GB2136430A - Production of 4,4'-Dinitrostilbene-2,2'-disulfonic Acid or a Salt Thereof - Google Patents

Abstract

4,4,-Dinitrostilbene-2,2'-disulfonic acid and salts thereof, useful as intermediates in the preparation of dyes and pigments, are prepared by oxidizing a compound of formula: <IMAGE> or a salt thereof in the presence of lithium and hydroxyl ions and, if desired, a catalyst.

Description

SPECIFICATION Production of 4,4'-Dinitrostilbene-2,2'-Disulfonic Acid or a Salt Thereof The present invention relates to a process for producing 4,4'-dinitrostilbene-2,2'-disulfonic acid or a salt thereof.

4,4'-diaminostilbene-2,2'-disulfonic acid, obtained by reducing 4,4'-dinitrostilbene-2,2'-disulfonic acid or its salt (hereinafter referred to as 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds), has been produced on a large scale and used as an intermediate for dyes and pigments such as fluorescent whitening agents.

Conventional processes for producing 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds, such as the process mentioned on page 511 of Yutaka Hosoda "Senryo Kagaku" published by Gihodo Co., Ltd. or in the Specification of Japanese Patent Laid-Open No. 38764/1 982, have defects in that the yield of product per unit volume of the reactor is very poor and a long reaction time is required.

According to the process mentioned in "Senryo Kagaku" or the Specification of Japanese Patent Laid-Open No. 38764/1982, the 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds are obtained in a yield of as low as about 6 wt. % based on the quantity of the reaction solution.

Further, a reaction time of 1 8 to 20 h is required in both processes. According to a process disclosed in the Specification of Japanese Patent Laid-Open No. 29561/1981, the intended product can be obtained in a yield of about 15% based on the reaction solution and the reaction time can be reduced to about 6 h. Though this process has improved to some extent the yield per unit volume of a reaction solution and the reaction time, it is costly since use of an organic solvent such as dimethylformamide or methanol is necessitated. Other industrial demerits of this process are that it includes the dangerous step of mixing the oxidizing agent with the organic solvent and that special care is necessary to avoid the presence of water when carrying out the reaction.

The present inventors have made intensive investigations for the purpose of developing an industrially advantageous process for producing the 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds in improved yield per unit volume of a reaction solution and in a reduced reaction time. A reason why the yield of the 4,4'-dinitrostilbene-2,2'-disulfonic acid compound per unit volume of reaction solution is poor when oxidation of 4-nitrotoluene-2-sulfonic acid is effected in an alkaline aqueous medium is that the solubilities of 4-nitrotoluene-2-sulfonic acid (starting material), 4,4' dinitrodibenzyl-2,2'-disulfonic acid (intermediate product) a nd and 4,4'-dinitrostilbene-2,2'-disulfonic acid (product) in water are low.The inventors have now found that when a lithium compound is incorporated in the oxidation reaction system, the amount of the starting material charged per unit volume of the reaction solution can be increased noticeably and the oxidation reaction rate can be increased sharply. According to the inventors knowledge, the process wherein 4-nitrotoluene-2sulfonic acid is oxidized in the presence of a lithium compound has not been known. Accordingly, the present invention provides a process for producing 4,4'-dinitrostilbene-2,2'-disulfonic acid or a salt thereof, which process comprises oxidising a compound of formula (I):

or a salt thereof in the presence of lithium and hydroxyl ions.

In carrying out the process of the present invention, 4-nitrotoluene-2-sulfonic acid or its alkali metal or alkaline earth metal salt, such as K, Na, Mg or Ca salt, is used as the starting material and water is used as a solvent. Water may be used in the form of a mixture with an organic solvent. The quantity of water used is about 0.8 to 20 parts by weight, preferably 1 to 10 parts by weight, per part by weight of 4-nitrotoluene-2-sulfonic acid.

