Research in the Chemistry of Carbazole Derivatives
Abstract Generated abstract
The study examines the addition of vinyl butyl ether to carbazole, a reaction related to earlier conflicting reports on the behavior of simple vinyl ethers with amines. Using acid catalysis, the authors compare mercury salts and sulfuric acid, then evaluate the effects of temperature, catalyst amount, reagent ratio, and solvent on formation of 9-(alpha-butoxy)ethylcarbazole. Concentrated sulfuric acid in acetone proved sufficient for rapid conversion under mild conditions, with optimal reaction at about 35 to 40°C using a slight excess of vinyl butyl ether. The product structure was supported by comparison with material prepared independently from 9-(alpha-acetoxy)ethylcarbazole and n-butanol, and under optimized conditions the isolated yield reached 98 percent.
Full Text
RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES
XVII. ON THE INTERACTION OF CARBAZOLE WITH VINYLBUTYL ETHER*
V. P. Lopatinskii, E. E. Sirotkina, A. N. Yushko
(Presented by the Scientific-Methodological Seminar of the Chemical-Technological Faculty)
Reactions between simple vinyl ethers and amines have been little studied, and the information about them is sometimes contradictory. Furukawa and Goi [1] suggested that, when carbazole is allowed to react with a small excess of vinylethyl ether in a solution of diethyl ether, benzene, or xylene in the presence of BF₃ etherate, the product formed is the addition product of vinylethyl ether to carbazole in position 3. Subsequently Furukawa, Onishi, and Tsuruta [2] described the reaction leading to the formation of 9-(α-ethoxy)ethylcarbazole upon heating carbazole with a sixfold excess of vinylethyl ether in an autoclave for 5 hours at 180°C, with a yield of 54% of crude substance. The similarity of the properties of the product of addition of vinylethyl ether to carbazole, which they had obtained earlier, to the properties of 9-(α-ethoxy)ethylcarbazole suggests the identity of both products obtained under different conditions.
In the present work, using the interaction of vinylbutyl ether and carbazole as an example, it is shown that similar products of addition of a simple vinyl ether to carbazole can be obtained under considerably milder conditions and in high yields. Assuming at first the possibility of vinylation of carbazole analogously to the reaction of carbazole with vinyl acetate, which we had studied earlier [3], we used in the reaction between vinylbutyl ether and carbazole such catalysts as mercury(II) acetate and mercury(II) sulfate. It turned out that the former only weakly accelerates the interaction, while the latter becomes most active when it is prepared directly in the reaction mixture from mercury(II) acetate and concentrated sulfuric acid. In subsequent experiments it was found that concentrated sulfuric acid alone has the same catalytic action; in the presence of dilute acid the reaction did not occur. As a result of the reaction, the addition product 9-(α-butoxy)ethylcarbazole is formed, the structure of which was confirmed by synthesis from 9-(α-acetoxy)ethylcarbazole and n-butanol [4]. In addition to studying the influence of the indicated catalysts on the process, we also studied the influence of other principal factors: temperature, the ratio between the reagents, and the influence of solvents.
Changing the temperature from 0 to 50°C showed that the best yields of the reaction product are achieved at 35–40°C, at which the reaction com-
* Communication XVII in the series “Interaction of amines with vinyl ethers.”
is completed in 30 minutes. When the temperature is raised, resinification increases, making isolation and purification of the product difficult. The amount of sulfuric acid (specific gravity 1.84) in the experiments was varied from 0.1 to 0.7% of the weight of carbazole. It was found that, for complete conversion of carbazole into 9-(α-butoxy)ethylcarbazole, 0.2% of catalyst is sufficient. Of the series of solvents investigated (acetone, methyl ethyl ketone, vinyl butyl ether), acetone proved to be the best; its optimum amount is 3 moles per mole of carbazole.
Vinyl butyl ether is preferably taken in excess (0.5 mole) in order to maintain a high reaction rate and achieve more complete conversion of carbazole. It should be noted that the reaction is accompanied by considerable evolution of heat, and therefore the vinyl butyl ether was introduced gradually. Since it immediately entered into the reaction, the duration of the process depended practically on the rate of addition of the ether. The results of several experiments are given in Table 1.
