Лако-красочные материалы — производство

Single Coupling Reactions with Hydroxy Compounds

Acid Orange A or Orange II

OH

HOsS—:

A solution of sulfanilic acid, equivalent to 17.3 grams (0.1 mole) of 100 per cent material, in 200 cc. water containing 6 grams of soda ash is boiled to drive off any aniline which may be present. The solution is filtered, treated with 30 cc. concentrated hydrochloric acid, and cooled to 20°C. The temperature is lowered to 10° by adding ice, and diazo — tization is carried out below 15° by adding 7 grams of 100 per cent sodium nitrite. The diazotization solution should give permanent tests with Congo red and starch-iodide papers.

While the diazotization reaction is being carried out, 14.4 grams (0.1 mole) of jS-naphthol is dissolved in 200 cc. water containing 15 grams of 30 per cent sodium hydroxide and 25 grams of soda ash; a clear solution should be obtained. This naphthol solution is cooled in an ice bath to 3°C., and the suspension of diazosulfanilic acid is added in a thin stream. The temperature of the mixture should not rise above 8°. After 1 hour, the reaction mixture is transferred to a porcelain dish and heated to boiling over a free flame. The hot solution is treated with 100 grams of salt added portionwise. The precipitate which has now separated completely can easily be filtered at 50° on a large suction funnel. The product is then pressed out in a screw press and dried at 100°. The yield, which is about 50 grams, can be determined accurately only by a comparison dyeing test.

Technical Observations. Acid orange A is one of the most widely used monoazo dyes because of its low cost and bright color. In large scale preparations, the coupling reaction is done in huge pitchpine vats having a capacity of 15,000 liters or more, or in concrete vats measuring up to 40 meters across and lined with refractory tile.

(Fig. 56, page 376, shows the general arrangement of a plant with diazotization and coupling vats in addition to the pressure equipment and filter press.) The filtered dye is not pressed out hydraulically, but is held under air pressure in the filter press for 1 to 3 hours and then dried on copper sheets. Drying is usually done in vacuum drying ovens which give rapid drying under mild conditions. A cost analysis for this dye is described in detail later (page 378 ff.).

In the case of this particular dye, the coupling reaction is usually carried out in a somewhat different manner whereby the soda is eliminated. The 0-naphthol is dissolved in the required amount of caustic soda and the solution is mixed with an almost neutral suspension of diazosulfanilic acid. The /З-naphthol is precipitated as fine crystals, and, as soon as the whole is thoroughly mixed, the amount of sodium hydroxide required to form the neutral sodium salt of the dye is added at 0°. Coupling takes place simultaneously, and the dye is filtered off cold without pre­viously wanning the mixture. The dye obtained is very concentrated and melts on the drying trays. This simple method was not given in detail here because most dyes cannot be made in this way. The procedure given, on the other hand, is appli­cable to almost all coupling reactions of 0-naphthol (roccelline, brilliant orange, etc.).

Acetyl-H Acid and Amidonaphthol Red G

An amount of H acid equivalent to 35 grams of 100 per cent material (0.1 mole) is dissolved at 50°C. in 200 cc. water containing 6 grams

of soda ash. With vigorous stirring, 17 grams of acetic anhydride is added over a period of 15 minutes. Complete acetylation of the amino group in H acid occurs, but simultaneously the hydroxyl group is partly acetylated. To test for completion of acetylation, a small test portion of the solution is acidified with hydrochloric acid, treated with a few drops of sodium nitrite, and then made alkaline with soda. If much H acid remains in the mixture, a blue coloration is formed (coupling of diazotized H acid with itself). As the acetylation proceeds, the color formed in the test becomes weaker and more reddish (coupling of diazotized H acid with acetyl-H acid). When the reaction mixture contains no more unchanged H acid, only a yellow coloration, formed by nitrosation, is obtained in the test. (The test can be carried out advantageously on filter paper.) When acetylation is complete, 25 grams of soda ash is added, and the mixture is heated and stirred at 90-95° for 1 hour, replacing the water lost by evaporation. This treatment hydro­lyzes the acetyl group on the oxygen but does not attack the acetyl — amino group. (If the treatment with soda is omitted, about 30 per cent of the starting material is lost, and the final dye is contaminated with decomposition products of the diazo compound.) The reaction can be controlled by titration with diazobenzene solution. The resulting soda solution is used directly in the coupling reaction. Acetyl-H acid com­bines with various diazo compounds to form beautiful azo dyes which are very fast to light and which level excellently. The important dye, amidonaphthol red G, for example, is formed with diazotized aniline.

Aniline (9.3 grams, 0.1 mole) is diazotized as described on page 259, and the diazo solution is mixed with the ice-cold soda solution of acetyl — H acid. The dye is salted out in the cold after 12 hours (20 per cent salt, calculated on the volume of the reaction mixture), filtered off, pressed in a screw press, and dried at 50°. The yield is about 50 grams.

If aminoacetanilide (page 132) is used in place of aniline, the excellent bluish tinted dye, amidonaphthol red 6B, is formed. This dye is more stable to light than the G brand.

Technical Observations. The dyes described above have largely replaced the analogous dyes from chromotropic acid (l,8dihydroxynaphthalene3,6disulfonic acid). They are cheaper and more stable to light.

It is interesting to note that the acetylation cannot be carried out in wooden containers in the plant. Especially when pitchpine is used, the final dyes almost always come out dull in color. The acetylation is done, therefore, in enameled vessels. The industrial process also uses somewhat less acetic anhydride. The final dyes are pressed out hydraulically and dried in vacuum drying ovens at 60°C. Hydrolysis of the dyes is minimized, not only by using the lower temperature, but also by drying as rapidly as possible.