EP0060437A1 - Electrochemical process for producing benzanthrones and planar polycyclic aromatic oxo compounds - Google Patents

Abstract

An electrochemical process for the production of benzanthrones and planar polycyclic aromatic oxy compounds is described. The process is carried out in acidic medium in an electrolysis cell separated by a diaphragm in the cathode and anode compartments. In the cathode compartment, anthraquinone or an anthraquinone derivative is electrolytically reduced to oxanthrone and this is converted with glycerin to the corresponding benzanthrone. In the anode compartment, a transition metal ion is simultaneously electrolytically transferred from the lower to the next higher oxidation state. The higher-value metal ion then serves as an oxidizing agent in the anolyte, with which the corresponding oxy compounds are obtained starting from planar polycyclic aromatic compounds.

Description

The present invention relates to an electrochemical redox process which is carried out in an electrolysis cell separated by a diaphragm in the cathode and anode compartments, cathodic benzanthrones and simultaneously anodically planar polycyclic aromatic oxy compounds being produced.

The oxy compounds obtainable according to the present invention have hitherto often been produced by means of reduction or oxidation reactions, in which heavy metals or heavy metal salts of higher value are frequently used as industrial reducing or oxidizing agents. After working up, diluted metal salt solutions remain, the disposal of which poses considerable ecological problems.

For example, metals such as iron, zinc, aluminum or copper in concentrated sulfuric acid are used for the reductive conversion of anthraquinone into the semiquinone form. Such processes are described, inter alia, in US Pat. No. 1,896,147 (reducing agent Fe), US Pat. No. 2,034,485 and USSR Patent 401,130 (reducing agent Fe and Cu), AM Lahin, Zhur. Obschei Khim. 18, 308 (1948), see. CA 44, 1079b (reducing agent Zn, Al, CuS0 ₄ ) and U.S. Patent 1,791,309 (reducing agent Zn and Al). Of these, iron has gained the greatest practical importance as a reducing agent. However, the use of iron as a reducing agent has major economic and ecological disadvantages, since at least 2 moles of iron must be used per mole of anthraquinone. This means that, for example, 2.0 moles of iron sulfate per mole of benzanthrone produced or at least 1320 g of iron sulfate per 1000 g of benzanthrone produced are produced as waste products. In addition, large amounts of waste sulfuric acid are produced, because in order to isolate the benzanthrone formed, the sulfuric acid has to be diluted to approx. 20%, which then either has to be regenerated to concentrated sulfuric acid in an energy-intensive manner or whose removal is also an environmental problem.

The oxidation of polycyclic aromatics has been carried out in many cases using higher-quality metal salts in an acidic medium. After the reaction, the organic solution is separated from the reduced metal salt, the reaction solution is strongly diluted with water, the organic product is filtered off or extracted with solvent, the removal of the waste acid together with the dissolved metal salt also causing considerable ecological problems.

For example, the production of 500 kg of dihydroxyviolanthrone produces 1200 kg of MnS0 ₄ in approx. 30,000 kg of 10% sulfuric acid. The processing of this mixture is uneconomical, so that only the plastering of the sulfuric acid and the landfill of the plaster remains.

The environmentally friendly electrochemical reaction procedure represents an alternative to the use of environmentally harmful reducing or oxidizing agents.

For example, the following electrochemical process for producing benzanthrone, starting from anthraquinone and glycerol, is known from European patent application 22062. Anthraquinone is reduced cathodically in an electrolytic cell in an acidic medium and thereby changes into the semiquinone form, the oxanthrone, which reacts with glycerol to form benzanthrone in a ring closure.

However, the oxidation potential of the anode is not used in this method.

The object of the invention is therefore to develop an electrochemical redox process which couples the already known reduction reaction taking place at the cathode with an oxidation reaction taking place simultaneously at the anode.

An electrochemical process for the preparation of benzidine from azoxybenzene and of anthraquinone from anthracene is known from US Pat. No. 1,544,357. Azoxybenzene is converted cathodically and anthracene anodically to the product mentioned. Both reactions take place simultaneously, in the electrolysis cell separated by a diaphragm in the cathode and anode space. The Electrolysis cell contains sulfuric acid in which a Cr-III salt is dissolved on the cathode side and a Cr-III or Cr-VI salt on the anode side.

