Лако-красочные материалы — производство

The reaction of diazotized sulfanilic acid with diphenylamine is an sible to carry out the* reaction in neutral or alkaline solution because interesting example of coupling in mineral acid solution. It is not pos — diazosulfanilic acid is immediately decomposed by soda and, surprising­ly, does not react at all in neutral solution. Furthermore, diphenylamine Coupling in alcohol solution is preferred, therefore, because the better yield compensates for the small loss of alcohol.

As already mentioned, the presence of diphenylamine as an impurity interferes with the nitration of orange IV, and other impurities have the same effect to a still greater degree. If tropaeoline is to be con­verted to azo yellow, it is essential that the tropaeoline acid be very pure. Small amounts of impurities lower the yield by 30 to 50 per cent. If the dye acid is pure, however, the nitration is not at all critical. The process is interesting in that the nitro compound is produced through nitrosoamine and nitroamine intermediate stages. The tropaeoline is nitrosated with nitrous acid and the nitroso compound is oxidized with very dilute nitric acid, going through an intermediate nitroamine which rearranges to the nitro compound under the influence of mineral acid. This rearrangement is exactly similar to that of phenylnitro — amine into o-nitroaniline (Bamberger). The same type of reaction is involved in the preparation of methylene green (q. v.).

Tropaeoline is widely used as a wool dye, giving pure tints and hav­ing adequate fastness to light and washing. It also has the property of increasing, to a considerable degree, the intensity of color produced by other dyes. This property is used especially in the widely used acid
black 4B, which is a mixture of about 45 per cent each of naphthol blue-black В and naphthylamine black D and 5 per cent each of tro — paeoline and fast red AV. Attempts to replace the tropaeoline in this mixture by other yellow dyes have shown that only metanil yellow, prepared from metanilic acid and diphenylamine, has the same effect. The intensification of color is as much as 30 per cent.

Azo yellow is acid fast and can be used satisfactorily for dyeing tin phosphate weighted silks. It is indispensible for producing water fast yellow and brown tints.

(a) Tropaeoline or Orange IV

N..

Diazosul — Diphenyl- fanilic acid amine

A solution of 52 grams (0.3 mole) of sulfanilic acid in 300 cc. water containing 16 grams of soda ash is boiled to steam out any aniline which may be present. The solution is filtered to remove insoluble impurities and acidified with 35 grams of concentrated sulfuric acid. The tempera­ture is lowered to 12°C. by external cooling, and 22 grams of sodium nitrite, dissolved in a small amount of water, is added. After 1 hour, the difficultly soluble diazosulfanilic acid is filtered off, rinsing the container out with the mother liquor. (Diazosulfanilic acid is harmless when moist, but is extremely explosive when dry.) The crystals are then stirred into a paste with 250 cc. 90 per cent alcohol, and the mixture is cooled to 12°. (The alcohol must not be denatured with pyridine bases; benzene has no deleterious action.) 38 grams of finely pow­dered diphenylamine is added. No dye formation occurs. The vessel is covered with a pasteboard lid or a lead plate, and 12 grams of con­centrated hydrochloric acid is added with good stirring. The tempera­ture is maintained at 12° for 1 hour, 14° for 2 hours, and 18° for 2 hours, after which the water bath is warmed to 35°. The dye which has splashed up on the walls of the beaker is washed down with alcohol. No generation of gas should occur during the reaction. If possible, the mixture is stirred for an additional 6 hours and allowed to stand over­night. It is then diluted with 1 liter water at 50°. The tropaeoline acid,
which is insoluble, is filtered off and washed thoroughly with watdr until the washings are pure yellow in color. When the acid is removed from the funnel, it is found to have a remarkable property; the appar­ently solid mass becomes fluid when it is worked. This property is re­garded in the plant as a sure indication of purity, the more fluid the paste formed from the solid press cake, the purer the product. The blue gray paste is stirred with 200 cc. water, and the mixture is heated to boiling and treated with 30 grams of potassium carbonate. The potas­sium salt of the dye crystallizes out completely within 24 hours and is filtered off and dried at 100°C. About 75 grams of concentrated product is obtained. (The sodium salt is difficultly soluble and poor in appear­ance; for this reason it is not used as a dye.)

