I. V. Gebler.

Professor of the Siberian Technological Institute.

On the Practice of Preparing $\alpha$ and $\beta$ Dinitronaphthalenes.

Direct nitration of naphthalene leads to the nitro-substituted 1,5- and 1,8-, i.e.

\[ \begin{array}{ccc} \text{NO}_2 && \text{NO}_2 \quad \text{NO}_2 \\ \text{[structural formula]} & \text{and} & \text{[structural formula]} \\ \text{NO}_2 && \end{array} \]

The first of these, also called $\alpha$-dinitronaphthalene, serves as the starting material for the synthesis of naphthazarin, while the second isomer, $\beta$-dinitronaphthalene, is used for preparing black dyes for cotton, having at once the character of sulfur and vat dyes; moreover, both dinitro products, on reduction, give the corresponding naphthylenediamines, which, among other things, are used in fur dyeing, and the 1,5-isomer is capable of being diazotized, the resulting diazo product, when coupled with amines and phenols, giving dyes of a substantive character.*) Both dinitronaphthalenes are always obtained with a considerable predominance of the $\beta$-isomer, namely in ratios $\alpha : \beta$ from 9 : 13 to 6 : 17.

In many cases it is desirable that some one product should predominate, for example the $\alpha$-isomer, as the more interesting and valuable one; and therefore it is of interest to determine the conditions of nitration of naphthalene on which the relative quantities of both isomers in the resulting mixture of nitro products depend.

In preparing dinitronaphthalenes one starts either from mononitronaphthalene or directly from the hydrocarbon; in the latter case the nitration reaction is usually conducted in stages, with the calculation that first the mononitro product is formed, which, without its isolation from the reaction mixture, is then converted into the dinitro derivative. For this purpose the nitration is first conducted for a certain time in the cold and is completed on a water bath.

As regards the calculation of the nitrating mixture, the recipes relating to this are quite varied. Thus, according to the method of Beilstein and Kurbatov, apparently first proposed in 1880,**) for 100 parts of naphthalene one takes 300 parts by weight of crude nitric acid and leaves it in the cold for 24 hours, after which 160 parts by weight of oil of vitriol are added and the mixture is heated for a day on a water bath. Taking the crude nitric acid as containing 65.3% $\mathrm{HNO_3}$ (sp. gr. 1.4), and the oil of vitriol (sp. gr. 1.84) as 97% monohydrate, and expressing these quantities in terms of anhydrous acids and water separately,

) N. N. Vorozhtsov, “Stages in the Synthesis of Dyes,” and also his article: “Prospects for the Synthesis of Substantive Azo Dyes.” Izvestiya I. V. P. N.*, No. 4.

) Zh. R. F. Kh. O. T. V., p. 142, and also A., 208, S. 219.

which makes it possible conveniently to compare the data of the various recipes; for the present case, in round numbers, we have:

For 100 parts of naphthalene:

\[ \begin{aligned} \mathrm{HNO_3} &: 283 \text{ parts}\\ \mathrm{H_2SO_4} &: 285 \quad " \\ \mathrm{H_2O} &: 160 \quad " \end{aligned} \]

Working by this method, we obtained very low yields of dinitronaphthalenes—on the average about 20% of theory; moreover, the crude nitro product always contains mononitronaphthalene (about 7% of theory), a considerable quantity of oxidized products and resins, and finally trinitronaphthalene, which was detected when the nitro product (after removal of mononitronaphthalene and resins) was extracted with chloroform, in which the isomer 1,3,5 is readily soluble, in contrast to $\alpha$- and $\beta$-dinitronaphthalenes. This last circumstance is, in all probability, due to too high a content of nitric acid in the nitrating mixture; the amount of $\mathrm{H_2SO_4}$, on the contrary, is not large in relation to $\mathrm{HNO_3}$ and is insufficient to convert part of the $\mathrm{HNO_3}$ into the anhydride form, which is what determines the nitrating effect alone—hence the formation of resins and oxidized substances. Thus the method of Beilstein and Kurbatov, which is cited everywhere in the special literature, handbooks, and encyclopedias*), can hardly be applied for the technical production of dinitronaphthalenes. It must be noted that in the work of the authors mentioned nothing is said about the yield of products.