Although this known electrochemical process relates to the simultaneous implementation of cathodic reduction and anodic oxidation, it cannot be used to solve the present problem, since it has been shown that the benzanthrone synthesis is inhibited by Cr-III ions. Furthermore, when using sulfuric acid at a concentration above 75% as the anolyte, the oxidation of Cr-III to Cr-VI described in the US patent could not be reworked.

Surprisingly, it has been shown that benzanthrone on the cathode side and polycyclic aromatic oxy compounds, such as dioxoviolanthrone on the anode side, are obtained even without the use of metal salts in the cathode compartment. I.e. with simultaneous use of the electrochemical potential of the anode and the cathode, the use of metal ions in the cathode compartment can be dispensed with in the present case. Furthermore, transition metal ions, e.g. of the elements manganese, cerium or cobalt proved to be suitable.

elektrochemisch in die Semichinonform überführt und diese mit Glyzerin zum Benzanthron der Formel

umsetzt, wobei die Benzolringe A und B substituiert sein können und gleichzeitig im Anodenraum die Kationen eines Uebergangsmetallsalzes von der niederen in eine höhere Oxidationsstufe überführt und diese Metallionen zur chemischen Oxidation von planaren polycyclischen aromatischen Verbindungen zu den entsprechenden Oxyverbindungen verwendet. Die Produkte werden nach beendeter Elektrolyse aus dem Katholyten und Anolyten isoliert.The process according to the invention thus consists in the simultaneous production of benzanthrones and polycyclic planar aromatic oxy compounds electrochemically by working in an electrolysis cell which contains an acid and is separated by a diaphragm into a cathode and an anode compartment, an anthraquinone of the formula being used in the cathode compartment

electrochemically converted into the semiquinone form and this with glycerin to the benzanthrone of the formula

implemented, the benzene rings A and B can be substituted and at the same time the cations of a transition metal salt in the anode space from the lower to a higher oxidation state and uses these metal ions for the chemical oxidation of planar polycyclic aromatic compounds to the corresponding oxy compounds. After the electrolysis has ended, the products are isolated from the catholyte and anolyte.

Unsubstituted anthraquinone is preferably used as the starting material for the production of benzanthrones in the cathode compartment, which are important as vat dye intermediates, but also those anthraquinones whose rings A and B have one or more of the following substituents: alkyl (C _l -C _4), such as methyl or ethyl, furthermore alkoxy (C ₁ -C _4), such as the methoxy, ethoxy, n-and iso-propoxy and n-, iso- and tert . -Butoxy residue; Finally, the hydroxyl group and the halogen atoms, such as chlorine, bromine and iodine, come into consideration as substituents.

Polycyclic planar aromatic compounds which correspond to the present invention in the anode compartment appropriate oxy compounds are, for example, those of the anthraquinone, benzanthrone and pyrene series. Such starting compounds can also have, for example, alkyl side chains which are terminally oxidized to the aldehyde or to the acid.

An example of the chemical oxidative reaction in the anode compartment is the conversion of 4,4'-bibenzanthrone to dioxoviolanthrone.

Dioxoviolanthrone can easily be reduced to dihydroxyviolanthrone, an important intermediate for the synthesis of vat dyes. It is advantageous for the recycling of the anolyte to carry out the reduction of dioxoviolanthrone to dihydroxyviolanthrone with SO _Z gas.

It is surprising that these large, poorly soluble aromatic molecules, such as the 4,4'-bibenzanthron or violanthron, can be easily oxidized using the new process. The oxidation can be carried out either directly in the anode compartment with a smaller than stoichiometrically required amount of metal salt, or preferably separately from the anode compartment with an anolyte solution containing more than the stoichiometric amount of metal salt as the oxidizing agent.

Any cell with a diaphragm can be selected as the electrolysis cell, the diaphragm being acid-resistant and concentrated and dilute mineral acid, such as sulfuric acid, phosphoric acid, and against organic acids, such as acetic acid. Materials from which the diaphragm is made are, for example, glass, clay, porous polytetrafluoroethylene or polymeric perfluorinated hydrocarbons in the form of an ion exchange membrane. The pore size of the diaphragm is in the range of 1 to 300 u.

You can work in a protective gas atmosphere in the cathode compartment so that there is no oxidative reaction. It is sufficient if the reaction vessel is slightly above the level, e.g. with nitrogen.

