EP0711851B1 - Process for manufacturing p-hydroxybenzaldehyde - Google Patents

Process for manufacturing p-hydroxybenzaldehyde Download PDF

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Publication number
EP0711851B1
EP0711851B1 EP95117495A EP95117495A EP0711851B1 EP 0711851 B1 EP0711851 B1 EP 0711851B1 EP 95117495 A EP95117495 A EP 95117495A EP 95117495 A EP95117495 A EP 95117495A EP 0711851 B1 EP0711851 B1 EP 0711851B1
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tert
butyl
mol
hydroxybenzaldehyde
phenol
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French (fr)
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EP0711851A1 (en
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Andreas Dr. Weiper-Idelmann
Karl-Heinz Dr. Grosse Brinkhaus
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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

Definitions

  • the present invention relates to an improved process for the preparation of p-hydroxybenzaldehydes of the general formula I. in which the aromatic ring can carry 2 to 4 inert substituents X, by electrochemical oxidation of a phenol of the general formula II in the presence of an alkanol R 1 -OH, the radical R 1 being a C 1 -C 6 alkyl radical.
  • the aldehydes I serve as intermediates for the production of pharmaceuticals, light and crop protection agents, stabilizers, Antioxidants, colors and fragrances.
  • the invention was based, the aldehydes I from the task To make phenols II selectively accessible in higher yields.
  • the starting compounds I can carry inert substituents such as alkyl, alkoxy, alkoxycarbonyl, cyano or halogen radicals.
  • substituents such as alkyl, alkoxy, alkoxycarbonyl, cyano or halogen radicals.
  • those compounds of the general formula III are preferred among the starting compounds in which the radicals R 2 and R 3 are independently of one another for C 1 -C 18 -alkyl radicals such as methyl, ethyl, n-propyl, isopropyl , n-butyl, iso-butyl and tert-butyl, but also for C 1 -C 18 alkoxy radicals such as methoxy or ethoxy.
  • the compounds of the formula II or III are commercially available or can be prepared by methods known per se.
  • the electrochemical oxidation is carried out in the presence of an alkanol R 1 -OH, the radical R 1 being a C 1 -C 6 alkyl radical.
  • Methanol is preferred.
  • the electrolyte can contain a solvent which is inert under the electrolysis conditions, such as acetonitrile; however, the electrolysis is preferably carried out without such a solvent.
  • concentration of the alkanol in the electrolyte is usually 50 to 98% by weight.
  • the electrolyte also contains an organic or inorganic one Base.
  • This base must be able to remove the phenol II or III to convert into the corresponding phenol ion.
  • amines e.g. tertiary amines, such as triethylamine, but preferably alkali metal hydroxides such as NaOH and KOH and alkali metal alcoholates such as sodium methoxide and ethanolate.
  • the bases are in substoichiometric amounts, based on the Phenol II or III used. 0.01 to 0.9 are preferred. particularly preferably 0.25 to 0.7 equivalents of base per equivalent Phenol II or III used.
  • auxiliary electrolyte such as weakly basic or neutral Salts are usually not required, so preferably without such auxiliary electrolytes is worked.
  • the process according to the invention is generally carried out at current densities of 0.1 to 20 A / dm 2 , preferably at 2 to 8 A / dm 2 .
  • the amount of charge is usually 4 to 6 F / mol of starting compound.
  • the temperature can be varied within wide limits. she can -20 to 180 ° C, preferred are 50 to 70 ° C. There prevails reduced pressure, normal pressure or positive pressure, but preferred Normal pressure or an overpressure up to 3 bar.
  • Precious metals such as platinum or oxides such as chromium and ruthenium oxide and mixed oxides such as Ti / RuO x can be considered as anode materials.
  • Graphite and platinum electrodes are preferred.
  • the electrolysis can be carried out batchwise or continuously will.
  • a partial stream the reaction solution is separated off and worked up, which generally makes up less than 5% by weight of the total current.
  • the reaction solution new starting solution added.
  • the reaction solution is advantageously worked up by distilling off the alkanol R 1 -OH.
  • the residue is worked up hydrolytically, preferably in neutral or acid.
  • Mineral acids such as sulfuric acid or organic acids such as acetic acid can be used for acidification. These acids are generally added to the reaction mixture in amounts of 1 to 10% by weight, based on the reaction mixture.
  • the product is then either separated off as a solid or, after extraction with an organic solvent such as methyl tert-butyl ether or toluene, obtained by distillation.
  • the alkanol R 1 -OH and optionally recovered starting material II or III can be used in further batches.
  • the method according to the invention allows selective production the aldehydes I in high yield.
  • Electrolyte composition 150 g (0.68 mol, 5% by weight) 2,6-di-tert-butyl-4-methylphenol 61.4 g (0.34 mol, 0.6% by weight) Sodium methylate as a 30% methanolic solution 2789 g Methanol Electrolysis conditions: temperature 58 ° C Current density 4 A / dm 2 Amount of charge 4.7 F / mol
  • the production was carried out in analogy to Example 1, but the current density was 8 A / dm 2 .
  • Electrolyte composition :
  • Electrolyte composition :
  • Electrolyte composition 150 g (0.68 mol, 5% by weight) 2,6-di-tert-butyl-4-methylphenol 19.1 g (0.34 mol, 0.6% by weight) Potassium hydroxide 2830 g Methanol
  • Electrolyte composition 150 g (1.1 mol, 10% by weight) 2,4,6-trimethylphenol 100 g (0.55 mol, 1% by weight) Sodium methylate as a 30% methanolic solution 2750 g Methanol Electrolysis conditions: temperature 58 ° C Current density 4 A / dm 2 Amount of charge 5 F / mol

