EP0198303B1 - Anodic oxidation process of water soluble leucotriphenyl methane dye compounds - Google Patents

Anodic oxidation process of water soluble leucotriphenyl methane dye compounds Download PDF

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EP0198303B1
EP0198303B1 EP86104339A EP86104339A EP0198303B1 EP 0198303 B1 EP0198303 B1 EP 0198303B1 EP 86104339 A EP86104339 A EP 86104339A EP 86104339 A EP86104339 A EP 86104339A EP 0198303 B1 EP0198303 B1 EP 0198303B1
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anodic oxidation
compounds
leuco
dye
leuco compound
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EP0198303A1 (en
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Horst Dr. Bruder
Wolfgang Habermann
Udo Dr. Mayer
Peter Dr. Hammes
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BASF SE
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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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  • JP-OS 130481/1 979 describes an electrochemical process for the preparation of triphenylmethane dyes by anodic oxidation of the corresponding leukotriphenylmethane compounds.
  • the oxidation takes place in an electrolysis cell, which is divided into two by a semi-permeable membrane made of unglazed porcelain.
  • a network of lead dioxide is used as the oxidation anode, the oxygen overvoltage of which is more than 700 mV at a current density of approximately 0.05 kA / m 2 .
  • the electrolysis takes place in the pH range between 6 and 7, current and material yields of 50 to 65%, based on the leuco compounds used, being obtained.
  • this process technology produces a cloudy and greenish blue dye which can only be used to a limited extent.
  • Type-specific products in high yield are obtained according to the prior art in the chemical oxidation of the leuco compound of the dye with CI N ° .42090 with alkali dichromates. Difficulties here arise in separating the chromium compounds from the color, so that the color produced in this way is unsuitable for the food sector.
  • the invention relates to a process for the preparation of water-soluble 2 to 4 sulfonic acid groups containing diamino-triphenylmethane dyes - by anodic oxidation of the leuco compounds in a two-part electrolytic cell, which is characterized in that the leuco compounds are at a pH _ 4, optionally in the presence of Mineral acid anions carrying oxygen atoms, anodically oxidized at an oxygen overvoltage of ⁇ 400 mV.
  • the process according to the invention gives diamino-triphenylmethane dyes containing sulfonic acid groups in very pure form and in high yield. Particularly pure dyes are achieved when using an exchange membrane as a partition.
  • the process according to the invention is generally carried out by pouring the solution of the leuco dye into the anode compartment of a divided electrolytic cell. A current-conducting solution is placed in the cathode compartment. The electrolysis takes place at an oxygen overvoltage of ⁇ 400 mV.
  • oxidizable leuco compounds come e.g. B. that of the dyes with the CI N °. 42045, 42051, 42052, 42053, 42075, 42080, 42085, 42090, 42095, 42100, 42105, 42120, 42135, 42150, 42155 and 42165.
  • the leuco compounds of the dyes with the CI N ° are preferred.
  • Possible mineral acid anions to be used are chlorates, perchlorates, nitrates, phosphates and mixtures thereof, preferably sulfates. These ions are the solutions of the leuco dyes in concentrations of 0.05 to 8 wt .-%, preferably 0.5 to 4 wt .-%, based on the solution, when using 10 to 35% solutions, in the form of acids or added salts.
  • the anodic oxidation of the leuco solutions takes place at pH values 4 4, preferably at pH values in the range from 0.5 to 2.5.
  • the oxygen overvoltage during the electrolytic oxidation is below 400 mV, in particular below 330 mV.
  • the dye is further oxidized by higher oxygen overvoltage, which reduces the yield.
  • Suitable anode materials are electrodes with a low oxygen overvoltage. The oxygen overvoltage must not exceed 400 mV.
  • anodes come e.g. B. electrically conductive, with non-stoichiometric, oxidic compounds of platinum and / or iridium or with compounds of the platinum metal group doped valve metals such as titanium, niobium or tantalum into consideration. Titanium or niobium electrodes doped with non-stoichiometric tantalum-iridium mixed oxides are particularly suitable.
  • activated carbon electrodes can also be used, e.g. B.
  • nitric acid anodized graphite which is doped with molybdenum (VI), tungsten (VI) and / or vanadium (V) compounds.
  • Such doped graphite electrodes are described in DE-OS 34 30 487.
  • Preferred dopants are those with molybdenum (VI) or vanadium (V) compounds which additionally contain titanium (III) and / or titanium (IV) compounds or iron (III) compounds.
  • Organic anion and cation exchangers have proven successful for separating the anode and cathode compartments.
  • Suitable ion exchangers are e.g. B. Polymers and copolymers of styrene, styrene and divinylbenzene, styrene and maleic anhydride, acrylic esters and divinylbenzene, olefins, perfluorinated olefins, vinyl chloride and acrylonitrile. which contain sulfonic acid and / or primary, secondary, tertiary or quaternary amine groups as charge-bearing groups.
  • Copolymers of tetrafluoroethylene with unsaturated perfluorinated ethers containing carboxylic acid ester and / or contain sulfonic acid fluoride groups and copolymers of styrene and divinylbenzene (DVB content 4 to 8% by weight) with quaternary ammonium groups or sulfonic acid groups as charge carriers.
  • Aqueous mineral acids, hydrochloric acids or alkalis can be used as catholytes when using cation exchange membranes, for separating the cathode and anode end spaces.
  • Aqueous sulfuric acid or alkali solutions are preferably used.
  • alkali lyes the lye corresponding to the alkali application of the leuco dye is used, so that 25 to 35% by weight of aqueous alkali lye can be obtained as a by-product.
  • anion exchange membranes aqueous alkali solutions, ammonia or alkali or ammonium carbonate or bicarbonate solutions are suitable as catholytes.
  • the alkali lyes are preferably primary, secondary or tertiary amines, e.g. B. those with C, -C 4 alkyl radicals on the nitrogen atom, which optionally have a hydroxyl and alkoxy group as substituents, in a concentration of 0.02 wt .-% to 10 wt .-%.
  • the aqueous solutions of the leuco compounds with the mineral acid anion additives are used as anolytes at a pH value of ⁇ 4.
  • the concentrations of leuco compounds in the anolyte should preferably be 5 to 30% by weight.
  • the current densities in the electrolysis can be 0.2 to 4 KA / m 2 , preferably 0.5 to 1.2 KA / m 2 .
  • the effective power supply for the leuco connection should be more than 100%, since oxygen is formed as a side reaction. Electricity offers of 105 to 130% based on the leuco connection used are preferred.
  • the anodic oxidation of the leuco compounds preferably takes place at temperatures below the boiling point of the water, preferably at temperatures from + 15 to + 45 ° C.
  • Cation exchange membranes and dilute sulfuric acid are preferably used as the catholyte.
  • concentration of sulfuric acid is preferably 2-10% by weight.
  • Electrodes made from intermediate titanium suboxide layers have proven to be favorable here.
  • a titanium flat profile electrode was used as the anode, which was surface-doped with a non-stoichiometric tantalum-iridium mixed oxide and had an intermediate titanium suboxide layer.
  • a Luggin capillary was attached to the surface of this anode and was connected to a silver / silver chloride reference electrode via a current key.
  • a copper electrode is used as the cathode.
  • Aqueous, 5% by weight sulfuric acid was added to the cathode compartment as the catholyte.
  • a 20% by weight aqueous solution of the leuco compound of the dye with CI N ° was used as the anolyte. 42 090 used.
  • the leuco dye was obtained by condensation from o-sulfobenzaldehyde and N-ethylsulfobenzylaniline).
  • the anolyte was circulated through the anode compartment at an average speed of approximately 0.5 m / s and electrolyzed at a current density of 0.6 KA / m 2 .
  • the electrolysis was carried out at a cell voltage of 3.5 V at temperatures between + 25 and + 32 ° C.
  • Example 2 The oxidation was carried out as indicated in Example 1, but the leuco dyes indicated in the table were used. The corresponding dyes were obtained in high yields, good purity and good coloristic properties.

