STUDIES IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES.

110. INTERACTION OF 3-CHLORO-SUBSTITUTED CARBAZOLES WITH FORMALDEHYDE

I. P. ZHEREBTSOV, N. A. KRYKINA, V. P. LOPATINSKII

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

In a recent work [1] it was shown that 9-alkylcarbazoles form formolite-type oligomers with formaldehyde; however, if position 3 in the carbazole ring is occupied by some substituent, then the principal reaction product is the corresponding dicarbazolylmethane, i.e., in this case polymeric products are no longer formed.

Oligomeric products based on carbazoles are of practical interest, since proposals have been made to use such formolite-like products as photosensitive materials [2].

In the present work we have studied the interaction of 3-chloro-9-ethylcarbazole and 3-chloro-9-(2-acetoxy)-ethylcarbazole with formaldehyde (formalin was used as the source of the latter) in acetic acid in the presence of phosphoric acid as catalyst. It was found that, depending on the temperature at which the process is carried out, both substances of the dicarbazolylmethane type and oligomers arising at elevated temperatures can be obtained; moreover, conditions may be found for obtaining predominantly one or another of these products by varying the temperature.

The formation of oligomers in the interaction of 3-chloro-substituted 9-alkylcarbazoles with formaldehyde indicates that positions 1 and 8 in the carbazole nucleus participate in the reaction; at the same time, apparently, the possible participation of positions 1 and 8 in the formation of dicarbazolylmethanes should also be taken into account, although the substances isolated by us as the principal products have the structure of 6,6′-dicarbazolylmethanes.

The structure of the dicarbazolylmethanes was confirmed by the results of IR and NMR spectroscopy.

The oligomers obtained by us have photosensitivity sufficient for practical use in electrophotography.

Dicarbazolylmethane based on 3-chloro-9-(2-acetoxy)-ethylcarbazole and the corresponding oligomers are readily saponified in an alkaline medium with the formation of alcohols, which may be used for introducing various functional groups at the alcoholic hydroxyl.

Experimental Part

Starting substances and reagents. The following were used in the work: carbazole—pure grade—a reagent from the Kharkov Coke-Chemical Plant; technical-

formalin with a formaldehyde content of 34%; acetic acid—glacial, chemically pure; phosphoric acid—chemically pure.

3-Chloro-9-ethylcarbazole. 257 g of 3-chlorocarbazole, prepared according to [3], 2600 ml of acetone, and 180 g of powdered caustic potash, with the addition of 238 ml of ethyl bromide, are shaken in a 1-l flask at 50–52°C for five hours, after which the reaction product is isolated by the method described for the preparation of 9-alkylcarbazoles [4]. Purification is carried out by distillation under vacuum with subsequent recrystallizations from isopropyl alcohol. 3-Chloro-9-ethylcarbazole is obtained, m.p. 68°C, in a yield of about 60% of theory.

In the IR spectrum (here and below: IKS-14 spectrophotometer, Vaseline oil) there are bands at 722, 737, and 806 cm\(^{-1}\), indicating both the presence of substitution in position 3 (806 cm\(^{-1}\)) and the presence of four adjacent hydrogen atoms in the carbazole nucleus (722 and 737 cm\(^{-1}\)). The spectrum lacks the band near 3450 cm\(^{-1}\) that reveals an unsubstituted amino group.

3-Chloro-9-(2-acetoxy)ethylcarbazole was prepared according to [5], m.p. 98–99°C. In the IR spectrum bands are observed at 722, 745, 802, and 825 cm\(^{-1}\) (the band corresponding to substitution in position 3 is often split into two), as well as a band at 1736 cm\(^{-1}\) (carbonyl group in an ester).

Bis-(6-chloro-9-ethyl-3-carbazolyl)methane. To 5 g of 3-chloro-9-ethylcarbazole, 30 ml of acetic acid, and 0.56 ml of phosphoric acid, 2.0 ml of formalin is added, after which the mixture is heated with stirring at 70°C for 3 hours. The precipitate that falls out on cooling is purified by recrystallizations from a mixture of alcohol with chloroform (1:1) and from benzene, giving bis-(6-chloro-9-ethyl-3-carbazolyl)methane, m.p. 189°C, in a yield of about 30% of theory.

In the IR spectrum, compared with the spectrum of 3-chloro-9-ethylcarbazole, the bands at 722 and 737 cm\(^{-1}\) disappear, with a simultaneous increase in the intensity of the band at 806 cm\(^{-1}\), which indicates substitution in position 6.

