EP0000495B1 - Process for the preparation of 1-amino-8-hydroxy naphthalene-3,6-disulphonic acids (h-acids). - Google Patents

Description

The present invention relates to a process for the preparation of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) as the monoalkali salt from 1-naphthylamino-3,6,8-trisulfonic acid by alkaline pressure hydrolysis.

1-Amino-8-naphthol-3,6-disulfonic acid, which is often also referred to as H-acid, is an important intermediate for the production of dyes (see Ullmanns Enzyklopadie der Technischen Chemie, 3rd edition, 12th volume, p . 621).

From FIAT Final Report No. 1016, pp. 32 to 39 it is known that H-acid can be produced as follows: naphthalene is made with sulfuric acid monohydrate (= 100% H _Z S0 ₄ ) and 65% oleum while maintaining a certain temperature program and stepwise addition of sulfuric acid monohydrate and oleum to a naphthalene-trisulfonic acid isomer mixture, which is nitrated with mixed acid. After dilution with water, expulsion of the nitrous gases and separation of the sulfuric acid as calcium sulfate, the isomer mixture of the nitronaphthalene trisulfonic acids is reduced with iron and then dissolved iron salts are precipitated with magnesium oxide and separated off. By adding rock salt and hydrochloric acid, the acidic calcium sodium salt of T-acid (1-naphthylamine-3,6,8-trisulfonic acid) is precipitated, which is filtered off and washed several times. This salt is added to the washing water and soda is added. Then the chalk that has precipitated is pressed and the salt solution is concentrated. The concentrated trisodium salt solution of the T-acid is reacted with 50% sodium hydroxide solution under pressure. Then sulfuric acid is added first, then water, and finally the H acid is obtained as the monosodium salt by filtration, washing and drying.

In this process, substantial amounts of by-products are formed in the alkaline hydrolysis of T-acid, e.g. 1-amino-6-naphthol-3,8-disulfonic acid, an isomer of H-acid known under the name W-acid, and 1,8-dihydroxy-naphthalene-3,6-disulfonic acid, one under the name Chromotrop Acid known secondary product of H acid. The yield of H acid in the process described above is generally only 70 to 72%, based on the T acid used.

A method has now been found for the preparation of 1-amino-8-naphthol-3,6-disulfonic acid monoalkali salts by reacting 1-naphthylamine-3,6,8-trisulfonic acid and / or its salts and / or naphthylamine-trisulfonic acid. Mixtures of isomers and / or their salts with alkali metal hydroxide solution at elevated pressure and elevated temperature and separation of 1-amino-8-naphthol-3,6-disulfonic acid monoalkali metal salts by acidification, which is characterized in that the reaction in the presence of alcohols and / or alcoholates and in the presence of nitric acid, nitrous acid, nitrogen oxides, nitrates, nitrites, nitro compounds or nitroso compounds.

In the process according to the invention, 1-naphthylamine-3,6,8-trisulfonic acid (T-acid) can be used in pure form and / or in the form of naphthylamine-trisulfonic acid isomer mixtures. The naphthylamine-trisulfonic acid isomer mixtures generally contain more than 65% by weight of 1-naphthylamine-3,6, B-trisulfonic acid, based on the total amount of diazotizable substance. If naphthylamine-trisulfonic acid isomer mixtures are used, preference is given to using those containing 70 to 90% by weight of 1-naphthylamine-3,6-B-trisulfonic acid. A naphthylamine-trisulfonic acid isomer mixture to be used with particular preference contains

Naphthylamine-trisulfonic acid isomer mixtures can contain other products in addition to the naphthylamine trisulfonic acids. Such products can in particular be by-products, decomposition products or unreacted intermediates from the production stages for naphthylamine-trisulfonic acid, for example naphthalene-di-, -tri- and -tetra-sulfonic acids, nitronaphthalene-mono-, -di and -trisulfonic acids, naphthylamine-mono- and disulfonic acids, e.g. 1-naphthylamine-3,6- and -5,7-disulfonic acid, also dinaphthylsulfonic sulfonic acids and their amino and nitrodivatives, and oxidation products of naphthalene and / or naphthalenesulfonic acids, which can be formed during sulfonation and / or nitration.