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Description

In der JP-OS 130481/1 979 wird ein elektrochemisches Verfahren zur Herstellung von Triphenylmethanfarbstoffen durch anodische Oxidation der entsprechenden Leukotriphenylmethanverbindungen beschrieben. Bei diesem Verfahren erfolgt die Oxidation in einer durch eine halbdurchlässige Membran aus unglasiertem Porzellan zweigeteilten Elektrolysezelle. Als Oxidationsanode wird ein Netz aus Bleidioxid verwendet, dessen Sauerstoffüberspannung bei einer Stromdichte von ungefähr 0,05 kA/m2 mehr als 700 mV beträgt. Die Elektrolyse erfolgt im pH-Bereich zwischen 6 und 7, wobei Strom- und Materialausbeuten von 50 bis 65%, bezogen auf die eingesetzten Leukoverbindungen erhalten werden. Bei der Oxidation der Leukoverbindung des Farbstoffs mit CI N°.42090 erhält man nach dieser Verfahrenstechnik einen trüben und grünstichigen Blaufarbstoff, der nur bedingt verwendet werden kann.JP-OS 130481/1 979 describes an electrochemical process for the preparation of triphenylmethane dyes by anodic oxidation of the corresponding leukotriphenylmethane compounds. In this process, the oxidation takes place in an electrolysis cell, which is divided into two by a semi-permeable membrane made of unglazed porcelain. A network of lead dioxide is used as the oxidation anode, the oxygen overvoltage of which is more than 700 mV at a current density of approximately 0.05 kA / m 2 . The electrolysis takes place in the pH range between 6 and 7, current and material yields of 50 to 65%, based on the leuco compounds used, being obtained. When the leuco compound of the dye is oxidized with CI N ° .42090, this process technology produces a cloudy and greenish blue dye which can only be used to a limited extent.