Suitable cathodes are the materials customary for electrochemical reactions, such as metals, metal alloys, activated metals, metal oxide electrodes, carbon electrodes, or electrodes made of glass-like sintered carbon.

As anode platinum, electrodes made of sintered carbon and Pb0 ₂ on titanium. The latter is particularly suitable for in situ reactions in the anode compartment.

The acidic reaction medium in particular mineral acids having a _pK a <2, such as sulfuric or phosphoric acid. Sulfuric acid with a concentration of 60 to 98% and especially a concentration of 80 to 95% is particularly suitable.

In addition to the acid, the electrolyte can also contain reaction-inert organic solvents as solubilizers.

The electrochemical synthesis takes place at a temperature between 50 and 150 ° C. Because of the solubility or However, in order to be able to work in technically interesting concentrations, operating temperatures in the range from about 80 to 120.degree. C., but in particular 90 to 105.degree. C., must be selected for suspending the quinoid compounds formed as an intermediate stage, for example in sulfuric acid electrolyte.

• Me = Metallion,
• n+x = Ladungszahl, wobeix = 1 bis 5, vorzugsweise jedoch 1 ist,
• e = Elektron,
• d.h. Metallionen werden an der Anode von einer niedrigen in die höhere Oxidationsstufe überführt.

The oxidation of planar polycyclic aromatic compounds to the corresponding oxy compounds takes place in the anolyte by means of transition metal ions, the oxidation potential of which in acidic solution is at least 10.5 volts. The metal ions thus serving as the oxidizing agent are generated in the anode compartment electrolytically according to the following scheme:

• Me = metal ion,
• n + x = number of charges, whereix = 1 to 5, but preferably 1,
• e = electron,
• ie metal ions are transferred from a low to a higher oxidation state at the anode.

gemessen gegen Wasserstoff-Normalelektrode.Transition metal redox pairs with an oxidation potential between +0.5 and +2.5 volts are particularly suitable; are mentioned in detail:

measured against hydrogen normal electrode.

In this case, a mixture of two redox pairs can also be present in the anode compartment, one of the two being present in each case in catalytic amounts, namely with molar ratios of 1: 100 to 1: 1000. To be favoured Redox couple mixtures are used in which the component used in lower concentration, namely 1 to 10 mmol per mole of transition metal sulfate, is a silver I salt, for example silver I sulfate, which forms silver II sulfate during the reaction at the anode is oxidized. The addition of catalytic amounts of silver salt increases the yield when the transition metal salt is converted to its higher valence level. In the case of the oxidation of manganese II to manganese III, the yield of manganese III can be increased by 20 to 50%, depending on the current density.

The electrochemically produced, higher-quality transition metal ions react in situ with the planar, polycyclic, aromatic compound dissolved in the anolyte and oxidize them to the corresponding oxy compounds, go back to the lower valence level even by taking up electrons, are finally reoxidized at the anode and stand again ready as an oxidizer. In this way, the oxidizing agent is conducted in a cyclic process, therefore a less than stoichiometric amount is sufficient to oxidize the organic starting compound in the anode compartment.

In a preferred variant of the method according to the invention, the anode compartment contains no organic compound in addition to the metal salt or salt mixture when current is passed. In this case, the electrolysis is stopped when the metal salt or the main component of the salt mixture is almost completely converted to the higher valence level. This salt solution or suspension can now be removed from the anode compartment and used in a separate reaction vessel for the oxidation of planar polycyclic aromatics. Since the oxidizing agent used is not regenerated in this case, stoichiometric ratios are required between the oxidizing agent and aromatics.

The oxidant consumed at the end of the chemical oxidation reaction, i.e. the solution of the metal salt now present in the lower oxidation state, after separation of the aromatic oxy compound, clarification by means of activated carbon and concentration, if appropriate, can be returned to the anode compartment and is again electrolytically oxidized here.

The products obtained can be isolated in the usual way from the catholyte, such as anolyte. When using sulfuric acid as the reaction medium, e.g. Diluted to 60%, the precipitated product is filtered off and washed until neutral, or the product is extracted from the 60% sulfuric acid with a commercially available solvent.

After product isolation, the anolyte is concentrated to the original concentration and used in the next oxidation cycle.

However, it can also be oxidized in dilute solution and the oxidized anolyte can then be brought to the original concentration.