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  • Organic Chemistry (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Description

Die vorliegende Erfindung betrifft ein verbessertes Verfahren zur Herstellung von p-Hydroxybenzaldehyden der allgemeinen Formel I

Figure 00010001
in der der aromatische Ring 2 bis 4 inerte Substituenten X tragen kann, durch elektrochemische Oxidation eines Phenols der allgemeinen Formel II
Figure 00010002
in Gegenwart eines Alkanols R1-OH, wobei der Rest R1 für einen C1-C6-Alkylrest steht.The present invention relates to an improved process for the preparation of p-hydroxybenzaldehydes of the general formula I.
Figure 00010001
in which the aromatic ring can carry 2 to 4 inert substituents X, by electrochemical oxidation of a phenol of the general formula II
Figure 00010002
in the presence of an alkanol R 1 -OH, the radical R 1 being a C 1 -C 6 alkyl radical.

Die Aldehyde I dienen als Zwischenprodukte für die Herstellung von Pharmazeutika, Licht- und Pflanzenschutzmitteln, Stabilisatoren, Antioxidantien, Farb- und Riechstoffen.The aldehydes I serve as intermediates for the production of pharmaceuticals, light and crop protection agents, stabilizers, Antioxidants, colors and fragrances.

Die elektrochemische Oxidation von 2,6-Di-tert.-butyl-4-methylphenol zu 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd beschreiben H. Ohmori et al. in Chem. Pharm. Bull. 33 (1985) 4007. Die Reaktion wird in einem Gemisch von Methanol und Diethylether in Gegenwart stöchiometrischer Mengen Natriummethanolat und eines weiteren Hilfselektrolyten bei konstantem Potential durchgeführt. Die erzielte Ausbeute von 68 % läßt jedoch für eine wirtschaftliche technische Umsetzung des Verfahrens Wünsche offen.The electrochemical oxidation of 2,6-di-tert-butyl-4-methylphenol to 3,5-di-tert-butyl-4-hydroxybenzaldehyde is described by H. Ohmori et al. in Chem. Pharm. Bull. 33 (1985) 4007. The reaction is carried out in a mixture of methanol and diethyl ether in the presence of stoichiometric amounts of sodium methoxide and another auxiliary electrolyte at constant potential. The yield of 68%, however, leaves something to be desired for an economical technical implementation of the process.

Der Erfindung lag die Aufgabe zugrunde, die Aldehyde I aus Phenolen II in höheren Ausbeuten selektiv zugänglich zu machen.The invention was based, the aldehydes I from the task To make phenols II selectively accessible in higher yields.

Demgemäß wurde eine Verbesserung des eingangs definierten Verfahrens gefunden, welche dadurch gekennzeichnet ist, daß man die Reaktion in Gegenwart von weniger als stöchiometrischen Mengen einer organischen oder anorganischen Base, die ein Phenol II in das entsprechende Phenolation überführen kann, durchführt, das Reaktionsgemisch hydrolytisch aufarbeitet und den Aldehyd I isoliert.Accordingly, an improvement in the process defined at the outset found, which is characterized in that the Reaction in the presence of less than stoichiometric amounts an organic or inorganic base containing a phenol II in can convert the corresponding phenolate ion, does that The reaction mixture is worked up hydrolytically and the aldehyde I isolated.