In the PMR spectrum (here and below: Varian-60A instrument; solvent, which simultaneously serves as internal standard—methylene chloride; \(\tau\) scale) the following signals are observed: 2.0 \(\tau\), relative intensity 2, protons in positions 4 and 5 of the carbazole nucleus; 2.60 \(\tau\), multiplet, relative intensity 4, protons in the remaining positions of the carbazole nucleus; 5.64 \(\tau\), quartet, protons of the methylene groups in the ethyl groups; 5.70 \(\tau\), singlet, protons of the methylene bridge between the carbazole nuclei, relative total intensity of the signals from the protons of the methylene groups—3; 8.62 \(\tau\), triplet, relative intensity 3, protons of the methyl groups in the ethyl groups.

Analyses: chlorine, %, found: 15.05. C\(_{29}\)H\(_{24}\)N\(_2\)Cl\(_2\), calculated: Cl, %, 15.07.

Bis-(6-chloro-9-(2-acetoxy)-ethyl-3-carbazolyl)methane. 30 g of 3-chloro-9-(2-acetoxy)-ethylcarbazole in 180 ml of acetic acid in the presence of 18 ml of phosphoric acid is heated with 34 ml of formalin at 70°C for 3 hours with stirring; the precipitate that falls out on cooling of the reaction mixture is washed free of acids with water, dried, and recrystallized from isopropyl alcohol, giving 21 g of substance in the form of small needles with m.p. 132–133°C. Molecular weight (cryoscopy in benzene)—597; ester number—186.5; elemental analysis, %, found: C—67.14; H—5.01; Cl—12.18. C\(_{32}\)H\(_{26}\)O\(_4\)N\(_2\)Cl\(_2\), calculated: C—67.77; H—4.80; Cl—11.90. In the IR spectrum there is disappearance of the bands at 722 and 745 cm\(^{-1}\), with a simultaneous increase in the intensity of the band near 806 cm\(^{-1}\). In the PMR spectrum the following signals are observed:

2.04 $\tau$, multiplet, protons in positions 4 and 5 of the carbazole nuclei; 2.64 $\tau$, multiplet, protons in the remaining positions of the carbazole nuclei; relative intensity of signals from aromatic protons — 2.08; 5.60 $\tau$, singlet, protons of methylene groups in oxoethyl residues; relative intensity — 1.45; 5.67 $\tau$, singlet, protons of the methylene bridge between the carbazole nuclei, relative intensity — 0.28; 8.10 $\tau$, singlet, protons of methyl groups, relative intensity — 1.

Oligomer from 3-chloro-9-ethylcarbazole and formaldehyde. 5 g of 3-chloro-9-ethylcarbazole, 30 ml of acetic acid, and 0.56 ml of phosphoric acid with 2.0 ml of formalin are boiled under a reflux condenser for 3 h, cooled, and the precipitate that separates is purified twice by reprecipitation from a benzene solution with hexane. This gives 2.0 g of a substance melting in a capillary at 160–165°C. The relative viscosity of a 1% solution in benzene in an Ostwald viscometer with a capillary diameter of 0.78–1.04 mm. The product has film-forming properties. When a 30% solution in toluene is applied to a steel substrate, a coating forms without visible inhomogeneities. The photosensitivity, determined analogously to [6], is about $15$ lux · sec · $10^{-3}$.

Molecular weight (by Rast) about 1100.

Oligomer from 3-chloro-9-(2-acetoxy)-ethylcarbazole and formaldehyde. 5 g of 3-chloro-9-(2-acetoxy)-ethylcarbazole, 30 ml of acetic acid, 5 ml of formalin, and 3 ml of phosphoric acid are boiled under a reflux condenser for 3 h. The precipitate that separates after cooling of the reaction mixture is purified by double reprecipitation from a benzene solution with octane. The relative viscosity of a 5% solution is 1.30. The tem— [[unclear: line continuation]] (formalin in acetic acid was used as the source of the latter) is 15–16 lux · sec · $10^{-3}$. Ester number — 165. Molecular weight (by Rast) about 1400.

Conclusions

It has been shown that, in the interaction of 3-chloro-9-ethylcarbazole and 3-chloro-9-(2-acetoxy)-ethylcarbazole, depending on the temperature, both substances of the dicarbazolylmethane type and oligomers of the formolite type can be obtained.

LITERATURE

1. Bruck P. J. Org. Chem. 35, 2222, 1970.
2. Fr. Pat. 1399095, C. A. 64, 5996, 1966.
3. Lopatinskii V. P., Zherebtsov I. P. Methods for obtaining chemical reagents and preparations, 11, 102. Moscow, IREA, 1964.
4. Lopatinskii V. P., Sirotkina E. E., Sukhoroslova M. M. Methods for obtaining chemical reagents and preparations, 11, 69, Moscow, IREA, 1964.
5. Lopatinskii V. P., Zherebtsov I. P., Shchelkovnikova L. I. Izvestiya TPI, 163, 22, 1970.
6. Lopatinskii V. P., Sirotkina E. E., Sutyagin V. M. Izvestiya TPI, 163, 176, 1970.