The 1-naphthylamine-3,6,8-trisulfonic acid or the naphthylamine trisulfonic acid isomer mixtures can be used in free form, in the form of neutral salts or in the form of acid salts will. Mixtures containing free acids and salts can also be used. If all or part of the 1-naphthylamine-3,6,8-trisulfonic acid or the naphthylamine-trisulfonic acid isomer mixtures are present as salts, the alkali and alkaline earth metal salts, in particular the sodium and potassium salts, are preferred.

Suitable 1-naphthylamine-3,6,8-trisulfonic acid or salts of this acid for use in the process according to the invention can be obtained by trisulfonating naphthalene, nitriding the resulting mixture, then reducing the nitro-naphthalene-trisulfonic acid mixture present, the acidic Calcium-sodium salt of the T-acid precipitates, this salt is mixed with soda in solution, the precipitated chalk is pressed out and the salt solution is concentrated. These reactions can be carried out according to the FIAT Final Report procedure described at the beginning or in any other way.

A naphthylamine-trisulfonic acid isomer mixture suitable for use in the process according to the invention can be obtained in a similar manner if the reaction sequence is terminated after the reduction of the nitro-naphthalenetrisulfonic acid mixture has ended.

The 1-naphthylamine-3,6,8-trisulfonic acid and / or its salts and / or the naphthylamine-trisulfonic acid isomer mixture and / or its salts can be, for example, in solid form or as an aqueous solution with a content of, for example, 20 to 50% by weight. -%, preferably 30 to 40% by weight, calculated as the free acid with the molecular weight 383, can be used.

Alkali hydroxide solutions for the process according to the invention are in particular aqueous potassium or sodium hydroxide solution. The use of potassium hydroxide leads to better yields compared to sodium hydroxide solution, but sodium hydroxide solution is generally cheaper. For example, 2.5 to 12 moles of alkali metal hydroxide can be used per mole of diazotizable substance (calculated with a molecular weight of 383 = T acid). The use of 6 to 9 moles of alkali metal hydroxide per mole of diazotizable substance is particularly preferred. The concentration of alkali hydroxide in the reaction mixture can be, for example, 10 to 50% by weight (based on the sum of alkali hydroxide plus water plus alcohol). This concentration is preferably 25 to 35%.

An essential aspect of the process according to the invention is that it is carried out in the presence of alcohols and / or alcoholates and in the presence of nitric acid, nitrous acid, nitrogen oxides, nitrates, nitrites, nitro compounds or nitroso compounds. The alcohols to be added can be added to the reaction mixture, for example in pure form, in a mixture with water or in the form of alcoholates, for example in the form of alkali alcoholates. Suitable alcohols are those alcoholic compounds which are miscible with water under the reaction conditions and which undergo no or only minor undesirable side reactions with strong alkali. In this case, the formation of alcoholate is not an undesirable side reaction. Aliphatic alcohols with, for example, 1-6 carbon atoms are preferred. For example, primary, secondary and tertiary monohydric and polyhydric alcohols can be used, the hydroxyl groups of which can also be wholly or partially etherified. Possible monohydric alcohols include: methanol, ethanol, n-propanol, 2-propanol, n-butanol, iso-butanol, tert-butanol. As polyhydric alcohols are e.g. in question: ethylene glycol, propanediols, butanediols, glycerol, butanetriols; Monoglyme, Digiyme, Of course, mixtures of alcohols can also be used. Methanol is particularly preferably used.

The amount of alcohol or alcoholate to be used can be granted, for example, in such a way that 10 to 80% by weight, preferably 25 to 60% by weight, of alcohol or alcoholate, based on the sum of water plus alcohol, is present.

Examples of suitable nitrogen oxides are N _z 0 ₅ , N ₂ 0 ₄ , N _z 0 ₃ , N0 ₂ and NO, preferably N ₂ 0 ₅ and N ₂ 0 ₄ or N0 ₂ . Suitable nitrates are, for example, alkali metal nitrates, ammonium nitrates, alkaline earth metal nitrates and other metal nitrates, including heavy metal nitrates. Alkali metal nitrates, in particular sodium or potassium nitrate, are preferably used. Examples of suitable nitrites are alkali metal nitrites, in particular sodium nitrite. Examples of suitable nitro compounds are aromatic and aliphatic nitro compounds, such as nitrobenzenes, nitronaphthalenes, nitrobenzenesulfonic acid, nitronaphthalene mono-, di- and trisulfonic acids, nitromethane, nitroethane and nitropropane. Examples of suitable nitroso compounds are nitrosobenzenes.