Die Ausgangsverbindungen I können inerte Substituenten wie Alkyl-, Alkoxy-, Alkoxycarbonyl-, Cyano- oder Halogenreste tragen. Im Hinblick auf ihre Verwendung als Zwischenprodukte sind unter den Ausgangsverbindungen solche Verbindungen der allgemeinen Formel III bevorzugt, in der die Reste R2 und R3 unabhängig voneinander für C1-C18-Alkylreste wie Methyl, Ethyl, n-Propyl, iso-Propyl, n-Butyl, iso-Butyl und tert.-Butyl, aber auch für C1-C18-Alkoxyreste wie Methoxy oder Ethoxy stehen. Die Verbindungen der Formel II bzw. III sind im Handel erhältlich oder nach an sich bekannten Methoden herstellbar.

Figure 00020001
The starting compounds I can carry inert substituents such as alkyl, alkoxy, alkoxycarbonyl, cyano or halogen radicals. With regard to their use as intermediates, those compounds of the general formula III are preferred among the starting compounds in which the radicals R 2 and R 3 are independently of one another for C 1 -C 18 -alkyl radicals such as methyl, ethyl, n-propyl, isopropyl , n-butyl, iso-butyl and tert-butyl, but also for C 1 -C 18 alkoxy radicals such as methoxy or ethoxy. The compounds of the formula II or III are commercially available or can be prepared by methods known per se.
Figure 00020001

Besonders bevorzugt ist die Herstellung folgender Verbindungen:
3-Methyl-5-tert.-Butyl-4-hydroxybenzaldehyd, 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd, 3,5-Di-n-butyl-4-hydroxybenzaldehyd, 3,5-Di-isopropyl-4-hydroxybenzaldehyd, 3,5-Diethyl-4-hydroxybenzaldehyd, 3,5-Dimethyl-4-hydroxybenzaldehyd, 3-tert.-Butyl-5-methyl-4-hydroxybenzaldehyd.The preparation of the following compounds is particularly preferred:
3-methyl-5-tert-butyl-4-hydroxybenzaldehyde, 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 3,5-di-n-butyl-4-hydroxybenzaldehyde, 3,5-di- isopropyl-4-hydroxybenzaldehyde, 3,5-diethyl-4-hydroxybenzaldehyde, 3,5-dimethyl-4-hydroxybenzaldehyde, 3-tert-butyl-5-methyl-4-hydroxybenzaldehyde.

Die elektrochemische Oxidation wird in Gegenwart eines Alkanols R1-OH vorgenommen, wobei der Rest R1 für einen C1-C6-Alkylrest steht. Bevorzugt ist Methanol. Der Elektrolyt kann ein unter den Elektrolysebedingungen inertes Lösungsmittel wie Acetonnitril enthalten; vorzugsweise führt man die Elektrolyse aber ohne ein solches Lösungsmittel aus. Die Konzentration des Alkanols im Elektrolyten beträgt in der Regel 50 bis 98 Gew.-%.The electrochemical oxidation is carried out in the presence of an alkanol R 1 -OH, the radical R 1 being a C 1 -C 6 alkyl radical. Methanol is preferred. The electrolyte can contain a solvent which is inert under the electrolysis conditions, such as acetonitrile; however, the electrolysis is preferably carried out without such a solvent. The concentration of the alkanol in the electrolyte is usually 50 to 98% by weight.

Weiterhin enthält der Elektrolyt eine organische oder anorganische Base. Diese Base muß in der Lage sein, das Phenol II bzw. III in das entsprechende Phenolation zu überführen. Im einzelnen kommen Amine, z.B. tertiäre Amine wie Triethylamin in Betracht, bevorzugt aber Alkalimetallhydroxide wie NaOH und KOH und Alkalimetallalkoholate wie Natriummethanolat und -ethanolat. Die Basen werden in unterstöchiometrischen Mengen, bezogen auf das Phenol II bzw. III, eingesetzt. Bevorzugt werden 0,01 bis 0,9, besonders bevorzugt 0,25 bis 0,7 Äquivalente Base pro Äquivalent Phenol II bzw. III verwendet.The electrolyte also contains an organic or inorganic one Base. This base must be able to remove the phenol II or III to convert into the corresponding phenol ion. In detail come amines, e.g. tertiary amines, such as triethylamine, but preferably alkali metal hydroxides such as NaOH and KOH and alkali metal alcoholates such as sodium methoxide and ethanolate. The bases are in substoichiometric amounts, based on the Phenol II or III used. 0.01 to 0.9 are preferred. particularly preferably 0.25 to 0.7 equivalents of base per equivalent Phenol II or III used.