Typgerechte Produkte in hoher Ausbeute erhält man nach dem Stand der Technik bei der chemischen Oxidation der Leukoverbindung des Farbstoffs mit CI N°.42090 mit Alkalidichromaten. Schwierigkeiten bereitet hier die Abtrennung der Chromverbindungen aus dem Farbstoff, so daß auf diesem Wege hergestellter Farbstoff für den Lebensmittelsektor ungeeignet ist.Type-specific products in high yield are obtained according to the prior art in the chemical oxidation of the leuco compound of the dye with CI N ° .42090 with alkali dichromates. Difficulties here arise in separating the chromium compounds from the color, so that the color produced in this way is unsuitable for the food sector.

Aufgabe der vorliegenden Erfindung war es, ein Verfahren zu entwickeln, nach welchem reine Sulfonsäuregruppen enthaltende Diamino-triphenylmethanfarbstoffe, vorzugsweise der Farbstoff mit CI N° 42090, in hoher Ausbeute hergestellt werden können.It was an object of the present invention to develop a process by which pure diamino-triphenylmethane dyes containing sulfonic acid groups, preferably the dye with CI N ° 42090, can be produced in high yield.

Diese Aufgabe wird mit Hilfe des erfindungsgemäßen Verfahrens durch Elektrolyse der entsprechenden Leukoverbindungen in einer zweigeteilten Elektrolysezelle gelöst. Dementsprechend betrifft die Erfindung ein Verfahren zur Herstellung von wasserlöslichen 2 bis 4 Sulfonsäuregruppen enthaltenden Diamino-triphenylmethanfarbstoffen - durch anodische Oxidation der Leukoverbindungen in einer zweigeteilten Elektrolysezelle, das dadurch gekennzeichnet ist, daß man die Leukoverbindungen bei einem pH-Wert _ 4, gegebenenfalls in Gegenwart von Sauerstoffatome tragenden Mineralsäureanionen, anodisch bei einer Sauerstoffüberspannung von≤ 400 mV oxidiert.This object is achieved with the aid of the method according to the invention by electrolysis of the corresponding leuco compounds in a two-part electrolysis cell. Accordingly, the invention relates to a process for the preparation of water-soluble 2 to 4 sulfonic acid groups containing diamino-triphenylmethane dyes - by anodic oxidation of the leuco compounds in a two-part electrolytic cell, which is characterized in that the leuco compounds are at a pH _ 4, optionally in the presence of Mineral acid anions carrying oxygen atoms, anodically oxidized at an oxygen overvoltage of ≤ 400 mV.

Nach dem erfindungsgemäßen Verfahren erhält man Sulfonsäuregruppen enthaltende Diamino-triphenylmethanfarbstoffe in sehr reiner Form und hoher Ausbeute. Besonders reine Farbstoffe werden bei Verwendung einer Austauschermembran als Trennwand erzielt.The process according to the invention gives diamino-triphenylmethane dyes containing sulfonic acid groups in very pure form and in high yield. Particularly pure dyes are achieved when using an exchange membrane as a partition.

Das Verfahren gemäß der Erfindung wird im allgemeinen so durchgeführt, daß man in den Anodenraum einer geteilten Elektrolysezelle die Lösung des Leukofarbstoffs einfüllt. In den Kathodenraum gibt man eine den Strom leitende Lösung. Die Elektrolyse erfolgt bei einer Sauerstoffüberspannung von < 400 mV.The process according to the invention is generally carried out by pouring the solution of the leuco dye into the anode compartment of a divided electrolytic cell. A current-conducting solution is placed in the cathode compartment. The electrolysis takes place at an oxygen overvoltage of <400 mV.