Preference is given to using compounds which themselves or their secondary products are soluble under the conditions for the precipitation of the H-acid monoalkali salt, such as nitrogen / oxygen acids, nitrogen oxides, nitrates, nitrites and nitro compounds which are soluble in an acid medium. No special precautions need to be taken to separate these additives, since these or their secondary products are then contained in the waste water after the H-acid has been removed as the monoalkali salt.

The process according to the invention is particularly preferably carried out in the presence of sodium nitrate or potassium nitrate.

The additives described above can be introduced into the process according to the invention in pure form or as a solution, for example as a solution in water, aqueous alkali or alcohol. Of course, 2 or more of the additives mentioned can also be used.

In general, it is sufficient if the above-mentioned NO-containing substances are present in small amounts in the reaction mixture. You can, for example, use as much of these substances Introduce into the reaction mixture that, based on 1 mol of 1-naphthylamine-3,6,8-trisulfonic acid or 1 mol of naphthylamine-trisulfonic acid isomer mixture or 1 mol of salts of these acids, there are 0.005 to 1 mol of these substances. These substances are preferably present in an amount of 0.01 to 0.5 mol, in particular in an amount of 0.01 to 0.1 mol (reference as above).

The process according to the invention can be carried out, for example, at temperatures from 150 to 250 ° C., preferably at 180 to 220 ° C., in a closed vessel. The pressure which arises is generally completely sufficient to carry out the process according to the invention in a satisfactory manner. Of course, the method according to the invention can also be carried out with pressures other than those which set themselves in closed vessels. For example, pressures in the range from 5 to 100 bar are possible for the process according to the invention.

The reaction time essentially depends on the reaction temperature and the alkali hydroxide concentration. It is shorter at relatively high reaction temperatures and at relatively high alkali hydroxide concentrations and longer at relatively low reaction temperatures and relatively low alkali hydroxide concentrations and is generally from 10 minutes to 10 hours. For example, good results are obtained at a reaction temperature of approx. 200 ° C. and an alkali hydroxide concentration of 30% by weight with a reaction time of 45-60 minutes.

The substances to be used in the process according to the invention are most conveniently introduced into the reaction vessel at a temperature such that the desired reaction temperature is present after the heat of mixture and optionally the heat of neutralization has been released. The substances to be entered can also be brought together at lower temperatures and heated to the desired reaction temperature in the reaction vessel.

After the reaction has ended and before the H acid has been separated off as the monoalkali metal salt, it is advantageous to cool the reaction mixture and / or to dilute it with water. You can, for example, on. Cool temperatures in the range of 20 to 150 ° C, preferably to temperatures in the range of 80 to 120 ° C '. The amount of water to be added depends on the reaction conditions, e.g. the type of alkali metal hydroxide, its amount and concentration, and the amount of alcohol that may still be present. It is advantageous to choose the amount of water so that the alkali sulfite formed in the reaction is dissolved or remains dissolved.

The H-acid can be separated off as the monoalkali salt by acidifying the reaction mixture with mineral acids.

Sulfuric acid is preferably used for this. Sufficient mineral acid is added to form the sparingly soluble monoalkali salt of H-acid. By appropriate selection of the concentration of the mineral acid and / or by adding water before and / or during the addition of the mineral acid, it is expediently ensured that the inorganic salt which forms, e.g. Sodium sulfate or potassium sulfate, does not fail. Good results can be obtained, for example, if a pH in the range 0 to 4, preferably 0.5 to 2.5, is set for the separation of the H-acid as the monoalkali salt and by dilution with water and / or by appropriate choice of the concentration the mineral acid, based on the weight of the mixture present in the pressure hydrolysis, which brings in 0.1 to 5 times, preferably 0.5 to 2 times the amount of water. The monoalkali salt of the H-acid can be separated off in a customary manner, for example by filtration. Before the monoalkali salt of H-acid is separated off, it is advantageous to set the temperature to less than 80 ° C. by cooling, for example by evaporative cooling, and to carry out the separation at a temperature of less than 80 ° C. The separation is preferably carried out at a temperature in the range from 20 to 60 ° C.