Ein weiterer Hilfselektrolyt wie schwach basische oder neutrale Salze ist in der Regel nicht erforderlich, so daß bevorzugt ohne solche Hilfselktrolyten gearbeitet wird.Another auxiliary electrolyte such as weakly basic or neutral Salts are usually not required, so preferably without such auxiliary electrolytes is worked.

Das erfindungsgemäße Verfahren wird im allgemeinen bei Stromdichten von 0,1 bis 20 A/dm2, bevorzugt bei 2 bis 8 A/dm2 durchgeführt. Die Ladungsmenge beträgt in der Regel 4 bis 6 F/mol Ausgangsverbindung.The process according to the invention is generally carried out at current densities of 0.1 to 20 A / dm 2 , preferably at 2 to 8 A / dm 2 . The amount of charge is usually 4 to 6 F / mol of starting compound.

Die Temperatur kann in weiten Grenzen variiert werden. Sie kann -20 bis 180°C betragen, bevorzugt sind 50 bis 70°C. Dabei herrscht verminderter Druck, Normaldruck oder Überdruck, bevorzugt aber Normaldruck oder ein Überdruck bis 3 bar.The temperature can be varied within wide limits. she can -20 to 180 ° C, preferred are 50 to 70 ° C. There prevails reduced pressure, normal pressure or positive pressure, but preferred Normal pressure or an overpressure up to 3 bar.

Als Reaktoren kommen geteilte oder ungeteilte Zellen in Betracht, von denen die letzteren bevorzugt sind.Divided or undivided cells come into consideration as reactors, the latter of which are preferred.

Als Anodenmaterialien kommen Edelmetalle wie Platin oder Oxide wie Chrom- und Rutheniumoxid sowie Mischoxide wie Ti/RuOx in Betracht. Bevorzugt sind Graphit- und Platinelektroden.Precious metals such as platinum or oxides such as chromium and ruthenium oxide and mixed oxides such as Ti / RuO x can be considered as anode materials. Graphite and platinum electrodes are preferred.

Als Kathodenmaterialien eignen sich allgemein Stahl, Eisen, Kupfer, Nickel, Zink und Kohle sowie Edelmetalle wie Platin; bevorzugt wird Graphit und Platin.Generally suitable steel, iron, Copper, nickel, zinc and coal as well as precious metals such as platinum; prefers becomes graphite and platinum.

Die Elektrolyse kann diskontinuierlich oder kontinuierlich ausgeführt werden. In einer kontinuierlichen Variante kann ein Teilstrom der Reaktionslösung abgetrennt und aufgearbeitet werden, der im allgemeinen weniger als 5 Gew.-% des Gesamtstroms ausmacht. In dem Maß wie Elektrolyt entnommen wird, wird der Reaktionslösung neue Ausgangslösung zugesetzt.The electrolysis can be carried out batchwise or continuously will. In a continuous variant, a partial stream the reaction solution is separated off and worked up, which generally makes up less than 5% by weight of the total current. As the electrolyte is removed, the reaction solution new starting solution added.

Die Aufarbeitung der Reaktionslösung geschieht vorteilhaft durch Abdestillieren des Alkanols R1-OH. Der Rückstand wird hydrolytisch, vorzugsweise im Neutralen oder Sauren, aufgearbeitet. Zum Ansäuren können beispielsweise Mineralsäuren wie Schwefelsäure oder organische Säuren wie Essigsäure dienen. Diese Säuren werden dem Reaktionsgemisch in der Regel in Mengen von 1 bis 10 Gew.-%, bezogen auf das Reaktionsgemisch, zugesetzt. Das Produkt wird dann entweder als Feststoff abgetrennt oder nach Extraktion mit einem organischen Lösungsmittel wie Methyl-tert.-Butylether oder Toluol destillativ gewonnen. Das Alkanol R1-OH und gegebenenfalls zurückgewonnes Ausgangsmaterial II bzw. III können in weiteren Ansätzen eingesetzt werden.The reaction solution is advantageously worked up by distilling off the alkanol R 1 -OH. The residue is worked up hydrolytically, preferably in neutral or acid. Mineral acids such as sulfuric acid or organic acids such as acetic acid can be used for acidification. These acids are generally added to the reaction mixture in amounts of 1 to 10% by weight, based on the reaction mixture. The product is then either separated off as a solid or, after extraction with an organic solvent such as methyl tert-butyl ether or toluene, obtained by distillation. The alkanol R 1 -OH and optionally recovered starting material II or III can be used in further batches.

