DE2320416C3 - Process for the preparation of 4,4'-diaminostilbenedisulfonic acid- (2,2 ') or their alkali or alkaline earth metal salts - Google Patents

Description

25th

The invention relates to a particularly advantageous process for the preparation of 4,4'-diaminostilbene disulfonic acid (2 £ ') - hereinafter referred to as diaminostilbene acid - or its alkali and alkaline earth metal salts from corresponding water-soluble salts dsr 4,4'-dinitrostilbene disulfonic acid (2.2 ') - hereinafter referred to as dinitrostilbene acid

The industrial production of diaminostilbene acid has hitherto been carried out by reducing dinitrostilbene acid with the help of iron flour or iron filings in acidic solution (H. E Fierz-David and L Blangey, Grundlegende Operations der Farbenchemie, 5th edition, Vienna 1943, page 161). After the reduction is complete, this process requires work-up in order to achieve the to separate the desired amino compound from the iron, which has dissolved in hydrochloric acid Working up with strong bases, the iron is precipitated as iron hydroxide which is difficult to filter and the removal of which requires considerable technical effort Another disadvantage of the iron reduction process can be seen in the fact that the amount obtained after the reduction Iron sludge or the iron oxide obtainable from it by drying or roasting is not unlimited Amount can be used in other technical processes. A smelting of iron residues like that requires a complex work-up beforehand. Due to the high demands placed on the Quality of the diaminostilbene acid is provided, an additional cleaning operation by intermediate isolation, for example of the sodium salts of the diamino nostilbene acid required to remove the last traces of iron.

A process has been found for the preparation of 4,4'-diaminostilbene disulfonic acid (2,2 ') or its alkali or alkaline earth metal salts by reducing the corresponding dinitro compound; which is characterized in that 4,4'-dinitrostilbene disulfonic acid (2,2 ') or their alkali or alkaline earth salts at a pH above 2.0 in water, methanol or a water-methanol mixture in the presence ⁶ ^ of metals of the 8th group of the Periodic Table of the Elements as catalysts, optionally on conventional porous supports, with hydrogen at a pressure of 1 to 250 bar in the temperature range from 15 to 120 ° C hydrogenated and then optionally acidified after removal of the catalyst

Preference is given to working in the temperature range from 40 ^° C. to 90 ^° C. and a hydrogen pressure of 10 to 150 bar

The sodium salt of dinitrostilbene acid is generally used for the process according to the invention at a pH greater than 2, preferably in the range from 5 to 8. If it is for reasons of apparatus it is advisable to work in the acidic reaction medium, the desired setting is made pH by adding mineral acid (preferably aqueous hydrochloric acid or sulfuric acid).

The feasibility of the method of the invention must in view of the prior art as are viewed as extremely surprising (catalytic hydrogenations in the Organisch-chemivräen Laboratorium Enke-Verlag 1965, page 90). It says there: “At In the case of unsaturated nitro compounds, it depends on the structural peculiarities of the respective compound whether both functions hydrogenate at the same time or which is attacked before the other. So you can use all unsaturated nitro compounds too hydrogenate saturated amines; Unsaturated amines are only obtained from a certain group in which the CC double bond difficult for steric and other reasons due to catalytically excited hydrogen can be tapped "

Furthermore, US Pat. No. 3,250,799 describes that 4-chloro-4'-nitro-2-cyano-stilbene can be obtained with nickel catalysts without attacking the stilbene double bond Can be hydrogenated Under the same conditions, this is also possible with the isomeric 4-chloro-4'-nitro-2'-cyano-stilbene according to Belgian patent 6 U 181. If one tries to transfer this hydrogenation with nickel catalysts to dinitrostilbene acid, the hydrogenation is like can be seen from the accompanying comparative example - only possible with the formation of considerable amounts of 4,4'-diaminodibenzyldisulfonic acid- (2,2 ').

The feasibility of the method of the invention was therefore by no means foreseeable.

The dinitrostilbene acid or its salts used for carrying out the process of the invention is known (Huang-Minlon, J. Am. Chem. Soc. 70 (1948), pages 2802, 2804). The starting compound can be used in the moist state, for example in the form in which it is obtained industrially with a content of approx. 50% of dinitrostilbene acid. For the implementation of the process takes place as a solution or. Diluent preferably water use. It is of course also possible to use organic solvents which are miscible with water and / or mixtures with water. Methanol may be mentioned as a preferred organic solvent. Of course, mixtures of methanol and water in any mixing ratio can also be used.

