Alkoholen der Formel R³OH steht R³ für einen niedermolekularen Alkylrest, insbesondere für einen Alkylrest mit 1 bis 5 Kohlenstoffatomen, vorzugsweise für einen Methyl- oder Ethylrest. Beispielsweise können n-oder iso Propanol, n-Butanol, n-Pentanol und bevorzugt Methanol oder Ethanol verwendet werden. Als ionogene Halogenide kommen Salze der Bromwasserstoff- und Chlorwasserstoffsäure in Betracht. Bevorzugt sind Salze der Bromwasserstoffsäure, wie Alkali, Erdalkalibromide sowie quartäre Ammonium-, insbesondere Tetraalkylammoniumbromide. Das Kation spielt keine erfindungswesentliche Rolle, es können daher auch andere ionogene Metallhalogenide verwendet werden, vorteilhaft wird man jedoch billige Halogenide wählen. Beispielsweise seien Natrium-, Kalium-, Calcium- und Ammoniumbromid, sowie Di-, Tri- und Tetramethyl- oder Tetraethylammoniumbromid genannt.In the alcohols of the formula R³OH, R³ represents a low molecular weight alkyl radical, in particular an alkyl radical having 1 to 5 carbon atoms, preferably a methyl or ethyl radical. For example, n- or iso-propanol, n-butanol, n-pentanol and preferably methanol or ethanol can be used. Salts of hydrobromic and hydrochloric acid are suitable as ionogenic halides. Salts of hydrobromic acid, such as alkali, alkaline earth bromides and quaternary ammonium, especially tetraalkylammonium bromides are preferred. The cation does not play an essential role in the invention, therefore other ionic metal halides can also be used, but cheap halides will advantageously be chosen. Examples include sodium, potassium, calcium and ammonium bromide, and di-, tri- and tetramethyl- or tetraethylammonium bromide.

Das erfindungsgemäße Verfahren kann in den technisch üblichen Elektrolysezellen durchgeführt werden. Vorteilhaft kann man es in einer ungeteilten Durchflußzelle durchführen, die es ermöglicht zur Minimierung der Zellspannung den Elektrodenabstand sehr gering zu halten. Die bevorzugten Elektrodenabstände liegen bei 1 mm oder darunter, insbesondere bei 0,25 bis 0,5 mm.The process according to the invention can be carried out in the industrially customary electrolysis cells. It can advantageously be carried out in an undivided flow cell, which makes it possible to keep the electrode spacing very small in order to minimize the cell voltage. The preferred electrode spacing is 1 mm or less, in particular 0.25 to 0.5 mm.

Bevorzugtes Anodenmaterial ist Graphit. Es können aber auch andere unter den Reaktionsbedingungen stabile Anodenmaterialien benutzt werden. Das Kathodenmaterial besteht z.B. aus Metallen wie Blei, Eisen, Stahl, Nickel oder Edelmetallen wie Platin. Bevorzugtes Kethodenmaterial ist ebenfalls Graphit.The preferred anode material is graphite. However, other anode materials which are stable under the reaction conditions can also be used. The cathode material is e.g. from metals such as lead, iron, steel, nickel or precious metals such as platinum. The preferred method material is also graphite.

Die Zusammensetzung des Elektrolyten kann in weiten Grenzen gewählt werden. So besteht der Elektrolyt beispielsweise aus
1 bis 80 Gew.% Hydroxialdehyd der Formel II
10 bis 95 Gew.% R³OH
0,1 bis 10 Gew.% HalogenidThe composition of the electrolyte can be chosen within wide limits. For example, the electrolyte consists of
1 to 80% by weight of hydroxy aldehyde of the formula II
10 to 95 wt% R³OH
0.1 to 10 wt% halide

