Лако-красочные материалы — производство

Cl ^ —N— N— OH — HO N^N—/ OH

HOOC COOH HOOC COOH

in. p. 288° (dec.) m. p. 277° (dec.)

A solution containing the equivalent of 17 grams of pure chloro — aminobenzoic acid, prepared, for example, as described on page 169, is acidified with 30 cc. 30 per cent hydrochloric acid and cooled to about —2°C. by addition of ice. To this solution is added, over a period of a few minutes, 35 cc. 20 per cent sodium nitrite solution. With good start­ing materials, the diazo solution remains colorless and clear. It is mixed with a solution of 15 grams of salicylic acid (10 per cent excess) in 300 cc. water containing 40 grams of soda ash and 15 cc. 30 per cent sodium hydroxide. After 2 hours, when the coupling reaction is completed, the mixture is heated to 80° and treated with 15 per cent (by volume) of salt and enough hydrochloric acid to precipitate the dye. The material is filtered off and pressed out in the screw press.

The resulting dye is of no value in itself and is carried directly into the next step. The broken-up press cake is placed in a rotating auto­clave with 50 cc. 30 per cent sodium hydroxide, 200 grams of water, and 1 gram of copper sulfate. The mixture is heated, with continuous agita­tion, for 10 hours at 140°C (pressure, 4 atmospheres), during which time the chlorine is replaced by a hydroxyl group.

The pure reddish brown solution is filtered to remove copper oxide, and the azosalicylic acid is precipitated at 80°C. by the addition of 15 per cent hydrochloric acid. The product is insoluble in water. The yield is about 28 grams, or 90 to 95 per cent of the theoretical amount. From 156 grams of pure chlorobenzoic acid, 230 grams of pure azosali­cylic acid can easily be obtained, whereas with impure starting materials and incorrect reduction of the nitro compound, the yield may fall to less than half this value.

For dyeing wool, the water-insoluble material is dissolved in am­monia and the solution is made distinctly acid with acetic acid. The dye is after-chromed with sodium bichromate, making the shade fuller and completely fast to boiling.

Technical Observations. Azosalicylic acid is a typical example of a dye spe­cifically designed to provide a use for a by-product. The problem here was to find a use for large quantities of o-chlorobenzoic acid formed as a by-product in the manufacture of o-sulfobenzaldehyde. The Geigy concern had about 30,000 kilo­grams of this by-product on hand before C. Mettler succeeded in solving the problem of its use. Azosalicylic acid is the fastest yellow chrome azo dye derived from salicylic acid. It approaches the previously described chromocitronine in fastness, and, con­trary to the behavior of chromocitronine, it levels well on wool. The corresponding dye from o-cresotinic acid is about 23 per cent stronger on wool.

The replacement of the chlorine by hydroxyl takes place under the catalytic influence of copper oxide. Instead of the oxide, “cement copper,” or finely divided sheet copper, can be used equally well.