For isolation by extraction of the reaction product formed and phase separation, higher-boiling, inert organic solvents, especially halogenated hydrocarbons, but especially chlorobenzenes, such as e.g. Monochlorobenzene, suitable.

The extraction temperature (absorption of the product in the organic solvent) is 70 to 110 ° C, advantageously 90 to 100 ° C.

• a) Kathoden- wie auch Anodenraum werden zur gleichzeitigen Durchführung von Redox-Reaktionen genutzt,
• b) durch die Verwendung von Uebergangsmetallsalzgemischen im Anodenraum wird eine hohe Oxidationsausbeute der Reaktion Meⁿ⁺→ Me (n+x)+ erreicht,
• c) der Anolyt kann nach Abtrennen des aromatischen Oxidationsproduktes, gegebenenfalls Reinigung und Aufkonzentrierung erneut verwendet werden und verursacht somit keine ökologischen Probleme.

The main advantages of the method according to the invention are as follows:

• a) cathode and anode compartments are used for simultaneous redox reactions,
• b) a high oxidation yield of the reaction Me ^{n +} → Me (n + x) + is achieved by using transition metal salt mixtures in the anode compartment,
• c) the anolyte can be reused after separating the aromatic oxidation product, if necessary cleaning and concentrating, and thus does not cause any ecological problems.

The invention is illustrated by the following examples.

example 1

46.8 g of anthraquinone (0.225 mol) are dissolved in 1300 g of 88% strength sulfuric acid on the cathode side in an electrolysis apparatus with a carbon cathode, Pt anode and sound diaphragm, and 31.05 g of glycerol are added dropwise during the electrolysis.

The anode side of the electrolysis cell contains 130 g of 88% strength sulfuric acid, in which 10 g of MnSO ₄ .H ₂ O (0.059 mol) are suspended. At 95 ° C 51 700 coulombs are used for electrolysis (3.5 V, 3A, 5 h).

After precipitation from the catholyte and sublimation of the crude benzanthrone, 44.0 g of benzanthrone, mp. 171-173 ° C., are isolated. This corresponds to a yield of 85% of theory with a cathodic current yield of 71.4%.

After the electrolysis has ended, the anolyte is poured into a beaker, 10.0 g (0.021 mol) of 4,4'-bibenzanthrone are added, and the reaction mixture is stirred at 30 ° C. for 4 hours. The dioxoviolanthrone formed is reduced in situ by dropwise addition of 400 ml of 40% sodium bisulfite solution to dihydroxyviolanthrone. The dihydroxyviolanthrone precipitate is finally filtered off, washed and dried.

Yield of dihydroxyviolanthrone 11.0 g = 76.4% of theory

der durch Methylierung von Dihydroxyviolanthron erhalten wird.Dihydroxyviolanthrone serves as an intermediate for the synthesis of the vat dye of the formula

which is obtained by methylation of dihydroxyviolanthrone.

The yield is approximately 99.5% when electrochemically represented dihydroxyviolanthrone is used.

Examples 2 to 5

As described in Example 1, the following substituted anthraquinones are first electrochemically converted to the semiquinone form in the same electrolysis cell instead of anthraquinone, which reacts in situ with glycerol to give the corresponding substituted benzanthrone.

Example 6

In an electrolysis apparatus with a carbon cathode, an anode made of sintered carbon and a clay diaphragm, 88.8% of 88.8% anthraquinone (0.225 mol) are dissolved in 1300 g of sulfuric acid on the cathode side, and 31.05 g of glycerin are added dropwise when the current is passed through.

The anode side of the electrolysis cell also contains 1300 g of 88% strength sulfuric acid, in which 100 g of MnSO ₄ .H ₂ O (0.59 mol) are suspended. At 95 ° C 51 600 coulombs are used for electrolysis (3.5 V, 3 A, 5 h).

After precipitation from the catholyte and sublimation of the crude benzanthrone, 37.08 g of benzanthrone, mp. 171-173 ° C., are isolated. This corresponds to a yield of 71.6% of theory with a cathodic current yield of 60%.

After the electrolysis has ended, the anolyte is used as described in Example 1 for the oxidation of 4,4'-bibenzanthrone.

Examples 7 to 13

If one works as described in Example 6, but the anthraquinone / glycerol ratio varies in the catholyte and the cation pair on the anode side and a platinum electrode is used as the anode, the following results are obtained with regard to the benzanthrone yield:

Example 14

In the electrolysis apparatus as described in Example 1, a Ti / Pb0 ₂ anode is used instead of a Pt anode.