To remove sulfur dioxide completely, it is advantageous, after the precipitation conditions have been set and before the monoalkali salt of the H-acid has been separated off, to reflux the acidified and diluted mixture for some time, for example 0.5 to 2 hours, or to keep it under vacuum or the sulfur dioxide with an inert gas, e.g. Nitrogen to blow out.

The monoalkali salt of H-acid present after the separation is usually washed with water and dried, for example in vacuo.

After the reaction, the alcohol can be separated off at various points during the working up of the reaction mixture. It is possible to separate the alcohol from an alkaline, neutral or acidic solution before or after the H-acid has been separated off as the monoalkali salt. The alcohol is preferably separated from alkaline or neutral solution and by distillation. It is particularly preferred to distill off the alcohol directly from the reaction mixture, optionally after cooling and / or dilution with water, via a column. If low-boiling alcohols, for example methanol, are used, it may be sufficient to start the distillation without external heat input by depressurization. If the alcohol used segregates from the reaction mixture at temperatures lower than the reaction temperature, it is also possible to separate the alcohol by phase separation after the reaction mixture has cooled.

The separated alcohol is preferably reused in the process according to the invention. It is then only necessary, possibly during the alkaline pressure hydrolysis and / or during the Processing to supplement lost alcohol content.

The process according to the invention provides the advantage over the known processes for the preparation of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) as the monoalkali salt that higher yields can be achieved and the formation of by-products, in particular the formation of 1-Amino-6-naphthol-3,8-disulfonic acid (W-acid) and the formation of 1,8-dihydroxynaphthalene-3,6- _. disulfonic acid (chromotropic acid) is significantly reduced. The reduced content of the W-acid, which is sparingly soluble in acidic solution, also means that the monoalkali salt of the H-acid can be isolated in a particularly pure form without intensive washing which is associated with losses in yield.

Examples example 1

• (%-Gehalte jeweils bezogen auf diazotierbare Substanz) das zusätzlich
• 0,3 Gew.-% 1-Naphthylamin-3,6-disulfonsäure-dinatriumsalz,
• 1,3 Gew.-% Naphthalin-1,3,6-trisulfonsäure-trinatriumsalz,
• 0,6 Gew.-% 1-Nitronaphthalin-3,6,8-trisulfonsäure-trinatriumsalz,
• 4,6 Gew.-% Wasser und quantitativ nicht bestimmbare Mengen an Amino- und Nitroderivaten der Dinaphthylsulfonsulfosäuren und an Oxidationsprodukten des Naphthalins und der Naphthalin-trisulfonsäuren enthält,
• 325 g Wasser, 310 g Methanol und
  • a) 8,5 g (0,1 Mol) Natriumnitrat
  • b) 4,2 g (0,05 Mol) Natriumnitrat
  • c) 0,8 g (0,01 Mol) Natriumnitrat
  • c) 6,9 g (0,1 Mol) Natriumnitrit

vorgelegt und auf 210°C aufgeheizt. In einem 1,3 I Stahl-Autoklav werden 474 g 70 gew.-%ige Natronlauge (8,3 Mol NaOH) auf 210°C aufgeheizt und mit Stickstoff quantitativ in den 2,7 I Autoklaven gedrückt, wodurch bezogen auf die Summe Wasser plus Methanol eine 30 gew.-%ige Natronlauge entsteht. Dabei stellt sich eine Temperatur von 220°C ein. Die Reaktionsmischung wird 20 Minuten bei 220°C gehalten, so schnell wie möglich abgekühlt, mit ca. 500 g Wasser verdünnt, das Methanol über eine Kolonne abdestilliert und das vom Methanol befreite Reaktionsgemisch durch Hochdruck-Flüssigkeits-Chromatographie quantitativ analysiert.580 g of a naphthylamine trisulfonic acid mixture in the form of the trisodium salts (content 11.9 g total nitrite / 100 g, 52.8% by weight T acid MG 383; a total of 69 g nitrite, 0.80 mol T acid) of the following composition:

• (% Contents based on diazotizable substance) this additionally
• 0.3% by weight of 1-naphthylamine-3,6-disulfonic acid disodium salt,
• 1.3% by weight of naphthalene-1,3,6-trisulfonic acid trisodium salt,
• 0.6% by weight 1-nitronaphthalene-3,6,8-trisulfonic acid trisodium salt,
• Contains 4.6% by weight of water and quantitatively undetermined quantities of amino and nitro derivatives of dinaphthylsulfonic sulfonic acids and of oxidation products of naphthalene and naphthalene trisulfonic acids,
• 325 g water, 310 g methanol and
  • a) 8.5 g (0.1 mol) of sodium nitrate
  • b) 4.2 g (0.05 mol) of sodium nitrate
  • c) 0.8 g (0.01 mol) of sodium nitrate
  • c) 6.9 g (0.1 mol) of sodium nitrite

submitted and heated to 210 ° C. In a 1.3 l steel autoclave, 474 g of 70% by weight sodium hydroxide solution (8.3 mol NaOH) are heated to 210 ° C. and quantitatively pressed into the 2.7 l autoclave with nitrogen, so that, based on the sum, water plus methanol a 30 wt .-% sodium hydroxide solution is formed. A temperature of 220 ° C is set. The reaction mixture is kept at 220 ° C. for 20 minutes, cooled as quickly as possible, diluted with about 500 g of water, the methanol is distilled off over a column and the reaction mixture freed from methanol is analyzed quantitatively by high pressure liquid chromatography.

The test results obtained are shown in Table 1:

The reaction mixtures freed from methanol are acidified at pH 1 to 1.5 in a pH-controlled manner, with about 1000 g of 50% strength by weight sulfuric acid, refluxed for one hour to remove sulfur dioxide, cooled to 40 ° C. under evaporative cooling and kept at 40 ° C for two hours. The product is filtered at 40 ° C, washed with a total of 500 g of water and dried at 80 ° C in a vacuum. The yields and the H-acid quality, which was determined by high pressure liquid chromatography, are listed in Table 2.

Examples 2a-2h

• 1. Molverhältnis NaOH zu T-Säure-Isomerengemisch-Trinatrium-Salz
• 2. NaOH-Konzentration
• 3. Gewichtsverhältnis Wasser zu Methanol
• 4. Menge des Natriumnitratzusatzes
• 5. Reaktionszeit

ergeben die in Tabelle 3 zusammengestellten Ergebnisse.Further reactions as in Example 1, but without analysis of the reaction mixture freed from methanol, carried out at 200 ° C. with variation of the reaction parameters:

• 1. Molar ratio NaOH to T-acid-isomer mixture-trisodium salt
• 2. NaOH concentration
• 3. Weight ratio of water to methanol
• 4. Amount of sodium nitrate added
• 5. Response time

give the results summarized in Table 3.

Example 3a-3e

580 g of the naphthylamine trisulfonic acid mixture given in Example 1, 275 g of water, 280 g of methanol and the amount of further additive given in the table below are placed in a 2.7 l nickel autoclave and heated to 190 ° C. 430 g of 70% strength by weight sodium hydroxide solution (7.5 mol NaOH) are heated to 190 ° C. in a 1.3 liter steel autoclave and quantitatively pressed into the 2.7 liter autoclave with nitrogen, as a result of which water and methanol are used a 30 wt .-% sodium hydroxide solution is formed. A temperature of 200 ° C is reached. The reaction mixture is kept at 200 ° C. for 50 minutes, cooled as quickly as possible, diluted with about 500 g of water, the methanol is distilled off over a column and the reaction mixture freed from methanol is analyzed quantitatively by high pressure liquid chromatography.

The test results obtained are shown in Table 4:

Example 4

450 g (1 mol) of T-acid trisodium salt (content 15.3 g of nitrite / 100 g, 85.1% by weight of T-acid MG 383; a total of 69 g of nitrite) are placed in a 2.7 I nickel autoclave. , 325 g of water, 310 g of methanol and 8.5 g (0.1 mol) of sodium nitrate and heated to 200 ° C. In a 1.3 l steel autoclave, 474 g of 70% by weight sodium hydroxide solution (8.3 mol NaOH) are heated to 215 ° C. and quantitatively pressed into the 2.7 l autoclave with nitrogen, causing water to be added to the total plus methanol a 30 wt .-% sodium hydroxide solution is formed. A temperature of 220 ° C is set. The reaction mixture is kept at 220 ° C. for 15 minutes, cooled as quickly as possible, diluted with about 500 g of water and the methanol is distilled off over a column. The hot reaction solution is run into a hot mixture of 325 ml of 96% sulfuric acid and 1.5 l of water. The resulting H-acid suspension is refluxed for one hour to remove sulfur dioxide, cooled to 40 to 45 ° C and kept at 40 to 45 ° C for one hour. The product is filtered at 40 ° C, washed with a total of 500 g of water and dried at 80 ° C in a vacuum. The yield is 82% of theory.