Als oxidierbare Leukoverbindungen kommen z. B. die der Farbstoffe mit den CI N°. 42045, 42051, 42052, 42053, 42075, 42080, 42085, 42090, 42095, 42100, 42105, 42120, 42135, 42150, 42155 und 42165 in Betracht. Bevorzugt sind die Leukoverbindungen der Farbstoffe mit den CI N°. 42090, 42045, 42051, 42052, 42053, 42080, 42105, 42135 und 42165, insbesondere mit CI N°. 42090.As oxidizable leuco compounds come e.g. B. that of the dyes with the CI N °. 42045, 42051, 42052, 42053, 42075, 42080, 42085, 42090, 42095, 42100, 42105, 42120, 42135, 42150, 42155 and 42165. The leuco compounds of the dyes with the CI N ° are preferred. 42090, 42045, 42051, 42052, 42053, 42080, 42105, 42135 and 42165, especially with CI N °. 42090.

Als gegebenenfalls anzuwendende Mineralsäureanionen kommen Chlorate, Perchlorate, Nitrate, Phosphate und deren Gemische, vorzugsweise Sulfate in Betracht. Diese ionen werden den Lösungen der Leukofarbstoffe in Konzentrationen von 0,05 bis 8 Gew.-%, vorzugsweise von 0,5 bis 4 Gew.-%, bezogen auf die Lösung, bei Verwendung 10 bis 35%iger Lösungen, in Form der Säuren oder Salze zugesetzt.Possible mineral acid anions to be used are chlorates, perchlorates, nitrates, phosphates and mixtures thereof, preferably sulfates. These ions are the solutions of the leuco dyes in concentrations of 0.05 to 8 wt .-%, preferably 0.5 to 4 wt .-%, based on the solution, when using 10 to 35% solutions, in the form of acids or added salts.

Die anodische Oxidation der Leukolösungen erfolgt bei pH-Werten ≤ 4, vorzugsweise bei pH-Werten im Bereich von 0,5 bis 2,5.The anodic oxidation of the leuco solutions takes place at pH values 4 4, preferably at pH values in the range from 0.5 to 2.5.

Die Sauerstoffüberspannung liegt während der elektrolytischen Oxidation bei unterhalb 400 mV, insbesondere bei unterhalb 330 mV. Durch höhere Sauerstoffüberspannung wird der Farbstoff weiter oxidiert, wodurch die Ausbeute sinkt.The oxygen overvoltage during the electrolytic oxidation is below 400 mV, in particular below 330 mV. The dye is further oxidized by higher oxygen overvoltage, which reduces the yield.

Geeignete Anodenmaterialien sind Elektroden mit einer geringen Sauerstoffüberspannung. Die Sauerstoffüberspannung darf Werte von 400 mV nicht übersteigen. Als Anoden kommen z. B. elektrisch leitende, mit nicht stöchiometrischen, oxidischen Verbindungen des Platins und/oder Iridiums oder mit Verbindungen der Platinmetallgruppe dotierte Ventilmetalle wie Titan, Niob oder Tantal in Betracht. Besonders geeignet sind mit nicht stöchiometrischen Tantal-Iridium-Mischoxiden dotierte Titan- oder Niobelektroden. An Stelle der dotierten Metallanoden können aber auch aktivierte Kohleelektroden verwendet werden, z. B. in Salpetersäure anodisch anoxidierter Graphit, der mit Molybdän(VI)-, Woltram(VI)- und/oder Vanadium(V)-Verbindungen dotiert ist. Solche dotierten Graphitelektroden sind in der DE-OS 34 30 487 beschrieben. Bevorzugte Dotierungen sind solche mit Molybdän(VI)- oder Vanadium(V)-Verbindungen, die zusätzlich Titan(III)- und/oder Titan(IV)-Verbindungen oder Eisen(III)-Verbindungen enthalten.Suitable anode materials are electrodes with a low oxygen overvoltage. The oxygen overvoltage must not exceed 400 mV. As anodes come e.g. B. electrically conductive, with non-stoichiometric, oxidic compounds of platinum and / or iridium or with compounds of the platinum metal group doped valve metals such as titanium, niobium or tantalum into consideration. Titanium or niobium electrodes doped with non-stoichiometric tantalum-iridium mixed oxides are particularly suitable. Instead of the doped metal anodes, activated carbon electrodes can also be used, e.g. B. in nitric acid anodized graphite, which is doped with molybdenum (VI), tungsten (VI) and / or vanadium (V) compounds. Such doped graphite electrodes are described in DE-OS 34 30 487. Preferred dopants are those with molybdenum (VI) or vanadium (V) compounds which additionally contain titanium (III) and / or titanium (IV) compounds or iron (III) compounds.

