Research in the Chemistry of Carbazole Derivatives
Abstract Generated abstract
This paper proposes a photochemically initiated method for condensing 9-hydroxymethylcarbazole without added acid catalysts, addressing contamination and coloration associated with conventional acid-catalyzed thermal polycondensation. Irradiation of an alcoholic solution containing slight moisture at reflux while passing air through the system produces small amounts of acidic oxidation products that initiate rapid polycondensation and precipitation of a comparatively pure polymer. IR spectroscopic, chemical, chromatographic, and comparison experiments indicate that the polymer is not formed by direct photochemical transformation, but through condensation promoted by in situ oxidation products under heated conditions. A typical procedure gave a white insoluble polymeric powder in up to about 50 percent yield after 3 hours, with melting behavior near 270 to 300°C and number-average molecular weight values of 250 to 400.
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RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES
81. PHOTOCHEMICAL INITIATION OF THE CONDENSATION OF 9-HYDROXYMETHYLCARBAZOLE
G. N. Ivanov, V. P. Lopatinskii, V. Ya. Tolmacheva
(Presented by the Scientific-Methodological Seminar of the organic departments and laboratories)
9-Hydroxymethylcarbazole [1] can enter into polycondensation reactions, giving various polymeric compounds. Such products may be used for various purposes, one of which is the use of the reaction products in photosensitive coatings for electrophotography.
The usual method of polycondensation of 9-hydroxymethylcarbazole is reduced to its thermal treatment in an acidic medium, where the acid acts as a catalyst. This simple method has such disadvantages as contamination of the product with acidic impurities and its coloration. Elimination of the noted disadvantages by available methods does not always achieve the goal.
In the present communication it is proposed to carry out the condensation reaction of 9-hydroxymethylcarbazole photochemically, without any catalytic additives. The essence of the method is that, upon irradiation of 9-hydroxymethylcarbazole with UV light in an alcoholic medium containing a small amount of moisture, at the boiling temperature of the solution and while air is passed through the reaction volume, small amounts of oxidation products are formed that exhibit an acidic reaction; the formation of small amounts of such impurities leads to the rapid course of polycondensation processes and to the precipitation of a polymeric sediment. As a rule, the concentration of oxidation products in the reaction is so low that in practice the polymeric substances obtained are very pure.
Investigation of the structure of the polymers by IR spectroscopy and chemical methods showed that the product contains no hydroxymethyl groups, has a carbazole framework, contains a small percentage of substituted benzene rings in the 3-position, and that an increased intensity of methylene groups and occupancy of the 9-position are observed. The listed facts made it possible to propose the composition of the polycondensate in the form of a mixture of two products
The product is not the result of a direct photochemical reaction, as was demonstrated by the identity of the IR spectra of compounds obtained by thermal condensation in an acidic medium and by condensation with the artificial addition of oxidation products without UV irradiation. Carrying out the experiment under the same conditions, but without heating, does not give a yield of polymers, which is also confirmed by chromatographic determination.
A typical experiment was carried out as follows.
An alcoholic solution of 9-hydroxymethylcarbazole with a concentration in the range of 0.1–10 g/l was poured into the reactor [2]. With vigorous initial purging of the volume with air, the reaction mixture was heated to boiling. The irradiation source (DRT-1000 lamp) and stirrer were switched on. Formation and precipitation of the polymeric product began 5–10 minutes after the start of irradiation. After 3 hours, the polymer yield reached 50% of the weight of the initial monomer. At the end of the experiment, the precipitate was filtered off, washed with hot alcohol, and dried at 60°C for 2 days.
In these experiments, 9-hydroxymethylcarbazole purified from ethanol, with m.p. 129°C, and isopropyl alcohol of “chemically pure” grade were used.
The reaction product was obtained as a white powder, insoluble in alcohols, acetone, benzene, hexane, and carbon tetrachloride. The product m.p. was from 270 to 300°C (depending on the initial concentration). The measured number-average molecular weight [3] had values of 250–400.
REFERENCES
- Kulev L. P., Lopatinskii V. P. Izvestiya TPI, 102, 103, 1959.
- Ivanov G. N., Tolmacheva V. Ya., Lopatinskii V. P. Author’s certificate for application No. 1454018, “Method for obtaining 1-acetylcarbazole.”
- Ivanov G. N., Budaeva V. A., Lopatinskii V. P. Izvestiya TPI, 136, 106, 1965.