RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

112. QUANTITATIVE DETERMINATION OF CARBAZOLE AND ANTHRACENE WHEN THEY ARE PRESENT TOGETHER

I. P. Zherebtsov, V. P. Lopatinskii, S. P. Yudina,
V. D. Pirogov, T. N. Zorina

(Presented by the scientific-methodological seminar
of the Chemical-Technological Faculty)

The problem of the quantitative determination of carbazole arises in the analysis of mixtures containing both substituted and unsubstituted at the nitrogen atom derivatives of carbazole. It was shown earlier [1] that one way of solving this problem may be the use of the acidic properties of the amino group in unsubstituted derivatives, with the ionization being followed by an indicator method.

In the present work a procedure is proposed for determining carbazole in the presence of nine of its substituted derivatives, phenanthrene, and anthracene, by the intrinsic absorption of the carbazole anion. Ionization of carbazole as an acid is carried out in N,N-dimethylformamide (DMFA) with the addition of aqueous caustic potash; in this process the carbazole anion is formed, whose maximum light absorption lies sufficiently far from the absorption maximum of the neutral molecule and is located in the near ultraviolet [2]. At the same time, 9-alkyl derivatives of carbazole and phenanthrene have insignificant absorption in the region of 360 nm and 413 nm and do not interfere with the determination of carbazole. Anthracene, however, practically does not absorb light only in the region of 413 nm, while in the region of 360 nm it has considerable absorption, which interferes with the determination of carbazole. Therefore it is advisable to determine carbazole in a mixture with anthracene using three calibration curves: for a mixture of equal amounts of carbazole and anthracene at 360 nm, where anthracene absorbs light, and at 413 nm, where it practically does not absorb, while the absorption of the carbazole anion is still considerable; and for anthracene at 360 nm.

Experimental Part

“Pure” phenanthrene contained no anthracene. Anthracene “for scientific work” was synthetic. 9-(2-Hydroxy)propylcarbazole was obtained according to [3], m.p. = 121°C. “Pure” carbazole was subjected to additional purification by the following procedure:

250 g of reagent-grade carbazole of “pure” qualification (MRTU 6-09-3815-67) are dissolved with boiling in 4.8 l of xylene, after which hot filtration is carried out in the usual manner and the solution is cooled to normal conditions. The precipitate that separates is filtered off and recrystallized from fresh portions of xylene (4.8 l for each recrystallization) until the solution is completely decolorized on heating (~4–6 operations). Upon completion of the last recrystallization

The purified carbazole is washed with benzene or alcohol (~600 ml) and dried at 60–70°C.

The carbazole obtained has a melting point in the range 246.5–246.8°C, and no anthracene impurities can be detected in it by TLC at a luminescence detection sensitivity of less than 1%.

Dimethylformamide (DMFA) for photometric measurements was used in “pure” grade and was not subjected to additional purification. A carbonate-free potassium hydroxide solution was prepared according to [4].

Construction of Calibration Curves

To construct calibration curves, a series of standard solutions of carbazole, its 9-alkyl derivatives, phenanthrene, and anthracene in DMFA is prepared in the concentration range from 0 to \(25.0 \cdot 10^{-4} M\). Into a 25-ml volumetric flask are added equal variable amounts (from 0 to 5 ml) of solutions of carbazole and anthracene, 2 ml of 0.47 N aqueous potassium hydroxide solution (variation in the alkali concentration within the range 0.3–0.7 N has practically no effect on the optical density), and DMFA to the mark. The mixture obtained is thoroughly stirred and allowed to stand for 10 min at room temperature. Under these conditions, as special experiments with carbazole showed, the optical density remains constant for at least 10 min and is directly proportional to the carbazole concentration within the indicated concentration limits.

The optical densities of the solutions are measured on an FEK-N-57 photoelectrocolorimeter with light filters No. 1 (360 nm) and No. 2 (413 nm) in 5-mm-thick cuvettes. The comparison cuvettes contain a mixture not containing the substances being analyzed.

The calibration curves for both light filters are obtained as straight lines expressing the dependence of optical density on carbazole content, with correlation coefficients of 0.998 and 0.996 for the first and second light filters, respectively.

A calibration curve for anthracene at 360 nm is constructed analogously; the correlation coefficient is 0.997.

Determination Procedure

A solution of the mixture to be analyzed in DMFA is prepared \((0.2994 \cdot 10^{-2}\ M)\). Into a 25-ml volumetric flask are placed 1 to 5 ml of the prepared solution so that the optical density measured with both light filters corresponds approximately to the middle of the calibration curves. Into the same flask are placed 2 ml of an aqueous potassium hydroxide solution of the same concentration as in the construction of the calibration curve, and DMFA is added to the mark. The resulting mixture is thoroughly stirred, allowed to stand for 10 min at room temperature, and the optical densities are measured with the 1st and 2nd light filters.

Since anthracene absorbs in the 360-nm region and practically does not absorb in the 413-nm region, the optical density of the solution measured with the 1st light filter is composed of the absorption of carbazole and anthracene, whereas with the 2nd light filter it corresponds to the absorption of only the carbazole anion. Thus, knowing the optical density with the 2nd light filter, and hence the carbazole content from the calibration curve for the 2nd light filter, one can find, using the calibration curve for the 1st light filter, the absorption corresponding to this amount of carbazole. By subtracting the optical density of carbazole measured with the 1st light filter from the optical density of the mixture, one can find the absorption of anthracene alone, and consequently its content.

Table 1

... content in the mixture, using the calibration graph for anthracene on the 1st light filter.

The results of typical determinations are given in Table 1. As can be seen from the table, 9-alkyl-substituted carbazoles, in particular 9-(2-hydroxy)propylcarbazole, and phenanthrene do not interfere with the determination of carbazole.

The accuracy of the determination is ±2.4% for carbazole and ±7.7% for anthracene.

REFERENCES

1. V. P. Lopatinskii, I. P. Zherebtsov, S. P. Yudina. Izvestiya TPI, vol. 257, 1972.
2. D. F. Bender, S. Sawicki, R. M. Wilson. Anal. Chem., 36, No. 6, 1011, 1964.
3. V. P. Lopatinskii. Izvestiya TPI, vol. 112, 1963, 10.
4. V. M. Suslennikova, E. K. Kiseleva. Manual for the Preparation of Titrated Solutions. Moscow–Leningrad, “Khimiya,” 1968.