I. V. Gebler and S. S. Maksimova.

Experience in the Catalytic Oxidation of Anthracene with Atmospheric Oxygen

The outstanding importance of anthraquinone in the dye industry creates a great demand for this product and raises the need to seek methods for obtaining it that are the most convenient and advantageous. At present very many such methods are known, but the majority of them, described in the patent literature, have not found application in industry, where, strictly speaking, only two methods are used:

1) Oxidation of pure anthracene with a chromic mixture, and
2) The synthetic method (in America), from phthalic anhydride and benzene via benzoylbenzoic acid.

Among other methods, the catalytic ones are of the greatest interest, in accordance with the tendency of modern chemical technology to make the broadest and fullest use of contact-catalytic processes, which in many cases ensures economical operation because of the simplicity of the principal reaction and the absence of expenditure of auxiliary materials.

The proposed methods for obtaining anthraquinone by catalytic oxidation of anthracene may be divided chiefly into two categories:

1) Oxidation of anthracene by oxides of nitrogen (sometimes together with air),¹ and 2) oxidation by atmospheric oxygen. The latter, of course, are of greater interest, since they should prove more economical.

With regard to them, the patent literature contains the following indications. Vapors of anthracene in a mixture with air and water vapor, or in a mixture with air and CO₂, are passed over a contact material, whereby anthracene is oxidized to anthraquinone; the temperatures necessary for the reaction are given as ranging from 240 to 650°; as catalysts there are proposed the oxides of Sb, Bi, Cr, V, Mo, B, Ur; also Pt (platinum black²); the substrates for depositing the catalysts are clay (for boron oxides) or pumice; anthracene may be used not only pure, but also with any content of phenanthrene. More definite data on the course of the oxidation reaction, on the yields of anthraquinone, and on the conditions are not available.

We undertook experiments on the oxidation of anthracene in the vapor state by atmospheric oxygen at ordinary pressure; a description of these is given below.

For the experiments on the oxidation of anthracene we used the following apparatus: a glass tube 20 cm in diameter and about 60 cm long was placed in a furnace constructed of black sheet iron and lined on the inside with asbestos to reduce thermal conductivity; the furnace was heated by means of gas burners from the bottom side; a thermometer introduced into the furnace—

from above in such a way that its bulb was in immediate proximity to the middle part of the tube, where the contact was located.

As the substrate on which the catalyst was deposited, pumice was used, crushed into grains of 0.1–0.2 cm. The pumice with the catalyst deposited on it was introduced in such an amount that the column formed by it in a tube of the indicated diameter was 20 to 30 cm long. The pumice was first crushed, impregnated with a solution of a salt of the corresponding metal serving as the catalyst, dried, and calcined in a glass tube in a current of air in order to obtain the corresponding oxide; by reweighing the pumice the amount of catalyst deposited on it was determined.

The reaction tube was connected on one side with a Wurtz flask, in which the anthracene was located; into this flask, through a stopper, tubes were introduced for the admission of superheated steam at \(T. 300—330^\circ\) and of air from a graduated gasometer. On the opposite side of the tube were placed a condenser and receivers.

The anthracene for the experiments was a technical product with \(T. P.: 203^\circ\), containing, according to analysis, 73.6% pure anthracene.

The vapors of anthracene, boiling in the Wurtz flask, entered together with air and steam into the reaction tube and, after passing through the contact, together with the anthraquinone formed, condensed and were collected in the receiver.

Preliminary experiments showed that without steam the transfer of anthracene is too difficult, and under such conditions it is impossible to carry out the work.

The determination of anthraquinone in the products collected together with water in the receivers was carried out as follows: the reaction product collected in the receivers was filtered off, dried at \(100^\circ\), weighed, then treated with fuming sulfuric acid (with a content of 15% anhydride) in an amount of 10 c.c. per 1 g of dry product, and the whole was heated on a water bath for 10 minutes, after which it was placed in a desiccator for 12 hours; then the mass was transferred to a beaker and diluted with 200 cu. cm of water.

The anthraquinone that precipitated was transferred to a weighed filter, washed with hot water, then with a hot solution of KOH (1 g per liter), and again with hot water; then the filter was dried in a weighing bottle at \(100^\circ\) to constant weight. The purity of the anthraquinone was checked by the melting point and, if necessary, sulfonation and all subsequent treatments were repeated; thus, for the isolation of anthraquinone we used those procedures which are prescribed by the known Luck method for the analysis of anthracene in the portion that follows oxidation. To use other methods, for example according to Nelson and Seusemann¹, proved impossible under our conditions.

Impregnation of the pumice was carried out with solutions of the following salts:

1) copper acetate;
2) ammonium molybdate;
3) ammonium vanadate.

With the corresponding further treatments, the following were deposited on the pumice: \(\mathrm{CuO}\), \(\mathrm{Mo_2O_5}\), \(\mathrm{V_2O_5}\).

With each of these catalysts, several experiments were carried out under the conditions indicated above, and the conditions were found under which the yields of anthraquinone proved to be the greatest.

The results of such typical experiments are given in the following table; in these experiments, per 1 g of sublimed anthracene, 20–50 g of steam and 40–60 liters of air were consumed.

As can be seen, under the given conditions the yield of anthraquinone depends on the nature of the catalyst used; the most active catalyst is vanadium pentoxide, with the use of which the greatest yield of anthraquinone is observed. Owing to the low volatility of anthracene, a considerable consumption of superheated steam is required, which accelerates the transition of anthracene.

1. CBl. 1923, vol. II, p. 163. ↩↩

2. G. P. 168291. CBl. 1922, II, pp. 574 and 1055; 1923, IV, 289. ↩