The catalysts optionally used for carrying out the process of the invention are used Sluggishly precipitated metals of the 6th group of the periodic table of the elements (K. A. Hofmann and U. R. Hofmann, Textbook of Inorganic Chemistry, Friedrich Vieweg & Sohn, Braunschweig, 12th edition (1948), page 83). Examples of catalysts are cobalt, ruthenium, rhodium, palladium and platinum or called the corresponding oxides. Platinum is particularly preferred. In the event that the catalyst is on

is deposited on a carrier, the usual porous carriers are used, as they are in Ullmann's Enzyklopadie der technischen Chemie, Volume 9, page 2 {j3 ff, Houben - Wey !, Methods of Organic Chemistry, Volume IV / 2, page 147 ff. and in Catalysis Vol. I ₁ page 251 ff. Reinhold Publishers, New York, 1954, are described. Activated carbons, aluminum oxide, silicon dioxide, aluminum silicates, optionally in combination with alkali and alkaline earth compounds, such as spinels, for example, may be mentioned. The catalysts are used in powdery, suspended, lumpy or shaped arrangements. The amount of the catalytically active metal on the support can be between 0.1 and 5% by weight, preferably 0.5 to 1% by weight. The amount of the catalyst used is based, if appropriate, on the salt used, calculated as dinitrostilbene acid with a molecular weight of 430. 0.1 to 5, preferably 0.5 to 2% by weight of catalyst are used.

The preferred catalyst carrier is a commercially available decolorizing carbon that does not contain any granular components and whose water content is <10% when packaged (methylene blue titer:> 11A determined based on the test specification of DAB VI; it is determined how many ml of 0.15% methylene blue - The solution can be decolorized within 5 minutes by shaking 0.10 g of dried activated charcoal or calculated on dry matter. This consumption is given as a titer in ml of 0.15% methylene blue solution per 0.1 g of activated charcoal); BET surface area 800 ± 50; pH 5.5 to 7.0; Ash content <1Λ% wc ~ soluble and acid-soluble, based on the substance dried for 2 hours at 120 ° C <0.5 or \ J5 * h grinding fineness>80; Vibrating weight DIN 53194 approx. 410 g / l; Fill weight, loose filling approx. 215 g / l.

To carry out the process, the free acid or the alkaline earth metal salt (preferably calcium salt) or alkali metal salt (sodium, potassium) is particularly useful preferably the disodium salt of dinitrostilbene acid, dissolved in water or a water-methanol mixture or suspended The solution or suspension is mixed with the catalyst in a pressure vessel which is usually used and under increased pressure Hydrogenated under pressure and optionally elevated temperature until the uptake of hydrogen has ceased The reaction mixture is then separated from the catalyst by settling or by filtration. in the Case of the use of dinitroitilbene acid Aqueous alkali metal hydroxide is added to salt mixtures to remove the catalyst and the catalyst is then filtered off. The catalyst can find use for further implementations. The method of the invention is therefore also of particular advantage because it can be carried out continuously in a simple manner. To work in the Swamp phase can, for example, according to Ulmann's Encyclopedia of Industrial Chemistry, Volume 10, Pages 508 and 560. For this purpose, the solution or suspension is pumped through one or more reactors connected in series in the presence of the required catalyst. Here can for example, the procedure is that the solution or suspension of dinitrostilbene acid or des Alkali or alkaline earth salt with the catalyst through a cascade of kettles or a system of tube furnaces, optionally under elevated temperature and under increased pressure is pumped. The one for the reaction necessary catalyst can either be used as a fresh catalyst for the solution or suspension of Dinitrostilbene acid or its salts are added. It is beneficial to use a catalyst again use, which is already used for the hydrogenation of dinitrosilbene acid or its salts according to the invention Hydrogen has served. In this case, it is expedient to carry part of the catalyst holding

ίο reaction mixture back into the starting solution, optionally with the addition of fresh catalyst.