The contents of the specified acids are calculated on free acids. The salts mentioned in Example 1 are in fact present.

Example 5

5.9 kg of a naphthylamine-trisulfonic acid mixture in the form of the trisodium salts (content 11.7 g Total nitrite / 100 g, 53.9% by weight T-acid with a molecular weight of 383, total 0.69 kg nitrite, 8.3 mol T-acid) of the following composition:

• 0,2 Gew.-% 1-Naphthylamin-3,6-disulfonsäure-dinatriumsalz
• 1,1 Gew.-% Naphthylamin-1,3,6-trisulfonsäure-trinatriumsalz
• 5,4 Gew.-% Wasser
  • und quantitativ nicht bestimmbare Mengen an Amino- und Nitroderivaten der Dinaphthylsulfon-sulfosäure und an Oxidationsprodukten des Naphthalins und der Naphthalin-trisulfonsäuren enthält, sowie
  • 2,8 kg Wasser, 2,8 kg Methanol und 64 g (0,75 Mol) Natriumnitrat werden in einem 20 I Nickel-Autoklaven auf 180°C aufgeheizt. Unter Stickstoff-überlagerung werden im Verlaufe von ca. 5 Minuten 4,3 kg 70 gew.-%ige Natronlauge 75 Mol NaOH) von 180°C eingepumpt, wobei sich eine Temperatur von 200°C eingstellt. Die Reaktionsmischung wird 55 Minuten bei 200°C gehalten und in einem 25 I Edelstahl-Kessel entspannt, in dem 10 1 kaltes Wasser vorgelegt sind. Das Methanol wird abdestilliert und die verdünnte H-Säure-Isomerengemisch-Lösung im Verlauf von 40 bis 60 Minuten mit Stickstoff in ein Fällungsgefäß aus Glas gedrückt, in dem ca. 4 kg Wasser (bzw. Waschwasser aus der Vorpartie) vorgelegt sind. Durch gleichzeitigen Zulauf von ca. 5,2 kg 100%iger Schwefelsäure wird der pH-Wert bei 1 bis 1,5 gehalten und die Reaktionsmischung zum Sieden gebracht. Die heiße, saure H-Säure-Suspension wird durch Anlegen von Vakuum vom restlichen Schwefeldioxid befreit, im Verlaufe von einer Stunde auf 40°C abgekühlt, eine Stunde bei 40°C gehalten und filtriert.

(Percentages based in each case on diazotizable substance), the additional

• 0.2% by weight 1-naphthylamine-3,6-disulfonic acid disodium salt
• 1.1% by weight of naphthylamine-1,3,6-trisulfonic acid trisodium salt
• 5.4% by weight of water
  • and quantitatively undetermined quantities of amino and nitro derivatives of dinaphthylsulfonic sulfonic acid and of oxidation products of naphthalene and naphthalene trisulfonic acids, and
  • 2.8 kg of water, 2.8 kg of methanol and 64 g (0.75 mol) of sodium nitrate are heated to 180 ° C. in a 20 l nickel autoclave. 4.3 kg of 70% strength by weight sodium hydroxide solution (75 mol NaOH) of 180 ° C. are pumped in over a period of about 5 minutes with a blanket of nitrogen, a temperature of 200 ° C. being established. The reaction mixture is held at 200 ° C. for 55 minutes and expanded in a 25 liter stainless steel kettle in which 10 liters of cold water are placed. The methanol is distilled off and the dilute H-acid isomer mixture solution is pressed over a period of 40 to 60 minutes with nitrogen into a glass precipitation vessel in which approx. 4 kg of water (or washing water from the previous batch) are placed. By simultaneously adding about 5.2 kg of 100% sulfuric acid, the pH is kept at 1 to 1.5 and the reaction mixture is brought to a boil. The hot, acidic H-acid suspension is freed of residual sulfur dioxide by applying a vacuum, cooled to 40 ° C. in the course of one hour, kept at 40 ° C. for one hour and filtered.