Examples of the lithium compounds releasing lithium ion are lithium oxide, lithium hydroxide, salts such as lithium carbonate and lithium acetate, lithium hypohalites and halides such as lithium chloride and lithium bromide. These lithium compounds form lithium salts of 4-nitrotoluene-2-sulfonic acid. The above mentioned lithium compounds are used in an amount of 1-5 moles per 1 mole of 4nitrotoluene-2-sulfonic acid.

The presence of hydroxyl ion (OH-) is indispensable in carrying out the oxidation reaction of the present invention. If, among the above-mentioned lithium compounds, lithium oxide and/or lithium hydroxide are used, since these compounds release hydroxyl group in water, the addition of another compound releasing a hydroxyl group, if desired, may be omitted. If lithium salts such as lithium carbonate and lithium acetate, lithium hypohalites and lithium halides such as lithium chloride and lithium bromide are used as lithium compounds, hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide or compounds capable of forming a hydroxide in water such as magnesium oxide and calcium oxide have to be added. In this case, the amount of a hydroxide or a compound capable of forming a hydroxide in water is about 0.3 to 5 mol/l.

Though the oxidation reaction of the present invention proceeds even in the absence of any catalyst, the reaction can be carried out more efficiently when a catalyst is used. The most suitable catalysts are manganese compounds. Further, compounds of transition metals such as Co, Fe, Ni, Pd, Pt, Cr, Ce, Ru, Rh, Ti, V, Zr, Pb, Th, Cu, Ag, Mo and W may also be used either alone or in the form of a mixture of them. The catalyst is used in an amount of about 1 x10-4 to 1 xl 0-1 mol/l. In addition, active carbon silica gel, alumina, urea, phase transfer catalysts and ion exchange resins are also usable as the effective catalysts.

The examples of oxidizing agents to be used are gases containing molecular oxygen, hypohalites, ozone and peroxides. From the economical viewpoint, gases containing molecular oxygen, particularly oxygen gas and air, are preferred.

The reaction temperature is 20 to 1000C, preferably 40 to 85cm.

The reaction may be carried out by a continuous process or a batch process under atmospheric pressure or elevated pressure. The reaction time is 4 to 10 h which is far shorter than those required in the conventional processes.

After-treatments of the reaction mixture are carried out according to an ordinary method. The following method is an example.

After completion of the oxidation reaction, water is added to the reaction mixture to dissolve the 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds. Then, carbon dioxide, an alkali carbonate or an alkali bicarbonate is added to the reaction mixture to precipitate the lithium ion in the form of a iess soluble salt thereof. After filtration, the intended 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds are obtained by an ordinary method such as deposition by acidification or salting out.

For easy understanding of the present invention, the process will now be elaborated in more detail.

Water, 4-nitrotoluene-2-sulfornic acid or its salt and, if necessary, a catalyst are charged in an alkali-resistant reactor. A lithium compound and an oxidizing agent are added thereto. After thorough stirring, a hydroxide or a compound releasing hydroxyl group is added thereto. (When lithium hydroxide is used, the addition of a hydroxide may be omitted). The hydroxide may be used in the form of solid or aqueous solution thereof.

Then, the stirring is continued at the reaction temperature mentioned above to effect the reaction. When the reaction temperature is elevated slowly, better result can be obtained compared with that obtained in a rapid temperature elevation. The reaction time is 4 to 10 h.

According to the pursuit of the reaction progress by a liquid chromatography analysis, it has been found that the amount of 4,4'-dinitrodibenzyl-2,2'-disulfonic acid (intermediate product) formed is far smaller than that formed in the conventional processes. This fact suggests that the mechanism of the process of the invention is different from that of the conventional processes. After completion of the reaction, 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds is filtered after cooling, and the filtrate which still contains the intended product can be recycled for the next reaction. But the reaction mixture, usually, is treated as follows. The reaction mixture is diluted with water until the intended 4,4'-dinitrostilbene-2,2'-disulfonic acid compounds have been dissolved completely.Then, carbon dioxide, an alkali carbonate or an alkali bicarbonate is added thereto in an oxidation atmosphere.