Another embodiment of the method of Invention consists in the overhead of the solution Dinitrostilbene acid or its salts via a

fixed catalyst, optionally at elevated temperature and at elevated pressure. Of the Advantage of this in Ullmann's Encyclopedia of Industrial Chemistry, Volume 7, page 448, described Process variant (trickle phase) is particularly important that a filtration of the catalyst as mentioned above not applicable

The process of the invention enables the diaminostilbenic acid in a particularly simple manner or their alkali and alkaline earth salts in high purity to manufacture. After the reaction has ended and filter off of the catalyst, in the present process, the reaction solution can be processed immediately, isolated or further processed into compound products. will. For example, can by acidifying the reaction solution with mineral acid

(e.g. aqueous sulfuric acid) immediately obtain the free diaminostilbenic acid. A complex work-up stage, such as that required by the iron reduction process, is therefore advantageously omitted in the Working up the reaction mixture is also that the hydrogen still dissolved in it, the one against oxygen sensitive diaminostilbene acid or its salts protect against the effects of atmospheric oxygen the process of the invention obtainable 4,4'-diaminostilbene disulfonic acid (2,2 ') or their alkali or Alkaline earth salt is a valuable intermediate product and is used in the production of organic dyes and optical brighteners used

1850 ml are filled into a 5 liter stirred autoclave Water and 527 g of the water-moist disodium salt of dinitrostilbene acid (content 49.51% determined by Diazotization; Molecular weight 430). This starting compound contained the following impurities:

Thin sheet chromatogram (güil00gl00% goods)

approx. 0.6 g 4,4'-dinitrodibenzyl * 2,2 '* disulfone-

acid (molecular weight 432) approx. 0.2 g 4-nitrotoluene-2-sulfonic acid,

0.2 g of 4-nitrobenzaldehyde'2-sulfonic acid, approx. 1.4 g of unknown impurities.

Add 6 g of the one described below

wet catalyst. Before adding the catalyst the pH of the solution at 70 ⁰ C is 7.3. It will be at

Starting at room temperature and increasing to 70 ° C

hydrogenated at a hydrogen pressure of 150 bar, wherein the hydrogen consumed in the reaction is topped up again to a pressure of 150 bar. The hydrogenation is essentially complete after 15 minutes. Then, 60 minutes at 70 ⁰ C and 150 bar hydrogen pressure is rehydrogenated. The catalyst is then filtered off and stored under water for BeisDiel 2.

The filtrate obtained is a light yellow solution and has a pH of 8.3, the analysis is as follows:

Content of disodium salt of 4,4'-DinitrobenzyI-2,2'-stilbene disulfonic acid calculated as the free acid from Molecular weight 370 = 9.03% (determined by diazotization).

Impurities detected by Thin layer chromatogram

(g in 100 g luü% iger goods)

approx. 0.6 g 4,4'-diaminodibenzyl-2 £ '-di-

sulfonic acid (molecular weight 372); Quantity identical to the starting material,

approx. 1 g 4-AnUnOiOlUoI-X-SuIfOnSaUrC,

approx. 1.0 g of 4-aminobenzaldehyde-2-sulfonic acid,

no nitro compounds.

Trace of azoxy compounds

The catalyst used for the hydrogenation was obtained as follows:

675 g of a commercially available activated flask (inner surface, determined by the BET method, 100 mVg; 80% of this coal have a grain size <40μπη) are stirred in 3 liters of water for 15 minutes. Then 100 ml of a platinum / hydrochloric acid solution are added, the content of which is 6.75 g of platinum The mixture is stirred for 1 hour at room temperature and the metallic platinum is beaten in the usual way by adding excess reducing agent, such as. B. 30% formaldehyde solution, 20% hydroxylamine solution or aqueous hydrazine hydrate solution of coal as metal. The catalyst is then filtered and washed with water for as long as until the outflowing filtrate is chlorine-free. The catalyst obtained in water-moist form becomes Used wet A sample of the catalyst, dried in a stream of air, shows a dry content of 38%.

Example 2

510 g of the disodium salt of dinitrostilbene acid (Content 53.7%, calculated on free acid with a molecular weight of 430) of the same analytical composition as described in Example 1 (thin-layer chromatogram) are added to 2 liters of water Starting at room temperature and increasing to 70 ° C at a hydrogen pressure of 150 bar, as described in Example 1, hydrogenated

The catalyst recovered from Example 1 is used as the catalyst, and 4 g of fresh catalyst (see above for preparation) are added. The hydrogenation is substantially complete after 30 minutes is 1 hour at 70 ° C and under 50 bar hydrogen pressure rehydrogenated The solution of Dinitrostilbensäuredinatriumsalzes hai before hydrogenation at 7O ⁰ C a pH of 7.3. The catalyst is filtered off and stored under water for example 3. The filtrate is a light yellow solution with a pH of 8.3. The analytical composition is as follows:

Disodium salt content 9.03%, calculated as free Acid from MO 370 determined by diazotization =

Thin layer chromatogram (g in 100 g in 100% goods)

approx. 0.6 g 4,4'-diaminobenzyl-2,2'-di-

sul ^f oic acid (molecular weight 372), approximately 0.1 g of 4-aminotoluene-2-sulfonic acid, about 1.0 g of 4-Amiru) benzaldehyde-2-sulfonic acid,

no nitro compounds Trace of azoxy compounds

Example 3

510 g of dinitrostilbene acid disodium salt (content 53.7%) are dissolved in 2000 ml of water in the presence of the recovered catalyst from Example 2 and an additional 4 g of fresh catalyst according to Example 1 150 bar hydrogen pressure between 30 and 80 ° C hydrogenated The hydrogenation is essentially after 30th Minutes ended; hydrogenation is continued for a further 60 minutes at 80 ° C. under 150 bar hydrogen pressure When the reaction is complete, the catalyst is filtered off and under water for reuse in the Example 4 stored The filtrate is slightly reddish in color and has a pH of 83- The analytical The composition is the same as that given in Example 2. Yield according to example 2.

Example 4

In the same way as in the Bendel 3, 510 g Dinitrostilbene acid sodium (content 53.7%, calculated as free acid with a molecular weight of 430) in the presence of from Example 3 recovered catalyst and additional addition of 4 g of fresh catalyst, such as down? Example 1 given, hydrogenated in the temperature range between 30 and 80 ° C. The main reaction is ended after 30 minutes. Subsequently, hydrogenation is carried out for 60 minutes at 150 bar and 80.degree. C. The The catalyst is filtered off (storage under water for example 5). The filtrate is slightly reddish colored and has a pH of 83. The analytical The composition of the solution of the diaminostilbene acid disodium salt corresponds to that of Example 2.

Yield according to example 2. Example 5

As indicated in Example 4, 510 g of dinitrostilbene acid disodium salt (content 53.7%, are calculated hydrogenated as a free acid with a molecular weight of 430) in the presence of the catalyst recovered from Example 4 with the addition of 4 g of fresh catalyst according to the procedure of Example 1 in the temperature range between 30 and 80 ^° C. The hydrogenation is essentially after 30 minutes is ended. Subsequently, hydrogenation is carried out for 60 minutes at 150 bar and 80 ° C. The catalyst is filtered off (storage under water for example 6). The filtrate is slightly reddish in color and has a pH of 83 · Analysis of the diamino compound and

Yield corresponds to example 2. Example 6

If example 5 is repeated using the d.vt recovered catalyst, this becomes achieved the same result.

Example 7

Repetition of Example 6 with the catalyst recovered there and the procedure according to Example 1 yields, after isolation of the catalyst, sin easy reddish colored filtrate of pH 8.3. Analytical composition and yield of diamine cotilbene acid according to Example 1.

_h , examples

Water-moist disodium salt of dinitrostilbene acid corresponding to 70.45 g of free dinitrostilbene acid from

Molecular weight 430 are suspended in 350 ml of water and, after the addition of 1.07 g of the catalyst described in Example I, ^{hydrogenated at 40 °} C. under a hydrogen pressure of 16 bar in accordance with Example I. After 3 hours the reaction has essentially ended. It is post-hydrogenated for half an hour at 4O ⁰ C and 210 bar hydrogen pressure, and then filtered off the catalyst. The pale yellow, clear reaction solution is diluted with the I, 5-fold amount of water and are 10 ° / o aqueous hydrochloric acid at 50 to 70 ⁰ C until a pH value of 2.5 to 3 added. The free diaminostilbene acid is then filtered off and dried. Yield 58.5 g (96.5% of theory) of free diaminostilbene acid (molecular weight 370).

Example 9

Water-moist dinitrostilbene acid sodium corresponds to 70.45 g of free acid with a molecular weight of 430

-J ~ _: _ Λ -: _ n ~: -: "i ο ι l ._: _ i \ w _: .._ l._:

ntlUbll Ht ULI III UVIjpi \ .l U UI.31. 111 IU \ J \, I IC 11 TTCI3C LfCI 80 ° C reduced under 10 bar hydrogen pressure. The main reaction is over after 1 hour. Subsequently, half an hour at 8O ⁰ C under 10 bar hydrogen pressure is rehydrogenated. Working up as in Example 8. Yield 58.7 g (97% of theory) of free diaminostilbene acid.

