Study in the Chemistry of Carbazole Derivatives
Abstract Generated abstract
This study examines the structure of a previously undescribed dichlorocarbazole isomer with melting point 111 to 113°C, formed in minor amount during chlorination of carbazole with sulfuryl chloride. The authors compare its formation in the chlorination of 3-chlorocarbazole, its melting behavior, and its infrared absorption bands with known dichlorocarbazole isomers and expected electrophilic substitution patterns in carbazole. The experiments show that the same low-yield isomer is obtained from 3-chlorocarbazole, indicating one chlorine atom is in the 3-position, while spectral evidence narrows the structure to 1,3- or 2,3-dichlorocarbazole. On chemical and positional grounds, the compound is assigned as 1,3-dichlorocarbazole.
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PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE, ORDER OF THE OCTOBER REVOLUTION AND ORDER OF THE RED BANNER OF LABOR,
named after S. M. Kirov
Vol. 198 1974
RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES
13. On the structure of dichlorocarbazoles formed by the action of sulfuryl chloride on carbazole
V. P. Lopatinskii, I. P. Zherebtsov
(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)
In one of the preceding works it was shown [1] that, upon chlorination of carbazole with two moles of sulfuryl chloride, it is possible to isolate at least two isomeric dichlorocarbazoles. One of them, formed in the largest amount, is 3,6-dichlorocarbazole, and its structure was proved by counter synthesis [2, 3]. The second isomer, with m.p. 111–113°, as is seen from Table 1, had not been described previously.
The isomer with m.p. 111–113° crystallizes in the form of plates, whereas the 1,6-dichlorocarbazole closest to it in m.p. crystallizes in the form of needles and has a higher melting point than the isomer under consideration. Moreover, in this case formation of the 1,4-isomer is unlikely, since usually in electrophilic substitution reactions in the carbazole molecule the positions 3, 6, 1, 8 are attacked first.
Table 1
Isomeric dichlorocarbazoles
| Name | M.p., °C | Literature |
|---|---|---|
| 3,6-dichlorocarbazole | 201–203 | [2] |
| 3,6-dichlorocarbazole | 204 | [3] |
| 3,6-dichlorocarbazole | 206 | [4] |
| 1,4-dichlorocarbazole | 84–85 | [5] |
| 1,6-dichlorocarbazole | 123–124 | [2] |
| 2,7-dichlorocarbazole | 204 | [6] |
| ??-dichlorocarbazole | 181 | [4] |
| ??-dichlorocarbazole | 111–113 | [1] |
This communication describes the results of several experiments aimed at establishing the structure of this isomer.
As our experiments showed, when 3-chlorocarbazole is chlorinated with one mole of sulfuryl chloride, the bulk of the starting substance…
is converted into 3,6-dichlorocarbazole. However, here too, as in the case of chlorination of carbazole with two moles of sulfuryl chloride, one and the same isomer of dichlorocarbazole, mp 111–113°, is formed in low yield. Consequently, this isomer contained one chlorine atom in position 3.
In its IR spectrum there are bands at 760 and 796 cm\(^{-1}\), corresponding to four adjacent hydrogen atoms in the aromatic ring of the carbazole molecule [8, 9]. The band at 823 cm\(^{-1}\) is characteristic of carbazole derivatives with two adjacent hydrogens in the benzene ring [10]. In our case, however, it is absent; the band at 768 cm\(^{-1}\) corresponds to an isolated hydrogen atom in the benzene ring.
Consequently, the isomer under study should be assigned the structure of 1,3- or 2,3-dichlorocarbazole. The latter is unlikely [7] for the reasons set forth above.
Experimental Part
Chlorination of 3-chlorocarbazole. To 100 g of 3-chlorocarbazole in 700 ml of dichloroethane are added 41 ml of sulfuryl chloride and (after stirring) 1 ml of a 5% solution of pyridine in dichloroethane. After the evolution of gases ceases, the mixture is heated to 70° and slowly cooled to room temperature. The precipitate that separates (84 g) is 3,6-dichlorocarbazole, mp 201–202°C.
Two-thirds of the initial volume of solvent is distilled off from the filtrate, and on cooling the residue a further 10 g of 3,6-dichlorocarbazole is isolated. The total yield of 3,6-dichlorocarbazole is 80% of theory. The residue is purified by vacuum distillation at 200–220°C (pressure 5 mm Hg) and by two successive recrystallizations from petroleum ether, giving 3.0 g of a substance with mp 111–113°, which shows no depression of the melting point in a mixture with the isomer obtained in the chlorination of carbazole [1].
The infrared spectrum of this substance was recorded in vaseline oil on an IKS-14 instrument. Absorption bands were found at the following frequencies: (cm\(^{-1}\)) 730 s, 766 s, 796 w, 844 w, 868 w, 903 w, 918 w, 1020 m. (s—strong band, w—weak band, m—medium band).
Conclusions
- One of the isomers formed in the chlorination of carbazole with two moles of sulfuryl chloride, and also in the chlorination of 3-chlorocarbazole, is 1,3-dichlorocarbazole.
LITERATURE
- V. P. Lopatinskii, I. P. Zherebtsov, S. F. Zelinskaya. Izvestiya TPI (in press).
- H. Grota, Ch. Riggle, A. Bearse. J. Org. Chem., 29 (8), 2474, 1964.
- S. Plant, J. Powell. J. Chem. Soc., 9379, 1947.
- F. Muzik. Z. Alban. Chem. Listy, 50, 1808, 1956.
- B. Barclay, N. Campbell. J. Chem. Soc., 530, 1945.
- H. Leditschke. Ber., 86, 522, 1953.
- Heterocyclic Compounds, vol. 3, ed. by Elderfield, IL, 1953.
- The Application of Spectroscopy in Chemistry, collection ed. by West, IL, 1959.
- Physical Methods in the Chemistry of Heterocyclic Compounds, ed. by Katritzky, “Khimiya,” 1966.
- D. Murphv, F. Schwartz, J. Picard, J. Kaufman. J. Am. Chem. Soc., 75, 4289.