Zur Trennung von Anoden- und Kathodenraum haben sich organische Anionen- und Kationenaustauscher bewährt. Geeignete Ionenaustauscher sind z. B. Polymerisate und Copolymerisate aus Styrol, Styrol und Divinylbenzol, Styrol und Maleinsäureanhydrid, Acrylester und Divinylbenzol, Olefinen, perfluorierten Olefinen, Vinylchlorid und Acrylnitril. die als ladungstragende Gruppen Sulfonsäure und/oder primäre, sekundäre, tertiäre oder quatäre Amingruppen enthalten. Bevorzugt geeignet sind Copolymerisate aus Tetrafluorethylen mit ungesättigten perfluorierten Ethern, die Carbonsäureester-und/oder Sulfonsäurefluorid-Gruppen enthalten, sowie Copolymerisate aus Styrol- und Divinylbenzol (DVB-Anteil 4 bis 8 Gew.-%) mit quaternären Ammoniumgruppen oder Sulfonsäuregruppen als Ladungsträgern.Organic anion and cation exchangers have proven successful for separating the anode and cathode compartments. Suitable ion exchangers are e.g. B. Polymers and copolymers of styrene, styrene and divinylbenzene, styrene and maleic anhydride, acrylic esters and divinylbenzene, olefins, perfluorinated olefins, vinyl chloride and acrylonitrile. which contain sulfonic acid and / or primary, secondary, tertiary or quaternary amine groups as charge-bearing groups. Copolymers of tetrafluoroethylene with unsaturated perfluorinated ethers containing carboxylic acid ester and / or contain sulfonic acid fluoride groups, and copolymers of styrene and divinylbenzene (DVB content 4 to 8% by weight) with quaternary ammonium groups or sulfonic acid groups as charge carriers.

Als Katolyte können bei Verwendung von Kationenaustauscher-Membranen, zur Trennung von Kathoden- und Anodendraum, wässrige Mineralsäuren, Salzsäuren oder Laugen benutzt werden. Vorzugsweise verwendet man wässrige Schwefelsäure oder Alkalilaugen. Im Falle der Anwendung von Alkalilaugen wird die dem Alkalikation des Leukofarbstoffs entsprechende Lauge verwendet, so daß als Nebenprodukt 25 bis 35 Gew.-% wässrige Alkalilauge gewonnen werden kann. Bei Verwendung von Anionenaustauscher-Membranen sind wässrige Alkalilaugen, Ammoniak oder Alkali- oder Ammoniumkarbonat- bzw. Bikarbonatlösungen als Katolyte geeignet. Um Schäden an den Membranen zu vermeiden setzt man den Alkalilaugen vorzugsweise primäre, sekundäre oder tertiäre Amine, z. B. solche mit C,-bis C4-Alkylresten am Stickstoffatom, die gegebenenfalls eine Hydroxyl- und Alkoxygruppe als Substituenten haben, in einer Konzentration von 0,02 Gew.-% bis 10 Gew.-% hinzu.Aqueous mineral acids, hydrochloric acids or alkalis can be used as catholytes when using cation exchange membranes, for separating the cathode and anode end spaces. Aqueous sulfuric acid or alkali solutions are preferably used. In the case of the use of alkali lyes, the lye corresponding to the alkali application of the leuco dye is used, so that 25 to 35% by weight of aqueous alkali lye can be obtained as a by-product. When using anion exchange membranes, aqueous alkali solutions, ammonia or alkali or ammonium carbonate or bicarbonate solutions are suitable as catholytes. In order to avoid damage to the membranes, the alkali lyes are preferably primary, secondary or tertiary amines, e.g. B. those with C, -C 4 alkyl radicals on the nitrogen atom, which optionally have a hydroxyl and alkoxy group as substituents, in a concentration of 0.02 wt .-% to 10 wt .-%.

Als Anolyte werden die wässrigen Lösungen der Leukoverbindungen mit den Mineralsäureanionenzusätzen bei einem pH-Wert ≤ 4 eingesetzt. Die Konzentrationen an Leukoverbindungen im Anolyten sollten vorzugsweise 5 bis 30 Gew.-% betragen.The aqueous solutions of the leuco compounds with the mineral acid anion additives are used as anolytes at a pH value of ≤ 4. The concentrations of leuco compounds in the anolyte should preferably be 5 to 30% by weight.