10

Example 13

salt (2.2 ') 16.5% calculated as free acid with a molecular weight of 370 from diazotization.

Thin layer chromatogram
,, (g in 100 g 100% goods)

2 g of 4,4'-diaminodibenzy / disulfonic acid (2.2 '),

5.0 g of 4-aminobenzaldehyde-2-sulfonic acid,

0.2 g of 4-aminotoluene-2-sulfonic acid.

0.1 g of azoxi compounds,

in 0.1 g of 4,4'-dinitrostilbene disulfonic acid (2.2 '),

0.1 g of nitroamido compounds.

Example 14

76 g (containing 55.7 g, calculated on the molecular weight Ii 430) of a mixture of the disodium salt of 4,4'-dinitrostilbene-disulfonic acid (2,2 ') and the free acid are in 344 g of water in the presence of 2 g a catalyst, as described in example 1, between 20 ° C and 80 ⁰ C and 150 bar hydrogen pressure

"" Ι i_:. r-v: _ ι υ ι *. J r »ι ..: ι:« λλ * ~ ·

i " iijui ici ι. Lsic camouflage itat vui uci i \ caiMiu * i uci au K ^ a pH value of 5. The main reaction is complete after 15 minutes. Hydrogenation is continued at 80 ^° C. and 150 bar for 1 hour.

The catalyst is filtered off and the 2 ·> is analyzed received solution:

8.58% molecular weight 370 by diazotization.

example

If example 9 is repeated, but under a hydrogen pressure of 25 bar, the main reaction is complete after 45 minutes. It is post-hydrogenated for 30 min at 80 ⁰ C and 25 bar hydrogen pressure. Working up as in Example 8 gives 58.3 g (95.5% of theory) of free diaminostilbene acid.

Example 11

If, following the procedure of Example 8, the previous Example 10 is repeated under one A hydrogen pressure of 50 bar means that the main reaction has ended after 40 minutes. It will take 30 minutes 50 bar hydrogen pressure at 80 ° C post-hydrogenated. Working up according to Example 8 gives 60 g of free Diaminostilbene acid (99% of theory).

Example 12

If example 11 is repeated and the system is operated at a hydrogen pressure of 100 bar, the main reaction is essentially ended after 30 minutes. It is half an hour at 80 = C and 100 bar hydrogen pressure rehydrated. After working up as in Example 8, 58.7 g (97% of theory) of free diaminostilbene acid are obtained.

55

110 g of the disodium salt of 4,4'Dinitrostilben-disulfonsäure- (2.2 ') (corresponding to a content of 74% free dinitrostilbene acid with a molecular weight of 430) are dissolved in 290 ml of water and hydrogenated in the presence of 0.5 g of a commercially available catalyst, the 5 wt .-% contains ruthenium on active clay (surface area 111 m ² / g, determined according to BET). It is hydrogenated under a hydrogen pressure of 150 bar at 90 to 100 ° C. for 25 minutes. Subsequently, hydrogenation is carried out at 100 ° C. for a further 30 minutes at 150 bar hydrogen pressure and the catalyst is removed by filtration. The filtrate is a light yellow solution with the following analytical composition: 4.4'-diaminostilbene disulfonic acid disodium thin layer chromatogram
(gin 100 g100% goods)

0.7 g of 4,4'-diaminodibenzyl-disulfonic acid (2.2 '),

0.1 g of 4-aminotoluene-2-sulfonic acid,

0.7 g of 4-aminobenzaldehyde-2-sulfonic acid,

no azoxy compounds,

no nitro compounds.

Example 15

76 g (containing 55.7%, calculated on the molecular weight of 430) of a mixture of the disodium salt of 4,4'-dinitrosilbene-disulfonic acid (2,2 ') and the free acid are in 344 g of water in the presence of 2 g of a Catalyst, as described in Example 1, ^{hydrogenated between 20 °} C. and 80 ^° C. and 150 bar hydrogen pressure. Before the reaction, the solution has ^{a pH of 2 at 80 °} C. The main reaction has ended after 17 minutes. It is hydrogenated at 80 ° C. and 150 bar 1 hour after.

The catalyst is filtered off and the solution obtained is analyzed:
8.42% molecular weight 370 by diazotization.

