Research in the Chemistry of Carbazole Derivatives
Abstract Generated abstract
This study examines chloromethylation of crosslinked copolymers of 9-vinylcarbazole with styrene and divinylbenzene, materials of interest as precursors to ion-exchange resins. Using monochlorodimethyl ether and zinc chloride, the authors evaluate how swelling time, reaction duration, catalyst amount, temperature, and degree of crosslinking affect chlorine incorporation into a copolymer containing 20 percent 9-vinylcarbazole, 75 percent styrene, and 5 percent divinylbenzene. The results indicate that longer swelling alone does not increase chlorine content, whereas reaction time and especially temperature have stronger effects, and excessive zinc chloride lowers chlorine incorporation, probably because of side crosslinking reactions. Lower crosslinking improves accessibility to chloromethylation, permitting substantially higher chlorine contents under otherwise comparable conditions.
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RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES
52. STUDY OF THE CHLOROMETHYLATION REACTION OF COPOLYMERS OF 9-VINYLCARBAZOLE WITH STYRENE AND DIVINYLBENZENE
V. P. Lopatinskii, E. E. Sirotkina, S. I. Kudinova
(Presented by the scientific-methodological seminar of the organic departments and problem laboratories)
Earlier we studied cross-linked copolymers of 9-vinylcarbazole with styrene [1], which are of interest for obtaining ion-exchange resins on their basis.
The subject of the present work is the study of the chloromethylation process of these copolymers.
The method of chloromethylation currently applied to copolymers of styrene with divinylbenzene proved unsatisfactory in our case. This is apparently explained by the fact that the chloromethylation reaction of 9-alkylcarbazoles and copolymers containing carbazole molecules often does not stop at the stage of formation of monosubstituted products; instead, as a result of secondary reactions of the chloromethyl groups, additional cross-links are formed, which ultimately leads to a decrease in the exchange capacity of the anionite [2].
The degree of chloromethylation is determined by the chlorine content in the chloromethylated copolymer and depends on a number of factors: the duration of swelling, the duration of the reaction, the reaction temperature, and the amount of catalyst. The chloromethylation reaction proceeds in the presence of Friedel–Crafts catalysts.
We used zinc chloride as the catalyst. For chloromethylation, a copolymer containing 20% 9-vinylcarbazole, 75% styrene, and 5% divinylbenzene was taken. Monochlorodimethyl ether was the chloromethylating agent.
To accelerate the chloromethylation process, the copolymer was subjected to preliminary swelling. From Table 1 it is evident that changing the swelling time from 2 to 8 hours does not lead to an increase in the chlorine content in the chloromethylated copolymer, whereas increasing the reaction time increases the chlorine content (Table 2).
Increasing the amount of catalyst above 0.4 mole per carbazole nucleus and 0.25 mole per styrene nucleus lowers the chlorine content, which can be explained by intensification of the side cross-linking reaction (Table 3).
As the data of Table 4 show, the reaction temperature has a significant effect on the chloromethylation process. The greatest number of chloromethyl groups is introduced into the copolymer at the boiling temperature of monochlorodimethyl ether. With a decrease in the degree of cross-linking of the copolymer, under otherwise equal conditions, the number of chloromethyl groups,
Table 1
Effect of swelling duration on the chloromethylation of the copolymer
| No. | Swelling duration, h | Reaction duration, h | Reaction temperature, °C | Amount of catalyst, % of copolymer weight | Amount of catalyst, mol per 1 mol of 9-vinylcarbazole | Amount of catalyst, mol per 1 mol of styrene | Chlorine content, % |
|---|---|---|---|---|---|---|---|
| 1 | 2 | 6 | 38 | 28.8 | 0.4 | 0.25 | 10.6 |
| 2 | 2 | 6 | 38 | 28.8 | 0.4 | 0.25 | 10.15 |
