Лако-красочные материалы — производство

The reduction is carried out in the manner described for the prepara­tion of aniline (page 75). The moist filter cake of nitrobenzene-2,5- disulfonic acid, obtained above, is added in small portions over the course of about 1 hour to a boiling, well stirred mixture of 200 grams of iron powder, 1 liter of water, and 20 cc. glacial acetic acid (Fig. 17, page 94). Stirring and boiling are continued for about 30 minutes, replacing the water lost by evaporation. The mixture is then made definitely alka­line with about 30 grams of soda ash and filtered hot to remove the iron sludge. The residue is boiled with a small amount of water and filtered, this process being repeated until the filtrate gives only a small amount of dye when it is diazotized and treated with an alkaline solution of /3- naphthol or R salt. The combined filtrate and washings are made just acid to litmus by the addition of concentrated hydrochloric acid, and then evaporated to about 800 cc. 60 grams of solid salt is now added and the solution is made strongly acid by the addition of 200 cc. concentrated hydrochloric acid, after which it is cooled overnight. The colorless white paste is filtered with suction and the precipitate washed with saturated salt solution, pressed out, dried and pulverized. In this way is obtained about 210 to 220 grams of the monosodium salt of aniline-2,5-disulfonic acid in the form of a white powder. 1 gram of the product is equivalent

to about 3 cc. 1 N nitrite solution. The yield is about 65 per cent of the theoretical amount based on chlorobenzene.

2-Nitrochlorobenzene-4-sulfonic acid can be prepared also by sulfonation of o-nitrochlorobenzene (see Table III).This method, however, is inherently more costly and less reliable than the one given above (nitration of chlorobenzene-4-sulfonic acid), because it requires the isolation of o-nifrochlorobenzene and its separation from the para isomer. Nevertheless, the second method may be preferable technically under those circumstances where the demand for p-nitrochlorobenzene is so large that a use for the by-product ortho isomer is needed. At the present time, the situ­ation is reversed. The manufacture of o-nitroanisole uses so much o-nitrochloroben­zene that the accumulated para compound is partly used in making p-nitroaniline.

Reduction of 2-nitrochIorobenzene-4-sulfonic acid gives o-chlorometanilic acid which is used in making azo dyes. The real technical value of nitrochlorobenzene — sulfonic acid, however, lies in the ability of its chlorine atom to be replaced by various groups. For example, o-nitrophenol-p-sulfonic acid is obtained by treat­ment with sodium hydroxide, and this product, on reduction, yields o-aminophenol — p-sulfonic acid. Analogously, nitrochlorobenzenesulfonic acid gives o-nitroanisole — p-sulfonic acid by treatment with alcoholic methanol, and from this is obtained o-anisidine-p-sulfonic acid. The action of ammonia on nitrochlorobenzenesulfonic acid produces o-nitroaniline-p-sulfonic acid; aniline and its derivatives produce о nitrodiphenylamine-p-sulfonic acids (cf. Table II).

Another replacement reaction of this same type is the reaction with neutral sulfite, whereby the chlorine is replaced by a sulfo group, leading to nitrobenzene — 2,5-disulfonic acid which can not be obtained by direct sulfonation.

Aniline-2,5-disulfonic acid, the preparation of which is described above, is used as a starting material for azo dyes, especially disazo and trisazo dyes of the type of Sirius light blue (see page 279).