Thin layer chromatogram
(g in 100 g 100% goods)

0.7 g of 4,4'-diaminodibenzyl-disulfonic acid- (2.2 ') _T

0.1 g of 4-aminotoluene-2-sulfonic acid,

2.5 g 3 g aminobenzaldehyde-2-sulfonic acid,

no azoxy compounds,

no nitro compounds.

Example 16

76 g (containing 55.7%, calculated on the molecular weight 430) of a mixture of the disodium salt of 4,4'-Γ ..trosti! Bendisulfonsäure- (2,2 ') and the free acid are in 344 g of methanol in the presence of as described in example 1, 2 g of a catalyst between 53 ° C and 80 = C and 150 bar Wasserstoffdnick The solution has hydrogenated at 80 ⁰ C a pH of 3. The main reaction is complete after 30 minutes. It is hydrogenated at 80 ° C. and 150 bar for 1 hour.

The catalyst is filtered off and the solution obtained is analyzed:

7.51% molecular weight 370 by diazolation. Thin layer chromatogram
(100% 100% goods). ■>

1 g 4,4'-diaminodibenzyl-disulfonic acid- (2,2 '), C ₁ I g' ♦ -aminotoluene ^ -sulfonic acid,

2 g ^ aminobenzaldehyde ^ -sulfonic acid, no azoxy compounds,

no nitro compounds. ^{l ()}

Example 17

Water-moist dinitrostilbene-acid sodium corresponding to 70.45 g of free acid with a molecular weight of 430 H are prepared in the manner described - Example 8 - at 40 ^° C. under 10 bar hydrogen pressure in the presence of 1.07 g of a catalyst composed of 5% rhodium on medicinal charcoal DAB 6 hydrogenated. The reaction is over after about 1 hour. Work-up as in Example 8. Almost quantitative yield.

Thin layer chromatogram
(100 g of 100% goods).

2 g of 4,4'-diaminodibenzyl-disulfonic acid- (2,2 '), 2 = 1 0.2 g of 4-aminobenzaldehyde-2-sulfonic acid.

Example 18

Water-moist dinitrostilbene acid sodium corresponds to 70.45 g of free acid with a molecular weight of 430 jo are in the manner described - Example 8 - at 170 ° C under 10 bar hydrogen in the presence of 1.07 g of a catalyst composed of 5% iridium on a charcoal, which is composed as described in Example 1 (. hydrogenated. The reaction is essentially complete after 3 hours. Work-up according to Example 8. Almost quantitative yield.

Example 19
(for comparison)

100 g of the disodium salt of 4,4'-DinitrostiIben-disulfonic acid- (2.2 ') (corresponding to a content of 90.0 g of dinitrostilbene acid with a molecular weight of 430 in 300 ml of water in the presence of 3 g of a 50% nickel-containing water-moist Raney nickel catalyst at 150 ° to 180 "C and a hydrogen pressure hydrogenated by 150 bar. The uptake of hydrogen is essentially over after 5 minutes. Man hydrogenated for 30 minutes at 180 ° C and 150 bar gradually filters off the catalyst. The filtrate is analyzed.

Content of the disodium salt of 4,4'-diaminostilbene-disulfonic acid- (2,2 ') calculated as free acid with a molecular weight of 370: 18.9% by diazotization.

Thin layer chromatogram
(gin 100 g100% goods)

30 g of 4,4'-diamino-dibenzyl-disulfonic acid- (2.2 ') molecular weight 372,

1 g aminobenzaldehyde sulfonic acid,

2 g aminotoluenesulfonic acid,
less than 0.1 azoxy compounds,
below 0.1 nitro compounds.

Claims (2)

Patent claims: 1, a process for the preparation of 4,4'-diaminostilbene disulfonic acid (2 £ ') or their alkali or alkaline earth metal salts by reducing the corresponding dinitro compound, characterized in that 4,4'-dinitrosüIbendisulfonsäure- (2,2') or Their alkali or alkaline earth metal salts at a pH value above 2.0 in water, ι ο methanol or a water-methanol mixture in the presence of metals from group 8 of the Periodic Table of the Elements as catalysts, optionally on conventional porous supports, and hydrogenated with hydrogen at a pressure of 1 to 250 bar in the temperature range of 15 to 120 ⁰ C after removal of the catalyst, optionally followed by acidification 2. The method according to claim 1, characterized in that one works at 40 to 90 ⁰ C and a hydrogen pressure of 10 to 150 bar