Carbon dioxide is used in the form of dry ice and carbon dioxide kept in a cylinder. The alkali carbonates include sodium carbonate, potassium carbonate and ammonium carbonate. The alkali bicarbonates include sodium hydrogencarbonate and ammonium hydrogencarbonate. They are used in an amount sufficient for the lithium ion in the reaction mixture to form a salt thereof perfectly. After stirring for about 30 min, the insolubie lithium salt is filtered off. Generally, the higher the temperature is, the higher the efficiency of lithium salt separation is. According to this process, a lithium recovery of at least about 75% can be attained. The filtrate from which the lithium salt has been separated is made acidic and the intended 4,4'-dinitrostilbene-2,2'-disuífonic acid compounds are separated by, for example, salting out.

The effects of the present invention will be shown in comparison with those of the conventional processes:

Conventional Process Present (Example 1 of Japanese Invention Pat. Laid-Open (Example 3) No. 38764/1982) Conc. of the intended product after completion 32.4% 6.6% of the oxidation reaction Reaction time 6.5 h 18h Yield L 86.5% 81% The following examples will further illustrate the present invention, which by no means limit the invention.

EXAMPLE 1 1 50 g of 4-nitrotoluene-2-sulfonic acid, 0.2 g of manganese acetate tetrahydrate and 640 g of water were charged in a four-necked glass flask and stirred while air was introduced therein at a rate of 1.6 1/min. 95.5 g of lithium hydroxide monohydrate was added slowly to the mixture. After completion of the addition, the temperature was elevated to 500C. The reaction was carried out at 50 to 550C for 2 h and then the temperature was elevated slowly to 700C in 4 h while air was introduced therein to effect the reaction.

Thereafter, the reaction mixture was transferred to a beaker. Hot water was added to the liquid and the resulting solution was stirred at 65 to 70 C while air was introduced therein. 121 g of anhydrous sodium carbonate was added to the solution and the resulting mixture was stirred for 30 min. Lithium carbonate thus precipitated was filtered off. The crystal was washed with 200 mi of hot water. The filtrates were gathered together and adjusted to pH 3 with conc. hydrochloric acid. 1 90 g of sodium chloride was added thereto. After cooling, sodium 4,4'-dinitrostilbene-2,2'-disulfonate was separated by filtration. After washing with about 400 ml of a 1 5% aqueous sodium chloride solution followed by drying, 1 52 g of a crystalline product was obtained.The purity of the product was 99% according to a liquid chromatography analysis and 92.3% according to a reduction analysis using TiCI3.

The yield of sodium 4,4'-dinitrostilbene-2,2'-disulfonate calculated from the latter purity was 85.5%.

It was confirmed that sodium 4,4'-diaminostilbene-2,2'-disulfonate obtained by reducing this product was sufficiently usable as an intermediate for a fluorescent dye.

The recovery of lithium in the form of lithium carbonate was 82.5%. According to an atomic absorption analysis, it had a sodium content of 0.23%.

EXAMPLE 2 The same procedure as in Example 1 was repeated except that the amount of lithium hydroxide monohydrate was altered to 103.7 g and that 264 g of anhydrous sodium carbonate was used for recovering lithium after completion of the reaction.

1 46 g of sodium 4,4'-dinitrostilbene-2,2'-disulfonate was obtained. This product had a purity of 99% according to a liquid chromatography analysis and 90.9% according to a reduction analysis with TiCI3. The yield of the intended product calculated from the latter purity was 80.9%. The recovery of lithium was 82.8%.

EXAMPLE 3 200 g of 4-nitrotoluene-2-sulfonic acid and 600 g of water were charged in a four-necked flask.

0.2 g of manganese acetate tetrahydrate was charged therein under stirring to obtain a solution. 98.3 g of lithium hydroxide monohydrate was added thereto slowly at 30 C while air was introduced therein at a rate of 4.8 1/min. After completion of the addition. the temperature was elevated to 460C. Then, the reaction was carried out by elevating the temperature slowly from 460C to 640C for 6.5 h.