Das erfindungsgemäße Verfahren erlaubt eine selektive Herstellung der Aldehyde I in hoher Ausbeute.The method according to the invention allows selective production the aldehydes I in high yield.

BeispieleExamples

Alle Beispiele wurden in einer von unten angeströmten ungeteilten Durchflußelektrolysezelle mit Graphitelektroden im Abstand von 1 mm durchgeführt.
Der Elektrolyt wurde mit 550 l/h umgepumpt.
Die Aufarbeitung erfolgte erfindungsgemäß durch Hydrolyse des Reaktionsgemisches.
Nicht umgesetztes Substrat und Zwischenprodukt wurden durch Extraktion der wäßrigen Mutterlauge mit Methyl-tert.-Butylether (MTBE) nach Filtration des Produktes und Eindampfen der Mutterlauge aus der Umkristallisation des Produktes gewonnen. Die Angaben in Gew.-% beziehen sich auf den Gesamtreaktionsansatz.All examples were carried out in an undivided flow-through electrolysis cell with graphite electrodes at a distance of 1 mm from below.
The electrolyte was pumped around at 550 l / h.
Working up was carried out according to the invention by hydrolysis of the reaction mixture.
Unreacted substrate and intermediate product were obtained from the recrystallization of the product by extraction of the aqueous mother liquor with methyl tert-butyl ether (MTBE) after filtration of the product and evaporation of the mother liquor. The percentages by weight relate to the overall reaction batch.

Beispiel 1example 1 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Elektrolytzusammensetzung:Electrolyte composition: 150 g (0,68 mol, 5 Gew.-%)150 g (0.68 mol, 5% by weight) 2,6-Di-tert.-butyl-4-methylphenol2,6-di-tert-butyl-4-methylphenol 61,4 g (0,34 mol, 0,6 Gew.-%)61.4 g (0.34 mol, 0.6% by weight) Natriummethylat als 30 %ige methanolische LösungSodium methylate as a 30% methanolic solution 2789 g2789 g MethanolMethanol Elektrolysebedingungen:Electrolysis conditions: Temperaturtemperature 58°C58 ° C StromdichteCurrent density 4 A/dm2 4 A / dm 2 LadungsmengeAmount of charge 4,7 F/mol4.7 F / mol

Die Aufarbeitung erfolgte durch destillative Abtrennung von 2380 g Methanol, gefolgt von der Hydrolyse des Reaktionsgemisches mit 450 g 4 %iger HCl und Abtrennung des Produktes durch Filtration, sowie Umkristallisation des Rohproduktes aus Cyclohexan.Working up was carried out by distillative removal of 2380 g of methanol, followed by hydrolysis of the reaction mixture with 450 g of 4% HCl and separation of the product by filtration, and recrystallization of the crude product from cyclohexane.

Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
148 g (0,66 mol, 93 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd Based on the substrate used, the following were isolated (data in mol%):
148 g (0.66 mol, 93%) 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Beispiel 2Example 2 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Die Herstellung erfolgte in Analogie zu Beispiel 1, die Stromdichte betrug jedoch 8 A/dm2.The production was carried out in analogy to Example 1, but the current density was 8 A / dm 2 .

Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
143 g (0,61 mol, 90 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehydBased on the substrate used, the following were isolated (data in mol%):
143 g (0.61 mol, 90%) 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Beispiel 3Example 3 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Die Herstellung erfolgte in Analogie zu Beispiel 1, jedoch betrug die Stromdichte 2 A/dm2.The production was carried out in analogy to Example 1, but the current density was 2 A / dm 2 .

Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
146 g (0,62 mol, 91 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehydBased on the substrate used, the following were isolated (data in mol%):
146 g (0.62 mol, 91%) of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

Beispiel 4Example 4 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde Elektrolytzusammensetzung:Electrolyte composition:

  • 300 g (1,36 mol, 10 Gew.-%) 2,6-Di-tert.-butyl-4-methylphenol,300 g (1.36 mol, 10% by weight) of 2,6-di-tert-butyl-4-methylphenol,
  • 122 g (0,68 mol) Natriummethylat als 30 %ige methanolische Lösung,122 g (0.68 mol) of sodium methylate as 30% methanolic Solution,
  • 2578 g Methanol.2578 g of methanol.

    • Die Elektrolyse und Aufarbeitung erfolgte in Analogie zu Beispiel 1.The electrolysis and workup were carried out in analogy to example 1.

    Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
    289 g (1,24 mol, 91 %) 3,5-Di-tert.-butyl-3-hydroxybenzaldehyd    Based on the substrate used, the following were isolated (data in mol%):
    289 g (1.24 mol, 91%) 3,5-di-tert-butyl-3-hydroxybenzaldehyde

    Beispiel 5Example 5 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

    Die Elektrolyse und Aufarbeitung erfolgte in Analogie zu Beispiel 4, jedoch betrug die Temperatur 40°C. The electrolysis and workup were carried out in analogy to example 4, but the temperature was 40 ° C.

    Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%(:
    258 g (1,1 mol, 81 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd    Relative to the substrate used were isolated (data in mol% (:
    258 g (1.1 mol, 81%) 3,5-di-tert-butyl-4-hydroxybenzaldehyde

    Beispiel 6Example 6 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde Elektrolytzusammensetzung:Electrolyte composition:

  • 300 g (1,36 mol, 10 Gew.-%) 2,6-Di-tert.-butyl-4-methylphenol300 g (1.36 mol, 10% by weight) of 2,6-di-tert-butyl-4-methylphenol
  • 20,5 g (0,51 mol, 0,7 Gew.-%) Natriumhydroxid20.5 g (0.51 mol, 0.7% by weight) sodium hydroxide
  • 2680 g Methanol2680 g of methanol

    • Elektrolyse und Aufarbeitung erfolgten in Analogie zu Beispiel 1.Electrolysis and workup were carried out in analogy to Example 1.

    Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
    271 g (1,2 mol, 85 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd    Based on the substrate used, the following were isolated (data in mol%):
    271 g (1.2 mol, 85%) 3,5-di-tert-butyl-4-hydroxybenzaldehyde

    Beispiel 7Example 7 Herstellung von 3,5-Di-tert.-butyl-4-hydroxybenzaldehydPreparation of 3,5-di-tert-butyl-4-hydroxybenzaldehyde

    Elektrolytzusammensetzung:Electrolyte composition: 150 g (0,68 mol, 5 Gew.-%)150 g (0.68 mol, 5% by weight) 2,6-Di-tert.-butyl-4-methylphenol2,6-di-tert-butyl-4-methylphenol 19,1 g (0,34 mol, 0,6 Gew.-%)19.1 g (0.34 mol, 0.6% by weight) KaliumhydroxidPotassium hydroxide 2830 g2830 g MethanolMethanol

    Elektrolyse und Aufarbeitung erfolgten in Analogie zu Beispiel 1.Electrolysis and workup were carried out in analogy to Example 1.

    Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
    119 g (0,51 mol, 75 %) 3,5-Di-tert.-butyl-4-hydroxybenzaldehyd    Based on the substrate used, the following were isolated (data in mol%):
    119 g (0.51 mol, 75%) 3,5-di-tert-butyl-4-hydroxybenzaldehyde

    Beispiel 8Example 8 Herstellung von 3,5-Dimethyl-4-hydroxybenzaldehydPreparation of 3,5-dimethyl-4-hydroxybenzaldehyde

    Elektrolytzusammensetzung:Electrolyte composition: 150 g (1,1 mol, 10 Gew.-%)150 g (1.1 mol, 10% by weight) 2,4,6-Trimethylphenol2,4,6-trimethylphenol 100 g (0,55 mol, 1 Gew.-%)100 g (0.55 mol, 1% by weight) Natriummethylat als 30 %ige methanolische LösungSodium methylate as a 30% methanolic solution 2750 g2750 g MethanolMethanol Elektrolysebedingungen:Electrolysis conditions: Temperaturtemperature 58°C58 ° C StromdichteCurrent density 4 A/dm2 4 A / dm 2 LadungsmengeAmount of charge 5 F/mol5 F / mol

