DIRECT IODINATION OF ANTHRAQUINONE

A. N. NOVIKOV, V. T. SLYUSARCHUK, G. A. CHAPLYGINA

(Presented by the scientific seminar of the Department of Organic Chemistry, KhTF)

Anthraquinone is used in the production of dyes, biologically active compounds, and other practically important substances. A number of anthraquinone derivatives are difficult to obtain, owing to the complexity of their preparation (multistage syntheses). Iodine-substituted anthraquinones in particular are little known, since they are prepared via nitro-, amino-, and diazonium compounds. The reaction of direct iodination [1] of anthraquinone is unknown.

In the present work, data are given on the interaction of anthraquinone with iodine in the presence of a sulfuric–nitric acid mixture, which leads in one stage to the formation of difficultly accessible iodine-substituted anthraquinones. The influence of various factors on the course of the reaction has been elucidated.

Analyzing the literature data on the chemical behavior of anthraquinone in nitration, chlorination, and sulfonation reactions, we expected to obtain a difficultly separable mixture of iodine-containing isomers. Introduction of a substituent into one of the anthraquinone nuclei does not lead to a marked decrease in the reactivity of the second nucleus, which should make it difficult to obtain a monosubstituted product. Monoidoanthraquinone could not be obtained by direct iodination in the presence of a mixture of sulfuric and nitric acids.

By fractional crystallization from the mixture of isomers, two compounds with melting points of 306 and 194°C were isolated. The first product corresponds to the 1,5-diiodoanthraquinone described in the literature. This isomer had previously been synthesized by a multistage route through diazo compounds [2]. The second compound, according to quantitative analysis, contains two iodine atoms and corresponds to 1,8-diiodoanthraquinone. According to literature data, the same isomers arise in other electrophilic substitution reactions—nitration, sulfonation, and chlorination.

Experimental Part

To 0.02 mole of anthraquinone, 0.02 mole of iodine, and 40 ml of sulfuric acid at a temperature of 75°C, nitric acid of specific gravity 1.4 was gradually added with vigorous stirring. The synthesis time was 3 hours. After completion of the reaction, the mixture was cooled, the precipitate was filtered off on a glass filter, washed with water and with a solution of sodium hyposulfite, and dried. The mixture was crystallized from glacial acetic acid. On

Fig. 1. Dependence of the yield of iodination products on the amount of nitric and sulfuric acids.

Fig. 2. Dependence of the yield of iodination products on the temperature and reaction time.

Figs. 1 and 2 present data on the dependence of the yield of iodination products on the amounts of nitric and sulfuric acids, and on the temperature and reaction time. The most favorable conditions for carrying out the iodination reaction of anthraquinone are: 0.02 mole of iodine, 0.02 mole of anthraquinone, 0.4 mole of sulfuric acid, 0.18 mole of nitric acid, reaction temperature 70°C, synthesis time 3 hours.

Conclusions

Under the conditions of the direct iodination reaction in the presence of a mixture of sulfuric and nitric acids, anthraquinone reacts with iodine. For the first time by this method, a mixture of iodine-containing isomers has been obtained. From the mixture, the difficultly accessible 2,5- and 1,8-diiodoanthraquinones were isolated.

References

1. Tronov B. V., Novikov A. N. Izv. vuzov, “Khim. i khim. tekhnologiya,” 3, 872 (1960); Novikov A. N., Khalimova T. A. Author’s certificate No. 159496, 162218; Byull. izobr., No. 10 (1954).

2. H. Scholl, G. Hass, Ber. 62, 113, 1929.