After completion of the reaction, the mixture was cooled to 550C and transferred to a beaker. 1.3 I of water was added thereto to control the total quantity to about 2.11. 1 57 g of sodium carbonate was added thereto at 50 to 550C and the mixture was stirred at 50 to 550C for about 30 min while air was introduced therein. A precipitate thus formed was filtered off at 550C. (It was found that the precipitate was lithium carbonate containing 0.18% of sodium compounds according to an atomic absorption analysis effected after drying. The recovery of lithium was 74.9%). Sulfuric acid was added to the filtrate to control its pH to 3 to 4. The total quantity was adjusted to 2.5 1.250 g of sodium chloride was added thereto and a crystalline product precipitated was filtered and washed with a 13% aqueous sodium chloride solution.After drying, 225 g of sodium .4,4'-dinitrostilbene-2,2'-disulfonate was obtained in the form of yellow crystal. The purity of the compound was 83.95% according to the nitro group-reduction analysis and the yield based on the purity was 86.5%. According to a liquid chromatographic analysis, the product had 100% purity.

Sodium 4,4'-diaminostilbene-2,2'-disulfonate obtained by reducing the above product had a purity sufficient for use as an intermediate for a fluorescent dye.

EXAMPLE 4 75 g of 4-nitrotoluene-2-sulfonic acid, 0.1 g of manganese acetate and 400 g of water were charged in a four-necked flask to obtain a solution. 14.5 g of lithium hydroxide monohydrate was added thereto and the mixture was stirred for a while with introduction of 4 1/min of air. Then, 18 g of sodium hydroxide was added slowly thereto. The reaction was carried out with introduction of air at 600C for 3 h and then at 680C for 4.5 h. After completion of the reaction, the same after-treatment as in Example 3 was effected to recover lithium carbonate. 74 g of sodium 4,4'-dinitrostilbene-2,2'disulfonate was obtained in the form of yellow crystals.

The yield of the product based on the purity was 80.7% according to the purity based on the nitro group-reduction analysis. According to a liquid chromatography analysis, the product had a 99% purity.

EXAMPLE 5 4-Nitrotoluene-2-sulfonic acid was oxidized in the same manner as in Example 3. After completion of the reaction, the reaction mixture was cooled to 600 C. Air and carbon dioxide were introduced therein each at a rate of 2 1/min for 1 h. Crystal thus formed was filtered at 600C and washed with about 200 ml hot water. 100 g of sodium carbonate was added to the filtrate while air was introduced therein at 60 C and the solution was stirred for 30 min. Crystal thus precipitated was filtered off. (The recovery of lithium carbonate was 87.0% in total). The filtrate was controlled to pH 3 with sulfuric acid and 1 25 g of sodium chloride was added thereto. After filtration, the crystal was dried, to obtain 221 g of sodium 4,4'-dinitrostilbene-2,2'-disulfonate in the form of yellow crystal. The purity of the product was 88.8% according to the nitro group-reduction analysis and the yield of the product based on the purity was 89.8%.

According to a liquid chromatography analysis, the product had 100% purity. Thus, the product had a quality to be sufficient for use as a starting material for a fluorescent dye.

Claims (6)

1. A process for producing 4,4'-dinitrostilbene-2,2'-disulfonic acid or a salt thereof, which process comprises oxidising a compound of formula (I):

or a salt thereof in the presence of lithium and hydroxyl ions.

2. A process according to claim 1, in which the compound of formula (I) or salt thereof is oxidised in the presence of a catalyst.

3. A process according to claim 2, in which the catalyst is a manganese compound or a transition metal compound.

4. A process according to claim 3, in which the catalyst is manganese acetate.

5. A process according to any one of the preceding claims, in which the compound of formula (I) or salt thereof is oxidised in the presence of lithium hydroxide and sodium hydroxide.

6. A process for producing 4,4'-dinitrostilbene-2,2'-disulfonic acid or a salt thereof, said process being substantially as hereinbefore described in any one of Examples 1 to 5.