Dem Elektrolyten kann, falls gewünscht, ein Lösungsmittel, etwa zur Verbesserung der Löslichkeit des Hydroxialdehyds oder des Halogenids zugesetzt werden. Geeignete Lösungsmittel sind z.B. Nitrile, wie Acetonitril und Ether, wie Tetrahydrofuran. Man gibt die Lösungsmittel z.B. in Mengen bis zu 30 Gew.%, bezogen auf den Elektrolyten, zu. Die Stromdichte ist kein begrenzender Faktor für das erfinungsgemäße Verfahren, sie beträgt z.B. 1 bis 25 A/dm². Vorzugsweise wird mit 3 bis 12 A/dm² elektrolysiert. Die Temperatur wird bei druckloser Fahrweise der Elektrolyse zweckmäßigerweise so gewählt, daß sie zumindest 5 bis 10°C unter dem Siedepunkt des Elektrolyten liegt. Bei Verwendung von Methanol oder Ethanol wird vorzugsweise bei Temperaturen von 20 bis 30°C elektrolysiert. Es wurde überraschend festgestellt, das das erfindungsgemäße Verfahren die Möglichkeit bietet, die Hydroxialdehyde weitgehend umzusetzen, ohne daß es zu Ausbeuteverlusten an Hydroxicarbonsäureester z.B. durch Folgeoxidationen kommt. Auch die Stromausbeuten sind bei dem erfindungsgemäßen Verfahren ungewöhnlich hoch. So ist der Hydroxialdehyd bei Elektrolyse mit 2 bis 2,5 F/Mol Hydroxialdehyd bereits vollständig umgesetzt.If desired, a solvent can be added to the electrolyte, for example to improve the solubility of the hydroxy aldehyde or the halide. Suitable solvents are, for example, nitriles such as acetonitrile and ethers such as tetrahydrofuran. The solvents are added, for example, in amounts of up to 30% by weight, based on the electrolyte. The current density is not a limiting factor for the method according to the invention, it is, for example, 1 to 25 A / dm 2. Electrolysis is preferably carried out at 3 to 12 A / dm 2. When the electrolysis is operated without pressure, the temperature is expediently chosen so that it is at least 5 to 10 ° C. below the boiling point of the electrolyte. When using methanol or ethanol is preferably electrolyzed at temperatures of 20 to 30 ° C. It was surprisingly found that the process according to the invention offers the possibility of largely converting the hydroxy aldehydes without there being any loss in yield of hydroxy carboxylic acid esters, for example as a result of subsequent oxidations. The current yields are also unusually high in the process according to the invention. In electrolysis, the hydroxy aldehyde is already completely converted with 2 to 2.5 F / mol hydroxy aldehyde.

Die Aufarbeitung der Elektrolyseausträge kann man nach an sich bekannten Methoden vornehmen. Zweckmäßigerweise wird der Elektrolyseaustrag destillativ aufgearbeitet. Überschüssiges Alkanol und evtl. eingesetztes Kolösungsmittel werden zunächst abdestiliert. Die Halogenide werden in bekannter Weise, z.B. durch Filtration oder Extraktion abgetrennt, und die Hydroxicarbonsäureester werden reindestilliert bzw. umkristallisiert. Alkanol, evtl. nicht umgesetzter Hydroxialdehyd und Kolösungsmittel sowie Halogenide können vorteilhaft zur Elektrolyse zurückgeführt werden. Das erfinungsgemäße Verfahren kann sowohl diskontinuierlich als auch kontinuierlich durchgeführt werden.The electrolysis discharges can be worked up by methods known per se. The electrolysis discharge is expediently worked up by distillation. Excess alkanol and any cosolvent used are first distilled off. The halides are made in a known manner, e.g. separated by filtration or extraction, and the hydroxy carboxylic acid esters are distilled or recrystallized. Alkanol, possibly unreacted hydroxy aldehyde and cosolvents as well as halides can advantageously be recycled to the electrolysis. The process according to the invention can be carried out batchwise or continuously.