Table 1
Results of Several Experiments on the Synthesis of 9-(α-Butoxy)ethylcarbazole
(In all experiments, 16.7 g (0.1 mole) of carbazole was taken into the reaction)
| No. | Acetone, ml | Vinyl butyl ether, ml | H₂SO₄, sp. gr. 1.84, ml | Reaction temperature, °C | Reaction duration, min | Yield, % of theoretical |
|---|---|---|---|---|---|---|
| 1 | 18.5 | 19.2 (0.15 M) | 0.01 | 40 | 25 | 98 |
| 2 | 18.5 | 19.2 | 0.005 | 40 | 25 | 72 |
| 3 | 18.5 | 19.2 | 0.002 | 40 | 25 | 45 |
| 4 | 18.5 | 19.2 | 0.003 | 40 | 25 | 92 |
| 5 | 18.5 | 12.8 (0.1 M) | 0.01 | 40 | 25 | 45 |
| 6 | 18.5 | 16 (0.125 M) | 0.01 | 40 | 25 | 95 |
| 7 | 18.5 | 19.2 (0.15 M) | 0.01 | 40 | 25 | 98 |
| 8 | 18.5 | 19.2 | 0.01 | 20 | 30 | 50 |
| 9 | 18.5 | 19.2 | 0.01 | 30 | 30 | 88 |
| 10 | 18.5 | 19.2 | 0.01 | 35 | 30 | 98 |
| 11 | 18.5 | 19.2 | 0.01 | 40 | 30 | 98 |
| 12 | 7.5 | 19.2 | 0.01 | 40 | 60 | 50 |
| 13 | 18.5 | 19.2 | 0.01 | 40 | 25 | 98 |
| 14 | 50 | 19.2 | 0.01 | 40 | 25 | 98 |
From the data obtained in Table 1 it is evident that, under optimum conditions, quantitative conversion of carbazole into 9-(α-butoxy)ethylcarbazole is achieved.
Experimental Part
9-(α-Butoxy)ethylcarbazole
Into a three-necked round-bottom flask equipped with a stirrer, reflux condenser, thermometer, and dropping funnel are introduced 18.5 ml of acetone (0.25 mole), 0.01 ml of sulfuric acid, specific gravity 1.84 (0.2% of the weight of carbazole), and 16.7 g (0.1 mole) of carbazole; with the stirrer switched on, 19.2 ml (0.5 mole) of vinyl butyl ether is added dropwise. The rate of addition of the vinyl butyl ether is regulated so that
so that the temperature of the reaction mixture does not rise above 40°C. After the carbazole has gone into solution, the reaction mixture is kept at 40°C for another 15 minutes and is then poured into water to wash out the sulfuric acid. The separated oily layer is extracted with ether; the ether extracts are dried over solid KOH, and after removal of the ether the residue is distilled in vacuo. At 183–185°C (3 mm Hg), 26.1 g (98% of theory) of a substance distilled over; it crystallizes from methanol as colorless transparent prisms with m.p. 52–53°C. The product is readily soluble in the usual organic solvents.
Analytical results. Found, %: C 80.23; 80.53; H 8.03; 8.00; N 5.28; 5.25. $\mathrm{C}_{18}\mathrm{H}_{21}\mathrm{NO}$; calculated, %: C 80.90; H 7.87; N 5.24. 9-($\alpha$-Butoxyethyl)carbazole, obtained by another method (by an exchange reaction of 9-($\alpha$-acetoxyethyl)carbazole with n-butanol) [4], had m.p. 52–53.5°C. The melting point of a mixture of the two products showed no depression.
Conclusions
-
The interaction of carbazole with vinyl butyl ether in the presence of sulfuric acid and mercury(II) sulfate has been studied.
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It has been established that the reaction product is 9-($\alpha$-butoxy)ethylcarbazole, obtained under optimum conditions in quantitative yield.
Literature
- J. Furukawa, M. Goi. Bull. Inst. Chem. Res. Kyoto Univ., 22, 84, 1950; C. A. 48, 6427, 1954.
- J. Furukawa et al., J. Org. Chem., 23, 672, 1958.
- V. P. Lopatinskii, E. E. Sirotkina. Izv. TPI, 111, 44, 1961.
- V. P. Lopatinskii, Yu. Shekhirev. Izv. TPI, 136, 1964.