Many experiments on the preparation of dinitronaphthalenes were carried out by Gassmann**). In his experiments the quantities of acids introduced into the nitrating mixture correspond to the following ratios:

per 100 parts of naphthalene.

For all cases except the third, the reaction began in the cold and ended by heating on a water bath for 12 hours.

Nitration according to recipe III was at first carried out at ordinary temperature with $\mathrm{HNO_3}$ alone, then, after addition of $\mathrm{H_2SO_4}$, for two hours on a water bath.

The yields of dinitronaphthalenes are given as follows:

% of theory.

We carried out the nitration of naphthalene under conditions analogous to those of the work itself, with a nitrating mixture of the composition:

\[ \begin{aligned} \mathrm{HNO_3} &: 125 \text{ parts}\\ \mathrm{H_2SO_4} &: 297 \text{ parts}\\ \mathrm{H_2O} &: 77 \text{ parts} \end{aligned} \qquad \text{per 100 parts of naphthalene.} \]

In this case we obtained $\alpha$: 32.6%, $\beta$: 62.7%.

The crude nitro product contained mononitronaphthalene—5%—and an insignificant amount of resins—0.5%; trinitronaphthalene was not detected. These results and Gassmann’s data, leaving aside in the latter the case III, which differs sharply from the others in the conditions of treatment and the yield of nitro products, we compare in the following table:

\[ \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \]

) Beilstein, Handb. d. Organ. Chemie; Schmetz, Die Chemie d. Steinkohlentheers, I. T.; Ullmann, Encyklopedie d. Technische Chemie*.

**) Ber. 29. S. 1243, 1522.

Thus, in all these cases the yields of dinitronaphthalenes are fairly high; consequently, the amount of HNO₃ in the nitrating mixture need only be taken with an excess of not more than 25% of theory. With an increase in the amount of H₂SO₄, nitration proceeds more completely (the mononitro product is absent) and at the same time the α : β ratio decreases, i.e., the β-isomer predominates in the mixture of nitro products.

In order to attain, if possible, higher yields of α-dinitronaphthalene, the amount of sulfuric acid should be as small as possible, but in this case one must reckon with the fact that undinitrated mononitronaphthalene remains in the reaction mixture of nitro products, which, before separation of the isomers, must be removed from the crude product by means of carbon disulfide or, in an extreme case, benzene.

Subsequently we made an experiment in obtaining dinitronaphthalene, taking as the water-removing agent, instead of sulfuric acid, sodium polysulfate, i.e., the acid sulfuric acid sodium salt of composition NaH₃(SO₄)₂.

The dehydrating capacity of this salt is very considerable; in some cases it may be used for the sulfonation of aromatic compounds.*) On the other hand, this salt melts at a temperature of about one hundred degrees and, consequently, under the conditions of nitrating naphthalene to the dinitro product, i.e., on heating on a boiling water bath, allows the possibility of forming a liquid homogeneous medium. The experiment was carried out as follows. For 1 mole of naphthalene, 2 moles of HNO₃ plus a 10% excess were taken, in the form of 65% acid (sp. gr. 1.4), and 1 mole of NaH₃(SO₄)₂. The mixture of HNO₃ and NaH₃(SO₄)₂ was heated to 100° and naphthalene was added to it in small portions with good stirring. Nitration was carried out for 6 hours on a boiling water bath. Further treatment of the crude product and separation of the isomers were carried out as before. It was found that the nitration product in this case contained:

Thus it turns out that in the presence of polysulfate, nitration, generally speaking, does proceed, and in a distinctive manner: along with a considerably larger amount of mononitro product, a relatively much larger amount of the α-isomer is obtained than we have when working with sulfuric acid.

) On this see T. P. No. 113784, and then my article: “On the Sulfonation of Aromatic Hydrocarbons with Polysulfate.” — Journal of the Chemical Industry*, T. P. No. 12, (1926).