Research in the Chemistry of Carbazole Derivatives

85. Use of Acid Ionization of 3-Nitrocarbazole for Its Quantitative Determination

V. P. Lopatinskii, I. P. Zherebtsov, S. P. Yudina, L. P. Belyanina

(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)

The problem of the quantitative determination of carbazoles unsubstituted in the ninth position arises in the analysis of mixtures containing both derivatives of carbazole substituted and unsubstituted at the nitrogen atom. As was shown earlier [1], one way of solving this problem may be to use the acidic properties of the amino group in unsubstituted derivatives.

Acid-type ionization of 3-nitrocarbazole proceeds in sufficiently basic media with formation of an anion whose light-absorption maximum is located sufficiently far from the absorption maximum of the neutral molecule and lies in the visible region of the spectrum [2]. On the other hand, 9-alkyl derivatives of 3-nitrocarbazole have insignificant absorption in the absorption region of the anion. An illustration of this phenomenon is given in Fig. 1. These circumstances make it possible to use a photometric method for determining 3-nitrocarbazole in a mixture with its 9-substituted derivatives.

The present communication describes the procedure we developed for determining 3-nitrocarbazole and the results of its verification.

Experimental Part

3-Nitrocarbazole was obtained according to [3], m.p. 216°C, and additionally recrystallized from nitrobenzene. According to the literature data, 3-nitrocarbazole melts, respectively, at 216°, 212°, 214°C [3, 4, 5].

Found N% — 13.25; C\(_{12}\)H\(_8\)N\(_2\)O\(_2\); calculated N% — 13.21. 3-Nitro-9-ethylcarbazole was obtained according to [6], m.p. 130°C. According to the literature data, [6] m.p. 128°C.

Found N% — 11.59; C\(_{14}\)H\(_{12}\)N\(_2\)O\(_2\); calculated N% — 11.67. 3-Nitro-9-(2-hydroxy)ethylcarbazole was obtained according to [7]. M.p. 183–184°C. According to [8] its m.p. is 183–184°C. Found N% — 11.06; C\(_{14}\)H\(_{12}\)N\(_2\)O\(_3\); calculated N% — 10.95.

3-Nitro-9-(2-hydroxy)propylcarbazole was obtained by reaction of 3-nitrocarbazole with propylene oxide in acetone in the presence of alkali.

Into a flask fitted with a reflux condenser and a stirrer were charged 10 g of 3-nitrocarbazole, 1.22 g of caustic potash ground to a powder, and 22 ml of acetone. The mixture was boiled for 10–15 minutes on a water bath, after which, at 45–50°C over 1 hour with stirring, 9.0 ml of propylene oxide was added. After this, stirring at the same temperature was continued for another hour. Then the reaction mixture was poured into a beaker.

Absorption spectra of 3-nitrocarbazole and its derivatives, recorded on an SF-10 instrument. Fig. 1. 1—3-nitrocarbazole in a neutral medium (in acetone), \(C=0.009M\), \(l=1\) mm. 2—3-nitrocarbazole in an alkaline medium (acetone: ethanol: KOH 0.4 N; 10:13:2), \(C=6.00\cdot10^{-5}\ M\), \(l=10.200\) mm. 3—3-nitro-9-(2-oxy)propylcarbazole in an alkaline medium (acetone: ethanol: KOH 0.4 N; 10:13:2), \(C=6.00\cdot10^{-5}\ M\), \(l=10.200\) mm.

with 100 ml of water. The precipitated sediment is washed with water, filtered off, and dried. Purification is carried out by recrystallization from ethyl alcohol, yielding a substance with m.p. 144.5°C.

Found N%—10.36; \(C_{15}H_{14}N_2O_3\); calculated N%—10.37.

For the photometric measurements the following solvents were used: acetone—“chemically pure,” rectified ethyl alcohol. A solution of caustic potash, free of carbonates, was prepared according to [9].

Construction of the Calibration Graph

To construct the calibration graph, a series of standard solutions is prepared, the concentrations of which cover the range from 0 to \(7.44\cdot10^{-5}\ M\) 3-nitrocarbazole. Into a 25 ml volumetric flask are added the necessary amount of a solution of 3-nitrocarbazole in acetone with an initial concentration of \(3.72\cdot10^{-4}\ M\), acetone in such an amount that its total quantity is 10 ml, 2.0 ml of 0.5 N caustic potash solution, and ethyl alcohol up to the mark.

The resulting mixture is thoroughly mixed and allowed to stand for 10 minutes at room temperature. The optical densities of the solutions are measured on an electrophotocalorimeter with a light filter whose transmission maximum is \(\lambda=460\) nm, in cuvettes with \(l=1\) cm. In the comparison cuvette is placed a mixture not containing 3-nitrocarbazole.

The calibration graph, in the form of the straight line \(D=f(C)\), is constructed from eight points, processing the results by the least-squares method [10].

Procedure of Determination

A solution of the analyzed mixture of 3-nitrocarbazole with its 9-alkyl-substituted derivatives is prepared in acetone or ethyl alcohol. Into a 25 ml volumetric flask are placed from 1 to 10 ml of the prepared solution so that

the measured optical density would correspond approximately to the middle of the calibration curve. Acetone is added to the same flask in such an amount that its total quantity is 10 ml, 2.0 ml of 0.5 N potassium hydroxide solution in water is added, and ethyl alcohol is added to the mark. The optical density is then measured by the method described above. From the graph, the amount of 3-nitrocarbazole corresponding to the optical density found for the solution is determined.

To study the influence of the presence of 9-substituted 3-nitrocarbazoles on the result of the analysis and to assess the accuracy and relative error of the method, a series of alkaline solutions was prepared with the same content of 3-nitrocarbazole in them, mixed with various amounts of 3-nitro-9-(2-hydroxy)propylcarbazole (from 0 to \(7.44 \cdot 10^{-5}\) M).

The results of the analyses are summarized in the table.

Table 1

Statistical processing of the results was carried out according to the recommendations given in the literature [11, 12, 13].

It was found that similar results are also obtained for mixtures containing, in addition to 3-nitrocarbazole, its 9-(2-hydroxy)ethyl derivative or 9-ethyl derivative.

Conclusions

A method has been proposed for determining 3-nitrocarbazole in mixtures with its 9-alkyl-substituted derivatives, and its accuracy has been evaluated.

REFERENCES

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