The product is washed with a total of 5.4 kg of water and dried in vacuo at 80 ° C. The yield is 82% based on T acid. The qualities of the product determined by high pressure liquid chromatography are listed in Table 5.

Example 6

A reaction carried out as in Example 5, but in which the reaction temperature is 190 ° C. and the reaction time is 100 minutes, gives a yield of 83%, based on T acid. The quality of the product, determined by high pressure liquid chromatography, is shown in Table 5.

Example 7 (comparative example)

• (%-Gehalte jeweils bezogen auf diazotierbare Substanz) das zusätzlich
• 0,3 Gew.-% 1-Naphthylamin-3,6-disulfonsäure-dinatriumsalz,
• 1,3 Gew.-% Naphthalin-1,3,6-trisulfonsäure-trinatriumsalz,
• 0,6 Gew.-% 1-Nitronaphthalin-3,6,8-trisulfonsäure-trinatriumsalz,
• 4,6 Gew.-% Wasser und quantitativ nicht bestimmbare Mengen an Amino- und Nitroderivaten der Dinaphthylsulfon-sulfosäure und an Oxidationsprodukten des Naphthalins und der Naphthalin-trisulfonsäuren enthält und 400 g Wasser vorgelegt und auf 180°C aufgeheizt. In einem 1,3 Liter Stahl-Autoklav werden 600 g 50 gew.-%ige Natronlauge (7,5 Mol NaOH) auf 185°C aufgeheizt und mit Stickstoff in den 2,7 Liter Autoklaven gedrückt, wodurch bezogen auf das gesamte Wasser eine 30 gew.-%ige Natronlauge entsteht. Dabei stellt sich eine Temperatur von 200°C ein. Die Reaktionsmischung wird 45 Minuten bei 200°C gehalten, so schnell wie möglich auf 100°C abgekühlt und mit 500 g Wasser verdünnt. Die heiße Reaktionslösung wird pH-kontrolliert (pH 1 bis 1,5) mit ca. 1000 g 50 gew.-%iger Schwefelsäure angesäuert, zur vollständigen Entfernung von Schwefeldioxid eine Stunde unter Rückfluß erhitzt, unter Verdampfungskühlung auf 40°C abgekühlt und 2 Stunden bei 40°C gehalten. Das Produkt wird bei 40°C filtriert, mit insgesamt 500 g Wasser gewaschen und bei 80°C im Vakuum getrocknet.

In a 2.7 liter nickel autoclave, 580 g of a naphthylamine trisulfonic acid mixture in the form of the trisodium salts (content 11.9 total nitrite / 100 g, 52.8% by weight T acid MG 383; a total of 69 g nitrite, 80 mol T acid) of the following composition:

• (% Contents based on diazotizable substance) this additionally
• 0.3% by weight of 1-naphthylamine-3,6-disulfonic acid disodium salt,
• 1.3% by weight of naphthalene-1,3,6-trisulfonic acid trisodium salt,
• 0.6% by weight 1-nitronaphthalene-3,6,8-trisulfonic acid trisodium salt,
• Contains 4.6% by weight of water and quantitatively undetermined quantities of amino and nitro derivatives of dinaphthylsulfone sulfonic acid and of oxidation products of naphthalene and naphthalene trisulfonic acids, and 400 g of water are introduced and heated to 180.degree. In a 1.3 liter steel autoclave, 600 g of 50% by weight sodium hydroxide solution (7.5 mol NaOH) are heated to 185 ° C. and pressed into the 2.7 liter autoclave with nitrogen, so that based on the total water, a 30% by weight sodium hydroxide solution is formed. A temperature of 200 ° C is reached. The reaction mixture is kept at 200 ° C. for 45 minutes, cooled to 100 ° C. as quickly as possible and diluted with 500 g of water. The hot reaction solution is acidified in a pH-controlled manner (pH 1 to 1.5) with about 1000 g of 50% strength by weight sulfuric acid, refluxed for one hour to remove sulfur dioxide completely, cooled to 40 ° C. under evaporative cooling and for 2 hours kept at 40 ° C. The product is filtered at 40 ° C, washed with a total of 500 g of water and dried at 80 ° C in a vacuum.

