Research in the Chemistry of Carbazole Derivatives

IX. Synthesis of 9-(β-Hydroxypropyl)carbazole

V. P. Lopatinskii, E. E. Sirotkina, N. A. Musorina

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

The interaction of carbazole with ethylene oxide, studied by us earlier [1], which leads to a quantitative yield of 9-(β-hydroxyethyl)carbazole, indicated the possibility of obtaining by this route also 9-(β-hydroxypropyl)carbazole, which is of practical interest for the synthesis of polymers of 9-propenylcarbazole, as well as a number of products of fine organic synthesis.

9-(β-Hydroxypropyl)carbazole was obtained by Flauers and Miller [2] through the interaction of carbazole with propylene chlorohydrin on boiling in an alkaline solution of methyl ethyl ketone for 31 hours, with a yield of 90%. The long duration of the process led us to seek other routes for the synthesis of this intermediate, among which we settled on the reaction of carbazole with propylene oxide. We carried out a systematic study of the influence of the principal factors on the hydroxypropylation of carbazole. The main results of this study are given in Table 1.

It was established that hydroxypropylation proceeds best in acetone and methyl ethyl ketone in the presence of alkalis, with acetone being the most convenient and leading to the production of a purer substance. The reaction is also possible without a solvent; however, in this case the yield of 9-(β-hydroxypropyl)carbazole does not exceed 25%. For conversion of carbazole into 9-(β-hydroxypropyl)carbazole to 95%, it is sufficient to use 2 moles of propylene oxide per mole of carbazole.

With a smaller amount of propylene oxide, the duration of the reaction and the amount of unreacted carbazole increase. It was established that 93–95% yields of the product can be obtained in 2 hours using caustic potash as catalyst in a molar amount three times smaller than the amount of carbazole. Further addition of alkali has no effect on the yields of the product and does not shorten the duration of the reaction, while with smaller amounts of caustic potash the rate of the process decreases noticeably and the yield of 9-(β-hydroxypropyl)carbazole does not rise above 75%. Caustic soda as catalyst is considerably worse than caustic potash. Temperature has a marked effect on the rate of hydroxypropylation, but raising it above 50°C is undesirable because of the intensification of resinification processes, which affects the purity of the product and increases its losses during isolation and purification.

The hydroxypropylation reaction must be carried out with continuous stirring. The product was identified as 9-(β-hydroxypropyl)

carbazole on the basis of elemental analyses, the melting point of the substance and of its acetyl derivative.

Table 1

Results of several experiments on the synthesis of 9-(β-oxypropyl)carbazole

Experimental Part

Carbazole with a melting point of 242–244° was used in the work (a reagent from the Kharkov Coke-Chemical Plant, twice recrystallized from ethanol). The propylene oxide was freshly distilled and had a boiling point of 34°C. The potassium hydroxide was of “chemically pure” grade, and the acetone was of “pure” grade.

9-(β-Oxypropyl)carbazole

Into a three-necked flask equipped with a mechanical stirrer, a dropping funnel, a reflux condenser, and a thermometer, and placed in a thermostat, were introduced 10 g of carbazole (0.06 mole), 1.122 g of potassium hydroxide (0.02 mole), and 22 ml of acetone. With the stirrer operating, the contents of the flask were kept at the boiling temperature of acetone for 10 minutes and then cooled to 45°C, after which 8.5 ml of propylene oxide (0.12 mole) was added dropwise. The reaction was carried out for 2 hours with continuous stirring at a temperature of 50 ± 1°C. After the reaction was complete, the contents of the flask were poured into water (150 ml) acidified with hydrochloric acid (15 ml, specific gravity 1.18). The crystalline precipitate that separated was filtered off, washed with water to a neutral reaction, dried, and subjected to vacuum distillation.

At 215–216°C (10 mm Hg), 12.95 g of a colorless oil distilled over (yield 95.3% of theoretical), which on standing crystallized into a product with a melting point of 114–117°C. After re-

Upon crystallization from ethanol, 9-(β-hydroxypropyl)carbazole was isolated in the form of colorless fine needles with a melting point of 119–120°C (according to the literature data [2], it melts at 120–121°C). Analyses: found, %: N 6.24; 6.30; calculated, %: N 6.40. Found, by Verley, %: OH 7.28; 7.42; calculated, %: OH 7.54. The picrate consists of fibrous red crystals with a melting point of 114–115°C.

9-(β-Acetoxypropyl)carbazole was obtained from 9-(β-hydroxypropyl)carbazole and acetyl bromide in the form of colorless needles with a melting point of 103–104°C (according to the literature data [2], it melts at 104–104.5°C).

Conclusions

1. The influence of the principal factors on the reaction of carbazole with propylene oxide in the presence of caustic potash has been investigated.

2. It has been shown that under optimal conditions a 95% yield of 9-(β-hydroxypropyl)carbazole can be achieved in 2 hours instead of 31 hours according to the previously known procedure.

Literature

1. V. P. Lopatinskii, E. E. Sirotkina, I. P. Zherebtsov. Izvestiya Tomskogo politekhnicheskogo instituta, 112, 1962.

2. R. Flowers, H. Miller, L. Flowers, J. Am. Ch. Soc., 70, 3019, 1948.