The clay diaphragm is replaced by an ion exchange membrane made of perfluorinated polymeric hydrocarbons. The cathodic reaction and the anodic reaction take place simultaneously.

The cathodic benzanthrone synthesis proceeds as described in Example 5. Yield benzanthrone sublimates 83.5% of theory Mp 170-172 ° C.

In the anode compartment, 130 g of H ₂ S0 ₄ 88% i ^g 2 ^{g of} MnSO4 .H ₂ O are dissolved and, shortly after the start of the electrolysis, the colorless solution has changed to pale violet (Mn ²⁺ → Mn ³⁺ ), 5 g 4,4'-Bibenzanthron (0.011 mol) dissolved in the 95 ° C anolyte. After passing 51500 coulombs

(7.5 V, 2 A, 7.5 h) the electrolysis is stopped. Current yield 70.2% of theory The anolyte is diluted to 60% with water and the dioxoviolanthrone formed is filtered off, washed neutral and dried. Yield 2.1 g = 39.28% of theory

Dioxoviolanthrone can be reduced to dihydroxyviolanthrone as usual.

Example 15

46.8 g of anthraquinone (0.225 mol) are dissolved in 1300 g of sulfuric acid in 1300 g of sulfuric acid in an electrolysis apparatus with a carbon cathode, Pt anode and sound diaphragm on the cathode side, and 31.05 g of glycerol are added dropwise when the current is passed through.

The anode side of the electrolytic cell contains 600 g of 88% sulfuric acid, in which 80 g of MnSO ₄ .H ₂ O (0.47 mol) and 0.62 g of Ag ₂ S0 ₄ (2 mmol) are suspended or dissolved.

At 95 ° C, 51700 coulombs are used for electrolysis (3.5 V, 3 A, 5 h).

After precipitation from the catholyte and sublimation of the crude benzanthrone, 44 g of benzanthrone, mp. 171-173 ° C., are isolated. This corresponds to a product yield of 85% of theory and a current efficiency of 71%.

After the electrolysis has ended, 25 g (0.055 mol) of 4,4'-bibenzanthrone are added and the mixture is stirred at 30 ° C. for 4 hours. After dilution of the reaction mass with 640 ml of water, the dioxoviolanthrone formed is reduced in situ by introducing 2.24 liters of SO ₂ (0.1 mol) at 60 ° C. to dihydroxyviolanthrone. The dihydroxyviolanthrone precipitate is filtered off, washed and dried. Yield of dihydroxyviolanthrone 24.1 g = 90% of theory (0.049 mol) with a total current yield of 73.4%.

Example 16

In 145 ml of anolyte containing 0.086 mol of Mn ³⁺ , 5.02 g (titer 90%) of bibenzanthrone are added within 1 hour and the mixture is left to react at 30 ° C. for 1½ hours (conversion of Mn ³⁺ → Mn ²⁺ = 85%) . Then 145 ml of water are added to the reaction mixture, the mixture is heated to 60 ° C. and 5.36 g of S0 _{2 are} gasified with stirring within 45 minutes, of which 0.694 g are used to reduce the dioxoviolanthrone formed. The reaction mixture is heated to 90 ° C. for 2 hours and excess SO _{2 is} blown out with nitrogen.

The reaction product is filtered through a frit and the mother liquor is concentrated again in vacuo (1 to 5 mm Hg). The reaction product is washed neutral with water and dried. Yield of dihydroxyviolanthrone 4.85 g = 90.67% of theory

Yield concentrated mother liquor 116 ml containing 198.4 g H ₂ SO ₄ and Mn ²⁺ . The mother liquor is made up to 145 ml with 98% H ₂ SO ₄ and water, filled into the anode compartment and the anodic oxidation cycle is repeated.

After 5 cycles, after separating off the product, the Mn-II-containing sulfuric acid is purified by adding 1 g of activated carbon, then heating to 40 ° C. and filtration. The clarified anolyte is light yellow again and can be used in further oxidation cycles after concentration.

The current efficiency of the reoxidation of the manganese-II to manganese-III sulfate is influenced positively by catalytic amounts of silver ions and is also dependent on the current density and the degree of conversion.