• H-Säure-Mononatriumsalz 88,2%
• 1-Naphthylamin-3,6-disulfonsäure-Mononatriumsalz 0,1-0,2%
• W-Säure-Mononatriumsalz 0,1-0,2%
• Chromotropsäure-Dinatriumsalz 1,1-1,2%
• T-Säure-Dinatriumsalz 0,1-0,2%
• Wasser 9,0%
• Natriumsulfat 0,5%

The yield is 58%, based on the T-acid isomer mixture or 72% based on T-acid. The H acid quality was determined by high pressure liquid chromatography as follows.

• H-acid monosodium salt 88.2%
• 1-naphthylamine-3,6-disulfonic acid monosodium salt 0.1-0.2%
• W acid monosodium salt 0.1-0.2%
• Chromotropic acid disodium salt 1.1-1.2%
• T-acid disodium salt 0.1-0.2%
• Water 9.0%
• Sodium sulfate 0.5%

Reaction products from the isomeric naphthylamine trisulfonic acids are not contained in the isolated product.

Example 8

A reaction carried out as in Example 7, but using pure T-acid trisodium salt, gives a yield of 73%, but an increased content of W- and T-acid.

• H-Säure-Mononatriumsalz 88,6%
• 1-Naphthylamin-3,6-disulfonsäure-Mononatriumsalz 0,2%
• W-Säure-Mononatriumsalz 2,0%
• Chromotropsäure-Dinatriumsalz 1,4%
• T-Säure-Dinatriumsalz 0,6%
• Wasser 6,8%
• Natriumsulfat 0,6%

Salary:

• H-acid monosodium salt 88.6%
• 1-naphthylamine-3,6-disulfonic acid monosodium salt 0.2%
• W acid monosodium salt 2.0%
• Chromotropic acid disodium salt 1.4%
• T-acid disodium salt 0.6%
• Water 6.8%
• Sodium sulfate 0.6%

Claims (11)

1. A process for the preparation of mono-alkali metal salts of I-amino-8-naphthol-3,6- disulphonic acid by reacting 1-naphthylamine-3,6,8-trisulphonic acid and/or the salts thereof and/or naphthylamine-trisulphonic acid isomer mixture and/or the salts thereof with an alkali metal hydroxide solution at elevated pressure and elevated temperature, and separating out the mono-alkali metal salts of 1-amino-8-naphthol-3,6-disulphonic acid by acidification, characterised in that the reaction is carried out in the presence of alcohols and/or alcoholates and in the presence of nitric acid, nitrous acid, nitrogen oxides, nitrates, nitrites, nitro compounds or nitroso compounds.

2. A process acccording to claim 1, characterised in that the reaction is carried out in the presence of aliphatic alcohols having 1 to 6 carbon atoms.

3. A process according to claim 1 and 2, characterised in that the reaction is carried out in the presence of methanol.

4. A process according to claim 1 to 3, characterised in that 10 to 80% by weight of alcohol and/or alcoholate, relative to the sum of water plus alcohol, is present during the reaction.

5. A process according to claim 1 to 4, characterised in that the process is carried out in the presence of sodium nitrate or potassium nitrate.

6. A process according to claim 1 to 5, characterised in that from 0.005 to 1 mol of nitric acid, nitrous acid, nitrogen oxides, nitrates, nitrites, nitro compounds or nitroso compounds is introduced into the reaction mixture per mol of 1-naphthylamine-3,6,8-trisulphonic acid used or per mol of naphthylamine-trisulphonic acid isomer mixture, or per mol of the salts of these acids.

7. A process according to claim 1 to 6, characterised in that the reaction is carried out at temperatures from 150 to 250°C.

8. A process according to claim 1 to 7, characterised in that the reaction is carried out in a closed vessel under the pressure which automatically forms.

9. A process according to claim 1 to 7, characterised in that the reaction is carried out under a pressure of from 5 to 100 bars.

10. A process according to claim 1 to 9, characterised in that after the reaction the alcohol is separated off from the alkaline or neutral solution by distillation.

11. A process according to claim 10, characterised in that the alcohol which is separated off is reused.