Die nach dem erfindungsgemäßen Verfahren hergestellten Hydroxicarbonsäure­ester sind vielfältig einsetzbare Zwischenprodukte für die Synthese von Pflanzenschutzmitteln oder Polymeren.The hydroxy carboxylic acid esters produced by the process according to the invention are versatile intermediates for the synthesis of crop protection agents or polymers.

Beispiele 1 bis 9Examples 1 to 9

Die Elektrooxidation wurde in einer ungeteilten Elektrolysezelle mit Anoden und Kathoden aus Graphit bei Temperaturen von 20 bis 25°C durchgeführt. Die Zusammensetzung des eingesetzten Elektrolyten sowie die Elektrolysebedingungen sind in der Tabelle zusammengefaßt. Während der Elektrolyse wurde der Elektrolyt mit 200 l/h über einen Wärmetauscher durch die Zelle gepumpt.The electrooxidation was carried out in an undivided electrolysis cell with anodes and cathodes made of graphite at temperatures of 20 to 25 ° C. The composition of the electrolyte used and the electrolysis conditions are summarized in the table. During the electrolysis, the electrolyte was pumped through the cell at 200 l / h via a heat exchanger.

Nach Beendigung der Elektrolyse wurde der Alkohol bei Normaldruck abdestilliert und der verbleibenden Rückstand bei 1 bis 40 mbar reindestilliert. Die Hydroxicarbonsäureester wurden bei einem Umsatz von > 98 % in Ausbeuten von 54 bis 81 %, bezogen auf den Ausgangsstoff (II), erhalten. Tabelle Nr. n Hydroxialdehyd der Formel II Alkanol der Formel R³OH Zusammensetzung des Elektrolyten Elektrizitätsmenge (F/mol) Stromdichte (A/dm²) Spannung (V) Umsatz (%) Ausbeute (%) R¹ R² R³ II Halogenid [Gew.%] R³OH 1 1 CH₃ CH₃ CH₃ 25 1 74 2.2 10 5.4 99 70 2 1 CH₃ C₂H₅ CH₃ 10 1 89 2.5 10 4.8 99 54 3 1 CH₃ CH₂OCH₃ CH₃ 10 1 89 2.5 10 5.0 100 81 4 1 CH₃ CH₂OH CH₃ 24 1 75 2.5 10 6.6 98 62 5 1 -(CH₂)₅- CH₃ 10 1 89 2.5 10 5.2 100 60 6 1 CH₃ CH₃ CH₃ 20 1 79 2.5 10 4.3 98 63 7 2 H H CH₃ 5 1 94 2.3 7.5 4.2 99 68 8 3 H H CH₃ 10 1 89 2.5 10 4.5 99 60 9 1 CH₃ C₃H₇ C₂H₅ 10 1 89 2.5 7.5 9.6 99 54 Anmerkung zur Tabelle: Im Beispiel 6 wurde als Halogenid LiCl eingesetzt. In allen anderen Beispielen wurde als Halogenid NaBr eingesetzt. Die in den Beispielen 3 und 4 angegebenen Ausbeuten wurden gaschromatographisch bestimmt. After the electrolysis had ended, the alcohol was distilled off at atmospheric pressure and the remaining residue was distilled off at 1 to 40 mbar. The hydroxy carboxylic acid esters were obtained with a conversion of> 98% in yields of 54 to 81%, based on the starting material (II). table No. n Hydroxy aldehyde of the formula II Alkanol of the formula R³OH Composition of the electrolyte Amount of electricity (F / mol) Current density (A / dm²) Voltage (V) Sales (%) Yield (%) R¹ R² R³ II Halide [wt%] R³OH 1 1 CH₃ CH₃ CH₃ 25th 1 74 2.2 10th 5.4 99 70 2nd 1 CH₃ C₂H₅ CH₃ 10th 1 89 2.5 10th 4.8 99 54 3rd 1 CH₃ CH₂OCH₃ CH₃ 10th 1 89 2.5 10th 5.0 100 81 4th 1 CH₃ CH₂OH CH₃ 24th 1 75 2.5 10th 6.6 98 62 5 1 - (CH₂) ₅- CH₃ 10th 1 89 2.5 10th 5.2 100 60 6 1 CH₃ CH₃ CH₃ 20th 1 79 2.5 10th 4.3 98 63 7 2nd H H CH₃ 5 1 94 2.3 7.5 4.2 99 68 8th 3rd H H CH₃ 10th 1 89 2.5 10th 4.5 99 60 9 1 CH₃ C₃H₇ C₂H₅ 10th 1 89 2.5 7.5 9.6 99 54 Note on the table: In example 6, LiCl was used as the halide. In all other examples, NaBr was used as the halide. The yields given in Examples 3 and 4 were determined by gas chromatography.