Zur Vermeidung von Diffusionsbehinderungen im Anodenbereich muß für eine gute Anströmung der Anode (turbulente Strömung und mittlere Strömungsgeschwindigkeiten -- 0,1 m/s) gesorgt werden. Die Stromdichten bei der Elektrolyse können 0,2 bis 4 KA/m2, vorzugsweise 0,5 bis 1,2 KA/m2 betragen. Das effektive Stromangebot für die Leukoverbindung sollte mehr als 100 % betragen, da als Nebenreaktion Sauerstoff gebildet wird. Bevorzugt wählt man Stromangebote von 105 bis 130 % bezogen auf die eingesetzte Leukoverbindung.In order to avoid diffusion impediments in the anode area, a good flow against the anode (turbulent flow and average flow velocities - 0.1 m / s) must be ensured. The current densities in the electrolysis can be 0.2 to 4 KA / m 2 , preferably 0.5 to 1.2 KA / m 2 . The effective power supply for the leuco connection should be more than 100%, since oxygen is formed as a side reaction. Electricity offers of 105 to 130% based on the leuco connection used are preferred.

Die anodische Oxidation der Leukoverbindungen erfolgt vorzugsweise bei den Temperaturen unterhalb des Siedepunktes des Wassers, vorzugsweise bei Temperaturen von + 15 bis + 45 °C.The anodic oxidation of the leuco compounds preferably takes place at temperatures below the boiling point of the water, preferably at temperatures from + 15 to + 45 ° C.

Bevorzugt verwendet man Kationenaustauscher-Membranen und verdünnte Schwefelsäure als Katolyt. Die Konzentration der Schwefelsäure beträgt vorzugsweise 2-10 Gew.-%. Mit dieser Kombination kann man die Farbstofflösungen während der Oxidation zusätzlich von Fremdmetallkationen reinigen und verhindert Schäden an der Membran.Cation exchange membranes and dilute sulfuric acid are preferably used as the catholyte. The concentration of sulfuric acid is preferably 2-10% by weight. With this combination, the dye solutions can also be cleaned of foreign metal cations during oxidation and prevent damage to the membrane.

Zur Vermeidung von Ablagerungen auf den Anodenoberflächen und einer Überoxidation des Farbstoffes ist es günstig, die Anoden bei einem Anstieg des Potentials auf Werte von s = 1 400 bis 1 500 mV kurzzeitig, d. h. 15 bis 30 Sekunden kathodisch zu schalten. Bei dieser Verfahrensweise ist es zweckmäßig, bei Verwendung von dotierten Titananoden umpolbare Elektroden einzusetzen, die Zwischenschichten aus Titan-, Tantal- oder Niobsuboxiden oder Carbiden, Siliciden oder Boriden dieser Metalle oder Wolfram und/oder Molybdän enthalten. Als günstig haben sich hier Elektroden aus Titansuboxidzwischenschichten erwiesen.In order to avoid deposits on the anode surfaces and overoxidation of the dye, it is expedient to briefly change the anodes when the potential rises to values of s = 1,400 to 1,500 mV, ie. H. Switch cathodically for 15 to 30 seconds. In this procedure, it is expedient to use electrodes which can be reversed when using doped titanium anodes and which contain intermediate layers of titanium, tantalum or niobium suboxides or carbides, silicides or borides of these metals or tungsten and / or molybdenum. Electrodes made from intermediate titanium suboxide layers have proven to be favorable here.

Das Verfahren soll durch die folgenden Ausführungsbeispiele zusätzliche erläutert werden.The method is intended to be further explained by the following exemplary embodiments.

