CH653671A5 - METHOD FOR PRODUCING 1-NAPHTHOL-3,6-DISULPHONIC ACID. - Google Patents

Description

The present invention relates to a process for the preparation of l-naphthol-3,6-disulfonic acid by reductive deamination.

For the preparation of l-naphthol-3,6-disulfonic acid, an important intermediate for dye synthesis, processes are already known which start from naphtha-lin-l, 3,6-trisulfonic acid (IG Farben regulation published in BIOS-FD 235 / 47,867), of l-naphthol-3,6,8-trisulfonic acid (SU 242 912 and SU 249 396) and of 1-aminonaphthalene-3,6-disulfonic acid (NN Woroshzow «Basis for the synthesis of intermediates and dyes »Akade-mie-Verlag Berlin 1966, page 472 ff.) The disadvantage of these processes described in the literature is that, in addition to l-naphthol-3,6-disulfonic acid, undesirable by-products are formed, such as, for example Large amounts of calcium sulfate in the production of naphthalene-1,3,6-trisulfonic acid, the starting material for the IG Farben process, or heavy metal salt solutions in the reductive elimination of sulfo groups according to the Russian patents.

The object of the invention was to develop a process for the preparation of 1-naphthol-3,6-disulfonic acid, according to which, if possible, no waste products and other undesirable by-products which are harmful to operational hygiene are formed.

The solution to this problem is given in the reductive deamination of l-amino-8-naphthol-3,6-disulfonic acid (H-acid) by first diazotizing it and then reducing the di-azo group reductively. There are no metal salt solutions that are difficult to remove with this process.

Reductive deamination has already been proposed in connection with the production of 2-naphthol-4-sulfonic acid starting from l-amino-2-naphthol-4-sulfonic acid (CH-PS 193 339, DRP 694 662, US Pat. No. 2,230 791, DBP 901 175 and DBP 905 014). However, a process for the reductive deamination of l-amino-8-naphthol-3,6-disulfonic acid cannot readily be derived from these known processes since, in contrast to l-amino-2-naphthol-4- sulfonic acid as the diazonium salt is not in the diazoxide form (P. Ruggii et al., Helv. Chim. Acta (1929) 12, 1034) and therefore to a considerable extent for self-condensation or for coupling to the reaction product, 1-naphthol disulfonic acid, should tend, especially since a-naphthols react much faster with diazonium salts than ß-naphthols. Surprisingly, however, it was found that l-amino-8-naphthol-3,6-disulfonic acid can be converted into l-naphthol-3,6-disulfonic acid with yields of approximately 70% as indicated.

The invention thus relates to a process for the preparation of l-naphthol-3,6-disulfonic acid, which is characterized in that l-amino-8-naphthol-3,6-disulphonic acid is reductively deaminated via the diazonium salt as intermediate 5 .

The l-amino-8-naph-thol-3,6-disulfonic acid used as the starting material is known and is obtained, for example, by the process described in DE-OS 27 32 291.

10 The diazotization of 1-amino-8-naphthol-3,6-disulfonic acid is preferably carried out with sodium nitrite in aqueous mineral acid solution at a temperature of about -10 to +10 ° C., at least 2 equivalents of mineral acid, e.g. Hydrochloric acid can be used. Instead of sodium nitrite, other alkali metal nitrites can of course also be used. Further suitable diazotizing agents are nitrogen oxides and nitrous acid derivatives such as nitrosyl chloride, nitrosylsulfuric acid or also their esters, such as, for example, butlynitrite.

20 If one works in aqueous mineral acid solution, the diazonium salt is obtained in the form of a suspension. The diazonium salt can be isolated from this by the customary methods and the diazo group can then be cleaved off under reductive conditions. However, it is also possible to continue working directly with the suspension of the diazonium salt. It is also possible to carry out the diazotization in the presence of a reducing compound and thus to obtain the 1-naphthol-3,6-disulfonic acid directly in one operation without separation of the diazo compound. The prerequisite here is, of course, that the reducing agent does not react with the diazotizing agent or that the diazotization reaction is difficult or even prevented.

As reducing agents which are suitable for exchanging the diazonium group for hydrogen, 35 heavy metal-free compounds, in particular the salts, esters or amides of formic acid or reducing sugar, especially alkaline glucose solution, are preferably used. The salts of formic acid are primarily the alkali metal formates, such as Sodium or potassium formate, but also ammonium formate in question. As esters of formic acid e.g. called the formic acid methyl, ethyl, propyl, isopropyl and butyl ester. As for the amides of formic acid, formamide or its N-alkylated derivatives, such as the dimethyl-45 formamide.

If alkali metal formates are used as the reducing agent, it is expedient to use them in excess, namely 2-5 mol of formate based on 1 mol of diazo-naphtholsulfonic acid.