In a three-necked flask equipped with stirrer, thermometer, and drop­ping funnel, 147 grams (1.0 mole) of coarsely pulverized p-dichloro­benzene (by-product of benzene chlorination, page 65) is covered with 300 grams of 100 per cent sulfuric acid. To this mixture is added with good stirring, over the course of 1 to 1.5 hours, a mixture of 68 grams of nitric acid (sp. gr. 1.52) and 68 grams of 100 per cent sulfuric acid. (The acid mixture is prepared by slowly adding the sulfuric acid to the nitric acid with cooling.) When the temperature reaches 30°C. the reaction flask is cooled slightly with water and the addition of acid is regulated so that the temperature remains between 30 and 35°. The crystals of p — dichlorobenzene gradually melt and when about half of the nitrating mixture has been added, an almost clear, oily layer is formed (eutectic mixture of p-dichlorobenzene and its nitro derivative). Vigorous stirring is necessary to achieve satisfactory mixing. Later, the nitro-p-dichloro — benzene begins to crystallize out. This may occur suddenly with the liberation of considerable heat, especially if the stirring has been in­adequate, and hence this phase of the reaction should be watched care­fully. If a rapid rise in temperature is observed, the addition of the nitrating mixture is interrupted and the cooling is increased in order to keep the temperature below 50° at the most. When the addition of the acids is completed, the reaction mixture is a thick, pale yellow, crystal­line mass. Stirring is continued for 3 or 4 hours, or until a nitrometer test shows that the residual nitric acid corresponds to the excess used. The end of the reaction can also be determined by diluting a test sample of the reaction mixture with water, filtering off the solid and determining its melting point (56-57°). A mixture of 700 grams of ice and 300 cc. water is now added, and the precipitated material is filtered off with suction and washed with cold water. In order to remove the last traces
of acids, the product is melted under 500 cc. hot water, stirred well, and allowed to cool to form a compact cake. This operation is repeated once more, and the acid-free, light yellow, crystalline material is then dried on filter paper at room temperature. The yield of product melting at 56-57° is 186 to 188 grams, or 97 to 98 per cent of the theoretical amount.

Remarks. N itro-pdichlorobenzene can be reduced to p-dichloroanilme in the usual way with iron and a small amount of acid. The chlorine ortho to the nitro group is labile and can be replaced by various substituents, less easily, however, than the chlorine in 2,4-dinitrocMorobenzene, but more easily than that in o-nitrochloro — benzene. The replacement of the chlorine by hydroxyl by the action of aqueous so­dium hydroxide is described in the following preparation. Reaction with sodium methylate yields 4-chloro-2-nitroanisole, which is reduced to 4-chloro-2-amsidine (chloramsidine P, or fast red R base). With ammonia under pressure, 4-chloro-2- nitroaniline (fast red 3CL base) is formed. These bases are important starting ma­terials for the preparation of azo dyes, especially pigment and lake colors, as well as ice colors.

(b)

4-Chloro-2-nitro phenol from IS itro-p^lichlorobeniene

Cl Cl

A mixture of 48 grams (0.25 mole) of nitro-p-dichlorobenzene, 86 grams (0.75 mole, 50 per cent excess) of sodium hydroxide solution (40° Вё), and 600 cc. water is placed in an autoclave, equipped with stirrer, and heated with good stirring for about 15 hours at 145°C. (internal temperature; oil bath, 186-190°). The pressure remains below 3 atmospheres. After cooling, the autoclave contents consist of a paste of well-formed red crystals of the difficultly soluble sodium salt of p- chloro-o-nitrophenol. These crystals are separated by filtration, washed with dilute salt solution and then dissolved in about 500 cc. of boiling water. The solution is filtered to remove traces of undissolved material, then strongly acidified with concentrated hydrochloric acid. After thor­oughly cooling the mixture, the coarsely crystalline precipitate of free chloronitrophenol is filtered off, washed with cold water, and dried on fil­ter paper at room temperature. If the reaction has been carried out properly, this product is light yellow in color and has the correct melting point of 87-88°. It can be used in the following reduction step without further purification. The original alkaline filtrate gives, on acidification, a few grams more of less pure product which can be purified by steam dis —

filiation. The total yield of product is about 37 grams, or 85 per cent of the theoretical amount.

To achieve good results in this preparation, it is absolutely essential: (I) to maintain as rapid stirring as possible in the autoclave, with the stirrer reaching to the bottom (the rotating autoclave described on page 359 is not suitable for this prepar­ation), (2) to maintain the prescribed temperature exactly, and (3) to use sodium hydroxide that is no more concentrated than described. If the alkali is too concen­trated or the temperature too high, reunification occurs and the yield is appreciably lowered.