RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

53. POLAROGRAPHIC DETERMINATION OF METHYL-ACETYL-CARBAZOLE

V. L. Ivasenko, V. P. Lopatinskii, E. E. Sirotkina

(Presented by the Scientific-Methodological Seminar of the Organic Departments and Problem Laboratories)

With the aim of studying the kinetics of the reduction of 9-methyl-3-acetylcarbazole, we studied the polarographic behavior of 9-methyl-3-acetylcarbazole and proposed a method for its quantitative determination in reaction mixtures. Polarographic determination of 9-methyl-3-acetylcarbazole had not previously been carried out.

The polarographic waves of 9-methyl-3-acetylcarbazole obtained by us against the background of acetate buffer solutions of composition CH₃COOH + CH₃COOLi, containing 50% ethanol, are presented in Fig. 1.

Dependence of the magnitude of the diffusion current on the concentration of 9-methyl-3-acetylcarbazole is linear (Fig. 2).

In Table 1 are given the values of the half-wave potentials of 9-methyl-3-acetylcarbazole at various background pH values.

Consideration of the polarograms of 9-methyl-3-acetylcarbazole obtained against the background of buffer solutions with different pH values shows that in acidic buffer solutions one polarographic wave is observed,

Fig. 1. 1 — pH = 2.8; 2 — pH = 5.2; 3 — pH = 8.4;
4 — pH = 12.2.

Fig. 2.

characterizing the reduction of 9-methyl-3-acetylcarbazole with the addition of one electron; in alkaline buffer solutions there is one two-valent wave, and in the region of pH ≃ 5 there are two one-electron waves.

Table 1

Half-wave potentials of 9-methyl-3-acetylcarbazole
at various background pH values

Experimental Part

The apparatus used: a type 7-77-4/V polarograph with a sensitivity of the order of \(10^{-9}\) A/mm.

All measurements were carried out in a thermostated cell using a dropping mercury electrode.

Reagents and solutions:

Acetic acid, chemically pure or analytical grade, GOST-61-51.
Lithium hydroxide, chemically pure or analytical grade, TsMTU 2062-48.
9-Methyl-3-acetylcarbazole, m.p. 101—102°, obtained by method (1).

An acetate buffer solution of composition \(\mathrm{CH_3COOH + CH_3COOLi}\), containing 50% ethanol, pH = 5 ÷ 6.

A 0.15 molar solution of lithium hydroxide.

A standard solution in ethanol containing 0.02—0.03 mol/L 9-methyl-3-acetylcarbazole.

Description of the determination

A weighed portion of ≃ 0.3 g of the substance to be analyzed is placed in a 25 ml volumetric flask and dissolved in 5 ml of dioxane. After dissolution, the contents of the flask are made up to the mark with ethanol; 0.2—0.5 ml of the resulting solution is added to 4—5 ml of acetate buffer background solution with pH 5—6, containing 50% ethanol, and, after nitrogen has been passed through for 10 min, polarography is carried out at a polarograph sensitivity of the order of \(10^{-7}\) A/mm, starting from a voltage of −0.6 V. Then the standard solution of 9-methyl-3-acetylcarbazole is added in an amount of 0.2—0.4 ml and, after nitrogen has been passed through for one minute, polarography is repeated.

The content of 9-methyl-3-acetylcarbazole (in %) in the mixture is determined by the formula [3]

\[ \frac{C_{\mathrm{st}}\cdot \Delta V \cdot h_0 \cdot 25} {10\left[h_1\cdot\left(\frac{V_0+\Delta V}{V_0}\right)-h_0\right]\cdot V\cdot g}, \]

where \(C_{\mathrm{st}}\) is the concentration of the standard solution, g/L;
\(V_0\) is the initial total volume of liquid in the electrolyzer, ml;
\(\Delta V\) is the volume of the added standard solution, ml;
\(h_0\) is the initial wave height of 9-methyl-3-acetylcarbazole, in mm;
\(h_1\) is the wave height after addition of the standard solution, in mm;

$V$ — volume of the analyzed solution added to the electrolyzer with the background electrolyte before polarography;

$h$ — weighed portion of the substance analyzed, in g.

Results of determination of 9-methyl-3-acetylcarbazole in the same mixture

Concentration in g/l: 3.75; 3.66; 3.72; 3.70; 3.66.

The analytical data were processed by the method of mathematical statistics and are presented in Table 2.

Table 2

Results of processing analyses of 9-methyl-3-acetylcarbazole

The following designations are adopted in Table 2:

$n$ — number of determinations,

$x$ — arithmetic mean of $n$ determinations,

$S$ — root-mean-square error of an individual determination

\[ S=\pm\sqrt{\frac{\sum(\bar{x}-x_i)^2}{n-1}}, \]

$\alpha$ — confidence,

$t$ — factor depending on $n$ and $\alpha$, found from the table [3],

$\varepsilon$ — accuracy of determination

\[ \varepsilon=\pm\frac{t_\alpha\cdot S}{\sqrt{n}}, \]

$\varepsilon_{\mathrm{rel}}$ — relative error of the method

\[ \varepsilon_{\mathrm{rel}}=\pm\frac{\varepsilon\cdot 100}{x}\%. \]

Conclusions

1. The method developed can be used to study the kinetics of the reduction of 9-methyl-3-acetylcarbazole. The confidence of the method of analysis is 0.95; the relative error is $\pm 1.87\%$.

Literature

1. V. P. Lopatinskii, E. E. Sirotkina. Izv. TPI, 126, 62, 1964.
2. Methods of Analysis of Chemical Reagents and Preparations. IREA, vol. 3, 1962.
3. G. A. Laitinen. Chemical Analysis. Khimiya, 1966.