Beispiel 1example 1

In einer durch eine Kationenaustauscher-Membran zweigeteilten Elektrolysezelle wurde als Anode eine Titanflachprofilelektrode verwendet, die oberflächlich mit einem nicht stöchiometrischen Tantal-Iridium-Mischoxid dotiert war und eine Titansuboxidzwischenschicht aufwies. Auf der Oberfläche dieser Anode war eine Luggin-Kapillare befestigt, die über einen Stromschlüssel mit einer Silber/Silberchlorid-Referenzelektrode Verbindung hatte. Als Kathode wird eine Kupferelektrode verwendet. In den Kathodenraum wurde wässrige, 5 Gew.-%ige Schwefelsäure als Katolyt gegeben. Als Anolyt wurde eine 20 Gew.- %ige wässrige Lösung der Leukoverbindung des Farbstoffs mit CI N°. 42 090 verwendet. (Der Leukofarbstoff wurde durch Kondensation aus o-Sulfobenzaldehyd und N-Ethylsulfobenzylanilin gewonnen). Der Anolyt wurde im Kreislauf mit einer mittleren Geschwindigkeit von ungefähr 0,5 m/s durch den Anodenraum gepumpt und bei einer Stromdichte von 0,6 KA/m2 elektrolysiert. Die Elektrolyse erfolgte bei einer Zellspannung von 3,5 V bei Temperaturen zwischen + 25 und + 32 °C. Das Anodenpotential betrug zu Beginn der Elektrolyse etwa s = 1 020 mV. Nach einem theoretischen Stromangebot von 120 %, bezogen auf die eingesetzte Leukoverbindung, stieg das Potential auf etwa s = 1 050 mV an. Zu diesem Zeitpunkt wurde die Elektrolyse abgebrochen und der Elektrolyt aufgearbeitet. Die Sauerstoffüberspannung betrug bei diesem Punkt 0 mV.In an electrolytic cell divided by a cation exchange membrane, a titanium flat profile electrode was used as the anode, which was surface-doped with a non-stoichiometric tantalum-iridium mixed oxide and had an intermediate titanium suboxide layer. A Luggin capillary was attached to the surface of this anode and was connected to a silver / silver chloride reference electrode via a current key. A copper electrode is used as the cathode. Aqueous, 5% by weight sulfuric acid was added to the cathode compartment as the catholyte. A 20% by weight aqueous solution of the leuco compound of the dye with CI N ° was used as the anolyte. 42 090 used. (The leuco dye was obtained by condensation from o-sulfobenzaldehyde and N-ethylsulfobenzylaniline). The anolyte was circulated through the anode compartment at an average speed of approximately 0.5 m / s and electrolyzed at a current density of 0.6 KA / m 2 . The electrolysis was carried out at a cell voltage of 3.5 V at temperatures between + 25 and + 32 ° C. The anode potential at the start of the electrolysis was approximately s = 1 020 mV. After a theoretical power supply of 120%, based on the leuco connection used, the potential rose to about s = 1 050 mV. At this point the electrolysis was stopped and the electrolyte was worked up. The oxygen overvoltage was 0 mV at this point.

Bezogen auf den eingesetzten Leukofarbstoff wurde 99 %iger reiner Farbstoff (CI N°. 42 090) mit den folgenden Daten erhalten :

  • xmax : 631 nm in 0,02 m Ammoniumacetatlösung.
Based on the leuco dye used, 99% pure dye (CI N °. 42 090) was obtained with the following data:
  • xmax: 631 nm in 0.02 m ammonium acetate solution.

Bei Verwendung von Titananoden, die mit Lithiumplatinat und nicht stöchiometrischen Tantaloxid-Iridiumoxid-Gemischen dotiert waren, wurden ähnliche Ergebnisse erzielt.Similar results were obtained using titanium anodes doped with lithium platinum and non-stoichiometric tantalum oxide-iridium oxide mixtures.

Beispiel 2Example 2

In einer Elektrolysezelle mit Anolyten und Katolyten wie in Beispiel 1 wurde eine Lösung des Leukofarbstoffs mit Cl N°. 42 090 mit verschiedenen theoretischen Stromangeboten elektrolysiert. In Abhängigkeit von den Stromangeboten bezogen auf den angewandten Leukofarbstoff wurden folgende Ausbeuten an Farbstoff (CI N°. 42 090) erhalten :

Figure imgb0001
In an electrolytic cell with anolytes and catolytes as in Example 1, a solution of the leuco dye with Cl N °. 42 090 electrolyzed with various theoretical currents. Depending on the electricity supply based on the leuco dye used, the following were: Yields of dye (CI N °. 42 090) obtained:
Figure imgb0001

Beispiel 3Example 3

In einer Elektrolysezelle mit Anolyten und Katolyten wie in Beispiel 1 wurde eine Lösung des Leukofarbstoffs aus Beispiel durch Variation der Stromdichte und damit bei unterschiedlichen Anodenpotentialen elektrolysiert. Bei diesen Versuchen ergaben sich in Abhängigkeit von den Anodenpotentialen und Überspannungen folgende Stromausbeuten für den Blaufarbstoff mit CI N°. 42 090 :

Figure imgb0002
In an electrolytic cell with anolytes and catolytes as in Example 1, a solution of the leuco dye from Example was electrolyzed by varying the current density and thus at different anode potentials. In these tests, depending on the anode potentials and overvoltages, the following current yields for the blue dye with CI N ° resulted. 42 090:
Figure imgb0002

Eine Überspannung von > 400 mV und eine Stromausbeute < 90 % führte zu coloristisch nicht mehr verwendbarem Farbstoff.An overvoltage of> 400 mV and a current efficiency <90% led to coloristically no longer usable dye.

