A Study in the Chemistry of Carbazole Derivatives

derivatives of the carbazole series are colored in various shades of yellow and green (with an identification limit of about a microgram).

IR spectra were recorded on an IKS-14 spectrophotometer in potassium bromide pellets and in solutions in carbon tetrachloride.

References

1. A. A. Petrov. Problems of chemical kinetics, catalysis, and reactivity. Collection of articles, 778. Publishing House of the Academy of Sciences of the USSR, Moscow, 1955.
2. L. Bellamy. Infrared Spectra of Complex Molecules. Moscow, IL, 1963.
3. K. Nakanishi. Infrared Spectra and the Structure of Organic Compounds. Moscow, “Mir,” 1965.
4. L. Bellamy. New Data on the Infrared Spectra of Complex Molecules. Moscow, “Mir,” 1971.
5. Methods of Organic Chemistry. Series of monographs edited by A. Weissberger, Vol. II. Determination of the Structure of Organic Compounds by Physical and Chemical Methods, Book 2. Moscow, “Khimiya,” 1967.
6. A. Akhrem, A. I. Kuznetsova. Thin-Layer Chromatography. Moscow, “Khimiya,” 1965.
7. I. M. Ezrielev, N. A. Larin. ZhOKh, 26, 791, 1956.
8. Thin-Layer Chromatography. Collection edited by E. Stahl. “Mir,” 1965.

RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

98. DETERMINATION OF CARBAZOLE AND ITS DERIVATIVES BY THE METHOD OF THIN-LAYER CHROMATOGRAPHY

I. P. Zherebtsov, V. P. Lopatinsky, S. P. Yudina, N. M. Rovkina,
E. N. Grabanchuk, V. I. Semenova

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

In studying the chemical transformations of carbazole and its derivatives, the need arises for their separate determination when they are present together. The most acceptable method for analyzing such mixtures is chromatography, which makes it possible to separate the mixture into individual components.

Among the chromatographic methods, thin-layer chromatography is convenient under our conditions.

This work presents the results of determining carbazole and its derivatives by thin-layer chromatography using an “internal standard” [1]. The composition of the mixtures separated is characterized in Table 1.

As sorbents, layers are used that consist of silica gel of various grades or aluminum oxide, fixed with gypsum. The selection of sorbents is given in Table 2.

As follows from Table 2, in the separation of mixtures B and O the best sorbent is fine-pored silica gel of grade KSM-6s. However, proceeding from the availability of the sorbents, all further work is carried out on silica gel of grade KSM and aluminum oxide.

The results of selecting mobile phases on the sorbents chosen by us, carried out analogously to work [2], are given in Table 3.

When using thin-layer chromatography for quantitative purposes, it is necessary to know the detection sensitivity. The detection sensitivity of carbazole and its derivatives, which is carried out by development in an iodine chamber and observation of luminescence under ultraviolet (UV) rays, is given in Table 4 (in micrograms).

Quantitative determination of the individual components in zones on thin-layer chromatograms can be performed by various methods [3,4].

Previously, the determination of 3-nitrocarbazole in mixtures with its 9-substituted derivatives by thin-layer chromatography using an “internal standard” had already been carried out. The eluates with 3-nitrocarbazole and the “standard” were photometered [5].

In the present work, the elution method is applied to the analysis of carbazole in a mixture containing carbazole, 9-oxymethylcarbazole, and 9-methylcarbazole—the “internal standard.” The determination of carbazole is carried out with the aid of a calibration graph constructed in the coordinates \(\lg \frac{D_1}{D_2}\)—concentration of the component being determined, where \(D_1\) and \(D_2\) are the optical densities of solutions of the reaction products of the “standard” and carbazole with xanthydrol, measured under constant conditions.

To construct the calibration graph, standard mixtures with different carbazole content and constant 9-methylcarbazole content are separated. Elution is carried out with acetic acid. The reaction of the eluates with xanthydrol is performed according to the procedure [6].

NOTE: the serial number of the components in mixtures in all tables corresponds to the order in which they are arranged on the chromatograms from the start to the front.

Table I

Table 2

NOTE: the quantities \(\Delta R_{f1-2}\), etc., denote the difference between the \(R_f\) of the first and second components, etc., respectively.