Claims (5)

1. Verfahren zur Herstellung von Hydroxicarbonsäureestern der allgemeinen Formel
Figure imgb0003
 in der n eine ganze Zahl von 0 bis 10 bedeutet, R¹ und R² Wasserstoff­atome, Hydroxigruppen, Alkoxigruppen oder aliphatische oder olefinische, geradkettige, verzweigte oder ringförmige Kohlenwasser­stoffreste bedeuten, wobei R¹ und R² auch gemeinsam für einen Alkylenrest stehen können, und die Kohlenwasserstoffreste noch durch Halogenatome, Hydroxi-, Epoxi- oder Nitrilgruppen substituiert sein können, und R³ für einen niedermolekularen Alkylrest steht, durch elektrochemische Oxidation von Hydroxialdehyden der allgemeinen Formel
Figure imgb0004
 in Gegenwart von Alkoholen der Formel R³OH, wobei n, R¹, R² und R³ die oben angegebene Bedeutung haben, dadurch gekennzeichnet, daß man die elektrochemische Oxidation in Gegenwart von ionogenen Bromide oder Chloriden in einer ungeteilten Elektrolysezelle durchführt.1. Process for the preparation of hydroxy carboxylic acid esters of the general formula
Figure imgb0003
 in which n is an integer from 0 to 10, R¹ and R² are hydrogen atoms, hydroxyl groups, alkoxy groups or aliphatic or olefinic, straight-chain, branched or ring-shaped hydrocarbon radicals, where R¹ and R² can also jointly represent an alkylene radical, and the hydrocarbon radicals still through Halogen atoms, hydroxyl, epoxy or nitrile groups can be substituted, and R³ represents a low molecular weight alkyl radical, by electrochemical oxidation of hydroxy aldehydes of the general formula
Figure imgb0004
 in the presence of alcohols of the formula R³OH, where n, R¹, R² and R³ have the meaning given above, characterized in that the electrochemical oxidation is carried out in the presence of ionogenic bromides or chlorides in an undivided electrolysis cell. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als ionogenes Bromid ein Alkali- oder Erdalkalibromid oder ein quartäres Ammoniumbromid verwendet.2. The method according to claim 1, characterized in that an alkali or alkaline earth bromide or a quaternary ammonium bromide is used as the ionogenic bromide. 3. Verfahren nach Anspruchen 1, dadurch gekennzeichnet, daß man die elektrochemische Oxidation an Graphitanoden vornimmt.3. The method according to claims 1, characterized in that one carries out the electrochemical oxidation on graphite anodes. 4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als Alkohol der Formel R³OH Methanol oder Ethanol verwendet.4. The method according to claim 1, characterized in that methanol or ethanol is used as the alcohol of the formula R³OH. 5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die elektrochemische Oxidation bei Stromdichten von 1 bis 25 A/dm² vornimmt.5. The method according to claim 1, characterized in that the electrochemical oxidation is carried out at current densities of 1 to 25 A / dm².
EP89107289A 1988-04-29 1989-04-22 Process for manufacturing hydroxycarboxylic-acid esters Expired - Lifetime EP0339523B1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2699937A1 (en) * 1992-12-29 1994-07-01 Ard Sa The prepn of galactaric acid from galacturonic acid

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