The freshly prepared, well washed tropaeoline acid is stirred with 300 cc. water and treated at 5°C. with 16 grams of 100 per cent sodium nitrite. Very slow stirring should be used since any foam that is formed causes difficulty in the subsequent nitration. After 2 hours, during which the light yellow nitrosoamine precipitates, 40 grams of 60 per cent nitric acid is added and stirring is continued for 2 hours. The temperature is then raised carefully to 68°. The mixture begins to foam and becomes darker in color, and all the solid dissolves in about 25 minutes. The mix­ture is heated for 10 minutes more at 71° and then diluted with 500 cc. water and neutralized with 25 grams of soda ash. Salt (200 grams) is added to precipitate the azo yellow. It separates in the course of a day as an orange-red, crumbly precipitate which is filtered off after 24 hours, pressed out, and dried at 60°. Higher temperatures cause de­composition. The yield is about 100 grams.

The mother liquor is always strongly colored because the nitration reaction is never clear-cut, some of the tropaeoline being converted to

nitrodiphenylamine and diazosulfanilic acid by the action of nitric acid. The formation of the diazo compound is easily recognized by placing a drop of the reaction mixture, at the beginning of the nitration, on filter paper and adding a drop of alkaline H acid solution to the light yellow ring. The red azo dye from sulfanilic acid and H acid is formed immediately.

The azo yellow prepared in this way is quite insensitive to dilute mineral acids, but is not satisfactory for certain purposes in silk dyeing. By using more nitric acid and more vigorous conditions, grades of azo yellow are produced which are more greenish in shade and completely fast to acids.

The preparation of azo yellow G is somewhat different. The nitra­tion is started at 40°C., and 90 grams of 60 per cent nitric acid is used instead of 40 grams. The temperature is raised to 70° in the course of 2 hours and held at this point for 2 horns more. This treatment makes the dye acid fast. At this point, the precipitate is slimy and not filterable. Salt (100 grams) is added, and the nitration mixture is diluted to 1 liter and stirred at 70° until the precipitate becomes light orange and pow­dery, requiring 1 to 2 hours. The mixture is then diluted further with 500 cc. water, and the process is continued as described above for azo yellow. The yield is about 95 grams.

The nitrated tropaeolines split off nitrous acid when dissolved in hot water and this acid attacks the copper equipment used by the dyers. There is a demand, therefore, for a nitrous acid-free azo yellow which is prepared in the following way. The freshly filtered azo yellow is heated to 90°C. with 4 parts of water, splitting off most of the nitrous and nitric acids. After about 3 hours, 5 per cent sodium bi­sulfite solution is added to remove the last traces of nitric acid. The mass gives off red fumes and foams strongly, so the process must be done in large vats. This treat­ment always results in a loss of 15 to 20 per cent of the dye. (See also azo flavine FF, page 272).

Technical Observations. The diazotization and coupling of sulfanilic acid are carried out in large enameled vessels. Thick glass rods carried in wood shafts which do not reach to the liquid level, are often used as stirrers. The diazosulfanilic acid is filtered off with suction (see Fig. 26, page 150). If the tropaeoline acid is of good quality, it is very fluid and can easily be pumped out of the coupling vessel. The moist tropaeoline acid from 38 kilograms of diphenylamine should weigh just about 200 kilograms after washing and strong pressing in the filter press. A variation of 10 kilograms, more or less, in this weight shows that impurities are present. The alcohol is recovered and rectified after neutralizing with soda; the loss in one operation is about 15 per cent.

The nitration is carried out in pitchpine vats of about 2500-liter capacity. They are equipped with good hoods (see Fig. 56, page 376) and last over a year. All parts of the equipment which come in contact with the vapors driven off during the heating operations should be covered with wooden boards held in place by wooden pegs.