| 3 | 3 | 6 | 35 | 28.8 | 0.4 | 0.25 | 9.9 |
| 4 | 3 | 6 | 35 | 28.8 | 0.4 | 0.25 | 10.3 |
| 5 | 4 | 6 | 35 | 28.8 | 0.4 | 0.25 | 8.9 |
| 6 | 4 | 6 | 35 | 28.8 | 0.4 | 0.25 | 8.82 |
| 7 | 8 | 6 | 35 | 28.8 | 0.4 | 0.25 | 10.7 |
Table 2
Effect of reaction duration on the process of chloromethylation of the copolymer
| No. | Swelling duration, h | Reaction duration, h | Reaction temperature, °C | Amount of catalyst, % of copolymer weight | Amount of catalyst, mol per 1 mol of 9-vinylcarbazole | Amount of catalyst, mol per 1 mol of styrene | Chlorine content, % |
|---|---|---|---|---|---|---|---|
| 1 | 6 | 4 | 35 | 28.8 | 0.4 | 0.25 | 7.1 |
| 2 | 6 | 4 | 35 | 28.8 | 0.4 | 0.25 | 6.5 |
| 3 | 6 | 6 | 35 | 28.8 | 0.4 | 0.25 | 8.2 |
| 4 | 6 | 8 | 35 | 28.8 | 0.4 | 0.25 | 10.9 |
| 5 | 6 | 10 | 35 | 28.8 | 0.4 | 0.25 | 9.1 |
Table 3
Effect of the amount of catalyst on the process of chloromethylation of the copolymer
| No. | Swelling duration, h | Reaction duration, h | Reaction temperature, °C | Amount of catalyst, % of copolymer weight | Amount of catalyst, mol per 1 mol of 9-vinylcarbazole | Amount of catalyst, mol per 1 mol of styrene | Chlorine content, % |
|---|---|---|---|---|---|---|---|
| 1 | 6 | 8 | 35 | 15.5 | 0.2 | 0.15 | 7.7 |
| 2 | 6 | 8 | 35 | 20 | 0.25 | 0.17 | 13.15 |
| 3 | 6 | 8 | 35 | 20 | 0.25 | 0.17 | 10.1 |
| 4 | 6 | 8 | 35 | 28.8 | 0.4 | 0.25 | 10.9 |
| 5 | 6 | 8 | 35 | 38 | 0.6 | 0.3 | 8.3 |
| 6 | 6 | 8 | 35 | 44.1 | 0.7 | 0.35 | 7.7 |
| 7 | 6 | 8 | 35 | 57 | 0.75 | 0.4 | 5.99 |
Table 4
Effect of reaction temperature on the chloromethylation process of the copolymer
| No. | Swelling duration, h | Reaction duration, h | Reaction temperature, °C | Amount of catalyst, % of copolymer weight | Amount of catalyst, mol per 1 mol of 9-vinylcarbazole | Amount of catalyst, mol per 1 mol of styrene | Chlorine content, % |
|---|---|---|---|---|---|---|---|
| 1 | 6 | 8 | 20 | 28.8 | 0.4 | 0.25 | 7.6 |
| 2 | 6 | 8 | 20 | 28.8 | 0.4 | 0.25 | 6.9 |
| 3 | 6 | 8 | 30 | 28.8 | 0.4 | 0.25 | 12.7 |
| 4 | 6 | 8 | 30 | 28.8 | 0.4 | 0.25 | 9.8 |
| 5 | 6 | 8 | 35 | 28.8 | 0.4 | 0.25 | 10.7 |
| 6 | 6 | 8 | 35 | 28.8 | 0.4 | 0.25 | 8.8 |
| 7 | 6 | 8 | 50 | 28.8 | 0.4 | 0.25 | 14.3 |
| 8 | 6 | 8 | 50 | 28.8 | 0.4 | 0.25 | 14 |
| 9 | 6 | 8 | 60 | 28.8 | 0.4 | 0.25 | 14.3 |
| 10 | 6 | 8 | 60 | 28.8 | 0.4 | 0.25 | 15.9 |
introduced into the copolymer increases. This can be explained by the greater swelling capacity of the copolymer and, consequently, by its greater accessibility for chloromethylation. Thus, with two-percent crosslinking it is possible to introduce up to 20–25% chlorine.
Chloromethylation was carried out in a round-bottom flask equipped with a stirrer, a reflux condenser, and placed in a thermostat. The copolymer and the calculated amount of monochlorodimethyl ether were introduced into the flask (2 mol per carbazole nucleus and 1 mol per styrene nucleus). After swelling of the copolymer, the temperature in the thermostat was brought to the specified value, the stirrer was switched on, and zinc chloride was introduced. The copolymer was filtered off and washed with a fivefold amount of methanol and a fourfold amount of 5% hydrochloric acid. After this, the chloromethylated copolymer was washed with distilled water until a negative reaction for chloride ion was obtained.
The air-dry copolymer was analyzed for chlorine content, and its swelling in xylene was determined.
The experimental data obtained are presented in Tables 1–4.
Conclusions
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The influence of the principal factors on the chloromethylation process of crosslinked copolymers of 9-vinylcarbazole with styrene has been investigated.
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The optimal conditions for the chloromethylation process of the indicated copolymers have been determined.
LITERATURE
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V. P. Lopatinskii, E. E. Sirotkina, S. I. Kudinova. Izv. TPI, in press.
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V. P. Lopatinskii, E. E. Sirotkina, M. P. Grosheva. Izv. TPI, in press.