Beispiel 4Example 4

Die Elektrolyse erfolgte wie in Beispiel 1 angegeben, jedoch wurde dem Anolyten zusätzliche 4 Gew.- % Schwefelsäure zugesetzt. Es wurde mit einer Stromdichte von 0,5 KA/m2 bei einem Potential von ε = 1 050 mV bis zu dem 1,2-fachen des erforderlichen elektrochemischen Äquivalentes elektrolysiert. Die Zellspannung betrug bei + 25 °C etwa 3,0 Volt. Die Sauerstoffüberspannung betrug bis Ende 200 mV. Bezogen auf den eingesetzten Leukofarbstoff wurde 99 %iger reiner Farbstoff (CI N°. 42 090) erhalten.The electrolysis was carried out as described in Example 1, but an additional 4% by weight of sulfuric acid was added to the anolyte. Electrolysis was carried out with a current density of 0.5 KA / m 2 at a potential of ε = 1 050 mV up to 1.2 times the required electrochemical equivalent. The cell voltage was approximately 3.0 volts at + 25 ° C. The oxygen overvoltage was 200 mV until the end. Based on the leuco dye used, 99% pure dye (CI N °. 42 090) was obtained.

Beispiele 5 bis 9Examples 5 to 9

Die Oxidation erfolgte wie in Beispiel 1 angegeben, jedoch wurden die in der Tabelle angegebenen Leukofarbstoffe verwendet. Die entsprechenden Farbstoffe wurden in hohen Ausbeuten, guter Reinheit und guten coloristischen Eigenschaften erhalten.The oxidation was carried out as indicated in Example 1, but the leuco dyes indicated in the table were used. The corresponding dyes were obtained in high yields, good purity and good coloristic properties.

(Siehe Tabelle Seite 5 f.)

Figure imgb0003
(See table on page 5 f.)
Figure imgb0003

Claims (6)

1. A process for the preparation of a water-soluble diaminotriphenylmethane dye containing from 2 to 4 sulfo groups by anodic oxidation of the leuco compound in an electrolysis cell which is divided into two compartments, wherein the leuco compound is subjected to anodic oxidation at an oxygen overvoltage of < 400 mV at a pH of < 4, in the presence or absence of mineral acid anions carrying oxygen atoms.
2. A process as claimed in claim 1, wherein the leuco compound of the dye with CI N°. 42 090 is oxidized.
3. A process as claimed in claim 1, wherein sulfate or phosphate is used as the mineral acid anion.
4. A process as claimed in claim 1 or 2 or 3, wherein the anodic oxidation of the leuco compound is carried out at a pH of 0.1-3.
5. A process as claimed in claim 1 or 2 or 3 or 4, wherein the anode material used is titanium which has been doped with electrically conductive non-stoichiometric oxidic compounds of tantalum and iridium or with electrically conductive compounds of the platinum group metals, which contain non-stoichiometric titanium, niobium and/or tantalum oxides, or is graphite which has been anodically oxidized on the surface in nitric and has been doped with molybdenum(VI), tungsten(VI) and/or vanadium(V) compounds.
6. A process as claimed in claim 1 or 2 or 3 or 4 or 5, wherein an anion or cation exchange membrane is used to separate the anode space from the cathode space.
EP86104339A 1985-04-13 1986-03-29 Anodic oxidation process of water soluble leucotriphenyl methane dye compounds Expired EP0198303B1 (en)

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DE19853513246 DE3513246A1 (en) 1985-04-13 1985-04-13 METHOD FOR ANODICALLY OXIDATING WATER-SOLUBLE LEUKOTRIPHENYLMETHANE DYE COMPOUNDS
DE3513246 1985-04-13

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JP2696565B2 (en) * 1988-10-28 1998-01-14 日本化薬株式会社 Electrolytic production of triphenylmethane dye.
JPH03107489A (en) * 1989-09-20 1991-05-07 Nippon Kayaku Co Ltd Production of xanthene dye by electrolysis
CN111763432B (en) * 2020-07-03 2021-08-10 浙江亿得新材料股份有限公司 Clean production method of brilliant blue dye

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