    Die Aufarbeitung erfolgte durch destillative Abtrennung von 2356 g Methanol, gefolgt von der Hydrolyse des Reaktionsgemisches mit 450 g 4 %iger HCl und Abtrennung des Produktes durch Filtration, sowie Umkristallisation des Rohproduktes aus Cyclohexan.Working up was carried out by distillative removal of 2356 g of methanol, followed by hydrolysis of the reaction mixture with 450 g of 4% HCl and separation of the product by filtration, and recrystallization of the crude product from cyclohexane.

    Bezogen auf eingesetztes Substrat wurden isoliert (Angaben in mol-%):
    114 g (0,76 mol, 69 %) 3,5-Di-methyl-4-hydroxybenzaldehyd    Based on the substrate used, the following were isolated (data in mol%):
    114 g (0.76 mol, 69%) 3,5-dimethyl-4-hydroxybenzaldehyde

    Claims (7)

    1. A process for preparing p-hydroxybenzaldehydes of the general formula I
      Figure 00100001
      in which the aromatic ring can carry from 2 to 4 inert substituents X, by electrochemical oxidation of a phenol of the general formula II
      Figure 00100002
      in the presence of an alkanol R1-OH, where R1 is C1-C6-alkyl, which comprises carrying out the reaction in the presence of less than stoichiometric amounts of an organic or inorganic base able to convert a phenol of the formula II into the corresponding phenolate ion, subjecting the reaction mixture to hydrolytic workup, and isolating the aldehyde of the formula I.
    2. A process as claimed in claim 1, wherein a phenol of the general formula III
      Figure 00110001
      where the R2 and R3 radicals are, independently of one another, C1-C18-alkyl or C1-C18-alkoxy, is oxidized.
    3. A process as claimed in claim 2, wherein the R2 and R3 radicals are a tert-butyl radical.
    4. A process as claimed in claims 1 to 3, wherein the electrochemical oxidation is carried out in undivided continuous flow cells.
    5. A process as claimed in claims 1 to 4, wherein electrolysis is carried out at from 50 to 70°C.
    6. A process as claimed in claims 1 to 5, wherein from 0.25 to 0.7 equivalent of base is employed per equivalent of phenol of the formula II.
    7. A process as claimed in claims 1 to 6, wherein alkali metal hydroxides or alkali metal alcoholates are employed as base.
    EP95117495A 1994-11-15 1995-11-07 Process for manufacturing p-hydroxybenzaldehyde Expired - Lifetime EP0711851B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    DE4440466A DE4440466A1 (en) 1994-11-15 1994-11-15 Process for the preparation of p-hydroxybenzaldehydes
    DE4440466 1994-11-15

    Publications (2)

    Publication Number Publication Date
    EP0711851A1 EP0711851A1 (en) 1996-05-15
    EP0711851B1 true EP0711851B1 (en) 1998-03-04

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    Application Number Title Priority Date Filing Date
    EP95117495A Expired - Lifetime EP0711851B1 (en) 1994-11-15 1995-11-07 Process for manufacturing p-hydroxybenzaldehyde

    Country Status (4)

    Country Link
    EP (1) EP0711851B1 (en)
    JP (1) JPH08209372A (en)
    DE (2) DE4440466A1 (en)
    ES (1) ES2113150T3 (en)

    Families Citing this family (1)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    WO2006077483A2 (en) * 2005-01-19 2006-07-27 Merisol Rsa (Pty) Ltd Method for the production of alkoxy-substituted phenols

    Family Cites Families (2)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    JPS5227739A (en) * 1975-08-26 1977-03-02 Takasago Corp Process for preparation of 3-substituted or non-substituted-4-hydroxyb enzaldehyde by electrolytic oxidation
    JPS572881A (en) * 1980-06-04 1982-01-08 Otsuka Chem Co Ltd Manufacture of 3,5-dialkoxy-4-hydroxybenzaldehyde

    Also Published As

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    ES2113150T3 (en) 1998-04-16
    EP0711851A1 (en) 1996-05-15
    DE4440466A1 (en) 1996-05-23
    DE59501538D1 (en) 1998-04-09
    JPH08209372A (en) 1996-08-13

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