Table 3

Table 4

Photometry is carried out on an FEK-N-57 instrument. The analytical wavelengths for carbazole are 584 nm, and for 9-methylcarbazole, 610 nm.

Because of the laboriousness of the elution method, measurement of the sizes of spots on the chromatogram is also used for quantitative determination. In this case, the use of an “internal standard” gives grounds to expect an increase in the accuracy of the determination, since errors associated with nonuniformity of the layers, with application of the initial samples, and with the chromatographic conditions, which are substantial in the usual variant of this determination, are largely eliminated.

Determination of carbazole derivatives is carried out with the aid of a calibration graph plotted in the coordinates \(\lg q - \frac{F_1}{F_2}\), where

$Q$ is the concentration or amount of the substance being determined in the sample;
$F_1$ is the spot area of the “internal standard”; $F_2$ is the spot area of the component being determined.

Since it is not possible to achieve complete identity of the conditions under which the analysis is carried out and, as a consequence, the slope of the calibration line varies from plate to plate, a calibration line is constructed for each plate.

The results of the determinations are presented in Table 5.

The proposed method makes it possible to determine both the absolute amounts of substances in the spots (Nos. I–15) and their concentrations in the original sample (Nos. 16–18). In the latter case, calibration of the capillary is not required; it is only important to use one and the same capillary for the entire determination.

The statistical treatment was carried out according to [7,8].

Experimental Part

To construct the calibration graph, a series of standard solutions is prepared with a constant content of the “standard” and different contents of the component being determined.

Samples of the prepared standard solutions and samples of the component being determined are applied to a plate by means of a calibrated capillary.

Chromatography is carried out by the ascending chromatography method in a saturated chamber [9]. The layers are applied according to Stahl [10]. After chromatography, the plates dried in air are developed with iodine vapors.

The spot sizes are determined as the product of the maximum dimensions along the direction of movement of the eluent and in the direction perpendicular to the movement of the eluent [11].

Knowing the ratio of the spot areas of the “internal standard” and of the substance being determined $\left(\dfrac{F_{\mathrm{st}}}{F}\right)$, the concentration of the desired component in the analyzed sample is determined from the calibration graph.

The sorbent layer is silica gel KSM or aluminum oxide, fixed with, respectively, 5% or 15% gypsum.

Layer thickness: about 0.5 mm.

Plate size: 13 × 18 cm.

“Start–front” distance: 10 cm.

Table 5

NOTE: \(a\) is the true content, \(\mu\)g (Nos. 1–15) and mg/ml (Nos. 16–18); \(n\) is the number of determinations; \(\overline{x}\) is the mean result, \(\mu\)g; \(S^2\) is the variance; \(\mathcal{E},\ \%\) is the relative error of the result at a confidence probability of 0.95.

Chromatographic plates, after application of the sorbent layer, are kept at room temperature in air for two days, after which they are used.

Literature

1. K. A. Gol'berg, M. S. Vidergauz. Course in Gas Chromatography. Moscow, “Khimiya,” 1964.

2. G. I. Bulenkov. Factory Laboratory, 4, 1967.

3. E. Shgard. Quantitative Chromatography on Paper and in Thin Layers. Moscow, “Mir,” 1971.

4. B. G. Belenskii. Journal of Analytical Chemistry, 27, no. 5, 883, 1972.

5. V. P. Lopatinskii, I. P. Zherebtsov, S. P. Udina. Proceedings of TPI.

6. G. Gilbert, R. M. Stickel, H. H. Morgan, Ann. Chem., 12, 1959.

7. L. P. Adamovich. Rational Methods for Compiling Analytical Prescriptions. Publishing House of Kharkov University, 1966.

8. K. Doerffel. Statistics in Analytical Chemistry. “Mir,” 1969.

9. A. Akhrem, A. I. Kuznetsova. Thin-Layer Chromatography. Moscow, “Khimiya,” 1967.

10. E. Stahl. Chromatography in Thin Layers. Moscow, “Mir,” 1965.

11. B. G. Belenskii, V. V. Nesterov. Problems of Analytical Chemistry. Collection, vol. I, Moscow, “Nauka,” 1970.