Example 17

In the electrolysis apparatus as described in Example 1, a Ti / Pb0 ₂ anode is used instead of a Pt anode. The clay diaphragm is replaced by an ion exchange membrane made of perfluorinated polymeric hydrocarbons. The cathodic reaction and the anodic reaction take place simultaneously in the electrolytic cell.

The cathodic benzanthrone synthesis proceeds as described in Example 1. Yield benzanthrone sublimates 81.5% of theory, mp. 171-172 ° C, cathodic current efficiency 68.4% of theory

In the anode compartment are dissolved in 130 g H ₂ SO ₄ 88% i ^g 2 ^g MnSO ₄ · H ₂ O and after the colorless solution has changed to pale violet (Mn ²⁺ → _Mn ³⁺ ) shortly after the start of the electrolysis, 2 g tetrachloropyrene (0.0058 mol) dissolved in the 95 ° C anolyte. After passing 51600 Coulomb (7.0 V, 4 A, 4 h), the electrolysis is stopped.

The anolyte is diluted with water to 50% H ₂ SO ₄ and the solid residue is filtered off, washed neutral and dried. Yield raw, after drying: 2.4 g.

According to mass spectrometric analysis, this dry residue contains the product naphthalene tetracarboxylic anhydride, naphthalene tetracarboxylic acid, and some starting material, tetrachloropyrene.

Example 18

As described in Example 1, in an electrolysis apparatus with carbon cathode, Pt anode and sound diaphragm on the cathode side 1300 g H ₂ SO ₄ 88% with 88.8 g anthraquinone and after dissolving the anthraquinone and applying a voltage of 3, 5 V, 31.05 g of glycerin added dropwise.

The anode side of the electrolytic cell contains 130 g of 88% strength sulfuric acid, in which 10 g of MnSO ₄ .H ₂ O are suspended.

At 95 ° C, 51900 coulombs are used for electrolysis (3.5 V, 3 A, 5 h).

Yield after working up the cathode compartment: benzanthrone 79.4% of theory, mp. 173-174 ° C. The cathodic current yield is 83.7% of theory

A portion of 14.0 g = 0.04 mol of tetrachloropyrene is added to the anolyte and the mixture is stirred at 30 ° C. for 6 hours. The product formed is diluted with 300 ml of water, suction filtered, washed neutral and dried.

Yield raw, after drying: 13.5 g.

According to mass spectrometric analysis, the dry residue contains naphthalene tetracarboxylic anhydride in addition to small amounts of starting material.

Example 19

200 g of sulfuric acid 90%, containing 0.09 mol of Mn-III sulfate, obtained by electrochemical oxidation of Mn-II sulfate according to Example 6, are mixed with 1.54 g (0.01 mol) of acenaphthene at room temperature while stirring, with a temperature increase of 2 ° C. After stirring for 5 hours at room temperature, the reaction mixture is diluted to a sulfuric acid concentration of 55% and the insoluble organic residue is filtered off with suction. The filter cake is washed with water and dried.

Yield of raw substance: 1 g (after drying)

The mass spectrometric analysis shows that the dry residue contains 1,8-naphthalenedicarboxylic acid anhydride.

Example 20

If, instead of acenaphthene, 1.28 g (0.01 mol) of naphthalene is used and the procedure is otherwise as described in Example 19, 0.5 g of a dry residue is obtained in which phthalic anhydride can be detected by mass spectroscopy.

Example 21

10 g (0.03 mol) of _L malachite green eukobase be 0.09 mol Mn-III-sulphate, dissolved in 200 g of sulfuric acid 90% as described in Example 19 oxidized. - The sulfuric acid Mn-III sulfate solution was obtained by electrochemical oxidation of Mn-II sulfate, according to Example 6.

The solution darkens within 10 minutes and the temperature rises to 53 ° C. The oxidation is complete after 1.5 hours and the undiluted 90% sulfuric acid is filtered off with a glass frit; 54.4 g of MnS0 ₄ xn H ₂ SO ₄ , moist, are recovered. The mother liquor will diluted to 55% sulfuric acid and this solution adjusted to pH 3 with 30% NaOH. Malachite green precipitates in dark green shiny crystals of the composition C ₂₃ H ₂₅ N ₂ ⁽⁺⁾ . (SO ₄ ^{2 -) /} ₂ xn Na ₂ SO ₄ .