The cleavage of the diazonium group is advantageously carried out at a temperature of 15 to 100 ° C., in particular 80 to 100 ° C. and at a pH in the range from 1 to 8; expediently one works at pH values around the neutral point. It is also possible to start at a pH 55 of 8 and to let it drop to a value of 3 to 4 during the reaction, for example.

Reductive deamination is achieved using a large number of other reducing agents (see Houben-Weyl Vol. 10/3 (1965) pages 115-144), which can in principle also be used in the present process.

The reaction mixture is worked up by known methods, for example by salting out the inorganic by-products, extracting the naphtholsulfonic acid and purifying it, e.g. by recrystallization. 65 The method according to the invention is carried out, for example, as follows:

l-Amino-8-naphthol-3,6-disulfonic acid is dissolved in aqueous solution at a temperature using sodium nitrite / hydrochloric acid.

diazotized from 0 to 5 C. After the reaction has ended, the diazonium salt is filtered off and introduced into an aqueous potassium formate solution. After a reaction time of several hours at a temperature of approximately 90 ° C., the diazo group is split off quantitatively. To separate the naphthol-3,6-disulfonic acid from the reaction mixture, this is mixed with 2 to 5 times the volume of ethanol and the precipitated inorganic The alcoholic-aqueous filtrate is evaporated and the product is optionally purified by recrystallization.

In this way, 1-naphthol-36-disulphonic acid is obtained with a yield of approximately 70% based on the 1-amino-8-naphthol-3,6-disulphonic acid used.

The invention is illustrated by the following examples.

example 1

20 g of l-amino-8-naphthoI-3,6-disulfonic acid (H-acid) are suspended in 95 ml of water in a beaker. A pH of 7 is set by adding 10N sodium hydroxide solution (5.7 ml), the H acid dissolving. The solution is then mixed with 15.96 ml of 4N sodium nitrite solution and mixed well. 78 g of ice are placed in a further beaker and 25 ml of 10 N hydrochloric acid are added. When the ice / hydrochloric acid mixture has reached a temperature of approx. -10 ° C, the H-acid / sodium nitrite solution is added dropwise within 4 hours. The temperature is kept in a range of 0-5 ° C. The diazonium salt precipitates out and forms a yellowish suspension. After excess nitrite has been destroyed using sulfamic acid, the diazonium salt is filtered off and the cleavage of the di-

3,653,671

azo group added within 8 hours in a freshly prepared potassium formate solution (3.3 molar excess of potassium formate based on diazonium salt), the pH of which was adjusted to 8 using potassium hydroxide solution. The 5 potassium formate solution has a temperature of 90 to 95 'C. when the diazonium salt is added. The temperature is maintained in this range for a total of 12 hours during the reaction time. For working up, the cooled reaction mixture is mixed with 250 ml of ethanol and the io precipitated salts are filtered off. These are dissolved in 0.1N hydrochloric acid and precipitated again by adding ethanol. This process is repeated two more times and then the combined filtrates are evaporated to dryness. This gives 28.7 g of l-naphthol-3,6-disulfonic acid with a content of 45.5%; i5 Yield: 69%; Rr value: 0.34.

Example 2

20 g of l-amino-8-naphthol-3,6-disulfonic acid are diazotized as described in Example 1. To split off the di-20 azo group, the diazonium salt is suspended in 105 ml of water and 8.33 g of glucose suspended in 20 ml of water are then added. The diazonium salt / glucose suspension prepared in this way is added within one hour to 80 ml of 12.5% sodium hydroxide solution, which has previously been heated to 80 ° C. 25 Allow to react for 3 hours at 80 ° C and then cool the reaction mixture to room temperature. After neutralization with dilute hydrochloric acid, the work-up is carried out as described in Example 1. The Rr value of the product thus obtained matches that of an authentic sample.

For thin-layer chromatographic analysis, silica gel plates with a UV indicator are used; Eluent: n-prop-anol / ammonia 20% in the ratio 2; 1.

C.

Claims (5)

653 671 PATENT CLAIMS 1. A process for the preparation of l-naphthol-3,6-disulphonic acid, characterized in that l-amino-8-naphthol-3,6-disulfonic acid is reductively deaminated via the diazonium salt. 2. The method according to claim 1, characterized in that a salt, ester or amide of formic acid or a reducing sugar is used as the reducing agent. 3. The method according to claim 1, characterized in that one carries out the diazotization and reductive deamination without intermediate isolation of the diazonium salt. 4. The method according to claim 2, characterized in that sodium or potassium formate or glucose is used as the reducing agent. 5. The l-naphthol-3,6-disulfonic acid obtained by the process according to claim 1.