Yield dried: 19 g

Claims (20)

1. Electrochemical process for the production of benzanthrones and planar polycyclic aromatic oxy compounds, characterized in that one works in an electrolysis cell which contains an acid and is separated by a diaphragm into a cathode and an anode space, an anthraquinone of the formula being used in the cathode space

electrochemically converted into the semiquinone form and this with glycerin to the benzanthrone of the formula

converts, where the benzene rings A and B can be substituted and at the same time the cations of a transition metal salt in the anode space from a lower to the higher oxidation state; these metal ions are used for the chemical oxidation of planar polycyclic aromatic compounds to the corresponding oxy compounds and the products formed are isolated from the catholyte and anolyte. 2. The method according to claim 1, characterized in that one starts from anthraquinones, the rings A and B of which have one or more of the following substituents, alkyl (C ₁ -C ₄ ), alkoxy (C ₁ -C ₄ ), hydroxy or halogen . 3. The method according to claim 1, characterized in that cathodically reduced anthraquinone to oxanthrone and this is reacted with glycerol with ring closure to benzanthrone. 4. The method according to claim 1, characterized in that in the anolyte during or after the electrolysis 4,4'-bibenzanthron is converted chemically oxidatively into dioxoviolanthrone. 5. The method according to claim 1, characterized in that one uses an electrolysis cell with a diaphragm with a pore size of 1 to 300 µ. 6. The method according to claim 1, characterized in that mineral acids with a pK _s <2 are used. 7. The method according to claim 6, characterized in that sulfuric acid concentration 60 to 98%, preferably 80 to 95%, is used. 8. The method according to claim 1, characterized in that one works at temperatures between 50 to 150 ° C, preferably 80 to 120 ° C, in particular 90 to 105 ° C. 9. The method according to claim 1, characterized in that anodically oxidizing transition metal ions and thus redox pairs with a potential of +0.5 to +2.5 volts are obtained. 10. The method according to claim 9, characterized in that one of the following redox pairs is present in the anode compartment: _Mn ²⁺ / _Mn ³⁺ , _Ce ³⁺ / _Ce ⁴⁺ , _Co ²⁺ / _Co ³⁺ , _Ag + / _Ag 2+. 11. The method according to claim 10, characterized in that the anode compartment contains manganese-II sulfate, which is oxidized to manganese-III sulfate during the electrolysis. 12. The method according to claim 10, characterized in that a mixture of two redox pairs in a molar ratio of 1: 100 to 1: 1000 is present in the anode compartment. 13. The method according to claim 1, characterized in that one carries out the anodic oxidation in the presence of catalytic amounts of a silver (I) salt, preferably silver I-sulfate, in a concentration of 1 to 10 mmol per mole of transition metal salt. 14 .. The method according to claim 1, characterized in that to carry out the chemical reaction, the contents of the cathode and anode compartment after the electrochemical redox reaction is transferred from the electrolytic cell into separate reactor vessels. 15. The method according to claim 14, characterized in that the anolyte used in the chemical oxidation reaction is cleaned, concentrated and returned to the anode compartment of the electrolytic cell, where the transition metal ions are again electrochemically oxidized. 16. The method according to claim 1, characterized in that anthraquinone is reduced cathodically in 80 to 90% sulfuric acid and at the same time glycerol is added in a molar ratio of 1: 1.1 to 1: 2, after the reaction has ended, the sulfuric acid is diluted to 60% and that fancy benzanthrone isolated. 17. The method according to claim 1, characterized in that anodically in 80- to 90% sulfuric acid, manganese-II-sulfate is oxidized in the presence of 4,4'-bibenzanthrone to manganese-III-sulfate, which acts in situ as an oxidizing agent and 4,4'-Bibenzanthron converted into dioxoviolanthron. 18. Process according to claims 1, 14 and 15, characterized in that manganese-II- is oxidized anodically in 80- to 90% sulfuric acid to manganese-III-sulfate, then the anolyte in a separate reactor vessel for the oxidative conversion of 4 , 4'-Bibenzanthron in Dioxoviolanthron used and the anolyte after isolation of the product for reoxidation in the anode compartment. 19. Process for working up the products, characterized in that either the mineral acid electrolyte is diluted and the precipitated product is isolated or the product is extracted from the dilute acid electrolyte by means of organic solvents and isolated by customary methods. 20. The benzanthrones and planar polycyclic aromatic oxy compounds prepared according to the reaction of claim 1.